COPT Defense Properties (CDP) 10-Q 27 Oct 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 20, 2017
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES TRUST
Entity Central Index Key	860,546
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		99,609,634
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Corporate Office Properties, L.P.
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES, L.P.
Entity Central Index Key	1,577,966
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Properties, net:
Operating properties, net	$ 2,690,712	$ 2,671,831
Projects in development or held for future development	406,319	401,531
Total properties, net	3,097,031	3,073,362
Assets held for sale, net	74,415	94,654
Cash and cash equivalents	10,858	209,863
Restricted cash and marketable securities	6,173	8,193
Investment in unconsolidated real estate joint venture	25,194	25,548
Accounts receivable (net of allowance for doubtful accounts of $639 and $603, respectively)	27,624	34,438
Deferred rent receivable (net of allowance of $255 and $373, respectively)	84,743	90,219
Intangible assets on real estate acquisitions, net	64,055	78,351
Deferred leasing costs (net of accumulated amortization of $28,590 and $65,988, respectively)	47,033	41,214
Investing receivables	56,108	52,279
Prepaid expenses and other assets, net	66,538	72,764
Total assets	3,559,772	3,780,885
Liabilities:
Debt, net	1,873,291	1,904,001
Accounts payable and accrued expenses	121,483	108,682
Rents received in advance and security deposits	26,223	29,798
Dividends and distributions payable	28,462	31,335
Deferred revenue associated with operating leases	12,047	12,666
Redeemable preferred shares/units	0	26,583
Capital lease obligation	16,347	0
Other liabilities	43,866	50,177
Total liabilities	2,121,719	2,163,242
Commitments and contingencies (Note 15)
Redeemable noncontrolling interests	23,269	22,979
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Shares of beneficial interest at liquidation preference ($0.01 par value; 25,000,000 shares authorized, 6,900,000 shares issued and outstanding at December 31, 2016 and none at September 30, 2017)	0	172,500
Common Shares of beneficial interest	996	985
Additional paid-in capital	2,150,067	2,116,581
Cumulative distributions in excess of net income	(800,290)	(765,276)
Accumulated other comprehensive loss	(859)	(1,731)
Total Corporate Office Properties Trust’s shareholders’ equity	1,349,914	1,523,059
Noncontrolling interests in subsidiaries:
Common units in COPLP	44,089	49,228
Preferred units in COPLP	8,800	8,800
Other consolidated entities	11,981	13,577
Noncontrolling interests in subsidiaries	64,870	71,605
Total equity	1,414,784	1,594,664
Total liabilities, redeemable noncontrolling interest and equity	3,559,772	3,780,885
Corporate Office Properties, L.P.
Properties, net:
Operating properties, net	2,690,712	2,671,831
Projects in development or held for future development	406,319	401,531
Total properties, net	3,097,031	3,073,362
Assets held for sale, net	74,415	94,654
Cash and cash equivalents	10,858	209,863
Restricted cash and marketable securities	1,766	2,756
Investment in unconsolidated real estate joint venture	25,194	25,548
Accounts receivable (net of allowance for doubtful accounts of $639 and $603, respectively)	27,624	34,438
Deferred rent receivable (net of allowance of $255 and $373, respectively)	84,743	90,219
Intangible assets on real estate acquisitions, net	64,055	78,351
Deferred leasing costs (net of accumulated amortization of $28,590 and $65,988, respectively)	47,033	41,214
Investing receivables	56,108	52,279
Prepaid expenses and other assets, net	66,538	72,764
Total assets	3,555,365	3,775,448
Liabilities:
Debt, net	1,873,291	1,904,001
Accounts payable and accrued expenses	121,483	108,682
Rents received in advance and security deposits	26,223	29,798
Dividends and distributions payable	28,462	31,335
Deferred revenue associated with operating leases	12,047	12,666
Redeemable preferred shares/units	0	26,583
Capital lease obligation	16,347	0
Other liabilities	39,459	44,740
Total liabilities	2,117,312	2,157,805
Commitments and contingencies (Note 15)
Redeemable noncontrolling interests	23,269	22,979
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest	1,394,911	1,401,597
Accumulated other comprehensive loss	(952)	(1,854)
Total Corporate Office Properties Trust’s shareholders’ equity	1,402,759	1,581,043
Noncontrolling interests in subsidiaries:
Noncontrolling interests in subsidiaries	12,025	13,621
Total equity	1,414,784	1,594,664
Total liabilities, redeemable noncontrolling interest and equity	3,555,365	3,775,448
General Partner | Corporate Office Properties, L.P.
Corporate Office Properties Trust’s shareholders’ equity:
Preferred partners' capital accounts	0	172,500
Limited Partner | Corporate Office Properties, L.P.
Corporate Office Properties Trust’s shareholders’ equity:
Preferred partners' capital accounts	$ 8,800	$ 8,800

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Allowance for doubtful accounts - AR	$ 639	$ 603
Deferred rent receivable	255	373
Deferred leasing costs, accumulated amortization	$ 28,590	$ 65,988
Preferred Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Shares of beneficial interest, shares authorized	25,000,000	25,000,000
Preferred Shares of beneficial interest, shares issued	0	6,900,000
Preferred Shares of beneficial interest, shares outstanding	0	6,900,000
Common Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Common Shares of beneficial interest, shares authorized	125,000,000	125,000,000
Common Shares of beneficial interest, shares issued	99,608,170	98,498,651
Common Shares of beneficial interest, shares outstanding	99,608,170	98,498,651
Redeemable Preferred Stock Liability Portion
Redeemable preferred units of general partner outstanding, in units	0	531,667
Preferred Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Corporate Office Properties, L.P.
Allowance for doubtful accounts - AR	$ 639	$ 603
Deferred rent receivable	255	373
Deferred leasing costs, accumulated amortization	$ 28,590	$ 65,988
Corporate Office Properties, L.P. | Redeemable Preferred Stock Liability Portion
Redeemable preferred units of general partner outstanding, in units	0	531,667
Corporate Office Properties, L.P. | General Partner
Common Shares of beneficial interest, shares outstanding	99,608,170	98,498,651
Preferred Units, Outstanding	0	6,900,000
Corporate Office Properties, L.P. | Limited Partner
Common Shares of beneficial interest, shares outstanding	3,253,391	3,590,391
Preferred Units, Outstanding	352,000	352,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues
Rental revenue	$ 102,275	$ 103,956	$ 304,237	$ 316,862
Tenant recoveries and other real estate operations revenue	24,956	26,998	78,058	81,103
Construction contract and other service revenues	29,786	11,149	65,958	34,372
Total revenues	157,017	142,103	448,253	432,337
Expenses
Property operating expenses	46,368	49,952	143,515	149,968
Depreciation and amortization associated with real estate operations	34,438	32,015	100,290	99,790
Construction contract and other service expenses	28,788	10,341	63,589	32,513
Impairment (recoveries) losses	(161)	27,699	1,464	99,837
General, administrative and leasing expenses	7,368	8,855	23,838	28,764
Business development expenses and land carry costs	1,277	1,716	4,567	6,497
Total operating expenses	118,078	130,578	337,263	417,369
Operating income	38,939	11,525	110,990	14,968
Interest expense	(19,615)	(18,301)	(57,772)	(64,499)
Interest and other income	1,508	1,391	4,817	3,877
Loss on early extinguishment of debt	0	(59)	(513)	(37)
Income (loss) before equity in income of unconsolidated entities and income taxes	20,832	(5,444)	57,522	(45,691)
Equity in income of unconsolidated entities	719	594	2,162	614
Income tax (expense) benefit	(57)	21	(145)	28
Income (loss) before gain on sales of real estate	21,494	(4,829)	59,539	(45,049)
Gain on sales of real estate	1,188	34,101	5,438	34,101
Net income (loss)	22,682	29,272	64,977	(10,948)
Net (income) loss attributable to noncontrolling interests:
Common units in COPLP	(704)	(901)	(1,611)	948
Preferred units in COPLP	(165)	(165)	(495)	(495)
Other consolidated entities	(897)	(907)	(2,738)	(2,799)
Net income (loss) attributable to COPT	20,916	27,299	60,133	(13,294)
Preferred share/unit dividends/distributions	0	(3,552)	(6,219)	(10,657)
Issuance costs associated with redeemed preferred shares	0	0	(6,847)	0
Net income (loss) attributable to COPT common shareholders	$ 20,916	$ 23,747	$ 47,067	$ (23,951)
Earnings per common share:
Net income (loss) attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)
Net income (loss) attributable to COPT common shareholders - diluted (in dollars per share/unit)	0.21	0.25	0.47	(0.26)
Dividends declared per common share/unit (in dollars per share)	$ 0.2750	$ 0.275	$ 0.825	$ 0.825
Corporate Office Properties, L.P.
Revenues
Rental revenue	$ 102,275	$ 103,956	$ 304,237	$ 316,862
Tenant recoveries and other real estate operations revenue	24,956	26,998	78,058	81,103
Construction contract and other service revenues	29,786	11,149	65,958	34,372
Total revenues	157,017	142,103	448,253	432,337
Expenses
Property operating expenses	46,368	49,952	143,515	149,968
Depreciation and amortization associated with real estate operations	34,438	32,015	100,290	99,790
Construction contract and other service expenses	28,788	10,341	63,589	32,513
Impairment (recoveries) losses	(161)	27,699	1,464	99,837
General, administrative and leasing expenses	7,368	8,855	23,838	28,764
Business development expenses and land carry costs	1,277	1,716	4,567	6,497
Total operating expenses	118,078	130,578	337,263	417,369
Operating income	38,939	11,525	110,990	14,968
Interest expense	(19,615)	(18,301)	(57,772)	(64,499)
Interest and other income	1,508	1,391	4,817	3,877
Loss on early extinguishment of debt	0	(59)	(513)	(37)
Income (loss) before equity in income of unconsolidated entities and income taxes	20,832	(5,444)	57,522	(45,691)
Equity in income of unconsolidated entities	719	594	2,162	614
Income tax (expense) benefit	(57)	21	(145)	28
Income (loss) before gain on sales of real estate	21,494	(4,829)	59,539	(45,049)
Gain on sales of real estate	1,188	34,101	5,438	34,101
Net income (loss)	22,682	29,272	64,977	(10,948)
Net (income) loss attributable to noncontrolling interests:
Net income attributable to noncontrolling interests in consolidated entities	(897)	(913)	(2,738)	(2,803)
Net income (loss) attributable to COPT	21,785	28,359	62,239	(13,751)
Preferred share/unit dividends/distributions	(165)	(3,717)	(6,714)	(11,152)
Issuance costs associated with redeemed preferred shares	0	0	(6,847)	0
Net income (loss) attributable to COPT common shareholders	$ 21,620	$ 24,642	$ 48,678	$ (24,903)
Earnings per common share:
Net income (loss) attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)
Net income (loss) attributable to COPT common shareholders - diluted (in dollars per share/unit)	0.21	0.25	0.47	(0.26)
Dividends declared per common share/unit (in dollars per share)	$ 0.275	$ 0.275	$ 0.825	$ 0.825

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income (loss)	$ 22,682	$ 29,272	$ 64,977	$ (10,948)
Other comprehensive income (loss)
Unrealized (loss) gain on interest rate derivatives	(301)	407	(1,877)	(16,581)
Loss on interest rate derivatives recognized in interest expense (effective portion)	615	1,043	2,652	2,763
Loss on interest rate derivatives recognized in interest expense (ineffective portion)	0	0	88	0
Equity in other comprehensive income (loss) of equity method investee	0	0	39	(184)
Other comprehensive income (loss)	314	1,450	902	(14,002)
Comprehensive income (loss)	22,996	30,722	65,879	(24,950)
Comprehensive income attributable to noncontrolling interests	(1,776)	(2,025)	(4,874)	(1,820)
Comprehensive income (loss) attributable to COPT	21,220	28,697	61,005	(26,770)
Corporate Office Properties, L.P.
Net income (loss)	22,682	29,272	64,977	(10,948)
Other comprehensive income (loss)
Unrealized (loss) gain on interest rate derivatives	(301)	407	(1,877)	(16,581)
Loss on interest rate derivatives recognized in interest expense (effective portion)	615	1,043	2,652	2,763
Loss on interest rate derivatives recognized in interest expense (ineffective portion)	0	0	88	0
Equity in other comprehensive income (loss) of equity method investee	0	0	39	(184)
Other comprehensive income (loss)	314	1,450	902	(14,002)
Comprehensive income (loss)	22,996	30,722	65,879	(24,950)
Comprehensive income attributable to noncontrolling interests	(897)	(913)	(2,738)	(2,803)
Comprehensive income (loss) attributable to COPT	$ 22,099	$ 29,809	$ 63,141	$ (27,753)

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Additional Paid-in Capital	Cumulative Distributions in Excess of Net Income	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.Common Shares	Corporate Office Properties, L.P.Accumulated Other Comprehensive Income (Loss)	Corporate Office Properties, L.P.Noncontrolling Interests	Corporate Office Properties, L.P.Limited Partner	Corporate Office Properties, L.P.Limited PartnerPreferred Shares	Corporate Office Properties, L.P.General Partner	Corporate Office Properties, L.P.General PartnerPreferred Shares
Balance (COPT: 94,531,512 shares and 98,498,651 shares as of December 31, 2015 and 2016, respectively) at Dec. 31, 2015	$ 1,616,564	$ 199,083	$ 945	$ 2,004,507	$ (657,172)	$ (2,838)	$ 72,039	$ 1,616,564	$ 1,400,745	$ (2,985)	$ 10,921		$ 8,800		$ 199,083
Balance (preferred units) at Dec. 31, 2015													352,000		7,431,667
Balance (in units/shares) at Dec. 31, 2015	94,531,512								98,208,903
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 87,000 and 337,000 shares as for the nine months ended September 30, 2016 and 2017, respectively)	$ 0		1	1,166			(1,167)
Costs associated with common shares issued to the public (in shares)									0
Costs associated with common shares issued to the public	$ (5)			(5)				(5)	$ (5)
Share-based compensation issuance, net of redemptions (in units/shares)	146,274								146,274
Share-based compensation issuance, net of redemptions (COPT: 146,274 and 176,477 shares issued, net of redemptions for the nine months ended September 30, 2016 and 2017, respectively)	$ 6,177		2	6,175				6,177	$ 6,177
Redemption of vested equity awards	(2,179)			(2,179)				(2,179)	(2,179)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(42)			42
Comprehensive income (loss)	(26,629)				(13,294)	(13,476)	141	(26,629)	(24,903)	(14,002)	1,124		$ 495		$ 10,657
Dividends / Distributions to owners of common and preferred units	(88,796)				(88,796)			(92,294)	(81,142)				$ (495)		$ (10,657)
Distributions to owners of common and preferred units in COPLP	(3,498)						(3,498)
Distributions to noncontrolling interests in subsidiaries	(12)						(12)	(12)			(12)
Adjustment to arrive at fair value of redeemable noncontrolling interests	(516)			(516)				(516)	(516)
Tax loss from share-based compensation	$ (319)			(319)				(319)	$ (319)
Balance (in units/shares) at Sep. 30, 2016	94,764,786								98,355,177
Balance (preferred units) at Sep. 30, 2016													352,000		7,431,667
Balance (COPT: 94,764,786 shares and 99,608,170 shares as of September 30, 2016 and 2017, respectively) at Sep. 30, 2016	$ 1,500,787	199,083	948	2,008,787	(759,262)	(16,314)	67,545	1,500,787	$ 1,297,858	(16,987)	12,033		$ 8,800		$ 199,083
Balance (COPT: 94,531,512 shares and 98,498,651 shares as of December 31, 2015 and 2016, respectively) at Dec. 31, 2016	$ 1,594,664	172,500	985	2,116,581	(765,276)	(1,731)	71,605	1,594,664	$ 1,401,597	(1,854)	13,621		$ 8,800		$ 172,500
Balance (preferred units) at Dec. 31, 2016												352,000	352,000	6,900,000	6,900,000
Balance (in units/shares) at Dec. 31, 2016	98,498,651								102,089,042			3,590,391		98,498,651
Increase (Decrease) in Shareholders' Equity
Redemption of preferred shares (6,900,000 shares)	$ (172,500)	$ (172,500)		6,847	(6,847)			(172,500)							$ (172,500)
Redemption of preferred units resulting from redemption of preferred shares (in units/shares)		(6,900,000)													(6,900,000)
Conversion of common units to common shares (COPT: 87,000 and 337,000 shares as for the nine months ended September 30, 2016 and 2017, respectively)	0		3	4,599			(4,602)
Issuance of common units resulting from common shares issued under at-the-market program (in units)									591,042
Issuance of common units resulting from common shares issued under at-the-market program (COPT: 591,042 shares for the nine months ended September 30, 2017)	$ 19,668		6	19,662				19,668	$ 19,668
Issuance of common units resulting from exercise of share options (COPT: 5,000 shares as for the nine months ended September 30, 2017)	5,000								5,000
Issuance of common units resulting from exercise of share options	$ 150			150				150	$ 150
Share-based compensation issuance, net of redemptions (in units/shares)	176,477								176,477
Share-based compensation issuance, net of redemptions (COPT: 146,274 and 176,477 shares issued, net of redemptions for the nine months ended September 30, 2016 and 2017, respectively)	$ 4,444		2	4,442				4,444	$ 4,444
Redemption of vested equity awards	(1,869)			(1,869)				(1,869)	(1,869)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(589)			589
Comprehensive income (loss)	64,159				60,133	872	3,154	64,159	55,525	902	1,018		$ 495		$ 6,219
Dividends / Distributions to owners of common and preferred units	(88,300)				(88,300)			(91,562)	(84,848)				$ (495)		$ (6,219)
Distributions to owners of common and preferred units in COPLP	(3,262)						(3,262)
Distributions to noncontrolling interests in subsidiaries	(2,614)						(2,614)	(2,614)			(2,614)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ 244			244				244	$ 244
Balance (in units/shares) at Sep. 30, 2017	99,608,170								102,861,561			3,253,391		99,608,170
Balance (preferred units) at Sep. 30, 2017												352,000	352,000	0	0
Balance (COPT: 94,764,786 shares and 99,608,170 shares as of September 30, 2016 and 2017, respectively) at Sep. 30, 2017	$ 1,414,784	$ 0	$ 996	$ 2,150,067	$ (800,290)	$ (859)	$ 64,870	$ 1,414,784	$ 1,394,911	$ (952)	$ 12,025		$ 8,800		$ 0

