Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities
Revenues from real estate operations received	$ 476,762	$ 453,847	$ 417,494
Construction contract and other service revenues received	88,433	112,644	346,281
Property operating expenses paid	(188,237)	(180,619)	(150,693)
Construction contract and other service expenses paid	(94,140)	(124,867)	(325,223)
General and administrative and business development expenses paid	(19,831)	(16,975)	(19,559)
Interest expense paid	(93,715)	(87,917)	(73,327)
Previously accreted interest expense paid	(17,314)
Interest and other income received	698	323	161
Payments in connection with early extinguishment of debt	(353)
Income taxes paid	(160)		(317)
Net cash provided by operating activities	152,143	156,436	194,817
Purchases of and additions to properties
Construction, development and redevelopment	(232,667)	(303,064)	(176,364)
Acquisitions of operating properties	(32,856)	(146,275)	(45,010)
Tenant improvements on operating properties	(37,195)	(20,826)	(14,622)
Other capital improvements on operating properties	(16,906)	(10,422)	(15,569)
Proceeds from sales of properties	79,638	27,576	65
Proceeds from sale of equity method investment	5,773
Mortgage and other loan receivables funded or acquired	(23,377)	(5,588)	(82,413)
Mortgage and other loan receivables payments received	16,759	1,568	680
Leasing costs paid	(15,997)	(14,403)	(8,786)
Investment in unconsolidated entities	(250)	(6,600)	(3,000)
Other	(3,309)	(1,133)	(4,057)
Net cash used in investing activities	(260,387)	(479,167)	(349,076)
Cash flows from financing activities
Proceeds from debt, including issuance of exchangeable senior notes	1,636,206	1,022,912	1,066,413
Repayments of debt
Scheduled principal amortization	(13,755)	(13,996)	(11,489)
Other repayments	(1,511,100)	(799,663)	(863,243)
Deferred financing costs paid	(13,113)	(8,570)	(3,388)
Net proceeds from issuance of common shares	147,828	250,196	77,052
Acquisition of noncontrolling interests in consolidated entities		(4,462)
Dividends paid	(130,745)	(109,894)	(100,095)
Distributions paid	(7,891)	(8,099)	(9,579)
Restricted share redemptions	(3,990)	(3,913)	(2,049)
Other	261	60	2,124
Net cash provided by financing activities	103,701	324,571	155,746
Net (decrease) increase in cash and cash equivalents	(4,543)	1,840	1,487
Cash and cash equivalents
Beginning of period	10,102	8,262	6,775
End of period	5,559	10,102	8,262
Reconciliation of net (loss) income to net cash provided by operating activities:
Net (loss) income	(124,318)	45,504	61,299
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and other amortization	136,594	125,819	111,811
Impairment losses	151,021
Loss on interest rate derivatives	29,805
Settlement of previously accreted interest expense	(17,314)
Amortization of deferred financing costs	6,596	5,871	4,214
Increase in deferred rent receivable	(10,102)	(5,706)	(1,296)
Amortization of net debt discounts	5,540	5,841	3,412
Gain on sales of real estate	(7,528)	(3,917)
Gain on equity method investment	(2,452)	(6,406)	(442)
Share-based compensation	11,920	11,845	10,602
Other	1,356	(3,872)	(5,693)
Changes in operating assets and liabilities:
Increase in accounts receivable	(7,094)	(1,680)	(3,634)
(Increase) decrease in restricted cash and marketable securities and prepaid expenses and other assets	(2,496)	3,799	(2,745)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(17,330)	(19,644)	15,787
(Decrease) increase in rents received in advance and security deposits	(2,055)	(1,018)	1,502
Net cash provided by operating activities	152,143	156,436	194,817
Supplemental schedule of non-cash investing and financing activities:
Increase in accrued capital improvements, leasing and other investing activity costs	11,719	4,576	6,256
Increase in property, debt and other liabilities in connection with acquisitions	3,040	74,244	3,085
Cancellation of mortgage loans receivable in connection with acquisitions			102,575
Increase in property and noncontrolling interests in connection with property contribution by a noncontrolling interest in a joint venture		9,000
Increase (decrease) in fair value of derivatives applied to AOCL and noncontrolling interests	1,438	(1,846)	3,365
Dividends/distributions payable	35,038	32,986	28,440
Decrease in noncontrolling interests and increase in shareholders' equity in connection with the conversion of common units into common shares	1,521	9,567	61,654
Adjustments to noncontrolling interests resulting from changes in ownership of Operating Partnership by COPT	$ 2,798	$ 10,274	$ 21,072