Brandywine Operating Partnership 10-K 23 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Entity Registrant Name	BRANDYWINE REALTY TRUST
Trading Symbol	BDN
Entity Central Index Key	790,816
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 3,040,624,004
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		178,442,517
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Entity Registrant Name	BRANDYWINE OPERATING PARTNERSHIP, L.P.
Entity Central Index Key	1,060,386
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Real estate investments:
Operating properties		$ 3,832,348	$ 3,586,295
Accumulated depreciation		(895,091)	(852,476)
Operating real estate investments, net		2,937,257	2,733,819
Construction-in-progress		121,188	297,462
Land held for development	[1]	98,242	150,970
Total real estate investments, net		3,156,687	3,182,251
Assets held for sale, net		392	41,718
Cash and cash equivalents		202,179	193,919
Accounts receivable, net of allowance of $3,467 and $2,373 in 2017 and 2016, respectively		17,938	12,446
Accrued rent receivable, net of allowance of $13,645 and $13,743 in 2017 and 2016, respectively		169,760	149,624
Investment in Real Estate Ventures, equity method		194,621	281,331
Deferred costs, net		96,695	91,342
Intangible assets, net		64,972	72,478
Other assets		92,204	74,104
Total assets		3,995,448	4,099,213
LIABILITIES AND EQUITY
Mortgage notes payable, net		317,216	321,549
Unsecured term loans, net		248,429	248,099
Unsecured senior notes, net		1,365,183	1,443,464
Accounts payable and accrued expenses		107,074	103,404
Distributions payable		32,456	30,032
Deferred income, gains and rent		42,593	31,620
Acquired lease intangibles, net		20,274	18,119
Liabilities related to assets held for sale		0	81
Other liabilities		15,623	19,408
Total liabilities		2,148,848	2,215,776
Commitments and contingencies
Equity:
6.90% Series E Preferred Shares, $0.01 par value; issued and outstanding- 0 in 2017 and 4,000,000 in 2016		0	40
Common Shares of Brandywine Realty Trust's beneficial interest, $0.01 par value; shares authorized 400,000,000; 178,285,236 and 175,140,760 issued and outstanding in 2017 and in 2016, respectively		1,784	1,752
Additional paid-in-capital		3,218,564	3,258,870
Deferred compensation payable in common shares		12,445	13,684
Common shares in grantor trust, 894,736 in 2017, 899,457 in 2016		(12,445)	(13,684)
Cumulative earnings		660,174	539,319
Accumulated other comprehensive income (loss)		2,399	(1,745)
Cumulative distributions		(2,053,741)	(1,931,892)
Total Brandywine Realty Trust's equity		1,829,180	1,866,344
Noncontrolling interests		17,420	17,093
Total beneficiaries' equity		1,846,600	1,883,437
Total liabilities and beneficiaries' equity		3,995,448	4,099,213
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Real estate investments:
Operating properties		3,832,348	3,586,295
Accumulated depreciation		(895,091)	(852,476)
Operating real estate investments, net		2,937,257	2,733,819
Construction-in-progress		121,188	297,462
Land held for development		98,242	150,970
Total real estate investments, net		3,156,687	3,182,251
Assets held for sale, net		392	41,718
Cash and cash equivalents		202,179	193,919
Accounts receivable, net of allowance of $3,467 and $2,373 in 2017 and 2016, respectively		17,938	12,446
Accrued rent receivable, net of allowance of $13,645 and $13,743 in 2017 and 2016, respectively		169,760	149,624
Investment in Real Estate Ventures, equity method		194,621	281,331
Deferred costs, net		96,695	91,342
Intangible assets, net		64,972	72,478
Other assets		92,204	74,104
Total assets		3,995,448	4,099,213
LIABILITIES AND EQUITY
Mortgage notes payable, net		317,216	321,549
Unsecured term loans, net		248,429	248,099
Unsecured senior notes, net		1,365,183	1,443,464
Accounts payable and accrued expenses		107,074	103,404
Distributions payable		32,456	30,032
Deferred income, gains and rent		42,593	31,620
Acquired lease intangibles, net		20,274	18,119
Liabilities related to assets held for sale		0	81
Other liabilities		15,623	19,408
Total liabilities		2,148,848	2,215,776
Commitments and contingencies
Redeemable limited partnership units at redemption value; 1,479,799 and 1,535,102 issued and outstanding in 2016 and 2015, respectively		26,918	23,795
Equity:
6.90% Series E Preferred Shares, $0.01 par value; issued and outstanding- 0 in 2017 and 4,000,000 in 2016		0	96,850
Redeemable limited partnership units at redemption value; 1,479,799 issued and outstanding in 2017 and 2016		1,815,411	1,762,764
Accumulated other comprehensive income (loss)		2,056	(2,122)
Total Brandywine Operating Partnership, L.P.'s equity		1,817,467	1,857,492
Noncontrolling interest - consolidated real estate ventures		2,215	2,150
Total partners' equity		1,819,682	1,859,642
Total liabilities and beneficiaries' equity		$ 3,995,448	$ 4,099,213
[1]	As of December 31, 2017, the Company categorized 13.1 acres of land held for development located in the Other segment as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3, “Real Estate Investments,” for further information.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts receivable, allowance	$ 3,467	$ 2,373
Accrued rent receivable, allowance	$ 13,645	$ 13,743
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Preferred Stock, Dividend Rate, Percentage	6.90%	6.90%
Preferred Stock, Par or Stated Value Per Share (USD per share)	$ 0.01	$ 0.01
Preferred Stock, Shares Issued	0	4,000,000
Preferred Stock, Shares Outstanding	0	4,000,000
Common Stock, Par or Stated Value Per Share (USD per share)	$ 0.01	$ 0.01
Common Stock, Shares Authorized	400,000,000	400,000,000
Common Stock, Shares, Issued	178,285,236	175,140,760
Common Stock, Shares, Outstanding	178,285,236	175,140,760
Common Shares in Grantor Trust	894,736	899,457
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Accounts receivable, allowance	$ 3,467	$ 2,373
Accrued rent receivable, allowance	$ 13,645	$ 13,743
Preferred Stock, Dividend Rate, Percentage	6.90%	6.90%
Preferred Stock, Shares Issued	0	4,000,000
Preferred Stock, Shares Outstanding	0	4,000,000
Redeemable Limited Partnership Units Issued	1,479,799	1,479,799
Redeemable Limited Partnership Units Outstanding	1,479,799	1,479,799
General Partners' Capital Account, Units Issued	178,285,236	175,140,760
General Partners' Capital Account, Units Outstanding	178,285,236	175,140,760

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue
Rents	$ 412,333	$ 421,505	$ 486,731
Tenant reimbursements	72,620	70,629	85,722
Termination fees	2,370	2,339	4,797
Third party management fees, labor reimbursement and leasing	28,345	26,674	18,764
Other	4,825	4,316	6,617
Total revenue	520,493	525,463	602,631
Operating expenses:
Property operating expenses	150,835	152,926	181,170
Real estate taxes	45,204	46,252	50,623
Third party management expenses	9,960	10,270	6,294
Depreciation and amortization	179,357	189,676	219,029
General and administrative expenses	28,538	26,596	29,406
Provision for impairment	3,057	40,517	82,208
Total operating expenses	416,951	466,237	568,730
Operating income	103,542	59,226	33,901
Other income (expense):
Interest income	1,113	1,236	1,224
Tax credit transaction income	0	0	19,955
Interest expense	(81,886)	(84,708)	(110,717)
Interest expense - amortization of deferred financing costs	(2,435)	(2,696)	(4,557)
Interest expense - financing obligation	0	(679)	(1,237)
Equity in loss of Real Estate Ventures	(8,306)	(11,503)	(811)
Net gain on disposition of real estate	31,657	116,983	20,496
Net gain on sale of undepreciated real estate	953	9,232	3,019
Net gain from remeasurement of investments in real estate ventures	0	0	758
Net gain on Real Estate Venture transactions	80,526	20,000	7,229
Loss on early extinguishment of debt	(3,933)	(66,590)	0
Net income (loss) before income taxes	121,231	40,501	(30,740)
Income tax benefit	628	0	0
Net income (loss)	121,859	40,501	(30,740)
Net (income) loss attributable to noncontrolling interests	(1,009)	(310)	339
Net income (loss) attributable to Brandywine Realty Trust	120,850	40,191	(30,401)
Distribution to preferred shareholders	(2,032)	(6,900)	(6,900)
Preferred share redemption charge	(3,181)	0	0
Nonforfeitable dividends allocated to unvested restricted shareholders	(327)	(341)	(329)
Net income (loss) attributable to Common Shareholders of Brandywine Realty Trust	$ 115,310	$ 32,950	$ (37,630)
Basic income (loss) per Common Share:	$ 0.66	$ 0.19	$ (0.21)
Diluted income (loss) per Common Share:	$ 0.65	$ 0.19	$ (0.21)
Basic weighted average shares outstanding	175,484,350	175,018,163	178,162,160
Diluted weighted average shares outstanding	176,808,166	176,010,814	178,162,160
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Revenue
Rents	$ 412,333	$ 421,505	$ 486,731
Tenant reimbursements	72,620	70,629	85,722
Termination fees	2,370	2,339	4,797
Third party management fees, labor reimbursement and leasing	28,345	26,674	18,764
Other	4,825	4,316	6,617
Total revenue	520,493	525,463	602,631
Operating expenses:
Property operating expenses	150,835	152,926	181,170
Real estate taxes	45,204	46,252	50,623
Third party management expenses	9,960	10,270	6,294
Depreciation and amortization	179,357	189,676	219,029
General and administrative expenses	28,538	26,596	29,406
Provision for impairment	3,057	40,517	82,208
Total operating expenses	416,951	466,237	568,730
Operating income	103,542	59,226	33,901
Other income (expense):
Interest income	1,113	1,236	1,224
Tax credit transaction income	0	0	19,955
Interest expense	(81,886)	(84,708)	(110,717)
Interest expense - amortization of deferred financing costs	(2,435)	(2,696)	(4,557)
Interest expense - financing obligation	0	(679)	(1,237)
Equity in loss of Real Estate Ventures	(8,306)	(11,503)	(811)
Net gain on disposition of real estate	31,657	116,983	20,496
Net gain on sale of undepreciated real estate	953	9,232	3,019
Net gain from remeasurement of investments in real estate ventures	0	0	758
Net gain on Real Estate Venture transactions	80,526	20,000	7,229
Loss on early extinguishment of debt	(3,933)	(66,590)	0
Net income (loss) before income taxes	121,231	40,501	(30,740)
Income tax benefit	628	0	0
Net income (loss)	121,859	40,501	(30,740)
Net (income) loss attributable to noncontrolling interests - consolidated real estate ventures	(29)	(15)	3
Net income (loss) attributable to Brandywine Realty Trust	121,830	40,486	(30,737)
Distribution to preferred shareholders	(2,032)	(6,900)	(6,900)
Preferred share redemption charge	(3,181)	0	0
Nonforfeitable dividends allocated to unvested restricted shareholders	(327)	(341)	(329)
Net income (loss) attributable to Common Shareholders of Brandywine Realty Trust	$ 116,290	$ 33,245	$ (37,966)
Basic income (loss) per Common Share:	$ 0.66	$ 0.19	$ (0.21)
Diluted income (loss) per Common Share:	$ 0.65	$ 0.19	$ (0.21)
Basic weighted average shares outstanding	176,964,149	176,523,800	179,697,262
Diluted weighted average shares outstanding	178,287,965	177,516,451	179,697,262
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income (loss)		$ 121,859	$ 40,501	$ (30,740)
Comprehensive income (loss):
Unrealized gain (loss) on derivative financial instruments		2,948	2,371	(1,010)
Reclassification of realized losses on derivative financial instruments to operations, net	[1]	1,230	1,104	420
Total comprehensive income (loss)		4,178	3,475	(590)
Comprehensive income (loss)		126,037	43,976	(31,330)
Comprehensive (income) loss attributable to noncontrolling interest		(1,043)	(338)	344
Comprehensive income (loss) attributable to reporting entity		124,994	43,638	(30,986)
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Net income (loss)		121,859	40,501	(30,740)
Comprehensive income (loss):
Unrealized gain (loss) on derivative financial instruments		2,948	2,371	(1,010)
Reclassification of realized losses on derivative financial instruments to operations, net	[2]	1,230	1,104	420
Total comprehensive income (loss)		4,178	3,475	(590)
Comprehensive income (loss)		126,037	43,976	(31,330)
Comprehensive (income) loss attributable to noncontrolling interest		(29)	(15)	3
Comprehensive income (loss) attributable to reporting entity		$ 126,008	$ 43,961	$ (31,327)
[1]	Amounts reclassified from comprehensive income to interest expense within the Consolidated Statements of Operations.
[2]	Amounts reclassified from comprehensive income to interest expense within the Consolidated Statement of Operations.

Consolidated Statements of Bene

Consolidated Statements of Beneficiaries' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Deferred Compensation, Share-based Payments [Member]	Additional Paid-in Capital [Member]	Common Stock In Grantor Trust [Member]	Cumulative Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
Beginning Balance at Dec. 31, 2014	$ 2,159,326	$ 40	$ 1,793	$ 6,219	$ 3,314,693	$ (6,219)	$ 529,487	$ (4,607)	$ (1,700,579)	$ 18,499
Beginning Balance, Shares at Dec. 31, 2014		4,000,000	179,293,160	384,536
Net income (loss)	(30,740)						(30,401)			(339)
Other comprehensive income (loss)	$ (590)							(585)		(5)
Issuance of Common Shares of Beneficial Interest, Shares	0
Repurchase and retirement of Common Shares of Beneficial Interest	$ (67,325)		$ (52)		(67,273)
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	(5,209,437)		(5,209,437)
Issuance of partnership interest in joint venture	$ 1,025									1,025
Bonus share issuance	125				125
Bonus share issuance, Shares			8,447
Equity issuance costs	(105)				(105)
Share-based compensation activity	5,097		$ 6		5,091
Share-based compensation activity, Shares			509,675	280,011
Share Issuance from/(to) Deferred Compensation Plan	(2)			$ 5,699	(2)	(5,699)
Share Issuance from/(to) Deferred Compensation Plan, Shares			88,146	81,139
Share Choice Plan Issuance, Shares			(1,423)
Reallocation of Noncontrolling Interest					93					(93)
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(107,820)								(106,899)	(921)
Ending Balance at Dec. 31, 2015	1,952,091	$ 40	$ 1,747	$ 11,918	3,252,622	(11,918)	499,086	(5,192)	(1,814,378)	18,166
Ending Balance, Shares at Dec. 31, 2015		4,000,000	174,688,568	745,686
Net income (loss)	40,501						40,191			310
Other comprehensive income (loss)	$ 3,475							3,447		28
Issuance of Common Shares of Beneficial Interest, Shares	0
Issuance of partnership interest in consolidated real estate venture	$ 108									108
Conversion of LP Units to Common Shares			$ 1		874					(875)
Conversion of LP Units to Common Shares, Shares			55,303
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	0
Share-based compensation activity	$ 5,764		$ 4		5,718		42
Share-based compensation activity, Shares			405,200
Share Issuance from/(to) Deferred Compensation Plan	(47)			$ 1,766	(47)	(1,766)
Share Issuance from/(to) Deferred Compensation Plan, Shares			(8,311)	153,771
Reallocation of Noncontrolling Interest					(297)					297
Preferred Share distributions	(6,900)								(6,900)
Distributions declared	(111,555)								(110,614)	(941)
Ending Balance at Dec. 31, 2016	1,883,437	$ 40	$ 1,752	$ 13,684	3,258,870	(13,684)	539,319	(1,745)	(1,931,892)	17,093
Ending Balance, Shares at Dec. 31, 2016		4,000,000	175,140,760	899,457
Net income (loss)	121,859						120,850			1,009
Other comprehensive income (loss)	4,178							4,144		34
Issuance of Common Shares of Beneficial Interest	51,225		$ 29		51,196
Issuance of Common Shares of Beneficial Interest, Shares			2,858,991
Redemption of Preferred Shares	(96,850)	$ (40)			(96,810)
Redemption of Preferred Shares, Shares		(4,000,000)
Issuance of partnership interest in consolidated real estate venture	85									85
Distributions from consolidated real estate venture	$ (48)									(48)
Repurchase and retirement of Common Shares of Beneficial Interest, Shares	0
Bonus share issuance	$ 110				110
Bonus share issuance, Shares			6,752
Equity issuance costs	(499)				(499)
Share-based compensation activity	6,697		$ 3		6,689		5
Share-based compensation activity, Shares			333,127	39,870
Share Issuance from/(to) Deferred Compensation Plan	(768)			$ (1,239)	(768)	1,239
Share Issuance from/(to) Deferred Compensation Plan, Shares			(52,971)	(44,591)
Share Choice Plan Issuance, Shares			(1,423)
Reallocation of Noncontrolling Interest					(224)					224
Preferred Share distributions	(2,032)								(2,032)
Preferred Share redemption charges	(3,181)								(3,181)
Distributions declared	(117,613)								(116,636)	(977)
Ending Balance at Dec. 31, 2017	$ 1,846,600		$ 1,784	$ 12,445	$ 3,218,564	$ (12,445)	$ 660,174	$ 2,399	$ (2,053,741)	$ 17,420
Ending Balance, Shares at Dec. 31, 2017			178,285,236	894,736

Consolidated Statements of Ben7

Consolidated Statements of Beneficiaries' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60
Cumulative Distributions [Member]
Distributions declared per Common Share	0.66	0.63	0.60
Noncontrolling Interest [Member]
Distributions declared per Common Share	$ 0.66	$ 0.63	$ 0.60

Consolidated Statements of Cash

Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Cash flows from operating activities:
Net income (loss)	$ 121,859	$ 40,501	$ (30,740)
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	179,357	189,676	219,029
Amortization of deferred financing costs	2,435	2,696	4,557
Amortization of debt discount/(premium), net	1,569	1,471	(755)
Amortization of stock compensation costs	4,883	4,310	5,065
Settlement of hedge transaction	0	0	(5,266)
Straight-line rent income	(27,115)	(28,351)	(23,668)
Amortization of acquired above (below) market leases, net	(3,071)	(6,529)	(7,960)
Straight-line ground rent expense	88	88	88
Provision for doubtful accounts	2,207	1,865	2,489
Net gain on real estate venture transactions	(80,526)	(20,000)	(7,418)
Net gain on sale of interests in real estate	(32,610)	(126,215)	(23,515)
Preacquisition cost write-off	0	0	1,299
Net gain from remeasurement of investment in real estate ventures	0	0	(758)
Loss on early extinguishment of debt	3,933	66,590	0
Provision for impairment	3,057	40,517	82,208
Tax credit transaction income	0	0	(19,955)
Other than temporary impairment	4,844	0	0
Real Estate Venture loss in excess of distributions	3,462	12,125	2,034
Deferred financing obligation	0	(679)	(1,237)
Income tax benefit	(628)	0	0
Changes in assets and liabilities:
Accounts receivable	(6,266)	2,373	(848)
Other assets	1,188	(155)	837
Accounts payable and accrued expenses	4,004	(8,004)	4,083
Deferred income, gains and rent	(1,482)	137	(521)
Other liabilities	829	685	(1,894)
Net cash provided by operating activities	182,017	173,101	197,154
Cash flows from investing activities:
Acquisition of properties	(72,523)	(20,406)	(150,472)
Acquisition of property - 1031 exchange funds applied	0	0	(62,812)
Proceeds from the sale of properties	171,860	784,331	247,228
Sale of property - 1031 exchange funds held in escrow	0	0	62,800
Net proceeds from the contribution of properties to an unconsolidated real estate venture	0	0	50,158
Proceeds from real estate venture sales	145,416	21,022	6,100
Issuance of mortgage note receivable	0	(3,380)	0
Proceeds from repayment of mortgage notes receivable	151	0	88,000
Capital expenditures for tenant improvements	(60,586)	(51,398)	(97,851)
Capital expenditures for redevelopments	(34,679)	(11,909)	(48,367)
Capital expenditures for developments	(66,915)	(191,184)	(179,927)
Advances for the purchase of tenant assets, net of repayments	18	(784)	308
Investment in unconsolidated Real Estate Ventures	(6,638)	(28,610)	(68,549)
Deposits for real estate	573	(746)	(878)
Escrowed cash	0	6,992	516
Cash distribution from unconsolidated Real Estate Ventures in excess of cumulative equity income	20,781	13,065	8,557
Leasing costs paid	(17,657)	(16,083)	(21,263)
Net cash provided by (used in) investing activities	79,801	500,910	(166,452)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	86,900	130,000
Repayments of mortgage notes payable	(4,931)	(357,151)	(222,836)
Proceeds from unsecured term loan borrowing	0	0	50,000
Proceeds from credit facility borrowings	341,000	195,000	89,000
Repayments of credit facility borrowings	(341,000)	(195,000)	(89,000)
Proceeds from unsecured notes	550,131	0	0
Repayments of unsecured notes	(628,590)	(149,919)	0
Debt financing costs paid	(4,727)	(495)	(5,202)
Net proceeds from issuance of common shares\units	51,225	0	0
Redemption of preferred shares	(100,000)	0	0
Proceeds from the exercise of stock options	1,229	1,286	127
Shares used for employee taxes upon vesting of share awards	(674)	(879)	(2,055)
Partner contributions to consolidated real estate venture	85	108	1,025
Partner distributions from consolidated real estate venture	(48)	0	0
Repurchase and retirement of common shares	0	0	(67,320)
Distributions paid to shareholders	(116,311)	(115,702)	(114,328)
Distributions to noncontrolling interest	(947)	(934)	(921)
Net cash used in financing activities	(253,558)	(536,786)	(231,510)
Increase (decrease) in cash and cash equivalents	8,260	137,225	(200,808)
Cash and cash equivalents at beginning of year	193,919	56,694	257,502
Cash and cash equivalents at end of period	202,179	193,919	56,694
Supplemental disclosure:
Cash paid for interest, net of capitalized interest during the years ended December 31, 2017, 2016 and 2015 of $3,527, $12,835 and $12,150, respectively	83,139	97,843	124,953
Cash paid for income taxes	225	0	0
Supplemental disclosure of non-cash activity:
Dividends and distributions declared but not paid	32,456	30,032	28,249
Change in investment in real estate ventures as a result of dispositions	(64,792)	(2,023)	0
Change in investment in real estate ventures related to non-cash disposition of property	0	25,165	(25,127)
Change in operating real estate related to non-cash property disposition	0	0	25,127
Change in real estate investments related to non-cash property acquisition	0	0	(66,324)
Change in investments in joint venture related to non-cash acquisition of property	0	0	66,324
Change in other liabilities from contingent consideration related to a business combination	0	0	1,585
Change in operating real estate from contingent consideration related to a business combination	0	0	(1,585)
Change in other liabilities from a deferred payment related to an asset acquisition	0	0	2,000
Change in operating real estate from a deferred payment related to an asset acquisition	0	0	(2,000)
Change in real estate ventures as a result of other than temporary impairment	(4,844)	0	0
Change in operating real estate from deconsolidation of 3141 Fairview Park Drive	0	44,313	0
Change in investment in real estate ventures from deconsolidation of 3141 Fairview Park Drive	0	(12,642)	0
Change in mortgage notes payable from deconsolidation of 3141 Fairview Park Drive	0	(20,582)	0
Change in other liabilities from deconsolidation of 3141 Fairview Park Drive	0	(12,384)	0
Change in capital expenditures financed through accounts payable at period end	(6,953)	8,222	(7,654)
Change in capital expenditures financed through retention payable at period end	(159)	848	6,104
Change in unfunded tenant allowance	0	0	(273)
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Cash flows from operating activities:
Net income (loss)	121,859	40,501	(30,740)
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	179,357	189,676	219,029
Amortization of deferred financing costs	2,435	2,696	4,557
Amortization of debt discount/(premium), net	1,569	1,471	(755)
Amortization of stock compensation costs	4,883	4,310	5,065
Settlement of hedge transaction	0	0	(5,266)
Straight-line rent income	(27,115)	(28,351)	(23,668)
Amortization of acquired above (below) market leases, net	(3,071)	(6,529)	(7,960)
Straight-line ground rent expense	88	88	88
Provision for doubtful accounts	2,207	1,865	2,489
Net gain on real estate venture transactions	(80,526)	(20,000)	(7,418)
Net gain on sale of interests in real estate	(32,610)	(126,215)	(23,515)
Preacquisition cost write-off	0	0	1,299
Net gain from remeasurement of investment in real estate ventures	0	0	(758)
Loss on early extinguishment of debt	3,933	66,590	0
Provision for impairment	3,057	40,517	82,208
Tax credit transaction income	0	0	(19,955)
Other than temporary impairment	4,844	0	0
Real Estate Venture loss in excess of distributions	3,462	12,125	2,034
Deferred financing obligation	0	(679)	(1,237)
Income tax benefit	(628)	0	0
Changes in assets and liabilities:
Accounts receivable	(6,266)	2,373	(848)
Other assets	1,188	(155)	837
Accounts payable and accrued expenses	4,004	(8,004)	4,083
Deferred income, gains and rent	(1,482)	137	(521)
Other liabilities	829	685	(1,894)
Net cash provided by operating activities	182,017	173,101	197,154
Cash flows from investing activities:
Acquisition of properties	(72,523)	(20,406)	(150,472)
Acquisition of property - 1031 exchange funds applied	0	0	(62,812)
Proceeds from the sale of properties	171,860	784,331	247,228
Sale of property - 1031 exchange funds held in escrow	0	0	62,800
Net proceeds from the contribution of properties to an unconsolidated real estate venture	0	0	50,158
Proceeds from real estate venture sales	145,416	21,022	6,100
Issuance of mortgage note receivable	0	(3,380)	0
Proceeds from repayment of mortgage notes receivable	151	0	88,000
Capital expenditures for tenant improvements	(60,586)	(51,398)	(97,851)
Capital expenditures for redevelopments	(34,679)	(11,909)	(48,367)
Capital expenditures for developments	(66,915)	(191,184)	(179,927)
Advances for the purchase of tenant assets, net of repayments	18	(784)	308
Investment in unconsolidated Real Estate Ventures	(6,638)	(28,610)	(68,549)
Deposits for real estate	573	(746)	(878)
Escrowed cash	0	6,992	516
Cash distribution from unconsolidated Real Estate Ventures in excess of cumulative equity income	20,781	13,065	8,557
Leasing costs paid	(17,657)	(16,083)	(21,263)
Net cash provided by (used in) investing activities	79,801	500,910	(166,452)
Cash flows from financing activities:
Proceeds from mortgage notes payable	0	86,900	130,000
Repayments of mortgage notes payable	(4,931)	(357,151)	(222,836)
Proceeds from unsecured term loan borrowing	0	0	50,000
Proceeds from credit facility borrowings	341,000	195,000	89,000
Repayments of credit facility borrowings	(341,000)	(195,000)	(89,000)
Proceeds from unsecured notes	550,131	0	0
Repayments of unsecured notes	(628,590)	(149,919)	0
Debt financing costs paid	(4,727)	(495)	(5,202)
Net proceeds from issuance of common shares\units	51,225	0	0
Redemption of preferred shares	(100,000)	0	0
Proceeds from the exercise of stock options	1,229	1,286	127
Shares used for employee taxes upon vesting of share awards	(674)	(879)	(2,055)
Partner contributions to consolidated real estate venture	85	108	1,025
Partner distributions from consolidated real estate venture	(48)	0	0
Repurchase and retirement of common shares	0	0	(67,320)
Distributions paid to shareholders	(117,258)	(116,636)	(115,249)
Net cash used in financing activities	(253,558)	(536,786)	(231,510)
Increase (decrease) in cash and cash equivalents	8,260	137,225	(200,808)
Cash and cash equivalents at beginning of year	193,919	56,694	257,502
Cash and cash equivalents at end of period	202,179	193,919	56,694
Supplemental disclosure:
Cash paid for interest, net of capitalized interest during the years ended December 31, 2017, 2016 and 2015 of $3,527, $12,835 and $12,150, respectively	83,139	97,843	124,953
Cash paid for income taxes	225	0	0
Supplemental disclosure of non-cash activity:
Dividends and distributions declared but not paid	32,456	30,032	28,249
Change in investment in real estate ventures as a result of dispositions	(64,792)	(2,023)	0
Change in investment in real estate ventures related to non-cash disposition of property	0	25,165	(25,127)
Change in operating real estate related to non-cash property disposition	0	0	25,127
Change in real estate investments related to non-cash property acquisition	0	0	(66,324)
Change in investments in joint venture related to non-cash acquisition of property	0	0	66,324
Change in other liabilities from contingent consideration related to a business combination	0	0	1,585
Change in operating real estate from contingent consideration related to a business combination	0	0	(1,585)
Change in other liabilities from a deferred payment related to an asset acquisition	0	0	2,000
Change in operating real estate from a deferred payment related to an asset acquisition	0	0	(2,000)
Change in real estate ventures as a result of other than temporary impairment	(4,844)	0	0
Change in operating real estate from deconsolidation of 3141 Fairview Park Drive	0	44,313	0
Change in investment in real estate ventures from deconsolidation of 3141 Fairview Park Drive	0	(12,642)	0
Change in mortgage notes payable from deconsolidation of 3141 Fairview Park Drive	0	(20,582)	0
Change in other liabilities from deconsolidation of 3141 Fairview Park Drive	0	(12,384)	0
Change in capital expenditures financed through accounts payable at period end	(6,953)	8,222	(7,654)
Change in capital expenditures financed through retention payable at period end	(159)	848	6,104
Change in unfunded tenant allowance	$ 0	$ 0	$ (273)

Consolidated Statements of Cas9

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental disclosure:
Capitalized interest	$ 3,527	$ 12,835	$ 12,150
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Supplemental disclosure:
Capitalized interest	$ 3,527	$ 12,835	$ 12,150

Consolidated Statements of Part

Consolidated Statements of Partners' Equity - USD ($) $ in Thousands	Total	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]	BRANDYWINE OPERATING PARTNERSHIP, L.P.	BRANDYWINE OPERATING PARTNERSHIP, L.P.General Partner Capital [Member]	BRANDYWINE OPERATING PARTNERSHIP, L.P.Series E-linked Preferred Stock [Member]	BRANDYWINE OPERATING PARTNERSHIP, L.P.Accumulated Other Comprehensive Income (Loss) [Member]	BRANDYWINE OPERATING PARTNERSHIP, L.P.Noncontrolling Interest [Member]	BRANDYWINE OPERATING PARTNERSHIP, L.P.Partners Equity [Member]
Beginning Balance at Dec. 31, 2014				$ 2,134,755	$ 2,041,902	$ 96,850	$ (5,007)	$ 1,010
Beginning Balance, Shares at Dec. 31, 2014					179,293,160	4,000,000
Net income (loss)	$ (30,740)		$ (339)	(30,740)	$ (30,740)			3	$ (30,737)
Other comprehensive income (loss)	(590)	$ (585)	(5)	(590)			(590)
Share Issuance from/(to) Deferred Compensation Plan	(2)			(2)	$ (2)
Share Issuance from/(to) Deferred Compensation Plan, Shares					88,146
Repurchase and retirement of LP units				(67,430)	$ (67,430)
Repurchase and retirement of LP units, Shares					(5,209,437)
Issuance of partnership interest in consolidated real estate venture				1,025				1,025
Bonus share issuance	125			125	$ 125
Bonus share issuance, Shares					8,447
Share Choice Plan Issuance, Shares					(1,423)
Share-based compensation activity	5,097			5,097	$ 5,097
Share-based compensation activity, Shares					509,675
Adjustment of redeemable partnership units to liquidation value at period end				1,533	$ 1,533
Reallocation of Noncontrolling Interest			(93)		6			(6)
Preferred Share distributions	(6,900)			(6,900)	(6,900)
Preferred share redemption charge	0			0
Distributions declared to general partnership unitholders				(106,899)	(106,899)
Ending Balance at Dec. 31, 2015				1,929,977	$ 1,836,692	$ 96,850	(5,597)	2,032
Ending Balance, Shares at Dec. 31, 2015					174,688,568	4,000,000
Net income (loss)	40,501		310	40,501	$ 40,486			15
Other comprehensive income (loss)	3,475	3,447	28	3,475			3,475
Share Issuance from/(to) Deferred Compensation Plan	(47)			(47)	$ (47)
Share Issuance from/(to) Deferred Compensation Plan, Shares					(8,311)
Issuance of partnership interest in consolidated real estate venture	108		108	109				109
Conversion of LP Units to Common Shares			(875)	875	$ 875
Conversion of LP Units to Common Shares, Shares					55,303
Share-based compensation activity	5,764			5,763	$ 5,763
Share-based compensation activity, Shares					405,200
Adjustment of redeemable partnership units to liquidation value at period end				(2,622)	$ (2,622)
Reallocation of Noncontrolling Interest			297		6			(6)
Redemption value of limited partnership units				(875)	(875)
Preferred Share distributions	(6,900)			(6,900)	(6,900)
Preferred share redemption charge	0			0
Distributions declared to general partnership unitholders				(110,614)	(110,614)
Ending Balance at Dec. 31, 2016				1,859,642	$ 1,762,764	$ 96,850	(2,122)	2,150
Ending Balance, Shares at Dec. 31, 2016					175,140,760	4,000,000
Net income (loss)	121,859		1,009	121,859	$ 121,830			29
Other comprehensive income (loss)	4,178	$ 4,144	34	4,178			4,178
Redemption of Preferred Mirror Units				(96,850)		$ (96,850)
Redemption of Preferred Mirror Units, Shares						(4,000,000)
Share Issuance from/(to) Deferred Compensation Plan	(768)			(768)	$ (768)
Share Issuance from/(to) Deferred Compensation Plan, Shares					(52,971)
Issuance of LP Units				50,726	$ 50,726
Issuance of LP Units, Shares					2,858,991
Issuance of partnership interest in consolidated real estate venture	85		85	85				85
Distributions from consolidated real estate venture	48		48	(48)				(48)
Bonus share issuance	110			110	$ 110
Bonus share issuance, Shares					6,752
Share Choice Plan Issuance, Shares					(1,423)
Share-based compensation activity	6,697			6,697	$ 6,697
Share-based compensation activity, Shares					333,127
Adjustment of redeemable partnership units to liquidation value at period end				(4,100)	$ (4,099)			(1)
Reallocation of Noncontrolling Interest			$ 224
Preferred Share distributions	(2,032)			(2,032)	(2,032)
Preferred share redemption charge	$ (3,181)			(3,181)	(3,181)
Distributions declared to general partnership unitholders				(116,636)	(116,636)
Ending Balance at Dec. 31, 2017				$ 1,819,682	$ 1,815,411		$ 2,056	$ 2,215
Ending Balance, Shares at Dec. 31, 2017					178,285,236

Consolidated Statements of Pa11

Consolidated Statements of Partners' Equity (Parenthetical) - BRANDYWINE OPERATING PARTNERSHIP, L.P. - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distributions to general partnership unitholders (USD per share)	$ 0.66	$ 0.63	$ 0.60
General Partner Capital [Member]
Distributions to general partnership unitholders (USD per share)	$ 0.66	$ 0.63	$ 0.60

Organization of the Parent Comp

Organization of the Parent Company and The Operating Partnership	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
ORGANIZATION OF THE PARENT COMPANY AND THE OPERATING PARTNERSHIP	1. ORGANIZATION OF THE PARENT COMPANY AND THE OPERATING PARTNERSHIP The Parent Company is a self-administered and self-managed real estate investment trust (“REIT”) that provides leasing, property management, development, redevelopment, acquisition and other tenant-related services for a portfolio of office, residential, retail and mixed-use properties. The Parent Company owns its assets and conducts its operations through the Operating Partnership and subsidiaries of the Operating Partnership. The Parent Company is the sole general partner of the Operating Partnership and, as of December 31, 2017, owned a 99.2% interest in the Operating Partnership. The Parent Company’s common shares of beneficial interest are publicly traded on the New York Stock Exchange under the ticker symbol “BDN.” As of December 31, 2017 93 16.4 81 five one 87 two four 2017 13 6.7 ubsequent to December 31, 2017, the Company completed transactions that reduced our interests in Real Estate Ventures and, as of the date of this Form 10-K, the Company owns interests in ten Real Estate Ventures. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. In addition to the Core Properties, a s of December 31, , the Company owned land held for development, comprised of 212 acres of undeveloped land, of which 13.1 acres were held for sale, and held options to purchase approximately 60 additional acres of undeveloped land. As of December 31, 2017, the total potential development that these land parcels could support, including the parcels under option, under current zoning and entitlements, amounted to an estimated 14.8 million square feet, of which 0.1 million square feet relates to the 13.1 acres held for sale. The Properties and the properties owned by the Real Estate Ventures are located in or near Philadelphia, Pennsylvania; Metropolitan Washington, D.C.; Southern New Jersey; Richmond, Virginia; Wilmington, Delaware and Austin, Texas. In addition to managing properties that the Company owns, as of December 31, 2017, the Company was managing approximately 8.8 million net rentable square feet of office and industrial properties for third parties and Real Estate Ventures. All references to building square footage, rentable square feet, acres, occupancy percentage the number of buildings and tax basis are unaudited. The Company conducts its third-party real estate management services business primarily through six management companies (collectively, the “Management Companies”): Brandywine Realty Services Corporation (“BRSCO”), BTRS, Inc. (“BTRS”), Brandywine Properties I Limited, Inc. (“BPI”), BDN Brokerage, LLC (“BBL”), Brandywine Properties Management, L.P. (“BPM”) and Brandywine Brokerage Services, LLC (“BBS”). BRSCO, BTRS and BPI are each a taxable REIT subsidiary. As of December 31, 2017, the Operating Partnership owns, directly and indirectly, 100% of each of BRSCO, BTRS, BPI, BBL, BPM and BBS. As of December 31, 2017, the Management Companies were managing properties containing an aggregate of approximately 25.2 million net rentable square feet, of which approximately 16.4 million net rentable square feet related to Properties owned by the Company and approximately 8.8 million net rentable square feet related to properties owned by third parties and Real Estate Ventures.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Out of Period Adjustment The Company recorded $1.2 million of impairment charges during the quarter ended December 31, 2016, which should have been recorded in the consolidated financial statements for the three-month period ended March 31, 2017 and the year ended December 31, 2017. Management concluded that these misstatements were not material to any prior period, nor were they material to the consolidated financial statements as of and for the twelve-month periods ended December 31, 2017 and 2016. Reclassifications During the first quarter of 2017, the Company adopted ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which requires the Company to reclassify employer tax payments on account of employee tax withholdings on share-based awards from operating activities to financing activities in the consolidated statement of cash flows. As a result of the adoption, $0.9 million and $2.1 million of cash outflows have been reclassified in the consolidated statements of cash flows for the years ended December 31, 2016 and 2015, respectively, from operating activities to financing activities. There was no other impact from the adoption of this guidance. Principles of Consolidation The Company consolidates variable interest entities (“VIEs”) in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have a controlling financial interest. The primary beneficiary is defined by the entity having both of the following characteristics: (i) the power to direct those matters that most significantly impact the activities of the VIE and (ii) the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE. For entities that the Company has the obligations to fund losses, its maximum exposure to loss is not limited to the carrying amount of its investments. As of December 31, 2017, the Company’s unconsolidated real estate ventures had aggregate indebtedness to third parties of $768.9 million. These loans are generally mortgage or construction loans, most of which are non-recourse to the Company. As of December 31, 2017, the loans for which there is recourse to the Company consists of the following: (i) a $55.4 million payment guaranty on the term loan for evo at Cira (guarantee cancelled upon the disposition of the Company’s interest in evo at Cira subsequent to December 31, 2017. See Note 20, “Subsequent Events,” When an entity is not deemed to be a VIE, the Company consolidates entities for which it has significant decision making control over the entity’s operations. The Company’s judgement with respect to its level of influence or control of an entity involves consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as managing member. The Company continuously assesses its determination of the primary beneficiary for each entity and assesses reconsideration events that may cause a change in the original determinations. The portion of the consolidated entities that are not owned by the Company is presented as noncontrolling interest as of and during the periods consolidated. All intercompany transactions have been eliminated in consolidation. As of December 31, 2017 and 2016, the Company included in its consolidated balance sheets consolidated VIEs having total assets of $412.9 million and $417.1 million, respectively, and total liabilities of $250.4 million and $254.6 million, respectively. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Management makes significant estimates regarding revenue, valuation of real estate and related intangible assets and liabilities, impairment of long-lived assets, land held for development, allowance for doubtful accounts and deferred costs. Operating Properties Operating properties are carried at historical cost less accumulated depreciation and impairment losses. The value of operating properties reflects their purchase price or development cost. Acquisition costs related to business combinations are expensed as incurred, whereas the costs related to asset acquisitions are capitalized as incurred. Costs incurred for the renovation and betterment of an operating property are capitalized to the Company’s investment in that property. Ordinary repairs and maintenance are expensed as incurred. Purchase Price Allocation For acquisitions of real estate or in-substance real estate that are accounted for as business combinations, we recognize the assets acquired (including the intangible value of acquired above- or below-market leases, acquired in-place leases, tenant relationships, and other intangible assets or liabilities), liabilities assumed, noncontrolling interests, and previously existing ownership interests at fair value as of the acquisition date. Any excess (deficit) of the consideration transferred relative to the fair value of the net assets acquired is accounted for as goodwill (bargain purchase gain). Acquisition costs related to business combinations are expensed as incurred. Acquisitions of real estate and in-substance real estate that do not meet the definition of a business are accounted for as asset acquisitions. The accounting model for asset acquisitions is similar to the accounting model for business combinations except that the acquisition consideration (including acquisition costs) is allocated to the individual assets acquired and liabilities assumed on a relative fair value basis. As a result, asset acquisitions do not result in recognition of goodwill or a bargain purchase gain. Additionally, because the accounting model for asset acquisitions is a cost accumulation model, preexisting interests in the acquired assets, if any, are not remeasured to fair value but continue to be accounted for at their historical cost. Direct acquisition costs are capitalized if an asset acquisition is probable. If we determine that an asset acquisition is no longer probable, no new costs are capitalized and all capitalized costs that are not recoverable are written off. The Company allocates the purchase price of properties considered to be business combinations and asset acquisitions to net tangible and identified intangible assets acquired based on fair values. Above-market and below-market in-place lease values for acquired properties are recorded based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases and (ii) the Company’s estimate of the fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining non-cancelable term of the lease (including the below market fixed renewal period, if applicable). Capitalized above-market lease values are amortized as a reduction of rental income over the remaining non-cancelable terms of the respective leases. Capitalized below-market lease values are amortized as an increase to rental income over the remaining non-cancelable terms of the respective leases, including any below market fixed-rate renewal option periods that are considered probable. Other intangible assets also include in-place leases based on the Company’s evaluation of the specific characteristics of each tenant’s lease and the Company’s overall relationship with the respective tenant. The Company estimates the cost to execute leases with terms similar to the remaining lease terms of the in-place leases, including leasing commissions, legal and other related expenses. This intangible asset is amortized to expense over the remaining term of the respective leases and any fixed-rate bargain renewal periods. Company estimates of value are made using methods similar to those used by independent appraisers or by using independent appraisals. Factors considered by the Company in this analysis include an estimate of the carrying costs during the expected lease-up periods considering current market conditions and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rents at market rates during the expected lease-up periods, which primarily range from four to twelve months. The Company also considers information obtained about each property as a result of its pre-acquisition due diligence, marketing and leasing activities in estimating the fair value of the tangible and intangible assets acquired. The Company also uses the information obtained as a result of its pre-acquisition due diligence as part of its consideration of the accounting standard governing asset retirement obligations and when necessary, will record a conditional asset retirement obligation as part of its purchase price. The Company also evaluates tenant relationships on a tenant-specific basis. On most of the Company’s acquisitions, this intangible has been deemed immaterial, in which case no related intangible asset value is assigned. In the event that a tenant terminates its lease, the unamortized portion of each intangible, including in-place lease values and tenant relationship values, is charged to expense and market rate adjustments (above or below) is recorded to revenue. The Company records development acquisitions that do not meet the accounting criteria to be accounted for as business combinations at the purchase price paid. Costs directly associated with development acquisitions accounted for as asset acquisitions are capitalized as part of the cost of the acquisition. Depreciation and Amortization The costs of buildings and improvements are depreciated using the straight-line method based on the following useful lives: buildings and improvements (5 to 55 years) and tenant improvements (the shorter of (i) the life of the asset, 1 to 16 years, or (ii) the lease term). Construction-in-Progress Project costs directly associated with the development and construction of a real estate project are capitalized as construction-in-progress. Construction-in-progress also includes costs related to ongoing tenant improvement projects. In addition, interest, real estate taxes and other expenses that are directly associated with the Company’s development activities are capitalized until the property is placed in service. Interest expense is capitalized using the Company’s weighted average interest rate. Internal direct costs are capitalized to projects in which qualifying expenditures are being incurred. Internal direct construction costs totaling $6.1 million in 2017, $6.7 million in 2016, $7.3 million in 2015 and interest totaling $3.1 million in 2017, $10.9 million in 2016, and $10.2 million in 2015 were capitalized related to the development of certain properties and land holdings. During the years ended December 31, 2017, 2016 and 2015, the Company’s internal direct construction costs are comprised entirely of capitalized salaries. The following table shows the amount of compensation costs (including bonuses and benefits) capitalized for the years presented (in thousands): December 31, 2017 2016 2015 Development $ 4,390 $ 3,182 $ 2,641 Redevelopment 319 144 221 Tenant Improvements 1,354 3,391 4,429 Total $ 6,063 $ 6,717 $ 7,291 Impairment or Disposal of Long-Lived Assets The Company reviews its long-lived assets for impairment following the end of each quarter using cash flow projections and estimated fair values for each of its properties where events or changes in circumstances indicate that the carrying amounts may not be recoverable. The Company updates leasing and other assumptions regularly, paying particular attention to properties where there is an event or change in circumstances that indicate an impairment in value. Additionally, the Company considers strategic decisions regarding the future development plans for property under development and other market factors. For long-lived assets to be held and used, the Company analyzes recoverability based on the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the assets over, in most cases, a 10-year hold period. If there is significant possibility that the Company will dispose of assets earlier, it analyzes the recoverability using a probability weighted analysis of the undiscounted future cash flows expected to be generated from the operations and eventual disposition of each asset using various probable hold periods. If the recovery analysis indicates that the carrying value of the tested property is not recoverable, the property is written down to its fair value and an impairment loss is recognized. In such case, an impairment loss is recognized in the amount of the excess of the carrying amount of the asset over its fair value. If and when the Company’s plans change, it revises its recoverability analysis to use cash flows expected from operations and eventual disposition of each asset using hold periods that are consistent with its revised plans. Estimated cash flows used in such analysis are based on the Company’s plans for the property and its views of market economic conditions. The estimates consider factors such as current and future rental rates, occupancies for the tested property and comparable properties, estimated operating and capital expenditures and recent sales data for comparable properties; most of these factors are influenced by market data obtained from real estate leasing and brokerage firms and the Company’s direct experience with the properties and their markets. The Company generally considers assets to be “held for sale” when the transaction has been approved by its Board of Trustees, or by officers vested with authority to approve the transaction, and there are no known significant contingencies relating to the sale of the property within one year of the consideration date and the consummation of the transaction is otherwise considered probable. When a property is designated as held for sale, the Company stops depreciating the property and estimates the property’s fair value, net of selling costs. If the determination is made that the estimated fair value, net of selling costs, is less than the net carrying value of the property, an impairment loss is recognized, reducing the net carrying value of the property to estimated fair value less selling costs. For periods in which a property is classified as held for sale, the Company classifies the assets and liabilities, as applicable, of the property as “held for sale” on the consolidated balance sheet for such periods. The relevant accounting guidance for impairments requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the disposal represents a strategic shift that has, or will have, a major effect on the Company’s operations and financial results. The components of the property’s net income that is reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan). Impairment of Land Held for Development When demand for build-to-suit office space declines and the ability to sell land held for development deteriorates, or other market factors indicate possible impairment in the recoverability of land held for development, it is reviewed for impairment by comparing its fair value to its carrying value. If the estimated sales value is less than the carrying value, the carrying value is written down to its estimated fair value. Cash and Cash Equivalents Cash and cash equivalents are highly-liquid investments with original maturities of three months or less. The Company maintains cash equivalents in money market accounts with financial institutions in excess of insured limits, but believes this risk is mitigated by only investing in or through major financial institutions. The Company does not invest its available cash balances in money market funds, as such available cash balances are appropriately reflected as cash and cash equivalents on its consolidated balance sheet. Restricted Cash Restricted cash consists of cash held as collateral to provide credit enhancement for the Company’s mortgage debt, cash for property taxes, capital expenditures and tenant improvements. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code in connection with sales of the Company’s properties. Restricted cash is included in the “Other assets” caption in the consolidated balance sheets. Accounts Receivable and Accrued Rent Receivable Generally, leases with tenants are accounted for as operating leases. Minimum annual rentals under tenant leases are recognized on a straight-line basis over the term of the related lease. The cumulative difference between lease revenue recognized under the straight-line method and contractual lease payment terms are recorded as “Accrued rent receivable, net” on the accompanying consolidated balance sheets. Included in current tenant receivables are tenant reimbursements which are comprised of amounts recoverable from tenants for common area maintenance expenses and certain other recoverable expenses that are recognized as revenue in the period in which the related expenses are incurred. As of December 31, 2017 and 2016, no tenant represented more than 10% of accounts receivable and accrued rent receivable. Tenant receivables and accrued rent receivables are carried net of the allowances for doubtful accounts of $3.5 million and $13.6 million in 2017, respectively, and $2.4 million and $13.7 million in 2016, respectively. The tenant receivables allowance is an estimate based on two calculations that are combined to determine the total amount reserved. First, the Company evaluates specific accounts where it has determined that a tenant may have an inability to meet its financial obligations. In these situations, the Company uses its judgment, based on the facts and circumstances, and records a specific reserve for that tenant against amounts due to reduce the receivable to the amount that the Company expects to collect. These reserves are reevaluated and adjusted as additional information becomes available. Second, a reserve is established for all tenants based on a range of percentages applied to receivable aging categories for tenant receivables. For accrued rent receivables, the Company considers the results of the evaluation of specific accounts and also considers other factors including assigning risk factors to different industries based on its tenants Standard Industrial Classification (SIC). The accrued rent receivable allowance percentages are also based on historical collection and write-off experience adjusted for current market conditions, which requires management’s judgments. Investments in Unconsolidated Real Estate Ventures Under the equity method, investments in unconsolidated Real Estate Ventures are recorded initially at cost, as Investments in unconsolidated Real Estate Ventures, and subsequently adjusted for equity in earnings, cash contributions, distributions and impairments. For Real Estate Ventures that are constructing assets to commence planned principal operations, the Company capitalizes interest expense using the Company’s weighted average interest rate of consolidated debt and its investment balance as a basis. Planned principal operations commence when a property is available to lease and at that point in time, the Company ceases capitalizing interest to its investment basis. During the twelve months ended December 31, 2017, 2016 and 2015, the Company capitalized interest expense of $0.4 million, $1.9 million and $2.0 million. On a periodic basis, management also assesses whether there are any indicators that the value of the Company’s investments in unconsolidated Real Estate Ventures may be other than temporarily impaired. An investment is impaired only if the value of the investment, as estimated by management, is less than the carrying value of the investment and the decline is other than temporary. To the extent that an impairment has occurred, the loss shall be measured as the excess of the carrying amount of the investment over the fair value of the investment, as estimated by management. Management is required to make significant judgements about the fair value of its ownership interests to determine if an impairment exists. Fair value is determined through various valuation techniques, including but not limited to, discounted cash flow models, quoted market values and third party appraisals. When the Company acquires an interest in or contributes assets to a real estate venture project, the difference between the Company’s cost basis in the investment and the value of the real estate venture or asset contributed is amortized over the life of the related assets, intangibles and liabilities and such adjustment is included in the Company’s share of equity in income of unconsolidated Real Estate Ventures. For purposes of cash flow presentation, distributions from unconsolidated Real Estate Ventures are presented as part of operating activities when they are considered as a return on investments. The Company elected, in connection with its adoption of ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15) during the fourth quarter of 2016, to continue to account for Deferred Costs Costs incurred in connection with property leasing are capitalized as deferred leasing costs. Deferred leasing costs consist primarily of leasing commissions and internal leasing costs that are amortized using the straight-line method over the life of the respective lease which generally ranges from 1 to 16 years. Management re-evaluates the remaining useful lives of leasing costs as economic and market conditions change. Notes Receivable The Company accounts for notes receivable on its balance sheet at amortized cost, net of allowance for loan losses. Interest income is recognized over the term of the notes receivable and is calculated based on the terms of the contractual terms of each note agreement. Notes receivable are placed on nonaccrual status when management determines, after considering economic and business conditions and collection efforts, that the loans are impaired or collection of interest is doubtful. Uncollectible interest previously accrued is recognized as bad debt expense. Interest income on nonaccrual loans is recognized only to the extent that cash payments are received. A note receivable was given to an unaffiliated third party during the third quarter of 2016 to facilitate its acquisition and development of an industrial facility located in Pennsauken, New Jersey. The loan matures three years after the payment commencement date, which is 90 days after substantial completion of the development, and bears interest at 6.3% during year one, 7.0% during year two and 8.0% during year three. The Company evaluated its investment in the note receivable under ASC 310, “Receivables” and determined that the loan was provided at market terms and the Company does not participate in the residual profit of the unaffiliated third party. Accordingly, the investment, totaling $3.5 million as of December 31, 2017 and $3.4 million as of December 31, 2016, has been classified on the Company’s balance sheet as a note receivable within the “Other assets” caption on the accompanying consolidated balance sheets. Deferred Financing Costs Costs incurred in connection with debt financing are capitalized as a direct deduction from the carrying value of the debt, except for costs capitalized related to the Company’s revolving credit facility, which are capitalized within the “Deferred costs, net” caption on the accompanying consolidated balance sheets. Deferred financing costs are charged to interest expense over the terms of the related debt agreements. Deferred financing costs consist primarily of loan fees which are amortized over the related loan term on a basis that approximates the effective interest method. Deferred financing costs are accelerated, when debt is extinguished, as part of the “Interest expense-amortization of deferred financing costs” caption within the Company’s consolidated statements of operations. Original issue discounts are recognized as part of the gain or loss on extinguishment of debt, as appropriate. Revenue Recognition Rental revenue is recognized on the straight-line basis, which averages minimum rent over the terms of the lease from the later of the date of the commencement of the lease or the date of acquisition of the property subject to existing leases. The straight-line rent adjustment increased revenue by approximately $24.9 million in 2017, $26.3 million in 2016 and $21.6 million in 2015. Deferred rents on the balance sheet represent rental revenue received prior to their due dates and amounts paid by the tenant for certain improvements considered to be landlord assets that will remain as the Company’s property at the end of the tenant’s lease term. The amortization of the amounts paid by the tenant for such improvements is calculated on a straight-line basis over the term of the tenant’s lease and is a component of straight-line rental income and increased revenue by $2.2 million in 2017, $2.1 million in 2016 and $2.0 million in 2015. Lease incentives, which are included as reductions of rental revenue in the accompanying consolidated statements of operations, are recognized on a straight-line basis over the term of the lease. Lease incentives decreased revenue by $1.8 million in 2017, $2.0 million in 2016 and $1.8 million in 2015. In addition, the Company’s rental revenue is impacted by the Company’s determination of whether improvements to the properties, whether made by the Company or by the tenant, are landlord assets. The determination of whether an improvement is a landlord asset requires judgment. In making this judgment, the Company’s primary consideration is whether the improvement would be utilizable by another tenant upon move out of the improved space by the then-existing tenant. If the Company has funded an improvement that it determines not to be landlord assets, then it treats the cost of the improvement as a lease incentive. If the tenant has funded the improvement that the Company determines to be landlord assets, then the Company treats the costs of the improvement as deferred revenue and amortizes this cost into revenue over the lease term. For certain leases, the Company makes significant assumptions and judgments in determining the lease term, including assumptions when the lease provides the tenant with an early termination option. The lease term impacts the period over which the Company determines and records minimum rents and also impacts the period over which the Company amortizes lease-related costs. The Company’s leases also typically provide for tenant reimbursement of a portion of common area maintenance expenses and other operating expenses to the extent that a tenant’s pro rata share of expenses exceeds a base year level set in the lease or to the extent that the tenant has a lease on a triple net basis. Recoveries from tenants, consisting of amounts due from tenants for common area maintenance expenses, real estate taxes and other recoverable costs are recognized as revenue in the period during which the expenses are incurred. Tenant reimbursements are recognized and presented in accordance with accounting guidance which requires that these reimbursements be recorded on a gross basis because the Company is generally the primary obligor with respect to the goods and services the purchase of which gives rise to the reimbursement obligation; because the Company has discretion in selecting the vendors and suppliers; and because the Company bears the credit risk in the event they do not reimburse the Company. The Company also receives payments from third parties for reimbursement of a portion of the payroll and payroll-related costs for certain of the Company’s personnel allocated to perform services for these third parties and reflects these payments on a gross basis. The Company recognizes gains on sales of real estate at times and in amounts determined in accordance with the accounting guidance for sales of real estate. The guidance takes into account the terms of the transaction and any continuing involvement, including in the form of management, leasing of space or financial assistance associated with the properties. If the sales criteria for the full accrual method are not met, then the Company defers some or all of the gain recognition and accounts for the continued operations of the property by applying the finance, leasing, profit sharing, deposit, installment or cost recovery method, as appropriate, until the sales criteria are met. The Company derives parking revenues from leases, monthly parking and transient parking. The Company recognizes parking revenue as earned. The Company’s flexible stay revenue consists of room revenue, food and beverage revenue, and revenue from other hotel operating departments (such as parking fees and other guest service fees). These revenues are recorded net of any sales and occupancy taxes collected from the hotel guests. All rebates or discounts are recorded as a reduction to revenue, and there are no material contingent obligations with respect to rebates and discounts offered by the hotel. All revenues are recorded on an accrual basis as they are earned. Any cash received prior to a guest’s arrival is recorded as an advance deposit from the guest and recognized as revenue at the time of the guest's occupancy at the hotel property. The Company receives leasing commission income, property management fees and third party development fees. Leasing commission income is earned based on a percentage of gross rental income upon a tenant signing a lease with a third party lessor. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis because such fees are contingent upon the collection of rents. The Company records development fees on a percentage of completion basis taking into account the risk associated with each project. The Company recognizes fees received for lease terminations as revenue and writes off against such revenue any deferred rents receivable. The resulting net amount is the net revenue from the early termination of the leases. When a tenant's lease for space in a property is terminated early but the tenant continues to lease such space under a new or modified lease in the property, the net revenue from the early termination of the lease is recognized evenly over the remaining life of the new or modified lease in place on that property, unless the Company cannot determine that collectability of the lease termination revenue is reasonably assured. No tenant represented greater than 10% of the Company’s rental revenue in 2017, 2016 or 2015. Income Taxes Parent Company The Parent Company has elected to be t

