COPT Defense Properties (CDP) 10-K 12 Feb 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 22, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-14023
Entity Registrant Name	CORPORATE OFFICE PROPERTIES TRUST
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	23-2947217
Entity Address, Address Line One	6711 Columbia Gateway Drive
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Columbia
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	21046
City Area Code	443
Local Phone Number	285-5400
Title of 12(b) Security	Common Shares of beneficial interest, $0.01 par value
Trading Symbol	OFC
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float				$ 2,200
Entity Common Stock, Shares Outstanding			112,181,219
Documents Incorporated by Reference	This report also includes separate sections under Part II, Item 9A. Controls and Procedures and separate Exhibit 31 and Exhibit 32 certifications for each of COPT and COPLP to establish that the Chief Executive Officer and the Chief Financial Officer of each entity have made the requisite certifications and that COPT and COPLP are compliant with Rule 13a-15 and Rule 15d-14 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and 18 U.S.C. §1350.
Entity Central Index Key	0000860546
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Corporate Office Properties, L.P
Entity Information [Line Items]
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Entity File Number	333-189188
Entity Registrant Name	CORPORATE OFFICE PROPERTIES, L.P.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	23-2930022
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float				$ 24.2
Entity Central Index Key	0001577966
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Common Units | Corporate Office Properties, L.P | COPT
Entity Information [Line Items]
Percentage ownership in operating partnership	98.60%	98.70%

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Properties, net:
Operating properties, net	$ 3,115,280	$ 2,772,647
Projects in development or held for future development	447,269	568,239
Total properties, net	3,562,549	3,340,886
Property - operating right-of-use assets	40,570	27,864
Property - finance right-of-use assets	40,425	40,458
Cash and cash equivalents	18,369	14,733
Investment in unconsolidated real estate joint ventures	29,303	51,949
Accounts receivable, net	41,637	35,444
Deferred rent receivable	92,876	87,736
Intangible assets on real estate acquisitions, net	19,344	27,392
Deferred leasing costs (net of accumulated amortization of $30,375 and $33,782, respectively)	58,613	58,392
Prepaid expenses and other assets, net	104,583	96,076
Total assets	4,077,023	3,854,453
Liabilities:
Debt, net	2,086,918	1,831,139
Accounts payable and accrued expenses	142,717	148,746
Rents received in advance and security deposits	33,425	33,620
Dividends and distributions payable	31,231	31,263
Deferred revenue associated with operating leases	10,832	7,361
Property - operating lease liabilities	30,746	17,317
Interest rate derivatives	9,522	25,682
Other liabilities	12,490	10,649
Total liabilities	2,357,881	2,105,777
Commitments and contingencies (Note 20)
Redeemable noncontrolling interests	25,430	29,431
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest ($0.01 par value; 150,000,000 shares authorized; shares issued and outstanding of 112,181,759 at December 31, 2020 and 112,068,705 at December 31, 2019)	1,122	1,121
Additional paid-in capital	2,478,906	2,481,558
Cumulative distributions in excess of net income	(809,836)	(778,275)
Accumulated other comprehensive loss	(9,157)	(25,444)
Total Corporate Office Properties Trust/L.P.'s equity	1,661,035	1,678,960
Noncontrolling interests in subsidiaries:
Common units in COPLP	20,465	19,597
Preferred units in COPLP	0	8,800
Other consolidated entities	12,212	11,888
Noncontrolling interests in subsidiaries	32,677	40,285
Total equity	1,693,712	1,719,245
Total liabilities, redeemable noncontrolling interests and equity	4,077,023	3,854,453
Investing Receivables
Properties, net:
Investing receivables (net of allowance for credit losses of $2,851 at December 31, 2020)	68,754	73,523
Corporate Office Properties, L.P
Properties, net:
Operating properties, net	3,115,280	2,772,647
Projects in development or held for future development	447,269	568,239
Total properties, net	3,562,549	3,340,886
Property - operating right-of-use assets	40,570	27,864
Property - finance right-of-use assets	40,425	40,458
Cash and cash equivalents	18,369	14,733
Investment in unconsolidated real estate joint ventures	29,303	51,949
Accounts receivable, net	41,637	35,444
Deferred rent receivable	92,876	87,736
Intangible assets on real estate acquisitions, net	19,344	27,392
Deferred leasing costs (net of accumulated amortization of $30,375 and $33,782, respectively)	58,613	58,392
Prepaid expenses and other assets, net	101,556	93,016
Total assets	4,073,996	3,851,393
Liabilities:
Debt, net	2,086,918	1,831,139
Accounts payable and accrued expenses	142,717	148,746
Rents received in advance and security deposits	33,425	33,620
Dividends and distributions payable	31,231	31,263
Deferred revenue associated with operating leases	10,832	7,361
Property - operating lease liabilities	30,746	17,317
Interest rate derivatives	9,522	25,682
Other liabilities	9,463	7,589
Total liabilities	2,354,854	2,102,717
Commitments and contingencies (Note 20)
Redeemable noncontrolling interests	25,430	29,431
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest ($0.01 par value; 150,000,000 shares authorized; shares issued and outstanding of 112,181,759 at December 31, 2020 and 112,068,705 at December 31, 2019)	1,690,610	1,724,159
Accumulated other comprehensive loss	(9,155)	(25,648)
Total Corporate Office Properties Trust/L.P.'s equity	1,681,455	1,707,311
Noncontrolling interests in subsidiaries:
Noncontrolling interests in subsidiaries	12,257	11,934
Total equity	1,693,712	1,719,245
Total liabilities, redeemable noncontrolling interests and equity	4,073,996	3,851,393
Corporate Office Properties, L.P | Investing Receivables
Properties, net:
Investing receivables (net of allowance for credit losses of $2,851 at December 31, 2020)	68,754	73,523
Corporate Office Properties, L.P | Limited Partner
Corporate Office Properties Trust’s shareholders’ equity:
Preferred units held by limited partner, 352,000 preferred units outstanding at December 31, 2019	$ 0	$ 8,800

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accumulated amortization of deferred leasing costs	$ 30,375	$ 33,782
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	112,181,759	112,068,705
Common Shares/units of beneficial interest, shares outstanding	112,181,759	112,068,705
Corporate Office Properties, L.P
Accumulated amortization of deferred leasing costs	$ 30,375	$ 33,782
General Partner | Corporate Office Properties, L.P
Common Shares/units of beneficial interest, shares outstanding	112,181,759	112,068,705
Limited Partner | Corporate Office Properties, L.P
Common Shares/units of beneficial interest, shares outstanding	1,352,430	1,482,425
Preferred units, outstanding		352,000
Investing Receivables
Investing receivable allowance for credit loss	$ 2,851	$ 0
Investing Receivables | Corporate Office Properties, L.P
Investing receivable allowance for credit loss	$ 2,851

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Lease revenue		$ 536,127	$ 522,472	$ 512,327
Construction contract and other service revenues		70,640	113,763	60,859
Total revenues		609,365	641,226	578,112
Operating expenses
Property operating expenses		203,840	198,143	201,035
Depreciation and amortization associated with real estate operations		138,193	137,069	137,116
Construction contract and other service expenses		67,615	109,962	58,326
Impairment losses		1,530	329	2,367
General, administrative and leasing expenses		33,001	35,402	28,900
Business development expenses and land carry costs		4,473	4,239	5,840
Total operating expenses		448,652	485,144	433,584
Interest expense		(67,937)	(71,052)	(75,385)
Interest and other income		8,574	7,894	4,358
Credit loss recoveries		933	0	0
Gain on sales of real estate		30,209	105,230	2,340
Gain on sale of investment in unconsolidated real estate joint venture		29,416	0	0
Loss on early extinguishment of debt		(7,306)	0	(258)
Loss on interest rate derivatives		(53,196)	0	0
Income before equity in income of unconsolidated entities and income taxes		101,406	198,154	75,583
Equity in income of unconsolidated entities		1,825	1,633	2,697
Income tax (expense) benefit		(353)	217	363
Net income		102,878	200,004	78,643
Net income attributable to noncontrolling interests:
Common units in COPLP		(1,180)	(2,363)	(1,742)
Preferred units in COPLP		(300)	(564)	(660)
Other consolidated entities		(4,024)	(5,385)	(3,940)
Net income attributable to COPT/COPLP		97,374	191,692	72,301
Net income attributable to COPT/COPLP common shareholders/unitholders		$ 97,374	$ 191,692	$ 72,301
Earnings per common share/unit:
Net income attributable to COPT/COPLP common share/unitholders - basic (in dollars per share/unit)	[1]	$ 0.87	$ 1.72	$ 0.69
Net income attributable to COPT/COPLP common share/unitholders - diluted (in dollars per share/unit)	[1]	$ 0.87	$ 1.71	$ 0.69
Revenue from Contract with Customer, Product and Service [Extensible List]		ofc:ConstructionContractAndOtherServiceRevenuesMember	ofc:ConstructionContractAndOtherServiceRevenuesMember	ofc:ConstructionContractAndOtherServiceRevenuesMember
Corporate Office Properties, L.P
Revenues
Lease revenue		$ 536,127	$ 522,472	$ 512,327
Construction contract and other service revenues		70,640	113,763	60,859
Total revenues		609,365	641,226	578,112
Operating expenses
Property operating expenses		203,840	198,143	201,035
Depreciation and amortization associated with real estate operations		138,193	137,069	137,116
Construction contract and other service expenses		67,615	109,962	58,326
Impairment losses		1,530	329	2,367
General, administrative and leasing expenses		33,001	35,402	28,900
Business development expenses and land carry costs		4,473	4,239	5,840
Total operating expenses		448,652	485,144	433,584
Interest expense		(67,937)	(71,052)	(75,385)
Interest and other income		8,574	7,894	4,358
Credit loss recoveries		933	0	0
Gain on sales of real estate		30,209	105,230	2,340
Gain on sale of investment in unconsolidated real estate joint venture		29,416	0	0
Loss on early extinguishment of debt		(7,306)	0	(258)
Loss on interest rate derivatives		(53,196)	0	0
Income before equity in income of unconsolidated entities and income taxes		101,406	198,154	75,583
Equity in income of unconsolidated entities		1,825	1,633	2,697
Income tax (expense) benefit		(353)	217	363
Net income		102,878	200,004	78,643
Net income attributable to noncontrolling interests in consolidated entities		(4,024)	(5,385)	(3,940)
Net income attributable to noncontrolling interests:
Net income attributable to COPT/COPLP		98,854	194,619	74,703
Preferred share/ unit dividends/ distributions		(300)	(564)	(660)
Net income attributable to COPT/COPLP common shareholders/unitholders		$ 98,554	$ 194,055	$ 74,043
Earnings per common share/unit:
Net income attributable to COPT/COPLP common share/unitholders - basic (in dollars per share/unit)	[2]	$ 0.87	$ 1.72	$ 0.69
Net income attributable to COPT/COPLP common share/unitholders - diluted (in dollars per share/unit)	[2]	$ 0.87	$ 1.71	$ 0.69
Other property revenue
Revenues
Total revenues		$ 2,598	$ 4,991	$ 4,926
Other property revenue | Corporate Office Properties, L.P
Revenues
Total revenues		$ 2,598	$ 4,991	$ 4,926
[1]	Basic and diluted earnings per common share are calculated based on amounts attributable to common shareholders of Corporate Office Properties Trust.
[2]	Basic and diluted earnings per common unit are calculated based on amounts attributable to common unitholders of Corporate Office Properties, L.P.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income	$ 102,878	$ 200,004	$ 78,643
Other comprehensive income (loss)
Unrealized loss on interest rate derivatives	(39,454)	(24,321)	(2,373)
Reclassification adjustments on interest rate derivatives recognized in interest expense	3,725	(1,415)	(407)
Reclassification adjustments on interest rate derivatives recognized in loss on interest rate derivatives	51,865	0	0
Equity in other comprehensive income of equity method investee	0	199	210
Total other comprehensive income (loss)	16,136	(25,537)	(2,570)
Comprehensive income	119,014	174,467	76,073
Comprehensive income attributable to noncontrolling interests	(5,353)	(7,981)	(6,453)
Comprehensive income attributable to COPT/COPLP	113,661	166,486	69,620
Corporate Office Properties, L.P
Net income	102,878	200,004	78,643
Other comprehensive income (loss)
Unrealized loss on interest rate derivatives	(39,454)	(24,321)	(2,373)
Reclassification adjustments on interest rate derivatives recognized in interest expense	3,725	(1,415)	(407)
Reclassification adjustments on interest rate derivatives recognized in loss on interest rate derivatives	51,865	0	0
Equity in other comprehensive income of equity method investee	0	199	210
Total other comprehensive income (loss)	16,136	(25,537)	(2,570)
Comprehensive income	119,014	174,467	76,073
Comprehensive income attributable to noncontrolling interests	(3,667)	(5,375)	(3,940)
Comprehensive income attributable to COPT/COPLP	$ 115,347	$ 169,092	$ 72,133

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Forward Equity Sale Agreement	Common Stock At-the-Market Program	Common Shares	Common SharesCumulative Effect, Period of Adoption, Adjusted Balance	Common SharesForward Equity Sale Agreement	Common SharesCommon Stock At-the-Market Program	Additional Paid-in Capital	Additional Paid-in CapitalCumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-in CapitalForward Equity Sale Agreement	Additional Paid-in CapitalCommon Stock At-the-Market Program	Cumulative Distributions in Excess of Net Income	Cumulative Distributions in Excess of Net IncomeCumulative Effect, Period of Adoption, Adjustment	Cumulative Distributions in Excess of Net IncomeCumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjusted Balance	Noncontrolling Interests	Noncontrolling InterestsCumulative Effect, Period of Adoption, Adjusted Balance	Corporate Office Properties, L.P	Corporate Office Properties, L.PCumulative Effect, Period of Adoption, Adjustment	Corporate Office Properties, L.PCumulative Effect, Period of Adoption, Adjusted Balance	Corporate Office Properties, L.PCommon Stock At-the-Market Program	Corporate Office Properties, L.PCommon Shares	Corporate Office Properties, L.PCommon SharesCumulative Effect, Period of Adoption, Adjustment	Corporate Office Properties, L.PCommon SharesCumulative Effect, Period of Adoption, Adjusted Balance	Corporate Office Properties, L.PCommon SharesCommon Stock At-the-Market Program	Corporate Office Properties, L.PAccumulated Other Comprehensive Income (Loss)	Corporate Office Properties, L.PAccumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjustment	Corporate Office Properties, L.PAccumulated Other Comprehensive Income (Loss)Cumulative Effect, Period of Adoption, Adjusted Balance	Corporate Office Properties, L.PNoncontrolling Interests	Corporate Office Properties, L.PNoncontrolling InterestsCumulative Effect, Period of Adoption, Adjusted Balance	Corporate Office Properties, L.PLimited Partner	Corporate Office Properties, L.PLimited PartnerPreferred Shares	Corporate Office Properties, L.PLimited PartnerPreferred SharesCumulative Effect, Period of Adoption, Adjusted Balance
Balance at Dec. 31, 2017	$ 1,468,307	$ 0	$ 1,468,307			$ 1,013	$ 1,013			$ 2,201,047	$ 2,201,047			$ (802,085)	$ (276)	$ (802,361)	$ 2,167	$ 276	$ 2,443	$ 66,165	$ 66,165	$ 1,468,307	$ 0	$ 1,468,307		$ 1,445,022	$ (276)	$ 1,444,746		$ 2,173	$ 276	$ 2,449	$ 12,312	$ 12,312		$ 8,800	$ 8,800
Balance (in units/ shares) at Dec. 31, 2017	101,292,299																									104,543,177		104,543,177
Balance (preferred units) at Dec. 31, 2017																																				352,000	352,000
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares	$ 0					19				27,394										(27,413)
Redemption of common units (in units)																										(13,377)
Redemption of common units	$ (339)																			(339)		(339)				$ (339)
Common shares issued during the period (in units/shares)				5,907,000	991,664																					5,907,000			991,664
Common shares issued during the period				$ 172,294	$ 29,732			$ 59	$ 10			$ 172,235	$ 29,722									172,294			$ 29,732	$ 172,294			$ 29,732
Share-based compensation issuance, net of redemptions (in shares/units)	146,290																									146,290
Share-based compensation issuance, net of redemptions	$ 6,963					1				6,962												6,963				$ 6,963
Redemption of vested equity awards	(1,702)									(1,702)												(1,702)				(1,702)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0									(2,466)										2,466
Comprehensive income	73,550													72,301			(2,681)			3,930		73,550				74,043				(2,570)			1,417			$ 660
Dividends/Distributions	(116,748)													(116,748)								(119,905)				(119,245)										$ (660)
Distributions to owners of common and preferred units in COPLP	(3,157)																			(3,157)
Distributions to noncontrolling interests in other consolidated entities	(15)																			(15)		(15)											(15)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ (1,837)									(1,837)												(1,837)				$ (1,837)
Balance (preferred units) at Dec. 31, 2018																																				352,000
Balance (in units/ shares) at Dec. 31, 2018	110,241,868																									111,574,754
Balance at Dec. 31, 2018	$ 1,627,048					1,102				2,431,355				(846,808)			(238)			41,637		1,627,048				$ 1,604,655				(121)			13,714			$ 8,800
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares	0					1				1,585										(1,586)
Redemption of common units (in units)																										(924)
Redemption of common units	$ (25)																			(25)		(25)				$ (25)
Common shares issued during the period (in units/shares)	1,000			1,614,087																						1,000			1,614,087
Common shares issued during the period	$ 29			$ 46,454				$ 16		29		$ 46,438										29			$ 46,454	$ 29			$ 46,454
Share-based compensation issuance, net of redemptions (in shares/units)	106,711																									362,213
Share-based compensation issuance, net of redemptions	$ 7,456					2				6,131										1,323		7,456				$ 7,456
Redemption of vested equity awards	(2,064)									(2,064)												(2,064)				(2,064)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0									(167)										167
Comprehensive income	170,632													191,692			(25,206)			4,146		170,632				194,055				(25,527)			1,540			564
Dividends/Distributions	(123,159)													(123,159)								(125,216)				(124,652)										$ (564)
Distributions to owners of common and preferred units in COPLP	(2,057)																			(2,057)
Contributions from noncontrolling interests in other consolidated entities/subsidiaries	2,570																			2,570		2,570											2,570
Distributions to noncontrolling interests in other consolidated entities	(5,890)																			(5,890)		(5,890)											(5,890)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ (1,749)									(1,749)												(1,749)				$ (1,749)
Balance (preferred units) at Dec. 31, 2019																																			352,000	352,000	352,000
Balance (in units/ shares) at Dec. 31, 2019	112,068,705																									113,551,130		113,551,130							1,482,425
Balance at Dec. 31, 2019	$ 1,719,245	$ (5,541)	$ 1,713,704			1,121	$ 1,121			2,481,558	$ 2,481,558			(778,275)	$ (5,541)	$ (783,816)	(25,444)		$ (25,444)	40,285	$ 40,285	$ 1,719,245	$ (5,541)	$ 1,713,704		$ 1,724,159	$ (5,541)	$ 1,718,618		(25,648)		$ (25,648)	11,934	$ 11,934		$ 8,800	$ 8,800
Increase (Decrease) in Shareholders' Equity
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member																					us-gaap:AccountingStandardsUpdate201613Member
Conversion of common units to common shares	$ 0									211										(211)
Redemption of preferred units (in units)																																				(352,000)
Redemption of preferred units	$ (8,800)																			(8,800)		$ (8,800)														$ (8,800)
Share-based compensation issuance, net of redemptions (in shares/units)	99,045																									280,315
Share-based compensation issuance, net of redemptions	$ 6,584					1				4,676										1,907		6,584				$ 6,584
Redemption of vested equity awards	(1,699)									(1,699)												(1,699)				(1,699)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0									767										(767)
Comprehensive income	115,588													97,374			16,287			1,927		115,588				98,554				16,493			241			300
Dividends/Distributions	(123,394)													(123,394)								(125,140)				(124,840)										$ (300)
Distributions to owners of common and preferred units in COPLP	(1,746)																			(1,746)
Contributions from noncontrolling interests in other consolidated entities/subsidiaries	112																			112		112											112
Distributions to noncontrolling interests in other consolidated entities	(30)																			(30)		(30)											(30)
Adjustment to arrive at fair value of redeemable noncontrolling interests	$ (6,607)									(6,607)												(6,607)				$ (6,607)
Balance (preferred units) at Dec. 31, 2020																																				0
Balance (in units/ shares) at Dec. 31, 2020	112,181,759																									113,831,445									1,352,430
Balance at Dec. 31, 2020	$ 1,693,712					$ 1,122				$ 2,478,906				$ (809,836)			$ (9,157)			$ 32,677		$ 1,693,712				$ 1,690,610				$ (9,155)			$ 12,257			$ 0

Consolidated Statements of Eq_2

Consolidated Statements of Equity (Parenthetical) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares outstanding (in units/ shares)	112,181,759	112,068,705	110,241,868	101,292,299
Conversion of common units to common shares (in shares/units)	14,009	105,039	1,904,615
Common shares issued during the period (in units/shares)		1,000
Share-based compensation issuance, net of redemptions (in shares/units)	99,045	106,711	146,290
Forward Equity Sale Agreement
Common shares issued during the period (in units/shares)		1,614,087	5,907,000
Common Stock At-the-Market Program
Common shares issued during the period (in units/shares)			991,664

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Revenues from real estate operations received	$ 542,727	$ 530,280	$ 528,066
Construction contract and other service revenues received	78,470	94,677	33,579
Property operating expenses paid	(202,660)	(196,611)	(197,647)
Construction contract and other service expenses paid	(67,760)	(96,789)	(79,386)
General, administrative, leasing, business development and land carry costs paid	(31,406)	(29,347)	(27,006)
Interest expense paid	(61,471)	(67,475)	(72,460)
Lease incentives paid	(11,925)	(9,482)	(7,679)
Sales-type lease costs paid	(10,747)	0	0
Income taxes paid	(4)	0	(21)
Other	3,200	3,305	3,036
Net cash provided by operating activities	238,424	228,558	180,482
Cash flows from investing activities
Development and redevelopment of properties	(344,401)	(394,444)	(159,994)
Tenant improvements on operating properties	(28,754)	(23,809)	(35,098)
Other capital improvements on operating properties	(32,756)	(24,659)	(24,223)
Proceeds from property dispositions
Distribution from unconsolidated real estate joint venture following contribution of properties	0	201,499	0
Sale of properties	83,165	108,128	0
Proceeds from sale of investment in unconsolidated real estate joint venture	59,841	0	0
Non-operating distributions from unconsolidated real estate joint venture	3,695	22,426	1,942
Investing receivables funded	(272)	(11,180)	(97)
Investing receivables payments received	8,000	0	4,455
Leasing costs paid	(16,938)	(16,825)	(10,926)
Settlement of interest rate derivatives	(53,130)	0	0
Other	(4,242)	849	(8,977)
Net cash used in investing activities	(325,792)	(138,015)	(232,918)
Proceeds from debt
Revolving Credit Facility	664,000	409,000	381,000
Unsecured senior notes	395,264	0	0
Other debt proceeds	206,931	43,615	13,406
Repayments of debt
Revolving Credit Facility	(698,000)	(445,000)	(294,000)
Unsecured senior notes	(300,000)	0	0
Scheduled principal amortization	(4,125)	(4,310)	(4,240)
Other debt repayments	(12,031)	(77)	(100,000)
Deferred financing costs paid	(2,400)	(448)	(8,292)
Payments on finance lease liabilities	(854)	(223)	(15,379)
Net proceeds from issuance of common shares	0	46,415	202,065
Common share/unit dividends/distributions paid	(123,367)	(122,657)	(114,286)
Distributions paid to noncontrolling interests in COPLP	(1,825)	(2,166)	(3,699)
Distributions paid to noncontrolling interests in other consolidated entities	(30)	(5,890)	(16)
Distributions paid to redeemable noncontrolling interests	(14,357)	(1,659)	(1,382)
Redemption of preferred units	(8,800)	0	0
Payments in connection with early extinguishment of debt	(7,029)	0	0
Other	(2,106)	(963)	(5,622)
Net cash provided by (used in) financing activities	91,271	(84,363)	49,555
Net increase (decrease) in cash and cash equivalents and restricted cash	3,903	6,180	(2,881)
Cash and cash equivalents and restricted cash
Beginning of year	18,130	11,950	14,831
End of year	22,033	18,130	11,950
Reconciliation of net income to net cash provided by operating activities:
Net income	102,878	200,004	78,643
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	140,031	138,903	139,063
Impairment losses	1,530	329	2,367
Amortization of deferred financing costs and net debt discounts	4,272	3,639	3,393
Increase in deferred rent receivable	(2,168)	(4,091)	(4,621)
Gain on sales of real estate	(30,209)	(105,230)	(2,340)
Gain on sale of investment in unconsolidated real estate joint venture	(29,416)	0	0
Share-based compensation	6,503	6,714	6,376
Loss on early extinguishment of debt	7,306	0	258
Loss on interest rate derivatives	53,196	0	0
Other	(7,855)	(6,022)	(2,991)
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(6,377)	(7,141)	5,673
Increase in prepaid expenses and other assets, net	(7,626)	(22,457)	(987)
Increase (decrease) in accounts payable, accrued expenses and other liabilities	6,554	20,369	(49,179)
(Decrease) increase in rents received in advance and security deposits	(195)	3,541	4,827
Net cash provided by operating activities	238,424	228,558	180,482
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents and restricted cash	18,130	11,950	14,831
Supplemental schedule of non-cash investing and financing activities:
(Decrease) increase in accrued capital improvements, leasing and other investing activity costs	(9,421)	35,913	6,570
Finance right-of-use asset contributed by noncontrolling interest in joint venture	0	2,570	0
Recognition of operating right-of-use assets and related lease liabilities	13,340	840	0
Non-cash changes from property dispositions:
Contribution of properties to unconsolidated real estate joint venture	0	158,542	0
Investment in unconsolidated real estate joint ventures retained in disposition	11,474	34,506	0
Non-cash changes from recognition of property sale previously accounted for as financing arrangement:
Decrease in assets held for sale, net	0	0	(42,226)
Decrease in deferred property sale	0	0	43,377
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income and noncontrolling interests	(35,728)	(25,817)	2,915
Equity in other comprehensive income of an equity method investee	0	199	210
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	211	1,586	27,413
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	(767)	167	2,466
Increase in redeemable noncontrolling interests and decrease in equity to carry redeemable noncontrolling interests at fair value	6,607	1,749	1,837
Corporate Office Properties, L.P
Cash flows from operating activities
Revenues from real estate operations received	542,727	530,280	528,066
Construction contract and other service revenues received	78,470	94,677	33,579
Property operating expenses paid	(202,660)	(196,611)	(197,647)
Construction contract and other service expenses paid	(67,760)	(96,789)	(79,386)
General, administrative, leasing, business development and land carry costs paid	(31,406)	(29,347)	(27,006)
Interest expense paid	(61,471)	(67,475)	(72,460)
Lease incentives paid	(11,925)	(9,482)	(7,679)
Sales-type lease costs paid	(10,747)	0	0
Income taxes paid	4	0	21
Other	3,200	3,305	3,036
Net cash provided by operating activities	238,424	228,558	180,482
Cash flows from investing activities
Development and redevelopment of properties	(344,401)	(394,444)	(159,994)
Tenant improvements on operating properties	(28,754)	(23,809)	(35,098)
Other capital improvements on operating properties	(32,756)	(24,659)	(24,223)
Proceeds from property dispositions
Distribution from unconsolidated real estate joint venture following contribution of properties	0	201,499	0
Sale of properties	83,165	108,128	0
Proceeds from sale of investment in unconsolidated real estate joint venture	59,841	0	0
Non-operating distributions from unconsolidated real estate joint venture	3,695	22,426	1,942
Investing receivables funded	(272)	(11,180)	(97)
Investing receivables payments received	8,000	0	4,455
Leasing costs paid	(16,938)	(16,825)	(10,926)
Settlement of interest rate derivatives	(53,130)	0	0
Other	(4,242)	849	(8,977)
Net cash used in investing activities	(325,792)	(138,015)	(232,918)
Proceeds from debt
Revolving Credit Facility	664,000	409,000	381,000
Unsecured senior notes	395,264	0	0
Other debt proceeds	206,931	43,615	13,406
Repayments of debt
Revolving Credit Facility	(698,000)	(445,000)	(294,000)
Unsecured senior notes	(300,000)	0	0
Scheduled principal amortization	(4,125)	(4,310)	(4,240)
Other debt repayments	(12,031)	(77)	(100,000)
Deferred financing costs paid	(2,400)	(448)	(8,292)
Payments on finance lease liabilities	(854)	(223)	(15,379)
Net proceeds from issuance of common shares	0	46,415	202,065
Common share/unit dividends/distributions paid	(124,815)	(124,171)	(117,325)
Distributions paid to noncontrolling interests in other consolidated entities	(30)	(5,890)	(16)
Distributions paid to redeemable noncontrolling interests	(14,357)	(1,659)	(1,382)
Redemption of preferred units	(8,800)	0	0
Payments in connection with early extinguishment of debt	(7,029)	0	0
Other	(2,483)	(1,615)	(6,282)
Net cash provided by (used in) financing activities	91,271	(84,363)	49,555
Net increase (decrease) in cash and cash equivalents and restricted cash	3,903	6,180	(2,881)
Cash and cash equivalents and restricted cash
Beginning of year	18,130	11,950	14,831
End of year	22,033	18,130	11,950
Reconciliation of net income to net cash provided by operating activities:
Net income	102,878	200,004	78,643
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	140,031	138,903	139,063
Impairment losses	1,530	329	2,367
Amortization of deferred financing costs and net debt discounts	4,272	3,639	3,393
Increase in deferred rent receivable	(2,168)	(4,091)	(4,621)
Gain on sales of real estate	(30,209)	(105,230)	(2,340)
Gain on sale of investment in unconsolidated real estate joint venture	(29,416)	0	0
Share-based compensation	6,503	6,714	6,376
Loss on early extinguishment of debt	7,306	0	258
Loss on interest rate derivatives	53,196	0	0
Other	(7,855)	(6,022)	(2,991)
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(6,377)	(7,141)	5,673
Increase in prepaid expenses and other assets, net	(7,659)	(23,255)	(1,735)
Increase (decrease) in accounts payable, accrued expenses and other liabilities	6,587	21,167	(48,431)
(Decrease) increase in rents received in advance and security deposits	(195)	3,541	4,827
Net cash provided by operating activities	238,424	228,558	180,482
Reconciliation of cash and cash equivalents and restricted cash:
Cash and cash equivalents and restricted cash	18,130	11,950	11,950
Supplemental schedule of non-cash investing and financing activities:
(Decrease) increase in accrued capital improvements, leasing and other investing activity costs	(9,421)	35,913	6,570
Finance right-of-use asset contributed by noncontrolling interest in joint venture	0	2,570	0
Recognition of operating right-of-use assets and related lease liabilities	13,340	840	0
Non-cash changes from property dispositions:
Contribution of properties to unconsolidated real estate joint venture	0	(158,542)	0
Investment in unconsolidated real estate joint ventures retained in disposition	11,474	34,506	0
Non-cash changes from recognition of property sale previously accounted for as financing arrangement:
Decrease in assets held for sale, net	0	0	(42,226)
Decrease in deferred property sale	0	0	43,377
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income and noncontrolling interests	(35,728)	(25,817)	2,915
Equity in other comprehensive income of an equity method investee	0	199	210
Increase in redeemable noncontrolling interests and decrease in equity to carry redeemable noncontrolling interests at fair value	$ 6,607	$ 1,749	$ 1,837

Organization

Organization	12 Months Ended
	Dec. 31, 2020
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 (“USG”) 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 December 31, 2020, our properties included the following (all references to number of properties, square footage, acres and megawatts are unaudited): • 181 properties totaling 21.0 million square feet comprised of 16.2 million square feet in 155 office properties and 4.7 million square feet in 26 single-tenant data center shell properties (“data center shells”). We owned 17 of these data center shells through unconsolidated real estate joint ventures; • a wholesale data center with a critical load of 19.25 megawatts; • 11 properties under development (nine office properties and two data center shells), including three partially-operational properties, that we estimate will total approximately 1.5 million square feet upon completion; and • approximately 830 acres of land controlled for future development that we believe could be developed into approximately 10.4 million square feet and 43 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, development and construction 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 December 31, 2020, COPT owned 98.6% of the outstanding COPLP common units (“common units”) and there were no preferred units outstanding. 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 common units to quarterly distributions and payments in liquidation is substantially the same as that of COPT common shareholders. 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	12 Months Ended
	Dec. 31, 2020
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. When we own an equity investment in an entity and cannot exert significant influence over its operations, we measure the investment at fair value, with changes recognized through net income. For an investment without a readily determinable fair value, we measure the investment at cost, less any impairments, plus or minus changes resulting from observable price changes for an identical or similar investment of the same issuer. Use of Estimates in the Preparation of Financial Statements We make estimates and assumptions when preparing financial statements under generally accepted accounting principles (“GAAP”). These estimates and assumptions affect various matters, including: • the reported amounts of assets and liabilities in our consolidated balance sheets as of the dates of the financial statements; • the disclosure of contingent assets and liabilities as of the dates of the financial statements; and • the reported amounts of revenues and expenses in our consolidated statements of operations during the reporting periods. Significant estimates are inherent in the presentation of our financial statements in a number of areas, including the evaluation of the collectability of accounts and deferred rent receivable, the determination of estimated useful lives of assets, the determination of lease terms, the evaluation of impairment of long-lived assets, the amount of impairment losses recognized, the allocation of property acquisition costs, the amount of revenue recognized relating to tenant improvements, the level of expense recognized in connection with share-based compensation and the determination of accounting method for investments. Actual results could differ from these and other estimates. Properties We report properties to be developed or held and used in operations at our depreciated cost, reduced for impairment losses. We capitalize direct and indirect project costs (including related compensation and other indirect costs), interest expense and real estate taxes associated with properties, or portions thereof, undergoing development or redevelopment activities. In capitalizing interest expense, if there is a specific borrowing for a property undergoing development or redevelopment activities, we apply the interest rate of that borrowing to the average accumulated expenditures that do not exceed such borrowing; for the portion of expenditures exceeding any such specific borrowing, we apply our weighted average interest rate on other borrowings to the expenditures. We continue to capitalize costs while development or redevelopment activities are underway until a property becomes “operational,” which occurs when lease terms commence (generally when the tenant has control of the leased space and we have delivered the premises to the tenant as required under the terms of such lease), but no later than one year after the cessation of major construction activities. When leases commence on portions of a newly-developed or redeveloped property in the period prior to one year from the cessation of major construction activities, we consider that property to be “partially operational.” When a property is partially operational, we allocate the costs associated with the property between the portion that is operational and the portion under development. We start depreciating costs associated with newly-developed or redeveloped properties as they become operational. Most of our leases provide for some form of improvements to leased space. When we are required to provide improvements under the terms of a lease, we determine whether the improvements constitute landlord assets or tenant assets. If the improvements are landlord assets, we capitalize the cost of the improvements and recognize depreciation expense over the shorter of the useful life of the assets or the term of the lease and recognize any payments from the tenant as rental revenue over the term of the lease. If the improvements are tenant assets, we defer the cost of improvements funded by us as a lease incentive asset and amortize it as a reduction of rental revenue over the term of the lease. In determining whether improvements constitute landlord or tenant assets, we consider numerous factors, including whether the economic substance of the lease terms is properly reflected and whether the improvements: have value to us as real estate; are unique to the tenant or reusable by other tenants; may be altered or removed by the tenant without our consent or without compensating us for any lost fair value; or are owned, and remain, with us or the tenant at the end of the lease term. We depreciate our fixed assets using the straight-line method over their estimated useful lives as follows: Estimated Useful Lives Buildings and building improvements 10-40 years Land improvements 10-20 years Tenant improvements on operating properties Shorter of remaining useful lives of assets or related lease term Equipment and personal property 3-10 years For periods in which a property is classified as held for sale, we classify the assets of the property’s asset group as held for sale on our consolidated balance sheet for such periods. When we dispose of, or classify as held for sale, a component (such as a reportable segment or sub-segment) or group of components that represents a strategic shift having a major effect on our operations and financial results (such as a major geographical area of operations or major line of business), we classify the associated results of operations as discontinued operations. We had no properties newly classified as discontinued operations in the last three years. Sales of Properties We recognize gains from sales of consolidated interests in properties to non-customer third parties when we have transferred control of such interests. Impairment of Properties We assess the asset groups associated with each of our properties, including operating properties, properties in development, land held for future development, related intangible assets, right-of-use assets, deferred rents receivable and lease liabilities for indicators of impairment quarterly or when circumstances indicate that an asset group may be impaired. If our analyses indicate that the carrying values of certain properties’ asset groups may be impaired, we perform a recovery analysis for such asset groups. For properties to be held and used, we analyze recoverability based on the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the properties over, in most cases, a ten-year holding period. If we believe it is more likely than not that we will dispose of the properties earlier, we analyze recoverability using a probability weighted analysis of the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the properties over the various possible holding periods. If the analysis indicates that the carrying value of a tested property’s asset group is not recoverable from its estimated future cash flows, the property’s asset group is written down to the property’s estimated fair value and an impairment loss is recognized. If and when our plans change, we revise our recoverability analyses to use the cash flows expected from the operations and eventual disposition of such property using holding periods that are consistent with our revised plans. Changes in holding periods may require us to recognize impairment losses. Fair values are estimated based on contract prices, indicative bids, discounted cash flow analyses, yield analyses or comparable sales analyses. Estimated cash flows used in our impairment analyses are based on our plans for the property and our views of market and economic conditions. The estimates consider items such as current and future market rental and occupancy rates, estimated operating and capital expenditures and recent sales data for comparable properties; most of these items are influenced by market data obtained from real estate leasing and brokerage firms and our direct experience with the properties and their markets. When we determine that a property is held for sale, we stop depreciating the property and estimate the property’s fair value, net of selling costs; if we then determine that the estimated fair value, net of selling costs, is less than the net book value of the property’s asset group, we recognize an impairment loss equal to the difference and reduce the net book value of the property’s asset group. Acquisition of Operating Properties Upon completion of operating property acquisitions, we allocate the purchase price to tangible and intangible assets and liabilities associated with such acquisitions based on our estimates of their fair values. We determine these fair values by using market data and independent appraisals available to us and making numerous estimates and assumptions. We allocate operating property acquisitions to the following components: • properties based on a valuation performed under the assumption that the property is vacant upon acquisition (the “if-vacant value”). The if-vacant value is allocated between land and buildings or, in the case of properties under development, development in progress. We also allocate additional amounts to properties for in-place tenant improvements based on our estimate of improvements per square foot provided under market leases that would be attributable to the remaining non-cancelable terms of the respective leases; • above- and below-market lease intangible assets or liabilities based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between: (1) the contractual amounts to be received pursuant to the in-place leases; and (2) our estimate of fair market lease rates for the corresponding space, measured over a period equal to the remaining non-cancelable term of the lease. The capitalized above- and below-market lease values are amortized as adjustments to lease revenue over the remaining lease terms of the respective leases, and to renewal periods in the case of below-market leases; • in-place lease value based on our estimates of: (1) the present value of additional income to be realized as a result of leases being in place on the acquired properties; and (2) costs to execute similar leases. Our estimate of costs to execute similar leases includes leasing commissions, legal and other related costs; • tenant relationship value based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with that respective tenant. Characteristics we consider in determining these values include the nature and extent of our existing business relationships with the tenant, growth prospects for developing new business with the tenant, the tenant’s credit quality and expectations of lease renewals, among other factors; and • above- and below-market cost arrangements (such as real estate tax treaties or above- or below-market ground leases) based on the present value of the expected benefit from any such arrangements in place on the property at the time of acquisition. Leased Assets, as a Lessee Effective January 1, 2019, we adopted guidance requiring lessees to classify 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. The guidance also requires us to recognize upon lease term commencement a right-of-use asset and lease liability for all leases with a term of greater than 12 months regardless of their classification. We adopted this guidance for leases on January 1, 2019 using a modified retrospective transition approach under which we elected to not adjust prior comparative reporting periods. We elected to apply a package of practical expedients that enabled us to carry forward upon adoption our historical assessments of: expired or existing leases regarding their lease classification; and whether any expired or existing contracts are, or contain, leases. We also elected a practical expedient that enabled us to avoid the need to assess whether expired or existing land easements not previously accounted for as leases are, or contain, a lease. In determining right-of-use assets and lease liabilities, we estimate an appropriate incremental borrowing rate on a fully-collateralized basis for the terms of the leases. Since the terms under our ground leases are usually significantly longer than the terms of borrowings available to us on a fully-collateralized basis, our estimate of this rate requires significant judgment, and considers factors such as interest rates available to us on a fully-collateralized basis for shorter-termed debt and U.S. Treasury rates. Cash and Cash Equivalents Cash and cash equivalents include all cash and liquid investments that mature three months or less from when they are purchased. Cash equivalents are reported at cost, which approximates fair value. We maintain our cash in bank accounts in amounts that may exceed Federally insured limits at times. We have not experienced any losses in these accounts in the past and believe that we are not exposed to significant credit risk because our accounts are deposited with major financial institutions. Investments in Marketable Securities We classify marketable securities as trading securities when we have the intent to sell such securities in the near term, and classify other marketable securities as available-for-sale securities. We determine the appropriate classification of investments in marketable securities at the acquisition date and re-evaluate the classification at each balance sheet date. We report investments in marketable securities classified as trading securities at fair value (which is included in the line entitled “Prepaid expenses and other assets, net” on our consolidated balance sheets), with unrealized gains and losses recognized through earnings; on our consolidated statements of cash flows, we classify cash flows from these securities as operating activities. Receivables and Credit Losses We evaluate our receivables from customers and borrowers for collectability and recognize estimated credit losses on these receivables. We use judgment in estimating these losses based upon the credit status of the entities associated with the individual receivables and payment history. Effective January 1, 2020, we adopted guidance issued by the Financial Accounting Standards Board (“FASB”) that changed how we measure credit losses for most financial assets and certain other instruments not measured at fair value through net income from an incurred loss model to an expected loss approach. Our items within the scope of this guidance included the following: • investing receivables, as disclosed in Note 8; • tenant notes receivable; • net investment in sales-type leases; • other assets comprised of non-lease revenue related accounts receivable (primarily from construction contract services) and contract assets from unbilled construction contract revenue; and • off-balance sheet credit exposures. Under this guidance, we recognize an estimate of our expected credit losses on these items as an allowance, as the guidance requires that financial assets be measured on an amortized cost basis and be presented at the net amount expected to be collected (or as a separate liability in the case of off-balance sheet credit exposures). The allowance represents the portion of the amortized cost basis that we do not expect to collect (or loss we expect to incur in the case of off-balance sheet credit exposures) due to credit over the contractual life based on available information relevant to assessing the collectability of cash flows, which includes consideration of past events, current conditions and reasonable and supportable forecasts of future economic conditions (including consideration of asset- or borrower-specific factors). The guidance requires the allowance for expected credit losses to reflect the risk of loss, even when that risk is remote. An allowance for credit losses is measured and recorded upon the initial recognition of a financial asset (or off-balance sheet credit exposure), regardless of whether it is originated or purchased. Quarterly, the expected losses are re-estimated, considering any cash receipts and changes in risks or assumptions, with resulting adjustments recognized as credit loss expense or recoveries on our consolidated statements of operations. We estimate expected credit losses for in-scope items using historical loss rate information developed for varying classifications of credit risk and contractual lives. Due to our limited quantity of items within the scope of this guidance and the unique risk characteristics of such items, we individually assign each in-scope item a credit risk classification. The credit risk classifications assigned by us are determined based on credit ratings assigned by ratings agencies (as available) or are internally-developed based on available financial information, historical payment experience, credit documentation, other publicly available information and current economic trends. In addition, for certain items in which the risk of credit loss is affected by the economic performance of a real estate development project, we develop probability weighted scenario analyses for varying levels of performance in estimating our credit loss allowance (applicable to our notes receivable from the City of Huntsville disclosed in Note 8 and a tax incremental financing obligation disclosed in Note 20). For lease revenue, if collectability is not probable, revenue recognized is limited to the lesser of revenue that would have been recognized if collectability was probable or lease payments collected. Losses on lease revenue receivables are presented on our consolidated statements of operation with property operating expenses for years prior to January 1, 2019, when we adopted new lease accounting guidance, and as reductions in lease revenue thereafter. Prior to our adoption of the credit loss guidance discussed above, we evaluated the collectability of both interest and principal of loans whenever events or changes in circumstances indicated such amounts may not be recoverable. A loan was impaired when it was probable that we would be unable to collect all amounts due according to the existing contractual terms. When a loan was impaired, the amount of the loss accrual was calculated by comparing the carrying amount of the investment to the present value of expected future cash flows discounted at the loan’s effective interest rate and the value of any collateral under such loan. When we believe that collection of interest income on an investing or tenant note receivable is not probable, we place the receivable on nonaccrual status, meaning interest income is recognized when payments are received rather than on an accrual basis. We write off receivables when we believe the facts and circumstances indicate that continued pursuit of collection is no longer warranted. When cash is received in connection with receivables for which we have previously recognized credit losses, we recognize reductions in our credit losses. Intangible Assets and Deferred Revenue on Real Estate Acquisitions We amortize the intangible assets and deferred revenue on real estate acquisitions discussed above as follows: Asset Type Amortization Period Above- and below-market leases Related lease terms In-place lease value Related lease terms Tenant relationship value Estimated period of time that tenant will lease space in property Above- and below-market cost arrangements Term of arrangements We recognize the amortization of acquired above- and below-market leases as adjustments to rental revenue. We recognize the amortization of above- and below-market cost arrangements as adjustments to property operating expenses. We recognize the amortization of other intangible assets on property acquisitions as amortization expense. Deferred Leasing Costs We defer costs incurred to obtain new tenant leases or extend existing tenant leases; our deferral of costs included related non-incremental compensation costs until January 1, 2019, when we adopted new lease accounting guidance. We amortize these costs evenly over the lease terms. We classify leasing costs paid as an investing activity on our statements of cash flows since such costs are necessary in order for us to generate long-term future cash flows from our properties. When tenant leases are terminated early, we expense any unamortized deferred leasing costs associated with those leases over the shortened term of the lease. Deferred Financing Costs We defer costs of financing arrangements and recognize these costs as interest expense over the related debt terms on a straight-line basis, which approximates the amortization that would occur under the effective interest method of amortization. We expense any unamortized loan costs when loans are retired early. We present deferred costs of financing arrangements as a direct deduction from the related debt liability, except for costs attributable to line-of-credit arrangements and interest rate derivatives, which we present in the balance sheet in the line entitled “prepaid expenses and other assets, net”. Interest Rate Derivatives Our primary objectives in using interest rate derivatives are to add stability to interest expense and to manage exposure to interest rate movements. To accomplish this objective, we use interest rate swaps as part of our interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable-rate amounts from a counterparty in exchange for our making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. We use interest rate swaps to hedge the cash flows associated with interest rates on variable-rate debt borrowings. We also use forward-starting interest rate swaps to hedge the cash flows associated with interest rates on forecasted fixed-rate borrowings. We recognize all derivatives as assets or liabilities on our consolidated balance sheet at fair value. We defer all changes in the fair value of designated cash flow hedges to accumulated other comprehensive income (“AOCI”) or loss (“AOCL”), reclassifying such deferrals to interest expense as interest expense is recognized on the hedged forecasted transactions. When an interest rate swap designated as a cash flow hedge no longer qualifies for hedge accounting and the hedged transactions are probable not to occur, we recognize changes in fair value of the hedge previously deferred to AOCI or AOCL, along with any changes in fair value occurring thereafter, through earnings. We do not use interest rate derivatives for trading or speculative purposes. We manage counter-party risk by only entering into contracts with major financial institutions based upon their credit ratings and other risk factors. We use standard market conventions and techniques such as discounted cash flow analysis, option pricing models, replacement cost and termination cost in computing the fair value of derivatives at each balance sheet date. We made an accounting policy election to use an exception provided for in the applicable accounting guidance with respect to measuring counterparty credit risk for derivative instruments; this election enables us to measure the fair value of groups of assets and liabilities associated with derivative instruments consistently with how market participants would price the net risk exposure as of the measurement date. Noncontrolling Interests COPT’s consolidated noncontrolling interests are comprised of interests in COPLP not owned by COPT (discussed further in Note 14) and interests in consolidated real estate joint ventures not owned by us (discussed further in Note 6). COPLP’s consolidated noncontrolling interests are comprised primarily of interests in our consolidated real estate joint ventures. We evaluate whether noncontrolling interests are subject to redemption features outside of our control. We classify noncontrolling interests that are currently redeemable for cash at the option of the holders or are probable of becoming redeemable as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheets; we adjust these interests each period to the greater of their fair value or carrying amount (initial amount as adjusted for allocations of income and losses and contributions and distributions), with a corresponding offset to additional paid-in capital on COPT’s consolidated balance sheets or common units on COPLP’s balance sheet. Our other noncontrolling interests are reported in the equity section of our consolidated balance sheets. Revenue Recognition Lease and Other Property Revenue We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. These leases usually include options under which the tenant may renew its lease based on market rates at the time of renewal, which are then typically subject to further negotiation. These leases occasionally provide the tenant with an option to terminate its lease early usually for a defined termination fee. Most of our lease revenue is from fixed contractual payments defined under the lease that, in most cases, escalate annually over the term of the lease. Our lease revenue also includes variable lease payments predominantly for tenant reimbursements of property operating expenses and lease termination fees. Property operating expense reimbursement structures vary, with some tenants responsible for all of a property’s expenses, while others are responsible for their share of a property’s expense only to the extent such expenses exceed amounts defined in the lease (which are derived from the property’s historical expense levels). Lease termination fees in most cases result from a tenant’s exercise of an existing right under a lease. Upon lease commencement, we evaluate leases to determine if they meet criteria set forth in lease accounting guidance for classification as sales-type leases or direct financing leases; when a lease meets none of these criteria, we classify the lease as an operating lease. Upon commencement of sales-type leases, we derecognize the underlying asset, recognizing in its place a net investment in the lease equal to the sum of the lease receivable and the present value of any unguaranteed residual asset and recognize any selling profit or loss created as a result of the difference between those two amounts. Similarly, for direct financing leases, the lessor derecognizes the underlying asset and recognizes a net investment in the lease, but, unlike in a sales-type lease, defers profit and amortizes it as interest income over the lease term. Our leases of properties as lessor are predominantly classified as operating leases, for which the underlying asset remains on our balance sheet and is depreciated consistently with other owned assets, with income recognized as described further below. We recognize minimum rents on operating leases, net of abatements, on a straight-line basis over the term of tenant leases. A lease term commences when: (1) the tenant has control of the leased space (legal right to use the property); and (2) we have delivered the premises to the tenant as required under the terms of such lease. The term of a lease includes the noncancellable periods of the lease along with periods covered by: (1) a tenant option to extend the lease if the tenant is reasonably certain to exercise that option; (2) a tenant option to terminate the lease if the tenant is reasonably certain not to exercise that option; and (3) an option to extend (or not to terminate) the lease in which exercise of the option is controlled by us as the lessor. When assessing the expected lease end date, we use judgment in contemplating the significance of: any penalties a tenant may incur should it choose not to exercise any existing options to extend the lease or exercise any existing options to terminate the lease; and economic incentives for the tenant based on any existing contract, asset, entity or market-based factors in the lease. While a significant portion of our portfolio is leased to the USG, and the majority of those leases consist of a series of one-year renewal options, or provide for early termination rights, we have concluded that exercise of existing renewal options, or continuation of such leases without exercising early termination rights, is reasonably certain for most of these leases. We report the amount by which our minimum rental revenue recognized on a straight-line basis under leases exceeds the contractual rent billings associated with such leases as deferred rent receivable on our consolidated balance sheets. Amounts by which our minimum rental revenue recognized on a straight-line basis under leases are less than the contractual rent billings associated with such leases are reported in liabilities as deferred revenue associated with operating leases on our consolidated balance sheets. In connection with a tenant’s entry into, or modification of, a lease, if we make cash payments to, or on behalf of, the tenant for purposes other than funding the construction of landlord assets, we defer the amount of such payments as lease incentives. As discussed above, when we are required to provide improvements under the terms of a lease, we determine whether the improvements constitute landlord assets or tenant assets; if the improvements are tenant assets, we defer the cost of improvements funded by us as a lease incentive asset. We amortize lease incentives as a reduction of rental revenue over the term of the lease. If collectability under a lease is not probable, revenue recognized is limited to the lesser of revenue that would have been recognized if collectability was probable or lease payments collected. We recognize lease revenue associated with tenant expense recoveries in the same periods in which we incur the related expenses, including tenant reimbursements of property taxes, utilities and other property operating expenses. We recognize fees received for lease terminations as revenue and write off against such revenue any (1) deferred rents receivable, and (2) deferred revenue, lease incentives and intangible assets that are amortizable into rental revenue associated with the leases; the resulting net amount is the net revenue from the early termination of the leases. When a tenant’s lease for space in a property is terminated early but the tenant continues to lease such space under a new or modified lease in the property, the net revenue from the early termination of the lease is recognized evenly over the remaining life of the new or modified lease in place on that property. Effective January 1, 2019, we adopted guidance issued by the FASB setting forth principles for the recognition, measurement, presentation and disclosure of leases, which required lessors of real estate to account for leases using an approach substantially equivalent to guidance previously in place for operating leases, direct financing leases and sales-type leases. We adopted this guidance for leases on January 1

