Consolidated Balance Sheets (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Properties, net:
Operating properties, net	$ 2,772,303	$ 2,802,773
Properties under construction or development	696,914	642,682
Total properties, net	3,469,217	3,445,455
Assets held for sale, net	72,767
Cash and cash equivalents	11,504	10,102
Restricted cash and marketable securities	39,232	22,582
Accounts receivable (net of allowance for doubtful accounts of $3,404 and $2,796, respectively)	20,991	18,938
Deferred rent receivable	87,148	79,160
Intangible assets on real estate acquisitions, net	97,954	113,735
Deferred leasing and financing costs, net	70,791	60,649
Prepaid expenses and other assets	95,788	93,896
Total assets	3,965,392	3,844,517
Liabilities:
Debt, net	2,420,073	2,323,681
Accounts payable and accrued expenses	114,834	99,699
Rents received in advance and security deposits	28,241	31,603
Dividends and distributions payable	35,029	32,986
Deferred revenue associated with operating leases	15,621	14,802
Distributions received in excess of investment in unconsolidated real estate joint venture	5,953	5,545
Interest rate derivatives	30,629	4,226
Other liabilities	7,389	8,837
Total liabilities	2,657,769	2,521,379
Commitments and contingencies (Note 16)
Corporate Office Properties Trust's shareholders' equity:
Preferred Shares of beneficial interest with an aggregate liquidation preference of $216,333 ($0.01 par value; 15,000,000 shares authorized and 8,121,667 shares issued and outstanding at September 30, 2011 and December 31, 2010)	81	81
Common Shares of beneficial interest ($0.01 par value; 125,000,000 shares authorized, shares issued and outstanding of 71,986,936 at September 30, 2011 and 66,931,582 at December 31, 2010)	720	669
Additional paid-in capital	1,663,850	1,511,844
Cumulative distributions in excess of net income	(416,342)	(281,794)
Accumulated other comprehensive loss	(28,618)	(4,163)
Total Corporate Office Properties Trust's shareholders' equity	1,219,691	1,226,637
Noncontrolling interests in subsidiaries:
Common units in the Operating Partnership	60,583	69,337
Preferred units in the Operating Partnership	8,800	8,800
Other consolidated entities	18,549	18,364
Noncontrolling interests in subsidiaries	87,932	96,501
Total equity	1,307,623	1,323,138
Total liabilities and equity	$ 3,965,392	$ 3,844,517