Consolidated Statements of Cash Flows (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Cash flows from operating activities
Revenues from real estate operations received	$ 350,593	$ 324,445
Construction contract and other service revenues received	73,382	92,817
Property operating expenses paid	(143,481)	(138,379)
Construction contract and other service expenses paid	(73,009)	(107,016)
General and administrative and business development expenses paid	(15,921)	(13,726)
Interest expense paid	(69,237)	(63,298)
Previously accreted interest expense paid	(17,314)
Interest and other income received	377	709
Payments in connection with early extinguishment of debt	(350)
Income taxes paid	(174)
Net cash provided by operating activities	104,866	95,552
Purchases of and additions to properties
Construction, development and redevelopment	(169,873)	(240,092)
Acquisitions of operating properties	(32,806)	(103,277)
Tenant improvements on operating properties	(27,421)	(11,259)
Other capital improvements on operating properties	(11,575)	(5,870)
Proceeds from sales of properties	27,312	27,580
Proceeds from sale of equity method investment	5,773
Mortgage and other loan receivables funded or acquired	(20,401)	(1,729)
Mortgage and other loan receivables payments received	5,203
Leasing costs paid	(10,357)	(7,717)
Investment in unconsolidated entities	(250)	(4,500)
Other	(3,330)	(2,241)
Net cash used in investing activities	(237,725)	(349,105)
Cash flows from financing activities
Proceeds from debt, including issuance of exchangeable senior notes	1,548,619	825,475
Repayments of debt
Scheduled principal amortization	(10,647)	(10,389)
Other repayments	(1,432,050)	(459,614)
Deferred financing costs paid	(12,771)	(7,086)
Net proceeds from issuance of common shares	147,781	4,378
Acquisition of noncontrolling interests in consolidated entities		(4,462)
Dividends paid	(97,047)	(81,376)
Distributions paid	(5,937)	(6,100)
Restricted share redemptions	(3,948)	(3,862)
Other	261	60
Net cash provided by financing activities	134,261	257,024
Net increase in cash and cash equivalents	1,402	3,471
Cash and cash equivalents
Beginning of period	10,102	8,262
End of period	11,504	11,733
Reconciliation of net (loss) income to net cash provided by operating activities:
Net (loss) income	(37,103)	28,752
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and other amortization	102,963	89,830
Impairment losses	72,347
Settlement of previously accreted interest expense	(17,314)
Amortization of deferred financing costs	5,090	4,175
Increase in deferred rent receivable	(7,587)	(3,295)
Amortization of net debt discounts	4,778	4,360
Gain on sales of real estate	(4,166)	(3,921)
Gain on equity method investment	(2,452)
Share-based compensation	8,156	8,726
Loss on early extinguishment of debt	1,670
Other	18	(2,194)
Changes in operating assets and liabilities:
Increase in accounts receivable	(1,311)	(1,648)
(Increase) decrease in restricted cash and marketable securities and prepaid expenses and other assets	(5,162)	8,165
Decrease in accounts payable, accrued expenses and other liabilities	(11,699)	(31,696)
Decrease in rents received in advance and security deposits	(3,362)	(5,702)
Net cash provided by operating activities	104,866	95,552
Supplemental schedule of non-cash investing and financing activities:
Increase in accrued capital improvements, leasing and other investing activity costs	25,314	4,308
Increase in property, debt and other liabilities in connection with acquisitions	3,040	74,244
Increase in property and noncontrolling interests in connection with property contribution by a noncontrolling interest in a joint venture		9,000
Decrease in fair value of derivatives applied to AOCL and noncontrolling interests	27,064	3,206
Dividends/distribution payable	35,029	29,899
Decrease in noncontrolling interests and increase in shareholders' equity in connection with the conversion of common units into common shares	1,276	8,970
Adjustments to noncontrolling interests resulting from changes in ownership of Operating Partnership by COPT	$ 2,542	$ 1,347