Consolidated Statements of Equ7

Consolidated Statements of Equity (Parenthetical) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Balance (in units/ shares)	99,608,170	94,764,786	98,498,651	94,531,512
Conversion of common units to common shares (in units/shares)	337,000	87,000
Issuance of common units resulting from exercise of share options (in shares or units)	5,000
Share-based compensation issuance, net of redemptions (in units/shares)	176,477	146,274
Common Shares
Issuance of common units resulting from common shares issued under at-the-market program (in units)	591,042
Preferred Shares
Redemption of preferred units resulting from redemption of preferred shares (in units/shares)	6,900,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Revenues from real estate operations received	$ 390,116	$ 393,300
Construction contract and other service revenues received	72,682	54,399
Property operating expenses paid	(144,187)	(154,203)
Construction contract and other service expenses paid	(57,189)	(33,169)
General, administrative, leasing, business development and land carry costs paid	(27,066)	(27,879)
Interest expense paid	(55,637)	(61,662)
Lease incentives	(9,414)	(1,789)
Other	1,373	976
Net cash provided by operating activities	170,678	169,973
Cash flows from investing activities
Construction, development and redevelopment	(113,678)	(121,297)
Tenant improvements on operating properties	(19,876)	(26,055)
Other capital improvements on operating properties	(15,174)	(22,063)
Proceeds from dispositions of properties	101,107	210,661
Proceeds from partial sale of properties, net of related debt	0	43,686
Leasing costs paid	(6,468)	(6,024)
Other	1,359	(991)
Net cash (used in) provided by investing activities	(52,730)	77,917
Proceeds from debt
Revolving Credit Facility	268,000	362,500
Other debt proceeds	0	105,000
Repayments of debt
Revolving Credit Facility	(98,000)	(406,000)
Scheduled principal amortization	(2,878)	(4,454)
Other debt repayments	(200,150)	(203,056)
Deferred financing costs paid	0	(825)
Net proceeds from issuance of common shares/units	19,834	(46)
Redemption of preferred shares/units	(199,083)	0
Common share/unit dividends/distributions paid	(81,779)	(78,072)
Preferred share/unit dividends/distributions paid	(9,305)	(10,657)
Distributions paid to noncontrolling interests in COPLP	(3,371)	(3,476)
Distributions paid to redeemable noncontrolling interests	(7,860)	(14,329)
Redemption of vested equity awards	(1,869)	(2,179)
Other	(492)	(5,032)
Net cash used in financing activities	(316,953)	(260,626)
Net decrease in cash and cash equivalents	(199,005)	(12,736)
Cash and cash equivalents
Beginning of period	209,863	60,310
End of period	10,858	47,574
Reconciliation of net income (loss) to net cash provided by operating activities:
Net income (loss)	64,977	(10,948)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	101,963	101,429
Impairment losses	1,457	99,797
(Gain) loss on interest rate derivatives	(43)	347
Amortization of deferred financing costs and net debt discounts	3,514	4,456
Increase in deferred rent receivable	(545)	(930)
Gain on sales of real estate	(5,438)	(34,101)
Share-based compensation	4,092	5,637
Other	(3,970)	(2,727)
Operating changes in assets and liabilities:
Decrease in accounts receivable	7,498	3,658
Decrease in restricted cash and marketable securities	2,778	18
Decrease (increase) in prepaid expenses and other assets, net	3,190	(19,778)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(5,220)	31,523
Decrease in rents received in advance and security deposits	(3,575)	(8,408)
Net cash provided by operating activities	170,678	169,973
Supplemental schedule of non-cash investing and financing activities:
Increase in accrued capital improvements, leasing and other investing activity costs	17,129	9,963
Increase in property in connection with capital lease obligation	16,127	0
Increase in property and redeemable noncontrolling interests in connection with property contributed in a joint venture	0	22,600
Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interest	0	6,683
Non-cash changes from partial sale of properties, net of debt:
Decrease in properties, net	0	(114,597)
Increase in investment in unconsolidated real estate joint venture	0	25,680
Decrease in debt	0	59,534
Other net decreases in assets and liabilities	0	3,619
Increase (decrease) in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests	774	(13,817)
Equity in other comprehensive income (loss) of an equity method investee	39	(184)
Dividends/distributions payable	28,462	30,225
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	4,602	1,167
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	589	42
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in equity to carry redeemable noncontrolling interest at fair value	(244)	516
Corporate Office Properties, L.P.
Cash flows from operating activities
Revenues from real estate operations received	390,116	393,300
Construction contract and other service revenues received	72,682	54,399
Property operating expenses paid	(144,187)	(154,203)
Construction contract and other service expenses paid	(57,189)	(33,169)
General, administrative, leasing, business development and land carry costs paid	(27,066)	(27,879)
Interest expense paid	(55,637)	(61,662)
Lease incentives	(9,414)	(1,789)
Other	1,373	976
Net cash provided by operating activities	170,678	169,973
Cash flows from investing activities
Construction, development and redevelopment	(113,678)	(121,297)
Tenant improvements on operating properties	(19,876)	(26,055)
Other capital improvements on operating properties	(15,174)	(22,063)
Proceeds from dispositions of properties	101,107	210,661
Proceeds from partial sale of properties, net of related debt	0	43,686
Leasing costs paid	(6,468)	(6,024)
Other	1,359	(991)
Net cash (used in) provided by investing activities	(52,730)	77,917
Proceeds from debt
Revolving Credit Facility	268,000	362,500
Other debt proceeds	0	105,000
Repayments of debt
Revolving Credit Facility	(98,000)	(406,000)
Scheduled principal amortization	(2,878)	(4,454)
Other debt repayments	(200,150)	(203,056)
Deferred financing costs paid	0	(825)
Net proceeds from issuance of common shares/units	19,834	(46)
Redemption of preferred shares/units	(199,083)	0
Common share/unit dividends/distributions paid	(84,655)	(81,053)
Preferred share/unit dividends/distributions paid	(9,800)	(11,152)
Distributions paid to redeemable noncontrolling interests	(7,860)	(14,329)
Redemption of vested equity awards	(1,869)	(2,179)
Other	(492)	(5,032)
Net cash used in financing activities	(316,953)	(260,626)
Net decrease in cash and cash equivalents	(199,005)	(12,736)
Cash and cash equivalents
Beginning of period	209,863	60,310
End of period	10,858	47,574
Reconciliation of net income (loss) to net cash provided by operating activities:
Net income (loss)	64,977	(10,948)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	101,963	101,429
Impairment losses	1,457	99,797
(Gain) loss on interest rate derivatives	(43)	347
Amortization of deferred financing costs and net debt discounts	3,514	4,456
Increase in deferred rent receivable	(545)	(930)
Gain on sales of real estate	(5,438)	(34,101)
Share-based compensation	4,092	5,637
Other	(3,970)	(2,727)
Operating changes in assets and liabilities:
Decrease in accounts receivable	7,498	3,658
Decrease in restricted cash and marketable securities	1,748	(495)
Decrease (increase) in prepaid expenses and other assets, net	3,190	(19,778)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(4,190)	32,036
Decrease in rents received in advance and security deposits	(3,575)	(8,408)
Net cash provided by operating activities	170,678	169,973
Supplemental schedule of non-cash investing and financing activities:
Increase in accrued capital improvements, leasing and other investing activity costs	17,129	9,963
Increase in property in connection with capital lease obligation	16,127	0
Increase in property and redeemable noncontrolling interests in connection with property contributed in a joint venture	0	22,600
Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interest	0	6,683
Non-cash changes from partial sale of properties, net of debt:
Decrease in properties, net	0	(114,597)
Increase in investment in unconsolidated real estate joint venture	0	25,680
Decrease in debt	0	59,534
Other net decreases in assets and liabilities	0	3,619
Increase (decrease) in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests	774	(13,817)
Equity in other comprehensive income (loss) of an equity method investee	39	(184)
Dividends/distributions payable	28,462	30,225
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in equity to carry redeemable noncontrolling interest at fair value	$ (244)	$ 516

Organization

Organization	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Corporate Office Properties Trust (“COPT”) and subsidiaries (collectively, the “Company”) is a fully-integrated and self-managed real estate investment trust (“REIT”). Corporate Office Properties, L.P. (“COPLP”) and subsidiaries (collectively, the “Operating Partnership”) is the entity through which COPT, the sole general partner of COPLP, conducts almost all of its operations and owns almost all of its assets. Unless otherwise expressly stated or the context otherwise requires, “we”, “us” and “our” as used herein refer to each of the Company and the Operating Partnership. We own, manage, lease, develop and selectively acquire office and data center properties. The majority of our portfolio is in locations that support the United States Government and its contractors, most of whom are engaged in national security, defense and information technology (“IT”) related activities servicing what we believe are growing, durable priority missions (“Defense/IT Locations”). We also own a portfolio of office properties located in select urban/urban-like submarkets within our regional footprint with durable Class-A office fundamentals and characteristics, as well as other properties supporting general commercial office tenants (“Regional Office”). As of September 30, 2017 , our properties included the following: • 159 operating office properties totaling 17.4 million square feet, including 15 triple-net leased, single-tenant data center properties. We owned six of these properties through an unconsolidated real estate joint venture; • ten office properties under construction or redevelopment that we estimate will total approximately 1.1 million square feet upon completion, including three triple-net leased, single-tenant data center properties, three partially operational properties and two properties completed but held for future lease to the United States Government; • 984 acres of land we controlled for future development that we believe could be developed into approximately 12.3 million square feet and an additional 152 acres of other land; and • a wholesale data center with a critical load of 19.25 megawatts. COPLP owns real estate directly and through subsidiary partnerships and limited liability companies (“LLCs”). In addition to owning real estate, COPLP also owns subsidiaries that provide real estate services such as property management and construction and development services primarily for our properties but also for third parties. Some of these services are performed by a taxable REIT subsidiary (“TRS”). Equity interests in COPLP are in the form of common and preferred units. As of September 30, 2017 , COPT owned 96.8% of the outstanding COPLP common units (“common units”) and none of the outstanding COPLP preferred units (“preferred units”); the remaining common and preferred units in COPLP were owned by third parties. Common units in COPLP not owned by COPT carry certain redemption rights. The number of common units in COPLP owned by COPT is equivalent to the number of outstanding common shares of beneficial interest (“common shares”) of COPT, and the entitlement of all COPLP common units to quarterly distributions and payments in liquidation is substantially the same as those of COPT common shareholders. Similarly, in the case of any series of preferred units in COPLP held by COPT, there is a series of preferred shares of beneficial interest (“preferred shares”) in COPT that is equivalent in number and carries substantially the same terms as such series of COPLP preferred units. COPT’s common shares are publicly traded on the New York Stock Exchange (“NYSE”) under the ticker symbol “OFC”. Because COPLP is managed by COPT, and COPT conducts substantially all of its operations through COPLP, we refer to COPT’s executive officers as COPLP’s executive officers, and although, as a partnership, COPLP does not have a board of trustees, we refer to COPT’s Board of Trustees as COPLP’s Board of Trustees.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The COPT consolidated financial statements include the accounts of COPT, the Operating Partnership, their subsidiaries and other entities in which COPT has a majority voting interest and control. The COPLP consolidated financial statements include the accounts of COPLP, its subsidiaries and other entities in which COPLP has a majority voting interest and control. We also consolidate certain entities when control of such entities can be achieved through means other than voting rights (“variable interest entities” or “VIEs”) if we are deemed to be the primary beneficiary of such entities. We eliminate all intercompany balances and transactions in consolidation. We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity. We use the cost method of accounting when we own an interest in an entity and cannot exert significant influence over its operations. These interim financial statements should be read together with the consolidated financial statements and notes thereto as of and for the year ended December 31, 2016 included in our 2016 Annual Report on Form 10-K. The unaudited consolidated financial statements include all adjustments that are necessary, in the opinion of management, to fairly state our financial position and results of operations. All adjustments are of a normal recurring nature. The consolidated financial statements have been prepared using the accounting policies described in our 2016 Annual Report on Form 10-K. Reclassification We reclassified certain amounts from prior periods to conform to the current period presentation of our consolidated financial statements with no effect on previously reported net income or equity. Recent Accounting Pronouncements We adopted guidance issued by the Financial Accounting Standards Board (“FASB”) effective January 1, 2017 intended to simplify various aspects related to the accounting and presentation for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the consolidated statement of cash flows. In connection with our adoption of this policy, we made an entity-wide accounting policy election to continue to account for potential future award forfeitures by estimating the number of awards that are expected to vest. Our adoption of this guidance did not have a material impact on our consolidated financial statements. We adopted guidance issued by the FASB prospectively effective January 1, 2017 that clarifies the definition of a business used by entities in determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill and consolidation. Under the new guidance, we expect that the majority of our future operating property acquisitions will be accounted for as asset acquisitions, whereas under the previous guidance our recent acquisitions were accounted for as business combinations; we believe that the primary effect of this change will be that transaction costs associated with future acquisitions will be capitalized rather than expensed as incurred. This guidance had no effect on our consolidated financial statements upon adoption. In May 2014, the FASB issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We will adopt this guidance for our annual and interim periods beginning January 1, 2018 and expect to use the modified retrospective method, under which the cumulative effect of initially applying the guidance is recognized at the date of initial application. We do not believe that our adoption of this guidance beginning on January 1, 2018 will have a material effect on our consolidated financial statements. However, as discussed further below, once the new guidance setting forth principles for the recognition, measurement, presentation and disclosure of leases goes into effect on January 1, 2019, we believe that the new revenue standard will apply to executory costs and other components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), which could affect our recognition pattern for such revenue. In February 2016, the FASB issued guidance that sets forth principles for the recognition, measurement, presentation and disclosure of leases. This guidance 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 of the leased asset by the lessee. The resulting classification determines whether the lease expense is recognized based on an effective interest method or straight-line basis over the term of the lease. 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 similar to existing guidance for operating leases. The guidance requires lessors of real estate to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. This guidance is effective for reporting periods beginning January 1, 2019 using a modified retrospective transition approach at the time of adoption. Early adoption is also permitted for this guidance. In addition, the guidance permits lessees and lessors to elect to apply a package of practical expedients that allow them not to reassess upon adoption: the lease classification for any expired or existing leases; their deferred recognition of incremental direct costs of leasing for any expired or existing leases; and whether any expired or existing contracts are, or contain, leases. While we are still completing our assessment of the impact of this guidance, below is a summary of the anticipated primary effects of this guidance on our accounting and reporting. • Real estate leases in which we are the lessor: ◦ Balance sheet reporting: We believe that we will apply an approach under the new guidance that is similar to the current accounting for operating leases, in which we will continue to recognize the underlying leased asset as property on our balance sheet. ◦ Deferral of non-incremental lease costs: Under the new lease guidance, we will no longer be able to defer the recognition of non-incremental costs in connection with new or extended tenant leases (refer to amounts reported in our 2016 Annual Report on Form 10-K for amounts deferred in 2014, 2015 and 2016). Upon adoption of the new guidance, we would expense previously deferred non-incremental lease costs for existing leases unless we elect the package of practical expedients, in which case such costs would remain deferred and amortized over the remaining lease terms. ◦ Lease revenue reporting: We believe that the new revenue standard will apply to executory costs and other components of revenue deemed to be non-lease components (such as common area maintenance and provision of utilities), even when the revenue for such activities is not separately stipulated in the lease. In that case, we would need to separate the lease components of revenue due under leases from the non-lease components and the revenue from these items previously recognized on a straight-line basis under current lease guidance would be recognized under the new revenue guidance as the related services are delivered. As a result, while the total revenue recognized over time would not differ under the new guidance, the recognition pattern could be different. We are in the process of evaluating the significance of the difference in the recognition pattern that would result from this change. • Leases in which we are the lessee: ◦ Our most significant leases as lessee are ground leases we have for certain properties; as of September 30, 2017 , our future minimum rental payments under these leases totaled $90.2 million , with various expiration dates extending to the year 2100. While we are still in the process of evaluating these leases under the new guidance, we believe that we will be required to recognize a right-of-use asset and a lease liability for the present value of these minimum lease payments. We also believe that these types of leases most likely would be classified as finance leases under the new guidance, which would result in the interest component of each lease payment being recorded as interest expense and the right-of-use asset being amortized into expense using the straight-line method over the life of the lease; however, if we elect to apply the package of practical expedients, we will continue to account for our existing ground leases as operating leases upon adoption of the guidance. 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 a more timely recognition of such losses. The guidance will apply to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loans, held-to-maturity debt securities, net investments in leases, and off-balance-sheet credit exposures (e.g. loan commitments). Under the new guidance, an entity will recognize its estimate of expected credit losses as an allowance, as the guidance requires that financial assets be measured on an amortized cost basis and to be presented at the net amount expected to be collected. The guidance is effective for us beginning January 1, 2020, with early adoption permitted after December 2018. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In August 2016, the FASB issued guidance that clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows with the objective of reducing the existing diversity in practice related to eight specific cash flow issues. The areas addressed in the new guidance relate to debt prepayment costs, settlement of zero-coupon debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned and bank-owned life insurance policies, distributions received from equity method investments, beneficial interest in securitization transactions and separately identifiable cash flows and application of the predominance principle. The guidance is effective for us beginning January 1, 2018, with early adoption permitted. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In November 2016, the FASB issued guidance that requires the statement of cash flows to explain the change during the period in the total of cash, cash equivalents and amounts described as restricted cash or restricted cash equivalents. Under the new guidance, amounts described as restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts shown on the statement of cash flows. The guidance is effective for us beginning January 1, 2018, with early adoption permitted. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In February 2017, the FASB issued guidance clarifying the scope of asset derecognition provisions and accounting for partial sales of nonfinancial assets. The new guidance requires recognition of a sale of real estate and resulting gain or loss when control transfers and the buyer has the ability to direct use of, or obtain substantially all of the remaining benefit from, the asset (which generally will occur on the closing date); the factor of continuing involvement is no longer a specific consideration for the timing of recognition. The new guidance eliminates the need to consider adequacy of buyer investment, which was replaced by additional judgments regarding collectability and intent and/or ability to pay. The new guidance also requires an entity to derecognize nonfinancial assets and in substance non financial assets once it transfers control of such assets. When an entity transfers its controlling interest in a nonfinancial asset, but retains a noncontrolling ownership interest, the entity is required to measure any non-controlling interest it receives or retains at fair value and recognize a full gain or loss on the transaction; as a result, sales and partial sales of real estate assets will now be subject to the same derecognition model as all other nonfinancial assets. As discussed further in our 2016 Annual Report on Form 10-K, we had a transaction in July 2016 accounted for as a partial sale under existing guidance that would meet the criteria for immediate full gain recognition under the new guidance; this would result in an additional $18 million in income being recognized in 2016 that is currently being amortized into income in subsequent periods under existing guidance. We do not believe that the recognition pattern for our other sales of real estate will be changed by the new guidance. We will adopt this guidance for our annual and interim periods beginning January 1, 2018 and expect to use the the full retrospective method, under which we would retrospectively restate each reporting period presented at the time of adoption. In August 2017, the FASB issued guidance that makes targeted improvements to hedge accounting. This new guidance simplifies the application of hedge accounting and better aligns financial reporting for hedging activities with companies’ economic objectives in undertaking those activities. Under the new guidance, all changes in the fair value of highly effective cash flow hedges will be recorded in other comprehensive income instead of income. The new guidance also eases the administrative burden of hedge documentation requirements and assessing hedge effectiveness. The guidance is effective for us beginning January 1, 2019, with early adoption permitted. We are currently evaluating the impact of this guidance, including transition elections and required disclosures, on our financial statements and the timing of adoption.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Recurring Fair Value Measurements COPT has a non-qualified elective deferred compensation plan for Trustees and certain members of our management team that permits participants to defer up to 100% of their compensation on a pre-tax basis and receive a tax-deferred return on such deferrals. The assets held in the plan (comprised primarily of mutual funds and equity securities) and the corresponding liability to the participants are measured at fair value on a recurring basis on COPT’s consolidated balance sheet using quoted market prices, as are other marketable securities that we hold. The balance of the plan, which was fully funded, totaled $4.4 million as of September 30, 2017 , and is included in the accompanying COPT consolidated balance sheets in the line entitled restricted cash and marketable securities. The offsetting liability associated with the plan is adjusted to fair value at the end of each accounting period based on the fair value of the plan assets and reported in other liabilities on COPT’s consolidated balance sheets. The assets of the plan and other marketable securities that we hold are classified in Level 1 of the fair value hierarchy. The liability associated with the plan is classified in Level 2 of the fair value hierarchy. The fair values of our interest rate derivatives are determined using widely accepted valuation techniques, including a 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 market data and implied volatilities in such interest rates. While we determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with our interest rate derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default. However, as of September 30, 2017 , we assessed the significance of the impact of the credit valuation adjustments on the overall valuation of our derivatives and determined that these adjustments are not significant. As a result, we determined that our interest rate derivative valuations in their entirety are classified in Level 2 of the fair value hierarchy. The carrying values of cash and cash equivalents, restricted cash, accounts receivable, other assets (excluding investing receivables) and accounts payable and accrued expenses are reasonable estimates of their fair values because of the short maturities of these instruments. As discussed in Note 6, we estimated the fair values of our investing receivables based on the discounted estimated future cash flows of the loans (categorized within Level 3 of the fair value hierarchy); the discount rates used approximate current market rates for loans with similar maturities and credit quality, and the estimated cash payments include scheduled principal and interest payments. For our disclosure of debt fair values in Note 8, we estimated the fair value of our unsecured senior notes based on quoted market rates for publicly-traded debt (categorized within Level 2 of the fair value hierarchy) and estimated the fair value of our other debt based on the discounted estimated future cash payments to be made on such debt (categorized within Level 3 of the fair value hierarchy); the discount rates used approximate current market rates for loans, or groups of loans, with similar maturities and credit quality, and the estimated future payments include scheduled principal and interest payments. Fair value estimates are made as of a specific point in time, are subjective in nature and involve uncertainties and matters of significant judgment. Settlement at such fair value amounts may not be possible and may not be a prudent management decision. For additional fair value information, please refer to Note 6 for investing receivables, Note 8 for debt and Note 9 for interest rate derivatives. COPT and Subsidiaries The table below sets forth financial assets and liabilities of COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2017 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 4,336 $ — $ — $ 4,336 Other 71 — — 71 Interest rate derivatives (2) — 126 — 126 Total assets $ 4,407 $ 126 $ — $ 4,533 Liabilities: Deferred compensation plan liability (3) $ — $ 4,407 $ — $ 4,407 Interest rate derivatives (3) — 316 — 316 Total liabilities $ — $ 4,723 $ — $ 4,723 (1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet. (2) Included in the line entitled “prepaid expenses and other assets” on COPT ’ s consolidated balance sheet. (3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet. COPLP and Subsidiaries The table below sets forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2017 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Interest rate derivatives (1) $ — $ 126 $ — $ 126 Liabilities: Interest rate derivatives (2) $ — $ 316 $ — $ 316 (1) Included in the line entitled “prepaid expenses and other assets” on COPLP ’ s consolidated balance sheet. (2) Included in the line entitled “other liabilities” on COPLP ’ s consolidated balance sheet. Nonrecurring Fair Value Measurements As part of our closing process for the first, second and third quarters of 2017, we conducted our quarterly review of our portfolio of long-lived assets to be held and used for indicators of impairment and found there to be no impairment losses. Further, for the respective quarters in 2017, we performed recoverability analyses for our properties classified as held for sale, which resulted in impairment losses of $1.6 million in the second quarter of 2017. These impairment losses were primarily on properties in White Marsh, Maryland (“White Marsh”) (included in our Regional Office and Other segments) that we reclassified to held for sale during the period and adjusted to fair value less costs to sell. These properties were sold in the third quarter. Changes in the expected future cash flows due to changes in our plans for specific properties (especially our expected holding period) could result in the recognition of impairment losses. In addition, because properties held for sale are carried at the lower of carrying value or estimated fair values less costs to sell, declines in their estimated fair values due to market conditions and other factors could result in the recognition of impairment losses.