Real Estate Investments

Real Estate Investments	12 Months Ended
	Dec. 31, 2017
Real Estate [Abstract]
REAL ESTATE INVESTMENTS	3. REAL ESTATE INVESTMENTS As of December 31, 2017 and 2016 the gross carrying value of the Company’s Properties was as follows (in thousands): December 31, December 31, 2017 2016 Land $ 492,197 $ 469,522 Building and improvements 2,896,113 2,683,087 Tenant improvements 444,038 433,686 Operating properties 3,832,348 3,586,295 Assets held for sale - real estate investments (a) - 73,591 Total $ 3,832,348 $ 3,659,886 (a) Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation, land held for development or other assets on the balance sheets of the properties held for sale. See 2016 Held for Sale section below. Acquisitions and Dispositions 2017 Acquisitions On October 13, 2017, the Company acquired, through a 99-year prepaid ground lease, the leasehold interest in an office property containing 282,709 rentable square feet located at 3025 Market Street in Philadelphia, Pennsylvania, known as One Drexel Plaza, for a gross purchase price of $35.0 million. The purchase of One Drexel Plaza is an asset acquisition under ASU 2017-01. The Company utilized a number of sources in making estimates of fair value for purposes of allocating the purchase price to tangible and intangibles assets acquired. October 13, 2017 Building and improvements $ 30,583 Construction-in-progress 672 Intangible assets acquired (a) 10,575 Below market lease liabilities assumed (b) (4,055 ) $ 37,775 (a) (b) One Drexel Plaza contributed approximately $1.2 million of revenue and approximately $0.4 million of net loss in the Company’s consolidated statements of operations, for the period from October 13, 2017 through December 31, 2017. On July 28, 2017, the Company acquired an office building containing 58,587 rentable square feet located at 3000 Market Street, in Philadelphia, Pennsylvania, for $32.7 million. The acquisition was the Section 1031 exchange receiver for the sale of Concord Airport Plaza. See property disposition table below. The purchase of 3000 Market Street is an asset acquisition under ASU 2017-01. As such, the Company capitalized $0.7 million of acquisition-related costs and allocated the purchase price, consisting of the contractual purchase price of $32.0 million and the acquisition related costs, to the tangible and intangible assets. The Company utilized a number of sources in making estimates of fair value for purposes of allocating the purchase price to tangible and intangibles assets acquired. The purchase price has been allocated as follows (in thousands): July 28, 2017 Building, land and improvements $ 32,004 Intangible assets acquired (a) 2,562 Below market lease liabilities assumed (b) (1,818 ) $ 32,748 (a) (b) 3000 Market Street contributed approximately $0.8 million of revenue and a $0.5 million of net loss in the Company’s consolidated statements of operations, for the period from July 28, 2017 through December 31, 2017. Dispositions The Company sold the following properties during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Type Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) November 22, 2017 11, 14, 15, 17 and 18 Campus Boulevard (Newtown Square) Newtown Square, PA Office 5 252,802 $ 42,000 $ 40,459 $ 19,642 October 31, 2017 630 Allendale Road King of Prussia, PA Office 1 150,000 17,500 16,580 3,605 June 27, 2017 Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) Marlton, NJ Office 4 134,794 9,700 8,650 (325 ) (b) June 12, 2017 7000 Midlantic Drive Mount Laurel, NJ Retail 1 10,784 8,200 7,714 1,413 March 30, 2017 200, 210 & 220 Lake Drive East (Woodland Falls) Cherry Hill, NJ Office 3 215,465 19,000 17,771 (249 ) (c) March 15, 2017 Philadelphia Marine Center (Marine Piers) Philadelphia, PA Mixed-use 1 181,900 21,400 11,182 6,498 (d) March 13, 2017 11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) Beltsville, MD Office 3 313,810 9,000 8,354 - (e) February 2, 2017 1200 & 1220 Concord Avenue (Concord Airport Plaza) Concord, CA Office 2 350,256 33,100 32,010 551 (f) Total Dispositions 20 1,609,811 $ 159,900 $ 142,720 $ 31,135 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, which reduced the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (c) As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (d) On March 15, 2017, the Company sold its sublease interest in the Piers at Penn’s Landing (the “Marine Piers”), which includes leasehold improvements containing 181,900 net rentable square feet, and a marina, located in Philadelphia, Pennsylvania for an aggregate sales price of $21.4 million. On the closing date, the buyer paid $12.0 million in cash. The $9.4 million balance of the purchase is due on (a) January 31, 2020, in the event that the tenant at the Marine Piers does not exercise an option it holds to extend the term of the sublease or (b) January 15, 2024, in the event that the tenant does exercise the option to extend the term of the sublease. In accordance with ASC 360-20, “Real Estate Sales,” the Company determined that it is appropriate to account for the sales transaction under the cost recovery method. The Company received cash proceeds of $11.2 million, after closing costs and prorations, and the net book value of the Marine Piers was $4.7 million, resulting in a gain on sale of $6.5 million. The remaining gain on sale of $9.4 million will be recognized on the second purchase price installment date. Prior to its sale, the Marine Piers had been classified as mixed-use within the Company’s property count. (e) During the fourth quarter of 2016, the Company recognized a $3.0 million impairment related to these properties. During the first quarter of 2017, there was a price reduction of $1.7 million under the agreement of sale and an additional impairment of $1.7 million was recognized. (f) During the fourth quarter of 2016, the Company recognized an $11.5 million impairment related to these properties. This sale was designated as a like-kind exchange under Section 1031 of the Internal Revenue Code (“IRC”) and, as such, the proceeds, totaling $32.0 million after closing costs and prorations, were deposited with a Qualified Intermediary, as defined under the IRC. The proceeds received at closing were recorded as “Other assets” in the Company’s consolidated balance sheets. During the third quarter of 2017, the Company acquired 3000 Market Street in Philadelphia, Pennsylvania using the full balance of the Section 1031 proceeds. See “Acquisition” section above. In addition to the amounts in the table above, the Company recorded a $0.5 million gain during the first quarter of 2017 from the receipt of additional proceeds from the disposition of Cira Square in 2016. For further information relating to this sale, see the dispositions table in the 2016 section below. The Company sold the following land parcels during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale September 13, 2017 50 E. Swedesford Square Malvern, PA 1 12.0 $ 7,200 $ 7,098 $ 882 July 18, 2017 Bishop's Gate Mount Laurel, NJ 1 49.5 6,000 5,640 71 (a) April 28, 2017 Garza Ranch - Multi-family Austin, TX 1 8.4 11,800 11,560 - (b) February 15, 2017 Gateway Land - Site C Richmond, VA 1 4.8 1,100 1,043 - (c) January 30, 2017 Garza Ranch - Hotel Austin, TX 1 1.7 3,500 3,277 - (b) Total Dispositions 5 76.4 $ 29,600 $ 28,618 $ 953 (a) During the fourth quarter of 2016, the Company recognized an impairment of $3.0 million. During the second quarter of 2017, the Company recorded a held for sale impairment charge of $0.3 million, reducing the aggregate carrying value of the land parcel from $5.9 million to its estimated fair value less costs to sell of $5.6 million. The fair value measurement is based on pricing in the purchase and sale agreement for the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the input utilized to determine fair value for the property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The land parcel was sold on July 18, 2017. (b) The Company has a continuing involvement in this property through a completion guaranty, which requires the Company, as developer, to complete certain infrastructure improvements on behalf of the buyers of the land parcels. The Company recorded the cash received at settlement as “Deferred income, gains and rent” on the Company’s consolidated balance sheet and the Company will recognize the sale upon completion of infrastructure improvements. See Note 19, “ Commitments and Contingencies ” for further discussion of the infrastructure improvements. (c) During the fourth quarter of 2016, the Company recognized a nominal impairment related to this land parcel. The sales of properties, land and the land parcel held for sale do not represent a strategic shift that has a major effect on the Company's operations and financial results. Accordingly, the operating results of these properties remain classified within continuing operations for all periods presented. Held for Use Impairment As of December 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment. Based on the analysis, no impairment charges were identified during the three-month period ended December 31, 2017. As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered an assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, reflected in the results for the twelve-month period ended December 31, 2017, reducing the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” Land Impairment As of December 31, 2017, the Company evaluated the recoverability of the carrying value of its land parcels that triggered assessment. Based on the analysis, no impairment charges were identified during the three-month period ended December 31, 2017. See above land disposition table for detail of the Bishop’s Gate land parcel, on which a $0.3 million impairment charge was recorded as of June 30, 2017. Held for Sale As of December 31, 2017, the Company had land held for development, consisting of a 13.1-acre parcel of land located in the Company’s Other segment, classified as held for sale but which did not meet the criteria to be classified within discontinued operations. Accordingly, as of December 31, 2017, $0.4 million was reclassified from ‘Land held for development’ to ‘Assets held for sale, net’ on the consolidated balance sheets. There were no other reclassifications related to this parcel of land. As of December 31, 2017, the carrying value of the land was less than the fair value less the anticipated costs of sale and, as such, the Company expects to record a nominal gain on sale. The fair value measurement is based on the pricing in the purchase and sale agreement. The sale of the Company’s fee interest in the property referenced above does not represent a strategic shift that has a major effect on the Company's operations and financial results. As a result, the operating results of this property remains classified within continuing operations for all periods presented. See Note 20, " Subsequent Events, 2016 Acquisition On July 1, 2016, the Company closed on the acquisition of 34.6 acres of land located in Austin, Texas known as the Garza Ranch for a gross purchase price of $20.6 million. The Company accounted for this transaction as an asset acquisition and capitalized approximately $1.9 million of acquisition related costs and closing costs as part of land held for development on its consolidated balance sheet. The Company funded the acquisition with $20.4 million of available corporate funds, net of prorations and other adjustments. As of December 31, 2017, the Company sold 9.5 acres (of the 34.6 acres) to two unaffiliated third parties. As of December 31, 2016, the land under this agreement of sale did not meet the criteria to be classified as held for sale. The Company has a continuing involvement through a completion guaranty, which requires the Company, as developer, to complete certain infrastructure improvements on behalf of the buyers of the land parcels. See “2017” section above for information related to the sale of 1.7 acres. Dispositions The Company sold the following properties during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) October 13, 2016 620, 640, 660 Allendale Road King of Prussia, PA 3 156,669 $ 12,800 $ 12,014 $ 2,382 September 1, 2016 1120 Executive Plaza Mt. Laurel, NJ 1 95,183 9,500 9,241 (18 ) (b) August 2, 2016 50 East Clementon Road Gibbsboro, NJ 1 3,080 1,100 1,011 (85 ) May 11, 2016 196/198 Van Buren Street (Herndon Metro Plaza I&II) Herndon, VA 2 197,225 44,500 43,412 (752 ) (c) February 5, 2016 2970 Market Street (Cira Square) Philadelphia, PA 1 862,692 354,000 350,150 115,828 February 4, 2016 Och-Ziff Portfolio Various 58 3,924,783 398,100 353,971 (372 ) (d) Total Dispositions 66 5,239,632 $ 820,000 $ 769,799 $ 116,983 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of June 30, 2016, the Company determined that the sale of the property was probable and classified this property as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the property exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized a provision for impairment totaling approximately $1.8 million during the three-month period ended June 30, 2016. The fair value measurement was based on the pricing in the purchase and sale agreement for the sale of the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the inputs utilized to determine fair value for this property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, "Fair Value Measurements and Disclosures.” The loss on sale represents additional closing costs recognized at closing. (c) During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing. (d) During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing The Company sold the following land parcels during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale (a) December 2, 2016 Oakland Lot B Oakland, CA 1 0.9 $ 13,750 $ 13,411 $ 9,039 August 19, 2016 Highlands Land Mt. Laurel, NJ 1 2.0 288 284 193 January 15, 2016 Greenhills Land Reading, PA 1 120.0 900 837 - (b) Total Dispositions 3 122.9 $ 14,938 $ 14,532 $ 9,232 (a) Gain on Sale is net of closing and other transaction related costs. (b) The carrying value of the land exceeded the fair value less the anticipated costs of sale as of December 31, 2015. Therefore the Company recognized an impairment loss of $0.3 million during the three-month period ended December 31, 2015. There was no gain or loss recognized on the sale during 2016. Held for Use Impairment As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” During the three-month period ended June 30, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered an assessment under the undiscounted cash flow model. Based on the analysis, the Company determined that due to the reduction in the Company’s intended hold period of a property located in the Metropolitan D.C. segment, the Company would not recover the carrying values of that property. Accordingly, the Company recorded an impairment charge on the property of $3.9 million at June 30, 2016, reducing the aggregate carrying value of the property from $37.4 million to its estimated fair value of $33.5 million. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rate and a discount rate of 7.75% and 8.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” During the three-month period ended March 31, 2016, the Company evaluated the recoverability of the carrying value of the properties that triggered an assessment under the undiscounted cash flow model. Based on the analysis, the Company determined that due to a reduction in the Company’s intended hold period, the Company would not recover the carrying value of two properties located in its Metropolitan D.C. segment. Accordingly, the Company recorded an impairment charge of Land Impairments As of December 31, 2016, the Company assessed the fair value of the land parcels within its Other segment that it intends to sell in the short-term and, based on that assessment, the Company determined that it would not recover the carrying value of five land parcels, consisting of 108 acres. Accordingly, the Company recorded impairment charges of $5.6 million at December 31, 2016, reducing the aggregate carrying value of the land parcels from $18.2 million to their estimated fair values of $12.6 million. The Company measured these impairments using indicative pricing in the markets in which each land parcel is located. The assumptions used to determine fair value under the market approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” Held for Sale The following is a summary of properties classified as held for sale at December 31, 2016 but which did not meet the criteria to be classified within discontinued operations at December 31, 2016 (in thousands): Held for Sale Properties Included in Continuing Operations December 31, 2016 Metropolitan D.C. - Office (a) Other Segment - Office (b) Other Segment - Land (c) Total ASSETS HELD FOR SALE Real estate investments: Operating properties $ 21,720 $ 51,871 $ - $ 73,591 Accumulated depreciation (11,935 ) (20,981 ) - (32,916 ) Operating real estate investments, net 9,785 30,890 - 40,675 Land held for development - - 1,043 1,043 Total real estate investments, net 9,785 30,890 1,043 41,718 Total assets held for sale, net $ 9,785 $ 30,890 $ 1,043 $ 41,718 LIABILITIES HELD FOR SALE Other liabilities $ 73 $ 8 $ - $ 81 Total liabilities held for sale $ 73 $ 8 $ - $ 81 (a) As of December 31, 2016, the Company determined that the sale of three office properties in the Metropolitan D.C. segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded their fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $3.0 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 10.00%, respectively. The results were comparable to indicative pricing in the market (b) As The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.75% and 9.75%, respectively. The results were comparable to indicative pricing in the market. (c) As of December 31, 2016, the Company determined that the sale of a land parcel in the Other segment was probable and classified the land parcel as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the land approximated the fair value less the anticipated costs of sale and the Company recorded a nominal impairment. The fair value measurement was based on the pricing in the purchase and sale The sales of the Company’s fee interests in the properties referenced above do not represent a strategic shift that has a major effect on the Company's operations and financial results. As a result, the operating results of these properties remain classified within continuing operations for all periods presented. See “2017” section above for further information regarding these dispositions. 2015 Acquisitions On July 7, 2015, the Company acquired a 0.8 acre parcel of land located at 2100 Market Street in Philadelphia, Pennsylvania for $18.8 million. The Company funded $16.8 million of the purchase price with available corporate funds and the remaining $2.0 million of the purchase price was funded in 2017. The Company accounted for this transaction as an asset acquisition and capitalized a nominal amount of acquisition related costs and other costs as part of land inventory on its consolidated balance sheet. In connection with the purchase agreement, if certain land parcels adjacent to 2100 Market Street are acquired from unaffiliated third parties, the Company may be required to pay additional consideration to the seller of 2100 Market Street. The unaffiliated third parties are not party to this transaction and any land parcels acquired will be acquired in arm’s length transactions. The amount of additional consideration, if any, payable to the seller of 2100 Market Street cannot be determined at this time. On June 22, 2015, through a series of transactions with International Business Machines ("IBM"), the Company acquired the remaining 50.0% interest in Broadmoor Austin Associates, consisting of seven office buildings and the 66.0 acre underlying land parcel located in Austin, Texas, for an aggregate purchase price of $211.4 million. The aggregate purchase price includes the carrying amount of the Company’s investment in Broadmoor Austin Associates of $66.3 million. The Company previously accounted for its 50.0% noncontrolling interest in Broadmoor Austin Associates under the equity method of accounting. As a result of acquiring IBM's remaining 50.0% common interest in Broadmoor Austin Associates, the Company obtained control of Broadmoor Austin Associates and the Company's existing investment balance was remeasured based on the fair value of the underlying properties acquired and the existing distribution provisions under the relevant partnership agreement. As a result, the Company recorded a $0.8 million gain on remeasurement. Broadmoor Austin Associates contributed revenue, included in the Company’s consolidated statements of operations, of $25.4 million, $26.4 million and $13.2 million and net income of $6.9 million, net losses of $5.2 million and $7.2 million for the twelve-months ended December 31, 2017, December 31, 2016 and December 31, 2015, respectively. The Company has treated its acquisition of the 50.0% ownership interest in Broadmoor Austin Associates as a business combination and allocated the purchase price to the tangible and intangible assets and liabilities. The Company utilized a number of sources in making estimates of fair values for purposes of allocating the purchase price to tangible and intangibles assets acquired and intangible liabilities assumed. The purchase price has been allocated as follows (in thousands): June 22, 2015 Building, land and improvements $ 163,271 Land inventory 6,045 Intangible assets acquired (a) 50,637 Below market lease liabilities assumed (b) (8,600 ) $ 211,353 Return of existing equity method investment (66,324 ) Gain on remeasurement (758 ) Net working capital assumed (450 ) Total cash payment at settlement $ 143,821 (a) Weighted average amortization period of 4.0 years. (b) Weighted average amortization period of 1.5 years The unaudited pro forma information below summarizes the Company’s combined results of operations for the year ended December 31, 2015 as though the acquisition of Broadmoor Austin Associates was completed on January 1, 2014. The supplemental pro forma operating data is not necessarily indicative of what the actual results of operations would have been assuming the transaction had been completed as set forth above, nor do they purport to represent the Company’s results of operations for future periods (in thousands, except for per share amounts). December 31, 2015 Pro forma revenue $ 612,649 Pro forma income (loss) from continuing operations (36,704 ) Pro forma net income (loss) available to common shareholders (43,594 ) Earnings (loss) per common share from continuing operations: Basic -- as reported $ (0.17 ) Basic -- as pro forma $ (0.21 ) Diluted -- as reported $ (0.17 ) Diluted -- as pro forma $ (0.21 ) Earnings (loss) per common share: Basic -- as reported $ (0.21 ) Basic -- as pro forma $ (0.24 ) Diluted -- as reported $ (0.21 ) Diluted -- as pro forma $ (0.24 ) On April 6, 2015, the Company acquired a 0.8 acre parcel of land, located at 25 M Street Southeast, Washington, D.C. for $20.3 million. The Company funded the cost of this acquisition with available corporate funds. The Company capitalized $0.3 million of acquisition related costs and these costs are included as part of land inventory on the Company's consolidated balance sheet. On May 12, 2015, the Company subsequently contributed the land parcel into a newly formed real estate venture known as 25 M Street Holdings, LLC (“25 M Street”), a joint venture between the Company and Jaco 25 M Investors, LLC (“Akridge”), an unaffiliated third party, with the intent to construct a 271,000 square foot Class A office property. The Company holds a 95.0% ownership interest in 25 M Street and Akridge contributed $1.0 million in cash for its 5.0% ownership interest in 25 M Street. The $1.0 million contribution from Akridge was distributed to the Company during 2015. 25 M Street is consolidated within the Company's financial statements. See Note 4, "Investment in Unconsolidated Real Estate Ventures," Based on the facts and circumstances at the formation of 25 M Street, the Company determined that 25 M Street is a variable interest entity (VIE) in accordance with the accounting standard for consolidation of VIEs. Accordingly, the Company used the variable interest model under the accounting standard for consolidation in order to determine whether to consolidate 25 M Street. Under the operating and related agreements, the Company has the power to control substantially all of the activities which most significantly impact the economics of 25 M Street, and accordingly, 25 M Street is consolidated within the Company’s financial statements. As of December 31, 2017 and December 31, 2016, the carrying value of the project, which is included in the land held for development caption of the consolidated balance sheets, was $23.1 million and $22.4 million, respectively. On April 2, 2015, the Company acquired, from an unaffiliated third party, a property located at 618 Market Street in Philadelphia, Pennsylvania, comprised of a 330-space parking garage and 14,404 net rentable square feet for $19.4 million. Although the property is currently fully operational, the Company intends to either redevelop the existing property or demolish and fully develop the property. As of December 31, 2017, the Company had not yet begun any such development or redevelopment plans. The purchase price includes contingent consideration, recorded at fair value and payable to the seller upon

Investment in Unconsolidated Re

Investment in Unconsolidated Real Estate Ventures	12 Months Ended
	Dec. 31, 2017
Equity Method Investments And Joint Ventures [Abstract]
INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES	4. INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES As of December 31, 2017, the Company held ownership interests in 13 unconsolidated Real Estate Ventures for an aggregate investment balance of $194.6 million. The Company formed or acquired interests in these Real Estate Ventures with unaffiliated third parties to develop or manage office, residential and/or mixed-use properties or to acquire land in anticipation of the possible development of office, residential and/or mixed-use properties. As of December 31, 2017, seven of the real estate ventures owned properties that contain an aggregate of approximately 6.7 million net rentable square feet of office space; three of the real estate ventures owned 4.4 acres of land held for development; one real estate venture owned 1.3 acres of land in active development; and two real estate ventures owned residential towers that contain 345 and 321 apartment units, respectively. Subsequent to December 31, 2017, the Company completed transactions that reduced its interests in Real Estate Ventures and, as of the date of this Form 10-K, the Company owns interests in ten Real Estate Ventures. See Note 20, “Subsequent Events,” The Company accounts for its unconsolidated interests in the Real Estate Ventures using the equity method. The Company’s unconsolidated interests range from 20% to 70%, subject to specified priority allocations of distributable cash in certain of the Real Estate Ventures. The Company earned management fees from its Real Estate Ventures of $6.4 million, $6.7 million and $4.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. The Company earned leasing commission income from its Real Estate Ventures of $4.5 million, $3.8 million and $2.1 million for the years ended December 31, 2017, 2016 and 2015, respectively. The Company has outstanding accounts receivable balances from its Real Estate Ventures of $0.9 million and $1.4 million for the years ended December 31, 2017 and 2016, respectively. The amounts reflected in the following tables (except for the Company’s share of equity and income) are based on the historical financial information of the individual Real Estate Ventures. The Company does not record operating losses of a Real Estate Venture in excess of its investment balance unless the Company is liable for the obligations of the Real Estate Venture or is otherwise committed to provide financial support to the Real Estate Venture. The Company’s investment in Real Estate Ventures as of December 31, 2017 and 2016, and the Company’s share of the Real Estate Ventures’ income (loss) for the years ended December 31, 2017 and 2016 was as follows (in thousands): Ownership Carrying Amount Company's Share of Real Estate Venture Income (Loss) Real Estate Venture Debt at 100% Current Interest Debt Percentage 2017 2016 2017 2016 2017 2016 Rate Maturity Office Properties Brandywine-AI Venture LLC (b) (h) 50% $ 43,560 $ 67,809 $ (4,465 ) $ (5,895 ) $ 93,117 $ 131,539 3.94 % (c) DRA (G&I) Austin (d) (h) 50% 13,972 52,886 (989 ) (1,880 ) 249,481 405,734 3.51 % (e) MAP Venture (f) 50% 15,450 20,893 (3,443 ) (4,218 ) 180,800 180,800 L+6.25% Feb 2018 (f) Four Tower Bridge (g) 65% 3,032 2,286 746 602 9,749 9,961 5.20 % Feb 2021 PJP VII 25% 1,156 980 175 233 4,792 4,956 L+2.65% Dec 2019 PJP II 30% 604 532 72 97 2,564 2,893 6.12 % Nov 2023 PJP VI 25% 179 142 38 97 7,370 7,652 6.08 % Apr 2023 1000 Chesterbrook Blvd. (h) - - - 160 - - PJP V (h) - - - 127 - - Invesco, L.P. (h) - - - 261 - - Coppell Associates - - - 12 - - Other HSRE-BDN I, LLC (d) 50% 17,671 21,228 449 843 110,886 105,000 L+2.25% Oct 2019 Brandywine 1919 Ventures (d) (i) 50% 22,268 27,462 (194 ) (1,529 ) 88,860 79,250 L+1.75% Oct 2018 TB-BDN Plymouth Apartments (h) - 12,450 99 119 - 53,967 Development Properties 4040 Wilson (j) 50% 37,179 36,356 (255 ) (270 ) 6,664 1,004 L+2.75% Dec 2021 51 N Street 70% 21,212 20,318 (176 ) (114 ) - - 1250 First Street Office 70% 17,867 17,304 (149 ) (15 ) - - Seven Tower Bridge (g) 20% 471 685 (214 ) (133 ) 14,629 14,710 3.17 % (k) $ 194,621 $ 281,331 $ (8,306 ) $ (11,503 ) $ 768,912 $ 997,466 ( a) Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable. (b) See “ Brandywine - AI Venture: 7101 Wisconsin Avenu e” and “ Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture. (c) The debt for these properties is comprised of two fixed rate mortgages: (1) $26.6 million with a 4.65% fixed interest rate due January 1, 2022, and (2) $66.5 million with a 3.22% fixed interest rate due August 1, 2019. (d) The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “ evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. (e) The debt for these properties includes three mortgages: (1) $133.6 million that was swapped to a 1.43% fixed rate (for an all-in fixed rate of 3.44% incorporating the 2.01% spread) due November 1, 2018, (2) $28.7 million with a 4.50% fixed interest rate due April 6, 2019 and (3) $87.1 million that was swapped to a 1.36% fixed rate (or all-in fixed rate of 3.36% incorporating the 2.00% spread) due February 10, 2020. On October 18, 2017, the venture sold eight office buildings, seven of which were encumbered by an aggregate of $151.0 million of mortgage debt. (f) In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option. The first option to extend the maturity date has been exercised and extends the maturity date through February 9, 2019. The two remaining unexercised options extend the maturity through February 9, 2021. (g) Subsequent to December 31, 2017, the Company exchanged its 20% interest in Seven Tower Bridge to acquire the remaining 35% interest in Four Tower Bridge. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. (h) On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions. (i) The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%. (j) During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million. (k) Comprised of two fixed rate mortgages totaling $8.0 million that matured on March 1, 2017, which are currently in default, and accrue interest at a current rate of 7.00%, a $0.7 million 3.00% fixed rate loan through its September 1, 2025 maturity, a $2.0 million 4.00% fixed rate loan with interest only through its February 7, 2018 maturity and a $3.9 million 3.25% fixed rate loan with interest only beginning March 11, 2018 through its March 11, 2020 maturity. The following is a summary of the financial position of the Real Estate Ventures as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 December 31, 2016 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Net property $ 263,557 $ 158,960 $ 661,448 $ 1,083,965 $ 493,960 $ 229,160 $ 733,883 $ 1,457,003 Other assets 42,272 24,181 95,479 161,932 82,725 33,205 113,987 229,917 Other liabilities 24,131 4,493 69,083 97,707 40,280 6,440 82,967 129,687 Debt, net 248,700 92,917 424,803 766,420 403,671 131,161 454,906 989,738 Equity (a) 32,998 85,731 263,041 381,770 132,734 124,764 309,997 567,495 (a) This amount includes the effect of the basis difference between the Company’s historical cost basis and the basis recorded at the Real Estate Venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from the impairment of investments, purchases of third party interests in existing Real Estate Ventures and upon the transfer of assets that were previously owned by the Company into a Real Estate Venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the Real Estate Venture level. The following is a summary of results of operations of the Real Estate Ventures in which the Company had interests as of December 31, 2017, 2016 and 2015 (in thousands): Twelve-month period ended December 31, 2017 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 85,500 $ 29,500 $ 101,271 $ 216,271 Operating expenses (35,997 ) (12,298 ) (51,045 ) (99,340 ) Interest expense, net (13,985 ) (4,707 ) (21,521 ) (40,213 ) Depreciation and amortization (34,026 ) (11,428 ) (32,986 ) (78,440 ) Loss on extinguishment of debt (2,613 ) (811 ) - (3,424 ) Net income (loss) $ (1,121 ) $ 256 $ (4,281 ) $ (5,146 ) Ownership interest % 50 % 50 % (a) Company's share of net income (loss) $ (560 ) $ 128 $ (1,432 ) $ (1,864 ) Other-than-temporary impairment (b) - (4,844 ) - (4,844 ) Basis adjustments and other (429 ) 251 (1,420 ) (1,598 ) Equity in loss of Real Estate Ventures $ (989 ) $ (4,465 ) $ (2,852 ) $ (8,306 ) Twelve-month period ended December 31, 2016 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 85,749 $ 31,047 $ 97,656 $ 214,452 Operating expenses (37,643 ) (13,654 ) (51,895 ) (103,192 ) Provision for impairment (c) - (10,476 ) - (10,476 ) Interest expense, net (15,052 ) (5,825 ) (19,437 ) (40,314 ) Depreciation and amortization (38,365 ) (12,811 ) (34,562 ) (85,738 ) Net loss (d) $ (5,311 ) $ (11,719 ) $ (8,238 ) $ (25,268 ) Ownership interest % 50 % 50 % (a) Company's share of net loss $ (2,656 ) $ (5,860 ) $ (3,985 ) $ (12,501 ) Basis adjustments and other 776 (35 ) 257 998 Equity in loss of Real Estate Ventures $ (1,880 ) $ (5,895 ) $ (3,728 ) $ (11,503 ) Twelve-month period ended December 31, 2015 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 78,367 $ 29,428 $ 57,133 $ 164,928 Operating expenses (33,194 ) (11,872 ) (25,070 ) (70,136 ) Interest expense, net (14,025 ) (5,310 ) (15,249 ) (34,584 ) Depreciation and amortization (36,809 ) (12,678 ) (18,613 ) (68,100 ) Net loss $ (5,661 ) $ (432 ) $ (1,799 ) $ (7,892 ) Ownership interest % 50 % 50 % (a) - Company's share of net income (loss) $ (2,831 ) $ (216 ) $ 455 $ (2,592 ) Basis adjustments and other 1,596 (13 ) 198 1,781 Equity in income (loss) of Real Estate Ventures $ (1,235 ) $ (229 ) $ 653 $ (811 ) (a) The Company’s unconsolidated ownership interests range from 20% to 70%, subject to specified priority allocations of distributable cash in certain of the Real Estate Ventures. (b) See “ Brandywine - AI Venture: Other Than Temporary Impairment” section below (c) See “ Brandywine - AI Venture: Station Square Impairment” (d) During the year ended December 31, 2016, there were $7.1 million of acquisition deal costs related to the formation of the MAP Venture. As of December 31, 2017, the aggregate principal payments of recourse and non-recourse debt payable to third-parties are as follows (in thousands): 2018 $ 236,468 2019 390,707 2020 92,679 2021 17,162 2022 25,372 Thereafter 6,524 Total principal payments 768,912 Net deferred financing costs (2,532 ) Outstanding indebtedness $ 766,380 Brandywine - AI Venture: 7101 Wisconsin Avenue On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, a property containing 230,904 rentable square feet located in Bethesda, Maryland, for a gross sales price of $105.7 million. At the time of sale, the property was encumbered by $37.4 million first mortgage financing, which was repaid in full at closing, resulting in a debt prepayment penalty of $0.8 million. Net of the first mortgage payoff and closing costs, BDN-AI Venture received cash proceeds of $63.6 million. For the Company’s 50% interest, it received net cash proceeds of $31.8 million and recognized a $13.8 million gain on the sale transaction. Subsequent to the sale transaction, the BDN-AI Venture continued to own five properties containing an aggregate of 874,479 rentable square feet. Brandywine - AI Venture: Other Than Temporary Impairment As of September 30, 2017, the Company evaluated the recoverability of its investment basis in BDN-AI Venture utilizing a discounted cash flow model. Based on the Company’s evaluation of the fair value of the Company’s investment in the five properties that remained owned by the BDN-AI Venture subsequent to the disposition of 7101 Wisconsin Avenue, the Company determined that a persistent weak demand for space and intense competition for tenants had reduced the Company’s share of the fair value of the remaining properties to be less than its investment basis in BDN-AI Venture. As a result, the Company concluded that the decline in value was other than temporary. As of September 30, 2017, the Company’s investment basis was $49.1 million, before a $4.8 million impairment charge. Subsequent to the recordation of this impairment charge, the Company had a net basis of $44.3 million in the venture. Determining the current fair value of the Company’s investment is based on a number of factors that are difficult to predict. The market may decline further and future impairment charges may be needed. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years, a residual capitalization rate of 7.5% and discount rates ranging from 7.8% to 8.5%. The assumptions to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” Brandywine - AI Venture: 3141 Fairview Park Drive On December 20, 2011, the Company formed a real estate venture, Brandywine - AI Venture LLC, (the "AICC Venture"), with Current Creek Investments, LLC ("Current Creek"), a wholly-owned subsidiary of Allstate Insurance Company. The Company and Current Creek each own a 50% interest in the AICC Venture. The AICC Venture owns three office properties, which the Company contributed to the AICC Venture upon its formation. The contributed office properties contain an aggregate of 587,317 net rentable square feet and consist of 3130 and 3141 Fairview Park Drive, both located in Falls Church, Virginia, and 7101 Wisconsin Avenue located in Bethesda, Maryland. The Company maintained a regional management and leasing office at 3141 Fairview Park Drive. Consistent with the other four properties owned by the AICC Venture, financial control was shared, however, pursuant to the accounting standard for sales-leaseback transactions, the lease that the Company maintained at 3141 Fairview Park Drive resulted in the Company having continuing involvement that required 3141 Fairview Park Drive and its related operations to be consolidated by the Company under the financing method of accounting for sales of real estate. At formation, the Company concluded under ASC 810, “ On August 31, 2016, the Company terminated its lease for the regional management and leasing office at 3141 Fairview Park Drive. Accordingly, the Company no longer has continuing involvement, other than the equity method investment and property management agreement, with 3141 Fairview Park Drive and recorded the partial sale under the full accrual method of accounting. As a result of the sale accounting, the Company deconsolidated net assets of $45.6 million, a mortgage loan of $20.6 million and a financing liability of $12.4 million related to the property from its consolidated balance sheet and recorded a $12.6 million equity method investment. Upon recognizing the sale, there was no gain or loss, as 3141 Fairview Park Drive was impaired to its fair value during the second quarter of 2016. On September 30, 2016, the Company funded a capital call totaling $10.3 million to the AICC Venture for its 50% share of the mortgage debt on 3141 Fairview Park Drive. Subsequently, the AICC Venture funded $20.6 million for the repayment of its mortgage debt. The Company determined that the partial sale recognition does not have an impact on the accounting standard for VIEs because the underlying real estate venture agreements are unchanged. The Venture is not a VIE in accordance with the accounting standard for the consolidation of VIEs. As a result, the Company continues to use the voting interest model under the accounting standard for consolidation in order to determine whether to consolidate the Venture. Based upon each member’s substantive participating rights over the activities of the Venture under its operating and related agreements, it is not consolidated by the Company, and is accounted for under the equity method of accounting. Brandywine - AI Venture: Station Square Impairment On July, 10, 2012, Brandywine – AI Venture (the “AISS Venture”), an unconsolidated real estate venture in which the Company owns a 50% interest, acquired a three building office portfolio totaling 497,896 net rentable square feet in Silver Spring, Maryland (“Station Square”) valued at $120.6 million. During the period ended September 30, 2016, the AISS Venture recorded a $10.4 million held for use impairment charge related to Station Square, which is included in the Company’s Metropolitan D.C. segment. The Company's share of this impairment charge was $5.2 million and is reflected in equity in loss of Real Estate Ventures in its consolidated statement of operations for the period ended December 31, 2016. The fair value of the Station Square properties was primarily determined based on offers received for the properties. The remaining properties in the AISS Venture were evaluated for impairment, and based on an undiscounted cash flow analysis, no additional other than temporary impairment was identified. All of the inputs used to determine the above-mentioned impairment charges are categorized Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The Company evaluated for other than temporary impairment in its investment in the AISS Venture in accordance with ASC 323, “ The Parc at Plymouth Meeting Venture On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, L.P., a real estate venture with Toll Brothers, at a gross sales value of $100.5 million, of which the Company was allocated 50% for its interest. The venture developed and operated a 398-unit multi-family complex in Plymouth Meeting, Pennsylvania encumbered by a $54.0 million construction loan. The construction loan was repaid commensurate with the sale of the Company’s 50% interest. As a result, the Company is no longer subject to a $3.2 million payment guarantee on the construction loan. The cash proceeds, after the payment of the Company’s share of the debt and closing costs, were $27.2 million. The carrying amount of the Company’s investment at the time of sale was $12.6 million, resulting in a $14.6 million gain on sale of an interest in the real estate venture. PJP V On September 22, 2016, the real estate venture known as PJP V sold its office property, comprised of 73,997 square feet, located in Charlottesville, Virginia. Also on September 22, 2016, using proceeds from the sale, the Company liquidated its entire 25% interest in the real estate venture for $3.4 million, net of closing costs. The carrying amount of the Company’s investment was $0.2 million at the time of sale, resulting in a recognized gain of $3.2 million related to the disposition. Invesco Venture On August 19, 2016, the Company assigned its residual profits interest in an unconsolidated real estate venture known as Invesco, L.P. to the general partner of Invesco L.P. for $7.0 million. At the time of sale, the Company’s investment basis in Invesco, L.P. was zero and the Company held no other ownership interest. As a result, the Company recorded the entire amount of the proceeds received as a gain on sale of unconsolidated real estate ventures in its consolidated statement of operations. 1000 Chesterbrook On June 30, 2016, the real estate venture known as 1000 Chesterbrook sold its office property, comprised of 172,286 square feet, located in Berwyn, Pennsylvania for a sales price of $32.1 million. As of June 30, 2016, the Company owned a 50% interest in the 1000 Chesterbrook real estate venture. The proceeds to 1000 Chesterbrook, net of closing costs, proration adjustments and $23.2 million of debt assumed by the buyer, were $9.8 million. The Company recorded $3.2 million for its proportionate share of the Venture’s gain which is reflected in “Gain on Real Estate Venture transactions” in the accompanying consolidated statement of operations. The proceeds from the sale, along with $0.2 million of working capital, were distributed to the Company during the third quarter of 2016. evo at Cira Centre South Venture On January 25, 2013, the Company formed HSRE-Campus Crest IX Real Estate Venture (“evo at Cira”), a joint venture among the Company and two unaffiliated third parties: Campus Crest Properties, LLC (“Campus Crest”) and HSRE-Campus Crest IXA, LLC (“HSRE”). evo at Cira constructed a 33-story, 850-bed student housing tower located in the University City submarket of Philadelphia, Pennsylvania. Each of the Company and Campus Crest owned a 30% interest in evo at Cira and HSRE owned a 40% interest. evo at Cira developed the project on a one-acre land parcel held under a long-term ground lease with a third party lessor. The Company contributed to evo at Cira its tenancy rights under a long-term ground lease, together with associated development rights, at an agreed-upon value of $8.5 million. The Company’s historical cost basis in the development rights that it contributed to the evo at Cira was $4.0 million, thus creating a $4.5 million basis difference at December 31, 2013 between the Company’s initial outside investment basis and its $8.5 million initial equity basis. As this basis difference is not related to a physical land parcel, but rather to development rights to construct evo at Cira, the Company will accrete the basis difference as a reduction of depreciation expense over the life of evo at Cira’s assets. On March 2, 2016, the Company paid $12.8 million of cash and HSRE paid $6.6 million of cash to purchase Campus Crest’s entire 30% interest in evo at Cira and, as a result, each of the Company and HSRE owned a 50% interest in evo at Cira. Subsequent to the transaction, the Company’s investment basis in evo at Cira was $28.3 million. In conjunction with the purchase, the Company and HSRE entered into an amended and restated operating agreement, changing the legal name of evo at Cira to HSRE-BDN I, LLC, to govern their rights and obligations as sole members of evo at Cira. On June 10, 2016, evo at Cira refinanced its $97.8 million construction facility maturing July 25, 2016 with a $117.0 million term loan bearing interest at LIBOR + 2.25% capped at a total maximum interest of 5.25% and maturing on October 31, 2019, with options to extend the term to June 30, 2021. evo at Cira received an advance of $105.0 million at closing. The additional $12.0 million capacity under the term loan may be funded if certain criteria relating to the operating performance of the student housing tower are met. The term loan is secured by a leasehold mortgage that holds an absolute assignment of leases and rents. Subsequent to refinancing and the receipt of amounts in escrow under the construction loan, evo at Cira distributed $6.3 million to the Company. Subsequent to December 31, 2017, evo at Cira sold the student housing tower, the real estate venture’s sole asset, and the Company disposed of its ownership 50% interest. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. The Company accounted for its investment in evo at Cira under the equity method of accounting. Based upon the reconsideration event caused by the refinancing of evo at Cira’s construction facility, the Company reassessed its consolidation conclusion. The Company determined that this Real Estate Venture was no longer a VIE in accordance with the accounting standard for the consolidation of VIEs because evo at Cira, through the refinancing of the construction facility and without further support from the Company or HSRE, demonstrated that it has sufficient equity at risk to finance its activities. As a result, the Company used the voting interest model under the accounting standard for consolidation in order to determine whether to consolidate evo at Cira. Based upon each member's substantive participating rights over the activities that significantly impact the operations and revenues of evo at Cira under the operating agreement and related agreements, evo at Cira is not consolidated by the Company, and is accounted for under the equity method of accounting. As a result of this transaction, the Company did not gain a controlling financial interest over evo at Cira; therefore, it was not required to remeasure its previously held equity interest to fair value at the date that it acquired the additional equity interest. MAP Venture On February 4, 2016, Brandywine Operating Partnership, L.P., together with subsidiaries of the Operating Partnership, entered into a series of related transactions (the “Och-Ziff Sale”) with affiliates of Och-Ziff Capital Management Group LLC (“Och-Ziff”) that resulted in the disposition by the Company of 58 office properties that contain an aggregate of 3,924,783 square feet for an aggregate purchase price of $398.1 million. The 58 properties are located in the Pennsylvania Suburbs, New Jersey/Delaware, Metropolitan Washington, D.C. and Richmond, Virginia. The related transactions involved: (i) the sale by the Company to MAP Fee Owner LLC, an affiliate of Och-Ziff (the “O-Z Land Purchaser”), of 100% of the Company’s fee interests in the land parcels (the “Land Parcels”) underlying the 58 office properties, together with rights to be the lessor under long-term ground leases (the “Ground Leases”) covering the Land Parcels and; (ii) the Company’s formation of MAP Ground Lease Venture LLC (the “MAP Venture”) with MAP Ground Lease Holdings The MAP Venture leases the Land Parcels from O-Z Land Purchaser through a ground lease that extends through February 2115. Annual payments by the MAP Venture, as tenant under the Ground Leases, initially total $11.9 million and increase 2.5% annually through November 2025. At closing on February 4, 2016, the MAP Venture obtained a third party non-recourse debt financing of approximately $180.8 million secured by mortgages on the Buildings of the MAP Venture. As a result of this transaction, the Company received $354.0 million in proceeds and maintains a 50% ownership interest in the MAP Venture valued as of February 4, 2016 at $25.2 million, which holds the leasehold interest in the Buildings. The MAP Venture was formed as a limited liability company in which the Company has been designated as the Managing Member. In addition, through an affiliate, the Company provides property management services at the Buildings on behalf of the MAP Venture for a market based management fee. The Company has determined that the MAP Venture is a VIE in accordance with the accounting standard for consolidation of VIE’s. As a result, the Company used the VIE model under the accounting standard for consolidations to determine if it will consolidate the MAP Venture. Based on the provisions in the limited liability company agreement, the Company determined that it shares with O-Z Venture Partner the power to control the activities that most significantly impact the economics of the MAP Venture. Since control is shared, the Buildings were deconsolidated by the Company and accounted for under the equity method of accounting. The Company is not required to fund the operating losses of the MAP Venture. Accordingly, it can only incur losses equal to its investment basis in the MAP Venture. The Company has determined that this transaction does not represent a significant shift in the Company’s operations that has a major impact on the Company’s economic performance. As a result, the properties are not classified as discontinued operations on the consolidated financial statements. Coppell Associates On January 29, 2016, the Company sold its entire 50% interest in an unconsolidated real estate venture known as Coppell Associates. The proceeds to the Company, net of closing costs and related debt payoff, were $4.6 million. The carrying amount of the Company’s investment in Coppell Associates was a $1.1 million liability at the sale date, resulting in a $5.7 million gain on sale of its interest in the real estate venture. The investment was in a liability position because the Company, as a general partner, was required to fund losses of Coppell Associates. The negative investment balance represented the Company’s share of unfunded cumulative losses incurred in excess of its investment basis as of the date of sale. Residence Inn Tower Bridge On December 30, 2015, the Company sold its entire 50% ownership interest in an unconsolidated real estate venture known as Residence Inn Tower Bridge (the “Residence Inn”). The proceeds to the Company, net of closing costs and related debt payoff, were $6.1 million. The carrying amount of the Company’s investment in the Residence Inn amounted to $0.9 million at the sale date, resulting in a $5.2 million gain on sale of its interest in the Real Estate Venture. JBG Ventures On May 29, 2015, the Company and an unaffiliated third party, JBG/DC Manager, LLC ("JBG"), formed 51 N 50 Patterson, Holdings, LLC Venture ("51 N Street") and 1250 First Street Office, LLC Venture ("1250 First Street"), as real estate ventures, with the Company owning a 70.0% interest and JBG owning a 30.0% interest in each of the two ventures. At formation, the Company and JBG made cash contributions of $15.2 million and $6.5 million, respectively, to 51 N Street, which was used to purchase 0.9 acres of undeveloped land. At formation, the Company and JBG made cash capital contributions of $13.2 million and $5.7 million, respectively, to 1250 First Street, which was used to purchase 0.5 acres of undeveloped land. Based on the facts and circumstances at the formation of each of the two ventures with JBG, the Company determined that each venture is a VIE in accordance with the accounting standard for the consolidation of VIEs. As a result, the Company used the variable interest model under the accounting standard for consolidation in order to determine whether to consolidate the JBG Ventures. JBG is the managing member of the ventures, and pursuant to the operating an

Deferred Costs

Deferred Costs	12 Months Ended
	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
DEFERRED COSTS	5. DEFERRED COSTS As of December 31, 2017 and 2016, the Company’s deferred costs (assets) were comprised of the following (in thousands): December 31, 2017 Total Cost Amortization Deferred Costs, net Leasing costs $ 154,481 $ (59,046 ) $ 95,435 Financing costs - Revolving Credit Facility 3,595 (2,335 ) 1,260 Total $ 158,076 $ (61,381 ) $ 96,695 December 31, 2016 Total Cost Accumulated Amortization Deferred Costs, net Leasing costs $ 146,135 $ (56,942 ) $ 89,193 Financing costs - Revolving Credit Facility 3,595 (1,446 ) 2,149 Total $ 149,730 $ (58,388 ) $ 91,342 During the years ended December 31, 2017, 2016 and 2015, the Company capitalized internal direct leasing costs of $4.6 million, $5.0 million and $6.6 million, respectively, in accordance with the accounting standard for the capitalization of leasing costs. Brokerage Commission Payments to Related Party In May 2015, the Company leased approximately 228,000 square feet of office space (the “2015 Lease”) to a third-party commercial tenant represented by a commercial real estate broker named WDL-EL Real Estate Advisory Group, LLC, which does business as “NorthMarq Advisors” (“NorthMarq”). Walter D’Alessio, who served until February 17, 2017 as our Chairman and Lead Independent Director, owns a 33.3% membership interest in WDL Real Estate Advisory Group, LLC (“WDL”), which in turn owns a 49% interest in NorthMarq. Mr. D’Alessio was also a Principal of NorthMarq and Chairman of the Board of the tenant when the 2015 Lease was executed. The tenant maintained a long-standing brokerage relationship with NorthMarq that pre-dated the Company’s commencement of discussions as to the 2015 Lease, and NorthMarq acted as the tenant’s exclusive broker in connection with the lease. Consistent with customary practice in the commercial real estate industry, the Company paid the tenant’s brokerage commission in the amount of $4.2 million, with one-half paid to NorthMarq in 2015 upon signing of the lease and the balance paid to NorthMarq in 2016 upon the tenant’s occupancy of the leased premises. As a principal of NorthMarq, Mr. D’Alessio received payments from NorthMarq aggregating approximately $1.0 million in connection with the brokerage commission, with one-half paid in 2015 and the balance paid in 2016.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS	6. INTANGIBLE ASSETS As of December 31, 2017 and 2016, the Company’s intangible assets were comprised of the following (in thousands): December 31, 2017 Total Cost Accumulated Amortization Intangible Assets, net Intangible assets, net: In-place lease value $ 108,060 $ (47,003 ) $ 61,057 Tenant relationship value 11,201 (9,275 ) 1,926 Above market leases acquired 4,545 (2,556 ) 1,989 Total intangible assets, net $ 123,806 $ (58,834 ) $ 64,972 Acquired lease intangibles, net: Below market leases acquired $ 36,213 $ (15,939 ) $ 20,274 December 31, 2016 Total Cost Accumulated Amortization Intangible Assets, net Intangible assets, net: In-place lease value $ 142,889 $ (75,696 ) $ 67,193 Tenant relationship value 13,074 (10,167 ) 2,907 Above market leases acquired 4,718 (2,340 ) 2,378 Total intangible assets, net $ 160,681 $ (88,203 ) $ 72,478 Acquired lease intangibles, net: Below market leases acquired $ 37,579 $ (19,460 ) $ 18,119 For both the years ended December 31, 2017 and 2016, the Company accelerated the amortization of intangible assets by approximately $0.6 million as a result of tenant move-outs prior to the end of the associated lease term. For the year ended December 31, 2015, this amount was $0.5 million. For the years ended December 31, 2017, 2016, and 2015, the Company accelerated the amortization of a nominal amount of intangible liabilities as a result of tenant move-outs. As of December 31, 2017, the Company’s annual amortization for its intangible assets/liabilities, assuming no early lease terminations, are as follows (dollars in thousands): Assets Liabilities 2018 $ 14,948 $ 3,553 2019 12,438 2,807 2020 9,770 2,042 2021 7,160 1,406 2022 5,093 1,238 Thereafter 15,563 9,228 Total $ 64,972 $ 20,274

Debt Obligations

Debt Obligations	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
DEBT OBLIGATIONS	7. DEBT OBLIGATIONS The following table sets forth information regarding the Company’s consolidated debt obligations outstanding at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Effective Interest Rate Maturity Date MORTGAGE DEBT: Two Logan Square $ 84,440 $ 86,012 3.98% May 2020 One Commerce Square 123,667 127,026 3.64% (a) Apr 2023 Two Commerce Square 112,000 112,000 4.51% (b) Apr 2023 Principal balance outstanding 320,107 325,038 Plus: fair market value premium (discount), net (2,325 ) (2,761 ) Less: deferred financing costs (566 ) (728 ) Mortgage indebtedness $ 317,216 $ 321,549 UNSECURED DEBT Seven-Year Term Loan - Swapped to fixed $ 250,000 $ 250,000 3.72% Oct 2022 $300.0M 5.70% Guaranteed Notes due 2017 (c) - 300,000 5.68% May 2017 $325.0M 4.95% Guaranteed Notes due 2018 (d) - 325,000 5.13% Apr 2018 $350.0M 3.95% Guaranteed Notes due 2023 (d) 350,000 250,000 3.87% Feb 2023 $250.0M 4.10% Guaranteed Notes due 2024 250,000 250,000 4.33% Oct 2024 $450.0M 3.95% Guaranteed Notes due 2027 (d) 450,000 - 4.03% Nov 2027 $250.0M 4.55% Guaranteed Notes due 2029 250,000 250,000 4.60% Oct 2029 Indenture IA (Preferred Trust I) (e) 27,062 27,062 LIBOR + 1.25% Mar 2035 Indenture IB (Preferred Trust I) - Swapped to fixed 25,774 25,774 3.30% Apr 2035 Indenture II (Preferred Trust II) - Swapped to fixed 25,774 25,774 3.09% Jul 2035 Principal balance outstanding 1,628,610 1,703,610 Plus: original issue premium (discount), net (4,423 ) (4,678 ) Less: deferred financing costs (10,575 ) (7,369 ) Total unsecured indebtedness $ 1,613,612 $ 1,691,563 Total Debt Obligations $ 1,930,828 $ 2,013,112 (a) T his loan was assumed upon acquisition of the related properties on December 19, 2013. On December 29, 2015, the Company refinanced the debt increasing the principal balance to $130.0 million and extended the scheduled maturity date from January 6, 2016 to April 5, 2023. A default under this loan will also constitute a default under the loan secured by Two Commerce Square. This loan is also secured by a lien on Two Commerce Square. (b) This loan was assumed upon acquisition of the related property on December 19, 2013. The interest rate reflects the market rate at the time of acquisition. A default under this loan will also constitute a default under the loan secured by One Commerce Square. This loan is also secured by a lien on (c) On May 1, 2017, the entire principal balance of the unsecured 5.70% Guaranteed Notes was repaid upon maturity. Available cash balances and the Credit Facility (as defined below) were used to fund the repayment of the unsecured notes. (d) On November 17, 2017, the Company completed an offering of $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. On November 17, 2017, the Company redeemed the remaining outstanding balance of the 4.95% Guaranteed Notes due 2018 (the “2018 Notes”) ahead of its scheduled maturity. See below for further discussion. (e) On September 30, 2017, the interest rate hedge contract for the Preferred Trust I expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%. During 2017, 2016, and 2015, the Company’s weighted-average effective interest rate on its mortgage notes payable was 4.04%, 4.03%, and 5.72%, respectively. As of December 31, 2017 and 2016, the gross carrying value of the mortgage indebtedness encumbering the Company’s Properties was $320.1 million and $325.0 million, respectively. The Parent Company unconditionally guarantees the unsecured debt obligations of the Operating Partnership (or is a co-borrower with the Operating Partnership) but does not by itself incur unsecured indebtedness. The Parent Company has no material assets other than its investment in the Operating Partnership. On November 17, 2017, the Company completed an underwriting offering of its $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes”) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. The 2027 Notes were priced at 99.25% of their face amount with a yield to maturity of 4.04%, representing a spread at the time of pricing of 1.70% over the ten-year treasury rate over the five-year treasury rate On November 17, 2017, the Company used a portion of the net proceeds from the offering of the 2027 Notes and 2023 Notes to repurchase $115.1 million aggregate principal amount of 2018 Notes, through a tender offer, which consists of a $113.4 million principal repayment of the 2018 Notes, $1.2 million of prepayment penalties and $0.5 million of accrued interest. The Company recognized a $1.4 million loss on early extinguishment of debt related to the total repurchase. On December 18, 2017, the Company redeemed in full the $211.6 million aggregate principal amount of 2018 Notes that remained outstanding following completion of the tender offer, at a cash redemption price of $215.7 million (inclusive of prepayment penalties of $2.3 million and accrued interest of $1.8 million). The Company recognized a $2.5 million loss on early extinguishment of debt related to the total repurchase. The following table provides additional information on the Company’s repurchase of $325.0 million in the aggregate principal amount of its outstanding unsecured notes (consisting of the 2018 Notes, as indicated above) during the twelve months ended December 31, 2017 (in thousands). There were no repurchases of unsecured debt during the twelve months ended December 31, 2016 and 2015. Notes Principal Repurchase Amount (a) Loss on Early Extinguishment of Debt (b) 2018 4.95% Notes $ 325,000 $ 330,792 $ (3,933 ) (a) Includes prepayment penalties with respect to the redemption of debt. (b) Includes unamortized balance of the original issue discount and deferred financing costs. On October 8, 2015, the Company amended and restated its $200.0 million seven-year term loan maturing February 1, 2019. Pursuant to the terms of the amendment, the Company increased the term loan by an additional $50.0 million, lengthened the maturity date to October 8, 2022, and exercised the option to increase the aggregate amount by up to $150.0 million. The loan bears interest at LIBOR plus 1.80%. Through a series of interest rate swaps, the $250.0 million outstanding balance of the term loan has a fixed interest rate of 3.72%. On May 15, 2015, the Company closed on a four-year unsecured revolving credit facility (the "Credit Facility") that provides for borrowings of up to $600.0 million. The Company expects to use advances under the Credit Facility for general business purposes, including to fund costs of acquisitions, developments and redevelopments of properties, fund share repurchases and to repay from time to time other debt. On terms and conditions specified in the credit agreement, the Company may enter into unsecured term loans and/or increase the initial amount of the credit facility by up to, in the aggregate for all such term loans and increases, an additional $400.0 million. The Credit Facility includes a $65.0 million sub-limit for the issuance of letters of credit and a $60.0 million sub-limit for swing-loans. The Credit Facility has a scheduled maturity date of May 15, 2019, and is subject to two six-month extensions on terms and conditions specified in the credit agreement. At the Company's option, loans outstanding under the Credit Facility will bear interest at a rate per annum equal to (1) LIBOR plus between 0.875% and 1.55% based on the Company's credit rating or (2) a base rate equal to the greatest of (a) the Administrative Agent's prime rate, (b) the Federal Funds rate plus 0.5% or (c) LIBOR for a one month period plus 1.00%, in each case, plus a margin ranging from 0.0% to 0.55% based on the Company's credit rating. The Credit Facility also contains a competitive bid option that allows banks that are part of the lender consortium to bid to make loan advances to the Company at a reduced interest rate. In addition, the Company is also obligated to pay (1) in quarterly installments a facility fee on the total commitment at a rate per annum ranging from 0.125% to 0.30% based on the Company's credit rating and (2) an annual fee on the undrawn amount of each letter or credit equal to the LIBOR Margin. Based on the Company's current credit rating, the LIBOR margin is 1.20% and the facility fee is 0.25%. As of December 31, 2017, the Company did not have any outstanding borrowings on its Credit Facility. During the twelve months ended December 31, 2017, the weighted-average interest rate on Credit Facility borrowings was 2.28%, resulting in $2.6 million of interest expense. As of and during the twelve-month period ended December 31, 2016, the Company had no borrowings under the Credit Facility. The Credit Facility contains financial and operating covenants and restrictions, including covenants that relate to the Company’s incurrence of additional debt; granting liens; consummation of mergers and consolidations; the disposition of assets and interests in subsidiaries; the making of loans and investments and the payment of dividends. The terms of the Credit Facility require that the Company maintain customary financial and other covenants, including (i) a fixed charge coverage ratio greater than or equal to 1.5 to 1.00; (ii) a minimum net worth; (iii) a leverage ratio less than or equal to 0.60 to 1.00, subject to specified exceptions; (iv) a ratio of unsecured indebtedness to unencumbered asset value less than or equal to 0.60 to 1.00, subject to specified exceptions; (v) a ratio of secured indebtedness to total asset value less than or equal to 0.40 to 1.00; and (vi) a ratio of unencumbered cash flow to interest expense on unsecured debt greater than 1.75 to 1.00. In addition, the Credit Facility restricts payments of dividends and distributions on shares in excess of 95% of the Company's funds from operations (FFO) except to the extent necessary to enable the Company to continue to qualify as a REIT for Federal income tax purposes. On December 31, 2017, the Company was in compliance with all covenants in the Credit Facility. Concurrently with its entry into the Credit Facility, the Company terminated its then existing unsecured revolving credit facility, which had a scheduled maturity date of February 1, 2016. The Term Loan contains the same financial and operating covenants and restrictions, including covenants that relate to the Company’s incurrence of additional debt; granting liens; consummation of mergers and consolidations; the disposition of assets and interests in subsidiaries; the making of loans and investments; negative pledges, transactions with affiliates and the payment of dividends, as the Credit Facility. The Company was in compliance with all financial covenants as of December 31, 2017. Management continuously monitors the Company’s compliance with and anticipated compliance with the covenants. Certain of the covenants restrict the Company’s ability to obtain alternative sources of capital. While the Company currently believes it will remain in compliance with its covenants, in the event that the economy deteriorates in the future, the Company may not be able to remain in compliance with such covenants, in which case a default would result absent a lender waiver. As of December 31, 2017, the Company’s aggregate scheduled principal payments of debt obligations, excluding amortization of discounts and premiums, are as follows (in thousands): 2018 $ 6,601 2019 7,360 2020 86,978 2021 6,099 2022 256,332 Thereafter 1,585,347 Total principal payments 1,948,717 Net unamortized premiums/(discounts) (6,748 ) Net deferred financing costs (11,141 ) Outstanding indebtedness $ 1,930,828

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE OF FINANCIAL INSTRUMENTS	8. FAIR VALUE OF FINANCIAL INSTRUMENTS The Company determined the fair values disclosed below using available market information and discounted cash flow analyses as of December 31, 2017 and 2016, respectively. The discount rate used in calculating fair value is the sum of the current risk free rate and the risk premium on the date of measurement of the instruments or obligations. Considerable judgment is necessary to interpret market data and to develop the related estimates of fair value. Accordingly, the estimates presented are not necessarily indicative of the amounts that the Company could realize upon disposition. The use of different estimation methodologies may have a material effect on the estimated fair value amounts shown. The Company believes that the carrying amounts reflected in the consolidated balance sheets at December 31, 2017 and 2016 approximate the fair values for cash and cash equivalents, accounts receivable, other assets, accounts payable and accrued expenses because they are short-term in duration. The following are financial instruments for which the Company’s estimates of fair value differ from the carrying amounts (in thousands): December 31, 2017 December 31, 2016 Carrying Amount (a) Fair Value Carrying Amount (a) Fair Value Unsecured notes payable $ 1,286,573 $ 1,314,900 $ 1,364,854 $ 1,372,758 Variable rate debt $ 327,039 $ 308,872 $ 326,709 $ 307,510 Mortgage notes payable $ 317,216 $ 304,665 $ 321,549 $ 328,853 Note receivable (b) $ 3,532 $ 3,605 $ 3,380 $ 3,717 (a) In April 2015, the FASB issued guidance requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct reduction from the carrying amount of the corresponding debt liability, consistent with debt discounts. As a result, the carrying amounts presented in the table above are net of deferred financing costs of $8.9 million and $5.5 million for unsecured notes payable, $1.6 million and $1.9 million for variable rate debt and $0.6 million and $0.7 million for mortgage notes payable as of December 31, 2017 and December 31, 2016, respectively. (b) The inputs to originate the note receivable are unobservable and, as a result, are categorized as Level 3. The Company determined fair value by calculating the present value of the cash payments to be received through the maturity date of the loan. See Note 2, “Significant Accounting Policies,” The inputs utilized to determine the fair value of the Company’s unsecured notes payable are categorized as Level 2. This is because the Company valued these instruments using quoted market prices as of December 31, 2017 and December 31, 2016. For the fair value of the Company’s unsecured notes, the Company uses a discount rate based on the indicative new issue pricing provided by lenders. The inputs utilized to determine the fair value of the Company’s mortgage notes payable and variable rate debt are categorized as Level 3. The fair value of the variable rate debt was estimated using a discounted cash flow analysis valuation on the borrowing rates currently available to the Company for loans with similar terms and maturities, as applicable. The fair value of the mortgage debt was determined by discounting the future contractual interest and principal payments by a blended market rate for loans with similar terms, maturities and loan-to-value. These inputs have been categorized as Level 3 because the Company considers the rates used in the valuation techniques to be unobservable inputs. For the Company’s mortgage loans, the Company uses an estimate based discounted cash flow analyses and its knowledge of the mortgage market. An increase in the discount rate used in the discounted cash flow model would result in a decrease in the fair value of the Company’s long-term debt. Conversely, a decrease in the discount rate used in the discounted cash flow model would result in an increase in the fair value of the Company’s long-term debt. Disclosure about the fair value of financial instruments is based upon pertinent information available to management as of December 31, 2017 and December 31, 2016. Although management is not aware of any factors that would significantly affect the fair value amounts, such amounts were not comprehensively revalued for purposes of these financial statements since December 31, 2017. Current estimates of fair value may differ from the amounts presented herein.

Risk Management and Use of Deri

Risk Management and Use of Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
RISK MANAGEMENT AND USE OF DERIVATIVE FINANCIAL INSTRUMENTS	9. RISK MANAGEMENT AND USE OF DERIVATIVE FINANCIAL INSTRUMENTS Risk Management In the course of its ongoing business operations, the Company encounters economic risk. There are three main components of economic risk: interest rate risk, credit risk and market risk. The Company is subject to interest rate risk on its interest-bearing liabilities. Credit risk is primarily the risk of inability or unwillingness of tenants to make contractually required payments and of counterparties on derivatives contracts to fulfill their obligations. Market risk is the risk of declines in the value of Company properties due to changes in rental rates, interest rates, supply and demand of similar products and other market factors affecting the valuation of properties. Risks and Uncertainties In the U.S., market and economic conditions have been improving, resulting in an increase of the volume of real estate transactions in the market. If the economy deteriorates, vacancy rates may increase through 2018 and possibly beyond. The financial markets also have an effect on the Company’s Real Estate Venture partners and contractual counterparties, including counterparties in derivative contracts. The Company’s Credit Facility, term loans and the indenture governing its unsecured public debt securities (See Note 7, “ Debt Obligations Availability of borrowings under the unsecured revolving credit facility is subject to a traditional material adverse effect clause. Each time the Company borrows it must represent to the lenders that there have been no events of a nature which would have a material adverse effect on the business, assets, operations, condition (financial or otherwise) or prospects of the Company taken as a whole or which could negatively affect the ability of the Company to perform its obligations under the unsecured revolving credit facility. While the Company believes that there are currently no material adverse effect events, it is possible that such an event could arise which would limit the Company’s borrowings under the unsecured revolving credit facility. If an event occurs which is considered to have a material adverse effect, the lenders could consider the Company in default under the terms of the unsecured revolving credit facility and any borrowings under the unsecured revolving credit facility would become unavailable. If the Company is unable to obtain a waiver, this would have a material adverse effect on the Company’s financial position and results of operations. The Company was in compliance with all financial covenants as of December 31, 2017. Management continuously monitors the Company’s compliance with and anticipated compliance with the covenants. Certain of the covenants restrict management’s ability to obtain alternative sources of capital. While the Company currently believes it will remain in compliance with its covenants, in the event that the economy deteriorates in the future, the Company may not be able to remain in compliance with such covenants, in which case a default would result absent a lender waiver. Use of Derivative Financial Instruments The Company’s use of derivative instruments is limited to the utilization of interest rate agreements or other instruments to manage interest rate risk exposures and not for speculative purposes. The principal objective of such arrangements is to minimize the risks and/or costs associated with the Company’s operating and financial structure, as well as to hedge specific transactions. The counterparties to these arrangements are major financial institutions with which the Company and its affiliates may also have other financial relationships. The Company is potentially exposed to credit loss in the event of non-performance by these counterparties. However, because of the high credit ratings of the counterparties, the Company does not anticipate that any of the counterparties will fail to meet these obligations as they come due. The Company does not hedge credit or property value market risks through derivative financial instruments. The Company formally assesses, both at the inception of a hedge and on an on-going basis, whether each derivative is highly-effective in offsetting changes in cash flows of the hedged item. If management determines that a derivative is not highly-effective as a hedge or if a derivative ceases to be a highly-effective hedge, the Company will discontinue hedge accounting prospectively for either the entire hedge or the portion of the hedge that is determined to be ineffective. The related ineffectiveness would be charged to the consolidated statement of operations. The valuation of these instruments is determined using widely accepted valuation techniques including discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate curves and implied volatilities. The fair values of interest rate swaps are determined using the market standard methodology of netting the discounted future fixed cash receipts (or payments) and the discounted expected variable cash payments (or receipts). The variable cash payments (or receipts) are based on an expectation of future interest rates (forward curves) derived from observable market interest rate curves. To comply with the provisions of the accounting standard for fair value measurements and disclosures, the Company incorporates credit valuation adjustments to appropriately reflect both its own nonperformance risk and the respective counterparty’s nonperformance risk in the fair value measurements. In adjusting the fair value of its derivative contracts for the effect of nonperformance risk, the Company has considered the impact of netting and any applicable credit enhancements, such as collateral postings, thresholds, mutual puts, and guarantees. The following table summarizes the terms and fair values of the Company’s derivative financial instruments as of December 31, 2017 and December 31, 2016. The notional amounts provide an indication of the extent of the Company’s involvement in these instruments at that time but do not represent exposure to credit, interest rate or market risks (amounts presented in thousands). Hedge Product Hedge Type Designation Notional Amount Strike Trade Date Maturity Date Fair value 12/31/2017 12/31/2016 12/31/2017 12/31/2016 Assets/(Liabilities) Swap Interest Rate Cash Flow (a) $ 250,000 $ 250,000 3.718 % October 8, 2015 October 8, 2022 $ 5,694 $ 3,733 Swap Interest Rate Cash Flow (a) 25,774 25,774 3.300 % December 22, 2011 January 30, 2021 25 (300 ) Swap Interest Rate Cash Flow (a) 25,774 25,774 3.090 % January 6, 2012 October 30, 2019 59 (214 ) Swap Interest Rate Cash Flow (b) - 27,062 2.750 % December 21, 2011 September 30, 2017 - (83 ) $ 301,548 $ 328,610 (a) Hedging unsecured variable rate debt. (b) On September 30, 2017, the interest rate hedge contract for this swap expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%. The Company measures its derivative instruments at fair value and records them in the “Other assets” and “Other liabilities” captions on the Company’s consolidated balance sheets. Although the Company has determined that the majority of the inputs used to value its derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with its derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default by itself and its counterparties. The Company has assessed the significance of the impact of the credit valuation adjustments on the overall valuation of its derivative positions and has determined that the credit valuation adjustments are not significant to the overall valuation of its derivatives. As a result, the Company has determined that the inputs utilized to determine the fair value of derivative instruments are classified in Level 2 of the fair value hierarchy. Disclosure about the fair value of derivative instruments is based upon pertinent information available to management as of December 31, 2017 and December 31, 2016. Although management is not aware of any factors that would significantly affect the fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since December 31, 2017. Current estimates of fair value may differ from the amounts presented herein. Concentration of Credit Risk Concentrations of credit risk arise for the Company when multiple tenants of the Company are engaged in similar business activities, or are located in the same geographic region, or have similar economic features that impact in a similar manner their ability to meet contractual obligations, including those to the Company. The Company regularly monitors its tenant base to assess potential concentrations of credit risk. Management believes the current credit risk portfolio is reasonably well diversified and does not contain an unusual concentration of credit risk. No tenant accounted for 10% or more of the Company’s rents during 2017, 2016 and 2015. Conditions in the general economy and the global credit markets have had a significant adverse effect on numerous industries. The Company has tenants concentrated in various industries that may be experiencing adverse effects from the current economic conditions and the Company could be adversely affected if such tenants were to default under their leases.

