COPT Defense Properties (CDP) 10-Q 1 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 20, 2018
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	Mar. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		102,144,334
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
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	Mar. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Properties, net:
Operating properties, net	$ 2,740,264	$ 2,737,611
Projects in development or held for future development	418,015	403,494
Total properties, net	3,158,279	3,141,105
Assets held for sale, net	42,226	42,226
Cash and cash equivalents	8,888	12,261
Investment in unconsolidated real estate joint venture	41,311	41,787
Accounts receivable (net of allowance for doubtful accounts of $742 and $607, respectively)	23,982	31,802
Deferred rent receivable (net of allowance of $375 and $364, respectively)	87,985	86,710
Intangible assets on real estate acquisitions, net	54,600	59,092
Deferred leasing costs (net of accumulated amortization of $29,435 and $29,560, respectively)	47,886	48,322
Investing receivables	58,800	57,493
Prepaid expenses and other assets, net	72,281	74,407
Total assets	3,596,238	3,595,205
Liabilities:
Debt, net	1,854,886	1,828,333
Accounts payable and accrued expenses	95,721	108,137
Rents received in advance and security deposits	26,569	25,648
Dividends and distributions payable	29,146	28,921
Deferred revenue associated with operating leases	11,246	11,682
Deferred property sale	43,377	43,377
Capital lease obligation	11,778	15,853
Other liabilities	17,643	41,822
Total liabilities	2,090,366	2,103,773
Commitments and contingencies (Note 16)
Redeemable noncontrolling interests	23,848	23,125
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest	1,022	1,013
Additional paid-in capital	2,221,427	2,201,047
Cumulative distributions in excess of net income	(813,302)	(802,085)
Accumulated other comprehensive income	7,204	2,167
Total Corporate Office Properties Trust’s shareholders’ equity	1,416,351	1,402,142
Noncontrolling interests in subsidiaries:
Common units in COPLP	44,327	45,097
Preferred units in COPLP	8,800	8,800
Other consolidated entities	12,546	12,268
Noncontrolling interests in subsidiaries	65,673	66,165
Total equity	1,482,024	1,468,307
Total liabilities, redeemable noncontrolling interests and equity	3,596,238	3,595,205
Corporate Office Properties, L.P.
Properties, net:
Operating properties, net	2,740,264	2,737,611
Projects in development or held for future development	418,015	403,494
Total properties, net	3,158,279	3,141,105
Assets held for sale, net	42,226	42,226
Cash and cash equivalents	8,888	12,261
Investment in unconsolidated real estate joint venture	41,311	41,787
Accounts receivable (net of allowance for doubtful accounts of $742 and $607, respectively)	23,982	31,802
Deferred rent receivable (net of allowance of $375 and $364, respectively)	87,985	86,710
Intangible assets on real estate acquisitions, net	54,600	59,092
Deferred leasing costs (net of accumulated amortization of $29,435 and $29,560, respectively)	47,886	48,322
Investing receivables	58,800	57,493
Prepaid expenses and other assets, net	67,800	69,791
Total assets	3,591,757	3,590,589
Liabilities:
Debt, net	1,854,886	1,828,333
Accounts payable and accrued expenses	95,721	108,137
Rents received in advance and security deposits	26,569	25,648
Dividends and distributions payable	29,146	28,921
Deferred revenue associated with operating leases	11,246	11,682
Deferred property sale	43,377	43,377
Capital lease obligation	11,778	15,853
Other liabilities	13,162	37,206
Total liabilities	2,085,885	2,099,157
Commitments and contingencies (Note 16)
Redeemable noncontrolling interests	23,848	23,125
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest	1,453,262	1,445,022
Accumulated other comprehensive income	7,370	2,173
Total Corporate Office Properties Trust’s shareholders’ equity	1,469,432	1,455,995
Noncontrolling interests in subsidiaries:
Noncontrolling interests in subsidiaries	12,592	12,312
Total equity	1,482,024	1,468,307
Total liabilities, redeemable noncontrolling interests and equity	3,591,757	3,590,589
Limited Partner | Corporate Office Properties, L.P.
Corporate Office Properties Trust’s shareholders’ equity:
Preferred units held by limited partner, 352,000 preferred units outstanding at March 31, 2018 and December 31, 2017	$ 8,800	$ 8,800

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Allowance for doubtful accounts - AR	$ 742	$ 607
Deferred rent receivable	375	364
Deferred leasing costs, accumulated amortization	$ 29,435	$ 29,560
Common Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Common Shares of beneficial interest, shares authorized	150,000,000	150,000,000
Common Shares of beneficial interest, shares issued	102,150,358	101,292,299
Common Shares of beneficial interest, shares outstanding	102,150,358	101,292,299
Corporate Office Properties, L.P.
Allowance for doubtful accounts - AR	$ 742	$ 607
Deferred rent receivable	375	364
Deferred leasing costs, accumulated amortization	$ 29,435	$ 29,560
Corporate Office Properties, L.P. | General Partner
Common Shares of beneficial interest, shares outstanding	102,150,358	101,292,299
Corporate Office Properties, L.P. | Limited Partner
Common Shares of beneficial interest, shares outstanding	3,197,061	3,250,878
Preferred Units, Outstanding	352,000	352,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Rental revenue	$ 100,834	$ 100,615
Tenant recoveries and other real estate operations revenue	27,444	26,152
Construction contract and other service revenues	27,198	13,034
Total revenues	155,476	139,801
Expenses
Property operating expenses	50,951	48,519
Depreciation and amortization associated with real estate operations	33,512	33,059
Construction contract and other service expenses	26,216	12,486
General, administrative and leasing expenses	7,292	8,611
Business development expenses and land carry costs	1,614	1,693
Total operating expenses	119,585	104,368
Operating income	35,891	35,433
Interest expense	(18,784)	(18,994)
Interest and other income	1,359	1,726
Income before equity in income of unconsolidated entities and income taxes	18,466	18,165
Equity in income of unconsolidated entities	373	377
Income tax expense	(55)	(40)
Income before gain on sales of real estate	18,784	18,502
Gain on sales of real estate	(4)	4,238
Net income	18,780	22,740
Net income attributable to noncontrolling interests:
Common units in COPLP	(544)	(622)
Preferred units in COPLP	(165)	(165)
Other consolidated entities	(921)	(934)
Net income attributable to COPT	17,150	21,019
Preferred share/unit dividends/distributions	0	(3,180)
Net income attributable to COPT common shareholders	$ 17,150	$ 17,839
Earnings per common share:
Net income attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.17	$ 0.18
Net income attributable to COPT common shareholders - diluted (in dollars per share/unit)	0.17	0.18
Dividends declared per common share/unit (in dollars per share)	$ 0.2750	$ 0.275
Corporate Office Properties, L.P.
Revenues
Rental revenue	$ 100,834	$ 100,615
Tenant recoveries and other real estate operations revenue	27,444	26,152
Construction contract and other service revenues	27,198	13,034
Total revenues	155,476	139,801
Expenses
Property operating expenses	50,951	48,519
Depreciation and amortization associated with real estate operations	33,512	33,059
Construction contract and other service expenses	26,216	12,486
General, administrative and leasing expenses	7,292	8,611
Business development expenses and land carry costs	1,614	1,693
Total operating expenses	119,585	104,368
Operating income	35,891	35,433
Interest expense	(18,784)	(18,994)
Interest and other income	1,359	1,726
Income before equity in income of unconsolidated entities and income taxes	18,466	18,165
Equity in income of unconsolidated entities	373	377
Income tax expense	(55)	(40)
Income before gain on sales of real estate	18,784	18,502
Gain on sales of real estate	(4)	4,238
Net income	18,780	22,740
Net income attributable to noncontrolling interests:
Net income attributable to noncontrolling interests in consolidated entities	(921)	(934)
Net income attributable to COPT	17,859	21,806
Preferred share/unit dividends/distributions	(165)	(3,345)
Net income attributable to COPT common shareholders	$ 17,694	$ 18,461
Earnings per common share:
Net income attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.17	$ 0.18
Net income attributable to COPT common shareholders - diluted (in dollars per share/unit)	0.17	0.18
Dividends declared per common share/unit (in dollars per share)	$ 0.275	$ 0.275

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 18,780	$ 22,740
Other comprehensive income
Unrealized gain on interest rate derivatives	4,676	224
Loss on interest rate derivatives recognized in interest expense	245	1,184
Other comprehensive income	4,921	1,408
Comprehensive income	23,701	24,148
Comprehensive income attributable to noncontrolling interests	(1,790)	(1,768)
Comprehensive income attributable to COPT	21,911	22,380
Corporate Office Properties, L.P.
Net income	18,780	22,740
Other comprehensive income
Unrealized gain on interest rate derivatives	4,676	224
Loss on interest rate derivatives recognized in interest expense	245	1,184
Other comprehensive income	4,921	1,408
Comprehensive income	23,701	24,148
Comprehensive income attributable to noncontrolling interests	(921)	(934)
Comprehensive income attributable to COPT	$ 22,780	$ 23,214

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock Issued to Public Under At-the-Market Program	Forward Equity Sale Agreement	Preferred Shares	Common Shares	Common SharesCommon Stock Issued to Public Under At-the-Market Program	Common SharesForward Equity Sale Agreement	Additional Paid-in Capital	Additional Paid-in CapitalCommon Stock Issued to Public Under At-the-Market Program	Additional Paid-in CapitalForward Equity Sale Agreement	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 Stock Issued to Public Under At-the-Market Program	Corporate Office Properties, L.P.Forward Equity Sale Agreement	Corporate Office Properties, L.P.Common Shares	Corporate Office Properties, L.P.Common SharesCommon Stock Issued to Public Under At-the-Market Program	Corporate Office Properties, L.P.Common SharesForward Equity Sale Agreement	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: 98,498,651 and 101,292,299 shares as of December 31, 2016 and 2017, respectively) at Dec. 31, 2016	$ 1,612,777			$ 172,500	$ 985			$ 2,116,581			$ (747,825)	$ (1,731)	$ 72,267	$ 1,612,777			$ 1,419,710			$ (1,854)	$ 13,621		$ 8,800		$ 172,500
Balance (preferred units) at Dec. 31, 2016																							352,000		6,900,000
Balance (in units/shares) at Dec. 31, 2016	98,498,651																102,089,042
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 185,000 and 53,817 shares as for the three months ended March 31, 2017 and 2018, respectively)	$ 0				2			2,535					(2,537)
Common shares issued during the period		$ 18,222				$ 5			$ 18,217						$ 18,222			$ 18,222
Common shares issued during the period (in shares)																		546,782
Share-based compensation issuance, net of redemptions (in units/shares)	159,801																159,801
Share-based compensation issuance, net of redemptions (COPT: 159,801 and 127,242 shares issued, net of redemptions for the three months ended March 31, 2017 and 2018, respectively)	$ 1,582				2			1,580						1,582			$ 1,582
Redemption of vested equity awards	(1,753)							(1,753)						(1,753)			(1,753)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0							(246)					246
Comprehensive income	23,581										21,019	1,361	1,201	23,581			18,461			1,408	367		$ 165		$ 3,180
Dividends / Distributions to owners of common and preferred units	(30,524)										(30,524)			(31,625)			(28,280)						$ (165)		$ (3,180)
Distributions to owners of common and preferred units in COPLP	(1,101)												(1,101)
Distributions to noncontrolling interests in subsidiaries	(2,606)												(2,606)	(2,606)							(2,606)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ (545)							(545)						(545)			$ (545)
Balance (in units/shares) at Mar. 31, 2017	99,390,234																102,795,625
Balance (preferred units) at Mar. 31, 2017																							352,000		6,900,000
Balance (COPT: 99,390,234 shares and 102,150,358 shares as of March 31, 2017 and 2018, respectively) at Mar. 31, 2017	$ 1,619,633			172,500	994			2,136,369			(757,330)	(370)	67,470	1,619,633			$ 1,427,397			(446)	11,382		$ 8,800		$ 172,500
Increase (Decrease) in Shareholders' Equity
Cumulative effect of accounting change for adoption of hedge accounting guidance											(276)	276					(276)			276
Balance, as adjusted	1,468,307			0	1,013			2,201,047			(802,361)	2,443	66,165	1,468,307			1,444,746			2,449	12,312		8,800		0
Balance (COPT: 98,498,651 and 101,292,299 shares as of December 31, 2016 and 2017, respectively) at Dec. 31, 2017	$ 1,468,307			0	1,013			2,201,047			(802,085)	2,167	66,165	1,468,307			$ 1,445,022			2,173	12,312		$ 8,800		$ 0
Balance (preferred units) at Dec. 31, 2017																						352,000	352,000		0
Balance (in units/shares) at Dec. 31, 2017	101,292,299																104,543,177					3,250,878		101,292,299
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 185,000 and 53,817 shares as for the three months ended March 31, 2017 and 2018, respectively)	$ 0				1			760					(761)
Common shares issued during the period			$ 19,976				$ 7			$ 19,969						$ 19,976			$ 19,976
Common shares issued during the period (in shares)			677,000																677,000
Share-based compensation issuance, net of redemptions (in units/shares)	127,242																127,242
Share-based compensation issuance, net of redemptions (COPT: 159,801 and 127,242 shares issued, net of redemptions for the three months ended March 31, 2017 and 2018, respectively)	$ 1,680				1			1,679						1,680			$ 1,680
Redemption of vested equity awards	(1,327)							(1,327)						(1,327)			(1,327)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0							(164)					164
Comprehensive income	23,063										17,150	4,761	1,152	23,063			17,694			4,921	283		$ 165		$ 0
Dividends / Distributions to owners of common and preferred units	(28,091)										(28,091)			(29,135)			(28,970)						$ (165)		$ 0
Distributions to owners of common and preferred units in COPLP	(1,044)												(1,044)
Distributions to noncontrolling interests in subsidiaries	(3)												(3)	(3)							(3)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ (537)							(537)						(537)			$ (537)
Balance (in units/shares) at Mar. 31, 2018	102,150,358																105,347,419					3,197,061		102,150,358
Balance (preferred units) at Mar. 31, 2018																						352,000	352,000		0
Balance (COPT: 99,390,234 shares and 102,150,358 shares as of March 31, 2017 and 2018, respectively) at Mar. 31, 2018	$ 1,482,024			$ 0	$ 1,022			$ 2,221,427			$ (813,302)	$ 7,204	$ 65,673	$ 1,482,024			$ 1,453,262			$ 7,370	$ 12,592		$ 8,800		$ 0