Properties, Net

Properties, Net	9 Months Ended
	Sep. 30, 2017
Real Estate [Abstract]
Properties, Net	Properties, Net Operating properties, net consisted of the following (in thousands): September 30, December 31, Land $ 440,771 $ 433,311 Buildings and improvements 3,009,203 2,944,905 Less: Accumulated depreciation (759,262 ) (706,385 ) Operating properties, net $ 2,690,712 $ 2,671,831 Projects in development or held for future development consisted of the following (in thousands): September 30, December 31, Land $ 216,108 $ 195,521 Development in progress, excluding land 190,211 206,010 Projects in development or held for future development $ 406,319 $ 401,531 Our properties held for sale included: • as of September 30, 2017 : two operating properties in our Data Center Shells sub-segment and one in our Fort Meade/BW Corridor sub-segment; and • as of December 31, 2016 : eight operating properties in White Marsh (included primarily in our Regional Office segment); one operating property in our Northern Virginia Defense/IT sub-segment; and land in White Marsh and Northern Virginia. The table below sets forth the components of assets held for sale on our consolidated balance sheet for these properties (in thousands): September 30, 2017 December 31, 2016 Properties, net $ 68,081 $ 85,402 Deferred rent receivable 5,582 4,241 Intangible assets on real estate acquisitions, net — 338 Deferred leasing costs, net 742 3,636 Lease incentives, net 10 1,037 Assets held for sale, net $ 74,415 $ 94,654 2017 Dispositions During the nine months ended September 30, 2017 , we sold the following operating properties (dollars in thousands): Project Name City, State Segment Date of Sale Number of Buildings Total Rentable Square Feet Transaction Value Gain on Sale 3120 Fairview Park Drive Falls Church, VA Northern Virginia Defense/IT 2/15/2017 1 190,000 $ 39,000 $ — 1334 Ashton Road Hanover, MD Fort Meade/BW Corridor 6/9/2017 1 37,000 2,300 — Remaining White Marsh Properties (1) White Marsh, MD Regional Office and Other 7/28/2017 8 412,000 47,500 1,180 Dispositions through 9/30/2017 10 639,000 $ 88,800 $ 1,180 (1) This sale also included land. We also sold other land in the nine months ended September 30, 2017 for $14.3 million and recognized a gain on sale of $4.2 million . On October 27, 2017, we sold: • 201 Technology Drive, an operating property totaling 103,000 square feet in Lebanon, Virginia (in our Data Center Shells sub-segment), for $29.2 million ; and • 11751 Meadowville Lane, an operating property totaling 193,000 square feet in Chester, Virginia (in our Data Center Shells sub-segment), for $44.3 million . We provided a financial guaranty to the buyer under which we would indemnify it for up to $20 million in losses it could incur related to a potential defined capital event occurring on the property by June 30, 2019. Accordingly, we will not recognize the sale of this property for accounting purposes, and will reflect the sale price of the property as a liability, until the guaranty expires. We do not expect to incur any losses under this financial guaranty. 2017 Construction Activities During the nine months ended September 30, 2017 , we placed into service 751,000 square feet in five newly constructed properties (including a partially operational property) and 88,000 square feet in three redeveloped properties (including a partially operational property). As of September 30, 2017 , we had eight office properties under construction, or for which we were contractually committed to construct, that we estimate will total 1.1 million square feet upon completion (including two properties completed but held for future lease to the United States Government) and two office properties under redevelopment that we estimate will total 36,000 square feet upon completion.

Real Estate Joint Ventures

Real Estate Joint Ventures	9 Months Ended
	Sep. 30, 2017
Equity Method Investments and Joint Ventures [Abstract]
Real Estate Joint Ventures	Real Estate Joint Ventures Consolidated Joint Ventures The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of September 30, 2017 (dollars in thousands): Nominal Ownership September 30, 2017 (1) Date % as of Total Encumbered Total Acquired 9/30/2017 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 158,937 $ 76,374 $ 50,344 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 70,767 45,813 46,895 Stevens Investors, LLC 8/11/2015 95% Development of real estate (4) 70,383 — 23,566 $ 300,087 $ 122,187 $ 120,805 (1) Excludes amounts eliminated in consolidation. (2) This joint venture’s properties are in Huntsville, Alabama. (3) This joint venture’s properties are in College Park, Maryland. (4) This joint venture’s property is in Washington, DC. Our partner in this joint venture received an additional distribution from the joint venture of $6.7 million in July 2017 that was reported in other liabilities on our consolidated balance sheet as of December 31, 2016. Unconsolidated Joint Venture As of September 30, 2017 , we owned a 50% interest in GI-COPT DC Partnership LLC (“GI-COPT”), a joint venture owning six triple-net leased, single-tenant data center properties in Virginia, that we account for using the equity method of accounting. As of September 30, 2017 , we had an investment balance in GI-COPT of $25.2 million . Our balance was $17.1 million lower than our share of the joint venture’s equity due to a difference between our cost basis and our share of the underlying equity in the net assets upon formation of the joint venture; we are amortizing this basis difference into equity in income from unconsolidated entities over the lives of the underlying assets.

Investing Receivables

Investing Receivables	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Investing Receivables	Investing Receivables Investing receivables, including accrued interest thereon, consisted of the following (in thousands): September 30, December 31, Notes receivable from the City of Huntsville $ 53,088 $ 49,258 Other investing loans receivable 3,020 3,021 $ 56,108 $ 52,279 Our notes receivable from the City of Huntsville funded infrastructure costs in connection with our LW Redstone Company, LLC joint venture (see Note 5) and carry an interest rate of 9.95% . We did not have an allowance for credit losses in connection with our investing receivables as of September 30, 2017 or December 31, 2016 . The fair value of these receivables approximated their carrying amounts as of September 30, 2017 and December 31, 2016 .

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Net	9 Months Ended
	Sep. 30, 2017
Prepaid Expense and Other Assets [Abstract]
Prepaid Expenses and Other Assets, Net	Prepaid Expenses and Other Assets, Net Prepaid expenses and other assets, net consisted of the following (in thousands): September 30, December 31, Prepaid expenses $ 30,932 $ 24,432 Lease incentives, net 17,202 18,276 Furniture, fixtures and equipment, net 5,422 5,204 Deferred tax asset, net (1) 2,851 3,036 Non-real estate equity method investments 2,413 2,355 Construction contract costs incurred in excess of billings 2,005 10,350 Deferred financing costs, net (2) 1,419 3,128 Other assets 4,294 5,983 Prepaid expenses and other assets, net $ 66,538 $ 72,764 (1) Includes a valuation allowance of $2.1 million . (2) Represents deferred costs, net of accumulated amortization, attributable to our Revolving Credit Facility and interest rate derivatives.

Debt, Net

Debt, Net	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Debt, Net	Debt, Net Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of September 30, December 31, Stated Interest Rates as of Scheduled Maturity as of September 30, 2017 September 30, 2017 Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 151,594 $ 154,143 3.82% - 7.87% (3) 2019-2026 Variable rate secured debt 13,200 13,448 LIBOR + 1.85% (4) October 2020 Total mortgage and other secured debt 164,794 167,591 Revolving Credit Facility 170,000 — LIBOR + 0.875% to 1.60% (5) May 2019 (6) Term Loan Facilities (7) 348,371 547,494 LIBOR + 0.90% to 2.40% (8) 2020-2022 Unsecured Senior Notes 3.600%, $350,000 aggregate principal 347,445 347,128 3.60% (9) May 2023 5.250%, $250,000 aggregate principal 246,525 246,176 5.25% (10) February 2024 3.700%, $300,000 aggregate principal 298,200 297,843 3.70% (11) June 2021 5.000%, $300,000 aggregate principal 296,639 296,368 5.00% (12) July 2025 Unsecured notes payable 1,317 1,401 0% (13) 2026 Total debt, net $ 1,873,291 $ 1,904,001 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $4.8 million as of September 30, 2017 and $6.1 million as of December 31, 2016 . (2) Certain fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying values of these loans reflect net unamortized premiums totaling $367,000 as of September 30, 2017 and $422,000 as of December 31, 2016 . (3) The weighted average interest rate on our fixed rate mortgage debt was 4.19% as of September 30, 2017 . (4) The interest rate on our variable rate secured debt as of September 30, 2017 was 3.09% . (5) The weighted average interest rate on the Revolving Credit Facility was 2.40% as of September 30, 2017 . (6) The facility matures in May 2019, with the ability for us to further extend such maturity by two six -month periods at our option, provided that there is no default under the facility and we pay an extension fee of 0.075% of the total availability under the facility for each extension period. (7) As of September 30, 2017 , we have the ability to borrow an additional $350.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders. On May 1, 2017, we repaid $200.0 million of the loan balance on a term loan scheduled to mature in 2020. (8) The weighted average interest rate on these loans was 2.93% as of September 30, 2017 . (9) The carrying value of these notes reflects an unamortized discount totaling $1.8 million as of September 30, 2017 and $2.0 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.70% . (10) The carrying value of these notes reflects an unamortized discount totaling $3.1 million as of September 30, 2017 and $3.4 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.49% . (11) The carrying value of these notes reflects an unamortized discount totaling $1.4 million as of September 30, 2017 and $1.7 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.85% . (12) The carrying value of these notes reflects an unamortized discount totaling $2.8 million as of September 30, 2017 and $3.0 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% . (13) These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying value of these notes reflects an unamortized discount totaling $394,000 as of September 30, 2017 and $460,000 as of December 31, 2016 . All debt is owed by the Operating Partnership. While COPT is not directly obligated by any debt, it has guaranteed the Operating Partnership’s Revolving Credit Facility, Term Loan Facilities and Unsecured Senior Notes. Certain of our debt instruments require that we comply with a number of restrictive financial covenants. As of September 30, 2017 , we were compliant with these covenants. We capitalized interest costs of $1.1 million in the three months ended September 30, 2017 , $1.2 million in the three months ended September 30, 2016 , $4.2 million in the nine months ended September 30, 2017 and $4.3 million in the nine months ended September 30, 2016 . The following table sets forth information pertaining to the fair value of our debt (in thousands): September 30, 2017 December 31, 2016 Carrying Fair Carrying Fair Amount Value Amount Value Fixed-rate debt Unsecured Senior Notes $ 1,188,809 $ 1,231,222 $ 1,187,515 $ 1,220,282 Other fixed-rate debt 152,911 154,781 155,544 156,887 Variable-rate debt 531,571 531,520 560,942 558,437 $ 1,873,291 $ 1,917,523 $ 1,904,001 $ 1,935,606

Interest Rate Derivatives

Interest Rate Derivatives	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Interest Rate Derivatives	Interest Rate Derivatives The following table sets forth the key terms and fair values of our interest rate swap derivatives, each of which was designated as a cash flow hedge of interest rate risk (dollars in thousands): Fair Value at Notional Amount Fixed Rate Floating Rate Index Effective Date Expiration Date September 30, December 31, $ 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 $ (237 ) $ (848 ) 13,311 (1) 1.3900% One-Month LIBOR 10/13/2015 10/1/2020 126 100 100,000 1.9013% One-Month LIBOR 9/1/2016 12/1/2022 (27 ) (23 ) 100,000 1.9050% One-Month LIBOR 9/1/2016 12/1/2022 (22 ) 48 50,000 1.9079% One-Month LIBOR 9/1/2016 12/1/2022 (30 ) 10 100,000 (2) 1.6730% One-Month LIBOR 9/1/2015 8/1/2019 — (701 ) $ (190 ) $ (1,414 ) (1) The notional amount of this instrument is scheduled to amortize to $12.1 million . (2) We cash settled this derivative and interest accrued thereon for $460,000 on May 1, 2017. Since the hedged transactions associated with this derivative were still probable to occur as of the settlement date, amounts in accumulated other comprehensive loss ( “ AOCL ” ) associated with this derivative will be reclassified to interest expense through August 2019. The table below sets forth the fair value of our interest rate derivatives as well as their classification on our consolidated balance sheets (in thousands): Fair Value at Derivatives Balance Sheet Location September 30, December 31, 2016 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets $ 126 $ 158 Interest rate swaps designated as cash flow hedges Other liabilities (316 ) (1,572 ) The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Unrealized (loss) gain recognized in AOCL (effective portion) $ (301 ) $ 407 $ (1,877 ) $ (16,581 ) Loss reclassified from AOCL into interest expense (effective portion) (615 ) (1,043 ) (2,652 ) (2,763 ) Gain (loss) on derivatives recognized in interest expense (ineffective portion) 34 1,523 132 (347 ) Loss reclassified from AOCL into interest expense (ineffective portion) (1) — — (88 ) — (1) Represents a loss recognized on certain interest rate swaps from the accelerated reclassification of amounts in AOCL on May 1, 2017, when we concluded that hedged forecasted transactions were probable not to occur. Over the next 12 months, we estimate that approximately $1.6 million of losses will be reclassified from AOCL as an increase to interest expense. We have agreements with each of our interest rate derivative counterparties that contain provisions under which, if we default or are capable of being declared in default on defined levels of our indebtedness, we could also be declared in default on our derivative obligations. Failure to comply with the loan covenant provisions could result in our being declared in default on any derivative instrument obligations covered by the agreements. As of September 30, 2017 , the fair value of interest rate derivatives in a liability position related to these agreements was $305,000 , excluding the effects of accrued interest and credit valuation adjustments. As of September 30, 2017 , we had not posted any collateral related to these agreements. We are not in default with any of these provisions. If we breached any of these provisions, we could be required to settle our obligations under the agreements at their termination value of $484,000 .