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value MeasurementsAccounting standards define fair value as the exit price, or the amount that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants as of the measurement date. The standards also establish a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs market participants would use in valuing the asset or liability developed based on market data obtained from sources independent of us. Unobservable inputs are inputs that reflect our assumptions about the factors market participants would use in valuing the asset or liability developed based upon the best information available in the circumstances. The hierarchy of these inputs is broken down into three levels: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs include (1) quoted prices for similar assets or liabilities in active markets, (2) quoted prices for identical or similar assets or liabilities in inactive markets and (3) inputs (other than quoted prices) that are observable for the asset or liability, either directly or indirectly; and Level 3 inputs are unobservable inputs for the asset or liability. Categorization within the valuation hierarchy is based upon the lowest level of input that is most significant to the fair value measurement. Recurring Fair Value Measurements COPT has a non-qualified elective deferred compensation plan for Trustees and certain members of our management team that, prior to December 31, 2019, permitted participants to defer up to 100% of their compensation on a pre-tax basis and receive a tax-deferred return on such deferrals. The Company froze additional entry into the plan effective December 31, 2019. 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 $3.0 million as of December 31, 2020 and $3.1 million as of December 31, 2019, and is included in the line entitled “prepaid expenses and other assets, net” on COPT’s consolidated balance sheets along with an insignificant amount of other marketable securities. The offsetting liability associated with the plan is adjusted to fair value at the end of each accounting period based on the fair value of the plan assets and reported in “other liabilities” on COPT’s consolidated balance sheets. The assets of the plan 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 December 31, 2020 and 2019, 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. The fair values of our investing receivables, as disclosed in Note 8, were 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 10, 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. For additional fair value information, refer to Note 8 for investing receivables, Note 10 for debt and Note 11 for interest rate derivatives. COPT and Subsidiaries The tables below set forth financial assets and liabilities of COPT and subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2020 and 2019 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 December 31, 2020: Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 3,008 $ — $ — $ 3,008 Other 19 — — 19 Other marketable securities (1) 30 — — 30 Total assets $ 3,057 $ — $ — $ 3,057 Liabilities: Deferred compensation plan liability (2) $ — $ 3,027 $ — $ 3,027 Interest rate derivatives — 9,522 — 9,522 Total liabilities $ — $ 12,549 $ — $ 12,549 December 31, 2019: Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 3,035 $ — $ — $ 3,035 Other 25 — — 25 Interest rate derivatives (1) — 23 — 23 Total assets $ 3,060 $ 23 $ — $ 3,083 Liabilities: Deferred compensation plan liability (2) $ — $ 3,060 $ — $ 3,060 Interest rate derivatives — 25,682 — 25,682 Total liabilities $ — $ 28,742 $ — $ 28,742 (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 tables below set forth financial assets and liabilities of COPLP and subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2020 and 2019 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 December 31, 2020: Assets: Other marketable securities (1) $ 30 $ — $ — $ 30 Liabilities: Interest rate derivatives $ — $ 9,522 $ — $ 9,522 December 31, 2019: Assets: Interest rate derivatives (1) $ — $ 23 $ — $ 23 Liabilities: Interest rate derivatives $ — $ 25,682 $ — $ 25,682 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPLP ’ s consolidated balance sheet. 2019 Nonrecurring Fair Value Measurements

Properties, Net

Properties, Net	12 Months Ended
	Dec. 31, 2020
Real Estate [Abstract]
Properties, Net	Properties, Net Operating properties, net consisted of the following (in thousands): December 31, 2020 2019 Land $ 528,269 $ 472,976 Buildings and improvements 3,711,264 3,306,791 Less: Accumulated depreciation (1,124,253) (1,007,120) Operating properties, net $ 3,115,280 $ 2,772,647 2020 Dispositions On October 30, 2020, we sold a 90% interest in two data center shell properties in Northern Virginia based on an aggregate property value of $89.7 million and retained a 10% interest in the properties through B RE COPT DC JV II LLC (“B RE COPT”), a newly-formed joint venture. Our partner in the joint venture acquired the 90% interest from us for $80.7 million. We account for our interest in the joint venture using the equity method of accounting as described further in Note 6. We recognized a gain on sale of $30.0 million. 2020 Development Activities In 2020, we placed into service 1.8 million square feet in 11 newly-developed properties, 42,000 square feet in expansions of three fully-operational properties and 21,000 square feet in a redeveloped property. As of December 31, 2020, we had 11 properties under development, including three partially-operational properties, that we estimate will total 1.5 million square feet upon completion. In the third quarter of 2020, we concluded that we no longer expected to develop a property in Baltimore, Maryland. As a result, we recognized an impairment loss on previously incurred pre-development costs of $1.5 million. 2019 Dispositions In 2019, we sold, through a series of transactions, a 90% interest in nine data center shells in Northern Virginia based on an aggregate property value of $345.1 million, retaining a 10% interest in the properties through BREIT COPT DC JV LLC (“BREIT-COPT”), a newly-formed joint venture. The transactions for seven of these properties were completed on June 20, 2019 and the remaining two properties on December 5, 2019. Our partner in the joint venture acquired the 90% interest from us for $310.6 million. We account for our interest in the joint venture using the equity method of accounting as described further in Note 6. We recognized a gain on sale of $105.2 million. 2019 Development Activities In 2019, we placed into service 1.1 million square feet in nine newly-developed properties and 85,000 square feet in one property under redevelopment. 2018 Dispositions In 2018, we sold 11751 Meadowville Lane, an operating property totaling 193,000 square feet in Chester, Virginia (in our Data Center Shells sub-segment). We contractually closed on the sale of this property on October 27, 2017 for $44.0 million. We provided a financial guaranty to the buyer under which we provided an indemnification for up to $20 million in losses it could incur related to a potential defined capital event occurring on the property; our financial guaranty to the buyer expired on October 1, 2018, resulting in no losses to us. We accounted for this transaction as a financing arrangement. Accordingly, we did not recognize the sale of this property for accounting purposes until the expiration of the guaranty on October 1, 2018. In the fourth quarter of 2018, we recognized a gain on this sale of $1.5 million. 2018 Development Activities In 2018, we placed into service 666,000 square feet in six newly-developed properties, 22,000 square feet in one redeveloped property and land under a long-term contract. In the fourth quarter of 2018, we abandoned plans to redevelop a property in our Fort Meade/BW Corridor sub-segment after we completed leasing on the property that did not require any redevelopment. Accordingly, we recognized an impairment loss of $2.4 million representing pre-development costs associated with the property.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases Lessor Arrangements We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. As of December 31, 2020, these leases, which may encompass all, or a portion of, a property, had remaining terms spanning from one month to 18 years and averaging approximately 5.4 years. Our lease revenue is comprised of: fixed lease revenue, including contractual rent billings under leases recognized on a straight-line basis over lease terms and amortization of lease incentives and above- and below- market lease intangibles; and variable lease revenue, including tenant expense recoveries, lease termination revenue and other revenue from tenants that is not fixed under the lease. The table below sets forth our composition of lease revenue recognized between fixed and variable lease revenue (in thousands): For the Years Ended December 31, Lease revenue 2020 2019 Fixed $ 425,593 $ 412,342 Variable 110,534 110,130 $ 536,127 $ 522,472 A significant concentration of our lease revenue in 2020 and 2019 was earned from our largest tenant, the USG, including 35% and 34% of our total lease revenue, respectively, and 25% of our fixed lease revenue in each of those years. Our lease revenue from the USG in 2020 and 2019 was earned primarily from properties in the Fort Meade/BW Corridor, Lackland Air Force Base and Northern Virginia Defense/IT reportable sub-segments (see Note 17). Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573 Lessee Arrangements As of December 31, 2020, our balance sheet included $81.0 million in right-of-use assets associated primarily with land leased from third parties underlying certain properties that we are operating or developing. The land leases have long durations with remaining terms ranging from 28 years (excluding extension options) to 95 years. As of December 31, 2020, our right-of-use assets included: • $37.8 million for land on which we are developing an office property in Washington, D.C. through our Stevens Investors, LLC joint venture, virtually all of the rent on which was previously paid. This lease has a 95-year remaining term, and we possess a bargain purchase option that we expect to exercise in 2021; • $11.3 million for land in a business park in Huntsville, Alabama under 15 leases through our LW Redstone Company, LLC joint venture, with remaining terms ranging from 42 to 51 years and options to renew for an additional 25 years that were not included in the term used in determining the asset balance; • $10.1 million for land underlying operating office properties in Washington, D.C. under two leases with remaining terms of approximately 79 years; • $6.6 million for land in a research park in College Park, Maryland under four leases through our M Square Associates, LLC joint venture, all of the rent on which was previously paid. These leases had remaining terms ranging from 62 to 73 years; • $6.5 million for land underlying a parking garage in Baltimore, Maryland under a lease with a remaining term of 28 years and an option to renew for an additional 49 years that was included in the term used in determining the asset balance; • $6.5 million for data center space in Phoenix, Arizona with a remaining term of 4 years and an option to renew for an additional five years that were not included in the term used in determining the asset balance; and • $2.2 million for other land underlying operating properties in our Fort Meade/BW Corridor sub-segment under two leases with remaining terms of approximately 47 years, all of the rent on which was previously paid. Our property right-of-use assets consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Right-of-use assets Operating leases - Property Property - operating right-of-use assets $ 40,570 $ 27,864 Finance leases - Property Property - finance right-of-use assets 40,425 40,458 Total right-of-use assets $ 80,995 $ 68,322 Property lease liabilities consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Lease liabilities Operating leases - Property Property - operating lease liabilities $ 30,746 $ 17,317 Finance leases - Property Other liabilities 28 702 Total lease liabilities $ 30,774 $ 18,019 The table below sets forth the weighted average terms and discount rates of our property leases as of December 31, 2020: Weighted average remaining lease term Operating leases 50 years Finance leases < 1 year Weighted average discount rate Operating leases 7.21 % Finance leases 3.62 % The table below presents our total property lease cost (in thousands): For the Years Ended December 31, Lease cost Statement of Operations Location 2020 2019 Operating lease cost Property leases - fixed Property operating expenses $ 2,413 $ 1,664 Property leases - variable Property operating expenses 127 4 Finance lease cost Amortization of property right-of-use assets Property operating expenses 34 30 $ 2,574 $ 1,698 The table below presents the effect of property lease payments on our consolidated statements of cash flows (in thousands): For the Years Ended December 31, Supplemental cash flow information 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 1,694 $ 1,004 Financing cash flows for financing leases $ 674 $ 14 Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019
Leases	Leases Lessor Arrangements We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. As of December 31, 2020, these leases, which may encompass all, or a portion of, a property, had remaining terms spanning from one month to 18 years and averaging approximately 5.4 years. Our lease revenue is comprised of: fixed lease revenue, including contractual rent billings under leases recognized on a straight-line basis over lease terms and amortization of lease incentives and above- and below- market lease intangibles; and variable lease revenue, including tenant expense recoveries, lease termination revenue and other revenue from tenants that is not fixed under the lease. The table below sets forth our composition of lease revenue recognized between fixed and variable lease revenue (in thousands): For the Years Ended December 31, Lease revenue 2020 2019 Fixed $ 425,593 $ 412,342 Variable 110,534 110,130 $ 536,127 $ 522,472 A significant concentration of our lease revenue in 2020 and 2019 was earned from our largest tenant, the USG, including 35% and 34% of our total lease revenue, respectively, and 25% of our fixed lease revenue in each of those years. Our lease revenue from the USG in 2020 and 2019 was earned primarily from properties in the Fort Meade/BW Corridor, Lackland Air Force Base and Northern Virginia Defense/IT reportable sub-segments (see Note 17). Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573 Lessee Arrangements As of December 31, 2020, our balance sheet included $81.0 million in right-of-use assets associated primarily with land leased from third parties underlying certain properties that we are operating or developing. The land leases have long durations with remaining terms ranging from 28 years (excluding extension options) to 95 years. As of December 31, 2020, our right-of-use assets included: • $37.8 million for land on which we are developing an office property in Washington, D.C. through our Stevens Investors, LLC joint venture, virtually all of the rent on which was previously paid. This lease has a 95-year remaining term, and we possess a bargain purchase option that we expect to exercise in 2021; • $11.3 million for land in a business park in Huntsville, Alabama under 15 leases through our LW Redstone Company, LLC joint venture, with remaining terms ranging from 42 to 51 years and options to renew for an additional 25 years that were not included in the term used in determining the asset balance; • $10.1 million for land underlying operating office properties in Washington, D.C. under two leases with remaining terms of approximately 79 years; • $6.6 million for land in a research park in College Park, Maryland under four leases through our M Square Associates, LLC joint venture, all of the rent on which was previously paid. These leases had remaining terms ranging from 62 to 73 years; • $6.5 million for land underlying a parking garage in Baltimore, Maryland under a lease with a remaining term of 28 years and an option to renew for an additional 49 years that was included in the term used in determining the asset balance; • $6.5 million for data center space in Phoenix, Arizona with a remaining term of 4 years and an option to renew for an additional five years that were not included in the term used in determining the asset balance; and • $2.2 million for other land underlying operating properties in our Fort Meade/BW Corridor sub-segment under two leases with remaining terms of approximately 47 years, all of the rent on which was previously paid. Our property right-of-use assets consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Right-of-use assets Operating leases - Property Property - operating right-of-use assets $ 40,570 $ 27,864 Finance leases - Property Property - finance right-of-use assets 40,425 40,458 Total right-of-use assets $ 80,995 $ 68,322 Property lease liabilities consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Lease liabilities Operating leases - Property Property - operating lease liabilities $ 30,746 $ 17,317 Finance leases - Property Other liabilities 28 702 Total lease liabilities $ 30,774 $ 18,019 The table below sets forth the weighted average terms and discount rates of our property leases as of December 31, 2020: Weighted average remaining lease term Operating leases 50 years Finance leases < 1 year Weighted average discount rate Operating leases 7.21 % Finance leases 3.62 % The table below presents our total property lease cost (in thousands): For the Years Ended December 31, Lease cost Statement of Operations Location 2020 2019 Operating lease cost Property leases - fixed Property operating expenses $ 2,413 $ 1,664 Property leases - variable Property operating expenses 127 4 Finance lease cost Amortization of property right-of-use assets Property operating expenses 34 30 $ 2,574 $ 1,698 The table below presents the effect of property lease payments on our consolidated statements of cash flows (in thousands): For the Years Ended December 31, Supplemental cash flow information 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 1,694 $ 1,004 Financing cash flows for financing leases $ 674 $ 14 Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019
Leases	Leases Lessor Arrangements We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. As of December 31, 2020, these leases, which may encompass all, or a portion of, a property, had remaining terms spanning from one month to 18 years and averaging approximately 5.4 years. Our lease revenue is comprised of: fixed lease revenue, including contractual rent billings under leases recognized on a straight-line basis over lease terms and amortization of lease incentives and above- and below- market lease intangibles; and variable lease revenue, including tenant expense recoveries, lease termination revenue and other revenue from tenants that is not fixed under the lease. The table below sets forth our composition of lease revenue recognized between fixed and variable lease revenue (in thousands): For the Years Ended December 31, Lease revenue 2020 2019 Fixed $ 425,593 $ 412,342 Variable 110,534 110,130 $ 536,127 $ 522,472 A significant concentration of our lease revenue in 2020 and 2019 was earned from our largest tenant, the USG, including 35% and 34% of our total lease revenue, respectively, and 25% of our fixed lease revenue in each of those years. Our lease revenue from the USG in 2020 and 2019 was earned primarily from properties in the Fort Meade/BW Corridor, Lackland Air Force Base and Northern Virginia Defense/IT reportable sub-segments (see Note 17). Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573 Lessee Arrangements As of December 31, 2020, our balance sheet included $81.0 million in right-of-use assets associated primarily with land leased from third parties underlying certain properties that we are operating or developing. The land leases have long durations with remaining terms ranging from 28 years (excluding extension options) to 95 years. As of December 31, 2020, our right-of-use assets included: • $37.8 million for land on which we are developing an office property in Washington, D.C. through our Stevens Investors, LLC joint venture, virtually all of the rent on which was previously paid. This lease has a 95-year remaining term, and we possess a bargain purchase option that we expect to exercise in 2021; • $11.3 million for land in a business park in Huntsville, Alabama under 15 leases through our LW Redstone Company, LLC joint venture, with remaining terms ranging from 42 to 51 years and options to renew for an additional 25 years that were not included in the term used in determining the asset balance; • $10.1 million for land underlying operating office properties in Washington, D.C. under two leases with remaining terms of approximately 79 years; • $6.6 million for land in a research park in College Park, Maryland under four leases through our M Square Associates, LLC joint venture, all of the rent on which was previously paid. These leases had remaining terms ranging from 62 to 73 years; • $6.5 million for land underlying a parking garage in Baltimore, Maryland under a lease with a remaining term of 28 years and an option to renew for an additional 49 years that was included in the term used in determining the asset balance; • $6.5 million for data center space in Phoenix, Arizona with a remaining term of 4 years and an option to renew for an additional five years that were not included in the term used in determining the asset balance; and • $2.2 million for other land underlying operating properties in our Fort Meade/BW Corridor sub-segment under two leases with remaining terms of approximately 47 years, all of the rent on which was previously paid. Our property right-of-use assets consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Right-of-use assets Operating leases - Property Property - operating right-of-use assets $ 40,570 $ 27,864 Finance leases - Property Property - finance right-of-use assets 40,425 40,458 Total right-of-use assets $ 80,995 $ 68,322 Property lease liabilities consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Lease liabilities Operating leases - Property Property - operating lease liabilities $ 30,746 $ 17,317 Finance leases - Property Other liabilities 28 702 Total lease liabilities $ 30,774 $ 18,019 The table below sets forth the weighted average terms and discount rates of our property leases as of December 31, 2020: Weighted average remaining lease term Operating leases 50 years Finance leases < 1 year Weighted average discount rate Operating leases 7.21 % Finance leases 3.62 % The table below presents our total property lease cost (in thousands): For the Years Ended December 31, Lease cost Statement of Operations Location 2020 2019 Operating lease cost Property leases - fixed Property operating expenses $ 2,413 $ 1,664 Property leases - variable Property operating expenses 127 4 Finance lease cost Amortization of property right-of-use assets Property operating expenses 34 30 $ 2,574 $ 1,698 The table below presents the effect of property lease payments on our consolidated statements of cash flows (in thousands): For the Years Ended December 31, Supplemental cash flow information 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 1,694 $ 1,004 Financing cash flows for financing leases $ 674 $ 14 Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019
Leases	Leases Lessor Arrangements We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. As of December 31, 2020, these leases, which may encompass all, or a portion of, a property, had remaining terms spanning from one month to 18 years and averaging approximately 5.4 years. Our lease revenue is comprised of: fixed lease revenue, including contractual rent billings under leases recognized on a straight-line basis over lease terms and amortization of lease incentives and above- and below- market lease intangibles; and variable lease revenue, including tenant expense recoveries, lease termination revenue and other revenue from tenants that is not fixed under the lease. The table below sets forth our composition of lease revenue recognized between fixed and variable lease revenue (in thousands): For the Years Ended December 31, Lease revenue 2020 2019 Fixed $ 425,593 $ 412,342 Variable 110,534 110,130 $ 536,127 $ 522,472 A significant concentration of our lease revenue in 2020 and 2019 was earned from our largest tenant, the USG, including 35% and 34% of our total lease revenue, respectively, and 25% of our fixed lease revenue in each of those years. Our lease revenue from the USG in 2020 and 2019 was earned primarily from properties in the Fort Meade/BW Corridor, Lackland Air Force Base and Northern Virginia Defense/IT reportable sub-segments (see Note 17). Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573 Lessee Arrangements As of December 31, 2020, our balance sheet included $81.0 million in right-of-use assets associated primarily with land leased from third parties underlying certain properties that we are operating or developing. The land leases have long durations with remaining terms ranging from 28 years (excluding extension options) to 95 years. As of December 31, 2020, our right-of-use assets included: • $37.8 million for land on which we are developing an office property in Washington, D.C. through our Stevens Investors, LLC joint venture, virtually all of the rent on which was previously paid. This lease has a 95-year remaining term, and we possess a bargain purchase option that we expect to exercise in 2021; • $11.3 million for land in a business park in Huntsville, Alabama under 15 leases through our LW Redstone Company, LLC joint venture, with remaining terms ranging from 42 to 51 years and options to renew for an additional 25 years that were not included in the term used in determining the asset balance; • $10.1 million for land underlying operating office properties in Washington, D.C. under two leases with remaining terms of approximately 79 years; • $6.6 million for land in a research park in College Park, Maryland under four leases through our M Square Associates, LLC joint venture, all of the rent on which was previously paid. These leases had remaining terms ranging from 62 to 73 years; • $6.5 million for land underlying a parking garage in Baltimore, Maryland under a lease with a remaining term of 28 years and an option to renew for an additional 49 years that was included in the term used in determining the asset balance; • $6.5 million for data center space in Phoenix, Arizona with a remaining term of 4 years and an option to renew for an additional five years that were not included in the term used in determining the asset balance; and • $2.2 million for other land underlying operating properties in our Fort Meade/BW Corridor sub-segment under two leases with remaining terms of approximately 47 years, all of the rent on which was previously paid. Our property right-of-use assets consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Right-of-use assets Operating leases - Property Property - operating right-of-use assets $ 40,570 $ 27,864 Finance leases - Property Property - finance right-of-use assets 40,425 40,458 Total right-of-use assets $ 80,995 $ 68,322 Property lease liabilities consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Lease liabilities Operating leases - Property Property - operating lease liabilities $ 30,746 $ 17,317 Finance leases - Property Other liabilities 28 702 Total lease liabilities $ 30,774 $ 18,019 The table below sets forth the weighted average terms and discount rates of our property leases as of December 31, 2020: Weighted average remaining lease term Operating leases 50 years Finance leases < 1 year Weighted average discount rate Operating leases 7.21 % Finance leases 3.62 % The table below presents our total property lease cost (in thousands): For the Years Ended December 31, Lease cost Statement of Operations Location 2020 2019 Operating lease cost Property leases - fixed Property operating expenses $ 2,413 $ 1,664 Property leases - variable Property operating expenses 127 4 Finance lease cost Amortization of property right-of-use assets Property operating expenses 34 30 $ 2,574 $ 1,698 The table below presents the effect of property lease payments on our consolidated statements of cash flows (in thousands): For the Years Ended December 31, Supplemental cash flow information 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 1,694 $ 1,004 Financing cash flows for financing leases $ 674 $ 14 Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019

Real Estate Joint Ventures

Real Estate Joint Ventures	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Real Estate Joint Ventures	Real Estate Joint Ventures Consolidated Real Estate Joint Ventures We consolidate the real estate joint ventures described below because of our: (1) power to direct the matters that most significantly impact their activities, including development, leasing and management of the properties developed by the VIEs; and (2) right to receive returns on our fundings and, in many cases, the obligation to fund the activities of the ventures to the extent that third-party financing is not obtained, both of which could be potentially significant to the VIEs. The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of December 31, 2020 (dollars in thousands): Nominal Ownership % December 31, 2020 (1) Date Acquired Total Encumbered Assets Total Liabilities Entity Location LW Redstone Company, LLC 3/23/2010 85% Huntsville, Alabama $ 403,448 $ 92,590 $ 100,334 Stevens Investors, LLC 8/11/2015 95% Washington, D.C. 161,735 158,286 88,028 M Square Associates, LLC 6/26/2007 50% College Park, Maryland 100,258 62,446 55,227 $ 665,441 $ 313,322 $ 243,589 (1) Excludes amounts eliminated in consolidation. Each of these joint ventures are engaged in the development and operation of real estate. With regard to these joint ventures: • for LW Redstone Company, LLC, we anticipate funding certain infrastructure costs (up to a maximum of $76.0 million excluding accrued interest thereon) due to be reimbursed by the City of Huntsville as discussed further in Note 8. We had advanced $61.0 million to the City through December 31, 2020 to fund such costs. We also expect to fund additional development costs through equity contributions to the extent that third party financing is not obtained. Our partner was credited with a $9.0 million in invested capital upon formation and is not required to make, nor has it made, additional equity contributions. In March 2020, the LW Redstone Company, LLC joint venture agreement was amended to change the distribution terms to allow the venture to distribute financing proceeds to satisfy our partner’s cumulative preferred return and to provide our partner a priority preferred return on its invested capital. While net cash flow distributions to the partners vary depending on the source of the funds distributed, cash flows are generally distributed to the partners as follows: (1) cumulative preferred returns of 13.5% on our partner’s invested capital; (2) cumulative preferred returns of 13.5% on our invested capital; (3) return of our invested capital; (4) return of our partner’s invested capital; and (5) any remaining residual 85% to us and 15% to our partner. Our partner has the right to require us to acquire its interest for fair value; accordingly, we classify the fair value of our partner’s interest as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheets. We have the right to acquire our partner’s interest at fair value upon the earlier of five years following the project’s achievement of a construction commencement threshold of 4.4 million square feet or March 2040; the project had achieved approximately 1.6 million square feet of construction commencement through December 31, 2020. Our partner has the right to receive some or all of the consideration for the acquisition of its interests in the form of common units in COPLP; • for Stevens Investors, LLC, net cash flows of this entity will be distributed to the partners as follows: (1) member loans and accrued interest; (2) pro rata return of the partners’ capital; (3) pro rata return of the partners’ respective unpaid preferred returns; and (4) varying splits of 85% to 60% to us and the balance to our partners as we reach specified return hurdles. Our partners have the right to require us to acquire some or all of their interests for fair value for a defined period of time following the property’s development completion (expected to occur in 2021) and stabilization (as defined in the operating agreement) of the joint venture’s office property; accordingly, we classify the fair value of our partners’ interest as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheets. We and our partners each have the right to acquire each other’s interests at fair value upon the second anniversary of the property’s stabilization date (as defined in the operating agreement). Our partners have the right to receive some or all of the consideration for the acquisition of their interests in the form of common units in COPLP; and • for M Square Associates, LLC, net cash flows of this entity are distributed to the partners as follows: (1) member loans and accrued interest; (2) our preferred return and capital contributions used to fund infrastructure costs; (3) the partners’ preferred returns and capital contributions used to fund all other costs, including the base land value credit, in proportion to the accrued returns and capital accounts; and (4) residual amounts distributed 50% to each member. We disclose the activity of our redeemable noncontrolling interests in Note 12. The ventures discussed above include only ones in which parties other than COPLP and COPT own interests. Unconsolidated Real Estate Joint Ventures The table below sets forth information pertaining to our investments in unconsolidated real estate joint ventures accounted for using the equity method of accounting (dollars in thousands): Date Acquired Nominal Ownership % Number of Properties Carrying Value of Investment (1) Entity December 31, 2020 December 31, 2019 B RE COPT DC JV II LLC (2) 10/30/2020 10% 8 $ 15,988 $ — BREIT COPT DC JV LLC 6/20/2019 10% 9 13,315 14,133 GI-COPT DC Partnership LLC 7/21/2016 50% N/A — 37,816 17 $ 29,303 $ 51,949 (1) Included in the line entitled “investment in unconsolidated real estate joint ventures” on our consolidated balance sheets. (2) As of December 31, 2020, our investment in B RE COPT was $7.4 million lower than our share of the joint venture’s equity due to a difference between our cost basis and our share of B RE COPT’s underlying equity in the net assets acquired from GI-COPT. These joint ventures operate triple-net leased, single-tenant data center shell properties in Northern Virginia. With regard to these joint ventures: • B RE COPT was formed in 2020, when, as described further in Note 4, we sold a 90% interest in two properties and retained a 10% interest in the properties through B RE COPT; • on December 22, 2020, we sold, through a series of transactions, 80% of our 50% interests in LLCs holding six properties and associated mortgage debt that we owned through GI-COPT DC Partnership LLC (“GI-COPT”). We received $60 million in proceeds and a 10% retained interest in the LLCs through B RE COPT, and recognized a gain of $29.4 million on the sale of these interests. GI-COPT was dissolved upon completion of these transactions; and • BREIT-COPT was formed in 2019, when, as described further in Note 4, we sold a 90% interest in nine properties and retained a 10% interest in the properties through the joint venture; We concluded that B RE COPT and BREIT-COPT are variable interest entities. Under the terms of the joint venture agreements, we and our partners receive returns in proportion to our investments, and our maximum exposure to losses is limited to our investments, subject to certain indemnification obligations with respect to nonrecourse debt secured by the properties. The nature of our involvement in the activities of the joint venture does not give us power over decisions that significantly affect its economic performance.

Intangible Assets on Real Estat

Intangible Assets on Real Estate Acquisitions	12 Months Ended
	Dec. 31, 2020
Intangible Assets on Real Estate Acquisitions
Intangible Assets on Real Estate Acquisitions	Intangible Assets on Real Estate Acquisitions Intangible assets on real estate acquisitions consisted of the following (in thousands): December 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net In-place lease value $ 131,974 $ 123,291 $ 8,683 $ 131,975 $ 120,894 $ 11,081 Tenant relationship value 59,069 49,055 10,014 59,131 43,544 15,587 Above-market leases 13,718 13,380 338 13,718 13,318 400 Other 1,333 1,024 309 1,333 1,009 324 $ 206,094 $ 186,750 $ 19,344 $ 206,157 $ 178,765 $ 27,392 Amortization of intangible assets on real estate acquisitions totaled $8.0 million in 2020, $8.7 million in 2019 and $15.6 million in 2018. The approximate weighted average amortization periods of the categories set forth above follow: in-place lease value: six years; tenant relationship value: eight years; above-market leases: eight years; and other: 22 years. The approximate weighted average amortization period for all of the categories combined is seven years. The estimated amortization (to amortization associated with real estate operations, rental revenue and property operating expenses) associated with the intangible asset categories set forth above for the next five years is: $4.7 million for 2021 ; $3.2 million for 2022 ; $2.8 million for 2023 ; $2.3 million for 2024 ; and $2.0 million for 2025

Investing Receivables

Investing Receivables	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Investing Receivables	Investing Receivables Investing receivables consisted of the following (in thousands): December 31, 2020 2019 Notes receivable from the City of Huntsville $ 65,564 $ 59,427 Other investing loans receivable 6,041 14,096 Amortized cost basis 71,605 73,523 Allowance for credit losses (2,851) — Investing receivables, net $ 68,754 $ 73,523 The balances above include accrued interest receivable, net of allowance for credit losses, of $4.8 million as of December 31, 2020 and $4.7 million as of December 31, 2019. 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%. These notes and the accrued and unpaid interest thereon, which is compounded annually on March 1, will be repaid using the real estate taxes generated by the properties developed by the joint venture. When these tax revenues are sufficient to cover the debt service on a certain increment of municipal bonds, the City of Huntsville will be required to issue bonds to repay the notes and the accrued and unpaid interest thereon. Each note has a maturity date of the earlier of 30 years from the date issued or the expiration of the tax increment district comprising the developed properties in 2045. Our other investing loans receivable carry an interest rate of 8.0% and mature in 2021. The fair value of these receivables was approximately $73 million as of December 31, 2020 and $74 million as of December 31, 2019.

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Net	12 Months Ended
	Dec. 31, 2020
Prepaid Expense and Other Assets [Abstract]
Prepaid Expenses and Other Assets, Net	Prepaid Expenses and Other Assets, Net Prepaid expenses and other assets, net consisted of the following (in thousands): December 31, 2020 2019 Lease incentives, net $ 35,642 $ 28,433 Prepaid expenses 19,690 18,835 Furniture, fixtures and equipment, net 10,433 7,823 Construction contract costs in excess of billings, net 10,343 17,223 Net investment in sales-type leases 6,573 — Non-real estate equity investments 5,509 6,705 Restricted cash 3,664 3,397 Deferred financing costs, net (1) 2,439 3,633 Deferred tax asset, net 1,989 2,328 Other assets 5,274 4,639 Total for COPLP and subsidiaries 101,556 93,016 Marketable securities in deferred compensation plan 3,027 3,060 Total for COPT and subsidiaries $ 104,583 $ 96,076 (1) Represents deferred costs, net of accumulated amortization, attributable to our Revolving Credit Facility and interest rate derivatives. Deferred tax asset, net reported above includes the following tax effects of temporary differences and carry forwards of our TRS (in thousands): December 31, 2020 2019 Operating loss carry forward $ 2,087 $ 2,885 Property 103 (77) Valuation allowance (201) (480) Deferred tax asset, net $ 1,989 $ 2,328 We recognize a valuation allowance on our deferred tax asset if we believe all or some portion of the asset may not be realized. An increase or decrease in the valuation allowance resulting from a change in circumstances that causes a change in our judgment about the realizability of our deferred tax asset is included in income. We believe it is more likely than not that the results of future operations in our TRS will generate sufficient taxable income to realize our December 31, 2020 net deferred tax asset.