Consolidated Statements of Equ7

Consolidated Statements of Equity (Parenthetical) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Balance (in units/ shares)	102,150,358	99,390,234	101,292,299	98,498,651
Conversion of common units to common shares (in units/shares)	53,817	185,000
Share-based compensation issuance, net of redemptions (in units/shares)	127,242	159,801
Forward Equity Sale Agreement
Common shares issued during the period (in shares)	677,000
Common Shares | Common Stock Issued to Public Under At-the-Market Program
Common shares issued during the period (in shares)		546,782

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Revenues from real estate operations received	$ 135,027	$ 132,985
Construction contract and other service revenues received	9,268	23,527
Property operating expenses paid	(43,212)	(40,837)
Construction contract and other service expenses paid	(41,128)	(14,790)
General, administrative, leasing, business development and land carry costs paid	(10,900)	(14,275)
Interest expense paid	(19,092)	(19,549)
Lease incentives paid	(4,204)	(7,729)
Other	436	750
Net cash provided by operating activities	26,195	60,082
Cash flows from investing activities
Construction, development and redevelopment	(17,540)	(35,795)
Tenant improvements on operating properties	(9,077)	(6,916)
Other capital improvements on operating properties	(5,198)	(5,203)
Proceeds from dispositions of properties	0	52,596
Leasing costs paid	(2,015)	(2,042)
Other	(974)	(630)
Net cash (used in) provided by investing activities	(34,804)	2,010
Proceeds from debt
Revolving Credit Facility	82,000	0
Repayments of debt
Revolving Credit Facility	(55,000)	0
Scheduled principal amortization	(1,052)	(1,008)
Payments on capital lease obligation	(4,202)	0
Net proceeds from issuance of common shares/units	19,989	18,237
Redemption of preferred shares/units	0	(26,583)
Common share/unit dividends/distributions paid	(27,855)	(27,100)
Preferred share/unit dividends/distributions paid	0	(3,581)
Distributions paid to noncontrolling interests in COPLP	(1,059)	(1,156)
Redemption of vested equity awards	(1,327)	(1,753)
Other	(5,183)	(3,009)
Net cash provided by (used in) financing activities	6,311	(45,953)
Net (decrease) increase in cash and cash equivalents and restricted cash	(2,298)	16,139
Cash and cash equivalents and restricted cash
Beginning of period	14,831	212,619
End of period	12,533	228,758
Reconciliation of net income to net cash provided by operating activities:
Net income	18,780	22,740
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	34,035	33,570
Amortization of deferred financing costs and net debt discounts	822	1,348
Increase in deferred rent receivable	(1,512)	(191)
Gain on sales of real estate	4	(4,238)
Share-based compensation	1,545	1,488
Other	(907)	(1,447)
Changes in operating assets and liabilities:
Decrease in accounts receivable	7,877	5,007
Decrease in prepaid expenses and other assets, net	8,533	15,479
Decrease in accounts payable, accrued expenses and other liabilities	(43,903)	(12,269)
Increase (decrease) in rents received in advance and security deposits	921	(1,405)
Net cash provided by operating activities	26,195	60,082
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents and restricted cash	14,831	212,619
Supplemental schedule of non-cash investing and financing activities:
Increase (decrease) in accrued capital improvements, leasing and other investing activity costs	12,232	(6,661)
Increase in fair value of derivatives applied to accumulated other comprehensive income and noncontrolling interests	4,887	1,408
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	761	2,537
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	164	246
Increase in redeemable noncontrolling interests and decrease in equity to carry redeemable noncontrolling interests at fair value	537	545
Corporate Office Properties, L.P.
Cash flows from operating activities
Revenues from real estate operations received	135,027	132,985
Construction contract and other service revenues received	9,268	23,527
Property operating expenses paid	(43,212)	(40,837)
Construction contract and other service expenses paid	(41,128)	(14,790)
General, administrative, leasing, business development and land carry costs paid	(10,900)	(14,275)
Interest expense paid	(19,092)	(19,549)
Lease incentives paid	(4,204)	(7,729)
Other	436	750
Net cash provided by operating activities	26,195	60,082
Cash flows from investing activities
Construction, development and redevelopment	(17,540)	(35,795)
Tenant improvements on operating properties	(9,077)	(6,916)
Other capital improvements on operating properties	(5,198)	(5,203)
Proceeds from dispositions of properties	0	52,596
Leasing costs paid	(2,015)	(2,042)
Other	(974)	(630)
Net cash (used in) provided by investing activities	(34,804)	2,010
Proceeds from debt
Revolving Credit Facility	82,000	0
Repayments of debt
Revolving Credit Facility	(55,000)	0
Scheduled principal amortization	(1,052)	(1,008)
Payments on capital lease obligation	(4,202)	0
Net proceeds from issuance of common shares/units	19,989	18,237
Redemption of preferred shares/units	0	(26,583)
Common share/unit dividends/distributions paid	(28,749)	(28,091)
Preferred share/unit dividends/distributions paid	(165)	(3,746)
Redemption of vested equity awards	(1,327)	(1,753)
Other	(5,183)	(3,009)
Net cash provided by (used in) financing activities	6,311	(45,953)
Net (decrease) increase in cash and cash equivalents and restricted cash	(2,298)	16,139
Cash and cash equivalents and restricted cash
Beginning of period	14,831	212,619
End of period	12,533	228,758
Reconciliation of net income to net cash provided by operating activities:
Net income	18,780	22,740
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	34,035	33,570
Amortization of deferred financing costs and net debt discounts	822	1,348
Increase in deferred rent receivable	(1,512)	(191)
Gain on sales of real estate	4	(4,238)
Share-based compensation	1,545	1,488
Other	(907)	(1,447)
Changes in operating assets and liabilities:
Decrease in accounts receivable	7,877	5,007
Decrease in prepaid expenses and other assets, net	8,398	14,193
Decrease in accounts payable, accrued expenses and other liabilities	(43,768)	(10,983)
Increase (decrease) in rents received in advance and security deposits	921	(1,405)
Net cash provided by operating activities	26,195	60,082
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents and restricted cash	14,831	212,619
Supplemental schedule of non-cash investing and financing activities:
Increase (decrease) in accrued capital improvements, leasing and other investing activity costs	12,232	(6,661)
Increase in fair value of derivatives applied to accumulated other comprehensive income and noncontrolling interests	4,887	1,408
Increase in redeemable noncontrolling interests and decrease in equity to carry redeemable noncontrolling interests at fair value	$ 537	$ 545

Organization

Organization	3 Months Ended
	Mar. 31, 2018
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 in the Greater Washington, DC/Baltimore region with durable Class-A office fundamentals and characteristics (“Regional Office”). As of March 31, 2018 , our properties included the following: • 159 properties totaling 17.6 million square feet comprised of 144 office properties and 15 single-tenant data center shell properties (“data center shells”). We owned six of these data center shells through an unconsolidated real estate joint venture; • a wholesale data center with a critical load of 19.25 megawatts; • seven properties under construction or redevelopment ( four office properties and three data center shells) that we estimate will total approximately 619,000 square feet upon completion, including one partially-operational property; and • approximately 1,000 acres of land controlled for future development that we believe could be developed into approximately 13.0 million square feet and 150 acres of other land. 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 March 31, 2018 , COPT owned 97.0% of the outstanding COPLP common units (“common units”); the remaining common units and all of the outstanding COPLP preferred units (“preferred units”) were owned by third parties. Common units not owned by COPT carry certain redemption rights. The number of common units owned by COPT is equivalent to the number of outstanding common shares of beneficial interest (“common shares”) of COPT, and the entitlement of all 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 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; similarly, although 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	3 Months Ended
	Mar. 31, 2018
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, 2017 included in our 2017 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 2017 Annual Report on Form 10-K as updated for our adoption of recent accounting pronouncements discussed below. 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, including restricted cash and marketable securities that were reclassified to the line entitled “prepaid expenses and other assets, net” on our consolidated balance sheets after having been reported on a separate line in our previous Quarterly Reports on Form 10-Q and Annual Reports on Form 10-K. Recent Accounting Pronouncements We adopted guidance issued by the Financial Accounting Standards Board (“FASB”) effective January 1, 2018 regarding the recognition of revenue from contracts with customers (“Topic 606”). Under this guidance, an entity recognizes 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 determined that Topic 606 is applicable to our construction contract and other service revenues, which includes predominantly construction and design projects performed primarily for tenants of our properties. We used the modified retrospective method for contracts that were not completed as of January 1, 2018. Under this method, the cumulative effect of initially applying the guidance is recognized as an adjustment to the opening balance of retained earnings as of the date of initial application. Our adoption of Topic 606 effective January 1, 2018 did not affect our consolidated financial statements other than additional disclosure provided in accordance with the guidance. We did not elect to use any of the practical expedients provided for under the guidance. 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, Topic 606 may 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). We adopted guidance issued by the FASB effective January 1, 2018 that requires entities to measure equity investments at fair value through net income, except for those that result in consolidation or are accounted for under the equity method of accounting. For equity investments without readily determinable fair values, the guidance permits the application of a measurement alternative using the cost of the investment, less any impairments, plus or minus changes resulting from observable price changes for an identical or similar investment of the same issuer. Our adoption of this guidance had no effect on our consolidated financial statements. We adopted guidance issued by the FASB retrospectively effective January 1, 2018 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. Our adoption of this guidance had no effect on our consolidated financial statements. We adopted guidance issued by the FASB retrospectively effective January 1, 2018 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. As a result of our adoption of this guidance, the change in restricted cash is no longer reported as either operating or investing activities on our statements of cash flows. Our restricted cash primarily consists of cash escrowed under mortgage debt for capital improvements and real estate taxes and certain tenant security deposits. Our adoption of this guidance had the following effects on our consolidated statements of cash flows for the three months ended March 31, 2017 (in thousands): As Previously Reported Impact of Adoption As Net cash provided by operating activities $ 60,637 $ (555 ) $ 60,082 Net cash provided by investing activities $ 1,923 $ 87 $ 2,010 Net increase in cash and cash equivalents and restricted cash $ 16,607 $ (468 ) $ 16,139 Beginning of period cash and cash equivalents and restricted cash $ 209,863 $ 2,756 $ 212,619 End of period cash and cash equivalents and restricted cash $ 226,470 $ 2,288 $ 228,758 We adopted guidance issued by the FASB that clarifies the scope of provisions and accounting for nonfinancial asset derecognition, including partial sales of real estate assets, effective January 1, 2018 using the full retrospective method. 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 nonfinancial 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 are now subject to the same derecognition model as all other nonfinancial assets. We had a transaction in July 2016 accounted for as a partial sale under the previous guidance that meets the criteria for immediate full gain recognition under the new guidance; as a result, we retrospectively recognized an additional $18 million in income in 2016 that was being amortized into income in subsequent periods under the previous guidance. The recognition pattern for our other sales of real estate were not changed by this new guidance. The full retrospective method requires adjustment of each reporting period presented at the time of adoption. The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPT and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolidated real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Cumulative distributions in excess of net income $ (818,190 ) $ 16,105 $ (802,085 ) $ (774,445 ) $ 17,115 $ (757,330 ) $ (765,276 ) $ 17,451 $ (747,825 ) Noncontrolling interests in subsidiaries $ 65,549 $ 616 $ 66,165 $ 66,820 $ 650 $ 67,470 $ 71,605 $ 662 $ 72,267 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to noncontrolling interests - Common units in COPLP $ (634 ) $ 12 $ (622 ) Net income attributable to COPT $ 21,355 $ (336 ) $ 21,019 Net income attributable to COPT common shareholders $ 18,175 $ (336 ) $ 17,839 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPT $ 22,716 $ (336 ) $ 22,380 The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPLP and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolid. real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Common units $ 1,428,301 $ 16,721 $ 1,445,022 $ 1,409,632 $ 17,765 $ 1,427,397 $ 1,401,597 $ 18,113 $ 1,419,710 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to COPLP $ 22,154 $ (348 ) $ 21,806 Net income attributable to COPLP common unitholders $ 18,809 $ (348 ) $ 18,461 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPLP $ 23,562 $ (348 ) $ 23,214 Adoption of this guidance had no impact to cash provided by or used in operating, financing or investing activities on our consolidated statements of cash flows for the three months ended March 31, 2017. We early adopted guidance issued by the FASB effective January 1, 2018 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. We adopted this guidance using the modified retrospective transition method under which we eliminated $276,000 in previously-recorded cumulative hedge ineffectiveness as of January 1, 2018 by means of a cumulative-effect adjustment to our beginning balance of accumulated other comprehensive income (“AOCI”), with a corresponding adjustment to the beginning balance of: cumulative distributions in excess of net income for COPT and subsidiaries; and common units for COPLP and subsidiaries. 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 2017 Annual Report on Form 10-K for amounts deferred in 2017, 2016 and 2015). 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: Under the issued and approved guidance, we believed that the new revenue standard would apply to executory costs and other components of revenue deemed to be non-lease components (such as common area maintenance and provision of utilities), in which case we would need: to separate the lease components of revenue due under leases from the non-lease components; and recognize revenue on the non-lease components as the related services are delivered, which could result in a change to our revenue recognition pattern. However, in March 2018, the FASB tentatively approved a practical expedient to provide lessors with an option to not separate lease components of revenue from non-lease components if: the timing and pattern of transfer of these components is the same as the related lease; and the lease would continue to be classified as an operating lease; • Leases in which we are the lessee: ◦ Our most significant leases as lessee are ground leases; as of March 31, 2018 , our future minimum rental payments under these leases totaled $89.7 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 right-of-use assets and lease liabilities 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, we expect to elect to apply the package of practical expedients under which we would 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.

