Corporate Office Properties Trust 10-Q 4 Nov 15 2015 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 16, 2015
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES TRUST
Entity Central Index Key	860,546
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		94,533,250
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Corporate Office Properties, L.P.
Entity Information [Line Items]
Entity Registrant Name	CORPORATE OFFICE PROPERTIES, L.P.
Entity Central Index Key	1,577,966
Document Type	10-Q
Document Period End Date	Sep. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Properties, net:
Operating properties, net	$ 2,932,843	$ 2,751,488
Projects in development or held for future development	414,757	545,426
Total properties, net	3,347,600	3,296,914
Assets held for sale, net	150,572	14,339
Cash and cash equivalents	3,840	6,077
Restricted cash and marketable securities	9,286	9,069
Accounts receivable (net of allowance for doubtful accounts of $2,010 and $717, respectively)	19,962	26,901
Deferred rent receivable (net of allowance of $1,816 and $1,418, respectively)	103,064	95,910
Intangible assets on real estate acquisitions, net	106,174	43,854
Deferred leasing and financing costs, net	64,367	64,797
Investing receivables	46,821	52,147
Prepaid expenses and other assets, net	66,787	60,249
Total assets	3,918,473	3,670,257
Liabilities:
Debt, net	2,121,240	1,920,057
Accounts payable and accrued expenses	98,551	123,035
Rents received in advance and security deposits	34,504	31,011
Dividends and distributions payable	30,182	29,862
Deferred revenue associated with operating leases	20,113	13,031
Interest rate derivatives	5,844	1,855
Other liabilities	8,524	12,105
Total liabilities	$ 2,318,958	$ 2,130,956
Commitments and contingencies
Redeemable noncontrolling interest	$ 19,608	$ 18,417
Corporate Office Properties Trust’s shareholders’ equity:
Preferred Shares of beneficial interest at liquidation preference ($0.01 par value; 25,000,000 shares authorized; issued and outstanding of 7,431,667 at September 30, 2015 and December 31, 2014)	199,083	199,083
Common Shares of beneficial interest	945	933
Additional paid-in capital	2,002,730	1,969,968
Cumulative distributions in excess of net income	(686,986)	(717,264)
Accumulated other comprehensive loss	(5,823)	(1,297)
Total Corporate Office Properties Trust’s shareholders’ equity	1,509,949	1,451,423
Noncontrolling interests in subsidiaries:
Common units in COPLP	50,992	51,534
Preferred units in COPLP	8,800	8,800
Other consolidated entities	10,166	9,127
Noncontrolling interests in subsidiaries	69,958	69,461
Total equity	1,579,907	1,520,884
Total liabilities, redeemable noncontrolling interest and equity	3,918,473	3,670,257
Corporate Office Properties, L.P.
Properties, net:
Operating properties, net	2,932,843	2,751,488
Projects in development or held for future development	414,757	545,426
Total properties, net	3,347,600	3,296,914
Assets held for sale, net	150,572	14,339
Cash and cash equivalents	3,840	6,077
Restricted cash and marketable securities	3,787	3,187
Accounts receivable (net of allowance for doubtful accounts of $2,010 and $717, respectively)	19,962	26,901
Deferred rent receivable (net of allowance of $1,816 and $1,418, respectively)	103,064	95,910
Intangible assets on real estate acquisitions, net	106,174	43,854
Deferred leasing and financing costs, net	64,367	64,797
Investing receivables	46,821	52,147
Prepaid expenses and other assets, net	66,787	60,249
Total assets	3,912,974	3,664,375
Liabilities:
Debt, net	2,121,240	1,920,057
Accounts payable and accrued expenses	98,551	123,035
Rents received in advance and security deposits	34,504	31,011
Dividends and distributions payable	30,182	29,862
Deferred revenue associated with operating leases	20,113	13,031
Interest rate derivatives	5,844	1,855
Other liabilities	3,025	6,223
Total liabilities	$ 2,313,459	$ 2,125,074
Commitments and contingencies
Redeemable noncontrolling interest	$ 19,608	$ 18,417
Corporate Office Properties Trust’s shareholders’ equity:
Common Shares of beneficial interest	1,367,904	1,305,219
Accumulated other comprehensive loss	(6,086)	(1,381)
Total Corporate Office Properties Trust’s shareholders’ equity	1,569,701	1,511,721
Noncontrolling interests in subsidiaries:
Noncontrolling interests in subsidiaries	10,206	9,163
Total equity	1,579,907	1,520,884
Total liabilities, redeemable noncontrolling interest and equity	3,912,974	3,664,375
General Partner | Corporate Office Properties, L.P.
Corporate Office Properties Trust’s shareholders’ equity:
Preferred partners' capital accounts	199,083	199,083
Limited Partner | Corporate Office Properties, L.P.
Corporate Office Properties Trust’s shareholders’ equity:
Preferred partners' capital accounts	$ 8,800	$ 8,800

