COPT Defense Properties (CDP) 10-K 18 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2014	Jan. 30, 2015	Jun. 30, 2014
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES TRUST
Entity Central Index Key	860546
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$1,600
Entity Common Stock, Shares Outstanding		93,414,408
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Corporate Office Properties, L.P.
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES, L.P.
Entity Central Index Key	1577966
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$99.50
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Properties, net:
Operating properties, net	$2,751,488	$2,702,693
Projects in development or held for future development	545,426	511,608
Total properties, net	3,296,914	3,214,301
Assets held for sale, net	14,339	0
Cash and cash equivalents	6,077	54,373
Restricted cash and marketable securities	9,069	11,448
Accounts receivable (net of allowance for doubtful accounts of $717 and $2,976, respectively)	26,901	27,000
Deferred rent receivable (net of allowance of $1,418 and $2,126, respectively)	95,910	89,456
Intangible assets on real estate acquisitions, net	43,854	59,258
Deferred leasing and financing costs, net	64,797	66,267
Investing receivables	52,147	53,663
Prepaid expenses and other assets	60,249	54,186
Total assets	3,670,257	3,629,952
Liabilities:
Debt, net	1,920,057	1,927,703
Accounts payable and accrued expenses	123,035	98,785
Rents received in advance and security deposits	31,011	31,492
Dividends and distributions payable	29,862	29,080
Deferred revenue associated with operating leases	13,031	10,369
Interest rate derivatives	1,855	3,309
Other liabilities	12,105	14,207
Total liabilities	2,130,956	2,114,945
Commitments and contingencies (Note 23)
Redeemable noncontrolling interest	18,417	17,758
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Shares of beneficial interest at liquidation preference	199,083	249,083
Common Shares of beneficial interest ($0.01 par value; 125,000,000 shares authorized, shares issued and outstanding of 93,255,284 at December 31, 2014 and 87,394,512 at December 31, 2013)	933	874
Additional paid-in capital	1,969,968	1,814,015
Cumulative distributions in excess of net income	-717,264	-641,868
Accumulated other comprehensive (loss) income	-1,297	3,480
Total Corporate Office Properties Trust’s shareholders’ equity	1,451,423	1,425,584
Noncontrolling interests in subsidiaries:
Common units in COPLP	51,534	53,468
Preferred units in COPLP	8,800	8,800
Other consolidated entities	9,127	9,397
Noncontrolling interests in subsidiaries	69,461	71,665
Total equity	1,520,884	1,497,249
Total liabilities, redeemable noncontrolling interest and equity	3,670,257	3,629,952
Corporate Office Properties, L.P.
Properties, net:
Operating properties, net	2,751,488	2,702,693
Projects in development or held for future development	545,426	511,608
Total properties, net	3,296,914	3,214,301
Assets held for sale, net	14,339	0
Cash and cash equivalents	6,077	54,373
Restricted cash and marketable securities	3,187	3,981
Accounts receivable (net of allowance for doubtful accounts of $717 and $2,976, respectively)	26,901	27,000
Deferred rent receivable (net of allowance of $1,418 and $2,126, respectively)	95,910	89,456
Intangible assets on real estate acquisitions, net	43,854	59,258
Deferred leasing and financing costs, net	64,797	66,267
Investing receivables	52,147	53,663
Prepaid expenses and other assets	60,249	54,186
Total assets	3,664,375	3,622,485
Liabilities:
Debt, net	1,920,057	1,927,703
Accounts payable and accrued expenses	123,035	98,785
Rents received in advance and security deposits	31,011	31,492
Dividends and distributions payable	29,862	29,080
Deferred revenue associated with operating leases	13,031	10,369
Interest rate derivatives	1,855	3,309
Other liabilities	6,223	6,740
Total liabilities	2,125,074	2,107,478
Commitments and contingencies (Note 23)
Redeemable noncontrolling interest	18,417	17,758
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Shares of beneficial interest at liquidation preference	199,083
Common Shares of beneficial interest ($0.01 par value; 125,000,000 shares authorized, shares issued and outstanding of 93,255,284 at December 31, 2014 and 87,394,512 at December 31, 2013)	1,305,219	1,226,318
Accumulated other comprehensive (loss) income	-1,381	3,605
Total Corporate Office Properties Trust’s shareholders’ equity	1,511,721	1,487,806
Noncontrolling interests in subsidiaries:
Noncontrolling interests in subsidiaries	9,163	9,443
Total equity	1,520,884	1,497,249
Total liabilities, redeemable noncontrolling interest and equity	3,664,375	3,622,485
Corporate Office Properties, L.P. | General Partner
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Units, Preferred Partners' Capital Accounts	199,083	249,083
Corporate Office Properties, L.P. | Limited Partner
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Units, Preferred Partners' Capital Accounts	$8,800	$8,800

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Allowance for doubtful accounts- AR	$717	$2,976
Allowance for deferred rent receivable	1,418	2,126
Common Shares of beneficial interest, par value (in dollars per share)	$0.01	$0.01
Common Shares of beneficial interest, shares authorized	125,000,000	125,000,000
Common Shares of beneficial interest, shares issued	93,255,284	87,394,512
Common Shares of beneficial interest, shares outstanding	93,255,284	87,394,512
Corporate Office Properties, L.P.
Allowance for doubtful accounts- AR	717	2,976
Allowance for deferred rent receivable	$1,418	$2,126
General Partner | Corporate Office Properties, L.P.
Preferred Units, Outstanding	7,431,667	9,431,667
Common Shares of beneficial interest, shares outstanding	93,255,284	87,394,512
Limited Partner | Corporate Office Properties, L.P.
Preferred Units, Outstanding	352,000	352,000
Common Shares of beneficial interest, shares outstanding	3,837,551	3,977,700

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues
Rental revenue	$386,396		$377,611		$353,080
Tenant recoveries and other real estate operations revenue	93,329		83,386		81,219
Construction contract and other service revenues	106,748		62,363		73,836
Total revenues	586,473		523,360		508,135
Expenses
Property operating expenses	179,934		167,199		159,206
Depreciation and amortization associated with real estate operations	136,086		113,214		107,998
Construction contract and other service expenses	100,058		58,875		70,576
Impairment losses	1,416		5,857		43,678
General, administrative and leasing expenses	31,794		30,869		31,900
Business development expenses and land carry costs	5,573		5,436		5,711
Total operating expenses	454,861		381,450		419,069
Operating income	131,612		141,910		89,066
Interest expense	-92,393		-82,010		-86,401
Interest and other income	4,923		3,834		7,172
Loss on early extinguishment of debt	-9,552		-27,030		-943
Income from continuing operations before equity in income (loss) of unconsolidated entities and income taxes	34,590		36,704		8,894
Equity in income (loss) of unconsolidated entities	229		2,110		-546
Income tax expense	-310		-1,978		-381
Income from continuing operations	34,509		36,836		7,967
Discontinued operations	26		55,692		12,353
Income before gain on sales of real estate	34,535		92,528		20,320
Gain on sales of real estate, net of income taxes	10,671		9,016		21
Net income	45,206		101,544		20,341
Net (income) loss attributable to noncontrolling interests:
Common units in COPLP	-1,006		-3,283		87
Preferred units in COPLP	-660		-660		-660
Other consolidated entities	-3,285		-3,894		1,209
Net income	40,255		93,707		20,977
Preferred share/ unit dividends/ distributions	-15,939		-19,971		-20,844
Issuance costs associated with redeemed preferred shares	-1,769		-2,904		-1,827
Net income (loss) attributable to COPT common shareholders	22,547		70,832		-1,694
Net income attributable to COPT:
Income from continuing operations	40,225		41,366		9,297
Discontinued operations, net	30		52,341		11,680
Net income	40,255		93,707		20,977
Basic earnings per common share
Income (loss) from continuing operations (in dollars per share/unit)	$0.25	[1]	$0.21	[1]	($0.19)	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.62	[1]	$0.16	[1]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Diluted earnings per common share
Income (loss) from continuing operations (in dollars per share/unit)	$0.25	[1]	$0.21	[1]	($0.19)	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.62	[1]	$0.16	[1]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Corporate Office Properties, L.P.
Revenues
Rental revenue	386,396		377,611		353,080
Tenant recoveries and other real estate operations revenue	93,329		83,386		81,219
Construction contract and other service revenues	106,748		62,363		73,836
Total revenues	586,473		523,360		508,135
Expenses
Property operating expenses	179,934		167,199		159,206
Depreciation and amortization associated with real estate operations	136,086		113,214		107,998
Construction contract and other service expenses	100,058		58,875		70,576
Impairment losses	1,416		5,857		43,678
General, administrative and leasing expenses	31,794		30,869		31,900
Business development expenses and land carry costs	5,573		5,436		5,711
Total operating expenses	454,861		381,450		419,069
Operating income	131,612		141,910		89,066
Interest expense	-92,393		-82,010		-86,401
Interest and other income	4,923		3,834		7,172
Loss on early extinguishment of debt	-9,552		-27,030		-943
Income from continuing operations before equity in income (loss) of unconsolidated entities and income taxes	34,590		36,704		8,894
Equity in income (loss) of unconsolidated entities	229		2,110		-546
Income tax expense	-310		-1,978		-381
Income from continuing operations	34,509		36,836		7,967
Discontinued operations	26		55,692		12,353
Income before gain on sales of real estate	34,535		92,528		20,320
Gain on sales of real estate, net of income taxes	10,671		9,016		21
Net income	45,206		101,544		20,341
Net (income) loss attributable to noncontrolling interests in consolidated entities	-3,276		-3,907		507
Net (income) loss attributable to noncontrolling interests:
Net income	41,930		97,637		20,848
Preferred share/ unit dividends/ distributions	-16,599		-20,631		-21,504
Issuance costs associated with redeemed preferred shares	-1,769		-2,904		-1,827
Net income (loss) attributable to COPT common shareholders	23,562		74,102		-2,483
Net income attributable to COPT:
Income from continuing operations	41,899		42,875		9,194
Discontinued operations, net	31		54,762		11,654
Net income	$41,930		$97,637		$20,848
Basic earnings per common share
Income (loss) from continuing operations (in dollars per share/unit)	$0.25	[2]	$0.21	[2]	($0.19)	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.62	[2]	$0.15	[2]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.25	[2]	$0.83	[2]	($0.04)	[2]
Diluted earnings per common share
Income (loss) from continuing operations (in dollars per share/unit)	$0.25	[2]	$0.21	[2]	($0.19)	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.62	[2]	$0.15	[2]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.25	[2]	$0.83	[2]	($0.04)	[2]
[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_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$45,206	$101,544	$20,341
Other comprehensive (loss) income
Unrealized (losses) gains on interest rate derivatives	-7,799	6,791	-7,676
Unrealized equity in other comprehensive income of equity method investee	0	1,070	0
Realized equity in other comprehensive income of equity method investee	0	-1,070	0
Other comprehensive (loss) income	-4,771	9,531	-3,979
Comprehensive income	40,435	111,075	16,362
Comprehensive (income) loss attributable to noncontrolling interests	-4,957	-8,453	961
Comprehensive income attributable to COPT	35,478	102,622	17,323
Interest expense
Other comprehensive (loss) income
Losses on interest rate derivatives	2,990	2,740	3,697
Loss on early extinguishment of debt
Other comprehensive (loss) income
Losses on interest rate derivatives	38	0	0
Corporate Office Properties, L.P.
Net income	45,206	101,544	20,341
Other comprehensive (loss) income
Unrealized (losses) gains on interest rate derivatives	-7,799	6,791	-7,676
Unrealized equity in other comprehensive income of equity method investee	0	1,070	0
Realized equity in other comprehensive income of equity method investee	0	-1,070	0
Other comprehensive (loss) income	-4,771	9,531	-3,979
Comprehensive income	40,435	111,075	16,362
Comprehensive (income) loss attributable to noncontrolling interests	-3,492	-4,125	615
Comprehensive income attributable to COPT	36,943	106,950	16,977
Corporate Office Properties, L.P. | Interest expense
Other comprehensive (loss) income
Losses on interest rate derivatives	2,990	2,740	3,697
Corporate Office Properties, L.P. | Loss on early extinguishment of debt
Other comprehensive (loss) income
Losses on interest rate derivatives	$38	$0	$0

Consolidated_Statements_of_Equ

Consolidated Statements of Equity (USD $)	Total	Preferred Shares	Common Shares	Preferred Shares	Common Shares	Additional Paid-in Capital	Additional Paid-in Capital	Additional Paid-in Capital	Cumulative Distributions in Excess of Net Income	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.
In Thousands, except Share data, unless otherwise specified	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	USD ($)	Preferred Shares	Common Shares	USD ($)	USD ($)	USD ($)	USD ($)	Preferred Shares	Common Shares	Common Shares	Common Shares	Common Shares	Accumulated Other Comprehensive Loss	Noncontrolling Interests	Limited Partner	Limited Partner	General Partner	General Partner
							USD ($)	USD ($)					USD ($)	USD ($)	USD ($)	Preferred Shares	USD ($)	USD ($)	USD ($)		Preferred Shares		Preferred Shares
																USD ($)					USD ($)		USD ($)
Balance at Dec. 31, 2011	$1,205,899			$216,333	$720	$1,451,078			($534,041)	($1,733)	$73,542	$1,205,899			$972,107			($1,837)	$10,496		$8,800		$216,333
Balance (preferred units) at Dec. 31, 2011																					352,000		8,121,667
Balance (in units/ shares) at Dec. 31, 2011	72,011,324														76,313,112
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (234,246, 311,343 and 140,149 shares in 2012, 2013 and 2014, respectively)	0				2	2,812					-2,814
Shares issued to the public (6,900,000 preferred shares in 2012, 8,625,000, 4,485,000 and 5,520,000 common shares in 2012, 2013 and 2014, respectively)(in dollars)		165,652	204,696	172,500	86		-6,848	204,610					165,652	204,696		-6,848	204,696						172,500
Shares issued to the public (in units/shares)				6,900,000	8,625,000										8,625,000								6,900,000
Stock redeemed or called during period (in units/ shares)				-2,200,000																			-2,200,000
Redemption of preferred shares/units (2,200,000, 3,390,000 and 2,000,000 shares in 2012, 2013 and 2014, respectively)	-55,000			-55,000		1,827			-1,827			-55,000											-55,000
Exercise of share options (in units/shares)	61,624														61,624
Exercise of share options ( 61,624, 39,331 and 62,888 shares in 2012, 2013 and 2014, respectively)(in dollars)	928				0	928						928			928
Share-based compensation	11,184				1	11,183						11,184			11,184
Share-based compensation (in shares/units)															160,643
Restricted common units/shares redemptions	-139,851														-139,851
Restricted common units/shares redemptions (139,851, 78,440 and 57,537 shares in 2012, 2013 and 2014, respectively) (in dollars)	-3,379					-3,379						-3,379			-3,379
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0					-4,627					4,627
Comprehensive income (loss)	18,927								20,977	-3,702	1,652	18,927			-656			-3,871	1,950		660		20,844
Dividends/Distributions	-102,564								-102,564			-107,841			-86,337						-660		-20,844
Distributions to owners of common and preferred units in COPLP	-5,277										-5,277
Distributions to noncontrolling interests	-655										-655	-655							-655
COPT contribution to COPLP of distribution from subsidiary												0			1,608				-1,608
Adjustment to arrive at fair value of redeemable noncontrolling interest	-3,955					-3,955						-3,955			-3,955
Tax benefit (loss) from share-based compensation	43					43						43			43
Balance at Dec. 31, 2012	1,436,499			333,833	809	1,653,672			-617,455	-5,435	71,075	1,436,499			1,089,391			-5,708	10,183		8,800		333,833
Balance (preferred units) at Dec. 31, 2012																					352,000		12,821,667
Balance (in units/ shares) at Dec. 31, 2012	80,952,986														85,020,528
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (234,246, 311,343 and 140,149 shares in 2012, 2013 and 2014, respectively)	0				3	3,994					-3,997
Shares issued to the public (6,900,000 preferred shares in 2012, 8,625,000, 4,485,000 and 5,520,000 common shares in 2012, 2013 and 2014, respectively)(in dollars)	117,961				45	117,916						117,961			117,961
Shares issued to the public (in units/shares)					4,485,000										4,485,000
Stock redeemed or called during period (in units/ shares)				-3,390,000																			-3,390,000
Redemption of preferred shares/units (2,200,000, 3,390,000 and 2,000,000 shares in 2012, 2013 and 2014, respectively)	-84,750			-84,750		2,904			-2,904			-84,750											-84,750
Issuance of common units resulting from common shares issued under at-the-market program (in units)															1,500,000
Issuance of common units resulting from common shares issued under at-the-market program (1,500,000 shares in 2013) (in dollars)	38,447				15	38,432						38,447			38,447
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units	1,369					-1,296					2,665
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in units)															221,501
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in dollars)												1,369			3,899				-2,530
Exercise of share options (in units/shares)	39,331														39,331
Exercise of share options ( 61,624, 39,331 and 62,888 shares in 2012, 2013 and 2014, respectively)(in dollars)	779				0	779						779			779
Share-based compensation	7,605				2	7,603						7,605			7,605
Share-based compensation (in shares/units)															184,292
Restricted common units/shares redemptions	-78,440														-78,440
Restricted common units/shares redemptions (139,851, 78,440 and 57,537 shares in 2012, 2013 and 2014, respectively) (in dollars)	-2,002					-2,002						-2,002			-2,002
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0					-744					744
Comprehensive income (loss)	109,699								93,707	8,915	7,077	109,699			77,006			9,313	2,749		660		19,971
Dividends/Distributions	-115,216								-115,216			-120,156			-99,525						-660		-19,971
Distributions to owners of common and preferred units in COPLP	-4,940										-4,940
Contributions from noncontrolling interests in other consolidates entities	86					0					86	86							86
Distributions to noncontrolling interests	-1,045										-1,045	-1,045							-1,045
Adjustment to arrive at fair value of redeemable noncontrolling interest	-7,121					-7,121						-7,121			-7,121
Tax benefit (loss) from share-based compensation	-122					-122						-122			-122
Balance at Dec. 31, 2013	1,497,249			249,083	874	1,814,015			-641,868	3,480	71,665	1,497,249			1,226,318			3,605	9,443		8,800		249,083
Balance (preferred units) at Dec. 31, 2013																				352,000	352,000	9,431,667	9,431,667
Balance (in units/ shares) at Dec. 31, 2013	87,394,512														91,372,212					3,977,700		87,394,512
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (234,246, 311,343 and 140,149 shares in 2012, 2013 and 2014, respectively)	0				2	1,841					-1,843
Shares issued to the public (6,900,000 preferred shares in 2012, 8,625,000, 4,485,000 and 5,520,000 common shares in 2012, 2013 and 2014, respectively)(in dollars)	148,666				55	148,611						148,666			148,666
Shares issued to the public (in units/shares)					5,520,000										5,520,000
Stock redeemed or called during period (in units/ shares)				-2,000,000																			-2,000,000
Redemption of preferred shares/units (2,200,000, 3,390,000 and 2,000,000 shares in 2012, 2013 and 2014, respectively)	-50,000			-50,000		1,769			-1,769			-50,000											-50,000
Exercise of share options (in units/shares)	62,888														62,888
Exercise of share options ( 61,624, 39,331 and 62,888 shares in 2012, 2013 and 2014, respectively)(in dollars)	1,489					1,489						1,489			1,489
Share-based compensation	7,050				2	7,048						7,050			7,050
Share-based compensation (in shares/units)															195,272
Restricted common units/shares redemptions	-57,537														-57,537
Restricted common units/shares redemptions (139,851, 78,440 and 57,537 shares in 2012, 2013 and 2014, respectively) (in dollars)	-1,554					-1,554						-1,554			-1,554
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0					-3,382					3,382
Comprehensive income (loss)	38,274								40,255	-4,777	2,796	38,274			25,331			-4,986	1,330		660		15,939
Dividends/Distributions	-113,882								-113,882			-118,811			-102,212						-660		-15,939
Distributions to owners of common and preferred units in COPLP	-4,929										-4,929
Contributions from noncontrolling interests in other consolidates entities	3										3	3							3
Distributions to noncontrolling interests	-1,613										-1,613	-1,613							-1,613
Adjustment to arrive at fair value of redeemable noncontrolling interest	134					134						134			134
Tax benefit (loss) from share-based compensation	-3					-3						-3			-3
Balance at Dec. 31, 2014	$1,520,884			$199,083	$933	$1,969,968			($717,264)	($1,297)	$69,461	$1,520,884			$1,305,219			($1,381)	$9,163		$8,800		$199,083
Balance (preferred units) at Dec. 31, 2014																				352,000	352,000	7,431,667	7,431,667
Balance (in units/ shares) at Dec. 31, 2014	93,255,284														97,092,835					3,837,551		93,255,284

Consolidated_Statements_of_Equ1

Consolidated Statements of Equity (Parenthetical)	1 Months Ended		12 Months Ended			0 Months Ended
	Nov. 30, 2014	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 16, 2013	Dec. 31, 2011
Balance (in units/ shares)			93,255,284	87,394,512	80,952,986		72,011,324
Conversion of common units to common shares (in shares/units)			140,149	311,343	234,246
Shares issued to the public (in units/shares)	5,520,000	4,485,000
Exercise of share options (in units/shares)			62,888	39,331	61,624
Restricted common units/shares redemptions			57,537	78,440	139,851
Preferred Shares
Shares issued to the public (in units/shares)					6,900,000
Stock redeemed or called during period (in units/ shares)			-2,000,000	-3,390,000	-2,200,000
Common Shares
Shares issued to the public (in units/shares)			5,520,000	4,485,000	8,625,000
Common Stock Issued to Public Under At-the-Market Program
Shares issued to the public (in units/shares)				1,500,000		1,500,000

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities
Revenues from real estate operations received	$479,605	$482,763	$483,421
Construction contract and other service revenues received	89,180	63,647	77,831
Property operating expenses paid	-178,803	-176,243	-174,683
Construction contract and other service expenses paid	-79,271	-63,853	-67,952
General, administrative, leasing, business development and land carry costs paid	-29,521	-28,022	-22,904
Interest expense paid	-79,095	-81,575	-87,394
Previously accreted interest expense paid	0	-11,116	0
Settlement of interest rate derivatives	0	0	-29,738
Proceeds from sale of trading marketable securities	0	298	18,975
Exit costs on property dispositions	0	-979	-4,146
Payments in connection with early extinguishment of debt	-9,017	-27,909	-2,637
Interest and other income received	607	1,962	1,073
Income taxes refunded (paid)	200	6	-8
Net cash provided by operating activities	193,885	158,979	191,838
Cash flows from investing activities
Construction, development and redevelopment	-200,385	-201,808	-165,275
Tenant improvements on operating properties	-27,037	-21,950	-27,103
Other capital improvements on operating properties	-28,720	-23,940	-20,066
Acquisitions of operating properties	0	0	-48,308
Proceeds from dispositions of properties	57,782	148,569	290,603
Investing receivables funded	-3,731	-14,077	-14,232
Investing receivables payments received	10,279	144	10,113
Leasing costs paid	-16,234	-14,429	-13,278
Decrease (increase) in restricted cash associated with investing activities	1,137	8,178	-872
Other	-2,780	-477	2,162
Net cash (used in) provided by investing activities	-209,689	-119,790	13,744
Proceeds from debt
Revolving Credit Facility	232,000	504,000	329,000
Unsecured senior notes	297,342	592,413	0
Other debt proceeds	11,569	94,049	403,117
Repayments of debt
Revolving Credit Facility	-149,000	-504,000	-991,000
Scheduled principal amortization	-6,517	-9,481	-11,684
Other debt repayments	-394,653	-612,093	-124,386
Deferred financing costs paid	-708	-9,361	-3,371
Net proceeds from issuance of preferred shares	0	0	165,652
Net proceeds from issuance of common shares	150,174	157,444	205,425
Redemption of preferred shares	-50,000	-84,750	-55,000
Common share/unit dividends/distributions paid	-96,330	-93,474	-89,161
Preferred share/unit dividends/distributions paid	-16,731	-21,335	-19,087
Distributions paid to noncontrolling interests in COPLP	-5,008	-4,958	-5,828
Restricted share redemptions	-1,554	-2,002	-3,379
Other	-3,076	-1,862	-845
Net cash (used in) provided by financing activities	-32,492	4,590	-200,547
Net increase (decrease) in cash and cash equivalents	-48,296	43,779	5,035
Cash and cash equivalents
Beginning of period	54,373	10,594	5,559
End of period	6,077	54,373	10,594
Reconciliation of net income (loss) to net cash provided by operating activities:
Net income	45,206	101,544	20,341
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	138,490	119,773	124,418
Impairment losses	1,419	31,068	62,702
Settlement of previously accreted interest expense	0	-11,116	0
Amortization of deferred financing costs	4,666	5,451	6,243
Increase in deferred rent receivable	-3,520	-5,196	-11,776
Amortization of net debt discounts	921	1,159	3,155
Gain on sales of real estate	-10,695	-11,687	-20,961
Share-based compensation	6,164	6,530	9,982
Loss (gain) on early extinguishment of debt	651	-68,689	-3,430
Other	-3,242	-3,093	-4,551
Changes in operating assets and liabilities:
Decrease (increase) in accounts receivable	94	-10,334	8,049
Decrease in restricted cash and marketable securities	1,352	576	14,934
(Increase) decrease in prepaid expenses and other assets	-12,231	-5,128	8,550
Increase in accounts payable, accrued expenses and other liabilities	25,091	3,960	4,101
(Decrease) increase in rents received in advance and security deposits	-481	4,161	-1,916
Decrease in interest rate derivatives in connection with cash settlement	0	0	-28,003
Net cash provided by operating activities	193,885	158,979	191,838
Supplemental schedule of non-cash investing and financing activities:
(Decrease) increase in accrued capital improvements, leasing and other investing activity costs	-3,779	2,947	-1,227
Decrease in property in connection with transfer of property in settlement of debt	0	73,780	12,042
Decrease in debt in connection with transfer of property in settlement of debt	0	146,500	16,304
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests	-4,866	9,470	4,040
Dividends/distribution payable	29,862	29,080	28,698
COPLP common units issued to acquire property and noncontrolling interest in other consolidated entity	0	5,194	0
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	1,843	3,997	2,814
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	3,382	744	4,627
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in equity to carry redeemable noncontrolling interest at fair value	-134	7,121	3,955
Corporate Office Properties, L.P.
Cash flows from operating activities
Revenues from real estate operations received	479,605	482,763	483,421
Construction contract and other service revenues received	89,180	63,647	77,831
Property operating expenses paid	-178,803	-176,243	-174,683
Construction contract and other service expenses paid	-79,271	-63,853	-67,952
General, administrative, leasing, business development and land carry costs paid	-29,521	-28,022	-22,904
Interest expense paid	-79,095	-81,575	-87,394
Previously accreted interest expense paid	0	-11,116	0
Settlement of interest rate derivatives	0	0	-29,738
Proceeds from sale of trading marketable securities	0	298	18,975
Exit costs on property dispositions	0	-979	-4,146
Payments in connection with early extinguishment of debt	-9,017	-27,909	-2,637
Interest and other income received	607	1,962	1,073
Income taxes refunded (paid)	200	6	-8
Net cash provided by operating activities	193,885	158,979	191,838
Cash flows from investing activities
Construction, development and redevelopment	-200,385	-201,808	-165,275
Tenant improvements on operating properties	-27,037	-21,950	-27,103
Other capital improvements on operating properties	-28,720	-23,940	-20,066
Acquisitions of operating properties	0	0	-48,308
Proceeds from dispositions of properties	57,782	148,569	290,603
Investing receivables funded	-3,731	-14,077	-14,232
Investing receivables payments received	10,279	144	10,113
Leasing costs paid	-16,234	-14,429	-13,278
Decrease (increase) in restricted cash associated with investing activities	1,137	8,178	-872
Other	-2,780	-477	2,162
Net cash (used in) provided by investing activities	-209,689	-119,790	13,744
Proceeds from debt
Revolving Credit Facility	232,000	504,000	329,000
Unsecured senior notes	297,342	592,413	0
Other debt proceeds	11,569	94,049	403,117
Repayments of debt
Revolving Credit Facility	-149,000	-504,000	-991,000
Scheduled principal amortization	-6,517	-9,481	-11,684
Other debt repayments	-394,653	-612,093	-124,386
Deferred financing costs paid	-708	-9,361	-3,371
Net proceeds from issuance of preferred shares	0	0	165,652
Net proceeds from issuance of common shares	150,174	157,444	205,425
Redemption of preferred shares	-50,000	-84,750	-55,000
Common share/unit dividends/distributions paid	-100,678	-97,772	-94,329
Preferred share/unit dividends/distributions paid	-17,391	-21,995	-19,747
Restricted share redemptions	-1,554	-2,002	-3,379
Other	-3,076	-1,862	-845
Net cash (used in) provided by financing activities	-32,492	4,590	-200,547
Net increase (decrease) in cash and cash equivalents	-48,296	43,779	5,035
Cash and cash equivalents
Beginning of period	54,373	10,594	5,559
End of period	6,077	54,373	10,594
Reconciliation of net income (loss) to net cash provided by operating activities:
Net income	45,206	101,544	20,341
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	138,490	119,773	124,418
Impairment losses	1,419	31,068	62,702
Settlement of previously accreted interest expense	0	-11,116	0
Amortization of deferred financing costs	4,666	5,451	6,243
Increase in deferred rent receivable	-3,520	-5,196	-11,776
Amortization of net debt discounts	921	1,159	3,155
Gain on sales of real estate	-10,695	-11,687	-20,961
Share-based compensation	6,164	6,530	9,982
Loss (gain) on early extinguishment of debt	651	-68,689	-3,430
Other	-3,242	-3,093	-4,551
Changes in operating assets and liabilities:
Decrease (increase) in accounts receivable	94	-10,334	8,049
Decrease in restricted cash and marketable securities	-234	1,267	14,122
(Increase) decrease in prepaid expenses and other assets	-12,231	-5,128	8,550
Increase in accounts payable, accrued expenses and other liabilities	26,677	3,269	4,913
(Decrease) increase in rents received in advance and security deposits	-481	4,161	-1,916
Decrease in interest rate derivatives in connection with cash settlement	0	0	-28,003
Net cash provided by operating activities	193,885	158,979	191,838
Supplemental schedule of non-cash investing and financing activities:
(Decrease) increase in accrued capital improvements, leasing and other investing activity costs	-3,779	2,947	-1,227
Decrease in property in connection with transfer of property in settlement of debt	0	73,780	12,042
Decrease in debt in connection with transfer of property in settlement of debt	0	146,500	16,304
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests	-4,866	9,470	4,040
Dividends/distribution payable	29,862	29,080	28,698
COPLP common units issued to acquire property and noncontrolling interest in other consolidated entity	0	5,194	0
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in equity to carry redeemable noncontrolling interest at fair value	($134)	$7,121	$3,955

Organization

Organization	12 Months Ended
	Dec. 31, 2014
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 focus primarily on serving the specialized requirements of United States Government agencies and their contractors, most of whom are engaged in national security and information technology related activities. We generally acquire, develop, manage and lease office and data center properties concentrated in large office parks located near knowledge-based government demand drivers and/or in targeted markets or submarkets in the Greater Washington, DC/Baltimore region. As of December 31, 2014, our properties included the following (all references to number of properties, square footage, acres and megawatts are unaudited):
	•	173 operating office properties totaling 16.8 million square feet (excluding two properties serving as collateral for a nonrecourse mortgage loan in default, as discussed further in Note 11);
	•	13 office properties under, or contractually committed for, construction or redevelopment that we estimate will total approximately 1.6 million square feet upon completion;
	•	1,464 acres of land we control that we believe are potentially developable into approximately 18.3 million square feet; and
	•	a partially operational, wholesale data center which upon completion and stabilization is expected to have a critical load of 19.25 megawatts.
	COPLP owns real estate both directly and through subsidiary partnerships and limited liability companies (“LLCs”).  In addition to owning real estate, COPLP also owns subsidiaries that provide real estate services such as property management and construction and development services primarily for our properties but also for third parties. Some of these services are performed by a taxable REIT subsidiary (“TRS”).
	Equity interests in COPLP are in the form of common and preferred units. As of December 31, 2014, COPT owned 96.0% of the outstanding COPLP common units (“common units”) and 95.5% of the outstanding COPLP preferred units (“preferred units”); the remaining common and preferred units in COPLP were owned by third parties. Common units in COPLP not owned by COPT carry certain redemption rights. The number of common units in COPLP owned by COPT is equivalent to the number of outstanding common shares of beneficial interest (“common shares”) of COPT, and the entitlement of all COPLP common units to quarterly distributions and payments in liquidation is substantially the same as those of COPT common shareholders. Similarly, in the case of each series of preferred units in COPLP held by COPT, there is a series of preferred shares of beneficial interest (“preferred shares”) in COPT that is equivalent in number and carries substantially the same terms as such series of COPLP preferred units. COPT’s common shares are publicly traded on the New York Stock Exchange (“NYSE”) under the ticker symbol “OFC”.
	Because COPLP is managed by COPT, and COPT conducts substantially all of its operations through COPLP, we refer to COPT’s executive officers as COPLP’s executive officers, and although, as a partnership, COPLP does not have a board of trustees, we refer to COPT’s Board of Trustees as COPLP’s Board of Trustees.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
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 significant intercompany balances and transactions in consolidation.
	We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity.
	We use the cost method of accounting when we own an interest in an entity and cannot exert significant influence over its operations.
	Prior Out of Period Adjustment
	During the second quarter of 2013, we identified an error related to the estimated fair value of a redeemable noncontrolling interest in a real estate joint venture. Changes in such fair value are reported as changes in equity with no impact to net income or comprehensive income. The error resulted in an understatement of the line entitled “redeemable noncontrolling interest” in the mezzanine section of our consolidated balance sheet and an overstatement of the line entitled “additional paid-in capital” in the equity section of our consolidated balance sheet of $3.7 million as of December 31, 2012. We have determined that this adjustment was not material to our financial statements for 2012 or 2013. Accordingly, this change is reported as an out-of-period adjustment in the consolidated statement of equity for the year ended December 31, 2013.
	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 at the dates of the financial statements;
	•	the disclosure of contingent assets and liabilities at 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 notes receivable, the allocation of property acquisition costs, the determination of estimated useful lives of assets, the determination of lease terms, the evaluation of impairment of long-lived assets, the amount of revenue recognized relating to tenant improvements and the level of expense recognized in connection with share-based compensation. Actual results could differ from these and other estimates.
	Acquisitions of Properties
	Upon completion of 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 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, construction 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-cancellable 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 rental revenue over the remaining lease terms of the respective 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 additional income to be realized includes carrying costs, such as real estate taxes, insurance and other operating expenses, and revenues during the expected lease-up periods considering current market conditions. 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.
	Properties
	We report properties to be developed or held and used in operations at our depreciated cost, reduced for impairment losses. The preconstruction stage of the development or redevelopment of an operating property includes efforts and related costs to secure land control and zoning, evaluate feasibility and complete other initial tasks which are essential to development.
	We capitalize interest expense, real estate taxes and direct and indirect project costs (including related compensation and other indirect costs) associated with properties, or portions thereof, undergoing construction, development and redevelopment activities. In capitalizing interest expense, if there is a specific borrowing for the property undergoing construction, development and 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 construction, 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-constructed 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 construction. We start depreciating newly-constructed and redeveloped properties as they become operational.
	Most of our leases involve 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 associated with such improvements 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 improvements are unique to the tenant or reusable by other tenants; whether the tenant is permitted to alter or remove the improvements without our consent or without compensating us for any lost fair value; whether the ownership of the improvements remains with us or remains with the tenant at the end of the lease term; and whether the economic substance of the lease terms is properly reflected.
	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		Related lease term
	Equipment and personal property		3-10 years
	We assess each of our operating properties for impairment quarterly using cash flow projections and estimated fair values that we derive for each of the properties.  We update the leasing and other assumptions used in these projections regularly, paying particular attention to properties that have experienced chronic vacancy or face significant market challenges.  We review our plans and intentions for our development projects and land parcels quarterly.  If our analyses indicate that the carrying values of operating properties, properties in development or land held for future development may be impaired, we perform a recovery analysis for such properties.  For long-lived assets 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 assets over, in most cases, a ten-year holding period.  If we believe there is a significant possibility that we might dispose of the assets 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 assets over the various possible holding periods.  If the recovery analysis indicates that the carrying value of a tested property is not recoverable from estimated future cash flows, it is written down to its 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 each asset using holding periods that are consistent with our revised plans. Changes in holding periods may require us to recognize significant impairment losses.
	Property fair values are determined based on contract prices, indicative bids, discounted cash flow analyses or yield analyses. Estimated cash flows used in such analyses are based on our plans for the property and our views of market and economic conditions. The estimates consider factors such as current and future rental rates, occupancies for the tested property and comparable properties, estimated operating and capital expenditures and recent sales data for comparable properties; most of these factors are influenced by market data obtained from real estate leasing and brokerage firms and our direct experience with the properties and their markets.
	When we determine that a property is held for sale, we discontinue the recording of depreciation expense on 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, we recognize an impairment loss equal to the difference and reduce the net book value of the property. For periods in which a property is classified as held for sale, we classify the assets of the property as held for sale on our consolidated balance sheet for such periods.
	For dispositions of operating properties occurring prior to the quarterly period ended June 30, 2014 in which we have no significant continuing involvement in such properties, or for operating properties held for sale prior to the quarterly period ended June 30, 2014, we classify the results of operations for such properties as discontinued operations; interest expense that is specifically identifiable to properties included in discontinued operations is used in the computation of interest expense attributable to discontinued operations. As discussed further below, we adopted guidance issued by the Financial Accounting Standards Board (“FASB”) related to the reporting of discontinued operations and disclosures of disposals of components of an entity effective for the quarterly period ended June 30, 2014. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale that represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity. We have had no properties newly classified as discontinued operations subsequent to our adoption of this guidance.
	Sales of Interests in Real Estate
	We recognize gains from sales of interests in real estate using the full accrual method, provided that various criteria relating to the terms of sale and any subsequent involvement by us with the real estate sold are met.
	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, 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. We report investments in marketable securities classified as available-for-sale securities at fair value, with net unrealized gains or losses deferred to accumulated other comprehensive income (loss) (“AOCI”) and realized gains and losses resulting from sales of such investments recognized through earnings; on our consolidated statements of cash flows, we classify cash flows from interest and dividends earned on these securities as operating activities and cash flows from purchases, sales and maturities of these securities as investing activities.
	Accounts and Deferred Rents Receivable and Investing Receivables
	We maintain allowances for estimated losses resulting from the failure of our customers or borrowers to satisfy their payment obligations. We use judgment in estimating these allowances based primarily upon the payment history and credit status of the entities associated with the individual receivables. We write off these receivables when we believe the facts and circumstances indicate that continued pursuit of collection is no longer warranted. When we earn interest income in connection with receivables for which we have established allowances, we establish allowances in connection with such interest income that is unpaid. When cash is received in connection with receivables for which we have established allowances, we reduce the amount of losses previously recognized.
	Intangible Assets and Deferred Revenue on Real Estate Acquisitions
	We capitalize intangible assets and deferred revenue on real estate acquisitions as described in the section above entitled “Acquisitions of Properties.” We amortize the intangible assets and deferred revenue 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
	Market concentration premium		40 years
	We recognize the amortization of acquired above-market 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 Financing Costs, Net
	We defer costs incurred to obtain new tenant leases or extend existing tenant leases, including related compensation costs. We amortize these costs evenly over the lease terms. When tenant leases are terminated early, we expense any unamortized deferred leasing costs associated with those leases over the shortened term of the lease.
	We defer costs of financing arrangements and recognize these costs as interest expense over the related loan 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.
	Noncontrolling Interests
	COPT’s consolidated noncontrolling interests are comprised of interests in COPLP not owned by COPT (discussed further in Note 15) and consolidated real estate joint ventures (discussed further in Note 6). COPLP’s consolidated noncontrolling interests are comprised primarily of interests in our consolidated real estate joint ventures. Also included in COPLP’s consolidated noncontrolling interests are interests in several real estate entities owned directly by COPT, or a wholly owned subsidiary of COPT, that generally do not exceed 1% of interests in such entities. We evaluate whether noncontrolling interests are subject to redemption features outside of our control. For noncontrolling interests that are currently redeemable for cash at the option of the holders of such interests or deemed probable to eventually become redeemable, we classify such interests 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, and only recognize reductions in such interests to the extent of their carrying amount. Our other noncontrolling interests are reported in the equity section of our consolidated balance sheets. The amounts reported for noncontrolling interests on our consolidated statements of operations represent the portion of these entities’ income or losses not attributable to us.
	Revenue Recognition
	We recognize minimum rents, net of abatements, on a straight-line basis over the term of tenant leases. A lease term generally 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 generally includes periods when a tenant: (1) may not terminate its lease obligation early; (2) may terminate its lease obligation early in exchange for a fee or penalty that we consider material enough such that termination would not be probable; (3) possesses renewal rights and the tenant’s failure to exercise such rights imposes a penalty on the tenant material enough such that renewal appears reasonably assured; or (4) possesses bargain renewal options for such periods. 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 included in 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.
	We recognize tenant recovery revenue in the same periods in which we incur the related expenses. Tenant recovery revenue includes payments from tenants as reimbursement for 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.
	We recognize fees for services provided by us once services are rendered, fees are determinable and collectability is assured. We recognize revenue under construction contracts using the percentage of completion method when the revenue and costs for such contracts can be estimated with reasonable accuracy; when these criteria do not apply to a contract, we recognize revenue on that contract using the completed contract method. Under the percentage of completion method, we recognize a percentage of the total estimated revenue on a contract based on the cost of services provided on the contract as of a point in time relative to the total estimated costs on the contract.
	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 primarily 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.  Derivatives are used to hedge the cash flows associated with interest rates on existing debt as well as future debt. We recognize all derivatives as assets or liabilities on our consolidated balance sheet at fair value. We defer the effective portion of changes in fair value of the designated cash flow hedges to AOCI and reclassify such deferrals to interest expense as interest expense is recognized on the hedged forecasted transactions. We recognize the ineffective portion of the change in fair value of interest rate derivatives directly in interest expense. When an interest rate swap designated as a cash flow hedge no longer qualifies for hedge accounting, we recognize changes in fair value of the hedge previously deferred to AOCI, 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.
Please refer to Note 12 for additional information pertaining to interest rate derivatives.
Expense Classification
We classify as property operations expense costs incurred for property taxes, ground rents, utilities, property management, insurance, repairs, exterior and interior maintenance and tenant revenue collection losses, as well as associated labor and indirect costs attributable to these costs.
We classify as general and 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, director and officers and key man life) and leasing prospects, as well as associated labor and indirect costs attributable to these costs.
Share-Based Compensation
We issue two forms of share-based compensation: restricted COPT common shares (“restricted shares”) and COPT performance share units (“PSUs”). We also issued options to purchase COPT common shares (“options”) in prior years. 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 construction and development activities.
When we adopted the authoritative guidance on accounting for share-based compensation, we elected to adopt the alternative transition method for calculating the tax effects of share-based compensation. This method enabled us to use a simplified method to establishing the beginning balance of the additional paid-in capital pool related to the tax effects of employee share-based compensation that was available to absorb tax deficiencies recognized subsequent to the adoption of this guidance.
We compute the fair value of options using the Black-Scholes option-pricing model. Under that model, the risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. The expected option life is based on our historical experience of employee exercise behavior. Expected volatility is based on historical volatility of COPT common shares. Expected dividend yield is based on the average historical dividend yield on our common shares over a period of time ending on the grant date of the options.
We compute the fair value of PSUs using a Monte Carlo model. Under that model, the baseline common share value is based on the market value on the grant date. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. Expected volatility is based on historical volatility of COPT’s common shares.
Recent Accounting Pronouncements
We adopted guidance issued by the FASB related to the reporting of discontinued operations and disclosures of disposals of components of an entity effective for the quarterly period ended June 30, 2014. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale that represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity. The guidance also provides for additional disclosure requirements in connection with both discontinued operations and other dispositions not qualifying as discontinued operations. The guidance applies prospectively to new disposals and new classifications of disposal groups as held for sale after the effective date. Our adoption of the guidance will result in fewer disposed or held for sale properties being reported as discontinued operations in our results of operations (including operating properties sold during the current period) but will not otherwise materially affect our consolidated financial statements.
In May 2014, the FASB issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Additionally, this guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We are required to adopt this guidance for our annual and interim periods beginning January 1, 2017, using one of two methods: retrospective restatement for each reporting period presented at the time of adoption, or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application. We are currently assessing the financial impact of this guidance on our consolidated financial statements.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	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.
	Recurring Fair Value Measurements
	The assets held in connection with a non-qualified elective deferred compensation plan held by COPT (comprised primarily of mutual funds and equity securities) and the corresponding liability to the participants are measured at fair value on a recurring basis on COPT’s consolidated balance sheet using quoted market prices, as are other marketable securities that we hold. The deferred compensation plan assets and other marketable securities are included in the line entitled restricted cash and marketable securities on COPT’s consolidated balance sheets. The offsetting liability associated with the deferred compensation 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 non-qualified elective deferred compensation plan and other marketable securities that we hold are classified in Level 1 of the fair value hierarchy. The liability associated with the deferred compensation plan is classified in Level 2 of the fair value hierarchy.
	The fair values of our interest rate derivatives are determined using widely accepted valuation techniques, including a discounted cash flow analysis on the expected cash flows of each derivative. This analysis reflects the contractual terms of the derivatives, including the period to maturity, and uses observable market-based inputs, including interest rate market data and implied volatilities in such interest rates. While we determined that the majority of the inputs used to value our derivatives fall within Level 2 of the fair value hierarchy, the credit valuation adjustments associated with our interest rate derivatives utilize Level 3 inputs, such as estimates of current credit spreads to evaluate the likelihood of default. However, as of December 31, 2014, 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.
	As of December 31, 2014 and 2013, we owned warrants to purchase 50,000 common shares in The KEYW Holding Corporation (“KEYW”) at an exercise price of $9.25 per share. KEYW is an entity supporting the intelligence community's operations and transformation to Cyber Age mission by providing engineering services and integrated platforms that support the intelligence process. We compute the fair value of these warrants using the Black-Scholes option-pricing model. Under that model, the risk-free interest rate is based on the U.S. Treasury yield curve in effect as of the valuation date. The expected life is based on the period of time until the expiration of the warrants. The expected volatility is based on an average of the historical volatility of companies in KEYW’s industry that we deem to be comparable. The expected dividend yield is based on the dividend yield on KEYW’s common shares as of the date of valuation. The warrants are classified in Level 2 of the fair value hierarchy.
	In addition to the warrants in KEYW described above, we also owned 1.9 million shares, or approximately 7%, of KEYW’s common stock as of December 31, 2011. We sold all of these shares in 2012 for $14.0 million. We recognized revenue from a lease with KEYW in one of our properties of $2.4 million in 2012.
	As discussed further in Note 6, our partner in a real estate joint venture has the right to require us to acquire its interest at fair value beginning in March 2020; accordingly, we classify the fair value of our partner’s interest as a redeemable noncontrolling interest in the mezzanine section of our consolidated balance sheet. We determine the fair value of the interest based on unobservable inputs after considering the assumptions that market participants would make in pricing the interest. We apply a discount rate to the estimated future cash flows allocable to our partner from the properties underlying the joint venture. Estimated cash flows used in such analyses are based on our plans for the properties and our views of market and economic conditions, and consider items such as current and future rental rates, occupancies for the properties and comparable properties and estimated operating and capital expenditures. In determining the fair value of our partner’s interest as of December 31, 2014 and 2013, we used a discount rate of 15.5%, which factored in risk appropriate to the level of future property development expected to be undertaken by the joint venture. A significant increase (decrease) in the discount rate used in determining the fair value would result in a significantly (lower) higher fair value. Given our reliance on the unobservable inputs, the valuations are classified in Level 3 of the fair value hierarchy.
	The carrying values of cash and cash equivalents, restricted cash, accounts receivable, other assets (excluding investing receivables) and accounts payable and accrued expenses are reasonable estimates of their fair values because of the short maturities of these instruments.  As discussed in Note 9, we estimated the fair values of our investing receivables based on the discounted estimated future cash flows of the loans (categorized within Level 3 of the fair value hierarchy); the discount rates used approximate current market rates for loans with similar maturities and credit quality, and the estimated cash payments include scheduled principal and interest payments.  For our disclosure of debt fair values in Note 11, we estimated the fair value of our unsecured senior notes and exchangeable 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 at a specific point in time, are subjective in nature and involve uncertainties and matters of significant judgment.  Settlement at such fair value amounts may not be possible and may not be a prudent management decision.
	For additional fair value information, please refer to Note 9 for investing receivables, Note 11 for debt and Note 12 for interest rate derivatives.
	COPT and Subsidiaries
	The tables below set forth financial assets and liabilities of COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2014 and 2013 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
			Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
			Identical Assets(Level 1)
	December 31, 2014:
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds		$	5,756	$	—		$	—	$	5,756
	Other		126		—			—		126
	Interest rate derivatives (2)		—		274			—		274
	Warrants to purchase common stock in KEYW (2)		—		164			—		164
	Total Assets		$	5,882	$	438		$	—	$	6,320
	Liabilities:
	Deferred compensation plan liability (3)		$	—	$	5,882		$	—	$	5,882
	Interest rate derivatives		—		1,855			—		1,855
	Total Liabilities		$	—	$	7,737		$	—	$	7,737
	Redeemable noncontrolling interest		$	—	$	—		$	18,417	$	18,417
	December 31, 2013:
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds		$	7,090	$	—		$	—	$	7,090
	Common stocks		176		—			—		176
	Other		201		—			—		201
	Common stock (1)		298		—			—		298
	Interest rate derivatives (2)		—		6,594					6,594
	Warrants to purchase common stock in KEYW (2)		—		301			—		301
	Total Assets		$	7,765	$	6,895		$	—	$	14,660
	Liabilities:
	Deferred compensation plan liability (3)		$	—	$	7,467		$	—	$	7,467
	Interest rate derivatives		—		3,309			—		3,309
	Total Liabilities		$	—	$	10,776		$	—	$	10,776
	Redeemable noncontrolling interest		$	—	$	—		$	17,758	$	17,758
	(1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet.
	(2) Included in the line entitled “prepaid expenses and other assets” on COPT’s consolidated balance sheet.
	(3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet.
	COPLP and Subsidiaries
	The tables below set forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2014 and 2013 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
			Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
			Identical Assets(Level 1)
	December 31, 2014:
	Assets:
	Interest rate derivatives (1)		$	—	$	274		$	—	$	274
	Warrants to purchase common stock in KEYW (1)		—		164			—		164
	Total Assets		$	—	$	438		$	—	$	438
	Liabilities:
	Interest rate derivatives		$	—	$	1,855		$	—	$	1,855
	Redeemable noncontrolling interest		$	—	$	—		$	18,417	$	18,417
	December 31, 2013:
	Assets:
	Common stock (2)		$	298	$	—		$	—	$	298
	Interest rate derivatives (1)		—		6,594			—		6,594
	Warrants to purchase common stock in KEYW (1)		—		301			—		301
Total Assets		$	298	$	6,895		$	—	$	7,193
Liabilities:
Interest rate derivatives		$	—	$	3,309		$	—	$	3,309
Redeemable noncontrolling interest		$	—	$	—		$	17,758	$	17,758
(1) Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet.
(2) Included in the line entitled “restricted cash and marketable securities” on COPLP’s consolidated balance sheet.
Nonrecurring Fair Value Measurements
In 2014, we recognized impairment losses totaling $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore, Maryland (“Greater Baltimore”) region that were disposed in the current period. After shortening our expected holding period for these properties during the year, we determined that the carrying amount of the properties would not likely be recovered from the cash flows from the operations and sales of the properties over the shortened period.
In 2013, we recognized the following impairment losses:
•	for certain of our operating properties that served as collateral for a nonrecourse loan, we expected that the cash flows to be generated by the properties would be insufficient to fund debt service requirements on the loan. While we sought to negotiate various alternatives with the lender, on December 23, 2013, we conveyed the properties to the lender to extinguish the loan. We recognized non-cash impairment losses of $11.0 million (all classified as discontinued operations and including $560,000 in exit costs) on these properties in 2013 resulting primarily from the carrying amount of certain of these properties located in Colorado Springs, Colorado (“Colorado Springs”) exceeding their fair value;
•	$15.2 million (all classified as discontinued operations and including $419,000 in exit costs) in connection with properties and land no longer aligned with our strategy that we sold, mostly in Colorado Springs; and
•	$5.9 million on two properties in the Greater Baltimore region that Management concluded no longer met our strategic investment criteria. After shortening our expected holding period for these properties during the period, we determined that the carrying amount of the properties would not likely be recovered from the cash flows from the operations and sales of the properties over the shortened period.
The table below sets forth the fair value hierarchy of the valuation technique we used to determine the fair values of the properties (dollars in thousands):
		Fair Value of Properties Held as of December 31, 2013
		Quoted Prices in					Significant				Impairment
		Active Markets for		Significant Other			Unobservable				Losses
		Identical Assets		Observable Inputs			Inputs				Recognized in
Description		(Level 1)		(Level 2)			(Level 3)		Total		2013 (1)
Assets (2):
Properties, net		$	—	$	—		$	4,459	$	4,459	$	31,068
(1) Represents aggregate impairment losses on non recurring fair value measurements resulting in such losses, excluding exit costs incurred of $979,000.
(2) Reflects balance sheet classifications of assets at time of fair value measurement, excluding the effect of held for sale classifications.
The table below sets forth quantitative information about significant unobservable inputs used for the Level 3 fair value measurements reported above as of December 31, 2013 (dollars in thousands):
Valuation Technique		Fair Value on		Unobservable Input		Range (Weighted Average)
		Measurement Date
Discounted cash flow		$	4,459	Discount rate		10.0% (1)
				Terminal capitalization rate		9.5% (1)
				Market rent growth rate		3.0% (1)
				Expense growth rate		3.0% (1)
(1) Only one value applied for this unobservable input.
2012 Impairment Losses
We recognized impairment losses in 2012 in connection with the following:
•	our office properties and developable land in Greater Philadelphia, Pennsylvania. Our Board of Trustees approved a plan by Management to shorten the holding period for these properties because they no longer met our strategic investment criteria. We determined that the carrying amounts of these properties would not likely be recovered from the cash flows from the operations and sales of such properties over the likely remaining holding period. Accordingly, we recognized aggregate non-cash impairment losses of $46.1 million in 2012 for the amounts by which the carrying values of the properties exceeded their respective estimated fair values. These losses contemplated our expectation that we would incur future cash expenditures of approximately $25.0 million to complete the redevelopment of certain of these properties;
•	properties sold, or identified for sale, that are no longer aligned with our strategy of $19.0 million ($23.2 million classified as discontinued operations and including $4.2 million in exit costs), including $6.9 million pertaining to certain properties in Colorado Springs classified as held for sale at December 31, 2012, and approximately $5.1 million related to our disposition of an additional property from which the cash flows were not sufficient to recover its carrying value; and
•	construction costs incurred on a property held for future development of $1.9 million.