Revenue Recognition on Construc

Revenue Recognition on Construction Contract and Other Service Revenues	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition on Construction Contract and Other Service Revenues	Revenue Recognition on Construction Contract and Other Service Revenues We enter into construction contracts to complete various design and construction services primarily for our United States Government tenants. The revenues and expenses from these services consist primarily of subcontracted costs that are reimbursed to us by our customers along with a fee. These services are an ancillary component of our overall operations, with small operating margins relative to the revenue. We review each contract to determine the performance obligations and allocate the transaction price. We recognize revenue under these contracts as services are performed in an amount that reflects the consideration we expect to receive in exchange for those services. Our performance obligations are satisfied over time as work progresses. Revenue recognition is determined using the input method based on costs incurred as of point in time relative to the total estimated costs at completion to measure progress toward satisfying our performance obligations. We believe incurred costs of work performed best depicts the transfer of control of the services being transferred to the customer. In determining whether the performance obligations of each construction contract should be accounted for separately versus together, we consider numerous factors that may require significant judgment, including: whether the components contracted are substantially the same with the same pattern of transfer; whether the customer could contract with another party to perform construction based on our design project; and whether the customer can elect not to move forward after the design phase of the contract. Most of our contracts have a single performance obligation as the promise to transfer the services is not separately identifiable from other obligations in the contracts and, therefore, are not distinct. Some contracts have multiple performance obligations, most commonly due to having distinct project phases for design and construction for which our customer is making decisions and managing separately. In these cases, we allocate the transaction price between these performance obligations based on the amounts separately set forth in the contracts for such obligations. Contract modifications, such as change orders, are routine for our construction contracts and are generally determined to be additions to the existing performance obligations because they would have been part of the initial performance obligations if they were identified at the initial contract date. We have three main types of compensation arrangements for our construction contracts: guaranteed maximum price (“GMP”); firm fixed price (“FFP”); and cost-plus fee. • GMP contracts provide for revenue equal to costs incurred plus a fee equal to a percentage of such costs, up to a maximum contract amount. We generally enter into GMP contracts for projects that are significant in nature based on the size of the project and total fees, and for which the full scope of the project has not been determined as of the contract date. GMP contracts are lower risk to us than FFP contracts since the costs and revenue move proportionately to one another; • FFP contracts provide for revenue equal to a fixed fee. These contracts are typically lower in value and scope relative to GMP contracts, and are generally entered into when the scope of the project is well defined. Typically, we assume more risk with FFP contracts than GMP contracts since the revenue is fixed and we could realize losses or less than expected profits if we incur more costs than originally estimated. However, these types of contracts offer the opportunity for additional profits when we complete the work for less than originally estimated. Determining the estimated total costs for contracts under an FFP compensation arrangement may require significant judgment and has a direct effect on our revenue recognition pattern; • Cost-plus fee contracts provide for revenue equal to costs incurred plus a fee equal to a percentage of such costs but, unlike GMP contracts, do not have a maximum contract amount. We do not frequently enter into cost-plus fee contracts. Similar to GMP contracts, cost-plus fee contracts are low risk to us since the costs and revenue move proportionately to one another. Construction contract cost estimates are based on various assumptions, such as performance of subcontractors and cost and availability of materials, to project the outcome of future events over the course of the project. We review and update these estimates regularly as a significant change could affect the profitability of our construction contracts. We recognize adjustments in estimated profit on contracts under the cumulative catch-up method as the modification does not create a new performance obligation. Under this method, the impact of the adjustment on profit recorded to date on a contract is recognized in the period the adjustment is identified. Revenue and profit in future periods are recognized using the adjusted estimate. If at any time the estimate of contract profitability indicates an anticipated loss on the contract, we recognize the total loss in the quarter it is identified. We disaggregate our construction contract and other service revenues by compensation arrangement and by service type as we believe it best depicts the nature, timing and uncertainty of our revenue. The table below reports construction contract and other service revenues by compensation arrangement (in thousands): For the Three Months Ended March 31, 2018 2017 Construction contract revenues: GMP $ 20,486 $ 6,589 FFP 6,435 6,198 Cost-plus fee 58 17 Other 219 230 $ 27,198 $ 13,034 The table below reports construction contract and other service revenues by service type (in thousands): For the Three Months Ended March 31, 2018 2017 Construction contract revenues: Construction $ 25,915 $ 10,091 Design 1,064 2,713 Other 219 230 $ 27,198 $ 13,034 We recognized revenue from performance obligations satisfied (or partially satisfied) in previous periods of $309,000 and $146,000 in three months ended March 31, 2018 and 2017 , respectively. Our timing of revenue recognition for construction contracts generally differs from the timing of invoicing to customers. We recognize such revenue as we satisfy our performance obligations. Payment terms and conditions vary by contract type. Under most of our contracts, we bill customers monthly, as work progresses, in accordance with the contract terms, with payment due in 30 days , although customers occasionally pay in advance of services being provided. We have determined that our contracts generally do not include a significant financing component. The primary purpose of the timing of our invoicing is for convenience, not to receive financing from our customers or to provide customers with financing. Additionally, the timing of transfer of the services is often at the discretion of the customer. We recognized no impairment losses on construction contracts receivable or unbilled construction revenue in the periods set forth herein. Accounts receivable related to our construction contract services is included in accounts receivable, net on our consolidated balance sheets. The beginning and ending balances of accounts receivable related to our construction contracts were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 4,577 $ 4,131 Ending balance $ 4,021 $ 7,376 Under most of our contracts, we bill customers one month subsequent to revenue recognition, resulting in contract assets representing unbilled construction revenue. Contract assets, which we refer to herein as construction costs in excess of billings, are included in prepaid expenses and other assets, net reported on our consolidated balance sheets. The beginning and ending balances of our contract assets were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 4,884 $ 10,350 Ending balance $ 4,250 $ 4,451 Our contract liabilities consist of advance payments from our customers or billings in excess of construction contract revenue recognized. Contract liabilities are included in other liabilities reported on our consolidated balance sheets. Changes in contract liabilities were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 27,402 $ 32,650 Ending balance $ 8,279 $ 40,485 Revenue recognized included in beginning balance $ 19,297 $ 4,199 The change in the contract liabilities balance reported above for the three months ended March 31, 2018 was due primarily to our satisfaction of performance obligations during the period on a contract on which we previously received advance payments from a customer. Revenue allocated to the remaining performance obligations under existing contracts as of March 31, 2018 that will be recognized as revenue in future periods was $23.5 million , all of which we expect to recognize during the remainder of 2018. We have no deferred incremental costs incurred to obtain or fulfill our construction contracts or other service revenues.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
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 sheets using quoted market prices, as are other marketable securities that we hold. The balance of the plan, which was fully funded, totaled $4.5 million as of March 31, 2018 , and is included in the accompanying COPT consolidated balance sheets in the line entitled “prepaid expenses and other assets, net”. 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 are classified in Level 1 of the fair value hierarchy, while the offsetting liability 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 March 31, 2018 , 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 7, 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 9, 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 7 for investing receivables, Note 9 for debt and Note 10 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 March 31, 2018 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 $ 4,433 $ — $ — $ 4,433 Other 48 — — 48 Interest rate derivatives (1) — 7,960 — 7,960 Total assets $ 4,481 $ 7,960 $ — $ 12,441 Liabilities: Deferred compensation plan liability (2) $ — $ 4,481 $ — $ 4,481 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPT’s consolidated balance sheet. (2) 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 March 31, 2018 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) $ — $ 7,960 $ — $ 7,960 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPLP ’ s consolidated balance sheet.

Properties, Net

Properties, Net	3 Months Ended
	Mar. 31, 2018
Real Estate [Abstract]
Properties, Net	Properties, Net Operating properties, net consisted of the following (in thousands): March 31, December 31, Land $ 457,459 $ 455,680 Buildings and improvements 3,096,262 3,068,124 Less: Accumulated depreciation (813,457 ) (786,193 ) Operating properties, net $ 2,740,264 $ 2,737,611 Projects in development or held for future development consisted of the following (in thousands): March 31, December 31, Land $ 239,141 $ 240,825 Development in progress, excluding land 178,874 162,669 Projects in development or held for future development $ 418,015 $ 403,494 Our property held for sale is 11751 Meadowville Lane, a property in our Data Center Shells sub-segment, the sale of which was not recognized for accounting purposes. We provided a financial guaranty to the buyer under which we provide an indemnification 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. We account for this transaction as a financing arrangement. Accordingly, we did not recognize the sale of this property for accounting purposes (and will not until the guaranty expires) and we reported the sales proceeds as a liability on the consolidated balance sheets as of March 31, 2018 and December 31, 2017 on the line entitled deferred property sale. We do not expect to incur any losses under this financial guaranty. The table below sets forth the components of this property’s assets as of March 31, 2018 and December 31, 2017 (in thousands): Properties, net $ 38,670 Deferred rent receivable 3,237 Deferred leasing costs, net 319 Assets held for sale, net $ 42,226 2018 Construction Activities During the three months ended March 31, 2018 , we placed into service 74,000 square feet in one newly-constructed property and 11,000 square feet in one partially-operational property under redevelopment. As of March 31, 2018 , we had six properties under construction, or which we were contractually committed to construct, that we estimate will total 597,000 square feet upon completion and one partially-operational property under redevelopment that we estimate will total 22,000 square feet upon completion.

Real Estate Joint Ventures

Real Estate Joint Ventures	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 (dollars in thousands): Nominal Ownership March 31, 2018 (1) Date % as of Total Encumbered Total Acquired 3/31/2018 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 161,290 $ 74,509 $ 52,511 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 71,556 44,909 45,436 Stevens Investors, LLC 8/11/2015 95% Development of real estate (4) 73,240 — 15,469 $ 306,086 $ 119,418 $ 113,416 (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. Unconsolidated Joint Venture As of March 31, 2018 , 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 shell properties in Virginia, that we account for using the equity method of accounting. As of March 31, 2018 , we had an investment balance in GI-COPT of $41.3 million .

Investing Receivables

Investing Receivables	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Investing Receivables	Investing Receivables Investing receivables, including accrued interest thereon, consisted of the following (in thousands): March 31, December 31, Notes receivable from the City of Huntsville $ 55,779 $ 54,472 Other investing loans receivable 3,021 3,021 $ 58,800 $ 57,493 Our notes receivable from the City of Huntsville funded infrastructure costs in connection with our LW Redstone Company, LLC joint venture (see Note 6) 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 March 31, 2018 or December 31, 2017 . The fair value of these receivables approximated their carrying amounts as of March 31, 2018 and December 31, 2017 .

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Net	3 Months Ended
	Mar. 31, 2018
Prepaid Expense and Other Assets [Abstract]
Prepaid Expenses and Other Assets, Net	Prepaid Expenses and Other Assets, Net Prepaid expenses and other assets, net of COPT and its subsidiaries consisted of the following (in thousands): March 31, December 31, Lease incentives, net $ 18,838 $ 19,011 Prepaid expenses 17,093 24,670 Interest rate derivatives 7,960 3,073 Furniture, fixtures and equipment, net 5,331 5,256 Marketable securities in deferred compensation plan 4,481 4,616 Construction contract costs incurred in excess of billings 4,250 4,884 Restricted cash 3,645 2,570 Non-real estate equity method investments 2,410 2,412 Deferred tax asset, net (1) 1,837 1,892 Other assets 6,436 6,023 Prepaid expenses and other assets, net $ 72,281 $ 74,407 (1) Includes a valuation allowance of $1.4 million .