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interests	9 Months Ended
	Sep. 30, 2017
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interests	Redeemable Noncontrolling Interests Our partners in two real estate joint ventures, LW Redstone Company, LLC and Stevens Investors, LLC (discussed further in Note 5), have the right to require us to acquire their respective interests at fair value; accordingly, we classify the fair value of our partners’ interests as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheet. We determine the fair value of the interests based on unobservable inputs after considering the assumptions that market participants would make in pricing the interest. We apply a discount rate to the estimated future cash flows allocable to our partners from the properties underlying the respective joint ventures. Estimated cash flows used in such analyses are based on our plans for the properties and our views of market and economic conditions, and consider items such as current and future rental rates, occupancies for the properties and comparable properties and estimated operating and capital expenditures. The table below sets forth the activity for these redeemable noncontrolling interests (in thousands): For the Nine Months Ended September 30, 2017 2016 Beginning balance $ 22,979 $ 19,218 Contributions from noncontrolling interests — 22,779 Distributions to noncontrolling interests (1,186 ) (21,344 ) Net income attributable to noncontrolling interests 1,720 1,679 Adjustment to arrive at fair value of interests (244 ) 516 Ending balance $ 23,269 $ 22,848

Equity

Equity	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Equity	Equity During the nine months ended September 30, 2017 , COPT redeemed all of the outstanding shares of its following series of preferred shares: • the 5.600% Series K Cumulative Redeemable Preferred Shares (the “Series K Preferred Shares”), redeemed effective January 21, 2017 at a price of $50.00 per share, or $26.6 million in the aggregate, plus accrued and unpaid dividends thereon through the date of redemption. Concurrently with this redemption, COPLP redeemed its Series K Preferred Units on the same terms. Since we made an irrevocable notification to holders of the Series K Preferred Shares in December 2016 of our intention to redeem such shares, we presented the liquidation preference of the shares/units as a liability on the consolidated balance sheets of COPT and COPLP as of December 31, 2016; we also recognized a $17,000 decrease to net income available to common shareholders/unitholders in the three months ended December 31, 2016 pertaining to the original issuance costs incurred on the shares/units; and • the 7.375% Series L Cumulative Preferred Shares (the “Series L Preferred Shares”), redeemed effective June 27, 2017 at a price of $25.00 per share, or $172.5 million in the aggregate, plus accrued and unpaid dividends thereon up to but not including the date of redemption. Concurrently with this redemption, COPLP redeemed its Series L Preferred Units on the same terms. We also recognized a $6.8 million decrease to net income available to common shareholders/unitholders in the nine months ended September 30, 2017 pertaining to the original issuance costs incurred on the shares/units. During the nine months ended September 30, 2017 , COPT issued 591,042 common shares at a weighted average price of $33.84 per share under its existing at-the-market (“ATM”) stock offering program. Net proceeds from the shares issued totaled $19.7 million , after payment of $300,000 in commissions to sales agents. COPT contributed the net proceeds from these issuances to COPLP in exchange for an equal number of units in COPLP. COPT’s remaining capacity under this ATM program is an aggregate gross sales price of $70.0 million in common share sales. During the nine months ended September 30, 2017 , certain COPLP limited partners converted 337,000 common units in COPLP for an equal number of common shares in COPT. See Note 13 for disclosure of COPT common share and COPLP common unit activity pertaining to our share-based compensation plans.

Information by Business Segment

Information by Business Segment	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Information by Business Segment	Information by Business Segment We have the following reportable segments: Defense/IT Locations; Regional Office; our operating wholesale data center; and other. We also report on Defense/IT Locations sub-segments, which include the following: Fort George G. Meade and the Baltimore/Washington Corridor (referred to herein as “Fort Meade/BW Corridor”); Northern Virginia Defense/IT Locations; Lackland Air Force Base (in San Antonio); locations serving the U.S. Navy (“Navy Support Locations”), which included properties proximate to the Washington Navy Yard, the Naval Air Station Patuxent River in Maryland and the Naval Surface Warfare Center Dahlgren Division in Virginia; Redstone Arsenal (in Huntsville); and data center shells (properties leased to tenants to be operated as data centers in which the tenants generally fund the costs for the power, fiber connectivity and data center infrastructure). We measure the performance of our segments through the measure we define as net operating income from real estate operations (“NOI from real estate operations”), which includes: real estate revenues and property operating expenses; and the net of revenues and property operating expenses of real estate operations owned through unconsolidated real estate joint ventures (“UJVs”) that is allocable to COPT’s ownership interest (“UJV NOI allocable to COPT”). Amounts reported for segment assets represent long-lived assets associated with consolidated operating properties (including the carrying value of properties, intangible assets, deferred leasing costs, deferred rents receivable and lease incentives) and the carrying value of investments in UJVs owning operating properties. Amounts reported as additions to long-lived assets represent additions to existing consolidated operating properties, excluding transfers from non-operating properties, which we report separately. The table below reports segment financial information for our reportable segments (in thousands): Operating Office Property Segments Defense/Information Technology Locations Fort Meade/BW Corridor Northern Virginia Defense/IT Lackland Air Force Base Navy Support Locations Redstone Arsenal Data Center Shells Total Defense/IT Locations Regional Office Operating Other Total Three Months Ended September 30, 2017 Revenues from real estate operations $ 61,254 $ 12,190 $ 11,024 $ 7,494 $ 3,532 $ 6,676 $ 102,170 $ 16,656 $ 7,398 $ 1,007 $ 127,231 Property operating expenses (19,708 ) (4,343 ) (6,193 ) (3,157 ) (1,432 ) (637 ) (35,470 ) (7,406 ) (3,175 ) (317 ) (46,368 ) UJV NOI allocable to COPT — — — — — 1,297 1,297 — — — 1,297 NOI from real estate operations $ 41,546 $ 7,847 $ 4,831 $ 4,337 $ 2,100 $ 7,336 $ 67,997 $ 9,250 $ 4,223 $ 690 $ 82,160 Additions to long-lived assets $ 5,810 $ 2,587 $ 55 $ 1,910 $ 843 $ — $ 11,205 $ 5,338 $ 9 $ 76 $ 16,628 Transfers from non-operating properties $ 5,519 $ 45,554 $ — $ 8 $ (62 ) $ 29,803 $ 80,822 $ 25 $ — $ — $ 80,847 Three Months Ended September 30 2016 Revenues from real estate operations $ 61,460 $ 12,231 $ 12,532 $ 7,232 $ 3,189 $ 5,175 $ 101,819 $ 20,499 $ 6,809 $ 1,827 $ 130,954 Property operating expenses (20,598 ) (4,462 ) (7,599 ) (3,374 ) (1,112 ) (528 ) (37,673 ) (8,155 ) (3,317 ) (807 ) (49,952 ) UJV NOI allocable to COPT — — — — — 1,008 1,008 — — — 1,008 NOI from real estate operations $ 40,862 $ 7,769 $ 4,933 $ 3,858 $ 2,077 $ 5,655 $ 65,154 $ 12,344 $ 3,492 $ 1,020 $ 82,010 Additions to long-lived assets $ 5,901 $ 7,153 $ — $ 2,207 $ 2,642 $ — $ 17,903 $ 4,168 $ 108 $ 53 $ 22,232 Transfers from non-operating properties $ 5,331 $ 308 $ 3 $ — $ 3,100 $ 25,513 $ 34,255 $ (4 ) $ 40 $ — $ 34,291 Nine Months Ended September 30, 2017 Revenues from real estate operations $ 183,393 $ 34,992 $ 35,687 $ 21,953 $ 10,616 $ 17,998 $ 304,639 $ 52,394 $ 21,201 $ 4,061 $ 382,295 Property operating expenses (60,357 ) (13,014 ) (21,125 ) (9,391 ) (4,294 ) (1,873 ) (110,054 ) (21,974 ) (10,041 ) (1,446 ) (143,515 ) UJV NOI allocable to COPT — — — — — 3,889 3,889 — — — 3,889 NOI from real estate operations $ 123,036 $ 21,978 $ 14,562 $ 12,562 $ 6,322 $ 20,014 $ 198,474 $ 30,420 $ 11,160 $ 2,615 $ 242,669 Additions to long-lived assets $ 15,085 $ 6,032 $ 71 $ 6,309 $ 1,059 $ — $ 28,556 $ 16,476 $ 3,588 $ 203 $ 48,823 Transfers from non-operating properties $ 37,094 $ 45,994 $ — $ 474 $ 1,643 $ 55,003 $ 140,208 $ — $ 8 $ 18 $ 140,234 Segment assets at September 30, 2017 $ 1,265,569 $ 400,855 $ 129,657 $ 194,801 $ 108,884 $ 258,611 $ 2,358,377 $ 398,579 $ 226,909 $ 13,347 $ 2,997,212 Nine Months Ended September 30, 2016 Revenues from real estate operations $ 184,881 $ 36,404 $ 34,408 $ 21,164 $ 9,496 $ 18,793 $ 305,146 $ 67,284 $ 20,106 $ 5,429 $ 397,965 Property operating expenses (64,222 ) (13,310 ) (19,863 ) (9,573 ) (3,050 ) (2,164 ) (112,182 ) (26,707 ) (8,629 ) (2,450 ) (149,968 ) UJV NOI allocable to COPT — — — — — 1,008 1,008 — — — 1,008 NOI from real estate operations $ 120,659 $ 23,094 $ 14,545 $ 11,591 $ 6,446 $ 17,637 $ 193,972 $ 40,577 $ 11,477 $ 2,979 $ 249,005 Additions to long-lived assets $ 19,516 $ 13,290 $ — $ 5,710 $ 3,561 $ — $ 42,077 $ 9,107 $ 108 $ 363 $ 51,655 Transfers from non-operating properties $ 41,850 $ 28,158 $ 240 $ — $ 3,315 $ 81,467 $ 155,030 $ 104 $ (391 ) $ (11 ) $ 154,732 Segment assets at September 30, 2016 $ 1,261,337 $ 416,886 $ 132,722 $ 195,244 $ 111,310 $ 189,746 $ 2,307,245 $ 453,766 $ 234,551 $ 31,563 $ 3,027,125 The following table reconciles our segment revenues to total revenues as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Segment revenues from real estate operations $ 127,231 $ 130,954 $ 382,295 $ 397,965 Construction contract and other service revenues 29,786 11,149 65,958 34,372 Total revenues $ 157,017 $ 142,103 $ 448,253 $ 432,337 The following table reconciles UJV NOI allocable to COPT to equity in income of unconsolidated entities as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 UJV NOI allocable to COPT $ 1,297 $ 1,008 $ 3,889 $ 1,008 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (577 ) (415 ) (1,724 ) (415 ) Add: Equity in (loss) income of unconsolidated non-real estate entities (1 ) 1 (3 ) 21 Equity in income of unconsolidated entities $ 719 $ 594 $ 2,162 $ 614 As previously discussed, we provide real estate services such as property management and construction and development services primarily for our properties but also for third parties. The primary manner in which we evaluate the operating performance of our service activities is through a measure we define as net operating income from service operations (“NOI from service operations”), which is based on the net of revenues and expenses from these activities. Construction contract and other service revenues and expenses consist primarily of subcontracted costs that are reimbursed to us by the customer along with a management fee. The operating margins from these activities are small relative to the revenue. We believe NOI from service operations is a useful measure in assessing both our level of activity and our profitability in conducting such operations. The table below sets forth the computation of our NOI from service operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Construction contract and other service revenues $ 29,786 $ 11,149 $ 65,958 $ 34,372 Construction contract and other service expenses (28,788 ) (10,341 ) (63,589 ) (32,513 ) NOI from service operations $ 998 $ 808 $ 2,369 $ 1,859 The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from before gain on sales of real estate as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 NOI from real estate operations $ 82,160 $ 82,010 $ 242,669 $ 249,005 NOI from service operations 998 808 2,369 1,859 Interest and other income 1,508 1,391 4,817 3,877 Equity in income of unconsolidated entities 719 594 2,162 614 Income tax (expense) benefit (57 ) 21 (145 ) 28 Depreciation and other amortization associated with real estate operations (34,438 ) (32,015 ) (100,290 ) (99,790 ) Impairment recoveries (losses) 161 (27,699 ) (1,464 ) (99,837 ) General, administrative and leasing expenses (7,368 ) (8,855 ) (23,838 ) (28,764 ) Business development expenses and land carry costs (1,277 ) (1,716 ) (4,567 ) (6,497 ) Interest expense (19,615 ) (18,301 ) (57,772 ) (64,499 ) Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities (1,297 ) (1,008 ) (3,889 ) (1,008 ) Loss on early extinguishment of debt — (59 ) (513 ) (37 ) Income (loss) before gain on sales of real estate $ 21,494 $ (4,829 ) $ 59,539 $ (45,049 ) The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): September 30, September 30, Segment assets $ 2,997,212 $ 3,027,125 Non-operating property assets 413,255 421,364 Other assets 149,305 185,705 Total COPT consolidated assets $ 3,559,772 $ 3,634,194 The accounting policies of the segments are the same as those used to prepare our consolidated financial statements, except that discontinued operations and UJV NOI allocable to COPT are not presented separately for segment purposes. In the segment reporting presented above, we did not allocate interest expense, depreciation and amortization, impairment (recoveries) losses, loss on early extinguishment of debt, gain on sales of real estate and equity in income of unconsolidated entities not included in NOI to our real estate segments since they are not included in the measure of segment profit reviewed by management. We also did not allocate general, administrative and leasing expenses, business development expenses and land carry costs, interest and other income, income taxes and noncontrolling interests because these items represent general corporate or non-operating property items not attributable to segments.

Share-Based Compensation and Ot

Share-Based Compensation and Other Compensation Matters	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation and Other Compensation Matters	Share-Based Compensation and Other Compensation Matters Performance-Based Share Units (“PSUs”) On January 1, 2017 , our Board of Trustees granted 36,525 PSUs with an aggregate grant date fair value of $1.4 million to our three executives (the “January Grants”). The PSUs have a performance period beginning on January 1, 2017 and concluding on the earlier of December 31, 2019 or the date of: (1) termination by us without cause, death or disability of the executive or constructive discharge of the executive (collectively, “qualified termination”); or (2) a sale event. The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned PSUs Payout % 75th or greater 200% of PSUs granted 50th or greater 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted If the percentile rank exceeds the 25th percentile and is between two of the percentile ranks set forth in the table above, then the percentage of the earned PSUs will be interpolated between the ranges set forth in the table above to reflect any performance between the listed percentiles. At the end of the performance period, we, in settlement of the award, will issue a number of fully-vested COPT common shares equal to the sum of: • the number of earned PSUs in settlement of the award plan; plus • the aggregate dividends that would have been paid with respect to the common shares issued in settlement of the earned PSUs through the date of settlement had such shares been issued on the grant date, divided by the share price on such settlement date, as defined under the terms of the agreement. If a performance period ends due to a sale event or qualified termination, the number of earned PSUs is prorated based on the portion of the three -year performance period that has elapsed. If employment is terminated by the employee or by us for cause, all PSUs are forfeited. PSUs do not carry voting rights. On August 23, 2017, the January Grants were modified to include a provision that limits the earned PSUs payout percentage to 100% of the PSUs granted if COPT’s total shareholder return is negative during the performance period irrespective of its percentile rank in the peer group (the “Negative TSR Modifier”). In addition, as a result of the modification to the January Grants, on August 23, 2017, we augmented the January Grants by issuing an aggregate of 2,826 additional PSUs to the executives. Each of the PSU Certificates also includes the Negative TSR Modifier. The incremental award to the executives on August 23, 2017 resulting from these modifications totaled $12,000 . For the January Grants, we computed a grant date fair value of $38.43 per PSU using a Monte Carlo model, which included assumptions of, among other things, the following: baseline common share value of $31.22 ; expected volatility for COPT common shares of 19.0% ; and a risk-free interest rate of 1.47% . For the award modification on August 23, 2017, we computed a pre-modification fair value of $49.66 per PSU and a post-modification fair value of $46.39 per PSU using a Monte Carlo model, which included assumptions of, among other things, the following: baseline common share value of $33.40 ; expected volatility for COPT common shares of 18.7% ; and a risk-free interest rate of 1.36% . We issued 9,763 common shares on February 7, 2017 to Mr. Stephen E. Budorick, our Chief Executive Officer, in settlement of PSUs issued in 2014, representing 100% of the target award for those PSUs. Restricted Shares During the nine months ended September 30, 2017 , certain employees and non-employee members of our Board of Trustees were granted a total of 230,635 restricted common shares with an aggregate grant date fair value of $7.8 million (weighted average of $33.96 per share). Restricted shares granted to employees vest based on increments and over periods of time set forth under the terms of the respective awards provided that the employees remain employed by us. Restricted shares granted to non-employee Trustees vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. During the nine months ended September 30, 2017 , forfeiture restrictions lapsed on 148,401 previously issued common shares; these shares had a weighted average grant date fair value of $26.18 per share, and the aggregate intrinsic value of the shares on the vesting dates was $5.0 million . Deferred Share Awards During the nine months ended September 30, 2017 , nonemployee members of our Board of Trustees were granted a total of 10,032 deferred share awards with an aggregate grant date fair value of $326,000 ( $32.47 per share). Deferred share awards vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. We settle deferred share awards by issuing an equivalent number of common shares upon vesting of the awards or a later date elected by the Trustee (generally upon cessation of being a Trustee). During the nine months ended September 30, 2017 , we issued 15,590 common shares in settlement of deferred share awards granted in 2016; these shares had a grant date fair value of $26.89 per share, and the aggregate intrinsic value of the shares on the settlement date was $508,000 . Options During the nine months ended September 30, 2017 , 5,000 options to purchase common shares (“options”) were exercised. The weighted average exercise price of these options was $29.98 per share, and the aggregate intrinsic value of the options exercised was $18,000 .