Concentration_of_Rental_Revenu

Concentration of Rental Revenue	12 Months Ended
	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Concentration of Rental Revenue	Concentration of Rental Revenue
	We derived large concentrations of our revenue from real estate operations from certain tenants during the periods set forth in our consolidated statements of operations. The following table summarizes the percentage of our rental revenue (which excludes tenant recoveries and other real estate operations revenue) earned from (1) individual tenants that accounted for at least 5% of our rental revenue from continuing and discontinued operations and (2) the aggregate of the five tenants from which we recognized the most rental revenue in the respective years:
		For the Years Ended December 31,
		2014		2013		2012
	United States Government	18	%	18	%	18	%
	Northrop Grumman Corporation (1)	6	%	8	%	7	%
	Booz Allen Hamilton, Inc.	6	%	6	%	6	%
	Computer Sciences Corporation (1)	N/A		5	%	5	%
	Five largest tenants	39	%	41	%	39	%
	(1) Includes affiliated organizations and agencies and predecessor companies.
	Our rental revenue from the United States Government was earned primarily from properties in the Baltimore/Washington Corridor, San Antonio, Texas (“San Antonio”), St. Mary’s & King George Counties and Colorado Springs regions. We also derived in excess of 90% of our construction contract revenue from the United States Government in each of the years set forth on the consolidated statements of operations.
	In addition, we derived large concentrations of our total revenue from real estate operations (defined as the sum of rental revenue and tenant recoveries and other real estate operations revenue) from certain geographic regions. These concentrations are set forth in the segment information provided in Note 18. Several of these regions, including the Baltimore/Washington Corridor, Northern Virginia, Washington, DC - Capitol Riverfront, St. Mary’s & King George Counties and Greater Baltimore, are within close proximity to each other, and all but three of our regions with real estate operations (San Antonio, Huntsville, Alabama (“Huntsville”) and Colorado Springs) are located in the Mid-Atlantic region of the United States.

Properties_net

Properties, net	12 Months Ended
	Dec. 31, 2014
Real Estate [Abstract]
Properties, net	Properties, net
	Operating properties, net consisted of the following (in thousands):
		December 31,
		2014				2013
	Land	$	439,355			$	430,472
	Buildings and improvements	3,015,216				2,869,870
	Less: accumulated depreciation	(703,083		)		(597,649		)
	Operating properties, net	$	2,751,488			$	2,702,693
	In 2014, we recognized $12.9 million in additional depreciation expense resulting from our revision of the useful life of a property in Greater Philadelphia that was removed from service for redevelopment.
	Projects we had in development or held for future development consisted of the following (in thousands):
		December 31,
		2014				2013
	Land	$	214,977			$	245,676
	Construction in progress, excluding land	330,449				265,932
	Projects in development or held for future development	$	545,426			$	511,608
	2014 Dispositions
	In 2014, we completed dispositions of the following operating properties (dollars in thousands):
	Project Name		Location		Date of Sale		Number of Buildings		Total Rentable Square Feet	Transaction Value		Gain on Disposition
	4969 and 4979 Mercantile Road		White Marsh, MD		7/14/14		2		96,721	$	5,960	$	2,124
	9930 and 9940 Franklin Square		White Marsh, MD		7/30/14		2		71,992	10,475		2,303
	5020, 5022, 5024 and 5026 Campbell Boulevard		White Marsh, MD		8/4/14		4		134,245	12,400		666
							8		302,958	$	28,835	$	5,093
	We also sold land in 2014 for $28.3 million and recognized gains of $5.6 million on the sales.
	2014 Construction Activities
	In 2014, we placed into service an aggregate of 692,000 square feet in five newly constructed office properties located in the Baltimore/Washington Corridor, Northern Virginia and Huntsville. As of December 31, 2014, we had eight office properties under construction, or for which we were contractually committed to construct, that we estimate will total 1.2 million square feet upon completion, including four in Northern Virginia, two in the Baltimore/Washington Corridor, one in San Antonio and one in Huntsville. We also had five office properties under redevelopment that we estimate will total 344,000 square feet upon completion, including three in the Baltimore/Washington Corridor, one in Greater Philadelphia and one in St. Mary’s County, Maryland.
	2013 Dispositions
	In April 2011, we completed a review of our portfolio and identified a number of properties that were no longer closely aligned with our strategy, and our Board of Trustees approved a plan by Management to dispose of some of these properties (the “Strategic Reallocation Plan”). In December 2011, we identified additional properties for disposal, and our Board of Trustees approved a plan by management to increase the scope of the Strategic Reallocation Plan to include the disposition of additional properties.  We completed dispositions of the following properties in 2013 primarily in connection with the Strategic Reallocation Plan (dollars in thousands):
	Project Name		Location		Date of Sale		Number of Buildings		Total Rentable Square Feet	Transaction Value		Gain on Disposition
	920 Elkridge Landing Road		Linthicum, MD		6/25/13		1		103,000	$	6,900	$	—
	4230 Forbes Boulevard		Lanham, MD		12/11/13		1		56,000	5,600		1,507
	December 2013 Colorado Springs Portfolio Disposition		Colorado Springs, CO		12/12/13		15		1,165,000	133,925		1,164
	December 2013 Portfolio Conveyance		Colorado Springs, CO and Linthicum, MD		12/23/13		14		1,021,000	146,876		—
							31		2,345,000	$	293,301	$	2,671
	Each of the above dispositions represents property sales except for the December 2013 Portfolio Conveyance, the disposition of which was completed in connection with a debt extinguishment, as described further below. We also had a disposition of a non-operating property in 2013 for an aggregate transaction value of $3.5 million. In addition to the gains on dispositions reflected above, we recognized impairment losses on certain of these assets that are disclosed in Note 3.
	On December 23, 2013, the mortgage lender on a $146.5 million nonrecourse mortgage loan that was secured by the December 2013 Portfolio Conveyance accepted a deed in lieu of foreclosure on the properties. As a result, we transferred title to the properties to the mortgage lender and we were relieved of the debt obligation plus accrued interest. As of the transfer date, the property had an estimated fair value of $74 million. Upon completion of this transfer, we recognized a gain on extinguishment of debt of $67.8 million, representing the excess of the mortgage loan and interest payable extinguished over the carrying values of the properties transferred as of the transfer date (which included the effect of previous impairment losses) and related closing costs.
	2013 Construction Activities
	In 2013, we placed into service an aggregate of 812,000 square feet in eight newly constructed office properties located in the Baltimore/Washington Corridor, Northern Virginia and Huntsville.

Real_Estate_Joint_Ventures

Real Estate Joint Ventures

12 Months Ended

Dec. 31, 2014

Equity Method Investments and Joint Ventures [Abstract]

Real Estate Joint Ventures

Real Estate Joint Ventures

Consolidated Real Estate Joint Ventures

The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of December 31, 2014 (dollars in thousands):

Nominal

Ownership

December 31, 2014

-1

Date

% as of

Total

Encumbered

Total

Acquired

12/31/14

Nature of Activity

Assets

Assets

Liabilities

LW Redstone Company, LLC

3/23/10

85%

Operates four buildings and developing others (2)

$

143,534

$

66,620

$

41,659

M Square Associates, LLC

6/26/07

50%

Operates two buildings and developing others (3)

59,414

48,856

39,077

$

202,948

$

115,476

$

80,736

(1) Excludes amounts eliminated in consolidation.

(2) This joint venture’s property is in Huntsville, Alabama.

(3) This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).

With regard to our consolidated joint ventures:

•

For LW Redstone, 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 9; as of December 31, 2014, we had advanced $49.1 million to the City to fund such costs (included in investing receivables on our consolidated balance sheets, and including accrued interest thereon).  We also expect to fund additional development and construction costs through equity contributions to the extent that third party financing is not obtained.  Our partner was credited with a $9.0 million capital account upon formation and is not required to make any future equity contributions. While net cash flow distributions to the partners vary depending on the source of the funds distributed, cash flows are generally distributed as follows:

•

cumulative preferred returns on capital invested to fund the project’s infrastructure costs on a pro rata basis to us and our partner;

•

cumulative preferred returns on our capital invested to fund the project’s vertical construction;

•

return of our invested capital;

•

return of our partner’s capital;

•

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 beginning in March 2020; accordingly, we classify the fair value of our partner’s interest as redeemable noncontrolling interests in the mezzanine section of our consolidated balance sheet. We disclose the activity for this redeemable noncontrolling interest in Note 13. We have the right to purchase 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 561,000 square feet of construction commencement through December 31, 2014; and

•

For M Square Associates, LLC, net cash flows of this entity will be 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.

The ventures discussed above include only ones in which parties other than COPLP and COPT own interests.

During the periods included herein, we also owned investments in the following consolidated real estate joint ventures:

•

Arundel Preserve #5, LLC, a joint venture owning property in Hanover, Maryland (in the Baltimore/Washington Corridor) and in which we had a 50% nominal ownership interest. On September 17, 2013, we acquired our partner’s noncontrolling interest, along with incremental additional land value in the venture, in exchange for 221,501 common units in COPLP valued at $5.2 million;

•

MOR Forbes 2 LLC, a joint venture owning property in Lanham, Maryland (in the Baltimore/Washington Corridor) and in which we had a 50% nominal ownership interest. On December 11, 2013, the joint venture sold the property, after which the proceeds were distributed to the partners and there was substantially no remaining business operations or property; and

•

COPT-FD Indian Head, LLC, a joint venture owning property in Charles County, Maryland (in our “Other” region). On August 7, 2014, the joint venture’s property was repurchased by Charles County under the terms of a development agreement for $6.4 million, after which the proceeds were distributed to the partners and there was no remaining business operations or assets.

We consolidate the real estate joint ventures described above because we have: (1) the power to direct the matters that most significantly impact the activities of the joint ventures, including development, leasing and management of the properties constructed by the VIEs; and (2) the 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.

Our commitments and contingencies pertaining to our real estate joint ventures are disclosed in Note 23.

Unconsolidated Real Estate Joint Venture

During the periods included herein, we had a 20% ownership interest in an unconsolidated real estate joint venture that operated 16 operating properties, and in which we had a negative investment balance of $6.4 million as of December 31, 2012. We historically accounted for the investment in the joint venture using the equity method of accounting primarily because: (1) we shared with our partner the power to direct the matters that most significantly impact the activities of the joint venture, including the management and operations of the properties and disposal rights with respect to such properties; and (2) our partner had the right to receive benefits and absorb losses that could be significant to the VIE through its proportionately larger investment. We deferred the gain on our initial contribution of property to the joint venture in a prior period due to certain guarantees described in Note 23, and we subsequently recognized losses in excess of our investment due to such guarantees and our intent to support the joint venture. During the fourth quarter of 2012, the holder of the mortgage debt encumbering all of the joint venture’s properties notified us of the debt’s default, initiated foreclosure proceedings and terminated responsibility that we carried for management of the properties; accordingly, we discontinued recognition of losses on this investment under the equity method effective in October 2012 due to our having neither the obligation nor intent to support the joint venture.  The carrying amount of our investment in this joint venture was lower than our share of the equity in the joint venture by $4.5 million as of December 31, 2012 due to our deferral of the gain on our contribution of the real estate into the joint venture upon its formation and our discontinuance of loss recognition under the equity method effective October 2012.

On December 6, 2013, the holder of the mortgage debt foreclosed on the properties. As a result, title to the properties was transferred to the mortgage lender and the joint venture was relieved of the debt obligation. The joint venture still had $5.6 million in nonrecourse mezzanine debt as of December 31, 2014; however, the joint venture no longer holds any property or other assets and has ceased all business operations. We continue to be subject to standard nonrecourse loan guarantees relating to this joint venture that are described further in Note 23; however, we assessed the nature of these guarantees and determined that the likelihood of us incurring any liability from these guarantees was remote. Therefore, we recognized a gain on the substantive disposition of our investment in the joint venture in 2013 of $6.3 million, which is included in the line entitled “gain on sales of real estate, net of income taxes” on our consolidated statements of operations.

Under the terms of the agreements governing the joint venture, net cash flows were to be distributed to the partners in proportion to their respective ownership interests. We did not recognize fees from the joint venture for property management, construction and leasing services we provided in 2012.

The following table sets forth the condensed statements of operations for this unconsolidated real estate joint venture (in thousands):

For the Years Ended

December 31,

2013

2012

Revenues

$

6,519

$

7,316

Property operating expenses

(2,818

)

(2,829

)

Interest expense

(10,463

)

(7,672

)

Depreciation and amortization expense

(2,067

)

(2,283

)

Gain on early extinguishment of debt

23,013

—

Net income (loss)

$

14,184

$

(5,468

)

Intangible_Assets_on_Real_Esta

Intangible Assets on Real Estate Acquisitions	12 Months Ended
	Dec. 31, 2014
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, 2014						31-Dec-13
		Gross Carrying Amount		Accumulated Amortization		Net		Gross Carrying Amount		Accumulated Amortization		Net
						Carrying Amount						Carrying Amount
	In-place lease value	$	123,759	$	101,040	$	22,719	$	125,504	$	93,885	$	31,619
	Tenant relationship value	42,301		28,492		13,809		44,414		25,962		18,452
	Below-market cost arrangements	12,415		5,984		6,431		12,416		5,136		7,280
	Above-market leases	8,659		8,159		500		8,925		7,970		955
	Market concentration premium	1,333		938		395		1,333		381		952
		$	188,467	$	144,613	$	43,854	$	192,592	$	133,334	$	59,258
	Amortization of the intangible asset categories set forth above totaled $15.2 million in 2014, $16.2 million in 2013 and $21.4 million in 2012. The approximate weighted average amortization periods of the categories set forth above follow: in-place lease value: six years; tenant relationship value: seven years; below-market cost arrangements: 31 years; above-market leases: two years; and market concentration premium: 28 years. The approximate weighted average amortization period for all of the categories combined is ten years. The estimated amortization expense associated with the intangible asset categories set forth above for the next five years is: $9.3 million for 2015; $8.4 million for 2016; $6.2 million for 2017; $3.8 million for 2018; and $3.4 million for 2019.

Deferred_Leasing_and_Financing

Deferred Leasing and Financing Costs	12 Months Ended
	Dec. 31, 2014
Deferred Leasing and Financing Costs [Abstract]
Deferred Leasing and Financing Costs	Deferred Leasing and Financing Costs
	Deferred leasing and financing costs, net consisted of the following (in thousands):
		December 31,
		2014			2013
	Deferred leasing costs	$	123,925		$	110,711
	Deferred financing costs	31,229			36,390
	Accumulated amortization	(90,357		)	(80,834		)
	Deferred leasing and financing costs, net	$	64,797		$	66,267

Investing_Receivables

Investing Receivables	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Investing Receivables	Investing Receivables
	Investing receivables, including accrued interest thereon, consisted of the following (in thousands):
		December 31,
		2014		2013
	Notes receivable from City of Huntsville	$	49,147	$	44,055
	Other investing loans receivable	3,000		9,608
		$	52,147	$	53,663
	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 1st, will be repaid using the real estate taxes generated by the properties constructed 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 receivable 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 constructed properties in 2045.
	We did not have an allowance for credit losses in connection with our investing receivables as of December 31, 2014 or December 31, 2013.  The fair value of these receivables approximated their carrying amounts as of December 31, 2014 and December 31, 2013.

Prepaid_Expenses_and_Other_Ass

Prepaid Expenses and Other Assets	12 Months Ended
	Dec. 31, 2014
Prepaid Expense and Other Assets [Abstract]
Prepaid Expenses and Other Assets	Prepaid Expenses and Other Assets
	Prepaid expenses and other assets consisted of the following (in thousands):
		December 31,
		2014		2013
	Prepaid expenses	$	20,570	$	19,308
	Lease incentives	13,344		8,435
	Construction contract costs incurred in excess of billings	6,656		2,462
	Furniture, fixtures and equipment, net	6,637		6,556
	Deferred tax asset, net (1)	4,002		4,305
	Operating notes receivable	3,797		1,692
	Other equity method investments	2,368		2,258
	Interest rate derivatives	274		6,594
	Other assets	2,601		2,576
	Prepaid expenses and other assets	$	60,249	$	54,186
	(1) See Note 19 for further disclosure.
	Operating notes receivable reported above includes amounts due from tenants with remaining terms exceeding one year totaling $3.6 million as of December 31, 2014 and $1.7 million as of December 31, 2013; we carried allowances for estimated losses for $252,000 of the December 31, 2014 balance and $87,000 of the December 31, 2013 balance.

Debt

Debt	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Debt	Debt
	Debt Summary
	Our debt consisted of the following (dollars in thousands):
		Maximum
		Availability as of			Carrying Value as of						Scheduled Maturity
		December 31,			December 31,		December 31,		Stated Interest Rates as of		as of
		2014			2014		2013		December 31, 2014		December 31, 2014
	Mortgage and Other Secured Loans:
	Fixed rate mortgage loans (1)				$	387,139	$	675,060	3.96% - 10.65% (2)		2015-2024
	Variable rate secured loan				36,877		37,691		LIBOR + 2.25% (3)		Nov-15
	Total mortgage and other secured loans				424,016		712,751
	Revolving Credit Facility (4)	$	800,000		83,000		—		LIBOR + 0.975% to 1.75%		Jul-17
	Term Loan Facilities	-5			520,000		620,000		LIBOR + 1.10% to 2.60% (6)		2015-2019
	Unsecured Senior Notes (4)
	3.600% Senior Notes				347,496		347,244		3.60%		May-23
	5.250% Senior Notes				245,797		245,445		5.25%		Feb-24
	3.700% Senior Notes				297,569		—		3.70%		Jun-21
	Unsecured notes payable				1,607		1,700		0% (7)		2026
	4.25% Exchangeable Senior Notes (4)				572		563		4.25%		Apr-30
	Total debt				$	1,920,057	$	1,927,703
	(1)	Several of the fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates.  The carrying values of these loans reflect net unamortized premiums totaling $42,000 as of December 31, 2014 and $69,000 as of December 31, 2013.
	-2	The maximum stated interest rate would be 7.87%, excluding the incremental additional interest rate associated with the default rate on a nonrecourse mortgage loan discussed further below. The weighted average interest rate on our fixed rate mortgage loans was 8.10% as of December 31, 2014 (or 6.16% excluding the incremental additional interest rate associated with the default rate on the loan discussed above).
	(3)	The interest rate on the loan outstanding was 2.41% as of December 31, 2014.
	-4	Refer to the paragraphs below for further disclosure.
	(5)	As discussed below, we have the ability to borrow an additional $180.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders.
	(6)	The weighted average interest rate on these loans was 1.80% as of December 31, 2014.
	(7)	These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates.  The carrying value of these notes reflects an unamortized discount totaling $654,000 as of December 31, 2014 and $761,000 as of December 31, 2013.
	All debt is owed by the Operating Partnership. While COPT is not directly obligated by any debt, it has guaranteed the Operating Partnership’s Revolving Credit Facility, Term Loan Facilities, Unsecured Senior Notes and 4.25% Exchangeable 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 net worth, 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, 2014, we were within the compliance requirements of these financial covenants.
	Our debt matures on the following schedule (in thousands):
	2015	$	343,545	-1
	2016	171,399
	2017	339,247		-2
	2018	2,036
	2019	122,094
	Thereafter	951,489
	Total	$	1,929,810	-3
	-1	Includes $150.0 million pertaining to a nonrecourse mortgage loan on which we defaulted on the payment terms as discussed further below. Also includes $150.0 million that may be extended for two one-year periods at our option, subject to certain conditions.
	(2)    Includes $333.0 million that may be extended for one year at our option, subject to certain conditions.
	(3)     Represents scheduled principal amortization and maturities only and therefore excludes net discounts of $9.8 million.
	We capitalized interest costs of $6.1 million in 2014, $8.8 million in 2013 and $13.9 million in 2012.
	The following table sets forth information pertaining to the fair value of our debt (in thousands):
		December 31, 2014					31-Dec-13
		Carrying			Estimated		Carrying		Estimated
		Amount			Fair Value		Amount		Fair Value
	Fixed-rate debt
	Unsecured Senior Notes	$	890,862		$	901,599	$	592,689	$	575,374
	4.25% Exchangeable Senior Notes	572			575		563		575
	Other fixed-rate debt	388,746			355,802		676,760		650,997
	Variable-rate debt	639,877			642,091		657,691		657,527
		$	1,920,057		$	1,900,067	$	1,927,703	$	1,884,473
	Mortgage and Other Secured Loans
	In April 2014, a wholly owned subsidiary defaulted on the payment terms of a $150.0 million nonrecourse mortgage loan secured by 15000 and 15010 Conference Center Drive, two operating properties in Northern Virginia with an aggregate estimated fair value that was less than the loan balance. This loan had an interest rate of 10.65% (including the effect of default interest) and was originally scheduled to mature in 2017. The lender subsequently accelerated the loan’s maturity date to July 2014. Additional disclosure regarding this loan is provided in the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of this Annual Report on Form 10-K.
	In December 2014, we completed the defeasance of, and full satisfaction of our obligations with respect to, (1) $103.0 million principal amount of secured nonrecourse mortgage loan due to mature on November 6, 2015 and bearing an interest rate of 5.53% and (2) $108.5 million principal amount of secured nonrecourse mortgage loan due to mature on January 1, 2016 and bearing an interest rate of 5.56%, as well as costs related to the defeasance and satisfaction. As a result, we recognized a loss on early extinguishment of debt of $9.1 million.
	Revolving Credit Facility
	We have a credit agreement providing for an unsecured revolving credit facility (the “Revolving Credit Facility”) with a group of lenders for which J.P. Morgan Securities LLC and KeyBanc Capital Markets acted as joint lead arrangers and joint book runners, KeyBank National Association acted as administrative agent and JPMorgan Chase Bank, N.A. and Bank of America, N.A. acted as co-syndication agents. The lenders’ aggregate commitment under the facility is $800.0 million, with the ability for us to increase the lenders’ aggregate commitment to $1.3 billion, provided that there is no default under the facility and subject to the approval of the lenders. Amounts available under the facility are computed based on 60% of our unencumbered asset value, as defined in the agreement.  The facility matures on July 1, 2017, and may be extended by one year at our option, provided that there is no default under the facility and we pay an extension fee of 0.15% of the total availability under the facility. The interest rate on the facility is based on LIBOR (customarily the 30-day rate) plus 0.975% to 1.750%, as determined by the credit ratings assigned to COPLP by Standard & Poor’s Rating Services, Moody’s Investor Services, 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 0.350%, as determined by the credit ratings assigned to COPLP by the Ratings Agencies. As of December 31, 2014, the maximum borrowing capacity under this facility totaled $800.0 million, of which $702.2 million was available.
	Weighted average borrowings under our Revolving Credit Facility totaled $15.9 million in 2014 and $55.5 million in 2013. The weighted average interest rate on our Revolving Credit Facility was 1.47% in 2014 and 1.74% in 2013.
	Term Loan Facilities
	Effective September 1, 2011, we entered into an unsecured term loan agreement with the same group of lenders as the Revolving Credit Facility under which we borrowed $400.0 million, with a right for us to borrow an additional $100.0 million, provided that there is no default under the agreement and subject to the approval of the lenders. In 2013, we amended this term loan and repaid $150.0 million of the loan balance. In 2014, we repaid an additional $100.0 million of the loan balance. The term loan matures on September 1, 2015, and may be extended by two one-year periods at our option, provided that there is no default and we pay an extension fee of 0.15% of the total availability of the agreement. The variable interest rate on the term loan is based on the LIBOR rate (customarily the 30-day rate) plus 1.10% to 2.00%, as determined by the credit ratings assigned to COPLP by the Ratings Agencies.
	Effective February 14, 2012, we entered into an unsecured term loan agreement with a group of lenders for which J.P. Morgan Securities LLC and KeyBank Capital Markets acted as joint lead arrangers and joint book runners, KeyBank National Association acted as administrative agent and JPMorgan Chase Bank, N.A. acted as syndication agent.  We borrowed $250.0 million under the term loan.  The term loan matures on February 14, 2017, and may be extended by one year at our option, provided that there is no default and we pay an extension fee of 0.15% of the total availability of the agreement.  The variable interest rate on the loan is based on the LIBOR rate (customarily the 30-day rate) plus 1.10% to 2.00%, as determined by the credit ratings assigned to COPLP by the Ratings Agencies.
	Effective August 3, 2012, we entered into an unsecured term loan agreement with a group of lenders for which Wells Fargo Securities, LLC acted as sole arranger and sole book runner, Wells Fargo Bank, National Association acted as administrative agent and Capital One, N.A. acted as documentation agent.  We borrowed $120.0 million under the term loan, with the ability for us to borrow an additional $80.0 million, provided that there is no default under the loan and subject to the approval of the lenders.  The term loan matures on August 2, 2019.  The variable interest rate on the loan is based on the LIBOR rate (customarily the 30-day rate) plus 2.10% to 2.60%, as determined by our leverage levels.
	Unsecured Senior Notes
	In 2013 and 2014, we issued the following senior notes:
	•	a $350.0 million aggregate principal amount of 3.600% Senior Notes at an initial offering price of 99.816% of their face value on May 6, 2013, resulting in proceeds, after deducting discounts of the initial purchasers of the notes, but before other offering expenses, of $347.1 million. The notes mature on May 15, 2023. The carrying value of these notes reflects an unamortized discount totaling $2.5 million as of December 31, 2014 and $2.8 million as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%;
•	a $250.0 million aggregate principal amount of 5.250% Senior Notes at an initial offering price of 98.783% of their face value on September 16, 2013, resulting in proceeds, after deducting underwriting discounts, but before other offering expenses, of $245.3 million. The notes mature on February 15, 2024. The carrying value of these notes reflects an unamortized discount totaling $4.2 million as of December 31, 2014 and $4.6 million as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%; and
•	a $300.0 million aggregate principal amount of 3.700% Senior Notes at an initial offering price of 99.739% of their face value on May 14, 2014, resulting in proceeds, after deducting underwriting discounts, but before other offering expenses, of $297.3 million. The notes mature on June 15, 2021. The carrying value of these notes reflects an unamortized discount totaling $2.4 million as of December 31, 2014. The effective interest rate under the notes, including amortization of the issuance costs, was 3.85%.
We may redeem these 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 3.600% Senior Notes, 40 basis points for the 5.250% Senior Notes and 25 basis points for the 3.700% 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 three months prior to the maturity date, 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.
Exchangeable Senior Notes
In 2010, COPLP issued a $240.0 million aggregate principal amount of 4.25% Exchangeable Senior Notes due 2030.  In 2013, we repaid $239.4 million principal amount of these notes and recognized a $25.9 million loss on early extinguishment of debt. The carrying value of these notes included a principal amount of $575,000 and an unamortized discount totaling $3,000 as of December 31, 2014 and $12,000 as of December 31, 2013.  Interest on the notes is payable on April 15 and October 15 of each year.  These notes have an exchange settlement feature that provides that the notes may, under certain circumstances, be exchangeable for cash and, at COPLP’s discretion, COPT common shares at an exchange rate (subject to adjustment) of 20.8513 shares per one thousand dollar principal amount of the notes (exchange rate is as of December 31, 2014 and is equivalent to an exchange price of $47.96 per common share) (the initial exchange rate of the notes was based on a 20% premium over the closing price on the NYSE on the transaction pricing date).  On or after April 20, 2015, COPLP may redeem the notes in cash in whole or in part. The holders of the notes have the right to require us to repurchase the notes in cash in whole or in part on each of April 15, 2015, April 15, 2020 and April 15, 2025, or in the event of a “fundamental change,” as defined under the terms of the notes, for a repurchase price equal to 100% of the principal amount of the notes plus accrued and unpaid interest.  The notes are general unsecured senior obligations of COPLP and rank equally in right of payment with all other senior unsecured indebtedness of COPLP and are guaranteed by COPT. The effective interest rate under the notes, including amortization of the issuance costs, was 6.05%.  Because the closing price of COPT’s common shares at December 31, 2014 and 2013 was less than the exchange price per common share applicable to these notes, the if-converted value of the notes did not exceed the principal amount.  The table below sets forth interest expense recognized on these notes (in thousands):
	For the Years Ended December 31,
	2014			2013		2012
Interest expense at stated interest rate	$	24		$	4,208	$	10,200
Interest expense associated with amortization of discount	10			1,615		3,651
Total	$	34		$	5,823	$	13,851

Interest_Rate_Derivatives

Interest Rate Derivatives	12 Months Ended
	Dec. 31, 2014
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 (dollars in thousands):
														Fair Value at
	Notional									Effective		Expiration		December 31,
	Amount				Fixed Rate			Floating Rate Index		Date		Date		2014			2013
	$	100,000			0.832	%		One-Month LIBOR		1/3/12		9/1/15		$	(407	)	$	(861	)
	100,000				0.832	%		One-Month LIBOR		1/3/12		9/1/15		(407		)	(861		)
	36,877			-1	3.83	%		One-Month LIBOR + 2.25%		11/2/10		11/2/15		(400		)	(832		)
	100,000				0.8055	%		One-Month LIBOR		9/2/14		9/1/16		(317		)	(94		)
	100,000				0.81	%		One-Month LIBOR		9/2/14		9/1/16		(324		)	(105		)
	100,000				1.673	%		One-Month LIBOR		9/1/15		8/1/19		239			3,377
	100,000				1.73	%		One-Month LIBOR		9/1/15		8/1/19		35			3,217
	100,000				0.6123	%		One-Month LIBOR		1/3/12		9/1/14		—			(279		)
	100,000				0.61	%		One-Month LIBOR		1/3/12		9/1/14		—			(277		)
														$	(1,581	)	$	3,285
	-1	The notional amount of this instrument is scheduled to amortize to $36.2 million.
	Each of the one-month LIBOR interest rate swaps set forth in the table above was designated as a cash flow hedge of interest rate risk.
	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):
			December 31, 2014						December 31, 2013
	Derivatives		Balance Sheet Location		Fair Value				Balance Sheet Location		Fair Value
	Interest rate swaps designated as cash flow hedges		Prepaid expenses and other assets		$	274			Prepaid expenses and other assets		$	6,594
	Interest rate swaps designated as cash flow hedges		Interest rate derivatives		(1,855		)		Interest rate derivatives		(3,309		)
	The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
	Amount of (losses) gains recognized in accumulated other comprehensive income (loss) (“AOCI”) (effective portion)	$	(7,799	)		$	6,791			$	(7,676	)
	Amount of losses reclassified from AOCI into interest expense (effective portion)	2,990				2,740				3,697
	Amount of loss reclassified from AOCI into loss on early extinguishment of debt	38				—				—
	Over the next 12 months, we estimate that approximately $2.9 million of losses will be reclassified from AOCI as an increase to interest expense.
	We have agreements with each of our interest rate derivative counterparties that contain provisions under which, if we default or are capable of being declared in default on defined levels of our indebtedness, we could also be declared in default on our derivative obligations.  These agreements also incorporate the loan covenant provisions of our indebtedness with a lender affiliate of the derivative counterparties.  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, 2014, the fair value of interest rate derivatives in a liability position related to these agreements was $1.9 million, excluding the effects of accrued interest. As of December 31, 2014, we had not posted any collateral related to these agreements.  We are not in default with any of these provisions.  If we breached any of these provisions, we could be required to settle our obligations under the agreements at their termination value of $2.1 million.

Redeemable_Noncontrolling_Inte

Redeemable Noncontrolling Interest	12 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest	Redeemable Noncontrolling Interest
	The table below sets forth the activity in a redeemable noncontrolling interest in a consolidated real estate joint venture described in Note 6 (in thousands):
		For the Years Ended December 31,
		2014			2013			2012
	Beginning balance	$	17,758		$	10,298		$	8,908
	Distribution to noncontrolling interest	(1,369		)	(1,037		)	—
	Net income (loss) attributable to noncontrolling interest	2,162			1,376			(2,565		)
	Adjustment to arrive at fair value of interest	(134		)	7,121			3,955
	Ending balance	$	18,417		$	17,758		$	10,298

Equity_COPT_and_Subsidiaries

Equity - COPT and Subsidiaries	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Equity - COPT and Subsidiaries	Equity - COPT and Subsidiaries
	Preferred Shares
	As of December 31, 2014, COPT had 25.0 million preferred shares authorized at $0.01 par value per share. The table below sets forth additional information pertaining to COPT’s outstanding preferred shares (dollars in thousands, except per share data):
	Series		# of Shares Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Dividend Yield		Annual Dividend Per Share		Earliest Redemption Date
	Series K		531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L		6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
			7,431,667	$	199,083
	Each series of preferred shares is nonvoting and redeemable for cash in the amount of its liquidation preference at COPT’s option on or after the earliest redemption date. The Series K Cumulative Redeemable Preferred Shares are also convertible, subject to certain conditions, into common shares on the basis of 0.8163 common shares for each preferred share. Holders of all preferred shares are entitled to cumulative dividends, payable quarterly (as and if declared by the Board of Trustees). In the case of each series of preferred shares, there is a series of COPLP preferred units owned by COPT that carries substantially the same terms.
	During 2013 and 2014, COPT redeemed all of the outstanding shares of its following series of preferred shares:
	•	the 7.625% Series J Preferred Shares on April 22, 2013 at a price of $25.00 per share, or $84.8 million in the aggregate, plus accrued and unpaid dividends thereon through the date of redemption, and recognized a $2.9 million decrease to net income available to common shareholders pertaining to the shares’ original issuance costs incurred at the time of the redemption; and
	•	the 7.500% Series H Preferred Shares on June 16, 2014 at a price of $25.00 per share, or $50.0 million in the aggregate, plus accrued and unpaid dividends thereon through the date of redemption, and recognized a $1.8 million decrease to net income available to common shareholders pertaining to the shares’ original issuance costs incurred at the time of the redemption.
	Common Shares
	During 2013 and 2014, COPT completed the following public offerings of common shares:
	•	4.485 million common shares in March 2013 at a public offering price of $26.34 per share for net proceeds of $118.1 million after underwriter discounts but before offering expenses; and
	•	5.52 million common shares in November 2014 at a public offering price of $27.30 per share for net proceeds of $148.9 million after underwriter discounts but before offering expenses.
	COPT contributed the net proceeds from these issuances to COPLP in exchange for an equal number of units in COPLP.
	In October 2012, COPT established an at-the-market (“ATM”) stock offering program under which it may, from time to time, offer and sell common shares in “at the market” stock offerings having an aggregate gross sales price of up to $150.0 million. Through December 31, 2014, COPT’s only issuance under the program was 1.5 million common shares issued on July 15, 2013 at a weighted average price of $26.05 per share under the ATM program; net proceeds from the shares issued totaled $38.5 million, after payment of $586,000 in commissions to sales agents; the proceeds from these shares were contributed to COPLP in exchange for an equal number of common units in COPLP. COPT’s remaining capacity under the ATM Plan is an aggregate gross sales price of $110.9 million in stock sales.
	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 140,149 in 2014 and 311,343 in 2013.
	COPT declared dividends per common share of $1.10 in 2014, 2013 and 2012.
	See Note 16 for disclosure of common share activity pertaining to our share-based compensation plans.

Equity_COPLP_and_Subsidiaries

Equity - COPLP and Subsidiaries	12 Months Ended
	Dec. 31, 2014
Class of Stock [Line Items]
Equity - COPLP and Subsidiaries	Equity - COPT and Subsidiaries
	Preferred Shares
	As of December 31, 2014, COPT had 25.0 million preferred shares authorized at $0.01 par value per share. The table below sets forth additional information pertaining to COPT’s outstanding preferred shares (dollars in thousands, except per share data):
	Series		# of Shares Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Dividend Yield		Annual Dividend Per Share		Earliest Redemption Date
	Series K		531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L		6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
			7,431,667	$	199,083
	Each series of preferred shares is nonvoting and redeemable for cash in the amount of its liquidation preference at COPT’s option on or after the earliest redemption date. The Series K Cumulative Redeemable Preferred Shares are also convertible, subject to certain conditions, into common shares on the basis of 0.8163 common shares for each preferred share. Holders of all preferred shares are entitled to cumulative dividends, payable quarterly (as and if declared by the Board of Trustees). In the case of each series of preferred shares, there is a series of COPLP preferred units owned by COPT that carries substantially the same terms.
	During 2013 and 2014, COPT redeemed all of the outstanding shares of its following series of preferred shares:
	•	the 7.625% Series J Preferred Shares on April 22, 2013 at a price of $25.00 per share, or $84.8 million in the aggregate, plus accrued and unpaid dividends thereon through the date of redemption, and recognized a $2.9 million decrease to net income available to common shareholders pertaining to the shares’ original issuance costs incurred at the time of the redemption; and
	•	the 7.500% Series H Preferred Shares on June 16, 2014 at a price of $25.00 per share, or $50.0 million in the aggregate, plus accrued and unpaid dividends thereon through the date of redemption, and recognized a $1.8 million decrease to net income available to common shareholders pertaining to the shares’ original issuance costs incurred at the time of the redemption.
	Common Shares
	During 2013 and 2014, COPT completed the following public offerings of common shares:
	•	4.485 million common shares in March 2013 at a public offering price of $26.34 per share for net proceeds of $118.1 million after underwriter discounts but before offering expenses; and
	•	5.52 million common shares in November 2014 at a public offering price of $27.30 per share for net proceeds of $148.9 million after underwriter discounts but before offering expenses.
	COPT contributed the net proceeds from these issuances to COPLP in exchange for an equal number of units in COPLP.
	In October 2012, COPT established an at-the-market (“ATM”) stock offering program under which it may, from time to time, offer and sell common shares in “at the market” stock offerings having an aggregate gross sales price of up to $150.0 million. Through December 31, 2014, COPT’s only issuance under the program was 1.5 million common shares issued on July 15, 2013 at a weighted average price of $26.05 per share under the ATM program; net proceeds from the shares issued totaled $38.5 million, after payment of $586,000 in commissions to sales agents; the proceeds from these shares were contributed to COPLP in exchange for an equal number of common units in COPLP. COPT’s remaining capacity under the ATM Plan is an aggregate gross sales price of $110.9 million in stock sales.
	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 140,149 in 2014 and 311,343 in 2013.
	COPT declared dividends per common share of $1.10 in 2014, 2013 and 2012.
	See Note 16 for disclosure of common share activity pertaining to our share-based compensation plans.
Corporate Office Properties, L.P.
Class of Stock [Line Items]
Equity - COPLP and Subsidiaries	Equity - COPLP and Subsidiaries
	General Partner Preferred Units
	The table below sets forth information pertaining to preferred units in COPLP held by COPT at December 31, 2014 (dollars in thousands, except per unit data):
	Series		# of Units Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Distribution Yield		Annual Distribution Per Unit		Earliest Redemption Date
	Series K		531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L		6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
			7,431,667	$	199,083
	In the case of each series of preferred units, COPT had preferred shares that carry substantially the same terms. Each series of preferred units are redeemable for cash in the amount of its liquidation preference at our option on or after the earliest redemption date. The Series K Preferred Units are also convertible, subject to certain conditions, into common units on the basis of 0.8163 common units for each preferred unit. COPT, as holder of these preferred units, is entitled to cumulative distributions, payable quarterly (as and if declared by the Board of Trustees).
	In 2013 and 2014, COPLP redeemed all of the outstanding units of its following series of preferred units held by COPT:
	•	the 7.625% Series J Preferred Units on April 22, 2013 at a price of $25.00 per unit, or $84.8 million in the aggregate, plus accrued and unpaid distributions thereon through the date of redemption, and recognized a $2.9 million decrease to net income available to common unitholders pertaining to the units’ original issuance costs at the time of the redemption; and
	•	the 7.500% Series H Preferred Units on June 16, 2014 at a price of $25.00 per unit, or $50.0 million in the aggregate, plus accrued and unpaid distributions thereon through the date of redemption, and recognized a $1.8 million decrease to net income available to common unitholders pertaining to the units’ original issuance costs at the time of the redemption.
	Limited Partner Preferred Units
	COPLP has 352,000 Series I Preferred Units issued to an unrelated party that have an aggregate liquidation preference of $8.8 million ($25.00 per unit), plus any accrued and unpaid distributions of return thereon (as described below), and may be redeemed for cash by COPLP at COPLP’s option any time after September 22, 2019. The owner of these units is entitled to a priority annual cumulative return equal to 7.5% of their liquidation preference through September 22, 2019; the annual cumulative preferred return increases for each subsequent five-year period, subject to certain maximum limits. These units are convertible into common units on the basis of 0.5 common units for each Series I Preferred Unit; the resulting common units would then be exchangeable for COPT common shares in accordance with the terms of COPLP’s agreement of limited partnership.
	Common Units
	COPT owned 96.0% of COPLP’s common units as of December 31, 2014 and 95.6% as of December 31, 2013.
	During 2013 and 2014, COPT acquired additional common units through the following public offerings of common shares:
	•	4.485 million common shares in March 2013 at a public offering price of $26.34 per share for net proceeds of $118.1 million (after underwriter discounts but before offering expenses) that were contributed to COPLP in exchange for an equal number of common units in COPLP; and
	•	5.52 million common shares in November 2014 at a public offering price of $27.30 per share for net proceeds of $148.9 million (after underwriter discounts but before offering expenses) that were contributed to COPLP in exchange for an equal number of common units in COPLP.
	On July 15, 2013, COPT issued 1.5 million common shares at a weighted average price of $26.05 per share, representing its only issuance under the ATM program through December 31, 2014. Net proceeds from the shares issued totaled $38.5 million, after payment of $586,000 in commissions to sales agents. The common shares were contributed to COPLP in exchange for 1.5 million common units.
	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). 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 140,149 in 2014 and 311,343 in 2013.
	We declared distributions per common unit of $1.10 in 2014, 2013 and 2012.