Debt, Net

Debt, Net	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt, Net	Debt, Net Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of March 31, December 31, Stated Interest Rates as of Scheduled Maturity as of March 31, 2018 March 31, 2018 Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 149,835 $ 150,723 3.82% - 7.87% (3) 2019-2026 Variable rate secured debt 13,029 13,115 LIBOR + 1.85% (4) October 2020 Total mortgage and other secured debt 162,864 163,838 Revolving Credit Facility 153,000 126,000 LIBOR + 0.875% to 1.60% (5) May 2019 (6) Term Loan Facilities (7) 348,072 347,959 LIBOR + 0.90% to 1.85% (8) 2020-2022 Unsecured Senior Notes 3.600%, $350,000 aggregate principal 347,659 347,551 3.60% (9) May 2023 5.250%, $250,000 aggregate principal 246,765 246,645 5.25% (10) February 2024 3.700%, $300,000 aggregate principal 298,444 298,322 3.70% (11) June 2021 5.000%, $300,000 aggregate principal 296,824 296,731 5.00% (12) July 2025 Unsecured note payable 1,258 1,287 0% (13) May 2026 Total debt, net $ 1,854,886 $ 1,828,333 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $4.8 million as of March 31, 2018 and $5.0 million as of December 31, 2017 . (2) Certain of the fixed rate mortgages carry interest rates that, upon assumption, were above or below market rates 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 $332,000 as of March 31, 2018 and $349,000 as of December 31, 2017 . (3) The weighted average interest rate on our fixed rate mortgage debt was 4.18% as of March 31, 2018 . (4) The interest rate on our variable rate secured debt was 3.51% as of March 31, 2018 . (5) The weighted average interest rate on the Revolving Credit Facility was 2.77% as of March 31, 2018 . (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 March 31, 2018 , 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. (8) The weighted average interest rate on these loans was 3.03% as of March 31, 2018 . (9) The carrying value of these notes reflects an unamortized discount totaling $1.6 million as of March 31, 2018 and $1.7 million as of December 31, 2017 . 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 $2.9 million as of March 31, 2018 and $3.0 million as of December 31, 2017 . 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 $1.2 million as of March 31, 2018 and $1.3 million as of December 31, 2017 . 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 $2.6 million as of March 31, 2018 and $2.7 million as of December 31, 2017 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% . (13) This note carries an interest rate that, upon assumption, was below market rates and it therefore was recorded at its fair value based on applicable effective interest rates. The carrying value of this note reflects an unamortized discount totaling $353,000 as of March 31, 2018 and $373,000 as of December 31, 2017 . 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 March 31, 2018 , we were within the compliance requirements of these financial covenants. We capitalized interest costs of $1.4 million in the three months ended March 31, 2018 and $1.5 million in the three months ended March 31, 2017 . The following table sets forth information pertaining to the fair value of our debt (in thousands): March 31, 2018 December 31, 2017 Carrying Fair Carrying Fair Amount Value Amount Value Fixed-rate debt Unsecured Senior Notes $ 1,189,692 $ 1,222,102 $ 1,189,249 $ 1,229,398 Other fixed-rate debt 151,093 151,271 152,010 152,485 Variable-rate debt 514,101 512,371 487,074 485,694 $ 1,854,886 $ 1,885,744 $ 1,828,333 $ 1,867,577

Interest Rate Derivatives

Interest Rate Derivatives	3 Months Ended
	Mar. 31, 2018
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 March 31, December 31, $ 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 $ 662 $ 252 13,121 (1) 1.3900% One-Month LIBOR 10/13/2015 10/1/2020 312 213 100,000 1.9013% One-Month LIBOR 9/1/2016 12/1/2022 2,794 1,046 100,000 1.9050% One-Month LIBOR 9/1/2016 12/1/2022 2,808 1,051 50,000 1.9079% One-Month LIBOR 9/1/2016 12/1/2022 1,384 511 $ 7,960 $ 3,073 (1) The notional amount of this instrument is scheduled to amortize to $12.1 million . 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 March 31, December 31, 2017 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets, net $ 7,960 $ 3,073 The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): Amount of Gain (Loss) Recognized in AOCI on Derivatives Amount of Gain (Loss) Reclassified from AOCI into Income For the Three Months Ended March 31, For the Three Months Ended March 31, Derivatives in Hedging Relationships 2018 2017 Statement of Operations Location 2018 2017 Interest rate derivatives $ 4,676 $ 224 Interest expense $ (245 ) $ (1,184 ) Over the next 12 months, we estimate that approximately $942,000 of gains will be reclassified from AOCI as a decrease 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. We are not in default with any of these provisions. As of March 31, 2018 , we did not have any derivatives in liability positions. As of March 31, 2018 , we had not posted any collateral related to these agreements.

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interests	3 Months Ended
	Mar. 31, 2018
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 6), 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 sheets. 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 Three Months Ended March 31, 2018 2017 Beginning balance $ 23,125 $ 22,979 Distributions to noncontrolling interests (452 ) (415 ) Net income attributable to noncontrolling interests 638 567 Adjustment to arrive at fair value of interests 537 545 Ending balance $ 23,848 $ 23,676

Equity

Equity	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
Equity	Equity During the three months ended March 31, 2018 , COPT issued 677,000 common shares under its forward equity sale agreements for net proceeds of $20.0 million . 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 the forward equity sale agreements was 6.8 million common shares as of March 31, 2018 . During the three months ended March 31, 2018 , certain COPLP limited partners converted 53,817 common units in COPLP for an equal number of common shares in COPT. As of March 31, 2018 , COPT had remaining capacity under its at-the-market stock offering program equal to an aggregate gross sales price of $70.0 million in common share sales. See Note 14 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	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Information by Business Segment	Information by Business Segment We have the following reportable segments: Defense/IT Locations; Regional Office; 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). As of March 31, 2018 and December 31, 2017 , our Regional Office segment included properties located in select urban/urban-like submarkets in the Greater Washington, DC/Baltimore region with durable Class-A office fundamentals and characteristics; during 2017, this segment also included suburban properties that did not meet these characteristics (that were since disposed). 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 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 Wholesale Other Total Three Months Ended March 31, 2018 Revenues from real estate operations $ 62,782 $ 12,561 $ 11,443 $ 7,870 $ 3,633 $ 5,831 $ 104,120 $ 15,284 $ 8,077 $ 797 $ 128,278 Property operating expenses (21,604 ) (4,723 ) (6,598 ) (3,304 ) (1,440 ) (794 ) (38,463 ) (7,878 ) (4,258 ) (352 ) (50,951 ) UJV NOI allocable to COPT — — — — — 1,199 1,199 — — — 1,199 NOI from real estate operations $ 41,178 $ 7,838 $ 4,845 $ 4,566 $ 2,193 $ 6,236 $ 66,856 $ 7,406 $ 3,819 $ 445 $ 78,526 Additions to long-lived assets $ 7,121 $ 1,940 $ — $ 1,108 $ 79 $ — $ 10,248 $ 3,884 $ 36 $ 127 $ 14,295 Transfers from non-operating properties $ 17,186 $ 341 $ — $ (3 ) $ 444 $ 1,114 $ 19,082 $ — $ 1,012 $ — $ 20,094 Segment assets at March 31, 2018 $ 1,273,359 $ 399,202 $ 127,855 $ 192,116 $ 107,096 $ 302,120 $ 2,401,748 $ 397,355 $ 222,738 $ 4,125 $ 3,025,966 Three Months Ended March 31, 2017 Revenues from real estate operations $ 60,855 $ 11,707 $ 11,634 $ 7,010 $ 3,460 $ 5,522 $ 100,188 $ 18,276 $ 6,770 $ 1,533 $ 126,767 Property operating expenses (20,520 ) (4,452 ) (6,802 ) (3,209 ) (1,371 ) (659 ) (37,013 ) (7,486 ) (3,365 ) (655 ) (48,519 ) UJV NOI allocable to COPT — — — — — 1,202 1,202 — — — 1,202 NOI from real estate operations $ 40,335 $ 7,255 $ 4,832 $ 3,801 $ 2,089 $ 6,065 $ 64,377 $ 10,790 $ 3,405 $ 878 $ 79,450 Additions to long-lived assets $ 3,422 $ 2,468 $ — $ 2,168 $ 132 $ — $ 8,190 $ 7,120 $ 1,574 $ 156 $ 17,040 Transfers from non-operating properties $ 13,416 $ 222 $ — $ — $ (4 ) $ (1,015 ) $ 12,619 $ — $ 8 $ 18 $ 12,645 Segment assets at March 31, 2017 $ 1,258,437 $ 361,449 $ 131,194 $ 195,892 $ 109,171 $ 224,254 $ 2,280,397 $ 439,079 $ 229,630 $ 21,011 $ 2,970,117 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 March 31, 2018 2017 Segment revenues from real estate operations $ 128,278 $ 126,767 Construction contract and other service revenues 27,198 13,034 Total revenues $ 155,476 $ 139,801 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 March 31, 2018 2017 UJV NOI allocable to COPT $ 1,199 $ 1,202 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (824 ) (824 ) Add: Equity in loss of unconsolidated non-real estate entities (2 ) (1 ) Equity in income of unconsolidated entities $ 373 $ 377 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 March 31, 2018 2017 Construction contract and other service revenues $ 27,198 $ 13,034 Construction contract and other service expenses (26,216 ) (12,486 ) NOI from service operations $ 982 $ 548 The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income before gain on sales of real estate as reported on our consolidated statements of operations (in thousands): For the Three Months Ended March 31, 2018 2017 NOI from real estate operations $ 78,526 $ 79,450 NOI from service operations 982 548 Interest and other income 1,359 1,726 Equity in income of unconsolidated entities 373 377 Income tax expense (55 ) (40 ) Depreciation and other amortization associated with real estate operations (33,512 ) (33,059 ) General, administrative and leasing expenses (7,292 ) (8,611 ) Business development expenses and land carry costs (1,614 ) (1,693 ) Interest expense (18,784 ) (18,994 ) Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities (1,199 ) (1,202 ) Income before gain on sales of real estate $ 18,784 $ 18,502 The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): March 31, March 31, Segment assets $ 3,025,966 $ 2,970,117 Non-operating property assets 425,951 429,690 Other assets 144,321 357,324 Total COPT consolidated assets $ 3,596,238 $ 3,757,131 The accounting policies of the segments are the same as those used to prepare our consolidated financial statements, except that 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, 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

Share-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Performance Share Awards (“PSUs”) On January 1, 2018 , our Board of Trustees granted 59,110 PSUs with an aggregate grant date fair value of $1.9 million to our three executives. The PSUs have a performance period beginning on January 1, 2018 and concluding on the earlier of December 31, 2020 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 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 number of earned PSUs in settlement of the award plan; and • pay cash equal to 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. 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. We computed a grant date fair value of $31.97 per PSU using a Monte Carlo model. Significant assumptions for that model included the following: baseline common share value of $29.20 ; expected volatility for COPT common shares of 17.0% ; and a risk-free interest rate of 2.04% . We issued 13,328 common shares on February 22, 2018 to executives in settlement of PSUs issued in 2015, representing 75% of the target award for those PSUs. Restricted Shares During the three months ended March 31, 2018 , certain employees were granted a total of 181,617 restricted common shares with an aggregate grant date fair value of $4.6 million (weighted average of $25.18 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. During the three months ended March 31, 2018 , forfeiture restrictions lapsed on 134,460 previously issued common shares; these shares had a weighted average grant date fair value of $29.49 per share, and the aggregate intrinsic value of the shares on the vesting dates was $3.4 million .

Earnings Per Share ("EPS") and

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU")	3 Months Ended
	Mar. 31, 2018
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 COPT’s forward equity sale agreements and our 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 March 31, 2018 2017 Numerator: Net income attributable to COPT $ 17,150 $ 21,019 Preferred share dividends — (3,180 ) Income attributable to share-based compensation awards (117 ) (125 ) Numerator for basic and diluted EPS on net income attributable to COPT common shareholders $ 17,033 $ 17,714 Denominator (all weighted averages): Denominator for basic EPS (common shares) 100,999 98,411 Dilutive effect of share-based compensation awards 144 155 Denominator for diluted EPS (common shares) 101,143 98,566 Basic EPS $ 0.17 $ 0.18 Diluted EPS $ 0.17 $ 0.18 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 March 31, 2018 2017 Conversion of common units 3,221 3,446 Conversion of Series I preferred units 176 176 The following securities were also excluded from the computation of diluted EPS because their effects were not dilutive: • weighted average shares related to COPT’s forward equity sale agreements for the three months ended March 31, 2018 of 7.5 million ; • weighted average restricted shares and deferred share awards for the three months ended March 31, 2018 and 2017 of 444,000 and 392,000 , respectively; and • weighted average options for the three months ended March 31, 2018 and 2017 of 60,000 and 140,000 , 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 COPT’s forward equity sale agreements and our 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 March 31, 2018 2017 Numerator: Net income attributable to COPLP $ 17,859 $ 21,806 Preferred unit distributions (165 ) (3,345 ) Income attributable to share-based compensation awards (117 ) (125 ) Numerator for basic and diluted EPU on net income attributable to COPLP common unitholders $ 17,577 $ 18,336 Denominator (all weighted averages): Denominator for basic EPU (common units) 104,220 101,857 Dilutive effect of share-based compensation awards 144 155 Denominator for diluted EPU (common units) 104,364 102,012 Basic EPU $ 0.17 $ 0.18 Diluted EPU $ 0.17 $ 0.18 Our diluted EPU computations do not include the effect of 176,000 common units resulting from an assumed conversion of the Series I preferred units since such a conversion would increase diluted EPU for the three months ended March 31, 2018 and 2017 . The following securities were also excluded from the computation of diluted EPU because their effects were not dilutive: • weighted average shares related to COPT’s forward equity sale agreements for the three months ended March 31, 2018 of 7.5 million ; • weighted average restricted units and deferred share awards for the three months ended March 31, 2018 and 2017 of 444,000 and 392,000 , respectively; and • weighted average options for the three months ended March 31, 2018 and 2017 of 60,000 and 140,000 , respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Litigation and Claims In the normal course of business, we are subject to legal actions and other claims. We record losses for specific legal proceedings and claims when we determine that a loss is probable and the amount of loss can be reasonably estimated. Management believes that it is reasonably possible that we could incur losses pursuant to such claims but do not believe such losses would materially affect our financial position, liquidity or our results of operations. 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. 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. 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 $995,000 liability through March 31, 2018 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 March 31, 2018 follow (in thousands): Year Ending December 31, 2018 (1) $ 961 2019 1,267 2020 1,260 2021 1,264 2022 1,151 Thereafter 84,611 $ 90,514 (1) Represents the nine months ending December 31, 2018 . Capital Lease On May 25, 2017, we entered into a ground lease on land under development in Washington, DC 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 March 31, 2018 follow (in thousands): Year Ending December 31, 2018 (1) $ 11,628 2020 135 2022 75 Total minimum rental payments 11,838 Less: Amount representing interest (60 ) Capital lease obligation $ 11,778 (1) Represents the nine months ending December 31, 2018 . Contractual Obligations We had amounts remaining to be incurred under various contractual obligations as of March 31, 2018 that included the following (excluding amounts incurred and therefore reflected as liabilities reported on our consolidated balance sheets): • new development and redevelopment obligations of $64.8 million ; • capital expenditures for operating properties of $45.9 million ; • third party construction and development of $14.3 million ; and • other obligations of $2.5 million .