Earnings Per Share ("EPS") and

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU")	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”)	Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”) COPT and Subsidiaries EPS We present both basic and diluted EPS. We compute basic EPS by dividing net income available to common shareholders allocable to unrestricted common shares under the two-class method by the weighted average number of unrestricted common shares outstanding during the period. Our computation of diluted EPS is similar except that: • the denominator is increased to include: (1) the weighted average number of potential additional common shares that would have been outstanding if securities that are convertible into COPT common shares were converted; and (2) the effect of dilutive potential common shares outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and • the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common shares that we added to the denominator. Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net income (loss) attributable to COPT $ 20,916 $ 27,299 $ 60,133 $ (13,294 ) Preferred share dividends — (3,552 ) (6,219 ) (10,657 ) Issuance costs associated with redeemed preferred shares — — (6,847 ) — Income attributable to share-based compensation awards (95 ) (105 ) (337 ) (319 ) Numerator for basic and diluted EPS on net income (loss) attributable to COPT common shareholders $ 20,821 $ 23,642 $ 46,730 $ (24,270 ) Denominator (all weighted averages): Denominator for basic EPS (common shares) 99,112 94,433 98,855 94,312 Dilutive effect of share-based compensation awards 146 81 154 — Denominator for diluted EPS (common shares) 99,258 94,514 99,009 94,312 Basic EPS: Net income (loss) attributable to COPT common shareholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Diluted EPS: Net income (loss) attributable to COPT common shareholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Our diluted EPS computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPS for the respective periods (in thousands): Weighted Average Shares Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Conversion of common units 3,350 3,591 3,400 3,648 Conversion of Series I Preferred Units 176 176 176 176 Conversion of Series K Preferred Shares — 434 — 434 The following share-based compensation securities were excluded from the computation of diluted EPS because their effects were antidilutive: • weighted average restricted shares and deferred share awards for the three months ended September 30, 2017 and 2016 of 445,000 and 375,000 , respectively, and for the nine months ended September 30, 2017 and 2016 of 431,000 and 394,000 , respectively; and • weighted average options for the three months ended September 30, 2017 and 2016 of 40,000 and 233,000 , respectively, and for the nine months ended September 30, 2017 and 2016 of 80,000 and 307,000 , respectively. COPLP and Subsidiaries EPU We present both basic and diluted EPU. We compute basic EPU by dividing net income available to common unitholders allocable to unrestricted common units under the two-class method by the weighted average number of unrestricted common units outstanding during the period. Our computation of diluted EPU is similar except that: • the denominator is increased to include: (1) the weighted average number of potential additional common units that would have been outstanding if securities that are convertible into our common units were converted; and (2) the effect of dilutive potential common units outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and • the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common units that we added to the denominator. Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net income (loss) attributable to COPLP common unitholders $ 21,785 $ 28,359 $ 62,239 $ (13,751 ) Preferred unit distributions (165 ) (3,717 ) (6,714 ) (11,152 ) Issuance costs associated with redeemed preferred units — — (6,847 ) — Income attributable to share-based compensation awards (95 ) (105 ) (337 ) (319 ) Numerator for basic and diluted EPU on net income (loss) attributable to COPLP common unitholders $ 21,525 $ 24,537 $ 48,341 $ (25,222 ) Denominator (all weighted averages): Denominator for basic EPU (common units) 102,462 98,024 102,255 97,960 Dilutive effect of share-based compensation awards 146 81 154 — Denominator for diluted EPU (common units) 102,608 98,105 102,409 97,960 Basic EPU: Net income (loss) attributable to COPLP common unitholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Diluted EPU: Net income (loss) attributable to COPLP common unitholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Conversion of Series I preferred units 176 176 176 176 Conversion of Series K preferred units — 434 — 434 The following share-based compensation securities were excluded from the computation of diluted EPU because their effects were antidilutive: • weighted average restricted units and deferred share awards for the three months ended September 30, 2017 and 2016 of 445,000 and 375,000 , respectively, and for the nine months ended September 30, 2017 and 2016 of 431,000 and 394,000 , respectively; and • weighted average options for the three months ended September 30, 2017 and 2016 of 40,000 and 233,000 , respectively, and for the nine months ended September 30, 2017 and 2016 of 80,000 and 307,000 , respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Litigation In the normal course of business, we are involved in legal actions arising from our ownership and administration of properties. We establish reserves for specific legal proceedings when we determine that the likelihood of an unfavorable outcome is probable and the amount of loss can be reasonably estimated. Management does not anticipate that any liabilities that may result from such proceedings will have a materially adverse effect on our financial position, operations or liquidity. Our assessment of the potential outcomes of these matters involves significant judgment and is subject to change based on future developments. Environmental We are subject to various Federal, state and local environmental regulations related to our property ownership and operation. We have performed environmental assessments of our properties, the results of which have not revealed any environmental liability that we believe would have a materially adverse effect on our financial position, operations or liquidity. Tax Incremental Financing Obligation In August 2010, Anne Arundel County, Maryland issued $30 million in tax incremental financing bonds to third-party investors in order to finance public improvements needed in connection with our project known as National Business Park North. The real estate taxes on increases in assessed value of a development district encompassing National Business Park North are to be transferred to a special fund pledged to the repayment of the bonds. We recognized a $685,000 liability through September 30, 2017 representing our estimated obligation to fund through a special tax any future shortfalls between debt service on the bonds and real estate taxes available to repay the bonds. Operating Leases We are obligated as lessee under operating leases (mostly ground leases) with various expiration dates extending to the year 2100. Future minimum rental payments due under the terms of these operating leases as of September 30, 2017 follow (in thousands): Year Ending December 31, 2017 (1) $ 320 2018 1,275 2019 1,263 2020 1,257 2021 1,260 Thereafter 85,761 $ 91,136 (1) Represents the three months ending December 31, 2017 . Capital Lease On May 25, 2017, we entered into a ground lease on land under development in Washington, D.C. for our Stevens Investors, LLC joint venture. The lease has a 99 -year term, and we possess an option to purchase the property for one dollar (estimated to occur between 2019 and 2020). Upon inception of the lease, we recorded a $16.1 million capital lease liability on our consolidated balance sheets based on the present value of the future minimum rental payments. Future minimum rental payments due under the term of this lease as of September 30, 2017 follow (in thousands): Year Ending December 31, 2017 (1) $ 700 2018 15,775 2020 135 Thereafter 75 Total minimum rental payments $ 16,685 Less: Amount representing interest (338 ) Capital lease obligation $ 16,347 (1) Represents the three months ending December 31, 2017 . Contractual Obligations We had amounts remaining to be incurred under various contractual obligations as of September 30, 2017 that included the following (excluding amounts incurred and therefore reflected as liabilities reported on our consolidated balance sheet): • new development and redevelopment obligations of $35.1 million ; • capital expenditures for operating properties of $45.8 million ; • third party construction and development of $67.4 million ; and • other obligations of $1.1 million . Environmental Indemnity Agreement In connection with a lease and subsequent sale in 2008 and 2010 of three properties in Dayton, New Jersey, we agreed to provide certain environmental indemnifications limited to $19 million in the aggregate. We have insurance coverage in place to mitigate much of any potential future losses that may result from these indemnification agreements.

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The COPT consolidated financial statements include the accounts of COPT, the Operating Partnership, their subsidiaries and other entities in which COPT has a majority voting interest and control. The COPLP consolidated financial statements include the accounts of COPLP, its subsidiaries and other entities in which COPLP has a majority voting interest and control. We also consolidate certain entities when control of such entities can be achieved through means other than voting rights (“variable interest entities” or “VIEs”) if we are deemed to be the primary beneficiary of such entities. We eliminate all intercompany balances and transactions in consolidation. We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity. We use the cost method of accounting when we own an interest in an entity and cannot exert significant influence over its operations. These interim financial statements should be read together with the consolidated financial statements and notes thereto as of and for the year ended December 31, 2016 included in our 2016 Annual Report on Form 10-K. The unaudited consolidated financial statements include all adjustments that are necessary, in the opinion of management, to fairly state our financial position and results of operations. All adjustments are of a normal recurring nature. The consolidated financial statements have been prepared using the accounting policies described in our 2016 Annual Report on Form 10-K.
Reclassification	Reclassification We reclassified certain amounts from prior periods to conform to the current period presentation of our consolidated financial statements with no effect on previously reported net income or equity.
Recent Accounting Pronouncements	Recent Accounting Pronouncements We adopted guidance issued by the Financial Accounting Standards Board (“FASB”) effective January 1, 2017 intended to simplify various aspects related to the accounting and presentation for employee share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the consolidated statement of cash flows. In connection with our adoption of this policy, we made an entity-wide accounting policy election to continue to account for potential future award forfeitures by estimating the number of awards that are expected to vest. Our adoption of this guidance did not have a material impact on our consolidated financial statements. We adopted guidance issued by the FASB prospectively effective January 1, 2017 that clarifies the definition of a business used by entities in determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill and consolidation. Under the new guidance, we expect that the majority of our future operating property acquisitions will be accounted for as asset acquisitions, whereas under the previous guidance our recent acquisitions were accounted for as business combinations; we believe that the primary effect of this change will be that transaction costs associated with future acquisitions will be capitalized rather than expensed as incurred. This guidance had no effect on our consolidated financial statements upon adoption. In May 2014, the FASB issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We will adopt this guidance for our annual and interim periods beginning January 1, 2018 and expect to use the modified retrospective method, under which the cumulative effect of initially applying the guidance is recognized at the date of initial application. We do not believe that our adoption of this guidance beginning on January 1, 2018 will have a material effect on our consolidated financial statements. However, as discussed further below, once the new guidance setting forth principles for the recognition, measurement, presentation and disclosure of leases goes into effect on January 1, 2019, we believe that the new revenue standard will apply to executory costs and other components of revenue due under leases that are deemed to be non-lease components (such as common area maintenance and provision of utilities), which could affect our recognition pattern for such revenue. In February 2016, the FASB issued guidance that sets forth principles for the recognition, measurement, presentation and disclosure of leases. This guidance 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 of the leased asset by the lessee. The resulting classification determines whether the lease expense is recognized based on an effective interest method or straight-line basis over the term of the lease. 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 similar to existing guidance for operating leases. The guidance requires lessors of real estate to account for leases using an approach that is substantially equivalent to existing guidance for sales-type leases, direct financing leases and operating leases. This guidance is effective for reporting periods beginning January 1, 2019 using a modified retrospective transition approach at the time of adoption. Early adoption is also permitted for this guidance. In addition, the guidance permits lessees and lessors to elect to apply a package of practical expedients that allow them not to reassess upon adoption: the lease classification for any expired or existing leases; their deferred recognition of incremental direct costs of leasing for any expired or existing leases; and whether any expired or existing contracts are, or contain, leases. While we are still completing our assessment of the impact of this guidance, below is a summary of the anticipated primary effects of this guidance on our accounting and reporting. • Real estate leases in which we are the lessor: ◦ Balance sheet reporting: We believe that we will apply an approach under the new guidance that is similar to the current accounting for operating leases, in which we will continue to recognize the underlying leased asset as property on our balance sheet. ◦ Deferral of non-incremental lease costs: Under the new lease guidance, we will no longer be able to defer the recognition of non-incremental costs in connection with new or extended tenant leases (refer to amounts reported in our 2016 Annual Report on Form 10-K for amounts deferred in 2014, 2015 and 2016). Upon adoption of the new guidance, we would expense previously deferred non-incremental lease costs for existing leases unless we elect the package of practical expedients, in which case such costs would remain deferred and amortized over the remaining lease terms. ◦ Lease revenue reporting: We believe that the new revenue standard will apply to executory costs and other components of revenue deemed to be non-lease components (such as common area maintenance and provision of utilities), even when the revenue for such activities is not separately stipulated in the lease. In that case, we would need to separate the lease components of revenue due under leases from the non-lease components and the revenue from these items previously recognized on a straight-line basis under current lease guidance would be recognized under the new revenue guidance as the related services are delivered. As a result, while the total revenue recognized over time would not differ under the new guidance, the recognition pattern could be different. We are in the process of evaluating the significance of the difference in the recognition pattern that would result from this change. • Leases in which we are the lessee: ◦ Our most significant leases as lessee are ground leases we have for certain properties; as of September 30, 2017 , our future minimum rental payments under these leases totaled $90.2 million , with various expiration dates extending to the year 2100. While we are still in the process of evaluating these leases under the new guidance, we believe that we will be required to recognize a right-of-use asset and a lease liability for the present value of these minimum lease payments. We also believe that these types of leases most likely would be classified as finance leases under the new guidance, which would result in the interest component of each lease payment being recorded as interest expense and the right-of-use asset being amortized into expense using the straight-line method over the life of the lease; however, if we elect to apply the package of practical expedients, we will continue to account for our existing ground leases as operating leases upon adoption of the guidance. 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 a more timely recognition of such losses. The guidance will apply to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loans, held-to-maturity debt securities, net investments in leases, and off-balance-sheet credit exposures (e.g. loan commitments). Under the new guidance, an entity will recognize its estimate of expected credit losses as an allowance, as the guidance requires that financial assets be measured on an amortized cost basis and to be presented at the net amount expected to be collected. The guidance is effective for us beginning January 1, 2020, with early adoption permitted after December 2018. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In August 2016, the FASB issued guidance that clarifies how entities should classify certain cash receipts and cash payments on the statement of cash flows with the objective of reducing the existing diversity in practice related to eight specific cash flow issues. The areas addressed in the new guidance relate to debt prepayment costs, settlement of zero-coupon debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of insurance claims, proceeds from the settlement of corporate-owned and bank-owned life insurance policies, distributions received from equity method investments, beneficial interest in securitization transactions and separately identifiable cash flows and application of the predominance principle. The guidance is effective for us beginning January 1, 2018, with early adoption permitted. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In November 2016, the FASB issued guidance that requires the statement of cash flows to explain the change during the period in the total of cash, cash equivalents and amounts described as restricted cash or restricted cash equivalents. Under the new guidance, amounts described as restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning of period and end of period total amounts shown on the statement of cash flows. The guidance is effective for us beginning January 1, 2018, with early adoption permitted. We do not expect the adoption of this guidance to have a material impact on our consolidated financial statements. In February 2017, the FASB issued guidance clarifying the scope of asset derecognition provisions and accounting for partial sales of nonfinancial assets. The new guidance requires recognition of a sale of real estate and resulting gain or loss when control transfers and the buyer has the ability to direct use of, or obtain substantially all of the remaining benefit from, the asset (which generally will occur on the closing date); the factor of continuing involvement is no longer a specific consideration for the timing of recognition. The new guidance eliminates the need to consider adequacy of buyer investment, which was replaced by additional judgments regarding collectability and intent and/or ability to pay. The new guidance also requires an entity to derecognize nonfinancial assets and in substance non financial assets once it transfers control of such assets. When an entity transfers its controlling interest in a nonfinancial asset, but retains a noncontrolling ownership interest, the entity is required to measure any non-controlling interest it receives or retains at fair value and recognize a full gain or loss on the transaction; as a result, sales and partial sales of real estate assets will now be subject to the same derecognition model as all other nonfinancial assets. As discussed further in our 2016 Annual Report on Form 10-K, we had a transaction in July 2016 accounted for as a partial sale under existing guidance that would meet the criteria for immediate full gain recognition under the new guidance; this would result in an additional $18 million in income being recognized in 2016 that is currently being amortized into income in subsequent periods under existing guidance. We do not believe that the recognition pattern for our other sales of real estate will be changed by the new guidance. We will adopt this guidance for our annual and interim periods beginning January 1, 2018 and expect to use the the full retrospective method, under which we would retrospectively restate each reporting period presented at the time of adoption. In August 2017, the FASB issued guidance that makes targeted improvements to hedge accounting. This new guidance simplifies the application of hedge accounting and better aligns financial reporting for hedging activities with companies’ economic objectives in undertaking those activities. Under the new guidance, all changes in the fair value of highly effective cash flow hedges will be recorded in other comprehensive income instead of income. The new guidance also eases the administrative burden of hedge documentation requirements and assessing hedge effectiveness. The guidance is effective for us beginning January 1, 2019, with early adoption permitted. We are currently evaluating the impact of this guidance, including transition elections and required disclosures, on our financial statements and the timing of adoption.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Schedule of fair value assets and liabilities measured on recurring basis	The table below sets forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2017 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Interest rate derivatives (1) $ — $ 126 $ — $ 126 Liabilities: Interest rate derivatives (2) $ — $ 316 $ — $ 316 (1) Included in the line entitled “prepaid expenses and other assets” on COPLP ’ s consolidated balance sheet. (2) Included in the line entitled “other liabilities” on COPLP ’ s consolidated balance sheet. The table below sets forth financial assets and liabilities of COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2017 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 4,336 $ — $ — $ 4,336 Other 71 — — 71 Interest rate derivatives (2) — 126 — 126 Total assets $ 4,407 $ 126 $ — $ 4,533 Liabilities: Deferred compensation plan liability (3) $ — $ 4,407 $ — $ 4,407 Interest rate derivatives (3) — 316 — 316 Total liabilities $ — $ 4,723 $ — $ 4,723 (1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet. (2) Included in the line entitled “prepaid expenses and other assets” on COPT ’ s consolidated balance sheet. (3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet.

Properties, Net (Tables)

Properties, Net (Tables)	9 Months Ended
	Sep. 30, 2017
Real Estate [Abstract]
Schedule of operating properties, net	Operating properties, net consisted of the following (in thousands): September 30, December 31, Land $ 440,771 $ 433,311 Buildings and improvements 3,009,203 2,944,905 Less: Accumulated depreciation (759,262 ) (706,385 ) Operating properties, net $ 2,690,712 $ 2,671,831
Schedule of projects in development or held for future development	Projects in development or held for future development consisted of the following (in thousands): September 30, December 31, Land $ 216,108 $ 195,521 Development in progress, excluding land 190,211 206,010 Projects in development or held for future development $ 406,319 $ 401,531
Components of assets held for sale	The table below sets forth the components of assets held for sale on our consolidated balance sheet for these properties (in thousands): September 30, 2017 December 31, 2016 Properties, net $ 68,081 $ 85,402 Deferred rent receivable 5,582 4,241 Intangible assets on real estate acquisitions, net — 338 Deferred leasing costs, net 742 3,636 Lease incentives, net 10 1,037 Assets held for sale, net $ 74,415 $ 94,654
Schedule of operating property dispositions	During the nine months ended September 30, 2017 , we sold the following operating properties (dollars in thousands): Project Name City, State Segment Date of Sale Number of Buildings Total Rentable Square Feet Transaction Value Gain on Sale 3120 Fairview Park Drive Falls Church, VA Northern Virginia Defense/IT 2/15/2017 1 190,000 $ 39,000 $ — 1334 Ashton Road Hanover, MD Fort Meade/BW Corridor 6/9/2017 1 37,000 2,300 — Remaining White Marsh Properties (1) White Marsh, MD Regional Office and Other 7/28/2017 8 412,000 47,500 1,180 Dispositions through 9/30/2017 10 639,000 $ 88,800 $ 1,180 (1) This sale also included land.

