Consolidated Statements of Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Preferred Shares USD ($)	Common Shares USD ($)	Additional Paid-in Capital USD ($)	Cumulative Distributions in Excess of Net Income USD ($)	Accumulated Other Comprehensive Income (Loss) USD ($)	Noncontrolling Interests USD ($)	Corporate Office Properties, L.P. USD ($)	Corporate Office Properties, L.P. Common Shares USD ($)	Corporate Office Properties, L.P. Accumulated Other Comprehensive Income (Loss) USD ($)	Corporate Office Properties, L.P. Noncontrolling Interests USD ($)	Corporate Office Properties, L.P. Limited Partner	Corporate Office Properties, L.P. Limited Partner Preferred Shares USD ($)	Corporate Office Properties, L.P. General Partner	Corporate Office Properties, L.P. General Partner Preferred Shares USD ($)
Balance (COPT: 87,394,512 shares and 93,255,284 shares as of December 31, 2013 and 2014, respectively) 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 (in units/ shares) at Dec. 31, 2013	87,394,512								91,372,212
Balance (preferred units) at Dec. 31, 2013													352,000		9,431,667
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 48,498 shares and 158,000 shares for the three months ended March 31, 2014 and 2015, respectively)	0		0	651			(651)
Exercise of share options (in units/shares)	26,614								26,614
Exercise of share options (COPT: 26,614 shares and 70,374 shares for the three months ended March 31, 2014 and 2015, respectively)	568			568				568	568
Share-based compensation issuance, net of redemptions (in units/shares)	125,307								125,307
Share-based compensation issuance, net of redemptions (COPT: 125,307 and 162,370 shares issued, net of redemptions for the three months ended March 31, 2014 and 2015, respectively)	1,856		2	1,854				1,856	1,856
Redemption of vested equity awards (in units/shares)									0
Redemption of vested equity awards	(1,092)			(1,092)				(1,092)	(1,092)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(69)			69
Comprehensive income	3,741				4,741	(1,408)	408	3,741	279	(1,472)	279		165		4,490
Dividends / Distributions to owners of common and preferred units	(28,581)				(28,581)			(29,827)	(25,172)				(165)		(4,490)
Distributions to owners of common and preferred units in COPLP	(1,246)						(1,246)
Adjustment to arrive at fair value of redeemable noncontrolling interest	540			540				540	540
Balance (COPT: 87,594,931 shares and 94,536,269 shares as of March 31, 2014 and 2015, respectively) at Mar. 31, 2014	1,473,035	249,083	876	1,816,467	(665,708)	2,072	70,245	1,473,035	1,203,297	2,133	9,722		8,800		249,083
Balance (in units/ shares) at Mar. 31, 2014	87,594,931								91,524,133
Balance (preferred units) at Mar. 31, 2014													352,000		9,431,667
Balance (COPT: 87,394,512 shares and 93,255,284 shares as of December 31, 2013 and 2014, respectively) 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 (in units/ shares) at Dec. 31, 2014	93,255,284								97,092,835			3,837,551		93,255,284
Balance (preferred units) at Dec. 31, 2014												352,000	352,000	7,431,667	7,431,667
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 48,498 shares and 158,000 shares for the three months ended March 31, 2014 and 2015, respectively)	0		2	2,120			(2,122)
Issuance of common units resulting from common shares issued under at-the-market program (in units)									890,241
Issuance of common units resulting from common shares issued under at-the-market program (COPT: 890,241 shares for the three months ended March 31, 2015)	26,535		9	26,526				26,535	26,535
Exercise of share options (in units/shares)	70,374								70,374
Exercise of share options (COPT: 26,614 shares and 70,374 shares for the three months ended March 31, 2014 and 2015, respectively)	1,845			1,845				1,845	1,845
Share-based compensation issuance, net of redemptions (in units/shares)	162,370								162,370
Share-based compensation issuance, net of redemptions (COPT: 125,307 and 162,370 shares issued, net of redemptions for the three months ended March 31, 2014 and 2015, respectively)	1,829		1	1,828				1,829	1,829
Redemption of vested equity awards (in units/shares)									0
Redemption of vested equity awards	(2,031)			(2,031)				(2,031)	(2,031)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(475)			475
Comprehensive income	11,472				13,355	(2,650)	767	11,472	10,200	(2,756)	311		165		3,552
Dividends / Distributions to owners of common and preferred units	(29,550)				(29,550)			(30,727)	(27,010)				(165)		(3,552)
Distributions to owners of common and preferred units in COPLP	(1,177)						(1,177)
Distributions to noncontrolling interests in subsidiaries	(4)						(4)	(4)			(4)
Adjustment to arrive at fair value of redeemable noncontrolling interest	(73)			(73)				(73)	(73)
Balance (COPT: 87,594,931 shares and 94,536,269 shares as of March 31, 2014 and 2015, respectively) at Mar. 31, 2015	$ 1,529,730	$ 199,083	$ 945	$ 1,999,708	$ (733,459)	$ (3,947)	$ 67,400	$ 1,529,730	$ 1,316,514	$ (4,137)	$ 9,470		$ 8,800		$ 199,083
Balance (in units/ shares) at Mar. 31, 2015	94,536,269								98,215,820			3,679,551		94,536,269
Balance (preferred units) at Mar. 31, 2015												352,000	352,000	7,431,667	7,431,667