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
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, 2017 included in our 2017 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 2017 Annual Report on Form 10-K as updated for our adoption of recent accounting pronouncements discussed below.
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, including restricted cash and marketable securities that were reclassified to the line entitled “prepaid expenses and other assets, net” on our consolidated balance sheets after having been reported on a separate line in our previous Quarterly Reports on Form 10-Q and Annual Reports on Form 10-K.
Recent Accounting Pronouncements	Recent Accounting Pronouncements We adopted guidance issued by the Financial Accounting Standards Board (“FASB”) effective January 1, 2018 regarding the recognition of revenue from contracts with customers (“Topic 606”). Under this guidance, an entity recognizes 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 determined that Topic 606 is applicable to our construction contract and other service revenues, which includes predominantly construction and design projects performed primarily for tenants of our properties. We used the modified retrospective method for contracts that were not completed as of January 1, 2018. Under this method, the cumulative effect of initially applying the guidance is recognized as an adjustment to the opening balance of retained earnings as of the date of initial application. Our adoption of Topic 606 effective January 1, 2018 did not affect our consolidated financial statements other than additional disclosure provided in accordance with the guidance. We did not elect to use any of the practical expedients provided for under the guidance. 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, Topic 606 may 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). We adopted guidance issued by the FASB effective January 1, 2018 that requires entities to measure equity investments at fair value through net income, except for those that result in consolidation or are accounted for under the equity method of accounting. For equity investments without readily determinable fair values, the guidance permits the application of a measurement alternative using the cost of the investment, less any impairments, plus or minus changes resulting from observable price changes for an identical or similar investment of the same issuer. Our adoption of this guidance had no effect on our consolidated financial statements. We adopted guidance issued by the FASB retrospectively effective January 1, 2018 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. Our adoption of this guidance had no effect on our consolidated financial statements. We adopted guidance issued by the FASB retrospectively effective January 1, 2018 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. As a result of our adoption of this guidance, the change in restricted cash is no longer reported as either operating or investing activities on our statements of cash flows. Our restricted cash primarily consists of cash escrowed under mortgage debt for capital improvements and real estate taxes and certain tenant security deposits. Our adoption of this guidance had the following effects on our consolidated statements of cash flows for the three months ended March 31, 2017 (in thousands): As Previously Reported Impact of Adoption As Net cash provided by operating activities $ 60,637 $ (555 ) $ 60,082 Net cash provided by investing activities $ 1,923 $ 87 $ 2,010 Net increase in cash and cash equivalents and restricted cash $ 16,607 $ (468 ) $ 16,139 Beginning of period cash and cash equivalents and restricted cash $ 209,863 $ 2,756 $ 212,619 End of period cash and cash equivalents and restricted cash $ 226,470 $ 2,288 $ 228,758 We adopted guidance issued by the FASB that clarifies the scope of provisions and accounting for nonfinancial asset derecognition, including partial sales of real estate assets, effective January 1, 2018 using the full retrospective method. 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 nonfinancial 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 are now subject to the same derecognition model as all other nonfinancial assets. We had a transaction in July 2016 accounted for as a partial sale under the previous guidance that meets the criteria for immediate full gain recognition under the new guidance; as a result, we retrospectively recognized an additional $18 million in income in 2016 that was being amortized into income in subsequent periods under the previous guidance. The recognition pattern for our other sales of real estate were not changed by this new guidance. The full retrospective method requires adjustment of each reporting period presented at the time of adoption. The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPT and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolidated real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Cumulative distributions in excess of net income $ (818,190 ) $ 16,105 $ (802,085 ) $ (774,445 ) $ 17,115 $ (757,330 ) $ (765,276 ) $ 17,451 $ (747,825 ) Noncontrolling interests in subsidiaries $ 65,549 $ 616 $ 66,165 $ 66,820 $ 650 $ 67,470 $ 71,605 $ 662 $ 72,267 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to noncontrolling interests - Common units in COPLP $ (634 ) $ 12 $ (622 ) Net income attributable to COPT $ 21,355 $ (336 ) $ 21,019 Net income attributable to COPT common shareholders $ 18,175 $ (336 ) $ 17,839 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPT $ 22,716 $ (336 ) $ 22,380 The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPLP and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolid. real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Common units $ 1,428,301 $ 16,721 $ 1,445,022 $ 1,409,632 $ 17,765 $ 1,427,397 $ 1,401,597 $ 18,113 $ 1,419,710 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to COPLP $ 22,154 $ (348 ) $ 21,806 Net income attributable to COPLP common unitholders $ 18,809 $ (348 ) $ 18,461 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPLP $ 23,562 $ (348 ) $ 23,214 Adoption of this guidance had no impact to cash provided by or used in operating, financing or investing activities on our consolidated statements of cash flows for the three months ended March 31, 2017. We early adopted guidance issued by the FASB effective January 1, 2018 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. We adopted this guidance using the modified retrospective transition method under which we eliminated $276,000 in previously-recorded cumulative hedge ineffectiveness as of January 1, 2018 by means of a cumulative-effect adjustment to our beginning balance of accumulated other comprehensive income (“AOCI”), with a corresponding adjustment to the beginning balance of: cumulative distributions in excess of net income for COPT and subsidiaries; and common units for COPLP and subsidiaries. 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 2017 Annual Report on Form 10-K for amounts deferred in 2017, 2016 and 2015). 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: Under the issued and approved guidance, we believed that the new revenue standard would apply to executory costs and other components of revenue deemed to be non-lease components (such as common area maintenance and provision of utilities), in which case we would need: to separate the lease components of revenue due under leases from the non-lease components; and recognize revenue on the non-lease components as the related services are delivered, which could result in a change to our revenue recognition pattern. However, in March 2018, the FASB tentatively approved a practical expedient to provide lessors with an option to not separate lease components of revenue from non-lease components if: the timing and pattern of transfer of these components is the same as the related lease; and the lease would continue to be classified as an operating lease; • Leases in which we are the lessee: ◦ Our most significant leases as lessee are ground leases; as of March 31, 2018 , our future minimum rental payments under these leases totaled $89.7 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 right-of-use assets and lease liabilities 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, we expect to elect to apply the package of practical expedients under which we would 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.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	Our adoption of this guidance had the following effects on our consolidated statements of cash flows for the three months ended March 31, 2017 (in thousands): As Previously Reported Impact of Adoption As Net cash provided by operating activities $ 60,637 $ (555 ) $ 60,082 Net cash provided by investing activities $ 1,923 $ 87 $ 2,010 Net increase in cash and cash equivalents and restricted cash $ 16,607 $ (468 ) $ 16,139 Beginning of period cash and cash equivalents and restricted cash $ 209,863 $ 2,756 $ 212,619 End of period cash and cash equivalents and restricted cash $ 226,470 $ 2,288 $ 228,758 The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPT and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolidated real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Cumulative distributions in excess of net income $ (818,190 ) $ 16,105 $ (802,085 ) $ (774,445 ) $ 17,115 $ (757,330 ) $ (765,276 ) $ 17,451 $ (747,825 ) Noncontrolling interests in subsidiaries $ 65,549 $ 616 $ 66,165 $ 66,820 $ 650 $ 67,470 $ 71,605 $ 662 $ 72,267 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to noncontrolling interests - Common units in COPLP $ (634 ) $ 12 $ (622 ) Net income attributable to COPT $ 21,355 $ (336 ) $ 21,019 Net income attributable to COPT common shareholders $ 18,175 $ (336 ) $ 17,839 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPT $ 22,716 $ (336 ) $ 22,380 The tables below set forth the impact of the adoption of this guidance for amounts previously reported on the consolidated financial statements of COPLP and subsidiaries (in thousands): As of December 31, 2017 As of March 31, 2017 As of December 31, 2016 Consolidated Balance Sheets As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As As Previously Reported Impact of Adoption As Investment in unconsolid. real estate joint venture $ 25,066 $ 16,721 $ 41,787 $ 25,417 $ 17,765 $ 43,182 $ 25,548 $ 18,113 $ 43,661 Common units $ 1,428,301 $ 16,721 $ 1,445,022 $ 1,409,632 $ 17,765 $ 1,427,397 $ 1,401,597 $ 18,113 $ 1,419,710 For the Three Months Ended March 31, 2017 Consolidated Statements of Operations and Comprehensive Income As Previously Reported Impact of Adoption As Equity in income of unconsolidated entities $ 725 $ (348 ) $ 377 Income before gain on sales of real estate $ 18,850 $ (348 ) $ 18,502 Net income $ 23,088 $ (348 ) $ 22,740 Net income attributable to COPLP $ 22,154 $ (348 ) $ 21,806 Net income attributable to COPLP common unitholders $ 18,809 $ (348 ) $ 18,461 Comprehensive income $ 24,496 $ (348 ) $ 24,148 Comprehensive income attributable to COPLP $ 23,562 $ (348 ) $ 23,214

Revenue Recognition on Constr27

Revenue Recognition on Construction Contract and Other Service Revenues (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The table below reports construction contract and other service revenues by compensation arrangement (in thousands): For the Three Months Ended March 31, 2018 2017 Construction contract revenues: GMP $ 20,486 $ 6,589 FFP 6,435 6,198 Cost-plus fee 58 17 Other 219 230 $ 27,198 $ 13,034 The table below reports construction contract and other service revenues by service type (in thousands): For the Three Months Ended March 31, 2018 2017 Construction contract revenues: Construction $ 25,915 $ 10,091 Design 1,064 2,713 Other 219 230 $ 27,198 $ 13,034
Schedule of Accounts Receivable	The beginning and ending balances of accounts receivable related to our construction contracts were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 4,577 $ 4,131 Ending balance $ 4,021 $ 7,376
Contract with Customer, Asset and Liability	The beginning and ending balances of our contract assets were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 4,884 $ 10,350 Ending balance $ 4,250 $ 4,451 Changes in contract liabilities were as follows (in thousands): For the Three Months Ended March 31, 2018 2017 Beginning balance $ 27,402 $ 32,650 Ending balance $ 8,279 $ 40,485 Revenue recognized included in beginning balance $ 19,297 $ 4,199

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
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 COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of March 31, 2018 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 $ 4,433 $ — $ — $ 4,433 Other 48 — — 48 Interest rate derivatives (1) — 7,960 — 7,960 Total assets $ 4,481 $ 7,960 $ — $ 12,441 Liabilities: Deferred compensation plan liability (2) $ — $ 4,481 $ — $ 4,481 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPT’s consolidated balance sheet. (2) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet. 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 March 31, 2018 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) $ — $ 7,960 $ — $ 7,960 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPLP ’ s consolidated balance sheet.

Properties, Net (Tables)

Properties, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Real Estate [Abstract]
Schedule of operating properties, net	Operating properties, net consisted of the following (in thousands): March 31, December 31, Land $ 457,459 $ 455,680 Buildings and improvements 3,096,262 3,068,124 Less: Accumulated depreciation (813,457 ) (786,193 ) Operating properties, net $ 2,740,264 $ 2,737,611
Schedule of projects in development or held for future development	Projects in development or held for future development consisted of the following (in thousands): March 31, December 31, Land $ 239,141 $ 240,825 Development in progress, excluding land 178,874 162,669 Projects in development or held for future development $ 418,015 $ 403,494
Components of assets held for sale	The table below sets forth the components of this property’s assets as of March 31, 2018 and December 31, 2017 (in thousands): Properties, net $ 38,670 Deferred rent receivable 3,237 Deferred leasing costs, net 319 Assets held for sale, net $ 42,226

Real Estate Joint Ventures (Tab

Real Estate Joint Ventures (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 (dollars in thousands): Nominal Ownership March 31, 2018 (1) Date % as of Total Encumbered Total Acquired 3/31/2018 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 161,290 $ 74,509 $ 52,511 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 71,556 44,909 45,436 Stevens Investors, LLC 8/11/2015 95% Development of real estate (4) 73,240 — 15,469 $ 306,086 $ 119,418 $ 113,416 (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.

Investing Receivables (Tables)

Investing Receivables (Tables)	3 Months Ended
	Mar. 31, 2018
Receivables [Abstract]
Schedule of investing receivables	Investing receivables, including accrued interest thereon, consisted of the following (in thousands): March 31, December 31, Notes receivable from the City of Huntsville $ 55,779 $ 54,472 Other investing loans receivable 3,021 3,021 $ 58,800 $ 57,493

Prepaid Expenses and Other As32

Prepaid Expenses and Other Assets, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Prepaid Expense and Other Assets [Abstract]
Schedule of prepaid expenses and other assets	Prepaid expenses and other assets, net of COPT and its subsidiaries consisted of the following (in thousands): March 31, December 31, Lease incentives, net $ 18,838 $ 19,011 Prepaid expenses 17,093 24,670 Interest rate derivatives 7,960 3,073 Furniture, fixtures and equipment, net 5,331 5,256 Marketable securities in deferred compensation plan 4,481 4,616 Construction contract costs incurred in excess of billings 4,250 4,884 Restricted cash 3,645 2,570 Non-real estate equity method investments 2,410 2,412 Deferred tax asset, net (1) 1,837 1,892 Other assets 6,436 6,023 Prepaid expenses and other assets, net $ 72,281 $ 74,407 (1) Includes a valuation allowance of $1.4 million .