Real Estate Joint Ventures (Tab

Real Estate Joint Ventures (Tables)	9 Months Ended
	Sep. 30, 2017
Equity Method Investments and Joint Ventures [Abstract]
Schedule of information related to investments in consolidated real estate joint ventures	The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of September 30, 2017 (dollars in thousands): Nominal Ownership September 30, 2017 (1) Date % as of Total Encumbered Total Acquired 9/30/2017 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 158,937 $ 76,374 $ 50,344 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 70,767 45,813 46,895 Stevens Investors, LLC 8/11/2015 95% Development of real estate (4) 70,383 — 23,566 $ 300,087 $ 122,187 $ 120,805 (1) Excludes amounts eliminated in consolidation. (2) This joint venture’s properties are in Huntsville, Alabama. (3) This joint venture’s properties are in College Park, Maryland. (4) This joint venture’s property is in Washington, DC. Our partner in this joint venture received an additional distribution from the joint venture of $6.7 million in July 2017 that was reported in other liabilities on our consolidated balance sheet as of December 31, 2016.

Investing Receivables (Tables)

Investing Receivables (Tables)	9 Months Ended
	Sep. 30, 2017
Receivables [Abstract]
Schedule of investing receivables	Investing receivables, including accrued interest thereon, consisted of the following (in thousands): September 30, December 31, Notes receivable from the City of Huntsville $ 53,088 $ 49,258 Other investing loans receivable 3,020 3,021 $ 56,108 $ 52,279

Prepaid Expenses and Other As29

Prepaid Expenses and Other Assets, Net (Tables)	9 Months Ended
	Sep. 30, 2017
Prepaid Expense and Other Assets [Abstract]
Schedule of prepaid expenses and other assets	Prepaid expenses and other assets, net consisted of the following (in thousands): September 30, December 31, Prepaid expenses $ 30,932 $ 24,432 Lease incentives, net 17,202 18,276 Furniture, fixtures and equipment, net 5,422 5,204 Deferred tax asset, net (1) 2,851 3,036 Non-real estate equity method investments 2,413 2,355 Construction contract costs incurred in excess of billings 2,005 10,350 Deferred financing costs, net (2) 1,419 3,128 Other assets 4,294 5,983 Prepaid expenses and other assets, net $ 66,538 $ 72,764 (1) Includes a valuation allowance of $2.1 million . (2) Represents deferred costs, net of accumulated amortization, attributable to our Revolving Credit Facility and interest rate derivatives.

Debt, Net (Tables)

Debt, Net (Tables)	9 Months Ended
	Sep. 30, 2017
Debt Disclosure [Abstract]
Schedule of debt	Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of September 30, December 31, Stated Interest Rates as of Scheduled Maturity as of September 30, 2017 September 30, 2017 Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 151,594 $ 154,143 3.82% - 7.87% (3) 2019-2026 Variable rate secured debt 13,200 13,448 LIBOR + 1.85% (4) October 2020 Total mortgage and other secured debt 164,794 167,591 Revolving Credit Facility 170,000 — LIBOR + 0.875% to 1.60% (5) May 2019 (6) Term Loan Facilities (7) 348,371 547,494 LIBOR + 0.90% to 2.40% (8) 2020-2022 Unsecured Senior Notes 3.600%, $350,000 aggregate principal 347,445 347,128 3.60% (9) May 2023 5.250%, $250,000 aggregate principal 246,525 246,176 5.25% (10) February 2024 3.700%, $300,000 aggregate principal 298,200 297,843 3.70% (11) June 2021 5.000%, $300,000 aggregate principal 296,639 296,368 5.00% (12) July 2025 Unsecured notes payable 1,317 1,401 0% (13) 2026 Total debt, net $ 1,873,291 $ 1,904,001 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $4.8 million as of September 30, 2017 and $6.1 million as of December 31, 2016 . (2) Certain fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying values of these loans reflect net unamortized premiums totaling $367,000 as of September 30, 2017 and $422,000 as of December 31, 2016 . (3) The weighted average interest rate on our fixed rate mortgage debt was 4.19% as of September 30, 2017 . (4) The interest rate on our variable rate secured debt as of September 30, 2017 was 3.09% . (5) The weighted average interest rate on the Revolving Credit Facility was 2.40% as of September 30, 2017 . (6) The facility matures in May 2019, with the ability for us to further extend such maturity by two six -month periods at our option, provided that there is no default under the facility and we pay an extension fee of 0.075% of the total availability under the facility for each extension period. (7) As of September 30, 2017 , we have the ability to borrow an additional $350.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders. On May 1, 2017, we repaid $200.0 million of the loan balance on a term loan scheduled to mature in 2020. (8) The weighted average interest rate on these loans was 2.93% as of September 30, 2017 . (9) The carrying value of these notes reflects an unamortized discount totaling $1.8 million as of September 30, 2017 and $2.0 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.70% . (10) The carrying value of these notes reflects an unamortized discount totaling $3.1 million as of September 30, 2017 and $3.4 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.49% . (11) The carrying value of these notes reflects an unamortized discount totaling $1.4 million as of September 30, 2017 and $1.7 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.85% . (12) The carrying value of these notes reflects an unamortized discount totaling $2.8 million as of September 30, 2017 and $3.0 million as of December 31, 2016 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% . (13) These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying value of these notes reflects an unamortized discount totaling $394,000 as of September 30, 2017 and $460,000 as of December 31, 2016 .
Schedule of the fair value of debt	The following table sets forth information pertaining to the fair value of our debt (in thousands): September 30, 2017 December 31, 2016 Carrying Fair Carrying Fair Amount Value Amount Value Fixed-rate debt Unsecured Senior Notes $ 1,188,809 $ 1,231,222 $ 1,187,515 $ 1,220,282 Other fixed-rate debt 152,911 154,781 155,544 156,887 Variable-rate debt 531,571 531,520 560,942 558,437 $ 1,873,291 $ 1,917,523 $ 1,904,001 $ 1,935,606

Interest Rate Derivatives (Tabl

Interest Rate Derivatives (Tables)	9 Months Ended
	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of key terms and fair values of interest rate swap derivatives	The following table sets forth the key terms and fair values of our interest rate swap derivatives, each of which was designated as a cash flow hedge of interest rate risk (dollars in thousands): Fair Value at Notional Amount Fixed Rate Floating Rate Index Effective Date Expiration Date September 30, December 31, $ 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 $ (237 ) $ (848 ) 13,311 (1) 1.3900% One-Month LIBOR 10/13/2015 10/1/2020 126 100 100,000 1.9013% One-Month LIBOR 9/1/2016 12/1/2022 (27 ) (23 ) 100,000 1.9050% One-Month LIBOR 9/1/2016 12/1/2022 (22 ) 48 50,000 1.9079% One-Month LIBOR 9/1/2016 12/1/2022 (30 ) 10 100,000 (2) 1.6730% One-Month LIBOR 9/1/2015 8/1/2019 — (701 ) $ (190 ) $ (1,414 ) (1) The notional amount of this instrument is scheduled to amortize to $12.1 million . (2) We cash settled this derivative and interest accrued thereon for $460,000 on May 1, 2017. Since the hedged transactions associated with this derivative were still probable to occur as of the settlement date, amounts in accumulated other comprehensive loss ( “ AOCL ” ) associated with this derivative will be reclassified to interest expense through August 2019.
Schedule of fair value and balance sheet classification of interest rate derivatives	The table below sets forth the fair value of our interest rate derivatives as well as their classification on our consolidated balance sheets (in thousands): Fair Value at Derivatives Balance Sheet Location September 30, December 31, 2016 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets $ 126 $ 158 Interest rate swaps designated as cash flow hedges Other liabilities (316 ) (1,572 )
Schedule of effect of interest rate derivatives on consolidated statements of operations and comprehensive income	The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Unrealized (loss) gain recognized in AOCL (effective portion) $ (301 ) $ 407 $ (1,877 ) $ (16,581 ) Loss reclassified from AOCL into interest expense (effective portion) (615 ) (1,043 ) (2,652 ) (2,763 ) Gain (loss) on derivatives recognized in interest expense (ineffective portion) 34 1,523 132 (347 ) Loss reclassified from AOCL into interest expense (ineffective portion) (1) — — (88 ) — (1) Represents a loss recognized on certain interest rate swaps from the accelerated reclassification of amounts in AOCL on May 1, 2017, when we concluded that hedged forecasted transactions were probable not to occur.

Redeemable Noncontrolling Int32

Redeemable Noncontrolling Interests (Tables)	9 Months Ended
	Sep. 30, 2017
Noncontrolling Interest [Abstract]
Schedule of activity for redeemable noncontrolling interest	The table below sets forth the activity for these redeemable noncontrolling interests (in thousands): For the Nine Months Ended September 30, 2017 2016 Beginning balance $ 22,979 $ 19,218 Contributions from noncontrolling interests — 22,779 Distributions to noncontrolling interests (1,186 ) (21,344 ) Net income attributable to noncontrolling interests 1,720 1,679 Adjustment to arrive at fair value of interests (244 ) 516 Ending balance $ 23,269 $ 22,848

Information by Business Segme33

Information by Business Segment (Tables)	9 Months Ended
	Sep. 30, 2017
Segment Reporting [Abstract]
Schedule of segment financial information for real estate operations	The table below reports segment financial information for our reportable segments (in thousands): Operating Office Property Segments Defense/Information Technology Locations Fort Meade/BW Corridor Northern Virginia Defense/IT Lackland Air Force Base Navy Support Locations Redstone Arsenal Data Center Shells Total Defense/IT Locations Regional Office Operating Other Total Three Months Ended September 30, 2017 Revenues from real estate operations $ 61,254 $ 12,190 $ 11,024 $ 7,494 $ 3,532 $ 6,676 $ 102,170 $ 16,656 $ 7,398 $ 1,007 $ 127,231 Property operating expenses (19,708 ) (4,343 ) (6,193 ) (3,157 ) (1,432 ) (637 ) (35,470 ) (7,406 ) (3,175 ) (317 ) (46,368 ) UJV NOI allocable to COPT — — — — — 1,297 1,297 — — — 1,297 NOI from real estate operations $ 41,546 $ 7,847 $ 4,831 $ 4,337 $ 2,100 $ 7,336 $ 67,997 $ 9,250 $ 4,223 $ 690 $ 82,160 Additions to long-lived assets $ 5,810 $ 2,587 $ 55 $ 1,910 $ 843 $ — $ 11,205 $ 5,338 $ 9 $ 76 $ 16,628 Transfers from non-operating properties $ 5,519 $ 45,554 $ — $ 8 $ (62 ) $ 29,803 $ 80,822 $ 25 $ — $ — $ 80,847 Three Months Ended September 30 2016 Revenues from real estate operations $ 61,460 $ 12,231 $ 12,532 $ 7,232 $ 3,189 $ 5,175 $ 101,819 $ 20,499 $ 6,809 $ 1,827 $ 130,954 Property operating expenses (20,598 ) (4,462 ) (7,599 ) (3,374 ) (1,112 ) (528 ) (37,673 ) (8,155 ) (3,317 ) (807 ) (49,952 ) UJV NOI allocable to COPT — — — — — 1,008 1,008 — — — 1,008 NOI from real estate operations $ 40,862 $ 7,769 $ 4,933 $ 3,858 $ 2,077 $ 5,655 $ 65,154 $ 12,344 $ 3,492 $ 1,020 $ 82,010 Additions to long-lived assets $ 5,901 $ 7,153 $ — $ 2,207 $ 2,642 $ — $ 17,903 $ 4,168 $ 108 $ 53 $ 22,232 Transfers from non-operating properties $ 5,331 $ 308 $ 3 $ — $ 3,100 $ 25,513 $ 34,255 $ (4 ) $ 40 $ — $ 34,291 Nine Months Ended September 30, 2017 Revenues from real estate operations $ 183,393 $ 34,992 $ 35,687 $ 21,953 $ 10,616 $ 17,998 $ 304,639 $ 52,394 $ 21,201 $ 4,061 $ 382,295 Property operating expenses (60,357 ) (13,014 ) (21,125 ) (9,391 ) (4,294 ) (1,873 ) (110,054 ) (21,974 ) (10,041 ) (1,446 ) (143,515 ) UJV NOI allocable to COPT — — — — — 3,889 3,889 — — — 3,889 NOI from real estate operations $ 123,036 $ 21,978 $ 14,562 $ 12,562 $ 6,322 $ 20,014 $ 198,474 $ 30,420 $ 11,160 $ 2,615 $ 242,669 Additions to long-lived assets $ 15,085 $ 6,032 $ 71 $ 6,309 $ 1,059 $ — $ 28,556 $ 16,476 $ 3,588 $ 203 $ 48,823 Transfers from non-operating properties $ 37,094 $ 45,994 $ — $ 474 $ 1,643 $ 55,003 $ 140,208 $ — $ 8 $ 18 $ 140,234 Segment assets at September 30, 2017 $ 1,265,569 $ 400,855 $ 129,657 $ 194,801 $ 108,884 $ 258,611 $ 2,358,377 $ 398,579 $ 226,909 $ 13,347 $ 2,997,212 Nine Months Ended September 30, 2016 Revenues from real estate operations $ 184,881 $ 36,404 $ 34,408 $ 21,164 $ 9,496 $ 18,793 $ 305,146 $ 67,284 $ 20,106 $ 5,429 $ 397,965 Property operating expenses (64,222 ) (13,310 ) (19,863 ) (9,573 ) (3,050 ) (2,164 ) (112,182 ) (26,707 ) (8,629 ) (2,450 ) (149,968 ) UJV NOI allocable to COPT — — — — — 1,008 1,008 — — — 1,008 NOI from real estate operations $ 120,659 $ 23,094 $ 14,545 $ 11,591 $ 6,446 $ 17,637 $ 193,972 $ 40,577 $ 11,477 $ 2,979 $ 249,005 Additions to long-lived assets $ 19,516 $ 13,290 $ — $ 5,710 $ 3,561 $ — $ 42,077 $ 9,107 $ 108 $ 363 $ 51,655 Transfers from non-operating properties $ 41,850 $ 28,158 $ 240 $ — $ 3,315 $ 81,467 $ 155,030 $ 104 $ (391 ) $ (11 ) $ 154,732 Segment assets at September 30, 2016 $ 1,261,337 $ 416,886 $ 132,722 $ 195,244 $ 111,310 $ 189,746 $ 2,307,245 $ 453,766 $ 234,551 $ 31,563 $ 3,027,125
Schedule of reconciliation of segment revenues to total revenues	The following table reconciles our segment revenues to total revenues as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Segment revenues from real estate operations $ 127,231 $ 130,954 $ 382,295 $ 397,965 Construction contract and other service revenues 29,786 11,149 65,958 34,372 Total revenues $ 157,017 $ 142,103 $ 448,253 $ 432,337
Schedule of reconciliation of unconsolidated joint venture net operating income to equity in income of unconsolidated entities	The following table reconciles UJV NOI allocable to COPT to equity in income of unconsolidated entities as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 UJV NOI allocable to COPT $ 1,297 $ 1,008 $ 3,889 $ 1,008 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (577 ) (415 ) (1,724 ) (415 ) Add: Equity in (loss) income of unconsolidated non-real estate entities (1 ) 1 (3 ) 21 Equity in income of unconsolidated entities $ 719 $ 594 $ 2,162 $ 614
Schedule of computation of net operating income from service operations	The table below sets forth the computation of our NOI from service operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Construction contract and other service revenues $ 29,786 $ 11,149 $ 65,958 $ 34,372 Construction contract and other service expenses (28,788 ) (10,341 ) (63,589 ) (32,513 ) NOI from service operations $ 998 $ 808 $ 2,369 $ 1,859
Schedule of reconciliation of net operating income from real estate operations and service operations to (loss) income from continuing operations	The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from before gain on sales of real estate as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 NOI from real estate operations $ 82,160 $ 82,010 $ 242,669 $ 249,005 NOI from service operations 998 808 2,369 1,859 Interest and other income 1,508 1,391 4,817 3,877 Equity in income of unconsolidated entities 719 594 2,162 614 Income tax (expense) benefit (57 ) 21 (145 ) 28 Depreciation and other amortization associated with real estate operations (34,438 ) (32,015 ) (100,290 ) (99,790 ) Impairment recoveries (losses) 161 (27,699 ) (1,464 ) (99,837 ) General, administrative and leasing expenses (7,368 ) (8,855 ) (23,838 ) (28,764 ) Business development expenses and land carry costs (1,277 ) (1,716 ) (4,567 ) (6,497 ) Interest expense (19,615 ) (18,301 ) (57,772 ) (64,499 ) Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities (1,297 ) (1,008 ) (3,889 ) (1,008 ) Loss on early extinguishment of debt — (59 ) (513 ) (37 ) Income (loss) before gain on sales of real estate $ 21,494 $ (4,829 ) $ 59,539 $ (45,049 )
Schedule of reconciliation of segment assets to total assets	The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): September 30, September 30, Segment assets $ 2,997,212 $ 3,027,125 Non-operating property assets 413,255 421,364 Other assets 149,305 185,705 Total COPT consolidated assets $ 3,559,772 $ 3,634,194

Share-Based Compensation and 34

Share-Based Compensation and Other Compensation Matters (Tables)	9 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of payouts for defined performance under performance-based awards of share-based compensation	The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned PSUs Payout % 75th or greater 200% of PSUs granted 50th or greater 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted

Earnings Per Share ("EPS") an35

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earnings per share	Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net income (loss) attributable to COPT $ 20,916 $ 27,299 $ 60,133 $ (13,294 ) Preferred share dividends — (3,552 ) (6,219 ) (10,657 ) Issuance costs associated with redeemed preferred shares — — (6,847 ) — Income attributable to share-based compensation awards (95 ) (105 ) (337 ) (319 ) Numerator for basic and diluted EPS on net income (loss) attributable to COPT common shareholders $ 20,821 $ 23,642 $ 46,730 $ (24,270 ) Denominator (all weighted averages): Denominator for basic EPS (common shares) 99,112 94,433 98,855 94,312 Dilutive effect of share-based compensation awards 146 81 154 — Denominator for diluted EPS (common shares) 99,258 94,514 99,009 94,312 Basic EPS: Net income (loss) attributable to COPT common shareholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Diluted EPS: Net income (loss) attributable to COPT common shareholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 )
Schedule of securities excluded from computation of diluted earnings per share	Our diluted EPS computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPS for the respective periods (in thousands): Weighted Average Shares Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Conversion of common units 3,350 3,591 3,400 3,648 Conversion of Series I Preferred Units 176 176 176 176 Conversion of Series K Preferred Shares — 434 — 434
Corporate Office Properties, L.P.
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earnings per share	Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Numerator: Net income (loss) attributable to COPLP common unitholders $ 21,785 $ 28,359 $ 62,239 $ (13,751 ) Preferred unit distributions (165 ) (3,717 ) (6,714 ) (11,152 ) Issuance costs associated with redeemed preferred units — — (6,847 ) — Income attributable to share-based compensation awards (95 ) (105 ) (337 ) (319 ) Numerator for basic and diluted EPU on net income (loss) attributable to COPLP common unitholders $ 21,525 $ 24,537 $ 48,341 $ (25,222 ) Denominator (all weighted averages): Denominator for basic EPU (common units) 102,462 98,024 102,255 97,960 Dilutive effect of share-based compensation awards 146 81 154 — Denominator for diluted EPU (common units) 102,608 98,105 102,409 97,960 Basic EPU: Net income (loss) attributable to COPLP common unitholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 ) Diluted EPU: Net income (loss) attributable to COPLP common unitholders $ 0.21 $ 0.25 $ 0.47 $ (0.26 )
Schedule of securities excluded from computation of diluted earnings per share	Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2017 2016 2017 2016 Conversion of Series I preferred units 176 176 176 176 Conversion of Series K preferred units — 434 — 434

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Future minimum rental payments for operating leases	Future minimum rental payments due under the terms of these operating leases as of September 30, 2017 follow (in thousands): Year Ending December 31, 2017 (1) $ 320 2018 1,275 2019 1,263 2020 1,257 2021 1,260 Thereafter 85,761 $ 91,136 (1) Represents the three months ending December 31, 2017 .
Future minimum lease payments for capital leases	Future minimum rental payments due under the term of this lease as of September 30, 2017 follow (in thousands): Year Ending December 31, 2017 (1) $ 700 2018 15,775 2020 135 Thereafter 75 Total minimum rental payments $ 16,685 Less: Amount representing interest (338 ) Capital lease obligation $ 16,347 (1) Represents the three months ending December 31, 2017 .