ShareBased_Compensation_and_Ot

Share-Based Compensation and Other Compensation Matters	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation and Other Compensation Matters	Share-Based Compensation and Other Compensation Matters
	Share-Based Compensation Plans
	In May 2010, COPT adopted the Amended and Restated 2008 Omnibus Equity and Incentive Plan. 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 5.9 million common shares in COPT to be issued in the form of options, share appreciation rights, deferred share awards, restricted share awards, unrestricted share awards, performance shares, dividend equivalent rights and other equity-based awards and for the granting of cash-based awards. The plan expires on May 13, 2020.
	In March 1998, COPT adopted a long-term incentive plan for our Trustees and employees. This plan, which expired in March 2008, provided for the award of options, restricted shares and dividend equivalents.
	Grants of restricted shares and options under these plans to nonemployee Trustees generally vest on the first anniversary of the grant date provided that the Trustee remains in his or her position. Restricted shares and options granted to employees vest based on increments and over periods of time set forth under the terms of the respective awards provided that the employees remain employed by us. Options expire ten years after the date of grant. Shares for each of the share-based compensation plans are issued under registration statements 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 such share-based compensation plans, COPLP issues to COPT an equal number of equity instruments with identical terms.
	The following table summarizes restricted share transactions under the share-based compensation plans for 2012, 2013 and 2014:
			Shares			Weighted Average Grant Date Fair Value
	Unvested at December 31, 2011		648,378			$	33.13
	Granted		177,662			23.64
	Forfeited		(17,019	)		31.43
	Vested		(374,378	)		32.72
	Unvested at December 31, 2012		434,643			29.67
	Granted		193,833			25.91
	Forfeited		(9,541	)		27.59
	Vested		(241,487	)		30.97
	Unvested at December 31, 2013		377,448			26.96
	Granted		216,607			26.73
	Forfeited		(21,335	)		25.1
	Vested		(182,213	)		28.56
	Unvested at December 31, 2014		390,507			$	26.19
	Unvested shares as of December 31, 2014 that are expected to vest		375,686			$	26.18
	The aggregate intrinsic value of restricted shares that vested was $4.9 million in 2014, $6.3 million in 2013 and $9.0 million in 2012.
	Our Board of Trustees made the following grants of PSUs to executives from 2011 through 2014 (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, 2014
	3/3/11		56,883			3/3/11		3/2/14		$	2,796			—
	3/1/12		54,070			1/1/12		12/31/14		1,772				54,070
	3/1/13		69,579			1/1/13		12/31/15		1,867				69,579
	3/6/14		49,103			1/1/14		12/31/16		1,723				49,103
	The PSUs each have 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 will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule:
	Percentile Rank		Earned PSUs Payout %
	75th or greater		200% of PSUs granted
	50th or greater		100% of PSUs granted
	25th		50% of PSUs granted
	Below 25th		0% of PSUs granted
	If the percentile rank exceeds the 25th percentile and is between two of the percentile ranks set forth in the table above, then the percentage of the earned PSUs will be interpolated between the ranges set forth in the table above to reflect any performance between the listed percentiles.  At the end of the performance period, we, in settlement of the award, will issue a number of fully-vested COPT common shares equal to the sum of:
	•	the number of earned PSUs in settlement of the award plan; plus
	•	the aggregate dividends that would have been paid with respect to the common shares issued in settlement of the earned PSUs through the date of settlement had such shares been issued on the grant date, divided by the share price on such settlement date, as defined under the terms of the agreement.
	If a performance period ends due to a sale event or qualified termination, the number of earned PSUs is prorated based on the portion of the three-year performance period that has elapsed.  If employment is terminated by the employee or by us for cause, all PSUs are forfeited.  PSUs do not carry voting rights.
	Based on COPT’s total shareholder return relative to its peer group of companies:
	•	for the 2011 PSUs that vested in 2014, there was no payout value in connection with the vesting; and
	•	for the 2012 PSUs that vested on December 31, 2014 to be paid out in 2015, approximately 40,000 shares will be issued in March 2015 in connection with the vesting.
	We computed grant date fair values for PSUs using Monte Carlo models and are recognizing these values over three-year periods that commenced on the respective grant dates. The grant date fair value and certain of the assumptions used in the Monte Carlo models for the PSUs granted in 2012, 2013 and 2014 are set forth below:
			For the Years Ended December 31,
			2014				2013				2012
	Grant date fair value		$	35.09			$	26.84			$	32.77
	Baseline common share value		$	26.52			$	25.85			$	24.39
	Expected volatility of common shares		28.6		%		29.5		%		43.2		%
	Risk-free interest rate		0.66		%		0.33		%		0.41		%
	The following table summarizes option transactions under the share-based compensation plans for 2012, 2013 and 2014 (dollars in thousands, except per share data):
			Shares			Range of Exercise Price per Share		Weighted Average Exercise Price per Share				Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
												(in Years)
	Outstanding at December 31, 2011		945,422			$13.40 - $57.00		$	36.63			4		$	510
	Forfeited/Expired – 2012		(85,588	)		$25.52 - $57.00		$	42.98
	Exercised – 2012		(61,624	)		$13.40 - $22.49		$	15.08
	Outstanding at December 31, 2012		798,210			$13.60 - $57.00		$	37.62			3		$	325
	Forfeited/Expired – 2013		(117,952	)		$18.08 - $51.62		$	40.91
	Exercised – 2013		(39,331	)		$13.60 - $26.24		$	19.67
	Outstanding at December 31, 2013		640,927			$19.63 - $56.00		$	38.11			2		$	68
	Forfeited/Expired – 2014		(18,303	)		$22.34 - $49.60		$	42.12
	Exercised – 2014		(62,888	)		$19.63 - $28.15		$	23.7
	Outstanding at December 31, 2014		559,736			$25.52 - $56.00		$	39.6			2		$	167
	Exercisable at December 31, 2012		798,210			-1		$	37.62
	Exercisable at December 31, 2013		640,927			-2		$	38.11
	Exercisable at December 31, 2014		559,736			-3		$	39.6
-1	9,500 of these options had an exercise price ranging from $13.60 to $16.73; 204,736 had an exercise price ranging from $16.74 to $30.04; 180,962 had an exercise price ranging from $30.05 to $41.28; and 403,012 had an exercise price ranging from $41.29 to $57.00.
-2	171,288 of these options had an exercise price ranging from $19.63 to $30.04; 145,187 had an exercise price ranging from$30.05 to $41.28; 160,402 had an exercise price ranging from $41.29 to $42.74; and 164,050 had an exercise price ranging from $42.75 to $56.00.
-3	105,672 of these options had an exercise price ranging from $25.52 to $30.04; 142,862 had an exercise price ranging from$30.05 to $41.28; 158,902 had an exercise price ranging from $41.29 to $42.74; and 152,300 had an exercise price ranging from $42.75 to $56.00.
The aggregate intrinsic value of options exercised was $225,000 in 2014, $258,000 in 2013 and $553,000 in 2012.
We own a taxable REIT subsidiary that is subject to Federal and state income taxes. We realized a windfall tax (loss) benefit of $(3,000) in 2014, $(122,000) in 2013 and $43,000 in 2012 on options exercised and vesting restricted shares in connection with employees of that subsidiary.
The table below sets forth our reporting for share based compensation expense (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
General, administrative and leasing expenses		$	5,307			$	5,412			$	8,611
Property operating expenses		857				1,118				1,371
Capitalized to development activities		886				1,075				1,202
Share-based compensation expense		$	7,050			$	7,605			$	11,184
The amounts included in our consolidated statements of operations for share-based compensation reflected an estimate of pre-vesting forfeitures of 0% for PSUs and 0% to 5% for restricted shares.
As of December 31, 2014, all of our options are vested and fully expensed. As of December 31, 2014, there was $6.3 million of unrecognized compensation cost related to unvested restricted shares that is expected to be recognized over a weighted average period of approximately two years. As of December 31, 2014, there was $1.9 million of unrecognized compensation cost related to PSUs that is expected to be recognized over a weighted average performance period of approximately two years.
401(k) Plan
We have a 401(k) defined contribution plan covering substantially all of our employees that permits participants to contribute up to 90% of their compensation, as defined in the Plan, per pay period on a before-tax basis or after-tax basis, or a combination of both, subject to limitations under the Internal Revenue Code of 1986 ( the “IRC”), as amended. Participants who are 50 years of age or older by the end of a particular plan year and have contributed the maximum 401(k) deferral amount allowed under the plan for that year are eligible to contribute an additional portion of their annual compensation on a before-tax basis as catch-up contributions, up to the annual limit under the IRC. We match 100% of the first 1% of pre-tax and/or after-tax contributions that participants contribute to the plan and 50% of the next 5% in participant contributions to the plan (representing an aggregate match by us of 3.5% on the first 6% of participant pre-tax and/or after-tax contributions to the plan).  Participants’ contributions are fully vested. Participants are 50% vested in matching contributions after one year of credited service and 100% vested after two years of credited service. We fund all contributions with cash. Our matching contributions under the plan totaled approximately $1.2 million in 2014, $1.1 million in 2013 and $1.1 million in 2012. The 401(k) plan is fully funded as of December 31, 2014.
Deferred Compensation Plan
COPT has a non-qualified elective deferred compensation plan for certain members of our management team that permits participants to defer up to 100% of their compensation on a pre-tax basis and receive a tax-deferred return on such deferrals. The balance of the plan, which was fully funded, totaled $5.9 million as of December 31, 2014 and $7.5 million as of December 31, 2013, and is included in the accompanying COPT consolidated balance sheets.
Executive Transition Costs
In connection with the departure on February 3, 2015 of Stephen E. Riffee, our Executive Vice President and Chief Financial Officer, and the retirement on March 31, 2012 of Randall M. Griffin, our former Chief Executive Officer, we recognized executive transition costs of $1.1 million in 2014 and $2.2 million in 2012. These costs, which are included in general administrative expense, represent incremental compensation costs associated with the executives’ employment separation, including cash and share-based compensation and post-employment benefits.

Operating_Leases

Operating Leases	12 Months Ended
	Dec. 31, 2014
Leases, Operating [Abstract]
Operating Leases	Operating Leases
	We lease our properties to tenants under operating leases with various expiration dates extending to the year 2030. Gross minimum future rentals on noncancelable leases in our properties as of December 31, 2014 were as follows (in thousands):
	Year Ending December 31,
	2015	$	349,099
	2016	301,184
	2017	263,428
	2018	202,661
	2019	154,044
	Thereafter	312,304
		$	1,582,720

Information_by_Business_Segmen

Information by Business Segment	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Information by Business Segment	Information by Business Segment
	We have ten reportable operating office property segments (comprised of: the Baltimore/Washington Corridor; Northern Virginia; San Antonio; Huntsville; Washington, DC — Capitol Riverfront; St. Mary’s and King George Counties; Greater Baltimore; Greater Philadelphia; Colorado Springs; and Other). We also have an operating wholesale data center segment.  The table below reports segment financial information for our reportable segments (in thousands).  We measure the performance of our segments through the measure we define as NOI from real estate operations, which is derived by subtracting property operating expenses from revenues from real estate operations.
		Operating Office Property Segments
		Baltimore/				Northern				San				Huntsville		Washington,		St. Mary’s &		Greater		Greater		Colorado			Other		Operating		Total
		Washington				Virginia				Antonio						DC - Capitol		King George		Baltimore		Philadelphia		Springs					Wholesale
		Corridor														Riverfront		Counties											Data Center
	Year Ended December 31, 2014
	Revenues from real estate operations	$	236,191			$	89,263			$	36,377			$	10,446	$	14,599	$	16,736	$	43,591	$	11,929	$	(1	)	$	10,150	$	10,430	$	479,711
	Property operating expenses	81,132				31,532				20,562				3,066		7,308		5,268		17,778		4,386		12			1,469		7,286		179,799
	NOI from real estate operations	$	155,059			$	57,731			$	15,815			$	7,380	$	7,291	$	11,468	$	25,813	$	7,543	$	(13	)	$	8,681	$	3,144	$	299,912
	Additions to long-lived assets	$	24,174			$	17,447			$	(6	)		$	4,077	$	1,185	$	8,825	$	7,925	$	952	$	—		$	—	$	22	$	64,601
	Transfers from non-operating properties	$	56,699			$	43,154			$	—			$	21,014	$	—	$	—	$	3,550	$	16,344	$	30		$	—	$	1,108	$	141,899
	Segment assets at December 31, 2014	$	1,277,600			$	642,429			$	116,252			$	97,209	$	95,195	$	100,777	$	274,091	$	106,931	$	—		$	77,834	$	163,177	$	2,951,495
	Year Ended December 31, 2013
	Revenues from real estate operations	$	237,869			$	92,010			$	33,060			$	5,050	$	16,863	$	16,568	$	42,653	$	11,924	$	25,290		$	10,075	$	7,271	$	498,633
	Property operating expenses	80,554				31,973				17,631				1,282		7,844		5,028		16,583		3,431		9,002			1,016		6,360		180,704
	NOI from real estate operations	$	157,315			$	60,037			$	15,429			$	3,768	$	9,019	$	11,540	$	26,070	$	8,493	$	16,288		$	9,059	$	911	$	317,929
	Additions to long-lived assets	$	28,087			$	13,090			$	335			$	3,563	$	2,604	$	2,341	$	2,913	$	406	$	2,940		$	—	$	598	$	56,877
	Transfers from non-operating properties	$	50,105			$	61,434			$	—			$	48,799	$	—	$	14	$	360	$	28,034	$	5,438		$	—	$	70,106	$	264,290
	Segment assets at December 31, 2013	$	1,243,099			$	616,082			$	118,299			$	77,773	$	98,962	$	96,143	$	303,823	$	104,657	$	—		$	80,002	$	166,790	$	2,905,630
	Year Ended December 31, 2012
	Revenues from real estate operations	$	238,488			$	79,574			$	32,018			$	3,867	$	16,697	$	16,392	$	52,616	$	9,698	$	24,987		$	12,116	$	6,647	$	493,100
	Property operating expenses	83,050				29,103				16,499				689		7,555		4,745		19,917		2,562		9,231			2,569		4,815		180,735
	NOI from real estate operations	$	155,438			$	50,471			$	15,519			$	3,178	$	9,142	$	11,647	$	32,699	$	7,136	$	15,756		$	9,547	$	1,832	$	312,365
	Additions to long-lived assets	$	25,921			$	65,157			$	280			$	26	$	317	$	1,844	$	9,690	$	286	$	2,929		$	152	$	199	$	106,801
	Transfers from non-operating properties	$	65,108			$	44,250			$	468			$	—	$	—	$	289	$	37,558	$	10,626	$	4,295		$	394	$	58,009	$	220,997
	Segment assets at December 31, 2012	$	1,267,357			$	569,860			$	119,369			$	28,730	$	104,544	$	98,027	$	320,548	$	78,798	$	175,830		$	82,090	$	100,777	$	2,945,930
	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,
			2014				2013				2012
	Segment revenues from real estate operations		$	479,711			$	498,633			$	493,100
	Construction contract and other service revenues		106,748				62,363				73,836
	Less: Revenues from discontinued operations (Note 20)		14				(37,636		)		(58,801		)
	Total revenues		$	586,473			$	523,360			$	508,135
	The following table reconciles our segment property operating expenses to property operating expenses as reported on our consolidated statements of operations (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	Segment property operating expenses		$	179,799			$	180,704			$	180,735
	Less: Property operating expenses from discontinued operations (Note 20)		135				(13,505		)		(21,529		)
	Total property operating expenses		$	179,934			$	167,199			$	159,206
	As previously discussed, we provide real estate services such as property management and construction and development services primarily for our properties but also for third parties.  The primary manner in which we evaluate the operating performance of our service activities is through a measure we define as net operating income from service operations (“NOI from service operations”), which is based on the net of revenues and expenses from these activities.  Construction contract and other service revenues and expenses consist primarily of subcontracted costs that are reimbursed to us by the customer along with a management fee. The operating margins from these activities are small relative to the revenue.  We believe NOI from service operations is a useful measure in assessing both our level of activity and our profitability in conducting such operations. The table below sets forth the computation of our NOI from service operations (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	Construction contract and other service revenues		$	106,748			$	62,363			$	73,836
	Construction contract and other service expenses		(100,058		)		(58,875		)		(70,576		)
	NOI from service operations		$	6,690			$	3,488			$	3,260
	The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from continuing operations as reported on our consolidated statements of operations (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	NOI from real estate operations		$	299,912			$	317,929			$	312,365
	NOI from service operations		6,690				3,488				3,260
	Interest and other income		4,923				3,834				7,172
	Equity in income (loss) of unconsolidated entities		229				2,110				(546		)
	Income tax expense		(310		)		(1,978		)		(381		)
	Other adjustments:		—
	Depreciation and other amortization associated with real estate operations		(136,086		)		(113,214		)		(107,998		)
	Impairment losses		(1,416		)		(5,857		)		(43,678		)
	General, administrative and leasing expenses		(31,794		)		(30,869		)		(31,900		)
	Business development expenses and land carry costs		(5,573		)		(5,436		)		(5,711		)
	Interest expense on continuing operations		(92,393		)		(82,010		)		(86,401		)
	NOI from discontinued operations		(121		)		(24,131		)		(37,272		)
	Loss on early extinguishment of debt		(9,552		)		(27,030		)		(943		)
	COPT consolidated income from continuing operations		$	34,509			$	36,836			$	7,967
	The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands):
	As of December 31,
	2014				2013
Segment assets	$	2,951,495			$	2,905,630
Non-operating property assets	567,586				517,564
Other assets	151,176				206,758
Total COPT consolidated assets	$	3,670,257			$	3,629,952
The accounting policies of the segments are the same as those used to prepare our consolidated financial statements, except that discontinued operations are not presented separately for segment purposes.  In the segment reporting presented above, we did not allocate interest expense, depreciation and amortization, impairment losses, loss on early extinguishment of debt and gain on sales of real estate 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 and administrative expenses, business development expenses and land carry costs, interest and other income, equity in income (loss) of unconsolidated entities, income taxes and noncontrolling interests because these items represent general corporate or non-operating property items not attributable to segments.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
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.
	The differences between taxable income reported on our income tax returns (estimated 2014 and actual 2013 and 2012) and net income as reported on our consolidated statements of operations are set forth below (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
		(Estimated)
	COPLP consolidated net income	$	45,206			$	101,544			$	20,341
	Adjustments:
	Rental revenue recognition	(3,932		)		1,303				(10,794		)
	Compensation expense recognition	1,912				8,987				(2,669		)
	Operating expense recognition	(2,260		)		(1,663		)		1,158
	Gain on sales of properties	(1,404		)		(50,860		)		(74,858		)
	Impairment losses	1,367				32,047				66,910
	Loss on interest rate derivatives	—				—				(29,805		)
	Gains from non-real estate investments	405				—				7,854
	Income from service operations	(391		)		1,650				1,500
	Income tax expense	310				1,978				381
	Depreciation and amortization	41,500				20,834				24,804
	Interest expense	920				2,057				3,978
	Income from unconsolidated entities	(187		)		3,148				(725		)
	COPLP consolidated noncontrolling interests	(3,285		)		(7,837		)		(636		)
	Other	2,346				1,529				(70		)
	COPLP consolidated taxable income	$	82,507			$	114,717			$	7,369
	Noncontrolling interests, other	(3,247		)		(4,061		)		(622		)
	Other	—				—				741
	COPT consolidated taxable income	$	79,260			$	110,656			$	7,488
	For Federal income tax purposes, dividends to shareholders may be characterized as ordinary income, capital gains or return of capital. The characterization of dividends declared on COPT’s common and preferred shares during each of the last three years was as follows:
		Common Shares									Preferred Shares
		For the Years Ended December 31,									For the Years Ended December 31,
		2014			2013			2012			2014		2013		2012
	Ordinary income	64.5	%		71.8	%		33.2	%		90.9	%	76.2	%	100	%
	Long-term capital gain	6.5	%		22.4	%		0	%		9.1	%	23.8	%	0	%
	Return of capital	29	%		5.8	%		66.8	%		0	%	0	%	0	%
	We distributed all of COPT’s REIT taxable income in 2014, 2013 and 2012 and, as a result, did not incur Federal income tax in those years on such income.
	The net basis of our consolidated assets and liabilities for tax reporting purposes is approximately $233 million lower than the amount reported on our consolidated balance sheet at December 31, 2014, which is primarily related to differences in basis for net properties, intangible assets on property acquisitions and deferred rent receivable.
	We own a TRS that is subject to Federal and state income taxes. Our TRS had income before income taxes under GAAP of $822,000 in 2014, $330,000 in 2013 and $11.3 million in 2012. Our TRS’ provision for income tax consisted of the following expenses (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
	Deferred
	Federal	$	258			$	1,742			$	312
	State	52				236				69
	Total income tax expense	$	310			$	1,978			$	381
	A reconciliation of our TRS’ Federal statutory rate to the effective tax rate for income tax reported on our statements of operations is set forth below:
		For the Years Ended December 31,
		2014			2013			2012
	Income taxes at U.S. statutory rate	34	%		34	%		34	%
	State and local, net of U.S. Federal tax benefit	4.2	%		4.5	%		4.6	%
	Increase in deferred tax asset valuation allowance	0	%		562.9	%		0	%
	Other	(0.4	)%		(1.1	)%		0	%
	Effective tax rate	37.8	%		600.3	%		38.6	%
	Items in our TRS contributing to temporary differences that lead to deferred taxes include depreciation and amortization, share-based compensation, certain accrued compensation, compensation paid in the form of contributions to a deferred nonqualified compensation plan, impairment losses and net operating losses that are not deductible until future periods. As of December 31, 2014, our TRS had a net operating loss carryforward for federal income tax purposes of approximately $13 million expiring in 2033. We believe that our TRS is no longer subject to income tax examinations for years prior to 2011.
	The table below sets forth the tax effects of temporary differences and carry forwards included in the net deferred tax asset of our TRS (in thousands):
		December 31,
		2014				2013
	Operating loss forward	$	5,012			$	5,382
	Share-based compensation	976				869
	Accrued payroll	195				221
	Property	(119		)		(105		)
	Valuation allowance	(2,062		)		(2,062		)
	Deferred tax asset, net	$	4,002			$	4,305
	We recognize a valuation allowance on our deferred tax asset if we believe all or some portion of the deferred tax 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. In 2013, we recognized a $1.9 million increase in our deferred tax asset valuation allowance due to a decrease in future projected operating income in our TRS resulting primarily from our dispositions of certain properties to which the TRS provided amenity services and our planned reduction in amenity services provided by the TRS at certain other properties. 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, 2014 net deferred tax asset.
	We are subject to certain state and local income and franchise taxes. The expense associated with these state and local taxes is included in general and administrative expense and property operating expenses on our consolidated statements of operations. We did not separately state these amounts on our consolidated statements of operations because they are insignificant.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations and Assets Held for Sale	Discontinued Operations and Assets Held for Sale
	Income from discontinued operations primarily includes revenues and expenses associated with the following:
	•	five properties in White Marsh, Maryland (in the Greater Baltimore region) that were sold on January 30, 2012;
	•	1101 Sentry Gateway in San Antonio that was sold on January 31, 2012;
	•	222 and 224 Schilling Circle in Greater Baltimore that were sold on February 10, 2012;
	•	15 and 45 West Gude Drive in the Baltimore/Washington Corridor that were sold on May 2, 2012;
	•	11800 Tech Road in the Baltimore/Washington Corridor that was sold on June 14, 2012;
	•	400 Professional Drive in the Baltimore/Washington Corridor for which the title to the property was transferred to the mortgage lender on July 2, 2012;
	•	23 operating properties primarily in the Baltimore/Washington Corridor and Greater Baltimore regions that were sold on July 24, 2012;
	•	920 Elkridge Landing Road in the Baltimore/Washington Corridor that was sold on June 25, 2013 (added to discontinued operations in 2013);
	•	4230 Forbes Boulevard in the Baltimore/Washington Corridor that was sold on December 11, 2013;
	•	15 operating properties in Colorado Springs that were sold on December 12, 2013; and
	•	nine operating properties in the Baltimore/Washington Corridor and five operating properties in Colorado Springs for which the title to the properties was transferred to the mortgage lender on December 23, 2013.
	The table below sets forth the components of discontinued operations reported on our consolidated statements of operations (in thousands):
			For the Years Ended December 31,
			2014			2013			2012
	Revenue from real estate operations		$	(14	)	$	37,636		$	58,801
	Property operating expenses		135			(13,505		)	(21,529		)
	Depreciation and amortization		—			(4,505		)	(13,939		)
	Impairment losses		(3		)	(26,190		)	(23,232		)
	General, administrative and leasing expenses		—			(4		)	(3		)
	Business development and land carry costs		—			—			(24		)
	Interest expense		—			(8,221		)	(10,397		)
	Gain on sales of real estate		24			2,671			20,940
	Gain on early extinguishment of debt		(116		)	67,810			1,736
	Discontinued operations		$	26		$	55,692		$	12,353
	As of December 31, 2014, we had two land parcels in the Greater Baltimore region classified as held for sale with a cost basis of $14.3 million.

Earnings_Per_Share_EPS_and_Ear

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”)	Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”)
	COPT and Subsidiaries EPS
	We present both basic and diluted EPS.  We compute basic EPS by dividing net income available to common shareholders allocable to unrestricted common shares under the two-class method by the weighted average number of unrestricted common shares outstanding during the period.  Our computation of diluted EPS is similar except that:
	•	the denominator is increased to include: (1) the weighted average number of potential additional common shares that would have been outstanding if securities that are convertible into COPT common shares were converted; and (2) the effect of dilutive potential common shares outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and
	•	the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common shares that we added to the denominator.
	Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data):
			For the Years Ended December 31,
			2014				2013			2012
	Numerator:
	Income from continuing operations		$	34,509			$	36,836		$	7,967
	Gain on sales of real estate, net		10,671				9,016			21
	Preferred share dividends		(15,939		)		(19,971		)	(20,844		)
	Issuance costs associated with redeemed preferred shares		(1,769		)		(2,904		)	(1,827		)
	(Income) loss from continuing operations attributable to noncontrolling interests		(4,955		)		(4,486		)	1,309
	Income from continuing operations attributable to restricted shares		(432		)		(414		)	(469		)
	Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders		$	22,085			$	18,077		$	(13,843	)
	Discontinued operations		26				55,692			12,353
	Discontinued operations attributable to noncontrolling interests		4				(3,351		)	(673		)
	Numerator for basic and diluted EPS on net income (loss)attributable to COPT common shareholders		$	22,115			$	70,418		$	(2,163	)
	Denominator (all weighted averages):
	Denominator for basic EPS (common shares)		88,092				85,167			73,454
	Dilutive effect of share-based compensation awards		171				57			—
	Denominator for basic and diluted EPS (common shares)		88,263				85,224			73,454
	Basic EPS:
	Income (loss) from continuing operations attributable to COPT common shareholders		$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPT common shareholders		—				0.62			0.16
	Net income (loss) attributable to COPT common shareholders		$	0.25			$	0.83		$	(0.03	)
	Diluted EPS:
	Income (loss) from continuing operations attributable to COPT common shareholders		$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPT common shareholders		—				0.62			0.16
	Net income (loss) attributable to COPT common shareholders		$	0.25			$	0.83		$	(0.03	)
	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,
			2014			2013			2012
	Conversion of common units		3,897			3,869			4,235
	Conversion of Series I preferred units		176			176			176
	Conversion of Series K preferred shares		434			434			434
	The following share-based compensation securities were excluded from the computation of diluted EPS because their effect was antidilutive:
	•	weighted average restricted shares of 401,000 for 2014, 385,000 for 2013 and 461,000 for 2012; and
	•	weighted average options of 492,000 for 2014, 636,000 for 2013 and 772,000 for 2012, respectively.
	As discussed in Note 11, we have outstanding senior notes that have an exchange settlement feature, but such notes did not affect our diluted EPS reported above since the weighted average closing price of COPT’s common shares during each of the periods was less than the exchange prices per common share applicable for such periods.
	COPLP and Subsidiaries EPU
	We present both basic and diluted EPU.  We compute basic EPU by dividing net income available to common unitholders allocable to unrestricted common units under the two-class method by the weighted average number of unrestricted common units outstanding during the period.  Our computation of diluted EPU is similar except that:
	•	the denominator is increased to include: (1) the weighted average number of potential additional common units that would have been outstanding if securities that are convertible into our common units were converted; and (2) the effect of dilutive potential common units outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and
	•	the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common units that we added to the denominator.
	Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data):
			For the Years Ended December 31,
			2014				2013			2012
	Numerator:
	Income from continuing operations		$	34,509			$	36,836		$	7,967
	Gain on sales of real estate, net		10,671				9,016			21
	Preferred unit distributions		(16,599		)		(20,631		)	(21,504		)
	Issuance costs associated with redeemed preferred units		(1,769		)		(2,904		)	(1,827		)
	(Income) loss from continuing operations attributable to noncontrolling interests		(3,281		)		(2,977		)	1,206
	Income from continuing operations attributable to restricted units		(432		)		(414		)	(469		)
	Numerator for basic and diluted EPU from continuing operations attributable to COPLP common unitholders		$	23,099			$	18,926		$	(14,606	)
	Discontinued operations		26				55,692			12,353
	Discontinued operations attributable to noncontrolling interests		5				(930		)	(699		)
	Numerator for basic and diluted EPU on net income (loss) attributable to COPLP common unitholders		$	23,130			$	73,688		$	(2,952	)
	Denominator (all weighted averages):
	Denominator for basic EPU (common units)		91,989				89,036			77,689
	Dilutive effect of share-based compensation awards		171				57			—
	Denominator for basic and diluted EPU (common units)		92,160				89,093			77,689
	Basic EPU:
Income (loss) from continuing operations attributable to COPLP common unitholders		$	0.25			$	0.21		$	(0.19	)
Discontinued operations attributable to COPLP common unitholders		—				0.62			0.15
Net income (loss) attributable to COPLP common unitholders		$	0.25			$	0.83		$	(0.04	)
Diluted EPU:
Income (loss) from continuing operations attributable to COPLP common unitholders		$	0.25			$	0.21		$	(0.19	)
Discontinued operations attributable to COPLP common unitholders		—				0.62			0.15
Net income (loss) attributable to COPLP common unitholders		$	0.25			$	0.83		$	(0.04	)
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,
		2014			2013			2012
Conversion of Series I preferred units		176			176			176
Conversion of Series K preferred units		434			434			434
The following share-based compensation securities were excluded from the computation of diluted EPU because their effect was antidilutive:
•	weighted average restricted units of 401,000 for 2014, 385,000 for 2013 and 461,000 for 2012; and
•	weighted average options of 492,000 for 2014, 636,000 for 2013 and 772,000 for 2012.
As discussed in Note 11, we have outstanding senior notes that have an exchange settlement feature, but such notes did not affect our diluted EPU reported above since the weighted average closing price of COPT’s common shares during each of the periods was less than the exchange prices per common share applicable for such periods.

Quarterly_Data_Unaudited

Quarterly Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Quarterly Data (Unaudited)	Quarterly Data (Unaudited)
	COPT and Subsidiaries
	The tables below set forth selected quarterly information for the years ended December 31, 2014 and 2013 (in thousands, except per share data). Certain of the amounts below have been reclassified to conform to the current period presentation of our consolidated financial statements.
		For the Year Ended December 31, 2014
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	146,667		$	139,820		$	153,015		$	146,971
	Operating income	$	25,206		$	31,836		$	37,422		$	37,148
	Income from continuing operations	$	5,660		$	9,248		$	13,727		$	5,874
	Discontinued operations	$	11		$	(198	)	$	191		$	22
	Net income	$	5,671		$	9,050		$	24,548		$	5,937
	Net income attributable to noncontrolling interests	(930		)	(1,160		)	(1,828		)	(1,033		)
	Net income attributable to COPT	4,741			7,890			22,720			4,904
	Preferred share dividends	(4,490		)	(4,344		)	(3,553		)	(3,552		)
	Issuance costs associated with redeemed preferred shares	—			(1,769		)	—			—
	Net income attributable to COPT common shareholders	$	251		$	1,777		$	19,167		$	1,352
	Basic earnings per common share	$	0		$	0.02		$	0.22		$	0.01
	Diluted earnings per common share	$	0		$	0.02		$	0.22		$	0.01
		For the Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	126,219		$	136,527		$	131,812		$	128,802
	Operating income	$	36,165		$	40,229		$	30,673		$	34,843
	Income (loss) from continuing operations	$	11,662		$	(232	)	$	10,974		$	14,432
	Discontinued operations	$	1,261		$	(4,502	)	$	(12,974	)	$	71,907
	Net income (loss)	$	15,277		$	(4,405	)	$	(2,000	)	$	92,672
	Net income attributable to noncontrolling interests	(257		)	(960		)	(964		)	(5,656		)
	Net income (loss) attributable to COPT	15,020			(5,365		)	(2,964		)	87,016
	Preferred share dividends	(6,106		)	(4,885		)	(4,490		)	(4,490		)
	Issuance costs associated with redeemed preferred shares	—			(2,904		)	—			—
	Net income (loss) attributable to COPT common shareholders	$	8,914		$	(13,154	)	$	(7,454	)	$	82,526
	Basic earnings per common share	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
	Diluted earnings per common share	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
	COPLP and Subsidiaries
	The tables below set forth selected quarterly information for the years ended December 31, 2014 and 2013 (in thousands, except per share data).
		For the Year Ended December 31, 2014
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	146,667		$	139,820		$	153,015		$	146,971
	Operating income	$	25,206		$	31,836		$	37,422		$	37,148
	Income from continuing operations	$	5,660		$	9,248		$	13,727		$	5,874
	Discontinued operations	$	11		$	(198	)	$	191		$	22
	Net income	$	5,671		$	9,050		$	24,548		$	5,937
	Net income attributable to noncontrolling interests	(737		)	(837		)	(897		)	(805		)
	Net income attributable to COPLP	4,934			8,213			23,651			5,132
	Preferred unit distributions	(4,655		)	(4,509		)	(3,718		)	(3,717		)
	Issuance costs associated with redeemed preferred units	—			(1,769		)	—			—
	Net income attributable to COPLP common unitholders	$	279		$	1,935		$	19,933		$	1,415
	Basic earnings per common unit	$	0		$	0.02		$	0.22		$	0.01
	Diluted earnings per common unit	$	0		$	0.02		$	0.22		$	0.01
		For the Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	126,219		$	136,527		$	131,812		$	128,802
	Operating income	$	36,165		$	40,229		$	30,673		$	34,843
	Income (loss) from continuing operations	$	11,662		$	(232	)	$	10,974		$	14,432
	Discontinued operations	$	1,261		$	(4,502	)	$	(12,974	)	$	71,907
	Net income (loss)	$	15,277		$	(4,405	)	$	(2,000	)	$	92,672
	Net loss (income) attributable to noncontrolling interests	336			(1,473		)	(1,035		)	(1,735		)
	Net income (loss) attributable to COPLP	15,613			(5,878		)	(3,035		)	90,937
	Preferred unit distributions	(6,271		)	(5,050		)	(4,655		)	(4,655		)
	Issuance costs associated with redeemed preferred units	—			(2,904		)	—			—
	Net income (loss) attributable to COPLP common unitholders	$	9,342		$	(13,832	)	$	(7,690	)	$	86,282
	Basic earnings per common unit	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
	Diluted earnings per common unit	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies
	Litigation
	In the normal course of business, we are involved in legal actions arising from our ownership and administration of properties.  We establish reserves for specific legal proceedings when we determine that the likelihood of an unfavorable outcome is probable and the amount of loss can be reasonably estimated.  Management does not anticipate that any liabilities that may result from such proceedings will have a materially adverse effect on our financial position, operations or liquidity.  Our assessment of the potential outcomes of these matters involves significant judgment and is subject to change based on future developments.
	Environmental
	We are subject to various Federal, state and local environmental regulations related to our property ownership and operation.  We have performed environmental assessments of our properties, the results of which have not revealed any environmental liability that we believe would have a materially adverse effect on our financial position, operations or liquidity.
	Joint Ventures
	In connection with our 2005 contribution of properties to an unconsolidated partnership in which we hold a joint venture interest, we entered into standard nonrecourse loan guarantees (environmental indemnifications and guarantees against fraud and misrepresentation, and springing guarantees of partnership debt in the event of a voluntary bankruptcy of the partnership).  On December 6, 2013, the holder of mortgage debt encumbering all of the joint venture’s properties foreclosed on the properties. As a result, title to the properties was transferred to the mortgage lender and the joint venture was relieved of the debt obligation plus accrued interest and penalties. The joint venture still had $5.6 million in nonrecourse mezzanine debt as of December 31, 2014; however, the joint venture no longer holds any property and has ceased all business operations. Management estimates there to be no fair value to the guarantees as of December 31, 2014 because the actions that would trigger performance are all within our control.
	Tax Incremental Financing Obligation
	In August 2010, Anne Arundel County, Maryland issued $30 million in tax incremental financing bonds to third-party investors in order to finance public improvements needed in connection with our project known as National Business Park North.  The real estate taxes on increases in assessed value of a development district encompassing National Business Park North are to be transferred to a special fund pledged to the repayment of the bonds.  We recognized a $1.3 million liability through December 31, 2014 representing our estimated obligation to fund through a special tax any future shortfalls between debt service on the bonds and real estate taxes available to repay the bonds.
	Operating Leases
	We are obligated as lessee under operating leases (mostly ground leases) with various expiration dates extending to the year 2100. Future minimum rental payments due under the terms of these operating leases as of December 31, 2014 follow (in thousands):
	Year Ending December 31,
	2015		$	905
	2016		839
	2017		768
	2018		735
	2019		728
	Thereafter		76,678
			$	80,653
	Environmental Indemnity Agreement
	We agreed to provide certain environmental indemnifications in connection with a lease and subsequent sale of three New Jersey properties. The prior owner of the properties, a Fortune 100 company that is responsible for groundwater contamination at such properties, previously agreed to indemnify us for (1) direct losses incurred in connection with the contamination and (2) its failure to perform remediation activities required by the State of New Jersey, up to the point that the state declares the remediation to be complete.  Under the environmental indemnification agreement, we agreed to the following:
	•	to indemnify the tenant against losses covered under the prior owner’s indemnity agreement if the prior owner fails to indemnify the tenant for such losses.  This indemnification is capped at $5.0 million in perpetuity after the State of New Jersey declares the remediation to be complete;
	•	to indemnify the tenant for consequential damages (e.g., business interruption) at one of the buildings in perpetuity and another of the buildings through 2025.  This indemnification is limited to $12.5 million; and
	•	to pay 50% of additional costs related to construction and environmental regulatory activities incurred by the tenant as a result of the indemnified environmental condition of the properties.  This indemnification is limited to $300,000 annually and $1.5 million in the aggregate.

Schedule_II_Valuation_and_Qual

Schedule II - Valuation and Qualifying Accounts (Notes)	12 Months Ended
	Dec. 31, 2014
Valuation and Qualifying Accounts [Abstract]
Schedule II—Valuation and Qualifying Accounts	Corporate Office Properties Trust and Subsidiaries and Corporate Office Properties, L.P. and Subsidiaries
	Schedule II—Valuation and Qualifying Accounts
	Years Ended December 31, 2014, 2013 and 2012
	(Dollars in thousands)
		Balance at		Charged to			Charged to Other Accounts (2)			Deductions (3)			Balance at End of Year
		Beginning		Costs and
		of Year		Expenses (1)
	Accounts Receivables-Allowance for doubtful accounts
	Year ended December 31, 2014	$	2,976	$	278		$	—		$	(2,537	)	$	717
	Year ended December 31, 2013	$	4,694	$	(65	)	$	—		$	(1,653	)	$	2,976
	Year ended December 31, 2012	$	3,546	$	1,532		$	232		$	(616	)	$	4,694
	Allowance for Deferred Rent Receivable
	Year ended December 31, 2014	$	2,126	$	—		$	(708	)	$	—		$	1,418
	Year ended December 31, 2013	$	913	$	—		$	1,213		$	—		$	2,126
	Year ended December 31, 2012	$	703	$	—		$	416		$	(206	)	$	913
	Allowance for Deferred Tax Asset
	Year ended December 31, 2014	$	2,062	$	—		$	—		$	—		$	2,062
	Year ended December 31, 2013	$	207	$	1,855		$	—		$	—		$	2,062
	Year ended December 31, 2012	$	207	$	—		$	—		$	—		$	207
	(1) Amounts charged to costs and expenses are net of recoveries.
	(2) Allowances for certain accounts receivables were charged to service company revenue. Deferred rent receivable allowances were charged to rental revenue.
	(3) Deductions reflect adjustments to reserves due to actual write-offs of accounts.