Debt, Net (Tables)

Debt, Net (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Schedule of debt	Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of March 31, December 31, Stated Interest Rates as of Scheduled Maturity as of March 31, 2018 March 31, 2018 Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 149,835 $ 150,723 3.82% - 7.87% (3) 2019-2026 Variable rate secured debt 13,029 13,115 LIBOR + 1.85% (4) October 2020 Total mortgage and other secured debt 162,864 163,838 Revolving Credit Facility 153,000 126,000 LIBOR + 0.875% to 1.60% (5) May 2019 (6) Term Loan Facilities (7) 348,072 347,959 LIBOR + 0.90% to 1.85% (8) 2020-2022 Unsecured Senior Notes 3.600%, $350,000 aggregate principal 347,659 347,551 3.60% (9) May 2023 5.250%, $250,000 aggregate principal 246,765 246,645 5.25% (10) February 2024 3.700%, $300,000 aggregate principal 298,444 298,322 3.70% (11) June 2021 5.000%, $300,000 aggregate principal 296,824 296,731 5.00% (12) July 2025 Unsecured note payable 1,258 1,287 0% (13) May 2026 Total debt, net $ 1,854,886 $ 1,828,333 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $4.8 million as of March 31, 2018 and $5.0 million as of December 31, 2017 . (2) Certain of the fixed rate mortgages carry interest rates that, upon assumption, were above or below market rates 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 $332,000 as of March 31, 2018 and $349,000 as of December 31, 2017 . (3) The weighted average interest rate on our fixed rate mortgage debt was 4.18% as of March 31, 2018 . (4) The interest rate on our variable rate secured debt was 3.51% as of March 31, 2018 . (5) The weighted average interest rate on the Revolving Credit Facility was 2.77% as of March 31, 2018 . (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 March 31, 2018 , 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. (8) The weighted average interest rate on these loans was 3.03% as of March 31, 2018 . (9) The carrying value of these notes reflects an unamortized discount totaling $1.6 million as of March 31, 2018 and $1.7 million as of December 31, 2017 . 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 $2.9 million as of March 31, 2018 and $3.0 million as of December 31, 2017 . 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 $1.2 million as of March 31, 2018 and $1.3 million as of December 31, 2017 . 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 $2.6 million as of March 31, 2018 and $2.7 million as of December 31, 2017 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% . (13) This note carries an interest rate that, upon assumption, was below market rates and it therefore was recorded at its fair value based on applicable effective interest rates. The carrying value of this note reflects an unamortized discount totaling $353,000 as of March 31, 2018 and $373,000 as of December 31, 2017 .
Schedule of the fair value of debt	The following table sets forth information pertaining to the fair value of our debt (in thousands): March 31, 2018 December 31, 2017 Carrying Fair Carrying Fair Amount Value Amount Value Fixed-rate debt Unsecured Senior Notes $ 1,189,692 $ 1,222,102 $ 1,189,249 $ 1,229,398 Other fixed-rate debt 151,093 151,271 152,010 152,485 Variable-rate debt 514,101 512,371 487,074 485,694 $ 1,854,886 $ 1,885,744 $ 1,828,333 $ 1,867,577

Interest Rate Derivatives (Tabl

Interest Rate Derivatives (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, December 31, $ 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 $ 662 $ 252 13,121 (1) 1.3900% One-Month LIBOR 10/13/2015 10/1/2020 312 213 100,000 1.9013% One-Month LIBOR 9/1/2016 12/1/2022 2,794 1,046 100,000 1.9050% One-Month LIBOR 9/1/2016 12/1/2022 2,808 1,051 50,000 1.9079% One-Month LIBOR 9/1/2016 12/1/2022 1,384 511 $ 7,960 $ 3,073 (1) The notional amount of this instrument is scheduled to amortize to $12.1 million .
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 March 31, December 31, 2017 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets, net $ 7,960 $ 3,073
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): Amount of Gain (Loss) Recognized in AOCI on Derivatives Amount of Gain (Loss) Reclassified from AOCI into Income For the Three Months Ended March 31, For the Three Months Ended March 31, Derivatives in Hedging Relationships 2018 2017 Statement of Operations Location 2018 2017 Interest rate derivatives $ 4,676 $ 224 Interest expense $ (245 ) $ (1,184 )

Redeemable Noncontrolling Int35

Redeemable Noncontrolling Interests (Tables)	3 Months Ended
	Mar. 31, 2018
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 Three Months Ended March 31, 2018 2017 Beginning balance $ 23,125 $ 22,979 Distributions to noncontrolling interests (452 ) (415 ) Net income attributable to noncontrolling interests 638 567 Adjustment to arrive at fair value of interests 537 545 Ending balance $ 23,848 $ 23,676

Information by Business Segme36

Information by Business Segment (Tables)	3 Months Ended
	Mar. 31, 2018
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 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 Wholesale Other Total Three Months Ended March 31, 2018 Revenues from real estate operations $ 62,782 $ 12,561 $ 11,443 $ 7,870 $ 3,633 $ 5,831 $ 104,120 $ 15,284 $ 8,077 $ 797 $ 128,278 Property operating expenses (21,604 ) (4,723 ) (6,598 ) (3,304 ) (1,440 ) (794 ) (38,463 ) (7,878 ) (4,258 ) (352 ) (50,951 ) UJV NOI allocable to COPT — — — — — 1,199 1,199 — — — 1,199 NOI from real estate operations $ 41,178 $ 7,838 $ 4,845 $ 4,566 $ 2,193 $ 6,236 $ 66,856 $ 7,406 $ 3,819 $ 445 $ 78,526 Additions to long-lived assets $ 7,121 $ 1,940 $ — $ 1,108 $ 79 $ — $ 10,248 $ 3,884 $ 36 $ 127 $ 14,295 Transfers from non-operating properties $ 17,186 $ 341 $ — $ (3 ) $ 444 $ 1,114 $ 19,082 $ — $ 1,012 $ — $ 20,094 Segment assets at March 31, 2018 $ 1,273,359 $ 399,202 $ 127,855 $ 192,116 $ 107,096 $ 302,120 $ 2,401,748 $ 397,355 $ 222,738 $ 4,125 $ 3,025,966 Three Months Ended March 31, 2017 Revenues from real estate operations $ 60,855 $ 11,707 $ 11,634 $ 7,010 $ 3,460 $ 5,522 $ 100,188 $ 18,276 $ 6,770 $ 1,533 $ 126,767 Property operating expenses (20,520 ) (4,452 ) (6,802 ) (3,209 ) (1,371 ) (659 ) (37,013 ) (7,486 ) (3,365 ) (655 ) (48,519 ) UJV NOI allocable to COPT — — — — — 1,202 1,202 — — — 1,202 NOI from real estate operations $ 40,335 $ 7,255 $ 4,832 $ 3,801 $ 2,089 $ 6,065 $ 64,377 $ 10,790 $ 3,405 $ 878 $ 79,450 Additions to long-lived assets $ 3,422 $ 2,468 $ — $ 2,168 $ 132 $ — $ 8,190 $ 7,120 $ 1,574 $ 156 $ 17,040 Transfers from non-operating properties $ 13,416 $ 222 $ — $ — $ (4 ) $ (1,015 ) $ 12,619 $ — $ 8 $ 18 $ 12,645 Segment assets at March 31, 2017 $ 1,258,437 $ 361,449 $ 131,194 $ 195,892 $ 109,171 $ 224,254 $ 2,280,397 $ 439,079 $ 229,630 $ 21,011 $ 2,970,117
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 March 31, 2018 2017 Segment revenues from real estate operations $ 128,278 $ 126,767 Construction contract and other service revenues 27,198 13,034 Total revenues $ 155,476 $ 139,801
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 March 31, 2018 2017 UJV NOI allocable to COPT $ 1,199 $ 1,202 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (824 ) (824 ) Add: Equity in loss of unconsolidated non-real estate entities (2 ) (1 ) Equity in income of unconsolidated entities $ 373 $ 377
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 March 31, 2018 2017 Construction contract and other service revenues $ 27,198 $ 13,034 Construction contract and other service expenses (26,216 ) (12,486 ) NOI from service operations $ 982 $ 548
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 before gain on sales of real estate as reported on our consolidated statements of operations (in thousands): For the Three Months Ended March 31, 2018 2017 NOI from real estate operations $ 78,526 $ 79,450 NOI from service operations 982 548 Interest and other income 1,359 1,726 Equity in income of unconsolidated entities 373 377 Income tax expense (55 ) (40 ) Depreciation and other amortization associated with real estate operations (33,512 ) (33,059 ) General, administrative and leasing expenses (7,292 ) (8,611 ) Business development expenses and land carry costs (1,614 ) (1,693 ) Interest expense (18,784 ) (18,994 ) Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities (1,199 ) (1,202 ) Income before gain on sales of real estate $ 18,784 $ 18,502
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): March 31, March 31, Segment assets $ 3,025,966 $ 2,970,117 Non-operating property assets 425,951 429,690 Other assets 144,321 357,324 Total COPT consolidated assets $ 3,596,238 $ 3,757,131

Share-Based Compensation (Table

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
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 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted

Earnings Per Share ("EPS") an38

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 2017 Numerator: Net income attributable to COPT $ 17,150 $ 21,019 Preferred share dividends — (3,180 ) Income attributable to share-based compensation awards (117 ) (125 ) Numerator for basic and diluted EPS on net income attributable to COPT common shareholders $ 17,033 $ 17,714 Denominator (all weighted averages): Denominator for basic EPS (common shares) 100,999 98,411 Dilutive effect of share-based compensation awards 144 155 Denominator for diluted EPS (common shares) 101,143 98,566 Basic EPS $ 0.17 $ 0.18 Diluted EPS $ 0.17 $ 0.18
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 March 31, 2018 2017 Conversion of common units 3,221 3,446 Conversion of Series I preferred units 176 176
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 March 31, 2018 2017 Numerator: Net income attributable to COPLP $ 17,859 $ 21,806 Preferred unit distributions (165 ) (3,345 ) Income attributable to share-based compensation awards (117 ) (125 ) Numerator for basic and diluted EPU on net income attributable to COPLP common unitholders $ 17,577 $ 18,336 Denominator (all weighted averages): Denominator for basic EPU (common units) 104,220 101,857 Dilutive effect of share-based compensation awards 144 155 Denominator for diluted EPU (common units) 104,364 102,012 Basic EPU $ 0.17 $ 0.18 Diluted EPU $ 0.17 $ 0.18

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2018
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 March 31, 2018 follow (in thousands): Year Ending December 31, 2018 (1) $ 961 2019 1,267 2020 1,260 2021 1,264 2022 1,151 Thereafter 84,611 $ 90,514 (1) Represents the nine months ending December 31, 2018 .
Future minimum lease payments for capital leases	Future minimum rental payments due under the term of this lease as of March 31, 2018 follow (in thousands): Year Ending December 31, 2018 (1) $ 11,628 2020 135 2022 75 Total minimum rental payments 11,838 Less: Amount representing interest (60 ) Capital lease obligation $ 11,778 (1) Represents the nine months ending December 31, 2018 .

Organization (Details)

Organization (Details) - Mar. 31, 2018 ft² in Thousands	a	ft²	MW	Property
Operating Properties
Investments in real estate
Number of real estate properties				159
Area of real estate property (in square feet or acres) | ft²		17,600
Operating Properties | Office Properties
Investments in real estate
Number of real estate properties				144
Operating Properties | Single-tenant data centers
Investments in real estate
Number of real estate properties				15
Properties under, or contractually committed for, construction or approved for redevelopment
Investments in real estate
Number of real estate properties				7
Area of real estate property (in square feet or acres) | ft²		619
Properties under, or contractually committed for, construction or approved for redevelopment | Office Properties
Investments in real estate
Number of real estate properties				4
Properties under, or contractually committed for, construction or approved for redevelopment | Single-tenant data centers
Investments in real estate
Number of real estate properties				3
Properties under, or contractually committed for, construction or approved for redevelopment | Partially operational properties
Investments in real estate
Number of real estate properties				1
Land controlled for future development
Investments in real estate
Area of real estate property (in square feet or acres)	1,000	13,000
Other Land
Investments in real estate
Area of real estate property (in square feet or acres) | a	150
Operating wholesale data centers
Investments in real estate
Critical load (in megawatts) | MW			19.25
GI-COPT | Operating Properties | Single-tenant data centers
Investments in real estate
Number of real estate properties				6

Organization (Details 2)

Organization (Details 2)	3 Months Ended
	Mar. 31, 2018
Corporate Office Properties, L.P. | Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	97.00%

Summary of Significant Accoun42

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum rental payments due		$ 90,514
Ground Leases
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Minimum rental payments due		$ 89,700
Accounting Standards Update 2017-05
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of change on net income	$ 18,000
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance				$ 276
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance			$ 276
Accumulated Other Comprehensive Income (Loss) | Corporate Office Properties, L.P.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance				276
Accumulated Other Comprehensive Income (Loss) | Corporate Office Properties, L.P. | Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance			0
Cumulative Distributions in Excess of Net Income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance				(276)
Cumulative Distributions in Excess of Net Income | Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance			(276)
Common Shares | Corporate Office Properties, L.P.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance				$ (276)
Common Shares | Corporate Office Properties, L.P. | Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of accounting change for adoption of hedge accounting guidance			$ 0

Summary of Significant Accoun43

Summary of Significant Accounting Policies (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities	$ 26,195	$ 60,082
Net cash provided by investing activities	(34,804)	2,010
Net increase in cash and cash equivalents and restricted cash	(2,298)	16,139
Beginning of period	14,831	212,619
End of period	$ 12,533	228,758
Accounting Standards Update 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		(555)
Net cash provided by investing activities		87
Net increase in cash and cash equivalents and restricted cash		(468)
Beginning of period		2,756
End of period		2,288
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net cash provided by operating activities		60,637
Net cash provided by investing activities		1,923
Net increase in cash and cash equivalents and restricted cash		16,607
Beginning of period		209,863
End of period		$ 226,470