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Allowance for doubtful accounts - AR	$ 2,010	$ 717
Allowance - Deferred rent receivable	$ 1,816	$ 1,418
Preferred Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Shares of beneficial interest, shares authorized	25,000,000	25,000,000
Preferred Shares of beneficial interest, shares issued	7,431,667	7,431,667
Preferred Shares of beneficial interest, shares outstanding	7,431,667	7,431,667
Common Shares of beneficial interest, par value (in dollars per share)	$ 0.01	$ 0.01
Common Shares of beneficial interest, shares authorized	125,000,000	125,000,000
Common Stock, Shares, Issued	94,533,670	93,255,284
Common Shares of beneficial interest, shares outstanding	94,533,670	93,255,284
Corporate Office Properties, L.P.
Allowance for doubtful accounts - AR	$ 2,010	$ 717
Allowance - Deferred rent receivable	$ 1,816	$ 1,418
Corporate Office Properties, L.P. | General Partner
Common Shares of beneficial interest, shares outstanding	94,533,670	93,255,284
Preferred Units, Outstanding	7,431,667	7,431,667
Corporate Office Properties, L.P. | Limited Partner
Common Shares of beneficial interest, shares outstanding	3,677,391	3,837,551
Preferred Units, Outstanding	352,000	352,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues
Rental revenue		$ 109,080	$ 96,207	$ 312,826	$ 288,574
Tenant recoveries and other real estate operations revenue		24,606	22,069	71,761	70,538
Construction contract and other service revenues		17,058	34,739	97,554	80,390
Total revenues		150,744	153,015	482,141	439,502
Expenses
Property operating expenses		48,897	43,056	145,996	136,600
Depreciation and amortization associated with real estate operations		38,403	30,237	103,788	104,728
Construction contract and other service expenses		16,132	33,593	94,923	75,353
Impairment losses		2,307	66	3,545	1,368
General, administrative and leasing expenses		7,439	7,211	22,864	22,882
Business development expenses and land carry costs		5,573	1,430	10,986	4,107
Total operating expenses		118,751	115,593	382,102	345,038
Operating income		31,993	37,422	100,039	94,464
Interest expense		(24,121)	(24,802)	(66,727)	(69,107)
Interest and other income		692	1,191	3,217	3,775
Gain (loss) on early extinguishment of debt		85,745	(176)	85,677	(446)
Income from continuing operations before equity in income of unconsolidated entities and income taxes		94,309	13,635	122,206	28,686
Equity in income of unconsolidated entities		18	193	52	206
Income tax expense		(48)	(101)	(153)	(257)
Income from continuing operations		94,279	13,727	122,105	28,635
Discontinued operations		0	191	156	4
Income before gain on sales of real estate		94,279	13,918	122,261	28,639
Gain on sales of real estate		15	10,630	4,000	10,630
Net income		94,294	24,548	126,261	39,269
Net income attributable to noncontrolling interests:
Common units in COPLP		(3,357)	(768)	(4,231)	(942)
Preferred units in COPLP		(165)	(165)	(495)	(495)
Other consolidated entities		(972)	(895)	(2,599)	(2,481)
Net income attributable to COPT		89,800	22,720	118,936	35,351
Preferred share/unit dividends/distributions		(3,552)	(3,553)	(10,657)	(12,387)
Issuance costs associated with redeemed preferred shares/unit		0	0	0	(1,769)
Net income attributable to COPT common shareholders		86,248	19,167	108,279	21,195
Net income attributable to COPT:
Income from continuing operations		89,800	22,537	118,783	35,342
Discontinued operations, net		0	183	153	9
Net income attributable to COPT		$ 89,800	$ 22,720	$ 118,936	$ 35,351
Basic earnings per common share
Income from continuing operations (in dollars per share/unit)	[1]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
Discontinued operations (in dollars per share/unit)	[1]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[1]	0.91	0.22	1.15	0.24
Diluted earnings per common share
Income from continuing operations (in dollars per share/unit)	[1]	0.91	0.22	1.15	0.24
Discontinued operations (in dollars per share/unit)	[1]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[1]	0.91	0.22	1.15	0.24
Dividends declared per common share/unit		$ 0.2750	$ 0.2750	$ 0.825	$ 0.825
Corporate Office Properties, L.P.
Revenues
Rental revenue		$ 109,080	$ 96,207	$ 312,826	$ 288,574
Tenant recoveries and other real estate operations revenue		24,606	22,069	71,761	70,538
Construction contract and other service revenues		17,058	34,739	97,554	80,390
Total revenues		150,744	153,015	482,141	439,502
Expenses
Property operating expenses		48,897	43,056	145,996	136,600
Depreciation and amortization associated with real estate operations		38,403	30,237	103,788	104,728
Construction contract and other service expenses		16,132	33,593	94,923	75,353
Impairment losses		2,307	66	3,545	1,368
General, administrative and leasing expenses		7,439	7,211	22,864	22,882
Business development expenses and land carry costs		5,573	1,430	10,986	4,107
Total operating expenses		118,751	115,593	382,102	345,038
Operating income		31,993	37,422	100,039	94,464
Interest expense		(24,121)	(24,802)	(66,727)	(69,107)
Interest and other income		692	1,191	3,217	3,775
Gain (loss) on early extinguishment of debt		85,745	(176)	85,677	(446)
Income from continuing operations before equity in income of unconsolidated entities and income taxes		94,309	13,635	122,206	28,686
Equity in income of unconsolidated entities		18	193	52	206
Income tax expense		(48)	(101)	(153)	(257)
Income from continuing operations		94,279	13,727	122,105	28,635
Discontinued operations		0	191	156	4
Income before gain on sales of real estate		94,279	13,918	122,261	28,639
Gain on sales of real estate		15	10,630	4,000	10,630
Net income		94,294	24,548	126,261	39,269
Net income attributable to noncontrolling interests:
Net income attributable to noncontrolling interests in consolidated entities		(972)	(897)	(2,602)	(2,471)
Net income attributable to COPT		93,322	23,651	123,659	36,798
Preferred share/unit dividends/distributions		(3,717)	(3,718)	(11,152)	(12,882)
Issuance costs associated with redeemed preferred shares/unit		0	0	0	(1,769)
Net income attributable to COPT common shareholders		89,605	19,933	112,507	22,147
Net income attributable to COPT:
Income from continuing operations		93,322	23,460	123,500	36,789
Discontinued operations, net		0	191	159	9
Net income attributable to COPT		$ 93,322	$ 23,651	$ 123,659	$ 36,798
Basic earnings per common share
Income from continuing operations (in dollars per share/unit)	[2]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
Discontinued operations (in dollars per share/unit)	[2]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[2]	0.91	0.22	1.15	0.24
Diluted earnings per common share
Income from continuing operations (in dollars per share/unit)	[2]	0.91	0.22	1.15	0.24
Discontinued operations (in dollars per share/unit)	[2]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[2]	0.91	0.22	1.15	0.24
Dividends declared per common share/unit		$ 0.275	$ 0.275	$ 0.825	$ 0.825
[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.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net income	$ 94,294	$ 24,548	$ 126,261	$ 39,269
Other comprehensive (loss) income
Unrealized (losses) gains on interest rate derivatives	(3,638)	1,015	(6,720)	(4,738)
Equity in other comprehensive loss of equity method investee	0	0	(264)	0
Other comprehensive (loss) income	(2,723)	1,771	(4,527)	(2,568)
Comprehensive income	91,571	26,319	121,734	36,701
Comprehensive income attributable to noncontrolling interests	(4,453)	(1,968)	(7,324)	(3,960)
Comprehensive income attributable to COPT	87,118	24,351	114,410	32,741
Interest Expense
Other comprehensive (loss) income
Losses on interest rate derivatives included in interest expense	915	756	2,457	2,170
Corporate Office Properties, L.P.
Net income	94,294	24,548	126,261	39,269
Other comprehensive (loss) income
Unrealized (losses) gains on interest rate derivatives	(3,638)	1,015	(6,720)	(4,738)
Equity in other comprehensive loss of equity method investee	0	0	(264)	0
Other comprehensive (loss) income	(2,723)	1,771	(4,527)	(2,568)
Comprehensive income	91,571	26,319	121,734	36,701
Comprehensive income attributable to noncontrolling interests	(1,035)	(964)	(2,780)	(2,630)
Comprehensive income attributable to COPT	90,536	25,355	118,954	34,071
Corporate Office Properties, L.P. | Interest Expense
Other comprehensive (loss) income
Losses on interest rate derivatives included in interest expense	$ 915	$ 756	$ 2,457	$ 2,170