Limited Partners' NonControllin

Limited Partners' NonControlling Interests in the Parent Company	12 Months Ended
	Dec. 31, 2017
Noncontrolling Interest [Abstract]
LIMITED PARTNERS' NONCONTROLLING INTERESTS IN THE PARENT COMPANY	10. LIMITED PARTNERS’ NONCONTROLLING INTERESTS IN THE PARENT COMPANY Noncontrolling interests in the Parent Company’s financial statements relate to redeemable common limited partnership interests in the Operating Partnership held by parties other than the Parent Company and properties which are consolidated but not wholly owned. Operating Partnership The aggregate book value of the noncontrolling interests associated with the redeemable common limited partnership interests that were consolidated in the accompanying consolidated balance sheet of the Parent Company as of December 31, 2017 and December 31, 2016, was $15.2 million and $14.9 million, respectively. Under the applicable accounting guidance, the redemption value of limited partnership units are carried at, on a limited partner basis, the greater of historical cost adjusted for the allocation of income and distributions or fair value. The Parent Company believes that the aggregate settlement value of these interests (based on the number of units outstanding and the closing price of the common shares on the balance sheet date) was approximately $26.9 million and $24.4 million, respectively, as of December 31, 2017 and December 31, 2016.

Beneficiaries Equity of the Par

Beneficiaries Equity of the Parent Company	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
BENEFICIARIES' EQUITY OF THE PARENT COMPANY	11. BENEFICIARIES’ EQUITY OF THE PARENT COMPANY Earnings per Share (EPS) The following tables detail the number of shares and net income used to calculate basic and diluted earnings per share (in thousands, except share and per share amounts; results may not add due to rounding): Year ended December 31, 2017 2016 2015 Basic Diluted Basic Diluted Basic Diluted Numerator Net income (loss) $ 121,859 $ 121,859 $ 40,501 $ 40,501 $ (30,740 ) $ (30,740 ) Net (income) loss attributable to noncontrolling interests (1,009 ) (1,009 ) (310 ) (310 ) 339 339 Nonforfeitable dividends allocated to unvested restricted shareholders (327 ) (327 ) (341 ) (341 ) (329 ) (329 ) Preferred share dividends (2,032 ) (2,032 ) (6,900 ) (6,900 ) (6,900 ) (6,900 ) Preferred share redemption charge (3,181 ) (3,181 ) - - - - Net income (loss) attributable to common shareholders $ 115,310 $ 115,310 $ 32,950 $ 32,950 $ (37,630 ) $ (37,630 ) Denominator Weighted-average shares outstanding 175,484,350 175,484,350 175,018,163 175,018,163 178,162,160 178,162,160 Contingent securities/Share based compensation - 1,323,816 - 992,651 - - Weighted-average shares outstanding 175,484,350 176,808,166 175,018,163 176,010,814 178,162,160 178,162,160 Earnings (loss) per Common Share: Net income (loss) attributable to common shareholders $ 0.66 $ 0.65 $ 0.19 $ 0.19 $ (0.21 ) $ (0.21 ) The contingent securities/share based compensation impact is calculated using the treasury stock method and relates to employee awards settled in shares of the Parent Company. The effect of these securities is anti-dilutive for periods that the Parent Company incurs a net loss from continuing operations available to common shareholders and therefore is excluded from the dilutive earnings per share calculation in such periods. Redeemable common limited partnership units, totaling 1,479,799 in both 2017 and 2016, and 1,535,102 in 2015, were excluded from the diluted earnings per share computations because they are not dilutive. Unvested restricted shares are considered participating securities which require the use of the two-class method for the computation of basic and diluted earnings per share. For the years ended December 31, 2017, 2016 and 2015, earnings representing nonforfeitable dividends were allocated to the unvested restricted shares issued to the Company’s executives and other employees under the Amended and Restated 1997 Long-Term Incentive Plan. Common and Preferred Shares On December 7, 2017, the Parent Company declared a distribution of $0.18 per common share, totaling $32.4 million, which was paid on January 23, 2018 to shareholders of record as of January 9, 2018. On April 11, 2017, the Parent Company redeemed all of its outstanding 4,000,000 Series E Preferred Shares at an aggregate redemption price of $25.51 per share, which includes $2.0 million of dividends accrued through the redemption date. The redemption was funded with existing cash balances on hand. Also on April 11, 2017, the Parent Company recognized a $3.2 million charge related to the underwriting discount and related expenses incurred at issuance of the Series E Preferred Shares on April 11, 2012. This charge is included in the earnings per share calculations above, as well as within the Parent Company’s consolidated income statements as a reduction in net income to arrive at net income attributable to common shareholders under the caption “Preferred share redemption charge.” There were no comparable charges for the years ended December 31, 2016 or 2015. Common Share Repurchases The Parent Company maintains a common share repurchase program under which the Board of Trustees has authorized the Parent Company to repurchase common shares. As of July 22, 2015, $100.0 million common share were authorized for repurchase under the program. During the years ended December 31, 2017 and 2016, there were no share repurchases under the program. During the year ended December 31, 2015, the Company repurchased and retired 5,209,437 common shares at an average purchase price of $12.90 per share and totaling $67.3 million. All of the repurchases under the current common share repurchase program occurred during 2015. The Company expects to fund any additional share repurchases with a combination of available cash balances and availability under its unsecured revolving credit facility. The timing and amounts of any purchases will depend on a variety of factors, including market conditions, regulatory requirements, share prices, capital availability and other factors as determined by the Company’s management team. The repurchase program does not require the purchase of any minimum number of shares and may be suspended or discontinued at any time without notice. In connection with the Parent Company’s common share repurchase program, one common unit of the Operating Partnership is retired for each common share repurchased. On July 22, 2015, the Parent Company's Board of Trustees authorized the repurchase of up to $100.0 million common shares, with a corresponding retirement of a number of common units equal to the number of common shares repurchased. The Company expects to fund the unit repurchases with a combination of available cash balances and availability under its unsecured revolving credit facility. During the years ended December 31, 2017 and 2016, there were no unit repurchases under the program. During the year ended December 31, 2015, the Company repurchased and retired 5,209,437 common units at an average purchase price of $12.90 per unit and totaling $67.3 million. All of the repurchases under the current common unit repurchase program occurred during 2015. The timing and amounts of any purchases will depend on a variety of factors, including market conditions, regulatory requirements, unit prices, capital availability and other factors as determined by the Company’s management team. The repurchase program does not require the purchase of any minimum number of units and may be suspended or discontinued at any time without notice. The common shares repurchased were retired and, as a result, were accounted for in accordance with Maryland law, which does not contemplate treasury stock. The repurchases were recorded as a reduction of common share (at $0.01 par value per share) and a decrease to additional paid-in-capital. Continuous Offering Program On January 10, 2017, the Parent Company entered into a continuous offering program (the “Offering Program”), under which it may sell up to an aggregate of 16,000,000 common shares until January 10, 2020 in at-the-market offerings. In connection with the commencement of the Offering Program, $0.2 million of upfront costs were recorded to Additional Paid-in Capital. This program is a replacement of a prior continuous offering program that expired on November 3, 2016. During 2017, the Parent Company issued 2,858,991 common shares under the Offering Program at a weighted average price per share of $18.19, receiving cash proceeds, net of issuance costs, of $51.2 million. No shares were issued during 2016 or 2015 under the Offering Program. The Parent Company has the ability to issue a total of 16,000,000 shares under the program through January 10, 2020, of which 13,141,009 common shares remain available for future issuance.

Partners Equity of The Operatin

Partners Equity of The Operating Partnership	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
PARTNERS' EQUITY OF THE OPERATING PARTNERSHIP	12. PARTNERS’ EQUITY OF THE OPERATING PARTNERSHIP Earnings per Common Partnership Unit The following tables detail the number of units and net income used to calculate basic and diluted earnings per common partnership unit (in thousands, except unit and per unit amounts; results may not add due to rounding): Year ended December 31, 2017 2016 2015 Basic Diluted Basic Diluted Basic Diluted Numerator Net income (loss) $ 121,859 $ 121,859 $ 40,501 $ 40,501 $ (30,740 ) $ (30,740 ) Nonforfeitable dividends allocated to unvested restricted unitholders (327 ) (327 ) (341 ) (341 ) (329 ) (329 ) Preferred unit dividends (2,032 ) (2,032 ) (6,900 ) (6,900 ) (6,900 ) (6,900 ) Preferred unit redemption charge (3,181 ) (3,181 ) - - - - Net (income) loss attributable to noncontrolling interests (29 ) (29 ) (15 ) (15 ) 3 3 Net income (loss) attributable to common unitholders $ 116,290 $ 116,290 $ 33,245 $ 33,245 $ (37,966 ) $ (37,966 ) Denominator Weighted-average units outstanding 176,964,149 176,964,149 176,523,800 176,523,800 179,697,262 179,697,262 Contingent securities/Share based compensation - 1,323,816 - 992,651 - - Total weighted-average units outstanding 176,964,149 178,287,965 176,523,800 177,516,451 179,697,262 179,697,262 Earnings (loss) per Common Partnership Unit: Net income (loss) attributable to common unitholders $ 0.66 $ 0.65 $ 0.19 $ 0.19 $ (0.21 ) $ (0.21 ) Unvested restricted units are considered participating securities which require the use of the two-class method for the computation of basic and diluted earnings per unit. For the years ended December 31, 2017, 2016 and 2015, earnings representing nonforfeitable dividends were allocated to the unvested restricted units issued to the Parent Company’s executives and other employees under the Parent Company’s shareholder-approved long-term incentive plan. Common Partnership Units and Preferred Mirror Units The Operating Partnership issues partnership units to the Parent Company in exchange for the contribution of the net proceeds of any equity security issuance by the Parent Company. The number and terms of such partnership units correspond to the number and terms of the related equity securities issued by the Parent Company. In addition, the Operating Partnership may also issue separate classes of partnership units. Historically, the Operating Partnership has had the following types of partnership units outstanding: (i) Preferred Partnership Units which have been issued to parties other than the Parent Company; (ii) Preferred Mirror Partnership Units which have been issued to the Parent Company; and (iii) Common Partnership Units which include both interests held by the Parent Company and those held by other limited partners. Preferred Mirror Partnership Units In exchange for the proceeds received in corresponding offerings by the Parent Company of preferred units of beneficial interest, the Operating Partnership has issued to the Parent Company a corresponding amount of Preferred Mirror Partnership Units with terms consistent with that of the preferred securities issued by the Parent Company. Common Partnership Units (Redeemable and General) The Operating Partnership has two classes of Common Partnership Units: (i) Class A Limited Partnership Interest which are held by both the Parent Company and outside third parties and (ii) General Partnership Interests which are held by the Parent Company (collectively, the Class A Limited Partnership Interest, and General Partnership Interests are referred to as “Common Partnership Units”). The holders of the Common Partnership Units are entitled to share in cash distributions from, and in profits and losses of, the Operating Partnership, in proportion to their respective percentage interests, subject to preferential distributions on the preferred mirror units and the preferred units. The Common Partnership Units held by the Parent Company (comprised of both General Partnership Units and Class A Limited Partnership Units) are presented as partner’s equity in the consolidated financial statements. Class A Limited Partnership Interest held by parties other than the Parent Company are redeemable at the option of the holder for a like number of common shares of the Parent Company, or cash, or a combination thereof, at the election of the Parent Company. Because the form of settlement of these redemption rights are not within the control of the Operating Partnership, these Common Partnership Units have been excluded from partner’s equity and are presented as redeemable limited partnership units measured at the potential cash redemption value as of the end of the periods presented based on the closing market price of the Parent Company’s common shares at December 31, 2017, 2016 and 2015, which was $18.19, $16.51, $13.66, respectively. As of both December 31, 2017 and 2016, 1,479,799 of Class A Units were outstanding and owned by outside limited partners of the Operating Partnership. As of December 31, 2015, 1,535,102 of Class A Units were outstanding and owned by outside limited partners of the Operating Partnership. On December 7, 2017, the Operating Partnership declared a distribution of $0.18 per common unit, totaling $32.4 million, which was paid on January 23, 2018 to unitholders of record as of January 9, 2018. On April 11, 2017, the Operating Partnership redeemed all of its outstanding 4,000,000 Series E-Linked Preferred Mirror Units at an aggregate redemption price of $25.51 per unit, which includes $2.0 million of dividends accrued through the redemption date. The redemption of preferred units was funded with existing cash balances on hand. Also on April 11, 2017, the Operating Partnership recognized a $3.2 million charge related to the underwriting discount and related expenses incurred at issuance of the Series E-Linked Preferred Mirror Units on April 11, 2012. This charge is included in the earnings per share calculations above, as well as within the Operating Partnership’s consolidated income statements as a reduction in net income to arrive at net income attributable to common partnership unitholders under the caption “Preferred unit redemption charge.” There were no comparable charges for years ended December 31, 2016 or 2015. Common Unit Repurchases In connection with the Parent Company’s common share repurchase program, one common unit is retired for each common share repurchased. As of July 22, 2015, $100.0 million common share were authorized for repurchase under the program, with a corresponding retirement of a number of common units equal to the number of common shares repurchased. During the years ended December 31, 2017 and 2016, there were no unit repurchases under the program. During the year ended December 31, 2015, the Company repurchased and retired 5,209,437 common units at an average purchase price of $12.90 per unit and totaling $67.3 million. All of the repurchases under the current common unit repurchase program occurred during 2015. The Company expects to fund the unit repurchases with a combination of available cash balances and availability under its unsecured revolving credit facility. The timing and amounts of any purchases will depend on a variety of factors, including market conditions, regulatory requirements, unit prices, capital availability and other factors as determined by the Company’s management team. The repurchase program does not require the purchase of any minimum number of units and may be suspended or discontinued at any time without notice. The common units repurchased were retired and, as a result, were accounted for in accordance with Maryland law, which does not contemplate treasury stock. The repurchases were recorded as a reduction of common units (at $0.01 par value per share) and a decrease to additional paid-in-capital. Continuous Offering Program On January 10, 2017, the Parent Company entered into a continuous offering program (the “Offering Program”), under which it may sell up to an aggregate of 16,000,000 common units until January 10, 2020 in at-the-market offerings. In connection with the commencement of the Offering Program, $0.2 million of upfront costs were recorded to General Partner Capital. This program is a replacement of a prior continuous offering program that expired on November 3, 2016. During 2017, the Parent Company issued 2,858,991 common units under the Offering Program at a weighted average price per unit of $18.19, receiving cash proceeds, net of issuance costs, of $51.2 million. No shares were issued during 2016 or 2015 under the Offering Program. The Parent Company has the ability to issue a total of 16,000,000 common units under the program through January 10, 2020, of which 13,141,009 common units remain available for future issuance.

Share Based Compensation, 401(k

Share Based Compensation, 401(k) Plan and Deferred Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
SHARE BASED COMPENSATION, 401(k) PLAN AND DEFERRED COMPENSATION	13. SHARE BASED COMPENSATION, 401(k) PLAN AND DEFERRED COMPENSATION Stock Options On December 31, 2017, options exercisable for 2,238,590 common shares were outstanding under the Parent Company’s shareholder approved equity incentive plan (referred to as the “Equity Incentive Plan”). During the years ended December 31, 2017, 2016 and 2015, the Company did not recognize any compensation expense related to unvested options. During the years ended December 31, 2017, 2016 and 2015, the Company did not capitalize any compensation expense related to stock options as part of the Company’s review of employee salaries eligible for capitalization. Option activity as of December 31, 2017 and changes during the year-ended December 31, 2017 were as follows: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at January 1, 2017 2,377,778 $ 15.36 2.15 Exercised (128,330 ) $ 9.59 $ 919,582 Forfeited/Expired (10,858 ) $ 20.61 Outstanding at December 31, 2017 2,238,590 $ 15.67 1.10 $ 8,735,293 Vested/Exercisable at December 31, 2017 2,238,590 $ 15.67 1.10 $ 8,735,293 401(k) Plan The Company sponsors a 401(k) defined contribution plan for its employees. Each employee may contribute up to 100% of annual compensation, subject to specific limitations under the Internal Revenue Code. At its discretion, the Company can make matching contributions equal to a percentage of the employee’s elective contribution and profit sharing contributions. The Company funds its 401(k) contributions annually and plan participants must be employed as of December 31 st Restricted Share Awards As of December 31, 2017, 455,643 restricted shares were outstanding under the Equity Incentive Plan and vest over two to three years from the initial grant dates. The remaining compensation expense to be recognized at December 31, 2017 was approximately $2.1 million and is expected to be recognized over a weighted average remaining vesting period of 1.3 years. During 2017, the Company recognized compensation expense related to outstanding restricted shares of $2.8 million, of which $0.4 million was capitalized as part of the Company’s review of employee salaries eligible for capitalization. For the years ended December 31, 2016 and 2015, the Company recognized $2.6 million (of which $0.4 million was capitalized) and $2.4 million (of which $0.7 million was capitalized), respectively, of compensation expense included in general and administrative expense in the respective periods related to outstanding restricted shares. The following table summarizes the Company’s restricted share activity during the year-ended December 31, 2017: Shares Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Non-vested at January 1, 2017 488,604 $ 14.10 $ 8,066,852 Granted 170,192 16.77 2,854,165 Vested (189,704 ) 14.40 3,227,342 Forfeited (13,449 ) 14.83 Non-vested at December 31, 2017 455,643 $ 14.95 $ 8,288,146 On March 1, 2017, the Compensation Committee of the Parent Company’s Board of Trustees awarded to officers of the Company an aggregate 109,629 restricted common shares, which cliff vest on April 15, 2020. On March 7, 2017, the Compensation Committee awarded non-officer employees an aggregate 32,122 restricted common shares, which vest in two equal annual installments on April 15 of 2018 and 2019. In addition, on May 18, 2017, the Compensation Committee awarded 28,441 restricted shares to the Board of Trustees which vest ratably over three years from the date of grant. Vesting of restricted common shares is subject to acceleration upon certain events, including if the recipient of the award were to die, become disabled or, in certain cases, retire in a qualifying retirement. Qualifying retirement generally means the recipient’s voluntary termination of employment after reaching at least age 57 and accumulating at least 15 years of service with the Company. In addition, in the case of the Company’s President and Chief Executive Officer, vesting would also accelerate if the Company were to terminate him without cause, or if he were to resign for good reason under his employment agreement. In addition, if the Company were to undergo a change of control, then unvested shares would also accelerate if, in connection with the change of control or within a specified period after the change of control, the holder’s employment were to terminate in a qualifying termination or resignation. In accordance with the accounting standard for share-based compensation, the Company amortizes share-based compensation costs through the qualifying retirement dates for those executives who meet the conditions for qualifying retirement during the scheduled vesting period and whose award agreements provide for vesting upon a qualifying retirement. Restricted Performance Share Units Plan The Compensation Committee of the Parent Company’s Board of Trustees has granted performance share-based awards (referred to as Restricted Performance Share Units, or RPSUs) to officers of the Parent Company. The RPSUs are settled in common shares, with the number of common shares issuable in settlement determined based on the Company’s total shareholder return over specified measurement periods compared to total shareholder returns of comparative groups over the measurement periods. The table below presents certain information as to unvested RPSU awards. RPSU Grant 2/23/2015 2/22/2016 3/1/2017 Total (Amounts below in shares, unless otherwise noted) Non-vested at January 1, 2017 147,589 231,388 - 378,977 Units Granted - - 174,854 174,854 Units Cancelled (2,274 ) (3,311 ) (2,443 ) (8,028 ) Non-vested at December 31, 2017 145,315 228,077 172,411 545,803 Measurement Period Commencement Date 1/1/2015 1/1/2016 1/1/2017 Measurement Period End Date 12/31/2017 12/31/2018 12/31/2019 Units Granted 186,395 231,388 174,854 Fair Value of Units on Grant Date (in thousands) $ 3,933 $ 3,558 $ 3,735 The Company values each RPSU on its grant date using a Monte Carlo simulation. The fair values of each award are being amortized over the three year cliff vesting period. The vesting of RPSUs is subject to acceleration upon a change in control or if the recipient of the award were to die, become disabled or retire in a qualifying retirement prior to the vesting date. In accordance with the accounting standard for share-based compensation, the Company amortizes stock-based compensation costs through the qualifying retirement date for those executives who meet the conditions for qualifying retirement during the schedule vesting period. For the year ended December 31, 2017, the Company recognized total compensation expense for the 2017, 2016 and 2015 RPSU awards of $3.4 million, of which $0.8 million was capitalized consistent with the Company’s policies for capitalizing eligible portions of employee compensation. For the year ended December 31, 2016, the Company recognized total compensation expense for the 2016, 2015 and 2014 RPSU awards of $2.8 million, of which $0.6 million was capitalized consistent with the Company’s policies for capitalizing eligible portions of employee compensation. For the year ended December 31, 2015, the Company recognized total compensation expense for the 2015, 2014 and 2013 RPSU awards of $4.2 million, of which $1.2 million was capitalized consistent with the Company’s policies for capitalizing eligible portions of employee compensation. The remaining compensation expense to be recognized at December 31, 2017 was approximately $1.7 million and is expected to be recognized over a weighted average remaining vesting period of 1.1 years. The Company issued 55,299 common shares on February 1, 2017 in settlement of RPSUs that had been awarded on March 11, 2014 and March 12, 2014 (with a three-year measurement period ended December 31, 2016). Holders of these RPSUs also received a cash dividend of $0.16 per share for these common shares on February 6, 2017. Employee Share Purchase Plan The Parent Company’s shareholders approved the 2007 Non-Qualified Employee Share Purchase Plan (the “ESPP”), which is intended to provide eligible employees with a convenient means to purchase common shares of the Parent Company through payroll deductions and voluntary cash purchases at an amount equal to 85% of the average closing price per share for a specified period. Under the plan document, the maximum participant contribution for the 2017 plan year is limited to the lesser of 20% of compensation or $50,000. The ESPP allows the Parent Company to make open market purchases, which reflects all purchases made under the plan to date. In addition, the number of shares separately reserved for issuance under the ESPP is 1.25 million. During the year ended December 31, 2017, employees made purchases under the ESPP of $0.4 million and the Company recognized $0.1 million of compensation expense related to the ESPP. During the years ended December 31, 2016 and 2015, employees made purchases under the ESPP of $0.4 million and $0.5 million, respectively, and the Company recognized $0.2 million and $0.1 million of compensation expense related to the ESPP, respectively. Compensation expense represents the 15% discount on the purchase price. The Board of Trustees of the Parent Company may terminate the ESPP at its sole discretion at any time. Deferred Compensation In January 2005, the Parent Company adopted a Deferred Compensation Plan (the “Plan”) that allows trustees and certain key employees to defer compensation voluntarily. Compensation expense is recorded for the deferred compensation and a related liability is recognized. Participants may elect designated benchmark investment options for the notional investment of their deferred compensation. The deferred compensation obligation is adjusted for deemed income or loss related to the investments selected. At the time the participants defer compensation, the Company records a liability, which is included in the Company’s consolidated balance sheet. The liability is adjusted for changes in the market value of the participant-selected investments at the end of each accounting period, and the impact of adjusting the liability is recorded as an increase or decrease to compensation cost. The Company has purchased mutual funds which can be utilized as a funding source for the Company’s obligations under the Plan. Participants in the Plan have no interest in any assets set aside by the Company to meet its obligations under the Plan. For each of the years ended December 31, 2017, December 31, 2016 and December 31, 2015, the Company recorded a nominal amount of deferred compensation costs, net of investments in the company-owned policies and mutual funds. Participants in the Plan may elect to have all or a portion of their deferred compensation invested in the Company’s common shares. The Company holds these shares in a rabbi trust, which is subject to the claims of the Company’s creditors in the event of the Company’s bankruptcy or insolvency. The Plan does not permit diversification of a participant’s deferral allocated to the Company common shares and deferrals allocated to Company common shares can only be settled with a fixed number of shares. In accordance with the accounting standard for deferred compensation arrangements where amounts earned are held in a rabbi trust and invested, the deferred compensation obligation associated with the Company’s common shares is classified as a component of shareholder’s equity and the related shares are treated as shares to be issued and are included in total shares outstanding. At both December 31, 2017 and 2016, 0.9 million of such shares were included in total shares outstanding. Subsequent changes in the fair value of the common shares are not reflected in operations or shareholders’ equity of the Company.

Distributions

Distributions	12 Months Ended
	Dec. 31, 2017
Distributions [Abstract]
DISTRIBUTIONS	14. DISTRIBUTIONS The following table provides the tax characteristics of the 2017, 2016 and 2015 distributions paid: Years ended December 31, 2017 2016 2015 (in thousands, except per share amounts) Common Share Distributions: Ordinary income $ 0.38 $ - $ 0.36 Capital gain 0.26 0.62 0.14 Non-taxable distributions - - 0.10 Distributions per share $ 0.64 $ 0.62 $ 0.60 Percentage classified as ordinary income 60.00 % 0.00 % 59.10 % Percentage classified as capital gain 40.00 % 100.00 % 23.50 % Percentage classified as non-taxable distribution 0.00 % 0.00 % 17.40 % Preferred Share Distributions: Total distributions paid $ 2,032 $ 6,900 $ 6,900 Percentage classified as ordinary income 60.00 % 0.00 % 71.60 % Percentage classified as capital gain 40.00 % 100.00 % 28.40 % Percentage classified as non-taxable distribution 0.00 % 0.00 % 0.00 %

Income Taxes and Tax Credit Tra

Income Taxes and Tax Credit Transactions	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES AND TAX CREDIT TRANSACTIONS	15. INCOME TAXES AND TAX CREDIT TRANSACTIONS Income Tax Provision/Benefit The Company accounts for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to the differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases, and for net operating loss, capital loss and tax credit carryforwards. The deferred tax assets and liabilities are measured using the enacted income tax rates in effect for the year in which those temporary differences are expected to be realized or settled. The effect on the deferred tax assets and liabilities from a change in tax rates is recognized in earnings in the period when the new rate is enacted. However, deferred tax assets are recognized only to the extent that it is more likely than not that they will be realized based on consideration of all available evidence, including the future reversals of existing taxable temporary differences, future projected taxable income and tax planning strategies. Valuation allowances are provided if, based upon the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. As of December 31, 2017, net deferred tax assets totaled $0.6 million and are included in the “Other assets” caption within the Company’s consolidated balance sheets. There was a nominal amount of deferred tax assets at December 31, 2016 included in the “Other Assets” caption within the Company’s consolidated balance sheets. In projecting future taxable income, the analysis begins with historical results and incorporates assumptions about the amount of future state and federal pretax operating income adjusted for items that do not have tax consequences. The assumptions about future taxable income require significant judgment and are consistent with the plans and estimates the Company is using to manage the underlying businesses. The Company considered all available evidence, both positive and negative, including a cumulative loss in recent years and its current forecast of future income in its analysis. While the Company believes its forecast of future taxable income is reasonable, it is inherently uncertain. If the Company’s projections of future income are lower than expected, the Company may need to establish a valuation allowance. The Company had no accruals for tax uncertainties as of December 31, 2017 and December 31, 2016. For the year ended December 31, 2017, there were $0.6 million of deferred income tax benefits. For the years ended December 31, 2016 and December 31, 2015, there were nominal amounts of income tax expense. Historic Tax Credit Transaction On November 17, 2008, the Company closed a transaction with US Bancorp (“USB”) related to the historic rehabilitation of the IRS Philadelphia Campus, an 862,692 square foot office building that is 100% leased to the IRS. On August 27, 2010, the Company completed the development of the IRS Philadelphia Campus and the IRS lease commenced. In connection with this completed development project, USB contributed to the Company $64.1 million of total project costs. In exchange for its contributions to the development of the IRS Philadelphia Campus, USB was entitled to substantially all of the benefits derived from the tax rehabilitation credits available under section 47 of the Internal Revenue Code. USB did not have a material interest in the underlying economics of the property. This transaction included a put/call provision whereby the Company was obligated or entitled to repurchase USB’s interest in the IRS Philadelphia Campus. The put option was exercised on September 30, 2015 and USB's interest in the IRS Philadelphia Campus was assigned to the Company. A purchase price of $3.2 million was attributed to that puttable noncontrolling interest obligation, which was funded with available corporate funds. Upon exercise of the put option, the Company funded USB's final 2% preferred return of $1.0 million. Based on the contractual arrangements that obligated the Company to deliver tax benefits and provide other guarantees to USB and that entitled the Company through fee arrangements to receive substantially all available cash flow from the IRS Philadelphia Campus, the Company concluded that the IRS Philadelphia Campus should be consolidated. The Company also concluded that capital contributions received from USB, in substance, were consideration that the Company received in exchange for its obligation to deliver tax credits and other tax benefits to USB. These receipts other than the amounts allocated to the put obligation were recognized as revenue in the consolidated financial statements beginning when the obligation to USB was relieved which occurred upon delivery of the expected tax benefits net of any associated costs. The tax credit was subject to 20% recapture per year beginning one year after the completion of the IRS Philadelphia Campus. Beginning September 2011 to September 2015, the Company recognized the cash received as revenue net of allocated expenses over the five year credit recapture period as defined in the Internal Revenue Code within other income (expense) in the consolidated statement of operations. The fifth and final recapture period ended September 30, 2015 and the Company recognized $11.9 million of cash received as revenue, net of $0.5 million of allocated expenses within other income (expense) it the consolidated statement of operations. As of December 31, 2017 and 2016, there were no USB contributions presented in the Company’s balance sheet Direct and incremental costs incurred in structuring the transaction were deferred and were recognized as an expense in the consolidated financial statements upon the recognition of the related revenue as discussed above. There were no deferred costs at December 31, 2016 and 2017. Amounts included in interest expense related to the accretion of the noncontrolling interest liability and the 2% return expected to be paid to USB on its noncontrolling interest aggregates to $1.1 million for the year ended December 31, 2015. There was no interest accretion for the year ended December 31, 2016. New Markets Tax Credit Transaction On December 30, 2008, the Company entered into a transaction with USB related to the Cira South Garage in Philadelphia, Pennsylvania and received a net benefit of $8.0 million under a qualified New Markets Tax Credit Program (“NMTC”). The NMTC was provided for in the Community Renewal Tax Relief Act of 2000 (the “Act”) and is intended to induce investment capital in under-served and impoverished areas of the United States. The Act permits taxpayers (whether companies or individuals) to claim credits against their Federal income taxes for up to 39% of qualified investments in qualified, active low-income businesses or ventures. USB contributed $13.3 million into the development of the Cira South Garage and as such it is entitled to substantially all of the benefits derived from the tax credit, but it does not have a material interest in the underlying economics of the Cira South Garage. This transaction also includes a put/call provision whereby the Company may be obligated or entitled to repurchase USB’s interest. The put option was exercised during 2017 and the Company’s obligation was relieved. Based on the contractual arrangements that obligate the Company to deliver tax benefits and provide various other guarantees to USB, the Company concluded that the investment entities established to facilitate the NMTC transaction should be consolidated. There were no USB contributions presented in the Company's consolidated balance sheets at December 31, 2017 and 2016. The contributions were recorded net of direct and incremental costs incurred in structuring the transaction are deferred and will be recognized as expense in the consolidated financial statements upon the recognition of the related revenue as discussed above. There were no deferred costs included within other assets on the balance sheet as of December 31, 2017 and December 31, 2016. The USB contribution other than the amount allocated to the put obligation was recognized as income in the consolidated financial statements when the tax benefits were delivered on December 30, 2015 without risk of recapture to the tax credit investors and the Company’s obligation was relieved. The NMTC is subject to 100% recapture for a period of seven years from the date that construction of the Cira South Garage commenced as provided in the Internal Revenue Code. The Company recognized the $8.1 million of net cash received as revenue within tax credit transaction income in the year ended December 31, 2015. During April of 2017, the put/call provision was exercised. As the tax credit transaction income was recognized during December of 2015 and the property was consolidated by the Company prior to December 31, 2016, there was no impact to the consolidated balance sheets and statements of operations for the years ended December 31, 2017 or December 31, 2016.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Accumulated Other Comprehensive Income (Loss)	16. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The following table details the components of accumulated other comprehensive income (loss) of the Parent Company and the Operating Partnership as of and for the three years ended December 31, 2017 (in thousands): Parent Company Cash Flow Hedges Balance at January 1, 2015 $ (4,607 ) Change in fair market value during year (1,010 ) Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests 5 Reclassification adjustments for (gains)/losses reclassified into operations 420 Balance at December 31, 2015 $ (5,192 ) Change in fair market value during year 2,371 Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests (28 ) Reclassification adjustments for (gains)/losses reclassified into operations 1,104 Balance at December 31, 2016 $ (1,745 ) Change in fair market value during year 2,948 Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests (34 ) Reclassification adjustments for (gains)/losses reclassified into operations 1,230 Balance at December 31, 2017 $ 2,399 Operating Partnership Cash Flow Hedges Balance at January 1, 2015 $ (5,007 ) Change in fair market value during year (1,010 ) Reclassification adjustments for (gains)/losses reclassified into operations 420 Balance at December 31, 2015 $ (5,597 ) Change in fair market value during year 2,371 Reclassification adjustments for (gains)/losses reclassified into operations 1,104 Balance at December 31, 2016 $ (2,122 ) Change in fair market value during year 2,948 Reclassification adjustments for (gains)/losses reclassified into operations 1,230 Balance at December 31, 2017 $ 2,056 Over time, the unrealized gains and losses held in Accumulated Other Comprehensive Income (“AOCI”) will be reclassified to interest expense when the related hedged items are recognized in earnings. The current balance held in AOCI is expected to be reclassified to interest expense for realized losses on forecasted debt transactions over the related term of the debt obligation, as applicable. The Company expects to reclassify $0.8 million from AOCI into interest expense within the next twelve months.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
SEGMENT INFORMATION	17. SEGMENT INFORMATION During the year ended December 31, 2017, the Company managed its portfolio within five segments: (1) Philadelphia Central Business District (Philadelphia CBD), (2) Pennsylvania Suburbs, (3) Metropolitan Washington, D.C., (4) Austin, Texas and (5) Other. The Philadelphia CBD segment includes properties located in the City of Philadelphia, Pennsylvania. The Pennsylvania Suburbs segment includes properties in Chester, Delaware, and Montgomery counties in the Philadelphia suburbs. The Metropolitan Washington, D.C. segment includes properties in the District of Columbia, Northern Virginia and southern Maryland. The Austin, Texas segment includes properties in the City of Austin, Texas. The Other segment includes properties located in Camden County in New Jersey and properties in New Castle County in Delaware. On February 2, 2017, the Company sold its last two remaining properties located in California, which were previously included in the Other segment. See Note 3, “Real Estate Investments,” The following tables provide selected asset information and results of operations of the Company’s reportable segments for the three years ended December 31, 2017, 2016 and 2015 (in thousands): Real estate investments, at cost: December 31, 2017 December 31, 2016 December 31, 2015 Philadelphia CBD $ 1,643,296 $ 1,320,974 $ 1,157,667 Pennsylvania Suburbs 958,796 1,005,446 1,019,280 Metropolitan Washington, D.C. 978,257 975,987 1,129,206 Austin, Texas 163,653 146,794 164,518 Other (a) 88,346 137,094 222,329 $ 3,832,348 $ 3,586,295 $ 3,693,000 Assets held for sale (b) - 73,591 794,588 Operating Properties $ 3,832,348 $ 3,659,886 $ 4,487,588 Corporate Construction-in-progress $ 121,188 $ 297,462 $ 268,983 Land held for development (c) $ 98,242 $ 150,970 $ 130,479 (a) As a result of the Och-Ziff Sale that occurred on February 4, 2016, the Company narrowed its segments to five segments: (1) Philadelphia Central Business District (“CBD”), (2) Pennsylvania Suburbs, (3) Metropolitan Washington, D.C. and (4) Austin, Texas and (5) Other. The Och-Ziff Sale disposed of the entire Richmond, Virginia segment. See Note 3, “Real Estate Investments,” for further information. (b) As of December 31, 2015, the Och-Ziff Portfolio and Cira Square were held for sale. As of December 31, 2016, the Concord Airport Plaza located in the Other segment and the Calverton portfolio located in the Metropolitan Washington, D.C. segment was held for sale. See Note 3, “Real Estate Investments,” for further information. (c) As of December 31, 2017, the Company categorized 13.1 acres of land held for development located in the Other segment as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3 , “Real Estate Investments,” None of the above aforementioned sales or properties classified as held for sale are considered significant dispositions under the accounting guidance for discontinued operations. Years ended December 31, 2017 2016 2015 Total revenue Operating expenses (a) Net operating income Total revenue Operating expenses (a) Net operating income Total revenue Operating expenses (a) Net Operating income Philadelphia CBD $ 226,673 $ (88,818 ) $ 137,855 $ 200,245 $ (78,708 ) $ 121,537 $ 209,298 $ (77,352 ) $ 131,946 Pennsylvania Suburbs 139,785 (47,769 ) 92,016 144,338 (49,208 ) 95,130 158,398 (57,319 ) 101,079 Metropolitan Washington, D.C. 92,024 (35,014 ) 57,010 99,781 (39,036 ) 60,745 110,657 (44,294 ) 66,363 Austin, Texas (b) 34,301 (15,456 ) 18,845 34,585 (13,222 ) 21,363 20,910 (8,010 ) 12,900 Other 18,347 (11,749 ) 6,598 39,359 (23,204 ) 16,155 98,799 (49,604 ) 49,195 Corporate 9,363 (7,193 ) 2,170 7,155 (6,070 ) 1,085 4,569 (1,508 ) 3,061 Operating properties $ 520,493 $ (205,999 ) $ 314,494 $ 525,463 $ (209,448 ) $ 316,015 $ 602,631 $ (238,087 ) $ 364,544 (a) Includes property operating expense, real estate taxes and third party management expense. (b) On June 22, 2015 the Company acquired the remaining 50.0% of the common interest in Broadmoor Austin Associates. As such, the Company has seven wholly owned properties in its Austin, Texas business segment. Net operating income for the years ended December 31, 2016 and 2015 includes management fees and related expenses for services provided by the Company to the Austin Venture, which are recorded in the Corporate segment. "Real Estate Investments," Unconsolidated real estate ventures: Investment in real estate ventures, at equity Equity in income (loss) of real estate ventures As of Years ended December 31, December 31, 2017 December 31, 2016 December 31, 2015 2017 2016 2015 Philadelphia CBD $ 39,939 $ 48,691 $ 44,089 $ 255 $ (686 ) $ (188 ) Pennsylvania Suburbs 3,503 15,421 16,408 631 748 310 Metropolitan Washington, D.C. (a) 119,817 141,786 118,422 (5,044 ) (6,293 ) (336 ) MAP Venture (b) 15,450 20,893 - (3,443 ) (4,218 ) - Other (c) 1,939 1,654 1,657 285 814 930 Austin, Texas (d) 13,973 52,886 60,428 (990 ) (1,868 ) (1,527 ) Total $ 194,621 $ 281,331 $ 241,004 $ (8,306 ) $ (11,503 ) $ (811 ) (a) On August 31, 2016, the Company terminated its lease for the regional management and leasing office at 3141 Fairview Park Drive, located in Falls Church, Virginia. Accordingly, the Company no longer has any continuing involvement with 3141 Fairview Park Drive and recorded the partial sale under the full accrual method of accounting. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” for further information. The years ended December 31, 2017 and 2016 include impairment charges related to the Brandywine - AI Venture. See Note 4 , “Investment in Unconsolidated Real Estate Ventures,” for further information. (b) The MAP Venture represents a joint venture formed between the Company and MAP Ground Lease Holdings LLC, an affiliate of Och-Ziff Capital Management Group, LLC, on February 4, 2016. The MAP Venture’s business operations, including properties in Richmond, Virginia; Metropolitan Washington, D.C.; New Jersey/Delaware and Pennsylvania Suburbs, are centrally managed with the results reported to management of the Company on a consolidated basis. As a result, the investment in the MAP Venture is separately presented. All other unconsolidated real estate ventures are managed consistently with the Company’s regional segments. (c) See footnote (a) to the “Real estate investments, at cost” table above for further information regarding this segment. (d) Investment in real estate ventures does not include the $1.1 million negative investment balance in one real estate venture as of December 31, 2015, which is included in the “Other Liabilities” caption of the consolidated balance sheets. The Company disposed of its interest in this venture during 2016. See Note 4, " Investment in Unconsolidated Real Estate Ventures ," for further information. The decrease in the Company’s investment balance primarily relates to distributions from the G&I VII Austin Office LLC real estate venture. See Note 4 , “Investment in Unconsolidated Real Estate Ventures,” for further information. Net operating income (“NOI”) is a non-GAAP financial measure defined as total revenue less property operating expenses, real estate taxes and third party management expenses. Property operating expenses that are included in determining NOI consist of costs that are necessary and allocable to our operating properties such as utilities, property-level salaries, repairs and maintenance, property insurance, management fees and bad debt expense. General and administrative expenses that are not reflected in NOI primarily consist of corporate-level salaries, amortization of share awards and professional fees that are incurred as part of corporate office management. All companies may not calculate NOI in the same manner. NOI is the measure that is used by the Company to evaluate the operating performance of its real estate assets by segment. The Company believes NOI provides useful information to investors regarding the financial condition and results of operations because it reflects only those income and expense items that are incurred at the property level. While NOI is a relevant and widely used measure of operating performance of real estate investment trusts, it does not represent cash flow from operations or net income as defined by GAAP and should not be considered as an alternative to those measures in evaluating our liquidity or operating performance. NOI does not reflect interest expenses, real estate impairment losses, depreciation and amortization costs, capital expenditures and leasing costs. The Company believes that net income (loss), as defined by GAAP, is the most appropriate earnings measure. The following is a reconciliation of consolidated net income (loss), as defined by GAAP, to consolidated NOI, (in thousands): Years Ended December 31, 2017 2016 2015 Net income (loss) $ 121,859 $ 40,501 $ (30,740 ) Plus: Interest expense 81,886 84,708 110,717 Interest expense - amortization of deferred financing costs 2,435 2,696 4,557 Interest expense - financing obligation - 679 1,237 Depreciation and amortization 179,357 189,676 219,029 General and administrative expenses 28,538 26,596 29,406 Equity in loss of Real Estate Ventures 8,306 11,503 811 Provision for impairment 3,057 40,517 82,208 Loss on early extinguishment of debt 3,933 66,590 - Less: Interest income 1,113 1,236 1,224 Income tax benefit 628 - - Tax credit transaction income - - 19,955 Net gain from remeasurement of investments in real estate ventures - - 758 Net gain on disposition of real estate 31,657 116,983 20,496 Net gain on sale of undepreciated real estate 953 9,232 3,019 Net gain on Real Estate Venture transactions 80,526 20,000 7,229 Consolidated net operating income $ 314,494 $ 316,015 $ 364,544

Operating Leases

Operating Leases	12 Months Ended
	Dec. 31, 2017
Leases Operating [Abstract]
OPERATING LEASES	18. OPERATING LEASES The Company leases properties to tenants under operating leases with various expiration dates extending to 2082. Minimum future rentals on non-cancelable leases at December 31, 2017 are as follows (in thousands): Year Minimum Rent 2018 $ 381,110 2019 370,211 2020 348,544 2021 323,654 2022 277,837 Thereafter 1,269,745 Total minimum future rentals presented above do not include amounts to be received as tenant reimbursements for operating costs.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	19. COMMITMENTS AND CONTINGENCIES Legal Proceedings The Company is involved from time to time in litigation on various matters, including disputes with tenants, disputes with vendors, employee disputes and disputes arising out of agreements to purchase or sell properties or joint ventures or disputes relating to state and local taxes. Given the nature of the Company’s business activities, these lawsuits are considered routine to the conduct of its business. The result of any particular lawsuit cannot be predicted, because of the very nature of litigation, the litigation process and its adversarial nature, and the jury system. The Company will establish reserves for specific legal proceedings when it determines that the likelihood of an unfavorable outcome is probable and when the amount of loss is reasonably estimable. The Company does not expect that the liabilities, if any, that may ultimately result from such legal actions will have a material adverse effect on the consolidated financial position, results of operations or cash flows of the Company. Letters-of-Credit Under certain mortgages, the Company has funded required leasing and capital reserve accounts for the benefit of the mortgage lenders with letters-of-credit. There were no associated letters-of-credit for a mortgage lender on December 31, 2017. On October 18, 2017, a $10.0 million letter-of-credit was released as a result of the disposition of eight office properties held by the Austin Venture, in which the Company holds a 50% interest. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” Environmental As an owner of real estate, the Company is subject to various environmental laws of federal, state, and local governments. The Company’s compliance with existing laws has not had a material adverse effect on its financial condition and results of operations, and the Company does not believe it will have a material adverse effect in the future. However, the Company cannot predict the impact of unforeseen environmental contingencies or new or changed laws or regulations on its current Properties or on properties that the Company may acquire. Ground Rent Future minimum rental payments under the terms of all non-cancellable ground leases under which the Company is the lessee are expensed on a straight-line basis regardless of when payments are due. The Company’s ground leases have remaining lease terms ranging from 11 to 71 years. Minimum future rental payments on non-cancelable leases at December 31, 2017 are as follows (in thousands): Year Minimum Rent 2018 $ 1,211 2019 1,211 2020 1,211 2021 1,211 2022 1,211 Thereafter 56,318 Total $ 62,373 The Company obtained ground tenancy rights related to three properties in Philadelphia, Pennsylvania, which provide for contingent rent participation by the lessor in certain capital transactions and net operating cash flows of the properties after certain returns are achieved by the Company. Such amounts, if any, will be reflected as contingent rent when incurred. The leases also provide for payment by the Company of certain operating costs relating to the land, primarily real estate taxes. The above schedule of future minimum rental payments does not include any contingent rent amounts or any reimbursed expenses. Put Agreement On May 4, 2015, the Company entered into a put agreement in the ordinary course of business that grants an unaffiliated third party the unilateral option to require the Company to purchase a property, at a predetermined price, until May 4, 2018. In addition to the $35.0 million purchase price, the Company would be responsible for the transaction and closing costs. There can be no assurance that the counterparty will exercise the option. Fair Value of Contingent Consideration On April 2, 2015, the Company purchased 618 Market Street in Philadelphia, Pennsylvania. The allocated purchase price included contingent consideration of $2.0 million payable to the seller upon commencement of development. The liability was recorded at a fair value of $1.6 million and will accrete through interest expense to $2.0 million over the expected period until development is commenced. The fair value of this contingent consideration was determined using a probability weighted discounted cash flow model. The significant inputs to the discounted cash flow model were the discount rate and weighted probability scenarios. As the inputs are unobservable, the Company determined the inputs used to value this liability fall within Level 3 for fair value reporting. As of December 31, 2017, the liability had accreted to $1.8 million. As there were no significant changes to the inputs, the liability remains within Level 3 for fair value reporting. Debt Guarantees As of December 31, 2017, the Company’s unconsolidated real estate ventures had aggregate indebtedness to third parties of $768.9 million. These loans are generally mortgage or construction loans, most of which are non-recourse to the Company. In addition, in certain instances, the Company provides non-recourse carve-out guarantees on these non-recourse loans. As of December 31, 2017, the loans for which there is recourse to the Company consists of the following: (i) a $55.4 million payment guaranty on the term loan for evo at Cira (guarantee cancelled upon the disposition of the Company’s interest in evo at Cira subsequent to December 31, 2017. See Note 20, “Subsequent Events,” Other Commitments or Contingencies On October 13, 2017, the Company acquired a leasehold interest in the office building known as One Drexel Plaza, in Philadelphia, Pennsylvania. See Note 3, “Real Estate Investments,” for further information. In connection with the acquisition, the Company is required to spend no less than $8.0 million in capital improvements to the property. The Company estimates that it will incur $37.3 million in excess of the funding requirement in the ground lease. Funding had not yet begun as of December 31, 2017. Also on October 13, 2017, the Company acquired a leasehold interest in the land parcel at 3001 Market Street in Philadelphia, Pennsylvania (“Drexel Square”). During the fourth quarter of 2017, the Company broke ground on the construction of a public park on the site, marking the commencement of construction at our Schuylkill Yards Project with Drexel. Under the terms of the Development Agreement with Drexel, we have until July 2019 to complete development of Drexel Square. If we are unable to complete such development within this timeframe, we may be subject to damages under the Development Agreement. During the fourth quarter of 2017, in connection with the Schuylkill Yards Project, the Company entered into a neighborhood engagement program and, as of December 31, 2017, had $3.6 million of future contractual obligations. In addition, the Company estimates $0.9 million of potential additional contributions for which the Company is not currently contractually obligated. On July 1, 2016, the Company closed on the acquisition of 34.6 acres of land located in Austin, Texas known as the Garza Ranch. As of December 31, 2017, the Company sold two parcels containing 8.4 acres and 1.7 acres (of the 34.6 acres) to two unaffiliated third parties. In connection with the agreements of sale, the Company entered into a development agreement and related completion guarantee to construct certain infrastructure improvements to the land on behalf of each buyer, estimated to cost $13.5 million. Total estimated costs related to the improvements are included in the sale price of each land parcel. Recognition of the sale of the land parcels is deferred until the improvements are completed. As of December 31, 2017, the costs incurred to complete the infrastructure improvements are less than the fixed sale price included in the agreements of sale for the land parcels. Accordingly, there are no indicators of impairment. On December 3, 2015, the Company entered into an agreement as development manager to construct Subaru of America’s (“Subaru”) corporate headquarters (the “Subaru Headquarters Development”), an office property containing five floors and approximately 250,000 square feet, on land owned by Subaru and located in Camden, New Jersey. In addition to development fees, the agreement provides the Company with the ability to earn an additional profit if total project costs are less than the not-to-exceed (“NTE”) amount. As of December 31, 2017, the Company has recognized $2.0 million of residual profit income related to the Subaru Headquarters Development. For the year ended December 31, 2017, the Company earned $1.5 million of residual profit income. The NTE amount, currently at $79.4 million, may be adjusted by change orders agreed upon by both Subaru and the Company. If construction costs exceed the NTE amount, the Company is obligated to pay the excess and the residual profit recognized will be reversed. As of December 31, 2017, the development was substantially completed and $67.1 million of the project costs had been funded. Also on December 3, 2015, the Company entered into an agreement to construct an 83,000 square foot build-to-suit service center (the “Subaru NSTC Development”) on land parcels owned by the Company for Subaru as the single tenant. On such date, Subaru entered into an 18-year lease for the service center. The lease contains a purchase option, which allows Subaru to purchase the property at the commencement of the lease, or five years subsequent to inception, at depreciated cost. The Company currently expects to deliver the building during the third quarter of 2018. At December 31, 2017, $15.5 million of the project costs, totaling $46.9 million, had been incurred and is included within the “Other Assets” caption of the consolidated balance sheets. As part of the Company’s September 2004 acquisition of a portfolio of properties from The Rubenstein Company (which the Company refers to as the “TRC acquisition”), the Company acquired its interest in Two Logan Square, a 708,844 square foot office building in Philadelphia, primarily through its ownership of a second and third mortgage secured by this property. This property is consolidated, as the borrower is a variable interest entity and the Company, through its ownership of the second and third mortgages, is the primary beneficiary. The Company currently does not expect to take title to Two Logan Square until, at the earliest, January 2020. If the Company takes fee title to Two Logan Square upon foreclosure of its mortgage, the Company has agreed to pay an unaffiliated third party that holds a residual interest in the fee owner of this property an amount equal to $2.9 million. On the TRC acquisition date, the Company recorded a liability of $0.7 million and this amount will accrete up to $2.9 million through January 2020. As of December 31, 2017, the Company had a balance of $2.4 million for this liability in its consolidated balance sheet. As part of the Company’s 2006 merger with Prentiss Properties Trust (“Prentiss”), the 2004 TRC acquisition and several of our other transactions, the Company agreed not to sell certain of the properties it acquired in transactions that would trigger taxable income to the former owners. In the case of the TRC acquisition, the Company agreed not to sell acquired properties in non-exempt transactions for periods up to 15 years from the date of the TRC acquisition as follows at December 31, 2017: One Logan Square, Two Logan Square and Radnor Corporate Center (January 2020). In the Prentiss acquisition, the Company assumed the obligation of Prentiss not to sell Concord Airport Plaza before March 2018. The Company’s agreements generally provide that it may dispose of the subject properties only in transactions that qualify as tax-free exchanges under Section 1031 of the Internal Revenue Code or in other tax deferred transactions. On February 2, 2017, the Company completed the disposition of Concord Airport Plaza in a transaction that qualified as a tax-free exchange under Section 1031 of the Internal Revenue Code. See Note 3, “Real Estate Investments,” As part of the Company’s acquisition of properties from time to time in tax-deferred transactions, the Company has agreed to provide certain of the prior owners of the acquired properties with the right to guarantee the Company’s indebtedness. If the Company were to seek to repay the indebtedness guaranteed by the prior owner before the expiration of the applicable agreement, the Company would be required to provide the prior owner an opportunity to guaranty qualifying replacement debt. These debt maintenance agreements may limit the Company’s ability to refinance indebtedness on terms favorable to the Company. As part of our 2013 acquisition of substantially all of the equity interests in the partnerships that own One and Two Commerce Square, the Company agreed, for the benefit of affiliates of the holder of the 1% residual ownership interest in these properties, to maintain qualifying mortgage debt through October 20, 2021, in the amounts of not less than $125.0 million on One Commerce Square and $100.0 million on Two Commerce Square. Similarly, the Company has agreements in place with other contributors of assets that obligate it to maintain debt available for them to guaranty. The Company invests in its properties and regularly incurs capital expenditures in the ordinary course of business to maintain the properties. The Company believes that such expenditures enhance its competitiveness. The Company also enters into construction, utility and service contracts in the ordinary course of business which may extend beyond one year. These contracts typically provide for cancellation with insignificant or no cancellation penalties.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	20. SUBSEQUENT EVENTS Four Tower Bridge Acquisition On January 5, 2018, the Company acquired, from its real estate venture partner in both the Four Tower Bridge real estate venture and the Seven Tower Bridge real estate venture, the remaining 35% ownership interest in the Four Tower Bridge real estate venture through a nonmonetary exchange for the Company's 20% ownership interest in the Seven Tower Bridge real estate venture. The Four Tower Bridge real estate venture owns an office property containing 86,021 square feet in Conshohocken, Pennsylvania encumbered with $9.7 million in debt. The Company previously accounted for its noncontrolling interest in Four Tower Bridge using the equity method. As a result of the exchange transaction, the Company obtained control of the Four Tower Bridge property. evo at Cira Disposition On January 10, 2018, evo at Cira, a real estate venture in which the Company held a 50% interest, sold its sole asset, a 345-unit student housing tower at a gross sales value of $197.5 million and the Company subsequently disposed of its 50% interest in the real estate venture with HSRE-Campus Crest IXA, LLC. The student housing tower, located in in Philadelphia, Pennsylvania, was encumbered by a secured loan with a principal balance of $110.9 million at the time of sale, which was repaid in full from the sale proceeds. The Company’s share of net cash proceeds from the sale, after debt repayment and closing costs, was $43.0 million. Westpark Land Sale On January 10, 2018, the Company disposed of 13.1 acres of land located in Durham, North Carolina, known as Westpark Land, for a sales price of $0.5 million.

Summary of Quarterly Results

Summary of Quarterly Results	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
SUMMARY OF QUARTERLY RESULTS (UNAUDITED)	21. SUMMARY OF QUARTERLY RESULTS (UNAUDITED) The following is a summary of quarterly financial information as of and for the years ended December 31, 2017 and 2016 (in thousands, except per share data): Brandywine Realty Trust 1st 2nd 3rd 4th Quarter Quarter Quarter Quarter 2017 Total revenue $ 130,920 $ 127,791 $ 128,438 $ 133,344 (a) Net income 21,271 7,698 19,046 73,844 (b) Net income allocated to Common Shares 19,278 4,092 18,803 73,137 Basic earnings per Common Share $ 0.11 $ 0.02 $ 0.11 $ 0.42 Diluted earnings per Common Share $ 0.11 $ 0.02 $ 0.11 $ 0.41 2016 Total revenue $ 136,502 $ 127,181 $ 129,694 $ 132,086 Net income (loss) 46,310 (1,323 ) 7,884 (12,370 ) Net income (loss) allocated to Common Shares 44,091 (3,105 ) 6,022 (14,058 ) Basic earnings (loss) per Common Share $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) Diluted earnings (loss) per Common Share $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) The summation of quarterly earnings per share amounts does not necessarily equal the full year amounts due to rounding. (a) The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania. (b) The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures." Brandywine Operating Partnership, L.P. 1st 2nd 3rd 4th Quarter Quarter Quarter Quarter 2017 Total revenue $ 130,920 $ 127,791 $ 128,438 $ 133,344 (a) Net income 21,271 7,698 19,046 73,844 (b) Net income attributable to Common Partnership Unitholders 19,442 4,129 18,961 73,758 Basic earnings per Common Partnership Unit $ 0.11 $ 0.02 $ 0.11 $ 0.42 Diluted earnings per Common Partnership Unit $ 0.11 $ 0.02 $ 0.11 $ 0.41 2016 Total revenue $ 136,502 $ 127,181 $ 129,694 $ 132,086 Net income (loss) 46,310 (1,323 ) 7,884 (12,370 ) Net income (loss) attributable to Common Partnership Unitholders 44,478 (3,131 ) 6,074 (14,176 ) Basic earnings (loss) per Common Partnership Unit $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) Diluted earnings (loss) per Common Partnership Unit $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) The summation of quarterly earnings per share amounts does not necessarily equal the full year amounts due to rounding. (a) The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania. (b) The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2017
Valuation And Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	Brandywine Realty Trust and Brandywine Operating Partnership, L.P. Schedule II Valuation and Qualifying Accounts (in thousands) Description Balance at Beginning of Year Additions Deductions (1) Balance at End of Year Allowance for doubtful accounts: Year-ended December 31, 2017 $ 16,116 $ 1,912 $ 916 $ 17,112 Year-ended December 31, 2016 $ 16,178 $ 2,207 $ 2,269 $ 16,116 Year-ended December 31, 2015 $ 15,347 $ 2,640 $ 1,809 $ 16,178 (1) Deductions represent amounts that the Company had fully reserved for in prior years and for which the pursuit of collection of such amounts was ceased during the year.

