Quarterly Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	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	$ 0.00	$ 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	$ 0.00	$ 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	$ 0.00	$ 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	$ 0.00	$ 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.