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Shares	Common Shares	Additional Paid-in Capital	Cumulative Distributions in Excess of Net Income	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Corporate Office Properties, L.P.	Corporate Office Properties, L.P.Common Shares	Corporate Office Properties, L.P.Accumulated Other Comprehensive Income (Loss)	Corporate Office Properties, L.P.Noncontrolling Interests	Corporate Office Properties, L.P.Limited Partner	Corporate Office Properties, L.P.Limited PartnerPreferred Shares	Corporate Office Properties, L.P.General Partner	Corporate Office Properties, L.P.General PartnerPreferred Shares
Balance (COPT: 87,394,512 shares and 93,255,284 shares as of December 31, 2013 and 2014, respectively) at Dec. 31, 2013	$ 1,497,249	$ 249,083	$ 874	$ 1,814,015	$ (641,868)	$ 3,480	$ 71,665	$ 1,497,249	$ 1,226,318	$ 3,605	$ 9,443		$ 8,800		$ 249,083
Balance (preferred units) at Dec. 31, 2013													352,000		9,431,667
Balance (in units/ shares) at Dec. 31, 2013	87,394,512								91,372,212
Increase (Decrease) in Shareholders' Equity
Redemption of preferred shares (in units/shares)															(2,000,000)
Redemption of preferred shares (in units/shares) (2,000,000 shares)	$ (50,000)	(50,000)		1,769	(1,769)			(50,000)							$ (50,000)
Conversion of common units to common shares (COPT: 117,149 shares and 160,160 shares for the nine months ended September 30, 2014 and 2015, respectively)	0		1	1,544			(1,545)
Costs associated with common shares issued to the public	$ (7)			(7)				(7)	$ (7)
Exercise of share options (in units/shares)	57,888								57,888
Exercise of share options (COPT: 57,888 shares and 76,474 shares for the nine months ended September 30, 2014 and 2015, respectively)	$ 1,359		0	1,359				1,359	$ 1,359
Share-based compensation issuance, net of redemptions (in units/shares)	142,182								142,182
Share-based compensation issuance, net of redemptions (COPT: 142,182 and 151,511 shares issued, net of redemptions for the nine months ended September 30, 2014 and 2015, respectively)	$ 5,249		2	5,247				5,249	$ 5,249
Redemption of vested equity awards (in units/shares)									0
Redemption of vested equity awards	(1,389)			(1,389)				(1,389)	$ (1,389)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(248)			248
Comprehensive income	35,055				35,351	(2,609)	2,313	35,055	23,916	(2,726)	983		$ 495		12,387
Dividends / Distributions to owners of common and preferred units	(84,692)				(84,692)			(88,402)	(75,520)				$ (495)		$ (12,387)
Distributions to owners of common and preferred units in COPLP	(3,710)						(3,710)
Distributions to noncontrolling interests in subsidiaries	(1,606)						(1,606)	(1,606)			(1,606)
Contributions from noncontrolling interests in subsidiaries	3			0			3	3			3
Adjustment to arrive at fair value of redeemable noncontrolling interest	$ (7)			(7)				(7)	$ (7)
Balance (in units/ shares) at Sep. 30, 2014	87,711,731								91,572,282
Balance (preferred units) at Sep. 30, 2014													352,000		7,431,667
Balance (COPT: 87,711,731 shares and 94,533,670 shares as of September 30, 2014 and 2015, respectively) at Sep. 30, 2014	$ 1,397,504	199,083	877	1,822,283	(692,978)	871	67,368	1,397,504	$ 1,179,919	879	8,823		$ 8,800		$ 199,083
Balance (COPT: 87,394,512 shares and 93,255,284 shares as of December 31, 2013 and 2014, respectively) at Dec. 31, 2014	$ 1,520,884	199,083	933	1,969,968	(717,264)	(1,297)	69,461	1,520,884	$ 1,305,219	(1,381)	9,163		$ 8,800		$ 199,083
Balance (preferred units) at Dec. 31, 2014												352,000	352,000	7,431,667	7,431,667
Balance (in units/ shares) at Dec. 31, 2014	93,255,284								97,092,835			3,837,551		93,255,284
Increase (Decrease) in Shareholders' Equity
Conversion of common units to common shares (COPT: 117,149 shares and 160,160 shares for the nine months ended September 30, 2014 and 2015, respectively)	$ 0		2	2,149			(2,151)
Issuance of common units resulting from common shares issued under at-the-market program (in units)									890,241
Issuance of common units resulting from common shares issued under at-the-market program (COPT: 890,241 shares for the nine months ended September 30, 2015)	$ 26,535		9	26,526				26,535	$ 26,535
Exercise of share options (in units/shares)	76,474								76,474
Exercise of share options (COPT: 57,888 shares and 76,474 shares for the nine months ended September 30, 2014 and 2015, respectively)	$ 2,008			2,008				2,008	$ 2,008
Share-based compensation issuance, net of redemptions (in units/shares)	151,511								151,511
Share-based compensation issuance, net of redemptions (COPT: 142,182 and 151,511 shares issued, net of redemptions for the nine months ended September 30, 2014 and 2015, respectively)	$ 5,600		1	5,599				5,600	$ 5,600
Redemption of vested equity awards (in units/shares)									0
Redemption of vested equity awards	(2,330)			(2,330)				(2,330)	$ (2,330)
Adjustments to noncontrolling interests resulting from changes in ownership of COPLP	0			(591)			591
Comprehensive income	120,044				118,936	(4,526)	5,634	120,044	112,507	(4,705)	1,090		$ 495		$ 10,657
Dividends / Distributions to owners of common and preferred units	(88,658)				(88,658)			(92,188)	(81,036)				$ (495)		$ (10,657)
Distributions to owners of common and preferred units in COPLP	(3,530)						(3,530)
Distributions to noncontrolling interests in subsidiaries	(47)						(47)	(47)			(47)
Adjustment to arrive at fair value of redeemable noncontrolling interest	$ (599)			(599)				(599)	$ (599)
Balance (in units/ shares) at Sep. 30, 2015	94,533,670								98,211,061			3,677,391		94,533,670
Balance (preferred units) at Sep. 30, 2015												352,000	352,000	7,431,667	7,431,667
Balance (COPT: 87,711,731 shares and 94,533,670 shares as of September 30, 2014 and 2015, respectively) at Sep. 30, 2015	$ 1,579,907	$ 199,083	$ 945	$ 2,002,730	$ (686,986)	$ (5,823)	$ 69,958	$ 1,579,907	$ 1,367,904	$ (6,086)	$ 10,206		$ 8,800		$ 199,083