Schedule_III_Real_Estate_and_A

Schedule III - Real Estate and Accumulated Depreciation	12 Months Ended
	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Schedule III-Real Estate and Accumulated Depreciation	Corporate Office Properties Trust and Subsidiaries and Corporate Office Properties, L.P. and Subsidiaries
	Schedule III—Real Estate and Accumulated Depreciation
	31-Dec-14
	(Dollars in thousands)
					Initial Cost								Gross Amounts Carried At Close of Period
	Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
	1000 Redstone Gateway (O)	Huntsville, AL	$	11,671	$	—		$	20,527		$	—	$	—		$	20,527	$	20,527	$	(924	)	2013	3/23/10
	1100 Redstone Gateway (O)	Huntsville, AL	12,057		—			19,501			—		—			19,501		19,501		(476		)	2014	3/23/10
	114 National Business Parkway (O)	Annapolis Junction, MD	—		364			3,109			46		364			3,155		3,519		(1,042		)	2002	6/30/00
	11751 Meadowville Lane (O)	Richmond, VA	—		1,305			52,098			112		1,305			52,210		53,515		(9,889		)	2007	9/15/06
	1200 Redstone Gateway (O)	Huntsville, AL	13,950		—			22,409			—		—			22,409		22,409		(586		)	2013	3/23/10
	1201 M Street (O)	Washington, DC	—		—			49,785			2,455		—			52,240		52,240		(7,255		)	2001	9/28/10
	1201 Winterson Road (O)	Linthicum, MD	—		1,288			5,452			460		1,288			5,912		7,200		(2,388		)	1985 (7)	4/30/98
	1220 12th Street, SE (O)	Washington, DC	—		—			42,464			2,014		—			44,478		44,478		(7,143		)	2003	9/28/10
	1243 Winterson Road (L)	Linthicum, MD	—		630			—			—		630			—		630		—			-8	12/19/01
	1302 Concourse Drive (O)	Linthicum, MD	—		2,078			8,313			5,008		2,078			13,321		15,399		(5,610		)	1996	11/18/99
	1304 Concourse Drive (O)	Linthicum, MD	—		1,999			12,934			2,594		1,999			15,528		17,527		(5,680		)	2002	11/18/99
	1306 Concourse Drive (O)	Linthicum, MD	—		2,796			11,186			5,745		2,796			16,931		19,727		(6,097		)	1990	11/18/99
	131 National Business Parkway (O)	Annapolis Junction, MD	—		1,906			7,623			3,288		1,906			10,911		12,817		(4,807		)	1990	9/28/98
	132 National Business Parkway (O)	Annapolis Junction, MD	—		2,917			12,259			2,977		2,917			15,236		18,153		(7,314		)	2000	5/28/99
	13200 Woodland Park Road (O)	Herndon, VA	—		10,428			41,711			13,985		10,428			55,696		66,124		(24,106		)	2002	6/2/03
	133 National Business Parkway (O)	Annapolis Junction, MD	—		2,517			10,068			4,920		2,517			14,988		17,505		(7,560		)	1997	9/28/98
	1331 Ashton Road (O)	Hanover, MD	—		587			2,347			1,474		587			3,821		4,408		(1,154		)	1989	4/28/99
	1334 Ashton Road (O)	Hanover, MD	—		736			1,488			2,634		736			4,122		4,858		(2,055		)	1989	4/28/99
	134 National Business Parkway (O)	Annapolis Junction, MD	—		3,684			7,517			1,282		3,684			8,799		12,483		(3,765		)	1999	11/13/98
	1340 Ashton Road (O)	Hanover, MD	—		905			3,620			1,466		905			5,086		5,991		(2,431		)	1989	4/28/99
	1341 Ashton Road (O)	Hanover, MD	—		306			1,223			601		306			1,824		2,130		(860		)	1989	4/28/99
	1343 Ashton Road (O)	Hanover, MD	—		193			774			405		193			1,179		1,372		(596		)	1989	4/28/99
	13450 Sunrise Valley Road (O)	Herndon, VA	—		1,386			5,576			3,335		1,386			8,911		10,297		(3,580		)	1998	7/25/03
	13454 Sunrise Valley Road (O)	Herndon, VA	—		2,899			11,986			5,447		2,899			17,433		20,332		(6,255		)	1998	7/25/03
	135 National Business Parkway (O)	Annapolis Junction, MD	11,418		2,484			9,750			4,742		2,484			14,492		16,976		(5,845		)	1998	12/30/98
	1362 Mellon Road (O)	Hanover, MD	—		1,706			8,670			119		1,706			8,789		10,495		(1,278		)	2006	2/10/06
	13857 McLearen Road (O)	Herndon, VA	—		3,507			30,177			1,557		3,507			31,734		35,241		(4,945		)	2007	7/11/12
	140 National Business Parkway (O)	Annapolis Junction, MD	—		3,407			24,167			643		3,407			24,810		28,217		(7,039		)	2003	12/31/03
	141 National Business Parkway (O)	Annapolis Junction, MD	11,871		2,398			9,590			2,995		2,398			12,585		14,983		(5,575		)	1990	9/28/98
	14280 Park Meadow Drive (O)	Chantilly, VA	—		3,731			15,953			1,754		3,731			17,707		21,438		(5,626		)	1999	9/29/04
	1460 Dorsey Road (L)	Hanover, MD	—		1,800			—			—		1,800			—		1,800		—			-8	2/28/06
	14840 Conference Center Drive (O)	Chantilly, VA	—		1,572			8,175			1,488		1,572			9,663		11,235		(3,885		)	2000	7/25/03
	14850 Conference Center Drive (O)	Chantilly, VA	—		1,615			8,358			2,896		1,615			11,254		12,869		(4,074		)	2000	7/25/03
	14900 Conference Center Drive (O)	Chantilly, VA	—		3,436			14,402			4,569		3,436			18,971		22,407		(7,396		)	1999	7/25/03
					Initial Cost								Gross Amounts Carried At Close of Period
	Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
	15000 Conference Center Drive (O)	Chantilly, VA	54,000		5,193			47,045			18,692		5,193			65,737		70,930		(25,365		)	1989	11/30/01
	1501 South Clinton Street (O)	Baltimore, MD	—		27,964			52,146			7,553		27,964			59,699		87,663		(11,059		)	2006	10/27/09
	15010 Conference Center Drive (O)	Chantilly, VA	96,000		3,500			41,921			498		3,500			42,419		45,919		(8,644		)	2006	11/30/01
	15049 Conference Center Drive (O)	Chantilly, VA	—		4,415			20,365			726		4,415			21,091		25,506		(8,781		)	1997	8/14/02
	15059 Conference Center Drive (O)	Chantilly, VA	—		5,753			13,615			1,780		5,753			15,395		21,148		(6,071		)	2000	8/14/02
	15395 John Marshall Highway (O)	Haymarket, VA	—		2,465			24,720			—		2,465			24,720		27,185		(576		)	2014	5/7/13
	1550 West Nursery Road (O)	Linthicum, MD	—		14,071			16,930			—		14,071			16,930		31,001		(3,038		)	2009	10/28/09
	1550 Westbranch Drive (O)	McLean, VA	—		5,595			26,212			116		5,595			26,328		31,923		(3,647		)	2002	6/28/10
	1560 West Nursery Road (O)	Linthicum, MD	—		1,441			96			—		1,441			96		1,537		(2		)	2014	10/28/09
	1560A Cable Ranch Road (O)	San Antonio, TX	—		1,097			3,770			352		1,097			4,122		5,219		(950		)	1985/2007	6/19/08
	1560B Cable Ranch Road (O)	San Antonio, TX	—		2,299			6,545			11		2,299			6,556		8,855		(1,532		)	1985/2006	6/19/08
	16442 Commerce Drive (O)	Dahlgren, VA	—		613			2,582			593		613			3,175		3,788		(1,153		)	2002	12/21/04
	16480 Commerce Drive (O)	Dahlgren, VA	—		1,856			7,425			167		1,856			7,592		9,448		(2,020		)	2000	12/28/04
	16501 Commerce Drive (O)	Dahlgren, VA	—		522			2,090			465		522			2,555		3,077		(714		)	2002	12/21/04
	16539 Commerce Drive (O)	Dahlgren, VA	—		688			2,860			1,469		688			4,329		5,017		(1,696		)	1990	12/21/04
	16541 Commerce Drive (O)	Dahlgren, VA	—		773			3,094			1,367		773			4,461		5,234		(1,529		)	1996	12/21/04
	16543 Commerce Drive (O)	Dahlgren, VA	—		436			1,742			172		436			1,914		2,350		(486		)	2002	12/21/04
	1751 Pinnacle Drive (O)	McLean, VA	—		10,486			42,339			22,325		10,486			64,664		75,150		(20,705		)	1989/1995	9/23/04
	1753 Pinnacle Drive (O)	McLean, VA	—		8,275			34,353			10,528		8,275			44,881		53,156		(14,406		)	1976/2004	9/23/04
	201 Technology Drive (O)	Lebanon, VA	—		726			31,091			60		726			31,151		31,877		(5,579		)	2007	10/5/07
	206 Research Boulevard (O)	Aberdeen, MD	—		1,813			17,485			—		1,813			17,485		19,298		(979		)	2012	9/14/07
	209 Research Boulevard (O)	Aberdeen, MD	—		1,045			16,087			32		1,045			16,119		17,164		(1,665		)	2010	9/14/07
210 Research Boulevard (O)	Aberdeen, MD	—		1,065			14,687			75		1,065			14,762		15,827		(1,191		)	2010	9/14/07
21267 Smith Switch Road (O)	Ashburn, VA	—		4,040			10,369			—		4,040			10,369		14,409		(106		)	2014	12/27/12
21271 Smith Switch Road (O)	Ashburn, VA	—		7,346			16,864			—		7,346			16,864		24,210		(447		)	2013	12/27/12
22289 Exploration Drive (O)	Lexington Park, MD	—		1,422			5,719			1,511		1,422			7,230		8,652		(2,512		)	2000	3/24/04
22299 Exploration Drive (O)	Lexington Park, MD	—		1,362			5,791			1,119		1,362			6,910		8,272		(2,433		)	1998	3/24/04
22300 Exploration Drive (O)	Lexington Park, MD	—		1,094			5,038			539		1,094			5,577		6,671		(1,878		)	1997	11/9/04
22309 Exploration Drive (O)	Lexington Park, MD	—		2,243			10,419			7,491		2,243			17,910		20,153		(3,999		)	1984/1997	3/24/04
23535 Cottonwood Parkway (O)	California, MD	—		692			3,051			223		692			3,274		3,966		(1,066		)	1984	3/24/04
2500 Riva Road (O)	Annapolis, MD	—		2,791			12,145			1		2,791			12,146		14,937		(4,073		)	2000	3/4/03
2691 Technology Drive (O)	Annapolis Junction, MD	—		2,098			17,334			5,115		2,098			22,449		24,547		(6,938		)	2005	5/26/00
2701 Technology Drive (O)	Annapolis Junction, MD	22,636		1,737			15,266			2,554		1,737			17,820		19,557		(6,641		)	2001	5/26/00
2711 Technology Drive (O)	Annapolis Junction, MD	17,606		2,251			21,611			1,451		2,251			23,062		25,313		(9,531		)	2002	11/13/00
2720 Technology Drive (O)	Annapolis Junction, MD	—		3,863			29,272			113		3,863			29,385		33,248		(7,577		)	2004	1/31/02
2721 Technology Drive (O)	Annapolis Junction, MD	—		4,611			14,597			1,226		4,611			15,823		20,434		(5,840		)	2000	10/21/99
2730 Hercules Road (O)	Annapolis Junction, MD	35,161		8,737			31,612			7,093		8,737			38,705		47,442		(14,268		)	1990	9/28/98
2900 Towerview Road (O)	Herndon, VA	—		3,207			16,379			6,419		3,207			22,798		26,005		(5,969		)	1982/2008	12/20/05
300 Sentinel Drive (O)	Annapolis Junction, MD	—		1,517			58,827			166		1,517			58,993		60,510		(6,977		)	2009	11/14/03
				Initial Cost								Gross Amounts Carried At Close of Period
Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
302 Sentinel Drive (O)	Annapolis Junction, MD	—		2,648			29,687			423		2,648			30,110		32,758		(5,210		)	2007	11/14/03
304 Sentinel Drive (O)	Annapolis Junction, MD	—		3,411			24,917			138		3,411			25,055		28,466		(5,655		)	2005	11/14/03
306 Sentinel Drive (O)	Annapolis Junction, MD	16,298		3,260			22,592			415		3,260			23,007		26,267		(4,687		)	2006	11/14/03
308 Sentinel Drive (O)	Annapolis Junction, MD	—		1,422			26,197			—		1,422			26,197		27,619		(2,395		)	2010	11/14/03
310 Sentinel Way (O)	Annapolis Junction, MD	—		2,372			33,953			—		2,372			33,953		36,325		—			-7	11/14/03
310 The Bridge Street (O)	Huntsville, AL	—		261			26,531			1,051		261			27,582		27,843		(4,310		)	2009	8/9/11
312 Sentinel Way (O)	Annapolis Junction, MD	—		3,138			23,793			—		3,138			23,793		26,931		(240		)	2014	11/14/03
3120 Fairview Park Drive (O)	Falls Church, VA	—		6,863			35,606			7,303		6,863			42,909		49,772		(5,456		)	2008	11/23/10
314 Sentinel Way (O)	Annapolis Junction, MD	—		1,254			1,325			—		1,254			1,325		2,579		(216		)	2008	11/14/03
316 Sentinel Way (O)	Annapolis Junction, MD	—		2,748			38,156			139		2,748			38,295		41,043		(2,602		)	2011	11/14/03
318 Sentinel Way (O)	Annapolis Junction, MD	—		2,185			28,426			—		2,185			28,426		30,611		(6,270		)	2005	11/14/03
320 Sentinel Way (O)	Annapolis Junction, MD	—		2,067			21,623			—		2,067			21,623		23,690		(3,770		)	2007	11/14/03
322 Sentinel Way (O)	Annapolis Junction, MD	21,680		2,605			22,827			—		2,605			22,827		25,432		(4,572		)	2006	11/14/03
324 Sentinel Way (O)	Annapolis Junction, MD	—		1,656			23,018			—		1,656			23,018		24,674		(2,503		)	2010	6/29/06
375 West Padonia Road (O)	Timonium, MD	—		2,483			10,415			4,857		2,483			15,272		17,755		(6,904		)	1986	12/21/99
410 National Business Parkway (O)	Annapolis Junction, MD	—		1,831			23,257			112		1,831			23,369		25,200		(1,127		)	2012	6/29/06
420 National Business Parkway (O)	Annapolis Junction, MD	—		2,370			27,161			101		2,370			27,262		29,632		(541		)	2013	6/29/06
430 National Business Parkway (O)	Annapolis Junction, MD	—		1,852			21,138			120		1,852			21,258		23,110		(1,494		)	2011	6/29/06
44408 Pecan Court (O)	California, MD	—		817			1,583			582		817			2,165		2,982		(405		)	1986	3/24/04
44414 Pecan Court (O)	California, MD	—		405			1,619			336		405			1,955		2,360		(641		)	1986	3/24/04
44417 Pecan Court (O)	California, MD	—		434			3,204			88		434			3,292		3,726		(1,037		)	1989 (7)	3/24/04
44420 Pecan Court (O)	California, MD	—		344			890			148		344			1,038		1,382		(199		)	1989	11/9/04
44425 Pecan Court (O)	California, MD	—		1,309			3,506			1,307		1,309			4,813		6,122		(1,492		)	1997	5/5/04
45310 Abell House Lane (O)	California, MD	—		2,272			13,808			—		2,272			13,808		16,080		(1,057		)	2011	8/30/10
46579 Expedition Drive (O)	Lexington Park, MD	—		1,406			5,796			1,335		1,406			7,131		8,537		(2,780		)	2002	3/24/04
46591 Expedition Drive (O)	Lexington Park, MD	—		1,200			7,199			803		1,200			8,002		9,202		(1,618		)	2005	3/24/04
4851 Stonecroft Boulevard (O)	Chantilly, VA	—		1,878			11,558			21		1,878			11,579		13,457		(2,959		)	2004	8/14/02
4940 Campbell Drive (O)	White Marsh, MD	—		1,379			3,858			1,373		1,379			5,231		6,610		(1,278		)	1990	1/9/07
525 Babcock Road (O)	Colorado Springs, CO	—		355			397			79		355			476		831		(153		)	1967	7/12/07
5325 Nottingham Drive (O)	White Marsh, MD	—		816			3,976			485		816			4,461		5,277		(1,076		)	2002	1/9/07
5355 Nottingham Drive (O)	White Marsh, MD	—		761			3,562			1,758		761			5,320		6,081		(1,874		)	2005	1/9/07
5520 Research Park Drive (O)	Catonsville, MD	—		—			20,072			38		—			20,110		20,110		(2,687		)	2009	4/4/06
5522 Research Park Drive (O)	Catonsville, MD	—		—			4,550			—		—			4,550		4,550		(842		)	2007	3/8/06
5825 University Research Court (O)	College Park, MD	15,615		—			22,522			60		—			22,582		22,582		(3,246		)	2008	1/29/08
5850 University Research Court (O)	College Park, MD	21,261		—			31,689			57		—			31,746		31,746		(3,763		)	2008	1/29/08
6700 Alexander Bell Drive (O)	Columbia, MD	—		1,755			7,019			5,550		1,755			12,569		14,324		(5,435		)	1988	5/14/01
6708 Alexander Bell Drive (O)	Columbia, MD	—		897			7,544			1,591		897			9,135		10,032		(3,319		)	1988 (7)	5/14/01
6711 Columbia Gateway Drive (O)	Columbia, MD	—		2,683			23,239			435		2,683			23,674		26,357		(4,765		)	2006-2007	9/28/00
6716 Alexander Bell Drive (O)	Columbia, MD	—		1,242			4,969			3,352		1,242			8,321		9,563		(3,992		)	1990	12/31/98
				Initial Cost								Gross Amounts Carried At Close of Period
Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
6721 Columbia Gateway Drive (O)	Columbia, MD	17,102		1,753			34,090			65		1,753			34,155		35,908		(4,941		)	2009	9/28/00
6724 Alexander Bell Drive (O)	Columbia, MD	—		449			5,039			368		449			5,407		5,856		(2,106		)	2001	5/14/01
6731 Columbia Gateway Drive (O)	Columbia, MD	—		2,807			19,098			2,046		2,807			21,144		23,951		(7,841		)	2002	3/29/00
6740 Alexander Bell Drive (O)	Columbia, MD	—		1,424			5,696			3,346		1,424			9,042		10,466		(4,644		)	1992	12/31/98
6741 Columbia Gateway Drive (O)	Columbia, MD	—		675			1,711			114		675			1,825		2,500		(303		)	2008	9/28/00
6750 Alexander Bell Drive (O)	Columbia, MD	—		1,263			12,461			3,419		1,263			15,880		17,143		(7,008		)	2001	12/31/98
6760 Alexander Bell Drive (O)	Columbia, MD	—		890			3,561			2,763		890			6,324		7,214		(2,989		)	1991	12/31/98
6940 Columbia Gateway Drive (O)	Columbia, MD	—		3,545			9,916			4,717		3,545			14,633		18,178		(6,463		)	1999	11/13/98
6950 Columbia Gateway Drive (O)	Columbia, MD	—		3,596			14,269			2,164		3,596			16,433		20,029		(6,965		)	1998	10/22/98
7000 Columbia Gateway Drive (O)	Columbia, MD	—		3,131			12,103			989		3,131			13,092		16,223		(4,056		)	1999	5/31/02
7005 Columbia Gateway Drive (O)	Columbia, MD	—		3,036			14			—		3,036			14		3,050		—			-8	6/26/14
7015 Albert Einstein Drive (O)	Columbia, MD	1,900		2,058			6,093			855		2,058			6,948		9,006		(2,669		)	1999	12/1/05
7061 Columbia Gateway Drive (O)	Columbia, MD	—		729			3,094			1,407		729			4,501		5,230		(1,657		)	2000	8/30/01
7063 Columbia Gateway Drive (O)	Columbia, MD	—		902			3,684			1,074		902			4,758		5,660		(2,272		)	2000	8/30/01
7065 Columbia Gateway Drive (O)	Columbia, MD	—		919			3,763			2,902		919			6,665		7,584		(2,343		)	2000	8/30/01
7067 Columbia Gateway Drive (O)	Columbia, MD	—		1,829			11,823			2,773		1,829			14,596		16,425		(5,461		)	2001	8/30/01
7125 Columbia Gateway Drive (L)	Columbia, MD	—		3,361			555			279		3,361			834		4,195		—			1973/1999 (8)	6/29/06
7125 Columbia Gateway Drive (O)	Columbia, MD	—		17,126			46,994			8,848		17,126			55,842		72,968		(14,434		)	1973/1999	6/29/06
7130 Columbia Gateway Drive (O)	Columbia, MD	—		1,350			4,359			1,802		1,350			6,161		7,511		(2,321		)	1989	9/19/05
7134 Columbia Gateway Drive (O)	Columbia, MD	—		704			1,971			310		704			2,281		2,985		(638		)	1990	9/19/05
7138 Columbia Gateway Drive (O)	Columbia, MD	—		1,104			3,518			1,975		1,104			5,493		6,597		(2,817		)	1990	9/19/05
7142 Columbia Gateway Drive (O)	Columbia, MD	—		1,342			3,978			2,494		1,342			6,472		7,814		(2,091		)	1994	9/19/05
7150 Columbia Gateway Drive (O)	Columbia, MD	—		1,032			3,429			579		1,032			4,008		5,040		(1,056		)	1991	9/19/05
7150 Riverwood Drive (O)	Columbia, MD	—		1,821			4,388			1,332		1,821			5,720		7,541		(1,742		)	2000	1/10/07
7160 Riverwood Drive (O)	Columbia, MD	—		2,732			7,006			1,605		2,732			8,611		11,343		(3,040		)	2000	1/10/07
7170 Riverwood Drive (O)	Columbia, MD	—		1,283			3,096			658		1,283			3,754		5,037		(1,218		)	2000	1/10/07
7175 Riverwood Drive (O)	Columbia, MD	—		1,788			7,270			—		1,788			7,270		9,058		(207		)	1996/2013	7/27/05
7200 Redstone Gateway (O)	Huntsville, AL	—		—			4,926			—		—			4,926		4,926		(133		)	2013	3/23/10
7200 Riverwood Road (O)	Columbia, MD	—		4,089			16,356			3,538		4,089			19,894		23,983		(7,933		)	1986	10/13/98
7205 Riverwood Drive (O)	Columbia, MD	—		1,367			24,114			—		1,367			24,114		25,481		(774		)	2013	7/27/05
7272 Park Circle Drive (O)	Hanover, MD	4,919		1,479			6,300			3,884		1,479			10,184		11,663		(2,461		)	1991/1996	1/10/07
7318 Parkway Drive (O)	Hanover, MD	—		972			3,888			926		972			4,814		5,786		(1,879		)	1984	4/16/99
7320 Parkway Drive (O)	Hanover, MD	—		905			3,570			4,018		905			7,588		8,493		(2,310		)	1983	4/4/02
7400 Redstone Gateway (O)	Huntsville, AL	—		—			4,163			—		—			4,163		4,163		—			-7	3/23/10
7467 Ridge Road (O)	Hanover, MD	—		1,629			6,517			2,402		1,629			8,919		10,548		(4,138		)	1990	4/28/99
7740 Milestone Parkway (O)	Hanover, MD	19,357		3,825			34,365			366		3,825			34,731		38,556		(4,003		)	2009	7/2/07
7770 Backlick Road (O)	Springfield, VA	—		6,387			74,325			140		6,387			74,465		80,852		(3,414		)	2012	3/10/10
7880 Milestone Parkway (O)	Hanover, MD	—		4,857			12,221			—		4,857			12,221		17,078		—			-7	9/17/13
8003 Corporate Drive (O)	White Marsh, MD	—		611			1,611			655		611			2,266		2,877		(396		)	1999	1/9/07
				Initial Cost								Gross Amounts Carried At Close of Period
Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
8007 Corporate Drive (O)	White Marsh, MD	—		1,434			3,336			1,034		1,434			4,370		5,804		(938		)	1995	1/9/07
8010 Corporate Drive (O)	White Marsh, MD	—		1,349			3,262			1,744		1,349			5,006		6,355		(1,282		)	1998	1/9/07
8013 Corporate Drive (O)	White Marsh, MD	—		642			1,536			1,809		642			3,345		3,987		(770		)	1990	1/9/07
8015 Corporate Drive (O)	White Marsh, MD	—		446			1,116			361		446			1,477		1,923		(428		)	1990	1/9/07
8019 Corporate Drive (O)	White Marsh, MD	—		680			1,898			739		680			2,637		3,317		(751		)	1990	1/9/07
8020 Corporate Drive (O)	White Marsh, MD	—		2,184			3,767			2,205		2,184			5,972		8,156		(1,499		)	1997	1/9/07
8023 Corporate Drive (O)	White Marsh, MD	—		651			1,603			5		651			1,608		2,259		(357		)	1990	1/9/07
8094 Sandpiper Circle (O)	White Marsh, MD	—		1,960			3,716			941		1,960			4,657		6,617		(1,125		)	1998	1/9/07
8098 Sandpiper Circle (O)	White Marsh, MD	—		1,797			3,651			639		1,797			4,290		6,087		(827		)	1998	1/9/07
8110 Corporate Drive (O)	White Marsh, MD	—		2,285			10,117			989		2,285			11,106		13,391		(2,870		)	2001	1/9/07
8140 Corporate Drive (O)	White Marsh, MD	—		2,158			8,457			3,008		2,158			11,465		13,623		(3,767		)	2003	1/9/07
8621 Robert Fulton Drive (O)	Columbia, MD	—		2,317			12,642			336		2,317			12,978		15,295		(3,015		)	2005-2006	6/10/05
8661 Robert Fulton Drive (O)	Columbia, MD	—		1,510			3,764			2,423		1,510			6,187		7,697		(1,848		)	2002	12/30/03
8671 Robert Fulton Drive (O)	Columbia, MD	—		1,718			4,280			1,981		1,718			6,261		7,979		(2,754		)	2002	12/30/03
870 Elkridge Landing Road (O)	Linthicum, MD	—		2,003			9,442			6,941		2,003			16,383		18,386		(7,965		)	1981	8/3/01
891 Elkridge Landing Road (O)	Linthicum, MD	—		1,165			4,772			2,295		1,165			7,067		8,232		(3,229		)	1984	7/2/01
900 Elkridge Landing Road (O)	Linthicum, MD	—		1,993			7,972			3,486		1,993			11,458		13,451		(5,655		)	1982	4/30/98
901 Elkridge Landing Road (O)	Linthicum, MD	—		1,156			4,437			2,419		1,156			6,856		8,012		(2,672		)	1984	7/2/01
911 Elkridge Landing Road (O)	Linthicum, MD	—		1,215			4,861			2,024		1,215			6,885		8,100		(3,239		)	1985	4/30/98
921 Elkridge Landing Road (O)	Linthicum, MD	—		1,044			4,239			748		1,044			4,987		6,031		(2,244		)	1983 (7)	4/30/98
938 Elkridge Landing Road (O)	Linthicum, MD	—		1,163			4,748			1,155		1,163			5,903		7,066		(1,928		)	1984	7/2/01
939 Elkridge Landing Road (O)	Linthicum, MD	—		939			3,756			3,074		939			6,830		7,769		(2,927		)	1983	4/30/98
940 Elkridge Landing Road (L)	Linthicum, MD	—		1,104			4,730			170		1,104			4,900		6,004		(4,884		)	-8	7/2/01
9651 Hornbaker Road (D)	Manassas, VA	—		6,050			204,176			853		6,050			205,029		211,079		(10,881		)	2010	9/14/10
9690 Deereco Road (O)	Timonium, MD	—		3,415			13,723			7,289		3,415			21,012		24,427		(9,585		)	1988	12/21/99
9900 Franklin Square Drive (O)	White Marsh, MD	—		979			3,466			325		979			3,791		4,770		(989		)	1999	1/9/07
9910 Franklin Square Drive (O)	White Marsh, MD	4,691		1,219			6,590			74		1,219			6,664		7,883		(1,952		)	2005	1/9/07
9920 Franklin Square Drive (O)	White Marsh, MD	—		1,058			5,293			1,436		1,058			6,729		7,787		(2,077		)	2006	1/9/07
Aerotech Commerce (L)	Colorado Springs, CO	—		900			—			—		900			—		900		—			-8	5/19/06
Arborcrest (O)	Blue Bell, PA	—		21,968			109,468			1,209		21,968			110,677		132,645		(22,043		)	1991-1996 (7)	10/14/97
Arundel Preserve (L)	Hanover, MD	—		13,401			7,238			—		13,401			7,238		20,639		—			-8	7/2/07
Ashburn Crossing - DC 10 (O)	Ashburn, VA	—		4,408			8,399			—		4,408			8,399		12,807		—			-7	12/27/12
Canton Crossing Land (L)	Baltimore, MD	—		16,085			905			—		16,085			905		16,990		—			-8	10/27/09
Canton Crossing Util Distr Ctr (O)	Baltimore, MD	—		7,300			15,556			878		7,300			16,434		23,734		(2,755		)	2006	10/27/09
Columbia Gateway - Southridge (L)	Columbia, MD	—		6,387			2,940			—		6,387			2,940		9,327		—			-8	9/20/04
Dahlgren Technology Center (L)	Dahlgren, VA	—		978			178			—		978			178		1,156		—			-8	3/16/05
Expedition VII (L)	Lexington Park, MD	—		705			727			—		705			727		1,432		—			-8	3/24/04
InterQuest (L)	Colorado Springs, CO	—		14,382			9			—		14,382			9		14,391		—			-8	9/28/05
M Square Research Park (L)	College Park, MD	—		—			3,129			—		—			3,129		3,129		—			-8	1/29/08
				Initial Cost								Gross Amounts Carried At Close of Period
Property (Type) (1)	Location	Encumbrances (2)		Land			Building and Land Improvements			Costs Capitalized Subsequent to Acquisition		Land			Building and Land Improvements		Total (3)(4)		Accumulated Depreciation (5)			Year Built or Renovated	Date Acquired (6)
National Business Park North (L)	Annapolis Junction, MD	—		27,785			47,411			—		27,785			47,411		75,196		—			-8	6/29/06
North Gate Business Park (L)	Aberdeen, MD	—		6,486			10,922			—		6,486			10,922		17,408		—			-8	9/14/07
Northwest Crossroads (L)	San Antonio, TX	—		7,430			836			—		7,430			836		8,266		—			-8	1/20/06
NOVA Office A (O) (9)	Chantilly, VA	—		2,096			38,142			—		2,096			38,142		40,238		—			-7	7/31/02
NOVA Office B (O) (9)	Chantilly, VA	—		739			18,858			—		739			18,858		19,597		—			-7	7/31/02
NOVA Office D (O)	Chantilly, VA	—		6,587			2			—		6,587			2		6,589		—			-7	7/31/02
Old Annapolis Road (O)	Columbia, MD	—		1,637			5,500			2,421		1,637			7,921		9,558		(2,756		)	1974/1985	12/14/00
Patriot Park (L)	Colorado Springs, CO	—		8,723			248			—		8,723			248		8,971		—			-8	7/8/05
Patriot Ridge (L)	Springfield, VA	—		18,517			14,440			—		18,517			14,440		32,957		—			-8	3/10/10
Redstone Gateway (L)	Huntsville, AL	—		—			14,087			—		—			14,087		14,087		—			-8	3/23/10
Route 15/Biggs Ford Road (L)	Frederick, MD	—		8,703			541			—		8,703			541		9,244		—			-8	8/28/08
Sentry Gateway (L)	San Antonio, TX	—		8,275			3,645			—		8,275			3,645		11,920		—			-8	3/30/05
Sentry Gateway - T (O)	San Antonio, TX	—		14,020			38,804			13		14,020			38,817		52,837		(7,646		)	1982/1985	3/30/05
Sentry Gateway - V (O)	San Antonio, TX	—		—			1,066			—		—			1,066		1,066		(161		)	2007	3/30/05
Sentry Gateway - W (O)	San Antonio, TX	—		—			1,884			—		—			1,884		1,884		(249		)	2009	3/30/05
Sentry Gateway - X (O)	San Antonio, TX	—		1,964			21,178			—		1,964			21,178		23,142		(2,204		)	2010	1/20/06
Sentry Gateway - Y (O)	San Antonio, TX	—		1,964			21,298			—		1,964			21,298		23,262		(2,213		)	2010	1/20/06
Sentry Gateway - Z (O)	San Antonio, TX	—		1,964			23,185			—		1,964			23,185		25,149		—			-7	6/14/05
Westfields - Park Center (L)	Chantilly, VA	—		16,418			8,584			—		16,418			8,584		25,002		—			-8	7/18/02
Westfields Corporate Center (L)	Chantilly, VA	—		7,141			1,415			—		7,141			1,415		8,556		—			-8	7/31/02
White Marsh (L)	White Marsh, MD	—		17,610			6,983			—		17,610			6,983		24,593		—			-8	1/9/07
Woodland Park (L)	Herndon, VA	—		9,614			81			—		9,614			81		9,695		—			-8	4/29/04
Other Developments, including intercompany eliminations (V)	Various	—		8			276			261		8			537		545		(26		)	Various	Various
		$	409,193	$	668,660		$	3,008,508		$	337,168	$	668,660		$	3,345,676	$	4,014,336	$	(703,083	)
-1	A legend for the Property Type follows: (O) =ffice Property; (L) =and held or pre-construction; (D) =ata Center; and (V) =arious.
-2	Excludes our Revolving Credit Facility of $83.0 million, term loan facilities of $520.0 million, unsecured senior notes of $890.9 million, exchangeable senior notes of $572,000, unsecured notes payable of $1.6 million, a letter of credit on a mortgage loan of $14.8 million, and net premiums on the remaining loans of $42,000.
-3	The aggregate cost of these assets for Federal income tax purposes was approximately $3.4 billion at December 31, 2014.
-4	As discussed in Note 3 to our Consolidated Financial Statements, we recognized impairment losses of $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore region that were disposed in the current period.
-5	The estimated lives over which depreciation is recognized follow: Building and land improvements: 10-40 years; and tenant improvements: related lease terms.
-6	The acquisition date of multi-parcel properties reflects the date of the earliest parcel acquisition.
-7	Under construction or redevelopment at December 31, 2014.
-8	Held or under pre-construction at December 31, 2014.
-9	The carrying amounts of these properties under construction exclude allocated costs of the garage being constructed to support the properties.
The following table summarizes our changes in cost of properties for the years ended December 31, 2014, 2013 and 2012 (in thousands):
					2014				2013			2012
	Beginning balance				$	3,811,950			$	3,859,960		$	4,038,932
	Acquisitions of operating properties				—				—			33,684
	Improvements and other additions				254,868				249,639			214,418
	Sales				(48,466		)		(141,045		)	(291,491		)
	Impairments				(3,042		)		(45,931		)	(121,557		)
	Other dispositions				(974		)		(110,673		)	(13,891		)
	Other				—				—			(135		)
	Ending balance				$	4,014,336			$	3,811,950		$	3,859,960
The following table summarizes our changes in accumulated depreciation for the same time periods (in thousands):
					2014				2013			2012
	Beginning balance				$	597,649			$	568,176		$	577,601
	Depreciation expense				111,326				92,677			93,158
	Sales				(3,129		)		(9,542		)	(40,346		)
	Impairments				(1,671		)		(14,863		)	(58,855		)
	Other dispositions				(1,092		)		(38,799		)	(3,247		)
	Other				—				—			(135		)
	Ending balance				$	703,083			$	597,649		$	568,176

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
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 significant intercompany balances and transactions in consolidation.
	We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity.
	We use the cost method of accounting when we own an interest in an entity and cannot exert significant influence over its operations.
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 at the dates of the financial statements;
	•	the disclosure of contingent assets and liabilities at 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 notes receivable, the allocation of property acquisition costs, the determination of estimated useful lives of assets, the determination of lease terms, the evaluation of impairment of long-lived assets, the amount of revenue recognized relating to tenant improvements and the level of expense recognized in connection with share-based compensation. Actual results could differ from these and other estimates.
Acquisitions of Properties	Acquisitions of Properties
	Upon completion of 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 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, construction 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-cancellable 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 rental revenue over the remaining lease terms of the respective 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 additional income to be realized includes carrying costs, such as real estate taxes, insurance and other operating expenses, and revenues during the expected lease-up periods considering current market conditions. 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.
Properties	Properties
	We report properties to be developed or held and used in operations at our depreciated cost, reduced for impairment losses. The preconstruction stage of the development or redevelopment of an operating property includes efforts and related costs to secure land control and zoning, evaluate feasibility and complete other initial tasks which are essential to development.
	We capitalize interest expense, real estate taxes and direct and indirect project costs (including related compensation and other indirect costs) associated with properties, or portions thereof, undergoing construction, development and redevelopment activities. In capitalizing interest expense, if there is a specific borrowing for the property undergoing construction, development and 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 construction, 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-constructed 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 construction. We start depreciating newly-constructed and redeveloped properties as they become operational.
	Most of our leases involve 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 associated with such improvements 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 improvements are unique to the tenant or reusable by other tenants; whether the tenant is permitted to alter or remove the improvements without our consent or without compensating us for any lost fair value; whether the ownership of the improvements remains with us or remains with the tenant at the end of the lease term; and whether the economic substance of the lease terms is properly reflected.
	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		Related lease term
	Equipment and personal property		3-10 years
	We assess each of our operating properties for impairment quarterly using cash flow projections and estimated fair values that we derive for each of the properties.  We update the leasing and other assumptions used in these projections regularly, paying particular attention to properties that have experienced chronic vacancy or face significant market challenges.  We review our plans and intentions for our development projects and land parcels quarterly.  If our analyses indicate that the carrying values of operating properties, properties in development or land held for future development may be impaired, we perform a recovery analysis for such properties.  For long-lived assets 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 assets over, in most cases, a ten-year holding period.  If we believe there is a significant possibility that we might dispose of the assets 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 assets over the various possible holding periods.  If the recovery analysis indicates that the carrying value of a tested property is not recoverable from estimated future cash flows, it is written down to its 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 each asset using holding periods that are consistent with our revised plans. Changes in holding periods may require us to recognize significant impairment losses.
	Property fair values are determined based on contract prices, indicative bids, discounted cash flow analyses or yield analyses. Estimated cash flows used in such analyses are based on our plans for the property and our views of market and economic conditions. The estimates consider factors such as current and future rental rates, occupancies for the tested property and comparable properties, estimated operating and capital expenditures and recent sales data for comparable properties; most of these factors are influenced by market data obtained from real estate leasing and brokerage firms and our direct experience with the properties and their markets.
	When we determine that a property is held for sale, we discontinue the recording of depreciation expense on 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, we recognize an impairment loss equal to the difference and reduce the net book value of the property. For periods in which a property is classified as held for sale, we classify the assets of the property as held for sale on our consolidated balance sheet for such periods.
	For dispositions of operating properties occurring prior to the quarterly period ended June 30, 2014 in which we have no significant continuing involvement in such properties, or for operating properties held for sale prior to the quarterly period ended June 30, 2014, we classify the results of operations for such properties as discontinued operations; interest expense that is specifically identifiable to properties included in discontinued operations is used in the computation of interest expense attributable to discontinued operations. As discussed further below, we adopted guidance issued by the Financial Accounting Standards Board (“FASB”) related to the reporting of discontinued operations and disclosures of disposals of components of an entity effective for the quarterly period ended June 30, 2014. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale that represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity.
Sale of Interests in Real Estate	Sales of Interests in Real Estate
	We recognize gains from sales of interests in real estate using the full accrual method, provided that various criteria relating to the terms of sale and any subsequent involvement by us with the real estate sold are met.
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 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, 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. We report investments in marketable securities classified as available-for-sale securities at fair value, with net unrealized gains or losses deferred to accumulated other comprehensive income (loss) (“AOCI”) and realized gains and losses resulting from sales of such investments recognized through earnings; on our consolidated statements of cash flows, we classify cash flows from interest and dividends earned on these securities as operating activities and cash flows from purchases, sales and maturities of these securities as investing activities.
Accounts and Deferred Rents Receivable and Investing Receivables	Accounts and Deferred Rents Receivable and Investing Receivables
	We maintain allowances for estimated losses resulting from the failure of our customers or borrowers to satisfy their payment obligations. We use judgment in estimating these allowances based primarily upon the payment history and credit status of the entities associated with the individual receivables. We write off these receivables when we believe the facts and circumstances indicate that continued pursuit of collection is no longer warranted. When we earn interest income in connection with receivables for which we have established allowances, we establish allowances in connection with such interest income that is unpaid. When cash is received in connection with receivables for which we have established allowances, we reduce the amount of losses previously recognized.
Intangible Assets and Deferred Revenue on Real Estate Acquisitions	Intangible Assets and Deferred Revenue on Real Estate Acquisitions
	We capitalize intangible assets and deferred revenue on real estate acquisitions as described in the section above entitled “Acquisitions of Properties.” We amortize the intangible assets and deferred revenue 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
	Market concentration premium		40 years
	We recognize the amortization of acquired above-market 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 Financing Costs, Net	Deferred Leasing and Financing Costs, Net
	We defer costs incurred to obtain new tenant leases or extend existing tenant leases, including related compensation costs. We amortize these costs evenly over the lease terms. When tenant leases are terminated early, we expense any unamortized deferred leasing costs associated with those leases over the shortened term of the lease.
	We defer costs of financing arrangements and recognize these costs as interest expense over the related loan 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.
Noncontrolling Interests	Noncontrolling Interests
	COPT’s consolidated noncontrolling interests are comprised of interests in COPLP not owned by COPT (discussed further in Note 15) and consolidated real estate joint ventures (discussed further in Note 6). COPLP’s consolidated noncontrolling interests are comprised primarily of interests in our consolidated real estate joint ventures. Also included in COPLP’s consolidated noncontrolling interests are interests in several real estate entities owned directly by COPT, or a wholly owned subsidiary of COPT, that generally do not exceed 1% of interests in such entities. We evaluate whether noncontrolling interests are subject to redemption features outside of our control. For noncontrolling interests that are currently redeemable for cash at the option of the holders of such interests or deemed probable to eventually become redeemable, we classify such interests 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, and only recognize reductions in such interests to the extent of their carrying amount. Our other noncontrolling interests are reported in the equity section of our consolidated balance sheets. The amounts reported for noncontrolling interests on our consolidated statements of operations represent the portion of these entities’ income or losses not attributable to us.
Revenue Recognition	Revenue Recognition
	We recognize minimum rents, net of abatements, on a straight-line basis over the term of tenant leases. A lease term generally 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 generally includes periods when a tenant: (1) may not terminate its lease obligation early; (2) may terminate its lease obligation early in exchange for a fee or penalty that we consider material enough such that termination would not be probable; (3) possesses renewal rights and the tenant’s failure to exercise such rights imposes a penalty on the tenant material enough such that renewal appears reasonably assured; or (4) possesses bargain renewal options for such periods. 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 included in 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.
	We recognize tenant recovery revenue in the same periods in which we incur the related expenses. Tenant recovery revenue includes payments from tenants as reimbursement for 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.
	We recognize fees for services provided by us once services are rendered, fees are determinable and collectability is assured. We recognize revenue under construction contracts using the percentage of completion method when the revenue and costs for such contracts can be estimated with reasonable accuracy; when these criteria do not apply to a contract, we recognize revenue on that contract using the completed contract method. Under the percentage of completion method, we recognize a percentage of the total estimated revenue on a contract based on the cost of services provided on the contract as of a point in time relative to the total estimated costs on the contract.
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 primarily 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.  Derivatives are used to hedge the cash flows associated with interest rates on existing debt as well as future debt. We recognize all derivatives as assets or liabilities on our consolidated balance sheet at fair value. We defer the effective portion of changes in fair value of the designated cash flow hedges to AOCI and reclassify such deferrals to interest expense as interest expense is recognized on the hedged forecasted transactions. We recognize the ineffective portion of the change in fair value of interest rate derivatives directly in interest expense. When an interest rate swap designated as a cash flow hedge no longer qualifies for hedge accounting, we recognize changes in fair value of the hedge previously deferred to AOCI, 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.
	Please refer to Note 12 for additional information pertaining to interest rate derivatives.
Expense Classification	Expense Classification
	We classify as property operations expense costs incurred for property taxes, ground rents, utilities, property management, insurance, repairs, exterior and interior maintenance and tenant revenue collection losses, as well as associated labor and indirect costs attributable to these costs.
	We classify as general and 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, director and officers and key man life) and leasing prospects, as well as associated labor and indirect costs attributable to these costs.
Share-Based Compensation	Share-Based Compensation
	We issue two forms of share-based compensation: restricted COPT common shares (“restricted shares”) and COPT performance share units (“PSUs”). We also issued options to purchase COPT common shares (“options”) in prior years. 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 construction and development activities.
	When we adopted the authoritative guidance on accounting for share-based compensation, we elected to adopt the alternative transition method for calculating the tax effects of share-based compensation. This method enabled us to use a simplified method to establishing the beginning balance of the additional paid-in capital pool related to the tax effects of employee share-based compensation that was available to absorb tax deficiencies recognized subsequent to the adoption of this guidance.
	We compute the fair value of options using the Black-Scholes option-pricing model. Under that model, the risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. The expected option life is based on our historical experience of employee exercise behavior. Expected volatility is based on historical volatility of COPT common shares. Expected dividend yield is based on the average historical dividend yield on our common shares over a period of time ending on the grant date of the options.
	We compute the fair value of PSUs using a Monte Carlo model. Under that model, the baseline common share value is based on the market value on the grant date. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant. Expected volatility is based on historical volatility of COPT’s common shares.
Recent Accounting Pronouncements	Recent Accounting Pronouncements
	We adopted guidance issued by the FASB related to the reporting of discontinued operations and disclosures of disposals of components of an entity effective for the quarterly period ended June 30, 2014. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale that represents a strategic shift that has (or will have) a major effect on an entity’s operations and financial results; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity. The guidance also provides for additional disclosure requirements in connection with both discontinued operations and other dispositions not qualifying as discontinued operations. The guidance applies prospectively to new disposals and new classifications of disposal groups as held for sale after the effective date. Our adoption of the guidance will result in fewer disposed or held for sale properties being reported as discontinued operations in our results of operations (including operating properties sold during the current period) but will not otherwise materially affect our consolidated financial statements.
	In May 2014, the FASB issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Additionally, this guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We are required to adopt this guidance for our annual and interim periods beginning January 1, 2017, using one of two methods: retrospective restatement for each reporting period presented at the time of adoption, or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application. We are currently assessing the financial impact of this guidance on our consolidated financial statements.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
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	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 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
	Market concentration premium	40 years

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
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 its subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2014 and 2013 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	December 31, 2014:
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds	$	5,756	$	—		$	—	$	5,756
	Other	126		—			—		126
	Interest rate derivatives (2)	—		274			—		274
	Warrants to purchase common stock in KEYW (2)	—		164			—		164
	Total Assets	$	5,882	$	438		$	—	$	6,320
	Liabilities:
	Deferred compensation plan liability (3)	$	—	$	5,882		$	—	$	5,882
	Interest rate derivatives	—		1,855			—		1,855
	Total Liabilities	$	—	$	7,737		$	—	$	7,737
	Redeemable noncontrolling interest	$	—	$	—		$	18,417	$	18,417
	December 31, 2013:
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds	$	7,090	$	—		$	—	$	7,090
	Common stocks	176		—			—		176
	Other	201		—			—		201
	Common stock (1)	298		—			—		298
	Interest rate derivatives (2)	—		6,594					6,594
	Warrants to purchase common stock in KEYW (2)	—		301			—		301
	Total Assets	$	7,765	$	6,895		$	—	$	14,660
	Liabilities:
	Deferred compensation plan liability (3)	$	—	$	7,467		$	—	$	7,467
	Interest rate derivatives	—		3,309			—		3,309
	Total Liabilities	$	—	$	10,776		$	—	$	10,776
	Redeemable noncontrolling interest	$	—	$	—		$	17,758	$	17,758
	(1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet.
	(2) Included in the line entitled “prepaid expenses and other assets” on COPT’s consolidated balance sheet.
	(3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet.
	The tables below set forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of December 31, 2014 and 2013 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	December 31, 2014:
	Assets:
	Interest rate derivatives (1)	$	—	$	274		$	—	$	274
	Warrants to purchase common stock in KEYW (1)	—		164			—		164
	Total Assets	$	—	$	438		$	—	$	438
	Liabilities:
	Interest rate derivatives	$	—	$	1,855		$	—	$	1,855
	Redeemable noncontrolling interest	$	—	$	—		$	18,417	$	18,417
	December 31, 2013:
	Assets:
	Common stock (2)	$	298	$	—		$	—	$	298
	Interest rate derivatives (1)	—		6,594			—		6,594
	Warrants to purchase common stock in KEYW (1)	—		301			—		301
	Total Assets	$	298	$	6,895		$	—	$	7,193
	Liabilities:
	Interest rate derivatives	$	—	$	3,309		$	—	$	3,309
	Redeemable noncontrolling interest	$	—	$	—		$	17,758	$	17,758
	(1) Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet.
	(2) Included in the line entitled “restricted cash and marketable securities” on COPLP’s consolidated balance sheet.
Schedule of fair value hierarchy of impaired properties and other assets associated with such properties	The table below sets forth the fair value hierarchy of the valuation technique we used to determine the fair values of the properties (dollars in thousands):
		Fair Value of Properties Held as of December 31, 2013
		Quoted Prices in					Significant				Impairment
		Active Markets for		Significant Other			Unobservable				Losses
		Identical Assets		Observable Inputs			Inputs				Recognized in
	Description	(Level 1)		(Level 2)			(Level 3)		Total		2013 (1)
	Assets (2):
	Properties, net	$	—	$	—		$	4,459	$	4,459	$	31,068
	(1) Represents aggregate impairment losses on non recurring fair value measurements resulting in such losses, excluding exit costs incurred of $979,000.
	(2) Reflects balance sheet classifications of assets at time of fair value measurement, excluding the effect of held for sale classifications.
Schedule of quantitative information about significant unobservable inputs used for Level 3 fair value measurements	The table below sets forth quantitative information about significant unobservable inputs used for the Level 3 fair value measurements reported above as of December 31, 2013 (dollars in thousands):
	Valuation Technique	Fair Value on		Unobservable Input		Range (Weighted Average)
		Measurement Date
	Discounted cash flow	$	4,459	Discount rate		10.0% (1)
				Terminal capitalization rate		9.5% (1)
				Market rent growth rate		3.0% (1)
				Expense growth rate		3.0% (1)
	(1) Only one value applied for this unobservable input.

Concentration_of_Rental_Revenu1

Concentration of Rental Revenue (Tables)	12 Months Ended
	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Schedule of percentage of the entity's rental revenue	The following table summarizes the percentage of our rental revenue (which excludes tenant recoveries and other real estate operations revenue) earned from (1) individual tenants that accounted for at least 5% of our rental revenue from continuing and discontinued operations and (2) the aggregate of the five tenants from which we recognized the most rental revenue in the respective years:
		For the Years Ended December 31,
		2014		2013		2012
	United States Government	18	%	18	%	18	%
	Northrop Grumman Corporation (1)	6	%	8	%	7	%
	Booz Allen Hamilton, Inc.	6	%	6	%	6	%
	Computer Sciences Corporation (1)	N/A		5	%	5	%
	Five largest tenants	39	%	41	%	39	%
	(1) Includes affiliated organizations and agencies and predecessor companies.