Debt, Net

Debt, Net	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt, Net	Debt, Net Debt Summary Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of December 31, 2020 December 31, December 31, 2019 Stated Interest Rates Scheduled Maturity Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 139,991 $ 143,430 3.82% - 4.62% (3) 2023-2026 Variable rate secured debt (4) 115,119 68,055 LIBOR + 1.45% to 2.35% (5) 2022-2026 Total mortgage and other secured debt 255,110 211,485 Revolving Credit Facility 143,000 177,000 LIBOR + 0.775% to 1.45% (6) March 2023 (7) Term Loan Facility 398,447 248,706 LIBOR + 1.00% to 1.65% (8) 2022 Unsecured Senior Notes (9) 3.60%, $350,000 aggregate principal 348,888 348,431 3.60% (10) May 2023 5.25%, $250,000 aggregate principal 248,194 247,652 5.25% (11) February 2024 5.00%, $300,000 aggregate principal 297,915 297,503 5.00% (12) July 2025 2.25%, $400,000 aggregate principal 394,464 — 2.25% (13) March 2026 3.70%, $300,000 aggregate principal — 299,324 3.70% (14) N/A (14) Unsecured note payable 900 1,038 0% (15) May 2026 Total debt, net $ 2,086,918 $ 1,831,139 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $5.9 million as of December 31, 2020 and $5.8 million as of December 31, 2019. (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 $155,000 as of December 31, 2020 and $217,000 as of December 31, 2019. (3) The weighted average interest rate on our fixed rate mortgage debt was 4.16% as of December 31, 2020. (4) Includes a construction loan with $29.1 million in remaining borrowing capacity as of December 31, 2020. (5) The weighted average interest rate on our variable rate secured debt was 2.28% as of December 31, 2020. (6) The weighted average interest rate on the Revolving Credit Facility was 1.20% as of December 31, 2020. (7) The facility matures in March 2023, 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. (8) The interest rate on this loan was 1.15% as of December 31, 2020. (9) Refer to the paragraphs below for further disclosure. (10) The carrying value of these notes reflects an unamortized discount totaling $781,000 as of December 31, 2020 and $1.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%. (11) The carrying value of these notes reflects an unamortized discount totaling $1.6 million as of December 31, 2020 and $2.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%. (12) The carrying value of these notes reflects an unamortized discount totaling $1.8 million as of December 31, 2020 and $2.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% (13) The carrying value of these notes reflects an unamortized discount totaling $4.5 million as of December 31, 2020 . (14) The carrying value of these notes reflects an unamortized discount totaling $534,000 as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 3.85%. (15) 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 $161,000 as of December 31, 2020 and $223,000 as of December 31, 2019. All debt is owed by the Operating Partnership. While COPT is not directly obligated by any debt, it has guaranteed COPLP’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, including maximum leverage ratio, unencumbered leverage ratio, minimum fixed charge coverage, minimum unencumbered interest coverage ratio, minimum debt service and maximum secured indebtedness ratio. In addition, the terms of some of COPLP’s debt may limit its ability to make certain types of payments and other distributions to COPT in the event of default or when such payments or distributions may prompt failure of debt covenants. As of December 31, 2020, we were compliant with these financial covenants. Our debt matures on the following schedule (in thousands): Year Ending December 31, December 31, 2020 2021 $ 3,955 2022 487,380 2023 560,130 2024 279,983 2025 323,717 Thereafter 446,300 Total $ 2,101,465 (1) (1) Represents scheduled principal amortization and maturities only and therefore excludes net discounts and deferred financing costs of $14.5 million. We capitalized interest costs of $12.1 million in 2020, $10.8 million in 2019 and $5.9 million in 2018. The following table sets forth information pertaining to the fair value of our debt (in thousands): December 31, 2020 December 31, 2019 Carrying Estimated Carrying Estimated Fixed-rate debt Unsecured Senior Notes $ 1,289,461 $ 1,334,342 $ 1,192,910 $ 1,227,441 Other fixed-rate debt 140,891 142,838 144,468 149,907 Variable-rate debt 656,566 654,102 493,761 495,962 $ 2,086,918 $ 2,131,282 $ 1,831,139 $ 1,873,310 Revolving Credit Facility On October 10, 2018, we entered into a credit agreement with a group of lenders to replace our existing unsecured revolving credit facility with a new facility (the prior facility and new facility are referred to collectively herein as our “Revolving Credit Facility”). The lenders’ aggregate commitment under the facility is $800.0 million, with the ability for us to increase the lenders’ aggregate commitment to $1.25 billion, provided that there is no default under the facility and subject to the approval of the lenders. The facility matures on March 10, 2023, 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. The interest rate on the facility is based on LIBOR plus 0.775% to 1.450%, as determined by the credit ratings assigned to COPLP by Standard & Poor’s Ratings Services, Moody’s Investors Service, Inc. or Fitch Ratings Ltd. (collectively, the “Ratings Agencies”). The facility also carries a quarterly fee that is based on the lenders’ aggregate commitment under the facility multiplied by a per annum rate of 0.125% to 0.300%, as determined by the credit ratings assigned to COPLP by the Ratings Agencies. As of December 31, 2020, the maximum borrowing capacity under this facility totaled $800.0 million, of which $657.0 million was available. Weighted average borrowings under our Revolving Credit Facility totaled $204.9 million in 2020 and $255.6 million in 2019. The weighted average interest rate on our Revolving Credit Facility was 1.55% in 2020 and 3.32% in 2019. Term Loan Facilities As of December 31, 2020, we had an unsecured term loan facility that we amended in 2020 to increase the loan amount by $150.0 million and change the interest terms. The loan carries a variable interest rate based on the LIBOR rate (customarily the 30-day rate) plus 1.00% to 1.65%, as determined by: a ratio of our debt to our assets; and the credit ratings assigned to COPLP by the Ratings Agencies. In addition to the term loan discussed above, we also had a term loan for which we repaid the remaining balance of $100.0 million in 2018. In connection with our Revolving Credit Facility discussed above, we have the ability to borrow up to $500.0 million under new term loans from the facility’s lender group provided that there is no default under the facility and subject to the approval of the lenders. Unsecured Senior Notes On September 17, 2020, we issued $400.0 million of 2.25% Senior Notes due 2026 (the “2.25% Notes”) at an initial offering price of 99.416% of their face value. The proceeds from this issuance, after deducting underwriting discounts, but before other offering expenses, were $395.3 million. The notes mature on March 15, 2026. The effective interest rate under the notes, including amortization of discount and issuance costs, was 2.48%. With regard to our 3.70% Senior Notes, we: • purchased $122.9 million of our 3.70% Senior Notes due 2021 (the “3.70% Notes”) on September 17, 2020 for $126.0 million, plus accrued interest, pursuant to a tender offer; and • redeemed the remaining $177.1 million of the 3.70% Notes on October 19, 2020 for $180.9 million plus accrued interest. In connection with this purchase and redemption, we recognized a loss on early extinguishment of debt of $7.3 million in 2020. We may redeem our unsecured senior notes, in whole at any time or in part from time to time, at our option, at a redemption price equal to the greater of (1) the aggregate principal amount of the notes being redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest thereon (not including any portion of such payments of interest accrued as of the date of redemption) discounted to its present value, on a semi-annual basis at an adjusted treasury rate plus a spread (30 basis points for the 3.60% Senior Notes, 40 basis points for the 5.25% Senior Notes, 45 basis points for the 5.00% Senior Notes and 35 basis points for the 2.25% Senior Notes), plus, in each case, accrued and unpaid interest thereon to the date of redemption. However, in each case, if this redemption occurs on or after a defined period of time prior to the maturity date (one month for the 2.25% Notes or three months for the other notes), the redemption price will be equal to 100% of the principal amount of the notes being redeemed, plus accrued and unpaid interest thereon to, but not including, the applicable redemption date. These notes are unconditionally guaranteed by COPT.

Interest Rate Derivatives

Interest Rate Derivatives	12 Months Ended
	Dec. 31, 2020
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): Notional Amount Effective Date Expiration Date Fair Value at December 31, Fixed Rate Floating Rate Index 2020 2019 $ 100,000 1.901 % One-Month LIBOR 9/1/2016 12/1/2022 $ (3,394) $ (1,028) 100,000 1.905 % One-Month LIBOR 9/1/2016 12/1/2022 (3,401) (1,037) 50,000 1.908 % One-Month LIBOR 9/1/2016 12/1/2022 (1,704) (524) 11,200 (1) 1.678 % One-Month LIBOR 8/1/2019 8/1/2026 (733) (20) 23,000 (2) 0.573 % One-Month LIBOR 4/1/2020 3/26/2025 (290) — 75,000 (3) 3.176 % Three-Month LIBOR 6/30/2020 N/A — (8,640) 75,000 (3) 3.192 % Three-Month LIBOR 6/30/2020 N/A — (8,749) 75,000 (3) 2.744 % Three-Month LIBOR 6/30/2020 N/A — (5,684) — 1.390 % One-Month LIBOR 10/13/2015 10/1/2020 — 23 $ (9,522) $ (25,659) (1) The notional amount of this instrument is scheduled to amortize to $10.0 million. (2) The notional amount of this instrument is scheduled to amortize to $22.1 million. (3) As discussed below, these instruments were cash settled in September 2020. 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 December 31, Derivatives Balance Sheet Location 2020 2019 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets, net $ — $ 23 Interest rate swaps designated as cash flow hedges Interest rate derivatives (liabilities) $ (9,522) $ (25,682) The tables below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): Amount of Loss Recognized in AOCL on Derivatives Amount of (Loss) Gain Reclassified from AOCL into Interest Expense on Statement of Operations For the Years Ended December 31, For the Years Ended December 31, Derivatives in Hedging Relationships 2020 2019 2018 2020 2019 2018 Interest rate derivatives $ (39,454) $ (24,321) $ (2,373) $ (3,725) $ 1,415 $ 407 Amount of Loss Reclassified from AOCL into Loss on Interest Rate Derivatives on Statement of Operations Amount of Loss Recognized on Undesignated Swaps in Loss on Interest Rate Derivatives on Statement of Operations For the Years Ended December 31, For the Years Ended December 31, Derivatives in Hedging Relationships 2020 2019 2018 2020 2019 2018 Interest rate derivatives $ (51,865) $ — — $ (1,265) $ — — As described further in Note 10, in September 2020, we completed our issuance of the 2.25% Notes. In August 2020, in anticipation of pursuing such an issuance, we determined that the forecasted transactions hedged by our three interest rate swaps with an effective date of June 30, 2020 and an aggregate notional amount of $225.0 million were no longer probable of occurring, resulting in our discontinuance of hedge accounting on these swaps. When we consummated the note issuance in September 2020, we determined that it was probable that the forecasted transactions would not occur, resulting in our reclassification of $51.9 million in losses from AOCL to loss on interest rate derivatives on our statements of operations. On September 22, 2020, we cash settled these swaps and accrued interest thereon for an aggregate amount of $53.1 million. Based on the fair value of our derivatives as of December 31, 2020, we estimate that approximately $4.8 million of losses will be reclassified from AOCL as an increase to interest expense over the next 12 months. We have agreements with each of our interest rate derivative counterparties that contain provisions under which, if we default or are capable of being declared in default on defined levels of our indebtedness, we could also be declared in default on our derivative obligations. Failure to comply with the loan covenant provisions could result in our being declared in default on any derivative instrument obligations covered by the agreements. As of December 31, 2020, we were not in default with any of these provisions. As of December 31, 2020, the fair value of interest rate derivatives in a liability position related to these agreements was $9.6 million, excluding the effects of accrued interest and credit valuation adjustments. As of December 31, 2020, we had not posted any collateral related to these agreements. If we breach any of these provisions, we could be required to settle our obligations under the agreements at their termination value, which was $10.0 million as of December 31, 2020.

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interests	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interests	Redeemable Noncontrolling InterestsAs discussed further in Note 6, our partners in two real estate joint ventures, LW Redstone Company, LLC and Stevens Investors, LLC, 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. The table below sets forth the activity for these redeemable noncontrolling interests (in thousands): For the Years Ended December 31, 2020 2019 2018 Beginning balance $ 29,431 $ 26,260 $ 23,125 Contributions from noncontrolling interests — — 186 Distributions to noncontrolling interests (14,034) (2,413) (1,411) Net income attributable to noncontrolling interests 3,426 3,835 2,523 Adjustment to arrive at fair value of interests 6,607 1,749 1,837 Ending balance $ 25,430 $ 29,431 $ 26,260

Equity - COPT and Subsidiaries

Equity - COPT and Subsidiaries	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity Note [Abstract]
Equity - COPT and Subsidiaries	Equity - COPT and Subsidiaries Preferred Shares As of December 31, 2020, COPT had 25.0 million preferred shares authorized and unissued at $0.01 par value per share. Common Shares In November 2018, COPT established an at-the-market (“ATM”) stock offering program under which it may offer and sell common shares in at-the-market stock offerings having an aggregate gross sales price of up to $300.0 million (the “2018 ATM Program”). Under the 2018 ATM Program, COPT may also, at its discretion, sell common shares under forward equity sales agreements. As of December 31, 2020, COPT had not issued any shares under the 2018 ATM Program. From 2018 to 2020, COPT completed the following share issuances under stock programs no longer in effect: • 1.6 million shares in 2019 for net proceeds of $46.5 million, and 5.9 million shares in 2018 for net proceeds of $172.5 million, under forward equity sale agreements originating on November 2, 2017 to issue shares at an initial gross offering price of $31.00 per share, before underwriting discounts, commissions and offering expenses. The forward sale price received upon physical settlement of the agreements was subject to adjustment on a daily basis based on a floating interest rate factor equal to the overnight bank funding rate less a spread, and was decreased on each of certain dates specified in the agreements during the term of the agreements; and • 992,000 common shares in 2018 at a weighted average price of $30.46 per share under an ATM program established in 2016. Net proceeds from the shares issued totaled $29.8 million, after payment of $0.5 million in commissions to sales agents. COPT contributed the net proceeds from these issuances to COPLP in exchange for an equal number of units in COPLP. Certain holders of COPLP common units converted their units into COPT common shares on the basis of one common share for each common unit in the amount of 14,009 in 2020, 105,039 in 2019 and 1.9 million in 2018. COPT declared dividends per common share of $1.10 in 2020, 2019 and 2018. COPT pays dividends at the discretion of its Board of Trustees. COPT’s ability to pay cash dividends will be dependent upon: (1) the cash flow generated from our operations; (2) cash generated or used by our financing and investing activities; and (3) the annual distribution requirements under the REIT provisions of the Code described in Note 2 and such other factors as the Board of Trustees deems relevant. COPT’s ability to make cash dividends will also be limited by the terms of COPLP’s Partnership Agreement, as well as by limitations imposed by state law. In addition, COPT is prohibited from paying cash dividends in excess of the amount necessary for it to qualify for taxation as a REIT if a default or event of default exists pursuant to the terms of our Revolving Credit Facility; this restriction does not currently limit COPT’s ability to pay dividends, and COPT does not believe that this restriction is reasonably likely to limit its ability to pay future dividends because it expects to comply with the terms of our Revolving Credit Facility. See Note 15 for disclosure of common share activity pertaining to our share-based compensation plans. Limited Partner Preferred Units On December 21, 2020, COPLP redeemed its 352,000 Series I Preferred Units from the third party unitholder at the units’ aggregate liquidation preference of $8.8 million ($25.00 per unit), plus accrued and unpaid distributions of return thereon up to the date of redemption. The owner of these units earned a priority annual cumulative return on the units equal to: 3.5% of their liquidation preference from September 23, 2019 up to the redemption date; and 7.5% of their liquidation preference prior to September 23, 2019. These units were convertible into common units on the basis of 0.5 common units for each Series I Preferred Unit, with the resulting common units being exchangeable for COPT common shares in accordance with the terms of COPLP’s agreement of limited partnership. Common Units COPT owned 98.6% of COPLP’s common units as of December 31, 2020 and 98.7% as of December 31, 2019. From 2018 to 2020, COPT acquired additional common units through the following common share issuances under stock programs no longer in effect: • 1.6 million shares in 2019 for net proceeds of $46.5 million, and 5.9 million shares in 2018 for net proceeds of $172.5 million, under forward equity sale agreements originating on November 2, 2017; and • 992,000 shares in 2018 at a weighted average price of $30.46 per share under an ATM program established in 2016. Net proceeds from the shares issued totaled $29.8 million, after payment of $0.5 million in commissions to sales agents. Limited partners in COPLP holding common units have the right to require COPLP to redeem all or a portion of their common units. COPLP (or COPT as the general partner) has the right, in its sole discretion, to deliver to such redeeming limited partners for each partnership unit either one COPT common share (subject to anti-dilution adjustment) or a cash payment equal to the then fair market value of such share (so adjusted) (based on the formula for determining such value set forth in the partnership agreement). Certain limited partners holding common units redeemed their units into common shares on the basis of one common share for each common unit in the amount of 14,009 in 2020, 105,039 in 2019 and 1.9 million in 2018. In addition, we redeemed 924 common units in 2019 for $25,000 and 13,377 in 2018 for $339,000. COPLP declared distributions per common unit of $1.10 in 2020, 2019 and 2018.

Equity - COPLP and Subsidiaries

Equity - COPLP and Subsidiaries	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity Note [Abstract]
Equity - COPLP and Subsidiaries	Equity - COPT and Subsidiaries Preferred Shares As of December 31, 2020, COPT had 25.0 million preferred shares authorized and unissued at $0.01 par value per share. Common Shares In November 2018, COPT established an at-the-market (“ATM”) stock offering program under which it may offer and sell common shares in at-the-market stock offerings having an aggregate gross sales price of up to $300.0 million (the “2018 ATM Program”). Under the 2018 ATM Program, COPT may also, at its discretion, sell common shares under forward equity sales agreements. As of December 31, 2020, COPT had not issued any shares under the 2018 ATM Program. From 2018 to 2020, COPT completed the following share issuances under stock programs no longer in effect: • 1.6 million shares in 2019 for net proceeds of $46.5 million, and 5.9 million shares in 2018 for net proceeds of $172.5 million, under forward equity sale agreements originating on November 2, 2017 to issue shares at an initial gross offering price of $31.00 per share, before underwriting discounts, commissions and offering expenses. The forward sale price received upon physical settlement of the agreements was subject to adjustment on a daily basis based on a floating interest rate factor equal to the overnight bank funding rate less a spread, and was decreased on each of certain dates specified in the agreements during the term of the agreements; and • 992,000 common shares in 2018 at a weighted average price of $30.46 per share under an ATM program established in 2016. Net proceeds from the shares issued totaled $29.8 million, after payment of $0.5 million in commissions to sales agents. COPT contributed the net proceeds from these issuances to COPLP in exchange for an equal number of units in COPLP. Certain holders of COPLP common units converted their units into COPT common shares on the basis of one common share for each common unit in the amount of 14,009 in 2020, 105,039 in 2019 and 1.9 million in 2018. COPT declared dividends per common share of $1.10 in 2020, 2019 and 2018. COPT pays dividends at the discretion of its Board of Trustees. COPT’s ability to pay cash dividends will be dependent upon: (1) the cash flow generated from our operations; (2) cash generated or used by our financing and investing activities; and (3) the annual distribution requirements under the REIT provisions of the Code described in Note 2 and such other factors as the Board of Trustees deems relevant. COPT’s ability to make cash dividends will also be limited by the terms of COPLP’s Partnership Agreement, as well as by limitations imposed by state law. In addition, COPT is prohibited from paying cash dividends in excess of the amount necessary for it to qualify for taxation as a REIT if a default or event of default exists pursuant to the terms of our Revolving Credit Facility; this restriction does not currently limit COPT’s ability to pay dividends, and COPT does not believe that this restriction is reasonably likely to limit its ability to pay future dividends because it expects to comply with the terms of our Revolving Credit Facility. See Note 15 for disclosure of common share activity pertaining to our share-based compensation plans. Limited Partner Preferred Units On December 21, 2020, COPLP redeemed its 352,000 Series I Preferred Units from the third party unitholder at the units’ aggregate liquidation preference of $8.8 million ($25.00 per unit), plus accrued and unpaid distributions of return thereon up to the date of redemption. The owner of these units earned a priority annual cumulative return on the units equal to: 3.5% of their liquidation preference from September 23, 2019 up to the redemption date; and 7.5% of their liquidation preference prior to September 23, 2019. These units were convertible into common units on the basis of 0.5 common units for each Series I Preferred Unit, with the resulting common units being exchangeable for COPT common shares in accordance with the terms of COPLP’s agreement of limited partnership. Common Units COPT owned 98.6% of COPLP’s common units as of December 31, 2020 and 98.7% as of December 31, 2019. From 2018 to 2020, COPT acquired additional common units through the following common share issuances under stock programs no longer in effect: • 1.6 million shares in 2019 for net proceeds of $46.5 million, and 5.9 million shares in 2018 for net proceeds of $172.5 million, under forward equity sale agreements originating on November 2, 2017; and • 992,000 shares in 2018 at a weighted average price of $30.46 per share under an ATM program established in 2016. Net proceeds from the shares issued totaled $29.8 million, after payment of $0.5 million in commissions to sales agents. Limited partners in COPLP holding common units have the right to require COPLP to redeem all or a portion of their common units. COPLP (or COPT as the general partner) has the right, in its sole discretion, to deliver to such redeeming limited partners for each partnership unit either one COPT common share (subject to anti-dilution adjustment) or a cash payment equal to the then fair market value of such share (so adjusted) (based on the formula for determining such value set forth in the partnership agreement). Certain limited partners holding common units redeemed their units into common shares on the basis of one common share for each common unit in the amount of 14,009 in 2020, 105,039 in 2019 and 1.9 million in 2018. In addition, we redeemed 924 common units in 2019 for $25,000 and 13,377 in 2018 for $339,000. COPLP declared distributions per common unit of $1.10 in 2020, 2019 and 2018.

Share-Based Compensation and Ot

Share-Based Compensation and Other Compensation Matters	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Share-Based Compensation and Other Compensation Matters	Share-Based Compensation and Other Compensation Matters Share-Based Compensation Plans In May 2017, COPT adopted the 2017 Omnibus Equity and Incentive Plan (the “2017 Plan”) following the approval of such plan by our common shareholders. COPT may issue equity-based awards under this plan to officers, employees, non-employee trustees and any other key persons of us and our subsidiaries, as defined in the plan. The plan provides for a maximum of 3.4 million common shares in COPT to be issued in the form of options, share appreciation rights, restricted share unit awards, restricted share awards, unrestricted share awards, dividend equivalent rights and other equity-based awards and for the granting of cash-based awards. In November 2018, we amended the 2017 Plan to provide for the future grant of awards in the form of PIUs; PIUs are a special class of common unit structured to qualify as “profit interests” for tax purposes which are similar to restricted shares and PSUs, except that upon vesting recipients will receive common units in COPLP. This plan expires on May 11, 2027. Shares for the 2017 Plan are issued under a registration statement on Form S-8 that became effective upon filing with the Securities and Exchange Commission. In connection with awards of common shares granted by COPT under the 2017 Plan, COPLP issues to COPT an equal number of equity instruments with identical terms. The table below sets forth our reporting for share based compensation cost (in thousands): For the Years Ended December 31, 2020 2019 2018 General, administrative and leasing expenses $ 5,385 $ 5,748 $ 5,415 Property operating expenses 1,119 966 961 Capitalized to development activities 556 742 587 Share-based compensation cost $ 7,060 $ 7,456 $ 6,963 The amounts included in our consolidated statements of operations for share-based compensation reflected an estimate of pre-vesting forfeitures of 0% for PSUs, PIUs and deferred share awards and 0% to 8% for restricted shares. As of December 31, 2020, unrecognized compensation costs related to unvested awards included: • $5.6 million on restricted shares expected to be recognized over a weighted average period of approximately two years; • $2.2 million on performance-based PIUs (“PB-PIUs”) expected to be recognized over a weighted average performance period of approximately two years; • $2.1 million on time-based PIUs (“TB-PIUs”) expected to be recognized over a weighted average period of approximately three years; and • $121,000 on deferred share awards expected to be recognized through October 2021. Restricted Shares The following table summarizes restricted shares under the share-based compensation plans for 2018, 2019 and 2020: Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2017 425,626 $ 30.37 Granted 219,716 25.62 Forfeited (25,419) 30.02 Vested (181,238) 29.49 Unvested as of December 31, 2018 438,685 28.38 Granted 195,520 26.56 Forfeited (56,341) 29.44 Vested (185,001) 28.01 Unvested as of December 31, 2019 392,863 27.49 Granted 166,918 25.22 Forfeited (25,773) (1) 27.12 Vested (173,191) 28.14 Unvested as of December 31, 2020 360,817 $ 26.16 Unvested shares as of December 31, 2020 that are expected to vest 330,605 $ 26.14 (1) Includes 9,064 restricted shares previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. 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 employee remains employed by us. Restricted shares granted to non-employee Trustees vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. The aggregate intrinsic value of restricted shares that vested was $4.4 million in 2020, $4.9 million in 2019 and $4.6 million in 2018. PIUs Commencing in 2019, we offered our executives and Trustees the opportunity to select PIUs as a form of long-term compensation in lieu of, or in combination with, other forms of share-based compensation awards (restricted shares, deferred share awards and PSUs). Our executives and certain of our Trustees selected PIUs as their form of share-based compensation for their 2019 and 2020 grants. We granted two forms of PIUs: TB-PIUs; and PB-PIUs. TB-PIUs are subject to forfeiture restrictions until the end of the requisite service period, at which time the TB-PIUs automatically convert into vested PIUs. PB-PIUs are subject to a market condition in that the number of earned awards are determined at the end of the performance period (as described further below) and then settled in vested PIUs. Vested PIUs carry substantially the same rights to redemption and distributions as non-PIU common units. TB-PIUs TB-PIUs granted to executives vest based on increments and over periods of time set forth under the terms of the respective awards provided that the employee remains employed by us. TB-PIUs granted to non-employee Trustees vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. Prior to vesting, TB-PIUs carry substantially the same rights to distributions as non-PIU common units but carry no redemption rights. The following table summarizes TB-PIUs under the share-based compensation plan for 2019 and 2020 : Number of TB-PIUs Weighted Average Grant Date Fair Value Unvested as of December 31, 2018 — N/A Granted 61,820 $ 26.01 Unvested as of December 31, 2019 61,820 26.01 Granted 98,318 25.47 Forfeited (20,622) (1) 25.50 Vested (25,182) 26.30 Unvested as of December 31, 2020 114,334 $ 25.57 Unvested TB-PIUs as of December 31, 2020 that are expected to vest 114,334 $ 25.57 (1) Represents TB-PIUs previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. The aggregate intrinsic value of TB-PIUs that vested was $640,000 in 2020. PB-PIUs We made the following grants of PB-PIUs to executives in 2019 and 2020 : (dollars in thousands, except per share data): Grant Date Number of PB-PIUs Granted Performance Period Commencement Date Performance Period End Date Grant Date Fair Value Number of PB-PIUs Outstanding as of December 31, 2020 (1) 1/1/2019 193,682 1/1/2019 12/31/2021 $ 2,415 156,104 1/1/2020 176,758 1/1/2020 12/31/2022 $ 2,891 141,152 (1) Excludes 73,184 PB-PIUs previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. The PB-PIUs each have a three-year performance period concluding on the earlier of the respective performance period end dates, 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 earned awards at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return (“TSR”) relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned Awards Payout % 75th or greater 100% of PB-PIUs granted 50th (target) 50% of PB-PIUs granted 25th 25% of PB-PIUs granted Below 25th 0% of PB-PIUs 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 awards will be interpolated between the ranges set forth in the table above to reflect any performance between the listed percentiles. If COPT’s TSR during the measurement period is negative, the maximum number of earned awards will be limited to the target level payout percentage. During the performance period, PB-PIUs carry rights to distributions equal to 10% of the distribution rights of non-PIU common units but carry no redemption rights. At the end of the performance period, we will settle the award by issuing vested PIUs equal to the number of earned awards in settlement of the award plan and paying cash equal to the excess, if any, of: the aggregate distributions that would have been paid with respect to vested PIUs issued in settlement of the earned awards through the date of settlement had such vested PIUs been issued on the grant date; over the aggregate distributions made on the PB-PIUs during the performance period. If a performance period ends due to a sale event or qualified termination, the number of earned awards 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 PB-PIUs are forfeited. We computed grant date fair values for PB-PIUs using Monte Carlo models and are recognizing these values over the respective performance periods. The grant date fair value and certain of the assumptions used in the Monte Carlo models for the PB-PIUs granted in 2019 and 2020 are set forth below: Grant Date Grant Date Fair Value Per PB-PIU Baseline Common Share Value Expected Volatility of Common Shares Risk-free Interest Rate 1/1/2019 $ 12.47 $ 21.03 21.0 % 2.51 % 1/1/2020 $ 16.36 $ 29.38 18.0 % 1.65 % PSUs We made the following grants of PSUs to executives from 2016 through 2018 (dollars in thousands): Grant Date Number of PSUs Granted Performance Period Commencement Date Performance Period End Date Grant Date Fair Value Number of PSUs Outstanding as of December 31, 2020 3/1/2016 26,299 1/1/2016 12/31/2018 $ 1,005 — 1/1/2017 39,351 1/1/2017 12/31/2019 $ 1,415 — 1/1/2018 59,110 1/1/2018 12/31/2020 $ 1,890 46,912 (1) (1) Excludes 12,198 PSUs previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. The PSUs each had three-year performance periods concluding on the earlier of the respective performance period end dates set forth above 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 were determined based on the percentile rank of COPT’s TSR 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 (target) 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted If the percentile rank exceeded the 25th percentile and was between two of the percentile ranks set forth in the table above, then the percentage of the earned PSUs was 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 settled the award by issuing fully-vested COPT shares equal to the number of earned PSUs in settlement of the award plan and either: • for awards granted January 1, 2017 and prior thereto, issuing fully-vested COPT shares 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, divided by the share price on such settlement date, as defined under the terms of the agreement; or • for awards issued subsequent to January 1, 2017, paying 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 was prorated based on the portion of the three-year performance period that had elapsed. If employment was terminated by the employee or by us for cause, all PSUs were forfeited. PSUs do not carry voting rights. Based on COPT’s TSR relative to its peer group of companies: • for the 2016 PSUs issued to executives that vested on December 31, 2018, we issued 44,757 common shares in settlement of the PSUs on January 18, 2019; • for the 2017 PSUs issued to executives that vested on December 31, 2019, we issued 23,181 common shares in settlement of the PSUs on January 13, 2020; and • for the 2018 PSUs issued to executives that vested on December 31, 2020, we issued 93,824 common shares in settlement of the PSUs on February 3, 2021. We computed grant date fair values for PSUs using Monte Carlo models and recognized these values over the performance periods. The 2018 grant date fair value of $31.97 was computed using a Monte Carlo model that included the following assumptions: baseline common share value of $29.20; expected volatility for common shares of 17.0%; and a risk-free interest rate of 2.04%. Deferred Share Awards We made the following grants of deferred share awards to nonemployee members of our Board of Trustees in 2018, 2019 and 2020 (dollars in thousands, except per share data): Year of Grant Number of Deferred Share Awards Granted Aggregate Grant Date Fair Value Grant Date Fair Value Per Share 2018 13,832 $ 388 $ 28.08 2019 3,432 $ 95 $ 27.60 2020 10,679 $ 253 $ 23.68 Deferred share awards vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. We settle deferred share awards by issuing an equivalent number of common shares upon vesting of the awards or a later date elected by the Trustee (generally upon cessation of being a Trustee). We issued the following common shares in settlement of deferred shares in 2018, 2019 and 2020 (dollars in thousands, except per share data): Year of Settlement Number of Common Shares Issued Grant Date Fair Value Per Share Aggregate Intrinsic Value 2018 5,515 $ 29.32 $ 154 2019 3,097 $ 26.77 $ 86 2020 — N/A N/A

Credit Losses, Financial Assets

Credit Losses, Financial Assets and Other Instruments	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Credit Losses, Financial Assets and Other Instruments	Credit Losses, Financial Assets and Other Instruments The table below sets forth the activity for the allowance for credit losses (in thousands): For the Year Ended December 31, 2020 Investing Receivables Tenant Notes Other Assets (2) Off-Balance Sheet Credit Exposures Total December 31, 2019 $ — $ 97 $ — $ — $ 97 Cumulative effect of change for adoption of credit loss guidance 3,732 325 144 1,340 5,541 Credit loss (recoveries) expense (881) 729 559 (1,340) (933) Other changes — 52 (60) — (8) December 31, 2020 $ 2,851 $ 1,203 $ 643 $ — $ 4,697 (1) Included in the line entitled “accounts receivable, net” on our consolidated balance sheets. (2) The balance as of December 31, 2020 included $257,000 in the line entitled “accounts receivable, net” and $386,000 in the line entitled “prepaid expenses and other assets, net” on our consolidated balance sheets. The following table presents the amortized cost basis of our investing receivables and tenants notes receivable by credit risk classification, by origination year as of December 31, 2020 (in thousands): Origination Year 2015 and Earlier 2016 2017 2018 2019 2020 Total Investing receivables: Credit risk classification: Investment grade $ 64,354 $ — $ 971 $ — $ — $ 239 $ 65,564 Non-investment grade — — — — 6,041 — 6,041 Total $ 64,354 $ — $ 971 $ — $ 6,041 $ 239 $ 71,605 Tenant notes receivable: Credit risk classification: Investment grade $ — $ 14 $ — $ 1,028 $ 84 $ 343 $ 1,469 Non-investment grade 97 165 — 164 1,883 1,803 4,112 Total $ 97 $ 179 $ — $ 1,192 $ 1,967 $ 2,146 $ 5,581 Sales-type lease receivable: Credit risk classification: Investment grade $ — $ — $ — $ — $ — $ 6,573 $ 6,573 Our investment grade credit risk classification represents entities with investment grade credit ratings from ratings agencies (such as Standard & Poor’s Ratings Services, Moody’s Investors Service, Inc. or Fitch Ratings Ltd.), meaning that they are considered to have at least an adequate capacity to meet their financial commitments, with credit risk ranging from minimal to moderate. Our non-investment grade credit risk classification represents entities with either no credit agency credit ratings or ratings deemed to be sub-investment grade; we believe that there is significantly more credit risk associated with this classification. The credit risk classifications of our investing receivables and tenant notes receivable were last updated in December 2020. An insignificant portion of the investing and tenant notes receivables set forth above was past due, which we define as being delinquent by more than three months from the due date.

Information by Business Segment

Information by Business Segment	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Information by Business Segment	Information by Business SegmentWe 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 (“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 fund the costs for the power, fiber connectivity and data center infrastructure). We measure the performance of our segments through the measure we define as net operating income from real estate operations (“NOI from real estate operations”), which includes: real estate revenues and property operating expenses; and the net of revenues and property operating expenses of real estate operations owned through unconsolidated real estate joint ventures (“UJVs”) that is allocable to COPT’s ownership interest (“UJV NOI allocable to COPT”). Amounts reported for segment assets represent long-lived assets associated with consolidated operating properties (including the carrying value of properties, right-of-use assets, net of related lease liabilities, 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 Operating Other Total Year Ended December 31, 2020 Revenues from real estate operations $ 254,197 $ 57,817 $ 50,982 $ 32,869 $ 22,515 $ 29,139 $ 447,519 $ 60,627 $ 27,788 $ 2,791 $ 538,725 Property operating expenses (85,032) (21,321) (29,055) (12,655) (8,119) (3,195) (159,377) (29,144) (14,171) (1,148) (203,840) UJV NOI allocable to COPT — — — — — 6,951 6,951 — — — 6,951 NOI from real estate operations $ 169,165 $ 36,496 $ 21,927 $ 20,214 $ 14,396 $ 32,895 $ 295,093 $ 31,483 $ 13,617 $ 1,643 $ 341,836 Additions to long-lived assets $ 31,295 $ 11,620 $ — $ 7,104 $ 2,905 $ — $ 52,924 $ 17,232 $ 11,158 $ 165 $ 81,479 Transfers from non-operating properties $ 21,859 $ 2,557 $ 456 $ — $ 138,122 $ 230,277 $ 393,271 $ 83,091 $ — $ — $ 476,362 Segment assets at December 31, 2020 $ 1,277,849 $ 392,714 $ 142,137 $ 178,897 $ 281,386 $ 419,929 $ 2,692,912 $ 490,422 $ 202,089 $ 3,555 $ 3,388,978 Year Ended December 31, 2019 Revenues from real estate operations $ 252,781 $ 55,742 $ 51,140 $ 32,659 $ 16,593 $ 26,571 $ 435,486 $ 59,611 $ 29,405 $ 2,961 $ 527,463 Property operating expenses (82,815) (19,779) (29,042) (13,579) (6,626) (1,962) (153,803) (29,682) (13,213) (1,445) (198,143) UJV NOI allocable to COPT — — — — — 5,705 5,705 — — — 5,705 NOI from real estate operations $ 169,966 $ 35,963 $ 22,098 $ 19,080 $ 9,967 $ 30,314 $ 287,388 $ 29,929 $ 16,192 $ 1,516 $ 335,025 Additions to long-lived assets $ 34,618 $ 9,326 $ — $ 8,912 $ 1,548 $ — $ 54,404 $ 20,925 $ 893 $ 128 $ 76,350 Transfers from non-operating properties $ 18,606 $ 4,548 $ 10,781 $ — $ 33,606 $ 159,472 $ 227,013 $ — $ (1,012) $ — $ 226,001 Segment assets at December 31, 2019 $ 1,280,656 $ 396,914 $ 146,592 $ 184,257 $ 138,501 $ 279,099 $ 2,426,019 $ 392,319 $ 202,935 $ 3,685 $ 3,024,958 Year Ended December 31, 2018 Revenues from real estate operations $ 248,927 $ 53,518 $ 46,286 $ 31,927 $ 14,745 $ 25,650 $ 421,053 $ 61,181 $ 31,892 $ 3,127 $ 517,253 Property operating expenses (82,975) (20,330) (26,888) (13,536) (6,050) (3,225) (153,004) (30,253) (16,342) (1,436) (201,035) UJV NOI allocable to COPT — — — — — 4,818 4,818 — — — 4,818 NOI from real estate operations $ 165,952 $ 33,188 $ 19,398 $ 18,391 $ 8,695 $ 27,243 $ 272,867 $ 30,928 $ 15,550 $ 1,691 $ 321,036 Additions to long-lived assets $ 38,612 $ 7,956 $ — $ 6,535 $ 573 $ — $ 53,676 $ 19,730 $ 856 $ 480 $ 74,742 Transfers from non-operating properties $ 35,648 $ 10,231 $ 14,718 $ (116) $ 4,167 $ 99,191 $ 163,839 $ — $ 2,304 $ — $ 166,143 Segment assets at December 31, 2018 $ 1,279,571 $ 399,339 $ 139,731 $ 188,911 $ 108,010 $ 353,165 $ 2,468,727 $ 395,380 $ 216,640 $ 4,115 $ 3,084,862 The following table reconciles our segment revenues to total revenues as reported on our consolidated statements of operations (in thousands): For the Years Ended December 31, 2020 2019 2018 Segment revenues from real estate operations $ 538,725 $ 527,463 $ 517,253 Construction contract and other service revenues 70,640 113,763 60,859 Total revenues $ 609,365 $ 641,226 $ 578,112 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 Years Ended December 31, 2020 2019 2018 UJV NOI allocable to COPT $ 6,951 $ 5,705 $ 4,818 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (5,120) (4,065) (3,314) Add: Equity in (loss) income of unconsolidated non-real estate entities (6) (7) 1,193 Equity in income of unconsolidated entities $ 1,825 $ 1,633 $ 2,697 As previously discussed, we provide real estate services such as property management, development and construction 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 Years Ended December 31, 2020 2019 2018 Construction contract and other service revenues $ 70,640 $ 113,763 $ 60,859 Construction contract and other service expenses (67,615) (109,962) (58,326) NOI from service operations $ 3,025 $ 3,801 $ 2,533 The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to net income as reported on our consolidated statements of operations (in thousands): For the Years Ended December 31, 2020 2019 2018 NOI from real estate operations $ 341,836 $ 335,025 $ 321,036 NOI from service operations 3,025 3,801 2,533 Interest and other income 8,574 7,894 4,358 Credit loss recoveries 933 — — Gain on sales of real estate 30,209 105,230 2,340 Gain on sale of investment in unconsolidated real estate joint venture 29,416 — — Equity in income of unconsolidated entities 1,825 1,633 2,697 Income tax (expense) benefit (353) 217 363 Depreciation and other amortization associated with real estate operations (138,193) (137,069) (137,116) Impairment losses (1,530) (329) (2,367) General, administrative and leasing expenses (33,001) (35,402) (28,900) Business development expenses and land carry costs (4,473) (4,239) (5,840) Interest expense (67,937) (71,052) (75,385) UJV NOI allocable to COPT included in equity in income of unconsolidated entities (6,951) (5,705) (4,818) Loss on early extinguishment of debt (7,306) — (258) Loss on interest rate derivatives (53,196) — — Net income $ 102,878 $ 200,004 $ 78,643 The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): As of December 31, 2020 2019 Segment assets $ 3,388,978 $ 3,024,958 Operating properties lease liabilities included in segment assets 30,721 17,317 Non-operating property assets 466,991 621,630 Other assets 190,333 190,548 Total COPT consolidated assets $ 4,077,023 $ 3,854,453 The accounting policies of the segments are the same as those used to prepare our consolidated financial statements. In the segment reporting presented above, we did not allocate interest expense, depreciation and amortization, impairment losses, gain on sales of real estate, gain on sale of investment in unconsolidated real estate joint venture, loss on early extinguishment of debt, loss on interest rate derivatives 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, credit loss recoveries (expense), income taxes and noncontrolling interests because these items represent general corporate or non-operating property items not attributable to segments.