Consolidated Statements of Equ7

Consolidated Statements of Equity (Parenthetical) - shares	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Balance (in units/ shares)	94,533,670	87,711,731	93,255,284	87,394,512
Conversion of common units to common shares (in units/ shares)	160,160	117,149
Exercise of share options (in units/shares)	76,474	57,888
Share-based compensation issuance, net of redemptions (in units/shares)	151,511	142,182
Common Shares
Issuance of common units resulting from common shares issued under at-the-market program (in units)	890,241
Preferred Shares
Redemption of preferred shares (in units/shares)		2,000,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities
Revenues from real estate operations received	$ 373,607	$ 358,212
Construction contract and other service revenues received	104,817	62,170
Property operating expenses paid	(146,274)	(141,489)
Construction contract and other service expenses paid	(112,614)	(58,218)
General, administrative, leasing, business development and land carry costs paid	(29,620)	(22,288)
Interest expense paid	(46,278)	(54,683)
Payments in connection with early extinguishment of debt	(18)	(104)
Interest and other income received	4,130	448
Income taxes (paid) refunded	(8)	200
Net cash provided by operating activities	147,742	144,248
Cash flows from investing activities
Acquisitions of operating properties and related intangible assets	(202,866)	0
Construction, development and redevelopment	(174,434)	(150,862)
Tenant improvements on operating properties	(18,129)	(17,754)
Other capital improvements on operating properties	(12,610)	(21,179)
Proceeds from dispositions of properties	45,066	57,973
Investing receivables funded	(22)	(3,610)
Investing receivables payments received	5,114	10,278
Leasing costs paid	(8,603)	(10,549)
Increase in prepaid expenses and other assets associated with investing activities	(4,348)	(1,260)
Other	(457)	(83)
Net cash used in investing activities	(371,289)	(137,046)
Proceeds from debt
Revolving Credit Facility	422,000	115,000
Unsecured senior notes	296,580	297,342
Other debt proceeds	50,000	11,569
Repayments of debt
Revolving Credit Facility	(418,000)	(115,000)
Scheduled principal amortization	(5,011)	(4,914)
Other debt repayments	(50,681)	(183,059)
Deferred financing costs paid	(5,377)	(694)
Net proceeds from issuance of common shares/units	28,567	1,352
Redemption of preferred shares/units	0	(50,000)
Common share/unit dividends/distributions paid	(77,641)	(72,217)
Preferred share/unit dividends/distributions paid	(10,657)	(13,179)
Distributions paid to noncontrolling interests in COPLP	(3,581)	(3,786)
Redemption of vested equity awards	(2,330)	(1,389)
Other	(2,559)	(2,582)
Net cash provided by (used in) financing activities	221,310	(21,557)
Net decrease in cash and cash equivalents	(2,237)	(14,355)
Cash and cash equivalents
Beginning of period	6,077	54,373
End of period	3,840	40,018
Reconciliation of net income to net cash provided by operating activities:
Net income	126,261	39,269
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	105,397	106,619
Impairment losses	3,779	1,371
Amortization of deferred financing costs	3,339	3,646
Increase in deferred rent receivable	(11,939)	(2,738)
Amortization of net debt discounts	805	659
Gain on sales of real estate	(4,000)	(10,654)
Share-based compensation	4,949	4,563
(Gain) loss on early extinguishment of debt	(86,075)	458
Other	1,922	(2,446)
Operating changes in assets and liabilities:
Decrease in accounts receivable	6,526	6,815
Increase in restricted cash and marketable securities	(1,102)	(2,591)
Increase in prepaid expenses and other assets, net	(5,228)	(26,553)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(655)	24,247
Increase in rents received in advance and security deposits	3,763	1,583
Net cash provided by operating activities	147,742	144,248
Supplemental schedule of non-cash investing and financing activities:
Decrease in accrued capital improvements, leasing and other investing activity costs	(11,722)	(174)
Debt assumed on acquisition of operating property	55,490	0
Other liabilities assumed on acquisition of operating properties	5,265	0
Decrease in property in connection with surrender of property in settlement of debt	(82,738)	0
Decrease in debt in connection with surrender of property in settlement of debt	(150,000)	0
Decrease in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests	(4,263)	(2,613)
Equity in other comprehensive loss of an equity method investee	(264)	0
Dividends/distributions payable	30,182	28,344
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	2,151	1,545
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	591	248
Increase in redeemable noncontrolling interest and decrease in equity to carry redeemable noncontrolling interest at fair value	599	7
Corporate Office Properties, L.P.
Cash flows from operating activities
Revenues from real estate operations received	373,607	358,212
Construction contract and other service revenues received	104,817	62,170
Property operating expenses paid	(146,274)	(141,489)
Construction contract and other service expenses paid	(112,614)	(58,218)
General, administrative, leasing, business development and land carry costs paid	(29,620)	(22,288)
Interest expense paid	(46,278)	(54,683)
Payments in connection with early extinguishment of debt	(18)	(104)
Interest and other income received	4,130	448
Income taxes (paid) refunded	(8)	200
Net cash provided by operating activities	147,742	144,248
Cash flows from investing activities
Acquisitions of operating properties and related intangible assets	(202,866)	0
Construction, development and redevelopment	(174,434)	(150,862)
Tenant improvements on operating properties	(18,129)	(17,754)
Other capital improvements on operating properties	(12,610)	(21,179)
Proceeds from dispositions of properties	45,066	57,973
Investing receivables funded	(22)	(3,610)
Investing receivables payments received	5,114	10,278
Leasing costs paid	(8,603)	(10,549)
Increase in prepaid expenses and other assets associated with investing activities	(4,348)	(1,260)
Other	(457)	(83)
Net cash used in investing activities	(371,289)	(137,046)
Proceeds from debt
Revolving Credit Facility	422,000	115,000
Unsecured senior notes	296,580	297,342
Other debt proceeds	50,000	11,569
Repayments of debt
Revolving Credit Facility	(418,000)	(115,000)
Scheduled principal amortization	(5,011)	(4,914)
Other debt repayments	(50,681)	(183,059)
Deferred financing costs paid	(5,377)	(694)
Net proceeds from issuance of common shares/units	28,567	1,352
Redemption of preferred shares/units	0	(50,000)
Common share/unit dividends/distributions paid	(80,727)	(75,508)
Preferred share/unit dividends/distributions paid	(11,152)	(13,674)
Redemption of vested equity awards	(2,330)	(1,389)
Other	(2,559)	(2,582)
Net cash provided by (used in) financing activities	221,310	(21,557)
Net decrease in cash and cash equivalents	(2,237)	(14,355)
Cash and cash equivalents
Beginning of period	6,077	54,373
End of period	3,840	40,018
Reconciliation of net income to net cash provided by operating activities:
Net income	126,261	39,269
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	105,397	106,619
Impairment losses	3,779	1,371
Amortization of deferred financing costs	3,339	3,646
Increase in deferred rent receivable	(11,939)	(2,738)
Amortization of net debt discounts	805	659
Gain on sales of real estate	(4,000)	(10,654)
Share-based compensation	4,949	4,563
(Gain) loss on early extinguishment of debt	(86,075)	458
Other	1,922	(2,446)
Operating changes in assets and liabilities:
Decrease in accounts receivable	6,526	6,815
Increase in restricted cash and marketable securities	(1,485)	(2,558)
Increase in prepaid expenses and other assets, net	(5,228)	(26,553)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(272)	24,214
Increase in rents received in advance and security deposits	3,763	1,583
Net cash provided by operating activities	147,742	144,248
Supplemental schedule of non-cash investing and financing activities:
Decrease in accrued capital improvements, leasing and other investing activity costs	(11,722)	(174)
Debt assumed on acquisition of operating property	55,490	0
Other liabilities assumed on acquisition of operating properties	5,265	0
Decrease in property in connection with surrender of property in settlement of debt	(82,738)	0
Decrease in debt in connection with surrender of property in settlement of debt	(150,000)	0
Decrease in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests	(4,263)	(2,613)
Equity in other comprehensive loss of an equity method investee	(264)	0
Dividends/distributions payable	30,182	28,344
Increase in redeemable noncontrolling interest and decrease in equity to carry redeemable noncontrolling interest at fair value	$ 599	$ 7