Properties_net_Tables

Properties, net (Tables)	12 Months Ended
	Dec. 31, 2014
Real Estate [Abstract]
Schedule of operating properties, net	Operating properties, net consisted of the following (in thousands):
		December 31,
		2014				2013
	Land	$	439,355			$	430,472
	Buildings and improvements	3,015,216				2,869,870
	Less: accumulated depreciation	(703,083		)		(597,649		)
	Operating properties, net	$	2,751,488			$	2,702,693
Schedule of projects in development or held for future development	Projects we had in development or held for future development consisted of the following (in thousands):
		December 31,
		2014				2013
	Land	$	214,977			$	245,676
	Construction in progress, excluding land	330,449				265,932
	Projects in development or held for future development	$	545,426			$	511,608
Schedule of operating property dispositions	In 2014, we completed dispositions of the following operating properties (dollars in thousands):
	Project Name		Location		Date of Sale		Number of Buildings		Total Rentable Square Feet	Transaction Value		Gain on Disposition
	4969 and 4979 Mercantile Road		White Marsh, MD		7/14/14		2		96,721	$	5,960	$	2,124
	9930 and 9940 Franklin Square		White Marsh, MD		7/30/14		2		71,992	10,475		2,303
	5020, 5022, 5024 and 5026 Campbell Boulevard		White Marsh, MD		8/4/14		4		134,245	12,400		666
							8		302,958	$	28,835	$	5,093
	We completed dispositions of the following properties in 2013 primarily in connection with the Strategic Reallocation Plan (dollars in thousands):
	Project Name		Location		Date of Sale		Number of Buildings		Total Rentable Square Feet	Transaction Value		Gain on Disposition
	920 Elkridge Landing Road		Linthicum, MD		6/25/13		1		103,000	$	6,900	$	—
	4230 Forbes Boulevard		Lanham, MD		12/11/13		1		56,000	5,600		1,507
	December 2013 Colorado Springs Portfolio Disposition		Colorado Springs, CO		12/12/13		15		1,165,000	133,925		1,164
	December 2013 Portfolio Conveyance		Colorado Springs, CO and Linthicum, MD		12/23/13		14		1,021,000	146,876		—
							31		2,345,000	$	293,301	$	2,671

Real_Estate_Joint_Ventures_Tab

Real Estate Joint Ventures (Tables)	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Schedule of information related to investments in consolidated real estate joint ventures	The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of December 31, 2014 (dollars in thousands):
			Nominal
			Ownership			December 31, 2014					-1
		Date	% as of			Total			Encumbered		Total
		Acquired	12/31/14		Nature of Activity	Assets			Assets		Liabilities
	LW Redstone Company, LLC	3/23/10	85%		Operates four buildings and developing others (2)	$	143,534		$	66,620	$	41,659
	M Square Associates, LLC	6/26/07	50%		Operates two buildings and developing others (3)	59,414			48,856		39,077
						$	202,948		$	115,476	$	80,736
	(1) Excludes amounts eliminated in consolidation.
	(2) This joint venture’s property is in Huntsville, Alabama.
	(3) This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).
Schedule of condensed statements of operations for unconsolidated real estate joint venture	The following table sets forth the condensed statements of operations for this unconsolidated real estate joint venture (in thousands):
			For the Years Ended
			December 31,
			2013			2012
	Revenues		$	6,519		$	7,316
	Property operating expenses		(2,818		)	(2,829		)
	Interest expense		(10,463		)	(7,672		)
	Depreciation and amortization expense		(2,067		)	(2,283		)
	Gain on early extinguishment of debt		23,013			—
	Net income (loss)		$	14,184		$	(5,468	)

Intangible_Assets_on_Real_Esta1

Intangible Assets on Real Estate Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2014
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, 2014						31-Dec-13
		Gross Carrying Amount		Accumulated Amortization		Net		Gross Carrying Amount		Accumulated Amortization		Net
						Carrying Amount						Carrying Amount
	In-place lease value	$	123,759	$	101,040	$	22,719	$	125,504	$	93,885	$	31,619
	Tenant relationship value	42,301		28,492		13,809		44,414		25,962		18,452
	Below-market cost arrangements	12,415		5,984		6,431		12,416		5,136		7,280
	Above-market leases	8,659		8,159		500		8,925		7,970		955
	Market concentration premium	1,333		938		395		1,333		381		952
		$	188,467	$	144,613	$	43,854	$	192,592	$	133,334	$	59,258

Deferred_Leasing_and_Financing1

Deferred Leasing and Financing Costs (Tables)	12 Months Ended
	Dec. 31, 2014
Deferred Leasing and Financing Costs [Abstract]
Schedule of deferred leasing and financing costs, net	Deferred leasing and financing costs, net consisted of the following (in thousands):
		December 31,
		2014			2013
	Deferred leasing costs	$	123,925		$	110,711
	Deferred financing costs	31,229			36,390
	Accumulated amortization	(90,357		)	(80,834		)
	Deferred leasing and financing costs, net	$	64,797		$	66,267

Investing_Receivables_Tables

Investing Receivables (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Schedule of investing receivables	nvesting receivables, including accrued interest thereon, consisted of the following (in thousands):
		December 31,
		2014		2013
	Notes receivable from City of Huntsville	$	49,147	$	44,055
	Other investing loans receivable	3,000		9,608
		$	52,147	$	53,663

Prepaid_Expenses_and_Other_Ass1

Prepaid Expenses and Other Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Prepaid Expense and Other Assets [Abstract]
Schedule of prepaid expenses and other assets	Prepaid expenses and other assets consisted of the following (in thousands):
		December 31,
		2014		2013
	Prepaid expenses	$	20,570	$	19,308
	Lease incentives	13,344		8,435
	Construction contract costs incurred in excess of billings	6,656		2,462
	Furniture, fixtures and equipment, net	6,637		6,556
	Deferred tax asset, net (1)	4,002		4,305
	Operating notes receivable	3,797		1,692
	Other equity method investments	2,368		2,258
	Interest rate derivatives	274		6,594
	Other assets	2,601		2,576
	Prepaid expenses and other assets	$	60,249	$	54,186
	(1) See Note 19 for further disclosure.

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Instrument [Line Items]
Schedule of debt	Our debt consisted of the following (dollars in thousands):
		Maximum
		Availability as of			Carrying Value as of						Scheduled Maturity
		December 31,			December 31,		December 31,		Stated Interest Rates as of		as of
		2014			2014		2013		December 31, 2014		December 31, 2014
	Mortgage and Other Secured Loans:
	Fixed rate mortgage loans (1)				$	387,139	$	675,060	3.96% - 10.65% (2)		2015-2024
	Variable rate secured loan				36,877		37,691		LIBOR + 2.25% (3)		Nov-15
	Total mortgage and other secured loans				424,016		712,751
	Revolving Credit Facility (4)	$	800,000		83,000		—		LIBOR + 0.975% to 1.75%		Jul-17
	Term Loan Facilities	-5			520,000		620,000		LIBOR + 1.10% to 2.60% (6)		2015-2019
	Unsecured Senior Notes (4)
	3.600% Senior Notes				347,496		347,244		3.60%		May-23
	5.250% Senior Notes				245,797		245,445		5.25%		Feb-24
	3.700% Senior Notes				297,569		—		3.70%		Jun-21
	Unsecured notes payable				1,607		1,700		0% (7)		2026
	4.25% Exchangeable Senior Notes (4)				572		563		4.25%		Apr-30
	Total debt				$	1,920,057	$	1,927,703
	(1)	Several of the fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates.  The carrying values of these loans reflect net unamortized premiums totaling $42,000 as of December 31, 2014 and $69,000 as of December 31, 2013.
	-2	The maximum stated interest rate would be 7.87%, excluding the incremental additional interest rate associated with the default rate on a nonrecourse mortgage loan discussed further below. The weighted average interest rate on our fixed rate mortgage loans was 8.10% as of December 31, 2014 (or 6.16% excluding the incremental additional interest rate associated with the default rate on the loan discussed above).
	(3)	The interest rate on the loan outstanding was 2.41% as of December 31, 2014.
	-4	Refer to the paragraphs below for further disclosure.
	(5)	As discussed below, we have the ability to borrow an additional $180.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders.
	(6)	The weighted average interest rate on these loans was 1.80% as of December 31, 2014.
	(7)	These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates.  The carrying value of these notes reflects an unamortized discount totaling $654,000 as of December 31, 2014 and $761,000 as of December 31, 2013.
Schedule of debt maturities	Our debt matures on the following schedule (in thousands):
	2015	$	343,545	-1
	2016	171,399
	2017	339,247		-2
	2018	2,036
	2019	122,094
	Thereafter	951,489
	Total	$	1,929,810	-3
	-1	Includes $150.0 million pertaining to a nonrecourse mortgage loan on which we defaulted on the payment terms as discussed further below. Also includes $150.0 million that may be extended for two one-year periods at our option, subject to certain conditions.
	(2)    Includes $333.0 million that may be extended for one year at our option, subject to certain conditions.
	(3)     Represents scheduled principal amortization and maturities only and therefore excludes net discounts of $9.8 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, 2014					31-Dec-13
		Carrying			Estimated		Carrying		Estimated
		Amount			Fair Value		Amount		Fair Value
	Fixed-rate debt
	Unsecured Senior Notes	$	890,862		$	901,599	$	592,689	$	575,374
	4.25% Exchangeable Senior Notes	572			575		563		575
	Other fixed-rate debt	388,746			355,802		676,760		650,997
	Variable-rate debt	639,877			642,091		657,691		657,527
		$	1,920,057		$	1,900,067	$	1,927,703	$	1,884,473
4.25% Exchangeable Senior Notes
Debt Instrument [Line Items]
Schedule of interest expense recognized on notes before deductions for amounts capitalized	The table below sets forth interest expense recognized on these notes (in thousands):
		For the Years Ended December 31,
		2014			2013		2012
	Interest expense at stated interest rate	$	24		$	4,208	$	10,200
	Interest expense associated with amortization of discount	10			1,615		3,651
	Total	$	34		$	5,823	$	13,851

Interest_Rate_Derivatives_Tabl

Interest Rate Derivatives (Tables)	12 Months Ended
	Dec. 31, 2014
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 (dollars in thousands):
														Fair Value at
	Notional									Effective		Expiration		December 31,
	Amount				Fixed Rate			Floating Rate Index		Date		Date		2014			2013
	$	100,000			0.832	%		One-Month LIBOR		1/3/12		9/1/15		$	(407	)	$	(861	)
	100,000				0.832	%		One-Month LIBOR		1/3/12		9/1/15		(407		)	(861		)
	36,877			-1	3.83	%		One-Month LIBOR + 2.25%		11/2/10		11/2/15		(400		)	(832		)
	100,000				0.8055	%		One-Month LIBOR		9/2/14		9/1/16		(317		)	(94		)
	100,000				0.81	%		One-Month LIBOR		9/2/14		9/1/16		(324		)	(105		)
	100,000				1.673	%		One-Month LIBOR		9/1/15		8/1/19		239			3,377
	100,000				1.73	%		One-Month LIBOR		9/1/15		8/1/19		35			3,217
	100,000				0.6123	%		One-Month LIBOR		1/3/12		9/1/14		—			(279		)
	100,000				0.61	%		One-Month LIBOR		1/3/12		9/1/14		—			(277		)
														$	(1,581	)	$	3,285
	-1	The notional amount of this instrument is scheduled to amortize to $36.2 million.
Schedule of fair value and balance sheet classification of interest rate derivatives	The table below sets forth the fair value of our interest rate derivatives as well as their classification on our consolidated balance sheets (in thousands):
			December 31, 2014						December 31, 2013
	Derivatives		Balance Sheet Location		Fair Value				Balance Sheet Location		Fair Value
	Interest rate swaps designated as cash flow hedges		Prepaid expenses and other assets		$	274			Prepaid expenses and other assets		$	6,594
	Interest rate swaps designated as cash flow hedges		Interest rate derivatives		(1,855		)		Interest rate derivatives		(3,309		)
Schedule of effect of interest rate derivatives on consolidated statements of operations and comprehensive income	The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
	Amount of (losses) gains recognized in accumulated other comprehensive income (loss) (“AOCI”) (effective portion)	$	(7,799	)		$	6,791			$	(7,676	)
	Amount of losses reclassified from AOCI into interest expense (effective portion)	2,990				2,740				3,697
	Amount of loss reclassified from AOCI into loss on early extinguishment of debt	38				—				—

Redeemable_Noncontrolling_Inte1

Redeemable Noncontrolling Interest (Tables)	12 Months Ended
	Dec. 31, 2014
Noncontrolling Interest [Abstract]
Schedule of activity for redeemable noncontrolling interest	The table below sets forth the activity in a redeemable noncontrolling interest in a consolidated real estate joint venture described in Note 6 (in thousands):
		For the Years Ended December 31,
		2014			2013			2012
	Beginning balance	$	17,758		$	10,298		$	8,908
	Distribution to noncontrolling interest	(1,369		)	(1,037		)	—
	Net income (loss) attributable to noncontrolling interest	2,162			1,376			(2,565		)
	Adjustment to arrive at fair value of interest	(134		)	7,121			3,955
	Ending balance	$	18,417		$	17,758		$	10,298

Equity_COPT_and_Subsidiaries_T

Equity - COPT and Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2014
Stockholders' Equity Note [Abstract]
Schedule of additional information pertaining to preferred shares	The table below sets forth additional information pertaining to COPT’s outstanding preferred shares (dollars in thousands, except per share data):
	Series	# of Shares Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Dividend Yield		Annual Dividend Per Share		Earliest Redemption Date
	Series K	531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L	6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
		7,431,667	$	199,083

Equity_COPLP_and_Subsidiaries_

Equity - COPLP and Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2014
Class of Stock [Line Items]
Schedule of additional information pertaining to preferred shares	The table below sets forth additional information pertaining to COPT’s outstanding preferred shares (dollars in thousands, except per share data):
	Series	# of Shares Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Dividend Yield		Annual Dividend Per Share		Earliest Redemption Date
	Series K	531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L	6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
		7,431,667	$	199,083
Corporate Office Properties, L.P.
Class of Stock [Line Items]
Schedule of additional information pertaining to preferred shares	The table below sets forth information pertaining to preferred units in COPLP held by COPT at December 31, 2014 (dollars in thousands, except per unit data):
	Series	# of Units Issued	Aggregate Liquidation Preference		Month of Issuance	Annual Distribution Yield		Annual Distribution Per Unit		Earliest Redemption Date
	Series K	531,667	$	26,583	Jan-07	5.6	%	$	2.8	1/9/17
	Series L	6,900,000	172,500		Jun-12	7.375	%	$	1.84375	6/27/17
		7,431,667	$	199,083

ShareBased_Compensation_and_Ot1

Share-Based Compensation and Other Compensation Matters (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of restricted share transactions under the entity's share-based compensation plans	The following table summarizes restricted share transactions under the share-based compensation plans for 2012, 2013 and 2014:
			Shares			Weighted Average Grant Date Fair Value
	Unvested at December 31, 2011		648,378			$	33.13
	Granted		177,662			23.64
	Forfeited		(17,019	)		31.43
	Vested		(374,378	)		32.72
	Unvested at December 31, 2012		434,643			29.67
	Granted		193,833			25.91
	Forfeited		(9,541	)		27.59
	Vested		(241,487	)		30.97
	Unvested at December 31, 2013		377,448			26.96
	Granted		216,607			26.73
	Forfeited		(21,335	)		25.1
	Vested		(182,213	)		28.56
	Unvested at December 31, 2014		390,507			$	26.19
	Unvested shares as of December 31, 2014 that are expected to vest		375,686			$	26.18
Schedule of PSU's Granted	Our Board of Trustees made the following grants of PSUs to executives from 2011 through 2014 (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, 2014
	3/3/11		56,883			3/3/11		3/2/14		$	2,796			—
	3/1/12		54,070			1/1/12		12/31/14		1,772				54,070
	3/1/13		69,579			1/1/13		12/31/15		1,867				69,579
	3/6/14		49,103			1/1/14		12/31/16		1,723				49,103
Schedule of payouts for defined performance under performance-based awards of share-based compensation	The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule:
	Percentile Rank		Earned PSUs Payout %
	75th or greater		200% of PSUs granted
	50th or greater		100% of PSUs granted
	25th		50% of PSUs granted
	Below 25th		0% of PSUs granted
Schedule of assumptions used in Monte Carlo models for PSUs	The grant date fair value and certain of the assumptions used in the Monte Carlo models for the PSUs granted in 2012, 2013 and 2014 are set forth below:
			For the Years Ended December 31,
			2014				2013				2012
	Grant date fair value		$	35.09			$	26.84			$	32.77
	Baseline common share value		$	26.52			$	25.85			$	24.39
	Expected volatility of common shares		28.6		%		29.5		%		43.2		%
	Risk-free interest rate		0.66		%		0.33		%		0.41		%
Summary of stock option transactions under the entity's share-based compensation plans	The following table summarizes option transactions under the share-based compensation plans for 2012, 2013 and 2014 (dollars in thousands, except per share data):
			Shares			Range of Exercise Price per Share		Weighted Average Exercise Price per Share				Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
												(in Years)
	Outstanding at December 31, 2011		945,422			$13.40 - $57.00		$	36.63			4		$	510
	Forfeited/Expired – 2012		(85,588	)		$25.52 - $57.00		$	42.98
	Exercised – 2012		(61,624	)		$13.40 - $22.49		$	15.08
	Outstanding at December 31, 2012		798,210			$13.60 - $57.00		$	37.62			3		$	325
	Forfeited/Expired – 2013		(117,952	)		$18.08 - $51.62		$	40.91
	Exercised – 2013		(39,331	)		$13.60 - $26.24		$	19.67
	Outstanding at December 31, 2013		640,927			$19.63 - $56.00		$	38.11			2		$	68
	Forfeited/Expired – 2014		(18,303	)		$22.34 - $49.60		$	42.12
	Exercised – 2014		(62,888	)		$19.63 - $28.15		$	23.7
	Outstanding at December 31, 2014		559,736			$25.52 - $56.00		$	39.6			2		$	167
	Exercisable at December 31, 2012		798,210			-1		$	37.62
	Exercisable at December 31, 2013		640,927			-2		$	38.11
	Exercisable at December 31, 2014		559,736			-3		$	39.6
	-1	9,500 of these options had an exercise price ranging from $13.60 to $16.73; 204,736 had an exercise price ranging from $16.74 to $30.04; 180,962 had an exercise price ranging from $30.05 to $41.28; and 403,012 had an exercise price ranging from $41.29 to $57.00.
	-2	171,288 of these options had an exercise price ranging from $19.63 to $30.04; 145,187 had an exercise price ranging from$30.05 to $41.28; 160,402 had an exercise price ranging from $41.29 to $42.74; and 164,050 had an exercise price ranging from $42.75 to $56.00.
	-3	105,672 of these options had an exercise price ranging from $25.52 to $30.04; 142,862 had an exercise price ranging from$30.05 to $41.28; 158,902 had an exercise price ranging from $41.29 to $42.74; and 152,300 had an exercise price ranging from $42.75 to $56.00.
Reporting for share-based compensation expense	The table below sets forth our reporting for share based compensation expense (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	General, administrative and leasing expenses		$	5,307			$	5,412			$	8,611
	Property operating expenses		857				1,118				1,371
	Capitalized to development activities		886				1,075				1,202
	Share-based compensation expense		$	7,050			$	7,605			$	11,184

Operating_Leases_Tables

Operating Leases (Tables)	12 Months Ended
	Dec. 31, 2014
Leases, Operating [Abstract]
Schedule of gross minimum future rentals on noncancelable leases in the entity's properties	Gross minimum future rentals on noncancelable leases in our properties as of December 31, 2014 were as follows (in thousands):
	Year Ending December 31,
	2015	$	349,099
	2016	301,184
	2017	263,428
	2018	202,661
	2019	154,044
	Thereafter	312,304
		$	1,582,720

Information_by_Business_Segmen1

Information by Business Segment (Tables)	12 Months Ended
	Dec. 31, 2014
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).  We measure the performance of our segments through the measure we define as NOI from real estate operations, which is derived by subtracting property operating expenses from revenues from real estate operations.
		Operating Office Property Segments
		Baltimore/				Northern				San				Huntsville		Washington,		St. Mary’s &		Greater		Greater		Colorado			Other		Operating		Total
		Washington				Virginia				Antonio						DC - Capitol		King George		Baltimore		Philadelphia		Springs					Wholesale
		Corridor														Riverfront		Counties											Data Center
	Year Ended December 31, 2014
	Revenues from real estate operations	$	236,191			$	89,263			$	36,377			$	10,446	$	14,599	$	16,736	$	43,591	$	11,929	$	(1	)	$	10,150	$	10,430	$	479,711
	Property operating expenses	81,132				31,532				20,562				3,066		7,308		5,268		17,778		4,386		12			1,469		7,286		179,799
	NOI from real estate operations	$	155,059			$	57,731			$	15,815			$	7,380	$	7,291	$	11,468	$	25,813	$	7,543	$	(13	)	$	8,681	$	3,144	$	299,912
	Additions to long-lived assets	$	24,174			$	17,447			$	(6	)		$	4,077	$	1,185	$	8,825	$	7,925	$	952	$	—		$	—	$	22	$	64,601
	Transfers from non-operating properties	$	56,699			$	43,154			$	—			$	21,014	$	—	$	—	$	3,550	$	16,344	$	30		$	—	$	1,108	$	141,899
	Segment assets at December 31, 2014	$	1,277,600			$	642,429			$	116,252			$	97,209	$	95,195	$	100,777	$	274,091	$	106,931	$	—		$	77,834	$	163,177	$	2,951,495
	Year Ended December 31, 2013
	Revenues from real estate operations	$	237,869			$	92,010			$	33,060			$	5,050	$	16,863	$	16,568	$	42,653	$	11,924	$	25,290		$	10,075	$	7,271	$	498,633
	Property operating expenses	80,554				31,973				17,631				1,282		7,844		5,028		16,583		3,431		9,002			1,016		6,360		180,704
	NOI from real estate operations	$	157,315			$	60,037			$	15,429			$	3,768	$	9,019	$	11,540	$	26,070	$	8,493	$	16,288		$	9,059	$	911	$	317,929
	Additions to long-lived assets	$	28,087			$	13,090			$	335			$	3,563	$	2,604	$	2,341	$	2,913	$	406	$	2,940		$	—	$	598	$	56,877
	Transfers from non-operating properties	$	50,105			$	61,434			$	—			$	48,799	$	—	$	14	$	360	$	28,034	$	5,438		$	—	$	70,106	$	264,290
	Segment assets at December 31, 2013	$	1,243,099			$	616,082			$	118,299			$	77,773	$	98,962	$	96,143	$	303,823	$	104,657	$	—		$	80,002	$	166,790	$	2,905,630
	Year Ended December 31, 2012
	Revenues from real estate operations	$	238,488			$	79,574			$	32,018			$	3,867	$	16,697	$	16,392	$	52,616	$	9,698	$	24,987		$	12,116	$	6,647	$	493,100
	Property operating expenses	83,050				29,103				16,499				689		7,555		4,745		19,917		2,562		9,231			2,569		4,815		180,735
	NOI from real estate operations	$	155,438			$	50,471			$	15,519			$	3,178	$	9,142	$	11,647	$	32,699	$	7,136	$	15,756		$	9,547	$	1,832	$	312,365
	Additions to long-lived assets	$	25,921			$	65,157			$	280			$	26	$	317	$	1,844	$	9,690	$	286	$	2,929		$	152	$	199	$	106,801
	Transfers from non-operating properties	$	65,108			$	44,250			$	468			$	—	$	—	$	289	$	37,558	$	10,626	$	4,295		$	394	$	58,009	$	220,997
	Segment assets at December 31, 2012	$	1,267,357			$	569,860			$	119,369			$	28,730	$	104,544	$	98,027	$	320,548	$	78,798	$	175,830		$	82,090	$	100,777	$	2,945,930
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,
			2014				2013				2012
	Segment revenues from real estate operations		$	479,711			$	498,633			$	493,100
	Construction contract and other service revenues		106,748				62,363				73,836
	Less: Revenues from discontinued operations (Note 20)		14				(37,636		)		(58,801		)
	Total revenues		$	586,473			$	523,360			$	508,135
Schedule of reconciliation of segment property operating expenses to total property operating expenses	The following table reconciles our segment property operating expenses to property operating expenses as reported on our consolidated statements of operations (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	Segment property operating expenses		$	179,799			$	180,704			$	180,735
	Less: Property operating expenses from discontinued operations (Note 20)		135				(13,505		)		(21,529		)
	Total property operating expenses		$	179,934			$	167,199			$	159,206
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,
			2014				2013				2012
	Construction contract and other service revenues		$	106,748			$	62,363			$	73,836
	Construction contract and other service expenses		(100,058		)		(58,875		)		(70,576		)
	NOI from service operations		$	6,690			$	3,488			$	3,260
Schedule of reconciliation of net operating income from real estate operations and service operations to (loss) income from continuing operations	The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from continuing operations as reported on our consolidated statements of operations (in thousands):
			For the Years Ended December 31,
			2014				2013				2012
	NOI from real estate operations		$	299,912			$	317,929			$	312,365
	NOI from service operations		6,690				3,488				3,260
	Interest and other income		4,923				3,834				7,172
	Equity in income (loss) of unconsolidated entities		229				2,110				(546		)
	Income tax expense		(310		)		(1,978		)		(381		)
	Other adjustments:		—
	Depreciation and other amortization associated with real estate operations		(136,086		)		(113,214		)		(107,998		)
	Impairment losses		(1,416		)		(5,857		)		(43,678		)
	General, administrative and leasing expenses		(31,794		)		(30,869		)		(31,900		)
	Business development expenses and land carry costs		(5,573		)		(5,436		)		(5,711		)
	Interest expense on continuing operations		(92,393		)		(82,010		)		(86,401		)
	NOI from discontinued operations		(121		)		(24,131		)		(37,272		)
	Loss on early extinguishment of debt		(9,552		)		(27,030		)		(943		)
	COPT consolidated income from continuing operations		$	34,509			$	36,836			$	7,967
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,
		2014				2013
	Segment assets	$	2,951,495			$	2,905,630
	Non-operating property assets	567,586				517,564
	Other assets	151,176				206,758
	Total COPT consolidated assets	$	3,670,257			$	3,629,952

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of differences between taxable income reported on income tax returns and net income as reported on consolidated statements of operations	The differences between taxable income reported on our income tax returns (estimated 2014 and actual 2013 and 2012) and net income as reported on our consolidated statements of operations are set forth below (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
		(Estimated)
	COPLP consolidated net income	$	45,206			$	101,544			$	20,341
	Adjustments:
	Rental revenue recognition	(3,932		)		1,303				(10,794		)
	Compensation expense recognition	1,912				8,987				(2,669		)
	Operating expense recognition	(2,260		)		(1,663		)		1,158
	Gain on sales of properties	(1,404		)		(50,860		)		(74,858		)
	Impairment losses	1,367				32,047				66,910
	Loss on interest rate derivatives	—				—				(29,805		)
	Gains from non-real estate investments	405				—				7,854
	Income from service operations	(391		)		1,650				1,500
	Income tax expense	310				1,978				381
	Depreciation and amortization	41,500				20,834				24,804
	Interest expense	920				2,057				3,978
	Income from unconsolidated entities	(187		)		3,148				(725		)
	COPLP consolidated noncontrolling interests	(3,285		)		(7,837		)		(636		)
	Other	2,346				1,529				(70		)
	COPLP consolidated taxable income	$	82,507			$	114,717			$	7,369
	Noncontrolling interests, other	(3,247		)		(4,061		)		(622		)
	Other	—				—				741
	COPT consolidated taxable income	$	79,260			$	110,656			$	7,488
Schedule of characterization of dividends declared on common and preferred shares	The characterization of dividends declared on COPT’s common and preferred shares during each of the last three years was as follows:
		Common Shares									Preferred Shares
		For the Years Ended December 31,									For the Years Ended December 31,
		2014			2013			2012			2014		2013		2012
	Ordinary income	64.5	%		71.8	%		33.2	%		90.9	%	76.2	%	100	%
	Long-term capital gain	6.5	%		22.4	%		0	%		9.1	%	23.8	%	0	%
	Return of capital	29	%		5.8	%		66.8	%		0	%	0	%	0	%
Components of provision for income tax	Our TRS’ provision for income tax consisted of the following expenses (in thousands):
		For the Years Ended December 31,
		2014				2013				2012
	Deferred
	Federal	$	258			$	1,742			$	312
	State	52				236				69
	Total income tax expense	$	310			$	1,978			$	381
Schedule of reconciliation of Federal statutory rate to effective tax rate	A reconciliation of our TRS’ Federal statutory rate to the effective tax rate for income tax reported on our statements of operations is set forth below:
		For the Years Ended December 31,
		2014			2013			2012
	Income taxes at U.S. statutory rate	34	%		34	%		34	%
	State and local, net of U.S. Federal tax benefit	4.2	%		4.5	%		4.6	%
	Increase in deferred tax asset valuation allowance	0	%		562.9	%		0	%
	Other	(0.4	)%		(1.1	)%		0	%
	Effective tax rate	37.8	%		600.3	%		38.6	%
Schedule of tax effects of temporary differences and carry forwards in net deferred tax assets	The table below sets forth the tax effects of temporary differences and carry forwards included in the net deferred tax asset of our TRS (in thousands):
		December 31,
		2014				2013
	Operating loss forward	$	5,012			$	5,382
	Share-based compensation	976				869
	Accrued payroll	195				221
	Property	(119		)		(105		)
	Valuation allowance	(2,062		)		(2,062		)
	Deferred tax asset, net	$	4,002			$	4,305

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]
Components of discontinued operations	The table below sets forth the components of discontinued operations reported on our consolidated statements of operations (in thousands):
		For the Years Ended December 31,
		2014			2013			2012
	Revenue from real estate operations	$	(14	)	$	37,636		$	58,801
	Property operating expenses	135			(13,505		)	(21,529		)
	Depreciation and amortization	—			(4,505		)	(13,939		)
	Impairment losses	(3		)	(26,190		)	(23,232		)
	General, administrative and leasing expenses	—			(4		)	(3		)
	Business development and land carry costs	—			—			(24		)
	Interest expense	—			(8,221		)	(10,397		)
	Gain on sales of real estate	24			2,671			20,940
	Gain on early extinguishment of debt	(116		)	67,810			1,736
	Discontinued operations	$	26		$	55,692		$	12,353

Earnings_Per_Share_EPS_and_Ear1

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earning 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,
		2014				2013			2012
	Numerator:
	Income from continuing operations	$	34,509			$	36,836		$	7,967
	Gain on sales of real estate, net	10,671				9,016			21
	Preferred share dividends	(15,939		)		(19,971		)	(20,844		)
	Issuance costs associated with redeemed preferred shares	(1,769		)		(2,904		)	(1,827		)
	(Income) loss from continuing operations attributable to noncontrolling interests	(4,955		)		(4,486		)	1,309
	Income from continuing operations attributable to restricted shares	(432		)		(414		)	(469		)
	Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders	$	22,085			$	18,077		$	(13,843	)
	Discontinued operations	26				55,692			12,353
	Discontinued operations attributable to noncontrolling interests	4				(3,351		)	(673		)
	Numerator for basic and diluted EPS on net income (loss)attributable to COPT common shareholders	$	22,115			$	70,418		$	(2,163	)
	Denominator (all weighted averages):
	Denominator for basic EPS (common shares)	88,092				85,167			73,454
	Dilutive effect of share-based compensation awards	171				57			—
	Denominator for basic and diluted EPS (common shares)	88,263				85,224			73,454
	Basic EPS:
	Income (loss) from continuing operations attributable to COPT common shareholders	$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPT common shareholders	—				0.62			0.16
	Net income (loss) attributable to COPT common shareholders	$	0.25			$	0.83		$	(0.03	)
	Diluted EPS:
	Income (loss) from continuing operations attributable to COPT common shareholders	$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPT common shareholders	—				0.62			0.16
	Net income (loss) attributable to COPT common shareholders	$	0.25			$	0.83		$	(0.03	)
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,
		2014			2013			2012
	Conversion of common units	3,897			3,869			4,235
	Conversion of Series I preferred units	176			176			176
	Conversion of Series K preferred shares	434			434			434
Corporate Office Properties, L.P.
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earning per share	Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data):
		For the Years Ended December 31,
		2014				2013			2012
	Numerator:
	Income from continuing operations	$	34,509			$	36,836		$	7,967
	Gain on sales of real estate, net	10,671				9,016			21
	Preferred unit distributions	(16,599		)		(20,631		)	(21,504		)
	Issuance costs associated with redeemed preferred units	(1,769		)		(2,904		)	(1,827		)
	(Income) loss from continuing operations attributable to noncontrolling interests	(3,281		)		(2,977		)	1,206
	Income from continuing operations attributable to restricted units	(432		)		(414		)	(469		)
	Numerator for basic and diluted EPU from continuing operations attributable to COPLP common unitholders	$	23,099			$	18,926		$	(14,606	)
	Discontinued operations	26				55,692			12,353
	Discontinued operations attributable to noncontrolling interests	5				(930		)	(699		)
	Numerator for basic and diluted EPU on net income (loss) attributable to COPLP common unitholders	$	23,130			$	73,688		$	(2,952	)
	Denominator (all weighted averages):
	Denominator for basic EPU (common units)	91,989				89,036			77,689
	Dilutive effect of share-based compensation awards	171				57			—
	Denominator for basic and diluted EPU (common units)	92,160				89,093			77,689
	Basic EPU:
	Income (loss) from continuing operations attributable to COPLP common unitholders	$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPLP common unitholders	—				0.62			0.15
	Net income (loss) attributable to COPLP common unitholders	$	0.25			$	0.83		$	(0.04	)
	Diluted EPU:
	Income (loss) from continuing operations attributable to COPLP common unitholders	$	0.25			$	0.21		$	(0.19	)
	Discontinued operations attributable to COPLP common unitholders	—				0.62			0.15
	Net income (loss) attributable to COPLP common unitholders	$	0.25			$	0.83		$	(0.04	)
Schedule of securities excluded from computation of diluted earnings per share	Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands):
		Weighted Average Units Excluded from Denominator for the Years Ended December 31,
		2014			2013			2012
	Conversion of Series I preferred units	176			176			176
	Conversion of Series K preferred units	434			434			434

Quarterly_Data_Unaudited_Table

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Data [Line Items]
Schedule of selected quarterly information	Certain of the amounts below have been reclassified to conform to the current period presentation of our consolidated financial statements.
		For the Year Ended December 31, 2014
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	146,667		$	139,820		$	153,015		$	146,971
	Operating income	$	25,206		$	31,836		$	37,422		$	37,148
	Income from continuing operations	$	5,660		$	9,248		$	13,727		$	5,874
	Discontinued operations	$	11		$	(198	)	$	191		$	22
	Net income	$	5,671		$	9,050		$	24,548		$	5,937
	Net income attributable to noncontrolling interests	(930		)	(1,160		)	(1,828		)	(1,033		)
	Net income attributable to COPT	4,741			7,890			22,720			4,904
	Preferred share dividends	(4,490		)	(4,344		)	(3,553		)	(3,552		)
	Issuance costs associated with redeemed preferred shares	—			(1,769		)	—			—
	Net income attributable to COPT common shareholders	$	251		$	1,777		$	19,167		$	1,352
	Basic earnings per common share	$	0		$	0.02		$	0.22		$	0.01
	Diluted earnings per common share	$	0		$	0.02		$	0.22		$	0.01
		For the Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	126,219		$	136,527		$	131,812		$	128,802
	Operating income	$	36,165		$	40,229		$	30,673		$	34,843
	Income (loss) from continuing operations	$	11,662		$	(232	)	$	10,974		$	14,432
	Discontinued operations	$	1,261		$	(4,502	)	$	(12,974	)	$	71,907
	Net income (loss)	$	15,277		$	(4,405	)	$	(2,000	)	$	92,672
	Net income attributable to noncontrolling interests	(257		)	(960		)	(964		)	(5,656		)
	Net income (loss) attributable to COPT	15,020			(5,365		)	(2,964		)	87,016
	Preferred share dividends	(6,106		)	(4,885		)	(4,490		)	(4,490		)
	Issuance costs associated with redeemed preferred shares	—			(2,904		)	—			—
	Net income (loss) attributable to COPT common shareholders	$	8,914		$	(13,154	)	$	(7,454	)	$	82,526
	Basic earnings per common share	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
	Diluted earnings per common share	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
Corporate Office Properties, L.P.
Quarterly Data [Line Items]
Schedule of selected quarterly information	The tables below set forth selected quarterly information for the years ended December 31, 2014 and 2013 (in thousands, except per share data).
		For the Year Ended December 31, 2014
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	146,667		$	139,820		$	153,015		$	146,971
	Operating income	$	25,206		$	31,836		$	37,422		$	37,148
	Income from continuing operations	$	5,660		$	9,248		$	13,727		$	5,874
	Discontinued operations	$	11		$	(198	)	$	191		$	22
	Net income	$	5,671		$	9,050		$	24,548		$	5,937
	Net income attributable to noncontrolling interests	(737		)	(837		)	(897		)	(805		)
	Net income attributable to COPLP	4,934			8,213			23,651			5,132
	Preferred unit distributions	(4,655		)	(4,509		)	(3,718		)	(3,717		)
	Issuance costs associated with redeemed preferred units	—			(1,769		)	—			—
	Net income attributable to COPLP common unitholders	$	279		$	1,935		$	19,933		$	1,415
	Basic earnings per common unit	$	0		$	0.02		$	0.22		$	0.01
	Diluted earnings per common unit	$	0		$	0.02		$	0.22		$	0.01
		For the Year Ended December 31, 2013
		First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	Revenues	$	126,219		$	136,527		$	131,812		$	128,802
	Operating income	$	36,165		$	40,229		$	30,673		$	34,843
	Income (loss) from continuing operations	$	11,662		$	(232	)	$	10,974		$	14,432
	Discontinued operations	$	1,261		$	(4,502	)	$	(12,974	)	$	71,907
	Net income (loss)	$	15,277		$	(4,405	)	$	(2,000	)	$	92,672
	Net loss (income) attributable to noncontrolling interests	336			(1,473		)	(1,035		)	(1,735		)
	Net income (loss) attributable to COPLP	15,613			(5,878		)	(3,035		)	90,937
	Preferred unit distributions	(6,271		)	(5,050		)	(4,655		)	(4,655		)
	Issuance costs associated with redeemed preferred units	—			(2,904		)	—			—
	Net income (loss) attributable to COPLP common unitholders	$	9,342		$	(13,832	)	$	(7,690	)	$	86,282
	Basic earnings per common unit	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94
	Diluted earnings per common unit	$	0.11		$	(0.16	)	$	(0.09	)	$	0.94

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum rental payments	Future minimum rental payments due under the terms of these operating leases as of December 31, 2014 follow (in thousands):
	Year Ending December 31,
	2015	$	905
	2016	839
	2017	768
	2018	735
	2019	728
	Thereafter	76,678
		$	80,653

Organization_Details

Organization (Details)	12 Months Ended
	Dec. 31, 2014
	acre
	sqft
Operating office properties
Investments in real estate
Number of real estate properties	173
Square footage of real estate properties (in square feet)	16,800,000
Office properties under, or contractually committed for, construction or approved for redevelopment
Investments in real estate
Number of real estate properties	13
Square footage of real estate properties (in square feet)	1,600,000
Land Controlled for Future Development [Member]
Investments in real estate
Area of land we control (in acres)	1,464
Developable square footage of real estate properties (in square feet)	18,300,000
Partially operational, wholesale data center
Investments in real estate
The expected stabilization critical load after completion of development (in megawatts)	19.25
Debt in Default of Payment Terms
Investments in real estate
Number of real estate properties	2

Organization_Details_2

Organization (Details 2) (Corporate Office Properties, L.P.)	12 Months Ended
	Dec. 31, 2014
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	96.00%
Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	95.50%

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2014
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 for recovery analysis of 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_Account4

Summary of Significant Accounting Policies (Details 1)	12 Months Ended
	Dec. 31, 2014
	Form
Cash and Cash Equivalents
Maximum term until original maturity to classify cash and liquid investments as cash and cash equivalent (in months)	3 months
Share-Based Compensation
Number of forms of share based compensation plans	2
Market concentration premium
Useful Lifes Related To Intangible Assets and Property [Abstract]
Finite-Lived Intangible Asset, Useful Life	40 years
Corporate Office Properties, L.P.
Noncontrolling Interest [Abstract]
Interests in several real estate entities owned directly by COPT	1.00%

Summary_of_Significant_Account5

Summary of Significant Accounting Policies (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Additional paid-in capital	$1,969,968	$1,814,015
Redeemable noncontrolling interest	18,417	17,758
Restatement Adjustment | Misapplication of Fair Value Assumptions
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Additional paid-in capital			-3,700
Redeemable noncontrolling interest			$3,700

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2011
KEYW Holding Corporation
Warrants
Number of warrants owned (in shares)		50,000	50,000
Exercise price of warrants (in dollars per share)		9.25	9.25
Number of shares owned in investee (in shares)				1,900,000
Percentage of common stock owned				7.00%
Amount of sale of owned shares	$14
Revenue earned from investee	$2.40
Redeemable non-controlling interest | Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)
Warrants
Discount rate		15.50%	15.50%

Fair_Value_Measurements_Detail1

Fair Value Measurements (Details 2) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Liabilities:
Interest rate derivatives	$1,855		$3,309
Redeemable noncontrolling interest	18,417		17,758		10,298	8,908
Corporate Office Properties, L.P.
Liabilities:
Interest rate derivatives	1,855		3,309
Fair value measurement on a recurring basis
Assets:
Common stocks			298	[1]
Interest rate derivatives	274	[2]	6,594	[2]
Warrants to purchase common stock in KEYW	164	[2]	301	[2]
Assets	6,320		14,660
Liabilities:
Deferred compensation plan liability	5,882	[3]	7,467	[3]
Interest rate derivatives	1,855		3,309
Liabilities	7,737		10,776
Redeemable noncontrolling interest	18,417		17,758
Fair value measurement on a recurring basis | Mutual funds
Assets:
Marketable securities in deferred compensation plan	5,756	[1]	7,090	[1]
Fair value measurement on a recurring basis | Common Shares
Assets:
Marketable securities in deferred compensation plan			176	[1]
Fair value measurement on a recurring basis | Other
Assets:
Marketable securities in deferred compensation plan	126	[1]	201	[1]
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Common stocks			298	[1]
Assets	5,882		7,765
Liabilities:
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	5,756	[1]	7,090	[1]
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Shares
Assets:
Marketable securities in deferred compensation plan			176	[1]
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	126	[1]	201	[1]
Fair value measurement on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	274	[2]	6,594	[2]
Warrants to purchase common stock in KEYW	164	[2]	301	[2]
Assets	438		6,895
Liabilities:
Deferred compensation plan liability	5,882	[3]	7,467	[3]
Interest rate derivatives	1,855		3,309
Liabilities	7,737		10,776
Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)
Liabilities:
Redeemable noncontrolling interest	18,417		17,758
Fair value measurement on a recurring basis | Corporate Office Properties, L.P.
Assets:
Common stocks			298	[4]
Interest rate derivatives	274	[5]	6,594	[5]
Warrants to purchase common stock in KEYW	164	[5]	301	[5]
Assets	438		7,193
Liabilities:
Interest rate derivatives	1,855		3,309
Redeemable noncontrolling interest	18,417		17,758
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Common stocks			298	[4]
Assets	0		298
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives	274	[5]	6,594	[5]
Warrants to purchase common stock in KEYW	164	[5]	301	[5]
Assets	438		6,895
Liabilities:
Interest rate derivatives	1,855		3,309
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Unobservable Inputs (Level 3)
Assets:
Assets	0		0
Liabilities:
Redeemable noncontrolling interest	$18,417		$17,758
[1]	Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet.
[2]	Included in the line entitled “prepaid expenses and other assets” on COPT’s consolidated balance sheet.
[3]	Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet.
[4]	Included in the line entitled “restricted cash and marketable securities” on COPLP’s consolidated balance sheet.
[5]	Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet.

Fair_Value_Measurements_Detail2

Fair Value Measurements (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair value of impaired properties and other assets
Impairment losses	$1,416,000	$5,857,000	$43,678,000
Exit costs included in impairment losses in connection with dispositions	0	979,000	4,146,000
Fair value measurement on a recurring basis
Fair value of impaired properties and other assets
Assets	6,320,000	14,660,000
Fair value measurement on a nonrecurring basis | Projects in development or held for future development
Fair value of impaired properties and other assets
Impairment losses			1,900,000
Fair value measurement on a nonrecurring basis | Property Conveyances
Fair value of impaired properties and other assets
Impairment losses		11,000,000
Exit costs included in impairment losses in connection with dispositions		560,000
Fair value measurement on a nonrecurring basis | Other Properties with Shortened Holding Periods
Fair value of impaired properties and other assets
Number of properties, shortened holding period		2
Fair value measurement on a nonrecurring basis | Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses			19,000,000
Exit costs included in impairment losses in connection with dispositions		419,000
Fair value measurement on a nonrecurring basis | Properties, Net
Fair value of impaired properties and other assets
Impairment losses		31,068,000
Assets		4,459,000
Fair value measurement on a nonrecurring basis | Additional Property Disposed [Member]
Fair value of impaired properties and other assets
Impairment losses			5,100,000
Fair value measurement on a nonrecurring basis | Significant Unobservable Inputs (Level 3) | Strategic Reallocation Plan
Fair value of impaired properties and other assets
Exit costs included in impairment losses in connection with dispositions			4,200,000
Fair value measurement on a nonrecurring basis | Significant Unobservable Inputs (Level 3) | Properties, Net
Fair value of impaired properties and other assets
Exit costs included in impairment losses in connection with dispositions		979,000
Assets		4,459,000
Fair value measurement on a nonrecurring basis | Discounted Cash Flow
Fair value of impaired properties and other assets
Discount rate		10.00%
Terminal capitalization rate		9.50%
Market rent growth rate		3.00%
Expense growth rate		3.00%
Fair value measurement on a nonrecurring basis | Discounted Cash Flow | Significant Unobservable Inputs (Level 3) | Properties, Net
Fair value of impaired properties and other assets
Assets		4,459,000
Fair value measurement on a nonrecurring basis | Discontinued Operations | Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses		15,200,000	23,200,000
Fair value measurement on a nonrecurring basis | Greater Baltimore | Other Properties with Shortened Holding Periods
Fair value of impaired properties and other assets
Impairment losses	1,371,000	5,900,000
Fair value measurement on a nonrecurring basis | Greater Philadelphia
Fair value of impaired properties and other assets
Impairment losses			46,100,000
Future expenditures for redevelopment			25,000,000
Fair value measurement on a nonrecurring basis | Colorado Springs | Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses			$6,900,000
Redeemable non-controlling interest | Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)
Fair value of impaired properties and other assets
Discount rate	15.50%	15.50%

Concentration_of_Rental_Revenu2

Concentration of Rental Revenue (Details)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Concentration Risk
Number of regions with real estate operations which are not located in the Mid-Atlantic region of the United States	3
Rental revenue | Tenants
Concentration Risk
Percentage required for qualification as major customer	5.00%
Number of tenants from which the entity has recognized the most rental revenue aggregated for revenue concentration disclosure	5
Rental revenue | Tenants | United States Government
Concentration Risk
Percentage of revenue	18.00%		18.00%		18.00%
Rental revenue | Tenants | Northrop Grumman Corporation
Concentration Risk
Percentage of revenue	6.00%	[1]	8.00%	[1]	7.00%	[1]
Rental revenue | Tenants | Booz Allen Hamilton, Inc.
Concentration Risk
Percentage of revenue	6.00%		6.00%		6.00%
Rental revenue | Tenants | Computer Sciences Corporation
Concentration Risk
Percentage of revenue			5.00%	[1]	5.00%	[1]
Rental revenue | Tenants | Five largest tenants
Concentration Risk
Percentage of revenue	39.00%		41.00%		39.00%
Construction contract revenue | United States Government
Concentration Risk
Percentage of revenue	90.00%		90.00%		90.00%
[1]	Includes affiliated organizations and agencies and predecessor companies.

Properties_net_Details

Properties, net (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Properties
Gross	$4,014,336	[1],[2]	$3,811,950	$3,859,960	$4,038,932
Operating properties, net	2,751,488		2,702,693
Operating properties, net
Properties
Less: accumulated depreciation	-703,083		-597,649
Operating properties, net | Land
Properties
Gross	439,355		430,472
Operating properties, net | Buildings and improvements
Properties
Gross	$3,015,216		$2,869,870
[1]	As discussed in Note 3 to our Consolidated Financial Statements, we recognized impairment losses of $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore region that were disposed in the current period.
[2]	The aggregate cost of these assets for Federal income tax purposes was approximately $3.4 billion at December 31, 2014.