Organization (Details)

Organization (Details) ft² in Thousands	Sep. 30, 2017aft²builldingPropertyMW
Operating office properties
Investments in real estate
Number of real estate properties	159
Area of real estate property (in square feet or acres) | ft²	17,400
Operating office properties | Single-tenant data centers
Investments in real estate
Number of real estate properties | buillding	15
Office properties under, or contractually committed for, construction or approved for redevelopment
Investments in real estate
Number of real estate properties	10
Area of real estate property (in square feet or acres) | ft²	1,087
Office properties under, or contractually committed for, construction or approved for redevelopment | Single-tenant data centers
Investments in real estate
Number of real estate properties | buillding	3
Office properties under, or contractually committed for, construction or approved for redevelopment | Partially operational properties
Investments in real estate
Number of real estate properties	3
Office properties under, or contractually committed for, construction or approved for redevelopment | Properties completed Held-for-future lease
Investments in real estate
Number of real estate properties	2
Land controlled for future development
Investments in real estate
Area of real estate property (in square feet or acres) | a	984
Developable square feet | ft²	12,300
Other Land
Investments in real estate
Area of real estate property (in square feet or acres) | a	152
Operating wholesale data centers
Investments in real estate
Critical load (in megawatts) | MW	19.25
GI-COPT | Operating office properties | Single-tenant data centers
Investments in real estate
Number of real estate properties	6

Organization (Details 2)

Organization (Details 2) - Corporate Office Properties, L.P.	9 Months Ended
	Sep. 30, 2017
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	96.80%
Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	0.00%

Summary of Significant Accoun39

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum rental payments due		$ 91,136
Ground Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum rental payments due		$ 90,200
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of change on net income	$ 18,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2017
Assets held for sale, net | Fair value measurement on a nonrecurring basis | White Marsh, Maryland
Assets and liabilities measured at fair value
Impairment losses	$ 1.6
Deferred compensation plan | Management
Assets and liabilities measured at fair value
Maximum percentage of participants' compensation which is deferrable (as a percent)		100.00%
Balance of the plan which was fully funded		$ 4.4

Fair Value Measurements (Deta41

Fair Value Measurements (Details 2) - Fair value measurement on a recurring basis $ in Thousands	Sep. 30, 2017USD ($)
Assets:
Interest rate derivatives	$ 126
Total assets	4,533
Liabilities:
Deferred compensation plan liability	4,407
Interest rate derivatives	316
Liabilities	4,723
Mutual funds
Assets:
Marketable securities in deferred compensation plan	4,336
Other
Assets:
Marketable securities in deferred compensation plan	71
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total assets	4,407
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Assets:
Marketable securities in deferred compensation plan	4,336
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Assets:
Marketable securities in deferred compensation plan	71
Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	126
Total assets	126
Liabilities:
Deferred compensation plan liability	4,407
Interest rate derivatives	316
Liabilities	4,723
Corporate Office Properties, L.P.
Assets:
Interest rate derivatives	126
Liabilities:
Interest rate derivatives	316
Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	126
Liabilities:
Interest rate derivatives	$ 316

Properties, Net (Details)

Properties, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Investments in real estate
Operating properties, net	$ 2,690,712	$ 2,671,831
Operating Properties
Investments in real estate
Less: accumulated depreciation	(759,262)	(706,385)
Operating properties, net	2,690,712	2,671,831
Operating Properties | Land
Investments in real estate
Gross	440,771	433,311
Operating Properties | Buildings and improvements
Investments in real estate
Gross	$ 3,009,203	$ 2,944,905

Properties, Net (Details 2)

Properties, Net (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Properties
Projects in development or held for future development	$ 406,319	$ 401,531
Projects in development or held for future development
Properties
Projects in development or held for future development	406,319	401,531
Projects in development or held for future development | Land in development or held for future development
Properties
Projects in development or held for future development	216,108	195,521
Projects in development or held for future development | Construction in progress, excluding land
Properties
Projects in development or held for future development	$ 190,211	$ 206,010

Properties, Net (Details 3)

Properties, Net (Details 3) $ in Thousands	Sep. 30, 2017USD ($)Property	Dec. 31, 2016USD ($)Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net	$ 74,415	$ 94,654
Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Properties, net	68,081	85,402
Deferred rent receivable	5,582	4,241
Intangible assets on real estate acquisitions, net	0	338
Deferred leasing costs, net	742	3,636
Lease incentives, net	10	1,037
Assets held for sale, net	$ 74,415	$ 94,654
Defense/Information Technology Locations | Data Center Shells | Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties | Property	2
Defense/Information Technology Locations | Northern Virginia Defense/IT | Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties | Property		1
Defense/Information Technology Locations | Fort Meade/BW Corridor | Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties | Property	1
Regional Office and Other [Member] | White Marsh, Maryland | Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties | Property		8

Properties, Net (Details 4)

Properties, Net (Details 4)	9 Months Ended
	Sep. 30, 2017USD ($)ft²Property	Oct. 27, 2017USD ($)ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price of land	$ 14,300,000
Gain on sale of land	$ 4,200,000
Operating Properties | Defense/Information Technology Locations | Data Center Shells | 201 Technology Drive | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square footage of real estate properties (in square feet) | ft²		103,000
Transaction value		$ 29,200,000
Operating Properties | Defense/Information Technology Locations | Data Center Shells | 11751 Meadowville Lane | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Square footage of real estate properties (in square feet) | ft²		193,000
Transaction value		$ 44,300,000
Indemnification amount		$ 20,000,000
Dispositions | Operating Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | Property	10
Square footage of real estate properties (in square feet) | ft²	639,000
Transaction value	$ 88,800,000
Gain on Sale	$ 1,180,000
Dispositions | Operating Properties | Defense/Information Technology Locations | Northern Virginia Defense/IT | 3120 Fairview Park Drive
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | Property	1
Square footage of real estate properties (in square feet) | ft²	190,000
Transaction value	$ 39,000,000
Gain on Sale	$ 0
Dispositions | Operating Properties | Defense/Information Technology Locations | Fort Meade/BW Corridor | 1334 Ashton Road
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | Property	1
Square footage of real estate properties (in square feet) | ft²	37,000
Transaction value	$ 2,300,000
Gain on Sale	$ 0
Dispositions | Operating Properties | Regional Office and Other [Member] | White Marsh, Maryland
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties | Property	8
Square footage of real estate properties (in square feet) | ft²	412,000
Transaction value	$ 47,500,000
Gain on Sale	$ 1,180,000

Properties, Net (Details 5)

Properties, Net (Details 5) ft² in Thousands	9 Months Ended
	Sep. 30, 2017ft²Property
Office properties under, or contractually committed for, construction or approved for redevelopment
Construction, Redevelopment and Dispositions
Number of real estate properties	10
Square footage of real estate properties (in square feet) | ft²	1,087
Newly constructed properties placed in service
Construction, Redevelopment and Dispositions
Square feet of properties placed in service | ft²	751
Number of real estate properties	5
Newly redeveloped properties placed in service
Construction, Redevelopment and Dispositions
Square feet of properties placed in service | ft²	88
Number of real estate properties	3
Properties under construction or contractually committed for construction
Construction, Redevelopment and Dispositions
Number of real estate properties	8
Square footage of real estate properties (in square feet) | ft²	1,051
Properties completed Held-for-future lease | Office properties under, or contractually committed for, construction or approved for redevelopment
Construction, Redevelopment and Dispositions
Number of real estate properties	2
Properties under or approved for redevelopment
Construction, Redevelopment and Dispositions
Number of real estate properties	2
Square footage of real estate properties (in square feet) | ft²	36

Real Estate Joint Ventures (Det

Real Estate Joint Ventures (Details) $ in Thousands	1 Months Ended	9 Months Ended
	Jul. 31, 2017USD ($)	Sep. 30, 2017USD ($)builldingProperty	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Investments in consolidated real estate joint ventures
Due to Affiliate		$ 7,860	$ 14,329
Real estate equity method investments		2,413		$ 2,355
GI-COPT
Investments in consolidated real estate joint ventures
Real estate equity method investments		25,200
Difference between cost basis and our share of the underlying equity		17,100
Consolidated real estate joint ventures
Investments in consolidated real estate joint ventures
Total Assets		300,087
Encumbered Assets		122,187
Total Liabilities		$ 120,805
Variable Interest Entity, Primary Beneficiary | LW Redstone Company, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)		85.00%
Total Assets		$ 158,937
Encumbered Assets		76,374
Total Liabilities		$ 50,344
Variable Interest Entity, Primary Beneficiary | M Square Associates, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)		50.00%
Total Assets		$ 70,767
Encumbered Assets		45,813
Total Liabilities		$ 46,895
Variable Interest Entity, Primary Beneficiary | Stevens Investors, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)		95.00%
Total Assets		$ 70,383
Encumbered Assets		0
Total Liabilities		$ 23,566
Due to Affiliate	$ 6,700
Operating office properties
Investments in consolidated real estate joint ventures
Number of real estate properties | Property		159
Single-tenant data centers | Operating office properties
Investments in consolidated real estate joint ventures
Number of real estate properties | buillding		15
Single-tenant data centers | Operating office properties | GI-COPT
Investments in consolidated real estate joint ventures
Ownership percentage (percent)		50.00%
Number of real estate properties | Property		6

Investing Receivables (Details)

Investing Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 56,108	$ 52,279
Notes Receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 53,088	49,258
Notes Receivable from City of Huntsville | LW Redstone Company, LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Stated interest rate (as a percent)	9.95%
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 3,020	$ 3,021

Prepaid Expenses and Other As49

Prepaid Expenses and Other Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Prepaid Expense and Other Assets [Abstract]
Prepaid expenses	$ 30,932	$ 24,432
Lease incentives, net	17,202	18,276
Furniture, fixtures and equipment, net	5,422	5,204
Deferred tax asset, net	2,851	3,036
Non-real estate equity method investments	2,413	2,355
Construction contract costs incurred in excess of billings	2,005	10,350
Deferred financing costs, net	1,419	3,128
Other assets	4,294	5,983
Prepaid expenses and other assets, net	66,538	72,764
Taxable REIT Subsidiary
Mortgage and Other Investing Receivables [Line Items]
Deferred tax assets, valuation allowance	$ 2,100	$ 2,100

Debt, Net (Details)

Debt, Net (Details)	May 01, 2017USD ($)	Sep. 30, 2017USD ($)extension	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)extension	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Debt
Carrying Value		$ 1,873,291,000		$ 1,873,291,000		$ 1,904,001,000
Deferred financing costs, net		1,419,000		1,419,000		3,128,000
Interest costs capitalized		1,100,000	$ 1,200,000	4,200,000	$ 4,300,000
Secured Debt
Debt
Carrying Value		$ 164,794,000		$ 164,794,000		167,591,000
Line of Credit [Member] | Revolving Credit Facility
Debt
Number of extensions | extension		2		2
Extension option period (in years)				6 months
Loans payable
Debt
Deferred financing costs, net		$ 4,800,000		$ 4,800,000		6,100,000
Credit Facility [Member] | Revolving Credit Facility
Debt
Line of credit facility, extension fee percentage				0.075%
Term Loan Facilities Maturing 2020
Debt
Repayments of long-term debt	$ 200,000,000
Fixed rate debt | Secured Debt
Debt
Carrying Value		151,594,000		$ 151,594,000		154,143,000
Unamortized premium included in carrying value		$ 367,000		$ 367,000		422,000
Weighted average interest rate (as a percent)		4.19%		4.19%
Fixed rate debt | Secured Debt | Minimum
Debt
Stated interest rate (as a percent)		3.82%		3.82%
Fixed rate debt | Secured Debt | Maximum
Debt
Stated interest rate (as a percent)		7.87%		7.87%
Variable-rate debt
Debt
Description of variable rate basis				LIBOR
Variable-rate debt | Secured Debt
Debt
Carrying Value		$ 13,200,000		$ 13,200,000		13,448,000
Stated interest rate (as a percent)		3.09%		3.09%
Variable-rate debt | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)				1.85%
Revolving Credit Facility
Debt
Carrying Value		$ 170,000,000		$ 170,000,000		0
Description of variable rate basis				LIBOR
Weighted average interest rate (as a percent)		2.40%		2.40%
Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)				0.875%
Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)				1.60%
Term Loan Facilities
Debt
Carrying Value		$ 348,371,000		$ 348,371,000		547,494,000
Description of variable rate basis				LIBOR
Weighted average interest rate (as a percent)		2.93%		2.93%
Aggregate additional borrowing capacity available		$ 350,000,000		$ 350,000,000
Term Loan Facilities | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)				0.90%
Term Loan Facilities | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)				2.40%
3.60% Senior Notes | Unsecured senior notes
Debt
Carrying Value		347,445,000		$ 347,445,000		347,128,000
Debt instrument, face amount		$ 350,000,000		$ 350,000,000
Stated interest rate (as a percent)		3.60%		3.60%
Unamortized discount included in carrying value		$ 1,800,000		$ 1,800,000		2,000,000
Interest rate on debt (as a percent)		3.70%		3.70%
5.250% Senior Notes | Unsecured senior notes
Debt
Carrying Value		$ 246,525,000		$ 246,525,000		246,176,000
Debt instrument, face amount		$ 250,000,000		$ 250,000,000
Stated interest rate (as a percent)		5.25%		5.25%
Unamortized discount included in carrying value		$ 3,100,000		$ 3,100,000		3,400,000
Interest rate on debt (as a percent)		5.49%		5.49%
3.70% Senior Notes | Unsecured senior notes
Debt
Carrying Value		$ 298,200,000		$ 298,200,000		297,843,000
Debt instrument, face amount		$ 300,000,000		$ 300,000,000
Stated interest rate (as a percent)		3.70%		3.70%
Unamortized discount included in carrying value		$ 1,400,000		$ 1,400,000		1,700,000
Interest rate on debt (as a percent)		3.85%		3.85%
5.000% Senior Notes | Unsecured senior notes
Debt
Carrying Value		$ 296,639,000		$ 296,639,000		296,368,000
Debt instrument, face amount		$ 300,000,000		$ 300,000,000
Stated interest rate (as a percent)		5.00%		5.00%
Unamortized discount included in carrying value		$ 2,800,000		$ 2,800,000		3,000,000
Interest rate on debt (as a percent)		5.15%		5.15%
Unsecured notes payable
Debt
Carrying Value		$ 1,317,000		$ 1,317,000		1,401,000
Stated interest rate (as a percent)		0.00%		0.00%
Unamortized discount included in carrying value		$ 394,000		$ 394,000		$ 460,000

Debt, Net (Details 2)

Debt, Net (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Carrying Amount
Carrying amount and estimated fair value of debt
Long-term debt	$ 1,873,291	$ 1,904,001
Carrying Amount | Unsecured senior notes
Carrying amount and estimated fair value of debt
Long-term debt	1,188,809	1,187,515
Carrying Amount | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	152,911	155,544
Carrying Amount | Variable-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	531,571	560,942
Estimated Fair Value
Carrying amount and estimated fair value of debt
Long-term debt	1,917,523	1,935,606
Estimated Fair Value | Unsecured senior notes
Carrying amount and estimated fair value of debt
Long-term debt	1,231,222	1,220,282
Estimated Fair Value | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	154,781	156,887
Estimated Fair Value | Variable-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	$ 531,520	$ 558,437