Construction Contract and Other

Construction Contract and Other Service Revenues	12 Months Ended
	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Construction Contract and Other Service Revenues	Construction Contract and Other Service Revenues 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 Years Ended December 31, 2020 2019 2018 Construction contract revenue: GMP $ 22,032 $ 67,708 $ 34,050 Cost-plus fee 34,025 34,386 5,540 FFP 12,373 10,688 20,327 Other 2,210 981 942 $ 70,640 $ 113,763 $ 60,859 The table below reports construction contract and other service revenues by service type (in thousands): For the Years Ended December 31, 2020 2019 2018 Construction contract revenue: Construction $ 66,087 $ 112,170 $ 57,986 Design 2,343 612 1,931 Other 2,210 981 942 $ 70,640 $ 113,763 $ 60,859 We derived 55% of our construction contract revenue from the USG in 2020, 74% in 2019 and 95% in 2018. We recognized an insignificant amount of revenue in 2020, 2019 and 2018 from performance obligations satisfied (or partially satisfied) in previous periods. 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 Years Ended December 31, 2020 2019 Beginning balance $ 12,378 $ 6,701 Ending balance $ 13,997 $ 12,378 Contract assets, which we refer to herein as construction contract 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 Years Ended December 31, 2020 2019 Beginning balance $ 17,223 $ 3,189 Ending balance $ 10,343 $ 17,223 Contract liabilities are included in other liabilities reported on our consolidated balance sheets. Changes in contract liabilities were as follows (in thousands): For the Years Ended December 31, 2020 2019 Beginning balance $ 1,184 $ 568 Ending balance $ 4,610 $ 1,184 Portion of beginning balance recognized in revenue during the year $ 757 $ 446

Earnings Per Share ("EPS") and

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”)	12 Months Ended
	Dec. 31, 2020
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 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, redeemable noncontrolling interests 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 add 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 Years Ended December 31, 2020 2019 2018 Numerator: Net income attributable to COPT $ 97,374 $ 191,692 $ 72,301 Income attributable to share-based compensation awards (431) (656) (462) Numerator for basic EPS on net income attributable to COPT common shareholders $ 96,943 $ 191,036 $ 71,839 Redeemable noncontrolling interests — 132 — Income attributable to share-based compensation awards 27 33 — Numerator for diluted EPS on net income attributable to COPT common shareholders $ 96,970 $ 191,201 $ 71,839 Denominator (all weighted averages): Denominator for basic EPS (common shares) 111,788 111,196 103,946 Dilutive effect of redeemable noncontrolling interests — 119 — Dilutive effect of share-based compensation awards 288 308 134 Dilutive effect of forward equity sale agreements — — 45 Denominator for diluted EPS (common shares) 112,076 111,623 104,125 Basic EPS $ 0.87 $ 1.72 $ 0.69 Diluted EPS $ 0.87 $ 1.71 $ 0.69 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 Years Ended December 31, 2020 2019 2018 Conversion of common units 1,236 1,299 2,468 Conversion of redeemable noncontrolling interests 957 896 936 Conversion of Series I Preferred Units 171 176 176 The following securities were also excluded from the computation of diluted EPS because their effect was antidilutive: • weighted average restricted shares and deferred share awards of 430,000 for 2020, 441,000 for 2019 and 452,000 for 2018; • weighted average unvested TB-PIUs of 89,000 for 2020 and 51,000 for 2019; • weighted average options of 12,000 for 2019 and 42,000 for 2018; and • weighted average shares related to COPT’s forward equity sale agreements of 376,000 for 2019. 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, redeemable noncontrolling interests 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 add 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 Years Ended December 31, 2020 2019 2018 Numerator: Net income attributable to COPLP $ 98,854 $ 194,619 $ 74,703 Preferred unit distributions (300) (564) (660) Income attributable to share-based compensation awards (511) (785) (462) Numerator for basic EPU on net income attributable to COPLP common unitholders 98,043 193,270 73,581 Redeemable noncontrolling interests — 132 — Income attributable to share-based compensation awards — 33 — Numerator for diluted EPU on net income attributable to COPLP common unitholders $ 98,043 $ 193,435 $ 73,581 Denominator (all weighted averages): Denominator for basic EPU (common units) 113,024 112,495 106,414 Dilutive effect of redeemable noncontrolling interests — 119 — Dilutive effect of share-based compensation awards 288 308 134 Dilutive effect of forward equity sale agreements — — 45 Denominator for diluted EPU (common units) 113,312 112,922 106,593 Basic EPU $ 0.87 $ 1.72 $ 0.69 Diluted EPU $ 0.87 $ 1.71 $ 0.69 Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator for the Years Ended December 31, 2020 2019 2018 Conversion of redeemable noncontrolling interests 957 896 936 Conversion of Series I Preferred Units 171 176 176 The following securities were also excluded from the computation of diluted EPU because their effect was antidilutive: • weighted average restricted units and deferred share awards of 430,000 for 2020, 441,000 for 2019 and 452,000 for 2018; • weighted average unvested TB-PIUs of 89,000 for 2020 and 51,000 for 2019; • weighted average options of 12,000 for 2019 and 42,000 for 2018; and • weighted average shares related to COPT’s forward equity sale agreements of 376,000 for 2019.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
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. As of December 31, 2020, management believes that it is reasonably possible that we could recognize a loss of up to $3.1 million for certain municipal tax claims. While we do not believe this loss would materially affect our financial position or liquidity, it could be material to our results of operations. Management believes that it is also reasonably possible that we could incur losses pursuant to other such claims but do not believe such losses would materially affect our financial position, liquidity or 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 Anne Arundel County, Maryland issued tax incremental financing bonds to third-party investors in order to finance public improvements needed in connection with our project known as the National Business Park. These bonds had a remaining principal balance of approximately $33 million as of December 31, 2020. The real estate taxes on increases in assessed values post-bond issuance of properties in development districts encompassing the National Business Park are transferred to a special fund pledged to the repayment of the bonds. While we are obligated to fund, through a special tax, any future shortfalls between debt service of the bonds and real estate taxes available to repay the bonds, as of December 31, 2020, we do not expect any such future fundings will be required. Effects of COVID-19 Since first being declared a pandemic by the World Health Organization in early March 2020, the coronavirus, or COVID-19, has spread worldwide. In an effort to control its spread, governments and other authorities imposed restrictive measures affecting freedom of movement and business operations, such as shelter-in-place orders and business closures. Strong restrictive measures were put into place in much of the United States beginning in March 2020, bringing many businesses to a halt while forcing others to change the way in which they conduct their operations, with much of the workforce working from their homes to the extent they were able. States and local governments began easing these measures to varying extents in late April 2020, with some lifting restrictive measures entirely, while others chose a more gradual, extended easing approach. While the easing of these measures enabled many businesses to gradually resume normal operations, most businesses continue to be hindered to varying extents by either measures still in effect, operational challenges resulting from social distancing requirements/expectations and/or a reluctance by much of the population to engage in certain activities while the pandemic is still active. As of the date of this filing, COVID-19 spread continues world- and nation-wide, and is expected to continue until vaccinations have been administered to much of the population, which is not expected to occur in the United States until at least mid- to late 2021. As a result, there continues to be significant uncertainty regarding the duration and extent of this pandemic. The outbreak significantly disrupted financial and economic markets worldwide, as well as in the United States at a national, regional and local level. These conditions could continue or further deteriorate as businesses feel the prolonged effects of stalled or reduced operations and uncertainty regarding the pandemic continues. COVID-19, and any similar pandemics should they occur, along with measures instituted to prevent spread, may adversely affect us in many ways, including, but not limited to: • disruption of our tenants’ operations, which could adversely affect their ability, or willingness, to sustain their businesses and/or fulfill their lease obligations; • our ability to maintain occupancy in our properties and obtain new leases for unoccupied and new development space at favorable terms or at all; • shortages in supply of products or services from our and our tenants’ vendors that are needed for us and our tenants to operate effectively, and which could lead to increased costs for such products and services; • access to debt and equity capital on attractive terms or at all. Severe disruption and instability in the global financial markets or deteriorations in credit and financing conditions may affect our or our tenants’ ability to access capital necessary to fund operations, refinance debt or fund planned investments on a timely basis, and may adversely affect the valuation of financial assets and liabilities; • our and our tenants’ ability to continue or complete planned development, including the potential for delays in the supply of materials or labor necessary for development; and • an increase in the pace of businesses implementing remote work arrangements over the long-term, which would adversely effect demand for office space.

Schedule III - Real Estate and

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III-Real Estate and Accumulated Depreciation	Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) 100 Light Street (O) Baltimore, MD $ 46,543 $ 26,715 $ 58,002 $ 21,859 $ 26,715 $ 79,861 $ 106,576 $ (20,981) 1973/2011 8/7/2015 100 Secured Gateway (O) Huntsville, AL — — 70,552 — — 70,552 70,552 (566) 2020 3/23/2010 1000 Redstone Gateway (O) Huntsville, AL 9,666 — 20,533 65 — 20,598 20,598 (4,007) 2013 3/23/2010 1100 Redstone Gateway (O) Huntsville, AL 10,263 — 19,593 66 — 19,659 19,659 (3,418) 2014 3/23/2010 114 National Business Parkway (O) Annapolis Junction, MD — 364 3,109 302 364 3,411 3,775 (1,584) 2002 6/30/2000 1200 Redstone Gateway (O) Huntsville, AL 11,851 — 22,389 60 — 22,449 22,449 (3,945) 2013 3/23/2010 1201 M Street SE (O) Washington, DC — — 49,785 9,621 — 59,406 59,406 (19,011) 2001 9/28/2010 1201 Winterson Road (O) Linthicum, MD — 2,130 17,007 901 2,130 17,908 20,038 (5,506) 1985/2017 4/30/1998 1220 12th Street SE (O) Washington, DC — — 42,464 8,795 — 51,259 51,259 (17,812) 2003 9/28/2010 1243 Winterson Road (L) Linthicum, MD — 630 — — 630 — 630 — (6) 12/19/2001 131 National Business Parkway (O) Annapolis Junction, MD — 1,906 7,623 5,075 1,906 12,698 14,604 (7,442) 1990 9/28/1998 132 National Business Parkway (O) Annapolis Junction, MD — 2,917 12,259 4,730 2,917 16,989 19,906 (10,566) 2000 5/28/1999 133 National Business Parkway (O) Annapolis Junction, MD — 2,517 10,068 6,274 2,517 16,342 18,859 (10,443) 1997 9/28/1998 134 National Business Parkway (O) Annapolis Junction, MD — 3,684 7,517 5,007 3,684 12,524 16,208 (7,329) 1999 11/13/1998 1340 Ashton Road (O) Hanover, MD — 905 3,620 2,042 905 5,662 6,567 (3,255) 1989 4/28/1999 13450 Sunrise Valley Drive (O) Herndon, VA — 1,386 5,576 4,636 1,386 10,212 11,598 (6,156) 1998 7/25/2003 13454 Sunrise Valley Drive (O) Herndon, VA — 2,847 11,986 9,184 2,847 21,170 24,017 (12,075) 1998 7/25/2003 135 National Business Parkway (O) Annapolis Junction, MD — 2,484 9,750 6,528 2,484 16,278 18,762 (10,164) 1998 12/30/1998 1362 Mellon Road (O) Hanover, MD — 950 3,864 1,065 950 4,929 5,879 (854) 2006 2/10/2006 13857 McLearen Road (O) Herndon, VA — 3,507 30,177 4,915 3,507 35,092 38,599 (12,784) 2007 7/11/2012 140 National Business Parkway (O) Annapolis Junction, MD — 3,407 24,167 1,751 3,407 25,918 29,325 (10,941) 2003 12/31/2003 141 National Business Parkway (O) Annapolis Junction, MD — 2,398 9,538 4,832 2,398 14,370 16,768 (9,190) 1990 9/28/1998 14280 Park Meadow Drive (O) Chantilly, VA — 3,731 15,953 5,485 3,731 21,438 25,169 (9,512) 1999 9/29/2004 1460 Dorsey Road (L) Hanover, MD — 1,577 76 — 1,577 76 1,653 — (6) 2/28/2006 14840 Conference Center Drive (O) Chantilly, VA — 1,572 8,175 5,751 1,572 13,926 15,498 (7,351) 2000 7/25/2003 14850 Conference Center Drive (O) Chantilly, VA — 1,615 8,358 3,873 1,615 12,231 13,846 (7,115) 2000 7/25/2003 14900 Conference Center Drive (O) Chantilly, VA — 3,436 14,402 8,659 3,436 23,061 26,497 (13,126) 1999 7/25/2003 1501 South Clinton Street (O) Baltimore, MD — 27,964 51,990 20,656 27,964 72,646 100,610 (28,175) 2006 10/27/2009 15049 Conference Center Drive (O) Chantilly, VA — 4,415 20,365 17,851 4,415 38,216 42,631 (18,061) 1997 8/14/2002 15059 Conference Center Drive (O) Chantilly, VA — 5,753 13,615 4,386 5,753 18,001 23,754 (10,079) 2000 8/14/2002 1550 West Nursery Road (O) Linthicum, MD — 14,071 16,930 — 14,071 16,930 31,001 (6,310) 2009 10/28/2009 1560 West Nursery Road (O) Linthicum, MD — 1,441 113 — 1,441 113 1,554 (19) 2014 10/28/2009 1610 West Nursery Road (O) Linthicum, MD — 259 246 — 259 246 505 (23) 2016 4/30/1998 1616 West Nursery Road (O) Linthicum, MD — 393 3,323 75 393 3,398 3,791 (268) 2017 4/30/1998 1622 West Nursery Road (O) Linthicum, MD — 393 2,542 — 393 2,542 2,935 (244) 2016 4/30/1998 16442 Commerce Drive (O) Dahlgren, VA — 613 2,582 980 613 3,562 4,175 (1,860) 2002 12/21/2004 Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) 16480 Commerce Drive (O) Dahlgren, VA — 1,856 7,425 2,602 1,856 10,027 11,883 (4,274) 2000 12/28/2004 16501 Commerce Drive (O) Dahlgren, VA — 522 2,090 1,040 522 3,130 3,652 (1,399) 2002 12/21/2004 16539 Commerce Drive (O) Dahlgren, VA — 688 2,860 2,326 688 5,186 5,874 (2,879) 1990 12/21/2004 16541 Commerce Drive (O) Dahlgren, VA — 773 3,094 2,594 773 5,688 6,461 (2,696) 1996 12/21/2004 16543 Commerce Drive (O) Dahlgren, VA — 436 1,742 838 436 2,580 3,016 (1,231) 2002 12/21/2004 1751 Pinnacle Drive (O) McLean, VA — 10,486 42,339 33,689 10,486 76,028 86,514 (38,872) 1989/1995 9/23/2004 1753 Pinnacle Drive (O) McLean, VA — 8,275 34,353 23,954 8,275 58,307 66,582 (25,248) 1976/2004 9/23/2004 206 Research Boulevard (O) Aberdeen, MD — — — — — — — (1) 2012 9/14/2007 209 Research Boulevard (O) Aberdeen, MD — 134 1,711 327 134 2,038 2,172 (599) 2010 9/14/2007 210 Research Boulevard (O) Aberdeen, MD — 113 1,402 248 113 1,650 1,763 (493) 2010 9/14/2007 2100 L Street (O) Washington, DC 82,882 19,024 92,387 — 19,024 92,387 111,411 — 2020 (7) 8/11/2015 2100 Rideout Road (O) Huntsville, AL — — 7,347 2,995 — 10,342 10,342 (1,786) 2016 3/23/2010 22289 Exploration Drive (O) Lexington Park, MD — 1,422 5,719 2,061 1,422 7,780 9,202 (4,126) 2000 3/24/2004 22299 Exploration Drive (O) Lexington Park, MD — 1,362 5,791 2,994 1,362 8,785 10,147 (4,888) 1998 3/24/2004 22300 Exploration Drive (O) Lexington Park, MD — 1,094 5,038 2,770 1,094 7,808 8,902 (3,624) 1997 11/9/2004 22309 Exploration Drive (O) Lexington Park, MD — 2,243 10,419 8,205 2,243 18,624 20,867 (8,227) 1984/1997 3/24/2004 23535 Cottonwood Parkway (O) California, MD — 692 3,051 648 692 3,699 4,391 (2,027) 1984 3/24/2004 250 W Pratt St (O) Baltimore, MD — 8,057 34,588 16,213 8,057 50,801 58,858 (15,418) 1985 3/19/2015 2500 Riva Road (O) Annapolis, MD — 2,791 12,155 1 2,791 12,156 14,947 (12,146) 2000 3/4/2003 2600 Park Tower Drive (O) Vienna, VA — 20,284 34,443 3,883 20,284 38,326 58,610 (7,108) 1999 4/15/2015 2691 Technology Drive (O) Annapolis Junction, MD — 2,098 17,334 5,565 2,098 22,899 24,997 (11,747) 2005 5/26/2000 2701 Technology Drive (O) Annapolis Junction, MD — 1,737 15,266 5,629 1,737 20,895 22,632 (12,487) 2001 5/26/2000 2711 Technology Drive (O) Annapolis Junction, MD — 2,251 21,611 4,332 2,251 25,943 28,194 (13,586) 2002 11/13/2000 2720 Technology Drive (O) Annapolis Junction, MD — 3,863 29,272 2,796 3,863 32,068 35,931 (13,249) 2004 1/31/2002 2721 Technology Drive (O) Annapolis Junction, MD — 4,611 14,597 3,247 4,611 17,844 22,455 (10,267) 2000 10/21/1999 2730 Hercules Road (O) Annapolis Junction, MD — 8,737 31,612 8,726 8,737 40,338 49,075 (22,740) 1990 9/28/1998 30 Light Street (O) Baltimore, MD 3,915 — 12,101 1,009 — 13,110 13,110 (1,894) 2009 8/7/2015 300 Sentinel Drive (O) Annapolis Junction, MD — 1,517 59,165 2,095 1,517 61,260 62,777 (16,564) 2009 11/14/2003 302 Sentinel Drive (O) Annapolis Junction, MD — 2,648 29,687 1,094 2,648 30,781 33,429 (10,028) 2007 11/14/2003 304 Sentinel Drive (O) Annapolis Junction, MD — 3,411 24,917 1,982 3,411 26,899 30,310 (11,186) 2005 11/14/2003 306 Sentinel Drive (O) Annapolis Junction, MD — 3,260 22,592 2,566 3,260 25,158 28,418 (9,147) 2006 11/14/2003 308 Sentinel Drive (O) Annapolis Junction, MD — 1,422 26,208 2,354 1,422 28,562 29,984 (7,003) 2010 11/14/2003 310 Sentinel Way (O) Annapolis Junction, MD — 2,372 42,584 — 2,372 42,584 44,956 (5,027) 2016 11/14/2003 310 The Bridge Street (O) Huntsville, AL — 261 26,531 5,135 261 31,666 31,927 (11,066) 2009 8/9/2011 312 Sentinel Way (O) Annapolis Junction, MD — 3,138 27,797 — 3,138 27,797 30,935 (4,389) 2014 11/14/2003 314 Sentinel Way (O) Annapolis Junction, MD — 1,254 7,741 — 1,254 7,741 8,995 (1,247) 2008 11/14/2003 Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) 316 Sentinel Way (O) Annapolis Junction, MD — 2,748 38,156 226 2,748 38,382 41,130 (8,426) 2011 11/14/2003 318 Sentinel Way (O) Annapolis Junction, MD — 2,185 28,426 560 2,185 28,986 31,171 (10,716) 2005 11/14/2003 320 Sentinel Way (O) Annapolis Junction, MD — 2,067 21,623 132 2,067 21,755 23,822 (7,029) 2007 11/14/2003 322 Sentinel Way (O) Annapolis Junction, MD — 2,605 22,827 1,900 2,605 24,727 27,332 (8,568) 2006 11/14/2003 324 Sentinel Way (O) Annapolis Junction, MD — 1,656 23,018 38 1,656 23,056 24,712 (5,956) 2010 6/29/2006 4000 Market Street (O) Huntsville, AL 6,052 — 9,207 — — 9,207 9,207 (394) 2018 3/23/2010 410 National Business Parkway (O) Annapolis Junction, MD — 1,831 23,257 2,080 1,831 25,337 27,168 (5,032) 2012 6/29/2006 4100 Market Street (O) Huntsville, AL 5,269 — 8,020 — — 8,020 8,020 (304) 2019 3/23/2010 420 National Business Parkway (O) Annapolis Junction, MD — 2,370 27,751 148 2,370 27,899 30,269 (4,752) 2013 6/29/2006 430 National Business Parkway (O) Annapolis Junction, MD — 1,852 21,563 830 1,852 22,393 24,245 (4,936) 2011 6/29/2006 44408 Pecan Court (O) California, MD — 817 1,583 1,706 817 3,289 4,106 (1,679) 1986 3/24/2004 44414 Pecan Court (O) California, MD — 405 1,619 1,138 405 2,757 3,162 (1,512) 1986 3/24/2004 44417 Pecan Court (O) California, MD — 434 3,822 180 434 4,002 4,436 (2,005) 1989/2015 3/24/2004 44420 Pecan Court (O) California, MD — 344 890 291 344 1,181 1,525 (546) 1989 11/9/2004 44425 Pecan Court (O) California, MD — 1,309 3,506 2,349 1,309 5,855 7,164 (3,431) 1997 5/5/2004 45310 Abell House Lane (O) California, MD — 2,272 13,808 816 2,272 14,624 16,896 (3,455) 2011 8/30/2010 4600 River Road (O) College Park, MD — — 23,294 — — 23,294 23,294 (19) 2020 (7) 1/29/2008 46579 Expedition Drive (O) Lexington Park, MD — 1,406 5,796 2,712 1,406 8,508 9,914 (4,231) 2002 3/24/2004 46591 Expedition Drive (O) Lexington Park, MD — 1,200 7,199 3,399 1,200 10,598 11,798 (3,932) 2005 3/24/2004 4851 Stonecroft Boulevard (O) Chantilly, VA — 1,878 11,558 299 1,878 11,857 13,735 (4,697) 2004 8/14/2002 540 National Business Parkway (O) Annapolis Junction, MD — 2,035 31,249 9 2,035 31,258 33,293 (2,521) 2017 6/29/2006 5520 Research Park Drive (O) Catonsville, MD — — 20,072 1,641 — 21,713 21,713 (6,375) 2009 4/4/2006 5522 Research Park Drive (O) Catonsville, MD — — 4,550 855 — 5,405 5,405 (1,652) 2007 3/8/2006 5801 University Research Court (O) College Park, MD 11,200 — 17,434 — — 17,434 17,434 (1,195) 2018 1/29/2008 5825 University Research Court (O) College Park, MD 20,011 — 22,771 1,780 — 24,551 24,551 (7,170) 2008 1/29/2008 5850 University Research Court (O) College Park, MD 21,171 — 31,906 405 — 32,311 32,311 (8,885) 2008 1/29/2008 6000 Redstone Gateway (O) Huntsville, AL — — 8,268 — — 8,268 8,268 (14) 2020 (7) 3/23/2010 610 Guardian Way (O) Annapolis Junction, MD — 6,946 14,597 — 6,946 14,597 21,543 — (7) 6/29/2006 6700 Alexander Bell Drive (O) Columbia, MD — 1,755 7,019 8,788 1,755 15,807 17,562 (8,825) 1988 5/14/2001 6708 Alexander Bell Drive (O) Columbia, MD — 897 12,644 1,618 897 14,262 15,159 (4,674) 1988/2016 5/14/2001 6711 Columbia Gateway Drive (O) Columbia, MD — 2,683 23,239 1,557 2,683 24,796 27,479 (9,200) 2006-2007 9/28/2000 6716 Alexander Bell Drive (O) Columbia, MD — 1,242 4,969 4,672 1,242 9,641 10,883 (6,123) 1990 12/31/1998 6721 Columbia Gateway Drive (O) Columbia, MD — 1,753 34,090 2,391 1,753 36,481 38,234 (10,096) 2009 9/28/2000 6724 Alexander Bell Drive (O) Columbia, MD — 449 5,039 2,507 449 7,546 7,995 (3,592) 2001 5/14/2001 6731 Columbia Gateway Drive (O) Columbia, MD — 2,807 19,098 5,605 2,807 24,703 27,510 (13,179) 2002 3/29/2000 6740 Alexander Bell Drive (O) Columbia, MD — 1,424 5,696 3,466 1,424 9,162 10,586 (6,236) 1992 12/31/1998 Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) 6741 Columbia Gateway Drive (O) Columbia, MD — 675 1,711 169 675 1,880 2,555 (639) 2008 9/28/2000 6750 Alexander Bell Drive (O) Columbia, MD — 1,263 12,461 5,075 1,263 17,536 18,799 (10,635) 2001 12/31/1998 6760 Alexander Bell Drive (O) Columbia, MD — 890 3,561 3,920 890 7,481 8,371 (4,859) 1991 12/31/1998 6940 Columbia Gateway Drive (O) Columbia, MD — 3,545 9,916 8,739 3,545 18,655 22,200 (10,795) 1999 11/13/1998 6950 Columbia Gateway Drive (O) Columbia, MD — 3,596 27,723 3,223 3,596 30,946 34,542 (11,991) 1998/2019 10/22/1998 7000 Columbia Gateway Drive (O) Columbia, MD — 3,131 12,103 7,537 3,131 19,640 22,771 (9,679) 1999 5/31/2002 7005 Columbia Gateway Drive (L) Columbia, MD — 3,036 747 — 3,036 747 3,783 — (6) 6/26/2014 7015 Albert Einstein Drive (O) Columbia, MD — 2,058 6,093 3,319 2,058 9,412 11,470 (4,585) 1999 12/1/2005 7061 Columbia Gateway Drive (O) Columbia, MD — 729 3,094 2,640 729 5,734 6,463 (3,393) 2000 8/30/2001 7063 Columbia Gateway Drive (O) Columbia, MD — 902 3,684 3,468 902 7,152 8,054 (4,450) 2000 8/30/2001 7065 Columbia Gateway Drive (O) Columbia, MD — 919 3,763 3,097 919 6,860 7,779 (4,565) 2000 8/30/2001 7067 Columbia Gateway Drive (O) Columbia, MD — 1,829 11,823 5,404 1,829 17,227 19,056 (8,693) 2001 8/30/2001 7100 Redstone Gateway (O) Huntsville, AL — — 9,101 — — 9,101 9,101 — (7) 3/23/2010 7125 Columbia Gateway Drive (O) Columbia, MD — 20,487 47,029 23,580 20,487 70,609 91,096 (27,691) 1973/1999 6/29/2006 7130 Columbia Gateway Drive (O) Columbia, MD — 1,350 4,359 2,896 1,350 7,255 8,605 (3,848) 1989 9/19/2005 7134 Columbia Gateway Drive (O) Columbia, MD — 704 4,700 668 704 5,368 6,072 (1,803) 1990/2016 9/19/2005 7138 Columbia Gateway Drive (O) Columbia, MD — 1,104 3,518 2,853 1,104 6,371 7,475 (4,072) 1990 9/19/2005 7142 Columbia Gateway Drive (O) Columbia, MD — 1,342 7,148 2,611 1,342 9,759 11,101 (4,052) 1994/2018 9/19/2005 7150 Columbia Gateway Drive (O) Columbia, MD — 1,032 3,429 813 1,032 4,242 5,274 (1,789) 1991 9/19/2005 7150 Riverwood Drive (O) Columbia, MD — 1,821 4,388 1,850 1,821 6,238 8,059 (3,016) 2000 1/10/2007 7160 Riverwood Drive (O) Columbia, MD — 2,732 7,006 4,405 2,732 11,411 14,143 (4,768) 2000 1/10/2007 7170 Riverwood Drive (O) Columbia, MD — 1,283 3,096 2,281 1,283 5,377 6,660 (2,576) 2000 1/10/2007 7175 Riverwood Drive (O) Columbia, MD — 1,788 7,269 — 1,788 7,269 9,057 (1,298) 1996/2013 7/27/2005 7200 Redstone Gateway (O) Huntsville, AL — — 8,348 81 — 8,429 8,429 (1,393) 2013 3/23/2010 7200 Riverwood Drive (O) Columbia, MD — 4,089 22,630 4,634 4,089 27,264 31,353 (12,592) 1986 10/13/1998 7205 Riverwood Drive (O) Columbia, MD — 1,367 21,419 — 1,367 21,419 22,786 (3,987) 2013 7/27/2005 7272 Park Circle Drive (O) Hanover, MD — 1,479 6,300 4,608 1,479 10,908 12,387 (5,467) 1991/1996 1/10/2007 7318 Parkway Drive (O) Hanover, MD — 972 3,888 1,324 972 5,212 6,184 (2,929) 1984 4/16/1999 7400 Redstone Gateway (O) Huntsville, AL — — 9,223 75 — 9,298 9,298 (1,281) 2015 3/23/2010 7467 Ridge Road (O) Hanover, MD — 1,565 3,116 5,041 1,565 8,157 9,722 (4,110) 1990 4/28/1999 7500 Advanced Gateway (O) Huntsville, AL — — 19,070 — — 19,070 19,070 (264) 2020 3/23/2010 7600 Advanced Gateway (O) Huntsville, AL — — 14,126 — — 14,126 14,126 (135) 2020 3/23/2010 7740 Milestone Parkway (O) Hanover, MD 16,902 3,825 34,176 1,084 3,825 35,260 39,085 (9,279) 2009 7/2/2007 7770 Backlick Road (O) Springfield, VA — 6,387 78,779 1,531 6,387 80,310 86,697 (14,971) 2012 3/10/2010 7880 Milestone Parkway (O) Hanover, MD — 4,857 25,916 321 4,857 26,237 31,094 (3,384) 2015 9/17/2013 8000 Rideout Road (O) Huntsville, AL — — 16,138 — — 16,138 16,138 — (7) 3/23/2010 Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) 8600 Advanced Gateway (O) Huntsville, AL — — 25,168 — — 25,168 25,168 (45) 2020 3/23/2010 8621 Robert Fulton Drive (O) Columbia, MD — 2,317 12,642 6,191 2,317 18,833 21,150 (6,700) 2005-2006 6/10/2005 8661 Robert Fulton Drive (O) Columbia, MD — 1,510 3,764 3,019 1,510 6,783 8,293 (3,528) 2002 12/30/2003 8671 Robert Fulton Drive (O) Columbia, MD — 1,718 4,280 4,294 1,718 8,574 10,292 (4,716) 2002 12/30/2003 870 Elkridge Landing Road (O) Linthicum, MD — 2,003 9,442 10,464 2,003 19,906 21,909 (11,574) 1981 8/3/2001 8800 Redstone Gateway (O) Huntsville, AL 11,679 — 18,446 — — 18,446 18,446 (511) 2019 3/23/2010 891 Elkridge Landing Road (O) Linthicum, MD — 1,165 4,772 3,512 1,165 8,284 9,449 (5,193) 1984 7/2/2001 901 Elkridge Landing Road (O) Linthicum, MD — 1,156 4,437 4,789 1,156 9,226 10,382 (4,687) 1984 7/2/2001 911 Elkridge Landing Road (O) Linthicum, MD — 1,215 4,861 3,431 1,215 8,292 9,507 (4,786) 1985 4/30/1998 938 Elkridge Landing Road (O) Linthicum, MD — 922 4,748 1,516 922 6,264 7,186 (3,221) 1984 7/2/2001 939 Elkridge Landing Road (O) Linthicum, MD — 939 3,756 4,444 939 8,200 9,139 (5,388) 1983 4/30/1998 9651 Hornbaker Road (D) Manassas, VA — 6,050 250,355 16,105 6,050 266,460 272,510 (72,246) 2010 9/14/2010 Arundel Preserve (L) Hanover, MD — 13,352 9,699 — 13,352 9,699 23,051 — (6) 7/2/2007 Canton Crossing Land (L) Baltimore, MD — 17,285 8,363 142 17,285 8,505 25,790 — (6) 10/27/2009 Canton Crossing Util Distr Ctr (O) Baltimore, MD — 6,100 10,450 1,689 6,100 12,139 18,239 (6,269) 2006 10/27/2009 Columbia Gateway - Southridge (L) Columbia, MD — 6,387 3,722 — 6,387 3,722 10,109 — (6) 9/20/2004 Dahlgren Technology Center (L) Dahlgren, VA — 978 178 — 978 178 1,156 — (6) 3/16/2005 Expedition VII (O) Lexington Park, MD — 705 862 — 705 862 1,567 — (7) 3/24/2004 IN 1 (O) Northern Virginia — 1,815 15,972 — 1,815 15,972 17,787 (735) 2019 8/31/2016 IN 2 (O) Northern Virginia — 2,627 28,829 — 2,627 28,829 31,456 (1,081) 2019 8/31/2016 M Square Research Park (L) College Park, MD — — 2,020 — — 2,020 2,020 — (6) 1/29/2008 MP 1 (O) Northern Virginia — 9,426 30,924 — 9,426 30,924 40,350 (1,240) 2019 11/20/2017 MP 2 (O) Northern Virginia — 9,426 29,989 — 9,426 29,989 39,415 (1,416) 2018 11/20/2017 MR Land (L) Northern Virginia — 9,038 514 — 9,038 514 9,552 — (6) 11/8/2018 National Business Park North (L) Annapolis Junction, MD — 21,898 35,639 — 21,898 35,639 57,537 — (6) 6/29/2006 North Gate Business Park (L) Aberdeen, MD — 1,755 5 — 1,755 5 1,760 — (6) 9/14/2007 NoVA Office A (O) (8) Chantilly, VA — 2,096 46,849 10 2,096 46,859 48,955 (6,926) 2015 7/18/2002 NoVA Office B (O) (8) Chantilly, VA — 739 38,376 — 739 38,376 39,115 (3,734) 2016 7/18/2002 NoVA Office C (O) (8) Chantilly, VA — 5,604 48,235 — 5,604 48,235 53,839 — (7) 7/18/2002 NoVA Office D (O) (8) Chantilly, VA — 6,587 40,559 — 6,587 40,559 47,146 (3,450) 2017 7/2/2013 Oak Grove A (O) Northern Virginia — 12,866 34,427 — 12,866 34,427 47,293 (494) 2020 11/1/2018 Oak Grove B (O) Northern Virginia — 12,866 40,550 — 12,866 40,550 53,416 (811) 2019 11/1/2018 Oak Grove Phase II (L) Northern Virginia — 23,483 8,833 — 23,483 8,833 32,316 — (6) 11/1/2018 Old Annapolis Road (O) Columbia, MD — 1,637 5,500 6,710 1,637 12,210 13,847 (4,870) 1974/1985 12/14/2000 P2 A (O) Northern Virginia — 16,878 39,934 — 16,878 39,934 56,812 (738) 2020 5/2/2019 P2 B (O) Northern Virginia — 22,866 35,960 — 22,866 35,960 58,826 (292) 2020 5/2/2019 Initial Cost Gross Amounts Carried Property (Type) (1) Location Encumbrances (2) Land Building Costs Capitalized Subsequent to Acquisition Land Building Total Accumulated Depreciation (4) Year Built or Renovated Date Acquired (5) P2 C (O) Northern Virginia — 14,842 30,272 — 14,842 30,272 45,114 (60) 2020 5/2/2019 Paragon Park (L) Northern Virginia — 7,738 462 — 7,738 462 8,200 — (6) 5/8/2017 Parkstone A (O) Northern Virginia — 3,942 1,257 — 3,942 1,257 5,199 — (7) 1/27/2005 Parkstone B (O) Northern Virginia — 3,346 1,074 — 3,346 1,074 4,420 — (7) 1/27/2005 Patriot Ridge (L) Springfield, VA — 18,517 14,562 — 18,517 14,562 33,079 — (6) 3/10/2010 Project EL (O) Confidential-USA — 7,430 7,479 — 7,430 7,479 14,909 — (7) 1/20/2006 Project EX (O) (9) Confidential-USA — 8,959 16,981 — 8,959 16,981 25,940 (698) 2018 7/16/2008 Redstone Gateway (L) Huntsville, AL — — 33,310 — — 33,310 33,310 (5) (6) 3/23/2010 Sentry Gateway (L) San Antonio, TX — 4,052 1,833 — 4,052 1,833 5,885 — (6) 3/30/2005 Sentry Gateway - T (O) San Antonio, TX — 14,020 38,804 13 14,020 38,817 52,837 (13,473) 1982/2008 3/30/2005 Sentry Gateway - V (O) San Antonio, TX — — 1,066 — — 1,066 1,066 (321) 2007 3/30/2005 Sentry Gateway - W (O) San Antonio, TX — — 1,884 71 — 1,955 1,955 (548) 2009 3/30/2005 Sentry Gateway - X (O) San Antonio, TX — 1,964 21,178 — 1,964 21,178 23,142 (5,375) 2010 1/20/2006 Sentry Gateway - Y (O) San Antonio, TX — 1,964 21,298 — 1,964 21,298 23,262 (5,407) 2010 1/20/2006 Sentry Gateway - Z (O) San Antonio, TX — 1,964 30,573 — 1,964 30,573 32,537 (4,438) 2015 6/14/2005 SP Manassas (L) Manassas, VA — 8,156 187 — 8,156 187 8,343 — (6) 7/24/2019 Westfields - Park Center (L) Chantilly, VA — 10,815 6,206 — 10,815 6,206 17,021 — (6) 7/2/2013 Other Developments, including intercompany eliminations (V) Various — — 282 257 — 539 539 (90) Various Various $ 257,404 $ 712,057 $ 3,427,401 $ 547,344 $ 712,057 $ 3,974,745 $ 4,686,802 $ (1,124,253) (1) A legend for the Property Type follows: (O) = Office or Data Center Shell Property; (L) = Land held or pre-development; (D) = Wholesale Data Center; and (V) = Various. (2) Excludes our Revolving Credit Facility of $143.0 million, term loan facilities of $398.4 million, unsecured senior notes of $1.3 billion, unsecured notes payable of $900,000, and deferred financing costs, net of premiums, on the remaining loans of $2.3 million. (3) The aggregate cost of these assets for Federal income tax purposes was approximately $3.6 billion as of December 31, 2020. (4) The estimated lives over which depreciation is recognized follow: Building and land improvements: 10-40 years; and tenant improvements: related lease terms. (5) The acquisition date of multi-parcel properties reflects the date of the earliest parcel acquisition. The acquisition date of properties owned through real estate joint ventures reflects the date of the formation of the joint venture. (6) Held as of December 31, 2020. (7) Under development or redevelopment as of December 31, 2020. (8) The carrying amounts of these properties exclude allocated costs of the garage being constructed to support the properties. (9) This property represents land under a long-term contract. The following table summarizes our changes in cost of properties for the years ended December 31, 2020, 2019 and 2018 (in thousands): 2020 2019 2018 Beginning balance $ 4,348,006 $ 4,148,529 $ 3,980,813 Improvements and other additions 405,940 480,418 224,524 Sales (1) (65,475) (242,497) (53,547) Impairments (1,530) (329) (2,493) Other dispositions (139) (340) (768) Reclassification to right-of use asset — (37,775) — Ending balance $ 4,686,802 $ 4,348,006 $ 4,148,529 The following table summarizes our changes in accumulated depreciation for the same time periods (in thousands): 2020 2019 2018 Beginning balance $ 1,007,120 $ 897,903 $ 801,038 Depreciation expense 119,377 117,973 112,610 Sales (1) (2,105) (8,416) (14,845) Impairments — — (132) Other dispositions (139) (340) (768) Ending balance $ 1,124,253 $ 1,007,120 $ 897,903 (1) Includes our sale, through a series of transactions, of ownership interests in data center shells through newly-formed unconsolidated real estate joint ventures in 2020 and 2019, as described in Note 4 to our consolidated financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
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.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements We make estimates and assumptions when preparing financial statements under generally accepted accounting principles (“GAAP”). These estimates and assumptions affect various matters, including: • the reported amounts of assets and liabilities in our consolidated balance sheets as of the dates of the financial statements; • the disclosure of contingent assets and liabilities as of the dates of the financial statements; and • the reported amounts of revenues and expenses in our consolidated statements of operations during the reporting periods.
Properties	Properties We report properties to be developed or held and used in operations at our depreciated cost, reduced for impairment losses. We capitalize direct and indirect project costs (including related compensation and other indirect costs), interest expense and real estate taxes associated with properties, or portions thereof, undergoing development or redevelopment activities. In capitalizing interest expense, if there is a specific borrowing for a property undergoing development or redevelopment activities, we apply the interest rate of that borrowing to the average accumulated expenditures that do not exceed such borrowing; for the portion of expenditures exceeding any such specific borrowing, we apply our weighted average interest rate on other borrowings to the expenditures. We continue to capitalize costs while development or redevelopment activities are underway until a property becomes “operational,” which occurs when lease terms commence (generally when the tenant has control of the leased space and we have delivered the premises to the tenant as required under the terms of such lease), but no later than one year after the cessation of major construction activities. When leases commence on portions of a newly-developed or redeveloped property in the period prior to one year from the cessation of major construction activities, we consider that property to be “partially operational.” When a property is partially operational, we allocate the costs associated with the property between the portion that is operational and the portion under development. We start depreciating costs associated with newly-developed or redeveloped properties as they become operational. Most of our leases provide for some form of improvements to leased space. When we are required to provide improvements under the terms of a lease, we determine whether the improvements constitute landlord assets or tenant assets. If the improvements are landlord assets, we capitalize the cost of the improvements and recognize depreciation expense over the shorter of the useful life of the assets or the term of the lease and recognize any payments from the tenant as rental revenue over the term of the lease. If the improvements are tenant assets, we defer the cost of improvements funded by us as a lease incentive asset and amortize it as a reduction of rental revenue over the term of the lease. In determining whether improvements constitute landlord or tenant assets, we consider numerous factors, including whether the economic substance of the lease terms is properly reflected and whether the improvements: have value to us as real estate; are unique to the tenant or reusable by other tenants; may be altered or removed by the tenant without our consent or without compensating us for any lost fair value; or are owned, and remain, with us or the tenant at the end of the lease term. We depreciate our fixed assets using the straight-line method over their estimated useful lives as follows: Estimated Useful Lives Buildings and building improvements 10-40 years Land improvements 10-20 years Tenant improvements on operating properties Shorter of remaining useful lives of assets or related lease term Equipment and personal property 3-10 years For periods in which a property is classified as held for sale, we classify the assets of the property’s asset group as held for sale on our consolidated balance sheet for such periods. When we dispose of, or classify as held for sale, a component (such as a reportable segment or sub-segment) or group of components that represents a strategic shift having a major effect on our operations and financial results (such as a major geographical area of operations or major line of business), we classify the associated results of operations as discontinued operations. We had no properties newly classified as discontinued operations in the last three years.
Sale of Properties	Sales of PropertiesWe recognize gains from sales of consolidated interests in properties to non-customer third parties when we have transferred control of such interests.
Impairment of Properties	Impairment of Properties We assess the asset groups associated with each of our properties, including operating properties, properties in development, land held for future development, related intangible assets, right-of-use assets, deferred rents receivable and lease liabilities for indicators of impairment quarterly or when circumstances indicate that an asset group may be impaired. If our analyses indicate that the carrying values of certain properties’ asset groups may be impaired, we perform a recovery analysis for such asset groups. For properties to be held and used, we analyze recoverability based on the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the properties over, in most cases, a ten-year holding period. If we believe it is more likely than not that we will dispose of the properties earlier, we analyze recoverability using a probability weighted analysis of the estimated undiscounted future cash flows expected to be generated from the operations and eventual disposition of the properties over the various possible holding periods. If the analysis indicates that the carrying value of a tested property’s asset group is not recoverable from its estimated future cash flows, the property’s asset group is written down to the property’s estimated fair value and an impairment loss is recognized. If and when our plans change, we revise our recoverability analyses to use the cash flows expected from the operations and eventual disposition of such property using holding periods that are consistent with our revised plans. Changes in holding periods may require us to recognize impairment losses. Fair values are estimated based on contract prices, indicative bids, discounted cash flow analyses, yield analyses or comparable sales analyses. Estimated cash flows used in our impairment analyses are based on our plans for the property and our views of market and economic conditions. The estimates consider items such as current and future market rental and occupancy rates, estimated operating and capital expenditures and recent sales data for comparable properties; most of these items are influenced by market data obtained from real estate leasing and brokerage firms and our direct experience with the properties and their markets.
Acquisition of Operating Properties	Acquisition of Operating Properties Upon completion of operating property acquisitions, we allocate the purchase price to tangible and intangible assets and liabilities associated with such acquisitions based on our estimates of their fair values. We determine these fair values by using market data and independent appraisals available to us and making numerous estimates and assumptions. We allocate operating property acquisitions to the following components: • properties based on a valuation performed under the assumption that the property is vacant upon acquisition (the “if-vacant value”). The if-vacant value is allocated between land and buildings or, in the case of properties under development, development in progress. We also allocate additional amounts to properties for in-place tenant improvements based on our estimate of improvements per square foot provided under market leases that would be attributable to the remaining non-cancelable terms of the respective leases; • above- and below-market lease intangible assets or liabilities based on the present value (using an interest rate which reflects the risks associated with the leases acquired) of the difference between: (1) the contractual amounts to be received pursuant to the in-place leases; and (2) our estimate of fair market lease rates for the corresponding space, measured over a period equal to the remaining non-cancelable term of the lease. The capitalized above- and below-market lease values are amortized as adjustments to lease revenue over the remaining lease terms of the respective leases, and to renewal periods in the case of below-market leases; • in-place lease value based on our estimates of: (1) the present value of additional income to be realized as a result of leases being in place on the acquired properties; and (2) costs to execute similar leases. Our estimate of costs to execute similar leases includes leasing commissions, legal and other related costs; • tenant relationship value based on our evaluation of the specific characteristics of each tenant’s lease and our overall relationship with that respective tenant. Characteristics we consider in determining these values include the nature and extent of our existing business relationships with the tenant, growth prospects for developing new business with the tenant, the tenant’s credit quality and expectations of lease renewals, among other factors; and • above- and below-market cost arrangements (such as real estate tax treaties or above- or below-market ground leases) based on the present value of the expected benefit from any such arrangements in place on the property at the time of acquisition.
Leased Assets, as a Lessee	Leased Assets, as a Lessee Effective January 1, 2019, we adopted guidance requiring lessees to classify 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. The guidance also requires us to recognize upon lease term commencement a right-of-use asset and lease liability for all leases with a term of greater than 12 months regardless of their classification. We adopted this guidance for leases on January 1, 2019 using a modified retrospective transition approach under which we elected to not adjust prior comparative reporting periods. We elected to apply a package of practical expedients that enabled us to carry forward upon adoption our historical assessments of: expired or existing leases regarding their lease classification; and whether any expired or existing contracts are, or contain, leases. We also elected a practical expedient that enabled us to avoid the need to assess whether expired or existing land easements not previously accounted for as leases are, or contain, a lease.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include all cash and liquid investments that mature three months or less from when they are purchased. Cash equivalents are reported at cost, which approximates fair value. We maintain our cash in bank accounts in amounts that may exceed Federally insured limits at times. We have not experienced any losses in these accounts in the past and believe that we are not exposed to significant credit risk because our accounts are deposited with major financial institutions.
Investments in Marketable Securities	Investments in Marketable SecuritiesWe classify marketable securities as trading securities when we have the intent to sell such securities in the near term, and classify other marketable securities as available-for-sale securities. We determine the appropriate classification of investments in marketable securities at the acquisition date and re-evaluate the classification at each balance sheet date. We report investments in marketable securities classified as trading securities at fair value (which is included in the line entitled “Prepaid expenses and other assets, net” on our consolidated balance sheets), with unrealized gains and losses recognized through earnings; on our consolidated statements of cash flows, we classify cash flows from these securities as operating activities.
Receivables and Credit Losses	Receivables and Credit Losses We evaluate our receivables from customers and borrowers for collectability and recognize estimated credit losses on these receivables. We use judgment in estimating these losses based upon the credit status of the entities associated with the individual receivables and payment history. Effective January 1, 2020, we adopted guidance issued by the Financial Accounting Standards Board (“FASB”) that changed how we measure credit losses for most financial assets and certain other instruments not measured at fair value through net income from an incurred loss model to an expected loss approach. Our items within the scope of this guidance included the following: • investing receivables, as disclosed in Note 8; • tenant notes receivable; • net investment in sales-type leases; • other assets comprised of non-lease revenue related accounts receivable (primarily from construction contract services) and contract assets from unbilled construction contract revenue; and • off-balance sheet credit exposures. Under this guidance, we recognize an estimate of our expected credit losses on these items as an allowance, as the guidance requires that financial assets be measured on an amortized cost basis and be presented at the net amount expected to be collected (or as a separate liability in the case of off-balance sheet credit exposures). The allowance represents the portion of the amortized cost basis that we do not expect to collect (or loss we expect to incur in the case of off-balance sheet credit exposures) due to credit over the contractual life based on available information relevant to assessing the collectability of cash flows, which includes consideration of past events, current conditions and reasonable and supportable forecasts of future economic conditions (including consideration of asset- or borrower-specific factors). The guidance requires the allowance for expected credit losses to reflect the risk of loss, even when that risk is remote. An allowance for credit losses is measured and recorded upon the initial recognition of a financial asset (or off-balance sheet credit exposure), regardless of whether it is originated or purchased. Quarterly, the expected losses are re-estimated, considering any cash receipts and changes in risks or assumptions, with resulting adjustments recognized as credit loss expense or recoveries on our consolidated statements of operations. We estimate expected credit losses for in-scope items using historical loss rate information developed for varying classifications of credit risk and contractual lives. Due to our limited quantity of items within the scope of this guidance and the unique risk characteristics of such items, we individually assign each in-scope item a credit risk classification. The credit risk classifications assigned by us are determined based on credit ratings assigned by ratings agencies (as available) or are internally-developed based on available financial information, historical payment experience, credit documentation, other publicly available information and current economic trends. In addition, for certain items in which the risk of credit loss is affected by the economic performance of a real estate development project, we develop probability weighted scenario analyses for varying levels of performance in estimating our credit loss allowance (applicable to our notes receivable from the City of Huntsville disclosed in Note 8 and a tax incremental financing obligation disclosed in Note 20). For lease revenue, if collectability is not probable, revenue recognized is limited to the lesser of revenue that would have been recognized if collectability was probable or lease payments collected. Losses on lease revenue receivables are presented on our consolidated statements of operation with property operating expenses for years prior to January 1, 2019, when we adopted new lease accounting guidance, and as reductions in lease revenue thereafter. Prior to our adoption of the credit loss guidance discussed above, we evaluated the collectability of both interest and principal of loans whenever events or changes in circumstances indicated such amounts may not be recoverable. A loan was impaired when it was probable that we would be unable to collect all amounts due according to the existing contractual terms. When a loan was impaired, the amount of the loss accrual was calculated by comparing the carrying amount of the investment to the present value of expected future cash flows discounted at the loan’s effective interest rate and the value of any collateral under such loan. When we believe that collection of interest income on an investing or tenant note receivable is not probable, we place the receivable on nonaccrual status, meaning interest income is recognized when payments are received rather than on an accrual basis. We write off receivables when we believe the facts and circumstances indicate that continued pursuit of collection is no longer warranted. When cash is received in connection with receivables for which we have previously recognized credit losses, we recognize reductions in our credit losses.
Intangible Assets and Deferred Revenue on Real Estate Acquisitions	Intangible Assets and Deferred Revenue on Real Estate Acquisitions We amortize the intangible assets and deferred revenue on real estate acquisitions discussed above as follows: Asset Type Amortization Period Above- and below-market leases Related lease terms In-place lease value Related lease terms Tenant relationship value Estimated period of time that tenant will lease space in property Above- and below-market cost arrangements Term of arrangements We recognize the amortization of acquired above- and below-market leases as adjustments to rental revenue. We recognize the amortization of above- and below-market cost arrangements as adjustments to property operating expenses. We recognize the amortization of other intangible assets on property acquisitions as amortization expense.
Deferred Leasing and Deferred Financing Costs	Deferred Leasing Costs We defer costs incurred to obtain new tenant leases or extend existing tenant leases; our deferral of costs included related non-incremental compensation costs until January 1, 2019, when we adopted new lease accounting guidance. We amortize these costs evenly over the lease terms. We classify leasing costs paid as an investing activity on our statements of cash flows since such costs are necessary in order for us to generate long-term future cash flows from our properties. When tenant leases are terminated early, we expense any unamortized deferred leasing costs associated with those leases over the shortened term of the lease. Deferred Financing Costs We defer costs of financing arrangements and recognize these costs as interest expense over the related debt terms on a straight-line basis, which approximates the amortization that would occur under the effective interest method of amortization. We expense any unamortized loan costs when loans are retired early. We present deferred costs of financing arrangements as a direct deduction from the related debt liability, except for costs attributable to line-of-credit arrangements and interest rate derivatives, which we present in the balance sheet in the line entitled “prepaid expenses and other assets, net”.
Interest Rate Derivatives	Interest Rate Derivatives Our primary objectives in using interest rate derivatives are to add stability to interest expense and to manage exposure to interest rate movements. To accomplish this objective, we use interest rate swaps as part of our interest rate risk management strategy. Interest rate swaps designated as cash flow hedges involve the receipt of variable-rate amounts from a counterparty in exchange for our making fixed-rate payments over the life of the agreements without exchange of the underlying notional amount. We use interest rate swaps to hedge the cash flows associated with interest rates on variable-rate debt borrowings. We also use forward-starting interest rate swaps to hedge the cash flows associated with interest rates on forecasted fixed-rate borrowings. We recognize all derivatives as assets or liabilities on our consolidated balance sheet at fair value. We defer all changes in the fair value of designated cash flow hedges to accumulated other comprehensive income (“AOCI”) or loss (“AOCL”), reclassifying such deferrals to interest expense as interest expense is recognized on the hedged forecasted transactions. When an interest rate swap designated as a cash flow hedge no longer qualifies for hedge accounting and the hedged transactions are probable not to occur, we recognize changes in fair value of the hedge previously deferred to AOCI or AOCL, along with any changes in fair value occurring thereafter, through earnings. We do not use interest rate derivatives for trading or speculative purposes. We manage counter-party risk by only entering into contracts with major financial institutions based upon their credit ratings and other risk factors.
Noncontrolling Interests	Noncontrolling InterestsCOPT’s consolidated noncontrolling interests are comprised of interests in COPLP not owned by COPT (discussed further in Note 14) and interests in consolidated real estate joint ventures not owned by us (discussed further in Note 6). COPLP’s consolidated noncontrolling interests are comprised primarily of interests in our consolidated real estate joint ventures. We evaluate whether noncontrolling interests are subject to redemption features outside of our control. We classify noncontrolling interests that are currently redeemable for cash at the option of the holders or are probable of becoming redeemable as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheets; we adjust these interests each period to the greater of their fair value or carrying amount (initial amount as adjusted for allocations of income and losses and contributions and distributions), with a corresponding offset to additional paid-in capital on COPT’s consolidated balance sheets or common units on COPLP’s balance sheet. Our other noncontrolling interests are reported in the equity section of our consolidated balance sheets.
Revenue Recognition	Revenue Recognition Lease and Other Property Revenue We lease real estate properties, comprised primarily of office properties and data center shells, to third parties. These leases usually include options under which the tenant may renew its lease based on market rates at the time of renewal, which are then typically subject to further negotiation. These leases occasionally provide the tenant with an option to terminate its lease early usually for a defined termination fee. Most of our lease revenue is from fixed contractual payments defined under the lease that, in most cases, escalate annually over the term of the lease. Our lease revenue also includes variable lease payments predominantly for tenant reimbursements of property operating expenses and lease termination fees. Property operating expense reimbursement structures vary, with some tenants responsible for all of a property’s expenses, while others are responsible for their share of a property’s expense only to the extent such expenses exceed amounts defined in the lease (which are derived from the property’s historical expense levels). Lease termination fees in most cases result from a tenant’s exercise of an existing right under a lease. Upon lease commencement, we evaluate leases to determine if they meet criteria set forth in lease accounting guidance for classification as sales-type leases or direct financing leases; when a lease meets none of these criteria, we classify the lease as an operating lease. Upon commencement of sales-type leases, we derecognize the underlying asset, recognizing in its place a net investment in the lease equal to the sum of the lease receivable and the present value of any unguaranteed residual asset and recognize any selling profit or loss created as a result of the difference between those two amounts. Similarly, for direct financing leases, the lessor derecognizes the underlying asset and recognizes a net investment in the lease, but, unlike in a sales-type lease, defers profit and amortizes it as interest income over the lease term. Our leases of properties as lessor are predominantly classified as operating leases, for which the underlying asset remains on our balance sheet and is depreciated consistently with other owned assets, with income recognized as described further below. We recognize minimum rents on operating leases, net of abatements, on a straight-line basis over the term of tenant leases. A lease term commences when: (1) the tenant has control of the leased space (legal right to use the property); and (2) we have delivered the premises to the tenant as required under the terms of such lease. The term of a lease includes the noncancellable periods of the lease along with periods covered by: (1) a tenant option to extend the lease if the tenant is reasonably certain to exercise that option; (2) a tenant option to terminate the lease if the tenant is reasonably certain not to exercise that option; and (3) an option to extend (or not to terminate) the lease in which exercise of the option is controlled by us as the lessor. When assessing the expected lease end date, we use judgment in contemplating the significance of: any penalties a tenant may incur should it choose not to exercise any existing options to extend the lease or exercise any existing options to terminate the lease; and economic incentives for the tenant based on any existing contract, asset, entity or market-based factors in the lease. While a significant portion of our portfolio is leased to the USG, and the majority of those leases consist of a series of one-year renewal options, or provide for early termination rights, we have concluded that exercise of existing renewal options, or continuation of such leases without exercising early termination rights, is reasonably certain for most of these leases. We report the amount by which our minimum rental revenue recognized on a straight-line basis under leases exceeds the contractual rent billings associated with such leases as deferred rent receivable on our consolidated balance sheets. Amounts by which our minimum rental revenue recognized on a straight-line basis under leases are less than the contractual rent billings associated with such leases are reported in liabilities as deferred revenue associated with operating leases on our consolidated balance sheets. In connection with a tenant’s entry into, or modification of, a lease, if we make cash payments to, or on behalf of, the tenant for purposes other than funding the construction of landlord assets, we defer the amount of such payments as lease incentives. As discussed above, when we are required to provide improvements under the terms of a lease, we determine whether the improvements constitute landlord assets or tenant assets; if the improvements are tenant assets, we defer the cost of improvements funded by us as a lease incentive asset. We amortize lease incentives as a reduction of rental revenue over the term of the lease. If collectability under a lease is not probable, revenue recognized is limited to the lesser of revenue that would have been recognized if collectability was probable or lease payments collected. We recognize lease revenue associated with tenant expense recoveries in the same periods in which we incur the related expenses, including tenant reimbursements of property taxes, utilities and other property operating expenses. We recognize fees received for lease terminations as revenue and write off against such revenue any (1) deferred rents receivable, and (2) deferred revenue, lease incentives and intangible assets that are amortizable into rental revenue associated with the leases; the resulting net amount is the net revenue from the early termination of the leases. When a tenant’s lease for space in a property is terminated early but the tenant continues to lease such space under a new or modified lease in the property, the net revenue from the early termination of the lease is recognized evenly over the remaining life of the new or modified lease in place on that property. Effective January 1, 2019, we adopted guidance issued by the FASB setting forth principles for the recognition, measurement, presentation and disclosure of leases, which required lessors of real estate to account for leases using an approach substantially equivalent to guidance previously in place for operating leases, direct financing leases and sales-type leases. We adopted this guidance for leases on January 1, 2019 using a modified retrospective transition approach under which we elected to not adjust prior comparative reporting periods (except for our presentation of lease revenue discussed below). We elected to apply a package of practical expedients that enabled us to carry forward upon adoption our historical assessments of: expired or existing leases regarding their lease classification and deferred recognition of non-incremental direct leasing costs; and whether any expired or existing contracts are, or contain, leases. We also elected a practical expedient that enabled us to avoid the need to assess whether expired or existing land easements not previously accounted for as leases are, or contain, a lease. In addition, we elected a practical expedient to avoid separating non-lease components that otherwise would need to be accounted for under revenue accounting guidance (such as tenant reimbursements of property operating expenses) from the associated lease component since (1) the non-lease components have the same timing and pattern of transfer as the associated lease component and (2) the lease component, if accounted for separately, would be classified as an operating lease; this enables us to account for the combination of the lease component and non-lease components as an operating lease since the lease component is the predominant component of the combined components. Construction Contract and Other Service Revenues We enter into construction contracts to complete various design and construction services primarily for our USG 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 based on the standalone selling price, as discussed further below. 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 a 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 relative standalone selling prices, which we determine by evaluating: the relative costs of each performance obligation; the expected operating margins (which typically do not vary significantly between obligations); and amounts set forth in the contracts for each obligation. 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. • 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. 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 primarily on contracts in place with subcontractors to complete most of the work, but may also include 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. 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. Under most of our contracts, we bill customers one month subsequent to revenue recognition, resulting in contract assets representing unbilled construction revenue.
Expense Classification	Expense Classification We classify as property operating expense costs incurred for property taxes, ground rents, utilities, property management, insurance, repairs and exterior and interior maintenance, as well as associated labor and indirect costs attributable to these costs. We classify as general, administrative and leasing expenses costs incurred for corporate-level management, public company administration, asset management, leasing, investor relations, marketing and corporate-level insurance (including general business and director and officers) and leasing prospects, as well as associated labor and indirect costs attributable to these expenses.
Share-Based Compensation	Share-Based Compensation We issue four forms of share-based compensation: restricted COPT common shares (“restricted shares”), deferred share awards (also known as restricted share units), performance share units (also known as performance share awards) (“PSUs”) and profit interest units (“PIUs”) (time-based and performance-based). We account for share-based compensation in accordance with authoritative guidance provided by the FASB that establishes standards for the accounting for transactions in which an entity exchanges its equity instruments for goods or services, focusing primarily on accounting for transactions in which an entity obtains employee services in share-based payment transactions. The guidance requires us to measure the cost of employee services received in exchange for an award of equity instruments based generally on the fair value of the award on the grant date; such cost is then recognized over the period during which the employee is required to provide service in exchange for the award. No compensation cost is recognized for equity instruments for which employees do not render the requisite service. The guidance also requires that share-based compensation be computed based on awards that are ultimately expected to vest; as a result, future forfeitures of awards are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. If an award is voluntarily cancelled by an employee, we recognize the previously unrecognized cost associated with the original award on the date of such cancellation. We capitalize costs associated with share-based compensation attributable to employees engaged in development and redevelopment activities. We compute the fair value of restricted shares, time-based PIUs and deferred share awards based on the fair value of COPT common shares on the grant date. We compute the fair value of PSUs and performance-based PIUs using a Monte Carlo
Income Taxes	Income Taxes COPT elected to be treated as a REIT under Sections 856 through 860 of the Internal Revenue Code. To qualify as a REIT, COPT must meet a number of organizational and operational requirements, including a requirement that it distribute at least 90% of the Company’s adjusted taxable income to its shareholders. As a REIT, COPT generally will not be subject to Federal income tax on taxable income that it distributes to its shareholders. If COPT fails to qualify as a REIT in any tax year, it will be subject to Federal income tax on its taxable income at regular corporate rates and may not be able to qualify as a REIT for four subsequent tax years. COPLP is a limited partnership and is not subject to federal income tax. Its partners are required to report their respective share of the Operating Partnership’s taxable income on their respective tax returns. COPT’s share of the Operating Partnership’s taxable income is reported on COPT’s income tax return. For Federal income tax purposes, dividends to shareholders may be characterized as ordinary income, capital gains or return of capital. The characterization of dividends paid on COPT’s common shares during each of the last three years was as follows: For the Years Ended December 31, 2020 2019 2018 Ordinary income 45.1 % 54.4 % 83.1 % Long-term capital gain 54.9 % 45.6 % — % Return of capital — % — % 16.9 % The dividends allocated to each of the above years for Federal income tax purposes included dividends paid on COPT’s common shares during each of those years except for the dividends paid on January 15, 2021 and 2020 (with a record date of December 31, 2020 and 2019, respectively), which were allocated for Federal income tax purposes to 2020 and 2019, respectively. We distributed all of COPT’s REIT taxable income in 2020, 2019 and 2018 and, as a result, did not incur Federal income tax in those years. The net basis of our consolidated assets and liabilities for tax reporting purposes was approximately $10 million higher than the amount reported on our consolidated balance sheet as of December 31, 2020.
Reclassifications	Reclassifications We reclassified certain amounts from prior periods to conform to the current period presentation of our consolidated financial statements with no effect on previously reported net income or equity.
Recent Accounting Pronouncements	Recent Accounting Pronouncements As discussed above, effective January 1, 2020, we adopted guidance issued by the FASB that changed how entities measure credit losses for most financial assets and certain other instruments not measured at fair value through net income. The guidance replaced the current incurred loss model with an expected loss approach, resulting in a more timely recognition of such losses. The guidance applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables (excluding those arising from operating leases), loans, held-to-maturity debt securities, net investments in leases and off-balance-sheet credit exposures. Under this guidance, we recognize an estimate of our expected credit losses on these asset types as an allowance, as the guidance requires that financial assets be measured on an amortized cost basis and be presented at the net amount expected to be collected. We adopted this guidance using the modified retrospective transition method under which we recognized a $5.5 million allowance for credit losses by means of a cumulative-effect adjustment to cumulative distributions in excess of net income of the Company (or common units of the Operating Partnership), and did not adjust prior comparative reporting periods. Our consolidated statements of operations reflect adjustments for changes in our expected credit losses occurring subsequent to adoption of this guidance. Effective January 1, 2020, we adopted guidance issued by the FASB that modifies disclosure requirements for fair value measurements. The resulting changes in disclosure did not have a material impact on our consolidated financial statements. Effective January 1, 2020, we adopted guidance issued by the FASB that aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. FASB guidance did not previously address the accounting for such implementation costs. Our adoption of this guidance did not have a material impact on our consolidated financial statements. In March 2020, the FASB issued guidance containing practical expedients for reference rate reform related activities pertaining to debt, leases, derivatives and other contracts. The guidance is optional and may be adopted over time as reference rate reform activities occur. During 2020, we elected to apply an expedient to treat any changes in loans resulting from reference rate reform as debt modifications (as opposed to extinguishments) and hedge accounting expedients related to probability and the assessments of effectiveness for future LIBOR-indexed cash flows to assume that the index upon which future hedged transactions will be based matches the index on the corresponding derivatives. Application of the hedge accounting expedients preserves the presentation of derivatives consistent with past presentation. We will continue to evaluate the impact of this guidance and may apply other elections as applicable as additional changes in the market occur.
Fair Value Measurement	Accounting standards define fair value as the exit price, or the amount that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants as of the measurement date. The standards also establish a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs are inputs market participants would use in valuing the asset or liability developed based on market data obtained from sources independent of us. Unobservable inputs are inputs that reflect our assumptions about the factors market participants would use in valuing the asset or liability developed based upon the best information available in the circumstances. The hierarchy of these inputs is broken down into three levels: Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; Level 2 inputs include (1) quoted prices for similar assets or liabilities in active markets, (2) quoted prices for identical or similar assets or liabilities in inactive markets and (3) inputs (other than quoted prices) that are observable for the asset or liability, either directly or indirectly; and Level 3 inputs are unobservable inputs for the asset or liability. Categorization within the valuation hierarchy is based upon the lowest level of input that is most significant to the fair value measurement.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of the estimated useful lives of fixed assets	We depreciate our fixed assets using the straight-line method over their estimated useful lives as follows: Estimated Useful Lives Buildings and building improvements 10-40 years Land improvements 10-20 years Tenant improvements on operating properties Shorter of remaining useful lives of assets or related lease term Equipment and personal property 3-10 years
Schedule of amortization of intangible assets and deferred revenue	We amortize the intangible assets and deferred revenue on real estate acquisitions discussed above as follows: Asset Type Amortization Period Above- and below-market leases Related lease terms In-place lease value Related lease terms Tenant relationship value Estimated period of time that tenant will lease space in property Above- and below-market cost arrangements Term of arrangements
Schedule of characterization of dividends declared on common and preferred shares	The characterization of dividends paid on COPT’s common shares during each of the last three years was as follows: For the Years Ended December 31, 2020 2019 2018 Ordinary income 45.1 % 54.4 % 83.1 % Long-term capital gain 54.9 % 45.6 % — % Return of capital — % — % 16.9 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of fair value assets and liabilities measured on recurring basis	The tables below set forth financial assets and liabilities of COPT and subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2020 and 2019 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 December 31, 2020: Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 3,008 $ — $ — $ 3,008 Other 19 — — 19 Other marketable securities (1) 30 — — 30 Total assets $ 3,057 $ — $ — $ 3,057 Liabilities: Deferred compensation plan liability (2) $ — $ 3,027 $ — $ 3,027 Interest rate derivatives — 9,522 — 9,522 Total liabilities $ — $ 12,549 $ — $ 12,549 December 31, 2019: Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 3,035 $ — $ — $ 3,035 Other 25 — — 25 Interest rate derivatives (1) — 23 — 23 Total assets $ 3,060 $ 23 $ — $ 3,083 Liabilities: Deferred compensation plan liability (2) $ — $ 3,060 $ — $ 3,060 Interest rate derivatives — 25,682 — 25,682 Total liabilities $ — $ 28,742 $ — $ 28,742 (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 tables below set forth financial assets and liabilities of COPLP and subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2020 and 2019 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 December 31, 2020: Assets: Other marketable securities (1) $ 30 $ — $ — $ 30 Liabilities: Interest rate derivatives $ — $ 9,522 $ — $ 9,522 December 31, 2019: Assets: Interest rate derivatives (1) $ — $ 23 $ — $ 23 Liabilities: Interest rate derivatives $ — $ 25,682 $ — $ 25,682 (1) Included in the line entitled “prepaid expenses and other assets, net” on COPLP ’ s consolidated balance sheet.

