Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Revenues
Rental revenue	$ 367,654		$ 348,006		$ 316,038
Tenant recoveries and other real estate operations revenue	86,517		80,490		71,521
Construction contract and other service revenues	73,836		84,345		104,675
Total revenues	528,007		512,841		492,234
Expenses
Property operating expenses	167,161		162,397		146,617
Depreciation and amortization associated with real estate operations	113,480		113,111		97,897
Construction contract and other service expenses	70,576		81,639		102,302
Impairment losses	43,214		83,478		0
General, administrative and leasing expenses	31,900		30,314		28,501
Business development expenses and land carry costs	5,711		6,122		6,403
Total operating expenses	432,042		477,061		381,720
Operating income	95,965		35,780		110,514
Interest expense	(94,624)		(98,222)		(95,729)
Interest and other income	7,172		5,603		9,568
Loss on early extinguishment of debt	(943)		(1,639)		0
Loss on interest rate derivatives	0		(29,805)		0
Income (loss) from continuing operations before equity in (loss) income of unconsolidated entities and income taxes	7,570		(88,283)		24,353
Equity in (loss) income of unconsolidated entities	(546)		(331)		1,376
Income tax (expense) benefit	(381)		6,710		(108)
Income (loss) from continuing operations	6,643		(81,904)		25,621
Discontinued operations	13,677		(48,404)		17,054
Income (loss) before gain on sales of real estate	20,320		(130,308)		42,675
Gain on sales of real estate, net of income taxes	21		2,732		2,829
Net income (loss)	20,341		(127,576)		45,504
Net loss (income) attributable to noncontrolling interests:
Common units in the Operating Partnership	87		8,439		(2,116)
Preferred units in the Operating Partnership	(660)		(660)		(660)
Other consolidated entities	1,209		369		32
Net income (loss) attributable to Corporate Office Properties Trust	20,977		(119,428)		42,760
Preferred share dividends	(20,844)		(16,102)		(16,102)
Issuance costs associated with redeemed preferred shares	(1,827)		0		0
Net (loss) income attributable to Corporate Office Properties Trust common shareholders	(1,694)		(135,530)		26,658
Net income (loss) attributable to Corporate Office Properties Trust:
Income (loss) from continuing operations	8,051		(73,884)		27,029
Discontinued operations, net	12,926		(45,544)		15,731
Net income (loss) attributable to Corporate Office Properties Trust	$ 20,977		$ (119,428)		$ 42,760
Basic earnings per common share
(Loss) income from continuing operations (in dollars per share)	$ (0.21)	[1]	$ (1.31)	[1]	$ 0.17	[1]
Discontinued operations (in dollars per share)	$ 0.18	[1]	$ (0.66)	[1]	$ 0.26	[1]
Net (loss) income attributable to COPT common shareholders (in dollars per share)	$ (0.03)	[1]	$ (1.97)	[1]	$ 0.43	[1]
Diluted earnings per common share
(Loss) income from continuing operations (in dollars per share)	$ (0.21)	[1]	$ (1.31)	[1]	$ 0.17	[1]
Discontinued operations (in dollars per share)	$ 0.18	[1]	$ (0.66)	[1]	$ 0.26	[1]
Net (loss) income attributable to COPT common shareholders (in dollars per share)	$ (0.03)	[1]	$ (1.97)	[1]	$ 0.43	[1]

[1] Basic and diluted earnings per common share are calculated based on amounts attributable to common shareholders of Corporate Office Properties Trust.