Properties_net_Details_2

Properties, net (Details 2) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Properties
Projects in development or held for future development	$545,426	$511,608
Projects in development or held for future development | Land in development or held for future development
Properties
Projects in development or held for future development	214,977	245,676
Projects in development or held for future development | Construction in progress, excluding land
Properties
Projects in development or held for future development	$330,449	$265,932

Properties_net_Details_3

Properties, net (Details 3) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 23, 2013
Dispositions
Gain on early extinguishment of debt	($9,552,000)	($27,030,000)	($943,000)
Non-operating Properties
Dispositions
Gain on Disposition	5,600,000
Sale price of non-operating properties	28,300,000	3,500,000
Secured Debt | December 2013 Portfolio Conveyance
Dispositions
Debt settled through the surrender of real estate assets				146,500,000
Gain on early extinguishment of debt				67,800,000
Secured Debt | Fair value measurement on a nonrecurring basis | December 2013 Portfolio Conveyance
Dispositions
Fair value of real estate disposed in settlement of debt				74,000,000
Operating properties
Dispositions
Number of Buildings Disposed	8	31
Total Rentable Square Feet	302,958	2,345,000
Transaction Value of Operating Property Dispositions	28,835,000	293,301,000
Gain on Disposition	5,093,000	2,671,000
Operating properties | 4969 and 4979 Mercantile Rd
Dispositions
Number of Buildings Disposed	2
Total Rentable Square Feet	96,721
Transaction Value of Operating Property Dispositions	5,960,000
Gain on Disposition	2,124,000
Operating properties | 9930 and 9940 Franklin Square
Dispositions
Number of Buildings Disposed	2
Total Rentable Square Feet	71,992
Transaction Value of Operating Property Dispositions	10,475,000
Gain on Disposition	2,303,000
Operating properties | 5020, 5022, 5024 and 5026 Campbell Boulevard
Dispositions
Number of Buildings Disposed	4
Total Rentable Square Feet	134,245
Transaction Value of Operating Property Dispositions	12,400,000
Gain on Disposition	666,000
Operating properties | 920 Elkridge Landing Road
Dispositions
Number of Buildings Disposed		1
Total Rentable Square Feet		103,000
Transaction Value of Operating Property Dispositions		6,900,000
Gain on Disposition		0
Operating properties | 4230 Forbes Boulevard
Dispositions
Number of Buildings Disposed		1
Total Rentable Square Feet		56,000
Transaction Value of Operating Property Dispositions		5,600,000
Gain on Disposition		1,507,000
Operating properties | December 2013 Colorado Springs Portfolio Disposition
Dispositions
Number of Buildings Disposed		15
Total Rentable Square Feet		1,165,000
Transaction Value of Operating Property Dispositions		133,925,000
Gain on Disposition		1,164,000
Operating properties | December 2013 Portfolio Conveyance
Dispositions
Number of Buildings Disposed		14
Total Rentable Square Feet		1,021,000
Transaction Value of Operating Property Dispositions		146,876,000
Gain on Disposition		$0

Properties_net_Details_4

Properties, net (Details 4) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	sqft	Property
	Property	sqft
Newly-constructed properties placed in service
Construction and Redevelopment Activities
Square Feet of Properties Placed in Service	692,000	812,000
Number of Real Estate Properties Placed In Service	5	8
Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties	8
Square footage of real estate properties (in square feet)	1,200,000
Properties under construction or contractually committed for construction | Northern Virginia
Construction and Redevelopment Activities
Number of real estate properties	4
Properties under construction or contractually committed for construction | Baltimore and Washington Corridor
Construction and Redevelopment Activities
Number of real estate properties	2
Properties under construction or contractually committed for construction | Huntsville
Construction and Redevelopment Activities
Number of real estate properties	1
Properties under construction or contractually committed for construction | San Antonio
Construction and Redevelopment Activities
Number of real estate properties	1
Properties under redevelopment
Construction and Redevelopment Activities
Number of real estate properties	5
Square footage of real estate properties (in square feet)	344,000
Properties under redevelopment | Baltimore and Washington Corridor
Construction and Redevelopment Activities
Number of real estate properties	3
Properties under redevelopment | Greater Philadelphia
Construction and Redevelopment Activities
Number of real estate properties	1
Properties under redevelopment | St Marys County
Construction and Redevelopment Activities
Number of real estate properties	1
Greater Philadelphia
Construction and Redevelopment Activities
Depreciation Expense Resulting From Useful Life Change	12.9

Real_Estate_Joint_Ventures_Det

Real Estate Joint Ventures (Details) (USD $)	12 Months Ended		0 Months Ended		12 Months Ended		0 Months Ended
	Dec. 31, 2014		Sep. 17, 2013	Dec. 11, 2013	Dec. 31, 2013	Dec. 31, 2012	Aug. 07, 2014
	buillding					Property
	sqft
Investments in consolidated real estate joint ventures
Investing receivables	$52,147,000				$53,663,000
LW Redstone Company, LLC
Investments in consolidated real estate joint ventures
Number of buildings operated by the joint venture	4
Partner's capital account upon formation	9,000,000
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)	4,400,000
Construction Commencement Threshold, Completed	561,000
LW Redstone Company, LLC | Maximum
Investments in consolidated real estate joint ventures
Infrastructure costs anticipated to be funded by entity for reimbursement by the City of Huntsville (in dollars)	76,000,000
M Square Associates, LLC
Investments in consolidated real estate joint ventures
Number of buildings operated by the joint venture	2
Percentage of residual amounts distributed to each member	50.00%
Consolidated real estate joint ventures
Investments in consolidated real estate joint ventures
Total Assets	202,948,000	[1]
Encumbered Assets	115,476,000	[1]
Total Liabilities	80,736,000	[1]
Arundel Preserve 5, LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)			50.00%
Arundel Preserve 5, LLC | Common Shares
Investments in consolidated real estate joint ventures
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in units)			221,501
Acquisition of property and noncontrolling interest in other consolidated entity for COPLP common units (in dollars)			5,200,000
MOR Forbes 2 LLC
Investments in consolidated real estate joint ventures
Ownership (as a percent)				50.00%
Unconsolidated real estate joint ventures
Investments in consolidated real estate joint ventures
Ownership (as a percent)						20.00%
Number of buildings operated by the joint venture						16
Investment balance						-6,400,000
Difference between carrying amount of investment and share of the equity in the joint venture						4,500,000
Gain on disposal					6,300,000
Condensed statements of operations for unconsolidated real estate joint venture
Revenues					6,519,000	7,316,000
Property operating expenses					-2,818,000	-2,829,000
Interest expense					-10,463,000	-7,672,000
Depreciation and amortization expense					-2,067,000	-2,283,000
Gain on early extinguishment of debt					23,013,000	0
Net income (loss)					14,184,000	-5,468,000
Unconsolidated real estate joint ventures | Nonrecourse loan guarantees of unconsolidated partnership | Nonrecourse mezzanine loan
Investments in consolidated real estate joint ventures
Nonrecourse mezzanine debt balance, equity method joint venture	5,600,000
LW Redstone Company, LLC | Variable Interest Entity, Primary Beneficiary
Investments in consolidated real estate joint ventures
Ownership (as a percent)	85.00%
Total Assets	143,534,000	[1],[2]
Encumbered Assets	66,620,000	[1],[2]
Total Liabilities	41,659,000	[1],[2]
M Square Associates, LLC | Variable Interest Entity, Primary Beneficiary
Investments in consolidated real estate joint ventures
Ownership (as a percent)	50.00%
Total Assets	59,414,000	[1],[3]
Encumbered Assets	48,856,000	[1],[3]
Total Liabilities	39,077,000	[1],[3]
COPT-FD Indian Head, LLC | Variable Interest Entity, Primary Beneficiary
Investments in consolidated real estate joint ventures
Proceeds from real estate and real estate joint ventures							6,400,000
Notes receivable from City of Huntsville
Investments in consolidated real estate joint ventures
Investing receivables	$49,147,000				$44,055,000
[1]	Excludes amounts eliminated in consolidation.
[2]	This joint venture’s property is in Huntsville, Alabama.
[3]	This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).

Intangible_Assets_on_Real_Esta2

Intangible Assets on Real Estate Acquisitions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Intangible assets on real estate acquisitions
Gross Carrying Amount	$188,467,000	$192,592,000
Accumulated Amortization	144,613,000	133,334,000
Net Carrying Amount	43,854,000	59,258,000
Amortization of the intangible assets	15,200,000	16,200,000	21,400,000
Weighted average amortization period of intangible assets	10 years
Estimated future amortization expense associated with the intangible asset categories for the next five years
2015	9,300,000
2016	8,400,000
2017	6,200,000
2018	3,800,000
2019	3,400,000
In-place lease value
Intangible assets on real estate acquisitions
Gross Carrying Amount	123,759,000	125,504,000
Accumulated Amortization	101,040,000	93,885,000
Net Carrying Amount	22,719,000	31,619,000
Weighted average amortization period of intangible assets	6 years
Tenant relationship value
Intangible assets on real estate acquisitions
Gross Carrying Amount	42,301,000	44,414,000
Accumulated Amortization	28,492,000	25,962,000
Net Carrying Amount	13,809,000	18,452,000
Weighted average amortization period of intangible assets	7 years
Below-market cost arrangements
Intangible assets on real estate acquisitions
Gross Carrying Amount	12,415,000	12,416,000
Accumulated Amortization	5,984,000	5,136,000
Net Carrying Amount	6,431,000	7,280,000
Weighted average amortization period of intangible assets	31 years
Above-market leases
Intangible assets on real estate acquisitions
Gross Carrying Amount	8,659,000	8,925,000
Accumulated Amortization	8,159,000	7,970,000
Net Carrying Amount	500,000	955,000
Weighted average amortization period of intangible assets	2 years
Market concentration premium
Intangible assets on real estate acquisitions
Gross Carrying Amount	1,333,000	1,333,000
Accumulated Amortization	938,000	381,000
Net Carrying Amount	$395,000	$952,000
Weighted average amortization period of intangible assets	28 years

Deferred_Leasing_and_Financing2

Deferred Leasing and Financing Costs (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred Leasing and Financing Costs [Abstract]
Deferred leasing costs	$123,925	$110,711
Deferred financing costs	31,229	36,390
Accumulated amortization	-90,357	-80,834
Deferred leasing and financing costs, net	$64,797	$66,267

Investing_Receivables_Details

Investing Receivables (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	52,147	$53,663
Notes receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	49,147	44,055
Notes receivable from City of Huntsville | LW Redstone Company, LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Stated interest rate (as a percent)	9.95%
Debt instrument, term	30 years
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	3,000	$9,608

Prepaid_Expenses_and_Other_Ass2

Prepaid Expenses and Other Assets (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Prepaid Expense and Other Assets [Abstract]
Prepaid expenses	$20,570		$19,308
Lease incentives	13,344		8,435
Construction contract costs incurred in excess of billings	6,656		2,462
Furniture, fixtures and equipment, net	6,637		6,556
Deferred tax asset, net	4,002	[1]	4,305	[1]
Operating notes receivable	3,797		1,692
Other equity method investments	2,368		2,258
Interest rate derivatives	274		6,594
Other assets	2,601		2,576
Prepaid expenses and other assets	60,249		54,186
Operating notes receivable
Mortgage and Other Investing Receivables [Line Items]
Operating notes receivables due from tenants with terms exceeding one year	3,600		1,700
Operating Notes Receivable Long-Term, Allowance for Estimated Losses	$252		$87
[1]	See Note 19 for further disclosure.

Debt_Details

Debt (Details) (USD $)	12 Months Ended				1 Months Ended		0 Months Ended			12 Months Ended	0 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014		Sep. 01, 2011	Feb. 14, 2012	Aug. 03, 2012	Dec. 31, 2010	6-May-13	Sep. 16, 2013	14-May-14	Apr. 30, 2014
Debt
Debt, net	$1,920,057,000		$1,927,703,000		$1,920,057,000
Loss on early extinguishment of debt	9,552,000		27,030,000	943,000
Principal amount of debt	1,929,810,000	[1]			1,929,810,000	[1]
Interest expense associated with amortization of discount	921,000		1,159,000	3,155,000
Secured Loans Due November 2015 and January 2016
Debt
Loss on early extinguishment of debt					9,100,000
Secured Loan Due January 2016
Debt
Stated interest rate (as a percent)	5.56%				5.56%
Amount of loans repaid upon entry into Revolving Credit Facility and Term Loan Agreement					108,500,000
Secured Loan Due November 2015
Debt
Stated interest rate (as a percent)	5.53%				5.53%
Amount of loans repaid upon entry into Revolving Credit Facility and Term Loan Agreement					103,000,000
Mortgage and Other Secured Loans:
Debt
Debt, net	424,016,000		712,751,000		424,016,000
Fixed rate mortgage loans
Debt
Debt, net	387,139,000		675,060,000		387,139,000
Stated Interest Rates, low end of range (as a percent)	3.96%	[2]
Stated Interest Rates, high end of range (as a percent)	10.65%	[2]
Unamortized premium included in carrying value	42,000		69,000		42,000
Weighted average interest rate (as a percent)	8.10%				8.10%
Weighted average interest rate excluding incremental rate	6.16%				6.16%
Variable rate secured loans
Debt
Debt, net	36,877,000		37,691,000		36,877,000
Stated interest rate (as a percent)	2.41%				2.41%
Description of variable rate basis	LIBOR	[3]
Variable rate, spread (as a percent)	2.25%	[3]
Revolving Credit Facility
Debt
Debt, net	83,000,000		0		83,000,000
Description of variable rate basis	LIBOR
Term Credit Facility Effective September 2011
Debt
Additional borrowing capacity available provided there is no default under the agreement							100,000,000
Extension option period (in years)							1 year
Initial amount borrowed							400,000,000
Extension fee as a percentage of total availability of the facility							0.15%
Repayments of Debt	100,000,000		150,000,000
Term Credit Facility Effective February 2012
Debt
Extension option period (in years)								1 year
Initial amount borrowed								250,000,000
Extension fee as a percentage of total availability of the facility								0.15%
Term Credit Facility Effective August 2012
Debt
Additional borrowing capacity available provided there is no default under the agreement									80,000,000
Initial amount borrowed									120,000,000
Term Loan Facilities
Debt
Debt, net	520,000,000		620,000,000		520,000,000
Description of variable rate basis	LIBOR	[4]
Weighted average interest rate (as a percent)	1.80%				1.80%
Additional borrowing capacity available provided there is no default under the agreement	180,000,000				180,000,000
4.25% Exchangeable Senior Notes
Debt
Debt, net	572,000		563,000		572,000
Stated interest rate (as a percent)	4.25%				4.25%					4.25%
Interest rate on debt (as a percent)	6.05%				6.05%
Unamortized discount included in carrying value	3,000		12,000		3,000
Initial amount borrowed										240,000,000
Exchange rate per $1000 principal amount (in common shares)	20.8513
Convertible debt principal amount, basis for exchange	1,000				1,000
Exchange price per common share based on exchange rate (in dollars per share)	$47.96				$47.96
Percentage over the entity's common stock price at the time of issuance which was used to determine the initial exchange rate	20.00%
Repurchase of notes, percentage of principal paid	100.00%				100.00%
Amount of loans repaid upon entry into Revolving Credit Facility and Term Loan Agreement			239,400,000
Loss on early extinguishment of debt			25,900,000
Principal amount of debt	575,000		575,000		575,000
Interest expense at stated interest rate	24,000		4,208,000	10,200,000
Interest expense associated with amortization of discount	10,000		1,615,000	3,651,000
Total interest expenses	34,000		5,823,000	13,851,000
Unsecured notes payable
Debt
Debt, net	1,607,000		1,700,000		1,607,000
Stated interest rate (as a percent)	0.00%				0.00%
Unamortized discount included in carrying value	654,000		761,000		654,000
Debt in Default of Payment Terms
Debt
Number of real estate properties	2				2
Senior Notes
Debt
Redemption percentage within three months of maturity	100.00%
Senior Notes | 3.60% Senior Notes
Debt
Debt, net	347,496,000		347,244,000		347,496,000
Stated interest rate (as a percent)	3.60%				3.60%						3.60%
Interest rate on debt (as a percent)	3.70%				3.70%
Unamortized discount included in carrying value	2,500,000		2,800,000		2,500,000
Initial amount borrowed											347,100,000
Loan amount											350,000,000
Debt issuance as a percentage of principal amount											99.82%
Senior Notes | 5.250% Senior Notes
Debt
Debt, net	245,797,000		245,445,000		245,797,000
Stated interest rate (as a percent)	5.25%				5.25%							5.25%
Interest rate on debt (as a percent)	5.49%				5.49%
Unamortized discount included in carrying value	4,200,000		4,600,000		4,200,000
Initial amount borrowed												245,300,000
Loan amount												250,000,000
Debt issuance as a percentage of principal amount												98.78%
Senior Notes | 3.70% Senior Notes
Debt
Debt, net	297,569,000		0		297,569,000
Stated interest rate (as a percent)													3.70%
Interest rate on debt (as a percent)	3.85%				3.85%
Unamortized discount included in carrying value	2,400,000				2,400,000
Initial amount borrowed													297,300,000
Loan amount													300,000,000
Debt issuance as a percentage of principal amount													99.74%
London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective September 2011
Debt
Description of variable rate basis	LIBOR
London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective February 2012
Debt
Description of variable rate basis	LIBOR
London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective August 2012
Debt
Description of variable rate basis	LIBOR
Adjusted Treasury | Senior Notes | 3.60% Senior Notes
Debt
Basis points used in determining redemption price prior to maturity	30.00%				30.00%
Adjusted Treasury | Senior Notes | 5.250% Senior Notes
Debt
Basis points used in determining redemption price prior to maturity	40.00%				40.00%
Adjusted Treasury | Senior Notes | 3.70% Senior Notes
Debt
Basis points used in determining redemption price prior to maturity	25.00%				25.00%
Revolving Credit Facility | Revolving Credit Facility
Debt
Maximum Availability	800,000,000				800,000,000
Weighted average interest rate (as a percent)	1.47%		1.74%		1.47%
Expansion right, maximum borrowing capacity	1,300,000,000				1,300,000,000
Amount available as a percentage of unencumbered Asset value	60.00%
Extension option period (in years)	1 year
Line of credit facility, extension fee percentage	0.15%
Remaining borrowing capacity	702,200,000				702,200,000
Weighted average borrowings	15,900,000		55,500,000
Minimum | Revolving Credit Facility
Debt
Variable rate, spread (as a percent)	0.98%
Minimum | Term Loan Facilities
Debt
Variable rate, spread (as a percent)	1.10%	[4]
Minimum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective September 2011
Debt
Variable rate, spread (as a percent)	1.10%
Minimum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective February 2012
Debt
Variable rate, spread (as a percent)	1.10%
Minimum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective August 2012
Debt
Variable rate, spread (as a percent)	2.10%
Minimum | Revolving Credit Facility | Revolving Credit Facility
Debt
Commitment fee percentage	0.13%
Minimum | Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt
Variable rate, spread (as a percent)	0.98%
Maximum | Fixed rate mortgage loans
Debt
Stated interest rate excluding incremental rate on default rate	7.87%				7.87%
Maximum | Revolving Credit Facility
Debt
Variable rate, spread (as a percent)	1.75%
Maximum | Term Loan Facilities
Debt
Variable rate, spread (as a percent)	2.60%	[4]
Maximum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective September 2011
Debt
Variable rate, spread (as a percent)	2.00%
Maximum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective February 2012
Debt
Variable rate, spread (as a percent)	2.00%
Maximum | London Interbank Offered Rate (LIBOR) | Term Credit Facility Effective August 2012
Debt
Variable rate, spread (as a percent)	2.60%
Maximum | Revolving Credit Facility | Revolving Credit Facility
Debt
Commitment fee percentage	0.35%
Maximum | Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility
Debt
Variable rate, spread (as a percent)	1.75%
Wholly Owned Subsidiary
Debt
Debt, net	$150,000,000				$150,000,000									$150,000,000
Wholly Owned Subsidiary | Debt in Default of Payment Terms
Debt
Stated interest rate (as a percent)														10.65%
Northern Virginia | Wholly Owned Subsidiary | Debt in Default of Payment Terms
Debt
Number of real estate properties														2
[1]	Represents scheduled principal amortization and maturities only and therefore excludes net discounts of $9.8 million.
[2]	The interest rate on the loan outstanding was 2.41% as of December 31, 2014.
[3]	Refer to the paragraphs below for further disclosure.
[4]	These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying value of these notes reflects an unamortized discount totaling $654,000 as of December 31, 2014 and $761,000 as of December 31, 2013.

Debt_Details_2

Debt (Details 2) (USD $)	0 Months Ended	12 Months Ended
	Sep. 01, 2011	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2014
	period	period
Schedule on basis of which debt matures
2015		$343,545,000	[1]
2016		171,399,000
2017		339,247,000	[2]
2018		2,036,000
2019		122,094,000
Thereafter		951,489,000
Total		1,929,810,000	[3]
Debt Instrument [Line Items]
Debt maturing in 2015 that may be extended for two one year periods		150,000,000
Number of extension option periods for year one long-term debt maturities repayments of principal	2	2
Extension option period for portion of debt maturing in 2015 (in years)		1 year
Debt maturing in 2017 that may be extended for a one year period		333,000,000
Extension option period for portion of debt maturing in 2017 (in years)		1 year
Net discounts		9,800,000
Capitalized interest costs		6,100,000		8,800,000	13,900,000
Wholly Owned Subsidiary
Debt Instrument [Line Items]
Debt, net		$150,000,000				$150,000,000
[1]	Includes $150.0 million pertaining to a nonrecourse mortgage loan on which we defaulted on the payment terms as discussed further below. Also includes $150.0 million that may be extended for two one-year periods at our option, subject to certain conditions.
[2]	Includes $333.0 million that may be extended for one year at our option, subject to certain conditions.
[3]	Represents scheduled principal amortization and maturities only and therefore excludes net discounts of $9.8 million.

Debt_Details_3

Debt (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Carrying amount and estimated fair value of debt
Debt, net	$1,920,057	$1,927,703
Senior Notes
Carrying amount and estimated fair value of debt
Debt, net	890,900
4.25% Exchangeable Senior Notes
Carrying amount and estimated fair value of debt
Debt, net	572	563
Carrying Amount
Carrying amount and estimated fair value of debt
Variable-rate debt	639,877	657,691
Debt, net	1,920,057	1,927,703
Carrying Amount | Senior Notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	890,862	592,689
Carrying Amount | 4.25% Exchangeable Senior Notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	572	563
Carrying Amount | Fixed-rate debt excluding other fixed rate debt not separately disclosed
Carrying amount and estimated fair value of debt
Fixed-rate debt	388,746	676,760
Total Estimated Fair Value
Carrying amount and estimated fair value of debt
Variable-rate debt	642,091	657,527
Debt, net	1,900,067	1,884,473
Total Estimated Fair Value | Senior Notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	901,599	575,374
Total Estimated Fair Value | 4.25% Exchangeable Senior Notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	575	575
Total Estimated Fair Value | Fixed-rate debt excluding other fixed rate debt not separately disclosed
Carrying amount and estimated fair value of debt
Fixed-rate debt	$355,802	$650,997

Interest_Rate_Derivatives_Deta

Interest Rate Derivatives (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair value of interest rate derivatives and balance sheet classification
Interest rate derivatives	$274,000	$6,594,000
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Unrealized (losses) gains on interest rate derivatives	-7,799,000	6,791,000	-7,676,000
Interest expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	2,990,000	2,740,000	3,697,000
Loss on early extinguishment of debt
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	38,000	0	0
Corporate Office Properties, L.P.
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Unrealized (losses) gains on interest rate derivatives	-7,799,000	6,791,000	-7,676,000
Corporate Office Properties, L.P. | Interest expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	2,990,000	2,740,000	3,697,000
Corporate Office Properties, L.P. | Loss on early extinguishment of debt
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	38,000	0	0
Interest rate swaps
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Unrealized (losses) gains on interest rate derivatives	-7,799,000	6,791,000	-7,676,000
Approximate amount of losses to be reclassified from AOCL to interest expense over the next 12 months	2,900,000
Interest rate derivatives in liability position, fair value	1,900,000
Termination value to settle obligations under interest rate derivative agreements	2,100,000
Interest rate swaps | Interest expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	2,990,000	2,740,000	3,697,000
Interest rate swaps | Loss on early extinguishment of debt
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Losses on interest rate derivatives	38,000	0	0
Interest rate swaps | Prepaid expenses and other assets
Fair value of interest rate derivatives and balance sheet classification
Interest rate derivatives	274,000	6,594,000
Interest rate swaps | Interest rate derivative [Member]
Fair value of interest rate derivatives and balance sheet classification
Fair value of Interest rate swaps classified as interest rate derivatives	-1,855,000	-3,309,000
Designated
Fair values of interest rate swap derivatives
Fair value of interest rate swaps	-1,581,000	3,285,000
Designated | Interest rate swap, effective date January 3, 2012, swap three
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.83%
Fair value of interest rate swaps	-407,000	-861,000
Designated | Interest rate swap, effective date January 3, 2012, swap four
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.83%
Fair value of interest rate swaps	-407,000	-861,000
Designated | Interest rate swap, effective date November 2, 2010
Fair values of interest rate swap derivatives
Notional Amount	36,877,000
Fixed Rate (as a percent)	3.83%
Fair value of interest rate swaps	-400,000	-832,000
Notional amount of interest rate derivatives after scheduled amortization	36,200,000
Designated | Interest rate swap, effective date November 2, 2010 | London Interbank Offered Rate (LIBOR)
Fair values of interest rate swap derivatives
Derivative, Basis Spread on Variable Rate	2.25%
Designated | Interest rate swap, effective date September 2, 2014, swap one
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.81%
Fair value of interest rate swaps	-317,000	-94,000
Designated | Interest rate swap, effective date September 2, 2014, swap two
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.81%
Fair value of interest rate swaps	-324,000	-105,000
Designated | Interest rate swap, effective date September 1, 2015, swap one
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	1.67%
Fair value of interest rate swaps	239,000	3,377,000
Designated | Interest rate swap, effective date September 1, 2015, swap two
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	1.73%
Fair value of interest rate swaps	35,000	3,217,000
Designated | Interest rate swap, effective date January 3, 2012, swap one
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.61%
Fair value of interest rate swaps	0	-279,000
Designated | Interest rate swap, effective date January 3, 2012, swap two
Fair values of interest rate swap derivatives
Notional Amount	100,000,000
Fixed Rate (as a percent)	0.61%
Fair value of interest rate swaps	$0	($277,000)

Redeemable_Noncontrolling_Inte2

Redeemable Noncontrolling Interest (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Redeemable Noncontrolling Interest [Roll Forward]
Redeemable noncontrolling interest, Beginning balance	$17,758	$10,298	$8,908
Distribution to noncontrolling interest	-1,369	-1,037	0
Net income (loss) attributable to noncontrolling interest	2,162	1,376	-2,565
Adjustment to arrive at fair value of redeemable noncontrolling interest	-134	7,121	3,955
Redeemable noncontrolling interest, Ending balance	$18,417	$17,758	$10,298

Equity_COPT_and_Subsidiaries_D

Equity - COPT and Subsidiaries (Details) (USD $)	1 Months Ended			12 Months Ended			0 Months Ended
	Nov. 30, 2014	Mar. 31, 2013	Oct. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 16, 2013	Jun. 16, 2014	Apr. 22, 2013
Preferred Stock
Number of shares issued				7,431,667
Aggregate liquidation preference				$199,083,000	$249,083,000
Stock redeemed or called during period value				50,000,000	84,750,000	55,000,000
Common Shares
Shares issued to the public	5,520,000	4,485,000
Per share value of common and preferred shares issued to the public (in dollars per share)	$27.30	$26.34
Net proceeds from issue of shares after underwriter discounts but before offering expenses	148,900,000	118,100,000		148,666,000	117,961,000
At-market-stock, offering program established, aggregate value			150,000,000
Number of common shares for each converted common unit (in shares)				1
Number of operating partnerships units converted into common shares (in units)				140,149	311,343	234,246
Dividends declared per common share				$1.10	$1.10	$1.10
Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public					1,500,000		1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses							38,500,000
Issuance of stock, weighted average price per share							$26.05
Payments of stock issuance costs							586,000
At-market stock, offering program established, remaining capacity				110,900,000
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
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses						165,652,000
Series H
Preferred Stock
Annual dividend yield								7.50%
Preferred stock, redemption price per share								$25
Stock redeemed or called during period value								50,000,000
Issuance costs associated with redeemed preferred shares								1,800,000
Series K
Preferred Stock
Number of shares issued				531,667
Aggregate liquidation preference				26,583,000
Annual dividend yield				5.60%
Annual dividend per share (in dollars per share)				$2.80
Number of common shares to be issued on conversion of each preferred share				0.8163
Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued				6,900,000
Aggregate liquidation preference				172,500,000
Annual dividend yield				7.38%
Annual dividend per share (in dollars per share)				$1.84
Series J
Preferred Stock
Annual dividend yield									7.63%
Preferred stock, redemption price per share									$25
Stock redeemed or called during period value									84,800,000
Issuance costs associated with redeemed preferred shares									2,900,000
Corporate Office Properties, L.P.
Preferred Stock
Number of shares issued				7,431,667
Aggregate liquidation preference				199,083,000
Stock redeemed or called during period value				50,000,000	84,750,000	55,000,000
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses				148,666,000	117,961,000
Number of common shares for each converted common unit (in shares)				1
Number of operating partnerships units converted into common shares (in units)				140,149	311,343
Dividends declared per common share				$1.10	$1.10	$1.10
Corporate Office Properties, L.P. | Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public							1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses							38,500,000
Issuance of stock, weighted average price per share							$26.05
Payments of stock issuance costs							586,000
Corporate Office Properties, L.P. | Preferred Shares
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses						165,652,000
Corporate Office Properties, L.P. | Series H
Preferred Stock
Annual dividend yield								7.50%
Preferred stock, redemption price per share								$25
Stock redeemed or called during period value								50,000,000
Issuance costs associated with redeemed preferred shares								1,800,000
Corporate Office Properties, L.P. | Series K
Preferred Stock
Number of shares issued				531,667
Aggregate liquidation preference				26,583,000
Annual dividend yield				5.60%
Annual dividend per share (in dollars per share)				$2.80
Number of common shares to be issued on conversion of each preferred share				0.8163
Corporate Office Properties, L.P. | Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued				6,900,000
Aggregate liquidation preference				172,500,000
Annual dividend yield				7.38%
Annual dividend per share (in dollars per share)				$1.84
Corporate Office Properties, L.P. | Series J
Preferred Stock
Annual dividend yield									7.63%
Preferred stock, redemption price per share									$25
Stock redeemed or called during period value									84,800,000
Issuance costs associated with redeemed preferred shares									$2,900,000

Equity_COPLP_and_Subsidiaries_1

Equity - COPLP and Subsidiaries (Details) (USD $)	1 Months Ended		12 Months Ended			0 Months Ended
	Nov. 30, 2014	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 16, 2013	Jun. 16, 2014	Apr. 22, 2013
Preferred Stock
Number of shares issued			7,431,667
Aggregate liquidation preference			$199,083,000	$249,083,000
Stock redeemed or called during period value			50,000,000	84,750,000	55,000,000
Common Shares
Shares issued to the public	5,520,000	4,485,000
Per share value of common and preferred shares issued to the public (in dollars per share)	$27.30	$26.34
Net proceeds from issue of shares after underwriter discounts but before offering expenses	148,900,000	118,100,000	148,666,000	117,961,000
Number of common shares for each converted common unit (in shares)			1
Number of operating partnerships units converted into common shares (in units)			140,149	311,343	234,246
Dividends declared per common share			$1.10	$1.10	$1.10
Preferred units in COPLP			8,800,000	8,800,000
Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public				1,500,000		1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses						38,500,000
Issuance of stock, weighted average price per share						$26.05
Payments of stock issuance costs						586,000
Preferred Shares
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses					165,652,000
Series H
Preferred Stock
Annual dividend yield							7.50%
Preferred stock, redemption price per share							$25
Stock redeemed or called during period value							50,000,000
Issuance costs associated with redeemed preferred shares							1,800,000
Series K
Preferred Stock
Number of shares issued			531,667
Aggregate liquidation preference			26,583,000
Annual dividend yield			5.60%
Annual dividend per share (in dollars per share)			$2.80
Number of common shares to be issued on conversion of each preferred share			0.8163
Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued			6,900,000
Aggregate liquidation preference			172,500,000
Annual dividend yield			7.38%
Annual dividend per share (in dollars per share)			$1.84
Series J
Preferred Stock
Annual dividend yield								7.63%
Preferred stock, redemption price per share								$25
Stock redeemed or called during period value								84,800,000
Issuance costs associated with redeemed preferred shares								2,900,000
Common Shares
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses					204,696,000
Corporate Office Properties, L.P.
Preferred Stock
Number of shares issued			7,431,667
Aggregate liquidation preference			199,083,000
Stock redeemed or called during period value			50,000,000	84,750,000	55,000,000
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses			148,666,000	117,961,000
Number of common shares for each converted common unit (in shares)			1
Number of operating partnerships units converted into common shares (in units)			140,149	311,343
Dividends declared per common share			$1.10	$1.10	$1.10
Corporate Office Properties, L.P. | Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public						1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses						38,500,000
Issuance of stock, weighted average price per share						$26.05
Payments of stock issuance costs						586,000
Corporate Office Properties, L.P. | Common Units
Common Shares
Percentage ownership in operating partnership			96.00%	95.60%
Corporate Office Properties, L.P. | Conversion of Series I preferred units
Preferred Stock
Annual dividend yield			7.50%
Annual cumulative preferred return increment frequency			5 years
Common Shares
Limited partners' capital account, units issued			352,000
Preferred units in COPLP			8,800,000
Preferred stock, liquidation preference per share			$25
Common units conversion basis units issuable			0.5
Corporate Office Properties, L.P. | Preferred Shares
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses					165,652,000
Corporate Office Properties, L.P. | Series H
Preferred Stock
Annual dividend yield							7.50%
Preferred stock, redemption price per share							$25
Stock redeemed or called during period value							50,000,000
Issuance costs associated with redeemed preferred shares							1,800,000
Corporate Office Properties, L.P. | Series K
Preferred Stock
Number of shares issued			531,667
Aggregate liquidation preference			26,583,000
Annual dividend yield			5.60%
Annual dividend per share (in dollars per share)			$2.80
Number of common shares to be issued on conversion of each preferred share			0.8163
Corporate Office Properties, L.P. | Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued			6,900,000
Aggregate liquidation preference			172,500,000
Annual dividend yield			7.38%
Annual dividend per share (in dollars per share)			$1.84
Corporate Office Properties, L.P. | Series J
Preferred Stock
Annual dividend yield								7.63%
Preferred stock, redemption price per share								$25
Stock redeemed or called during period value								84,800,000
Issuance costs associated with redeemed preferred shares								2,900,000
Corporate Office Properties, L.P. | Common Shares
Common Shares
Shares issued to the public	5,520,000	4,485,000
Per share value of common and preferred shares issued to the public (in dollars per share)	$27.30	$26.34
Net proceeds from issue of shares after underwriter discounts but before offering expenses	$148,900,000	$118,100,000			$204,696,000

ShareBased_Compensation_and_Ot2

Share-Based Compensation and Other Compensation Matters (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 03, 2011	Mar. 02, 2012	Mar. 01, 2013	Mar. 06, 2014	31-May-10
Stock Options
Share-Based Compensation
Expiration period	10 years
Restricted shares
Shares
Unvested at the beginning of the period (in shares)	377,448	434,643	648,378
Stock awards granted (in shares or units)	216,607	193,833	177,662
Forfeited (in shares)	-21,335	-9,541	-17,019
Vested (in shares)	182,213	241,487	374,378
Unvested at the end of the period (in shares)	390,507	377,448	434,643
Restricted shares expected to vest (in shares)	375,686
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)	26.96	$29.67	$33.13
Grant date fair value (in dollars per share)	26.73	$25.91	$23.64
Forfeited (in dollars per share)	25.1	$27.59	$31.43
Vested (in dollars per share)	28.56	$30.97	$32.72
Unvested at the end of the period (in dollars per share)	26.19	$26.96	$29.67
Restricted shares expected to vest (in dollars per share)	26.18
Other Share-based Compensation Additional Disclosures
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed	4,900,000	$6,300,000	$9,000,000
Performance share units
Weighted Average Grant Date Fair Value
Grant date fair value (in dollars per share)	35.09	$26.84	$32.77
Potential earned PSUs payout for defined levels of performance under awards
Earned PSUs payout (as a percent of PSUs granted) on 75th or greater percentile rank	200.00%
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank	100.00%
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank	50.00%
Performance share units granted on percentile rank below 25th (as a percent)	0.00%
Performance period of the award	3 years
Assumptions used to value stock awards
Baseline value per common share (in dollars per share)	26.52	$25.85	$24.39
Expected volatility of common shares (as a percent)	28.60%	29.50%	43.20%
Risk-free interest rate (as a percent)	0.66%	0.33%	0.41%
Performance share units | 2011 PSU Grants
Shares
Stock awards granted (in shares or units)				56,883
Unvested at the end of the period (in shares)	0
Other Share-based Compensation Additional Disclosures
Aggregate grant date fair value				2,796,000
Performance share units | 2012 PSU Grants
Shares
Stock awards granted (in shares or units)					54,070
Unvested at the end of the period (in shares)	54,070
Other Share-based Compensation Additional Disclosures
Aggregate grant date fair value					1,772,000
Potential earned PSUs payout for defined levels of performance under awards
Shares issued for PSU Awards Vested in Period (in shares)	40,000
Performance share units | 2013 PSU Grants
Shares
Stock awards granted (in shares or units)						69,579
Unvested at the end of the period (in shares)	69,579
Other Share-based Compensation Additional Disclosures
Aggregate grant date fair value						1,867,000
Performance share units | 2014 PSU Grants
Shares
Stock awards granted (in shares or units)							49,103
Unvested at the end of the period (in shares)	49,103
Other Share-based Compensation Additional Disclosures
Aggregate grant date fair value							$1,723,000
Potential earned PSUs payout for defined levels of performance under awards
The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25%	2
Performance period of the award	3 years
Maximum | Amended and Restated 2008 Omnibus Equity and Incentive Plan
Share-Based Compensation
Number of common shares of beneficial interest authorized to be issued								5,900,000

ShareBased_Compensation_and_Ot3

Share-Based Compensation and Other Compensation Matters (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Stock Options
Exercised (in shares)	-62,888		-39,331		-61,624
Aggregate Intrinsic Value
Increase (decrease) in tax benefit from share-based compensation	($3,000)		($122,000)		$43,000
Options
Stock Options
Outstanding at the beginning of the period (in shares)	640,927		798,210		945,422
Forfeited/Expired (in shares)	-18,303		-117,952		-85,588
Exercised (in shares)	-62,888		-39,331		-61,624
Outstanding at the end of the period (in shares)	559,736		640,927		798,210		945,422
Exercisable at the end of the period (in shares)	559,736	[1]	640,927	[2]	798,210	[3]
Exercise price range, options outstanding, low end of range (in dollars per share)	$25.52		$19.63		$13.60		$13.40
Exercise price range, options outstanding, high end of range (in dollars per share)	$56		$56		$57		$57
Weighted Average Exercise Price per Share
Outstanding at the beginning of the period (in dollars per share)	$38.11		$37.62		$36.63
Forfeited/Expired (in dollars per share)	$42.12		$40.91		$42.98
Exercised (in dollars per share)	$23.70		$19.67		$15.08
Outstanding at the end of the period (in dollars per share)	$39.60		$38.11		$37.62		$36.63
Exercisable at the end of the period (in dollars per share)	$39.60	[1]	$38.11	[2]	$37.62	[3]
Weighted Average Remaining Contractual Term
Weighted average remaining contractual term	2 years		2 years		3 years		4 years
Aggregate Intrinsic Value
Balance outstanding	167,000		68,000		325,000		510,000
Aggregate intrinsic value of options exercised	225,000		258,000		600,000
Options | Range of Exercise Price One | Vested
Stock Options
Exercisable at the end of the period (in shares)	105,672		171,288		9,500
Exercise price range, options outstanding, low end of range (in dollars per share)	$25.52		$19.63		$13.60
Exercise price range, options outstanding, high end of range (in dollars per share)	$30.04		$30.04		$16.73
Options | Range of Exercise Price Two | Vested
Stock Options
Exercisable at the end of the period (in shares)	142,862		145,187		204,736
Exercise price range, options outstanding, low end of range (in dollars per share)	$30.05		$30.05		$16.74
Exercise price range, options outstanding, high end of range (in dollars per share)	$41.28		$41.28		$30.04
Options | Range of Exercise Price Three | Vested
Stock Options
Exercisable at the end of the period (in shares)	158,902		160,402		180,962
Exercise price range, options outstanding, low end of range (in dollars per share)	$41.29		$41.29		$30.05
Exercise price range, options outstanding, high end of range (in dollars per share)	$42.74		$42.74		$41.28
Options | Range of Exercise Price Four | Vested
Stock Options
Exercisable at the end of the period (in shares)	152,300		164,050		403,012
Exercise price range, options outstanding, low end of range (in dollars per share)	$42.75		$42.75		$41.29
Exercise price range, options outstanding, high end of range (in dollars per share)	$56		$56		$57
Performance share units
Aggregate Intrinsic Value
Estimated pre-vesting forfeitures (as a percent)	0.00%
Unrecognized compensation cost	1,900,000
Expected weighted average period during which unrecognized compensation cost will be recognized	2 years
Restricted shares
Aggregate Intrinsic Value
Unrecognized compensation cost	$6,300,000
Expected weighted average period during which unrecognized compensation cost will be recognized	2 years
Minimum | Options
Stock Options
Exercise price range, options forfeited (in dollars per share)	$22.34		$18.08		$25.52
Exercise price range, options exercised (in dollars per share)	$19.63		$13.60		$13.40
Minimum | Restricted shares
Aggregate Intrinsic Value
Estimated pre-vesting forfeitures (as a percent)	0.00%
Maximum | Options
Stock Options
Exercise price range, options forfeited (in dollars per share)	$49.60		$51.62		$57
Exercise price range, options exercised (in dollars per share)	$28.15		$26.24		$22.49
Maximum | Restricted shares
Aggregate Intrinsic Value
Estimated pre-vesting forfeitures (as a percent)	5.00%
[1]	105,672 of these options had an exercise price ranging from $25.52 to $30.04; 142,862 had an exercise price ranging from$30.05 to $41.28; 158,902 had an exercise price ranging from $41.29 to $42.74; and 152,300 had an exercise price ranging from $42.75 to $56.00.
[2]	171,288 of these options had an exercise price ranging from $19.63 to $30.04; 145,187 had an exercise price ranging from$30.05 to $41.28; 160,402 had an exercise price ranging from $41.29 to $42.74; and 164,050 had an exercise price ranging from $42.75 to $56.00.
[3]	9,500 of these options had an exercise price ranging from $13.60 to $16.73; 204,736 had an exercise price ranging from $16.74 to $30.04; 180,962 had an exercise price ranging from $30.05 to $41.28; and 403,012 had an exercise price ranging from $41.29 to $57.00.