Summary of Significant Accoun44

Summary of Significant Accounting Policies (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture	$ 41,311	$ 43,182	$ 41,787	$ 43,661
Cumulative distributions in excess of net income	(813,302)	(757,330)	(802,085)	(747,825)
Noncontrolling interests in subsidiaries	65,673	67,470	66,165	72,267
Common units	1,022		1,013
Equity in income of unconsolidated entities	373	377
Income before gain on sales of real estate	18,784	18,502
Net income	18,780	22,740
Net income attributable to noncontrolling interests - Common units in COPLP	(544)	(622)
Net income attributable to COPT	17,150	21,019
Net income attributable to COPT common shareholders	17,150	17,839
Comprehensive income	23,701	24,148
Comprehensive income attributable to COPT	21,911	22,380
Corporate Office Properties, L.P.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture	41,311	43,182	41,787	43,661
Noncontrolling interests in subsidiaries	12,592		12,312
Common units	1,453,262	1,427,397	1,445,022	1,419,710
Equity in income of unconsolidated entities	373	377
Income before gain on sales of real estate	18,784	18,502
Net income	18,780	22,740
Net income attributable to COPT	17,859	21,806
Net income attributable to COPT common shareholders	17,694	18,461
Comprehensive income	23,701	24,148
Comprehensive income attributable to COPT	$ 22,780	23,214
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture		25,417	25,066	25,548
Cumulative distributions in excess of net income		(774,445)	(818,190)	(765,276)
Noncontrolling interests in subsidiaries		66,820	65,549	71,605
Equity in income of unconsolidated entities		725
Income before gain on sales of real estate		18,850
Net income		23,088
Net income attributable to noncontrolling interests - Common units in COPLP		(634)
Net income attributable to COPT		21,355
Net income attributable to COPT common shareholders		18,175
Comprehensive income		24,496
Comprehensive income attributable to COPT		22,716
As Previously Reported | Corporate Office Properties, L.P.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture		25,417	25,066	25,548
Common units		1,409,632	1,428,301	1,401,597
Equity in income of unconsolidated entities		725
Income before gain on sales of real estate		18,850
Net income		23,088
Net income attributable to COPT		22,154
Net income attributable to COPT common shareholders		18,809
Comprehensive income		24,496
Comprehensive income attributable to COPT		23,562
Accounting Standards Update 2017-05
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture		17,765	16,721	18,113
Cumulative distributions in excess of net income		17,115	16,105	17,451
Noncontrolling interests in subsidiaries		650	616	662
Equity in income of unconsolidated entities		(348)
Income before gain on sales of real estate		(348)
Net income		(348)
Net income attributable to noncontrolling interests - Common units in COPLP		12
Net income attributable to COPT		(336)
Net income attributable to COPT common shareholders		(336)
Comprehensive income		(348)
Comprehensive income attributable to COPT		(336)
Accounting Standards Update 2017-05 | Corporate Office Properties, L.P.
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investment in unconsolidated real estate joint venture		17,765	16,721	18,113
Common units		17,765	$ 16,721	$ 18,113
Equity in income of unconsolidated entities		(348)
Income before gain on sales of real estate		(348)
Net income		(348)
Net income attributable to COPT		(348)
Net income attributable to COPT common shareholders		(348)
Comprehensive income		(348)
Comprehensive income attributable to COPT		$ (348)

Revenue Recognition on Constr45

Revenue Recognition on Construction Contract and Other Service Revenues (Details) - Construction Contract Revenue $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)compensation_arrangement	Mar. 31, 2017USD ($)
Disaggregation of Revenue [Line Items]
Number of compensation arrangement types | compensation_arrangement	3
Performance obligations satisfied or already satisfied	$ 309	$ 146
Customers payment period	30 days
Remaining performance obligations	$ 23,500

Revenue Recognition on Constr46

Revenue Recognition on Construction Contract and Other Service Revenues (Details 1) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	$ 27,198	$ 13,034
Construction
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	25,915	10,091
Design
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	1,064	2,713
Other
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	219	230
GMP
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	20,486	6,589
FFP
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	6,435	6,198
Cost-plus fee
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	58	17
Other
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	$ 219	$ 230

Revenue Recognition on Constr47

Revenue Recognition on Construction Contract and Other Service Revenues (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in Accounts Receivable
Beginning balance	$ 23,982		$ 31,802
Ending balance	23,982		31,802
Construction Contract Revenue
Change in Accounts Receivable
Beginning balance	4,021	$ 7,376	4,577	$ 4,131
Ending balance	4,021	7,376	4,577	4,131
Change in Contract with Customer, Asset
Beginning balance	4,250	4,451	4,884	10,350
Ending balance	4,250	4,451	4,884	10,350
Change in Contract with Customer, Liability
Beginning balance	8,279	40,485	27,402	32,650
Ending balance	8,279	40,485	$ 27,402	$ 32,650
Revenue recognized included in beginning balance	$ 19,297	$ 4,199

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Assets and liabilities measured at fair value
Marketable securities in deferred compensation plan	$ 4,481	$ 4,616
Deferred compensation plan | Management
Assets and liabilities measured at fair value
Maximum percentage of participants' compensation which is deferrable (as a percent)	100.00%
Marketable securities in deferred compensation plan	$ 4,500

Fair Value Measurements (Deta49

Fair Value Measurements (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Marketable securities in deferred compensation plan	$ 4,481	$ 4,616
Fair value measurement on a recurring basis
Assets:
Interest rate derivatives	7,960
Total assets	12,441
Liabilities:
Deferred compensation plan liability	4,481
Fair value measurement on a recurring basis | Mutual funds
Assets:
Marketable securities in deferred compensation plan	4,433
Fair value measurement on a recurring basis | Other
Assets:
Marketable securities in deferred compensation plan	48
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Total assets	4,481
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Assets:
Marketable securities in deferred compensation plan	4,433
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Assets:
Marketable securities in deferred compensation plan	48
Fair value measurement on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	7,960
Total assets	7,960
Liabilities:
Deferred compensation plan liability	4,481
Fair value measurement on a recurring basis | Corporate Office Properties, L.P.
Assets:
Interest rate derivatives	7,960
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	$ 7,960

Properties, Net (Details)

Properties, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments in real estate
Operating properties, net	$ 2,740,264	$ 2,737,611
Operating Properties
Investments in real estate
Less: accumulated depreciation	(813,457)	(786,193)
Operating properties, net	2,740,264	2,737,611
Operating Properties | Land
Investments in real estate
Gross	457,459	455,680
Operating Properties | Buildings and improvements
Investments in real estate
Gross	$ 3,096,262	$ 3,068,124

Properties, Net (Details 2)

Properties, Net (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Properties
Projects in development or held for future development	$ 418,015	$ 403,494
Projects in development or held for future development
Properties
Projects in development or held for future development	418,015	403,494
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	239,141	240,825
Projects in development or held for future development | Construction in progress, excluding land
Properties
Projects in development or held for future development	$ 178,874	$ 162,669

Properties, Net (Details 3)

Properties, Net (Details 3) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net	$ 42,226	$ 42,226
Assets held for sale, net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Properties, net	38,670	38,670
Deferred rent receivable	3,237	3,237
Deferred leasing costs, net	319	319
Assets held for sale, net	42,226	$ 42,226
11751 Meadowville Lane | Operating Properties | 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]
Indemnification amount	$ 20,000

Properties, Net (Details 4)

Properties, Net (Details 4) ft² in Thousands	Mar. 31, 2018ft²Property
Newly constructed properties placed in service
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) | ft²	74
Number of real estate properties | Property	1
Newly redeveloped properties placed in service
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) | ft²	11
Number of real estate properties | Property	1
Properties under construction or contractually committed for construction
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) | ft²	597
Number of real estate properties | Property	6
Properties under or approved for redevelopment
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) | ft²	22
Number of real estate properties | Property	1

Real Estate Joint Ventures (Det

Real Estate Joint Ventures (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)Property	Dec. 31, 2017USD ($)
Investments in consolidated real estate joint ventures
Real estate equity method investments	$ 2,410	$ 2,412
GI-COPT
Investments in consolidated real estate joint ventures
Real estate equity method investments	41,300
Consolidated real estate joint ventures
Investments in consolidated real estate joint ventures
Total Assets	306,086
Encumbered Assets	119,418
Total Liabilities	$ 113,416
Variable Interest Entity, Primary Beneficiary | LW Redstone Company, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)	85.00%
Total Assets	$ 161,290
Encumbered Assets	74,509
Total Liabilities	$ 52,511
Variable Interest Entity, Primary Beneficiary | M Square Associates, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)	50.00%
Total Assets	$ 71,556
Encumbered Assets	44,909
Total Liabilities	$ 45,436
Variable Interest Entity, Primary Beneficiary | Stevens Investors, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)	95.00%
Total Assets	$ 73,240
Encumbered Assets	0
Total Liabilities	$ 15,469
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	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 58,800	$ 57,493
Notes Receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 55,779	54,472
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	$ 3,021	$ 3,021

Prepaid Expenses and Other As56

Prepaid Expenses and Other Assets, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Prepaid Expense and Other Assets [Abstract]
Lease incentives, net	$ 18,838	$ 19,011
Prepaid expenses	17,093	24,670
Interest rate derivatives	7,960	3,073
Furniture, fixtures and equipment, net	5,331	5,256
Marketable securities in deferred compensation plan	4,481	4,616
Construction contract costs incurred in excess of billings	4,250	4,884
Restricted cash	3,645	2,570	$ 2,288	$ 2,756
Non-real estate equity method investments	2,410	2,412
Deferred tax asset, net	1,837	1,892
Other assets	6,436	6,023
Prepaid expenses and other assets, net	72,281	74,407
Taxable REIT Subsidiary
Mortgage and Other Investing Receivables [Line Items]
Deferred tax assets, valuation allowance	$ 1,400	$ 1,400

Debt, Net (Details)

Debt, Net (Details)	3 Months Ended
	Mar. 31, 2018USD ($)extension	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Debt
Carrying Value	$ 1,854,886,000		$ 1,828,333,000
Interest costs capitalized	1,400,000	$ 1,500,000
Secured Debt
Debt
Carrying Value	$ 162,864,000		163,838,000
Line of Credit | Revolving Credit Facility
Debt
Number of extensions | extension	2
Extension option period (in years)	6 months
Line of credit facility, extension fee percentage	0.075%
Loans payable
Debt
Deferred financing costs, net	$ 4,800,000		5,000,000
Fixed rate debt | Secured Debt
Debt
Carrying Value	149,835,000		150,723,000
Unamortized premium included in carrying value	$ 332,000		349,000
Weighted average interest rate (as a percent)	4.18%
Fixed rate debt | Secured Debt | Minimum
Debt
Stated interest rate (as a percent)	3.82%
Fixed rate debt | Secured Debt | Maximum
Debt
Stated interest rate (as a percent)	7.87%
Variable-rate debt | Secured Debt
Debt
Carrying Value	$ 13,029,000		13,115,000
Stated interest rate (as a percent)	3.51%
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	$ 153,000,000		126,000,000
Weighted average interest rate (as a percent)	2.77%
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	$ 348,072,000		347,959,000
Weighted average interest rate (as a percent)	3.03%
Aggregate additional borrowing capacity available	$ 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)	1.85%
3.60% Senior Notes | Unsecured senior notes
Debt
Carrying Value	$ 347,659,000		347,551,000
Debt instrument, face amount	$ 350,000,000
Stated interest rate (as a percent)	3.60%
Unamortized discount included in carrying value	$ 1,600,000		1,700,000
Interest rate on debt (as a percent)	3.70%
5.250% Senior Notes | Unsecured senior notes
Debt
Carrying Value	$ 246,765,000		246,645,000
Debt instrument, face amount	$ 250,000,000
Stated interest rate (as a percent)	5.25%
Unamortized discount included in carrying value	$ 2,900,000		3,000,000
Interest rate on debt (as a percent)	5.49%
3.70% Senior Notes | Unsecured senior notes
Debt
Carrying Value	$ 298,444,000		298,322,000
Debt instrument, face amount	$ 300,000,000
Stated interest rate (as a percent)	3.70%
Unamortized discount included in carrying value	$ 1,200,000		1,300,000
Interest rate on debt (as a percent)	3.85%
5.000% Senior Notes | Unsecured senior notes
Debt
Carrying Value	$ 296,824,000		296,731,000
Debt instrument, face amount	$ 300,000,000
Stated interest rate (as a percent)	5.00%
Unamortized discount included in carrying value	$ 2,600,000		2,700,000
Interest rate on debt (as a percent)	5.15%
Unsecured notes payable
Debt
Carrying Value	$ 1,258,000		1,287,000
Stated interest rate (as a percent)	0.00%
Unamortized discount included in carrying value	$ 353,000		$ 373,000

Debt, Net (Details 2)

Debt, Net (Details 2) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Carrying Amount
Carrying amount and estimated fair value of debt
Long-term debt	$ 1,854,886	$ 1,828,333
Carrying Amount | Unsecured senior notes
Carrying amount and estimated fair value of debt
Long-term debt	1,189,692	1,189,249
Carrying Amount | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	151,093	152,010
Carrying Amount | Variable-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	514,101	487,074
Estimated Fair Value
Carrying amount and estimated fair value of debt
Long-term debt	1,885,744	1,867,577
Estimated Fair Value | Unsecured senior notes
Carrying amount and estimated fair value of debt
Long-term debt	1,222,102	1,229,398
Estimated Fair Value | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	151,271	152,485
Estimated Fair Value | Variable-rate debt
Carrying amount and estimated fair value of debt
Long-term debt	$ 512,371	$ 485,694