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2017
Real Estate And Accumulated Depreciation Disclosure [Abstract]
Real Estate and Accumulated Depreciation Disclosure	BRANDYWINE REALTY TRUST AND BRANDYWINE OPERATING PARTNERSHIP, L.P. Schedule III Real Estate and Accumulated Depreciation — December 31, 2017 (in thousands) Initial Cost Gross Amount Which Carried December 31, 2017 Property Name City State Encumbrances (a) Land Building & Improvements Net Improvements (Retirements) Since Acquisition Land Building & Improvements Total (b) Accumulated Depreciation at December 31, 2017 (c) Year of Construction Year Acquired Depreciable Life PENNSYLVANIA SUBURBS 400 Berwyn Park Berwyn PA - 2,657 4,462 12,982 2,657 17,444 20,101 7,366 1999 1999 40 300 Berwyn Park Berwyn PA - 2,206 13,422 3,119 2,206 16,541 18,747 9,112 1989 1997 40 1050 Westlakes Drive Berwyn PA - 2,611 10,445 2,511 2,611 12,956 15,567 5,622 1984 1999 40 1200 Swedesford Road Berwyn PA - 2,595 11,809 3,439 2,595 15,248 17,843 8,739 1994 2001 40 200 Berwyn Park Berwyn PA - 1,533 9,460 2,042 1,533 11,502 13,035 6,235 1987 1997 40 1180 Swedesford Road Berwyn PA - 2,086 8,342 3,110 2,086 11,452 13,538 4,962 1987 2001 40 100 Berwyn Park Berwyn PA - 1,180 7,290 1,404 1,180 8,694 9,874 4,643 1986 1997 40 1160 Swedesford Road Berwyn PA - 1,781 7,124 6,635 2,045 13,495 15,540 5,036 1986 2001 40 1100 Cassett Road Berwyn PA - 1,695 6,779 1,271 1,695 8,050 9,745 3,419 1997 2001 40 Six Tower Bridge (181 Washington Street) Conshohocken PA - 6,927 14,722 1,762 6,237 17,174 23,411 2,623 1999 2013 40 52 Swedesford Square East Whiteland Twp. PA - 4,241 16,579 5,340 4,241 21,919 26,160 9,736 1988 1998 40 640 Freedom Business Center King Of Prussia PA - 4,222 16,891 3,934 4,222 20,825 25,047 10,685 1991 1998 40 620 Freedom Business Center King Of Prussia PA - 2,770 11,014 1,444 2,770 12,458 15,228 6,595 1986 1998 40 1000 First Avenue King Of Prussia PA - 2,772 10,936 3,670 2,772 14,606 17,378 6,600 1980 1998 40 1060 First Avenue King Of Prussia PA - 2,712 10,953 4,289 2,712 15,242 17,954 7,384 1987 1998 40 630 Freedom Business Center King Of Prussia PA - 2,773 11,144 3,340 2,773 14,484 17,257 6,850 1989 1998 40 1020 First Avenue King Of Prussia PA - 2,168 8,576 3,939 2,168 12,515 14,683 5,513 1984 1998 40 1040 First Avenue King Of Prussia PA - 2,860 11,282 5,037 2,860 16,319 19,179 7,320 1985 1998 40 610 Freedom Business Center King Of Prussia PA - 2,017 8,070 2,895 2,017 10,965 12,982 5,199 1985 1998 40 650 Park Avenue King Of Prussia PA - 1,916 4,378 1,569 1,916 5,947 7,863 3,401 1968 1998 40 600 Park Avenue King Of Prussia PA - 1,012 4,048 385 1,012 4,433 5,445 2,406 1964 1998 40 933 First Avenue King Of Prussia PA - 3,127 20,794 (1,301) 3,127 19,493 22,620 482 2017 N/A 40 401 Plymouth Road Plymouth Meeting PA - 6,199 16,131 16,905 6,199 33,036 39,235 13,795 2001 2000 40 Metroplex (4000 Chemical Road) Plymouth Meeting PA - 4,373 24,546 679 4,373 25,225 29,598 6,437 2007 2001 40 610 West Germantown Pike Plymouth Meeting PA - 3,651 14,514 3,172 3,651 17,686 21,337 7,309 1987 2002 40 600 West Germantown Pike Plymouth Meeting PA - 3,652 15,288 2,251 3,652 17,539 21,191 6,877 1986 2002 40 630 West Germantown Pike Plymouth Meeting PA - 3,558 14,743 2,172 3,558 16,915 20,473 6,645 1988 2002 40 620 West Germantown Pike Plymouth Meeting PA - 3,572 14,435 1,199 3,572 15,634 19,206 6,262 1990 2002 40 660 West Germantown Pike Plymouth Meeting PA - 3,694 5,487 20,715 5,405 24,491 29,896 4,429 1987 2012 30 351 Plymouth Road Plymouth Meeting PA - 1,043 555 - 1,043 555 1,598 177 N/A 2000 40 150 Radnor Chester Road Radnor PA - 11,925 36,986 12,659 11,897 49,673 61,570 21,400 1983 2004 29 One Radnor Corporate Center Radnor PA - 7,323 28,613 22,440 7,323 51,053 58,376 26,157 1998 2004 29 201 King of Prussia Road Radnor PA - 8,956 29,811 3,800 8,949 33,618 42,567 18,855 2001 2004 25 555 Lancaster Avenue Radnor PA - 8,014 16,508 16,861 8,609 32,774 41,383 15,517 1973 2004 24 Four Radnor Corporate Center Radnor PA - 5,406 21,390 12,190 5,705 33,281 38,986 13,192 1995 2004 30 Five Radnor Corporate Center Radnor PA - 6,506 25,525 4,373 6,578 29,826 36,404 10,451 1998 2004 38 Three Radnor Corporate Center Radnor PA - 4,773 17,961 2,790 4,791 20,733 25,524 10,342 1998 2004 29 Two Radnor Corporate Center Radnor PA - 3,937 15,484 3,440 3,942 18,919 22,861 8,458 1998 2004 29 130 Radnor Chester Road Radnor PA - 2,573 8,338 3,460 2,567 11,804 14,371 5,948 1983 2004 25 170 Radnor Chester Road Radnor PA - 2,514 8,147 2,132 2,509 10,284 12,793 3,739 1983 2004 25 200 Radnor Chester Road Radnor PA - 3,366 - 3,572 3,366 3,572 6,938 503 2014 2005 40 101 West Elm Street W. Conshohocken PA - 6,251 25,209 2,872 6,251 28,081 34,332 8,968 1999 2005 40 1 West Elm Street W. Conshohocken PA - 3,557 14,249 3,151 3,557 17,400 20,957 5,290 1999 2005 40 PHILADELPHIA CBD Cira Centre (2929 Arch Street) Philadelphia PA - - 208,570 (6,931) 12,586 189,053 201,639 68,099 2005 N/A 40 Three Logan Square (1717 Arch Street) Philadelphia PA - - 98,188 61,060 25,195 134,053 159,248 31,079 1990 2010 40 Two Commerce Square (2001 Market Street) Philadelphia PA 112,000 15,323 120,200 21,892 15,323 142,092 157,415 17,086 1992 2013 40 One Logan Square (130 North 18th Street) Philadelphia PA - 14,496 107,736 28,938 14,473 136,697 151,170 52,506 1998 2004 34 Two Logan Square (100 North 18th Street) Philadelphia PA 84,440 16,066 100,255 19,733 16,066 119,988 136,054 42,317 1988 2004 36 One Commerce Square (2005 Market Street) Philadelphia PA 123,667 15,161 105,021 22,924 15,160 127,946 143,106 15,828 1987 2013 40 Cira Centre South Garage Philadelphia PA - - 76,008 8,114 - 84,122 84,122 14,732 2010 N/A 40 1900 Market Street Philadelphia PA - 7,768 17,263 46,556 7,768 63,819 71,587 7,484 1981 2012 30 3020 Market Street Philadelphia PA - - 21,417 7,603 - 29,020 29,020 7,511 1959 2011 26 The Lift at Juniper Street (101 - 103 Juniper Street) Philadelphia PA - - 14,401 (3,329) 478 10,594 11,072 2,803 2010 2006 40 618-634 Market Street (d) Philadelphia PA - 13,365 5,791 490 13,365 6,281 19,646 3,258 1966 2015 5 FMC Tower at Cira Centre South (2929 Walnut Street) Philadelphia PA - - 400,294 (7,976) - 392,318 392,318 16,218 2016 N/A 40 2100 Market Street (e) Philadelphia PA - 18,827 - 5,494 18,854 5,467 24,321 121 N/A 2015 N/A 3000 Market Street (f) Philadelphia PA - 18,924 13,080 8 18,924 13,088 32,012 569 1937 2017 12 One Drexel Plaza (f) Philadelphia PA - - 24,377 6,206 - 30,583 30,583 194 1953 2017 40 METROPOLITAN WASHINGTON, D.C. 6600 Rockledge Drive Bethesda MD - - 37,421 10,841 - 48,262 48,262 13,299 1981 2006 50 2340 Dulles Corner Boulevard Herndon VA - 16,345 65,379 3,710 16,129 69,305 85,434 21,809 1987 2006 40 2291 Wood Oak Drive Herndon VA - 8,243 52,413 12,549 8,782 64,423 73,205 19,549 1999 2006 55 2251 Corporate Park Drive Herndon VA - 11,472 45,893 3,412 11,472 49,305 60,777 14,191 2000 2006 40 2355 Dulles Corner Boulevard Herndon VA - 10,365 43,876 7,299 10,365 51,175 61,540 16,202 1988 2006 40 2411 Dulles Corner Park Herndon VA - 7,279 46,340 17,626 7,417 63,828 71,245 16,736 1990 2006 50 13880 Dulles Corner Lane Herndon VA - 7,236 39,213 5,904 7,373 44,980 52,353 11,525 1997 2006 55 2121 Cooperative Way Herndon VA - 5,598 38,639 3,186 5,795 41,628 47,423 11,035 2000 2006 54 2201 Cooperative Way Herndon VA - 4,809 34,093 6,018 4,809 40,111 44,920 10,205 1990 2006 54 13825 Sunrise Valley Drive Herndon VA - 3,794 19,365 1,454 3,866 20,747 24,613 6,202 1989 2006 46 1676 International Drive Mclean VA - 18,437 97,538 3,744 18,785 100,934 119,719 23,545 1999 2006 55 8260 Greensboro Drive Mclean VA - 7,952 33,964 3,184 8,102 36,998 45,100 10,182 1980 2006 52 2273 Research Boulevard Rockville MD - 5,167 31,110 4,098 5,237 35,138 40,375 9,332 1999 2006 45 2275 Research Boulevard Rockville MD - 5,059 29,668 8,093 5,154 37,666 42,820 10,989 1990 2006 45 2277 Research Boulevard Rockville MD - 4,649 26,952 18,867 4,733 45,735 50,468 12,369 1986 2006 45 1900 Gallows Road Vienna VA - 7,797 47,817 12,333 7,944 60,003 67,947 17,697 1989 2006 52 8521 Leesburg Pike Vienna VA - 4,316 30,885 6,846 4,397 37,650 42,047 9,854 1984 2006 51 AUSTIN, TX 11501 Burnet Road - Building 1 Austin TX - 3,755 22,702 130 3,755 22,832 26,587 1,783 1991 2015 35 11501 Burnet Road - Building 2 Austin TX - 2,732 16,305 1,572 2,732 17,877 20,609 1,606 1991 2015 35 11501 Burnet Road - Building 3 Austin TX - 3,688 22,348 128 3,688 22,476 26,164 1,755 1991 2015 35 11501 Burnet Road - Building 4 Austin TX - 2,614 15,740 90 2,614 15,830 18,444 1,236 1991 2015 35 11501 Burnet Road - Building 5 Austin TX - 3,689 22,354 128 3,689 22,482 26,171 1,755 1991 2015 35 11501 Burnet Road - Building 6 (g) Austin TX - 2,676 15,972 (1,835) 2,676 14,137 16,813 121 1991 2015 40 11501 Burnet Road - Building 8 Austin TX - 1,400 7,422 104 1,400 7,526 8,926 591 1991 2015 35 11501 Burnet Road - Parking Garage Austin TX - - 19,826 113 - 19,939 19,939 2,070 1991 2015 35 OTHER 20 East Clementon Road Gibbsboro NJ - 769 3,055 506 719 3,611 4,330 1,892 1986 1997 40 10 Foster Avenue Gibbsboro NJ - 244 971 69 244 1,040 1,284 571 1983 1997 40 7 Foster Avenue Gibbsboro NJ - 231 921 17 231 938 1,169 501 1983 1997 40 2 Foster Avenue Gibbsboro NJ - 185 730 11 185 741 926 741 1974 1997 40 4 Foster Avenue Gibbsboro NJ - 183 726 6 183 732 915 732 1974 1997 40 1 Foster Avenue Gibbsboro NJ - 93 364 8 93 372 465 372 1972 1997 40 5 U.S. Avenue Gibbsboro NJ - 21 81 2 21 83 104 45 1987 1997 40 5 Foster Avenue Gibbsboro NJ - 9 32 26 9 58 67 33 1968 1997 40 Main Street - Plaza 1000 Voorhees NJ - 2,732 10,942 376 2,732 11,318 14,050 11,037 1988 1997 40 Main Street - Piazza Voorhees NJ - 696 2,802 3,446 700 6,244 6,944 2,741 1990 1997 40 Main Street - Promenade Voorhees NJ - 532 2,052 404 532 2,456 2,988 1,357 1988 1997 40 920 North King Street Wilmington DE - 6,141 21,140 5,003 6,141 26,143 32,284 10,185 1989 2004 30 300 Delaware Avenue Wilmington DE - 6,369 13,739 2,708 6,369 16,447 22,816 8,762 1989 2004 23 Total: $ 320,107 $ 449,911 $ 2,815,831 $ 566,606 $ 492,197 $ 3,340,151 $ 3,832,348 $ 895,091 ( a ) Excludes the effect of any net interest premium/(discount) and deferred financing costs. (b) Reconciliation of Real Estate: The following table reconciles the real estate investments from January 1, 2015 to December 31, 2017 (in thousands): 2017 2016 2015 Balance at beginning of year $ 3,659,886 $ 4,487,588 $ 4,631,128 Additions: Acquisitions 62,586 - 182,381 Capital expenditures and assets placed into service 356,857 213,996 165,941 Less: Dispositions/impairments/placed into redevelopment (189,395 ) (962,676 ) (442,327 ) Retirements (57,586 ) (79,022 ) (49,535 ) Balance at end of year $ 3,832,348 $ 3,659,886 $ 4,487,588 Less: Assets held for sale - (73,591 ) (794,588 ) Per consolidated balance sheet $ 3,832,348 $ 3,586,295 $ 3,693,000 The aggregate cost for federal income tax purposes is $3.1 billion as of December 31, 2017. (c) Reconciliation of Accumulated Depreciation: The following table reconciles the accumulated depreciation on real estate investments from January 1, 2015 to December 31, 2017 (in thousands): 2017 2016 2015 Balance at beginning of year $ 885,392 $ 1,080,616 $ 1,078,996 Additions: Depreciation expense 135,823 131,859 159,080 Less: Dispositions/impairments/placed into redevelopment (74,178 ) (250,110 ) (109,243 ) Retirements (51,946 ) (76,973 ) (48,217 ) Balance at end of year $ 895,091 $ 885,392 $ 1,080,616 Less: Assets held for sale - (32,916 ) (213,581 ) Per consolidated balance sheet $ 895,091 $ 852,476 $ 867,035 (d) At acquisition it was determined that the useful life of the parking structure is five years, which reflects the expected demolition date. (e) Building and improvements consists of capital improvements, which are depreciated over the lease term. (f) Reflects original construction date. Significant improvements were made to 3000 Market Street in 1988 and One Drexel Plaza in 2012. (g) The property was partially placed into service during 2017.

Summary of Significant Accoun35

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Out of Period Adjustment	Out of Period Adjustment The Company recorded $1.2 million of impairment charges during the quarter ended December 31, 2016, which should have been recorded in the consolidated financial statements for the three-month period ended March 31, 2017 and the year ended December 31, 2017. Management concluded that these misstatements were not material to any prior period, nor were they material to the consolidated financial statements as of and for the twelve-month periods ended December 31, 2017 and 2016.
Reclassifications	Reclassifications During the first quarter of 2017, the Company adopted ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which requires the Company to reclassify employer tax payments on account of employee tax withholdings on share-based awards from operating activities to financing activities in the consolidated statement of cash flows. As a result of the adoption, $0.9 million and $2.1 million of cash outflows have been reclassified in the consolidated statements of cash flows for the years ended December 31, 2016 and 2015, respectively, from operating activities to financing activities. There was no other impact from the adoption of this guidance.
Principles of Consolidation	Principles of Consolidation The Company consolidates variable interest entities (“VIEs”) in which it is considered to be the primary beneficiary. VIEs are entities in which the equity investors do not have sufficient equity at risk to finance their endeavors without additional financial support or that the holders of the equity investment at risk do not have a controlling financial interest. The primary beneficiary is defined by the entity having both of the following characteristics: (i) the power to direct those matters that most significantly impact the activities of the VIE and (ii) the obligation to absorb losses or the right to receive benefits of the VIE that could potentially be significant to the VIE. For entities that the Company has the obligations to fund losses, its maximum exposure to loss is not limited to the carrying amount of its investments. As of December 31, 2017, the Company’s unconsolidated real estate ventures had aggregate indebtedness to third parties of $768.9 million. These loans are generally mortgage or construction loans, most of which are non-recourse to the Company. As of December 31, 2017, the loans for which there is recourse to the Company consists of the following: (i) a $55.4 million payment guaranty on the term loan for evo at Cira (guarantee cancelled upon the disposition of the Company’s interest in evo at Cira subsequent to December 31, 2017. See Note 20, “Subsequent Events,” When an entity is not deemed to be a VIE, the Company consolidates entities for which it has significant decision making control over the entity’s operations. The Company’s judgement with respect to its level of influence or control of an entity involves consideration of various factors including the form of the Company’s ownership interest, its representation in the entity’s governance, the size of its investment (including loans), estimates of future cash flows, its ability to participate in policy making decisions and the rights of the other investors to participate in the decision making process and to replace the Company as manager and/or liquidate the venture, if applicable. The Company’s assessment of its influence or control over an entity affects the presentation of these investments in the Company’s consolidated financial statements. In addition to evaluating control rights, the Company consolidates entities in which the outside partner has no substantive kick-out rights to remove the Company as managing member. The Company continuously assesses its determination of the primary beneficiary for each entity and assesses reconsideration events that may cause a change in the original determinations. The portion of the consolidated entities that are not owned by the Company is presented as noncontrolling interest as of and during the periods consolidated. All intercompany transactions have been eliminated in consolidation. As of December 31, 2017 and 2016, the Company included in its consolidated balance sheets consolidated VIEs having total assets of $412.9 million and $417.1 million, respectively, and total liabilities of $250.4 million and $254.6 million, respectively.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Management makes significant estimates regarding revenue, valuation of real estate and related intangible assets and liabilities, impairment of long-lived assets, land held for development, allowance for doubtful accounts and deferred costs.
Operating Properties	Operating Properties Operating properties are carried at historical cost less accumulated depreciation and impairment losses. The value of operating properties reflects their purchase price or development cost. Acquisition costs related to business combinations are expensed as incurred, whereas the costs related to asset acquisitions are capitalized as incurred. Costs incurred for the renovation and betterment of an operating property are capitalized to the Company’s investment in that property. Ordinary repairs and maintenance are expensed as incurred.
Purchase Price Allocation	Purchase Price Allocation For acquisitions of real estate or in-substance real estate that are accounted for as business combinations, we recognize the assets acquired (including the intangible value of acquired above- or below-market leases, acquired in-place leases, tenant relationships, and other intangible assets or liabilities), liabilities assumed, noncontrolling interests, and previously existing ownership interests at fair value as of the acquisition date. Any excess (deficit) of the consideration transferred relative to the fair value of the net assets acquired is accounted for as goodwill (bargain purchase gain). Acquisition costs related to business combinations are expensed as incurred. Acquisitions of real estate and in-substance real estate that do not meet the definition of a business are accounted for as asset acquisitions. The accounting model for asset acquisitions is similar to the accounting model for business combinations except that the acquisition consideration (including acquisition costs) is allocated to the individual assets acquired and liabilities assumed on a relative fair value basis. As a result, asset acquisitions do not result in recognition of goodwill or a bargain purchase gain. Additionally, because the accounting model for asset acquisitions is a cost accumulation model, preexisting interests in the acquired assets, if any, are not remeasured to fair value but continue to be accounted for at their historical cost. Direct acquisition costs are capitalized if an asset acquisition is probable. If we determine that an asset acquisition is no longer probable, no new costs are capitalized and all capitalized costs that are not recoverable are written off. The Company allocates the purchase price of properties considered to be business combinations and asset acquisitions to net tangible and identified intangible assets acquired based on fair values. Above-market and below-market in-place lease values for acquired properties are recorded based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between (i) the contractual amounts to be paid pursuant to the in-place leases and (ii) the Company’s estimate of the fair market lease rates for the corresponding in-place leases, measured over a period equal to the remaining non-cancelable term of the lease (including the below market fixed renewal period, if applicable). Capitalized above-market lease values are amortized as a reduction of rental income over the remaining non-cancelable terms of the respective leases. Capitalized below-market lease values are amortized as an increase to rental income over the remaining non-cancelable terms of the respective leases, including any below market fixed-rate renewal option periods that are considered probable. Other intangible assets also include in-place leases based on the Company’s evaluation of the specific characteristics of each tenant’s lease and the Company’s overall relationship with the respective tenant. The Company estimates the cost to execute leases with terms similar to the remaining lease terms of the in-place leases, including leasing commissions, legal and other related expenses. This intangible asset is amortized to expense over the remaining term of the respective leases and any fixed-rate bargain renewal periods. Company estimates of value are made using methods similar to those used by independent appraisers or by using independent appraisals. Factors considered by the Company in this analysis include an estimate of the carrying costs during the expected lease-up periods considering current market conditions and costs to execute similar leases. In estimating carrying costs, the Company includes real estate taxes, insurance and other operating expenses and estimates of lost rents at market rates during the expected lease-up periods, which primarily range from four to twelve months. The Company also considers information obtained about each property as a result of its pre-acquisition due diligence, marketing and leasing activities in estimating the fair value of the tangible and intangible assets acquired. The Company also uses the information obtained as a result of its pre-acquisition due diligence as part of its consideration of the accounting standard governing asset retirement obligations and when necessary, will record a conditional asset retirement obligation as part of its purchase price. The Company also evaluates tenant relationships on a tenant-specific basis. On most of the Company’s acquisitions, this intangible has been deemed immaterial, in which case no related intangible asset value is assigned. In the event that a tenant terminates its lease, the unamortized portion of each intangible, including in-place lease values and tenant relationship values, is charged to expense and market rate adjustments (above or below) is recorded to revenue. The Company records development acquisitions that do not meet the accounting criteria to be accounted for as business combinations at the purchase price paid. Costs directly associated with development acquisitions accounted for as asset acquisitions are capitalized as part of the cost of the acquisition.
Depreciation and Amortization	Depreciation and Amortization The costs of buildings and improvements are depreciated using the straight-line method based on the following useful lives: buildings and improvements (5 to 55 years) and tenant improvements (the shorter of (i) the life of the asset, 1 to 16 years, or (ii) the lease term).
Construction-in-Progress	Construction-in-Progress Project costs directly associated with the development and construction of a real estate project are capitalized as construction-in-progress. Construction-in-progress also includes costs related to ongoing tenant improvement projects. In addition, interest, real estate taxes and other expenses that are directly associated with the Company’s development activities are capitalized until the property is placed in service. Interest expense is capitalized using the Company’s weighted average interest rate. Internal direct costs are capitalized to projects in which qualifying expenditures are being incurred. Internal direct construction costs totaling $6.1 million in 2017, $6.7 million in 2016, $7.3 million in 2015 and interest totaling $3.1 million in 2017, $10.9 million in 2016, and $10.2 million in 2015 were capitalized related to the development of certain properties and land holdings. During the years ended December 31, 2017, 2016 and 2015, the Company’s internal direct construction costs are comprised entirely of capitalized salaries. The following table shows the amount of compensation costs (including bonuses and benefits) capitalized for the years presented (in thousands): December 31, 2017 2016 2015 Development $ 4,390 $ 3,182 $ 2,641 Redevelopment 319 144 221 Tenant Improvements 1,354 3,391 4,429 Total $ 6,063 $ 6,717 $ 7,291
Impairment or Disposal of Long-Lived Assets	Impairment or Disposal of Long-Lived Assets The Company reviews its long-lived assets for impairment following the end of each quarter using cash flow projections and estimated fair values for each of its properties where events or changes in circumstances indicate that the carrying amounts may not be recoverable. The Company updates leasing and other assumptions regularly, paying particular attention to properties where there is an event or change in circumstances that indicate an impairment in value. Additionally, the Company considers strategic decisions regarding the future development plans for property under development and other market factors. For long-lived assets to be held and used, the Company analyzes recoverability based on the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the assets over, in most cases, a 10-year hold period. If there is significant possibility that the Company will dispose of assets earlier, it analyzes the recoverability using a probability weighted analysis of the undiscounted future cash flows expected to be generated from the operations and eventual disposition of each asset using various probable hold periods. If the recovery analysis indicates that the carrying value of the tested property is not recoverable, the property is written down to its fair value and an impairment loss is recognized. In such case, an impairment loss is recognized in the amount of the excess of the carrying amount of the asset over its fair value. If and when the Company’s plans change, it revises its recoverability analysis to use cash flows expected from operations and eventual disposition of each asset using hold periods that are consistent with its revised plans. Estimated cash flows used in such analysis are based on the Company’s plans for the property and its views of market economic conditions. The estimates consider factors such as current and future rental rates, occupancies for the tested property and comparable properties, estimated operating and capital expenditures and recent sales data for comparable properties; most of these factors are influenced by market data obtained from real estate leasing and brokerage firms and the Company’s direct experience with the properties and their markets. The Company generally considers assets to be “held for sale” when the transaction has been approved by its Board of Trustees, or by officers vested with authority to approve the transaction, and there are no known significant contingencies relating to the sale of the property within one year of the consideration date and the consummation of the transaction is otherwise considered probable. When a property is designated as held for sale, the Company stops depreciating the property and estimates the property’s fair value, net of selling costs. If the determination is made that the estimated fair value, net of selling costs, is less than the net carrying value of the property, an impairment loss is recognized, reducing the net carrying value of the property to estimated fair value less selling costs. For periods in which a property is classified as held for sale, the Company classifies the assets and liabilities, as applicable, of the property as “held for sale” on the consolidated balance sheet for such periods. The relevant accounting guidance for impairments requires that qualifying assets and liabilities and the results of operations that have been sold, or otherwise qualify as “held for sale,” be presented as discontinued operations in all periods presented if the disposal represents a strategic shift that has, or will have, a major effect on the Company’s operations and financial results. The components of the property’s net income that is reflected as discontinued operations include the net gain (or loss) upon the disposition of the property held for sale, operating results, depreciation and interest expense (if the property is subject to a secured loan).
Impairment of Land Held for Development	Impairment of Land Held for Development When demand for build-to-suit office space declines and the ability to sell land held for development deteriorates, or other market factors indicate possible impairment in the recoverability of land held for development, it is reviewed for impairment by comparing its fair value to its carrying value. If the estimated sales value is less than the carrying value, the carrying value is written down to its estimated fair value.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are highly-liquid investments with original maturities of three months or less. The Company maintains cash equivalents in money market accounts with financial institutions in excess of insured limits, but believes this risk is mitigated by only investing in or through major financial institutions. The Company does not invest its available cash balances in money market funds, as such available cash balances are appropriately reflected as cash and cash equivalents on its consolidated balance sheet.
Restricted Cash	Restricted Cash Restricted cash consists of cash held as collateral to provide credit enhancement for the Company’s mortgage debt, cash for property taxes, capital expenditures and tenant improvements. Escrows also include cash held by qualified intermediaries for possible investments in like-kind exchanges in accordance with Section 1031 of the Internal Revenue Code in connection with sales of the Company’s properties. Restricted cash is included in the “Other assets” caption in the consolidated balance sheets.
Accounts Receivable And Accrued Rent Receivable	Accounts Receivable and Accrued Rent Receivable Generally, leases with tenants are accounted for as operating leases. Minimum annual rentals under tenant leases are recognized on a straight-line basis over the term of the related lease. The cumulative difference between lease revenue recognized under the straight-line method and contractual lease payment terms are recorded as “Accrued rent receivable, net” on the accompanying consolidated balance sheets. Included in current tenant receivables are tenant reimbursements which are comprised of amounts recoverable from tenants for common area maintenance expenses and certain other recoverable expenses that are recognized as revenue in the period in which the related expenses are incurred. As of December 31, 2017 and 2016, no tenant represented more than 10% of accounts receivable and accrued rent receivable. Tenant receivables and accrued rent receivables are carried net of the allowances for doubtful accounts of $3.5 million and $13.6 million in 2017, respectively, and $2.4 million and $13.7 million in 2016, respectively. The tenant receivables allowance is an estimate based on two calculations that are combined to determine the total amount reserved. First, the Company evaluates specific accounts where it has determined that a tenant may have an inability to meet its financial obligations. In these situations, the Company uses its judgment, based on the facts and circumstances, and records a specific reserve for that tenant against amounts due to reduce the receivable to the amount that the Company expects to collect. These reserves are reevaluated and adjusted as additional information becomes available. Second, a reserve is established for all tenants based on a range of percentages applied to receivable aging categories for tenant receivables. For accrued rent receivables, the Company considers the results of the evaluation of specific accounts and also considers other factors including assigning risk factors to different industries based on its tenants Standard Industrial Classification (SIC). The accrued rent receivable allowance percentages are also based on historical collection and write-off experience adjusted for current market conditions, which requires management’s judgments.
Investments in Unconsolidated Real Estate Ventures	Investments in Unconsolidated Real Estate Ventures Under the equity method, investments in unconsolidated Real Estate Ventures are recorded initially at cost, as Investments in unconsolidated Real Estate Ventures, and subsequently adjusted for equity in earnings, cash contributions, distributions and impairments. For Real Estate Ventures that are constructing assets to commence planned principal operations, the Company capitalizes interest expense using the Company’s weighted average interest rate of consolidated debt and its investment balance as a basis. Planned principal operations commence when a property is available to lease and at that point in time, the Company ceases capitalizing interest to its investment basis. During the twelve months ended December 31, 2017, 2016 and 2015, the Company capitalized interest expense of $0.4 million, $1.9 million and $2.0 million. On a periodic basis, management also assesses whether there are any indicators that the value of the Company’s investments in unconsolidated Real Estate Ventures may be other than temporarily impaired. An investment is impaired only if the value of the investment, as estimated by management, is less than the carrying value of the investment and the decline is other than temporary. To the extent that an impairment has occurred, the loss shall be measured as the excess of the carrying amount of the investment over the fair value of the investment, as estimated by management. Management is required to make significant judgements about the fair value of its ownership interests to determine if an impairment exists. Fair value is determined through various valuation techniques, including but not limited to, discounted cash flow models, quoted market values and third party appraisals. When the Company acquires an interest in or contributes assets to a real estate venture project, the difference between the Company’s cost basis in the investment and the value of the real estate venture or asset contributed is amortized over the life of the related assets, intangibles and liabilities and such adjustment is included in the Company’s share of equity in income of unconsolidated Real Estate Ventures. For purposes of cash flow presentation, distributions from unconsolidated Real Estate Ventures are presented as part of operating activities when they are considered as a return on investments. The Company elected, in connection with its adoption of ASU 2016-15, “Classification of Certain Cash Receipts and Cash Payments” (ASU 2016-15) during the fourth quarter of 2016, to continue to account for
Deferred Costs	Deferred Costs Costs incurred in connection with property leasing are capitalized as deferred leasing costs. Deferred leasing costs consist primarily of leasing commissions and internal leasing costs that are amortized using the straight-line method over the life of the respective lease which generally ranges from 1 to 16 years. Management re-evaluates the remaining useful lives of leasing costs as economic and market conditions change.
Notes Receivable	Notes Receivable The Company accounts for notes receivable on its balance sheet at amortized cost, net of allowance for loan losses. Interest income is recognized over the term of the notes receivable and is calculated based on the terms of the contractual terms of each note agreement. Notes receivable are placed on nonaccrual status when management determines, after considering economic and business conditions and collection efforts, that the loans are impaired or collection of interest is doubtful. Uncollectible interest previously accrued is recognized as bad debt expense. Interest income on nonaccrual loans is recognized only to the extent that cash payments are received. A note receivable was given to an unaffiliated third party during the third quarter of 2016 to facilitate its acquisition and development of an industrial facility located in Pennsauken, New Jersey. The loan matures three years after the payment commencement date, which is 90 days after substantial completion of the development, and bears interest at 6.3% during year one, 7.0% during year two and 8.0% during year three. The Company evaluated its investment in the note receivable under ASC 310, “Receivables” and determined that the loan was provided at market terms and the Company does not participate in the residual profit of the unaffiliated third party. Accordingly, the investment, totaling $3.5 million as of December 31, 2017 and $3.4 million as of December 31, 2016, has been classified on the Company’s balance sheet as a note receivable within the “Other assets” caption on the accompanying consolidated balance sheets.
Deferred Financing Costs	Deferred Financing Costs Costs incurred in connection with debt financing are capitalized as a direct deduction from the carrying value of the debt, except for costs capitalized related to the Company’s revolving credit facility, which are capitalized within the “Deferred costs, net” caption on the accompanying consolidated balance sheets. Deferred financing costs are charged to interest expense over the terms of the related debt agreements. Deferred financing costs consist primarily of loan fees which are amortized over the related loan term on a basis that approximates the effective interest method. Deferred financing costs are accelerated, when debt is extinguished, as part of the “Interest expense-amortization of deferred financing costs” caption within the Company’s consolidated statements of operations. Original issue discounts are recognized as part of the gain or loss on extinguishment of debt, as appropriate.
Revenue Recognition	Revenue Recognition Rental revenue is recognized on the straight-line basis, which averages minimum rent over the terms of the lease from the later of the date of the commencement of the lease or the date of acquisition of the property subject to existing leases. The straight-line rent adjustment increased revenue by approximately $24.9 million in 2017, $26.3 million in 2016 and $21.6 million in 2015. Deferred rents on the balance sheet represent rental revenue received prior to their due dates and amounts paid by the tenant for certain improvements considered to be landlord assets that will remain as the Company’s property at the end of the tenant’s lease term. The amortization of the amounts paid by the tenant for such improvements is calculated on a straight-line basis over the term of the tenant’s lease and is a component of straight-line rental income and increased revenue by $2.2 million in 2017, $2.1 million in 2016 and $2.0 million in 2015. Lease incentives, which are included as reductions of rental revenue in the accompanying consolidated statements of operations, are recognized on a straight-line basis over the term of the lease. Lease incentives decreased revenue by $1.8 million in 2017, $2.0 million in 2016 and $1.8 million in 2015. In addition, the Company’s rental revenue is impacted by the Company’s determination of whether improvements to the properties, whether made by the Company or by the tenant, are landlord assets. The determination of whether an improvement is a landlord asset requires judgment. In making this judgment, the Company’s primary consideration is whether the improvement would be utilizable by another tenant upon move out of the improved space by the then-existing tenant. If the Company has funded an improvement that it determines not to be landlord assets, then it treats the cost of the improvement as a lease incentive. If the tenant has funded the improvement that the Company determines to be landlord assets, then the Company treats the costs of the improvement as deferred revenue and amortizes this cost into revenue over the lease term. For certain leases, the Company makes significant assumptions and judgments in determining the lease term, including assumptions when the lease provides the tenant with an early termination option. The lease term impacts the period over which the Company determines and records minimum rents and also impacts the period over which the Company amortizes lease-related costs. The Company’s leases also typically provide for tenant reimbursement of a portion of common area maintenance expenses and other operating expenses to the extent that a tenant’s pro rata share of expenses exceeds a base year level set in the lease or to the extent that the tenant has a lease on a triple net basis. Recoveries from tenants, consisting of amounts due from tenants for common area maintenance expenses, real estate taxes and other recoverable costs are recognized as revenue in the period during which the expenses are incurred. Tenant reimbursements are recognized and presented in accordance with accounting guidance which requires that these reimbursements be recorded on a gross basis because the Company is generally the primary obligor with respect to the goods and services the purchase of which gives rise to the reimbursement obligation; because the Company has discretion in selecting the vendors and suppliers; and because the Company bears the credit risk in the event they do not reimburse the Company. The Company also receives payments from third parties for reimbursement of a portion of the payroll and payroll-related costs for certain of the Company’s personnel allocated to perform services for these third parties and reflects these payments on a gross basis. The Company recognizes gains on sales of real estate at times and in amounts determined in accordance with the accounting guidance for sales of real estate. The guidance takes into account the terms of the transaction and any continuing involvement, including in the form of management, leasing of space or financial assistance associated with the properties. If the sales criteria for the full accrual method are not met, then the Company defers some or all of the gain recognition and accounts for the continued operations of the property by applying the finance, leasing, profit sharing, deposit, installment or cost recovery method, as appropriate, until the sales criteria are met. The Company derives parking revenues from leases, monthly parking and transient parking. The Company recognizes parking revenue as earned. The Company’s flexible stay revenue consists of room revenue, food and beverage revenue, and revenue from other hotel operating departments (such as parking fees and other guest service fees). These revenues are recorded net of any sales and occupancy taxes collected from the hotel guests. All rebates or discounts are recorded as a reduction to revenue, and there are no material contingent obligations with respect to rebates and discounts offered by the hotel. All revenues are recorded on an accrual basis as they are earned. Any cash received prior to a guest’s arrival is recorded as an advance deposit from the guest and recognized as revenue at the time of the guest's occupancy at the hotel property. The Company receives leasing commission income, property management fees and third party development fees. Leasing commission income is earned based on a percentage of gross rental income upon a tenant signing a lease with a third party lessor. Property management fees are recorded and earned based on a percentage of collected rents at the properties under management, and not on a straight-line basis because such fees are contingent upon the collection of rents. The Company records development fees on a percentage of completion basis taking into account the risk associated with each project. The Company recognizes fees received for lease terminations as revenue and writes off against such revenue any deferred rents receivable. The resulting net amount is the net revenue from the early termination of the leases. When a tenant's lease for space in a property is terminated early but the tenant continues to lease such space under a new or modified lease in the property, the net revenue from the early termination of the lease is recognized evenly over the remaining life of the new or modified lease in place on that property, unless the Company cannot determine that collectability of the lease termination revenue is reasonably assured. No tenant represented greater than 10% of the Company’s rental revenue in 2017, 2016 or 2015.
Income Taxes	Income Taxes Parent Company The Parent Company has elected to be treated as a REIT under Sections 856 through 860 of the Internal Revenue Code of 1986, as amended (the “Code”). In order to continue to qualify as a REIT, the Parent Company is required to, among other things, distribute at least 90% of its annual REIT taxable income to its shareholders and meet certain tests regarding the nature of its income and assets. As a REIT, the Parent Company is not subject to federal and state (in states that follow federal rules) income taxes with respect to the portion of its income that meets certain criteria and is distributed annually to its shareholders. Accordingly, a nominal provision for federal and state (as applicable) income taxes is included in the accompanying consolidated financial statements with respect to the operations of the Parent Company. The Parent Company intends to continue to operate in a manner that allows it to meet the requirements for taxation as a REIT. If the Parent Company fails to qualify as a REIT in any taxable year, it will be subject to federal and state (as applicable) income taxes and may not be able to qualify as a REIT for the four subsequent tax years. The Parent Company is subject to certain local income taxes. Provision for federal income taxes is recorded in the income tax provision line item and state and local income taxes have been included in operating expenses in the Parent Company’s Consolidated Statements of Operations and Comprehensive Income. The tax basis of the Parent Company’s assets was $3.1 billion and $3.0 billion for the years ended December 31, 2017 and December 31, 2016, respectively. The Parent Company is subject to a 4% federal excise tax if sufficient taxable income is not distributed within prescribed time limits. The excise tax equals 4% of the annual amount, if any, by which the sum of (a) 85% of the Parent Company’s ordinary income and (b) 95% of the Parent Company’s net capital gain exceeds cash distributions and certain taxes paid by the Parent Company. No excise tax was incurred in 2017, 2016 or 2015. The Parent Company has elected to treat several of its subsidiaries as taxable REIT subsidiaries (each a “TRS”). A TRS is subject to federal, state and local income tax. In general, a TRS may perform non-customary services for tenants, hold assets that the Parent Company, as a REIT, cannot hold directly and generally may engage in any real estate or non-real estate related business. The Company’s taxable REIT subsidiaries did not have significant tax provisions or deferred income tax items as of December 31, 2017 and December 31, 2016. During January 2017, the Company placed into service the hotel operations at FMC Tower. In order for the income from hotel property investments to constitute “ rents from real property Legislation commonly known as the Tax Cuts and Jobs Act (the “TCJA”) was signed into law on December 22, 2017. The TCJA makes significant changes to the U.S. federal income tax rules for taxation of individuals and corporations (including REITs), generally effective for taxable years beginning after December 31, 2017. Operating Partnership In general, the Operating Partnership is not subject to federal and state income taxes, and accordingly, no provision for income taxes has been made in the accompanying consolidated financial statements. The partners of the Operating Partnership are required to include their respective share of the Operating Partnership’s profits or losses in their respective tax returns. The Operating Partnership’s tax returns and the amount of allocable Partnership profits and losses are subject to examination by federal and state taxing authorities. If such examination results in changes to the Operating Partnership profits or losses, then the tax liability of the partners would be changed accordingly. The tax basis of the Operating Partnership’s assets was $3.1 billion and $3.0 billion for the years ended December 31, 2017 and December 31, 2016, respectively. The Operating Partnership may elect to treat a subsidiary REIT under Sections 856 through 860 of the Code, if applicable. Each subsidiary REIT would be required to meet the requirements for treatment as a REIT under Sections 856 through 860 of the Code. If a subsidiary REIT fails to qualify as a REIT in any taxable year, that subsidiary REIT would be subject to federal and state income taxes and would not be able to qualify as a REIT for the four subsequent taxable years. Also, each subsidiary REIT would be subject to certain local income taxes. The Operating Partnership has elected to treat several of its subsidiaries as TRSs, which are subject to federal, state and local income tax. The Company accounts for income taxes using the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to the differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases, and for net operating loss, capital loss and tax credit carryforwards. The deferred tax assets and liabilities are measured using the enacted income tax rates in effect for the year in which those temporary differences are expected to be realized or settled. The effect on the deferred tax assets and liabilities from a change in tax rates is recognized in earnings in the period when the new rate is enacted. However, deferred tax assets are recognized only to the extent that it is more likely than not that they will be realized based on consideration of all available evidence, including the future reversals of existing taxable temporary differences, future projected taxable income and tax planning strategies. Valuation allowances are provided if, based upon the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.
Earnings Per Share	Earnings Per Share Basic earnings per share (“EPS”) is computed by dividing net income available to common shareholders, as adjusted for unallocated earnings, if any, of certain securities, by the weighted average number of common shares outstanding during the year. Diluted EPS reflects the potential dilution that could occur from common shares issuable in connection with awards under share-based compensation plans, including upon the exercise of stock options, and conversion of the noncontrolling interests in the Operating Partnership. Anti-dilutive shares are excluded from the calculation. Earnings Per Unit Basic EPS is computed by dividing net income available to common unitholders, as adjusted for unallocated earnings, if any, of certain securities issued by the Operating Partnership, by the weighted average number of common unit equivalents outstanding during the year. Diluted EPS reflects the potential dilution that could occur from units issuable in connection with awards under share-based compensation plans, including upon the exercise of stock options. Anti-dilutive units are excluded from the calculation.
Share-Based Compensation Plans	Share-Based Compensation Plans The Parent Company maintains a shareholder-approved equity-incentive plan known as the Amended and Restated 1997 Long-Term Incentive Plan (the “1997 Plan”). The 1997 Plan is administered by the Compensation Committee of the Parent Company’s Board of Trustees. Under the 1997 Plan, the Compensation Committee is authorized to award equity and equity-based awards, including incentive stock options, non-qualified stock options, restricted shares and performance-based shares. On May 18, 2017, an additional 2,663,886 awards were authorized for issuance, bringing the total authorized awards to 6,500,000. As of December 31, 2017, 3,838,008 awards had been granted, which included 2,238,590 awards for options and share appreciation rights, leaving 2,661,992 awards available for future issuance under the 1997 Plan. The Company incurred share-based compensation expense of $6.3 million during 2017, of which $1.2 million was capitalized as part of the Company’s review of employee salaries eligible for capitalization. The Company incurred share-based compensation expense of $5.6 million and $7.3 million during 2016 and 2015, of which $1.0 million and $1.9 million, respectively, were also capitalized. The expensed amounts are included in general and administrative expense on the Company’s consolidated income statement in the respective periods.
Comprehensive Income	Comprehensive Income Comprehensive income is recorded in accordance with the provisions of the accounting standard for comprehensive income. The accounting standard establishes standards for reporting comprehensive income and its components in the financial statements. Comprehensive income includes the effective portions of changes in the fair value of derivatives.
Accounting for Derivative Instruments and Hedging Activities	Accounting for Derivative Instruments and Hedging Activities The Company accounts for its derivative instruments and hedging activities in accordance with the accounting standard for derivative and hedging activities. The accounting standard requires the Company to measure every derivative instrument (including certain derivative instruments embedded in other contracts) at fair value and record them on the balance sheet as either an asset or liability. See disclosures below related to the accounting standard for fair value measurements and disclosures. For derivatives designated as cash flow hedges, the effective portions of changes in the fair value of the derivative are reported in other comprehensive income while the ineffective portions are recognized in earnings. The Company actively manages its ratio of fixed-to-floating rate debt. To manage its fixed and floating rate debt in a cost-effective manner, the Company, from time to time, enters into interest rate swap agreements as cash flow hedges, under which it agrees to exchange various combinations of fixed and/or variable interest rates based on agreed upon notional amounts.
Fair Value Measurements	Fair Value Measurements The Company estimates the fair value of its derivatives in accordance with the accounting standard for fair value measurements and disclosures. The accounting standard defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. It also establishes a fair value hierarchy which requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. The standard describes three levels of inputs that may be used to measure fair value. Financial assets and liabilities recorded on the consolidated balance sheets are categorized based on the inputs to the valuation techniques as follows: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access; • Level 2 inputs are inputs, other than quoted prices included in Level 1, which are observable for the asset or liability, either directly or indirectly. Level 2 inputs may include quoted prices for similar assets and liabilities in active markets, as well as inputs that are observable for the asset or liability (other than quoted prices), such as interest rates, foreign exchange rates, and yield curves that are observable at commonly quoted intervals; and • Level 3 inputs are unobservable inputs for the asset or liability, which is typically based on an entity’s own assumptions, as there is little if any, related market activity or information. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment, and considers factors specific to the asset or liability. Non-financial assets and liabilities recorded at fair value on a non-recurring basis include non-financial assets and liabilities measured at fair value in a business combination and the impairment or disposal of long-lived assets measured at fair value. The Company periodically reviews its long-lived assets and equity method investments for other than temporary impairment. Any impairments recorded on equity method investments would be recorded at fair value on a non-recurring basis. The fair values assigned to the Company's purchase price allocations primarily utilize Level 3 inputs. The fair value assigned to the long-lived assets for which there was impairment recorded utilize Level 3 inputs.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2017, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2017-12 (“ASU 2017-12”) to simplify the application of hedge accounting guidance and improve the financial reporting of hedging relationships to better portray the economic results of an entity’s risk management activities in its financial statements. In addition, ASU 2017-12 requires an entity to present the earnings effect of the hedging instrument in the same income statement line item in which the earnings effect of the hedged item is reported. The transition guidance provides companies with the option of early adopting the new standard using a modified retrospective transition method in any interim period after issuance of the update, or alternatively requires adoption for fiscal years beginning after December 15, 2018. This adoption method requires companies to recognize the cumulative effect of initially applying the guidance as an adjustment to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year that an entity adopts the update. The Company is in the process of evaluating the impact of this new guidance on its consolidated financial statements. In May 2017, the FASB issued ASU No. 2017-09 (“ASU 2017-09”) to provide guidance to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new guidance, modification accounting is required only if the fair value, the vesting conditions, or the classification of the award (as equity or liability) changes as a result of the changes in terms or conditions. ASU 2017-09 is effective for all entities for annual periods, and interim periods within those annual periods, beginning after December 15, 2017. Early adoption is permitted and application is prospective. As the application is prospective, there is no impact on the consolidated financial statement presented herein. In February 2017, the FASB issued ASU No. 2017-05 (“ASU 2017-05”) to provide guidance for recognizing gains and losses from the transfer of nonfinancial assets and in-substance nonfinancial assets in contracts with non-customers, unless other specific guidance applies. The standard requires a company to derecognize nonfinancial assets once it transfers control of a distinct nonfinancial asset or distinct in substance nonfinancial asset. Additionally, when a company transfers its controlling interest in a nonfinancial asset, but retains a noncontrolling ownership interest, the company is required to measure any noncontrolling interest it receives or retains at fair value. The guidance requires companies to recognize a full gain or loss on the transaction. As a result of the new guidance, the guidance specific to real estate sales in ASC 360-20 will be eliminated. ASU 2017-05 is effective for annual periods beginning after December 15, 2017, including interim periods within that reporting period. The effective date of this guidance coincides with revenue recognition guidance. The Company expects to utilize the modified retrospective approach. Under the modified retrospective approach, the Company is required to evaluate incomplete contracts as of December 31, 2017 to determine if the sale recognition of nonfinancial assets under ASU 2017-05 differs from ASC 360-20. The Company has identified three sale contracts that may not be considered completed contracts, as defined under ASU 2017-05 by December 31, 2017. Based on our final assessment of these sale contracts, the revenue and remaining gain on sale for each of these property sales will be recognized when the Company fulfills its performance obligations under each contract. Accordingly, the derecognition of nonfinancial assets and revenue recognition patterns are not expected to change under ASU 2017-05 when compared to ASC 360-20. In January 2017, the FASB issued ASU 2017-01, “Business Combinations (Topic 805): Clarifying the Definition of a Business” (“ASU 2017-01”). ASU 2017-01 clarifies the framework for determining whether an integrated set of assets and activities meets the definition of a business. The revised framework establishes a screen for determining whether an integrated set of assets and activities is a business and narrows the definition of a business, which is expected to result in fewer transactions being accounted for as business combinations. Acquisitions of integrated sets of assets and activities that do not meet the definition of a business are accounted for as asset acquisitions. This update is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2017, with early adoption permitted for transactions that have not been reported in previously issued (or available to be issued) financial statements and shall be applied on a prospective basis. The Company early adopted ASU 2017-01 during the first quarter of 2017. The Company expects that acquisitions of real estate or in-substance real estate will not meet the revised definition of a business because substantially all of the fair value is concentrated in a single identifiable asset or group of similar identifiable assets (i.e. land, buildings, and related intangible assets) or because the acquisition does not include a substantive process in the form of an acquired workforce or an acquired contract that cannot be replaced without significant cost, effort or delay. In November 2016, the FASB issued guidance requiring that the statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts described as restricted cash or cash equivalents. Beginning-of-period and end-of-period total amounts shown on the statement of cash flows should include restricted cash, cash equivalents and amounts described as restricted cash or cash equivalents. The guidance does not provide a definition of restricted cash or restricted cash equivalents. The guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. As of December 31, 2017 and December 31, 2016, we had $1.3 million and $0.7 million of restricted cash, respectively, on our consolidated balance sheets. Subsequent to the adoption of this ASU, restricted cash balances will be included with cash and cash equivalents balances as of the beginning and ending of each period presented in our consolidated statements of cash flows; separate line items reconciling changes in restricted cash balances to the changes in cash and cash equivalents will no longer be presented within the operating and investing sections of our consolidated statements of cash flows In June 2016, the FASB issued guidance that changes how entities measure credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. The guidance replaces the current incurred loss model with an expected loss approach, resulting in more timely recognition of such losses. The guidance is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted after December 2018. The Company is in the process of evaluating the impact of this new guidance and determined that the adoption of the guidance will have an impact on the Company’s estimation of its allowance for doubtful accounts. The Company has not quantified the impact that this guidance will have on its consolidated financial statements. In May 2016, the FASB issued guidance amending the revenue from contracts with customers standard issued in May 2014. The amendments are intended to address implementation issues that were raised by stakeholders and discussed by the Joint Transition Resource Group, and provide additional practical expedients on collectability, noncash consideration, presentation of sales tax and contract modifications and completed contracts at transition. In accordance with the FASB election to defer the effective date of the revenue recognition standard by one year, reporting entities may choose to adopt the standard as of its original effective date or for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Calendar year-end reporting entities are therefore required to apply the new revenue guidance beginning in their 2018 interim and annual financial statements. The Company has evaluated the impact of this new guidance and has determined that the impact of the adoption of this guidance is not material to its financial results. In order to evaluate this standard, the Company analyzed all of its revenue streams except for rental revenue because rental revenue recognition is under the scope of ASC 842. The results of the final assessment are as follows: • The Company analyzed its tenant reimbursement revenue and determined that the performance obligations set forth in the Company’s lease agreements will not change the revenue recognition pattern. • The Company identified similar performance obligations under this standard as compared with deliverables and separate units of account previously identified for leasing commissions, management fees, parking revenue, hotel and restaurant revenues and other sundry revenues. As a result, the Company determined that the timing of its leasing commissions, management fees, parking revenue, hotel and restaurant revenues and other sundry revenues will remain the same. • The Company determined that its revenue recognition pattern for development fee revenues will change under the revenue from contracts with customers standard. For all contracts that are not complete as of December 31, 2017, the Company will adopt the input method under the accounting standard. This methodology replaces the percentage of completion method under the current revenue recognition accounting guidance. Although the accounting under the input method is similar to the percentage of completion method, variable income components are evaluated differently under revenue with contracts from customers when compared to the current revenue recognition standard. Additionally, the Company currently recognizes development fee revenue related to its development services provided for certain third party customers under the completed contract method of accounting. This concept is no longer relevant under the new standard because the Company can measure the inputs that are included in the construction services provided to third party customers and will recognize development fee revenue over time rather than at a point in time. As of December 31, 2017, there are no open development contracts, as defined by the accounting standard. As a result, there is no impact of this standard on current development fee income. • Currently, the Company is evaluating the disclosure requirements in the guidance and has not determined the impact on the footnote disclosures to its consolidated financial statements. In February 2016, the FASB issued guidance modifying the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease, respectively. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for in the same manner as operating leases today. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. The guidance supersedes previously issued guidance under ASC Topic 840 “Leases.” The guidance is effective on January 1, 2019, with early adoption permitted. The ASU is expected to have the following impact on the Company’s consolidated financial statements: • The Company is in the process of separating lease components due under its leases from non-lease components. Under ASC 842 as a lessor, lease components will be recognized on a straight line basis, while non-lease components will be recognized in accordance with the new revenue standard. The Company is in the process of evaluating the impact the ASU will have on its consolidated financial statements. • The Company’s tenant reimbursement revenues generated from common area and maintenance services that are provided to its tenants are considered a non-lease component that must be separated, allocated based on the transaction price allocation guidance and accounted for according to the new revenue standard. • ASC 842 is expected to impact the Company’s consolidated financial statements as the Company has land lease arrangements for which it is the lessee. • The Company will expense additional costs related to leasing efforts under ASC 842 compared to the previous GAAP because certain activities performed by personnel involved in the leasing process will no longer be considered incremental costs to execute a lease agreement. • The Company’s equity-method investments may adopt the standard using the timeline otherwise afforded private companies. The Company anticipates the impact of ASC 842 will be similar to the items described above. In January 2018, the FASB issued a proposed amendment to the lease ASU that would allow lessors to elect, as a practical expedient, not to allocate the total consideration to lease and nonlease components based on their relative standalone selling prices. If adopted, this practical expedient will allow lessors to elect a combined single lease component presentation if (i) the timing and pattern of the revenue recognition of the combined single lease component is the same, and (ii) the related lease component and, the combined single lease component would be classified as an operating lease. We have not completed our analysis of this ASU. If the proposed practical expedient mentioned above is adopted and we elect it, we expect tenant recoveries that qualify as nonlease components will be presented under a single lease component presentation. However, without the proposed practical expedient, we expect that our tenant recoveries would be separated into lease and nonlease components. Tenant recoveries that qualify as lease components, which relate to the right to use the leased asset (e.g., property taxes, and insurance), would be accounted for under the new lease ASU. Tenant recoveries that qualify as nonlease components, which relate to payments for goods or services that are transferred separately from the right to use the underlying asset, including tenant recoveries pertaining to payments for maintenance activities and common area expenses, would be accounted for under the new revenue recognition ASU upon adoption of the new lease ASU.

Summary of Significant Accoun36

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Compensation Costs (Including Bonuses and Benefits) Capitalized	During the years ended December 31, 2017, 2016 and 2015, the Company’s internal direct construction costs are comprised entirely of capitalized salaries. The following table shows the amount of compensation costs (including bonuses and benefits) capitalized for the years presented (in thousands): December 31, 2017 2016 2015 Development $ 4,390 $ 3,182 $ 2,641 Redevelopment 319 144 221 Tenant Improvements 1,354 3,391 4,429 Total $ 6,063 $ 6,717 $ 7,291

Real Estate Investments (Tables

Real Estate Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Real Estate Properties [Line Items]
Gross Carrying Value Of Company's Properties	As of December 31, 2017 and 2016 the gross carrying value of the Company’s Properties was as follows (in thousands): December 31, December 31, 2017 2016 Land $ 492,197 $ 469,522 Building and improvements 2,896,113 2,683,087 Tenant improvements 444,038 433,686 Operating properties 3,832,348 3,586,295 Assets held for sale - real estate investments (a) - 73,591 Total $ 3,832,348 $ 3,659,886 (a) Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation, land held for development or other assets on the balance sheets of the properties held for sale. See 2016 Held for Sale section below.
Schedule of Purchase Price Allocation	The purchase price has been allocated as follows (in thousands): October 13, 2017 Building and improvements $ 30,583 Construction-in-progress 672 Intangible assets acquired (a) 10,575 Below market lease liabilities assumed (b) (4,055 ) $ 37,775 (a) (b) The purchase price has been allocated as follows (in thousands): July 28, 2017 Building, land and improvements $ 32,004 Intangible assets acquired (a) 2,562 Below market lease liabilities assumed (b) (1,818 ) $ 32,748 (a) (b) The purchase price has been allocated as follows (in thousands): June 22, 2015 Building, land and improvements $ 163,271 Land inventory 6,045 Intangible assets acquired (a) 50,637 Below market lease liabilities assumed (b) (8,600 ) $ 211,353 Return of existing equity method investment (66,324 ) Gain on remeasurement (758 ) Net working capital assumed (450 ) Total cash payment at settlement $ 143,821 (a) Weighted average amortization period of 4.0 years. (b) Weighted average amortization period of 1.5 years
Dispositions	The Company sold the following properties during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Type Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) November 22, 2017 11, 14, 15, 17 and 18 Campus Boulevard (Newtown Square) Newtown Square, PA Office 5 252,802 $ 42,000 $ 40,459 $ 19,642 October 31, 2017 630 Allendale Road King of Prussia, PA Office 1 150,000 17,500 16,580 3,605 June 27, 2017 Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) Marlton, NJ Office 4 134,794 9,700 8,650 (325 ) (b) June 12, 2017 7000 Midlantic Drive Mount Laurel, NJ Retail 1 10,784 8,200 7,714 1,413 March 30, 2017 200, 210 & 220 Lake Drive East (Woodland Falls) Cherry Hill, NJ Office 3 215,465 19,000 17,771 (249 ) (c) March 15, 2017 Philadelphia Marine Center (Marine Piers) Philadelphia, PA Mixed-use 1 181,900 21,400 11,182 6,498 (d) March 13, 2017 11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) Beltsville, MD Office 3 313,810 9,000 8,354 - (e) February 2, 2017 1200 & 1220 Concord Avenue (Concord Airport Plaza) Concord, CA Office 2 350,256 33,100 32,010 551 (f) Total Dispositions 20 1,609,811 $ 159,900 $ 142,720 $ 31,135 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, which reduced the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (c) As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (d) On March 15, 2017, the Company sold its sublease interest in the Piers at Penn’s Landing (the “Marine Piers”), which includes leasehold improvements containing 181,900 net rentable square feet, and a marina, located in Philadelphia, Pennsylvania for an aggregate sales price of $21.4 million. On the closing date, the buyer paid $12.0 million in cash. The $9.4 million balance of the purchase is due on (a) January 31, 2020, in the event that the tenant at the Marine Piers does not exercise an option it holds to extend the term of the sublease or (b) January 15, 2024, in the event that the tenant does exercise the option to extend the term of the sublease. In accordance with ASC 360-20, “Real Estate Sales,” the Company determined that it is appropriate to account for the sales transaction under the cost recovery method. The Company received cash proceeds of $11.2 million, after closing costs and prorations, and the net book value of the Marine Piers was $4.7 million, resulting in a gain on sale of $6.5 million. The remaining gain on sale of $9.4 million will be recognized on the second purchase price installment date. Prior to its sale, the Marine Piers had been classified as mixed-use within the Company’s property count. (e) During the fourth quarter of 2016, the Company recognized a $3.0 million impairment related to these properties. During the first quarter of 2017, there was a price reduction of $1.7 million under the agreement of sale and an additional impairment of $1.7 million was recognized. (f) During the fourth quarter of 2016, the Company recognized an $11.5 million impairment related to these properties. This sale was designated as a like-kind exchange under Section 1031 of the Internal Revenue Code (“IRC”) and, as such, the proceeds, totaling $32.0 million after closing costs and prorations, were deposited with a Qualified Intermediary, as defined under the IRC. The proceeds received at closing were recorded as “Other assets” in the Company’s consolidated balance sheets. During the third quarter of 2017, the Company acquired 3000 Market Street in Philadelphia, Pennsylvania using the full balance of the Section 1031 proceeds. See “Acquisition” section above. The Company sold the following land parcels during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale September 13, 2017 50 E. Swedesford Square Malvern, PA 1 12.0 $ 7,200 $ 7,098 $ 882 July 18, 2017 Bishop's Gate Mount Laurel, NJ 1 49.5 6,000 5,640 71 (a) April 28, 2017 Garza Ranch - Multi-family Austin, TX 1 8.4 11,800 11,560 - (b) February 15, 2017 Gateway Land - Site C Richmond, VA 1 4.8 1,100 1,043 - (c) January 30, 2017 Garza Ranch - Hotel Austin, TX 1 1.7 3,500 3,277 - (b) Total Dispositions 5 76.4 $ 29,600 $ 28,618 $ 953 (a) During the fourth quarter of 2016, the Company recognized an impairment of $3.0 million. During the second quarter of 2017, the Company recorded a held for sale impairment charge of $0.3 million, reducing the aggregate carrying value of the land parcel from $5.9 million to its estimated fair value less costs to sell of $5.6 million. The fair value measurement is based on pricing in the purchase and sale agreement for the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the input utilized to determine fair value for the property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The land parcel was sold on July 18, 2017. (b) The Company has a continuing involvement in this property through a completion guaranty, which requires the Company, as developer, to complete certain infrastructure improvements on behalf of the buyers of the land parcels. The Company recorded the cash received at settlement as “Deferred income, gains and rent” on the Company’s consolidated balance sheet and the Company will recognize the sale upon completion of infrastructure improvements. See Note 19, “ Commitments and Contingencies ” for further discussion of the infrastructure improvements. (c) During the fourth quarter of 2016, the Company recognized a nominal impairment related to this land parcel. The sales of properties, land and the land parcel held for sale do not represent a strategic shift that has a major effect on the Company's operations and financial results. Accordingly, the operating results of these properties remain classified within continuing operations for all periods presented. The Company sold the following properties during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) October 13, 2016 620, 640, 660 Allendale Road King of Prussia, PA 3 156,669 $ 12,800 $ 12,014 $ 2,382 September 1, 2016 1120 Executive Plaza Mt. Laurel, NJ 1 95,183 9,500 9,241 (18 ) (b) August 2, 2016 50 East Clementon Road Gibbsboro, NJ 1 3,080 1,100 1,011 (85 ) May 11, 2016 196/198 Van Buren Street (Herndon Metro Plaza I&II) Herndon, VA 2 197,225 44,500 43,412 (752 ) (c) February 5, 2016 2970 Market Street (Cira Square) Philadelphia, PA 1 862,692 354,000 350,150 115,828 February 4, 2016 Och-Ziff Portfolio Various 58 3,924,783 398,100 353,971 (372 ) (d) Total Dispositions 66 5,239,632 $ 820,000 $ 769,799 $ 116,983 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of June 30, 2016, the Company determined that the sale of the property was probable and classified this property as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the property exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized a provision for impairment totaling approximately $1.8 million during the three-month period ended June 30, 2016. The fair value measurement was based on the pricing in the purchase and sale agreement for the sale of the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the inputs utilized to determine fair value for this property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, "Fair Value Measurements and Disclosures.” The loss on sale represents additional closing costs recognized at closing. (c) During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing. (d) During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing The Company sold the following land parcels during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale (a) December 2, 2016 Oakland Lot B Oakland, CA 1 0.9 $ 13,750 $ 13,411 $ 9,039 August 19, 2016 Highlands Land Mt. Laurel, NJ 1 2.0 288 284 193 January 15, 2016 Greenhills Land Reading, PA 1 120.0 900 837 - (b) Total Dispositions 3 122.9 $ 14,938 $ 14,532 $ 9,232 (a) Gain on Sale is net of closing and other transaction related costs. (b) The carrying value of the land exceeded the fair value less the anticipated costs of sale as of December 31, 2015. Therefore the Company recognized an impairment loss of $0.3 million during the three-month period ended December 31, 2015. There was no gain or loss recognized on the sale during 2016. The Company sold the following office properties during the twelve-month period ended December 31, 2015 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain on Sale (a) December 31, 2015 5707 Southwest Parkway (Encino Trace) Austin, TX 2 320,000 $ 76,700 $ 50,158 $ 2,008 (b) December 29, 2015 Laurel Corporate Center Mt. Laurel, NJ 6 560,147 56,500 56,253 2,901 December 18, 2015 Carlsbad Properties Carlsbad, CA 3 196,075 30,400 29,568 - (c) December 18, 2015 751-761 Fifth Ave King of Prussia, PA 1 158,000 4,600 4,245 894 September 29, 2015 1000 Howard Boulevard Mt. Laurel, NJ 1 105,312 16,500 15,780 4,828 August 13, 2015 Bay Colony Office Park Wayne, PA 4 247,294 37,500 36,386 269 August 11, 2015 741 First Avenue King of Prussia, PA 1 77,184 4,900 4,640 372 June 10, 2015 100 Gateway Centre Parkway Richmond, VA 1 74,991 4,100 3,911 - (d) April 24, 2015 Christina & Delaware Corporate Centers Wilmington, DE 5 485,182 50,100 49,579 1,749 April 9, 2015 Lake Merritt Tower Oakland, CA 1 204,336 65,000 62,800 - (e) January 8, 2015 1000 Atrium Way / 457 Haddonfield Road (Atrium I / Libertyview) Mt. Laurel, NJ / Cherry Hill, NJ 2 221,405 28,300 26,778 8,981 Total Dispositions 27 2,649,926 $ 374,600 $ 340,098 $ 22,002 (f) (a) Gain on Sale is net of closing and other transaction related costs. (b) On December 31, 2015, the Company contributed two newly constructed four-story, Class A office buildings, commonly known as “Encino Trace,” containing an aggregate of approximately 320,000 square feet in Austin, Texas to one of its existing real estate ventures (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). When these two properties were contributed to the Austin Venture the Company had incurred a total of $76.7 million of development costs, representing the contribution value. In conjunction with the contribution: (i) the Austin Venture obtained a $30.0 million mortgage loan; (ii) DRA contributed $25.1 million in net cash to the capital of the Austin Venture, including a $1.8 million working capital contribution; and (iii) the Austin Venture distributed $50.2 million to the Company and credited the Company with a $23.3 million capital contribution to the Austin Venture. In addition to the contribution of the properties, the Company also made a $1.8 million cash contribution to the Austin Venture for working capital. The Company recognized a $2.0 million gain on the contribution. Under the Encino Trace loan agreement, the Austin Venture has the option, subject to certain leasing and loan-to-value requirements, to borrow an additional $29.7 million to fund tenant improvements and leasing commissions. (c) The Company recorded an impairment loss of $6.3 million for the Carlsbad office properties during the fourth quarter of 2015. As such, there was no gain at disposition for this property. (d) The Company recorded an impairment loss of $0.8 million for 100 Gateway Centre Parkway during the second quarter of 2015. As such, there was no gain at disposition for this property. (e) The Company recorded an impairment loss of $1.7 million for Lake Merritt Tower on March 31, 2015. As such, there was no gain at disposition for this property. Sales proceeds were deposited in escrow under Section 1031 of the Internal Revenue Code and applied to purchase the Broadmoor Austin portfolio. Refer to Broadmoor Austin Associates acquisition summary, above, for further details. (f) Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale. The Company sold the following land parcels during the twelve-month period ended December 31, 2015 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) December 18, 2015 Two Christina Centre Wilmington, DE 1 1.6 $ 6,500 $ 5,986 $ - (b) September 1, 2015 7000 Midlantic Mt. Laurel, NJ 1 3.5 2,200 1,742 (169 ) August 31, 2015 Four Points Austin, TX 1 8.6 2,500 2,344 71 August 25, 2015 Two Kaiser Plaza Oakland, CA 1 1.0 11,100 11,016 3,117 Total Dispositions 4 14.7 $ 22,300 $ 21,088 $ 3,019 (a) Gain/(Loss) on sale includes closing and other transaction related costs. (b) The Company recorded an impairment loss of $0.3 million for Two Christina Centre during the fourth quarter of 2015. As such, there was no gain/(loss) at disposition for this land parcel.
Schedule of Pro Forma Information	The supplemental pro forma operating data is not necessarily indicative of what the actual results of operations would have been assuming the transaction had been completed as set forth above, nor do they purport to represent the Company’s results of operations for future periods (in thousands, except for per share amounts). December 31, 2015 Pro forma revenue $ 612,649 Pro forma income (loss) from continuing operations (36,704 ) Pro forma net income (loss) available to common shareholders (43,594 ) Earnings (loss) per common share from continuing operations: Basic -- as reported $ (0.17 ) Basic -- as pro forma $ (0.21 ) Diluted -- as reported $ (0.17 ) Diluted -- as pro forma $ (0.21 ) Earnings (loss) per common share: Basic -- as reported $ (0.21 ) Basic -- as pro forma $ (0.24 ) Diluted -- as reported $ (0.21 ) Diluted -- as pro forma $ (0.24 )
Held for Sale Properties Included in Continuing Operations [Member]
Real Estate Properties [Line Items]
Summary of Properties Classified as Held for Sale but Which did not Meet the Criteria to be Classified within Discontinued Operations	The following is a summary of properties classified as held for sale at December 31, 2016 but which did not meet the criteria to be classified within discontinued operations at December 31, 2016 (in thousands): Held for Sale Properties Included in Continuing Operations December 31, 2016 Metropolitan D.C. - Office (a) Other Segment - Office (b) Other Segment - Land (c) Total ASSETS HELD FOR SALE Real estate investments: Operating properties $ 21,720 $ 51,871 $ - $ 73,591 Accumulated depreciation (11,935 ) (20,981 ) - (32,916 ) Operating real estate investments, net 9,785 30,890 - 40,675 Land held for development - - 1,043 1,043 Total real estate investments, net 9,785 30,890 1,043 41,718 Total assets held for sale, net $ 9,785 $ 30,890 $ 1,043 $ 41,718 LIABILITIES HELD FOR SALE Other liabilities $ 73 $ 8 $ - $ 81 Total liabilities held for sale $ 73 $ 8 $ - $ 81 (a) As of December 31, 2016, the Company determined that the sale of three office properties in the Metropolitan D.C. segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded their fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $3.0 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 10.00%, respectively. The results were comparable to indicative pricing in the market (b) As The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.75% and 9.75%, respectively. The results were comparable to indicative pricing in the market. (c) As of December 31, 2016, the Company determined that the sale of a land parcel in the Other segment was probable and classified the land parcel as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the land approximated the fair value less the anticipated costs of sale and the Company recorded a nominal impairment. The fair value measurement was based on the pricing in the purchase and sale The following is a summary of properties classified as held for sale but which did it not meet the criteria to be classified within discontinued operations at December 31, 2015 (in thousands ): Held for Sale Properties Included in Continuing Operations December 31, 2015 Och-Ziff Properties (a) 2970 Market Street (b) Greenhills Land (c) Total ASSETS HELD FOR SALE Real estate investments: Operating properties $ 526,099 $ 268,489 $ - $ 794,588 Accumulated depreciation (179,092 ) (34,489 ) - (213,581 ) Operating real estate investments, net 347,007 234,000 - 581,007 Construction-in-progress 1,915 25 - 1,940 Land held for development - - 837 837 Total real estate investments, net 348,922 234,025 837 583,784 Intangible assets 581 - - 581 Total assets held for sale, net $ 349,503 $ 234,025 $ 837 $ 584,365 LIABILITIES HELD FOR SALE Acquired lease intangibles, net $ 192 $ - $ - $ 192 Other liabilities 1,959 - - 1,959 Total liabilities held for sale $ 2,151 $ - $ - $ 2,151 (a) On February 4, 2016, the Company disposed of its interests in 58 properties located in the Pennsylvania Suburbs, New Jersey/Delaware, Metropolitan Washington, D.C. and Richmond, Virginia segments in a series of related transactions with Och Ziff Real Estate. During the fourth quarter of 2015, significant provisions were agreed upon by both the Company and Och Ziff Real Estate and, as a result, the Company determined that the sale of the portfolio was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $45.4 million during the year ended December 31, 2015. The fair value measurement was based on the pricing in the purchase and sale agreement. As the significant inputs to the model are unobservable, the Company determined that the value determined for these real estate investments fall within Level 3 for fair value reporting. (b) On December 23, 2015 the Company entered into a purchase and sale agreement to dispose of its equity interests in the office property located at 2970 Market Street in Philadelphia commonly known as 30 th (c) On January 15, 2016, the Company sold the fee interest in a 120 acre land parcel located in Berks County, Pennsylvania for $0.9 million. As of December 31, 2015, the Company classified this land parcel as held for sale in accordance with the applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $0.3 million during the year ended December 31, 2015.