Properties, Net (Tables)

Properties, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Real Estate [Abstract]
Schedule of operating properties, net	Operating properties, net consisted of the following (in thousands): December 31, 2020 2019 Land $ 528,269 $ 472,976 Buildings and improvements 3,711,264 3,306,791 Less: Accumulated depreciation (1,124,253) (1,007,120) Operating properties, net $ 3,115,280 $ 2,772,647

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Operating Lease Revenue Recognized	The table below sets forth our composition of lease revenue recognized between fixed and variable lease revenue (in thousands): For the Years Ended December 31, Lease revenue 2020 2019 Fixed $ 425,593 $ 412,342 Variable 110,534 110,130 $ 536,127 $ 522,472
Sales-type leases fixed contractual payments due	Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573
Operating leases fixed contractual payments due	Fixed contractual payments due under our property leases were as follows (in thousands): As of December 31, 2020 Year Ending December 31, Operating leases Sales-type leases 2021 $ 424,585 $ 871 2022 378,573 949 2023 324,917 949 2024 276,488 949 2025 197,677 949 Thereafter 745,303 4,464 Total contractual payments $ 2,347,543 9,131 Less: Amount representing interest (2,558) Net investment in sales-type leases $ 6,573
Right-of-Use Assets and Lease Liabilities	Our property right-of-use assets consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Right-of-use assets Operating leases - Property Property - operating right-of-use assets $ 40,570 $ 27,864 Finance leases - Property Property - finance right-of-use assets 40,425 40,458 Total right-of-use assets $ 80,995 $ 68,322 Property lease liabilities consisted of the following (in thousands): As of December 31, Leases Balance Sheet Location 2020 2019 Lease liabilities Operating leases - Property Property - operating lease liabilities $ 30,746 $ 17,317 Finance leases - Property Other liabilities 28 702 Total lease liabilities $ 30,774 $ 18,019
Lease Costs	The table below sets forth the weighted average terms and discount rates of our property leases as of December 31, 2020: Weighted average remaining lease term Operating leases 50 years Finance leases < 1 year Weighted average discount rate Operating leases 7.21 % Finance leases 3.62 % The table below presents our total property lease cost (in thousands): For the Years Ended December 31, Lease cost Statement of Operations Location 2020 2019 Operating lease cost Property leases - fixed Property operating expenses $ 2,413 $ 1,664 Property leases - variable Property operating expenses 127 4 Finance lease cost Amortization of property right-of-use assets Property operating expenses 34 30 $ 2,574 $ 1,698 The table below presents the effect of property lease payments on our consolidated statements of cash flows (in thousands): For the Years Ended December 31, Supplemental cash flow information 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ 1,694 $ 1,004 Financing cash flows for financing leases $ 674 $ 14
Finance Lease, Liability, Maturity	Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019
Operating Lease, Liability, Maturity	Payments on property leases were due as follows (in thousands): As of December 31, 2020 As of December 31, 2019 Year Ending December 31, Operating Finance Total Operating Finance Total 2020 N/A N/A N/A $ 1,092 $ 674 $ 1,766 2021 $ 3,211 $ 14 $ 3,225 1,138 14 1,152 2022 3,332 14 3,346 1,162 14 1,176 2023 3,382 — 3,382 1,167 — 1,167 2024 3,434 — 3,434 1,173 — 1,173 2025 1,780 — 1,780 N/A N/A N/A Thereafter 126,350 — 126,350 100,609 — 100,609 Total lease payments 141,489 28 141,517 106,341 702 107,043 Less: Amount representing interest (110,743) — (110,743) (89,024) — (89,024) Lease liability $ 30,746 $ 28 $ 30,774 $ 17,317 $ 702 $ 18,019

Real Estate Joint Ventures (Tab

Real Estate Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Real estate joint ventures	The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of December 31, 2020 (dollars in thousands): Nominal Ownership % December 31, 2020 (1) Date Acquired Total Encumbered Assets Total Liabilities Entity Location LW Redstone Company, LLC 3/23/2010 85% Huntsville, Alabama $ 403,448 $ 92,590 $ 100,334 Stevens Investors, LLC 8/11/2015 95% Washington, D.C. 161,735 158,286 88,028 M Square Associates, LLC 6/26/2007 50% College Park, Maryland 100,258 62,446 55,227 $ 665,441 $ 313,322 $ 243,589 (1) Excludes amounts eliminated in consolidation.
Schedule of information related to investments in unconsolidated real estate joint ventures	The table below sets forth information pertaining to our investments in unconsolidated real estate joint ventures accounted for using the equity method of accounting (dollars in thousands): Date Acquired Nominal Ownership % Number of Properties Carrying Value of Investment (1) Entity December 31, 2020 December 31, 2019 B RE COPT DC JV II LLC (2) 10/30/2020 10% 8 $ 15,988 $ — BREIT COPT DC JV LLC 6/20/2019 10% 9 13,315 14,133 GI-COPT DC Partnership LLC 7/21/2016 50% N/A — 37,816 17 $ 29,303 $ 51,949 (1) Included in the line entitled “investment in unconsolidated real estate joint ventures” on our consolidated balance sheets. (2) As of December 31, 2020, our investment in B RE COPT was $7.4 million lower than our share of the joint venture’s equity due to a difference between our cost basis and our share of B RE COPT’s underlying equity in the net assets acquired from GI-COPT.

Intangible Assets on Real Est_2

Intangible Assets on Real Estate Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2020
Intangible Assets on Real Estate Acquisitions
Schedule of intangible assets on real estate acquisitions	Intangible assets on real estate acquisitions consisted of the following (in thousands): December 31, 2020 December 31, 2019 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net In-place lease value $ 131,974 $ 123,291 $ 8,683 $ 131,975 $ 120,894 $ 11,081 Tenant relationship value 59,069 49,055 10,014 59,131 43,544 15,587 Above-market leases 13,718 13,380 338 13,718 13,318 400 Other 1,333 1,024 309 1,333 1,009 324 $ 206,094 $ 186,750 $ 19,344 $ 206,157 $ 178,765 $ 27,392

Investing Receivables (Tables)

Investing Receivables (Tables)	12 Months Ended
	Dec. 31, 2020
Receivables [Abstract]
Schedule of investing receivables	Investing receivables consisted of the following (in thousands): December 31, 2020 2019 Notes receivable from the City of Huntsville $ 65,564 $ 59,427 Other investing loans receivable 6,041 14,096 Amortized cost basis 71,605 73,523 Allowance for credit losses (2,851) — Investing receivables, net $ 68,754 $ 73,523

Prepaid Expenses and Other As_2

Prepaid Expenses and Other Assets, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Prepaid Expense and Other Assets [Abstract]
Schedule of prepaid expenses and other assets	Prepaid expenses and other assets, net consisted of the following (in thousands): December 31, 2020 2019 Lease incentives, net $ 35,642 $ 28,433 Prepaid expenses 19,690 18,835 Furniture, fixtures and equipment, net 10,433 7,823 Construction contract costs in excess of billings, net 10,343 17,223 Net investment in sales-type leases 6,573 — Non-real estate equity investments 5,509 6,705 Restricted cash 3,664 3,397 Deferred financing costs, net (1) 2,439 3,633 Deferred tax asset, net 1,989 2,328 Other assets 5,274 4,639 Total for COPLP and subsidiaries 101,556 93,016 Marketable securities in deferred compensation plan 3,027 3,060 Total for COPT and subsidiaries $ 104,583 $ 96,076 (1) Represents deferred costs, net of accumulated amortization, attributable to our Revolving Credit Facility and interest rate derivatives.
Schedule of tax effects of temporary differences and carry forwards in net deferred tax assets	Deferred tax asset, net reported above includes the following tax effects of temporary differences and carry forwards of our TRS (in thousands): December 31, 2020 2019 Operating loss carry forward $ 2,087 $ 2,885 Property 103 (77) Valuation allowance (201) (480) Deferred tax asset, net $ 1,989 $ 2,328

Debt, Net (Tables)

Debt, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of debt	Our debt consisted of the following (dollars in thousands): Carrying Value (1) as of December 31, 2020 December 31, December 31, 2019 Stated Interest Rates Scheduled Maturity Mortgage and Other Secured Debt: Fixed rate mortgage debt (2) $ 139,991 $ 143,430 3.82% - 4.62% (3) 2023-2026 Variable rate secured debt (4) 115,119 68,055 LIBOR + 1.45% to 2.35% (5) 2022-2026 Total mortgage and other secured debt 255,110 211,485 Revolving Credit Facility 143,000 177,000 LIBOR + 0.775% to 1.45% (6) March 2023 (7) Term Loan Facility 398,447 248,706 LIBOR + 1.00% to 1.65% (8) 2022 Unsecured Senior Notes (9) 3.60%, $350,000 aggregate principal 348,888 348,431 3.60% (10) May 2023 5.25%, $250,000 aggregate principal 248,194 247,652 5.25% (11) February 2024 5.00%, $300,000 aggregate principal 297,915 297,503 5.00% (12) July 2025 2.25%, $400,000 aggregate principal 394,464 — 2.25% (13) March 2026 3.70%, $300,000 aggregate principal — 299,324 3.70% (14) N/A (14) Unsecured note payable 900 1,038 0% (15) May 2026 Total debt, net $ 2,086,918 $ 1,831,139 (1) The carrying values of our debt other than the Revolving Credit Facility reflect net deferred financing costs of $5.9 million as of December 31, 2020 and $5.8 million as of December 31, 2019. (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 $155,000 as of December 31, 2020 and $217,000 as of December 31, 2019. (3) The weighted average interest rate on our fixed rate mortgage debt was 4.16% as of December 31, 2020. (4) Includes a construction loan with $29.1 million in remaining borrowing capacity as of December 31, 2020. (5) The weighted average interest rate on our variable rate secured debt was 2.28% as of December 31, 2020. (6) The weighted average interest rate on the Revolving Credit Facility was 1.20% as of December 31, 2020. (7) The facility matures in March 2023, 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. (8) The interest rate on this loan was 1.15% as of December 31, 2020. (9) Refer to the paragraphs below for further disclosure. (10) The carrying value of these notes reflects an unamortized discount totaling $781,000 as of December 31, 2020 and $1.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%. (11) The carrying value of these notes reflects an unamortized discount totaling $1.6 million as of December 31, 2020 and $2.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%. (12) The carrying value of these notes reflects an unamortized discount totaling $1.8 million as of December 31, 2020 and $2.1 million as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% (13) The carrying value of these notes reflects an unamortized discount totaling $4.5 million as of December 31, 2020 . (14) The carrying value of these notes reflects an unamortized discount totaling $534,000 as of December 31, 2019. The effective interest rate under the notes, including amortization of the issuance costs, was 3.85%. (15) 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 $161,000 as of December 31, 2020 and $223,000 as of December 31, 2019.
Schedule of debt maturities	Our debt matures on the following schedule (in thousands): Year Ending December 31, December 31, 2020 2021 $ 3,955 2022 487,380 2023 560,130 2024 279,983 2025 323,717 Thereafter 446,300 Total $ 2,101,465 (1) (1) Represents scheduled principal amortization and maturities only and therefore excludes net discounts and deferred financing costs of $14.5 million.
Schedule of the fair value of debt	The following table sets forth information pertaining to the fair value of our debt (in thousands): December 31, 2020 December 31, 2019 Carrying Estimated Carrying Estimated Fixed-rate debt Unsecured Senior Notes $ 1,289,461 $ 1,334,342 $ 1,192,910 $ 1,227,441 Other fixed-rate debt 140,891 142,838 144,468 149,907 Variable-rate debt 656,566 654,102 493,761 495,962 $ 2,086,918 $ 2,131,282 $ 1,831,139 $ 1,873,310

Interest Rate Derivatives (Tabl

Interest Rate Derivatives (Tables)	12 Months Ended
	Dec. 31, 2020
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): Notional Amount Effective Date Expiration Date Fair Value at December 31, Fixed Rate Floating Rate Index 2020 2019 $ 100,000 1.901 % One-Month LIBOR 9/1/2016 12/1/2022 $ (3,394) $ (1,028) 100,000 1.905 % One-Month LIBOR 9/1/2016 12/1/2022 (3,401) (1,037) 50,000 1.908 % One-Month LIBOR 9/1/2016 12/1/2022 (1,704) (524) 11,200 (1) 1.678 % One-Month LIBOR 8/1/2019 8/1/2026 (733) (20) 23,000 (2) 0.573 % One-Month LIBOR 4/1/2020 3/26/2025 (290) — 75,000 (3) 3.176 % Three-Month LIBOR 6/30/2020 N/A — (8,640) 75,000 (3) 3.192 % Three-Month LIBOR 6/30/2020 N/A — (8,749) 75,000 (3) 2.744 % Three-Month LIBOR 6/30/2020 N/A — (5,684) — 1.390 % One-Month LIBOR 10/13/2015 10/1/2020 — 23 $ (9,522) $ (25,659) (1) The notional amount of this instrument is scheduled to amortize to $10.0 million. (2) The notional amount of this instrument is scheduled to amortize to $22.1 million. (3) As discussed below, these instruments were cash settled in September 2020.
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 December 31, Derivatives Balance Sheet Location 2020 2019 Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets, net $ — $ 23 Interest rate swaps designated as cash flow hedges Interest rate derivatives (liabilities) $ (9,522) $ (25,682)
Schedule of effect of interest rate derivatives on consolidated statements of operations and comprehensive income	The tables below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): Amount of Loss Recognized in AOCL on Derivatives Amount of (Loss) Gain Reclassified from AOCL into Interest Expense on Statement of Operations For the Years Ended December 31, For the Years Ended December 31, Derivatives in Hedging Relationships 2020 2019 2018 2020 2019 2018 Interest rate derivatives $ (39,454) $ (24,321) $ (2,373) $ (3,725) $ 1,415 $ 407 Amount of Loss Reclassified from AOCL into Loss on Interest Rate Derivatives on Statement of Operations Amount of Loss Recognized on Undesignated Swaps in Loss on Interest Rate Derivatives on Statement of Operations For the Years Ended December 31, For the Years Ended December 31, Derivatives in Hedging Relationships 2020 2019 2018 2020 2019 2018 Interest rate derivatives $ (51,865) $ — — $ (1,265) $ — —

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2020
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 Years Ended December 31, 2020 2019 2018 Beginning balance $ 29,431 $ 26,260 $ 23,125 Contributions from noncontrolling interests — — 186 Distributions to noncontrolling interests (14,034) (2,413) (1,411) Net income attributable to noncontrolling interests 3,426 3,835 2,523 Adjustment to arrive at fair value of interests 6,607 1,749 1,837 Ending balance $ 25,430 $ 29,431 $ 26,260

Share-Based Compensation and _2

Share-Based Compensation and Other Compensation Matters (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Reporting for share-based compensation expense	The table below sets forth our reporting for share based compensation cost (in thousands): For the Years Ended December 31, 2020 2019 2018 General, administrative and leasing expenses $ 5,385 $ 5,748 $ 5,415 Property operating expenses 1,119 966 961 Capitalized to development activities 556 742 587 Share-based compensation cost $ 7,060 $ 7,456 $ 6,963
Summary of restricted share and TB-PIU transactions under the entity's share-based compensation plans	The following table summarizes restricted shares under the share-based compensation plans for 2018, 2019 and 2020: Shares Weighted Average Grant Date Fair Value Unvested as of December 31, 2017 425,626 $ 30.37 Granted 219,716 25.62 Forfeited (25,419) 30.02 Vested (181,238) 29.49 Unvested as of December 31, 2018 438,685 28.38 Granted 195,520 26.56 Forfeited (56,341) 29.44 Vested (185,001) 28.01 Unvested as of December 31, 2019 392,863 27.49 Granted 166,918 25.22 Forfeited (25,773) (1) 27.12 Vested (173,191) 28.14 Unvested as of December 31, 2020 360,817 $ 26.16 Unvested shares as of December 31, 2020 that are expected to vest 330,605 $ 26.14 (1) Includes 9,064 restricted shares previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. 2020 : Number of TB-PIUs Weighted Average Grant Date Fair Value Unvested as of December 31, 2018 — N/A Granted 61,820 $ 26.01 Unvested as of December 31, 2019 61,820 26.01 Granted 98,318 25.47 Forfeited (20,622) (1) 25.50 Vested (25,182) 26.30 Unvested as of December 31, 2020 114,334 $ 25.57 Unvested TB-PIUs as of December 31, 2020 that are expected to vest 114,334 $ 25.57
Schedule of PB-PIU/PSUs Granted	We made the following grants of PB-PIUs to executives in 2019 and 2020 : (dollars in thousands, except per share data): Grant Date Number of PB-PIUs Granted Performance Period Commencement Date Performance Period End Date Grant Date Fair Value Number of PB-PIUs Outstanding as of December 31, 2020 (1) 1/1/2019 193,682 1/1/2019 12/31/2021 $ 2,415 156,104 1/1/2020 176,758 1/1/2020 12/31/2022 $ 2,891 141,152 (1) Excludes 73,184 PB-PIUs previously awarded to our former Executive Vice President and Chief Operating Officer that were forfeited upon his resignation. We made the following grants of PSUs to executives from 2016 through 2018 (dollars in thousands): Grant Date Number of PSUs Granted Performance Period Commencement Date Performance Period End Date Grant Date Fair Value Number of PSUs Outstanding as of December 31, 2020 3/1/2016 26,299 1/1/2016 12/31/2018 $ 1,005 — 1/1/2017 39,351 1/1/2017 12/31/2019 $ 1,415 — 1/1/2018 59,110 1/1/2018 12/31/2020 $ 1,890 46,912 (1)
Schedule of payouts for defined performance under PB-PIU/PSUs	The number of earned awards at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return (“TSR”) relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned Awards Payout % 75th or greater 100% of PB-PIUs granted 50th (target) 50% of PB-PIUs granted 25th 25% of PB-PIUs granted Below 25th 0% of PB-PIUs granted Percentile Rank Earned PSUs Payout % 75th or greater 200% of PSUs granted 50th (target) 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted
Schedule of assumptions used in Monte Carlo models for PB-PIUs	The grant date fair value and certain of the assumptions used in the Monte Carlo models for the PB-PIUs granted in 2019 and 2020 are set forth below: Grant Date Grant Date Fair Value Per PB-PIU Baseline Common Share Value Expected Volatility of Common Shares Risk-free Interest Rate 1/1/2019 $ 12.47 $ 21.03 21.0 % 2.51 % 1/1/2020 $ 16.36 $ 29.38 18.0 % 1.65 %
Deferred Shares Granted	We made the following grants of deferred share awards to nonemployee members of our Board of Trustees in 2018, 2019 and 2020 (dollars in thousands, except per share data): Year of Grant Number of Deferred Share Awards Granted Aggregate Grant Date Fair Value Grant Date Fair Value Per Share 2018 13,832 $ 388 $ 28.08 2019 3,432 $ 95 $ 27.60 2020 10,679 $ 253 $ 23.68
Share-based compensation, common shares issued in settlement of vested deferred share awards	We issued the following common shares in settlement of deferred shares in 2018, 2019 and 2020 (dollars in thousands, except per share data): Year of Settlement Number of Common Shares Issued Grant Date Fair Value Per Share Aggregate Intrinsic Value 2018 5,515 $ 29.32 $ 154 2019 3,097 $ 26.77 $ 86 2020 — N/A N/A

Credit Losses, Financial Asse_2

Credit Losses, Financial Assets and Other Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Schedule of Credit Losses, Financial Assets and Other Instruments, Allowance for Credit Loss	The table below sets forth the activity for the allowance for credit losses (in thousands): For the Year Ended December 31, 2020 Investing Receivables Tenant Notes Other Assets (2) Off-Balance Sheet Credit Exposures Total December 31, 2019 $ — $ 97 $ — $ — $ 97 Cumulative effect of change for adoption of credit loss guidance 3,732 325 144 1,340 5,541 Credit loss (recoveries) expense (881) 729 559 (1,340) (933) Other changes — 52 (60) — (8) December 31, 2020 $ 2,851 $ 1,203 $ 643 $ — $ 4,697 (1) Included in the line entitled “accounts receivable, net” on our consolidated balance sheets. (2) The balance as of December 31, 2020 included $257,000 in the line entitled “accounts receivable, net” and $386,000 in the line entitled “prepaid expenses and other assets, net” on our consolidated balance sheets.
Financing Receivable Credit Quality Indicators	The following table presents the amortized cost basis of our investing receivables and tenants notes receivable by credit risk classification, by origination year as of December 31, 2020 (in thousands): Origination Year 2015 and Earlier 2016 2017 2018 2019 2020 Total Investing receivables: Credit risk classification: Investment grade $ 64,354 $ — $ 971 $ — $ — $ 239 $ 65,564 Non-investment grade — — — — 6,041 — 6,041 Total $ 64,354 $ — $ 971 $ — $ 6,041 $ 239 $ 71,605 Tenant notes receivable: Credit risk classification: Investment grade $ — $ 14 $ — $ 1,028 $ 84 $ 343 $ 1,469 Non-investment grade 97 165 — 164 1,883 1,803 4,112 Total $ 97 $ 179 $ — $ 1,192 $ 1,967 $ 2,146 $ 5,581 Sales-type lease receivable: Credit risk classification: Investment grade $ — $ — $ — $ — $ — $ 6,573 $ 6,573