Organization

Organization	9 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Corporate Office Properties Trust (“COPT”) and subsidiaries (collectively, the “Company”) is a fully-integrated and self-managed real estate investment trust (“REIT”). Corporate Office Properties, L.P. (“COPLP”) and subsidiaries (collectively, the “Operating Partnership”) is the entity through which COPT, the sole general partner of COPLP, conducts almost all of its operations and owns almost all of its assets. Unless otherwise expressly stated or the context otherwise requires, “we”, “us” and “our” as used herein refer to each of the Company and the Operating Partnership. We focus primarily on serving the specialized requirements of United States Government agencies and their contractors, most of whom are engaged in national security and information technology related activities. We generally acquire, develop, manage and lease office and data center properties concentrated in large office parks located near knowledge-based government demand drivers and/or in targeted markets or submarkets in the Greater Washington, DC/Baltimore region. As of September 30, 2015 , our properties included the following: • 183 operating office properties totaling 18.8 million square feet; • 10 office properties under, or contractually committed for, construction or redevelopment that we estimate will total approximately 1.2 million square feet upon completion, including one partially operational property included above; • 1,450 acres of land we control that we believe are potentially developable into approximately 17.7 million square feet; and • a wholesale data center with a critical load of 19.25 megawatts. COPLP owns real estate both directly and through subsidiary partnerships and limited liability companies (“LLCs”). In addition to owning real estate, COPLP also owns subsidiaries that provide real estate services such as property management and construction and development services primarily for our properties but also for third parties. Some of these services are performed by a taxable REIT subsidiary (“TRS”). Equity interests in COPLP are in the form of common and preferred units. As of September 30, 2015 , COPT owned 96.3% of the outstanding COPLP common units (“common units”) and 95.5% of the outstanding COPLP preferred units (“preferred units”); the remaining common and preferred units in COPLP were owned by third parties. Common units in COPLP not owned by COPT carry certain redemption rights. The number of common units in COPLP owned by COPT is equivalent to the number of outstanding common shares of beneficial interest (“common shares”) of COPT, and the entitlement of all COPLP common units to quarterly distributions and payments in liquidation is substantially the same as those of COPT common shareholders. Similarly, in the case of each series of preferred units in COPLP held by COPT, there is a series of preferred shares of beneficial interest (“preferred shares”) in COPT that is equivalent in number and carries substantially the same terms as such series of COPLP preferred units. COPT’s common shares are publicly traded on the New York Stock Exchange (“NYSE”) under the ticker symbol “OFC”. Because COPLP is managed by COPT, and COPT conducts substantially all of its operations through COPLP, we refer to COPT’s executive officers as COPLP’s executive officers, and although, as a partnership, COPLP does not have a board of trustees, we refer to COPT’s Board of Trustees as COPLP’s Board of Trustees.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The COPT consolidated financial statements include the accounts of COPT, the Operating Partnership, their subsidiaries and other entities in which COPT has a majority voting interest and control. The COPLP consolidated financial statements include the accounts of COPLP, its subsidiaries and other entities in which COPLP has a majority voting interest and control. We also consolidate certain entities when control of such entities can be achieved through means other than voting rights (“variable interest entities” or “VIEs”) if we are deemed to be the primary beneficiary of such entities. We eliminate all significant intercompany balances and transactions in consolidation. We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity. These interim financial statements should be read together with the consolidated financial statements and notes thereto as of and for the year ended December 31, 2014 included in our 2014 Annual Report on Form 10-K. The unaudited consolidated financial statements include all adjustments that are necessary, in the opinion of management, to fairly present our financial position and results of operations. All adjustments are of a normal recurring nature. The consolidated financial statements have been prepared using the accounting policies described in our 2014 Annual Report on Form 10-K. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Additionally, this guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We are required to adopt this guidance for our annual and interim periods beginning January 1, 2018 using one of two methods: retrospective restatement for each reporting period presented at the time of adoption, or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In January 2015, the FASB issued guidance regarding the presentation of extraordinary and unusual items in statements of operations. This guidance eliminates the concept of extraordinary items. However, the presentation and disclosure requirements for items that are either unusual in nature or infrequent in occurrence remain and will be expanded to include items that are both unusual in nature and infrequent in occurrence. This guidance is effective for periods beginning after December 15, 2015. We expect that the application of this guidance will have no effect on our reported consolidated financial statements. In February 2015, the FASB issued guidance regarding amendments to the consolidation analysis. This guidance amends the criteria for determining which entities are considered variable interest entities (“VIE”), amends the criteria for determining if a service provider possesses a variable interest in a VIE and ends the deferral granted to investment companies for application of the VIE consolidation model. This guidance is effective for annual periods, and interim periods therein, beginning after December 15, 2015. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In April 2015, the FASB issued guidance that changes the presentation of debt issuance costs in financial statements. This guidance requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than as an asset. Amortization of the costs will continue to be reported as interest expense. This guidance was further updated in August 2015 with respect to debt issuance costs of line-of-credit arrangements to note that it will be permissible for an entity to defer and present debt issuance costs as an asset and subsequently amortize the deferred debt issuance costs ratably over the term of a line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. This guidance is effective for annual reporting periods beginning after December 15, 2016. Early adoption is permitted. This guidance will be applied retrospectively to each prior period presented. We expect that the application of this guidance will not materially affect our consolidated financial statements. In September 2015, the FASB issued guidance that eliminates the requirement to restate prior period financial statements for measurement period adjustments following a business combination. The guidance requires that the cumulative impact of a measurement period adjustment (including the impact on prior periods) be recognized in the reporting period in which the adjustment is identified. The prior period impact of the adjustment should be either presented separately on the face of the statement of operations or disclosed in the notes. This guidance is effective for annual reporting periods beginning after December 15, 2015. This guidance will be applied prospectively for measurement period adjustments that occur after the effective date. We expect that the application of this guidance will not materially affect our consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements For a description on how we estimate fair value, see Note 3 to the consolidated financial statements in our 2014 Annual Report on Form 10-K. Recurring Fair Value Measurements Our partner in a real estate joint venture has the right to require us to acquire its interest at fair value beginning in March 2020; accordingly, we classify the fair value of our partner’s interest as a redeemable noncontrolling interest in the mezzanine section of our consolidated balance sheet. In determining the fair value of our partner’s interest as of September 30, 2015 , we used a discount rate of 15.5% which factored in risk appropriate to the level of future property development expected to be undertaken by the joint venture. A significant increase (decrease) in the discount rate used in determining the fair value would result in a significantly (lower) higher fair value. Given our reliance on the unobservable inputs, the valuations are classified in Level 3 of the fair value hierarchy. Please refer to Note 11 for a rollforward of the activity for redeemable noncontrolling interest. The carrying values of cash and cash equivalents, restricted cash, accounts receivable, other assets (excluding investing receivables) and accounts payable and accrued expenses are reasonable estimates of their fair values because of the short maturities of these instruments. As discussed in Note 7, we estimated the fair values of our investing receivables based on the discounted estimated future cash flows of the loans (categorized within Level 3 of the fair value hierarchy); the discount rates used approximate current market rates for loans with similar maturities and credit quality, and the estimated cash payments include scheduled principal and interest payments. For our disclosure of debt fair values in Note 9, we estimated the fair value of our unsecured senior notes and exchangeable senior notes based on quoted market rates for publicly-traded debt (categorized within Level 2 of the fair value hierarchy) and estimated the fair value of our other debt based on the discounted estimated future cash payments to be made on such debt (categorized within Level 3 of the fair value hierarchy); the discount rates used approximate current market rates for loans, or groups of loans, with similar maturities and credit quality, and the estimated future payments include scheduled principal and interest payments. Fair value estimates are made at a specific point in time, are subjective in nature and involve uncertainties and matters of significant judgment. Settlement at such fair value amounts may not be possible and may not be a prudent management decision. For additional fair value information, please refer to Note 7 for investing receivables, Note 9 for debt and Note 10 for interest rate derivatives. COPT and Subsidiaries The table below sets forth financial assets and liabilities of COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2015 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 5,395 $ — $ — $ 5,395 Other 104 — — 104 Warrants to purchase common stock (2) — 42 — 42 Total assets $ 5,499 $ 42 $ — $ 5,541 Liabilities: Deferred compensation plan liability (3) $ — $ 5,499 $ — $ 5,499 Interest rate derivatives — 5,844 — 5,844 Total liabilities $ — $ 11,343 $ — $ 11,343 Redeemable noncontrolling interest $ — $ — $ 19,608 $ 19,608 (1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet. (2) Included in the line entitled “prepaid expenses and other assets” on COPT’s consolidated balance sheet. (3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet. COPLP and Subsidiaries The table below sets forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2015 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Warrants to purchase common stock (1) $ — $ 42 $ — $ 42 Liabilities: Interest rate derivatives $ — $ 5,844 $ — $ 5,844 Redeemable noncontrolling interest $ — $ — $ 19,608 $ 19,608 (1) Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet. Nonrecurring Fair Value Measurements During the nine months ended September 30, 2015, we recognized the following impairment losses resulting from nonrecurring fair value measurements: • $1.3 million primarily in the three months ended June 30, 2015 on a property in Northern Virginia that we sold on July 27, 2015 following receipt of an unsolicited offer. This property’s carrying value exceeded its fair value less costs to sell; and • $2.3 million in the three months ended September 30, 2015 on three properties in the Greater Baltimore, Maryland (“Greater Baltimore”) region that we concluded no longer met our investment criteria during the period and whose carrying amounts exceeded their estimated fair values less costs to sell. These properties were reclassified as held for sale. The table below sets forth the fair value hierarchy of the valuation technique we used to determine the fair values of these properties (dollars in thousands): Fair Values of Properties Held as of September 30, 2015 Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Description (Level 1) (Level 2) (Level 3) Total Assets: Assets held for sale, net (1) $ — $ — $ 7,225 $ 7,225 (1) Represents estimated fair values less costs to sell. The table below sets forth quantitative information about significant unobservable inputs used for the Level 3 fair value measurements reported above as of September 30, 2015 (dollars in thousands): Valuation Technique Fair Values on Measurement Date Unobservable Input Range (Weighted Average) (1) Discounted cash flow $ 7,225 Discount rate 8.25% Terminal capitalization rate 7.75% Market rent growth rate 2.0% Expense growth rate 2.0% (1) Only one value applied for these unobservable inputs. During the nine months ended September 30, 2014, we recognized impairment losses totaling $1.4 million primarily in connection with certain of our operating properties in the Greater Baltimore region that were disposed of during the period. After shortening our expected holding period for these properties during the period, we determined that the carrying amount of the properties would not likely be recovered from the cash flows from the operations and sales of the properties over the shortened period.