Investment in Unconsolidated 38

Investment in Unconsolidated Real Estate Ventures (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss)	The Company’s investment in Real Estate Ventures as of December 31, 2017 and 2016, and the Company’s share of the Real Estate Ventures’ income (loss) for the years ended December 31, 2017 and 2016 was as follows (in thousands): Ownership Carrying Amount Company's Share of Real Estate Venture Income (Loss) Real Estate Venture Debt at 100% Current Interest Debt Percentage 2017 2016 2017 2016 2017 2016 Rate Maturity Office Properties Brandywine-AI Venture LLC (b) (h) 50% $ 43,560 $ 67,809 $ (4,465 ) $ (5,895 ) $ 93,117 $ 131,539 3.94 % (c) DRA (G&I) Austin (d) (h) 50% 13,972 52,886 (989 ) (1,880 ) 249,481 405,734 3.51 % (e) MAP Venture (f) 50% 15,450 20,893 (3,443 ) (4,218 ) 180,800 180,800 L+6.25% Feb 2018 (f) Four Tower Bridge (g) 65% 3,032 2,286 746 602 9,749 9,961 5.20 % Feb 2021 PJP VII 25% 1,156 980 175 233 4,792 4,956 L+2.65% Dec 2019 PJP II 30% 604 532 72 97 2,564 2,893 6.12 % Nov 2023 PJP VI 25% 179 142 38 97 7,370 7,652 6.08 % Apr 2023 1000 Chesterbrook Blvd. (h) - - - 160 - - PJP V (h) - - - 127 - - Invesco, L.P. (h) - - - 261 - - Coppell Associates - - - 12 - - Other HSRE-BDN I, LLC (d) 50% 17,671 21,228 449 843 110,886 105,000 L+2.25% Oct 2019 Brandywine 1919 Ventures (d) (i) 50% 22,268 27,462 (194 ) (1,529 ) 88,860 79,250 L+1.75% Oct 2018 TB-BDN Plymouth Apartments (h) - 12,450 99 119 - 53,967 Development Properties 4040 Wilson (j) 50% 37,179 36,356 (255 ) (270 ) 6,664 1,004 L+2.75% Dec 2021 51 N Street 70% 21,212 20,318 (176 ) (114 ) - - 1250 First Street Office 70% 17,867 17,304 (149 ) (15 ) - - Seven Tower Bridge (g) 20% 471 685 (214 ) (133 ) 14,629 14,710 3.17 % (k) $ 194,621 $ 281,331 $ (8,306 ) $ (11,503 ) $ 768,912 $ 997,466 ( a) Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable. (b) See “ Brandywine - AI Venture: 7101 Wisconsin Avenu e” and “ Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture. (c) The debt for these properties is comprised of two fixed rate mortgages: (1) $26.6 million with a 4.65% fixed interest rate due January 1, 2022, and (2) $66.5 million with a 3.22% fixed interest rate due August 1, 2019. (d) The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “ evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. (e) The debt for these properties includes three mortgages: (1) $133.6 million that was swapped to a 1.43% fixed rate (for an all-in fixed rate of 3.44% incorporating the 2.01% spread) due November 1, 2018, (2) $28.7 million with a 4.50% fixed interest rate due April 6, 2019 and (3) $87.1 million that was swapped to a 1.36% fixed rate (or all-in fixed rate of 3.36% incorporating the 2.00% spread) due February 10, 2020. On October 18, 2017, the venture sold eight office buildings, seven of which were encumbered by an aggregate of $151.0 million of mortgage debt. (f) In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option. The first option to extend the maturity date has been exercised and extends the maturity date through February 9, 2019. The two remaining unexercised options extend the maturity through February 9, 2021. (g) Subsequent to December 31, 2017, the Company exchanged its 20% interest in Seven Tower Bridge to acquire the remaining 35% interest in Four Tower Bridge. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information. (h) On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions. (i) The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%. (j) During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million. (k) Comprised of two fixed rate mortgages totaling $8.0 million that matured on March 1, 2017, which are currently in default, and accrue interest at a current rate of 7.00%, a $0.7 million 3.00% fixed rate loan through its September 1, 2025 maturity, a $2.0 million 4.00% fixed rate loan with interest only through its February 7, 2018 maturity and a $3.9 million 3.25% fixed rate loan with interest only beginning March 11, 2018 through its March 11, 2020 maturity. The following is a summary of the financial position of the Real Estate Ventures as of December 31, 2017 and December 31, 2016 (in thousands): December 31, 2017 December 31, 2016 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Net property $ 263,557 $ 158,960 $ 661,448 $ 1,083,965 $ 493,960 $ 229,160 $ 733,883 $ 1,457,003 Other assets 42,272 24,181 95,479 161,932 82,725 33,205 113,987 229,917 Other liabilities 24,131 4,493 69,083 97,707 40,280 6,440 82,967 129,687 Debt, net 248,700 92,917 424,803 766,420 403,671 131,161 454,906 989,738 Equity (a) 32,998 85,731 263,041 381,770 132,734 124,764 309,997 567,495 (a) This amount includes the effect of the basis difference between the Company’s historical cost basis and the basis recorded at the Real Estate Venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from the impairment of investments, purchases of third party interests in existing Real Estate Ventures and upon the transfer of assets that were previously owned by the Company into a Real Estate Venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the Real Estate Venture level. The following is a summary of results of operations of the Real Estate Ventures in which the Company had interests as of December 31, 2017, 2016 and 2015 (in thousands): Twelve-month period ended December 31, 2017 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 85,500 $ 29,500 $ 101,271 $ 216,271 Operating expenses (35,997 ) (12,298 ) (51,045 ) (99,340 ) Interest expense, net (13,985 ) (4,707 ) (21,521 ) (40,213 ) Depreciation and amortization (34,026 ) (11,428 ) (32,986 ) (78,440 ) Loss on extinguishment of debt (2,613 ) (811 ) - (3,424 ) Net income (loss) $ (1,121 ) $ 256 $ (4,281 ) $ (5,146 ) Ownership interest % 50 % 50 % (a) Company's share of net income (loss) $ (560 ) $ 128 $ (1,432 ) $ (1,864 ) Other-than-temporary impairment (b) - (4,844 ) - (4,844 ) Basis adjustments and other (429 ) 251 (1,420 ) (1,598 ) Equity in loss of Real Estate Ventures $ (989 ) $ (4,465 ) $ (2,852 ) $ (8,306 ) Twelve-month period ended December 31, 2016 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 85,749 $ 31,047 $ 97,656 $ 214,452 Operating expenses (37,643 ) (13,654 ) (51,895 ) (103,192 ) Provision for impairment (c) - (10,476 ) - (10,476 ) Interest expense, net (15,052 ) (5,825 ) (19,437 ) (40,314 ) Depreciation and amortization (38,365 ) (12,811 ) (34,562 ) (85,738 ) Net loss (d) $ (5,311 ) $ (11,719 ) $ (8,238 ) $ (25,268 ) Ownership interest % 50 % 50 % (a) Company's share of net loss $ (2,656 ) $ (5,860 ) $ (3,985 ) $ (12,501 ) Basis adjustments and other 776 (35 ) 257 998 Equity in loss of Real Estate Ventures $ (1,880 ) $ (5,895 ) $ (3,728 ) $ (11,503 ) Twelve-month period ended December 31, 2015 DRA (G&I) Austin Brandywine-AI Venture LLC Other Total Revenue $ 78,367 $ 29,428 $ 57,133 $ 164,928 Operating expenses (33,194 ) (11,872 ) (25,070 ) (70,136 ) Interest expense, net (14,025 ) (5,310 ) (15,249 ) (34,584 ) Depreciation and amortization (36,809 ) (12,678 ) (18,613 ) (68,100 ) Net loss $ (5,661 ) $ (432 ) $ (1,799 ) $ (7,892 ) Ownership interest % 50 % 50 % (a) - Company's share of net income (loss) $ (2,831 ) $ (216 ) $ 455 $ (2,592 ) Basis adjustments and other 1,596 (13 ) 198 1,781 Equity in income (loss) of Real Estate Ventures $ (1,235 ) $ (229 ) $ 653 $ (811 ) (a) The Company’s unconsolidated ownership interests range from 20% to 70%, subject to specified priority allocations of distributable cash in certain of the Real Estate Ventures. (b) See “ Brandywine - AI Venture: Other Than Temporary Impairment” section below (c) See “ Brandywine - AI Venture: Station Square Impairment” (d) During the year ended December 31, 2016, there were $7.1 million of acquisition deal costs related to the formation of the MAP Venture.
Schedule of Maturities of Long-term Debt	As of December 31, 2017, the Company’s aggregate scheduled principal payments of debt obligations, excluding amortization of discounts and premiums, are as follows (in thousands): 2018 $ 6,601 2019 7,360 2020 86,978 2021 6,099 2022 256,332 Thereafter 1,585,347 Total principal payments 1,948,717 Net unamortized premiums/(discounts) (6,748 ) Net deferred financing costs (11,141 ) Outstanding indebtedness $ 1,930,828
Dispositions	The Company sold the following properties during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Type Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) November 22, 2017 11, 14, 15, 17 and 18 Campus Boulevard (Newtown Square) Newtown Square, PA Office 5 252,802 $ 42,000 $ 40,459 $ 19,642 October 31, 2017 630 Allendale Road King of Prussia, PA Office 1 150,000 17,500 16,580 3,605 June 27, 2017 Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) Marlton, NJ Office 4 134,794 9,700 8,650 (325 ) (b) June 12, 2017 7000 Midlantic Drive Mount Laurel, NJ Retail 1 10,784 8,200 7,714 1,413 March 30, 2017 200, 210 & 220 Lake Drive East (Woodland Falls) Cherry Hill, NJ Office 3 215,465 19,000 17,771 (249 ) (c) March 15, 2017 Philadelphia Marine Center (Marine Piers) Philadelphia, PA Mixed-use 1 181,900 21,400 11,182 6,498 (d) March 13, 2017 11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) Beltsville, MD Office 3 313,810 9,000 8,354 - (e) February 2, 2017 1200 & 1220 Concord Avenue (Concord Airport Plaza) Concord, CA Office 2 350,256 33,100 32,010 551 (f) Total Dispositions 20 1,609,811 $ 159,900 $ 142,720 $ 31,135 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, which reduced the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (c) As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs. (d) On March 15, 2017, the Company sold its sublease interest in the Piers at Penn’s Landing (the “Marine Piers”), which includes leasehold improvements containing 181,900 net rentable square feet, and a marina, located in Philadelphia, Pennsylvania for an aggregate sales price of $21.4 million. On the closing date, the buyer paid $12.0 million in cash. The $9.4 million balance of the purchase is due on (a) January 31, 2020, in the event that the tenant at the Marine Piers does not exercise an option it holds to extend the term of the sublease or (b) January 15, 2024, in the event that the tenant does exercise the option to extend the term of the sublease. In accordance with ASC 360-20, “Real Estate Sales,” the Company determined that it is appropriate to account for the sales transaction under the cost recovery method. The Company received cash proceeds of $11.2 million, after closing costs and prorations, and the net book value of the Marine Piers was $4.7 million, resulting in a gain on sale of $6.5 million. The remaining gain on sale of $9.4 million will be recognized on the second purchase price installment date. Prior to its sale, the Marine Piers had been classified as mixed-use within the Company’s property count. (e) During the fourth quarter of 2016, the Company recognized a $3.0 million impairment related to these properties. During the first quarter of 2017, there was a price reduction of $1.7 million under the agreement of sale and an additional impairment of $1.7 million was recognized. (f) During the fourth quarter of 2016, the Company recognized an $11.5 million impairment related to these properties. This sale was designated as a like-kind exchange under Section 1031 of the Internal Revenue Code (“IRC”) and, as such, the proceeds, totaling $32.0 million after closing costs and prorations, were deposited with a Qualified Intermediary, as defined under the IRC. The proceeds received at closing were recorded as “Other assets” in the Company’s consolidated balance sheets. During the third quarter of 2017, the Company acquired 3000 Market Street in Philadelphia, Pennsylvania using the full balance of the Section 1031 proceeds. See “Acquisition” section above. The Company sold the following land parcels during the twelve-month period ended December 31, 2017 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale September 13, 2017 50 E. Swedesford Square Malvern, PA 1 12.0 $ 7,200 $ 7,098 $ 882 July 18, 2017 Bishop's Gate Mount Laurel, NJ 1 49.5 6,000 5,640 71 (a) April 28, 2017 Garza Ranch - Multi-family Austin, TX 1 8.4 11,800 11,560 - (b) February 15, 2017 Gateway Land - Site C Richmond, VA 1 4.8 1,100 1,043 - (c) January 30, 2017 Garza Ranch - Hotel Austin, TX 1 1.7 3,500 3,277 - (b) Total Dispositions 5 76.4 $ 29,600 $ 28,618 $ 953 (a) During the fourth quarter of 2016, the Company recognized an impairment of $3.0 million. During the second quarter of 2017, the Company recorded a held for sale impairment charge of $0.3 million, reducing the aggregate carrying value of the land parcel from $5.9 million to its estimated fair value less costs to sell of $5.6 million. The fair value measurement is based on pricing in the purchase and sale agreement for the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the input utilized to determine fair value for the property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The land parcel was sold on July 18, 2017. (b) The Company has a continuing involvement in this property through a completion guaranty, which requires the Company, as developer, to complete certain infrastructure improvements on behalf of the buyers of the land parcels. The Company recorded the cash received at settlement as “Deferred income, gains and rent” on the Company’s consolidated balance sheet and the Company will recognize the sale upon completion of infrastructure improvements. See Note 19, “ Commitments and Contingencies ” for further discussion of the infrastructure improvements. (c) During the fourth quarter of 2016, the Company recognized a nominal impairment related to this land parcel. The sales of properties, land and the land parcel held for sale do not represent a strategic shift that has a major effect on the Company's operations and financial results. Accordingly, the operating results of these properties remain classified within continuing operations for all periods presented. The Company sold the following properties during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) October 13, 2016 620, 640, 660 Allendale Road King of Prussia, PA 3 156,669 $ 12,800 $ 12,014 $ 2,382 September 1, 2016 1120 Executive Plaza Mt. Laurel, NJ 1 95,183 9,500 9,241 (18 ) (b) August 2, 2016 50 East Clementon Road Gibbsboro, NJ 1 3,080 1,100 1,011 (85 ) May 11, 2016 196/198 Van Buren Street (Herndon Metro Plaza I&II) Herndon, VA 2 197,225 44,500 43,412 (752 ) (c) February 5, 2016 2970 Market Street (Cira Square) Philadelphia, PA 1 862,692 354,000 350,150 115,828 February 4, 2016 Och-Ziff Portfolio Various 58 3,924,783 398,100 353,971 (372 ) (d) Total Dispositions 66 5,239,632 $ 820,000 $ 769,799 $ 116,983 (a) Gain/(Loss) on Sale is net of closing and other transaction related costs. (b) As of June 30, 2016, the Company determined that the sale of the property was probable and classified this property as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the property exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized a provision for impairment totaling approximately $1.8 million during the three-month period ended June 30, 2016. The fair value measurement was based on the pricing in the purchase and sale agreement for the sale of the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the inputs utilized to determine fair value for this property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, "Fair Value Measurements and Disclosures.” The loss on sale represents additional closing costs recognized at closing. (c) During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing. (d) During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing The Company sold the following land parcels during the twelve-month period ended December 31, 2016 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain on Sale (a) December 2, 2016 Oakland Lot B Oakland, CA 1 0.9 $ 13,750 $ 13,411 $ 9,039 August 19, 2016 Highlands Land Mt. Laurel, NJ 1 2.0 288 284 193 January 15, 2016 Greenhills Land Reading, PA 1 120.0 900 837 - (b) Total Dispositions 3 122.9 $ 14,938 $ 14,532 $ 9,232 (a) Gain on Sale is net of closing and other transaction related costs. (b) The carrying value of the land exceeded the fair value less the anticipated costs of sale as of December 31, 2015. Therefore the Company recognized an impairment loss of $0.3 million during the three-month period ended December 31, 2015. There was no gain or loss recognized on the sale during 2016. The Company sold the following office properties during the twelve-month period ended December 31, 2015 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Properties Rentable Square Feet Sales Price Net Proceeds on Sale Gain on Sale (a) December 31, 2015 5707 Southwest Parkway (Encino Trace) Austin, TX 2 320,000 $ 76,700 $ 50,158 $ 2,008 (b) December 29, 2015 Laurel Corporate Center Mt. Laurel, NJ 6 560,147 56,500 56,253 2,901 December 18, 2015 Carlsbad Properties Carlsbad, CA 3 196,075 30,400 29,568 - (c) December 18, 2015 751-761 Fifth Ave King of Prussia, PA 1 158,000 4,600 4,245 894 September 29, 2015 1000 Howard Boulevard Mt. Laurel, NJ 1 105,312 16,500 15,780 4,828 August 13, 2015 Bay Colony Office Park Wayne, PA 4 247,294 37,500 36,386 269 August 11, 2015 741 First Avenue King of Prussia, PA 1 77,184 4,900 4,640 372 June 10, 2015 100 Gateway Centre Parkway Richmond, VA 1 74,991 4,100 3,911 - (d) April 24, 2015 Christina & Delaware Corporate Centers Wilmington, DE 5 485,182 50,100 49,579 1,749 April 9, 2015 Lake Merritt Tower Oakland, CA 1 204,336 65,000 62,800 - (e) January 8, 2015 1000 Atrium Way / 457 Haddonfield Road (Atrium I / Libertyview) Mt. Laurel, NJ / Cherry Hill, NJ 2 221,405 28,300 26,778 8,981 Total Dispositions 27 2,649,926 $ 374,600 $ 340,098 $ 22,002 (f) (a) Gain on Sale is net of closing and other transaction related costs. (b) On December 31, 2015, the Company contributed two newly constructed four-story, Class A office buildings, commonly known as “Encino Trace,” containing an aggregate of approximately 320,000 square feet in Austin, Texas to one of its existing real estate ventures (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). When these two properties were contributed to the Austin Venture the Company had incurred a total of $76.7 million of development costs, representing the contribution value. In conjunction with the contribution: (i) the Austin Venture obtained a $30.0 million mortgage loan; (ii) DRA contributed $25.1 million in net cash to the capital of the Austin Venture, including a $1.8 million working capital contribution; and (iii) the Austin Venture distributed $50.2 million to the Company and credited the Company with a $23.3 million capital contribution to the Austin Venture. In addition to the contribution of the properties, the Company also made a $1.8 million cash contribution to the Austin Venture for working capital. The Company recognized a $2.0 million gain on the contribution. Under the Encino Trace loan agreement, the Austin Venture has the option, subject to certain leasing and loan-to-value requirements, to borrow an additional $29.7 million to fund tenant improvements and leasing commissions. (c) The Company recorded an impairment loss of $6.3 million for the Carlsbad office properties during the fourth quarter of 2015. As such, there was no gain at disposition for this property. (d) The Company recorded an impairment loss of $0.8 million for 100 Gateway Centre Parkway during the second quarter of 2015. As such, there was no gain at disposition for this property. (e) The Company recorded an impairment loss of $1.7 million for Lake Merritt Tower on March 31, 2015. As such, there was no gain at disposition for this property. Sales proceeds were deposited in escrow under Section 1031 of the Internal Revenue Code and applied to purchase the Broadmoor Austin portfolio. Refer to Broadmoor Austin Associates acquisition summary, above, for further details. (f) Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale. The Company sold the following land parcels during the twelve-month period ended December 31, 2015 (dollars in thousands): Disposition Date Property/Portfolio Name Location Number of Parcels Acres Sales Price Net Proceeds on Sale Gain/(Loss) on Sale (a) December 18, 2015 Two Christina Centre Wilmington, DE 1 1.6 $ 6,500 $ 5,986 $ - (b) September 1, 2015 7000 Midlantic Mt. Laurel, NJ 1 3.5 2,200 1,742 (169 ) August 31, 2015 Four Points Austin, TX 1 8.6 2,500 2,344 71 August 25, 2015 Two Kaiser Plaza Oakland, CA 1 1.0 11,100 11,016 3,117 Total Dispositions 4 14.7 $ 22,300 $ 21,088 $ 3,019 (a) Gain/(Loss) on sale includes closing and other transaction related costs. (b) The Company recorded an impairment loss of $0.3 million for Two Christina Centre during the fourth quarter of 2015. As such, there was no gain/(loss) at disposition for this land parcel.
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Schedule of Maturities of Long-term Debt	As of December 31, 2017, the aggregate principal payments of recourse and non-recourse debt payable to third-parties are as follows (in thousands): 2018 $ 236,468 2019 390,707 2020 92,679 2021 17,162 2022 25,372 Thereafter 6,524 Total principal payments 768,912 Net deferred financing costs (2,532 ) Outstanding indebtedness $ 766,380
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Dispositions	The summary of the transaction is as follows (in thousands); October 18, 2017 Gross sales price $ 333,250 Debt principal (150,968 ) Debt prepayment penalties (2,120 ) Closing costs and net prorations (7,420 ) Cash to Austin Venture $ 172,742 Company's ownership interest 50 % Cash to the Company $ 86,371 Cash to Austin Venture $ 172,742 Austin Venture basis of sold properties (92,559 ) Austin Venture gain on sale $ 80,183 Company's ownership interest 50 % Company's share of gain $ 40,092 Company's share of gain $ 40,092 Deferred gain from partial sale 12,072 Gain on real estate venture transactions $ 52,164

Deferred Costs (Assets) (Tables

Deferred Costs (Assets) (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure	As of December 31, 2017 and 2016, the Company’s deferred costs (assets) were comprised of the following (in thousands): December 31, 2017 Total Cost Amortization Deferred Costs, net Leasing costs $ 154,481 $ (59,046 ) $ 95,435 Financing costs - Revolving Credit Facility 3,595 (2,335 ) 1,260 Total $ 158,076 $ (61,381 ) $ 96,695 December 31, 2016 Total Cost Accumulated Amortization Deferred Costs, net Leasing costs $ 146,135 $ (56,942 ) $ 89,193 Financing costs - Revolving Credit Facility 3,595 (1,446 ) 2,149 Total $ 149,730 $ (58,388 ) $ 91,342

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	As of December 31, 2017 and 2016, the Company’s intangible assets were comprised of the following (in thousands): December 31, 2017 Total Cost Accumulated Amortization Intangible Assets, net Intangible assets, net: In-place lease value $ 108,060 $ (47,003 ) $ 61,057 Tenant relationship value 11,201 (9,275 ) 1,926 Above market leases acquired 4,545 (2,556 ) 1,989 Total intangible assets, net $ 123,806 $ (58,834 ) $ 64,972 Acquired lease intangibles, net: Below market leases acquired $ 36,213 $ (15,939 ) $ 20,274 December 31, 2016 Total Cost Accumulated Amortization Intangible Assets, net Intangible assets, net: In-place lease value $ 142,889 $ (75,696 ) $ 67,193 Tenant relationship value 13,074 (10,167 ) 2,907 Above market leases acquired 4,718 (2,340 ) 2,378 Total intangible assets, net $ 160,681 $ (88,203 ) $ 72,478 Acquired lease intangibles, net: Below market leases acquired $ 37,579 $ (19,460 ) $ 18,119
Summary of Amortization for Intangible Assets and Liabilities	As of December 31, 2017, the Company’s annual amortization for its intangible assets/liabilities, assuming no early lease terminations, are as follows (dollars in thousands): Assets Liabilities 2018 $ 14,948 $ 3,553 2019 12,438 2,807 2020 9,770 2,042 2021 7,160 1,406 2022 5,093 1,238 Thereafter 15,563 9,228 Total $ 64,972 $ 20,274

Debt Obligations (Tables)

Debt Obligations (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Consolidated debt obligations	The following table sets forth information regarding the Company’s consolidated debt obligations outstanding at December 31, 2017 and 2016 (in thousands): December 31, 2017 December 31, 2016 Effective Interest Rate Maturity Date MORTGAGE DEBT: Two Logan Square $ 84,440 $ 86,012 3.98% May 2020 One Commerce Square 123,667 127,026 3.64% (a) Apr 2023 Two Commerce Square 112,000 112,000 4.51% (b) Apr 2023 Principal balance outstanding 320,107 325,038 Plus: fair market value premium (discount), net (2,325 ) (2,761 ) Less: deferred financing costs (566 ) (728 ) Mortgage indebtedness $ 317,216 $ 321,549 UNSECURED DEBT Seven-Year Term Loan - Swapped to fixed $ 250,000 $ 250,000 3.72% Oct 2022 $300.0M 5.70% Guaranteed Notes due 2017 (c) - 300,000 5.68% May 2017 $325.0M 4.95% Guaranteed Notes due 2018 (d) - 325,000 5.13% Apr 2018 $350.0M 3.95% Guaranteed Notes due 2023 (d) 350,000 250,000 3.87% Feb 2023 $250.0M 4.10% Guaranteed Notes due 2024 250,000 250,000 4.33% Oct 2024 $450.0M 3.95% Guaranteed Notes due 2027 (d) 450,000 - 4.03% Nov 2027 $250.0M 4.55% Guaranteed Notes due 2029 250,000 250,000 4.60% Oct 2029 Indenture IA (Preferred Trust I) (e) 27,062 27,062 LIBOR + 1.25% Mar 2035 Indenture IB (Preferred Trust I) - Swapped to fixed 25,774 25,774 3.30% Apr 2035 Indenture II (Preferred Trust II) - Swapped to fixed 25,774 25,774 3.09% Jul 2035 Principal balance outstanding 1,628,610 1,703,610 Plus: original issue premium (discount), net (4,423 ) (4,678 ) Less: deferred financing costs (10,575 ) (7,369 ) Total unsecured indebtedness $ 1,613,612 $ 1,691,563 Total Debt Obligations $ 1,930,828 $ 2,013,112 (a) T his loan was assumed upon acquisition of the related properties on December 19, 2013. On December 29, 2015, the Company refinanced the debt increasing the principal balance to $130.0 million and extended the scheduled maturity date from January 6, 2016 to April 5, 2023. A default under this loan will also constitute a default under the loan secured by Two Commerce Square. This loan is also secured by a lien on Two Commerce Square. (b) This loan was assumed upon acquisition of the related property on December 19, 2013. The interest rate reflects the market rate at the time of acquisition. A default under this loan will also constitute a default under the loan secured by One Commerce Square. This loan is also secured by a lien on (c) On May 1, 2017, the entire principal balance of the unsecured 5.70% Guaranteed Notes was repaid upon maturity. Available cash balances and the Credit Facility (as defined below) were used to fund the repayment of the unsecured notes. (d) On November 17, 2017, the Company completed an offering of $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. On November 17, 2017, the Company redeemed the remaining outstanding balance of the 4.95% Guaranteed Notes due 2018 (the “2018 Notes”) ahead of its scheduled maturity. See below for further discussion. (e) On September 30, 2017, the interest rate hedge contract for the Preferred Trust I expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%.
Summary of debt repurchases	The following table provides additional information on the Company’s repurchase of $325.0 million in the aggregate principal amount of its outstanding unsecured notes (consisting of the 2018 Notes, as indicated above) during the twelve months ended December 31, 2017 (in thousands). There were no repurchases of unsecured debt during the twelve months ended December 31, 2016 and 2015. Notes Principal Repurchase Amount (a) Loss on Early Extinguishment of Debt (b) 2018 4.95% Notes $ 325,000 $ 330,792 $ (3,933 ) (a) Includes prepayment penalties with respect to the redemption of debt. (b) Includes unamortized balance of the original issue discount and deferred financing costs.
Schedule of Maturities of Long-term Debt	As of December 31, 2017, the Company’s aggregate scheduled principal payments of debt obligations, excluding amortization of discounts and premiums, are as follows (in thousands): 2018 $ 6,601 2019 7,360 2020 86,978 2021 6,099 2022 256,332 Thereafter 1,585,347 Total principal payments 1,948,717 Net unamortized premiums/(discounts) (6,748 ) Net deferred financing costs (11,141 ) Outstanding indebtedness $ 1,930,828

Fair Value of Financial Instr42

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments With Fair Values Different From Their Carrying Amount	The following are financial instruments for which the Company’s estimates of fair value differ from the carrying amounts (in thousands): December 31, 2017 December 31, 2016 Carrying Amount (a) Fair Value Carrying Amount (a) Fair Value Unsecured notes payable $ 1,286,573 $ 1,314,900 $ 1,364,854 $ 1,372,758 Variable rate debt $ 327,039 $ 308,872 $ 326,709 $ 307,510 Mortgage notes payable $ 317,216 $ 304,665 $ 321,549 $ 328,853 Note receivable (b) $ 3,532 $ 3,605 $ 3,380 $ 3,717 (a) In April 2015, the FASB issued guidance requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct reduction from the carrying amount of the corresponding debt liability, consistent with debt discounts. As a result, the carrying amounts presented in the table above are net of deferred financing costs of $8.9 million and $5.5 million for unsecured notes payable, $1.6 million and $1.9 million for variable rate debt and $0.6 million and $0.7 million for mortgage notes payable as of December 31, 2017 and December 31, 2016, respectively. (b) The inputs to originate the note receivable are unobservable and, as a result, are categorized as Level 3. The Company determined fair value by calculating the present value of the cash payments to be received through the maturity date of the loan. See Note 2, “Significant Accounting Policies,”

Risk Management and Use of De43

Risk Management and Use of Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The following table summarizes the terms and fair values of the Company’s derivative financial instruments as of December 31, 2017 and December 31, 2016. The notional amounts provide an indication of the extent of the Company’s involvement in these instruments at that time but do not represent exposure to credit, interest rate or market risks (amounts presented in thousands). Hedge Product Hedge Type Designation Notional Amount Strike Trade Date Maturity Date Fair value 12/31/2017 12/31/2016 12/31/2017 12/31/2016 Assets/(Liabilities) Swap Interest Rate Cash Flow (a) $ 250,000 $ 250,000 3.718 % October 8, 2015 October 8, 2022 $ 5,694 $ 3,733 Swap Interest Rate Cash Flow (a) 25,774 25,774 3.300 % December 22, 2011 January 30, 2021 25 (300 ) Swap Interest Rate Cash Flow (a) 25,774 25,774 3.090 % January 6, 2012 October 30, 2019 59 (214 ) Swap Interest Rate Cash Flow (b) - 27,062 2.750 % December 21, 2011 September 30, 2017 - (83 ) $ 301,548 $ 328,610 (a) Hedging unsecured variable rate debt. (b) On September 30, 2017, the interest rate hedge contract for this swap expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%.

Beneficiaries Equity of the P44

Beneficiaries Equity of the Parent Company (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Earnings Per Share (EPS), Basic and Diluted	The following tables detail the number of shares and net income used to calculate basic and diluted earnings per share (in thousands, except share and per share amounts; results may not add due to rounding): Year ended December 31, 2017 2016 2015 Basic Diluted Basic Diluted Basic Diluted Numerator Net income (loss) $ 121,859 $ 121,859 $ 40,501 $ 40,501 $ (30,740 ) $ (30,740 ) Net (income) loss attributable to noncontrolling interests (1,009 ) (1,009 ) (310 ) (310 ) 339 339 Nonforfeitable dividends allocated to unvested restricted shareholders (327 ) (327 ) (341 ) (341 ) (329 ) (329 ) Preferred share dividends (2,032 ) (2,032 ) (6,900 ) (6,900 ) (6,900 ) (6,900 ) Preferred share redemption charge (3,181 ) (3,181 ) - - - - Net income (loss) attributable to common shareholders $ 115,310 $ 115,310 $ 32,950 $ 32,950 $ (37,630 ) $ (37,630 ) Denominator Weighted-average shares outstanding 175,484,350 175,484,350 175,018,163 175,018,163 178,162,160 178,162,160 Contingent securities/Share based compensation - 1,323,816 - 992,651 - - Weighted-average shares outstanding 175,484,350 176,808,166 175,018,163 176,010,814 178,162,160 178,162,160 Earnings (loss) per Common Share: Net income (loss) attributable to common shareholders $ 0.66 $ 0.65 $ 0.19 $ 0.19 $ (0.21 ) $ (0.21 )

Partners Equity of the Operat45

Partners Equity of the Operating Partnership (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share (EPS), Basic and Diluted	The following tables detail the number of shares and net income used to calculate basic and diluted earnings per share (in thousands, except share and per share amounts; results may not add due to rounding): Year ended December 31, 2017 2016 2015 Basic Diluted Basic Diluted Basic Diluted Numerator Net income (loss) $ 121,859 $ 121,859 $ 40,501 $ 40,501 $ (30,740 ) $ (30,740 ) Net (income) loss attributable to noncontrolling interests (1,009 ) (1,009 ) (310 ) (310 ) 339 339 Nonforfeitable dividends allocated to unvested restricted shareholders (327 ) (327 ) (341 ) (341 ) (329 ) (329 ) Preferred share dividends (2,032 ) (2,032 ) (6,900 ) (6,900 ) (6,900 ) (6,900 ) Preferred share redemption charge (3,181 ) (3,181 ) - - - - Net income (loss) attributable to common shareholders $ 115,310 $ 115,310 $ 32,950 $ 32,950 $ (37,630 ) $ (37,630 ) Denominator Weighted-average shares outstanding 175,484,350 175,484,350 175,018,163 175,018,163 178,162,160 178,162,160 Contingent securities/Share based compensation - 1,323,816 - 992,651 - - Weighted-average shares outstanding 175,484,350 176,808,166 175,018,163 176,010,814 178,162,160 178,162,160 Earnings (loss) per Common Share: Net income (loss) attributable to common shareholders $ 0.66 $ 0.65 $ 0.19 $ 0.19 $ (0.21 ) $ (0.21 )
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Share (EPS), Basic and Diluted	The following tables detail the number of units and net income used to calculate basic and diluted earnings per common partnership unit (in thousands, except unit and per unit amounts; results may not add due to rounding): Year ended December 31, 2017 2016 2015 Basic Diluted Basic Diluted Basic Diluted Numerator Net income (loss) $ 121,859 $ 121,859 $ 40,501 $ 40,501 $ (30,740 ) $ (30,740 ) Nonforfeitable dividends allocated to unvested restricted unitholders (327 ) (327 ) (341 ) (341 ) (329 ) (329 ) Preferred unit dividends (2,032 ) (2,032 ) (6,900 ) (6,900 ) (6,900 ) (6,900 ) Preferred unit redemption charge (3,181 ) (3,181 ) - - - - Net (income) loss attributable to noncontrolling interests (29 ) (29 ) (15 ) (15 ) 3 3 Net income (loss) attributable to common unitholders $ 116,290 $ 116,290 $ 33,245 $ 33,245 $ (37,966 ) $ (37,966 ) Denominator Weighted-average units outstanding 176,964,149 176,964,149 176,523,800 176,523,800 179,697,262 179,697,262 Contingent securities/Share based compensation - 1,323,816 - 992,651 - - Total weighted-average units outstanding 176,964,149 178,287,965 176,523,800 177,516,451 179,697,262 179,697,262 Earnings (loss) per Common Partnership Unit: Net income (loss) attributable to common unitholders $ 0.66 $ 0.65 $ 0.19 $ 0.19 $ (0.21 ) $ (0.21 )

Share Based Compensation, 40146

Share Based Compensation, 401(k) Plan and Deferred Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Option Activity	Option activity as of December 31, 2017 and changes during the year-ended December 31, 2017 were as follows: Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at January 1, 2017 2,377,778 $ 15.36 2.15 Exercised (128,330 ) $ 9.59 $ 919,582 Forfeited/Expired (10,858 ) $ 20.61 Outstanding at December 31, 2017 2,238,590 $ 15.67 1.10 $ 8,735,293 Vested/Exercisable at December 31, 2017 2,238,590 $ 15.67 1.10 $ 8,735,293
Company's Restricted Share Activity	The following table summarizes the Company’s restricted share activity during the year-ended December 31, 2017: Shares Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Non-vested at January 1, 2017 488,604 $ 14.10 $ 8,066,852 Granted 170,192 16.77 2,854,165 Vested (189,704 ) 14.40 3,227,342 Forfeited (13,449 ) 14.83 Non-vested at December 31, 2017 455,643 $ 14.95 $ 8,288,146
Schedule of Restricted Performance Share Units Plan	The table below presents certain information as to unvested RPSU awards. RPSU Grant 2/23/2015 2/22/2016 3/1/2017 Total (Amounts below in shares, unless otherwise noted) Non-vested at January 1, 2017 147,589 231,388 - 378,977 Units Granted - - 174,854 174,854 Units Cancelled (2,274 ) (3,311 ) (2,443 ) (8,028 ) Non-vested at December 31, 2017 145,315 228,077 172,411 545,803 Measurement Period Commencement Date 1/1/2015 1/1/2016 1/1/2017 Measurement Period End Date 12/31/2017 12/31/2018 12/31/2019 Units Granted 186,395 231,388 174,854 Fair Value of Units on Grant Date (in thousands) $ 3,933 $ 3,558 $ 3,735

Distributions (Tables)

Distributions (Tables)	12 Months Ended
	Dec. 31, 2017
Distributions [Abstract]
Schedule of Dividends Payable	The following table provides the tax characteristics of the 2017, 2016 and 2015 distributions paid: Years ended December 31, 2017 2016 2015 (in thousands, except per share amounts) Common Share Distributions: Ordinary income $ 0.38 $ - $ 0.36 Capital gain 0.26 0.62 0.14 Non-taxable distributions - - 0.10 Distributions per share $ 0.64 $ 0.62 $ 0.60 Percentage classified as ordinary income 60.00 % 0.00 % 59.10 % Percentage classified as capital gain 40.00 % 100.00 % 23.50 % Percentage classified as non-taxable distribution 0.00 % 0.00 % 17.40 % Preferred Share Distributions: Total distributions paid $ 2,032 $ 6,900 $ 6,900 Percentage classified as ordinary income 60.00 % 0.00 % 71.60 % Percentage classified as capital gain 40.00 % 100.00 % 28.40 % Percentage classified as non-taxable distribution 0.00 % 0.00 % 0.00 %

Accumulated Other Comprehensi48

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table details the components of accumulated other comprehensive income (loss) of the Parent Company and the Operating Partnership as of and for the three years ended December 31, 2017 (in thousands): Parent Company Cash Flow Hedges Balance at January 1, 2015 $ (4,607 ) Change in fair market value during year (1,010 ) Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests 5 Reclassification adjustments for (gains)/losses reclassified into operations 420 Balance at December 31, 2015 $ (5,192 ) Change in fair market value during year 2,371 Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests (28 ) Reclassification adjustments for (gains)/losses reclassified into operations 1,104 Balance at December 31, 2016 $ (1,745 ) Change in fair market value during year 2,948 Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests (34 ) Reclassification adjustments for (gains)/losses reclassified into operations 1,230 Balance at December 31, 2017 $ 2,399 Operating Partnership Cash Flow Hedges Balance at January 1, 2015 $ (5,007 ) Change in fair market value during year (1,010 ) Reclassification adjustments for (gains)/losses reclassified into operations 420 Balance at December 31, 2015 $ (5,597 ) Change in fair market value during year 2,371 Reclassification adjustments for (gains)/losses reclassified into operations 1,104 Balance at December 31, 2016 $ (2,122 ) Change in fair market value during year 2,948 Reclassification adjustments for (gains)/losses reclassified into operations 1,230 Balance at December 31, 2017 $ 2,056

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Real Estate Investments, Net Operating Income and Unconsolidated Real Estate Ventures of Reportable Segments	The following tables provide selected asset information and results of operations of the Company’s reportable segments for the three years ended December 31, 2017, 2016 and 2015 (in thousands): Real estate investments, at cost: December 31, 2017 December 31, 2016 December 31, 2015 Philadelphia CBD $ 1,643,296 $ 1,320,974 $ 1,157,667 Pennsylvania Suburbs 958,796 1,005,446 1,019,280 Metropolitan Washington, D.C. 978,257 975,987 1,129,206 Austin, Texas 163,653 146,794 164,518 Other (a) 88,346 137,094 222,329 $ 3,832,348 $ 3,586,295 $ 3,693,000 Assets held for sale (b) - 73,591 794,588 Operating Properties $ 3,832,348 $ 3,659,886 $ 4,487,588 Corporate Construction-in-progress $ 121,188 $ 297,462 $ 268,983 Land held for development (c) $ 98,242 $ 150,970 $ 130,479 (a) As a result of the Och-Ziff Sale that occurred on February 4, 2016, the Company narrowed its segments to five segments: (1) Philadelphia Central Business District (“CBD”), (2) Pennsylvania Suburbs, (3) Metropolitan Washington, D.C. and (4) Austin, Texas and (5) Other. The Och-Ziff Sale disposed of the entire Richmond, Virginia segment. See Note 3, “Real Estate Investments,” for further information. (b) As of December 31, 2015, the Och-Ziff Portfolio and Cira Square were held for sale. As of December 31, 2016, the Concord Airport Plaza located in the Other segment and the Calverton portfolio located in the Metropolitan Washington, D.C. segment was held for sale. See Note 3, “Real Estate Investments,” for further information. (c) As of December 31, 2017, the Company categorized 13.1 acres of land held for development located in the Other segment as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3 , “Real Estate Investments,” None of the above aforementioned sales or properties classified as held for sale are considered significant dispositions under the accounting guidance for discontinued operations. Years ended December 31, 2017 2016 2015 Total revenue Operating expenses (a) Net operating income Total revenue Operating expenses (a) Net operating income Total revenue Operating expenses (a) Net Operating income Philadelphia CBD $ 226,673 $ (88,818 ) $ 137,855 $ 200,245 $ (78,708 ) $ 121,537 $ 209,298 $ (77,352 ) $ 131,946 Pennsylvania Suburbs 139,785 (47,769 ) 92,016 144,338 (49,208 ) 95,130 158,398 (57,319 ) 101,079 Metropolitan Washington, D.C. 92,024 (35,014 ) 57,010 99,781 (39,036 ) 60,745 110,657 (44,294 ) 66,363 Austin, Texas (b) 34,301 (15,456 ) 18,845 34,585 (13,222 ) 21,363 20,910 (8,010 ) 12,900 Other 18,347 (11,749 ) 6,598 39,359 (23,204 ) 16,155 98,799 (49,604 ) 49,195 Corporate 9,363 (7,193 ) 2,170 7,155 (6,070 ) 1,085 4,569 (1,508 ) 3,061 Operating properties $ 520,493 $ (205,999 ) $ 314,494 $ 525,463 $ (209,448 ) $ 316,015 $ 602,631 $ (238,087 ) $ 364,544 (a) Includes property operating expense, real estate taxes and third party management expense. (b) On June 22, 2015 the Company acquired the remaining 50.0% of the common interest in Broadmoor Austin Associates. As such, the Company has seven wholly owned properties in its Austin, Texas business segment. Net operating income for the years ended December 31, 2016 and 2015 includes management fees and related expenses for services provided by the Company to the Austin Venture, which are recorded in the Corporate segment. "Real Estate Investments," Unconsolidated real estate ventures: Investment in real estate ventures, at equity Equity in income (loss) of real estate ventures As of Years ended December 31, December 31, 2017 December 31, 2016 December 31, 2015 2017 2016 2015 Philadelphia CBD $ 39,939 $ 48,691 $ 44,089 $ 255 $ (686 ) $ (188 ) Pennsylvania Suburbs 3,503 15,421 16,408 631 748 310 Metropolitan Washington, D.C. (a) 119,817 141,786 118,422 (5,044 ) (6,293 ) (336 ) MAP Venture (b) 15,450 20,893 - (3,443 ) (4,218 ) - Other (c) 1,939 1,654 1,657 285 814 930 Austin, Texas (d) 13,973 52,886 60,428 (990 ) (1,868 ) (1,527 ) Total $ 194,621 $ 281,331 $ 241,004 $ (8,306 ) $ (11,503 ) $ (811 ) (a) On August 31, 2016, the Company terminated its lease for the regional management and leasing office at 3141 Fairview Park Drive, located in Falls Church, Virginia. Accordingly, the Company no longer has any continuing involvement with 3141 Fairview Park Drive and recorded the partial sale under the full accrual method of accounting. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” for further information. The years ended December 31, 2017 and 2016 include impairment charges related to the Brandywine - AI Venture. See Note 4 , “Investment in Unconsolidated Real Estate Ventures,” for further information. (b) The MAP Venture represents a joint venture formed between the Company and MAP Ground Lease Holdings LLC, an affiliate of Och-Ziff Capital Management Group, LLC, on February 4, 2016. The MAP Venture’s business operations, including properties in Richmond, Virginia; Metropolitan Washington, D.C.; New Jersey/Delaware and Pennsylvania Suburbs, are centrally managed with the results reported to management of the Company on a consolidated basis. As a result, the investment in the MAP Venture is separately presented. All other unconsolidated real estate ventures are managed consistently with the Company’s regional segments. (c) See footnote (a) to the “Real estate investments, at cost” table above for further information regarding this segment. (d) Investment in real estate ventures does not include the $1.1 million negative investment balance in one real estate venture as of December 31, 2015, which is included in the “Other Liabilities” caption of the consolidated balance sheets. The Company disposed of its interest in this venture during 2016. See Note 4, " Investment in Unconsolidated Real Estate Ventures ," for further information. The decrease in the Company’s investment balance primarily relates to distributions from the G&I VII Austin Office LLC real estate venture. See Note 4 , “Investment in Unconsolidated Real Estate Ventures,” for further information.
Reconciliation of Consolidated Net Income (Loss) to Consolidated NOI	The following is a reconciliation of consolidated net income (loss), as defined by GAAP, to consolidated NOI, (in thousands): Years Ended December 31, 2017 2016 2015 Net income (loss) $ 121,859 $ 40,501 $ (30,740 ) Plus: Interest expense 81,886 84,708 110,717 Interest expense - amortization of deferred financing costs 2,435 2,696 4,557 Interest expense - financing obligation - 679 1,237 Depreciation and amortization 179,357 189,676 219,029 General and administrative expenses 28,538 26,596 29,406 Equity in loss of Real Estate Ventures 8,306 11,503 811 Provision for impairment 3,057 40,517 82,208 Loss on early extinguishment of debt 3,933 66,590 - Less: Interest income 1,113 1,236 1,224 Income tax benefit 628 - - Tax credit transaction income - - 19,955 Net gain from remeasurement of investments in real estate ventures - - 758 Net gain on disposition of real estate 31,657 116,983 20,496 Net gain on sale of undepreciated real estate 953 9,232 3,019 Net gain on Real Estate Venture transactions 80,526 20,000 7,229 Consolidated net operating income $ 314,494 $ 316,015 $ 364,544

Operating Leases (Tables)

Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Leases Operating [Abstract]
Operating Leases Future Minimum Payments Receivable	The Company leases properties to tenants under operating leases with various expiration dates extending to 2082. Minimum future rentals on non-cancelable leases at December 31, 2017 are as follows (in thousands): Year Minimum Rent 2018 $ 381,110 2019 370,211 2020 348,544 2021 323,654 2022 277,837 Thereafter 1,269,745

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Minimum Future Rental Payments on Non-cancelable Leases	Minimum future rental payments on non-cancelable leases at December 31, 2017 are as follows (in thousands): Year Minimum Rent 2018 $ 1,211 2019 1,211 2020 1,211 2021 1,211 2022 1,211 Thereafter 56,318 Total $ 62,373

Summary of Quarterly Results (T

Summary of Quarterly Results (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Quarterly Financial Information	The following is a summary of quarterly financial information as of and for the years ended December 31, 2017 and 2016 (in thousands, except per share data): Brandywine Realty Trust 1st 2nd 3rd 4th Quarter Quarter Quarter Quarter 2017 Total revenue $ 130,920 $ 127,791 $ 128,438 $ 133,344 (a) Net income 21,271 7,698 19,046 73,844 (b) Net income allocated to Common Shares 19,278 4,092 18,803 73,137 Basic earnings per Common Share $ 0.11 $ 0.02 $ 0.11 $ 0.42 Diluted earnings per Common Share $ 0.11 $ 0.02 $ 0.11 $ 0.41 2016 Total revenue $ 136,502 $ 127,181 $ 129,694 $ 132,086 Net income (loss) 46,310 (1,323 ) 7,884 (12,370 ) Net income (loss) allocated to Common Shares 44,091 (3,105 ) 6,022 (14,058 ) Basic earnings (loss) per Common Share $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) Diluted earnings (loss) per Common Share $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) The summation of quarterly earnings per share amounts does not necessarily equal the full year amounts due to rounding. (a) The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania. (b) The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Schedule of Quarterly Financial Information	1st 2nd 3rd 4th Quarter Quarter Quarter Quarter 2017 Total revenue $ 130,920 $ 127,791 $ 128,438 $ 133,344 (a) Net income 21,271 7,698 19,046 73,844 (b) Net income attributable to Common Partnership Unitholders 19,442 4,129 18,961 73,758 Basic earnings per Common Partnership Unit $ 0.11 $ 0.02 $ 0.11 $ 0.42 Diluted earnings per Common Partnership Unit $ 0.11 $ 0.02 $ 0.11 $ 0.41 2016 Total revenue $ 136,502 $ 127,181 $ 129,694 $ 132,086 Net income (loss) 46,310 (1,323 ) 7,884 (12,370 ) Net income (loss) attributable to Common Partnership Unitholders 44,478 (3,131 ) 6,074 (14,176 ) Basic earnings (loss) per Common Partnership Unit $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) Diluted earnings (loss) per Common Partnership Unit $ 0.25 $ (0.02 ) $ 0.03 $ (0.08 ) The summation of quarterly earnings per share amounts does not necessarily equal the full year amounts due to rounding. (a) The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania. (b) The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Organization of The Parent Co53

Organization of The Parent Company and The Operating Partnership (Textual) (Details)	Jan. 10, 2018Real_Estate_Investment	Dec. 31, 2017	Dec. 31, 2017property	Dec. 31, 2017ft²	Dec. 31, 2017Real_Estate_Investment	Dec. 31, 2017a	Dec. 31, 2017Apartment_unit	Dec. 31, 2016ft²	Dec. 31, 2015ft²
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			93
Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Acreage of land | a						13.1
Subsequent Event [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Investments in Real Estate Ventures | Real_Estate_Investment	10
Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			81
Rentable Square Feet								5,239,632	2,649,926
Mixed Use Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			5
Retail Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			1
Core Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			87
Development Property [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			2
Redevelopment Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Properties | property			4
Unconsolidated Real Estate Ventures [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment					13
Unconsolidated Real Estate Ventures [Member] | Seven Real Estate Ventures [Member] | Office Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment					7
Rentable Square Feet				6,700,000
Unconsolidated Real Estate Ventures [Member] | Three Real Estate Ventures [Member] | Land Held For Development [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment					3
Acreage of land | a						4.4
Unconsolidated Real Estate Ventures [Member] | One Real Estate Venture [Member] | Active Development Land [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment					1
Acreage of land | a						1.3
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower One [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures					1		1
Number of Property units			345				345
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower Two [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures					1		1
Number of Property units			321				321
Parent Company [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the Operating Partnership		99.20%
Net Rentable Square Feet				16,400,000
Undeveloped Parcels of Land | a						212
Undeveloped Land Held for Sale | a						13.1
Area of Additional Undeveloped Parcels of Land With Option to Purchase | a						60
Total Potential Development Capacity				14,800,000
Parent Company [Member] | Assets Held-for-sale [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Total Potential Development Capacity				100,000
Wholly-owned Management Company Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net Rentable Square Feet				25,200,000
Wholly-owned Management Company Subsidiaries [Member] | Partially Owned Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net Rentable Square Feet				8,800,000
Wholly-owned Management Company Subsidiaries [Member] | Wholly Owned Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net Rentable Square Feet				16,400,000
Wholly-owned Management Company Subsidiaries [Member] | Office and Industrial Properties [Member] | Partially Owned Properties [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Net Rentable Square Feet				8,800,000
Subsidiaries [Member]
Organization of The Parent Company and The Operating Partnership [Line Items]
Ownership in the Operating Partnership		100.00%

Summary of Significant Accoun54

Summary of Significant Accounting Policies (Textual) (Details)		May 18, 2017shares	Dec. 31, 2016USD ($)Customer	Dec. 31, 2017USD ($)Customershares	Dec. 31, 2016USD ($)Customer	Dec. 31, 2015USD ($)Customer
Summary Of Significant Accounting Policies (Textual) [Abstract]
Shares used for employee taxes upon vesting of share awards				$ 674,000	$ 879,000	$ 2,055,000
Real estate ventures aggregate indebtedness to third parties			$ 997,466,000	768,912,000	997,466,000
Variable interest entity, assets			417,100,000	412,900,000	417,100,000
Variable interest entity, liabilities			254,600,000	250,400,000	254,600,000
Revenue increased by straight-line rent adjustment				24,900,000	26,300,000	21,600,000
Increased revenue due to amortization of deferred rent				2,200,000	2,100,000	2,000,000
Decrease in revenue due to amortization of lease incentives				1,800,000	2,000,000	1,800,000
Share-based compensation expense				6,300,000	5,600,000	7,300,000
Share-based compensation expense, capitalized				$ 1,200,000	1,000,000	$ 1,900,000
Common shares for future awards | shares				2,661,992
Additional shares authorized for issuance | shares		2,663,886
Total number of shares authorized for issuance | shares		6,500,000
Number of awards granted | shares				3,838,008
Restricted cash			$ 700,000	$ 1,300,000	$ 700,000
Employee Stock Option And Share Appreciation Rights
Summary Of Significant Accounting Policies (Textual) [Abstract]
Common shares for future awards | shares				2,238,590
Customer Concentration Risk [Member] | Rental Revenue [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Number of tenant accounted for 10% or more of the Company's rents | Customer			0	0	0	0
Maximum [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Property, Plant and Equipment, Useful Life				55 years
Tenant Improvements Useful Lives				16 years
Minimum [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Property, Plant and Equipment, Useful Life				5 years
Tenant Improvements Useful Lives				1 year
Unconsolidated Real Estate Ventures [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties				$ 768,912,000
Capitalized interest				400,000	$ 1,900,000	$ 2,000,000
evo at Cira Centre South Venture [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Guarantees, maximum exposure amount				55,400,000
PJP VII [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties			$ 4,956,000	4,792,000	4,956,000
Guarantees, maximum exposure amount				400,000
4040 Wilson Venture [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties	[1]		1,004,000	6,664,000	1,004,000
Guarantees, maximum exposure amount				$ 41,300,000
ASU 2016-09 [Member] | Reclassified from Operating Activities to Financing Activities [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Shares used for employee taxes upon vesting of share awards					$ 900,000	$ 2,100,000
Impairment Charges [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Out-of-period error immaterial in current year			$ 1,200,000
[1]	During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million.

Summary of Significant Accoun55

Summary of Significant Accounting Policies - Construction-in-Progress (Textual) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	$ 6,063	$ 6,717	$ 7,291
Development [Member]
Construction in Progress [Line Items]
Internal direct construction costs capitalized related to development of properties and land holdings	4,390	3,182	2,641
Capitalized interest	$ 3,100	$ 10,900	$ 10,200

Summary of Significant Accoun56

Summary of Significant Accounting Policies - Compensation Costs (Including Bonuses and Benefits) Capitalized (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	$ 6,063	$ 6,717	$ 7,291
Development [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	4,390	3,182	2,641
Redevelopment [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	319	144	221
Tenant Improvements [Member]
Construction in Progress [Line Items]
Salaries including bonuses and benefits, capitalized during the period	$ 1,354	$ 3,391	$ 4,429

Summary of Significant Accoun57

Summary of Significant Accounting Policies - Impairment or Disposal of Long-Lived Assets (Textual) (Details)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Disposition of assets, holding period	10 years

Summary of Significant Accoun58

Summary of Significant Accounting Policies - Accounts Receivable and Accrued Rent Receivable (Textual) (Details) $ in Thousands	Dec. 31, 2017USD ($)Customer	Dec. 31, 2016USD ($)Customer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable	$ 3,467	$ 2,373
Accrued rent receivable, allowance	13,645	13,743
Tenant Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable	$ 3,500	$ 2,400
Accounts Receivable [Member] | Customer Concentration Risk [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of tenant accounted for 10% or more of the Company's accounts receivable | Customer	0	0

Summary of Significant Accoun59

Summary of Significant Accounting Policies - Deferred Costs (Textual) (Details)	12 Months Ended
	Dec. 31, 2017
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Remaining Lease Period - Minimum	1 year
Remaining Lease Period - Maximum	16 years

Summary of Significant Accoun60

Summary of Significant Accounting Policies - Notes Receivable (Textual) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan maturity term	3 years
Note receivable	$ 3.5	$ 3.4
Note Receivable Year One [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan bears interest rate	6.30%
Note Receivable Year Two [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan bears interest rate	7.00%
Note Receivable Year Three [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan bears interest rate	8.00%

Summary of Significant Accoun61

Summary of Significant Accounting Policies - Income Taxes (Textual) (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Distributable Income Minimum Percentage	90.00%
Tax Basis of Assets, Cost for Income Tax Purposes	$ 3.1	$ 3
Federal excise tax if sufficient taxable income is not distributed within prescribed time limits	4.00%
Excise tax equal to annual amount	4.00%
Excise tax, if sum of ordinary income	85.00%
Excise tax, if Net capital gain exceeds cash distributions and certain taxes paid	95.00%
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Income Tax Contingency [Line Items]
Tax Basis of Assets, Cost for Income Tax Purposes	$ 3.1	$ 3

Real Estate Investments - Gross

Real Estate Investments - Gross Carrying Value of Company's Properties (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Property, Plant and Equipment, Gross [Abstract]
Land		$ 492,197	$ 469,522
Tenant improvements		444,038	433,686
Operating properties		3,832,348	3,586,295
Assets held for sale - real estate investments	[1]	0	73,591	[2]	$ 794,588
Total		3,832,348	3,659,886
Building and Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Operating properties		$ 2,896,113	$ 2,683,087
[1]	As of December 31, 2015, the Och-Ziff Portfolio and Cira Square were held for sale. As of December 31, 2016, the Concord Airport Plaza located in the Other segment and the Calverton portfolio located in the Metropolitan Washington, D.C. segment was held for sale. See Note 3, “Real Estate Investments,” for further information.
[2]	Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation, land held for development or other assets on the balance sheets of the properties held for sale. See 2016 Held for Sale section below.