Interest Rate Derivatives (Deta

Interest Rate Derivatives (Details) - USD ($) $ in Thousands	May 01, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Unrealized (loss) gain recognized in AOCL (effective portion)		$ (301)	$ 407	$ (1,877)	$ (16,581)
Interest rate swaps
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Approximate loss amount to be reclassified from AOCI to interest expense over the next 12 months		1,600		1,600
Interest rate derivatives in liability position, fair value		305		305
Termination value to settle obligations under interest rate derivative agreements		484		484
Interest rate swaps | Interest Expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Loss reclassified from AOCL into interest expense (effective portion)		(615)	(1,043)	(2,652)	(2,763)
Gain (loss) on derivatives recognized in interest expense (ineffective portion)		34	1,523	132	(347)
Loss reclassified from AOCL into interest expense (ineffective portion)		0	$ 0	(88)	$ 0
Interest rate swaps | Prepaid expenses and other current assets
Fair value of interest rate derivatives and balance sheet classification
Interest rate swaps designated as cash flow hedges		126		126		$ 158
Interest rate swaps | Other Liabilities
Fair value of interest rate derivatives and balance sheet classification
Interest rate swaps designated as cash flow hedges		(316)		(316)		(1,572)
Designated
Fair values of interest rate swap derivatives
Fair value of interest rate swaps		(190)		(190)		(1,414)
Designated | Interest rate swap, effective date September 1, 2015, swap two
Fair values of interest rate swap derivatives
Notional Amount		$ 100,000		$ 100,000
Fixed rate (as a percent)		1.73%		1.73%
Fair value of interest rate swaps		$ (237)		$ (237)		(848)
Designated | Interest rate swap, effective October 13, 2015
Fair values of interest rate swap derivatives
Notional Amount		$ 13,311		$ 13,311
Fixed rate (as a percent)		1.39%		1.39%
Fair value of interest rate swaps		$ 126		$ 126		100
Notional amount of interest rate derivatives after scheduled amortization		12,100		12,100
Designated | Interest rate swap, effective September 1, 2016, swap one
Fair values of interest rate swap derivatives
Notional Amount		$ 100,000		$ 100,000
Fixed rate (as a percent)		1.9013%		1.9013%
Fair value of interest rate swaps		$ (27)		$ (27)		(23)
Designated | Interest rate swap, effective September 1, 2016, swap two
Fair values of interest rate swap derivatives
Notional Amount		$ 100,000		$ 100,000
Fixed rate (as a percent)		1.905%		1.905%
Fair value of interest rate swaps		$ (22)		$ (22)		48
Designated | Interest rate swap, effective September 1, 2016, swap three
Fair values of interest rate swap derivatives
Notional Amount		$ 50,000		$ 50,000
Fixed rate (as a percent)		1.9079%		1.9079%
Fair value of interest rate swaps		$ (30)		$ (30)		10
Designated | Interest rate swap, effective date September 1, 2015, swap one
Fair values of interest rate swap derivatives
Notional Amount		$ 100,000		$ 100,000
Fixed rate (as a percent)		1.673%		1.673%
Fair value of interest rate swaps		$ 0		$ 0		$ (701)
Interest rate swap cash settled	$ 460

Redeemable Noncontrolling Int53

Redeemable Noncontrolling Interests (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017USD ($)joint_venture	Sep. 30, 2016USD ($)
Noncontrolling Interest [Abstract]
Number of joint ventures with redeemable noncontrolling interests | joint_venture	2
Redeemable Noncontrolling Interest [Roll Forward]
Beginning balance	$ 22,979	$ 19,218
Contributions from noncontrolling interests	0	22,779
Distributions to noncontrolling interests	(1,186)	(21,344)
Net income attributable to noncontrolling interests	1,720	1,679
Adjustment to arrive at fair value of interests	(244)	516
Ending balance	$ 23,269	$ 22,848

Equity (Details)

Equity (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 27, 2017	Jan. 21, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Redemption of preferred shares (6,900,000 shares)				$ 172,500
Conversion of common units to common shares (in units/shares)				337,000	87,000
Common Stock Issued to Public Under At-the-Market Program
Class of Stock [Line Items]
Shares issued to the public (in shares)				591,042
Issuance of stock, weighted average price per share (in dollars per share)				$ 33.84
Net proceeds from shares issued				$ 19,700
Payments of stock issuance costs				300
At-market stock, offering program established, remaining capacity				70,000
Series K Cumulative Preferred Stock
Class of Stock [Line Items]
Dividend rate (percent)		5.60%
Preferred stock, redemption price per share (in dollars per share)		$ 50
Redemption of preferred shares (6,900,000 shares)		$ 26,600
Issuance costs associated with redeemed preferred shares			$ 17
Series L Cumulative Preferred Stock
Class of Stock [Line Items]
Dividend rate (percent)	7.375%
Preferred stock, redemption price per share (in dollars per share)	$ 25
Redemption of preferred shares (6,900,000 shares)	$ 172,500
Issuance costs associated with redeemed preferred shares				$ 6,800

Information by Business Segme55

Information by Business Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment financial information for real estate operations
Revenues from real estate operations	$ 127,231	$ 130,954	$ 382,295	$ 397,965
Property operating expenses	(46,368)	(49,952)	(143,515)	(149,968)
UJV NOI allocable to COPT	1,297	1,008	3,889	1,008
NOI from real estate operations	82,160	82,010	242,669	249,005
Additions to long-lived assets	16,628	22,232	48,823	51,655
Transfers from non-operating properties	80,847	34,291	140,234	154,732
Segment assets	3,559,772	3,634,194	3,559,772	3,634,194	$ 3,780,885
Defense/Information Technology Locations
Segment financial information for real estate operations
Revenues from real estate operations	102,170	101,819	304,639	305,146
Property operating expenses	(35,470)	(37,673)	(110,054)	(112,182)
UJV NOI allocable to COPT	1,297	1,008	3,889	1,008
NOI from real estate operations	67,997	65,154	198,474	193,972
Additions to long-lived assets	11,205	17,903	28,556	42,077
Transfers from non-operating properties	80,822	34,255	140,208	155,030
Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Revenues from real estate operations	61,254	61,460	183,393	184,881
Property operating expenses	(19,708)	(20,598)	(60,357)	(64,222)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	41,546	40,862	123,036	120,659
Additions to long-lived assets	5,810	5,901	15,085	19,516
Transfers from non-operating properties	5,519	5,331	37,094	41,850
Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Revenues from real estate operations	12,190	12,231	34,992	36,404
Property operating expenses	(4,343)	(4,462)	(13,014)	(13,310)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	7,847	7,769	21,978	23,094
Additions to long-lived assets	2,587	7,153	6,032	13,290
Transfers from non-operating properties	45,554	308	45,994	28,158
Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Revenues from real estate operations	11,024	12,532	35,687	34,408
Property operating expenses	(6,193)	(7,599)	(21,125)	(19,863)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	4,831	4,933	14,562	14,545
Additions to long-lived assets	55	0	71	0
Transfers from non-operating properties	0	3	0	240
Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Revenues from real estate operations	7,494	7,232	21,953	21,164
Property operating expenses	(3,157)	(3,374)	(9,391)	(9,573)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	4,337	3,858	12,562	11,591
Additions to long-lived assets	1,910	2,207	6,309	5,710
Transfers from non-operating properties	8	0	474	0
Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Revenues from real estate operations	3,532	3,189	10,616	9,496
Property operating expenses	(1,432)	(1,112)	(4,294)	(3,050)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	2,100	2,077	6,322	6,446
Additions to long-lived assets	843	2,642	1,059	3,561
Transfers from non-operating properties	(62)	3,100	1,643	3,315
Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Revenues from real estate operations	6,676	5,175	17,998	18,793
Property operating expenses	(637)	(528)	(1,873)	(2,164)
UJV NOI allocable to COPT	1,297	1,008	3,889	1,008
NOI from real estate operations	7,336	5,655	20,014	17,637
Additions to long-lived assets	0	0	0	0
Transfers from non-operating properties	29,803	25,513	55,003	81,467
Regional Office
Segment financial information for real estate operations
Revenues from real estate operations	16,656	20,499	52,394	67,284
Property operating expenses	(7,406)	(8,155)	(21,974)	(26,707)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	9,250	12,344	30,420	40,577
Additions to long-lived assets	5,338	4,168	16,476	9,107
Transfers from non-operating properties	25	(4)	0	104
Operating wholesale data centers
Segment financial information for real estate operations
Revenues from real estate operations	7,398	6,809	21,201	20,106
Property operating expenses	(3,175)	(3,317)	(10,041)	(8,629)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	4,223	3,492	11,160	11,477
Additions to long-lived assets	9	108	3,588	108
Transfers from non-operating properties	0	40	8	(391)
Other Segments
Segment financial information for real estate operations
Revenues from real estate operations	1,007	1,827	4,061	5,429
Property operating expenses	(317)	(807)	(1,446)	(2,450)
UJV NOI allocable to COPT	0	0	0	0
NOI from real estate operations	690	1,020	2,615	2,979
Additions to long-lived assets	76	53	203	363
Transfers from non-operating properties	0	0	18	(11)
Segment assets
Segment financial information for real estate operations
Segment assets	2,997,212	3,027,125	2,997,212	3,027,125
Segment assets | Defense/Information Technology Locations
Segment financial information for real estate operations
Segment assets	2,358,377	2,307,245	2,358,377	2,307,245
Segment assets | Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Segment assets	1,265,569	1,261,337	1,265,569	1,261,337
Segment assets | Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Segment assets	400,855	416,886	400,855	416,886
Segment assets | Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Segment assets	129,657	132,722	129,657	132,722
Segment assets | Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Segment assets	194,801	195,244	194,801	195,244
Segment assets | Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Segment assets	108,884	111,310	108,884	111,310
Segment assets | Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Segment assets	258,611	189,746	258,611	189,746
Segment assets | Regional Office
Segment financial information for real estate operations
Segment assets	398,579	453,766	398,579	453,766
Segment assets | Operating wholesale data centers
Segment financial information for real estate operations
Segment assets	226,909	234,551	226,909	234,551
Segment assets | Other Segments
Segment financial information for real estate operations
Segment assets	$ 13,347	$ 31,563	$ 13,347	$ 31,563

Information by Business Segme56

Information by Business Segment (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of segment revenues to total revenues
Segment revenues from real estate operations	$ 127,231	$ 130,954	$ 382,295	$ 397,965
Construction contract and other service revenues	29,786	11,149	65,958	34,372
Total revenues	157,017	142,103	448,253	432,337
Reconciliation of UJV NOI allocable to COPT to Equity Income in Unconsolidated Entities
UJV NOI allocable to COPT	1,297	1,008	3,889	1,008
Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense	(577)	(415)	(1,724)	(415)
Add: Equity in (loss) income of unconsolidated non-real estate entities	(1)	1	(3)	21
Equity in income of unconsolidated entities	719	594	2,162	614
Computation of net operating income from service operations
Construction contract and other service revenues	29,786	11,149	65,958	34,372
Construction contract and other service expenses	(28,788)	(10,341)	(63,589)	(32,513)
NOI from service operations	$ 998	$ 808	$ 2,369	$ 1,859

Information by Business Segme57

Information by Business Segment (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of NOI from real estate operations and NOI from service operations to (loss) income from continuing operations
NOI from real estate operations	$ 82,160	$ 82,010	$ 242,669	$ 249,005
NOI from service operations	998	808	2,369	1,859
Interest and other income	1,508	1,391	4,817	3,877
Equity in income of unconsolidated entities	719	594	2,162	614
Income tax (expense) benefit	(57)	21	(145)	28
Depreciation and other amortization associated with real estate operations	(34,438)	(32,015)	(100,290)	(99,790)
Impairment recoveries (losses)	161	(27,699)	(1,464)	(99,837)
General, administrative and leasing expenses	(7,368)	(8,855)	(23,838)	(28,764)
Business development expenses and land carry costs	(1,277)	(1,716)	(4,567)	(6,497)
Interest expense	(19,615)	(18,301)	(57,772)	(64,499)
Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities	(1,297)	(1,008)	(3,889)	(1,008)
Loss on early extinguishment of debt	0	(59)	(513)	(37)
Income (loss) before gain on sales of real estate	$ 21,494	$ (4,829)	$ 59,539	$ (45,049)

Information by Business Segme58

Information by Business Segment (Details 4) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Reconciliation of segment assets to total assets
Assets	$ 3,559,772	$ 3,780,885	$ 3,634,194
Segment assets
Reconciliation of segment assets to total assets
Assets	2,997,212		3,027,125
Non-operating property assets
Reconciliation of segment assets to total assets
Assets	413,255		421,364
Other assets
Reconciliation of segment assets to total assets
Assets	$ 149,305		$ 185,705

Share-Based Compensation and 59

Share-Based Compensation and Other Compensation Matters (Details)	Aug. 23, 2017USD ($)$ / sharesshares	Aug. 22, 2017$ / shares	Feb. 07, 2017shares	Jan. 01, 2017USD ($)employeePercentile_Rank$ / sharesshares	Sep. 30, 2017USD ($)$ / sharesshares
Other Share-based Compensation Additional Disclosures
Options exercised in period (in shares or units)					5,000
Restricted shares
Share-Based Compensation
Stock awards granted (in shares or units)					230,635
Aggregate grant date fair value | $					$ 7,800,000
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares					$ 33.96
Other Share-based Compensation Additional Disclosures
Shares vested (in shares)					148,401
Weighted average fair value of shares vested (in dollars per share) | $ / shares					$ 26.18
Aggregate intrinsic value of awards upon vesting | $					$ 5,000,000
Deferred share awards
Share-Based Compensation
Stock awards granted (in shares or units)					10,032
Aggregate grant date fair value | $					$ 326,000
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares					$ 32.47
Other Share-based Compensation Additional Disclosures
Shares vested (in shares)					15,590
Weighted average fair value of shares vested (in dollars per share) | $ / shares					$ 26.89
Aggregate intrinsic value of awards upon vesting | $					$ 508,000
Options
Other Share-based Compensation Additional Disclosures
Options exercised in period (in shares or units)					5,000
Options exercised weighted average exercise price (in dollars per share) | $ / shares					$ 29.98
Intrinsic value of options exercised | $					$ 18,000
2017 PSU Grants | Performance share units
Share-Based Compensation
Stock awards granted (in shares or units)	2,826			36,525
Aggregate grant date fair value | $				$ 1,400,000
Potential earned PSUs payout for defined levels of performance under awards
Earned PSUs payout (as a percent of PSUs granted) on 75th or greater percentile rank				200.00%
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank				100.00%
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank				50.00%
Performance share units granted on percentile rank below 25th (as a percent)				0.00%
The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25% | Percentile_Rank				2
Assumptions used to value stock awards
Performance period of the award				3 years
Negative TSR Modifier payout percentage	100.00%
Incremental value of awards | $	$ 12,000
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 46.39	$ 49.66		$ 38.43
Baseline value per common share (in dollars per share) | $ / shares	$ 33.40			$ 31.22
Expected volatility of common shares (as a percent)	18.70%			19.00%
Risk-free interest rate (as a percent)	1.36%			1.47%
2017 PSU Grants | Performance share units | Executive Officer [Member]
Share-Based Compensation
Number of employees affected | employee				3
2014 PSU Grants | Performance share units | Chief Executive Officer
Other Share-based Compensation Additional Disclosures
Shares issued (in shares)			9,763
Percentage of target			100.00%

Earnings Per Share ("EPS") an60

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income (loss) attributable to COPT	$ 20,916	$ 27,299	$ 60,133	$ (13,294)
Preferred share/unit dividends/distributions	0	(3,552)	(6,219)	(10,657)
Issuance costs associated with redeemed preferred shares	0	0	(6,847)	0
Income attributable to share-based compensation awards	(95)	(105)	(337)	(319)
Numerator for basic and diluted EPS on net income (loss) attributable to COPT common shareholders	$ 20,821	$ 23,642	$ 46,730	$ (24,270)
Denominator (all weighted averages):
Denominator for basic EPS (common shares)	99,112	94,433	98,855	94,312
Dilutive effect of share-based compensation awards (shares)	146	81	154	0
Denominator for diluted EPS (common shares)	99,258	94,514	99,009	94,312
Basic EPS:
Net income (loss) attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)
Diluted EPS:
Net income (loss) attributable to COPT common shareholders - diluted (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)
Corporate Office Properties, L.P.
Numerator:
Net income (loss) attributable to COPT	$ 21,785	$ 28,359	$ 62,239	$ (13,751)
Preferred share/unit dividends/distributions	(165)	(3,717)	(6,714)	(11,152)
Issuance costs associated with redeemed preferred shares	0	0	(6,847)	0
Income attributable to share-based compensation awards	(95)	(105)	(337)	(319)
Numerator for basic and diluted EPS on net income (loss) attributable to COPT common shareholders	$ 21,525	$ 24,537	$ 48,341	$ (25,222)
Denominator (all weighted averages):
Denominator for basic EPS (common shares)	102,462	98,024	102,255	97,960
Dilutive effect of share-based compensation awards (shares)	146	81	154	0
Denominator for diluted EPS (common shares)	102,608	98,105	102,409	97,960
Basic EPS:
Net income (loss) attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)
Diluted EPS:
Net income (loss) attributable to COPT common shareholders - diluted (in dollars per share/unit)	$ 0.21	$ 0.25	$ 0.47	$ (0.26)

Earnings Per Share ("EPS") an61

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details 2) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Conversion of common units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,350,000	3,591,000	3,400,000	3,648,000
Conversion of Series I Preferred Units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176,000	176,000	176,000	176,000
Conversion of Series K Preferred Shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	0	434,000	0	434,000
Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	445,000	375,000	431,000	394,000
Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	40,000	233,000	80,000	307,000
Corporate Office Properties, L.P. | Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	445,000	375,000	431,000	394,000
Corporate Office Properties, L.P. | Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	40,000	233,000	80,000	307,000
Corporate Office Properties, L.P. | Conversion of Series I preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176,000	176,000	176,000	176,000
Corporate Office Properties, L.P. | Conversion of Series K preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	0	434,000	0	434,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	May 25, 2017USD ($)	Sep. 30, 2017USD ($)Property	Dec. 31, 2016USD ($)	Aug. 31, 2010USD ($)
Capital Leases
Capital lease term	99 years
Purchase option	$ 1
Capital lease obligation	$ 16,100,000	$ 16,347,000	$ 0
Environmental Indemnity Agreement
Number of properties which were provided environmental indemnifications | Property		3
Maximum additional costs agreed to be paid by the entity under environmental indemnification agreement		$ 19,000,000
New Development and Redevelopment Obligations
Capital Leases
Purchase obligations		35,100,000
Capital Expenditures For Operating Properties
Capital Leases
Purchase obligations		45,800,000
Third Party Construction and Development
Capital Leases
Purchase obligations		67,400,000
Other Obligations
Capital Leases
Purchase obligations		1,100,000
Specialty Tax Guarantee
Tax incremental financing obligation
Liability recognized with regard to tax incremental financing obligation at end of current period		$ 685,000
Specialty Tax Guarantee | Anne Arundel County, Maryland | Tax Incremental Financing Bond
Loss Contingencies [Line Items]
Loan amount				$ 30,000,000

Commitments and Contingencies63

Commitments and Contingencies - Operating Leases Future Minimum Payments (Details) $ in Thousands	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 320
2,018	1,275
2,019	1,263
2,020	1,257
2,021	1,260
Thereafter	85,761
Total	$ 91,136

Commitments and Contingencies64

Commitments and Contingencies - Capital Leases Future Minimum Payments (Details) $ in Thousands	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 700
2,018	15,775
2,020	135
Thereafter	75
Total minimum rental payments	16,685
Less: Amount representing interest	(338)
Capital lease obligation	$ 16,347