Information by Business Segme_2

Information by Business Segment (Tables)	12 Months Ended
	Dec. 31, 2020
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 Operating Other Total Year Ended December 31, 2020 Revenues from real estate operations $ 254,197 $ 57,817 $ 50,982 $ 32,869 $ 22,515 $ 29,139 $ 447,519 $ 60,627 $ 27,788 $ 2,791 $ 538,725 Property operating expenses (85,032) (21,321) (29,055) (12,655) (8,119) (3,195) (159,377) (29,144) (14,171) (1,148) (203,840) UJV NOI allocable to COPT — — — — — 6,951 6,951 — — — 6,951 NOI from real estate operations $ 169,165 $ 36,496 $ 21,927 $ 20,214 $ 14,396 $ 32,895 $ 295,093 $ 31,483 $ 13,617 $ 1,643 $ 341,836 Additions to long-lived assets $ 31,295 $ 11,620 $ — $ 7,104 $ 2,905 $ — $ 52,924 $ 17,232 $ 11,158 $ 165 $ 81,479 Transfers from non-operating properties $ 21,859 $ 2,557 $ 456 $ — $ 138,122 $ 230,277 $ 393,271 $ 83,091 $ — $ — $ 476,362 Segment assets at December 31, 2020 $ 1,277,849 $ 392,714 $ 142,137 $ 178,897 $ 281,386 $ 419,929 $ 2,692,912 $ 490,422 $ 202,089 $ 3,555 $ 3,388,978 Year Ended December 31, 2019 Revenues from real estate operations $ 252,781 $ 55,742 $ 51,140 $ 32,659 $ 16,593 $ 26,571 $ 435,486 $ 59,611 $ 29,405 $ 2,961 $ 527,463 Property operating expenses (82,815) (19,779) (29,042) (13,579) (6,626) (1,962) (153,803) (29,682) (13,213) (1,445) (198,143) UJV NOI allocable to COPT — — — — — 5,705 5,705 — — — 5,705 NOI from real estate operations $ 169,966 $ 35,963 $ 22,098 $ 19,080 $ 9,967 $ 30,314 $ 287,388 $ 29,929 $ 16,192 $ 1,516 $ 335,025 Additions to long-lived assets $ 34,618 $ 9,326 $ — $ 8,912 $ 1,548 $ — $ 54,404 $ 20,925 $ 893 $ 128 $ 76,350 Transfers from non-operating properties $ 18,606 $ 4,548 $ 10,781 $ — $ 33,606 $ 159,472 $ 227,013 $ — $ (1,012) $ — $ 226,001 Segment assets at December 31, 2019 $ 1,280,656 $ 396,914 $ 146,592 $ 184,257 $ 138,501 $ 279,099 $ 2,426,019 $ 392,319 $ 202,935 $ 3,685 $ 3,024,958 Year Ended December 31, 2018 Revenues from real estate operations $ 248,927 $ 53,518 $ 46,286 $ 31,927 $ 14,745 $ 25,650 $ 421,053 $ 61,181 $ 31,892 $ 3,127 $ 517,253 Property operating expenses (82,975) (20,330) (26,888) (13,536) (6,050) (3,225) (153,004) (30,253) (16,342) (1,436) (201,035) UJV NOI allocable to COPT — — — — — 4,818 4,818 — — — 4,818 NOI from real estate operations $ 165,952 $ 33,188 $ 19,398 $ 18,391 $ 8,695 $ 27,243 $ 272,867 $ 30,928 $ 15,550 $ 1,691 $ 321,036 Additions to long-lived assets $ 38,612 $ 7,956 $ — $ 6,535 $ 573 $ — $ 53,676 $ 19,730 $ 856 $ 480 $ 74,742 Transfers from non-operating properties $ 35,648 $ 10,231 $ 14,718 $ (116) $ 4,167 $ 99,191 $ 163,839 $ — $ 2,304 $ — $ 166,143 Segment assets at December 31, 2018 $ 1,279,571 $ 399,339 $ 139,731 $ 188,911 $ 108,010 $ 353,165 $ 2,468,727 $ 395,380 $ 216,640 $ 4,115 $ 3,084,862
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 Years Ended December 31, 2020 2019 2018 Segment revenues from real estate operations $ 538,725 $ 527,463 $ 517,253 Construction contract and other service revenues 70,640 113,763 60,859 Total revenues $ 609,365 $ 641,226 $ 578,112
Reconciliation of UJV NOI allocable to COPT 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 Years Ended December 31, 2020 2019 2018 UJV NOI allocable to COPT $ 6,951 $ 5,705 $ 4,818 Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense (5,120) (4,065) (3,314) Add: Equity in (loss) income of unconsolidated non-real estate entities (6) (7) 1,193 Equity in income of unconsolidated entities $ 1,825 $ 1,633 $ 2,697
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 Years Ended December 31, 2020 2019 2018 Construction contract and other service revenues $ 70,640 $ 113,763 $ 60,859 Construction contract and other service expenses (67,615) (109,962) (58,326) NOI from service operations $ 3,025 $ 3,801 $ 2,533
Schedule of reconciliation of net operating income from real estate operations and service operations to net income	The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to net income as reported on our consolidated statements of operations (in thousands): For the Years Ended December 31, 2020 2019 2018 NOI from real estate operations $ 341,836 $ 335,025 $ 321,036 NOI from service operations 3,025 3,801 2,533 Interest and other income 8,574 7,894 4,358 Credit loss recoveries 933 — — Gain on sales of real estate 30,209 105,230 2,340 Gain on sale of investment in unconsolidated real estate joint venture 29,416 — — Equity in income of unconsolidated entities 1,825 1,633 2,697 Income tax (expense) benefit (353) 217 363 Depreciation and other amortization associated with real estate operations (138,193) (137,069) (137,116) Impairment losses (1,530) (329) (2,367) General, administrative and leasing expenses (33,001) (35,402) (28,900) Business development expenses and land carry costs (4,473) (4,239) (5,840) Interest expense (67,937) (71,052) (75,385) UJV NOI allocable to COPT included in equity in income of unconsolidated entities (6,951) (5,705) (4,818) Loss on early extinguishment of debt (7,306) — (258) Loss on interest rate derivatives (53,196) — — Net income $ 102,878 $ 200,004 $ 78,643
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): As of December 31, 2020 2019 Segment assets $ 3,388,978 $ 3,024,958 Operating properties lease liabilities included in segment assets 30,721 17,317 Non-operating property assets 466,991 621,630 Other assets 190,333 190,548 Total COPT consolidated assets $ 4,077,023 $ 3,854,453

Construction Contract and Oth_2

Construction Contract and Other Service Revenues (Tables)	12 Months Ended
	Dec. 31, 2020
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 Years Ended December 31, 2020 2019 2018 Construction contract revenue: GMP $ 22,032 $ 67,708 $ 34,050 Cost-plus fee 34,025 34,386 5,540 FFP 12,373 10,688 20,327 Other 2,210 981 942 $ 70,640 $ 113,763 $ 60,859 The table below reports construction contract and other service revenues by service type (in thousands): For the Years Ended December 31, 2020 2019 2018 Construction contract revenue: Construction $ 66,087 $ 112,170 $ 57,986 Design 2,343 612 1,931 Other 2,210 981 942 $ 70,640 $ 113,763 $ 60,859
Contract Asset, Contract Liability and Receivable	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 Years Ended December 31, 2020 2019 Beginning balance $ 12,378 $ 6,701 Ending balance $ 13,997 $ 12,378 Contract assets, which we refer to herein as construction contract 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 Years Ended December 31, 2020 2019 Beginning balance $ 17,223 $ 3,189 Ending balance $ 10,343 $ 17,223 Contract liabilities are included in other liabilities reported on our consolidated balance sheets. Changes in contract liabilities were as follows (in thousands): For the Years Ended December 31, 2020 2019 Beginning balance $ 1,184 $ 568 Ending balance $ 4,610 $ 1,184 Portion of beginning balance recognized in revenue during the year $ 757 $ 446

Earnings Per Share ("EPS") an_2

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
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 Years Ended December 31, 2020 2019 2018 Numerator: Net income attributable to COPT $ 97,374 $ 191,692 $ 72,301 Income attributable to share-based compensation awards (431) (656) (462) Numerator for basic EPS on net income attributable to COPT common shareholders $ 96,943 $ 191,036 $ 71,839 Redeemable noncontrolling interests — 132 — Income attributable to share-based compensation awards 27 33 — Numerator for diluted EPS on net income attributable to COPT common shareholders $ 96,970 $ 191,201 $ 71,839 Denominator (all weighted averages): Denominator for basic EPS (common shares) 111,788 111,196 103,946 Dilutive effect of redeemable noncontrolling interests — 119 — Dilutive effect of share-based compensation awards 288 308 134 Dilutive effect of forward equity sale agreements — — 45 Denominator for diluted EPS (common shares) 112,076 111,623 104,125 Basic EPS $ 0.87 $ 1.72 $ 0.69 Diluted EPS $ 0.87 $ 1.71 $ 0.69 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 Years Ended December 31, 2020 2019 2018 Numerator: Net income attributable to COPLP $ 98,854 $ 194,619 $ 74,703 Preferred unit distributions (300) (564) (660) Income attributable to share-based compensation awards (511) (785) (462) Numerator for basic EPU on net income attributable to COPLP common unitholders 98,043 193,270 73,581 Redeemable noncontrolling interests — 132 — Income attributable to share-based compensation awards — 33 — Numerator for diluted EPU on net income attributable to COPLP common unitholders $ 98,043 $ 193,435 $ 73,581 Denominator (all weighted averages): Denominator for basic EPU (common units) 113,024 112,495 106,414 Dilutive effect of redeemable noncontrolling interests — 119 — Dilutive effect of share-based compensation awards 288 308 134 Dilutive effect of forward equity sale agreements — — 45 Denominator for diluted EPU (common units) 113,312 112,922 106,593 Basic EPU $ 0.87 $ 1.72 $ 0.69 Diluted EPU $ 0.87 $ 1.71 $ 0.69
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 Years Ended December 31, 2020 2019 2018 Conversion of common units 1,236 1,299 2,468 Conversion of redeemable noncontrolling interests 957 896 936 Conversion of Series I Preferred Units 171 176 176 Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator for the Years Ended December 31, 2020 2019 2018 Conversion of redeemable noncontrolling interests 957 896 936 Conversion of Series I Preferred Units 171 176 176

Organization (Narrative) (Detai

Organization (Narrative) (Details) ft² in Millions	12 Months Ended
	Dec. 31, 2020property	Dec. 31, 2019	Dec. 31, 2020ft²	Dec. 31, 2020MW	Dec. 31, 2020a	Dec. 31, 2020shares
Corporate Office Properties, L.P | COPT | Preferred units
Investments in real estate
Limited partners' capital account, units outstanding (in shares) | shares						0
Common Units | Corporate Office Properties, L.P | COPT
Investments in real estate
Percentage ownership in operating partnership	98.60%	98.70%
Operating properties
Investments in real estate
Number of real estate properties	181
Area of real estate property (in sqft or acres) | ft²			21
Operating properties | Office Properties
Investments in real estate
Number of real estate properties	155
Area of real estate property (in sqft or acres) | ft²			16.2
Operating properties | Single-tenant data centers
Investments in real estate
Number of real estate properties	26
Area of real estate property (in sqft or acres) | ft²			4.7
Operating Wholesale Data Center
Investments in real estate
Critical load (in megawatts) | MW				19.25
Properties under development
Investments in real estate
Number of real estate properties	11
Area of real estate property (in sqft or acres) | ft²			1.5
Properties under development | Office Properties
Investments in real estate
Number of real estate properties	9
Properties under development | Single-tenant data centers
Investments in real estate
Number of real estate properties	2
Properties Under Development, Partially-Operational
Investments in real estate
Number of real estate properties	3
Land controlled for future development
Investments in real estate
Area of real estate property (in sqft or acres)			10.4		830
Other land
Investments in real estate
Area of real estate property (in sqft or acres) | a					43
Unconsolidated Real Estate Joint Ventures
Investments in real estate
Number of real estate properties	17
Unconsolidated Real Estate Joint Ventures | Operating properties | Single-tenant data centers
Investments in real estate
Number of real estate properties	17

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Properties and Impairment) (Details)	12 Months Ended
	Dec. 31, 2020
Properties
Period after the cessation of major construction activities for considering property as operational if leases have not commenced earlier (in years)	1 year
Period after the cessation of major construction activities for considering property as partially operational if leases have commenced earlier (in years)	1 year
Property, Plant and Equipment [Line Items]
Period used recovery analysis for long-lived assets to be held and used that may be impaired (in years)	10 years
Minimum | Buildings and building improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Minimum | Land improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years
Minimum | Equipment and personal property
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum | Buildings and building improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Maximum | Land improvements
Property, Plant and Equipment [Line Items]
Estimated useful life	20 years
Maximum | Equipment and personal property
Property, Plant and Equipment [Line Items]
Estimated useful life	10 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies (Revenue Recognition) (Details)	Dec. 31, 2020
United States Government
Lessor, Lease, Description [Line Items]
Renewal term	1 year

Summary of Significant Accoun_6

Summary of Significant Accounting Policies (Share-Based Compensation) (Details)	12 Months Ended
	Dec. 31, 2020form
Accounting Policies [Abstract]
Number of forms of share based compensation plans	4

Summary of Significant Accoun_7

Summary of Significant Accounting Policies (Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Approximate amount by which basis of assets and liabilities for tax reporting purposes is higher (lower) than amount reported on consolidated balance sheet	$ 10
Common Shares
Income Tax Disclosure [Line Items]
Ordinary income	45.10%	54.40%	83.10%
Long-term capital gain	54.90%	45.60%	0.00%
Return of capital	0.00%	0.00%	16.90%

Summary of Significant Accoun_8

Summary of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss impact		$ 5,541
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit loss impact	$ 5,500

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2020
Assets and liabilities measured at fair value on a recurring basis
Marketable securities in deferred compensation plan		$ 3,060	$ 3,027
Fair Value, Recurring | Deferred compensation plan | Trustees and Management
Assets and liabilities measured at fair value on a recurring basis
Maximum percentage of participants' compensation which is deferrable (as a percent)		100.00%
Marketable securities in deferred compensation plan		$ 3,100	$ 3,000
Fair Value, Nonrecurring | Frederick, Maryland
Assets and liabilities measured at fair value on a recurring basis
Impairment losses	$ 327

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Marketable securities in deferred compensation plan	$ 3,027	$ 3,060
Fair value measurement on a recurring basis
Assets:
Other marketable securities	30
Interest rate derivatives		23
Total assets	3,057	3,083
Liabilities:
Deferred compensation plan liability	3,027	3,060
Interest rate derivatives	9,522	25,682
Total liabilities	12,549	28,742
Fair value measurement on a recurring basis | Mutual funds
Assets:
Marketable securities in deferred compensation plan	3,008	3,035
Fair value measurement on a recurring basis | Other
Assets:
Marketable securities in deferred compensation plan	19	25
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Other marketable securities	30
Interest rate derivatives		0
Total assets	3,057	3,060
Liabilities:
Deferred compensation plan liability	0	0
Interest rate derivatives	0	0
Total liabilities	0	0
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	3,008	3,035
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	19	25
Fair value measurement on a recurring basis | Significant Other Observable Inputs(Level 2)
Assets:
Other marketable securities	0
Interest rate derivatives		23
Total assets	0	23
Liabilities:
Deferred compensation plan liability	3,027	3,060
Interest rate derivatives	9,522	25,682
Total liabilities	12,549	28,742
Fair value measurement on a recurring basis | Significant Other Observable Inputs(Level 2) | Mutual funds
Assets:
Marketable securities in deferred compensation plan	0	0
Fair value measurement on a recurring basis | Significant Other Observable Inputs(Level 2) | Other
Assets:
Marketable securities in deferred compensation plan	0	0
Fair value measurement on a recurring basis | Significant Unobservable  Inputs (Level 3)
Assets:
Other marketable securities	0
Interest rate derivatives		0
Total assets	0	0
Liabilities:
Deferred compensation plan liability	0	0
Interest rate derivatives	0	0
Total liabilities	0	0
Fair value measurement on a recurring basis | Significant Unobservable  Inputs (Level 3) | Mutual funds
Assets:
Marketable securities in deferred compensation plan	0	0
Fair value measurement on a recurring basis | Significant Unobservable  Inputs (Level 3) | Other
Assets:
Marketable securities in deferred compensation plan	0	0
Corporate Office Properties, L.P | Fair value measurement on a recurring basis
Assets:
Other marketable securities	30
Interest rate derivatives		23
Liabilities:
Interest rate derivatives	9,522	25,682
Corporate Office Properties, L.P | Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Other marketable securities	30
Interest rate derivatives		0
Liabilities:
Interest rate derivatives	0	0
Corporate Office Properties, L.P | Fair value measurement on a recurring basis | Significant Other Observable Inputs(Level 2)
Assets:
Other marketable securities	0
Interest rate derivatives		23
Liabilities:
Interest rate derivatives	9,522	25,682
Corporate Office Properties, L.P | Fair value measurement on a recurring basis | Significant Unobservable  Inputs (Level 3)
Assets:
Other marketable securities	0
Interest rate derivatives		0
Liabilities:
Interest rate derivatives	$ 0	$ 0

Properties, Net (Operating prop

Properties, Net (Operating properties, net) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating properties, net
Gross	$ 4,686,802	$ 4,348,006	$ 4,148,529	$ 3,980,813
Operating properties, net	3,115,280	2,772,647
Operating properties, net
Operating properties, net
Less: accumulated depreciation	(1,124,253)	(1,007,120)
Operating properties, net	3,115,280	2,772,647
Operating properties, net | Land
Operating properties, net
Gross	528,269	472,976
Operating properties, net | Buildings and improvements
Operating properties, net
Gross	$ 3,711,264	$ 3,306,791

Properties, Net (Narrative) (De

Properties, Net (Narrative) (Details) ft² in Thousands	Oct. 30, 2020USD ($)property	Sep. 30, 2020USD ($)	Dec. 31, 2018USD ($)ft²property	Dec. 31, 2019USD ($)ft²property	Dec. 31, 2018USD ($)ft²property	Dec. 31, 2020ft²property	Dec. 22, 2020	Dec. 05, 2019property	Jun. 20, 2019property	Oct. 27, 2017USD ($)ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage sold	90.00%			90.00%
Number of properties sold	2			9
B RE COPT DC JV II LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage	10.00%					10.00%	10.00%
Number of real estate properties						8
BREIT COPT DC JV LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage				10.00%		10.00%
Number of real estate properties						9
Baltimore, Maryland
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges | $		$ 1,500,000
Expansion of Fully-Operational Properties Placed in Service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in sqft or acres) | ft²						42
Number of real estate properties						3
Properties Under Development, Partially-Operational
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties						3
Newly-developed properties placed in service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in sqft or acres) | ft²			666	1,100	666	1,800
Number of real estate properties			6	9	6	11
Redeveloped Property Placed in Service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in sqft or acres) | ft²						21
Properties under development
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in sqft or acres) | ft²						1,500
Number of real estate properties						11
Newly redeveloped properties placed In service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in sqft or acres) | ft²			22	85	22
Number of real estate properties			1	1	1
Fort Meade/BW Corridor sub-segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges | $					$ 2,400,000
Data Center Shells in Northern Virginia | Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage sold	90.00%			90.00%
Number of properties sold	2			9				2	7
Transaction value | $	$ 89,700,000			$ 345,100,000
Proceeds from sale | $	80,700,000			310,600,000
Gain on disposal | $	$ 30,000,000			$ 105,200,000
Data Center Shells in Chester, Virginia | Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transaction value | $										$ 44,000,000
Gain on disposal | $			$ 1,500,000
Area of real estate property (in sqft or acres) | ft²										193
Maximum exposure | $										$ 20,000,000

Leases (Lessor Arrangements) (D

Leases (Lessor Arrangements) (Details)	12 Months Ended
	Dec. 31, 2020
Lessor, Lease, Description [Line Items]
Average term of contract	5 years 4 months 24 days
Minimum
Lessor, Lease, Description [Line Items]
Term of contract	1 month
Maximum
Lessor, Lease, Description [Line Items]
Term of contract	18 years

Leases (Lease Revenue) (Details

Leases (Lease Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Fixed	$ 425,593	$ 412,342
Variable	110,534	110,130
Lease revenue	536,127	$ 522,472	$ 512,327
Operating leases
2021	424,585
2022	378,573
2023	324,917
2024	276,488
2025	197,677
Thereafter	745,303
Total contractual payments	2,347,543
Sales-type leases
2021	871
2022	949
2023	949
2024	949
2025	949
Thereafter	4,464
Total contractual payments	9,131
Less: Amount representing interest	(2,558)
Net investment in sales-type leases	$ 6,573

Leases (Percentage of Revenue)

Leases (Percentage of Revenue) (Details) - United States Government - Concentration risk	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lease Revenue, Risk Benchmark
Concentration Risk [Line Items]
Percentage of revenue	35.00%	34.00%
Fixed Lease Revenue Benchmark
Concentration Risk [Line Items]
Percentage of revenue	25.00%	25.00%

Leases (Lessee Arrangements) (D

Leases (Lessee Arrangements) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)Lease
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 81
Minimum | Land Leases
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	28 years
Maximum | Land Leases
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	95 years
Washington DC
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 10.1
Lessee, Remaining term of contract	79 years
Lessee, Number of lease contracts | Lease	2
Baltimore, Maryland
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 6.5
Lessee, Remaining term of contract	28 years
Optional renewal term	49 years
Phoenix, Arizona
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 6.5
Lessee, Remaining term of contract	4 years
Optional renewal term	5 years
Stevens Investors, LLC | Washington DC
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 37.8
Lessee, Remaining term of contract	95 years
LW Redstone Company, LLC | Huntsville, Alabama
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 11.3
Lessee, Number of lease contracts | Lease	15
Optional renewal term	25 years
LW Redstone Company, LLC | Huntsville, Alabama | Minimum
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	42 years
LW Redstone Company, LLC | Huntsville, Alabama | Maximum
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	51 years
M Square Associates, LLC | College Park, Maryland
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 6.6
Lessee, Number of lease contracts | Lease	4
M Square Associates, LLC | College Park, Maryland | Minimum
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	62 years
M Square Associates, LLC | College Park, Maryland | Maximum
Lessee, Lease, Description [Line Items]
Lessee, Remaining term of contract	73 years
Fort Meade/BW Corridor
Lessee, Lease, Description [Line Items]
Lessee, Right-of-use asset	$ 2.2
Lessee, Remaining term of contract	47 years
Lessee, Number of lease contracts | Lease	2

Leases (Property right-of-use A

Leases (Property right-of-use Assets ) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating leases - Property	$ 40,570	$ 27,864
Finance leases - Property	40,425	40,458
Total right-of-use assets	80,995	68,322
Property - operating lease liabilities	30,746	17,317
Finance leases - Property	28	702
Total lease liabilities	$ 30,774	$ 18,019
Finance Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilities

Leases (Weighted Average Terms

Leases (Weighted Average Terms and Discount Rates) (Details)	Dec. 31, 2020
Leases [Abstract]
Operating leases, Weighted average remaining lease term	50 years
Finance leases, Weighted average remaining lease term (less than)	1 year
Operating lease, Weighted average discount rate	7.21%
Finance lease, Weighted average discount rate	3.62%

Leases (Property Lease Cost) (D

Leases (Property Lease Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Lease costs	$ 2,574	$ 1,698
Property operating expenses
Lessee, Lease, Description [Line Items]
Property leases - fixed	2,413	1,664
Property leases - variable	127	4
Finance lease - Amortization of property right-of-use assets	$ 34	$ 30

Leases (Supplemental Cash Flow

Leases (Supplemental Cash Flow Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Financing cash flows for financing leases	$ 854	$ 223	$ 15,379
Real estate related leases
Lessee, Lease, Description [Line Items]
Operating cash flows for operating leases	1,694	1,004
Financing cash flows for financing leases	$ 674	$ 14

Leases (Property Leases Due) (D

Leases (Property Leases Due) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating leases
Year 1	$ 3,211	$ 1,092
Year 2	3,332	1,138
Year 3	3,382	1,162
Year 4	3,434	1,167
Year 5	1,780	1,173
Thereafter	126,350	100,609
Total lease payments	141,489	106,341
Less: Amount representing interest	(110,743)	(89,024)
Lease liability	30,746	17,317
Finance leases
Year 1	14	674
Year 2	14	14
Year 3	0	14
Year 4	0	0
Year 5	0	0
Thereafter	0	0
Total lease payments	28	702
Less: Amount representing interest	0	0
Lease liability	28	702
Total
Total, year 1	3,225	1,766
Total, year 2	3,346	1,152
Total, year 3	3,382	1,176
Total, year 4	3,434	1,167
Total, year 5	1,780	1,173
Total, thereafter	126,350	100,609
Total lease payments	141,517	107,043
Less: Amount representing interest	(110,743)	(89,024)
Total lease liabilities	$ 30,774	$ 18,019

Real Estate Joint Ventures (Con

Real Estate Joint Ventures (Consolidated Real Estate Joint Ventures) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Total Assets	$ 4,077,023	$ 3,854,453
Total Liabilities	2,357,881	$ 2,105,777
Variable Interest Entity, Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Total Assets	665,441
Encumbered Assets	313,322
Total Liabilities	$ 243,589
Variable Interest Entity, Primary Beneficiary | LW Redstone Company, LLC
Schedule of Equity Method Investments [Line Items]
Nominal Ownership %	85.00%
Total Assets	$ 403,448
Encumbered Assets	92,590
Total Liabilities	$ 100,334
Variable Interest Entity, Primary Beneficiary | Stevens Investors, LLC
Schedule of Equity Method Investments [Line Items]
Nominal Ownership %	95.00%
Total Assets	$ 161,735
Encumbered Assets	158,286
Total Liabilities	$ 88,028
Variable Interest Entity, Primary Beneficiary | M Square Associates, LLC
Schedule of Equity Method Investments [Line Items]
Nominal Ownership %	50.00%
Total Assets	$ 100,258
Encumbered Assets	62,446
Total Liabilities	$ 55,227

Real Estate Joint Ventures (Nar

Real Estate Joint Ventures (Narrative) (Details) $ in Thousands, ft² in Millions	Dec. 22, 2020USD ($)property	Dec. 31, 2020USD ($)ft²	Dec. 31, 2019USD ($)property	Dec. 31, 2018USD ($)	Dec. 21, 2020	Oct. 30, 2020property
Investments in real estate joint ventures
Ownership percentage sold			90.00%			90.00%
Number of properties sold | property			9			2
Gain on sale of investment in unconsolidated real estate joint venture		$ 29,416	$ 0	$ 0
GI-COPT DC Partnership LLC
Investments in real estate joint ventures
Ownership interest sold of the original 50% owned	80.00%
Ownership percentage			50.00%		50.00%
Proceeds from sale of investment in unconsolidated real estate joint venture	$ 60,000
Gain on sale of investment in unconsolidated real estate joint venture	$ 29,400
BREIT COPT DC JV LLC
Investments in real estate joint ventures
Ownership percentage		10.00%	10.00%
B RE COPT DC JV II LLC
Investments in real estate joint ventures
Ownership percentage	10.00%	10.00%				10.00%
LW Redstone Company, LLC
Investments in real estate joint ventures
Partner's capital account upon formation		$ 9,000
Percentage of cumulative preferred returns of cash flows on partners' invested capital		13.50%
Percentage of cumulative preferred returns of cash flows on our invested capital		13.50%
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the company		85.00%
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the entity's partners		15.00%
Number of years following construction commencement threshold achievement before partner's interest can be purchased at fair value		5 years
Construction commencement threshold (in square feet) | ft²		4.4
Construction commencement completed (in sqft) | ft²		1.6
LW Redstone Company, LLC | Maximum
Investments in real estate joint ventures
Infrastructure costs anticipated to be funded by entity for reimbursement by the City of Huntsville (in dollars)		$ 76,000
LW Redstone Company, LLC | Notes receivable from the City of Huntsville
Investments in real estate joint ventures
Infrastructure costs funded to date for reimbursement by the City of Huntsville		$ 61,000
Stevens Investors, LLC | Maximum
Investments in real estate joint ventures
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the company		85.00%
Stevens Investors, LLC | Minimum
Investments in real estate joint ventures
Percentage of residual distributable cash flows in excess of unpaid cumulative preferred returns and return of invested capital entitled to the company		60.00%
M Square Associates, LLC
Investments in real estate joint ventures
Percentage of residual amounts distributed to each member		50.00%
GI-COPT DC Partnership LLC | B RE COPT DC JV II LLC
Investments in real estate joint ventures
Number of properties sold | property	6

Real Estate Joint Ventures (Unc

Real Estate Joint Ventures (Unconsolidated Real Estate Joint Ventures) (Details) $ in Thousands	Dec. 31, 2020USD ($)property	Dec. 22, 2020	Dec. 21, 2020	Oct. 30, 2020	Dec. 31, 2019USD ($)
Unconsolidated Real Estate Joint Ventures
Schedule of Equity Method Investments [Line Items]
Number of real estate properties | property	17
Real estate equity method investments	$ 29,303				$ 51,949
B RE COPT DC JV II LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage	10.00%	10.00%		10.00%
Number of real estate properties | property	8
Real estate equity method investments	$ 15,988				$ 0
Difference between the joint venture's cost basis and the entity's share of B RE COPT’s underlying equity in the net assets acquired from GI-COPT	$ 7,400
BREIT COPT DC JV LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage	10.00%				10.00%
Number of real estate properties | property	9
Real estate equity method investments	$ 13,315				$ 14,133
GI-COPT DC Partnership LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage			50.00%		50.00%
Real estate equity method investments	$ 0				$ 37,816

Intangible Assets on Real Est_3

Intangible Assets on Real Estate Acquisitions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 206,094	$ 206,157
Accumulated Amortization	186,750	178,765
Net Carrying Amount	19,344	27,392
Amortization of the intangible assets	$ 8,000	8,700	$ 15,600
Weighted average amortization period of intangible assets	7 years
Estimated future amortization expense associated with the intangible asset categories for the next five years
2021	$ 4,700
2022	3,200
2023	2,800
2024	2,300
2025	2,000
In-place lease value
Intangible assets on real estate acquisitions
Gross Carrying Amount	131,974	131,975
Accumulated Amortization	123,291	120,894
Net Carrying Amount	$ 8,683	11,081
Weighted average amortization period of intangible assets	6 years
Tenant relationship value
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 59,069	59,131
Accumulated Amortization	49,055	43,544
Net Carrying Amount	$ 10,014	15,587
Weighted average amortization period of intangible assets	8 years
Above-market leases
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 13,718	13,718
Accumulated Amortization	13,380	13,318
Net Carrying Amount	$ 338	400
Weighted average amortization period of intangible assets	8 years
Other
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 1,333	1,333
Accumulated Amortization	1,024	1,009
Net Carrying Amount	$ 309	$ 324
Weighted average amortization period of intangible assets	22 years

Investing Receivables (Details)

Investing Receivables (Details) - Investing Receivables - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis	$ 71,605	$ 73,523
Allowance for credit losses	(2,851)	0
Investing receivables, net	68,754	73,523
Notes receivable from the City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis	65,564	59,427
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost basis	$ 6,041	$ 14,096

Investing Receivables (Narrativ

Investing Receivables (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable, fair value disclosure	$ 73	$ 74
Notes receivable from the City of Huntsville | LW Redstone Company, LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate	9.95%
Note receivable term	30 years
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate	8.00%
Investing Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable, net of allowance for credit losses	$ 4.8	$ 4.7

Prepaid Expenses and Other As_3

Prepaid Expenses and Other Assets, Net (Prepaid Expenses and Other Assets, Net) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Restricted cash	$ 3,664	$ 3,397	$ 3,884	$ 2,570
Marketable securities in deferred compensation plan	3,027	3,060
Total	104,583	96,076
Corporate Office Properties, L.P
Property, Plant and Equipment [Line Items]
Lease incentives, net	35,642	28,433
Prepaid expenses	19,690	18,835
Furniture, fixtures and equipment, net	10,433	7,823
Construction contract costs in excess of billings, net	10,343	17,223
Net investment in sales-type leases	6,573	0
Non-real estate equity investments	5,509	6,705
Restricted cash	3,664	3,397	$ 3,884	$ 2,570
Deferred financing costs, net	2,439	3,633
Deferred tax asset, net	1,989	2,328
Other assets	5,274	4,639
Total	$ 101,556	$ 93,016

Prepaid Expenses and Other As_4

Prepaid Expenses and Other Assets, Net (Deferred Tax Assets) (Details) - TRS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Tax Credit Carryforward [Line Items]
Operating loss carry forward	$ 2,087	$ 2,885
Property	103
Property		(77)
Valuation allowance	(201)	(480)
Deferred tax asset, net	$ 1,989	$ 2,328

Debt, Net (Debt Schedule) (Deta

Debt, Net (Debt Schedule) (Details)	Oct. 10, 2018extension	Dec. 31, 2020USD ($)	Sep. 17, 2020USD ($)	Dec. 31, 2019USD ($)
Debt
Carrying Value		$ 2,086,918,000		$ 1,831,139,000
Revolving Credit Facility
Debt
Carrying Value		$ 143,000,000		177,000,000
Weighted average interest rate		1.20%
Term Loan Facility
Debt
Interest rate		1.15%
Carrying Value		$ 398,447,000		248,706,000
Unsecured note payable
Debt
Interest rate		0.00%
Carrying Value		$ 900,000		1,038,000
Unamortized discount included in carrying value		$ 161,000		223,000
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Minimum
Debt
Variable rate, spread		0.775%
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | Maximum
Debt
Variable rate, spread		1.45%
London Interbank Offered Rate (LIBOR) | Term Loan Facility | Minimum
Debt
Variable rate, spread		1.00%
London Interbank Offered Rate (LIBOR) | Term Loan Facility | Maximum
Debt
Variable rate, spread		1.65%
Mortgage and other secured debt
Debt
Carrying Value		$ 255,110,000		211,485,000
Mortgage and other secured debt | Fixed rate mortgage debt
Debt
Carrying Value		139,991,000		143,430,000
Unamortized premium included in carrying value		$ 155,000		217,000
Weighted average interest rate		4.16%
Mortgage and other secured debt | Fixed rate mortgage debt | Minimum
Debt
Interest rate		3.82%
Mortgage and other secured debt | Fixed rate mortgage debt | Maximum
Debt
Interest rate		4.62%
Mortgage and other secured debt | Variable rate secured loans
Debt
Carrying Value		$ 115,119,000		68,055,000
Weighted average interest rate		2.28%
Mortgage and other secured debt | London Interbank Offered Rate (LIBOR) | Variable rate secured loans | Minimum
Debt
Variable rate, spread		1.45%
Mortgage and other secured debt | London Interbank Offered Rate (LIBOR) | Variable rate secured loans | Maximum
Debt
Variable rate, spread		2.35%
Mortgage and other secured debt | London Interbank Offered Rate (LIBOR) | Construction Loan Payable
Debt
Remaining borrowing capacity		$ 29,100,000
Senior Notes | 3.60%, $350,000 aggregate principal
Debt
Interest rate		3.60%
Debt instrument, face amount		$ 350,000,000
Carrying Value		348,888,000		348,431,000
Unamortized discount included in carrying value		$ 781,000		1,100,000
Effective interest rate on debt		3.70%
Senior Notes | 5.25%, $250,000 aggregate principal
Debt
Interest rate		5.25%
Debt instrument, face amount		$ 250,000,000
Carrying Value		248,194,000		247,652,000
Unamortized discount included in carrying value		$ 1,600,000		2,100,000
Effective interest rate on debt		5.49%
Senior Notes | 5.00%, $300,000 aggregate principal
Debt
Interest rate		5.00%
Debt instrument, face amount		$ 300,000,000
Carrying Value		297,915,000		297,503,000
Unamortized discount included in carrying value		$ 1,800,000		2,100,000
Effective interest rate on debt		5.15%
Senior Notes | 2.25%, $400,000 aggregate principal
Debt
Interest rate		2.25%
Debt instrument, face amount		$ 400,000,000	$ 400,000,000
Carrying Value		394,464,000		$ 0
Unamortized discount included in carrying value		$ 4,500,000
Effective interest rate on debt		2.48%
Senior Notes | 3.70%, $300,000 aggregate principal
Debt
Interest rate				3.70%
Debt instrument, face amount				$ 300,000,000
Carrying Value		$ 0		299,324,000
Unamortized discount included in carrying value				$ 534,000
Effective interest rate on debt				3.85%
Loans Payable
Debt
Net deferred financing costs		$ 5,900,000		$ 5,800,000
Line of Credit | Revolving Credit Facility
Debt
Number of extensions | extension	2
Extension option period	6 months	6 months
Line of credit facility, extension fee	0.075%
Line of Credit | London Interbank Offered Rate (LIBOR) | Minimum | Revolving Credit Facility
Debt
Variable rate, spread	0.775%
Line of Credit | London Interbank Offered Rate (LIBOR) | Maximum | Revolving Credit Facility
Debt
Variable rate, spread	1.45%

Debt, Net (Debt Maturities) (De

Debt, Net (Debt Maturities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule on basis of which debt matures
2021	$ 3,955
2022	487,380
2023	560,130
2024	279,983
2025	323,717
Thereafter	446,300
Total	2,101,465
Net discounts and deferred financing costs	14,500
Capitalized interest costs	$ 12,100	$ 10,800	$ 5,900

Debt, Net (Fair Value of Debt)

Debt, Net (Fair Value of Debt) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount
Debt Instrument [Line Items]
Long-term debt	$ 2,086,918	$ 1,831,139
Carrying Amount | Unsecured Senior Notes
Debt Instrument [Line Items]
Long-term debt	1,289,461	1,192,910
Carrying Amount | Other fixed-rate debt
Debt Instrument [Line Items]
Long-term debt	140,891	144,468
Carrying Amount | Variable-rate debt
Debt Instrument [Line Items]
Long-term debt	656,566	493,761
Estimated Fair Value
Debt Instrument [Line Items]
Long-term debt	2,131,282	1,873,310
Estimated Fair Value | Unsecured Senior Notes
Debt Instrument [Line Items]
Long-term debt	1,334,342	1,227,441
Estimated Fair Value | Other fixed-rate debt
Debt Instrument [Line Items]
Long-term debt	142,838	149,907
Estimated Fair Value | Variable-rate debt
Debt Instrument [Line Items]
Long-term debt	$ 654,102	$ 495,962

Debt, Net (Narrative) (Details)

Debt, Net (Narrative) (Details)	Sep. 17, 2020USD ($)	Oct. 10, 2018USD ($)extension	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Oct. 19, 2020USD ($)
Debt Instrument [Line Items]
Loss on early extinguishment of debt			$ (7,306,000)	$ 0	$ (258,000)
Revolving Credit Facility
Debt Instrument [Line Items]
Weighted average interest rate			1.20%
Aggregate additional borrowing capacity			$ 500,000,000
Term Loan Facility
Debt Instrument [Line Items]
Loan increase			$ 150,000,000
Repayments of term loan					$ 100,000,000
Minimum | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread			0.775%
Minimum | Term Loan Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread			1.00%
Maximum | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread			1.45%
Maximum | Term Loan Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread			1.65%
Revolving Credit Facility | Revolving Credit Facility
Debt Instrument [Line Items]
Weighted average borrowings			$ 204,900,000	$ 255,600,000
Weighted average interest rate			1.55%	3.32%
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Current borrowing capacity		$ 800,000,000	$ 800,000,000
Maximum availability		$ 1,250,000,000
Number of extensions | extension		2
Extension option period		6 months	6 months
Line of credit facility, extension fee		0.075%
Remaining borrowing capacity			$ 657,000,000
Line of Credit | Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread		0.775%
Commitment fee percentage		0.125%
Line of Credit | Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable rate, spread		1.45%
Commitment fee percentage		0.30%
Senior Notes
Debt Instrument [Line Items]
Redemption period before maturity date for 100% redemption price			3 months
Redemption price			100.00%
Senior Notes | 2.25% Senior Notes
Debt Instrument [Line Items]
Loan amount	$ 400,000,000		$ 400,000,000
Initial offering price	99.416%
Proceeds from issuance of debt	$ 395,300,000
Effective interest rate on debt			2.48%
Basis point used in determining redemption price prior to maturity	0.35%
Redemption period before maturity date for 100% redemption price			1 month
Senior Notes | 3.70% Senior Notes
Debt Instrument [Line Items]
Loan amount				$ 300,000,000
Effective interest rate on debt				3.85%
Repurchased face amount	$ 122,900,000					$ 177,100,000
Repurchase face amount including accrued interest	$ 126,000,000					$ 180,900,000
Loss on early extinguishment of debt			$ 7,300,000
Senior Notes | 3.60% Senior Notes
Debt Instrument [Line Items]
Loan amount			$ 350,000,000
Effective interest rate on debt			3.70%
Senior Notes | 3.60% Senior Notes | Adjusted Treasury
Debt Instrument [Line Items]
Basis point used in determining redemption price prior to maturity			0.30%
Senior Notes | 5.250% Senior Notes
Debt Instrument [Line Items]
Loan amount			$ 250,000,000
Effective interest rate on debt			5.49%
Senior Notes | 5.250% Senior Notes | Adjusted Treasury
Debt Instrument [Line Items]
Basis point used in determining redemption price prior to maturity			0.40%
Senior Notes | 5.0% Senior Notes
Debt Instrument [Line Items]
Loan amount			$ 300,000,000
Effective interest rate on debt			5.15%
Senior Notes | 5.0% Senior Notes | Adjusted Treasury
Debt Instrument [Line Items]
Basis point used in determining redemption price prior to maturity			0.45%

Interest Rate Derivatives (Deta

Interest Rate Derivatives (Details) $ in Thousands	Sep. 22, 2020USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Aug. 31, 2020USD ($)derivative
Derivatives in Hedging Relationships
Amount of Loss Recognized in AOCL on Derivatives			$ (39,454)	$ (24,321)	$ (2,373)
Amount of (Loss) Gain Reclassified from AOCL into Interest Expense on Statement of Operations			(3,725)	1,415	407
Gain (loss) on derivative instruments, net			(53,196)	0	0
Reclassification adjustments on interest rate derivatives recognized in loss on interest rate derivatives			(51,865)	0	0
Payments for hedge, investing activities			53,130	0	0
Interest rate swaps
Derivatives in Hedging Relationships
Number of interest rate derivatives discontinued due to forecasted transaction not probable of occurring | derivative						3
Notional amount of forecasted transaction not probable of occurring						$ 225,000
Reclassification adjustments on interest rate derivatives recognized in loss on interest rate derivatives		$ 51,900
Payments for hedge, investing activities	$ 53,100
Interest rate swaps | Reclassification out of Accumulated Other Comprehensive Income | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest
Derivatives in Hedging Relationships
Gain (loss) on derivative instruments, net			(51,865)	0	0
Interest rate swaps | Interest Expense
Derivatives in Hedging Relationships
Amount of (Loss) Gain Reclassified from AOCL into Interest Expense on Statement of Operations			(3,725)	1,415	407
Interest rate swaps | Prepaid expenses and other assets, net
Fair value of interest rate derivatives and balance sheet classification
Interest rate swaps designated as cash flow hedges			0	23
Interest rate swaps | Interest rate derivatives (liabilities)
Fair value of interest rate derivatives and balance sheet classification
Interest rate swaps designated as cash flow hedges			(9,522)	(25,682)
Undesignated Swaps
Derivatives in Hedging Relationships
Gain (loss) on derivative instruments, net			(1,265)	0	$ 0
Designated
Fair values of interest rate swap derivatives
Fair value of interest rate swaps			(9,522)	(25,659)
Designated | Interest rate swaps
Derivatives in Hedging Relationships
Approximate amount to be reclassified from AOCL to interest expense over the next 12 months			4,800
Fair value of derivative liability			9,600
Settlement amount of derivative obligation at termination value			10,000
Designated | Interest rate swap, effective September 1, 2016, swap one
Fair values of interest rate swap derivatives
Notional Amount			$ 100,000
Fixed Rate			1.901%
Fair value of interest rate swaps			$ (3,394)	(1,028)
Designated | Interest rate swap, effective September 1, 2016, swap two
Fair values of interest rate swap derivatives
Notional Amount			$ 100,000
Fixed Rate			1.905%
Fair value of interest rate swaps			$ (3,401)	(1,037)
Designated | Interest rate swap, effective September 1, 2016, swap three
Fair values of interest rate swap derivatives
Notional Amount			$ 50,000
Fixed Rate			1.908%
Fair value of interest rate swaps			$ (1,704)	(524)
Designated | Interest rate swap, effective August 1, 2019
Fair values of interest rate swap derivatives
Notional Amount			$ 11,200
Fixed Rate			1.678%
Fair value of interest rate swaps			$ (733)	(20)
Notional amount of interest rate derivatives after scheduled amortization			10,000
Designated | Interest rate swap, effective April 2020, swap two
Fair values of interest rate swap derivatives
Notional Amount			$ 23,000
Fixed Rate			0.573%
Fair value of interest rate swaps			$ (290)	0
Notional amount of interest rate derivatives after scheduled amortization			22,100
Designated | Interest rate swap, effective June 30, 2020, swap one
Fair values of interest rate swap derivatives
Notional Amount			$ 75,000
Fixed Rate			3.176%
Fair value of interest rate swaps			$ 0	(8,640)
Designated | Interest rate swap, effective June 30, 2020, swap two
Fair values of interest rate swap derivatives
Notional Amount			$ 75,000
Fixed Rate			3.192%
Fair value of interest rate swaps			$ 0	(8,749)
Designated | Interest rate swap, effective June 30, 2020, swap three
Fair values of interest rate swap derivatives
Notional Amount			$ 75,000
Fixed Rate			2.744%
Fair value of interest rate swaps			$ 0	(5,684)
Designated | Interest rate swap, effective October 13, 2015
Fair values of interest rate swap derivatives
Notional Amount			$ 0
Fixed Rate			1.39%
Fair value of interest rate swaps			$ 0	$ 23