Real Estate Investments - Acqui

Real Estate Investments - Acquisitions (Textual) (Details) $ in Thousands		Oct. 13, 2017USD ($)ft²	Jul. 28, 2017USD ($)ft²	Jul. 02, 2016USD ($)a	Jul. 07, 2015USD ($)a	Jun. 22, 2015USD ($)ft²aproperty	May 12, 2015USD ($)ft²	Apr. 06, 2015USD ($)a	Apr. 02, 2015USD ($)ft²	Dec. 31, 2017USD ($)a		Dec. 31, 2017USD ($)a	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)ft²	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)a	Dec. 31, 2017USD ($)a	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)ft²	Jan. 30, 2017a	Jul. 01, 2016a
Business Acquisition [Line Items]
Revenue										$ 133,344	[1]		$ 128,438	$ 127,791	$ 130,920	$ 132,086	$ 129,694	$ 127,181	$ 136,502		$ 520,493	$ 525,463	$ 602,631
Net losses										73,137			$ 18,803	$ 4,092	$ 19,278	(14,058)	$ 6,022	$ (3,105)	$ 44,091		120,850	40,191	(30,401)
Amount funded by corporate funds																					72,523	20,406	150,472
Net gain from remeasurement of investments in real estate ventures																					0	0	758
Land held for development	[2]									98,242		$ 98,242				150,970				$ 98,242	98,242	150,970	$ 130,479
2100 Market Street [Member]
Business Acquisition [Line Items]
Acreage of land | a					0.8
Payments to Acquire Land					$ 18,800
Amount funded by corporate funds					16,800
Amount Deferred					$ 2,000
25 M Street [Member]
Business Acquisition [Line Items]
Capitalized transaction costs								$ 300
Area of Real Estate Property | ft²							271,000
Acreage of land | a								0.8
Payments to Acquire Land								$ 20,300
Land held for development										$ 23,100		23,100				$ 22,400				23,100	$ 23,100	$ 22,400
25 M Street [Member] | Brandywine 25 M Street [Member]
Business Acquisition [Line Items]
Percent of Acquired Entity							95.00%
Garza Land Sale [Member]
Business Acquisition [Line Items]
Area of land under agreement to sell | a																								1.7
Office Properties [Member]
Business Acquisition [Line Items]
Rentable Square Feet | ft²																5,239,632						5,239,632	2,649,926
One Drexel Plaza [Member]
Business Acquisition [Line Items]
Lease agreement term		99 years
Rentable Square Feet | ft²		282,709
Gross purchase value of office property		$ 35,000
Capitalized transaction costs		2,800
Revenue												1,200
Net losses												$ (400)
Building, land and improvements		$ 30,583
3000 Market Street [Member]
Business Acquisition [Line Items]
Gross purchase value of office property			$ 32,700
Capitalized transaction costs			700
Revenue																				800
Net losses																				$ (500)
Contractual sale price of real estate acquired			32,000
Building, land and improvements			$ 32,004
3000 Market Street [Member] | Office Properties [Member]
Business Acquisition [Line Items]
Area of Real Estate Property | ft²			58,587
Garza Land Acquisition [Member]
Business Acquisition [Line Items]
Acreage of land | a				34.6																					34.6
Gross purchase value of assets				$ 20,600
Acquisition costs				1,900
Amount funded by corporate funds				$ 20,400
Area of land under agreement to sell | a										9.5		9.5								9.5	9.5
Broadmoor Austin Associates [Member]
Business Acquisition [Line Items]
Rentable Square Feet | ft²						1,112,236
Revenue																					$ 25,400	$ 26,400	$ 13,200
Net losses																					$ 6,900	$ (5,200)	$ (7,200)
Acreage of land | a						66
Payments to Acquire Land						$ 143,800
Amount funded by corporate funds						$ 81,000
Percentage of ownership interests						50.00%
Number of Property units | property						7
Purchase Price of Assets						$ 211,400
Carrying amount of Investment						$ 66,300
Lease percentage of acquired property						100.00%
Funds Held in Escrow						$ 62,800
Mortgage Debt Paid at Closing						51,200
Acquisition Costs						$ 200
Ownership percentage						50.00%
Net gain from remeasurement of investments in real estate ventures						$ 800
Building, land and improvements						$ 163,271
25 M Street [Member] | 25 M Street [Member]
Business Acquisition [Line Items]
Payments to Acquire Land							$ 1,000
Asset Acquisition Ownership Percent							5.00%
618 Market Street [Member]
Business Acquisition [Line Items]
Area of Real Estate Property | ft²									14,404
Payments to Acquire Land									$ 19,400
Number of Parking Spaces | ft²									330
Fair Value of Contingent Consideration									$ 1,600
Consideration, Cash									17,800
Building, land and improvements									19,200
Intangible Assets									$ 200
[1]	The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania.
[2]	As of December 31, 2017, the Company categorized 13.1 acres of land held for development located in the Other segment as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3, “Real Estate Investments,” for further information.

Real Estate Investments - Purch

Real Estate Investments - Purchase Price Allocation (Details) - USD ($) $ in Thousands		Oct. 13, 2017	Jul. 28, 2017	Jun. 22, 2015
One Drexel Plaza [Member]
Business Acquisition [Line Items]
Building, land and improvements		$ 30,583
Construction-in-progress		672
Intangible assets acquired	[1]	10,575
Below market lease liabilities assumed	[2]	(4,055)
Total purchase price		$ 37,775
3000 Market Street [Member]
Business Acquisition [Line Items]
Building, land and improvements			$ 32,004
Intangible assets acquired	[3]		2,562
Below market lease liabilities assumed	[4]		(1,818)
Total purchase price			$ 32,748
Broadmoor Austin Associates [Member]
Business Acquisition [Line Items]
Building, land and improvements				$ 163,271
Land inventory				6,045
Intangible assets acquired	[5]			50,637
Below market lease liabilities assumed	[6]			(8,600)
Total purchase price				211,353
Return of existing equity method investment				(66,324)
Gain on remeasurement				(758)
Net working capital assumed				(450)
Total cash payment at settlement				$ 143,821
[1]	Weighted average amortization period of 7.9 years.
[2]	Weighted average amortization period of 7.0 years.
[3]	Weighted average amortization period of 5.9 years.
[4]	Weighted average amortization period of 6.0 years.
[5]	Weighted average amortization period of 4.0 years.
[6]	Weighted average amortization period of 1.5 years

Real Estate Investments - Pur65

Real Estate Investments - Purchase Price Allocation (Parenthetical) (Details)	Oct. 13, 2017	Jul. 28, 2017	Jun. 22, 2015
One Drexel Plaza [Member] | Intangible Assets Acquired [Member]
Business Acquisition [Line Items]
Weighted average amortization period	7 years 10 months 24 days
One Drexel Plaza [Member] | Below Market Lease [Member]
Business Acquisition [Line Items]
Weighted average amortization period	7 years
3000 Market Street [Member] | Intangible Assets Acquired [Member]
Business Acquisition [Line Items]
Weighted average amortization period		5 years 10 months 24 days
3000 Market Street [Member] | Below Market Lease [Member]
Business Acquisition [Line Items]
Weighted average amortization period		6 years
Broadmoor Austin Associates [Member] | Intangible Assets Acquired [Member]
Business Acquisition [Line Items]
Weighted average amortization period			4 years
Broadmoor Austin Associates [Member] | Below Market Lease [Member]
Business Acquisition [Line Items]
Weighted average amortization period			1 year 6 months

Real Estate Investments - Summa

Real Estate Investments - Summary of Office Properties Sold (Details)		Feb. 02, 2017property	Mar. 31, 2017USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2017USD ($)ft²property	Dec. 31, 2016USD ($)ft²property		Dec. 31, 2015USD ($)ft²property		Dec. 23, 2015ft²
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from the sale of properties						$ 171,860,000	$ 784,331,000		$ 247,228,000
Gain (Loss) on Sale						$ 31,657,000	$ 116,983,000		$ 20,496,000
Philadelphia Marine Center (Marine Piers) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						181,900
Sales Price						$ 21,400,000
Proceeds from the sale of properties						11,200,000
Gain (Loss) on Sale						$ 6,500,000
2970 Market Street (Cira Square) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²											862,692
Gain (Loss) on Sale			$ 500,000
Encino Trace [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									2
Rentable Square Feet | ft²									320,000
Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							66		27
Rentable Square Feet | ft²							5,239,632		2,649,926
Sales Price							$ 820,000,000		$ 374,600,000
Proceeds from the sale of properties							769,799,000		340,098,000
Gain (Loss) on Sale							$ 116,983,000	[1]	$ 22,002,000	[2],[3]
Office Properties [Member] | 11, 14, 15, 17 and 18 Campus Boulevard (Newtown Square) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						5
Rentable Square Feet | ft²						252,802
Sales Price						$ 42,000,000
Proceeds from the sale of properties						40,459,000
Gain (Loss) on Sale	[1]					$ 19,642,000
Office Properties [Member] | 630 Allendale Road [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						1
Rentable Square Feet | ft²						150,000
Sales Price						$ 17,500,000
Proceeds from the sale of properties						16,580,000
Gain (Loss) on Sale	[1]					$ 3,605,000
Office Properties [Member] | Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						4
Rentable Square Feet | ft²						134,794
Sales Price						$ 9,700,000
Proceeds from the sale of properties						8,650,000
Gain (Loss) on Sale	[1],[4]					$ (325,000)
Office Properties [Member] | 200, 210 & 220 Lake Drive East (Woodland Falls) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						3
Rentable Square Feet | ft²						215,465
Sales Price						$ 19,000,000
Proceeds from the sale of properties						17,771,000
Gain (Loss) on Sale	[1],[5]					$ (249,000)
Office Properties [Member] | 11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						3
Rentable Square Feet | ft²						313,810
Sales Price						$ 9,000,000
Proceeds from the sale of properties						8,354,000
Gain (Loss) on Sale	[1],[6]					$ 0
Office Properties [Member] | 1200 & 1220 Concord Avenue (Concord Airport Plaza) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property		2				2
Rentable Square Feet | ft²						350,256
Sales Price						$ 33,100,000
Proceeds from the sale of properties						32,010,000
Gain (Loss) on Sale	[1],[7]					$ 551,000
Office Properties [Member] | 620, 640, 660 Allendale Road [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							3
Rentable Square Feet | ft²							156,669
Sales Price							$ 12,800,000
Proceeds from the sale of properties							12,014,000
Gain (Loss) on Sale	[1]						$ 2,382,000
Office Properties [Member] | 1120 Executive Plaza [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							1
Rentable Square Feet | ft²							95,183
Sales Price							$ 9,500,000
Proceeds from the sale of properties							9,241,000
Gain (Loss) on Sale	[1],[8]						$ (18,000)
Office Properties [Member] | 50 East Clementon Road [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							1
Rentable Square Feet | ft²							3,080
Sales Price							$ 1,100,000
Proceeds from the sale of properties							1,011,000
Gain (Loss) on Sale	[1]						$ (85,000)
Office Properties [Member] | 196/198 Van Buren Street (Herndon Metro Plaza I&II) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							2
Rentable Square Feet | ft²							197,225
Sales Price							$ 44,500,000
Proceeds from the sale of properties							43,412,000
Gain (Loss) on Sale	[1],[9]						$ (752,000)
Office Properties [Member] | 2970 Market Street (Cira Square) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							1
Rentable Square Feet | ft²							862,692
Sales Price							$ 354,000,000
Proceeds from the sale of properties							350,150,000
Gain (Loss) on Sale	[1]						$ 115,828,000
Office Properties [Member] | Och Ziff Portfolio [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property							58
Rentable Square Feet | ft²							3,924,783
Sales Price							$ 398,100,000
Proceeds from the sale of properties							353,971,000
Gain (Loss) on Sale	[1],[10]						$ (372,000)
Office Properties [Member] | Encino Trace [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									2
Rentable Square Feet | ft²									320,000
Sales Price									$ 76,700,000
Proceeds from the sale of properties									50,158,000
Gain (Loss) on Sale	[2],[11]								$ 2,008,000
Office Properties [Member] | Laurel Corporate Center [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									6
Rentable Square Feet | ft²									560,147
Sales Price									$ 56,500,000
Proceeds from the sale of properties									56,253,000
Gain (Loss) on Sale	[2]								$ 2,901,000
Office Properties [Member] | Carlsbad Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									3
Rentable Square Feet | ft²									196,075
Sales Price									$ 30,400,000
Proceeds from the sale of properties									29,568,000
Gain (Loss) on Sale	[2],[12]								$ 0
Office Properties [Member] | 751-761 Fifth Ave [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									1
Rentable Square Feet | ft²									158,000
Sales Price									$ 4,600,000
Proceeds from the sale of properties									4,245,000
Gain (Loss) on Sale	[2]								$ 894,000
Office Properties [Member] | 1000 Howard Boulevard [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									1
Rentable Square Feet | ft²									105,312
Sales Price									$ 16,500,000
Proceeds from the sale of properties									15,780,000
Gain (Loss) on Sale	[2]								$ 4,828,000
Office Properties [Member] | Bay Colony Office Park [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									4
Rentable Square Feet | ft²									247,294
Sales Price									$ 37,500,000
Proceeds from the sale of properties									36,386,000
Gain (Loss) on Sale	[2]								$ 269,000
Office Properties [Member] | 741 First Avenue [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									1
Rentable Square Feet | ft²									77,184
Sales Price									$ 4,900,000
Proceeds from the sale of properties									4,640,000
Gain (Loss) on Sale	[2]								$ 372,000
Office Properties [Member] | 100 Gateway Centre Parkway [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									1
Rentable Square Feet | ft²									74,991
Sales Price									$ 4,100,000
Proceeds from the sale of properties									3,911,000
Gain (Loss) on Sale				$ 0					$ 0	[2],[13]
Office Properties [Member] | Christina & Delaware Corporate Centers [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									5
Rentable Square Feet | ft²									485,182
Sales Price									$ 50,100,000
Proceeds from the sale of properties									49,579,000
Gain (Loss) on Sale	[2]								$ 1,749,000
Office Properties [Member] | Lake Merritt Tower [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									1
Rentable Square Feet | ft²									204,336
Sales Price									$ 65,000,000
Proceeds from the sale of properties									62,800,000
Gain (Loss) on Sale					$ 0				$ 0	[2],[14]
Office Properties [Member] | 1000 Atrium Way / 457 Haddonfield Road (Atrium I / Libertyview) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property									2
Rentable Square Feet | ft²									221,405
Sales Price									$ 28,300,000
Proceeds from the sale of properties									26,778,000
Gain (Loss) on Sale	[2]								$ 8,981,000
Retail Properties [Member] | 7000 Midlantic Drive [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						1
Rentable Square Feet | ft²						10,784
Sales Price						$ 8,200,000
Proceeds from the sale of properties						7,714,000
Gain (Loss) on Sale	[1]					$ 1,413,000
Mixed Use Properties [Member] | Philadelphia Marine Center (Marine Piers) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						1
Rentable Square Feet | ft²						181,900
Sales Price						$ 21,400,000
Proceeds from the sale of properties						11,182,000
Gain (Loss) on Sale	[1],[15]					$ 6,498,000
Office, Retail and Mixed-use Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property						20
Rentable Square Feet | ft²						1,609,811
Sales Price						$ 159,900,000
Proceeds from the sale of properties						142,720,000
Gain (Loss) on Sale	[1]					$ 31,135,000
[1]	Gain/(Loss) on Sale is net of closing and other transaction related costs.
[2]	Gain on Sale is net of closing and other transaction related costs.
[3]	Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.
[4]	As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, which reduced the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs.
[5]	As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs.
[6]	During the fourth quarter of 2016, the Company recognized a $3.0 million impairment related to these properties. During the first quarter of 2017, there was a price reduction of $1.7 million under the agreement of sale and an additional impairment of $1.7 million was recognized.
[7]	During the fourth quarter of 2016, the Company recognized an $11.5 million impairment related to these properties. This sale was designated as a like-kind exchange under Section 1031 of the Internal Revenue Code (“IRC”) and, as such, the proceeds, totaling $32.0 million after closing costs and prorations, were deposited with a Qualified Intermediary, as defined under the IRC. The proceeds received at closing were recorded as “Other assets” in the Company’s consolidated balance sheets. During the third quarter of 2017, the Company acquired 3000 Market Street in Philadelphia, Pennsylvania using the full balance of the Section 1031 proceeds. See “Acquisition” section above.
[8]	As of June 30, 2016, the Company determined that the sale of the property was probable and classified this property as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the property exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized a provision for impairment totaling approximately $1.8 million during the three-month period ended June 30, 2016. The fair value measurement was based on the pricing in the purchase and sale agreement for the sale of the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the inputs utilized to determine fair value for this property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, "Fair Value Measurements and Disclosures.” The loss on sale represents additional closing costs recognized at closing.
[9]	During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing.
[10]	During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing.
[11]	On December 31, 2015, the Company contributed two newly constructed four-story, Class A office buildings, commonly known as “Encino Trace,” containing an aggregate of approximately 320,000 square feet in Austin, Texas to one of its existing real estate ventures (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). When these two properties were contributed to the Austin Venture the Company had incurred a total of $76.7 million of development costs, representing the contribution value. In conjunction with the contribution: (i) the Austin Venture obtained a $30.0 million mortgage loan; (ii) DRA contributed $25.1 million in net cash to the capital of the Austin Venture, including a $1.8 million working capital contribution; and (iii) the Austin Venture distributed $50.2 million to the Company and credited the Company with a $23.3 million capital contribution to the Austin Venture. In addition to the contribution of the properties, the Company also made a $1.8 million cash contribution to the Austin Venture for working capital. The Company recognized a $2.0 million gain on the contribution. Under the Encino Trace loan agreement, the Austin Venture has the option, subject to certain leasing and loan-to-value requirements, to borrow an additional $29.7 million to fund tenant improvements and leasing commissions.
[12]	The Company recorded an impairment loss of $6.3 million for the Carlsbad office properties during the fourth quarter of 2015. As such, there was no gain at disposition for this property.
[13]	The Company recorded an impairment loss of $0.8 million for 100 Gateway Centre Parkway during the second quarter of 2015. As such, there was no gain at disposition for this property.
[14]	The Company recorded an impairment loss of $1.7 million for Lake Merritt Tower on March 31, 2015. As such, there was no gain at disposition for this property. Sales proceeds were deposited in escrow under Section 1031 of the Internal Revenue Code and applied to purchase the Broadmoor Austin portfolio. Refer to Broadmoor Austin Associates acquisition summary, above, for further details.
[15]	On March 15, 2017, the Company sold its sublease interest in the Piers at Penn’s Landing (the “Marine Piers”), which includes leasehold improvements containing 181,900 net rentable square feet, and a marina, located in Philadelphia, Pennsylvania for an aggregate sales price of $21.4 million. On the closing date, the buyer paid $12.0 million in cash. The $9.4 million balance of the purchase is due on (a) January 31, 2020, in the event that the tenant at the Marine Piers does not exercise an option it holds to extend the term of the sublease or (b) January 15, 2024, in the event that the tenant does exercise the option to extend the term of the sublease. In accordance with ASC 360-20, “Real Estate Sales,” the Company determined that it is appropriate to account for the sales transaction under the cost recovery method. The Company received cash proceeds of $11.2 million, after closing costs and prorations, and the net book value of the Marine Piers was $4.7 million, resulting in a gain on sale of $6.5 million. The remaining gain on sale of $9.4 million will be recognized on the second purchase price installment date. Prior to its sale, the Marine Piers had been classified as mixed-use within the Company’s property count.

Real Estate Investments - Sum67

Real Estate Investments - Summary of Office Properties Sold (Parenthetical) (Details)		Oct. 18, 2017USD ($)ft²property	Oct. 17, 2017property	Mar. 31, 2017USD ($)propertysegment	Feb. 02, 2017property	Dec. 31, 2017USD ($)ft²property	Mar. 31, 2017USD ($)propertysegment	Dec. 31, 2016USD ($)ft²property	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)ft²Storey	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2017USD ($)ft²property	Dec. 31, 2016USD ($)ft²property		Dec. 31, 2015USD ($)ft²propertyStorey		Oct. 17, 2014ft²property	Jul. 31, 2014ft²property
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property						93								93
Provision for impairment									$ 1,800,000					$ 3,057,000	$ 40,517,000		$ 82,208,000
Proceeds from the sale of properties														171,860,000	784,331,000		247,228,000
Assets held for sale, net						$ 392,000		$ 41,718,000						392,000	41,718,000
Gain (Loss) on Sale														31,657,000	116,983,000		20,496,000
Proceeds after closing costs and prorations														0	0		62,800,000
Gain (loss) on real estate venture transactions														$ 80,526,000	$ 20,000,000		$ 7,229,000
Austin Joint Venture [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property																			7	2
Rentable Square Feet | ft²		1,164,496				1,570,123								1,570,123					590,881	232,274
Sales Price		$ 333,250,000
Number of Properties Sold | property		8	7			8
Gain (loss) on real estate venture transactions		$ 40,092,000				$ 52,200,000
Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property						81								81
Rentable Square Feet | ft²								5,239,632			2,649,926				5,239,632		2,649,926
Sales Price								$ 820,000,000			$ 374,600,000				$ 820,000,000		$ 374,600,000
Proceeds from the sale of properties															769,799,000		340,098,000
Gain (Loss) on Sale															$ 116,983,000	[1]	22,002,000	[2],[3]
Deferred gain on sale											500,000						$ 500,000
Number of Properties Sold | property															66		27
Deferred gain											500,000						$ 500,000
Other Segments
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties				4			4	3							3
Provision for impairment						$ 0
Carrying value of real estate prior to impairment						$ 10,200,000		$ 25,800,000						$ 10,200,000	$ 25,800,000
Aggregate carrying value								18,500,000							$ 18,500,000
Impairment Hold Period				10 years											10 years
Residual Capitalization Rates				9.00%											8.75%
Discount Rates				9.25%											9.00%
Impairment of properties held for use				$ 1,000,000											$ 7,300,000
Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment							$ 1,000,000
Carrying value of real estate prior to impairment				10,200,000			10,200,000
Aggregate carrying value				$ 9,200,000			$ 9,200,000
Impairment Hold Period							10 years
Residual Capitalization Rates							9.00%
Discount Rates							9.25%
Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						134,794								134,794
Sales Price						$ 9,700,000								$ 9,700,000
Proceeds from the sale of properties														8,650,000
Gain (Loss) on Sale	[1],[4]													$ (325,000)
Number of Properties Sold | property														4
Two, Four A, Four B and Five Eves Drive (Evesham Corporate Center) [Member] | Other Segments
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property				4			4
200, 210 & 220 Lake Drive East (Woodland Falls) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment								7,300,000
Carrying value of real estate prior to impairment								25,800,000							25,800,000
Aggregate carrying value								$ 18,500,000							$ 18,500,000
Impairment Hold Period								10 years
Residual Capitalization Rates								8.75%
Discount Rates								9.00%
200, 210 & 220 Lake Drive East (Woodland Falls) [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						215,465								215,465
Sales Price						$ 19,000,000								$ 19,000,000
Proceeds from the sale of properties														17,771,000
Gain (Loss) on Sale	[1],[5]													$ (249,000)
Number of Properties Sold | property														3
200, 210 & 220 Lake Drive East (Woodland Falls) [Member] | Other Segments
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property								3							3
Philadelphia Marine Center (Marine Piers) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						181,900								181,900
Sales Price						$ 21,400,000								$ 21,400,000
Payment by cash on purchases														12,000,000
Balance payment on purchases						9,400,000								$ 9,400,000
Date of second installment payment														Jan. 31, 2020
Proceeds from the sale of properties														$ 11,200,000
Assets held for sale, net						4,700,000								4,700,000
Gain (Loss) on Sale														6,500,000
Deferred gain on sale						9,400,000								9,400,000
Deferred gain						$ 9,400,000								$ 9,400,000
11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale							$ 1,700,000	$ 3,000,000
Purchase price reduction							$ 1,700,000
11700, 11710, 11720 & 11740 Beltsville Drive (Calverton) [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						313,810								313,810
Sales Price						$ 9,000,000								$ 9,000,000
Proceeds from the sale of properties														8,354,000
Gain (Loss) on Sale	[1],[6]													$ 0
Number of Properties Sold | property														3
1200 & 1220 Concord Avenue (Concord Airport Plaza) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale														$ 32,000
Proceeds after closing costs and prorations								$ 11,500
1200 & 1220 Concord Avenue (Concord Airport Plaza) [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²						350,256								350,256
Sales Price						$ 33,100,000								$ 33,100,000
Proceeds from the sale of properties														32,010,000
Gain (Loss) on Sale	[1],[7]													$ 551,000
Number of Properties Sold | property					2									2
196/198 Van Buren Street (Herndon Metro Plaza I&II) [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²								197,225							197,225
Sales Price								$ 44,500,000							$ 44,500,000
Proceeds from the sale of properties															43,412,000
Gain (Loss) on Sale	[1],[8]														$ (752,000)
Impairment of properties held for use										$ 7,400,000
Number of Properties Sold | property															2
Och Ziff Portfolio [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²								3,924,783							3,924,783
Sales Price								$ 398,100,000							$ 398,100,000
Proceeds from the sale of properties															353,971,000
Gain (Loss) on Sale	[1],[9]														$ (372,000)
Provision for impairment on assets held for sale											$ 45,400,000
Number of Properties Sold | property															58
Encino Trace [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²											320,000						320,000
Number of floors of a building | Storey											4						4
Number of Properties Sold | property																	2
Encino Trace [Member] | Austin Joint Venture [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Non-Recourse Debt											$ 30,000,000						$ 30,000,000
Amount Of Participant Contribution											1,800,000						1,800,000
Encino Trace [Member] | Brandywine Realty Trust [Member] | Austin Joint Venture [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Development costs											76,700,000						76,700,000
Proceeds from Equity Method Investment, Dividends or Distributions																	50,200,000
Capital contribution											23,300,000						23,300,000
Gain (loss) on real estate venture transactions																	2,000,000
Additional borrowing fund to tenant improvements and leasing commissions											29,700,000						29,700,000
Encino Trace [Member] | DRA Advisors LLC [Member] | Austin Joint Venture [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Working capital contribution											1,800,000						1,800,000
Encino Trace [Member] | DRA Advisors LLC [Member] | Brandywine Realty Trust [Member] | Austin Joint Venture [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Amount Of Participant Contribution											$ 25,100,000						$ 25,100,000
Encino Trace [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²											320,000						320,000
Sales Price											$ 76,700,000						$ 76,700,000
Proceeds from the sale of properties																	50,158,000
Gain (Loss) on Sale	[2],[10]																$ 2,008,000
Number of Properties Sold | property																	2
Carlsbad, CA [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (Loss) on Sale											0
Provision for impairment on assets held for sale											$ 6,300,000
100 Gateway Centre Parkway [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²											74,991						74,991
Sales Price											$ 4,100,000						$ 4,100,000
Proceeds from the sale of properties																	3,911,000
Gain (Loss) on Sale												$ 0					$ 0	[2],[11]
Provision for impairment on assets held for sale												$ 800,000
Number of Properties Sold | property																	1
Lake Merritt Tower [Member] | Office Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²											204,336						204,336
Sales Price											$ 65,000,000						$ 65,000,000
Proceeds from the sale of properties																	62,800,000
Gain (Loss) on Sale													$ 0				$ 0	[2],[12]
Provision for impairment on assets held for sale													$ 1,700,000
Number of Properties Sold | property																	1
[1]	Gain/(Loss) on Sale is net of closing and other transaction related costs.
[2]	Gain on Sale is net of closing and other transaction related costs.
[3]	Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.
[4]	As of March 31, 2017, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of four properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $1.0 million at March 31, 2017, which reduced the aggregate carrying values of the properties from $10.2 million to their estimated fair value of $9.2 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 9.25%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs.
[5]	As of December 31, 2016, the Company evaluated the recoverability of the carrying value of its properties that triggered assessment under the undiscounted cash flow model. Based on the Company’s evaluation, it was determined that due to the reduction in the Company’s intended hold period of three properties located in the Other segment, the Company would not recover the carrying values of these properties. Accordingly, the Company recorded impairment charges on these properties of $7.3 million at December 31, 2016, reducing the aggregate carrying values of the properties from $25.8 million to their estimated fair value of $18.5 million. The Company measured these impairments based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 8.75% and 9.00%, respectively. The results were comparable to indicative pricing in the market. The assumptions used to determine fair value under the income approach are Level 3 inputs in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The loss on sale in the table above represents additional closing costs.
[6]	During the fourth quarter of 2016, the Company recognized a $3.0 million impairment related to these properties. During the first quarter of 2017, there was a price reduction of $1.7 million under the agreement of sale and an additional impairment of $1.7 million was recognized.
[7]	During the fourth quarter of 2016, the Company recognized an $11.5 million impairment related to these properties. This sale was designated as a like-kind exchange under Section 1031 of the Internal Revenue Code (“IRC”) and, as such, the proceeds, totaling $32.0 million after closing costs and prorations, were deposited with a Qualified Intermediary, as defined under the IRC. The proceeds received at closing were recorded as “Other assets” in the Company’s consolidated balance sheets. During the third quarter of 2017, the Company acquired 3000 Market Street in Philadelphia, Pennsylvania using the full balance of the Section 1031 proceeds. See “Acquisition” section above.
[8]	During the three-month period ended March 31, 2016, the Company recognized a provision for impairment totaling approximately $7.4 million on the properties. See “Held for Use Impairment” section below. The loss on sale primarily relates to additional closing costs recognized at closing.
[9]	During the three-month period ended December 31, 2015, the Company recognized a provision for impairment totaling approximately $45.4 million. The loss on sale represents additional closing costs recognized at closing.
[10]	On December 31, 2015, the Company contributed two newly constructed four-story, Class A office buildings, commonly known as “Encino Trace,” containing an aggregate of approximately 320,000 square feet in Austin, Texas to one of its existing real estate ventures (the “Austin Venture”) that the Company formed in 2013 with G&I VII Austin Office LLC, an investment vehicle advised by DRA Advisors LLC (“DRA”). When these two properties were contributed to the Austin Venture the Company had incurred a total of $76.7 million of development costs, representing the contribution value. In conjunction with the contribution: (i) the Austin Venture obtained a $30.0 million mortgage loan; (ii) DRA contributed $25.1 million in net cash to the capital of the Austin Venture, including a $1.8 million working capital contribution; and (iii) the Austin Venture distributed $50.2 million to the Company and credited the Company with a $23.3 million capital contribution to the Austin Venture. In addition to the contribution of the properties, the Company also made a $1.8 million cash contribution to the Austin Venture for working capital. The Company recognized a $2.0 million gain on the contribution. Under the Encino Trace loan agreement, the Austin Venture has the option, subject to certain leasing and loan-to-value requirements, to borrow an additional $29.7 million to fund tenant improvements and leasing commissions.
[11]	The Company recorded an impairment loss of $0.8 million for 100 Gateway Centre Parkway during the second quarter of 2015. As such, there was no gain at disposition for this property.
[12]	The Company recorded an impairment loss of $1.7 million for Lake Merritt Tower on March 31, 2015. As such, there was no gain at disposition for this property. Sales proceeds were deposited in escrow under Section 1031 of the Internal Revenue Code and applied to purchase the Broadmoor Austin portfolio. Refer to Broadmoor Austin Associates acquisition summary, above, for further details.

Real Estate Investments - Dispo

Real Estate Investments - Dispositions (Textual) (Details)		Mar. 31, 2017USD ($)segment	Dec. 31, 2017USD ($)apropertyParcel	Mar. 31, 2017USD ($)segment	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)property	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)apropertyParcel	Dec. 31, 2016USD ($)apropertyParcel	Dec. 31, 2015USD ($)apropertyParcel
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net gain on disposition of real estate								$ 31,657,000	$ 116,983,000	$ 20,496,000
Impairment charges					$ 1,800,000			$ 3,057,000	40,517,000	82,208,000
Number of Properties | property			93					93
Aggregate carrying values of properties			$ 3,832,348,000					$ 3,832,348,000	3,586,295,000
Assets held for sale, net			$ 392,000					$ 392,000	41,718,000
Assets Held-for-sale [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Acreage of land | a			13.1					13.1
Assets held for sale, net									$ 41,718,000	$ 584,365,000
Land Held For Development [Member] | Assets Held-for-sale [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Assets held for sale, net			$ 400,000					$ 400,000
Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Acreage of land | a			76.4					76.4	122.9	14.7
Number of Parcels | Parcel			5					5	3	4
Other Segments
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Impairment charges			$ 0
Number of Properties		4		4					3
Impairment of properties held for use		$ 1,000,000							$ 7,300,000
Carrying value of real estate prior to impairment			10,200,000					$ 10,200,000	$ 25,800,000
Impairment Hold Period		10 years							10 years
Residual Capitalization Rates		9.00%							8.75%
Discount Rates		9.25%							9.00%
Aggregate carrying value									$ 18,500,000
Other Segments | Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Impairment charges			0				$ 300,000
Impairment of properties held for use									5,600,000
Carrying value of real estate prior to impairment									$ 18,200,000
Acreage of land | a									108
Aggregate carrying value									$ 12,600,000
Number of Parcels | Parcel									5
Other Segments | Impairment on Held for Use Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Aggregate carrying values of properties			$ 9,200,000					$ 9,200,000
Metropolitan DC [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties | property						2				3
Impairment of properties held for use					3,900,000	$ 7,400,000				$ 27,500,000
Carrying value of real estate prior to impairment					$ 37,400,000	$ 51,900,000
Impairment Hold Period					10 years	10 years				10 years
Residual Capitalization Rates					7.75%	7.00%				8.00%
Discount Rates					8.25%	7.00%				8.00%
Aggregate carrying value					$ 33,500,000	$ 44,500,000				$ 40,400,000
Estimated Fair Value Of Impaired Property										12,900,000
2970 Market Street (Cira Square) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net gain on disposition of real estate				$ 500,000
2970 Market Street (Cira Square) [Member] | Assets Held-for-sale [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Assets held for sale, net	[1]									$ 234,025,000
[1]	On December 23, 2015 the Company entered into a purchase and sale agreement to dispose of its equity interests in the office property located at 2970 Market Street in Philadelphia commonly known as 30th Street Main Post Office (“Cira Square”), which includes 862,692 square feet of rentable space and is fully leased to a single tenant. As of December 31, 2015, the Company determined the sale was probable and classified the property as held for sale in accordance with applicable accounting standards for long lived assets. As the fair value less anticipated costs to sell exceeded the carrying value of the property no impairment loss was recorded. The fair value measurement was based on the pricing in the purchase and sale agreement. As the sales price is unobservable, the Company determined that the significant inputs used to value this real estate investment are Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” On February 5, 2016 the Company completed the disposition of its equity interests in Cira Square.

Real Estate Investments - Sum69

Real Estate Investments - Summary of Land Parcels Sold (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017USD ($)aParcel	Dec. 31, 2016USD ($)aParcel		Dec. 31, 2015USD ($)aParcel		Jan. 15, 2016Parcel
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from the sale of properties		$ 171,860	$ 784,331		$ 247,228
Gain (Loss) on Sale		$ 953	$ 9,232		$ 3,019
Greenhills Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel							120
Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		5	3		4
Acreage of land | a		76.4	122.9		14.7
Sales Price		$ 29,600	$ 14,938		$ 22,300
Proceeds from the sale of properties		28,618	14,532		21,088
Gain (Loss) on Sale		$ 953	$ 9,232	[1]	$ 3,019	[2]
Land [Member] | 50 E. Swedesford Square [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		1
Acreage of land | a		12
Sales Price		$ 7,200
Proceeds from the sale of properties		7,098
Gain (Loss) on Sale		$ 882
Land [Member] | Bishops Gate [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		1
Acreage of land | a		49.5
Sales Price		$ 6,000
Proceeds from the sale of properties		5,640
Gain (Loss) on Sale	[3]	$ 71
Land [Member] | Garza Ranch - Multi-family [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		1
Acreage of land | a		8.4
Sales Price		$ 11,800
Proceeds from the sale of properties		11,560
Gain (Loss) on Sale	[4]	$ 0
Land [Member] | Gateway Land - Site C [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		1
Acreage of land | a		4.8
Sales Price		$ 1,100
Proceeds from the sale of properties		1,043
Gain (Loss) on Sale	[5]	$ 0
Land [Member] | Garza Ranch - Hotel [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel		1
Acreage of land | a		1.7
Sales Price		$ 3,500
Proceeds from the sale of properties		3,277
Gain (Loss) on Sale	[4]	$ 0
Land [Member] | Oakland Lot B [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel			1
Acreage of land | a			0.9
Sales Price			$ 13,750
Proceeds from the sale of properties			13,411
Gain (Loss) on Sale	[1]		$ 9,039
Land [Member] | Highlands Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel			1
Acreage of land | a			2
Sales Price			$ 288
Proceeds from the sale of properties			284
Gain (Loss) on Sale	[1]		$ 193
Land [Member] | Greenhills Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel			1
Acreage of land | a			120
Sales Price			$ 900
Proceeds from the sale of properties			837
Gain (Loss) on Sale	[1],[6]		$ 0
Land [Member] | Two Christina Centre [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel					1
Acreage of land | a					1.6
Sales Price					$ 6,500
Proceeds from the sale of properties					5,986
Gain (Loss) on Sale	[2],[7]				$ 0
Land [Member] | A7000 Midlantic [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel					1
Acreage of land | a					3.5
Sales Price					$ 2,200
Proceeds from the sale of properties					1,742
Gain (Loss) on Sale	[2]				$ (169)
Land [Member] | Four Points Centre [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel					1
Acreage of land | a					8.6
Sales Price					$ 2,500
Proceeds from the sale of properties					2,344
Gain (Loss) on Sale	[2]				$ 71
Land [Member] | Two Kaiser Plaza [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Parcels | Parcel					1
Acreage of land | a					1
Sales Price					$ 11,100
Proceeds from the sale of properties					11,016
Gain (Loss) on Sale	[2]				$ 3,117
[1]	Gain on Sale is net of closing and other transaction related costs.
[2]	Gain/(Loss) on sale includes closing and other transaction related costs.
[3]	During the fourth quarter of 2016, the Company recognized an impairment of $3.0 million. During the second quarter of 2017, the Company recorded a held for sale impairment charge of $0.3 million, reducing the aggregate carrying value of the land parcel from $5.9 million to its estimated fair value less costs to sell of $5.6 million. The fair value measurement is based on pricing in the purchase and sale agreement for the property. As the pricing in the purchase and sale agreement is unobservable, the Company determined that the input utilized to determine fair value for the property falls within Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” The land parcel was sold on July 18, 2017.
[4]	The Company has a continuing involvement in this property through a completion guaranty, which requires the Company, as developer, to complete certain infrastructure improvements on behalf of the buyers of the land parcels. The Company recorded the cash received at settlement as “Deferred income, gains and rent” on the Company’s consolidated balance sheet and the Company will recognize the sale upon completion of infrastructure improvements. See Note 19, “Commitments and Contingencies” for further discussion of the infrastructure improvements.
[5]	During the fourth quarter of 2016, the Company recognized a nominal impairment related to this land parcel.
[6]	The carrying value of the land exceeded the fair value less the anticipated costs of sale as of December 31, 2015. Therefore the Company recognized an impairment loss of $0.3 million during the three-month period ended December 31, 2015. There was no gain or loss recognized on the sale during 2016.
[7]	The Company recorded an impairment loss of $0.3 million for Two Christina Centre during the fourth quarter of 2015. As such, there was no gain/(loss) at disposition for this land parcel.

Real Estate Investments - Sum70

Real Estate Investments - Summary of Land Parcels Sold (Parenthetical) (Details) - USD ($)	3 Months Ended			12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Gain (Loss) on Sale				$ 31,657,000	$ 116,983,000	$ 20,496,000
Bishops Gate [Member] | Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale	$ 300,000	$ 3,000,000
Carrying value of real estate prior to impairment	5,900,000
Aggregate carrying value	$ 5,600,000
Greenhills Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale						$ 300,000
Greenhills Land [Member] | Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale			$ 300,000
Gain (Loss) on Sale					$ 0
Two Christina Centre [Member] | Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale			300,000
Gain (Loss) on Sale			$ 0

Real Estate Investments - Sum71

Real Estate Investments - Summary of Properties Classified as Held for Sale Included in Continuing Operations (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS HELD FOR SALE
Total assets held for sale, net		$ 392	$ 41,718
LIABILITIES HELD FOR SALE
Total liabilities held for sale		$ 0	81
Held for Sale Properties Included in Continuing Operations [Member]
ASSETS HELD FOR SALE
Operating properties			73,591	$ 794,588
Accumulated depreciation			(32,916)	(213,581)
Operating real estate investments, net			40,675	581,007
Construction-in-progress				1,940
Land held for development			1,043	837
Total real estate investments, net			41,718	583,784
Intangible assets				581
Total assets held for sale, net			41,718	584,365
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net				192
Other liabilities			81	1,959
Total liabilities held for sale			81	2,151
Held for Sale Properties Included in Continuing Operations [Member] | Metropolitan D.C. - Office [Member]
ASSETS HELD FOR SALE
Operating properties	[1]		21,720
Accumulated depreciation	[1]		(11,935)
Operating real estate investments, net	[1]		9,785
Land held for development	[1]		0
Total real estate investments, net	[1]		9,785
Total assets held for sale, net	[1]		9,785
LIABILITIES HELD FOR SALE
Other liabilities	[1]		73
Total liabilities held for sale	[1]		73
Held for Sale Properties Included in Continuing Operations [Member] | Other Segment - Office [Member]
ASSETS HELD FOR SALE
Operating properties	[2]		51,871
Accumulated depreciation	[2]		(20,981)
Operating real estate investments, net	[2]		30,890
Land held for development	[2]		0
Total real estate investments, net	[2]		30,890
Total assets held for sale, net	[2]		30,890
LIABILITIES HELD FOR SALE
Other liabilities	[2]		8
Total liabilities held for sale	[2]		8
Held for Sale Properties Included in Continuing Operations [Member] | Other Segment - Land [Member]
ASSETS HELD FOR SALE
Operating properties	[3]		0
Accumulated depreciation	[3]		0
Operating real estate investments, net	[3]		0
Land held for development	[3]		1,043
Total real estate investments, net	[3]		1,043
Total assets held for sale, net	[3]		1,043
LIABILITIES HELD FOR SALE
Other liabilities	[3]		0
Total liabilities held for sale	[3]		$ 0
Held for Sale Properties Included in Continuing Operations [Member] | Och Ziff Properties [Member]
ASSETS HELD FOR SALE
Operating properties	[4]			526,099
Accumulated depreciation	[4]			(179,092)
Operating real estate investments, net	[4]			347,007
Construction-in-progress	[4]			1,915
Land held for development	[4]			0
Total real estate investments, net	[4]			348,922
Intangible assets	[4]			581
Total assets held for sale, net	[4]			349,503
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[4]			192
Other liabilities	[4]			1,959
Total liabilities held for sale	[4]			2,151
Held for Sale Properties Included in Continuing Operations [Member] | 2970 Market Street (Cira Square) [Member]
ASSETS HELD FOR SALE
Operating properties	[5]			268,489
Accumulated depreciation	[5]			(34,489)
Operating real estate investments, net	[5]			234,000
Construction-in-progress	[5]			25
Land held for development	[5]			0
Total real estate investments, net	[5]			234,025
Intangible assets	[5]			0
Total assets held for sale, net	[5]			234,025
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[5]			0
Other liabilities	[5]			0
Total liabilities held for sale	[5]			0
Held for Sale Properties Included in Continuing Operations [Member] | Greenhills Land [Member]
ASSETS HELD FOR SALE
Operating properties	[6]			0
Accumulated depreciation	[6]			0
Operating real estate investments, net	[6]			0
Construction-in-progress	[6]			0
Land held for development	[6]			837
Total real estate investments, net	[6]			837
Intangible assets	[6]			0
Total assets held for sale, net	[6]			837
LIABILITIES HELD FOR SALE
Acquired lease intangibles, net	[6]			0
Other liabilities	[6]			0
Total liabilities held for sale	[6]			$ 0
[1]	As of December 31, 2016, the Company determined that the sale of three office properties in the Metropolitan D.C. segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded their fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $3.0 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.00% and 10.00%, respectively. The results were comparable to indicative pricing in the market. As significant inputs to the model are unobservable, the Company determined that the value determined for this property falls within Level 3 fair value reporting.
[2]	As of December 31, 2016, the Company determined that the sale of two office properties in the Other segment was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $11.5 million during the three-month period ended December 31, 2016. The Company measured this impairment based on a discounted cash flow analysis, using a hold period of 10 years and residual capitalization rates and discount rates of 9.75% and 9.75%, respectively. The results were comparable to indicative pricing in the market. As significant inputs to the model are unobservable, the Company determined that the value determined for this property falls within Level 3 fair value reporting.
[3]	As of December 31, 2016, the Company determined that the sale of a land parcel in the Other segment was probable and classified the land parcel as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the land approximated the fair value less the anticipated costs of sale and the Company recorded a nominal impairment. The fair value measurement was based on the pricing in the purchase and sale.
[4]	On February 4, 2016, the Company disposed of its interests in 58 properties located in the Pennsylvania Suburbs, New Jersey/Delaware, Metropolitan Washington, D.C. and Richmond, Virginia segments in a series of related transactions with Och Ziff Real Estate. During the fourth quarter of 2015, significant provisions were agreed upon by both the Company and Och Ziff Real Estate and, as a result, the Company determined that the sale of the portfolio was probable and classified these properties as held for sale in accordance with applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $45.4 million during the year ended December 31, 2015. The fair value measurement was based on the pricing in the purchase and sale agreement. As the significant inputs to the model are unobservable, the Company determined that the value determined for these real estate investments fall within Level 3 for fair value reporting.
[5]	On December 23, 2015 the Company entered into a purchase and sale agreement to dispose of its equity interests in the office property located at 2970 Market Street in Philadelphia commonly known as 30th Street Main Post Office (“Cira Square”), which includes 862,692 square feet of rentable space and is fully leased to a single tenant. As of December 31, 2015, the Company determined the sale was probable and classified the property as held for sale in accordance with applicable accounting standards for long lived assets. As the fair value less anticipated costs to sell exceeded the carrying value of the property no impairment loss was recorded. The fair value measurement was based on the pricing in the purchase and sale agreement. As the sales price is unobservable, the Company determined that the significant inputs used to value this real estate investment are Level 3 in accordance with the fair value hierarchy established by Accounting Standards Codification (ASC) Topic 820, “Fair Value Measurements and Disclosures.” On February 5, 2016 the Company completed the disposition of its equity interests in Cira Square.
[6]	On January 15, 2016, the Company sold the fee interest in a 120 acre land parcel located in Berks County, Pennsylvania for $0.9 million. As of December 31, 2015, the Company classified this land parcel as held for sale in accordance with the applicable accounting standards for long lived assets. At such date, the carrying value of the properties exceeded the fair value less the anticipated costs of sale. As a result, the Company recognized an impairment loss totaling approximately $0.3 million during the year ended December 31, 2015.

Real Estate Investments - Sum72

Real Estate Investments - Summary of Properties Classified as Held for Sale Included in Continuing Operations (Parenthetical) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2016property	Dec. 31, 2015USD ($)	Feb. 04, 2016property	Jan. 15, 2016USD ($)Parcel	Dec. 23, 2015ft²
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Real Estate Properties | property				58
Och Ziff Properties [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale			$ 45,400,000
2970 Market Street (Cira Square) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale			$ 0
Purchase and Sale Agreement Date			Dec. 23, 2015
Rentable Square Feet | ft²						862,692
Greenhills Land [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale			$ 300,000
Number of Parcels | Parcel					120
Contractual Sales Price					$ 900,000
Held for Sale Properties Included in Continuing Operations [Member] | Metropolitan D.C. - Office [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property		3
Provision for impairment on assets held for sale	$ 3,000,000
Impairment Hold Period		10 years
Residual Capitalization Rates		9.00%
Discount Rates		10.00%
Held for Sale Properties Included in Continuing Operations [Member] | Other Segment - Office [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold | property		2
Provision for impairment on assets held for sale	$ 11,500,000
Impairment Hold Period		10 years
Residual Capitalization Rates		9.75%
Discount Rates		9.75%

Real Estate Investments - Pro F

Real Estate Investments - Pro Forma (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings (loss) per common share from continuing operations:
Basic -- as reported									$ 0.66	$ 0.19	$ (0.21)
Diluted -- as reported									0.65	0.19	(0.21)
Earnings (loss) per common share:
Basic -- as reported	$ 0.42	$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	0.66	0.19	(0.21)
Diluted -- as reported	$ 0.41	$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
Broadmoor Austin Associates [Member]
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma revenue											$ 612,649
Pro forma income (loss) from continuing operations											(36,704)
Pro forma net income (loss) available to common shareholders											$ (43,594)
Earnings (loss) per common share from continuing operations:
Basic -- as reported											$ (0.17)
Basic -- as pro forma											(0.21)
Diluted -- as reported											(0.17)
Diluted -- as pro forma											(0.21)
Earnings (loss) per common share:
Basic -- as reported											(0.21)
Basic -- as pro forma											(0.24)
Diluted -- as reported											(0.21)
Diluted -- as pro forma											$ (0.24)

Investment in Unconsolidated 74

Investment in Unconsolidated Real Estate Ventures (Textual) (Details)		Jan. 10, 2018USD ($)Real_Estate_Investment	Oct. 18, 2017USD ($)ft²property	Oct. 17, 2017USD ($)property	Sep. 14, 2017USD ($)ft²property	Jan. 31, 2017USD ($)property	Sep. 30, 2016USD ($)ft²Apartment_unitNumberofCar.	Sep. 22, 2016USD ($)ft²	Aug. 31, 2016USD ($)	Aug. 19, 2016USD ($)	Jun. 30, 2016USD ($)ft²	Jun. 10, 2016USD ($)	Mar. 02, 2016USD ($)	Feb. 04, 2016USD ($)ft²property	Jan. 29, 2016USD ($)	Dec. 30, 2015USD ($)	Jun. 22, 2015USD ($)ft²apropertyBuilding	May 29, 2015USD ($)a	Jan. 30, 2015USD ($)	Oct. 21, 2014USD ($)	Oct. 17, 2014USD ($)ft²property	Oct. 15, 2014USD ($)	Jul. 31, 2014USD ($)ft²propertyStorey	Oct. 16, 2013USD ($)ft²property	Jul. 31, 2013USD ($)ft²aproperty	Sep. 30, 2016USD ($)	Dec. 31, 2017USD ($)property	Dec. 31, 2016USD ($)ft²	Jun. 30, 2016USD ($)ft²	Sep. 30, 2017USD ($)ft²property	Sep. 30, 2016USD ($)	Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)ft²property		Dec. 31, 2015USD ($)ft²propertyStorey		Dec. 31, 2011USD ($)	Dec. 31, 2017		Dec. 31, 2017property	Dec. 31, 2017ft²	Dec. 31, 2017Real_Estate_Investment	Dec. 31, 2017a	Dec. 31, 2017Apartment_unit	Dec. 31, 2014USD ($)	Oct. 27, 2014Storey	Apr. 03, 2014ft²propertyStorey	Dec. 31, 2013USD ($)	Jan. 25, 2013USD ($)aStoreyBed	Jul. 10, 2012USD ($)ft²property	Dec. 20, 2011property	Jan. 20, 2011a
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											$ 194,621,000	$ 281,331,000				$ 194,621,000		$ 281,331,000		$ 241,004,000
Management fees																																28,345,000		26,674,000		18,764,000
Accounts receivable																											17,938,000	12,446,000				17,938,000		12,446,000
Property encumbered at the time of venture sale																											320,107,000					320,107,000
Proceeds from real estate venture sales																																145,416,000		21,022,000		6,100,000
Net gain on Real Estate Venture transactions																																80,526,000		20,000,000		7,229,000
Deconsolidated mortgage loan																																0		(20,582,000)		0
Deconsolidated financing liability																																0		(12,384,000)		0
Capital funded to venture for mortgage debt																																6,638,000		28,610,000		68,549,000
Repayment of mortgage debt																																4,931,000		357,151,000		222,836,000
Number of Properties | property																																									93
Cash proceeds after the payment of share of the debt and closing costs																																145,416,000		21,022,000		6,100,000
Advance received for refinancing																																341,000,000		195,000,000		89,000,000
Cash distribution from unconsolidated real estate ventures																																20,781,000		13,065,000		8,557,000
Proceeds from the sale of properties																																171,860,000		784,331,000		247,228,000
Gain (Loss) on Sale																																31,657,000		116,983,000		20,496,000
Amount funded by corporate funds																																72,523,000		20,406,000		150,472,000
Proceeds from repayment of mortgage notes receivable																																151,000		0		$ 88,000,000
Real estate ventures aggregate indebtedness to third parties																											768,912,000	$ 997,466,000				768,912,000		$ 997,466,000
Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																	1,112,236
Acreage of land | a																	66
Number of Property units | property																	7
Equity method investment percentage																	50.00%
Payments to Acquire Land																	$ 143,800,000
Encino Trace - Land [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																				320,000
Number of Properties | property																																				2
Number of floors of a building | Storey																																				4
Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																	50.00%
TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Gross sales price						$ 100,500,000
Proceeds from real estate venture sales						27,200,000
Net gain on Real Estate Venture transactions						$ 14,600,000
Sale of ownership interest percentage						50.00%
Allocated gross sales value of ownership interest, percentage						50.00%
Number of Properties Sold | property						398
Guarantee obligations cancelled						$ 3,200,000
Cash proceeds after the payment of share of the debt and closing costs						27,200,000
TB-BDN Plymouth Apartments [Member] | Pennsylvania [Member]
Schedule Of Equity Method Investments [Line Items]
Construction Loan						54,000,000
Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | property																																																2
Number of floors of a building | Storey																																																3
Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																												5,239,632						5,239,632		2,649,926
Gross sales price																												$ 820,000,000						$ 820,000,000		$ 374,600,000
Number of Properties | property																																									81
Number of Properties Sold | property																																		66		27
Proceeds from the sale of properties																																		$ 769,799,000		$ 340,098,000
Gain (Loss) on Sale																																		116,983,000	[1]	22,002,000	[2],[3]
Office Properties [Member] | Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | Building																	7
Office Properties [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																										587,317
Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees																																6,400,000		6,700,000		4,400,000
Accounts receivable																											900,000	$ 1,400,000				900,000		1,400,000
Real Estate Venture [Member] | Lease Commission Income [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees																																4,500,000		$ 3,800,000		$ 2,100,000
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											13
Investment in Real Estate Ventures, equity method																											194,600,000					194,600,000
Equity method investment percentage																												0.00%						0.00%		0.00%			0.00%
Equity method investment other than temporary impairment charge	[4]																															4,844,000
Real estate ventures aggregate indebtedness to third parties																											768,912,000					768,912,000
Unconsolidated Real Estate Ventures [Member] | TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Equity in income (loss) of Real Estate Ventures						$ 12,600,000
Unconsolidated Real Estate Ventures [Member] | Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																												20.00%						20.00%		20.00%			20.00%
Unconsolidated Real Estate Ventures [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																												70.00%						70.00%		70.00%			70.00%
Unconsolidated Real Estate Ventures [Member] | Land Under Active Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											1
Acreage of land | a																																												1.3
Unconsolidated Real Estate Ventures [Member] | Seven Real Estate Ventures [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											7
Rentable Square Feet | ft²																																										6,700,000
Unconsolidated Real Estate Ventures [Member] | Three Real Estate Ventures [Member] | Land Held For Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											3
Acreage of land | a																																												4.4
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower One [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures																																											1		1
Number of Property units																																									345				345
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower Two [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures																																											1		1
Number of Property units																																									321				321
BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[5],[6]																										43,560,000	$ 67,809,000				43,560,000		$ 67,809,000
Rentable Square Feet | ft²					874,479
Equity method investment percentage																												50.00%						50.00%		50.00%			50.00%	[5],[6],[7]												50.00%
Number of office properties owned | property					5																									5
Cost of equity method investment																														$ 49,100,000
Equity method investment other than temporary impairment charge																														4,800,000		4,844,000	[4]
Cost of equity method investment after recordation of impairment charge																														$ 44,300,000
Impairment Hold Period																														10 years
Residual Capitalization Rates																														7.50%
Effective interest rate	[5],[6]																																						3.94%
Real estate ventures aggregate indebtedness to third parties	[5],[6]																										93,117,000	$ 131,539,000				93,117,000		$ 131,539,000
BDN - Al Venture [Member] | Current Creek Investments, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																																				50.00%
BDN - Al Venture [Member] | 7101 Wisconsin Property Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²					230,904																									239,904
Equity method investment percentage					50.00%
Gross sales price					$ 105,700,000																									$ 105,700,000
Property encumbered at the time of venture sale					37,400,000
Debt instrument prepayment penalty					800,000
Cash proceeds received from sale of venture					63,600,000
Proceeds from real estate venture sales					31,800,000
Net gain on Real Estate Venture transactions					13,800,000
Cash proceeds after the payment of share of the debt and closing costs					$ 31,800,000
BDN - Al Venture [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method									$ 12,600,000
Deconsolidated net assets									45,600,000
Deconsolidated mortgage loan									20,600,000
Deconsolidated financing liability									$ 12,400,000
Recognizing gain or loss on sale																													$ 0
Capital funded to venture for mortgage debt																										$ 10,300,000
Repayment of mortgage debt																												20,600,000
BDN - Al Venture [Member] | Station Square [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																																			497,896
Equity method investment percentage																																																			50.00%
Cost of equity method investment																																																			$ 120,600,000
Equity method investment other than temporary impairment charge																															$ 5,200,000
Provision for impairment of investment in real estate ventures																															10,400,000
Number of Properties | property																																																			3
BDN - Al Venture [Member] | Remaining Properties in Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment other than temporary impairment charge																																0
BDN - Al Venture [Member] | Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Discount Rates																														7.80%
BDN - Al Venture [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Discount Rates																														8.50%
BDN - Al Venture [Member] | Office Properties [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Number of office properties owned | property																																																				3
PJP V [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage								25.00%
Proceeds from real estate venture sales								$ 3,400,000
Net gain on Real Estate Venture transactions								3,200,000
Cash proceeds after the payment of share of the debt and closing costs								3,400,000
Equity in income (loss) of Real Estate Ventures								$ 200,000
PJP V [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²								73,997
Invesco Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net gain on Real Estate Venture transactions										$ 7,000,000
Equity in income (loss) of Real Estate Ventures										0
Amount of proceeds, net of closing costs										$ 7,000,000
1000 Chesterbrook [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage											50.00%																		50.00%
Gross sales price											$ 32,100,000																		$ 32,100,000
Proceeds from real estate venture sales											9,800,000
Net gain on Real Estate Venture transactions											3,200,000
Cash proceeds after the payment of share of the debt and closing costs											9,800,000
Debt assumed by buyer											$ 23,200,000
Working capital contribution							$ 200,000																			$ 200,000					$ 200,000
1000 Chesterbrook [Member] | One Real Estate Venture [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Area of Real Estate Property | ft²											172,286																		172,286
evo at Cira Centre South Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method													$ 28,300,000
Equity method investment percentage													50.00%																																					30.00%
Cost of equity method investment																																																		$ 4,000,000
Construction Loan												$ 97,800,000
Number of floors of a building | Storey																																																		33
Student housing bed capacity | Bed																																																		850
Area of developed parcels of land (in acres) owned by a Real Estate Venture | a																																																		1
Equity Method Investment, Underlying Equity in Net Assets																																																		$ 8,500,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																																																		$ 4,500,000
Cash paid to acquire real estate ventures													$ 12,800,000
Equity method investment percentage of interests acquired by the Company and HSRE													30.00%
Debt instrument maturity date												Jul. 25, 2016
Cash distribution from unconsolidated real estate ventures												$ 6,300,000
Guarantees, maximum exposure amount																											55,400,000					55,400,000
Guarantor obligations, current carrying value																											55,400,000					$ 55,400,000
evo at Cira Centre South Venture [Member] | Secured Debt [Member]
Schedule Of Equity Method Investments [Line Items]
Debt instrument maturity date												Oct. 31, 2019
Term loans												$ 117,000,000
Debt instrument, description of variable rate basis																																LIBOR + 2.25
Debt instrument optional extended maturity date												Jun. 30, 2021
Advance received for refinancing												$ 105,000,000
Additional capacity under the term loan may be funded if certain criterion relating to the operating performance of the student housing tower are met												$ 12,000,000
evo at Cira Centre South Venture [Member] | Secured Debt [Member] | LIBOR [Member]
Schedule Of Equity Method Investments [Line Items]
Debt instrument, basis spread on variable rate												2.25%
evo at Cira Centre South Venture [Member] | Campus Crest Properties, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																																		30.00%
evo at Cira Centre South Venture [Member] | HSRE, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage													50.00%																																					40.00%
Cash paid to acquire real estate ventures													$ 6,600,000
evo at Cira Centre South Venture [Member] | Maximum [Member] | Secured Debt [Member]
Schedule Of Equity Method Investments [Line Items]
Effective interest rate												5.25%
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[8]																										15,450,000	20,893,000				$ 15,450,000		20,893,000
Equity method investment percentage	[7],[8]																																						50.00%
Real estate ventures aggregate indebtedness to third parties	[8]																										180,800,000	180,800,000				180,800,000		180,800,000
MAP Venture [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²														3,924,783
Equity method investment percentage														50.00%
Gross sales price														$ 398,100,000
Number of Properties Sold | property														58
Percentage of fee interests in land sold														100.00%
Ground lease annual payments																																$ 11,900,000
Ground lease annual rent expense increase percentage																																							2.50%
Reassessment period for change in ground lease annual payments																																10 years
Ground Lease Terms																																Annual payments by the MAP Venture, as tenant under the Ground Leases, initially total $11.9 million and increase 2.5% annually through November 2025.
Non-Recourse Debt														$ 180,800,000
Proceeds from the sale of properties														354,000,000
Ownership percentage value														$ 25,200,000
Coppell Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage															50.00%
Proceeds from real estate venture sales															$ 4,600,000
Cash proceeds after the payment of share of the debt and closing costs															4,600,000
Gain (Loss) on Sale															5,700,000
Coppell Associates [Member] | Other Liabilities [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method															$ 1,100,000
Residence Inn Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																$ 900,000
Equity method investment percentage																50.00%
Proceeds from real estate venture sales																$ 6,100,000
Cash proceeds after the payment of share of the debt and closing costs																6,100,000
Gain (Loss) on Sale																$ 5,200,000
51 N 50 Patterson [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											21,212,000	20,318,000				$ 21,212,000		20,318,000
Equity method investment percentage																		70.00%																					70.00%	[7]
Payments to Acquire Land																		$ 15,200,000
Area owned by real estate venture of undeveloped parcels of land | a																		0.9
Real estate ventures aggregate indebtedness to third parties																											0	0				0		0
51 N 50 Patterson [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																		30.00%
Payments to Acquire Land																		$ 6,500,000
1250 First Street Office [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											17,867,000	17,304,000				17,867,000		17,304,000
Equity method investment percentage																		70.00%																					70.00%	[7]
Payments to Acquire Land																		$ 13,200,000
Area owned by real estate venture of undeveloped parcels of land | a																		0.5
Real estate ventures aggregate indebtedness to third parties																											0	0				0		0
1250 First Street Office [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																		30.00%
Payments to Acquire Land																		$ 5,700,000
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[9],[10]																										22,268,000	27,462,000				$ 22,268,000		27,462,000
Equity method investment percentage																																							50.00%	[7],[9],[10]													50.00%
Number of floors of a building | Storey																																															29
Area of developed parcels of land (in acres) owned by a Real Estate Venture | a																																																					1
Debt instrument, description of variable rate basis																																LIBOR + 1.75
Payments to Acquire Land																																						$ 9,300,000
Remeasurement gain or loss on investments																						$ 0
Square foot of contemporary glass tower development | ft²							455,000
Number of luxury apartments | Apartment_unit							321
Square feet of commercial space | ft²							24,000
Number of Car Structured Parking Facility | NumberofCar.							215
Real estate ventures aggregate indebtedness to third parties	[9],[10]																										88,860,000	79,250,000				$ 88,860,000		79,250,000
Brandywine Nineteen Nineteen Ventures [Member] | LCOR/CalSTRS [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																				50.00%
Aggregate gross sales price of a joint venture																				$ 16,400,000
General Partners' Contributed Capital																				5,200,000
Net gain on sale of undepreciated real estate																				$ 8,200,000
Outstanding construction loan																											88,900,000					88,900,000
Equity method investments, Cash contributions																																29,600,000
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											14,000,000					14,000,000
Rentable Square Feet | ft²			1,164,496																		590,881		232,274																			1,570,123
Equity method investment percentage			50.00%
Gross sales price			$ 333,250,000
Proceeds from real estate venture sales			172,742,000
Net gain on Real Estate Venture transactions			$ 40,092,000																								$ 52,200,000
Number of office properties owned | property																																									11
Number of Properties | property																					7		2
Number of Properties Sold | property			8	7																							8
Cash proceeds after the payment of share of the debt and closing costs			$ 172,742,000
Amount of proceeds, net of closing costs			86,371,000
Equity method investments, Cash contributions																					$ 18,900,000		$ 12,800,000
Equity method investments, Closing costs																					200,000		100,000
Equity method investment, Consideration transferred																							48,200,000
Mortgage loans outstanding																							$ 34,500,000
Mortgage loans interest rate																							3.87%
Equity Method Investments Purchase Adjustments																							$ 900,000
Business acquisition cost of acquired entity transaction costs borne by seller																							600,000
Amount funded by corporate funds																					128,100,000
Short-term Bank Loans and Notes Payable																					$ 88,000,000
Real estate ventures aggregate indebtedness to third parties			150,968,000	$ 151,000,000
Cash proceeds after the payment of mortgage debt, closing costs and prorations			86,400,000
Deferred gain on sale			$ 12,072,000
Austin Joint Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																							50.00%
Area of Real Estate Property | ft²																								1,398,826
Aggregate gross sales price of a joint venture																								$ 330,000,000
Equity method investments, Cash contributions																							$ 6,400,000
Number of properties contributed to a joint venture | property																								7
Equity method investment, agreement to pay future capital expenditures																								$ 5,200,000																									$ 800,000
Equity Method Investment, Additional Distribution Rights																																							10.00%
Austin Joint Venture [Member] | DRA Advisors LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																							50.00%
Non-Recourse Debt																								230,600,000
Equity Method Investment, Distribution, Net of Initial Funding Agreement																								266,300,000
Amount Of Participant Contribution																								49,700,000
Equity method investments, Closing costs																								1,900,000
Closing Prorations and Lender Holdbacks																								6,900,000
Proceeds from Equity Method Investment, Dividends or Distributions																								$ 271,500,000
Austin Joint Venture [Member] | Office Properties [Member] | Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																																192,396
Austin, Texas [Member]
Schedule Of Equity Method Investments [Line Items]
Number of floors of a building | Storey																							3
Austin, Texas [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, agreement to pay future capital expenditures																																														$ 4,400,000
River Place [Member]
Schedule Of Equity Method Investments [Line Items]
Proceeds from repayment of mortgage notes receivable																			$ 88,000,000
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[11]																										$ 37,179,000	$ 36,356,000				37,179,000		$ 36,356,000
Equity method investment percentage																												50.00%						50.00%					50.00%	[7],[11]
Capital funded to venture for mortgage debt																																6,700,000
Area owned by real estate venture of undeveloped parcels of land | a																									1.3
Real estate ventures aggregate indebtedness to third parties	[11]																										6,664,000	$ 1,004,000				6,664,000		$ 1,004,000
Additional borrowing fund to tenant improvements and leasing commissions																											150,000,000					150,000,000
Guarantees, maximum exposure amount																											41,300,000					41,300,000
4040 Wilson Venture [Member] | Mixed Use Property [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | property																									8
Area of Real Estate Property | ft²																									427,500
4040 Wilson Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Cash paid to acquire real estate ventures																									$ 36,000,000
Capital contribution to venture																											36,900,000					36,900,000
4040 Wilson Venture [Member] | Ashton Park
Schedule Of Equity Method Investments [Line Items]
Capital contribution to venture																											36,900,000					36,900,000
PJP VII [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											1,156,000	980,000				1,156,000		980,000
Equity method investment percentage	[7]																																						25.00%
Real estate ventures aggregate indebtedness to third parties																											4,792,000	$ 4,956,000				4,792,000		$ 4,956,000
Guarantees, maximum exposure amount																											$ 400,000					$ 400,000
Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Investments in Real Estate Ventures | Real_Estate_Investment		10
Subsequent Event [Member] | Evo at Cira Disposition [Member]
Schedule Of Equity Method Investments [Line Items]
Gross sales price		$ 197,500,000
Proceeds from real estate venture sales		$ 43,000,000
Sale of ownership interest percentage		50.00%
Cash proceeds after the payment of share of the debt and closing costs		$ 43,000,000
[1]	Gain/(Loss) on Sale is net of closing and other transaction related costs.
[2]	Gain on Sale is net of closing and other transaction related costs.
[3]	Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.
[4]	See “Brandywine - AI Venture: Other Than Temporary Impairment” section below.
[5]	On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions.
[6]	See “Brandywine - AI Venture: 7101 Wisconsin Avenue” and “Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture.
[7]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.
[8]	In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.
[9]	The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.
[10]	The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%.
[11]	During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million.