Interest Rate Derivatives (Deta

Interest Rate Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair value of interest rate derivatives and balance sheet classification
Interest rate swaps designated as cash flow hedges	$ 7,960		$ 3,073
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Interest rate derivatives	4,676	$ 224
Interest rate swaps | Interest Expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Amount of Gain (Loss) Reclassified from AOCI into Income	(245)	$ (1,184)
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	7,960		3,073
Designated
Fair values of interest rate swap derivatives
Fair value of interest rate swaps	7,960		3,073
Designated | 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	(942)
Designated | Interest rate swap, effective date September 1, 2015, swap two
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000
Fixed rate (as a percent)	1.73%
Fair value of interest rate swaps	$ 662		252
Designated | Interest rate swap, effective October 13, 2015
Fair values of interest rate swap derivatives
Notional Amount	$ 13,121
Fixed rate (as a percent)	1.39%
Fair value of interest rate swaps	$ 312		213
Notional amount of interest rate derivatives after scheduled amortization	12,100
Designated | Interest rate swap, effective September 1, 2016, swap one
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000
Fixed rate (as a percent)	1.9013%
Fair value of interest rate swaps	$ 2,794		1,046
Designated | Interest rate swap, effective September 1, 2016, swap two
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000
Fixed rate (as a percent)	1.905%
Fair value of interest rate swaps	$ 2,808		1,051
Designated | Interest rate swap, effective September 1, 2016, swap three
Fair values of interest rate swap derivatives
Notional Amount	$ 50,000
Fixed rate (as a percent)	1.9079%
Fair value of interest rate swaps	$ 1,384		$ 511

Redeemable Noncontrolling Int60

Redeemable Noncontrolling Interests (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)joint_venture	Mar. 31, 2017USD ($)
Noncontrolling Interest [Abstract]
Number of joint ventures with redeemable noncontrolling interests | joint_venture	2
Redeemable Noncontrolling Interest [Roll Forward]
Beginning balance	$ 23,125	$ 22,979
Distributions to noncontrolling interests	(452)	(415)
Net income attributable to noncontrolling interests	638	567
Adjustment to arrive at fair value of interests	537	545
Ending balance	$ 23,848	$ 23,676

Equity (Details)

Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Class of Stock [Line Items]
Conversion of common units to common shares (in units/shares)	53,817	185,000
Forward Equity Sale Agreement
Class of Stock [Line Items]
Common shares issued under forward equity sale agreements	$ 19,976
Forward Equity Sale Agreement | Common Shares
Class of Stock [Line Items]
Number of shares issued	677,000
Common shares issued under forward equity sale agreements	$ 7
Remaining capacity under forward equity sale agreements	6,800,000
Common Stock Issued to Public Under At-the-Market Program
Class of Stock [Line Items]
Common shares issued under forward equity sale agreements		$ 18,222
Common Stock Issued to Public Under At-the-Market Program | Common Shares
Class of Stock [Line Items]
Common shares issued under forward equity sale agreements		$ 5
At-market stock, offering program established, remaining capacity	$ 70,000

Information by Business Segme62

Information by Business Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment financial information for real estate operations
Revenues from real estate operations	$ 128,278	$ 126,767
Property operating expenses	(50,951)	(48,519)
UJV NOI allocable to COPT	1,199	1,202
NOI from real estate operations	78,526	79,450
Additions to long-lived assets	14,295	17,040
Transfers from non-operating properties	20,094	12,645
Segment assets	3,596,238	3,757,131	$ 3,595,205
Defense/Information Technology Locations
Segment financial information for real estate operations
Revenues from real estate operations	104,120	100,188
Property operating expenses	(38,463)	(37,013)
UJV NOI allocable to COPT	1,199	1,202
NOI from real estate operations	66,856	64,377
Additions to long-lived assets	10,248	8,190
Transfers from non-operating properties	19,082	12,619
Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Revenues from real estate operations	62,782	60,855
Property operating expenses	(21,604)	(20,520)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	41,178	40,335
Additions to long-lived assets	7,121	3,422
Transfers from non-operating properties	17,186	13,416
Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Revenues from real estate operations	12,561	11,707
Property operating expenses	(4,723)	(4,452)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	7,838	7,255
Additions to long-lived assets	1,940	2,468
Transfers from non-operating properties	341	222
Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Revenues from real estate operations	11,443	11,634
Property operating expenses	(6,598)	(6,802)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	4,845	4,832
Additions to long-lived assets	0	0
Transfers from non-operating properties	0	0
Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Revenues from real estate operations	7,870	7,010
Property operating expenses	(3,304)	(3,209)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	4,566	3,801
Additions to long-lived assets	1,108	2,168
Transfers from non-operating properties	(3)	0
Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Revenues from real estate operations	3,633	3,460
Property operating expenses	(1,440)	(1,371)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	2,193	2,089
Additions to long-lived assets	79	132
Transfers from non-operating properties	444	(4)
Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Revenues from real estate operations	5,831	5,522
Property operating expenses	(794)	(659)
UJV NOI allocable to COPT	1,199	1,202
NOI from real estate operations	6,236	6,065
Additions to long-lived assets	0	0
Transfers from non-operating properties	1,114	(1,015)
Regional Office
Segment financial information for real estate operations
Revenues from real estate operations	15,284	18,276
Property operating expenses	(7,878)	(7,486)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	7,406	10,790
Additions to long-lived assets	3,884	7,120
Transfers from non-operating properties	0	0
Operating wholesale data centers
Segment financial information for real estate operations
Revenues from real estate operations	8,077	6,770
Property operating expenses	(4,258)	(3,365)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	3,819	3,405
Additions to long-lived assets	36	1,574
Transfers from non-operating properties	1,012	8
Other Segments
Segment financial information for real estate operations
Revenues from real estate operations	797	1,533
Property operating expenses	(352)	(655)
UJV NOI allocable to COPT	0	0
NOI from real estate operations	445	878
Additions to long-lived assets	127	156
Transfers from non-operating properties	0	18
Segment assets
Segment financial information for real estate operations
Segment assets	3,025,966	2,970,117
Segment assets | Defense/Information Technology Locations
Segment financial information for real estate operations
Segment assets	2,401,748	2,280,397
Segment assets | Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Segment assets	1,273,359	1,258,437
Segment assets | Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Segment assets	399,202	361,449
Segment assets | Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Segment assets	127,855	131,194
Segment assets | Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Segment assets	192,116	195,892
Segment assets | Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Segment assets	107,096	109,171
Segment assets | Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Segment assets	302,120	224,254
Segment assets | Regional Office
Segment financial information for real estate operations
Segment assets	397,355	439,079
Segment assets | Operating wholesale data centers
Segment financial information for real estate operations
Segment assets	222,738	229,630
Segment assets | Other Segments
Segment financial information for real estate operations
Segment assets	$ 4,125	$ 21,011

Information by Business Segme63

Information by Business Segment (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reconciliation of segment revenues to total revenues
Segment revenues from real estate operations	$ 128,278	$ 126,767
Construction contract and other service revenues	27,198	13,034
Total revenues	155,476	139,801
Reconciliation of UJV NOI allocable to COPT to Equity Income in Unconsolidated Entities
UJV NOI allocable to COPT	1,199	1,202
Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense	(824)	(824)
Add: Equity in loss of unconsolidated non-real estate entities	(2)	(1)
Equity in income of unconsolidated entities	373	377
Computation of net operating income from service operations
Construction contract and other service revenues	27,198	13,034
Construction contract and other service expenses	(26,216)	(12,486)
NOI from service operations	$ 982	$ 548

Information by Business Segme64

Information by Business Segment (Details 3) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reconciliation of NOI from real estate operations and NOI from service operations to (loss) income from continuing operations
NOI from real estate operations	$ 78,526	$ 79,450
NOI from service operations	982	548
Interest and other income	1,359	1,726
Equity in income of unconsolidated entities	373	377
Income tax expense	(55)	(40)
Depreciation and other amortization associated with real estate operations	(33,512)	(33,059)
General, administrative and leasing expenses	(7,292)	(8,611)
Business development expenses and land carry costs	(1,614)	(1,693)
Interest expense	(18,784)	(18,994)
Less: UJV NOI allocable to COPT included in equity in income of unconsolidated entities	(1,199)	(1,202)
Income before gain on sales of real estate	$ 18,784	$ 18,502

Information by Business Segme65

Information by Business Segment (Details 4) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Reconciliation of segment assets to total assets
Assets	$ 3,596,238	$ 3,595,205	$ 3,757,131
Segment assets
Reconciliation of segment assets to total assets
Assets	3,025,966		2,970,117
Non-operating property assets
Reconciliation of segment assets to total assets
Assets	425,951		429,690
Other assets
Reconciliation of segment assets to total assets
Assets	$ 144,321		$ 357,324

Share-Based Compensation (Detai

Share-Based Compensation (Details) $ / shares in Units, $ in Millions	Feb. 22, 2018shares	Jan. 01, 2018USD ($)Percentile_Rankemployee$ / sharesshares	Mar. 31, 2018USD ($)$ / sharesshares
Restricted shares
Share-Based Compensation
Stock awards granted (in shares or units) | shares			181,617
Aggregate grant date fair value | $			$ 4.6
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares			$ 25.18
Other Share-based Compensation Additional Disclosures
Shares vested (in shares) | shares			134,460
Weighted average fair value of shares vested (in dollars per share) | $ / shares			$ 29.49
Aggregate intrinsic value of awards upon vesting | $			$ 3.4
2018 PSU Grants | Performance share units
Share-Based Compensation
Stock awards granted (in shares or units) | shares		59,110
Aggregate grant date fair value | $		$ 1.9
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
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 31.97
Baseline value per common share (in dollars per share) | $ / shares		$ 29.20
Expected volatility of common shares (as a percent)		17.00%
Risk-free interest rate (as a percent)		2.04%
2018 PSU Grants | Performance share units | Executives
Share-Based Compensation
Number of employees affected | employee		3
2015 PSU Grants | Performance share units | Executives
Other Share-based Compensation Additional Disclosures
Shares issued (in shares) | shares	13,328
Percentage of target	75.00%

Earnings Per Share ("EPS") an67

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income attributable to COPT	$ 17,150	$ 21,019
Preferred share/unit dividends/distributions	0	(3,180)
Income attributable to share-based compensation awards	(117)	(125)
Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	$ 17,033	$ 17,714
Denominator (all weighted averages):
Denominator for basic EPS (common shares)	100,999	98,411
Dilutive effect of share-based compensation awards (shares)	144	155
Denominator for diluted EPS (common shares)	101,143	98,566
Basic EPS:
Net income attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.17	$ 0.18
Diluted EPS:
Net income attributable to COPT common shareholders - diluted (in dollars per share/unit)	$ 0.17	$ 0.18
Corporate Office Properties, L.P.
Numerator:
Net income attributable to COPT	$ 17,859	$ 21,806
Preferred share/unit dividends/distributions	(165)	(3,345)
Income attributable to share-based compensation awards	(117)	(125)
Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	$ 17,577	$ 18,336
Denominator (all weighted averages):
Denominator for basic EPS (common shares)	104,220	101,857
Dilutive effect of share-based compensation awards (shares)	144	155
Denominator for diluted EPS (common shares)	104,364	102,012
Basic EPS:
Net income attributable to COPT common shareholders - basic (in dollars per share/unit)	$ 0.17	$ 0.18
Diluted EPS:
Net income attributable to COPT common shareholders - diluted (in dollars per share/unit)	$ 0.17	$ 0.18

Earnings Per Share ("EPS") an68

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details 2) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Conversion of common units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,221	3,446
Conversion of Series I preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176
Forward Equity Sale Agreement
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	7,500
Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	444	392
Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	60	140
Corporate Office Properties, L.P. | Forward Equity Sale Agreement
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	7,500
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)	444	392
Corporate Office Properties, L.P. | Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	60	140
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	176

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	May 25, 2017USD ($)	Mar. 31, 2018USD ($)Property	Dec. 31, 2017USD ($)	Aug. 31, 2010USD ($)
Capital Leases
Capital lease term	99 years
Purchase option	$ 1
Capital lease obligation	$ 16,100,000	$ 11,778,000	$ 15,853,000
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		64,800,000
Capital Expenditures For Operating Properties
Capital Leases
Purchase obligations		45,900,000
Third Party Construction and Development
Capital Leases
Purchase obligations		14,300,000
Other Obligations
Capital Leases
Purchase obligations		2,500,000
Specialty Tax Guarantee
Tax incremental financing obligation
Liability recognized with regard to tax incremental financing obligation at end of current period		$ 995,000
Specialty Tax Guarantee | Anne Arundel County, Maryland | Tax Incremental Financing Bond
Loss Contingencies [Line Items]
Loan amount				$ 30,000,000

Commitments and Contingencies70

Commitments and Contingencies - Operating Leases Future Minimum Payments (Details) $ in Thousands	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 961
2,019	1,267
2,020	1,260
2,021	1,264
2,022	1,151
Thereafter	84,611
Total	$ 90,514

Commitments and Contingencies71

Commitments and Contingencies - Capital Leases Future Minimum Payments (Details) $ in Thousands	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 11,628
2,020	135
2,022	75
Total minimum rental payments	11,838
Less: Amount representing interest	(60)
Capital lease obligation	$ 11,778

Uncategorized Items - ofc-20180

Label	Element	Value
Subsidiaries [Member]
Restricted Cash	us-gaap_RestrictedCash	$ 2,756,000
Restricted Cash	us-gaap_RestrictedCash	2,288,000
Restricted Cash	us-gaap_RestrictedCash	2,570,000
Restricted Cash	us-gaap_RestrictedCash	$ 3,645,000