Redeemable Noncontrolling Int_3

Redeemable Noncontrolling Interests (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)joint_venture	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Noncontrolling Interest [Abstract]
Number of joint ventures with redeemable noncontrolling interests | joint_venture	2
Redeemable Noncontrolling Interest [Roll Forward]
Beginning balance	$ 29,431	$ 26,260	$ 23,125
Contributions from noncontrolling interests	0	0	186
Distributions to noncontrolling interests	(14,034)	(2,413)	(1,411)
Net income attributable to noncontrolling interests	3,426	3,835	2,523
Adjustment to arrive at fair value of interests	6,607	1,749	1,837
Ending balance	$ 25,430	$ 29,431	$ 26,260

Equity - COPT and Subsidiaries

Equity - COPT and Subsidiaries (Details) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 02, 2017
Common Shares
Number of common shares for each converted common unit (in shares)		1	1	1
Number of operating partnerships units converted into common shares (in units)		14,009	105,039	1,904,615
Dividends declared per common share (in dollars per share)		$ 1.10	$ 1.10	$ 1.10
Preferred Shares
Preferred Stock
Number of preferred shares authorized		25,000,000
Number of preferred shares of beneficial interest authorized (in dollars per share)		$ 0.01
2018 ATM Program | Common Shares
Common Shares
At-market-stock, offering program established, aggregate value	$ 300,000,000
Shares issued to the public (in shares)		0
Forward Equity Sale Agreement | Common Shares
Common Shares
Shares issued to the public (in shares)			1,600,000	5,900,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses			$ 46,500,000	$ 172,500,000
Initial gross offering price per share (in dollars per share)					$ 31
2016 ATM Program | Common Shares
Common Shares
Shares issued to the public (in shares)				992,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses				$ 29,800,000
Issuance of stock, weighted average price per share (in dollars per share)				$ 30.46
Payments of stock issuance costs				$ 500,000

Equity - COPLP and Subsidiari_2

Equity - COPLP and Subsidiaries (Details) $ / shares in Units, $ in Thousands	Dec. 21, 2020USD ($)$ / sharesshares	Dec. 20, 2020	Sep. 23, 2019	Sep. 22, 2019	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Preferred Stock
Redemption of preferred units					$ 8,800
Common Shares
Number of common shares for each converted common unit (in shares) | shares					1	1	1
Number of operating partnerships units converted into common shares (in units) | shares					14,009	105,039	1,904,615
Redemption of common units						$ 25	$ 339
Dividends declared per common share (in dollars per share) | $ / shares					$ 1.10	$ 1.10	$ 1.10
Common Shares | Forward Equity Sale Agreement
Common Shares
Shares issued to the public (in units) | shares						1,600,000	5,900,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses						$ 46,500	$ 172,500
Common Shares | 2016 ATM Program
Common Shares
Shares issued to the public (in units) | shares							992,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses							$ 29,800
Issuance of stock, weighted average price per share (in dollars per share) | $ / shares							$ 30.46
Payments of stock issuance costs							$ 500
Corporate Office Properties, L.P
Preferred Stock
Redemption of preferred units					$ 8,800
Common Shares
Number of common shares for each converted common unit (in shares) | shares					1	1	1
Number of operating partnerships units converted into common shares (in units) | shares					14,009	105,039	1,900,000
Redemption of common units						$ 25	$ 339
Dividends declared per common share (in dollars per share) | $ / shares					$ 1.10	$ 1.10	$ 1.10
Corporate Office Properties, L.P | Common Shares
Common Shares
Stock redeemed or called during period (in units/ shares) | shares						924	13,377
Redemption of common units						$ 25	$ 339
Corporate Office Properties, L.P | Common Units
Common Shares
Stock redeemed or called during period (in units/ shares) | shares						924	13,377
Redemption of common units						$ 25	$ 339
Corporate Office Properties, L.P | Common Units | COPT
Common Shares
Percentage ownership in operating partnership					98.60%	98.70%
Corporate Office Properties, L.P | Conversion of Series I preferred units
Preferred Stock
Redemption of preferred units (in units) | shares	352,000
Redemption of preferred units	$ 8,800
Preferred stock, redemption price per share (in dollars per share) | $ / shares	$ 25
Annual dividend yield			3.50%	7.50%
Limited partner preferred units conversion rate to shares		0.5

Share-Based Compensation and _3

Share-Based Compensation and Other Compensation Matters (Narrative) (Details) $ / shares in Units, $ in Thousands	Feb. 03, 2021shares	Jan. 13, 2020shares	Jan. 18, 2019shares	Jan. 01, 2018$ / shares	Dec. 31, 2020USD ($)rankformPercentile_Rank$ / shares	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)$ / shares	May 31, 2017shares
Performance Shares, Profit Interest Units and Deferred Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated pre-vesting forfeitures					0.00%	0.00%	0.00%
Restricted shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost					$ 5,600
Expected weighted average period during which unrecognized compensation cost will be recognized					2 years
Aggregate intrinsic value of shares that vested					$ 4,400	$ 4,900	$ 4,600
Grant date fair value (in dollars per share) | $ / shares					$ 25.22	$ 26.56	$ 25.62
Restricted shares | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated pre-vesting forfeitures					0.00%	0.00%	0.00%
Restricted shares | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated pre-vesting forfeitures					8.00%	8.00%	8.00%
Performance-based PIUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost					$ 2,200
Expected weighted average period during which unrecognized compensation cost will be recognized					2 years
Vesting period					3 years
Percentile ranks to fall between for PIUs | rank					2
Percent of award distribution rights					10.00%
Performance period of the award					3 years
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
Time-based PIUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost					$ 2,100
Expected weighted average period during which unrecognized compensation cost will be recognized					3 years
Aggregate intrinsic value of shares that vested					$ 640
Grant date fair value (in dollars per share) | $ / shares					$ 25.47	$ 26.01
Deferred Share Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost					$ 121
Aggregate intrinsic value of shares that vested						$ 86	$ 154
Grant date fair value (in dollars per share) | $ / shares					$ 23.68	$ 27.60	$ 28.08
Profit Interest Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of forms of profit interest units available to executives and trustees | form					2
Performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period of the award					3 years
2017 Omnibus Equity and Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common shares of beneficial interest authorized to be issued | shares								3,400,000
2016 PSU Grants | Performance share units | Executives
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for PSU awards vested in period (in shares) | shares			44,757
2017 PSU Grants | Performance share units | Executives
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for PSU awards vested in period (in shares) | shares		23,181
2018 PSU Grants | Performance share units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value (in dollars per share) | $ / shares				$ 31.97
Baseline Common Share Value (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 | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued for PSU awards vested in period (in shares) | shares	93,824

Share-Based Compensation and _4

Share-Based Compensation and Other Compensation Matters (Compensation Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-Based Compensation
Share-based compensation cost	$ 7,060	$ 7,456	$ 6,963
General, administrative and leasing expenses
Share-Based Compensation
Share-based compensation cost	5,385	5,748	5,415
Property operating expenses
Share-Based Compensation
Share-based compensation cost	1,119	966	961
Capitalized to development activities
Share-Based Compensation
Share-based compensation cost	$ 556	$ 742	$ 587

Share-Based Compensation and _5

Share-Based Compensation and Other Compensation Matters (Restricted Shares and TB-PIUs Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted shares
Shares
Unvested at the beginning of the period (in shares)	392,863	438,685	425,626
Stock awards granted (in shares or units)	166,918	195,520	219,716
Forfeited (in shares)	(25,773)	(56,341)	(25,419)
Vested (in shares)	(173,191)	(185,001)	(181,238)
Unvested at the end of the period (in shares)	360,817	392,863	438,685
Unvested shares as of December 31, 2020 that are expected to vest (in shares)	330,605
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 27.49	$ 28.38	$ 30.37
Grant date fair value (in dollars per share)	25.22	26.56	25.62
Forfeited (in dollars per share)	27.12	29.44	30.02
Vested (in dollars per share)	28.14	28.01	29.49
Unvested at the end of the period (in dollars per share)	26.16	$ 27.49	$ 28.38
Unvested shares as of December 31, 2020 that are expected to vest (in dollars per share)	$ 26.14
Restricted shares | Former Executive Vice President and Chief Operating Officer
Shares
Forfeited (in shares)	(9,064)
Time-based PIUs
Shares
Unvested at the beginning of the period (in shares)	61,820	0
Stock awards granted (in shares or units)	98,318	61,820
Forfeited (in shares)	(20,622)
Vested (in shares)	(25,182)
Unvested at the end of the period (in shares)	114,334	61,820	0
Unvested shares as of December 31, 2020 that are expected to vest (in shares)	114,334
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	$ 26.01
Grant date fair value (in dollars per share)	25.47	$ 26.01
Forfeited (in dollars per share)	25.50
Vested (in dollars per share)	26.30
Unvested at the end of the period (in dollars per share)	25.57	$ 26.01
Unvested shares as of December 31, 2020 that are expected to vest (in dollars per share)	$ 25.57

Share-Based Compensation and _6

Share-Based Compensation and Other Compensation Matters (Grants to Executives) (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Jan. 01, 2019	Jan. 01, 2018	Jan. 01, 2017	Mar. 01, 2016	Dec. 31, 2020
Performance-based PIUs | Former Executive Vice President and Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeitures (in shares)						73,184
Performance-based PIUs | 2019 PB PIU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares or units)		193,682
Grant Date Fair Value		$ 2,415
Unvested at the end of the period (in shares)						156,104
Performance-based PIUs | 2020 PB PIU
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares or units)	176,758
Grant Date Fair Value	$ 2,891
Unvested at the end of the period (in shares)						141,152
Performance share units | 2016 PSU Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares or units)					26,299
Grant Date Fair Value					$ 1,005
Unvested at the end of the period (in shares)						0
Performance share units | 2017 PSU Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares or units)				39,351
Grant Date Fair Value				$ 1,415
Unvested at the end of the period (in shares)						0
Performance share units | 2018 PSU Grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards granted (in shares or units)			59,110
Grant Date Fair Value			$ 1,890
Unvested at the end of the period (in shares)						46,912
Performance share units | 2018 PSU Grants | Former Executive Vice President and Chief Operating Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeitures (in shares)						12,198

Share-Based Compensation and _7

Share-Based Compensation and Other Compensation Matters (Percentile Grant and Assumptions) (Details) - $ / shares	Jan. 01, 2020	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2020
Performance-based PIUs
Potential earned payout for defined levels of performance under awards
Earned payout (as a percent of PSUs/ PIUs granted) on 75th or greater percentile rank				100.00%
Earned payout (as a percent of PSUs/ PIUs granted) on 50th percentile rank (target)				50.00%
Earned payout (as a percent of PSUs/ PIUs granted) on 25th percentile rank				25.00%
Performance share units/ PB PIUs granted on percentile rank below 25th (as a percent)				0.00%
Performance-based PIUs | 2019 PB PIU
Assumptions used to value stock awards
Grant date fair value (in dollars per share)		$ 12.47
Baseline Common Share Value (in dollars per share)		$ 21.03
Expected Volatility of Common Shares		21.00%
Risk-free Interest Rate		2.51%
Performance-based PIUs | 2020 PB PIU
Assumptions used to value stock awards
Grant date fair value (in dollars per share)	$ 16.36
Baseline Common Share Value (in dollars per share)	$ 29.38
Expected Volatility of Common Shares	18.00%
Risk-free Interest Rate	1.65%
Performance share units
Potential earned payout for defined levels of performance under awards
Earned payout (as a percent of PSUs/ PIUs granted) on 75th or greater percentile rank				200.00%
Earned payout (as a percent of PSUs/ PIUs granted) on 50th percentile rank (target)				100.00%
Earned payout (as a percent of PSUs/ PIUs granted) on 25th percentile rank				50.00%
Performance share units/ PB PIUs granted on percentile rank below 25th (as a percent)				0.00%
Performance share units | 2018 PSU Grants
Assumptions used to value stock awards
Grant date fair value (in dollars per share)			$ 31.97
Baseline Common Share Value (in dollars per share)			$ 29.20
Expected Volatility of Common Shares			17.00%
Risk-free Interest Rate			2.04%

Share-Based Compensation and _8

Share-Based Compensation and Other Compensation Matters (Deferred Share Awards) (Details) - Deferred Share Awards - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Deferred Share Awards Granted (in shares or units)	10,679	3,432	13,832
Aggregate Grant Date Fair Value	$ 253	$ 95	$ 388
Grant Date Fair Value Per Share (in dollars per share)	$ 23.68	$ 27.60	$ 28.08
Number of common shares issued (in shares)	0	3,097	5,515
Grant date fair value (in dollars per share)		$ 26.77	$ 29.32
Aggregate Intrinsic Value		$ 86	$ 154

Credit Losses, Financial Asse_3

Credit Losses, Financial Assets and Other Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Off-Balance Sheet, Credit Loss, Exposure, Credit Loss Expense (Reversal) Allowance for Credit Loss [Roll Forward]
December 31, 2019	$ 0
Cumulative effect of change for adoption of credit loss guidance	1,340
Credit loss (recoveries) expense	(1,340)
Other changes	0
December 31, 2020	0	$ 0
Credit Losses, Financial Assets and Other Instruments [Roll Forward]
December 31, 2019	97
Cumulative effect of change for adoption of credit loss guidance	5,541
Credit loss (recoveries) expense	(933)	0	$ 0
Other changes	(8)
December 31, 2020	4,697	97
Other Assets
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
December 31, 2019	0
Cumulative effect of change for adoption of credit loss guidance	144
Credit loss (recoveries) expense	559
Other changes	(60)
December 31, 2020	643	0
Accounts receivable, allowance for credit loss	643	0
Other Assets | Accounts Receivable, Net
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
December 31, 2020	257
Accounts receivable, allowance for credit loss	257
Other Assets | Prepaid expenses and other assets, net
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
December 31, 2020	386
Accounts receivable, allowance for credit loss	386
Investing Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
December 31, 2019	0
Cumulative effect of change for adoption of credit loss guidance	3,732
Credit loss (recoveries) expense	(881)
Other changes	0
December 31, 2020	2,851	0
Tenant Notes Receivables
Financing Receivable, Allowance for Credit Loss [Roll Forward]
December 31, 2019	97
Cumulative effect of change for adoption of credit loss guidance	325
Credit loss (recoveries) expense	729
Other changes	52
December 31, 2020	$ 1,203	$ 97

Credit Losses, Financial Asse_4

Credit Losses, Financial Assets and Other Instruments (Credit Risk Classification) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Investing Receivables
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	$ 64,354
2016	0
2017	971
2018	0
2019	6,041
2020	239
Total	71,605	$ 73,523
Investing Receivables | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	64,354
2016	0
2017	971
2018	0
2019	0
2020	239
Total	65,564
Investing Receivables | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	0
2016	0
2017	0
2018	0
2019	6,041
2020	0
Total	6,041
Tenant Notes Receivables
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	97
2016	179
2017	0
2018	1,192
2019	1,967
2020	2,146
Total	5,581
Tenant Notes Receivables | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	0
2016	14
2017	0
2018	1,028
2019	84
2020	343
Total	1,469
Tenant Notes Receivables | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	97
2016	165
2017	0
2018	164
2019	1,883
2020	1,803
Total	4,112
Sales-Type Lease Receivables | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2015 and Earlier	0
2016	0
2017	0
2018	0
2019	0
2020	6,573
Total	$ 6,573

Information by Business Segme_3

Information by Business Segment (Segment Financial Information for Our Reportable Segments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment financial information for real estate operations
Revenues from real estate operations	$ 609,365	$ 641,226	$ 578,112
Property operating expenses	(203,840)	(198,143)	(201,035)
UJV NOI allocable to COPT	6,951	5,705	4,818
Segment assets	4,077,023	3,854,453
Segment assets
Segment financial information for real estate operations
Segment assets	3,388,978	3,024,958
Real estate operations
Segment financial information for real estate operations
Revenues from real estate operations	538,725	527,463	517,253
Property operating expenses	(203,840)	(198,143)	(201,035)
UJV NOI allocable to COPT	6,951	5,705	4,818
NOI from real estate operations	341,836	335,025	321,036
Additions to long-lived assets	81,479	76,350	74,742
Transfers from non-operating properties	476,362	226,001	166,143
Real estate operations | Defense/Information Technology Locations
Segment financial information for real estate operations
Revenues from real estate operations	447,519	435,486	421,053
Property operating expenses	(159,377)	(153,803)	(153,004)
UJV NOI allocable to COPT	6,951	5,705	4,818
NOI from real estate operations	295,093	287,388	272,867
Additions to long-lived assets	52,924	54,404	53,676
Transfers from non-operating properties	393,271	227,013	163,839
Real estate operations | Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Revenues from real estate operations	254,197	252,781	248,927
Property operating expenses	(85,032)	(82,815)	(82,975)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	169,165	169,966	165,952
Additions to long-lived assets	31,295	34,618	38,612
Transfers from non-operating properties	21,859	18,606	35,648
Real estate operations | Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Revenues from real estate operations	57,817	55,742	53,518
Property operating expenses	(21,321)	(19,779)	(20,330)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	36,496	35,963	33,188
Additions to long-lived assets	11,620	9,326	7,956
Transfers from non-operating properties	2,557	4,548	10,231
Real estate operations | Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Revenues from real estate operations	50,982	51,140	46,286
Property operating expenses	(29,055)	(29,042)	(26,888)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	21,927	22,098	19,398
Additions to long-lived assets	0	0	0
Transfers from non-operating properties	456	10,781	14,718
Real estate operations | Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Revenues from real estate operations	32,869	32,659	31,927
Property operating expenses	(12,655)	(13,579)	(13,536)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	20,214	19,080	18,391
Additions to long-lived assets	7,104	8,912	6,535
Transfers from non-operating properties	0	0	(116)
Real estate operations | Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Revenues from real estate operations	22,515	16,593	14,745
Property operating expenses	(8,119)	(6,626)	(6,050)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	14,396	9,967	8,695
Additions to long-lived assets	2,905	1,548	573
Transfers from non-operating properties	138,122	33,606	4,167
Real estate operations | Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Revenues from real estate operations	29,139	26,571	25,650
Property operating expenses	(3,195)	(1,962)	(3,225)
UJV NOI allocable to COPT	6,951	5,705	4,818
NOI from real estate operations	32,895	30,314	27,243
Additions to long-lived assets	0	0	0
Transfers from non-operating properties	230,277	159,472	99,191
Real estate operations | Regional Office
Segment financial information for real estate operations
Revenues from real estate operations	60,627	59,611	61,181
Property operating expenses	(29,144)	(29,682)	(30,253)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	31,483	29,929	30,928
Additions to long-lived assets	17,232	20,925	19,730
Transfers from non-operating properties	83,091	0	0
Real estate operations | Operating Wholesale Data Center
Segment financial information for real estate operations
Revenues from real estate operations	27,788	29,405	31,892
Property operating expenses	(14,171)	(13,213)	(16,342)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	13,617	16,192	15,550
Additions to long-lived assets	11,158	893	856
Transfers from non-operating properties	0	(1,012)	2,304
Real estate operations | Other
Segment financial information for real estate operations
Revenues from real estate operations	2,791	2,961	3,127
Property operating expenses	(1,148)	(1,445)	(1,436)
UJV NOI allocable to COPT	0	0	0
NOI from real estate operations	1,643	1,516	1,691
Additions to long-lived assets	165	128	480
Transfers from non-operating properties	0	0	0
Real estate operations | Segment assets
Segment financial information for real estate operations
Segment assets	3,388,978	3,024,958	3,084,862
Real estate operations | Segment assets | Defense/Information Technology Locations
Segment financial information for real estate operations
Segment assets	2,692,912	2,426,019	2,468,727
Real estate operations | Segment assets | Defense/Information Technology Locations | Fort Meade/BW Corridor
Segment financial information for real estate operations
Segment assets	1,277,849	1,280,656	1,279,571
Real estate operations | Segment assets | Defense/Information Technology Locations | Northern Virginia Defense/IT
Segment financial information for real estate operations
Segment assets	392,714	396,914	399,339
Real estate operations | Segment assets | Defense/Information Technology Locations | Lackland Air Force Base
Segment financial information for real estate operations
Segment assets	142,137	146,592	139,731
Real estate operations | Segment assets | Defense/Information Technology Locations | Navy Support Locations
Segment financial information for real estate operations
Segment assets	178,897	184,257	188,911
Real estate operations | Segment assets | Defense/Information Technology Locations | Redstone Arsenal
Segment financial information for real estate operations
Segment assets	281,386	138,501	108,010
Real estate operations | Segment assets | Defense/Information Technology Locations | Data Center Shells
Segment financial information for real estate operations
Segment assets	419,929	279,099	353,165
Real estate operations | Segment assets | Regional Office
Segment financial information for real estate operations
Segment assets	490,422	392,319	395,380
Real estate operations | Segment assets | Operating Wholesale Data Center
Segment financial information for real estate operations
Segment assets	202,089	202,935	216,640
Real estate operations | Segment assets | Other
Segment financial information for real estate operations
Segment assets	$ 3,555	$ 3,685	$ 4,115

Information by Business Segme_4

Information by Business Segment (Reconciliation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of segment revenues to total revenues
Construction contract and other service revenues	$ 70,640	$ 113,763	$ 60,859
Total revenues	609,365	641,226	578,112
Reconciliation of UJV NOI allocable to COPT to Equity Income in Unconsolidated entities [Abstract]
UJV NOI allocable to COPT	6,951	5,705	4,818
Less: Income from UJV allocable to COPT attributable to depreciation and amortization expense and interest expense	(5,120)	(4,065)	(3,314)
Add: Equity in (loss) income of unconsolidated non-real estate entities	(6)	(7)	1,193
Equity in income of unconsolidated entities	1,825	1,633	2,697
Computation of net operating income from service operations
Construction contract and other service revenues	70,640	113,763	60,859
Construction contract and other service expenses	(67,615)	(109,962)	(58,326)
Real estate operations
Reconciliation of segment revenues to total revenues
Total revenues	538,725	527,463	517,253
Reconciliation of UJV NOI allocable to COPT to Equity Income in Unconsolidated entities [Abstract]
UJV NOI allocable to COPT	6,951	5,705	4,818
Service operations
Computation of net operating income from service operations
NOI from service operations	$ 3,025	$ 3,801	$ 2,533

Information by Business Segme_5

Information by Business Segment (NOI Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment financial information for real estate operations
Interest and other income	$ 8,574	$ 7,894	$ 4,358
Credit loss recoveries	933	0	0
Gain on sales of real estate	30,209	105,230	2,340
Gain on sale of investment in unconsolidated real estate joint venture	29,416	0	0
Equity in income of unconsolidated entities	1,825	1,633	2,697
Income tax (expense) benefit	(353)	217	363
Depreciation and other amortization associated with real estate operations	(138,193)	(137,069)	(137,116)
Impairment losses	(1,530)	(329)	(2,367)
General, administrative and leasing expenses	(33,001)	(35,402)	(28,900)
Business development expenses and land carry costs	(4,473)	(4,239)	(5,840)
Interest expense	(67,937)	(71,052)	(75,385)
UJV NOI allocable to COPT included in equity in income of unconsolidated entities	(6,951)	(5,705)	(4,818)
Loss on early extinguishment of debt	(7,306)	0	(258)
Loss on interest rate derivatives	(53,196)	0	0
Net income	102,878	200,004	78,643
Real estate operations
Segment financial information for real estate operations
NOI from real estate operations	341,836	335,025	321,036
UJV NOI allocable to COPT included in equity in income of unconsolidated entities	$ (6,951)	$ (5,705)	$ (4,818)

Information by Business Segme_6

Information by Business Segment (Assets Reconciliation) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of segment assets to total assets
Total COPT consolidated assets	$ 4,077,023	$ 3,854,453
Operating properties lease liabilities included in segment assets	30,746	17,317
Segment assets
Reconciliation of segment assets to total assets
Total COPT consolidated assets	3,388,978	3,024,958
Operating properties lease liabilities included in segment assets	30,721	17,317
Non-operating property assets
Reconciliation of segment assets to total assets
Total COPT consolidated assets	466,991	621,630
Other assets
Reconciliation of segment assets to total assets
Total COPT consolidated assets	$ 190,333	$ 190,548

Construction Contract and Oth_3

Construction Contract and Other Service Revenues (Construction Contract and Other Service Revenues by Compensation Arrangement) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	$ 70,640	$ 113,763	$ 60,859
Construction
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	66,087	112,170	57,986
Design
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	2,343	612	1,931
Other
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	2,210	981	942
GMP
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	22,032	67,708	34,050
Cost-plus fee
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	34,025	34,386	5,540
FFP
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	12,373	10,688	20,327
Other
Disaggregation of Revenue [Line Items]
Construction contract and other service revenues	$ 2,210	$ 981	$ 942

Construction Contract and Oth_4

Construction Contract and Other Service Revenues (Percentage of Revenue - Narrative) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Construction contract revenue | Revenue from Contract with Customer Benchmark | Concentration risk | United States Government
Concentration Risk [Line Items]
Percentage of revenue	55.00%	74.00%	95.00%

Construction Contract and Oth_5

Construction Contract and Other Service Revenues (Rollforwards) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Change in Accounts Receivable
Beginning balance	$ 35,444
Ending balance	41,637	$ 35,444
Construction contract revenue
Change in Accounts Receivable
Beginning balance	12,378	6,701
Ending balance	13,997	12,378
Change in Contract with Customer, Asset
Beginning balance	17,223	3,189
Ending balance	10,343	17,223
Change in Contract with Customer, Liability
Beginning balance	1,184	568
Ending balance	4,610	1,184
Portion of beginning balance recognized in revenue during the year	$ 757	$ 446

Construction Contract and Oth_6

Construction Contract and Other Service Revenues (Remaining Performance Obligations) (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 $ in Millions	Dec. 31, 2020USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligations	$ 81.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing	1 year

Construction Contract and Oth_7

Construction Contract and Other Service Revenues (Deferred Incremental Costs Incurred) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Construction contract revenue
Disaggregation of Revenue [Line Items]
Deferred incremental costs incurred	$ 0	$ 0	$ 0

Earnings Per Share ("EPS") an_3

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Basic and Diluted Calculation) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income attributable to COPT/COPLP		$ 97,374	$ 191,692	$ 72,301
Income attributable to share-based compensation awards		(431)	(656)	(462)
Numerator for basic EPS/EPU on net income attributable to COPT/COPLP common share/unitholders		96,943	191,036	71,839
Redeemable noncontrolling interests		0	132	0
Income attributable to share-based compensation awards		27	33	0
Numerator for diluted EPS/EPU on net income attributable to COPT/COPLP common share/unitholders		$ 96,970	$ 191,201	$ 71,839
Denominator (all weighted averages):
Denominator for basic EPS/EPU (common shares/units)		111,788	111,196	103,946
Dilutive effect of redeemable noncontrolling interests (common shares/units)		0	119	0
Dilutive effect of share-based compensation awards (common shares/units)		288	308	134
Dilutive effect of forward equity sale agreements (common shares/units)		0	0	45
Denominator for diluted EPS/EPU (common shares/units)		112,076	111,623	104,125
Basic EPS/EPU (in dollars per share)	[1]	$ 0.87	$ 1.72	$ 0.69
Diluted EPS/EPU (in dollars per share)	[1]	$ 0.87	$ 1.71	$ 0.69
Corporate Office Properties, L.P
Numerator:
Net income attributable to COPT/COPLP		$ 98,854	$ 194,619	$ 74,703
Preferred share/ unit dividends/ distributions		(300)	(564)	(660)
Income attributable to share-based compensation awards		(511)	(785)	(462)
Numerator for basic EPS/EPU on net income attributable to COPT/COPLP common share/unitholders		98,043	193,270	73,581
Redeemable noncontrolling interests		0	132	0
Income attributable to share-based compensation awards		0	33	0
Numerator for diluted EPS/EPU on net income attributable to COPT/COPLP common share/unitholders		$ 98,043	$ 193,435	$ 73,581
Denominator (all weighted averages):
Denominator for basic EPS/EPU (common shares/units)		113,024	112,495	106,414
Dilutive effect of redeemable noncontrolling interests (common shares/units)		0	119	0
Dilutive effect of share-based compensation awards (common shares/units)		288	308	134
Dilutive effect of forward equity sale agreements (common shares/units)		0	0	45
Denominator for diluted EPS/EPU (common shares/units)		113,312	112,922	106,593
Basic EPS/EPU (in dollars per share)	[2]	$ 0.87	$ 1.72	$ 0.69
Diluted EPS/EPU (in dollars per share)	[2]	$ 0.87	$ 1.71	$ 0.69
[1]	Basic and diluted earnings per common share are calculated based on amounts attributable to common shareholders of Corporate Office Properties Trust.
[2]	Basic and diluted earnings per common unit are calculated based on amounts attributable to common unitholders of Corporate Office Properties, L.P.

Earnings Per Share ("EPS") an_4

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Anti-Dilutive Securities) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Conversion of common units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	1,236	1,299	2,468
Conversion of redeemable noncontrolling interests
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	957	896	936
Conversion of Series I preferred units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	171	176	176
Weighted average restricted shares/units and deferred share awards
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	430	441	452
Weighted average unvested TB-PIUs
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	89	51
Weighted average options
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)		12	42
Weighted average shares related to forward equity sale agreements
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)		376
Corporate Office Properties, L.P | Conversion of redeemable noncontrolling interests
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	957	896	936
Corporate Office Properties, L.P | Conversion of Series I preferred units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	171	176	176
Corporate Office Properties, L.P | Weighted average restricted shares/units and deferred share awards
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	430	441	452
Corporate Office Properties, L.P | Weighted average unvested TB-PIUs
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)	89	51
Corporate Office Properties, L.P | Weighted average options
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)		12	42
Corporate Office Properties, L.P | Weighted average shares related to forward equity sale agreements
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares/units)		376

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2020USD ($)property
Commitments and Contingencies
Estimate of possible loss	$ 3.1
Environmental Indemnity Agreement
Number of lease properties which were provided environmental indemnifications | property	3
Maximum environmental indemnification to the tenant against consequential damages after acquisition of property	$ 19
Anne Arundel County, Maryland | Tax Incremental Financing Bond
Environmental Indemnity Agreement
Maximum exposure	$ 33