Investment in Unconsolidated 75

Investment in Unconsolidated Real Estate Ventures - Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss) (Details) - USD ($) $ in Thousands

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Sep. 22, 2016

Jun. 30, 2016

Jan. 29, 2016

May 29, 2015

Dec. 20, 2011

Jan. 20, 2011

Schedule Of Equity Method Investments [Line Items]

Investment in Real Estate Ventures, equity method

$ 194,621

$ 281,331

$ 241,004

Company’s share of income (loss) (Company’s basis)

(8,306)

(11,503)

$ (811)

Equity Method Investments including net liabilities

281,331

Equity Method Investment Summarized Financial Information Debt

$ 768,912

$ 997,466

Brandywine - AI Venture LLC [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

50.00%

[1],[2],[3]

50.00%

50.00%

50.00%

Investment in Real Estate Ventures, equity method

[1],[3]

$ 43,560

$ 67,809

Company’s share of income (loss) (Company’s basis)

(4,465)

[1],[3]

(5,895)

[1],[3]

$ (229)

Equity Method Investment Summarized Financial Information Debt

[1],[3]

$ 93,117

131,539

Debt Instrument, Interest Rate, Effective Percentage

[1],[3]

3.94%

DRA (G&I) Austin [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[1],[2],[4]

50.00%

Investment in Real Estate Ventures, equity method

[1],[4]

$ 13,972

52,886

Company’s share of income (loss) (Company’s basis)

[1],[4]

(989)

(1,880)

Equity Method Investment Summarized Financial Information Debt

[1],[4]

$ 249,481

405,734

Debt Instrument, Interest Rate, Effective Percentage

[1],[4]

3.51%

MAP Venture [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2],[5]

50.00%

Investment in Real Estate Ventures, equity method

[5]

$ 15,450

20,893

Company’s share of income (loss) (Company’s basis)

[5]

(3,443)

(4,218)

Equity Method Investment Summarized Financial Information Debt

[5]

$ 180,800

180,800

Debt Instrument, Interest Rate Terms

[5]

L+6.25%

Debt Instrument, Maturity Date, Month and Year

[5]

2018-02

Four Tower Bridge [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2],[6]

65.00%

Investment in Real Estate Ventures, equity method

[6]

$ 3,032

2,286

Company’s share of income (loss) (Company’s basis)

[6]

746

602

Equity Method Investment Summarized Financial Information Debt

[6]

$ 9,749

9,961

Debt Instrument, Interest Rate, Effective Percentage

[6]

5.20%

Debt Instrument, Maturity Date, Month and Year

[6]

2021-02

PJP VII [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2]

25.00%

Investment in Real Estate Ventures, equity method

$ 1,156

980

Company’s share of income (loss) (Company’s basis)

175

233

Equity Method Investment Summarized Financial Information Debt

$ 4,792

4,956

Debt Instrument, Interest Rate Terms

L+2.65%

Debt Instrument, Maturity Date, Month and Year

2019-12

PJP Two [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2]

30.00%

Investment in Real Estate Ventures, equity method

$ 604

532

Company’s share of income (loss) (Company’s basis)

72

97

Equity Method Investment Summarized Financial Information Debt

$ 2,564

2,893

Debt Instrument, Interest Rate, Effective Percentage

6.12%

Debt Instrument, Maturity Date, Month and Year

2023-11

PJP VI [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2]

25.00%

Investment in Real Estate Ventures, equity method

$ 179

142

Company’s share of income (loss) (Company’s basis)

38

97

Equity Method Investment Summarized Financial Information Debt

$ 7,370

7,652

Debt Instrument, Interest Rate, Effective Percentage

6.08%

Debt Instrument, Maturity Date, Month and Year

2023-04

1000 Chesterbrook Blvd. [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

50.00%

Company’s share of income (loss) (Company’s basis)

[1]

160

PJP V [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

25.00%

Company’s share of income (loss) (Company’s basis)

[1]

127

Invesco, L.P. [Member]

Schedule Of Equity Method Investments [Line Items]

Company’s share of income (loss) (Company’s basis)

[1]

261

Coppell Associates [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

50.00%

Company’s share of income (loss) (Company’s basis)

12

HSRE BDN I, LLC [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2],[4]

50.00%

Investment in Real Estate Ventures, equity method

[4]

$ 17,671

21,228

Company’s share of income (loss) (Company’s basis)

[4]

449

843

Equity Method Investment Summarized Financial Information Debt

[4]

$ 110,886

105,000

Debt Instrument, Interest Rate Terms

[4]

L+2.25%

Debt Instrument, Maturity Date, Month and Year

[4]

2019-10

Brandywine Nineteen Nineteen Ventures [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

50.00%

[2],[4],[7]

50.00%

Investment in Real Estate Ventures, equity method

[4],[7]

$ 22,268

27,462

Company’s share of income (loss) (Company’s basis)

[4],[7]

(194)

(1,529)

Equity Method Investment Summarized Financial Information Debt

[4],[7]

$ 88,860

79,250

Debt Instrument, Interest Rate Terms

[4],[7]

L+1.75%

Debt Instrument, Maturity Date, Month and Year

[4],[7]

2018-10

TB-BDN Plymouth Apartments [Member]

Schedule Of Equity Method Investments [Line Items]

Investment in Real Estate Ventures, equity method

[1]

12,450

Company’s share of income (loss) (Company’s basis)

[1]

$ 99

119

Equity Method Investment Summarized Financial Information Debt

[1]

$ 53,967

4040 Wilson Venture [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

50.00%

[2],[8]

50.00%

Investment in Real Estate Ventures, equity method

[8]

$ 37,179

$ 36,356

Company’s share of income (loss) (Company’s basis)

[8]

(255)

(270)

Equity Method Investment Summarized Financial Information Debt

[8]

$ 6,664

1,004

Debt Instrument, Interest Rate Terms

[8]

L+2.75%

Debt Instrument, Maturity Date, Month and Year

[8]

2021-12

51 N 50 Patterson [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

70.00%

[2]

70.00%

Investment in Real Estate Ventures, equity method

$ 21,212

20,318

Company’s share of income (loss) (Company’s basis)

(176)

(114)

Equity Method Investment Summarized Financial Information Debt

$ 0

0

Seven Tower Bridge [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

[2],[6]

20.00%

Investment in Real Estate Ventures, equity method

[6]

$ 471

685

Company’s share of income (loss) (Company’s basis)

[6]

(214)

(133)

Equity Method Investment Summarized Financial Information Debt

[6]

$ 14,629

14,710

Debt Instrument, Interest Rate, Effective Percentage

[6]

3.17%

1250 First Street Office [Member]

Schedule Of Equity Method Investments [Line Items]

Equity Method Investment, Ownership Percentage

70.00%

[2]

70.00%

Investment in Real Estate Ventures, equity method

$ 17,867

17,304

Company’s share of income (loss) (Company’s basis)

(149)

(15)

Equity Method Investment Summarized Financial Information Debt

$ 0

$ 0

[1]

On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions.

[2]

Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.

[3]

See “Brandywine - AI Venture: 7101 Wisconsin Avenue” and “Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture.

[4]

The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.

[5]

In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.

[6]

Subsequent to December 31, 2017, the Company exchanged its 20% interest in Seven Tower Bridge to acquire the remaining 35% interest in Four Tower Bridge. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.

[7]

The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%.

[8]

During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million.

Investment in Unconsolidated 76

Investment in Unconsolidated Real Estate Ventures - Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss) (Parenthetical) (Details) $ in Thousands		Oct. 18, 2017USD ($)ft²property	Oct. 17, 2017USD ($)property	Jan. 31, 2017USD ($)property	Mar. 02, 2016USD ($)optionterm	Dec. 31, 2017USD ($)ft²propertyoption		Dec. 31, 2017USD ($)ft²propertyoption		Jan. 05, 2018	Sep. 30, 2017USD ($)ft²	Sep. 14, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Sep. 22, 2016	Jun. 30, 2016	Dec. 31, 2015	Oct. 17, 2014ft²	Jul. 31, 2014ft²	Dec. 20, 2011	Jan. 20, 2011
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment Summarized Financial Information Debt						$ 768,912		$ 768,912					$ 997,466
Notional amount						301,548		301,548					328,610
Mortgage notes payable, net						$ 317,216		$ 317,216					$ 321,549
DRA Austin Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage						50.00%		50.00%					50.00%			50.00%
Number of Properties Sold | property		8
Equity Method Investment Summarized Financial Information Debt		$ 151,000
Rentable Square Feet | ft²		1,164,496
Sales Price		$ 333,300
TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties Sold | property				398
Sale of ownership interest percentage				50.00%
Sales Price				$ 100,500
Percentage of ownership interests				50.00%
BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage						50.00%	[1],[2],[3]	50.00%	[1],[2],[3]				50.00%			50.00%			50.00%
Debt Instrument, Interest Rate, Effective Percentage	[1],[3]					3.94%		3.94%
Equity Method Investment Summarized Financial Information Debt	[1],[3]					$ 93,117		$ 93,117					$ 131,539
Rentable Square Feet | ft²												874,479
BDN - Al Venture [Member] | 7101 Wisconsin Property Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage												50.00%
Rentable Square Feet | ft²											239,904	230,904
Sales Price											$ 105,700	$ 105,700
HSRE BDN I, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[2],[4]					50.00%		50.00%
Equity Method Investment Summarized Financial Information Debt	[4]					$ 110,886		$ 110,886					105,000
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage		50.00%
Number of Properties Sold | property		8	7			8
Equity Method Investment Summarized Financial Information Debt		$ 150,968	$ 151,000
Rentable Square Feet | ft²		1,164,496				1,570,123		1,570,123									590,881	232,274
Sales Price		$ 333,250
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[2],[5]					50.00%		50.00%
Equity Method Investment Summarized Financial Information Debt	[5]					$ 180,800		$ 180,800					180,800
Seven Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[2],[6]					20.00%		20.00%
Debt Instrument, Interest Rate, Effective Percentage	[6]					3.17%		3.17%
Equity Method Investment Summarized Financial Information Debt	[6]					$ 14,629		$ 14,629					14,710
Seven Tower Bridge [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Sale of ownership interest percentage										20.00%
Four Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[2],[6]					65.00%		65.00%
Debt Instrument, Interest Rate, Effective Percentage	[6]					5.20%		5.20%
Equity Method Investment Summarized Financial Information Debt	[6]					$ 9,749		$ 9,749					9,961
Four Tower Bridge [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage										35.00%
PJP V [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage														25.00%
1000 Chesterbrook Blvd. [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage															50.00%
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage						50.00%	[2],[4],[7]	50.00%	[2],[4],[7]											50.00%
Equity Method Investment Summarized Financial Information Debt	[4],[7]					$ 88,860		$ 88,860					$ 79,250
Interest rate protection cap								4.50%
Debt Instrument, Interest Rate Terms								LIBOR + 1.75
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage						50.00%	[2],[8]	50.00%	[2],[8]				50.00%
Equity Method Investment Summarized Financial Information Debt	[8]					$ 6,664		$ 6,664					$ 1,004
Mortgage notes payable, net						$ 150,000		$ 150,000
Secured JV Debt [Member] | BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Number of Fixed Rate Mortgages						2		2
Secured JV Debt [Member] | BDN - Al Venture [Member] | Fixed rate loan maturing January 1, 2022 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount						$ 26,600		$ 26,600
Debt Instrument, Interest Rate, Stated Percentage						4.65%		4.65%
Debt Instrument Maturity Date								Jan. 1, 2022
Secured JV Debt [Member] | BDN - Al Venture [Member] | Fixed rate loan maturing August 1, 2019 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount						$ 66,500		$ 66,500
Debt Instrument, Interest Rate, Stated Percentage						3.22%		3.22%
Debt Instrument Maturity Date								Aug. 1, 2019
Secured JV Debt [Member] | HSRE BDN I, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage					50.00%
Secured JV Debt [Member] | Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties Sold | property		8						8
Debt Instrument, Number of Mortgages						3		3
Number of Real Estate Properties Encumbered by Mortgage Debt | property		7
Equity Method Investment Summarized Financial Information Debt		$ 151,000
Secured JV Debt [Member] | Austin Joint Venture [Member] | First mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount						$ 133,600		$ 133,600
Debt Instrument Maturity Date								Nov. 1, 2018
Derivative, Fixed Interest Rate						1.43%		1.43%
Debt Instrument, Interest Rate, Effective Percentage						3.44%		3.44%
Derivative, Basis Spread on Variable Rate						2.01%		2.01%
Secured JV Debt [Member] | Austin Joint Venture [Member] | Second mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount						$ 28,700		$ 28,700
Debt Instrument, Interest Rate, Stated Percentage						4.50%		4.50%
Debt Instrument Maturity Date								Apr. 6, 2019
Secured JV Debt [Member] | Austin Joint Venture [Member] | Third mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount						$ 87,100		$ 87,100
Debt Instrument Maturity Date								Feb. 10, 2020
Derivative, Fixed Interest Rate						1.36%		1.36%
Debt Instrument, Interest Rate, Effective Percentage						3.36%		3.36%
Derivative, Basis Spread on Variable Rate						2.00%		2.00%
Secured JV Debt [Member] | MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument Maturity Date								Feb. 9, 2018
Interest rate protection cap					1.75%
Notional amount					$ 200,800
Debt instrument, number of options to extend maturity date | option					3
Debt instrument, number of successive terms | term					3
Debt instrument, first option extended maturity date								Feb. 9, 2019
Debt instrument, remaining unexercised options extended maturity date								Feb. 9, 2021
Debt instrument, number of options exercised to extend maturity date | option						2		2
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Mortgage Maturing March 2017 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						7.00%		7.00%
Debt Instrument Maturity Date								Mar. 1, 2017
Debt Instrument, Number of Fixed Rate Mortgages						2		2
Equity Method Investment Summarized Financial Information Debt						$ 8,000		$ 8,000
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing September 2025 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.00%		3.00%
Debt Instrument Maturity Date								Sep. 1, 2025
Equity Method Investment Summarized Financial Information Debt						$ 700		$ 700
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing February 2017 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						4.00%		4.00%
Debt Instrument Maturity Date								Feb. 7, 2018
Equity Method Investment Summarized Financial Information Debt						$ 2,000		$ 2,000
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing March 2020 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						3.25%		3.25%
Debt Instrument Maturity Date								Mar. 11, 2020
Equity Method Investment Summarized Financial Information Debt						$ 3,900		$ 3,900
[1]	On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions.
[2]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.
[3]	See “Brandywine - AI Venture: 7101 Wisconsin Avenue” and “Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture.
[4]	The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.
[5]	In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.
[6]	Subsequent to December 31, 2017, the Company exchanged its 20% interest in Seven Tower Bridge to acquire the remaining 35% interest in Four Tower Bridge. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.
[7]	The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%.
[8]	During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million.

Investment in Unconsolidated 77

Investment in Unconsolidated Real Estate Ventures - Summary of Financial Position of Real Estate Ventures (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
Net property		$ 1,083,965	$ 1,457,003
Other assets		161,932	229,917
Other liabilities		97,707	129,687
Debt, net		766,420	989,738
Equity	[1]	381,770	567,495
DRA Austin Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		263,557	493,960
Other assets		42,272	82,725
Other liabilities		24,131	40,280
Debt, net		248,700	403,671
Equity	[1]	32,998	132,734
Other [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		661,448	733,883
Other assets		95,479	113,987
Other liabilities		69,083	82,967
Debt, net		424,803	454,906
Equity	[1]	263,041	309,997
BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net property		158,960	229,160
Other assets		24,181	33,205
Other liabilities		4,493	6,440
Debt, net		92,917	131,161
Equity	[1]	$ 85,731	$ 124,764
[1]	This amount includes the effect of the basis difference between the Company’s historical cost basis and the basis recorded at the Real Estate Venture level, which is typically amortized over the life of the related assets and liabilities. Basis differentials occur from the impairment of investments, purchases of third party interests in existing Real Estate Ventures and upon the transfer of assets that were previously owned by the Company into a Real Estate Venture. In addition, certain acquisition, transaction and other costs may not be reflected in the net assets at the Real Estate Venture level.

Investment in Unconsolidated 78

Investment in Unconsolidated Real Estate Ventures - Summary of Results of Operations of Real Estate Ventures with Interests (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015	Dec. 20, 2011
Schedule Of Equity Method Investments [Line Items]
Equity in income (loss) of Real Estate Ventures			$ (8,306)		$ (11,503)		$ (811)
DRA Austin Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Revenue			85,500		85,749		78,367
Operating expenses			(35,997)		(37,643)		(33,194)
Provision for impairment	[1]				0
Interest expense, net			(13,985)		(15,052)		(14,025)
Depreciation and amortization			(34,026)		(38,365)		(36,809)
Loss on extinguishment of debt			(2,613)
Net income (loss)			$ (1,121)		$ (5,311)	[2]	$ (5,661)
Ownership interest %			50.00%		50.00%		50.00%
Company's share of net income (loss)			$ (560)		$ (2,656)		$ (2,831)
Other-than-temporary impairment	[3]		0
Basis adjustments and other			(429)		776		1,596
Equity in income (loss) of Real Estate Ventures			(989)		(1,880)		(1,235)
Brandywine - AI Venture LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Revenue			29,500		31,047		29,428
Operating expenses			(12,298)		(13,654)		(11,872)
Provision for impairment	[1]				(10,476)
Interest expense, net			(4,707)		(5,825)		(5,310)
Depreciation and amortization			(11,428)		(12,811)		(12,678)
Loss on extinguishment of debt			(811)
Net income (loss)			$ 256		$ (11,719)	[2]	$ (432)
Ownership interest %			50.00%	[4],[5],[6]	50.00%		50.00%	50.00%
Company's share of net income (loss)			$ 128		$ (5,860)		$ (216)
Other-than-temporary impairment		$ (4,800)	(4,844)	[3]
Basis adjustments and other			251		(35)		(13)
Equity in income (loss) of Real Estate Ventures			(4,465)	[4],[6]	(5,895)	[4],[6]	(229)
Other [Member]
Schedule Of Equity Method Investments [Line Items]
Revenue			101,271		97,656		57,133
Operating expenses			(51,045)		(51,895)		(25,070)
Provision for impairment	[1]				0
Interest expense, net			(21,521)		(19,437)		(15,249)
Depreciation and amortization			(32,986)		(34,562)		(18,613)
Loss on extinguishment of debt			0
Net income (loss)			$ (4,281)		$ (8,238)	[2]	$ (1,799)
Ownership interest %	[7]		0.00%		0.00%		0.00%
Company's share of net income (loss)			$ (1,432)		$ (3,985)		$ 455
Other-than-temporary impairment	[3]		0
Basis adjustments and other			(1,420)		257		198
Equity in income (loss) of Real Estate Ventures			(2,852)		(3,728)		653
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Revenue			216,271		214,452		164,928
Operating expenses			(99,340)		(103,192)		(70,136)
Provision for impairment	[1]				(10,476)
Interest expense, net			(40,213)		(40,314)		(34,584)
Depreciation and amortization			(78,440)		(85,738)		(68,100)
Loss on extinguishment of debt			(3,424)
Net income (loss)			$ (5,146)		$ (25,268)	[2]	$ (7,892)
Ownership interest %			0.00%		0.00%		0.00%
Company's share of net income (loss)			$ (1,864)		$ (12,501)		$ (2,592)
Other-than-temporary impairment	[3]		(4,844)
Basis adjustments and other			(1,598)		998		1,781
Equity in income (loss) of Real Estate Ventures			$ (8,306)		$ (11,503)		$ (811)
[1]	See “Brandywine - AI Venture: Station Square Impairment” section below.
[2]	During the year ended December 31, 2016, there were $7.1 million of acquisition deal costs related to the formation of the MAP Venture.
[3]	See “Brandywine - AI Venture: Other Than Temporary Impairment” section below.
[4]	On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions.
[5]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.
[6]	See “Brandywine - AI Venture: 7101 Wisconsin Avenue” and “Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture.
[7]	The Company’s unconsolidated ownership interests range from 20% to 70%, subject to specified priority allocations of distributable cash in certain of the Real Estate Ventures.

Investment in Unconsolidated 79

Investment in Unconsolidated Real Estate Ventures - Summary of Results of Operations of Real Estate Ventures with Interests (Parenthetical) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2015
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage		0.00%	0.00%	0.00%
Unconsolidated Real Estate Ventures [Member] | Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage		20.00%	20.00%	20.00%
Unconsolidated Real Estate Ventures [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage		70.00%	70.00%	70.00%
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage	[1],[2]		50.00%
Acquisition deal costs		$ 7.1
[1]	In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.
[2]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.

Investment in Unconsolidated 80

Investment in Unconsolidated Real Estate Ventures - Aggregate Principal Payments of Recourse and Non-recourse Debt Payable to Third-parties (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Equity Method Investments [Line Items]
2,018	$ 6,601
2,019	7,360
2,020	86,978
2,021	6,099
2,022	256,332
Thereafter	1,585,347
Total principal payments	768,912	$ 997,466
Net deferred financing costs	(11,141)
Outstanding indebtedness	766,420	$ 989,738
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
2,018	236,468
2,019	390,707
2,020	92,679
2,021	17,162
2,022	25,372
Thereafter	6,524
Total principal payments	768,912
Net deferred financing costs	(2,532)
Outstanding indebtedness	$ 766,380

Investment in Unconsolidated 81

Investment in Unconsolidated Real Estate Ventures - Summary of Transaction (Details) - USD ($) $ in Thousands	Oct. 18, 2017	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 17, 2017
Schedule Of Equity Method Investments [Line Items]
Debt principal		$ (768,912)	$ (768,912)	$ (997,466)
Debt prepayment penalties			(3,933)	(66,590)	$ 0
Proceeds from real estate venture sales			145,416	21,022	6,100
Company's share of gain			$ 80,526	$ 20,000	$ 7,229
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Gross sales price	$ 333,250
Debt principal	(150,968)					$ (151,000)
Debt prepayment penalties	(2,120)
Closing costs and net prorations	(7,420)
Proceeds from real estate venture sales	$ 172,742
Ownership percentage	50.00%
Cash to the Company	$ 86,371
Austin Venture basis of sold properties	(92,559)
Austin Venture gain on sale	80,183
Company's share of gain	40,092	$ 52,200
Deferred gain on sale	12,072
Gain on real estate venture transactions	$ 52,164

Deferred Costs - Deferred Costs

Deferred Costs - Deferred Costs (Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components of Deferred Costs Net [Abstract]
Leasing costs, Total Cost	$ 154,481	$ 146,135
Total Cost	158,076	149,730
Leasing costs, Accumulated Amortization	(59,046)	(56,942)
Total, Accumulated Amortization	(61,381)	(58,388)
Leasing costs, Deferred Costs, net	95,435	89,193
Financing costs, Deferred Costs, net	11,141
Deferred Costs	96,695	91,342
Revolving Credit Facility [Member]
Components of Deferred Costs Net [Abstract]
Financing costs, Total Cost	3,595	3,595
Financing costs, Accumulated Amortization	(2,335)	(1,446)
Financing costs, Deferred Costs, net	$ 1,260	$ 2,149

Deferred Costs (Textual) (Detai

Deferred Costs (Textual) (Details) $ in Thousands	1 Months Ended	8 Months Ended	12 Months Ended			20 Months Ended
	May 31, 2015ft²	Dec. 31, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)
Deferred Costs (Textual) [Abstract]
Capitalized internal direct leasing costs			$ 4,600	$ 5,000	$ 6,600
2015 Lease [Member]
Deferred Costs (Textual) [Abstract]
Square feet of office space leased | ft²	228,000
Brokerage commission						$ 4,200
2015 Lease [Member] | Chairman and Lead Independent Director [Member]
Deferred Costs (Textual) [Abstract]
Membership interest	33.30%
Brokerage commission		$ 500		$ 500		$ 1,000
2015 Lease [Member] | WDL Real Estate Advisory Group, LLC [Member]
Deferred Costs (Textual) [Abstract]
Membership interest	49.00%

Intangible Assets - Intangible

Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Intangible Assets, Total Cost	$ 123,806	$ 160,681
Intangible Assets, Accumulated Amortization	(58,834)	(88,203)
Intangible Assets, net	64,972	72,478
Acquired Lease Intangibles, Net	20,274	18,119
Below market leases [Member]
Intangible Assets [Line Items]
Acquired Lease Intangibles, Gross	36,213	37,579
Acquired Lease Intangibles, Accumulated Amortization	(15,939)	(19,460)
Acquired Lease Intangibles, Net	20,274	18,119
In-place lease value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	108,060	142,889
Intangible Assets, Accumulated Amortization	(47,003)	(75,696)
Intangible Assets, net	61,057	67,193
Tenant relationship value [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	11,201	13,074
Intangible Assets, Accumulated Amortization	(9,275)	(10,167)
Intangible Assets, net	1,926	2,907
Above market leases acquired [Member]
Intangible Assets [Line Items]
Intangible Assets, Total Cost	4,545	4,718
Intangible Assets, Accumulated Amortization	(2,556)	(2,340)
Intangible Assets, net	$ 1,989	$ 2,378

Intangible Assets (Textual) (De

Intangible Assets (Textual) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tenant Move-Outs Prior to End of the Lease Term [Member]
Finite Lived Intangible Assets [Line Items]
Intangible Assets Written Off Through Accelerated Amortization	$ 0.6	$ 0.6	$ 0.5

Intangible Assets and Liabiliti

Intangible Assets and Liabilities - Annual Amortization of Intangible Assets, Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
2,018	$ 14,948
2,019	12,438
2,020	9,770
2,021	7,160
2,022	5,093
Thereafter	15,563
Intangible Assets, net	64,972	$ 72,478
Liabilities
2,018	3,553
2,019	2,807
2,020	2,042
2,021	1,406
2,022	1,238
Thereafter	9,228
Acquired Lease Intangibles, Net	$ 20,274	$ 18,119

Debt Obligations - Consolidated

Debt Obligations - Consolidated Debt Obligations Outstanding (Details) - USD ($) $ in Thousands		Oct. 08, 2015	Sep. 30, 2017	Oct. 07, 2015	Dec. 31, 2017		Nov. 09, 2017	Dec. 31, 2016
Consolidated debt obligations
Plus: premiums/(discounts), net					$ (6,748)
Less: deferred financing costs					(11,141)
Total Debt Obligations					1,930,828			$ 2,013,112
Secured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					320,107			325,038
Plus: premiums/(discounts), net					(2,325)			(2,761)
Less: deferred financing costs					(566)			(728)
Total mortgage indebtedness					317,216			321,549
Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					1,628,610			1,703,610
Plus: premiums/(discounts), net					(4,423)			(4,678)
Less: deferred financing costs					(10,575)			(7,369)
Total unsecured indebtedness					1,613,612			1,691,563
Two Logan Square [Member] | Secured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 84,440			86,012
Effective interest rate					3.98%
Debt instrument maturity date					May 1, 2020
One Commerce Square [Member] | Secured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 123,667			127,026
Effective interest rate	[1]				3.64%
Debt instrument maturity date					Apr. 5, 2023
Two Commerce Square [Member] | Secured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 112,000			112,000
Effective interest rate	[2]				4.51%
Debt instrument maturity date					Apr. 5, 2023
$300.0M 5.70% Guaranteed Notes due 2017 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross	[3]				$ 0			300,000
Effective interest rate	[3]				5.68%
Debt instrument maturity date	[3]				May 1, 2017
$325.0M 4.95% Guaranteed Notes due 2018 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross	[4]				$ 0			325,000
Effective interest rate	[4]				5.13%
Debt instrument maturity date	[4]				Apr. 15, 2018
$250M 3.95% Guaranteed Notes due 2023 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross	[4]				$ 350,000			250,000
Effective interest rate	[4]				3.87%
Debt instrument maturity date	[4]				Feb. 15, 2023
Seven Year Term Loan - Swapped to fixed [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross		$ 250,000		$ 200,000	$ 250,000			250,000
Effective interest rate		3.72%			3.72%
Debt instrument maturity date		Oct. 8, 2022		Feb. 1, 2019	Oct. 1, 2022
250.0M 4.10% Guaranteed Notes due 2024 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 250,000			250,000
Effective interest rate					4.33%
Debt instrument maturity date					Oct. 1, 2024
$450.0M 3.95% Guaranteed Notes due 2027 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 450,000	[4]	$ 450,000	0	[4]
Effective interest rate	[4]				4.03%
Debt instrument maturity date	[4]				Nov. 30, 2027
$250M 4.55% Guaranteed Notes due 2029 [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 250,000			250,000
Effective interest rate					4.60%
Debt instrument maturity date					Oct. 1, 2029
Indenture IA (Preferred Trust I) [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross	[5]				$ 27,062			27,062
Debt instrument, description of variable rate basis			LIBOR + 1.25%		LIBOR + 1.25%	[5]
Spread on variable rate			1.25%		1.25%	[5]
Debt instrument maturity date	[5]				Mar. 30, 2035
Indenture IB (Preferred Trust I) - Swapped to fixed [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 25,774			25,774
Effective interest rate					3.30%
Debt instrument maturity date					Apr. 30, 2035
Indenture II (Preferred Trust II) - Swapped to fixed [Member] | Unsecured Debt [Member]
Consolidated debt obligations
Long-term Debt, Gross					$ 25,774			$ 25,774
Effective interest rate					3.09%
Debt instrument maturity date					Jul. 30, 2035
[1]	This loan was assumed upon acquisition of the related properties on December 19, 2013. On December 29, 2015, the Company refinanced the debt increasing the principal balance to $130.0 million and extended the scheduled maturity date from January 6, 2016 to April 5, 2023.  A default under this loan will also constitute a default under the loan secured by Two Commerce Square. This loan is also secured by a lien on Two Commerce Square.
[2]	This loan was assumed upon acquisition of the related property on December 19, 2013. The interest rate reflects the market rate at the time of acquisition. A default under this loan will also constitute a default under the loan secured by One Commerce Square. This loan is also secured by a lien on One Commerce Square.
[3]	On May 1, 2017, the entire principal balance of the unsecured 5.70% Guaranteed Notes was repaid upon maturity. Available cash balances and the Credit Facility (as defined below) were used to fund the repayment of the unsecured notes.
[4]	On November 17, 2017, the Company completed an offering of $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. On November 17, 2017, the Company redeemed the remaining outstanding balance of the 4.95% Guaranteed Notes due 2018 (the “2018 Notes”) ahead of its scheduled maturity. See below for further discussion.
[5]	On September 30, 2017, the interest rate hedge contract for the Preferred Trust I expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%.

Debt Obligations - Consolidat88

Debt Obligations - Consolidated Debt Obligations Outstanding (Parenthetical) (Details) - USD ($) $ in Thousands		Dec. 29, 2015	Sep. 30, 2017	Dec. 31, 2017		Nov. 17, 2017	Nov. 09, 2017	May 01, 2017	Dec. 31, 2016
Secured Debt [Member]
Debt Instrument [Line Items]
Underwriting offering amount				$ 320,107					$ 325,038
Unsecured Debt [Member]
Debt Instrument [Line Items]
Underwriting offering amount				$ 1,628,610					1,703,610
One Commerce Square [Member] | Secured Debt [Member]
Debt Instrument [Line Items]
Debt instrument increase in principal		$ 130,000
Debt Instrument Maturity Date				Apr. 5, 2023
Underwriting offering amount				$ 123,667					127,026
$300.0M 5.70% Guaranteed Notes due 2017 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity Date	[1]			May 1, 2017
Debt Instrument Interest Rate Stated Percentage								5.70%
Underwriting offering amount	[1]			$ 0					300,000
$450.0M 3.95% Guaranteed Notes due 2027 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity Date	[2]			Nov. 30, 2027
Debt Instrument Interest Rate Stated Percentage							3.95%
Underwriting offering amount				$ 450,000	[2]		$ 450,000		0	[2]
$250M 3.95% Guaranteed Notes due 2023 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity Date	[2]			Feb. 15, 2023
Debt Instrument Interest Rate Stated Percentage							3.95%
Underwriting offering amount	[2]			$ 350,000					250,000
Debt Instrument, Face Amount							$ 100,000
$325.0M 4.95% Guaranteed Notes due 2018 [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity Date	[2]			Apr. 15, 2018
Debt Instrument Interest Rate Stated Percentage						4.95%
Underwriting offering amount	[2]			$ 0					325,000
Indenture IA (Preferred Trust I) [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt Instrument Maturity Date	[3]			Mar. 30, 2035
Underwriting offering amount	[3]			$ 27,062					$ 27,062
Debt Instrument, Interest Rate Terms			LIBOR + 1.25%	LIBOR + 1.25%	[3]
Spread on variable rate			1.25%	1.25%	[3]
[1]	On May 1, 2017, the entire principal balance of the unsecured 5.70% Guaranteed Notes was repaid upon maturity. Available cash balances and the Credit Facility (as defined below) were used to fund the repayment of the unsecured notes.
[2]	On November 17, 2017, the Company completed an offering of $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. On November 17, 2017, the Company redeemed the remaining outstanding balance of the 4.95% Guaranteed Notes due 2018 (the “2018 Notes”) ahead of its scheduled maturity. See below for further discussion.
[3]	On September 30, 2017, the interest rate hedge contract for the Preferred Trust I expired. Subsequent to this expiration, the debt bears interest at a variable rate of LIBOR + 1.25%.

Debt Obligations (Textual) (Det

Debt Obligations (Textual) (Details) - USD ($)

Dec. 18, 2017

Nov. 16, 2017

Nov. 09, 2017

Oct. 08, 2015

May 12, 2015

Oct. 07, 2015

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Nov. 17, 2017

May 15, 2015

Debt Instrument [Line Items]

Loss on early extinguishment of debt

$ (3,933,000)

$ (66,590,000)

$ 0

Extinguishment of Debt, Amount

$ 325,000,000

0

$ 0

New Credit Facility [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Long-term Debt, Weighted Average Interest Rate

2.28%

Debt term

4 years

Maximum borrowing capacity

$ 600,000,000

Increase in limit

400,000,000

Minimum Credit Spread on a LIBOR Rate Loan

0.00%

Maximum Credit Spread on a LIBOR Rate Loan

0.55%

Commitment fee percentage

0.25%

Line of credit

$ 0

$ 0

Interest expense borrowings

$ 2,600,000

Minimum fixed charge coverage ratio

1.5

Maximum leverage ratio

0.60

Maximum unsecured indebtedness to unencumbered asset value ratio

0.60

Maximum secured indebtedness to total asset value ratio

0.40

Minimum unencumbered cash flow to interest expense on unsecured debt ratio

1.75

Maximum percent of payments of dividends and distributions

95.00%

New Credit Facility [Member] | Revolving Credit Facility [Member] | Minimum [Member]

Debt Instrument [Line Items]

Commitment fee percentage

0.125%

New Credit Facility [Member] | Revolving Credit Facility [Member] | Maximum [Member]

Debt Instrument [Line Items]

Commitment fee percentage

0.30%

New Credit Facility [Member] | Letter of Credit [Member]

Debt Instrument [Line Items]

Maximum borrowing capacity

65,000,000

New Credit Facility [Member] | Swing-Loans [Member]

Debt Instrument [Line Items]

Maximum borrowing capacity

$ 60,000,000

New Credit Facility [Member] | LIBOR [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Variable interest rate

1.20%

Basis spread on variable rate

1.00%

New Credit Facility [Member] | LIBOR [Member] | Revolving Credit Facility [Member] | Minimum [Member]

Debt Instrument [Line Items]

Variable interest rate

0.875%

New Credit Facility [Member] | LIBOR [Member] | Revolving Credit Facility [Member] | Maximum [Member]

Debt Instrument [Line Items]

Variable interest rate

1.55%

New Credit Facility [Member] | Federal Funds Rate [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Basis spread on variable rate

0.50%

Secured Debt [Member]

Debt Instrument [Line Items]

Long-term Debt, Weighted Average Interest Rate

4.04%

4.03%

5.72%

Long-term Debt, Gross

$ 320,107,000

$ 325,038,000

Unsecured Debt [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

1,628,610,000

1,703,610,000

Repayment of prepayment penalities

$ 1,200,000

Repayment of accrued interest

500,000

Unsecured Debt [Member] | $450.0M 3.95% Guaranteed Notes due 2027 [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

$ 450,000,000

$ 450,000,000

[1]

0

[1]

Debt Instrument, Interest Rate, Stated Percentage

3.95%

Debt instrument, Unamortized discount, Percent of face amount

99.25%

Debt instrument, Yield to maturity

4.04%

Debt instrument, Yield to maturity spread at time of pricing

1.70%

Treasury note rate term

10 years

Debt Instrument Maturity Date

[1]

Nov. 30, 2027

Effective interest rate

[1]

4.03%

Unsecured Debt [Member] | $250M 3.95% Guaranteed Notes due 2023 [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

[1]

$ 350,000,000

250,000,000

Debt Instrument, Interest Rate, Stated Percentage

3.95%

Debt Instrument, Face Amount

$ 100,000,000

Debt instrument, Unamortized discount, Percent of face amount

102.497%

Debt instrument, Yield to maturity

3.40%

Debt instrument, Yield to maturity spread at time of pricing

1.40%

Treasury note rate term

5 years

Debt Instrument Maturity Date

[1]

Feb. 15, 2023

Effective interest rate

[1]

3.87%

Unsecured Debt [Member] | Notes 2027 and 2023 [Member]

Debt Instrument [Line Items]

Debt Instrument, Unamortized Discount

$ 3,400,000

Debt Instrument, Unamortized Premium

2,500,000

Proceeds from Notes Payable

$ 546,600,000

Loss on early extinguishment of debt

(1,400,000)

Unsecured Debt [Member] | $325.0M 4.95% Guaranteed Notes due 2018 [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

[1]

$ 0

325,000,000

Debt Instrument, Interest Rate, Stated Percentage

4.95%

Debt Instrument, Repurchased Face Amount

$ 211,600,000

115,100,000

Repayments of debt

$ 113,400,000

Repayment of prepayment penalities

2,300,000

Repayment of accrued interest

1,800,000

Loss on early extinguishment of debt

(2,500,000)

Debt instrument, cash redemption price

$ 215,700,000

Debt Instrument Maturity Date

[1]

Apr. 15, 2018

Effective interest rate

[1]

5.13%

Unsecured Debt [Member] | Seven Year Term Loan - Swapped to fixed [Member]

Debt Instrument [Line Items]

Long-term Debt, Gross

$ 250,000,000

$ 200,000,000

$ 250,000,000

$ 250,000,000

Debt Instrument Maturity Date

Oct. 8, 2022

Feb. 1, 2019

Oct. 1, 2022

Increase in debt

$ 50,000,000

Increase in limit

$ 150,000,000

Effective interest rate

3.72%

3.72%

Unsecured Debt [Member] | Seven Year Term Loan - Swapped to fixed [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Variable interest rate

1.80%

Unsecured Debt [Member] | New Credit Facility [Member]

Debt Instrument [Line Items]

Debt Instrument Maturity Date

May 15, 2019

[1]

On November 17, 2017, the Company completed an offering of $450.0 million 3.95% Guaranteed Notes due 2027 (the “2027 Notes) and reopened the 3.95% Guaranteed Notes due 2023 (the “2023 Notes”) for an additional $100.0 million. On November 17, 2017, the Company redeemed the remaining outstanding balance of the 4.95% Guaranteed Notes due 2018 (the “2018 Notes”) ahead of its scheduled maturity. See below for further discussion.

Debt Obligations - Additional I

Debt Obligations - Additional Information on Repurchase of Outstanding Unsecured Notes (Details) - USD ($)		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Extinguishment Of Debt [Line Items]
Principal		$ 325,000,000	$ 0	$ 0
Repurchase Amount		628,590,000	149,919,000	0
Loss on early extinguishment of debt		(3,933,000)	$ (66,590,000)	$ 0
$250.0M 5.400% Guaranteed Notes due 2014 [Member]
Extinguishment Of Debt [Line Items]
Principal		325,000,000
Repurchase Amount	[1]	330,792,000
Loss on early extinguishment of debt	[2]	$ (3,933,000)
[1]	Includes prepayment penalties with respect to the redemption of debt.
[2]	Includes unamortized balance of the original issue discount and deferred financing costs.

Debt Obligations - Aggregate Sc

Debt Obligations - Aggregate Scheduled Principal Payments of Debt Obligation, Excluding Amortization of Discounts and Premiums (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
2,018	$ 6,601
2,019	7,360
2,020	86,978
2,021	6,099
2,022	256,332
Thereafter	1,585,347
Total principal payments	1,948,717
Net unamortized premiums/(discounts)	(6,748)
Net deferred financing costs	(11,141)
Total Debt Obligations	$ 1,930,828	$ 2,013,112

Fair Value of Financial Instr92

Fair Value of Financial Instruments - Financial Instruments for which Estimates of Fair Value Differ from Carrying Amounts (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Mortgage notes payable, net		$ 317,216	$ 321,549
Note receivable		3,500	3,400
Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable	[1],[2]	3,532	3,380
Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Note receivable, fair value	[2]	3,605	3,717
Unsecured Notes Payable [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured notes payable	[1]	1,286,573	1,364,854
Unsecured Notes Payable [Member] | Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		1,314,900	1,372,758
Variable Rate Debt [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Variable rate debt	[1]	327,039	326,709
Variable Rate Debt [Member] | Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		308,872	307,510
Mortgages Notes Payable [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Mortgage notes payable, net	[1]	317,216	321,549
Mortgages Notes Payable [Member] | Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument, fair value		$ 304,665	$ 328,853
[1]	In April 2015, the FASB issued guidance requiring that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct reduction from the carrying amount of the corresponding debt liability, consistent with debt discounts. As a result, the carrying amounts presented in the table above are net of deferred financing costs of $8.9 million and $5.5 million for unsecured notes payable, $1.6 million and $1.9 million for variable rate debt and $0.6 million and $0.7 million for mortgage notes payable as of December 31, 2017 and December 31, 2016, respectively.
[2]	The inputs to originate the note receivable are unobservable and, as a result, are categorized as Level 3. The Company determined fair value by calculating the present value of the cash payments to be received through the maturity date of the loan. See Note 2, “Significant Accounting Policies,” for further information regarding the note origination.

Fair Value of Financial Instr93

Fair Value of Financial Instruments - Financial Instruments for which Estimates of Fair Value Differ from Carrying Amounts (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deferred financing costs, net	$ 11,141
Unsecured Notes Payable [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deferred financing costs, net	10,575	$ 7,369
Unsecured Notes Payable [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deferred financing costs, net	8,900	5,500
Variable Rate Debt [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deferred financing costs, net	1,600	1,900
Mortgages Notes Payable [Member] | Carrying Amount [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Deferred financing costs, net	$ 600	$ 700

Risk Management and Use of De94

Risk Management and Use of Derivative Financial Instruments - Terms and Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives Fair Value [Line Items]
Notional Amount	$ 301,548	$ 328,610
3.300% Interest Rate Swap Maturing January 30, 2021 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.30%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(300)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 25
3.090% Interest Rate Swap Maturing October 30, 2019 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount	$ 25,774	25,774
Derivative, Fixed Interest Rate	3.09%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(214)
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 59
2.750% Interest Rate Swap Maturing September 30, 2017 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Notional Amount		$ 27,062
Derivative, Fixed Interest Rate		2.75%
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		$ (83)
3.718% Interest Rate Swap Maturing October 8, 2022 [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Derivative, Fixed Interest Rate	3.718%
Derivative Asset, Notional Amount	$ 250,000	250,000
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	$ 5,694	$ 3,733

Risk Management and Use of De95

Risk Management and Use of Derivative Financial Instruments - Terms and Fair Values of Derivative Financial Instruments (Parenthetical) (Details)	Dec. 31, 2017
Indenture IA (Preferred Trust I) [Member] | LIBOR [Member]
Derivatives Fair Value [Line Items]
Derivative, Basis Spread on Variable Rate	1.25%

Risk Management and Use of De96

Risk Management and Use of Derivative Financial Instruments (Textual) (Details) - Customer	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rental Revenue [Member] | Customer Concentration Risk [Member]
Derivatives Fair Value [Line Items]
Number of tenant accounted for 10% or more of the Company's rents	0	0	0

Limited Partners' NonControll97

Limited Partners' NonControlling Interests in the Parent Company (Textual) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Abstract]
Aggregate amount related to non-controlling interests classified within equity	$ 15.2	$ 14.9
Settlement value of non controlling interest in operating partnership	$ 26.9	$ 24.4

Beneficiaries Equity of the P98

Beneficiaries Equity of the Parent Company - Number of Shares and Net Income Used to Calculate Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss)	$ 73,844	[1]	$ 19,046	$ 7,698	$ 21,271	$ (12,370)	$ 7,884	$ (1,323)	$ 46,310	$ 121,859	$ 40,501	$ (30,740)
Net (income) loss attributable to noncontrolling interests, Basic										(1,009)	(310)	339
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic										(327)	(341)	(329)
Distribution to preferred shareholders										(2,032)	(6,900)	(6,900)
Preferred share redemption charge										(3,181)	0	0
Net income (loss) attributable to Common Shareholders of Brandywine Realty Trust										115,310	32,950	(37,630)
Net (income) loss attributable to noncontrolling interests, Diluted										(1,009)	(310)	339
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted										(327)	(341)	(329)
Net income (loss) attributable to common shareholders, Diluted										$ 115,310	$ 32,950	$ (37,630)
Denominator
Basic weighted average shares outstanding (in shares)										175,484,350	175,018,163	178,162,160
Contingent securities/Share based compensation (in shares)										1,323,816	992,651	0
Diluted weighted average shares outstanding (in shares)										176,808,166	176,010,814	178,162,160
Earnings (loss) per Common Share:
Net income (loss) attributable to common shareholders, Basic (USD per share)	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Net income (loss) attributable to common shareholders, Diluted (USD per share)	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
[1]	The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Beneficiaries Equity of the P99

Beneficiaries Equity of the Parent Company (Textual) (Details) - USD ($)	Dec. 07, 2017	Apr. 11, 2017	Jan. 10, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 22, 2015
Class of Stock [Line Items]
Dividends, Common Stock	$ 32,400,000
Dividends payable, date to be paid	Jan. 23, 2018
Dividends payable, date of record	Jan. 9, 2018
Preferred share redemption charge				$ 3,181,000	$ 0	$ 0
Authorized Amount							$ 100,000,000
Repurchased and Retired, Shares				0	0	5,209,437
Share Price						$ 12.90
Repurchased and Retired, Value						$ 67,325,000
Common stock price per share				$ 0.01	$ 0.01
Common Stock, Shares Authorized				400,000,000	400,000,000
Upfront costs				$ 499,000		$ 105,000
Common shares issued under offering program					0	0
Cash proceeds, net of issuance costs				$ 51,225,000	$ 0	$ 0
Offering Program [Member]
Class of Stock [Line Items]
Common Stock, Shares Authorized			16,000,000
Upfront costs			$ 200,000
Common shares issued under offering program				2,858,991	0	0
Weighted average price per share				$ 18.19
Cash proceeds, net of issuance costs				$ 51,200,000
Common shares remain available for future issuance				13,141,009
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Class of Stock [Line Items]
Dividends, Common Stock	$ 32,400,000
Dividends payable, date to be paid	Jan. 23, 2018
Dividends payable, date of record	Jan. 9, 2018
Preferred share redemption charge				$ 3,181,000	$ 0	$ 0
Repurchase program, number of common unit retired for each common share repurchased				1
Cash proceeds, net of issuance costs				$ 51,225,000	$ 0	$ 0
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Series E Preferred Stock [Member]
Class of Stock [Line Items]
Redemption outstanding shares		4,000,000
Redemption price per share		$ 25.51
Accrued dividends paid in cash		$ 2,000,000
Preferred share redemption charge		$ 3,200,000
Dividend Declared [Member]
Class of Stock [Line Items]
Dividends Payable, Amount Per Share	$ 0.18
Dividend Declared [Member] | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Class of Stock [Line Items]
Dividends Payable, Amount Per Share	$ 0.18
Redeemable Common Limited Partnership Units [Member]
Class of Stock [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share				1,479,799	1,479,799	1,535,102

Partners Equity of the Opera100

Partners Equity of the Operating Partnership - Number of Units and Net Income Used to Calculate Basic and Diluted Earnings Per Common Partnership Unit (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator
Net income (loss)	$ 73,844	[1]	$ 19,046	$ 7,698	$ 21,271	$ (12,370)	$ 7,884	$ (1,323)	$ 46,310	$ 121,859	$ 40,501	$ (30,740)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic										(327)	(341)	(329)
Distribution to preferred shareholders										(2,032)	(6,900)	(6,900)
Preferred share redemption charge										(3,181)	0	0
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted										$ (327)	$ (341)	$ (329)
Denominator
Basic weighted average shares outstanding (in shares)										175,484,350	175,018,163	178,162,160
Contingent securities/Share based compensation (in shares)										1,323,816	992,651	0
Diluted weighted average shares outstanding (in shares)										176,808,166	176,010,814	178,162,160
Earnings (loss) per Common Partnership Unit:
Net income (loss) attributable to common shareholders, Basic (USD per share)	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Net income (loss) attributable to common shareholders, Diluted (USD per share)	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Numerator
Net income (loss)	$ 73,844	[1]	$ 19,046	$ 7,698	$ 21,271	$ (12,370)	$ 7,884	$ (1,323)	$ 46,310	$ 121,859	$ 40,501	$ (30,740)
Nonforfeitable dividends allocated to unvested restricted shareholders, Basic										(327)	(341)	(329)
Distribution to preferred shareholders										(2,032)	(6,900)	(6,900)
Preferred share redemption charge										(3,181)	0	0
Net (income) loss attributable to noncontrolling interests										(29)	(15)	3
Net income (loss) attributable to common unitholders, Basic										116,290	33,245	(37,966)
Nonforfeitable dividends allocated to unvested restricted shareholders, Diluted										(327)	(341)	(329)
Net income attributable to common unitholders, Diluted										$ 116,290	$ 33,245	$ (37,966)
Denominator
Basic weighted average shares outstanding (in shares)										176,964,149	176,523,800	179,697,262
Contingent securities/Share based compensation (in shares)										1,323,816	992,651	0
Diluted weighted average shares outstanding (in shares)										178,287,965	177,516,451	179,697,262
Earnings (loss) per Common Partnership Unit:
Net income (loss) attributable to common shareholders, Basic (USD per share)	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Net income (loss) attributable to common shareholders, Diluted (USD per share)	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
[1]	The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Partners Equity of the Opera101

Partners Equity of the Operating Partnership (Textual) (Details) - USD ($)	Dec. 07, 2017	Apr. 11, 2017	Jan. 10, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 22, 2015
Earnings Per Common Partnership Unit [Line Items]
Dividends, Common Stock	$ 32,400,000
Dividends payable, date to be paid	Jan. 23, 2018
Dividends payable, date of record	Jan. 9, 2018
Preferred share redemption charge				$ 3,181,000	$ 0	$ 0
Authorized Amount							$ 100,000,000
Repurchased and Retired, Shares				0	0	5,209,437
Share Price						$ 12.90
Repurchased and Retired, Value						$ 67,325,000
Common Stock, Par or Stated Value Per Share (USD per share)				$ 0.01	$ 0.01
Common Stock, Shares Authorized				400,000,000	400,000,000
Upfront costs				$ 499,000		$ 105,000
Common shares issued under offering program					0	0
Cash proceeds, net of issuance costs				$ 51,225,000	$ 0	$ 0
Offering Program [Member]
Earnings Per Common Partnership Unit [Line Items]
Common Stock, Shares Authorized			16,000,000
Upfront costs			$ 200,000
Common shares issued under offering program				2,858,991	0	0
Weighted average price per share				$ 18.19
Cash proceeds, net of issuance costs				$ 51,200,000
Common shares remain available for future issuance				13,141,009
Dividend Declared [Member]
Earnings Per Common Partnership Unit [Line Items]
Dividends Payable, Amount Per Share	$ 0.18
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Common Partnership Unit [Line Items]
Dividends, Common Stock	$ 32,400,000
Dividends payable, date to be paid	Jan. 23, 2018
Dividends payable, date of record	Jan. 9, 2018
Preferred share redemption charge				$ 3,181,000	$ 0	$ 0
Repurchase program, number of mirror unit retired for each common share repurchased				1
Cash proceeds, net of issuance costs				$ 51,225,000	$ 0	$ 0
BRANDYWINE OPERATING PARTNERSHIP, L.P. | Dividend Declared [Member]
Earnings Per Common Partnership Unit [Line Items]
Dividends Payable, Amount Per Share	$ 0.18
Class A Units [Member]
Earnings Per Common Partnership Unit [Line Items]
Redeemable Limited Partnership Units Potential Cash Redemption Value Closing Market Price				$ 18.19	$ 16.51	$ 13.66
Limited Partners' Capital Account, Units Outstanding				1,479,799	1,479,799	1,535,102
Series E Preferred Stock [Member] | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings Per Common Partnership Unit [Line Items]
Redemption outstanding shares		4,000,000
Redemption price per share		$ 25.51
Accrued dividends paid in cash		$ 2,000,000
Preferred share redemption charge		$ 3,200,000

Share Based Compensation, 40102

Share Based Compensation, 401(k) Plan and Deferred Compensation (Textual) (Details)	May 18, 2017shares	Mar. 07, 2017Installmentshares	Mar. 01, 2017shares	Feb. 01, 2017shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)	Feb. 06, 2017$ / shares	Feb. 22, 2016shares	Feb. 23, 2015shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | shares					2,238,590	2,377,778
Share-based compensation expense | $					$ 6,300,000	$ 5,600,000	$ 7,300,000
Share-based compensation expense, capitalized | $					1,200,000	1,000,000	1,900,000
Defined Contribution Plan, Employer Discretionary Contribution Amount | $					$ 500,000	$ 400,000	400,000
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent					100.00%
Aggregate share-based awards awarded to executives | shares	6,500,000
Number of shares to be issued under deferred compensation plan included in total shares outstanding | shares					900,000	900,000
Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | shares					2,238,590
Share-based compensation expense | $					$ 0	$ 0
Share-based compensation expense, capitalized | $					0	0
Restricted Share Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense | $					2,800,000	2,600,000	2,400,000
Share-based compensation expense, capitalized | $					$ 400,000	$ 400,000	700,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | shares					455,643	488,604
Unrecognized compensation expenses | $					$ 2,100,000
Weighted average period over which options will be recognized					1 year 3 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					two to three years from the initial grant dates
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares					170,192
Voluntary Termination Of Employment Terms					after reaching at least age 57 and accumulating at least 15 years of service with the Company
Accumulated Service Period For Voluntary Termination					15 years
Restricted Share Awards [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Voluntary Termination of Employment Age Limit					57 years
Restricted Share Awards [Member] | Non-Officer Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares		32,122
Number of Vesting Installments | Installment		2
Restricted Share Awards [Member] | Cliff Vest [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares			109,629
Share Based Compensation Arrangement By Share Based Payment Award, Vesting Date			Apr. 15, 2020
Restricted Share Awards [Member] | Installment One [Member] | Non-Officer Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award, Vesting Date		Apr. 15, 2018
Restricted Share Awards [Member] | Installment Two [Member] | Non-Officer Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award, Vesting Date		Apr. 15, 2019
Restricted Share Awards [Member] | Ratable Vesting
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares	28,441
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights					ratably over three years
Restricted Share Awards [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period					3 years
Restricted Share Awards [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period					2 years
Restricted Performance Share Units Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense | $					$ 3,400,000	$ 2,800,000	4,200,000
Share-based compensation expense, capitalized | $					$ 800,000	600,000	1,200,000
Unrecognized compensation expenses | $						$ 1,700,000
Weighted average period over which options will be recognized					1 year 1 month 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					3 year
Common shares issued for share based compensation | shares				55,299
Dividends Payable, Amount Per Share | $ / shares								$ 0.16
Restricted Performance Share Units Plan [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number | shares					545,803	378,977
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares					174,854
Aggregate share-based awards awarded to executives | shares			174,854						231,388	186,395
Restricted Performance Share Units Plan [Member] | Cliff Vest [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights					three year cliff vesting period
Employee Share Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense | $					$ 100,000	$ 200,000	100,000
Share purchases made by employees under ESPP					85% of the average closing price per share for a specified period
Maximum participant contribution, percentage of compensation					20.00%
Maximum participant contribution, dollar amount | $					$ 50,000
Aggregate share-based awards awarded to executives | shares					1,250,000
Stock Issued During Period, Value, Employee Stock Purchase Plan | $					$ 400,000	$ 400,000	$ 500,000
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date					15.00%

Share Based Compensation, 40103

Share Based Compensation, 401(k) Plan and Deferred Compensation - Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Option activity
Outstanding at beginning of year, shares	2,377,778
Exercised, shares	(128,330)
Forfeited/Expired, shares	(10,858)
Outstanding at end of year, shares	2,238,590	2,377,778
Vested/Exercisable at end of year, shares	2,238,590
Outstanding at beginning of year, Weighted Average Exercise Price	$ 15.36
Exercised, Weighted Average Exercise Price	9.59
Forfeited/Expired, Weighted Average Exercise Price	20.61
Outstanding at end of year, Weighted Average Exercise Price	15.67	$ 15.36
Vested/Exercisable at end of period, Weighted Average Exercise Price	$ 15.67
Weighted Average Remaining Contractual Term (in years)	1 year 1 month 6 days	2 years 1 month 24 days
Vested/Exercisable at end of period, Weighted Average Remaining Contractual Term (in years)	1 year 1 month 6 days
Exercised, Aggregated Intrinsic Value	$ 919,582
Outstanding at end of year, Aggregate Intrinsic Value	8,735,293
Vested/Exercisable at end of year, Aggregate Intrinsic Value	$ 8,735,293

Share Based Compensation, 40104

Share Based Compensation, 401(k) Plan and Deferred Compensation - Restricted Share Activity (Details) - Restricted Share Awards [Member]	12 Months Ended
	Dec. 31, 2017USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at January 1, 2017, shares | shares	488,604
Granted, shares | shares	170,192
Vested, shares | shares	(189,704)
Forfeited, shares | shares	(13,449)
Non-vested at December 31, 2017, shares | shares	455,643
Non-vested at January 1, 2017, Weighted Average Grant Date Fair Value | $ / shares	$ 14.10
Granted, Weighted Average Grant Date Fair Value | $ / shares	16.77
Vested, Weighted Average Grant Date Fair Value | $ / shares	14.40
Forfeited, Weighted Average Grant Date Fair Value | $ / shares	14.83
Non-vested at December 31, 2017, Weighted Average Grant Date Fair Value | $ / shares	$ 14.95
Non-vested at January 1, 2017, Aggregate Intrinsic Value | $	$ 8,066,852
Granted, Aggregate Intrinsic Value | $	2,854,165
Vested, Aggregate Intrinsic Value | $	3,227,342
Non-vested at December 31, 2017, Aggregate Intrinsic Value | $	$ 8,288,146

Share Based Compensation, 40105

Share Based Compensation, 401(k) Plan and Deferred Compensation - Restricted Performance Share Units (Details) - USD ($) $ in Thousands	Mar. 01, 2017	Feb. 22, 2016	Feb. 23, 2015	Dec. 31, 2017	May 18, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Units Granted					6,500,000
Restricted Performance Share Units Plan [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at January 1, 2017, shares				378,977
Granted, shares				174,854
Units Cancelled				(8,028)
Non-vested at December 31, 2017, shares				545,803
Units Granted	174,854	231,388	186,395
Fair Value of Units on Grant Date (in thousands)	$ 3,735	$ 3,558	$ 3,933
Restricted Performance Share Units Plan [Member] | February 23, 2015 RSPU Grant [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at January 1, 2017, shares				147,589
Granted, shares				0
Units Cancelled				(2,274)
Non-vested at December 31, 2017, shares				145,315
Measurement Period Commencement Date				Jan. 1, 2015
Measurement Period End Date				Dec. 31, 2017
Restricted Performance Share Units Plan [Member] | February 22, 2016 RSPU Grant [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at January 1, 2017, shares				231,388
Granted, shares				0
Units Cancelled				(3,311)
Non-vested at December 31, 2017, shares				228,077
Measurement Period Commencement Date				Jan. 1, 2016
Measurement Period End Date				Dec. 31, 2018
Restricted Performance Share Units Plan [Member] | March 01, 2017 RSPU Grant [Member] | Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Non-vested at January 1, 2017, shares				0
Granted, shares				174,854
Units Cancelled				(2,443)
Non-vested at December 31, 2017, shares				172,411
Measurement Period Commencement Date				Jan. 1, 2017
Measurement Period End Date				Dec. 31, 2019

Distributions - Tax Characteris

Distributions - Tax Characteristics of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distributions [Abstract]
Common Share Distributions Payments of Ordinary Dividends	$ 0.38	$ 0	$ 0.36
Common Share Distributions Capital Gain	0.26	0.62	0.14
Common Share Distributions Non-taxable Distributions	0	0	0.10
Common Stock, Dividends, Per Share, Paid	$ 0.64	$ 0.62	$ 0.60
Percentage Of Distributions classified as ordinary income	60.00%	0.00%	59.10%
Percentage Of Distributions classified as capital gain	40.00%	100.00%	23.50%
Percentage Of Distributions classified as non-taxable distribution	0.00%	0.00%	17.40%
Dividends, Preferred Stock	$ 2,032	$ 6,900	$ 6,900
Percentage Of Preferred Distributions classified as ordinary income	60.00%	0.00%	71.60%
Percentage Of Preferred Distributions classified as capital gain	40.00%	100.00%	28.40%
Percentage Of Preferred Distributions classified as non-taxable distribution	0.00%	0.00%	0.00%

Income Taxes and Tax Credit 107

Income Taxes and Tax Credit Transactions (Textual) (Details)	Dec. 30, 2008USD ($)	Sep. 30, 2015USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Aug. 27, 2010USD ($)	Nov. 17, 2008ft²
Tax Credit Carryforward [Line Items]
Accruals for tax uncertainties			$ 0	$ 0
Deferred income tax benefit			628,000	0	$ 0
Tax credit transaction income			$ 0	0	(19,955,000)
Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Area Of IRS Campus Building | ft²							862,692
Percentage of building leased to IRS							100.00%
Purchase price for noncontrolling interest obligation put option		$ 3,200,000
Rate of return on noncontrolling interest		2.00%
Percentage of tax credit recapture		20.00%
Tax credit transaction income		$ 11,900,000
Other income (expense)		$ (500,000)
Recognition of cash received as revenue net of allocated expenses on or after September 2011, period			over the five year credit recapture period as defined in the Internal Revenue Code
Recognition of cash received as revenue net of allocated expenses on or after September 2011, period in years		5 years
Accretion of noncontrolling interest liability				0	1,100,000
Historic Tax Credit Transaction [Member] | U S B [Member]
Tax Credit Carryforward [Line Items]
Agreed contribution in project cost						$ 64,100,000
USB contributions			$ 0	0
New Markets Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Percentage of tax credit recapture			100.00%
Tax credit transaction income	$ 8,000,000				$ 8,100,000
Recognition of cash received as revenue net of allocated expenses on or after September 2011, period in years			7 years
Percentage of qualified investments	39.00%
New Markets Tax Credit Transaction [Member] | U S B [Member]
Tax Credit Carryforward [Line Items]
USB contributions	$ 13,300,000
Other Assets [Member]
Tax Credit Carryforward [Line Items]
Net deferred tax assets			$ 600,000
Other Assets [Member] | Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Deferred Costs			0	0
Other Assets [Member] | New Markets Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Deferred Costs			$ 0	$ 0
Other Liabilities [Member] | Historic Tax Credit Transaction [Member]
Tax Credit Carryforward [Line Items]
Preferred return		$ 1,000,000

Accumulated Other Comprehens108

Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Accumulated other comprehensive income (loss) [Line Items]
Balance at January 1		$ (1,745)
Reclassification of realized losses on derivative financial instruments to operations, net	[1]	1,230	$ 1,104	$ 420
Balance at December 31,		2,399	(1,745)
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Schedule of Accumulated other comprehensive income (loss) [Line Items]
Balance at January 1		(2,122)
Reclassification of realized losses on derivative financial instruments to operations, net	[2]	1,230	1,104	420
Balance at December 31,		2,056	(2,122)
Accumulated Other Comprehensive Income (Loss) [Member]
Schedule of Accumulated other comprehensive income (loss) [Line Items]
Balance at January 1		(1,745)	(5,192)	(4,607)
Change in fair market value during year		2,948	2,371	(1,010)
Allocation of unrealized (gains)/losses on derivative financial instruments to noncontrolling interests		(34)	(28)	5
Reclassification of realized losses on derivative financial instruments to operations, net		1,230	1,104	420
Balance at December 31,		2,399	(1,745)	(5,192)
Accumulated Other Comprehensive Income (Loss) [Member] | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Schedule of Accumulated other comprehensive income (loss) [Line Items]
Balance at January 1		(2,122)	(5,597)	(5,007)
Change in fair market value during year		2,948	2,371	(1,010)
Reclassification of realized losses on derivative financial instruments to operations, net		1,230	1,104	420
Balance at December 31,		$ 2,056	$ (2,122)	$ (5,597)
[1]	Amounts reclassified from comprehensive income to interest expense within the Consolidated Statements of Operations.
[2]	Amounts reclassified from comprehensive income to interest expense within the Consolidated Statement of Operations.