ShareBased_Compensation_and_Ot4

Share-Based Compensation and Other Compensation Matters (Details 3) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-Based Compensation
Share-based compensation expense	$7,050	$7,605	$11,184
General, adminstrative and leasing expenses
Share-Based Compensation
Share-based compensation expense	5,307	5,412	8,611
Property operating expenses
Share-Based Compensation
Share-based compensation expense	857	1,118	1,371
Capitalized to development activities
Share-Based Compensation
Share-based compensation expense	$886	$1,075	$1,202

ShareBased_Compensation_and_Ot5

Share-Based Compensation and Other Compensation Matters Share-Based Compensation and Other Compensation Matters (Details 4) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Maximum percentage of compensation employees can contribute to the 401K plan	90.00%
Minimum age of participants who are eligible to contribute an additional portion of their annual compensation	50 years
Employer matching contribution for the first 1% of the participants' eligible compensation (as a percent)	100.00%
Maximum percentage of participants' compensation eligible for 100% employer matching contribution (as a percent)	1.00%
Employer matching contribution for the next 5% after first 1% of the participants' eligible compensation (as a percent)	50.00%
Maximum percentage of participants' compensation eligible for 50% employer matching contribution (as a percent)	5.00%
Employer's aggregate matching contribution for the first 6% of the participants' eligible compensation (as a percent)	3.50%
Maximum percentage of participants' compensation eligible for 3.5% aggregate employer matching contribution	6.00%
Participants' vesting portion in employer matching contribution after one year of credited service (as a percent)	50.00%
Period of credited service after which participants are 50% vested in employer matching contribution	1 year
Participants' vesting portion in employer matching contribution after two years of credited service (as a percent)	100.00%
Period of credited service after which participants are 100% vested in employer matching contribution	2 years
Matching contribution under the plan	$1.20	$1.10	$1.10

ShareBased_Compensation_and_Ot6

Share-Based Compensation and Other Compensation Matters (Details 5) (Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member], Management, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Management
Deferred Compensation Plan
Maximum percentage of participants' compensation which is deferrable (as a percent)	100.00%
Balance of the plan which was fully funded	$5.90	$7.50

ShareBased_Compensation_and_Ot7

Share-Based Compensation and Other Compensation Matters (Details 6) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2012
Chief Financial Officer
Defined Benefit Plan Disclosure [Line Items]
Executive transition costs	$1.10
Former Chief Executive Officer
Defined Benefit Plan Disclosure [Line Items]
Executive transition costs		$2.20

Operating_Leases_Details

Operating Leases (Details) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Gross minimum future rentals
2015	$349,099
2016	301,184
2017	263,428
2018	202,661
2019	154,044
Thereafter	312,304
Total	$1,582,720

Information_by_Business_Segmen2

Information by Business Segment (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	segment
Segment Reporting [Abstract]
Number of primary office property segments (in number of segments)	10
Segment financial information for real estate operations
Revenues from real estate operations	$479,711	$498,633	$493,100
Property operating expenses	179,799	180,704	180,735
NOI from real estate operations	299,912	317,929	312,365
Segment assets	3,670,257	3,629,952
Operating Segment Total
Segment financial information for real estate operations
Revenues from real estate operations	479,711	498,633	493,100
Property operating expenses	179,799	180,704	180,735
NOI from real estate operations	299,912	317,929	312,365
Additions to long-lived assets	64,601	56,877	106,801
Transfers from non-operating properties	141,899	264,290	220,997
Segment assets	2,951,495	2,905,630	2,945,930
Baltimore and Washington Corridor
Segment financial information for real estate operations
Revenues from real estate operations	236,191	237,869	238,488
Property operating expenses	81,132	80,554	83,050
NOI from real estate operations	155,059	157,315	155,438
Additions to long-lived assets	24,174	28,087	25,921
Transfers from non-operating properties	56,699	50,105	65,108
Segment assets	1,277,600	1,243,099	1,267,357
Northern Virginia
Segment financial information for real estate operations
Revenues from real estate operations	89,263	92,010	79,574
Property operating expenses	31,532	31,973	29,103
NOI from real estate operations	57,731	60,037	50,471
Additions to long-lived assets	17,447	13,090	65,157
Transfers from non-operating properties	43,154	61,434	44,250
Segment assets	642,429	616,082	569,860
San Antonio
Segment financial information for real estate operations
Revenues from real estate operations	36,377	33,060	32,018
Property operating expenses	20,562	17,631	16,499
NOI from real estate operations	15,815	15,429	15,519
Additions to long-lived assets	-6	335	280
Transfers from non-operating properties	0	0	468
Segment assets	116,252	118,299	119,369
Huntsville
Segment financial information for real estate operations
Revenues from real estate operations	10,446	5,050	3,867
Property operating expenses	3,066	1,282	689
NOI from real estate operations	7,380	3,768	3,178
Additions to long-lived assets	4,077	3,563	26
Transfers from non-operating properties	21,014	48,799	0
Segment assets	97,209	77,773	28,730
Washington, DC - Capitol Riverfront
Segment financial information for real estate operations
Revenues from real estate operations	14,599	16,863	16,697
Property operating expenses	7,308	7,844	7,555
NOI from real estate operations	7,291	9,019	9,142
Additions to long-lived assets	1,185	2,604	317
Transfers from non-operating properties	0	0	0
Segment assets	95,195	98,962	104,544
St. Mary's and King George Counties
Segment financial information for real estate operations
Revenues from real estate operations	16,736	16,568	16,392
Property operating expenses	5,268	5,028	4,745
NOI from real estate operations	11,468	11,540	11,647
Additions to long-lived assets	8,825	2,341	1,844
Transfers from non-operating properties	0	14	289
Segment assets	100,777	96,143	98,027
Greater Baltimore
Segment financial information for real estate operations
Revenues from real estate operations	43,591	42,653	52,616
Property operating expenses	17,778	16,583	19,917
NOI from real estate operations	25,813	26,070	32,699
Additions to long-lived assets	7,925	2,913	9,690
Transfers from non-operating properties	3,550	360	37,558
Segment assets	274,091	303,823	320,548
Greater Philadelphia
Segment financial information for real estate operations
Revenues from real estate operations	11,929	11,924	9,698
Property operating expenses	4,386	3,431	2,562
NOI from real estate operations	7,543	8,493	7,136
Additions to long-lived assets	952	406	286
Transfers from non-operating properties	16,344	28,034	10,626
Segment assets	106,931	104,657	78,798
Colorado Springs
Segment financial information for real estate operations
Revenues from real estate operations	-1	25,290	24,987
Property operating expenses	12	9,002	9,231
NOI from real estate operations	-13	16,288	15,756
Additions to long-lived assets	0	2,940	2,929
Transfers from non-operating properties	30	5,438	4,295
Segment assets	0	0	175,830
Other
Segment financial information for real estate operations
Revenues from real estate operations	10,150	10,075	12,116
Property operating expenses	1,469	1,016	2,569
NOI from real estate operations	8,681	9,059	9,547
Additions to long-lived assets	0	0	152
Transfers from non-operating properties	0	0	394
Segment assets	77,834	80,002	82,090
Operating Wholesale Data Center
Segment financial information for real estate operations
Revenues from real estate operations	10,430	7,271	6,647
Property operating expenses	7,286	6,360	4,815
NOI from real estate operations	3,144	911	1,832
Additions to long-lived assets	22	598	199
Transfers from non-operating properties	1,108	70,106	58,009
Segment assets	$163,177	$166,790	$100,777

Information_by_Business_Segmen3

Information by Business Segment (Details 2) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of segment revenues to total revenues
Segment revenues from real estate operations									$479,711	$498,633	$493,100
Construction contract and other service revenues									106,748	62,363	73,836
Less: Revenues from discontinued operations (Note 20)									14	-37,636	-58,801
Total revenues	146,971	153,015	139,820	146,667	128,802	131,812	136,527	126,219	586,473	523,360	508,135
Reconciliation of segment property operating expenses to property operating expenses
Segment property operating expenses									179,799	180,704	180,735
Less: Property operating expenses from discontinued operations									135	-13,505	-21,529
Total property operating expenses									179,934	167,199	159,206
Computation of net operating income from service operations
Construction contract and other service revenues									106,748	62,363	73,836
Construction contract and other service expenses									-100,058	-58,875	-70,576
NOI from service operations									6,690	3,488	3,260
Reconciliation of NOI from real estate operations and NOI from service operations to (loss) income from continuing operations
NOI from real estate operations									299,912	317,929	312,365
NOI from service operations									6,690	3,488	3,260
Interest and other income									4,923	3,834	7,172
Equity in income (loss) of unconsolidated entities									229	2,110	-546
Income tax expense									-310	-1,978	-381
Other adjustments:
Depreciation and amortization associated with real estate operations									-136,086	-113,214	-107,998
Impairment losses									-1,416	-5,857	-43,678
General, administrative and leasing expenses									-31,794	-30,869	-31,900
Business development expenses and land carry costs									-5,573	-5,436	-5,711
Interest expense on continuing operations									-92,393	-82,010	-86,401
NOI from discontinued operations									-121	-24,131	-37,272
Loss on early extinguishment of debt									-9,552	-27,030	-943
Income from continuing operations	$5,874	$13,727	$9,248	$5,660	$14,432	$10,974	($232)	$11,662	$34,509	$36,836	$7,967

Information_by_Business_Segmen4

Information by Business Segment (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Reconciliation of segment assets to total assets
Assets	$3,670,257	$3,629,952
Segment assets
Reconciliation of segment assets to total assets
Assets	2,951,495	2,905,630	2,945,930
Non-operating property assets
Reconciliation of segment assets to total assets
Assets	567,586	517,564
Other assets
Reconciliation of segment assets to total assets
Assets	$151,176	$206,758

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax [Line Items]
Minimum adjusted taxable income to be distributed to shareholders to qualify as a REIT (as a percent)									90.00%
Subsequent period during which entity would be disqualified as a REIT if during any tax year entity fails to qualify as a REIT (in years)									4 years
Net income	$5,937	$24,548	$9,050	$5,671	$92,672	($2,000)	($4,405)	$15,277	$45,206	$101,544	$20,341
Adjustments:
Noncontrolling interests, gross									-3,247	-4,061	-622
Other									0	0	741
Taxable income									79,260	110,656	7,488
Corporate Office Properties, L.P.
Income Tax [Line Items]
Net income	5,937	24,548	9,050	5,671	92,672	-2,000	-4,405	15,277	45,206	101,544	20,341
Adjustments:
Rental revenue recognition									-3,932	1,303	-10,794
Compensation expense recognition									1,912	8,987	-2,669
Operating expense recognition									-2,260	-1,663	1,158
Gain on sales of properties									-1,404	-50,860	-74,858
Impairment losses									1,367	32,047	66,910
Loss on interest rate derivatives									0	0	-29,805
Gains from non-real estate investments									405	0	7,854
Income from service operations									-391	1,650	1,500
Income tax expense									310	1,978	381
Depreciation and amortization									41,500	20,834	24,804
Interest expense									920	2,057	3,978
Income from unconsolidated entities									-187	3,148	-725
Noncontrolling interests, gross									-3,285	-7,837	-636
Other									2,346	1,529	-70
Taxable income									$82,507	$114,717	$7,369

Income_Taxes_Details_2

Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other income tax information
Approximate amount by which basis of assets and liabilities for tax reporting purposes is lower than amount reported on consolidated balance sheet	$233,000,000
Deferred income tax (benefit) expense
Total income tax expense	310,000	1,978,000	381,000
Deferred Tax Assets, Net [Abstract]
Increase in deferred tax asset valuation		1,900,000
TRS
Other income tax information
(Loss) income before income taxes	822,000	300,000	11,300,000
Deferred income tax (benefit) expense
Federal	258,000	1,742,000	312,000
State	52,000	236,000	69,000
Total income tax expense	310,000	1,978,000	381,000
Reconciliation of Federal statutory rate to the effective tax rate
Income taxes at U.S. statutory rate (as a percent)	34.00%	34.00%	34.00%
State and local, net of U.S. Federal tax benefit (as a percent)	4.20%	4.50%	4.60%
Increase in deferred tax asset valuation allowance (as a percent)	0.00%	562.90%	0.00%
Other (as a percent)	-0.40%	-1.10%	0.00%
Effective tax rate (as a percent)	37.80%	600.30%	38.60%
Operating Loss Carryforwards	13,000,000
Deferred Tax Assets, Net [Abstract]
Operating loss forward	5,012,000	5,382,000
Share-based compensation	976,000	869,000
Accrued payroll	195,000	221,000
Property	-119,000	-105,000
Valuation allowance	-2,062,000	-2,062,000
Deferred tax asset, net	$4,002,000	$4,305,000
Common Shares
Income Tax [Line Items]
Ordinary income (as a percent)	64.50%	71.80%	33.20%
Long-term capital gain (as a percent)	6.50%	22.40%	0.00%
Return of capital (as a percent)	29.00%	5.80%	66.80%
Preferred Shares
Income Tax [Line Items]
Ordinary income (as a percent)	90.90%	76.20%	100.00%
Long-term capital gain (as a percent)	9.10%	23.80%	0.00%
Return of capital (as a percent)	0.00%	0.00%	0.00%

Discontinued_Operations_Detail

Discontinued Operations (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 30, 2012	Jul. 24, 2012	Dec. 12, 2013	Dec. 23, 2013
												Property	Property	Property	Property
Properties
Revenue from real estate operations									($14)	$37,636	$58,801
Property operating expenses									135	-13,505	-21,529
Depreciation and amortization									0	-4,505	-13,939
Impairment losses									-3	-26,190	-23,232
General, administrative and leasing expenses									0	-4	-3
Business development and land carry costs									0	0	-24
Interest expense									0	-8,221	-10,397
Gain on sales of real estate									24	2,671	20,940
Gain (loss) on early extinguishment of debt									-116	67,810	1,736
Discontinued operations	22	191	-198	11	71,907	-12,974	-4,502	1,261	26	55,692	12,353
Assets held for sale, net	14,339				0				14,339	0
White Marsh Portfolio Disposition Property
Properties
Number of properties sold												5
July 2012 Portfolio Disposition
Properties
Number of properties sold													23
December 2013 Colorado Springs Portfolio Disposition
Properties
Number of properties sold														15
Baltimore and Washington Corridor
Properties
Number of properties transferred															9
Colorado Springs
Properties
Number of properties transferred															5
Greater Baltimore
Properties
Number of land parcels held-for-sale	2								2
Assets held for sale, net	$14,339								$14,339

Earnings_Per_Share_EPS_and_Ear2

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Numerator:
Income (loss) from continuing operations	$5,874	$13,727	$9,248	$5,660	$14,432	$10,974	($232)	$11,662	$34,509		$36,836		$7,967
Gain on sales of real estate, net									10,671		9,016		21
Preferred share/ unit dividends/ distributions	-3,552	-3,553	-4,344	-4,490	-4,490	-4,490	-4,885	-6,106	-15,939		-19,971		-20,844
Issuance costs associated with redeemed preferred shares	0	0	-1,769	0	0	0	-2,904	0	-1,769		-2,904		-1,827
(Income) loss from continuing operations attributable to noncontrolling interests									-4,955		-4,486		1,309
Income from continuing operations attributable to restricted units									-432		-414		-469
Numerator for basic and diluted EPS/EPU from continuing operations attributable to COPT/COPLP common shareholders/unitholders									22,085		18,077		-13,843
Discontinued operations	22	191	-198	11	71,907	-12,974	-4,502	1,261	26		55,692		12,353
Discontinued operations attributable to noncontrolling interests									4		-3,351		-673
Numerator for basic and diluted EPS/EPU on net income (loss)attributable to COPT/COPLP common shareholders/common unitholders									22,115		70,418		-2,163
Denominator (all weighted averages):
Denominator for basic EPS (common shares)									88,092		85,167		73,454
Dilutive effect of share-based compensation awards									171		57		0
Denominator for basic and diluted EPS (common shares)									88,263		85,224		73,454
Basic EPS:
Income (loss) from continuing operations (in dollars per share/unit)									$0.25	[1]	$0.21	[1]	($0.19)	[1]
Discontinued operations (in dollars per share/unit)									$0	[1]	$0.62	[1]	$0.16	[1]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Diluted EPS:
Income (loss) from continuing operations (in dollars per share/unit)									$0.25	[1]	$0.21	[1]	($0.19)	[1]
Discontinued operations (in dollars per share/unit)									$0	[1]	$0.62	[1]	$0.16	[1]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Corporate Office Properties, L.P.
Numerator:
Income (loss) from continuing operations	5,874	13,727	9,248	5,660	14,432	10,974	-232	11,662	34,509		36,836		7,967
Gain on sales of real estate, net									10,671		9,016		21
Preferred share/ unit dividends/ distributions	-3,717	-3,718	-4,509	-4,655	-4,655	-4,655	-5,050	-6,271	-16,599		-20,631		-21,504
Issuance costs associated with redeemed preferred shares	0	0	-1,769	0	0	0	-2,904	0	-1,769		-2,904		-1,827
(Income) loss from continuing operations attributable to noncontrolling interests									-3,281		-2,977		1,206
Income from continuing operations attributable to restricted units									-432		-414		-469
Numerator for basic and diluted EPS/EPU from continuing operations attributable to COPT/COPLP common shareholders/unitholders									23,099		18,926		-14,606
Discontinued operations	22	191	-198	11	71,907	-12,974	-4,502	1,261	26		55,692		12,353
Discontinued operations attributable to noncontrolling interests									5		-930		-699
Numerator for basic and diluted EPS/EPU on net income (loss)attributable to COPT/COPLP common shareholders/common unitholders									$23,130		$73,688		($2,952)
Denominator (all weighted averages):
Denominator for basic EPS (common shares)									91,989		89,036		77,689
Dilutive effect of share-based compensation awards									171		57		0
Denominator for basic and diluted EPS (common shares)									92,160		89,093		77,689
Basic EPS:
Income (loss) from continuing operations (in dollars per share/unit)									$0.25	[2]	$0.21	[2]	($0.19)	[2]
Discontinued operations (in dollars per share/unit)									$0	[2]	$0.62	[2]	$0.15	[2]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[2]	$0.83	[2]	($0.04)	[2]
Diluted EPS:
Income (loss) from continuing operations (in dollars per share/unit)									$0.25	[2]	$0.21	[2]	($0.19)	[2]
Discontinued operations (in dollars per share/unit)									$0	[2]	$0.62	[2]	$0.15	[2]
Net income (loss) attributable to COPT common shareholders (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[2]	$0.83	[2]	($0.04)	[2]
[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_and_Ear3

Earnings Per Share ("EPS") and Earnings Per Unit (“EPU”) (Details 2)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Conversion of common units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,897	3,869	4,235
Conversion of Series I preferred units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176	176
Conversion of Series K preferred shares
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	434	434	434
Restricted Stock
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	401	385	461
Stock Options
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	492	636	772
Corporate Office Properties, L.P. | Restricted Stock
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	401	385	461
Corporate Office Properties, L.P. | Stock Options
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	492	636	772
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)	176	176	176
Corporate Office Properties, L.P. | Conversion of Series K preferred units
Antidilutive securities
Weighted average antidilutive securities excluded from computation of diluted earnings per share (in shares)	434	434	434

Quarterly_Data_Unaudited_Detai

Quarterly Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues	$146,971	$153,015	$139,820	$146,667	$128,802	$131,812	$136,527	$126,219	$586,473		$523,360		$508,135
Operating income (loss)	37,148	37,422	31,836	25,206	34,843	30,673	40,229	36,165	131,612		141,910		89,066
Income (loss) from continuing operations	5,874	13,727	9,248	5,660	14,432	10,974	-232	11,662	34,509		36,836		7,967
Discontinued operations	22	191	-198	11	71,907	-12,974	-4,502	1,261	26		55,692		12,353
Net income	5,937	24,548	9,050	5,671	92,672	-2,000	-4,405	15,277	45,206		101,544		20,341
Net (income) loss attributable to noncontrolling interests in consolidated entities	-1,033	-1,828	-1,160	-930	-5,656	-964	-960	-257
Net income	4,904	22,720	7,890	4,741	87,016	-2,964	-5,365	15,020	40,255		93,707		20,977
Preferred share/ unit dividends/ distributions	-3,552	-3,553	-4,344	-4,490	-4,490	-4,490	-4,885	-6,106	-15,939		-19,971		-20,844
Issuance costs associated with redeemed preferred shares	0	0	-1,769	0	0	0	-2,904	0	-1,769		-2,904		-1,827
Net income (loss) attributable to COPT common shareholders	1,352	19,167	1,777	251	82,526	-7,454	-13,154	8,914	22,547		70,832		-1,694
Basic earnings per common share/unit (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Diluted earnings per common share/unit (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[1]	$0.83	[1]	($0.03)	[1]
Corporate Office Properties, L.P.
Revenues	146,971	153,015	139,820	146,667	128,802	131,812	136,527	126,219	586,473		523,360		508,135
Operating income (loss)	37,148	37,422	31,836	25,206	34,843	30,673	40,229	36,165	131,612		141,910		89,066
Income (loss) from continuing operations	5,874	13,727	9,248	5,660	14,432	10,974	-232	11,662	34,509		36,836		7,967
Discontinued operations	22	191	-198	11	71,907	-12,974	-4,502	1,261	26		55,692		12,353
Net income	5,937	24,548	9,050	5,671	92,672	-2,000	-4,405	15,277	45,206		101,544		20,341
Net (income) loss attributable to noncontrolling interests in consolidated entities	-805	-897	-837	-737	-1,735	-1,035	-1,473	336	-3,276		-3,907		507
Net income	5,132	23,651	8,213	4,934	90,937	-3,035	-5,878	15,613	41,930		97,637		20,848
Preferred share/ unit dividends/ distributions	-3,717	-3,718	-4,509	-4,655	-4,655	-4,655	-5,050	-6,271	-16,599		-20,631		-21,504
Issuance costs associated with redeemed preferred shares	0	0	-1,769	0	0	0	-2,904	0	-1,769		-2,904		-1,827
Net income (loss) attributable to COPT common shareholders	$1,415	$19,933	$1,935	$279	$86,282	($7,690)	($13,832)	$9,342	$23,562		$74,102		($2,483)
Basic earnings per common share/unit (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[2]	$0.83	[2]	($0.04)	[2]
Diluted earnings per common share/unit (in dollars per share/unit)	$0.01	$0.22	$0.02	$0	$0.94	($0.09)	($0.16)	$0.11	$0.25	[2]	$0.83	[2]	($0.04)	[2]
[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.

Commitments_and_Contingencies_1

Commitments and Contingencies (Details) (USD $)	1 Months Ended
	Aug. 31, 2010	Dec. 31, 2014
		Property
Tax incremental financing obligation
The amount of tax incremental financing bonds issued by Anne Arundel County, Maryland	$30,000,000
Liability recognized with regard to tax incremental financing obligation at end of current period		1,300,000
Future minimum rental payments due:
2015		905,000
2016		839,000
2017		768,000
2018		735,000
2019		728,000
Thereafter		76,678,000
Total		80,653,000
Environmental Indemnity Agreement
Number of lease properties which were provided environmental indemnifications		3
Environmental indemnification to the tenant against losses covered under prior owner's indemnity agreement		5,000,000
Maximum environmental indemnification to the tenant against consequential damages after acquisition of property		12,500,000
Additional costs agreed to be paid by the entity related to construction and environmental regulatory activities (as a percent)		50.00%
Maximum annual additional costs agreed to be paid by the entity related to construction and environmental regulatory activities		300,000
Maximum additional costs agreed to be paid by the entity related to construction and environmental regulatory activities		$1,500,000

Schedule_II_Valuation_and_Qual1

Schedule II - Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accounts Receivables-Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$2,976		$4,694		$3,546
Charged to Costs and Expenses	278	[1]	-65	[1]	1,532	[1]
Charged to Other Accounts	0	[2]	0	[2]	232	[2]
Deductions	-2,537	[3]	-1,653	[3]	-616	[3]
Balance at End of Year	717		2,976		4,694
Allowance for Deferred Rent Receivable
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,126		913		703
Charged to Costs and Expenses	0	[1]	0	[1]	0	[1]
Charged to Other Accounts	-708	[2]	1,213	[2]	416	[2]
Deductions	0	[3]	0	[3]	-206	[3]
Balance at End of Year	1,418		2,126		913
Allowance for Deferred Tax Asset
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	2,062		207		207
Charged to Costs and Expenses	0	[1]	1,855	[1]	0	[1]
Charged to Other Accounts	0	[2]	0	[2]	0	[2]
Deductions	0	[3]	0	[3]	0	[3]
Balance at End of Year	$2,062		$2,062		$207
[1]	Amounts charged to costs and expenses are net of recoveries.
[2]	Allowances for certain accounts receivables were charged to service company revenue. Deferred rent receivable allowances were charged to rental revenue.
[3]	Deductions reflect adjustments to reserves due to actual write-offs of accounts.