Properties, Net

Properties, Net	9 Months Ended
	Sep. 30, 2015
Real Estate [Abstract]
Properties, Net	Properties, Net Operating properties, net consisted of the following (in thousands): September 30, December 31, Land $ 466,701 $ 439,355 Buildings and improvements 3,141,889 3,015,216 Less: Accumulated depreciation (675,747 ) (703,083 ) Operating properties, net $ 2,932,843 $ 2,751,488 During the nine months ended September 30, 2014, we recognized $12.9 million in additional depreciation expense resulting from our revision of the useful life of a property in Greater Philadelphia, Pennsylvania (“Greater Philadelphia”) that was removed from service for redevelopment. Projects in development or held for future development consisted of the following (in thousands): September 30, December 31, Land $ 207,748 $ 214,977 Development in progress, excluding land 207,009 330,449 Projects in development or held for future development $ 414,757 $ 545,426 As of September 30, 2015 , we had 18 operating properties in Greater Baltimore and one in Northern Virginia classified as held for sale. The table below sets forth the components of assets held for sale on our consolidated balance sheet for these properties (in thousands): September 30, 2015 Properties, net $ 142,817 Deferred rent receivable 3,998 Intangible assets on real estate acquisitions, net 799 Deferred leasing costs, net 2,053 Lease incentives, net 905 Assets held for sale, net $ 150,572 As of December 31, 2014, we had two land parcels in the Greater Baltimore region classified as held for sale with aggregate carrying amounts of $14.3 million that were sold during the nine months ended September 30, 2015. 2015 Acquisitions In the nine months ended September 30, 2015 , we acquired the following operating properties: • 250 W. Pratt Street, a 367,000 square foot office property in Baltimore, Maryland that was 96.2% leased, for $61.9 million on March 19, 2015; • 2600 Park Tower Drive, a 237,000 square foot office property in Vienna, Virginia (in the Northern Virginia region) that was 100% leased, for $80.5 million on April 15, 2015; and • 100 Light Street, a 558,000 square foot office property in Baltimore, Maryland that was 93.5% leased, and its structured parking garage, 30 Light Street, for $121.2 million on August 7, 2015. In connection with that acquisition, we assumed a $55.0 million mortgage loan with a fair value at assumption of $55.5 million . The table below sets forth the allocation of the aggregate acquisition costs of these properties (in thousands): Land, operating properties $ 55,076 Building and improvements 139,520 Intangible assets on real estate acquisitions 75,846 Total assets 270,442 Below-market leases (6,820 ) Total acquisition cost $ 263,622 Intangible assets recorded in connection with these acquisitions included the following (dollars in thousands): Weighted Average Amortization Period (in Years) Tenant relationship value $ 31,208 12 In-place lease value 35,231 7 Above-market leases 6,720 4 Below-market cost arrangements 2,687 40 $ 75,846 10 These properties contributed revenues of $6.9 million for the three months ended September 30, 2015 and $11.2 million for the nine months ended September 30, 2015 , and contributed net income from continuing operations of $487,000 for the three months ended September 30, 2015 and $697,000 for the nine months ended September 30, 2015 . We expensed operating property acquisition costs of $2.7 million during the three months ended September 30, 2015 and $4.1 million during the nine months ended September 30, 2015 that are included in business development expenses and land carry costs on our consolidated statements of operations. We accounted for these acquisitions as business combinations. We included the results of operations for the acquisitions in our consolidated statements of operations from their respective purchase dates through September 30, 2015 . The following table presents pro forma information for COPT and subsidiaries as if these acquisitions had occurred on January 1, 2014. This pro forma information also includes adjustments to reclassify the operating property acquisition costs disclosed above from the 2015 periods in which they were incurred to the nine months ended September 30, 2014. The pro forma financial information was prepared for comparative purposes only and is not necessarily indicative of what would have occurred had these acquisitions been made at that time or of results which may occur in the future (in thousands, except per shares amounts). For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) Pro forma total revenues $ 152,736 $ 162,085 $ 498,657 $ 467,224 Pro forma net income attributable to COPT common shareholders $ 88,836 $ 19,683 $ 112,941 $ 19,266 Pro forma EPS: Basic $ 0.94 $ 0.22 $ 1.20 $ 0.22 Diluted $ 0.94 $ 0.22 $ 1.20 $ 0.22 2015 Dispositions In the nine months ended September 30, 2015 , we completed the following dispositions of operating properties: • 1550 Westbranch Drive, a 160,000 square foot office property in McLean, Virginia (in the Northern Virginia region) for $27.8 million on July 27, 2015; and • 15000 and 15010 Conference Center Drive, two office properties in Chantilly, Virginia (in the Northern Virginia region) totaling 665,000 square feet. On August 28, 2015, ownership in these properties was transferred to the mortgage lender on a $150.0 million nonrecourse mortgage loan that was secured by the properties and we removed the debt obligation and accrued interest from our balance sheet. The properties had an estimated fair value of $99 million on the transfer date. Upon completion of this transfer, we recognized a gain on early extinguishment of debt of $84.8 million , representing the difference between the mortgage loan and accrued interest payable extinguished over the carrying value of the properties transferred as of the transfer date and related closing costs. We also sold land during the nine months ended September 30, 2015 for $18.1 million and recognized gains of $4.0 million on the sales. 2015 Construction Activities During the nine months ended September 30, 2015 , we placed into service an aggregate of 897,000 square feet in seven newly constructed office properties located in Northern Virginia, San Antonio, Texas (“San Antonio”), Huntsville, Alabama (“Huntsville”) and the Baltimore/Washington Corridor, and 170,000 square feet in two properties redeveloped in Greater Philadelphia and St. Mary’s County, Maryland. As of September 30, 2015 , we had six office properties under construction, or for which we were contractually committed to construct, that we estimate will total 1.0 million square feet upon completion (including one partially operational property), including four in Northern Virginia and two in the Baltimore/Washington Corridor. We also had four office properties under redevelopment that we estimate will total 156,000 square feet upon completion, all of which were located in the Baltimore/Washington Corridor.

Real Estate Joint Ventures

Real Estate Joint Ventures	9 Months Ended
	Sep. 30, 2015
Equity Method Investments and Joint Ventures [Abstract]
Real Estate Joint Ventures	Real Estate Joint Ventures The table below sets forth information pertaining to our material investments in consolidated real estate joint ventures as of September 30, 2015 (dollars in thousands): Nominal Ownership September 30, 2015 (1) Date % as of Total Encumbered Total Acquired 9/30/2015 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 144,906 $ 64,395 $ 39,093 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 58,840 48,301 38,117 $ 203,746 $ 112,696 $ 77,210 (1) Excludes amounts eliminated in consolidation. (2) This joint venture’s properties are in Huntsville. (3) This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).

Intangible Assets on Real Estat

Intangible Assets on Real Estate Acquisition, Net	9 Months Ended
	Sep. 30, 2015
Intangible Assets on Real Estate Acquisitions [Abstract]
Intangible Assets on Real Estate Acquisition, Net	Intangible Assets on Real Estate Acquisitions, Net Intangible assets on real estate acquisitions consisted of the following, excluding amounts for properties held for sale (in thousands): September 30, 2015 December 31, 2014 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount In-place lease value $ 138,410 $ 87,667 $ 50,743 $ 123,759 $ 101,040 $ 22,719 Tenant relationship value 63,117 22,525 40,592 42,301 28,492 13,809 Below-market cost arrangements 15,102 6,505 8,597 12,415 5,984 6,431 Above-market leases 13,844 7,987 5,857 8,659 8,159 500 Market concentration premium 1,333 948 385 1,333 938 395 $ 231,806 $ 125,632 $ 106,174 $ 188,467 $ 144,613 $ 43,854 Amortization of the intangible asset categories set forth above totaled $11.9 million in the nine months ended September 30, 2015 and $10.8 million in the nine months ended September 30, 2014 . The approximate weighted average amortization periods of the categories set forth above follow (excluding amounts for properties held for sale): in-place lease value: six years; tenant relationship value: 11 years; below-market cost arrangements: 35 years; above-market leases: four years; and market concentration premium: 27 years. The approximate weighted average amortization period for all of the categories combined is 10 years. Estimated amortization expense associated with the intangible asset categories set forth above through 2020 follows (excluding amounts for properties held for sale): $5.1 million for the three months ending December 31, 2015; $19.7 million for 2016; $17.1 million for 2017; $12.3 million for 2018; $9.3 million for 2019; and $7.3 million for 2020.