Accumulated Other Comprehens109

Accumulated Other Comprehensive Income (Loss) (Textual) (Details) $ in Millions	Dec. 31, 2017USD ($)
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Gains (losses) expected to be reclassified from AOCI into interest expense within the next twelve months	$ 0.8

Segment Information (Textual) (

Segment Information (Textual) (Details)	Feb. 02, 2017property	Dec. 31, 2017propertysegment	Dec. 31, 2016property	Dec. 31, 2015property
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment		5
Office Properties [Member]
Segment Reporting Information [Line Items]
Number of Properties Sold			66	27
Office Properties [Member] | 1200 & 1220 Concord Avenue (Concord Airport Plaza) [Member]
Segment Reporting Information [Line Items]
Number of Properties Sold	2	2

Segment Information - Real Esta

Segment Information - Real Estate Investments, at Cost of Company's Reportable Segments (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Segment Reporting Information [Line Items]
Operating properties		$ 3,832,348	$ 3,586,295		$ 3,693,000
Assets held for sale - real estate investments	[1]	0	73,591	[2]	794,588
Operating Properties		3,832,348	3,659,886		4,487,588
Construction-in-progress		121,188	297,462		268,983
Land held for development	[3]	98,242	150,970		130,479
Philadelphia CBD [Member]
Segment Reporting Information [Line Items]
Operating properties		1,643,296	1,320,974		1,157,667
Pennsylvania Suburbs [Member]
Segment Reporting Information [Line Items]
Operating properties		958,796	1,005,446		1,019,280
Metropolitan DC [Member]
Segment Reporting Information [Line Items]
Operating properties		978,257	975,987		1,129,206
Austin, Texas [Member]
Segment Reporting Information [Line Items]
Operating properties		163,653	146,794		164,518
Other [Member]
Segment Reporting Information [Line Items]
Operating properties	[4]	$ 88,346	$ 137,094		$ 222,329
[1]	As of December 31, 2015, the Och-Ziff Portfolio and Cira Square were held for sale. As of December 31, 2016, the Concord Airport Plaza located in the Other segment and the Calverton portfolio located in the Metropolitan Washington, D.C. segment was held for sale. See Note 3, “Real Estate Investments,” for further information.
[2]	Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation, land held for development or other assets on the balance sheets of the properties held for sale. See 2016 Held for Sale section below.
[3]	As of December 31, 2017, the Company categorized 13.1 acres of land held for development located in the Other segment as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3, “Real Estate Investments,” for further information.
[4]	As a result of the Och-Ziff Sale that occurred on February 4, 2016, the Company narrowed its segments to five segments: (1) Philadelphia Central Business District (“CBD”), (2) Pennsylvania Suburbs, (3) Metropolitan Washington, D.C. and (4) Austin, Texas and (5) Other. The Och-Ziff Sale disposed of the entire Richmond, Virginia segment. See Note 3, “Real Estate Investments,” for further information.

Segment Information - Real E112

Segment Information - Real Estate Investments, at Cost of Company's Reportable Segments (Parenthetical) (Details) - Assets Held-for-sale [Member]	Dec. 31, 2017a
Segment Reporting Information [Line Items]
Acreage of land	13.1
Other [Member] | Land Held For Development [Member]
Segment Reporting Information [Line Items]
Acreage of land	13.1

Segment Information - Net Opera

Segment Information - Net Operating Income of Company's Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended									12 Months Ended
		Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenue		$ 133,344		$ 128,438	$ 127,791	$ 130,920	$ 132,086	$ 129,694	$ 127,181	$ 136,502	$ 520,493	$ 525,463	$ 602,631
Operating expenses	[2]										(205,999)	(209,448)	(238,087)
Net operating income											314,494	316,015	364,544
Operating Segments [Member] | Philadelphia CBD [Member]
Segment Reporting Information [Line Items]
Total revenue											226,673	200,245	209,298
Operating expenses	[2]										(88,818)	(78,708)	(77,352)
Net operating income											137,855	121,537	131,946
Operating Segments [Member] | Pennsylvania Suburbs [Member]
Segment Reporting Information [Line Items]
Total revenue											139,785	144,338	158,398
Operating expenses	[2]										(47,769)	(49,208)	(57,319)
Net operating income											92,016	95,130	101,079
Operating Segments [Member] | Metropolitan DC [Member]
Segment Reporting Information [Line Items]
Total revenue											92,024	99,781	110,657
Operating expenses	[2]										(35,014)	(39,036)	(44,294)
Net operating income											57,010	60,745	66,363
Operating Segments [Member] | Austin, Texas [Member]
Segment Reporting Information [Line Items]
Total revenue	[3]										34,301	34,585	20,910
Operating expenses	[2],[3]										(15,456)	(13,222)	(8,010)
Net operating income	[3]										18,845	21,363	12,900
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Total revenue											18,347	39,359	98,799
Operating expenses	[2]										(11,749)	(23,204)	(49,604)
Net operating income											6,598	16,155	49,195
Corporate [Member]
Segment Reporting Information [Line Items]
Total revenue											9,363	7,155	4,569
Operating expenses	[2]										(7,193)	(6,070)	(1,508)
Net operating income											$ 2,170	$ 1,085	$ 3,061
[1]	The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania.
[2]	Includes property operating expense, real estate taxes and third party management expense.
[3]	On June 22, 2015 the Company acquired the remaining 50.0% of the common interest in Broadmoor Austin Associates. As such, the Company has seven wholly owned properties in its Austin, Texas business segment. Net operating income for the years ended December 31, 2016 and 2015 includes management fees and related expenses for services provided by the Company to the Austin Venture, which are recorded in the Corporate segment. See Note 3, "Real Estate Investments," for further information regarding these transactions.

Segment Information - Net Op114

Segment Information - Net Operating Income of Company's Reportable Segments (Parenthetical) (Details) - property	Dec. 31, 2017	Dec. 31, 2016	Jun. 22, 2015
Segment Reporting Information [Line Items]
Number of Properties	93
Austin, Texas [Member]
Segment Reporting Information [Line Items]
Number of Properties		7
Broadmoor Austin Associates [Member]
Segment Reporting Information [Line Items]
Percentage of ownership interests			50.00%

Segment Information - Unconsoli

Segment Information - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity		$ 194,621	$ 281,331	$ 241,004
Equity in loss of Real Estate Ventures		(8,306)	(11,503)	(811)
Philadelphia CBD [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity		39,939	48,691	44,089
Equity in loss of Real Estate Ventures		255	(686)	(188)
Pennsylvania Suburbs [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity		3,503	15,421	16,408
Equity in loss of Real Estate Ventures		631	748	310
Metropolitan DC [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	[1]	119,817	141,786	118,422
Equity in loss of Real Estate Ventures	[1]	(5,044)	(6,293)	(336)
MAP Venture [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	[2]	15,450	20,893	0
Equity in loss of Real Estate Ventures	[2]	(3,443)	(4,218)	0
Other [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	[3]	1,939	1,654	1,657
Equity in loss of Real Estate Ventures	[3]	285	814	930
Austin, Texas [Member]
Segment Reporting Information [Line Items]
Investment in real estate ventures, at equity	[4]	13,973	52,886	60,428
Equity in loss of Real Estate Ventures	[4]	$ (990)	$ (1,868)	$ (1,527)
[1]	On August 31, 2016, the Company terminated its lease for the regional management and leasing office at 3141 Fairview Park Drive, located in Falls Church, Virginia. Accordingly, the Company no longer has any continuing involvement with 3141 Fairview Park Drive and recorded the partial sale under the full accrual method of accounting. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” for further information. The years ended December 31, 2017 and 2016 include impairment charges related to the Brandywine - AI Venture. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” for further information.
[2]	The MAP Venture represents a joint venture formed between the Company and MAP Ground Lease Holdings LLC, an affiliate of Och-Ziff Capital Management Group, LLC, on February 4, 2016. The MAP Venture’s business operations, including properties in Richmond, Virginia; Metropolitan Washington, D.C.; New Jersey/Delaware and Pennsylvania Suburbs, are centrally managed with the results reported to management of the Company on a consolidated basis. As a result, the investment in the MAP Venture is separately presented. All other unconsolidated real estate ventures are managed consistently with the Company’s regional segments.
[3]	See footnote (a) to the “Real estate investments, at cost” table above for further information regarding this segment.
[4]	Investment in real estate ventures does not include the $1.1 million negative investment balance in one real estate venture as of December 31, 2015, which is included in the “Other Liabilities” caption of the consolidated balance sheets. The Company disposed of its interest in this venture during 2016. See Note 4, "Investment in Unconsolidated Real Estate Ventures," for further information. The decrease in the Company’s investment balance primarily relates to distributions from the G&I VII Austin Office LLC real estate venture. See Note 4, “Investment in Unconsolidated Real Estate Ventures,” for further information.

Segment Information - Uncons116

Segment Information - Unconsolidated Real Estate Ventures of Company's Reportable Segments (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Other liabilities	$ 15,623	$ 19,408
Coppell Associates [Member]
Segment Reporting Information [Line Items]
Other liabilities			$ 1,100

Segment Information - Reconcili

Segment Information - Reconciliation of Consolidated Net Income (Loss) to Consolidated NOI (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017	[1]	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting [Abstract]
Net income (loss)	$ 73,844		$ 19,046	$ 7,698	$ 21,271	$ (12,370)	$ 7,884	$ (1,323)	$ 46,310	$ 121,859	$ 40,501	$ (30,740)
Plus:
Interest expense										81,886	84,708	110,717
Interest expense - amortization of deferred financing costs										2,435	2,696	4,557
Interest expense - financing obligation										0	679	1,237
Depreciation and amortization										179,357	189,676	219,029
General and administrative expenses										28,538	26,596	29,406
Equity in loss of Real Estate Ventures										8,306	11,503	811
Provision for impairment								$ 1,800		3,057	40,517	82,208
Loss on early extinguishment of debt										3,933	66,590	0
Less:
Interest income										1,113	1,236	1,224
Income tax benefit										628	0	0
Tax credit transaction income										0	0	19,955
Net gain from remeasurement of investments in real estate ventures										0	0	758
Net gain on disposition of real estate										31,657	116,983	20,496
Net gain on sale of undepreciated real estate										953	9,232	3,019
Net gain on Real Estate Venture transactions										80,526	20,000	7,229
Consolidated net operating income										$ 314,494	$ 316,015	$ 364,544
[1]	The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Operating Leases - Minimum Futu

Operating Leases - Minimum Future Rentals on Non-cancelable Leases of Company properties leased to Tenants (Details) $ in Thousands	Dec. 31, 2017USD ($)
Operating Leases, Future Minimum Payments Receivable [Abstract]
2,018	$ 381,110
2,019	370,211
2,020	348,544
2,021	323,654
2,022	277,837
Thereafter	$ 1,269,745

Commitments and Contingencie119

Commitments and Contingencies (Textual) (Details)		Oct. 18, 2017USD ($)ft²property	Oct. 17, 2017USD ($)property	Dec. 03, 2015ft²	Apr. 02, 2015USD ($)	Dec. 31, 2017USD ($)ft²apropertyParcel	Sep. 30, 2004USD ($)	Dec. 31, 2017USD ($)ft²aParcel	Dec. 03, 2017ft²Floor	Oct. 13, 2017USD ($)ft²	Dec. 31, 2016USD ($)	Jul. 02, 2016a	Jul. 01, 2016a	Dec. 31, 2015	Oct. 17, 2014ft²	Jul. 31, 2014ft²
Property Subject to or Available for Operating Lease [Line Items]
Letter of credit outstanding amount released		$ 10,000,000
Real estate ventures aggregate indebtedness to third parties						$ 768,912,000		$ 768,912,000			$ 997,466,000
Agreed holding period (not to sell) for properties acquired as part of the TRC acquisition								15 years
Subaru Corporate Headquarters Project [Member]
Property Subject to or Available for Operating Lease [Line Items]
Number of floors | Floor									5
Area of office property | ft²									250,000
Residual profit recognized						2,000,000		$ 2,000,000
Residual profit earned								1,500,000
NTE Amount						79,400,000		79,400,000
Project costs funded						67,100,000		67,100,000
Subaru Build-to-Service Center Project [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lease terms				18 years
Project costs funded						15,500,000		15,500,000
Rentable Square Feet | ft²				83,000
Purchase option of lease from inception period				5 years
Project costs						46,900,000		46,900,000
evo at Cira Centre South Venture [Member]
Property Subject to or Available for Operating Lease [Line Items]
Guarantees, maximum exposure amount						55,400,000		55,400,000
4040 Wilson Venture [Member]
Property Subject to or Available for Operating Lease [Line Items]
Guarantees, maximum exposure amount						41,300,000		41,300,000
618 Market Street [Member]
Property Subject to or Available for Operating Lease [Line Items]
Contingent consideration, liability					$ 2,000,000	1,800,000		1,800,000
Fair value of contingent consideration					1,600,000
Interest expense					$ 2,000,000
One Drexel Plaza [Member]
Property Subject to or Available for Operating Lease [Line Items]
Estimated of funding In the ground lease										$ 37,300,000
Rentable Square Feet | ft²										282,709
Drexel Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Required spending in capital improvements to property						3,600,000		3,600,000
Estimated potential additional contribution obligation						$ 900,000		$ 900,000
Garza Land Acquisition [Member]
Property Subject to or Available for Operating Lease [Line Items]
Acreage of land | a												34.6	34.6
Number of Parcels | Parcel						2		2
Infrastructure improvements to land, estimated cost						$ 13,500,000		$ 13,500,000
Garza Land Acquisition [Member] | Parcel One [Member]
Property Subject to or Available for Operating Lease [Line Items]
Area of land sold | a						8.4		8.4
Garza Land Acquisition [Member] | Parcel Two [Member]
Property Subject to or Available for Operating Lease [Line Items]
Area of land sold | a						1.7		1.7
Two Logan Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Leased Area Of Building | ft²								708,844
Amount to be paid if the Company takes fee title to Two Logan Square upon foreclosure of related mortgage						$ 2,900,000		$ 2,900,000
Liability related to acquisition of TRC							$ 700,000	$ 2,400,000
Commerce Square [Member] | Prentiss Properties Trust [Member]
Property Subject to or Available for Operating Lease [Line Items]
Non-controlling interest, ownership percentage by non-controlling Owners						1.00%		1.00%
One Commerce Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Tax guarantee obligation						$ 125,000,000		$ 125,000,000
Two Commerce Square [Member]
Property Subject to or Available for Operating Lease [Line Items]
Tax guarantee obligation						100,000,000		100,000,000
Put Agreement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Purchase price						35,000,000		$ 35,000,000
Minimum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lease terms								11 years
Minimum [Member] | One Drexel Plaza [Member]
Property Subject to or Available for Operating Lease [Line Items]
Required spending in capital improvements to property						$ 8,000,000		$ 8,000,000
Maximum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lease terms								71 years
Austin Joint Venture [Member]
Property Subject to or Available for Operating Lease [Line Items]
Number of Properties Sold | property		8	7			8
Equity method investment percentage		50.00%
Real estate ventures aggregate indebtedness to third parties		$ 150,968,000	$ 151,000,000
Rentable Square Feet | ft²		1,164,496				1,570,123		1,570,123							590,881	232,274
Unconsolidated Real Estate Ventures [Member]
Property Subject to or Available for Operating Lease [Line Items]
Equity method investment percentage						0.00%		0.00%			0.00%			0.00%
Real estate ventures aggregate indebtedness to third parties						$ 768,912,000		$ 768,912,000
Unconsolidated Real Estate Ventures [Member] | Minimum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Equity method investment percentage						20.00%		20.00%			20.00%			20.00%
Unconsolidated Real Estate Ventures [Member] | Maximum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Equity method investment percentage						70.00%		70.00%			70.00%			70.00%
PJP VII [Member]
Property Subject to or Available for Operating Lease [Line Items]
Equity method investment percentage	[1]					25.00%		25.00%
Real estate ventures aggregate indebtedness to third parties						$ 4,792,000		$ 4,792,000			$ 4,956,000
Guarantees, maximum exposure amount						400,000		400,000
Mortgage Lenders [Member]
Property Subject to or Available for Operating Lease [Line Items]
Associated letter of credit						$ 0		$ 0
[1]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.

Commitments and Contingencies -

Commitments and Contingencies - Minimum Future Rental Payments on Non-cancelable Leases (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments And Contingencies Disclosure [Abstract]
2,018	$ 1,211
2,019	1,211
2,020	1,211
2,021	1,211
2,022	1,211
Thereafter	56,318
Total	$ 62,373

Subsequent Events (Textual) (De

Subsequent Events (Textual) (Details) $ in Thousands		Jan. 10, 2018USD ($)aproperty	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Jan. 05, 2018USD ($)ft²
Subsequent Event [Line Items]
Cash proceeds after the payment of share of the debt and closing costs			$ 145,416	$ 21,022	$ 6,100
Four Tower Bridge [Member]
Subsequent Event [Line Items]
Ownership percentage	[1],[2]		65.00%
Seven Tower Bridge [Member]
Subsequent Event [Line Items]
Ownership percentage	[1],[2]		20.00%
Subsequent Event [Member] | Evo at Cira Disposition [Member]
Subsequent Event [Line Items]
Sale of ownership interest percentage		50.00%
Gross sales price		$ 197,500
Number of property units sold | property		345
Cash proceeds after the payment of share of the debt and closing costs		$ 43,000
Subsequent Event [Member] | Philadelphia [Member] | Pennsylvania [Member] | Evo at Cira Disposition [Member]
Subsequent Event [Line Items]
Principal balance of secured loan		110,900
Subsequent Event [Member] | Durham, North Carolina [Member] | Westpark Land [Member]
Subsequent Event [Line Items]
Gross sales price		$ 500
Acreage of land | a		13.1
Subsequent Event [Member] | Four Tower Bridge [Member]
Subsequent Event [Line Items]
Ownership percentage						35.00%
Subsequent Event [Member] | Four Tower Bridge [Member] | Conshohocken [Member] | Pennsylvania [Member]
Subsequent Event [Line Items]
Area of Real Estate Property | ft²						86,021
Real estate property debt						$ 9,700
Subsequent Event [Member] | Seven Tower Bridge [Member]
Subsequent Event [Line Items]
Sale of ownership interest percentage						20.00%
[1]	Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.
[2]	Subsequent to December 31, 2017, the Company exchanged its 20% interest in Seven Tower Bridge to acquire the remaining 35% interest in Four Tower Bridge. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.

Summary of Quarterly Results (D

Summary of Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information [Line Items]
Total revenue	$ 133,344	[1]	$ 128,438	$ 127,791	$ 130,920	$ 132,086	$ 129,694	$ 127,181	$ 136,502	$ 520,493	$ 525,463	$ 602,631
Net income (loss)	73,844	[2]	19,046	7,698	21,271	(12,370)	7,884	(1,323)	46,310	121,859	40,501	(30,740)
Net income (loss) allocated to Common Shares/ Partnership Unitholders	$ 73,137		$ 18,803	$ 4,092	$ 19,278	$ (14,058)	$ 6,022	$ (3,105)	$ 44,091	$ 120,850	$ 40,191	$ (30,401)
Basic earnings (loss) per Common Shares/Partnership Unitholders	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Diluted earnings (loss) per Common Share/ Partnership Unitholders	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Quarterly Financial Information [Line Items]
Total revenue	$ 133,344	[1]	$ 128,438	$ 127,791	$ 130,920	$ 132,086	$ 129,694	$ 127,181	$ 136,502	$ 520,493	$ 525,463	$ 602,631
Net income (loss)	73,844	[2]	19,046	7,698	21,271	(12,370)	7,884	(1,323)	46,310	121,859	40,501	(30,740)
Net income (loss) allocated to Common Shares/ Partnership Unitholders	$ 73,758		$ 18,961	$ 4,129	$ 19,442	$ (14,176)	$ 6,074	$ (3,131)	$ 44,478	$ 121,830	$ 40,486	$ (30,737)
Basic earnings (loss) per Common Shares/Partnership Unitholders	$ 0.42		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.66	$ 0.19	$ (0.21)
Diluted earnings (loss) per Common Share/ Partnership Unitholders	$ 0.41		$ 0.11	$ 0.02	$ 0.11	$ (0.08)	$ 0.03	$ (0.02)	$ 0.25	$ 0.65	$ 0.19	$ (0.21)
[1]	The increase in fourth quarter revenues primarily relates to the operating performance of 1900 Market Street in Philadelphia, Pennsylvania and the acquisition of One Drexel Plaza in Philadelphia, Pennsylvania.
[2]	The increase in net income for the fourth quarter primarily relates to the gain of $52.2 million from the disposition of eight office properties by the Austin Venture. For further details, see Note 4, "Investment in Unconsolidated Real Estate Ventures."

Summary of Quarterly Results (P

Summary of Quarterly Results (Parenthetical) (Details) $ in Thousands	Oct. 18, 2017USD ($)property	Oct. 17, 2017property	Dec. 31, 2017USD ($)property	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions				$ 80,526	$ 20,000	$ 7,229
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions				$ 80,526	$ 20,000	$ 7,229
Austin Joint Venture [Member]
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions	$ 40,092		$ 52,200
Number of Properties Sold | property	8	7	8
Austin Joint Venture [Member] | BRANDYWINE OPERATING PARTNERSHIP, L.P.
Quarterly Financial Information [Line Items]
Net gain on Real Estate Venture transactions			$ 52,200
Number of Properties Sold | property			8

Schedule II - Valuation and 124

Schedule II - Valuation and Qualifying Accounts (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Valuation Allowances and Reserves, Balance at Beginning of Period	$ 16,116	$ 16,178	$ 15,347
Valuation Allowances and Reserves, Additions	1,912	2,207	2,640
Valuation Allowances and Reserves, Deductions	916	2,269	1,809
Valuation Allowances and Reserves, Balance at End of Period	$ 17,112	$ 16,116	$ 16,178

Schedule III - Real Estate a125

Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 320,107
Initial Cost [Abstract]
Land	449,911
Buildings and Improvements	2,815,831
Net Improvements (Retirements) Since Acquisition	566,606
Carrying Amount at Which Carried [Abstract]
Land	492,197
Buildings and Improvements	3,340,151
Total	3,832,348	$ 3,659,886	$ 4,487,588	$ 4,631,128
Accumulated Depreciation at December 31, 2017	895,091	$ 885,392	$ 1,080,616	$ 1,078,996
PENNSYLVANIA SUBURBS [Member] | 400 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	0
Initial Cost [Abstract]
Land	2,657
Buildings and Improvements	4,462
Net Improvements (Retirements) Since Acquisition	12,982
Carrying Amount at Which Carried [Abstract]
Land	2,657
Buildings and Improvements	17,444
Total	20,101
Accumulated Depreciation at December 31, 2017	$ 7,366
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	1,999
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 300 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,206
Buildings and Improvements	13,422
Net Improvements (Retirements) Since Acquisition	3,119
Carrying Amount at Which Carried [Abstract]
Land	2,206
Buildings and Improvements	16,541
Total	18,747
Accumulated Depreciation at December 31, 2017	$ 9,112
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1050 Westlakes Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,611
Buildings and Improvements	10,445
Net Improvements (Retirements) Since Acquisition	2,511
Carrying Amount at Which Carried [Abstract]
Land	2,611
Buildings and Improvements	12,956
Total	15,567
Accumulated Depreciation at December 31, 2017	$ 5,622
Real Estate And Accumulated Depreciation Construction Year	1,984
Real Estate And Accumulated Depreciation Year Of Acquisition	1,999
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1200 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,595
Buildings and Improvements	11,809
Net Improvements (Retirements) Since Acquisition	3,439
Carrying Amount at Which Carried [Abstract]
Land	2,595
Buildings and Improvements	15,248
Total	17,843
Accumulated Depreciation at December 31, 2017	$ 8,739
Real Estate And Accumulated Depreciation Construction Year	1,994
Real Estate And Accumulated Depreciation Year Of Acquisition	2,001
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 200 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,533
Buildings and Improvements	9,460
Net Improvements (Retirements) Since Acquisition	2,042
Carrying Amount at Which Carried [Abstract]
Land	1,533
Buildings and Improvements	11,502
Total	13,035
Accumulated Depreciation at December 31, 2017	$ 6,235
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1180 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,086
Buildings and Improvements	8,342
Net Improvements (Retirements) Since Acquisition	3,110
Carrying Amount at Which Carried [Abstract]
Land	2,086
Buildings and Improvements	11,452
Total	13,538
Accumulated Depreciation at December 31, 2017	$ 4,962
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	2,001
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 100 Berwyn Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,180
Buildings and Improvements	7,290
Net Improvements (Retirements) Since Acquisition	1,404
Carrying Amount at Which Carried [Abstract]
Land	1,180
Buildings and Improvements	8,694
Total	9,874
Accumulated Depreciation at December 31, 2017	$ 4,643
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1160 Swedesford Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,781
Buildings and Improvements	7,124
Net Improvements (Retirements) Since Acquisition	6,635
Carrying Amount at Which Carried [Abstract]
Land	2,045
Buildings and Improvements	13,495
Total	15,540
Accumulated Depreciation at December 31, 2017	$ 5,036
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	2,001
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1100 Cassett Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,695
Buildings and Improvements	6,779
Net Improvements (Retirements) Since Acquisition	1,271
Carrying Amount at Which Carried [Abstract]
Land	1,695
Buildings and Improvements	8,050
Total	9,745
Accumulated Depreciation at December 31, 2017	$ 3,419
Real Estate And Accumulated Depreciation Construction Year	1,997
Real Estate And Accumulated Depreciation Year Of Acquisition	2,001
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | Six Tower Bridge (181 Washington Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,927
Buildings and Improvements	14,722
Net Improvements (Retirements) Since Acquisition	1,762
Carrying Amount at Which Carried [Abstract]
Land	6,237
Buildings and Improvements	17,174
Total	23,411
Accumulated Depreciation at December 31, 2017	$ 2,623
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,013
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 52 Swedesford Square [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,241
Buildings and Improvements	16,579
Net Improvements (Retirements) Since Acquisition	5,340
Carrying Amount at Which Carried [Abstract]
Land	4,241
Buildings and Improvements	21,919
Total	26,160
Accumulated Depreciation at December 31, 2017	$ 9,736
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 640 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,222
Buildings and Improvements	16,891
Net Improvements (Retirements) Since Acquisition	3,934
Carrying Amount at Which Carried [Abstract]
Land	4,222
Buildings and Improvements	20,825
Total	25,047
Accumulated Depreciation at December 31, 2017	$ 10,685
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 620 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,770
Buildings and Improvements	11,014
Net Improvements (Retirements) Since Acquisition	1,444
Carrying Amount at Which Carried [Abstract]
Land	2,770
Buildings and Improvements	12,458
Total	15,228
Accumulated Depreciation at December 31, 2017	$ 6,595
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1000 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,772
Buildings and Improvements	10,936
Net Improvements (Retirements) Since Acquisition	3,670
Carrying Amount at Which Carried [Abstract]
Land	2,772
Buildings and Improvements	14,606
Total	17,378
Accumulated Depreciation at December 31, 2017	$ 6,600
Real Estate And Accumulated Depreciation Construction Year	1,980
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1060 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,712
Buildings and Improvements	10,953
Net Improvements (Retirements) Since Acquisition	4,289
Carrying Amount at Which Carried [Abstract]
Land	2,712
Buildings and Improvements	15,242
Total	17,954
Accumulated Depreciation at December 31, 2017	$ 7,384
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 630 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,773
Buildings and Improvements	11,144
Net Improvements (Retirements) Since Acquisition	3,340
Carrying Amount at Which Carried [Abstract]
Land	2,773
Buildings and Improvements	14,484
Total	17,257
Accumulated Depreciation at December 31, 2017	$ 6,850
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1020 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,168
Buildings and Improvements	8,576
Net Improvements (Retirements) Since Acquisition	3,939
Carrying Amount at Which Carried [Abstract]
Land	2,168
Buildings and Improvements	12,515
Total	14,683
Accumulated Depreciation at December 31, 2017	$ 5,513
Real Estate And Accumulated Depreciation Construction Year	1,984
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1040 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,860
Buildings and Improvements	11,282
Net Improvements (Retirements) Since Acquisition	5,037
Carrying Amount at Which Carried [Abstract]
Land	2,860
Buildings and Improvements	16,319
Total	19,179
Accumulated Depreciation at December 31, 2017	$ 7,320
Real Estate And Accumulated Depreciation Construction Year	1,985
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 610 Freedom Business Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,017
Buildings and Improvements	8,070
Net Improvements (Retirements) Since Acquisition	2,895
Carrying Amount at Which Carried [Abstract]
Land	2,017
Buildings and Improvements	10,965
Total	12,982
Accumulated Depreciation at December 31, 2017	$ 5,199
Real Estate And Accumulated Depreciation Construction Year	1,985
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 650 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,916
Buildings and Improvements	4,378
Net Improvements (Retirements) Since Acquisition	1,569
Carrying Amount at Which Carried [Abstract]
Land	1,916
Buildings and Improvements	5,947
Total	7,863
Accumulated Depreciation at December 31, 2017	$ 3,401
Real Estate And Accumulated Depreciation Construction Year	1,968
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 600 Park Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,012
Buildings and Improvements	4,048
Net Improvements (Retirements) Since Acquisition	385
Carrying Amount at Which Carried [Abstract]
Land	1,012
Buildings and Improvements	4,433
Total	5,445
Accumulated Depreciation at December 31, 2017	$ 2,406
Real Estate And Accumulated Depreciation Construction Year	1,964
Real Estate And Accumulated Depreciation Year Of Acquisition	1,998
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 933 First Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,127
Buildings and Improvements	20,794
Net Improvements (Retirements) Since Acquisition	(1,301)
Carrying Amount at Which Carried [Abstract]
Land	3,127
Buildings and Improvements	19,493
Total	22,620
Accumulated Depreciation at December 31, 2017	$ 482
Real Estate And Accumulated Depreciation Construction Year	2,017
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 401 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,199
Buildings and Improvements	16,131
Net Improvements (Retirements) Since Acquisition	16,905
Carrying Amount at Which Carried [Abstract]
Land	6,199
Buildings and Improvements	33,036
Total	39,235
Accumulated Depreciation at December 31, 2017	$ 13,795
Real Estate And Accumulated Depreciation Construction Year	2,001
Real Estate And Accumulated Depreciation Year Of Acquisition	2,000
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | Metroplex (4000 Chemical Road) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,373
Buildings and Improvements	24,546
Net Improvements (Retirements) Since Acquisition	679
Carrying Amount at Which Carried [Abstract]
Land	4,373
Buildings and Improvements	25,225
Total	29,598
Accumulated Depreciation at December 31, 2017	$ 6,437
Real Estate And Accumulated Depreciation Construction Year	2,007
Real Estate And Accumulated Depreciation Year Of Acquisition	2,001
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 610 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,651
Buildings and Improvements	14,514
Net Improvements (Retirements) Since Acquisition	3,172
Carrying Amount at Which Carried [Abstract]
Land	3,651
Buildings and Improvements	17,686
Total	21,337
Accumulated Depreciation at December 31, 2017	$ 7,309
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	2,002
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 600 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,652
Buildings and Improvements	15,288
Net Improvements (Retirements) Since Acquisition	2,251
Carrying Amount at Which Carried [Abstract]
Land	3,652
Buildings and Improvements	17,539
Total	21,191
Accumulated Depreciation at December 31, 2017	$ 6,877
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	2,002
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 630 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,558
Buildings and Improvements	14,743
Net Improvements (Retirements) Since Acquisition	2,172
Carrying Amount at Which Carried [Abstract]
Land	3,558
Buildings and Improvements	16,915
Total	20,473
Accumulated Depreciation at December 31, 2017	$ 6,645
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	2,002
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 620 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,572
Buildings and Improvements	14,435
Net Improvements (Retirements) Since Acquisition	1,199
Carrying Amount at Which Carried [Abstract]
Land	3,572
Buildings and Improvements	15,634
Total	19,206
Accumulated Depreciation at December 31, 2017	$ 6,262
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	2,002
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 660 West Germantown Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,694
Buildings and Improvements	5,487
Net Improvements (Retirements) Since Acquisition	20,715
Carrying Amount at Which Carried [Abstract]
Land	5,405
Buildings and Improvements	24,491
Total	29,896
Accumulated Depreciation at December 31, 2017	$ 4,429
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	2,012
Depreciable Life (Years)	30 years
PENNSYLVANIA SUBURBS [Member] | 351 Plymouth Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,043
Buildings and Improvements	555
Net Improvements (Retirements) Since Acquisition	0
Carrying Amount at Which Carried [Abstract]
Land	1,043
Buildings and Improvements	555
Total	1,598
Accumulated Depreciation at December 31, 2017	$ 177
Real Estate And Accumulated Depreciation Year Of Acquisition	2,000
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 150 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	11,925
Buildings and Improvements	36,986
Net Improvements (Retirements) Since Acquisition	12,659
Carrying Amount at Which Carried [Abstract]
Land	11,897
Buildings and Improvements	49,673
Total	61,570
Accumulated Depreciation at December 31, 2017	$ 21,400
Real Estate And Accumulated Depreciation Construction Year	1,983
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	29 years
PENNSYLVANIA SUBURBS [Member] | One Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,323
Buildings and Improvements	28,613
Net Improvements (Retirements) Since Acquisition	22,440
Carrying Amount at Which Carried [Abstract]
Land	7,323
Buildings and Improvements	51,053
Total	58,376
Accumulated Depreciation at December 31, 2017	$ 26,157
Real Estate And Accumulated Depreciation Construction Year	1,998
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	29 years
PENNSYLVANIA SUBURBS [Member] | 201 King of Prussia Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	8,956
Buildings and Improvements	29,811
Net Improvements (Retirements) Since Acquisition	3,800
Carrying Amount at Which Carried [Abstract]
Land	8,949
Buildings and Improvements	33,618
Total	42,567
Accumulated Depreciation at December 31, 2017	$ 18,855
Real Estate And Accumulated Depreciation Construction Year	2,001
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	25 years
PENNSYLVANIA SUBURBS [Member] | 555 Lancaster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	8,014
Buildings and Improvements	16,508
Net Improvements (Retirements) Since Acquisition	16,861
Carrying Amount at Which Carried [Abstract]
Land	8,609
Buildings and Improvements	32,774
Total	41,383
Accumulated Depreciation at December 31, 2017	$ 15,517
Real Estate And Accumulated Depreciation Construction Year	1,973
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	24 years
PENNSYLVANIA SUBURBS [Member] | Four Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	5,406
Buildings and Improvements	21,390
Net Improvements (Retirements) Since Acquisition	12,190
Carrying Amount at Which Carried [Abstract]
Land	5,705
Buildings and Improvements	33,281
Total	38,986
Accumulated Depreciation at December 31, 2017	$ 13,192
Real Estate And Accumulated Depreciation Construction Year	1,995
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	30 years
PENNSYLVANIA SUBURBS [Member] | Five Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,506
Buildings and Improvements	25,525
Net Improvements (Retirements) Since Acquisition	4,373
Carrying Amount at Which Carried [Abstract]
Land	6,578
Buildings and Improvements	29,826
Total	36,404
Accumulated Depreciation at December 31, 2017	$ 10,451
Real Estate And Accumulated Depreciation Construction Year	1,998
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	38 years
PENNSYLVANIA SUBURBS [Member] | Three Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,773
Buildings and Improvements	17,961
Net Improvements (Retirements) Since Acquisition	2,790
Carrying Amount at Which Carried [Abstract]
Land	4,791
Buildings and Improvements	20,733
Total	25,524
Accumulated Depreciation at December 31, 2017	$ 10,342
Real Estate And Accumulated Depreciation Construction Year	1,998
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	29 years
PENNSYLVANIA SUBURBS [Member] | Two Radnor Corporate Center [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,937
Buildings and Improvements	15,484
Net Improvements (Retirements) Since Acquisition	3,440
Carrying Amount at Which Carried [Abstract]
Land	3,942
Buildings and Improvements	18,919
Total	22,861
Accumulated Depreciation at December 31, 2017	$ 8,458
Real Estate And Accumulated Depreciation Construction Year	1,998
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	29 years
PENNSYLVANIA SUBURBS [Member] | 130 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,573
Buildings and Improvements	8,338
Net Improvements (Retirements) Since Acquisition	3,460
Carrying Amount at Which Carried [Abstract]
Land	2,567
Buildings and Improvements	11,804
Total	14,371
Accumulated Depreciation at December 31, 2017	$ 5,948
Real Estate And Accumulated Depreciation Construction Year	1,983
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	25 years
PENNSYLVANIA SUBURBS [Member] | 170 Radnor Chester Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,514
Buildings and Improvements	8,147
Net Improvements (Retirements) Since Acquisition	2,132
Carrying Amount at Which Carried [Abstract]
Land	2,509
Buildings and Improvements	10,284
Total	12,793
Accumulated Depreciation at December 31, 2017	$ 3,739
Real Estate And Accumulated Depreciation Construction Year	1,983
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	25 years
PENNSYLVANIA SUBURBS [Member] | 200 N. Radnor Chester Rd. [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,366
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	3,572
Carrying Amount at Which Carried [Abstract]
Land	3,366
Buildings and Improvements	3,572
Total	6,938
Accumulated Depreciation at December 31, 2017	$ 503
Real Estate And Accumulated Depreciation Construction Year	2,014
Real Estate And Accumulated Depreciation Year Of Acquisition	2,005
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 101 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,251
Buildings and Improvements	25,209
Net Improvements (Retirements) Since Acquisition	2,872
Carrying Amount at Which Carried [Abstract]
Land	6,251
Buildings and Improvements	28,081
Total	34,332
Accumulated Depreciation at December 31, 2017	$ 8,968
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,005
Depreciable Life (Years)	40 years
PENNSYLVANIA SUBURBS [Member] | 1 West Elm Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,557
Buildings and Improvements	14,249
Net Improvements (Retirements) Since Acquisition	3,151
Carrying Amount at Which Carried [Abstract]
Land	3,557
Buildings and Improvements	17,400
Total	20,957
Accumulated Depreciation at December 31, 2017	$ 5,290
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,005
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | Cira Centre (2929 Arch Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	208,570
Net Improvements (Retirements) Since Acquisition	(6,931)
Carrying Amount at Which Carried [Abstract]
Land	12,586
Buildings and Improvements	189,053
Total	201,639
Accumulated Depreciation at December 31, 2017	$ 68,099
Real Estate And Accumulated Depreciation Construction Year	2,005
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | Three Logan Square (1717 Arch Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	98,188
Net Improvements (Retirements) Since Acquisition	61,060
Carrying Amount at Which Carried [Abstract]
Land	25,195
Buildings and Improvements	134,053
Total	159,248
Accumulated Depreciation at December 31, 2017	$ 31,079
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	2,010
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | Two Commerce Square (2001 Market Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 112,000
Initial Cost [Abstract]
Land	15,323
Buildings and Improvements	120,200
Net Improvements (Retirements) Since Acquisition	21,892
Carrying Amount at Which Carried [Abstract]
Land	15,323
Buildings and Improvements	142,092
Total	157,415
Accumulated Depreciation at December 31, 2017	$ 17,086
Real Estate And Accumulated Depreciation Construction Year	1,992
Real Estate And Accumulated Depreciation Year Of Acquisition	2,013
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | One Logan Square (130 North 18th Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	14,496
Buildings and Improvements	107,736
Net Improvements (Retirements) Since Acquisition	28,938
Carrying Amount at Which Carried [Abstract]
Land	14,473
Buildings and Improvements	136,697
Total	151,170
Accumulated Depreciation at December 31, 2017	$ 52,506
Real Estate And Accumulated Depreciation Construction Year	1,998
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	34 years
Philadelphia CBD [Member] | Two Logan Square (100 North 18th Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 84,440
Initial Cost [Abstract]
Land	16,066
Buildings and Improvements	100,255
Net Improvements (Retirements) Since Acquisition	19,733
Carrying Amount at Which Carried [Abstract]
Land	16,066
Buildings and Improvements	119,988
Total	136,054
Accumulated Depreciation at December 31, 2017	$ 42,317
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	36 years
Philadelphia CBD [Member] | One Commerce Square (2005 Market Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 123,667
Initial Cost [Abstract]
Land	15,161
Buildings and Improvements	105,021
Net Improvements (Retirements) Since Acquisition	22,924
Carrying Amount at Which Carried [Abstract]
Land	15,160
Buildings and Improvements	127,946
Total	143,106
Accumulated Depreciation at December 31, 2017	$ 15,828
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	2,013
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | Cira Centre South Garage [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	76,008
Net Improvements (Retirements) Since Acquisition	8,114
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	84,122
Total	84,122
Accumulated Depreciation at December 31, 2017	$ 14,732
Real Estate And Accumulated Depreciation Construction Year	2,010
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | 1900 Market [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,768
Buildings and Improvements	17,263
Net Improvements (Retirements) Since Acquisition	46,556
Carrying Amount at Which Carried [Abstract]
Land	7,768
Buildings and Improvements	63,819
Total	71,587
Accumulated Depreciation at December 31, 2017	$ 7,484
Real Estate And Accumulated Depreciation Construction Year	1,981
Real Estate And Accumulated Depreciation Year Of Acquisition	2,012
Depreciable Life (Years)	30 years
Philadelphia CBD [Member] | 3020 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	21,417
Net Improvements (Retirements) Since Acquisition	7,603
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	29,020
Total	29,020
Accumulated Depreciation at December 31, 2017	$ 7,511
Real Estate And Accumulated Depreciation Construction Year	1,959
Real Estate And Accumulated Depreciation Year Of Acquisition	2,011
Depreciable Life (Years)	26 years
Philadelphia CBD [Member] | The Lift at Juniper Street (101 - 103 Juniper Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	14,401
Net Improvements (Retirements) Since Acquisition	(3,329)
Carrying Amount at Which Carried [Abstract]
Land	478
Buildings and Improvements	10,594
Total	11,072
Accumulated Depreciation at December 31, 2017	$ 2,803
Real Estate And Accumulated Depreciation Construction Year	2,010
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | 618-634 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	13,365
Buildings and Improvements	5,791
Net Improvements (Retirements) Since Acquisition	490
Carrying Amount at Which Carried [Abstract]
Land	13,365
Buildings and Improvements	6,281
Total	19,646
Accumulated Depreciation at December 31, 2017	$ 3,258
Real Estate And Accumulated Depreciation Construction Year	1,966
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	5 years
Philadelphia CBD [Member] | FMC Tower at Cira Centre South (2929 Walnut Street) [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	400,294
Net Improvements (Retirements) Since Acquisition	(7,976)
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	392,318
Total	392,318
Accumulated Depreciation at December 31, 2017	$ 16,218
Real Estate And Accumulated Depreciation Construction Year	2,016
Depreciable Life (Years)	40 years
Philadelphia CBD [Member] | 2100 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	18,827
Buildings and Improvements	0
Net Improvements (Retirements) Since Acquisition	5,494
Carrying Amount at Which Carried [Abstract]
Land	18,854
Buildings and Improvements	5,467
Total	24,321
Accumulated Depreciation at December 31, 2017	$ 121
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Philadelphia CBD [Member] | 3000 Market Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	18,924
Buildings and Improvements	13,080
Net Improvements (Retirements) Since Acquisition	8
Carrying Amount at Which Carried [Abstract]
Land	18,924
Buildings and Improvements	13,088
Total	32,012
Accumulated Depreciation at December 31, 2017	$ 569
Real Estate And Accumulated Depreciation Construction Year	1,937
Real Estate And Accumulated Depreciation Year Of Acquisition	2,017
Depreciable Life (Years)	12 years
Philadelphia CBD [Member] | One Drexel Plaza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	24,377
Net Improvements (Retirements) Since Acquisition	6,206
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	30,583
Total	30,583
Accumulated Depreciation at December 31, 2017	$ 194
Real Estate And Accumulated Depreciation Construction Year	1,953
Real Estate And Accumulated Depreciation Year Of Acquisition	2,017
Depreciable Life (Years)	40 years
Metropolitan DC [Member] | 6600 Rockledge Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	37,421
Net Improvements (Retirements) Since Acquisition	10,841
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	48,262
Total	48,262
Accumulated Depreciation at December 31, 2017	$ 13,299
Real Estate And Accumulated Depreciation Construction Year	1,981
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	50 years
Metropolitan DC [Member] | 2340 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	16,345
Buildings and Improvements	65,379
Net Improvements (Retirements) Since Acquisition	3,710
Carrying Amount at Which Carried [Abstract]
Land	16,129
Buildings and Improvements	69,305
Total	85,434
Accumulated Depreciation at December 31, 2017	$ 21,809
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	40 years
Metropolitan DC [Member] | 2291 Wood Oak Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	8,243
Buildings and Improvements	52,413
Net Improvements (Retirements) Since Acquisition	12,549
Carrying Amount at Which Carried [Abstract]
Land	8,782
Buildings and Improvements	64,423
Total	73,205
Accumulated Depreciation at December 31, 2017	$ 19,549
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	55 years
Metropolitan DC [Member] | 2251 Corporate Park Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	11,472
Buildings and Improvements	45,893
Net Improvements (Retirements) Since Acquisition	3,412
Carrying Amount at Which Carried [Abstract]
Land	11,472
Buildings and Improvements	49,305
Total	60,777
Accumulated Depreciation at December 31, 2017	$ 14,191
Real Estate And Accumulated Depreciation Construction Year	2,000
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	40 years
Metropolitan DC [Member] | 2355 Dulles Corner Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	10,365
Buildings and Improvements	43,876
Net Improvements (Retirements) Since Acquisition	7,299
Carrying Amount at Which Carried [Abstract]
Land	10,365
Buildings and Improvements	51,175
Total	61,540
Accumulated Depreciation at December 31, 2017	$ 16,202
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	40 years
Metropolitan DC [Member] | 2411 Dulles Corner Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,279
Buildings and Improvements	46,340
Net Improvements (Retirements) Since Acquisition	17,626
Carrying Amount at Which Carried [Abstract]
Land	7,417
Buildings and Improvements	63,828
Total	71,245
Accumulated Depreciation at December 31, 2017	$ 16,736
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	50 years
Metropolitan DC [Member] | 13880 Dulles Corner Lane [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,236
Buildings and Improvements	39,213
Net Improvements (Retirements) Since Acquisition	5,904
Carrying Amount at Which Carried [Abstract]
Land	7,373
Buildings and Improvements	44,980
Total	52,353
Accumulated Depreciation at December 31, 2017	$ 11,525
Real Estate And Accumulated Depreciation Construction Year	1,997
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	55 years
Metropolitan DC [Member] | 2121 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	5,598
Buildings and Improvements	38,639
Net Improvements (Retirements) Since Acquisition	3,186
Carrying Amount at Which Carried [Abstract]
Land	5,795
Buildings and Improvements	41,628
Total	47,423
Accumulated Depreciation at December 31, 2017	$ 11,035
Real Estate And Accumulated Depreciation Construction Year	2,000
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	54 years
Metropolitan DC [Member] | 2201 Cooperative Way [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,809
Buildings and Improvements	34,093
Net Improvements (Retirements) Since Acquisition	6,018
Carrying Amount at Which Carried [Abstract]
Land	4,809
Buildings and Improvements	40,111
Total	44,920
Accumulated Depreciation at December 31, 2017	$ 10,205
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	54 years
Metropolitan DC [Member] | 13825 Sunrise Valley Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,794
Buildings and Improvements	19,365
Net Improvements (Retirements) Since Acquisition	1,454
Carrying Amount at Which Carried [Abstract]
Land	3,866
Buildings and Improvements	20,747
Total	24,613
Accumulated Depreciation at December 31, 2017	$ 6,202
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	46 years
Metropolitan DC [Member] | 1676 International Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	18,437
Buildings and Improvements	97,538
Net Improvements (Retirements) Since Acquisition	3,744
Carrying Amount at Which Carried [Abstract]
Land	18,785
Buildings and Improvements	100,934
Total	119,719
Accumulated Depreciation at December 31, 2017	$ 23,545
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	55 years
Metropolitan DC [Member] | 8260 Greensboro Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,952
Buildings and Improvements	33,964
Net Improvements (Retirements) Since Acquisition	3,184
Carrying Amount at Which Carried [Abstract]
Land	8,102
Buildings and Improvements	36,998
Total	45,100
Accumulated Depreciation at December 31, 2017	$ 10,182
Real Estate And Accumulated Depreciation Construction Year	1,980
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	52 years
Metropolitan DC [Member] | 2273 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	5,167
Buildings and Improvements	31,110
Net Improvements (Retirements) Since Acquisition	4,098
Carrying Amount at Which Carried [Abstract]
Land	5,237
Buildings and Improvements	35,138
Total	40,375
Accumulated Depreciation at December 31, 2017	$ 9,332
Real Estate And Accumulated Depreciation Construction Year	1,999
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	45 years
Metropolitan DC [Member] | 2275 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	5,059
Buildings and Improvements	29,668
Net Improvements (Retirements) Since Acquisition	8,093
Carrying Amount at Which Carried [Abstract]
Land	5,154
Buildings and Improvements	37,666
Total	42,820
Accumulated Depreciation at December 31, 2017	$ 10,989
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	45 years
Metropolitan DC [Member] | 2277 Research Boulevard [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,649
Buildings and Improvements	26,952
Net Improvements (Retirements) Since Acquisition	18,867
Carrying Amount at Which Carried [Abstract]
Land	4,733
Buildings and Improvements	45,735
Total	50,468
Accumulated Depreciation at December 31, 2017	$ 12,369
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	45 years
Metropolitan DC [Member] | 1900 Gallows Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	7,797
Buildings and Improvements	47,817
Net Improvements (Retirements) Since Acquisition	12,333
Carrying Amount at Which Carried [Abstract]
Land	7,944
Buildings and Improvements	60,003
Total	67,947
Accumulated Depreciation at December 31, 2017	$ 17,697
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	52 years
Metropolitan DC [Member] | 8521 Leesburg Pike [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	4,316
Buildings and Improvements	30,885
Net Improvements (Retirements) Since Acquisition	6,846
Carrying Amount at Which Carried [Abstract]
Land	4,397
Buildings and Improvements	37,650
Total	42,047
Accumulated Depreciation at December 31, 2017	$ 9,854
Real Estate And Accumulated Depreciation Construction Year	1,984
Real Estate And Accumulated Depreciation Year Of Acquisition	2,006
Depreciable Life (Years)	51 years
Austin, Texas [Member] | 11501 Burnet Road - Building 1 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,755
Buildings and Improvements	22,702
Net Improvements (Retirements) Since Acquisition	130
Carrying Amount at Which Carried [Abstract]
Land	3,755
Buildings and Improvements	22,832
Total	26,587
Accumulated Depreciation at December 31, 2017	$ 1,783
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Building 2 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,732
Buildings and Improvements	16,305
Net Improvements (Retirements) Since Acquisition	1,572
Carrying Amount at Which Carried [Abstract]
Land	2,732
Buildings and Improvements	17,877
Total	20,609
Accumulated Depreciation at December 31, 2017	$ 1,606
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Building 3 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,688
Buildings and Improvements	22,348
Net Improvements (Retirements) Since Acquisition	128
Carrying Amount at Which Carried [Abstract]
Land	3,688
Buildings and Improvements	22,476
Total	26,164
Accumulated Depreciation at December 31, 2017	$ 1,755
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Building 4 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,614
Buildings and Improvements	15,740
Net Improvements (Retirements) Since Acquisition	90
Carrying Amount at Which Carried [Abstract]
Land	2,614
Buildings and Improvements	15,830
Total	18,444
Accumulated Depreciation at December 31, 2017	$ 1,236
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Building 5 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	3,689
Buildings and Improvements	22,354
Net Improvements (Retirements) Since Acquisition	128
Carrying Amount at Which Carried [Abstract]
Land	3,689
Buildings and Improvements	22,482
Total	26,171
Accumulated Depreciation at December 31, 2017	$ 1,755
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Building 6 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,676
Buildings and Improvements	15,972
Net Improvements (Retirements) Since Acquisition	(1,835)
Carrying Amount at Which Carried [Abstract]
Land	2,676
Buildings and Improvements	14,137
Total	16,813
Accumulated Depreciation at December 31, 2017	$ 121
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	40 years
Austin, Texas [Member] | 11501 Burnet Road - Building 8 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	1,400
Buildings and Improvements	7,422
Net Improvements (Retirements) Since Acquisition	104
Carrying Amount at Which Carried [Abstract]
Land	1,400
Buildings and Improvements	7,526
Total	8,926
Accumulated Depreciation at December 31, 2017	$ 591
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Austin, Texas [Member] | 11501 Burnet Road - Parking Garage [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	0
Buildings and Improvements	19,826
Net Improvements (Retirements) Since Acquisition	113
Carrying Amount at Which Carried [Abstract]
Land	0
Buildings and Improvements	19,939
Total	19,939
Accumulated Depreciation at December 31, 2017	$ 2,070
Real Estate And Accumulated Depreciation Construction Year	1,991
Real Estate And Accumulated Depreciation Year Of Acquisition	2,015
Depreciable Life (Years)	35 years
Other [Member] | 20 East Clementon Road [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	769
Buildings and Improvements	3,055
Net Improvements (Retirements) Since Acquisition	506
Carrying Amount at Which Carried [Abstract]
Land	719
Buildings and Improvements	3,611
Total	4,330
Accumulated Depreciation at December 31, 2017	$ 1,892
Real Estate And Accumulated Depreciation Construction Year	1,986
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 10 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	244
Buildings and Improvements	971
Net Improvements (Retirements) Since Acquisition	69
Carrying Amount at Which Carried [Abstract]
Land	244
Buildings and Improvements	1,040
Total	1,284
Accumulated Depreciation at December 31, 2017	$ 571
Real Estate And Accumulated Depreciation Construction Year	1,983
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 7 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	231
Buildings and Improvements	921
Net Improvements (Retirements) Since Acquisition	17
Carrying Amount at Which Carried [Abstract]
Land	231
Buildings and Improvements	938
Total	1,169
Accumulated Depreciation at December 31, 2017	$ 501
Real Estate And Accumulated Depreciation Construction Year	1,983
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 2 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	185
Buildings and Improvements	730
Net Improvements (Retirements) Since Acquisition	11
Carrying Amount at Which Carried [Abstract]
Land	185
Buildings and Improvements	741
Total	926
Accumulated Depreciation at December 31, 2017	$ 741
Real Estate And Accumulated Depreciation Construction Year	1,974
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 4 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	183
Buildings and Improvements	726
Net Improvements (Retirements) Since Acquisition	6
Carrying Amount at Which Carried [Abstract]
Land	183
Buildings and Improvements	732
Total	915
Accumulated Depreciation at December 31, 2017	$ 732
Real Estate And Accumulated Depreciation Construction Year	1,974
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 1 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	93
Buildings and Improvements	364
Net Improvements (Retirements) Since Acquisition	8
Carrying Amount at Which Carried [Abstract]
Land	93
Buildings and Improvements	372
Total	465
Accumulated Depreciation at December 31, 2017	$ 372
Real Estate And Accumulated Depreciation Construction Year	1,972
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 5 U.S. Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	21
Buildings and Improvements	81
Net Improvements (Retirements) Since Acquisition	2
Carrying Amount at Which Carried [Abstract]
Land	21
Buildings and Improvements	83
Total	104
Accumulated Depreciation at December 31, 2017	$ 45
Real Estate And Accumulated Depreciation Construction Year	1,987
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 5 Foster Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	9
Buildings and Improvements	32
Net Improvements (Retirements) Since Acquisition	26
Carrying Amount at Which Carried [Abstract]
Land	9
Buildings and Improvements	58
Total	67
Accumulated Depreciation at December 31, 2017	$ 33
Real Estate And Accumulated Depreciation Construction Year	1,968
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | Main Street-Plaza 1000 [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	2,732
Buildings and Improvements	10,942
Net Improvements (Retirements) Since Acquisition	376
Carrying Amount at Which Carried [Abstract]
Land	2,732
Buildings and Improvements	11,318
Total	14,050
Accumulated Depreciation at December 31, 2017	$ 11,037
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | Main Street-Piazza [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	696
Buildings and Improvements	2,802
Net Improvements (Retirements) Since Acquisition	3,446
Carrying Amount at Which Carried [Abstract]
Land	700
Buildings and Improvements	6,244
Total	6,944
Accumulated Depreciation at December 31, 2017	$ 2,741
Real Estate And Accumulated Depreciation Construction Year	1,990
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | Main Street-Promenade [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	532
Buildings and Improvements	2,052
Net Improvements (Retirements) Since Acquisition	404
Carrying Amount at Which Carried [Abstract]
Land	532
Buildings and Improvements	2,456
Total	2,988
Accumulated Depreciation at December 31, 2017	$ 1,357
Real Estate And Accumulated Depreciation Construction Year	1,988
Real Estate And Accumulated Depreciation Year Of Acquisition	1,997
Depreciable Life (Years)	40 years
Other [Member] | 920 North King Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,141
Buildings and Improvements	21,140
Net Improvements (Retirements) Since Acquisition	5,003
Carrying Amount at Which Carried [Abstract]
Land	6,141
Buildings and Improvements	26,143
Total	32,284
Accumulated Depreciation at December 31, 2017	$ 10,185
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	30 years
Other [Member] | 300 Delaware Avenue [Member]
Real Estate and Accumulated Depreciation [Line Items]
Encumbrances	$ 0
Initial Cost [Abstract]
Land	6,369
Buildings and Improvements	13,739
Net Improvements (Retirements) Since Acquisition	2,708
Carrying Amount at Which Carried [Abstract]
Land	6,369
Buildings and Improvements	16,447
Total	22,816
Accumulated Depreciation at December 31, 2017	$ 8,762
Real Estate And Accumulated Depreciation Construction Year	1,989
Real Estate And Accumulated Depreciation Year Of Acquisition	2,004
Depreciable Life (Years)	23 years

Schedule III - Real Estate a126

Schedule III - Real Estate and Accumulated Depreciation (Reconciliation of Real Estate Investments and Accumulated Depreciation) (Parentheticals) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at the Beginning of the Year		$ 3,659,886	$ 4,487,588		$ 4,631,128
Additions:
Acquisitions		62,586	0		182,381
Capital expenditures and assets placed into service		356,857	213,996		165,941
Less:
Dispositions/impairments/placed into redevelopment		(189,395)	(962,676)		(442,327)
Retirements		(57,586)	(79,022)		(49,535)
Balance at the end of the year		3,832,348	3,659,886		4,487,588
Assets held for sale	[1]	0	(73,591)	[2]	(794,588)
Operating properties		3,832,348	3,586,295		3,693,000
Tax Basis of Assets, Cost for Income Tax Purposes		3,100,000	3,000,000
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the beginning of the year		885,392	1,080,616		1,078,996
Real Estate Accumulated Depreciation Additions [Abstract]
Depreciation expense		135,823	131,859		159,080
Real Estate Accumulated Depreciation Less Dispositions [Abstract]
Dispositions/impairments/placed into redevelopment		(74,178)	(250,110)		(109,243)
Retirements		(51,946)	(76,973)		(48,217)
Balance at the end of the year		895,091	885,392		1,080,616
Assets held for sale		0	(32,916)		(213,581)
Real Estate Investment Property, Accumulated Depreciation		895,091	852,476
Accumulated Depreciation, including HFS [Member]
Real Estate Accumulated Depreciation Less Dispositions [Abstract]
Real Estate Investment Property, Accumulated Depreciation		$ 895,091	$ 852,476		$ 867,035
[1]	As of December 31, 2015, the Och-Ziff Portfolio and Cira Square were held for sale. As of December 31, 2016, the Concord Airport Plaza located in the Other segment and the Calverton portfolio located in the Metropolitan Washington, D.C. segment was held for sale. See Note 3, “Real Estate Investments,” for further information.
[2]	Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation, land held for development or other assets on the balance sheets of the properties held for sale. See 2016 Held for Sale section below.