Schedule_III_Real_Estate_and_A1

Schedule III - Real Estate and Accumulated Depreciation (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Real Estate and Accumulated Depreciation
Encumbrances	$409,193,000	[1]
Initial Cost
Land	668,660,000
Building and Land Improvements	3,008,508,000
Costs Capitalized Subsequent to Acquisition	337,168,000
Gross Amounts Carried at Close of Period
Land	668,660,000
Building and Land Improvements	3,345,676,000
Total	4,014,336,000	[2],[3]	3,811,950,000	3,859,960,000	4,038,932,000
Accumulated Depreciation	-703,083,000	[4]	-597,649,000	-568,176,000	-577,601,000
Additional information
Debt excluded from encumbrances	1,920,057,000		1,927,703,000
Aggregate cost of assets for federal income tax purposes	3,400,000,000
Impairment losses	1,416,000		5,857,000	43,678,000
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 excluded from encumbrances	83,000,000		0
Term Loan Facilities
Additional information
Debt excluded from encumbrances	520,000,000		620,000,000
Senior Unsecured Notes
Additional information
Debt excluded from encumbrances	890,900,000
4.25% Exchangeable Senior Notes
Additional information
Debt excluded from encumbrances	572,000		563,000
Unsecured notes payable
Additional information
Debt excluded from encumbrances	1,607,000		1,700,000
Letter of Credit
Additional information
Debt excluded from encumbrances	14,800,000
Fixed rate mortgage loans
Additional information
Debt excluded from encumbrances	387,139,000		675,060,000
Unamortized premium included in carrying value	42,000		69,000
1000 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	11,671,000	[1]
Initial Cost
Building and Land Improvements	20,527,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	20,527,000
Total	20,527,000	[2],[3]
Accumulated Depreciation	-924,000	[4]
1100 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	12,057,000	[1]
Initial Cost
Building and Land Improvements	19,501,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	19,501,000
Total	19,501,000	[2],[3]
Accumulated Depreciation	-476,000	[4]
114 National Business Parkway
Initial Cost
Land	364,000
Building and Land Improvements	3,109,000
Costs Capitalized Subsequent to Acquisition	46,000
Gross Amounts Carried at Close of Period
Land	364,000
Building and Land Improvements	3,155,000
Total	3,519,000	[2],[3]
Accumulated Depreciation	-1,042,000	[4]
11751 Meadowville Lane
Initial Cost
Land	1,305,000
Building and Land Improvements	52,098,000
Costs Capitalized Subsequent to Acquisition	112,000
Gross Amounts Carried at Close of Period
Land	1,305,000
Building and Land Improvements	52,210,000
Total	53,515,000	[2],[3]
Accumulated Depreciation	-9,889,000	[4]
1200 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	13,950,000	[1]
Initial Cost
Building and Land Improvements	22,409,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	22,409,000
Total	22,409,000	[2],[3]
Accumulated Depreciation	-586,000	[4]
1201 M Street
Initial Cost
Building and Land Improvements	49,785,000
Costs Capitalized Subsequent to Acquisition	2,455,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	52,240,000
Total	52,240,000	[2],[3]
Accumulated Depreciation	-7,255,000	[4]
1201 Winterson Road
Initial Cost
Land	1,288,000	[5]
Building and Land Improvements	5,452,000	[5]
Costs Capitalized Subsequent to Acquisition	460,000	[5]
Gross Amounts Carried at Close of Period
Land	1,288,000	[5]
Building and Land Improvements	5,912,000	[5]
Total	7,200,000	[2],[3],[5]
Accumulated Depreciation	-2,388,000	[4],[5]
1220 12th Street, SE
Initial Cost
Building and Land Improvements	42,464,000
Costs Capitalized Subsequent to Acquisition	2,014,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	44,478,000
Total	44,478,000	[2],[3]
Accumulated Depreciation	-7,143,000	[4]
1243 Winterson Road
Initial Cost
Land	630,000	[6]
Gross Amounts Carried at Close of Period
Land	630,000	[6]
Total	630,000	[2],[3],[6]
1302 Concourse Drive
Initial Cost
Land	2,078,000
Building and Land Improvements	8,313,000
Costs Capitalized Subsequent to Acquisition	5,008,000
Gross Amounts Carried at Close of Period
Land	2,078,000
Building and Land Improvements	13,321,000
Total	15,399,000	[2],[3]
Accumulated Depreciation	-5,610,000	[4]
1304 Concourse Drive
Initial Cost
Land	1,999,000
Building and Land Improvements	12,934,000
Costs Capitalized Subsequent to Acquisition	2,594,000
Gross Amounts Carried at Close of Period
Land	1,999,000
Building and Land Improvements	15,528,000
Total	17,527,000	[2],[3]
Accumulated Depreciation	-5,680,000	[4]
1306 Concourse Drive
Initial Cost
Land	2,796,000
Building and Land Improvements	11,186,000
Costs Capitalized Subsequent to Acquisition	5,745,000
Gross Amounts Carried at Close of Period
Land	2,796,000
Building and Land Improvements	16,931,000
Total	19,727,000	[2],[3]
Accumulated Depreciation	-6,097,000	[4]
131 National Business Parkway
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,906,000
Building and Land Improvements	7,623,000
Costs Capitalized Subsequent to Acquisition	3,288,000
Gross Amounts Carried at Close of Period
Land	1,906,000
Building and Land Improvements	10,911,000
Total	12,817,000	[2],[3]
Accumulated Depreciation	-4,807,000	[4]
132 National Business Parkway
Initial Cost
Land	2,917,000
Building and Land Improvements	12,259,000
Costs Capitalized Subsequent to Acquisition	2,977,000
Gross Amounts Carried at Close of Period
Land	2,917,000
Building and Land Improvements	15,236,000
Total	18,153,000	[2],[3]
Accumulated Depreciation	-7,314,000	[4]
13200 Woodland Park Road
Initial Cost
Land	10,428,000
Building and Land Improvements	41,711,000
Costs Capitalized Subsequent to Acquisition	13,985,000
Gross Amounts Carried at Close of Period
Land	10,428,000
Building and Land Improvements	55,696,000
Total	66,124,000	[2],[3]
Accumulated Depreciation	-24,106,000	[4]
133 National Business Parkway
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,517,000
Building and Land Improvements	10,068,000
Costs Capitalized Subsequent to Acquisition	4,920,000
Gross Amounts Carried at Close of Period
Land	2,517,000
Building and Land Improvements	14,988,000
Total	17,505,000	[2],[3]
Accumulated Depreciation	-7,560,000	[4]
1331 Ashton Road
Initial Cost
Land	587,000
Building and Land Improvements	2,347,000
Costs Capitalized Subsequent to Acquisition	1,474,000
Gross Amounts Carried at Close of Period
Land	587,000
Building and Land Improvements	3,821,000
Total	4,408,000	[2],[3]
Accumulated Depreciation	-1,154,000	[4]
1334 Ashton Road
Initial Cost
Land	736,000
Building and Land Improvements	1,488,000
Costs Capitalized Subsequent to Acquisition	2,634,000
Gross Amounts Carried at Close of Period
Land	736,000
Building and Land Improvements	4,122,000
Total	4,858,000	[2],[3]
Accumulated Depreciation	-2,055,000	[4]
134 National Business Parkway
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	3,684,000
Building and Land Improvements	7,517,000
Costs Capitalized Subsequent to Acquisition	1,282,000
Gross Amounts Carried at Close of Period
Land	3,684,000
Building and Land Improvements	8,799,000
Total	12,483,000	[2],[3]
Accumulated Depreciation	-3,765,000	[4]
1340 Ashton Road
Initial Cost
Land	905,000
Building and Land Improvements	3,620,000
Costs Capitalized Subsequent to Acquisition	1,466,000
Gross Amounts Carried at Close of Period
Land	905,000
Building and Land Improvements	5,086,000
Total	5,991,000	[2],[3]
Accumulated Depreciation	-2,431,000	[4]
1341 Ashton Road
Initial Cost
Land	306,000
Building and Land Improvements	1,223,000
Costs Capitalized Subsequent to Acquisition	601,000
Gross Amounts Carried at Close of Period
Land	306,000
Building and Land Improvements	1,824,000
Total	2,130,000	[2],[3]
Accumulated Depreciation	-860,000	[4]
1343 Ashton Road
Initial Cost
Land	193,000
Building and Land Improvements	774,000
Costs Capitalized Subsequent to Acquisition	405,000
Gross Amounts Carried at Close of Period
Land	193,000
Building and Land Improvements	1,179,000
Total	1,372,000	[2],[3]
Accumulated Depreciation	-596,000	[4]
13450 Sunrise Valley Road
Initial Cost
Land	1,386,000
Building and Land Improvements	5,576,000
Costs Capitalized Subsequent to Acquisition	3,335,000
Gross Amounts Carried at Close of Period
Land	1,386,000
Building and Land Improvements	8,911,000
Total	10,297,000	[2],[3]
Accumulated Depreciation	-3,580,000	[4]
13454 Sunrise Valley Road
Initial Cost
Land	2,899,000
Building and Land Improvements	11,986,000
Costs Capitalized Subsequent to Acquisition	5,447,000
Gross Amounts Carried at Close of Period
Land	2,899,000
Building and Land Improvements	17,433,000
Total	20,332,000	[2],[3]
Accumulated Depreciation	-6,255,000	[4]
135 National Business Parkway
Real Estate and Accumulated Depreciation
Encumbrances	11,418,000	[1]
Initial Cost
Land	2,484,000
Building and Land Improvements	9,750,000
Costs Capitalized Subsequent to Acquisition	4,742,000
Gross Amounts Carried at Close of Period
Land	2,484,000
Building and Land Improvements	14,492,000
Total	16,976,000	[2],[3]
Accumulated Depreciation	-5,845,000	[4]
1362 Mellon Road
Initial Cost
Land	1,706,000
Building and Land Improvements	8,670,000
Costs Capitalized Subsequent to Acquisition	119,000
Gross Amounts Carried at Close of Period
Land	1,706,000
Building and Land Improvements	8,789,000
Total	10,495,000	[2],[3]
Accumulated Depreciation	-1,278,000	[4]
13857 McLearen Road
Initial Cost
Land	3,507,000
Building and Land Improvements	30,177,000
Costs Capitalized Subsequent to Acquisition	1,557,000
Gross Amounts Carried at Close of Period
Land	3,507,000
Building and Land Improvements	31,734,000
Total	35,241,000	[2],[3]
Accumulated Depreciation	-4,945,000	[4]
140 National Business Parkway
Initial Cost
Land	3,407,000
Building and Land Improvements	24,167,000
Costs Capitalized Subsequent to Acquisition	643,000
Gross Amounts Carried at Close of Period
Land	3,407,000
Building and Land Improvements	24,810,000
Total	28,217,000	[2],[3]
Accumulated Depreciation	-7,039,000	[4]
141 National Business Parkway
Real Estate and Accumulated Depreciation
Encumbrances	11,871,000	[1]
Initial Cost
Land	2,398,000
Building and Land Improvements	9,590,000
Costs Capitalized Subsequent to Acquisition	2,995,000
Gross Amounts Carried at Close of Period
Land	2,398,000
Building and Land Improvements	12,585,000
Total	14,983,000	[2],[3]
Accumulated Depreciation	-5,575,000	[4]
14280 Park Meadow Drive
Initial Cost
Land	3,731,000
Building and Land Improvements	15,953,000
Costs Capitalized Subsequent to Acquisition	1,754,000
Gross Amounts Carried at Close of Period
Land	3,731,000
Building and Land Improvements	17,707,000
Total	21,438,000	[2],[3]
Accumulated Depreciation	-5,626,000	[4]
1460 Dorsey Road
Initial Cost
Land	1,800,000	[6]
Gross Amounts Carried at Close of Period
Land	1,800,000	[6]
Total	1,800,000	[2],[3],[6]
14840 Conference Center Drive
Initial Cost
Land	1,572,000
Building and Land Improvements	8,175,000
Costs Capitalized Subsequent to Acquisition	1,488,000
Gross Amounts Carried at Close of Period
Land	1,572,000
Building and Land Improvements	9,663,000
Total	11,235,000	[2],[3]
Accumulated Depreciation	-3,885,000	[4]
14850 Conference Center Drive
Initial Cost
Land	1,615,000
Building and Land Improvements	8,358,000
Costs Capitalized Subsequent to Acquisition	2,896,000
Gross Amounts Carried at Close of Period
Land	1,615,000
Building and Land Improvements	11,254,000
Total	12,869,000	[2],[3]
Accumulated Depreciation	-4,074,000	[4]
14900 Conference Center Drive
Initial Cost
Land	3,436,000
Building and Land Improvements	14,402,000
Costs Capitalized Subsequent to Acquisition	4,569,000
Gross Amounts Carried at Close of Period
Land	3,436,000
Building and Land Improvements	18,971,000
Total	22,407,000	[2],[3]
Accumulated Depreciation	-7,396,000	[4]
15000 Conference Center Drive
Real Estate and Accumulated Depreciation
Encumbrances	54,000,000	[1]
Initial Cost
Land	5,193,000
Building and Land Improvements	47,045,000
Costs Capitalized Subsequent to Acquisition	18,692,000
Gross Amounts Carried at Close of Period
Land	5,193,000
Building and Land Improvements	65,737,000
Total	70,930,000	[2],[3]
Accumulated Depreciation	-25,365,000	[4]
1501 South Clinton Street
Initial Cost
Land	27,964,000
Building and Land Improvements	52,146,000
Costs Capitalized Subsequent to Acquisition	7,553,000
Gross Amounts Carried at Close of Period
Land	27,964,000
Building and Land Improvements	59,699,000
Total	87,663,000	[2],[3]
Accumulated Depreciation	-11,059,000	[4]
15010 Conference Center Drive
Real Estate and Accumulated Depreciation
Encumbrances	96,000,000	[1]
Initial Cost
Land	3,500,000
Building and Land Improvements	41,921,000
Costs Capitalized Subsequent to Acquisition	498,000
Gross Amounts Carried at Close of Period
Land	3,500,000
Building and Land Improvements	42,419,000
Total	45,919,000	[2],[3]
Accumulated Depreciation	-8,644,000	[4]
15049 Conference Center Drive
Initial Cost
Land	4,415,000
Building and Land Improvements	20,365,000
Costs Capitalized Subsequent to Acquisition	726,000
Gross Amounts Carried at Close of Period
Land	4,415,000
Building and Land Improvements	21,091,000
Total	25,506,000	[2],[3]
Accumulated Depreciation	-8,781,000	[4]
15059 Conference Center Drive
Initial Cost
Land	5,753,000
Building and Land Improvements	13,615,000
Costs Capitalized Subsequent to Acquisition	1,780,000
Gross Amounts Carried at Close of Period
Land	5,753,000
Building and Land Improvements	15,395,000
Total	21,148,000	[2],[3]
Accumulated Depreciation	-6,071,000	[4]
15395 John Marshall Highway
Initial Cost
Land	2,465,000
Building and Land Improvements	24,720,000
Gross Amounts Carried at Close of Period
Land	2,465,000
Building and Land Improvements	24,720,000
Total	27,185,000	[2],[3]
Accumulated Depreciation	-576,000	[4]
1550 West Nursery Road
Initial Cost
Land	14,071,000
Building and Land Improvements	16,930,000
Gross Amounts Carried at Close of Period
Land	14,071,000
Building and Land Improvements	16,930,000
Total	31,001,000	[2],[3]
Accumulated Depreciation	-3,038,000	[4]
1550 Westbranch Drive
Initial Cost
Land	5,595,000
Building and Land Improvements	26,212,000
Costs Capitalized Subsequent to Acquisition	116,000
Gross Amounts Carried at Close of Period
Land	5,595,000
Building and Land Improvements	26,328,000
Total	31,923,000	[2],[3]
Accumulated Depreciation	-3,647,000	[4]
1560 West Nursery Road
Initial Cost
Land	1,441,000
Building and Land Improvements	96,000
Costs Capitalized Subsequent to Acquisition	0
Gross Amounts Carried at Close of Period
Land	1,441,000
Building and Land Improvements	96,000
Total	1,537,000	[2],[3]
Accumulated Depreciation	-2,000	[4]
1560A Cable Ranch Road
Initial Cost
Land	1,097,000
Building and Land Improvements	3,770,000
Costs Capitalized Subsequent to Acquisition	352,000
Gross Amounts Carried at Close of Period
Land	1,097,000
Building and Land Improvements	4,122,000
Total	5,219,000	[2],[3]
Accumulated Depreciation	-950,000	[4]
1560B Cable Ranch Road
Initial Cost
Land	2,299,000
Building and Land Improvements	6,545,000
Costs Capitalized Subsequent to Acquisition	11,000
Gross Amounts Carried at Close of Period
Land	2,299,000
Building and Land Improvements	6,556,000
Total	8,855,000	[2],[3]
Accumulated Depreciation	-1,532,000	[4]
16442 Commerce Drive
Initial Cost
Land	613,000
Building and Land Improvements	2,582,000
Costs Capitalized Subsequent to Acquisition	593,000
Gross Amounts Carried at Close of Period
Land	613,000
Building and Land Improvements	3,175,000
Total	3,788,000	[2],[3]
Accumulated Depreciation	-1,153,000	[4]
16480 Commerce Drive
Initial Cost
Land	1,856,000
Building and Land Improvements	7,425,000
Costs Capitalized Subsequent to Acquisition	167,000
Gross Amounts Carried at Close of Period
Land	1,856,000
Building and Land Improvements	7,592,000
Total	9,448,000	[2],[3]
Accumulated Depreciation	-2,020,000	[4]
16501 Commerce Drive
Initial Cost
Land	522,000
Building and Land Improvements	2,090,000
Costs Capitalized Subsequent to Acquisition	465,000
Gross Amounts Carried at Close of Period
Land	522,000
Building and Land Improvements	2,555,000
Total	3,077,000	[2],[3]
Accumulated Depreciation	-714,000	[4]
16539 Commerce Drive
Initial Cost
Land	688,000
Building and Land Improvements	2,860,000
Costs Capitalized Subsequent to Acquisition	1,469,000
Gross Amounts Carried at Close of Period
Land	688,000
Building and Land Improvements	4,329,000
Total	5,017,000	[2],[3]
Accumulated Depreciation	-1,696,000	[4]
16541 Commerce Drive
Initial Cost
Land	773,000
Building and Land Improvements	3,094,000
Costs Capitalized Subsequent to Acquisition	1,367,000
Gross Amounts Carried at Close of Period
Land	773,000
Building and Land Improvements	4,461,000
Total	5,234,000	[2],[3]
Accumulated Depreciation	-1,529,000	[4]
16543 Commerce Drive
Initial Cost
Land	436,000
Building and Land Improvements	1,742,000
Costs Capitalized Subsequent to Acquisition	172,000
Gross Amounts Carried at Close of Period
Land	436,000
Building and Land Improvements	1,914,000
Total	2,350,000	[2],[3]
Accumulated Depreciation	-486,000	[4]
1751 Pinnacle Drive
Initial Cost
Land	10,486,000
Building and Land Improvements	42,339,000
Costs Capitalized Subsequent to Acquisition	22,325,000
Gross Amounts Carried at Close of Period
Land	10,486,000
Building and Land Improvements	64,664,000
Total	75,150,000	[2],[3]
Accumulated Depreciation	-20,705,000	[4]
1753 Pinnacle Drive
Initial Cost
Land	8,275,000
Building and Land Improvements	34,353,000
Costs Capitalized Subsequent to Acquisition	10,528,000
Gross Amounts Carried at Close of Period
Land	8,275,000
Building and Land Improvements	44,881,000
Total	53,156,000	[2],[3]
Accumulated Depreciation	-14,406,000	[4]
201 Technology Drive
Initial Cost
Land	726,000
Building and Land Improvements	31,091,000
Costs Capitalized Subsequent to Acquisition	60,000
Gross Amounts Carried at Close of Period
Land	726,000
Building and Land Improvements	31,151,000
Total	31,877,000	[2],[3]
Accumulated Depreciation	-5,579,000	[4]
206 Research Boulevard
Initial Cost
Land	1,813,000
Building and Land Improvements	17,485,000
Gross Amounts Carried at Close of Period
Land	1,813,000
Building and Land Improvements	17,485,000
Total	19,298,000	[2],[3]
Accumulated Depreciation	-979,000	[4]
209 Research Boulevard
Initial Cost
Land	1,045,000
Building and Land Improvements	16,087,000
Costs Capitalized Subsequent to Acquisition	32,000
Gross Amounts Carried at Close of Period
Land	1,045,000
Building and Land Improvements	16,119,000
Total	17,164,000	[2],[3]
Accumulated Depreciation	-1,665,000	[4]
210 Research Boulevard
Initial Cost
Land	1,065,000
Building and Land Improvements	14,687,000
Costs Capitalized Subsequent to Acquisition	75,000
Gross Amounts Carried at Close of Period
Land	1,065,000
Building and Land Improvements	14,762,000
Total	15,827,000	[2],[3]
Accumulated Depreciation	-1,191,000	[4]
21267 Smith Switch Road
Initial Cost
Land	4,040,000
Building and Land Improvements	10,369,000
Gross Amounts Carried at Close of Period
Land	4,040,000
Building and Land Improvements	10,369,000
Total	14,409,000	[2],[3]
Accumulated Depreciation	-106,000	[4]
21271 Smith Switch Road
Initial Cost
Land	7,346,000
Building and Land Improvements	16,864,000
Gross Amounts Carried at Close of Period
Land	7,346,000
Building and Land Improvements	16,864,000
Total	24,210,000	[2],[3]
Accumulated Depreciation	-447,000	[4]
22289 Exploration Drive
Initial Cost
Land	1,422,000
Building and Land Improvements	5,719,000
Costs Capitalized Subsequent to Acquisition	1,511,000
Gross Amounts Carried at Close of Period
Land	1,422,000
Building and Land Improvements	7,230,000
Total	8,652,000	[2],[3]
Accumulated Depreciation	-2,512,000	[4]
22299 Exploration Drive
Initial Cost
Land	1,362,000
Building and Land Improvements	5,791,000
Costs Capitalized Subsequent to Acquisition	1,119,000
Gross Amounts Carried at Close of Period
Land	1,362,000
Building and Land Improvements	6,910,000
Total	8,272,000	[2],[3]
Accumulated Depreciation	-2,433,000	[4]
22300 Exploration Drive
Initial Cost
Land	1,094,000
Building and Land Improvements	5,038,000
Costs Capitalized Subsequent to Acquisition	539,000
Gross Amounts Carried at Close of Period
Land	1,094,000
Building and Land Improvements	5,577,000
Total	6,671,000	[2],[3]
Accumulated Depreciation	-1,878,000	[4]
22309 Exploration Drive
Initial Cost
Land	2,243,000
Building and Land Improvements	10,419,000
Costs Capitalized Subsequent to Acquisition	7,491,000
Gross Amounts Carried at Close of Period
Land	2,243,000
Building and Land Improvements	17,910,000
Total	20,153,000	[2],[3]
Accumulated Depreciation	-3,999,000	[4]
23535 Cottonwood Parkway
Initial Cost
Land	692,000
Building and Land Improvements	3,051,000
Costs Capitalized Subsequent to Acquisition	223,000
Gross Amounts Carried at Close of Period
Land	692,000
Building and Land Improvements	3,274,000
Total	3,966,000	[2],[3]
Accumulated Depreciation	-1,066,000	[4]
2500 Riva Road
Initial Cost
Land	2,791,000
Building and Land Improvements	12,145,000
Costs Capitalized Subsequent to Acquisition	1,000
Gross Amounts Carried at Close of Period
Land	2,791,000
Building and Land Improvements	12,146,000
Total	14,937,000	[2],[3]
Accumulated Depreciation	-4,073,000	[4]
2691 Technology Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,098,000
Building and Land Improvements	17,334,000
Costs Capitalized Subsequent to Acquisition	5,115,000
Gross Amounts Carried at Close of Period
Land	2,098,000
Building and Land Improvements	22,449,000
Total	24,547,000	[2],[3]
Accumulated Depreciation	-6,938,000	[4]
2701 Technology Drive
Real Estate and Accumulated Depreciation
Encumbrances	22,636,000	[1]
Initial Cost
Land	1,737,000
Building and Land Improvements	15,266,000
Costs Capitalized Subsequent to Acquisition	2,554,000
Gross Amounts Carried at Close of Period
Land	1,737,000
Building and Land Improvements	17,820,000
Total	19,557,000	[2],[3]
Accumulated Depreciation	-6,641,000	[4]
2711 Technology Drive
Real Estate and Accumulated Depreciation
Encumbrances	17,606,000	[1]
Initial Cost
Land	2,251,000
Building and Land Improvements	21,611,000
Costs Capitalized Subsequent to Acquisition	1,451,000
Gross Amounts Carried at Close of Period
Land	2,251,000
Building and Land Improvements	23,062,000
Total	25,313,000	[2],[3]
Accumulated Depreciation	-9,531,000	[4]
2720 Technology Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	3,863,000
Building and Land Improvements	29,272,000
Costs Capitalized Subsequent to Acquisition	113,000
Gross Amounts Carried at Close of Period
Land	3,863,000
Building and Land Improvements	29,385,000
Total	33,248,000	[2],[3]
Accumulated Depreciation	-7,577,000	[4]
2721 Technology Drive
Initial Cost
Land	4,611,000
Building and Land Improvements	14,597,000
Costs Capitalized Subsequent to Acquisition	1,226,000
Gross Amounts Carried at Close of Period
Land	4,611,000
Building and Land Improvements	15,823,000
Total	20,434,000	[2],[3]
Accumulated Depreciation	-5,840,000	[4]
2730 Hercules Road
Real Estate and Accumulated Depreciation
Encumbrances	35,161,000	[1]
Initial Cost
Land	8,737,000
Building and Land Improvements	31,612,000
Costs Capitalized Subsequent to Acquisition	7,093,000
Gross Amounts Carried at Close of Period
Land	8,737,000
Building and Land Improvements	38,705,000
Total	47,442,000	[2],[3]
Accumulated Depreciation	-14,268,000	[4]
2900 Towerview Road
Initial Cost
Land	3,207,000
Building and Land Improvements	16,379,000
Costs Capitalized Subsequent to Acquisition	6,419,000
Gross Amounts Carried at Close of Period
Land	3,207,000
Building and Land Improvements	22,798,000
Total	26,005,000	[2],[3]
Accumulated Depreciation	-5,969,000	[4]
300 Sentinel Drive
Initial Cost
Land	1,517,000
Building and Land Improvements	58,827,000
Costs Capitalized Subsequent to Acquisition	166,000
Gross Amounts Carried at Close of Period
Land	1,517,000
Building and Land Improvements	58,993,000
Total	60,510,000	[2],[3]
Accumulated Depreciation	-6,977,000	[4]
302 Sentinel Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,648,000
Building and Land Improvements	29,687,000
Costs Capitalized Subsequent to Acquisition	423,000
Gross Amounts Carried at Close of Period
Land	2,648,000
Building and Land Improvements	30,110,000
Total	32,758,000	[2],[3]
Accumulated Depreciation	-5,210,000	[4]
304 Sentinel Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	3,411,000
Building and Land Improvements	24,917,000
Costs Capitalized Subsequent to Acquisition	138,000
Gross Amounts Carried at Close of Period
Land	3,411,000
Building and Land Improvements	25,055,000
Total	28,466,000	[2],[3]
Accumulated Depreciation	-5,655,000	[4]
306 Sentinel Drive
Real Estate and Accumulated Depreciation
Encumbrances	16,298,000	[1]
Initial Cost
Land	3,260,000
Building and Land Improvements	22,592,000
Costs Capitalized Subsequent to Acquisition	415,000
Gross Amounts Carried at Close of Period
Land	3,260,000
Building and Land Improvements	23,007,000
Total	26,267,000	[2],[3]
Accumulated Depreciation	-4,687,000	[4]
308 Sentinel Drive
Initial Cost
Land	1,422,000
Building and Land Improvements	26,197,000
Gross Amounts Carried at Close of Period
Land	1,422,000
Building and Land Improvements	26,197,000
Total	27,619,000	[2],[3]
Accumulated Depreciation	-2,395,000	[4]
310 Sentinel Way
Initial Cost
Land	2,372,000	[5]
Building and Land Improvements	33,953,000	[5]
Gross Amounts Carried at Close of Period
Land	2,372,000	[5]
Building and Land Improvements	33,953,000	[5]
Total	36,325,000	[2],[3],[5]
Accumulated Depreciation	0	[4],[5]
310 The Bridge Street
Initial Cost
Land	261,000
Building and Land Improvements	26,531,000
Costs Capitalized Subsequent to Acquisition	1,051,000
Gross Amounts Carried at Close of Period
Land	261,000
Building and Land Improvements	27,582,000
Total	27,843,000	[2],[3]
Accumulated Depreciation	-4,310,000	[4]
312 Sentinel Way
Initial Cost
Land	3,138,000
Building and Land Improvements	23,793,000
Gross Amounts Carried at Close of Period
Land	3,138,000
Building and Land Improvements	23,793,000
Total	26,931,000	[2],[3]
Accumulated Depreciation	-240,000	[4]
3120 Fairview Park Drive
Initial Cost
Land	6,863,000
Building and Land Improvements	35,606,000
Costs Capitalized Subsequent to Acquisition	7,303,000
Gross Amounts Carried at Close of Period
Land	6,863,000
Building and Land Improvements	42,909,000
Total	49,772,000	[2],[3]
Accumulated Depreciation	-5,456,000	[4]
314 Sentinel Way
Initial Cost
Land	1,254,000
Building and Land Improvements	1,325,000
Gross Amounts Carried at Close of Period
Land	1,254,000
Building and Land Improvements	1,325,000
Total	2,579,000	[2],[3]
Accumulated Depreciation	-216,000	[4]
316 Sentinel Way
Initial Cost
Land	2,748,000
Building and Land Improvements	38,156,000
Costs Capitalized Subsequent to Acquisition	139,000
Gross Amounts Carried at Close of Period
Land	2,748,000
Building and Land Improvements	38,295,000
Total	41,043,000	[2],[3]
Accumulated Depreciation	-2,602,000	[4]
318 Sentinel Way
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,185,000
Building and Land Improvements	28,426,000
Gross Amounts Carried at Close of Period
Land	2,185,000
Building and Land Improvements	28,426,000
Total	30,611,000	[2],[3]
Accumulated Depreciation	-6,270,000	[4]
320 Sentinel Way
Initial Cost
Land	2,067,000
Building and Land Improvements	21,623,000
Gross Amounts Carried at Close of Period
Land	2,067,000
Building and Land Improvements	21,623,000
Total	23,690,000	[2],[3]
Accumulated Depreciation	-3,770,000	[4]
322 Sentinel Way
Real Estate and Accumulated Depreciation
Encumbrances	21,680,000	[1]
Initial Cost
Land	2,605,000
Building and Land Improvements	22,827,000
Gross Amounts Carried at Close of Period
Land	2,605,000
Building and Land Improvements	22,827,000
Total	25,432,000	[2],[3]
Accumulated Depreciation	-4,572,000	[4]
324 Sentinel Way
Initial Cost
Land	1,656,000
Building and Land Improvements	23,018,000
Gross Amounts Carried at Close of Period
Land	1,656,000
Building and Land Improvements	23,018,000
Total	24,674,000	[2],[3]
Accumulated Depreciation	-2,503,000	[4]
375 West Padonia Road
Initial Cost
Land	2,483,000
Building and Land Improvements	10,415,000
Costs Capitalized Subsequent to Acquisition	4,857,000
Gross Amounts Carried at Close of Period
Land	2,483,000
Building and Land Improvements	15,272,000
Total	17,755,000	[2],[3]
Accumulated Depreciation	-6,904,000	[4]
410 National Business Parkway
Initial Cost
Land	1,831,000
Building and Land Improvements	23,257,000
Costs Capitalized Subsequent to Acquisition	112,000
Gross Amounts Carried at Close of Period
Land	1,831,000
Building and Land Improvements	23,369,000
Total	25,200,000	[2],[3]
Accumulated Depreciation	-1,127,000	[4]
420 National Business Parkway
Initial Cost
Land	2,370,000
Building and Land Improvements	27,161,000
Costs Capitalized Subsequent to Acquisition	101,000
Gross Amounts Carried at Close of Period
Land	2,370,000
Building and Land Improvements	27,262,000
Total	29,632,000	[2],[3]
Accumulated Depreciation	-541,000	[4]
430 National Business Parkway
Initial Cost
Land	1,852,000
Building and Land Improvements	21,138,000
Costs Capitalized Subsequent to Acquisition	120,000
Gross Amounts Carried at Close of Period
Land	1,852,000
Building and Land Improvements	21,258,000
Total	23,110,000	[2],[3]
Accumulated Depreciation	-1,494,000	[4]
44408 Pecan Court
Initial Cost
Land	817,000
Building and Land Improvements	1,583,000
Costs Capitalized Subsequent to Acquisition	582,000
Gross Amounts Carried at Close of Period
Land	817,000
Building and Land Improvements	2,165,000
Total	2,982,000	[2],[3]
Accumulated Depreciation	-405,000	[4]
44414 Pecan Court
Initial Cost
Land	405,000
Building and Land Improvements	1,619,000
Costs Capitalized Subsequent to Acquisition	336,000
Gross Amounts Carried at Close of Period
Land	405,000
Building and Land Improvements	1,955,000
Total	2,360,000	[2],[3]
Accumulated Depreciation	-641,000	[4]
44417 Pecan Court
Initial Cost
Land	434,000	[5]
Building and Land Improvements	3,204,000	[5]
Costs Capitalized Subsequent to Acquisition	88,000	[5]
Gross Amounts Carried at Close of Period
Land	434,000	[5]
Building and Land Improvements	3,292,000	[5]
Total	3,726,000	[2],[3],[5]
Accumulated Depreciation	-1,037,000	[4],[5]
44420 Pecan Court
Initial Cost
Land	344,000
Building and Land Improvements	890,000
Costs Capitalized Subsequent to Acquisition	148,000
Gross Amounts Carried at Close of Period
Land	344,000
Building and Land Improvements	1,038,000
Total	1,382,000	[2],[3]
Accumulated Depreciation	-199,000	[4]
44425 Pecan Court
Initial Cost
Land	1,309,000
Building and Land Improvements	3,506,000
Costs Capitalized Subsequent to Acquisition	1,307,000
Gross Amounts Carried at Close of Period
Land	1,309,000
Building and Land Improvements	4,813,000
Total	6,122,000	[2],[3]
Accumulated Depreciation	-1,492,000	[4]
45310 Abell House Lane
Initial Cost
Land	2,272,000
Building and Land Improvements	13,808,000
Gross Amounts Carried at Close of Period
Land	2,272,000
Building and Land Improvements	13,808,000
Total	16,080,000	[2],[3]
Accumulated Depreciation	-1,057,000	[4]
46579 Expedition Drive
Initial Cost
Land	1,406,000
Building and Land Improvements	5,796,000
Costs Capitalized Subsequent to Acquisition	1,335,000
Gross Amounts Carried at Close of Period
Land	1,406,000
Building and Land Improvements	7,131,000
Total	8,537,000	[2],[3]
Accumulated Depreciation	-2,780,000	[4]
46591 Expedition Drive
Initial Cost
Land	1,200,000
Building and Land Improvements	7,199,000
Costs Capitalized Subsequent to Acquisition	803,000
Gross Amounts Carried at Close of Period
Land	1,200,000
Building and Land Improvements	8,002,000
Total	9,202,000	[2],[3]
Accumulated Depreciation	-1,618,000	[4]
4851 Stonecroft Boulevard
Initial Cost
Land	1,878,000
Building and Land Improvements	11,558,000
Costs Capitalized Subsequent to Acquisition	21,000
Gross Amounts Carried at Close of Period
Land	1,878,000
Building and Land Improvements	11,579,000
Total	13,457,000	[2],[3]
Accumulated Depreciation	-2,959,000	[4]
4940 Campbell Drive
Initial Cost
Land	1,379,000
Building and Land Improvements	3,858,000
Costs Capitalized Subsequent to Acquisition	1,373,000
Gross Amounts Carried at Close of Period
Land	1,379,000
Building and Land Improvements	5,231,000
Total	6,610,000	[2],[3]
Accumulated Depreciation	-1,278,000	[4]
525 Babcock Road
Initial Cost
Land	355,000
Building and Land Improvements	397,000
Costs Capitalized Subsequent to Acquisition	79,000
Gross Amounts Carried at Close of Period
Land	355,000
Building and Land Improvements	476,000
Total	831,000	[2],[3]
Accumulated Depreciation	-153,000	[4]
5325 Nottingham Drive
Initial Cost
Land	816,000
Building and Land Improvements	3,976,000
Costs Capitalized Subsequent to Acquisition	485,000
Gross Amounts Carried at Close of Period
Land	816,000
Building and Land Improvements	4,461,000
Total	5,277,000	[2],[3]
Accumulated Depreciation	-1,076,000	[4]
5355 Nottingham Drive
Initial Cost
Land	761,000
Building and Land Improvements	3,562,000
Costs Capitalized Subsequent to Acquisition	1,758,000
Gross Amounts Carried at Close of Period
Land	761,000
Building and Land Improvements	5,320,000
Total	6,081,000	[2],[3]
Accumulated Depreciation	-1,874,000	[4]
5520 Research Park Drive
Initial Cost
Building and Land Improvements	20,072,000
Costs Capitalized Subsequent to Acquisition	38,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	20,110,000
Total	20,110,000	[2],[3]
Accumulated Depreciation	-2,687,000	[4]
5522 Research Park Drive
Initial Cost
Building and Land Improvements	4,550,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	4,550,000
Total	4,550,000	[2],[3]
Accumulated Depreciation	-842,000	[4]
5825 University Research Court
Real Estate and Accumulated Depreciation
Encumbrances	15,615,000	[1]
Initial Cost
Building and Land Improvements	22,522,000
Costs Capitalized Subsequent to Acquisition	60,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	22,582,000
Total	22,582,000	[2],[3]
Accumulated Depreciation	-3,246,000	[4]
5850 University Research Court
Real Estate and Accumulated Depreciation
Encumbrances	21,261,000	[1]
Initial Cost
Building and Land Improvements	31,689,000
Costs Capitalized Subsequent to Acquisition	57,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	31,746,000
Total	31,746,000	[2],[3]
Accumulated Depreciation	-3,763,000	[4]
6700 Alexander Bell Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,755,000
Building and Land Improvements	7,019,000
Costs Capitalized Subsequent to Acquisition	5,550,000
Gross Amounts Carried at Close of Period
Land	1,755,000
Building and Land Improvements	12,569,000
Total	14,324,000	[2],[3]
Accumulated Depreciation	-5,435,000	[4]
6708 Alexander Bell Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1],[5]
Initial Cost
Land	897,000	[5]
Building and Land Improvements	7,544,000	[5]
Costs Capitalized Subsequent to Acquisition	1,591,000	[5]
Gross Amounts Carried at Close of Period
Land	897,000	[5]
Building and Land Improvements	9,135,000	[5]
Total	10,032,000	[2],[3],[5]
Accumulated Depreciation	-3,319,000	[4],[5]
6711 Columbia Gateway Drive
Initial Cost
Land	2,683,000
Building and Land Improvements	23,239,000
Costs Capitalized Subsequent to Acquisition	435,000
Gross Amounts Carried at Close of Period
Land	2,683,000
Building and Land Improvements	23,674,000
Total	26,357,000	[2],[3]
Accumulated Depreciation	-4,765,000	[4]
6716 Alexander Bell Drive
Initial Cost
Land	1,242,000
Building and Land Improvements	4,969,000
Costs Capitalized Subsequent to Acquisition	3,352,000
Gross Amounts Carried at Close of Period
Land	1,242,000
Building and Land Improvements	8,321,000
Total	9,563,000	[2],[3]
Accumulated Depreciation	-3,992,000	[4]
6721 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	17,102,000	[1]
Initial Cost
Land	1,753,000
Building and Land Improvements	34,090,000
Costs Capitalized Subsequent to Acquisition	65,000
Gross Amounts Carried at Close of Period
Land	1,753,000
Building and Land Improvements	34,155,000
Total	35,908,000	[2],[3]
Accumulated Depreciation	-4,941,000	[4]
6724 Alexander Bell Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	449,000
Building and Land Improvements	5,039,000
Costs Capitalized Subsequent to Acquisition	368,000
Gross Amounts Carried at Close of Period
Land	449,000
Building and Land Improvements	5,407,000
Total	5,856,000	[2],[3]
Accumulated Depreciation	-2,106,000	[4]
6731 Columbia Gateway Drive
Initial Cost
Land	2,807,000
Building and Land Improvements	19,098,000
Costs Capitalized Subsequent to Acquisition	2,046,000
Gross Amounts Carried at Close of Period
Land	2,807,000
Building and Land Improvements	21,144,000
Total	23,951,000	[2],[3]
Accumulated Depreciation	-7,841,000	[4]
6740 Alexander Bell Drive
Initial Cost
Land	1,424,000
Building and Land Improvements	5,696,000
Costs Capitalized Subsequent to Acquisition	3,346,000
Gross Amounts Carried at Close of Period
Land	1,424,000
Building and Land Improvements	9,042,000
Total	10,466,000	[2],[3]
Accumulated Depreciation	-4,644,000	[4]
6741 Columbia Gateway Drive
Initial Cost
Land	675,000
Building and Land Improvements	1,711,000
Costs Capitalized Subsequent to Acquisition	114,000
Gross Amounts Carried at Close of Period
Land	675,000
Building and Land Improvements	1,825,000
Total	2,500,000	[2],[3]
Accumulated Depreciation	-303,000	[4]
6750 Alexander Bell Drive
Initial Cost
Land	1,263,000
Building and Land Improvements	12,461,000
Costs Capitalized Subsequent to Acquisition	3,419,000
Gross Amounts Carried at Close of Period
Land	1,263,000
Building and Land Improvements	15,880,000
Total	17,143,000	[2],[3]
Accumulated Depreciation	-7,008,000	[4]
6760 Alexander Bell Drive
Initial Cost
Land	890,000
Building and Land Improvements	3,561,000
Costs Capitalized Subsequent to Acquisition	2,763,000
Gross Amounts Carried at Close of Period
Land	890,000
Building and Land Improvements	6,324,000
Total	7,214,000	[2],[3]
Accumulated Depreciation	-2,989,000	[4]
6940 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	3,545,000
Building and Land Improvements	9,916,000
Costs Capitalized Subsequent to Acquisition	4,717,000
Gross Amounts Carried at Close of Period
Land	3,545,000
Building and Land Improvements	14,633,000
Total	18,178,000	[2],[3]
Accumulated Depreciation	-6,463,000	[4]
6950 Columbia Gateway Drive
Initial Cost
Land	3,596,000
Building and Land Improvements	14,269,000
Costs Capitalized Subsequent to Acquisition	2,164,000
Gross Amounts Carried at Close of Period
Land	3,596,000
Building and Land Improvements	16,433,000
Total	20,029,000	[2],[3]
Accumulated Depreciation	-6,965,000	[4]
7000 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	3,131,000
Building and Land Improvements	12,103,000
Costs Capitalized Subsequent to Acquisition	989,000
Gross Amounts Carried at Close of Period
Land	3,131,000
Building and Land Improvements	13,092,000
Total	16,223,000	[2],[3]
Accumulated Depreciation	-4,056,000	[4]
7005 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1],[6]
Initial Cost
Land	3,036,000	[6]
Building and Land Improvements	14,000	[6]
Costs Capitalized Subsequent to Acquisition	0	[6]
Gross Amounts Carried at Close of Period
Land	3,036,000	[6]
Building and Land Improvements	14,000	[6]
Total	3,050,000	[2],[3],[6]
Accumulated Depreciation	0	[4],[6]
7015 Albert Einstein Drive
Real Estate and Accumulated Depreciation
Encumbrances	1,900,000	[1]
Initial Cost
Land	2,058,000
Building and Land Improvements	6,093,000
Costs Capitalized Subsequent to Acquisition	855,000
Gross Amounts Carried at Close of Period
Land	2,058,000
Building and Land Improvements	6,948,000
Total	9,006,000	[2],[3]
Accumulated Depreciation	-2,669,000	[4]
7061 Columbia Gateway Drive
Initial Cost
Land	729,000
Building and Land Improvements	3,094,000
Costs Capitalized Subsequent to Acquisition	1,407,000
Gross Amounts Carried at Close of Period
Land	729,000
Building and Land Improvements	4,501,000
Total	5,230,000	[2],[3]
Accumulated Depreciation	-1,657,000	[4]
7063 Columbia Gateway Drive
Initial Cost
Land	902,000
Building and Land Improvements	3,684,000
Costs Capitalized Subsequent to Acquisition	1,074,000
Gross Amounts Carried at Close of Period
Land	902,000
Building and Land Improvements	4,758,000
Total	5,660,000	[2],[3]
Accumulated Depreciation	-2,272,000	[4]
7065 Columbia Gateway Drive
Initial Cost
Land	919,000
Building and Land Improvements	3,763,000
Costs Capitalized Subsequent to Acquisition	2,902,000
Gross Amounts Carried at Close of Period
Land	919,000
Building and Land Improvements	6,665,000
Total	7,584,000	[2],[3]
Accumulated Depreciation	-2,343,000	[4]
7067 Columbia Gateway Drive
Initial Cost
Land	1,829,000
Building and Land Improvements	11,823,000
Costs Capitalized Subsequent to Acquisition	2,773,000
Gross Amounts Carried at Close of Period
Land	1,829,000
Building and Land Improvements	14,596,000
Total	16,425,000	[2],[3]
Accumulated Depreciation	-5,461,000	[4]
7125 Columbia Gateway Drive Land
Initial Cost
Land	3,361,000	[6]
Building and Land Improvements	555,000	[6]
Costs Capitalized Subsequent to Acquisition	279,000	[6]
Gross Amounts Carried at Close of Period
Land	3,361,000	[6]
Building and Land Improvements	834,000	[6]
Total	4,195,000	[2],[3],[6]
7125 Columbia Gateway Drive
Initial Cost
Land	17,126,000
Building and Land Improvements	46,994,000
Costs Capitalized Subsequent to Acquisition	8,848,000
Gross Amounts Carried at Close of Period
Land	17,126,000
Building and Land Improvements	55,842,000
Total	72,968,000	[2],[3]
Accumulated Depreciation	-14,434,000	[4]
7130 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,350,000
Building and Land Improvements	4,359,000
Costs Capitalized Subsequent to Acquisition	1,802,000
Gross Amounts Carried at Close of Period
Land	1,350,000
Building and Land Improvements	6,161,000
Total	7,511,000	[2],[3]
Accumulated Depreciation	-2,321,000	[4]
7134 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	704,000
Building and Land Improvements	1,971,000
Costs Capitalized Subsequent to Acquisition	310,000
Gross Amounts Carried at Close of Period
Land	704,000
Building and Land Improvements	2,281,000
Total	2,985,000	[2],[3]
Accumulated Depreciation	-638,000	[4]
7138 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,104,000
Building and Land Improvements	3,518,000
Costs Capitalized Subsequent to Acquisition	1,975,000
Gross Amounts Carried at Close of Period
Land	1,104,000
Building and Land Improvements	5,493,000
Total	6,597,000	[2],[3]
Accumulated Depreciation	-2,817,000	[4]
7142 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,342,000
Building and Land Improvements	3,978,000
Costs Capitalized Subsequent to Acquisition	2,494,000
Gross Amounts Carried at Close of Period
Land	1,342,000
Building and Land Improvements	6,472,000
Total	7,814,000	[2],[3]
Accumulated Depreciation	-2,091,000	[4]
7150 Columbia Gateway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,032,000
Building and Land Improvements	3,429,000
Costs Capitalized Subsequent to Acquisition	579,000
Gross Amounts Carried at Close of Period
Land	1,032,000
Building and Land Improvements	4,008,000
Total	5,040,000	[2],[3]
Accumulated Depreciation	-1,056,000	[4]
7150 Riverwood Drive
Initial Cost
Land	1,821,000
Building and Land Improvements	4,388,000
Costs Capitalized Subsequent to Acquisition	1,332,000
Gross Amounts Carried at Close of Period
Land	1,821,000
Building and Land Improvements	5,720,000
Total	7,541,000	[2],[3]
Accumulated Depreciation	-1,742,000	[4]
7160 Riverwood Drive
Initial Cost
Land	2,732,000
Building and Land Improvements	7,006,000
Costs Capitalized Subsequent to Acquisition	1,605,000
Gross Amounts Carried at Close of Period
Land	2,732,000
Building and Land Improvements	8,611,000
Total	11,343,000	[2],[3]
Accumulated Depreciation	-3,040,000	[4]
7170 Riverwood Drive
Initial Cost
Land	1,283,000
Building and Land Improvements	3,096,000
Costs Capitalized Subsequent to Acquisition	658,000
Gross Amounts Carried at Close of Period
Land	1,283,000
Building and Land Improvements	3,754,000
Total	5,037,000	[2],[3]
Accumulated Depreciation	-1,218,000	[4]
7175 Riverwood Drive
Initial Cost
Land	1,788,000
Building and Land Improvements	7,270,000
Gross Amounts Carried at Close of Period
Land	1,788,000
Building and Land Improvements	7,270,000
Total	9,058,000	[2],[3]
Accumulated Depreciation	-207,000	[4]
7200 Redstone Gateway
Initial Cost
Building and Land Improvements	4,926,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	4,926,000
Total	4,926,000	[2],[3]
Accumulated Depreciation	-133,000	[4]
7200 Riverwood Road
Initial Cost
Land	4,089,000
Building and Land Improvements	16,356,000
Costs Capitalized Subsequent to Acquisition	3,538,000
Gross Amounts Carried at Close of Period
Land	4,089,000
Building and Land Improvements	19,894,000
Total	23,983,000	[2],[3]
Accumulated Depreciation	-7,933,000	[4]
7205 Riverwood Drive
Initial Cost
Land	1,367,000
Building and Land Improvements	24,114,000
Gross Amounts Carried at Close of Period
Land	1,367,000
Building and Land Improvements	24,114,000
Total	25,481,000	[2],[3]
Accumulated Depreciation	-774,000	[4]
7272 Park Circle Drive
Real Estate and Accumulated Depreciation
Encumbrances	4,919,000	[1]
Initial Cost
Land	1,479,000
Building and Land Improvements	6,300,000
Costs Capitalized Subsequent to Acquisition	3,884,000
Gross Amounts Carried at Close of Period
Land	1,479,000
Building and Land Improvements	10,184,000
Total	11,663,000	[2],[3]
Accumulated Depreciation	-2,461,000	[4]
7318 Parkway Drive
Initial Cost
Land	972,000
Building and Land Improvements	3,888,000
Costs Capitalized Subsequent to Acquisition	926,000
Gross Amounts Carried at Close of Period
Land	972,000
Building and Land Improvements	4,814,000
Total	5,786,000	[2],[3]
Accumulated Depreciation	-1,879,000	[4]
7320 Parkway Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	905,000
Building and Land Improvements	3,570,000
Costs Capitalized Subsequent to Acquisition	4,018,000
Gross Amounts Carried at Close of Period
Land	905,000
Building and Land Improvements	7,588,000
Total	8,493,000	[2],[3]
Accumulated Depreciation	-2,310,000	[4]
7400 Redstone Gateway
Real Estate and Accumulated Depreciation
Encumbrances	0	[1],[5]
Initial Cost
Land	0	[5]
Building and Land Improvements	4,163,000	[5]
Costs Capitalized Subsequent to Acquisition	0	[5]
Gross Amounts Carried at Close of Period
Land	0	[5]
Building and Land Improvements	4,163,000	[5]
Total	4,163,000	[2],[3],[5]
Accumulated Depreciation	0	[4],[5]
7467 Ridge Road
Initial Cost
Land	1,629,000
Building and Land Improvements	6,517,000
Costs Capitalized Subsequent to Acquisition	2,402,000
Gross Amounts Carried at Close of Period
Land	1,629,000
Building and Land Improvements	8,919,000
Total	10,548,000	[2],[3]
Accumulated Depreciation	-4,138,000	[4]
7740 Milestone Parkway
Real Estate and Accumulated Depreciation
Encumbrances	19,357,000	[1]
Initial Cost
Land	3,825,000
Building and Land Improvements	34,365,000
Costs Capitalized Subsequent to Acquisition	366,000
Gross Amounts Carried at Close of Period
Land	3,825,000
Building and Land Improvements	34,731,000
Total	38,556,000	[2],[3]
Accumulated Depreciation	-4,003,000	[4]
7770 Backlick Road
Initial Cost
Land	6,387,000
Building and Land Improvements	74,325,000
Costs Capitalized Subsequent to Acquisition	140,000
Gross Amounts Carried at Close of Period
Land	6,387,000
Building and Land Improvements	74,465,000
Total	80,852,000	[2],[3]
Accumulated Depreciation	-3,414,000	[4]
7880 Milestone Parkway
Initial Cost
Land	4,857,000	[5]
Building and Land Improvements	12,221,000	[5]
Costs Capitalized Subsequent to Acquisition	0	[5]
Gross Amounts Carried at Close of Period
Land	4,857,000	[5]
Building and Land Improvements	12,221,000	[5]
Total	17,078,000	[2],[3],[5]
Accumulated Depreciation	0	[4],[5]
8003 Corporate Drive
Initial Cost
Land	611,000
Building and Land Improvements	1,611,000
Costs Capitalized Subsequent to Acquisition	655,000
Gross Amounts Carried at Close of Period
Land	611,000
Building and Land Improvements	2,266,000
Total	2,877,000	[2],[3]
Accumulated Depreciation	-396,000	[4]
8007 Corporate Drive
Initial Cost
Land	1,434,000
Building and Land Improvements	3,336,000
Costs Capitalized Subsequent to Acquisition	1,034,000
Gross Amounts Carried at Close of Period
Land	1,434,000
Building and Land Improvements	4,370,000
Total	5,804,000	[2],[3]
Accumulated Depreciation	-938,000	[4]
8010 Corporate Drive
Initial Cost
Land	1,349,000
Building and Land Improvements	3,262,000
Costs Capitalized Subsequent to Acquisition	1,744,000
Gross Amounts Carried at Close of Period
Land	1,349,000
Building and Land Improvements	5,006,000
Total	6,355,000	[2],[3]
Accumulated Depreciation	-1,282,000	[4]
8013 Corporate Drive
Initial Cost
Land	642,000
Building and Land Improvements	1,536,000
Costs Capitalized Subsequent to Acquisition	1,809,000
Gross Amounts Carried at Close of Period
Land	642,000
Building and Land Improvements	3,345,000
Total	3,987,000	[2],[3]
Accumulated Depreciation	-770,000	[4]
8015 Corporate Drive
Initial Cost
Land	446,000
Building and Land Improvements	1,116,000
Costs Capitalized Subsequent to Acquisition	361,000
Gross Amounts Carried at Close of Period
Land	446,000
Building and Land Improvements	1,477,000
Total	1,923,000	[2],[3]
Accumulated Depreciation	-428,000	[4]
8019 Corporate Drive
Initial Cost
Land	680,000
Building and Land Improvements	1,898,000
Costs Capitalized Subsequent to Acquisition	739,000
Gross Amounts Carried at Close of Period
Land	680,000
Building and Land Improvements	2,637,000
Total	3,317,000	[2],[3]
Accumulated Depreciation	-751,000	[4]
8020 Corporate Drive
Initial Cost
Land	2,184,000
Building and Land Improvements	3,767,000
Costs Capitalized Subsequent to Acquisition	2,205,000
Gross Amounts Carried at Close of Period
Land	2,184,000
Building and Land Improvements	5,972,000
Total	8,156,000	[2],[3]
Accumulated Depreciation	-1,499,000	[4]
8023 Corporate Drive
Initial Cost
Land	651,000
Building and Land Improvements	1,603,000
Costs Capitalized Subsequent to Acquisition	5,000
Gross Amounts Carried at Close of Period
Land	651,000
Building and Land Improvements	1,608,000
Total	2,259,000	[2],[3]
Accumulated Depreciation	-357,000	[4]
8094 Sandpiper Circle
Initial Cost
Land	1,960,000
Building and Land Improvements	3,716,000
Costs Capitalized Subsequent to Acquisition	941,000
Gross Amounts Carried at Close of Period
Land	1,960,000
Building and Land Improvements	4,657,000
Total	6,617,000	[2],[3]
Accumulated Depreciation	-1,125,000	[4]
8098 Sandpiper Circle
Initial Cost
Land	1,797,000
Building and Land Improvements	3,651,000
Costs Capitalized Subsequent to Acquisition	639,000
Gross Amounts Carried at Close of Period
Land	1,797,000
Building and Land Improvements	4,290,000
Total	6,087,000	[2],[3]
Accumulated Depreciation	-827,000	[4]
8110 Corporate Drive
Initial Cost
Land	2,285,000
Building and Land Improvements	10,117,000
Costs Capitalized Subsequent to Acquisition	989,000
Gross Amounts Carried at Close of Period
Land	2,285,000
Building and Land Improvements	11,106,000
Total	13,391,000	[2],[3]
Accumulated Depreciation	-2,870,000	[4]
8140 Corporate Drive
Initial Cost
Land	2,158,000
Building and Land Improvements	8,457,000
Costs Capitalized Subsequent to Acquisition	3,008,000
Gross Amounts Carried at Close of Period
Land	2,158,000
Building and Land Improvements	11,465,000
Total	13,623,000	[2],[3]
Accumulated Depreciation	-3,767,000	[4]
8621 Robert Fulton Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,317,000
Building and Land Improvements	12,642,000
Costs Capitalized Subsequent to Acquisition	336,000
Gross Amounts Carried at Close of Period
Land	2,317,000
Building and Land Improvements	12,978,000
Total	15,295,000	[2],[3]
Accumulated Depreciation	-3,015,000	[4]
8661 Robert Fulton Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,510,000
Building and Land Improvements	3,764,000
Costs Capitalized Subsequent to Acquisition	2,423,000
Gross Amounts Carried at Close of Period
Land	1,510,000
Building and Land Improvements	6,187,000
Total	7,697,000	[2],[3]
Accumulated Depreciation	-1,848,000	[4]
8671 Robert Fulton Drive
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	1,718,000
Building and Land Improvements	4,280,000
Costs Capitalized Subsequent to Acquisition	1,981,000
Gross Amounts Carried at Close of Period
Land	1,718,000
Building and Land Improvements	6,261,000
Total	7,979,000	[2],[3]
Accumulated Depreciation	-2,754,000	[4]
870 Elkridge Landing Road
Real Estate and Accumulated Depreciation
Encumbrances	0	[1]
Initial Cost
Land	2,003,000
Building and Land Improvements	9,442,000
Costs Capitalized Subsequent to Acquisition	6,941,000
Gross Amounts Carried at Close of Period
Land	2,003,000
Building and Land Improvements	16,383,000
Total	18,386,000	[2],[3]
Accumulated Depreciation	-7,965,000	[4]
891 Elkridge Landing Road
Initial Cost
Land	1,165,000
Building and Land Improvements	4,772,000
Costs Capitalized Subsequent to Acquisition	2,295,000
Gross Amounts Carried at Close of Period
Land	1,165,000
Building and Land Improvements	7,067,000
Total	8,232,000	[2],[3]
Accumulated Depreciation	-3,229,000	[4]
900 Elkridge Landing Road
Initial Cost
Land	1,993,000
Building and Land Improvements	7,972,000
Costs Capitalized Subsequent to Acquisition	3,486,000
Gross Amounts Carried at Close of Period
Land	1,993,000
Building and Land Improvements	11,458,000
Total	13,451,000	[2],[3]
Accumulated Depreciation	-5,655,000	[4]
901 Elkridge Landing Road
Initial Cost
Land	1,156,000
Building and Land Improvements	4,437,000
Costs Capitalized Subsequent to Acquisition	2,419,000
Gross Amounts Carried at Close of Period
Land	1,156,000
Building and Land Improvements	6,856,000
Total	8,012,000	[2],[3]
Accumulated Depreciation	-2,672,000	[4]
911 Elkridge Landing Road
Initial Cost
Land	1,215,000
Building and Land Improvements	4,861,000
Costs Capitalized Subsequent to Acquisition	2,024,000
Gross Amounts Carried at Close of Period
Land	1,215,000
Building and Land Improvements	6,885,000
Total	8,100,000	[2],[3]
Accumulated Depreciation	-3,239,000	[4]
921 Elkridge Landing Road
Initial Cost
Land	1,044,000	[5]
Building and Land Improvements	4,239,000	[5]
Costs Capitalized Subsequent to Acquisition	748,000	[5]
Gross Amounts Carried at Close of Period
Land	1,044,000	[5]
Building and Land Improvements	4,987,000	[5]
Total	6,031,000	[2],[3],[5]
Accumulated Depreciation	-2,244,000	[4],[5]
938 Elkridge Landing Road
Initial Cost
Land	1,163,000
Building and Land Improvements	4,748,000
Costs Capitalized Subsequent to Acquisition	1,155,000
Gross Amounts Carried at Close of Period
Land	1,163,000
Building and Land Improvements	5,903,000
Total	7,066,000	[2],[3]
Accumulated Depreciation	-1,928,000	[4]
939 Elkridge Landing Road
Initial Cost
Land	939,000
Building and Land Improvements	3,756,000
Costs Capitalized Subsequent to Acquisition	3,074,000
Gross Amounts Carried at Close of Period
Land	939,000
Building and Land Improvements	6,830,000
Total	7,769,000	[2],[3]
Accumulated Depreciation	-2,927,000	[4]
940 Elkridge Landing Road
Initial Cost
Land	1,104,000	[6]
Building and Land Improvements	4,730,000	[6]
Costs Capitalized Subsequent to Acquisition	170,000	[6]
Gross Amounts Carried at Close of Period
Land	1,104,000	[6]
Building and Land Improvements	4,900,000	[6]
Total	6,004,000	[2],[3],[6]
Accumulated Depreciation	-4,884,000	[4],[6]
9651 Hornbaker Road
Initial Cost
Land	6,050,000
Building and Land Improvements	204,176,000
Costs Capitalized Subsequent to Acquisition	853,000
Gross Amounts Carried at Close of Period
Land	6,050,000
Building and Land Improvements	205,029,000
Total	211,079,000	[2],[3]
Accumulated Depreciation	-10,881,000	[4]
9690 Deereco Road
Initial Cost
Land	3,415,000
Building and Land Improvements	13,723,000
Costs Capitalized Subsequent to Acquisition	7,289,000
Gross Amounts Carried at Close of Period
Land	3,415,000
Building and Land Improvements	21,012,000
Total	24,427,000	[2],[3]
Accumulated Depreciation	-9,585,000	[4]
9900 Franklin Square Drive
Initial Cost
Land	979,000
Building and Land Improvements	3,466,000
Costs Capitalized Subsequent to Acquisition	325,000
Gross Amounts Carried at Close of Period
Land	979,000
Building and Land Improvements	3,791,000
Total	4,770,000	[2],[3]
Accumulated Depreciation	-989,000	[4]
9910 Franklin Square Drive
Real Estate and Accumulated Depreciation
Encumbrances	4,691,000	[1]
Initial Cost
Land	1,219,000
Building and Land Improvements	6,590,000
Costs Capitalized Subsequent to Acquisition	74,000
Gross Amounts Carried at Close of Period
Land	1,219,000
Building and Land Improvements	6,664,000
Total	7,883,000	[2],[3]
Accumulated Depreciation	-1,952,000	[4]
9920 Franklin Square Drive
Initial Cost
Land	1,058,000
Building and Land Improvements	5,293,000
Costs Capitalized Subsequent to Acquisition	1,436,000
Gross Amounts Carried at Close of Period
Land	1,058,000
Building and Land Improvements	6,729,000
Total	7,787,000	[2],[3]
Accumulated Depreciation	-2,077,000	[4]
Aerotech Commerce
Initial Cost
Land	900,000	[6]
Gross Amounts Carried at Close of Period
Land	900,000	[6]
Total	900,000	[2],[3],[6]
Arborcrest
Initial Cost
Land	21,968,000	[5]
Building and Land Improvements	109,468,000	[5]
Costs Capitalized Subsequent to Acquisition	1,209,000	[5]
Gross Amounts Carried at Close of Period
Land	21,968,000	[5]
Building and Land Improvements	110,677,000	[5]
Total	132,645,000	[2],[3],[5]
Accumulated Depreciation	-22,043,000	[4],[5]
Arundel Preserve
Initial Cost
Land	13,401,000	[6]
Building and Land Improvements	7,238,000	[6]
Gross Amounts Carried at Close of Period
Land	13,401,000	[6]
Building and Land Improvements	7,238,000	[6]
Total	20,639,000	[2],[3],[6]
Ashburn Crossing - DC 10
Initial Cost
Land	4,408,000	[5]
Building and Land Improvements	8,399,000	[5]
Gross Amounts Carried at Close of Period
Land	4,408,000	[5]
Building and Land Improvements	8,399,000	[5]
Total	12,807,000	[2],[3],[5]
Accumulated Depreciation	0	[4],[5]
Canton Crossing Land
Initial Cost
Land	16,085,000	[6]
Building and Land Improvements	905,000	[6]
Gross Amounts Carried at Close of Period
Land	16,085,000	[6]
Building and Land Improvements	905,000	[6]
Total	16,990,000	[2],[3],[6]
Canton Crossing Util Distr Ctr
Initial Cost
Land	7,300,000
Building and Land Improvements	15,556,000
Costs Capitalized Subsequent to Acquisition	878,000
Gross Amounts Carried at Close of Period
Land	7,300,000
Building and Land Improvements	16,434,000
Total	23,734,000	[2],[3]
Accumulated Depreciation	-2,755,000	[4]
Columbia Gateway - Southridge
Initial Cost
Land	6,387,000	[6]
Building and Land Improvements	2,940,000	[6]
Gross Amounts Carried at Close of Period
Land	6,387,000	[6]
Building and Land Improvements	2,940,000	[6]
Total	9,327,000	[2],[3],[6]
Dahlgren Technology Center
Initial Cost
Land	978,000	[6]
Building and Land Improvements	178,000	[6]
Gross Amounts Carried at Close of Period
Land	978,000	[6]
Building and Land Improvements	178,000	[6]
Total	1,156,000	[2],[3],[6]
Expedition VII
Initial Cost
Land	705,000	[6]
Building and Land Improvements	727,000	[6]
Gross Amounts Carried at Close of Period
Land	705,000	[6]
Building and Land Improvements	727,000	[6]
Total	1,432,000	[2],[3],[6]
InterQuest
Initial Cost
Land	14,382,000	[6]
Building and Land Improvements	9,000	[6]
Gross Amounts Carried at Close of Period
Land	14,382,000	[6]
Building and Land Improvements	9,000	[6]
Total	14,391,000	[2],[3],[6]
M Square Research Park
Initial Cost
Building and Land Improvements	3,129,000	[6]
Gross Amounts Carried at Close of Period
Building and Land Improvements	3,129,000	[6]
Total	3,129,000	[2],[3],[6]
National Business Park North
Initial Cost
Land	27,785,000	[6]
Building and Land Improvements	47,411,000	[6]
Gross Amounts Carried at Close of Period
Land	27,785,000	[6]
Building and Land Improvements	47,411,000	[6]
Total	75,196,000	[2],[3],[6]
North Gate Business Park
Initial Cost
Land	6,486,000	[6]
Building and Land Improvements	10,922,000	[6]
Gross Amounts Carried at Close of Period
Land	6,486,000	[6]
Building and Land Improvements	10,922,000	[6]
Total	17,408,000	[2],[3],[6]
Northwest Crossroads
Initial Cost
Land	7,430,000	[6]
Building and Land Improvements	836,000	[6]
Gross Amounts Carried at Close of Period
Land	7,430,000	[6]
Building and Land Improvements	836,000	[6]
Total	8,266,000	[2],[3],[6]
NOVA Office A
Initial Cost
Land	2,096,000	[5],[7]
Building and Land Improvements	38,142,000	[5],[7]
Gross Amounts Carried at Close of Period
Land	2,096,000	[5],[7]
Building and Land Improvements	38,142,000	[5],[7]
Total	40,238,000	[2],[3],[5],[7]
NOVA Office B
Initial Cost
Land	739,000	[5],[7]
Building and Land Improvements	18,858,000	[5],[7]
Gross Amounts Carried at Close of Period
Land	739,000	[5],[7]
Building and Land Improvements	18,858,000	[5],[7]
Total	19,597,000	[2],[3],[5],[7]
NOVA Office D
Initial Cost
Land	6,587,000	[5]
Building and Land Improvements	2,000	[5]
Gross Amounts Carried at Close of Period
Land	6,587,000	[5]
Building and Land Improvements	2,000	[5]
Total	6,589,000	[2],[3],[5]
Old Annapolis Road
Initial Cost
Land	1,637,000
Building and Land Improvements	5,500,000
Costs Capitalized Subsequent to Acquisition	2,421,000
Gross Amounts Carried at Close of Period
Land	1,637,000
Building and Land Improvements	7,921,000
Total	9,558,000	[2],[3]
Accumulated Depreciation	-2,756,000	[4]
Patriot Park
Initial Cost
Land	8,723,000	[6]
Building and Land Improvements	248,000	[6]
Gross Amounts Carried at Close of Period
Land	8,723,000	[6]
Building and Land Improvements	248,000	[6]
Total	8,971,000	[2],[3],[6]
Patriot Ridge
Initial Cost
Land	18,517,000	[6]
Building and Land Improvements	14,440,000	[6]
Gross Amounts Carried at Close of Period
Land	18,517,000	[6]
Building and Land Improvements	14,440,000	[6]
Total	32,957,000	[2],[3],[6]
Redstone Gateway
Initial Cost
Building and Land Improvements	14,087,000	[6]
Gross Amounts Carried at Close of Period
Building and Land Improvements	14,087,000	[6]
Total	14,087,000	[2],[3],[6]
Route 15/Biggs Ford Road
Initial Cost
Land	8,703,000	[6]
Building and Land Improvements	541,000	[6]
Gross Amounts Carried at Close of Period
Land	8,703,000	[6]
Building and Land Improvements	541,000	[6]
Total	9,244,000	[2],[3],[6]
Sentry Gateway
Initial Cost
Land	8,275,000	[6]
Building and Land Improvements	3,645,000	[6]
Gross Amounts Carried at Close of Period
Land	8,275,000	[6]
Building and Land Improvements	3,645,000	[6]
Total	11,920,000	[2],[3],[6]
Sentry Gateway - T
Initial Cost
Land	14,020,000
Building and Land Improvements	38,804,000
Costs Capitalized Subsequent to Acquisition	13,000
Gross Amounts Carried at Close of Period
Land	14,020,000
Building and Land Improvements	38,817,000
Total	52,837,000	[2],[3]
Accumulated Depreciation	-7,646,000	[4]
Sentry Gateway - V
Initial Cost
Building and Land Improvements	1,066,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	1,066,000
Total	1,066,000	[2],[3]
Accumulated Depreciation	-161,000	[4]
Sentry Gateway - W
Initial Cost
Building and Land Improvements	1,884,000
Gross Amounts Carried at Close of Period
Building and Land Improvements	1,884,000
Total	1,884,000	[2],[3]
Accumulated Depreciation	-249,000	[4]
Sentry Gateway - X
Initial Cost
Land	1,964,000
Building and Land Improvements	21,178,000
Gross Amounts Carried at Close of Period
Land	1,964,000
Building and Land Improvements	21,178,000
Total	23,142,000	[2],[3]
Accumulated Depreciation	-2,204,000	[4]
Sentry Gateway - Y
Initial Cost
Land	1,964,000
Building and Land Improvements	21,298,000
Gross Amounts Carried at Close of Period
Land	1,964,000
Building and Land Improvements	21,298,000
Total	23,262,000	[2],[3]
Accumulated Depreciation	-2,213,000	[4]
Sentry Gateway - Z
Initial Cost
Land	1,964,000	[5]
Building and Land Improvements	23,185,000	[5]
Gross Amounts Carried at Close of Period
Land	1,964,000	[5]
Building and Land Improvements	23,185,000	[5]
Total	25,149,000	[2],[3],[5]
Westfields - Park Center
Initial Cost
Land	16,418,000	[6]
Building and Land Improvements	8,584,000	[6]
Gross Amounts Carried at Close of Period
Land	16,418,000	[6]
Building and Land Improvements	8,584,000	[6]
Total	25,002,000	[2],[3],[6]
Westfields Corporate Center
Initial Cost
Land	7,141,000	[6]
Building and Land Improvements	1,415,000	[6]
Gross Amounts Carried at Close of Period
Land	7,141,000	[6]
Building and Land Improvements	1,415,000	[6]
Total	8,556,000	[2],[3],[6]
White Marsh
Initial Cost
Land	17,610,000	[6]
Building and Land Improvements	6,983,000	[6]
Gross Amounts Carried at Close of Period
Land	17,610,000	[6]
Building and Land Improvements	6,983,000	[6]
Total	24,593,000	[2],[3],[6]
Woodland Park
Initial Cost
Land	9,614,000	[6]
Building and Land Improvements	81,000	[6]
Gross Amounts Carried at Close of Period
Land	9,614,000	[6]
Building and Land Improvements	81,000	[6]
Total	9,695,000	[2],[3],[6]
Other Developments, including intercompany eliminations
Initial Cost
Land	8,000
Building and Land Improvements	276,000
Costs Capitalized Subsequent to Acquisition	261,000
Gross Amounts Carried at Close of Period
Land	8,000
Building and Land Improvements	537,000
Total	545,000	[2],[3]
Accumulated Depreciation	-26,000	[4]
Other Properties with Shortened Holding Periods | Fair value measurement on a nonrecurring basis | Greater Baltimore
Additional information
Impairment losses	$1,371,000		$5,900,000
[1]	Excludes our Revolving Credit Facility of $83.0 million, term loan facilities of $520.0 million, unsecured senior notes of $890.9 million, exchangeable senior notes of $572,000, unsecured notes payable of $1.6 million, a letter of credit on a mortgage loan of $14.8 million, and net premiums on the remaining loans of $42,000.
[2]	As discussed in Note 3 to our Consolidated Financial Statements, we recognized impairment losses of $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore region that were disposed in the current period.
[3]	The aggregate cost of these assets for Federal income tax purposes was approximately $3.4 billion at December 31, 2014.
[4]	The estimated lives over which depreciation is recognized follow: Building and land improvements: 10-40 years; and tenant improvements: related lease terms.
[5]	Under construction or redevelopment at December 31, 2014.
[6]	Held or under pre-construction at December 31, 2014.
[7]	The carrying amounts of these properties under construction exclude allocated costs of the garage being constructed to support the properties.

Schedule_III_Real_Estate_and_A2

Schedule III - Real Estate and Accumulated Depreciation (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Changes in cost of properties
Beginning balance	$3,811,950		$3,859,960	$4,038,932
Acquisitions of operating properties	0		0	33,684
Building and land improvements	254,868		249,639	214,418
Sales	-48,466		-141,045	-291,491
Impairments	-3,042		-45,931	-121,557
Other dispositions	-974		-110,673	-13,891
Other	0		0	-135
Ending balance	4,014,336	[1],[2]	3,811,950	3,859,960
Changes in accumulated depreciation
Beginning balance	597,649		568,176	577,601
Depreciation expense	111,326		92,677	93,158
Sales	-3,129		-9,542	-40,346
Impairments	-1,671		-14,863	-58,855
Other dispositions	-1,092		-38,799	-3,247
Other	0		0	-135
Ending balance	$703,083	[3]	$597,649	$568,176
[1]	As discussed in Note 3 to our Consolidated Financial Statements, we recognized impairment losses of $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore region that were disposed in the current period.
[2]	The aggregate cost of these assets for Federal income tax purposes was approximately $3.4 billion at December 31, 2014.
[3]	The estimated lives over which depreciation is recognized follow: Building and land improvements: 10-40 years; and tenant improvements: related lease terms.