Schedule III - Real Estate an_2

Schedule III - Real Estate and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Real Estate and Accumulated Depreciation
Encumbrances	$ 257,404
Initial Cost
Land	712,057
Building and Land Improvements	3,427,401
Costs Capitalized Subsequent to Acquisition	547,344
Gross Amounts Carried At Close of Period
Land	712,057
Building and Land Improvements	3,974,745
Total	4,686,802	$ 4,348,006	$ 4,148,529	$ 3,980,813
Accumulated Depreciation	(1,124,253)	(1,007,120)	$ (897,903)	$ (801,038)
Additional information
Debt, net	2,086,918	1,831,139
Net discounts and deferred financing costs	14,500
Aggregate cost of assets for federal income tax purposes	$ 3,600,000
Buildings improvements | Minimum
Additional information
Estimated lives over which depreciation is recognized	10 years
Buildings improvements | Maximum
Additional information
Estimated lives over which depreciation is recognized	40 years
Revolving Credit Facility
Additional information
Debt, net	$ 143,000	177,000
Term Loan Facility
Additional information
Debt, net	398,447	$ 248,706
Unsecured Senior Notes
Additional information
Debt, net	1,300,000
Unsecured notes payable
Additional information
Debt, net	900
Fixed rate mortgage loans
Additional information
Net discounts and deferred financing costs	2,300
100 Light Street
Real Estate and Accumulated Depreciation
Encumbrances	46,543
Initial Cost
Land	26,715
Building and Land Improvements	58,002
Costs Capitalized Subsequent to Acquisition	21,859
Gross Amounts Carried At Close of Period
Land	26,715
Building and Land Improvements	79,861
Total	106,576
Accumulated Depreciation	(20,981)
100 Secured Gateway
Initial Cost
Building and Land Improvements	70,552
Gross Amounts Carried At Close of Period
Building and Land Improvements	70,552
Total	70,552
Accumulated Depreciation	(566)
1000 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	9,666
Initial Cost
Building and Land Improvements	20,533
Costs Capitalized Subsequent to Acquisition	65
Gross Amounts Carried At Close of Period
Building and Land Improvements	20,598
Total	20,598
Accumulated Depreciation	(4,007)
1100 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	10,263
Initial Cost
Building and Land Improvements	19,593
Costs Capitalized Subsequent to Acquisition	66
Gross Amounts Carried At Close of Period
Building and Land Improvements	19,659
Total	19,659
Accumulated Depreciation	(3,418)
114 National Business Parkway
Initial Cost
Land	364
Building and Land Improvements	3,109
Costs Capitalized Subsequent to Acquisition	302
Gross Amounts Carried At Close of Period
Land	364
Building and Land Improvements	3,411
Total	3,775
Accumulated Depreciation	(1,584)
1200 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	11,851
Initial Cost
Building and Land Improvements	22,389
Gross Amounts Carried At Close of Period
Building and Land Improvements	22,449
Total	22,449
Accumulated Depreciation	(3,945)
1201 M Street SE
Initial Cost
Building and Land Improvements	49,785
Costs Capitalized Subsequent to Acquisition	9,621
Gross Amounts Carried At Close of Period
Building and Land Improvements	59,406
Total	59,406
Accumulated Depreciation	(19,011)
1201 Winterson Road
Initial Cost
Land	2,130
Building and Land Improvements	17,007
Costs Capitalized Subsequent to Acquisition	901
Gross Amounts Carried At Close of Period
Land	2,130
Building and Land Improvements	17,908
Total	20,038
Accumulated Depreciation	(5,506)
1220 12th Street, SE
Initial Cost
Building and Land Improvements	42,464
Costs Capitalized Subsequent to Acquisition	8,795
Gross Amounts Carried At Close of Period
Building and Land Improvements	51,259
Total	51,259
Accumulated Depreciation	(17,812)
1243 Winterson Road
Initial Cost
Land	630
Gross Amounts Carried At Close of Period
Land	630
Total	630
131 National Business Parkway
Initial Cost
Land	1,906
Building and Land Improvements	7,623
Costs Capitalized Subsequent to Acquisition	5,075
Gross Amounts Carried At Close of Period
Land	1,906
Building and Land Improvements	12,698
Total	14,604
Accumulated Depreciation	(7,442)
132 National Business Parkway
Initial Cost
Land	2,917
Building and Land Improvements	12,259
Costs Capitalized Subsequent to Acquisition	4,730
Gross Amounts Carried At Close of Period
Land	2,917
Building and Land Improvements	16,989
Total	19,906
Accumulated Depreciation	(10,566)
133 National Business Parkway
Initial Cost
Land	2,517
Building and Land Improvements	10,068
Costs Capitalized Subsequent to Acquisition	6,274
Gross Amounts Carried At Close of Period
Land	2,517
Building and Land Improvements	16,342
Total	18,859
Accumulated Depreciation	(10,443)
134 National Business Parkway
Initial Cost
Land	3,684
Building and Land Improvements	7,517
Costs Capitalized Subsequent to Acquisition	5,007
Gross Amounts Carried At Close of Period
Land	3,684
Building and Land Improvements	12,524
Total	16,208
Accumulated Depreciation	(7,329)
1340 Ashton Road
Initial Cost
Land	905
Building and Land Improvements	3,620
Costs Capitalized Subsequent to Acquisition	2,042
Gross Amounts Carried At Close of Period
Land	905
Building and Land Improvements	5,662
Total	6,567
Accumulated Depreciation	(3,255)
13450 Sunrise Valley Drive
Initial Cost
Land	1,386
Building and Land Improvements	5,576
Costs Capitalized Subsequent to Acquisition	4,636
Gross Amounts Carried At Close of Period
Land	1,386
Building and Land Improvements	10,212
Total	11,598
Accumulated Depreciation	(6,156)
13454 Sunrise Valley Drive
Initial Cost
Land	2,847
Building and Land Improvements	11,986
Costs Capitalized Subsequent to Acquisition	9,184
Gross Amounts Carried At Close of Period
Land	2,847
Building and Land Improvements	21,170
Total	24,017
Accumulated Depreciation	(12,075)
135 National Business Parkway
Initial Cost
Land	2,484
Building and Land Improvements	9,750
Costs Capitalized Subsequent to Acquisition	6,528
Gross Amounts Carried At Close of Period
Land	2,484
Building and Land Improvements	16,278
Total	18,762
Accumulated Depreciation	(10,164)
1362 Mellon Road
Initial Cost
Land	950
Building and Land Improvements	3,864
Costs Capitalized Subsequent to Acquisition	1,065
Gross Amounts Carried At Close of Period
Land	950
Building and Land Improvements	4,929
Total	5,879
Accumulated Depreciation	(854)
13857 McLearen Road
Initial Cost
Land	3,507
Building and Land Improvements	30,177
Costs Capitalized Subsequent to Acquisition	4,915
Gross Amounts Carried At Close of Period
Land	3,507
Building and Land Improvements	35,092
Total	38,599
Accumulated Depreciation	(12,784)
140 National Business Parkway
Initial Cost
Land	3,407
Building and Land Improvements	24,167
Costs Capitalized Subsequent to Acquisition	1,751
Gross Amounts Carried At Close of Period
Land	3,407
Building and Land Improvements	25,918
Total	29,325
Accumulated Depreciation	(10,941)
141 National Business Parkway
Initial Cost
Land	2,398
Building and Land Improvements	9,538
Costs Capitalized Subsequent to Acquisition	4,832
Gross Amounts Carried At Close of Period
Land	2,398
Building and Land Improvements	14,370
Total	16,768
Accumulated Depreciation	(9,190)
14280 Park Meadow Drive
Initial Cost
Land	3,731
Building and Land Improvements	15,953
Costs Capitalized Subsequent to Acquisition	5,485
Gross Amounts Carried At Close of Period
Land	3,731
Building and Land Improvements	21,438
Total	25,169
Accumulated Depreciation	(9,512)
1460 Dorsey Road
Initial Cost
Land	1,577
Building and Land Improvements	76
Gross Amounts Carried At Close of Period
Land	1,577
Building and Land Improvements	76
Total	1,653
14840 Conference Center Drive
Initial Cost
Land	1,572
Building and Land Improvements	8,175
Costs Capitalized Subsequent to Acquisition	5,751
Gross Amounts Carried At Close of Period
Land	1,572
Building and Land Improvements	13,926
Total	15,498
Accumulated Depreciation	(7,351)
14850 Conference Center Drive
Initial Cost
Land	1,615
Building and Land Improvements	8,358
Costs Capitalized Subsequent to Acquisition	3,873
Gross Amounts Carried At Close of Period
Land	1,615
Building and Land Improvements	12,231
Total	13,846
Accumulated Depreciation	(7,115)
14900 Conference Center Drive
Initial Cost
Land	3,436
Building and Land Improvements	14,402
Costs Capitalized Subsequent to Acquisition	8,659
Gross Amounts Carried At Close of Period
Land	3,436
Building and Land Improvements	23,061
Total	26,497
Accumulated Depreciation	(13,126)
1501 South Clinton Street
Initial Cost
Land	27,964
Building and Land Improvements	51,990
Costs Capitalized Subsequent to Acquisition	20,656
Gross Amounts Carried At Close of Period
Land	27,964
Building and Land Improvements	72,646
Total	100,610
Accumulated Depreciation	(28,175)
15049 Conference Center Drive
Initial Cost
Land	4,415
Building and Land Improvements	20,365
Costs Capitalized Subsequent to Acquisition	17,851
Gross Amounts Carried At Close of Period
Land	4,415
Building and Land Improvements	38,216
Total	42,631
Accumulated Depreciation	(18,061)
15059 Conference Center Drive
Initial Cost
Land	5,753
Building and Land Improvements	13,615
Costs Capitalized Subsequent to Acquisition	4,386
Gross Amounts Carried At Close of Period
Land	5,753
Building and Land Improvements	18,001
Total	23,754
Accumulated Depreciation	(10,079)
1550 West Nursery Road
Initial Cost
Land	14,071
Building and Land Improvements	16,930
Gross Amounts Carried At Close of Period
Land	14,071
Building and Land Improvements	16,930
Total	31,001
Accumulated Depreciation	(6,310)
1560 West Nursery Road
Initial Cost
Land	1,441
Building and Land Improvements	113
Gross Amounts Carried At Close of Period
Land	1,441
Building and Land Improvements	113
Total	1,554
Accumulated Depreciation	(19)
1610 West Nursery Road
Initial Cost
Land	259
Building and Land Improvements	246
Gross Amounts Carried At Close of Period
Land	259
Building and Land Improvements	246
Total	505
Accumulated Depreciation	(23)
1616 West Nursery Road
Initial Cost
Land	393
Building and Land Improvements	3,323
Costs Capitalized Subsequent to Acquisition	75
Gross Amounts Carried At Close of Period
Land	393
Building and Land Improvements	3,398
Total	3,791
Accumulated Depreciation	(268)
1622 West Nursery Road
Initial Cost
Land	393
Building and Land Improvements	2,542
Gross Amounts Carried At Close of Period
Land	393
Building and Land Improvements	2,542
Total	2,935
Accumulated Depreciation	(244)
16442 Commerce Drive
Initial Cost
Land	613
Building and Land Improvements	2,582
Costs Capitalized Subsequent to Acquisition	980
Gross Amounts Carried At Close of Period
Land	613
Building and Land Improvements	3,562
Total	4,175
Accumulated Depreciation	(1,860)
16480 Commerce Drive
Initial Cost
Land	1,856
Building and Land Improvements	7,425
Costs Capitalized Subsequent to Acquisition	2,602
Gross Amounts Carried At Close of Period
Land	1,856
Building and Land Improvements	10,027
Total	11,883
Accumulated Depreciation	(4,274)
16501 Commerce Drive
Initial Cost
Land	522
Building and Land Improvements	2,090
Costs Capitalized Subsequent to Acquisition	1,040
Gross Amounts Carried At Close of Period
Land	522
Building and Land Improvements	3,130
Total	3,652
Accumulated Depreciation	(1,399)
16539 Commerce Drive
Initial Cost
Land	688
Building and Land Improvements	2,860
Costs Capitalized Subsequent to Acquisition	2,326
Gross Amounts Carried At Close of Period
Land	688
Building and Land Improvements	5,186
Total	5,874
Accumulated Depreciation	(2,879)
16541 Commerce Drive
Initial Cost
Land	773
Building and Land Improvements	3,094
Costs Capitalized Subsequent to Acquisition	2,594
Gross Amounts Carried At Close of Period
Land	773
Building and Land Improvements	5,688
Total	6,461
Accumulated Depreciation	(2,696)
16543 Commerce Drive
Initial Cost
Land	436
Building and Land Improvements	1,742
Costs Capitalized Subsequent to Acquisition	838
Gross Amounts Carried At Close of Period
Land	436
Building and Land Improvements	2,580
Total	3,016
Accumulated Depreciation	(1,231)
1751 Pinnacle Drive
Initial Cost
Land	10,486
Building and Land Improvements	42,339
Costs Capitalized Subsequent to Acquisition	33,689
Gross Amounts Carried At Close of Period
Land	10,486
Building and Land Improvements	76,028
Total	86,514
Accumulated Depreciation	(38,872)
1753 Pinnacle Drive
Initial Cost
Land	8,275
Building and Land Improvements	34,353
Costs Capitalized Subsequent to Acquisition	23,954
Gross Amounts Carried At Close of Period
Land	8,275
Building and Land Improvements	58,307
Total	66,582
Accumulated Depreciation	(25,248)
206 Research Boulevard
Initial Cost
Land	0
Building and Land Improvements	0
Costs Capitalized Subsequent to Acquisition	0
Gross Amounts Carried At Close of Period
Land	0
Building and Land Improvements	0
Total	0
Accumulated Depreciation	(1)
209 Research Boulevard
Initial Cost
Land	134
Building and Land Improvements	1,711
Costs Capitalized Subsequent to Acquisition	327
Gross Amounts Carried At Close of Period
Land	134
Building and Land Improvements	2,038
Total	2,172
Accumulated Depreciation	(599)
210 Research Boulevard
Initial Cost
Land	113
Building and Land Improvements	1,402
Costs Capitalized Subsequent to Acquisition	248
Gross Amounts Carried At Close of Period
Land	113
Building and Land Improvements	1,650
Total	1,763
Accumulated Depreciation	(493)
2100 L Street
Real Estate and Accumulated Depreciation
Encumbrances	82,882
Initial Cost
Land	19,024
Building and Land Improvements	92,387
Gross Amounts Carried At Close of Period
Land	19,024
Building and Land Improvements	92,387
Total	111,411
2100 Rideout Road
Initial Cost
Land	0
Building and Land Improvements	7,347
Costs Capitalized Subsequent to Acquisition	2,995
Gross Amounts Carried At Close of Period
Land	0
Building and Land Improvements	10,342
Total	10,342
Accumulated Depreciation	(1,786)
22289 Exploration Drive
Initial Cost
Land	1,422
Building and Land Improvements	5,719
Costs Capitalized Subsequent to Acquisition	2,061
Gross Amounts Carried At Close of Period
Land	1,422
Building and Land Improvements	7,780
Total	9,202
Accumulated Depreciation	(4,126)
22299 Exploration Drive
Initial Cost
Land	1,362
Building and Land Improvements	5,791
Costs Capitalized Subsequent to Acquisition	2,994
Gross Amounts Carried At Close of Period
Land	1,362
Building and Land Improvements	8,785
Total	10,147
Accumulated Depreciation	(4,888)
22300 Exploration Drive
Initial Cost
Land	1,094
Building and Land Improvements	5,038
Costs Capitalized Subsequent to Acquisition	2,770
Gross Amounts Carried At Close of Period
Land	1,094
Building and Land Improvements	7,808
Total	8,902
Accumulated Depreciation	(3,624)
22309 Exploration Drive
Initial Cost
Land	2,243
Building and Land Improvements	10,419
Costs Capitalized Subsequent to Acquisition	8,205
Gross Amounts Carried At Close of Period
Land	2,243
Building and Land Improvements	18,624
Total	20,867
Accumulated Depreciation	(8,227)
23535 Cottonwood Parkway
Initial Cost
Land	692
Building and Land Improvements	3,051
Costs Capitalized Subsequent to Acquisition	648
Gross Amounts Carried At Close of Period
Land	692
Building and Land Improvements	3,699
Total	4,391
Accumulated Depreciation	(2,027)
250 W Pratt St
Initial Cost
Land	8,057
Building and Land Improvements	34,588
Costs Capitalized Subsequent to Acquisition	16,213
Gross Amounts Carried At Close of Period
Land	8,057
Building and Land Improvements	50,801
Total	58,858
Accumulated Depreciation	(15,418)
2500 Riva Road
Initial Cost
Land	2,791
Building and Land Improvements	12,155
Costs Capitalized Subsequent to Acquisition	1
Gross Amounts Carried At Close of Period
Land	2,791
Building and Land Improvements	12,156
Total	14,947
Accumulated Depreciation	(12,146)
2600 Park Tower Drive
Initial Cost
Land	20,284
Building and Land Improvements	34,443
Costs Capitalized Subsequent to Acquisition	3,883
Gross Amounts Carried At Close of Period
Land	20,284
Building and Land Improvements	38,326
Total	58,610
Accumulated Depreciation	(7,108)
2691 Technology Drive
Initial Cost
Land	2,098
Building and Land Improvements	17,334
Costs Capitalized Subsequent to Acquisition	5,565
Gross Amounts Carried At Close of Period
Land	2,098
Building and Land Improvements	22,899
Total	24,997
Accumulated Depreciation	(11,747)
2701 Technology Drive
Initial Cost
Land	1,737
Building and Land Improvements	15,266
Costs Capitalized Subsequent to Acquisition	5,629
Gross Amounts Carried At Close of Period
Land	1,737
Building and Land Improvements	20,895
Total	22,632
Accumulated Depreciation	(12,487)
2711 Technology Drive
Initial Cost
Land	2,251
Building and Land Improvements	21,611
Costs Capitalized Subsequent to Acquisition	4,332
Gross Amounts Carried At Close of Period
Land	2,251
Building and Land Improvements	25,943
Total	28,194
Accumulated Depreciation	(13,586)
2720 Technology Drive
Initial Cost
Land	3,863
Building and Land Improvements	29,272
Costs Capitalized Subsequent to Acquisition	2,796
Gross Amounts Carried At Close of Period
Land	3,863
Building and Land Improvements	32,068
Total	35,931
Accumulated Depreciation	(13,249)
2721 Technology Drive
Initial Cost
Land	4,611
Building and Land Improvements	14,597
Costs Capitalized Subsequent to Acquisition	3,247
Gross Amounts Carried At Close of Period
Land	4,611
Building and Land Improvements	17,844
Total	22,455
Accumulated Depreciation	(10,267)
2730 Hercules Road
Initial Cost
Land	8,737
Building and Land Improvements	31,612
Costs Capitalized Subsequent to Acquisition	8,726
Gross Amounts Carried At Close of Period
Land	8,737
Building and Land Improvements	40,338
Total	49,075
Accumulated Depreciation	(22,740)
30 Light Street
Real Estate and Accumulated Depreciation
Encumbrances	3,915
Initial Cost
Land	0
Building and Land Improvements	12,101
Costs Capitalized Subsequent to Acquisition	1,009
Gross Amounts Carried At Close of Period
Land	0
Building and Land Improvements	13,110
Total	13,110
Accumulated Depreciation	(1,894)
300 Sentinel Drive
Initial Cost
Land	1,517
Building and Land Improvements	59,165
Costs Capitalized Subsequent to Acquisition	2,095
Gross Amounts Carried At Close of Period
Land	1,517
Building and Land Improvements	61,260
Total	62,777
Accumulated Depreciation	(16,564)
302 Sentinel Drive
Initial Cost
Land	2,648
Building and Land Improvements	29,687
Costs Capitalized Subsequent to Acquisition	1,094
Gross Amounts Carried At Close of Period
Land	2,648
Building and Land Improvements	30,781
Total	33,429
Accumulated Depreciation	(10,028)
304 Sentinel Drive
Initial Cost
Land	3,411
Building and Land Improvements	24,917
Costs Capitalized Subsequent to Acquisition	1,982
Gross Amounts Carried At Close of Period
Land	3,411
Building and Land Improvements	26,899
Total	30,310
Accumulated Depreciation	(11,186)
306 Sentinel Drive
Initial Cost
Land	3,260
Building and Land Improvements	22,592
Costs Capitalized Subsequent to Acquisition	2,566
Gross Amounts Carried At Close of Period
Land	3,260
Building and Land Improvements	25,158
Total	28,418
Accumulated Depreciation	(9,147)
308 Sentinel Drive
Initial Cost
Land	1,422
Building and Land Improvements	26,208
Costs Capitalized Subsequent to Acquisition	2,354
Gross Amounts Carried At Close of Period
Land	1,422
Building and Land Improvements	28,562
Total	29,984
Accumulated Depreciation	(7,003)
310 Sentinel Way
Initial Cost
Land	2,372
Building and Land Improvements	42,584
Gross Amounts Carried At Close of Period
Land	2,372
Building and Land Improvements	42,584
Total	44,956
Accumulated Depreciation	(5,027)
310 The Bridge Street
Initial Cost
Land	261
Building and Land Improvements	26,531
Costs Capitalized Subsequent to Acquisition	5,135
Gross Amounts Carried At Close of Period
Land	261
Building and Land Improvements	31,666
Total	31,927
Accumulated Depreciation	(11,066)
312 Sentinel Way
Initial Cost
Land	3,138
Building and Land Improvements	27,797
Gross Amounts Carried At Close of Period
Land	3,138
Building and Land Improvements	27,797
Total	30,935
Accumulated Depreciation	(4,389)
314 Sentinel Way
Initial Cost
Land	1,254
Building and Land Improvements	7,741
Gross Amounts Carried At Close of Period
Land	1,254
Building and Land Improvements	7,741
Total	8,995
Accumulated Depreciation	(1,247)
316 Sentinel Way
Initial Cost
Land	2,748
Building and Land Improvements	38,156
Costs Capitalized Subsequent to Acquisition	226
Gross Amounts Carried At Close of Period
Land	2,748
Building and Land Improvements	38,382
Total	41,130
Accumulated Depreciation	(8,426)
318 Sentinel Way
Initial Cost
Land	2,185
Building and Land Improvements	28,426
Costs Capitalized Subsequent to Acquisition	560
Gross Amounts Carried At Close of Period
Land	2,185
Building and Land Improvements	28,986
Total	31,171
Accumulated Depreciation	(10,716)
320 Sentinel Way
Initial Cost
Land	2,067
Building and Land Improvements	21,623
Costs Capitalized Subsequent to Acquisition	132
Gross Amounts Carried At Close of Period
Land	2,067
Building and Land Improvements	21,755
Total	23,822
Accumulated Depreciation	(7,029)
322 Sentinel Way
Initial Cost
Land	2,605
Building and Land Improvements	22,827
Costs Capitalized Subsequent to Acquisition	1,900
Gross Amounts Carried At Close of Period
Land	2,605
Building and Land Improvements	24,727
Total	27,332
Accumulated Depreciation	(8,568)
324 Sentinel Way
Initial Cost
Land	1,656
Building and Land Improvements	23,018
Costs Capitalized Subsequent to Acquisition	38
Gross Amounts Carried At Close of Period
Land	1,656
Building and Land Improvements	23,056
Total	24,712
Accumulated Depreciation	(5,956)
4000 Market Street
Real Estate and Accumulated Depreciation
Encumbrances	6,052
Initial Cost
Building and Land Improvements	9,207
Gross Amounts Carried At Close of Period
Building and Land Improvements	9,207
Total	9,207
Accumulated Depreciation	(394)
410 National Business Parkway
Initial Cost
Land	1,831
Building and Land Improvements	23,257
Costs Capitalized Subsequent to Acquisition	2,080
Gross Amounts Carried At Close of Period
Land	1,831
Building and Land Improvements	25,337
Total	27,168
Accumulated Depreciation	(5,032)
4100 Market Street
Real Estate and Accumulated Depreciation
Encumbrances	5,269
Initial Cost
Building and Land Improvements	8,020
Gross Amounts Carried At Close of Period
Building and Land Improvements	8,020
Total	8,020
Accumulated Depreciation	(304)
420 National Business Parkway
Initial Cost
Land	2,370
Building and Land Improvements	27,751
Costs Capitalized Subsequent to Acquisition	148
Gross Amounts Carried At Close of Period
Land	2,370
Building and Land Improvements	27,899
Total	30,269
Accumulated Depreciation	(4,752)
430 National Business Parkway
Initial Cost
Land	1,852
Building and Land Improvements	21,563
Costs Capitalized Subsequent to Acquisition	830
Gross Amounts Carried At Close of Period
Land	1,852
Building and Land Improvements	22,393
Total	24,245
Accumulated Depreciation	(4,936)
44408 Pecan Court
Initial Cost
Land	817
Building and Land Improvements	1,583
Costs Capitalized Subsequent to Acquisition	1,706
Gross Amounts Carried At Close of Period
Land	817
Building and Land Improvements	3,289
Total	4,106
Accumulated Depreciation	(1,679)
44414 Pecan Court
Initial Cost
Land	405
Building and Land Improvements	1,619
Costs Capitalized Subsequent to Acquisition	1,138
Gross Amounts Carried At Close of Period
Land	405
Building and Land Improvements	2,757
Total	3,162
Accumulated Depreciation	(1,512)
44417 Pecan Court
Initial Cost
Land	434
Building and Land Improvements	3,822
Costs Capitalized Subsequent to Acquisition	180
Gross Amounts Carried At Close of Period
Land	434
Building and Land Improvements	4,002
Total	4,436
Accumulated Depreciation	(2,005)
44420 Pecan Court
Initial Cost
Land	344
Building and Land Improvements	890
Costs Capitalized Subsequent to Acquisition	291
Gross Amounts Carried At Close of Period
Land	344
Building and Land Improvements	1,181
Total	1,525
Accumulated Depreciation	(546)
44425 Pecan Court
Initial Cost
Land	1,309
Building and Land Improvements	3,506
Costs Capitalized Subsequent to Acquisition	2,349
Gross Amounts Carried At Close of Period
Land	1,309
Building and Land Improvements	5,855
Total	7,164
Accumulated Depreciation	(3,431)
45310 Abell House Lane
Initial Cost
Land	2,272
Building and Land Improvements	13,808
Costs Capitalized Subsequent to Acquisition	816
Gross Amounts Carried At Close of Period
Land	2,272
Building and Land Improvements	14,624
Total	16,896
Accumulated Depreciation	(3,455)
4600 River Road
Initial Cost
Land	0
Building and Land Improvements	23,294
Gross Amounts Carried At Close of Period
Building and Land Improvements	23,294
Total	23,294
Accumulated Depreciation	(19)
46579 Expedition Drive
Initial Cost
Land	1,406
Building and Land Improvements	5,796
Costs Capitalized Subsequent to Acquisition	2,712
Gross Amounts Carried At Close of Period
Land	1,406
Building and Land Improvements	8,508
Total	9,914
Accumulated Depreciation	(4,231)
46591 Expedition Drive
Initial Cost
Land	1,200
Building and Land Improvements	7,199
Costs Capitalized Subsequent to Acquisition	3,399
Gross Amounts Carried At Close of Period
Land	1,200
Building and Land Improvements	10,598
Total	11,798
Accumulated Depreciation	(3,932)
4851 Stonecroft Boulevard
Initial Cost
Land	1,878
Building and Land Improvements	11,558
Costs Capitalized Subsequent to Acquisition	299
Gross Amounts Carried At Close of Period
Land	1,878
Building and Land Improvements	11,857
Total	13,735
Accumulated Depreciation	(4,697)
540 National Business Parkway
Initial Cost
Land	2,035
Building and Land Improvements	31,249
Costs Capitalized Subsequent to Acquisition	9
Gross Amounts Carried At Close of Period
Land	2,035
Building and Land Improvements	31,258
Total	33,293
Accumulated Depreciation	(2,521)
5520 Research Park Drive
Initial Cost
Building and Land Improvements	20,072
Costs Capitalized Subsequent to Acquisition	1,641
Gross Amounts Carried At Close of Period
Building and Land Improvements	21,713
Total	21,713
Accumulated Depreciation	(6,375)
5522 Research Park Drive
Initial Cost
Building and Land Improvements	4,550
Costs Capitalized Subsequent to Acquisition	855
Gross Amounts Carried At Close of Period
Building and Land Improvements	5,405
Total	5,405
Accumulated Depreciation	(1,652)
5801 University Research Court
Real Estate and Accumulated Depreciation
Encumbrances	11,200
Initial Cost
Building and Land Improvements	17,434
Gross Amounts Carried At Close of Period
Building and Land Improvements	17,434
Total	17,434
Accumulated Depreciation	(1,195)
5825 University Research Court
Real Estate and Accumulated Depreciation
Encumbrances	20,011
Initial Cost
Building and Land Improvements	22,771
Costs Capitalized Subsequent to Acquisition	1,780
Gross Amounts Carried At Close of Period
Building and Land Improvements	24,551
Total	24,551
Accumulated Depreciation	(7,170)
5850 University Research Court
Real Estate and Accumulated Depreciation
Encumbrances	21,171
Initial Cost
Building and Land Improvements	31,906
Costs Capitalized Subsequent to Acquisition	405
Gross Amounts Carried At Close of Period
Building and Land Improvements	32,311
Total	32,311
Accumulated Depreciation	(8,885)
6000 Redstone Gateway
Initial Cost
Building and Land Improvements	8,268
Gross Amounts Carried At Close of Period
Building and Land Improvements	8,268
Total	8,268
Accumulated Depreciation	(14)
610 Guardian Way
Initial Cost
Land	6,946
Building and Land Improvements	14,597
Gross Amounts Carried At Close of Period
Land	6,946
Building and Land Improvements	14,597
Total	21,543
6700 Alexander Bell Drive
Initial Cost
Land	1,755
Building and Land Improvements	7,019
Costs Capitalized Subsequent to Acquisition	8,788
Gross Amounts Carried At Close of Period
Land	1,755
Building and Land Improvements	15,807
Total	17,562
Accumulated Depreciation	(8,825)
6708 Alexander Bell Drive
Initial Cost
Land	897
Building and Land Improvements	12,644
Costs Capitalized Subsequent to Acquisition	1,618
Gross Amounts Carried At Close of Period
Land	897
Building and Land Improvements	14,262
Total	15,159
Accumulated Depreciation	(4,674)
6711 Columbia Gateway Drive
Initial Cost
Land	2,683
Building and Land Improvements	23,239
Costs Capitalized Subsequent to Acquisition	1,557
Gross Amounts Carried At Close of Period
Land	2,683
Building and Land Improvements	24,796
Total	27,479
Accumulated Depreciation	(9,200)
6716 Alexander Bell Drive
Initial Cost
Land	1,242
Building and Land Improvements	4,969
Costs Capitalized Subsequent to Acquisition	4,672
Gross Amounts Carried At Close of Period
Land	1,242
Building and Land Improvements	9,641
Total	10,883
Accumulated Depreciation	(6,123)
6721 Columbia Gateway Drive
Initial Cost
Land	1,753
Building and Land Improvements	34,090
Costs Capitalized Subsequent to Acquisition	2,391
Gross Amounts Carried At Close of Period
Land	1,753
Building and Land Improvements	36,481
Total	38,234
Accumulated Depreciation	(10,096)
6724 Alexander Bell Drive
Initial Cost
Land	449
Building and Land Improvements	5,039
Costs Capitalized Subsequent to Acquisition	2,507
Gross Amounts Carried At Close of Period
Land	449
Building and Land Improvements	7,546
Total	7,995
Accumulated Depreciation	(3,592)
6731 Columbia Gateway Drive
Initial Cost
Land	2,807
Building and Land Improvements	19,098
Costs Capitalized Subsequent to Acquisition	5,605
Gross Amounts Carried At Close of Period
Land	2,807
Building and Land Improvements	24,703
Total	27,510
Accumulated Depreciation	(13,179)
6740 Alexander Bell Drive
Initial Cost
Land	1,424
Building and Land Improvements	5,696
Costs Capitalized Subsequent to Acquisition	3,466
Gross Amounts Carried At Close of Period
Land	1,424
Building and Land Improvements	9,162
Total	10,586
Accumulated Depreciation	(6,236)
6741 Columbia Gateway Drive
Initial Cost
Land	675
Building and Land Improvements	1,711
Costs Capitalized Subsequent to Acquisition	169
Gross Amounts Carried At Close of Period
Land	675
Building and Land Improvements	1,880
Total	2,555
Accumulated Depreciation	(639)
6750 Alexander Bell Drive
Initial Cost
Land	1,263
Building and Land Improvements	12,461
Costs Capitalized Subsequent to Acquisition	5,075
Gross Amounts Carried At Close of Period
Land	1,263
Building and Land Improvements	17,536
Total	18,799
Accumulated Depreciation	(10,635)
6760 Alexander Bell Drive
Initial Cost
Land	890
Building and Land Improvements	3,561
Costs Capitalized Subsequent to Acquisition	3,920
Gross Amounts Carried At Close of Period
Land	890
Building and Land Improvements	7,481
Total	8,371
Accumulated Depreciation	(4,859)
6940 Columbia Gateway Drive
Initial Cost
Land	3,545
Building and Land Improvements	9,916
Costs Capitalized Subsequent to Acquisition	8,739
Gross Amounts Carried At Close of Period
Land	3,545
Building and Land Improvements	18,655
Total	22,200
Accumulated Depreciation	(10,795)
6950 Columbia Gateway Drive
Initial Cost
Land	3,596
Building and Land Improvements	27,723
Costs Capitalized Subsequent to Acquisition	3,223
Gross Amounts Carried At Close of Period
Land	3,596
Building and Land Improvements	30,946
Total	34,542
Accumulated Depreciation	(11,991)
7000 Columbia Gateway Drive
Initial Cost
Land	3,131
Building and Land Improvements	12,103
Costs Capitalized Subsequent to Acquisition	7,537
Gross Amounts Carried At Close of Period
Land	3,131
Building and Land Improvements	19,640
Total	22,771
Accumulated Depreciation	(9,679)
7005 Columbia Gateway Drive
Initial Cost
Land	3,036
Building and Land Improvements	747
Gross Amounts Carried At Close of Period
Land	3,036
Building and Land Improvements	747
Total	3,783
7015 Albert Einstein Drive
Initial Cost
Land	2,058
Building and Land Improvements	6,093
Costs Capitalized Subsequent to Acquisition	3,319
Gross Amounts Carried At Close of Period
Land	2,058
Building and Land Improvements	9,412
Total	11,470
Accumulated Depreciation	(4,585)
7061 Columbia Gateway Drive
Initial Cost
Land	729
Building and Land Improvements	3,094
Costs Capitalized Subsequent to Acquisition	2,640
Gross Amounts Carried At Close of Period
Land	729
Building and Land Improvements	5,734
Total	6,463
Accumulated Depreciation	(3,393)
7063 Columbia Gateway Drive
Initial Cost
Land	902
Building and Land Improvements	3,684
Costs Capitalized Subsequent to Acquisition	3,468
Gross Amounts Carried At Close of Period
Land	902
Building and Land Improvements	7,152
Total	8,054
Accumulated Depreciation	(4,450)
7065 Columbia Gateway Drive
Initial Cost
Land	919
Building and Land Improvements	3,763
Costs Capitalized Subsequent to Acquisition	3,097
Gross Amounts Carried At Close of Period
Land	919
Building and Land Improvements	6,860
Total	7,779
Accumulated Depreciation	(4,565)
7067 Columbia Gateway Drive
Initial Cost
Land	1,829
Building and Land Improvements	11,823
Costs Capitalized Subsequent to Acquisition	5,404
Gross Amounts Carried At Close of Period
Land	1,829
Building and Land Improvements	17,227
Total	19,056
Accumulated Depreciation	(8,693)
7100 Redstone Gateway
Initial Cost
Building and Land Improvements	9,101
Gross Amounts Carried At Close of Period
Building and Land Improvements	9,101
Total	9,101
7125 Columbia Gateway Drive
Initial Cost
Land	20,487
Building and Land Improvements	47,029
Costs Capitalized Subsequent to Acquisition	23,580
Gross Amounts Carried At Close of Period
Land	20,487
Building and Land Improvements	70,609
Total	91,096
Accumulated Depreciation	(27,691)
7130 Columbia Gateway Drive
Initial Cost
Land	1,350
Building and Land Improvements	4,359
Costs Capitalized Subsequent to Acquisition	2,896
Gross Amounts Carried At Close of Period
Land	1,350
Building and Land Improvements	7,255
Total	8,605
Accumulated Depreciation	(3,848)
7134 Columbia Gateway Drive
Initial Cost
Land	704
Building and Land Improvements	4,700
Costs Capitalized Subsequent to Acquisition	668
Gross Amounts Carried At Close of Period
Land	704
Building and Land Improvements	5,368
Total	6,072
Accumulated Depreciation	(1,803)
7138 Columbia Gateway Drive
Initial Cost
Land	1,104
Building and Land Improvements	3,518
Costs Capitalized Subsequent to Acquisition	2,853
Gross Amounts Carried At Close of Period
Land	1,104
Building and Land Improvements	6,371
Total	7,475
Accumulated Depreciation	(4,072)
7142 Columbia Gateway Drive
Initial Cost
Land	1,342
Building and Land Improvements	7,148
Costs Capitalized Subsequent to Acquisition	2,611
Gross Amounts Carried At Close of Period
Land	1,342
Building and Land Improvements	9,759
Total	11,101
Accumulated Depreciation	(4,052)
7150 Columbia Gateway Drive
Initial Cost
Land	1,032
Building and Land Improvements	3,429
Costs Capitalized Subsequent to Acquisition	813
Gross Amounts Carried At Close of Period
Land	1,032
Building and Land Improvements	4,242
Total	5,274
Accumulated Depreciation	(1,789)
7150 Riverwood Drive
Initial Cost
Land	1,821
Building and Land Improvements	4,388
Costs Capitalized Subsequent to Acquisition	1,850
Gross Amounts Carried At Close of Period
Land	1,821
Building and Land Improvements	6,238
Total	8,059
Accumulated Depreciation	(3,016)
7160 Riverwood Drive
Initial Cost
Land	2,732
Building and Land Improvements	7,006
Costs Capitalized Subsequent to Acquisition	4,405
Gross Amounts Carried At Close of Period
Land	2,732
Building and Land Improvements	11,411
Total	14,143
Accumulated Depreciation	(4,768)
7170 Riverwood Drive
Initial Cost
Land	1,283
Building and Land Improvements	3,096
Costs Capitalized Subsequent to Acquisition	2,281
Gross Amounts Carried At Close of Period
Land	1,283
Building and Land Improvements	5,377
Total	6,660
Accumulated Depreciation	(2,576)
7175 Riverwood Drive
Initial Cost
Land	1,788
Building and Land Improvements	7,269
Gross Amounts Carried At Close of Period
Land	1,788
Building and Land Improvements	7,269
Total	9,057
Accumulated Depreciation	(1,298)
7200 Redstone Gateway
Initial Cost
Building and Land Improvements	8,348
Costs Capitalized Subsequent to Acquisition	81
Gross Amounts Carried At Close of Period
Building and Land Improvements	8,429
Total	8,429
Accumulated Depreciation	(1,393)
7200 Riverwood Drive
Initial Cost
Land	4,089
Building and Land Improvements	22,630
Costs Capitalized Subsequent to Acquisition	4,634
Gross Amounts Carried At Close of Period
Land	4,089
Building and Land Improvements	27,264
Total	31,353
Accumulated Depreciation	(12,592)
7205 Riverwood Drive
Initial Cost
Land	1,367
Building and Land Improvements	21,419
Gross Amounts Carried At Close of Period
Land	1,367
Building and Land Improvements	21,419
Total	22,786
Accumulated Depreciation	(3,987)
7272 Park Circle Drive
Initial Cost
Land	1,479
Building and Land Improvements	6,300
Costs Capitalized Subsequent to Acquisition	4,608
Gross Amounts Carried At Close of Period
Land	1,479
Building and Land Improvements	10,908
Total	12,387
Accumulated Depreciation	(5,467)
7318 Parkway Drive
Initial Cost
Land	972
Building and Land Improvements	3,888
Costs Capitalized Subsequent to Acquisition	1,324
Gross Amounts Carried At Close of Period
Land	972
Building and Land Improvements	5,212
Total	6,184
Accumulated Depreciation	(2,929)
7400 Redstone Gateway
Initial Cost
Building and Land Improvements	9,223
Costs Capitalized Subsequent to Acquisition	75
Gross Amounts Carried At Close of Period
Building and Land Improvements	9,298
Total	9,298
Accumulated Depreciation	(1,281)
7467 Ridge Road
Initial Cost
Land	1,565
Building and Land Improvements	3,116
Costs Capitalized Subsequent to Acquisition	5,041
Gross Amounts Carried At Close of Period
Land	1,565
Building and Land Improvements	8,157
Total	9,722
Accumulated Depreciation	(4,110)
7500 Advanced Gateway
Initial Cost
Building and Land Improvements	19,070
Gross Amounts Carried At Close of Period
Building and Land Improvements	19,070
Total	19,070
Accumulated Depreciation	(264)
7600 Advanced Gateway
Initial Cost
Building and Land Improvements	14,126
Gross Amounts Carried At Close of Period
Building and Land Improvements	14,126
Total	14,126
Accumulated Depreciation	(135)
7740 Milestone Parkway
Real Estate and Accumulated Depreciation
Encumbrances	16,902
Initial Cost
Land	3,825
Building and Land Improvements	34,176
Costs Capitalized Subsequent to Acquisition	1,084
Gross Amounts Carried At Close of Period
Land	3,825
Building and Land Improvements	35,260
Total	39,085
Accumulated Depreciation	(9,279)
7770 Backlick Road
Initial Cost
Land	6,387
Building and Land Improvements	78,779
Costs Capitalized Subsequent to Acquisition	1,531
Gross Amounts Carried At Close of Period
Land	6,387
Building and Land Improvements	80,310
Total	86,697
Accumulated Depreciation	(14,971)
7880 Milestone Parkway
Initial Cost
Land	4,857
Building and Land Improvements	25,916
Costs Capitalized Subsequent to Acquisition	321
Gross Amounts Carried At Close of Period
Land	4,857
Building and Land Improvements	26,237
Total	31,094
Accumulated Depreciation	(3,384)
8000 Rideout Road
Initial Cost
Building and Land Improvements	16,138
Gross Amounts Carried At Close of Period
Building and Land Improvements	16,138
Total	16,138
8600 Advanced Gateway
Initial Cost
Building and Land Improvements	25,168
Gross Amounts Carried At Close of Period
Building and Land Improvements	25,168
Total	25,168
Accumulated Depreciation	(45)
8621 Robert Fulton Drive
Initial Cost
Land	2,317
Building and Land Improvements	12,642
Costs Capitalized Subsequent to Acquisition	6,191
Gross Amounts Carried At Close of Period
Land	2,317
Building and Land Improvements	18,833
Total	21,150
Accumulated Depreciation	(6,700)
8661 Robert Fulton Drive
Initial Cost
Land	1,510
Building and Land Improvements	3,764
Costs Capitalized Subsequent to Acquisition	3,019
Gross Amounts Carried At Close of Period
Land	1,510
Building and Land Improvements	6,783
Total	8,293
Accumulated Depreciation	(3,528)
8671 Robert Fulton Drive
Initial Cost
Land	1,718
Building and Land Improvements	4,280
Costs Capitalized Subsequent to Acquisition	4,294
Gross Amounts Carried At Close of Period
Land	1,718
Building and Land Improvements	8,574
Total	10,292
Accumulated Depreciation	(4,716)
870 Elkridge Landing Road
Initial Cost
Land	2,003
Building and Land Improvements	9,442
Costs Capitalized Subsequent to Acquisition	10,464
Gross Amounts Carried At Close of Period
Land	2,003
Building and Land Improvements	19,906
Total	21,909
Accumulated Depreciation	(11,574)
8800 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	11,679
Initial Cost
Building and Land Improvements	18,446
Gross Amounts Carried At Close of Period
Building and Land Improvements	18,446
Total	18,446
Accumulated Depreciation	(511)
891 Elkridge Landing Road
Initial Cost
Land	1,165
Building and Land Improvements	4,772
Costs Capitalized Subsequent to Acquisition	3,512
Gross Amounts Carried At Close of Period
Land	1,165
Building and Land Improvements	8,284
Total	9,449
Accumulated Depreciation	(5,193)
901 Elkridge Landing Road
Initial Cost
Land	1,156
Building and Land Improvements	4,437
Costs Capitalized Subsequent to Acquisition	4,789
Gross Amounts Carried At Close of Period
Land	1,156
Building and Land Improvements	9,226
Total	10,382
Accumulated Depreciation	(4,687)
911 Elkridge Landing Road
Initial Cost
Land	1,215
Building and Land Improvements	4,861
Costs Capitalized Subsequent to Acquisition	3,431
Gross Amounts Carried At Close of Period
Land	1,215
Building and Land Improvements	8,292
Total	9,507
Accumulated Depreciation	(4,786)
938 Elkridge Landing Road
Initial Cost
Land	922
Building and Land Improvements	4,748
Costs Capitalized Subsequent to Acquisition	1,516
Gross Amounts Carried At Close of Period
Land	922
Building and Land Improvements	6,264
Total	7,186
Accumulated Depreciation	(3,221)
939 Elkridge Landing Road
Initial Cost
Land	939
Building and Land Improvements	3,756
Costs Capitalized Subsequent to Acquisition	4,444
Gross Amounts Carried At Close of Period
Land	939
Building and Land Improvements	8,200
Total	9,139
Accumulated Depreciation	(5,388)
9651 Hornbaker Road
Initial Cost
Land	6,050
Building and Land Improvements	250,355
Costs Capitalized Subsequent to Acquisition	16,105
Gross Amounts Carried At Close of Period
Land	6,050
Building and Land Improvements	266,460
Total	272,510
Accumulated Depreciation	(72,246)
Arundel Preserve
Initial Cost
Land	13,352
Building and Land Improvements	9,699
Gross Amounts Carried At Close of Period
Land	13,352
Building and Land Improvements	9,699
Total	23,051
Canton Crossing Land
Initial Cost
Land	17,285
Building and Land Improvements	8,363
Costs Capitalized Subsequent to Acquisition	142
Gross Amounts Carried At Close of Period
Land	17,285
Building and Land Improvements	8,505
Total	25,790
Canton Crossing Util Distr Ctr
Initial Cost
Land	6,100
Building and Land Improvements	10,450
Costs Capitalized Subsequent to Acquisition	1,689
Gross Amounts Carried At Close of Period
Land	6,100
Building and Land Improvements	12,139
Total	18,239
Accumulated Depreciation	(6,269)
Columbia Gateway - Southridge
Initial Cost
Land	6,387
Building and Land Improvements	3,722
Gross Amounts Carried At Close of Period
Land	6,387
Building and Land Improvements	3,722
Total	10,109
Dahlgren Technology Center
Initial Cost
Land	978
Building and Land Improvements	178
Gross Amounts Carried At Close of Period
Land	978
Building and Land Improvements	178
Total	1,156
Expedition VII
Initial Cost
Land	705
Building and Land Improvements	862
Gross Amounts Carried At Close of Period
Land	705
Building and Land Improvements	862
Total	1,567
IN 1
Initial Cost
Land	1,815
Building and Land Improvements	15,972
Gross Amounts Carried At Close of Period
Land	1,815
Building and Land Improvements	15,972
Total	17,787
Accumulated Depreciation	(735)
IN 2
Initial Cost
Land	2,627
Building and Land Improvements	28,829
Gross Amounts Carried At Close of Period
Land	2,627
Building and Land Improvements	28,829
Total	31,456
Accumulated Depreciation	(1,081)
M Square Research Park
Initial Cost
Building and Land Improvements	2,020
Gross Amounts Carried At Close of Period
Building and Land Improvements	2,020
Total	2,020
MP 1
Initial Cost
Land	9,426
Building and Land Improvements	30,924
Gross Amounts Carried At Close of Period
Land	9,426
Building and Land Improvements	30,924
Total	40,350
Accumulated Depreciation	(1,240)
MP 2
Initial Cost
Land	9,426
Building and Land Improvements	29,989
Gross Amounts Carried At Close of Period
Land	9,426
Building and Land Improvements	29,989
Total	39,415
Accumulated Depreciation	(1,416)
MR Land
Initial Cost
Land	9,038
Building and Land Improvements	514
Gross Amounts Carried At Close of Period
Land	9,038
Building and Land Improvements	514
Total	9,552
National Business Park North
Initial Cost
Land	21,898
Building and Land Improvements	35,639
Gross Amounts Carried At Close of Period
Land	21,898
Building and Land Improvements	35,639
Total	57,537
North Gate Business Park
Initial Cost
Land	1,755
Building and Land Improvements	5
Gross Amounts Carried At Close of Period
Land	1,755
Building and Land Improvements	5
Total	1,760
NOVA Office A
Initial Cost
Land	2,096
Building and Land Improvements	46,849
Costs Capitalized Subsequent to Acquisition	10
Gross Amounts Carried At Close of Period
Land	2,096
Building and Land Improvements	46,859
Total	48,955
Accumulated Depreciation	(6,926)
NOVA Office B
Initial Cost
Land	739
Building and Land Improvements	38,376
Gross Amounts Carried At Close of Period
Land	739
Building and Land Improvements	38,376
Total	39,115
Accumulated Depreciation	(3,734)
Nova Office C
Initial Cost
Land	5,604
Building and Land Improvements	48,235
Gross Amounts Carried At Close of Period
Land	5,604
Building and Land Improvements	48,235
Total	53,839
NOVA Office D
Initial Cost
Land	6,587
Building and Land Improvements	40,559
Gross Amounts Carried At Close of Period
Land	6,587
Building and Land Improvements	40,559
Total	47,146
Accumulated Depreciation	(3,450)
Oak Grove A
Initial Cost
Land	12,866
Building and Land Improvements	34,427
Gross Amounts Carried At Close of Period
Land	12,866
Building and Land Improvements	34,427
Total	47,293
Accumulated Depreciation	(494)
Oak Grove B
Initial Cost
Land	12,866
Building and Land Improvements	40,550
Gross Amounts Carried At Close of Period
Land	12,866
Building and Land Improvements	40,550
Total	53,416
Accumulated Depreciation	(811)
Oak Grove Phase II
Initial Cost
Land	23,483
Building and Land Improvements	8,833
Gross Amounts Carried At Close of Period
Land	23,483
Building and Land Improvements	8,833
Total	32,316
Old Annapolis Road
Initial Cost
Land	1,637
Building and Land Improvements	5,500
Costs Capitalized Subsequent to Acquisition	6,710
Gross Amounts Carried At Close of Period
Land	1,637
Building and Land Improvements	12,210
Total	13,847
Accumulated Depreciation	(4,870)
P2 A
Initial Cost
Land	16,878
Building and Land Improvements	39,934
Gross Amounts Carried At Close of Period
Land	16,878
Building and Land Improvements	39,934
Total	56,812
Accumulated Depreciation	(738)
P2 B
Initial Cost
Land	22,866
Building and Land Improvements	35,960
Gross Amounts Carried At Close of Period
Land	22,866
Building and Land Improvements	35,960
Total	58,826
Accumulated Depreciation	(292)
P2 C
Initial Cost
Land	14,842
Building and Land Improvements	30,272
Gross Amounts Carried At Close of Period
Land	14,842
Building and Land Improvements	30,272
Total	45,114
Accumulated Depreciation	(60)
Paragon Park
Initial Cost
Land	7,738
Building and Land Improvements	462
Gross Amounts Carried At Close of Period
Land	7,738
Building and Land Improvements	462
Total	8,200
Parkstone A
Initial Cost
Land	3,942
Building and Land Improvements	1,257
Gross Amounts Carried At Close of Period
Land	3,942
Building and Land Improvements	1,257
Total	5,199
Parkstone B
Initial Cost
Land	3,346
Building and Land Improvements	1,074
Gross Amounts Carried At Close of Period
Land	3,346
Building and Land Improvements	1,074
Total	4,420
Patriot Ridge
Initial Cost
Land	18,517
Building and Land Improvements	14,562
Gross Amounts Carried At Close of Period
Land	18,517
Building and Land Improvements	14,562
Total	33,079
Project EL
Initial Cost
Land	7,430
Building and Land Improvements	7,479
Gross Amounts Carried At Close of Period
Land	7,430
Building and Land Improvements	7,479
Total	14,909
Project EX
Initial Cost
Land	8,959
Building and Land Improvements	16,981
Gross Amounts Carried At Close of Period
Land	8,959
Building and Land Improvements	16,981
Total	25,940
Accumulated Depreciation	(698)
Redstone Gateway
Initial Cost
Building and Land Improvements	33,310
Gross Amounts Carried At Close of Period
Building and Land Improvements	33,310
Total	33,310
Accumulated Depreciation	(5)
Sentry Gateway
Initial Cost
Land	4,052
Building and Land Improvements	1,833
Gross Amounts Carried At Close of Period
Land	4,052
Building and Land Improvements	1,833
Total	5,885
Sentry Gateway - T
Initial Cost
Land	14,020
Building and Land Improvements	38,804
Costs Capitalized Subsequent to Acquisition	13
Gross Amounts Carried At Close of Period
Land	14,020
Building and Land Improvements	38,817
Total	52,837
Accumulated Depreciation	(13,473)
Sentry Gateway - V
Initial Cost
Building and Land Improvements	1,066
Gross Amounts Carried At Close of Period
Building and Land Improvements	1,066
Total	1,066
Accumulated Depreciation	(321)
Sentry Gateway - W
Initial Cost
Building and Land Improvements	1,884
Costs Capitalized Subsequent to Acquisition	71
Gross Amounts Carried At Close of Period
Building and Land Improvements	1,955
Total	1,955
Accumulated Depreciation	(548)
Sentry Gateway - X
Initial Cost
Land	1,964
Building and Land Improvements	21,178
Gross Amounts Carried At Close of Period
Land	1,964
Building and Land Improvements	21,178
Total	23,142
Accumulated Depreciation	(5,375)
Sentry Gateway - Y
Initial Cost
Land	1,964
Building and Land Improvements	21,298
Gross Amounts Carried At Close of Period
Land	1,964
Building and Land Improvements	21,298
Total	23,262
Accumulated Depreciation	(5,407)
Sentry Gateway - Z
Initial Cost
Land	1,964
Building and Land Improvements	30,573
Gross Amounts Carried At Close of Period
Land	1,964
Building and Land Improvements	30,573
Total	32,537
Accumulated Depreciation	(4,438)
SP Manassas
Initial Cost
Land	8,156
Building and Land Improvements	187
Gross Amounts Carried At Close of Period
Land	8,156
Building and Land Improvements	187
Total	8,343
Westfields - Park Center
Initial Cost
Land	10,815
Building and Land Improvements	6,206
Gross Amounts Carried At Close of Period
Land	10,815
Building and Land Improvements	6,206
Total	17,021
Other Developments, including intercompany eliminations
Initial Cost
Building and Land Improvements	282
Costs Capitalized Subsequent to Acquisition	257
Gross Amounts Carried At Close of Period
Building and Land Improvements	539
Total	539
Accumulated Depreciation	$ (90)

Schedule III - Real Estate an_3

Schedule III - Real Estate and Accumulated Depreciation (Rollforward) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in cost of properties
Beginning balance	$ 4,348,006	$ 4,148,529	$ 3,980,813
Improvements and other additions	405,940	480,418	224,524
Sales	(65,475)	(242,497)	(53,547)
Impairments	(1,530)	(329)	(2,493)
Other dispositions	(139)	(340)	(768)
Reclassification to right-of use asset	0	(37,775)	0
Ending balance	4,686,802	4,348,006	4,148,529
Changes in accumulated depreciation
Beginning balance	1,007,120	897,903	801,038
Depreciation expense	119,377	117,973	112,610
Sales	(2,105)	(8,416)	(14,845)
Impairments	0	0	(132)
Other dispositions	(139)	(340)	(768)
Ending balance	$ 1,124,253	$ 1,007,120	$ 897,903

Uncategorized Items - ofc-20201

Label	Element	Value
Accounting Standards Update [Extensible List]	us-gaap_AccountingStandardsUpdateExtensibleList	us-gaap:AccountingStandardsUpdate201712Member
Subsidiaries [Member]
Accounting Standards Update [Extensible List]	us-gaap_AccountingStandardsUpdateExtensibleList	us-gaap:AccountingStandardsUpdate201712Member