Investing Receivables

Investing Receivables	9 Months Ended
	Sep. 30, 2015
Receivables [Abstract]
Investing Receivables	Investing Receivables Investing receivables, including accrued interest thereon, consisted of the following (in thousands): September 30, December 31, Notes receivable from the City of Huntsville $ 43,821 $ 49,147 Other investing loans receivable 3,000 3,000 $ 46,821 $ 52,147 Our notes receivable from the City of Huntsville funded infrastructure costs in connection with our LW Redstone Company, LLC joint venture (see Note 5) and carry an interest rate of 9.95% . We did not have an allowance for credit losses in connection with our investing receivables as of September 30, 2015 or December 31, 2014 . The fair value of these receivables approximated their carrying amounts as of September 30, 2015 and December 31, 2014 .

Prepaid Expenses and Other Asse

Prepaid Expenses and Other Assets, Net	9 Months Ended
	Sep. 30, 2015
Prepaid Expense and Other Assets [Abstract]
Prepaid Expenses and Other Assets, Net	Prepaid Expenses and Other Assets, Net Prepaid expenses and other assets consisted of the following (in thousands): September 30, December 31, Prepaid expenses $ 28,655 $ 20,570 Lease incentives, net 11,589 13,344 Furniture, fixtures and equipment, net 5,941 6,637 Construction contract costs incurred in excess of billings 4,722 6,656 Deferred tax asset, net (1) 4,015 4,002 Operating notes receivable 3,744 3,797 Equity method investments 1,626 2,368 Other assets 6,495 2,875 Prepaid expenses and other assets, net $ 66,787 $ 60,249 (1) Includes a valuation allowance of $2.1 million . Operating notes receivable reported above includes amounts due from tenants with remaining terms exceeding one year totaling $3.7 million as of September 30, 2015 and $3.6 million as of December 31, 2014 ; we carried allowances for estimated losses for $278,000 of the September 30, 2015 balance and $252,000 of the December 31, 2014 balance.

Debt, Net

Debt, Net	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Debt, Net	Debt, Net Our debt consisted of the following (dollars in thousands): Maximum Availability at Carrying Value at Scheduled Maturity September 30, September 30, December 31, Stated Interest Rates as of as of September 30, 2015 September 30, 2015 Mortgage and Other Secured Loans: Fixed rate mortgage loans (1) $ 288,217 $ 387,139 3.96% - 7.87% (2) 2016-2024 Variable rate secured loan 36,249 36,877 LIBOR + 2.25% (3) November 2015 Total mortgage and other secured loans 324,466 424,016 Revolving Credit Facility $ 800,000 87,000 83,000 LIBOR + 0.875% to 1.60% (4) May 2019 Term Loan Facilities (5) 520,000 520,000 LIBOR + 0.90% to 2.60% (6) 2016-2020 Unsecured Senior Notes 3.600% Senior Notes (7) 347,691 347,496 3.60% May 2023 5.250% Senior Notes (8) 246,074 245,797 5.25% February 2024 3.700% Senior Notes (9) 297,830 297,569 3.70% June 2021 5.000% Senior Note (10) 296,646 — 5.00% July 2025 Unsecured notes payable 1,533 1,607 0% (11) 2026 4.25% Exchangeable Senior Notes (12) — 572 N/A (12) Total debt, net $ 2,121,240 $ 1,920,057 (1) Several of the fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying values of these loans reflect net unamortized premiums totaling $24,000 as of September 30, 2015 and $42,000 as of December 31, 2014 . Please refer to Note 4 for disclosure pertaining to the removal of a $150.0 million nonrecourse mortgage loan from our balance sheet on August 28, 2015. (2) The weighted average interest rate on our fixed rate mortgage loans was 6.07% as of September 30, 2015 . (3) The interest rate on the loan outstanding was 2.45% as of September 30, 2015 . (4) The weighted average interest rate on the Revolving Credit Facility was 1.48% as of September 30, 2015 . (5) We have the ability to borrow an additional $380.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders. (6) The weighted average interest rate on these loans was 1.78% as of September 30, 2015 . (7) The carrying value of these notes included a principal amount of $350.0 million and an unamortized discount totaling $2.3 million as of September 30, 2015 and $2.5 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.70% . (8) The carrying value of these notes included a principal amount of $250.0 million and an unamortized discount totaling $3.9 million as of September 30, 2015 and $4.2 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.49% . (9) The carrying value of these notes included a principal amount of $300.0 million and an unamortized discount totaling $2.2 million as of September 30, 2015 and $2.4 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.85% . (10) Refer to the paragraph below for disclosure pertaining to these notes. (11) These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying value of these notes reflects an unamortized discount totaling $578,000 as of September 30, 2015 and $654,000 as of December 31, 2014 . (12) On April 20, 2015, we redeemed these notes at 100% of their principal amount. All debt is owed by the Operating Partnership. While COPT is not directly obligated by any debt, it has guaranteed the Operating Partnership’s Revolving Credit Facility, Term Loan Facilities and Unsecured Senior Notes. On May 6, 2015, we entered into a credit agreement with a group of lenders for which KeyBanc Capital Markets and J.P. Morgan Securities LLC acted as joint lead arrangers and joint book runners, KeyBank National Association acted as administrative agent and JPMorgan Chase Bank, N.A. acted as syndication agent (the “Consolidated Credit Agreement”) to amend, restate and consolidate the terms of our Revolving Credit Facility and one of our term loan facilities. In addition to consolidating the terms of these loan facilities, the Consolidated Credit Agreement included the following provisions: For the Revolving Credit Facility: • an extension of the maturity date from July 14, 2017 to May 6, 2019, with the ability for us to further extend such maturity by two six -month periods at our option, provided that there is no default under the facility and we pay an extension fee based on the total availability of the facility for each extension; • changes to the interest terms of the facility such that the variable interest rate is based on LIBOR (customarily the 30-day rate) plus 0.875% to 1.600% , as determined by the credit ratings assigned to COPLP by Standard & Poor’s Ratings Services, Moody’s Investors Service, Inc. or Fitch Ratings Ltd. (collectively, the “Ratings Agencies”); • changes to the quarterly fee carried by the facility. Such fee is based on the average daily amount of the lenders’ aggregate commitment multiplied by a per annum rate of 0.125% to 0.300% , as determined by the credit ratings assigned to COPLP by the Ratings Agencies; and • certain changes to the financial covenants of the facility. For the term loan facility: • an increase in the loan amount from $250.0 million to $300.0 million , with a right for us to borrow up to an additional $200.0 million during the term for an aggregate maximum loan of $500.0 million , subject to certain conditions. We used the proceeds from the $50.0 million increase in the facility to repay a portion of another existing unsecured term loan; • an extension of the maturity date of the loan from February 14, 2017 to May 6, 2020; • changes to the interest terms of the facility such that the variable interest rate is based on LIBOR (customarily the 30-day rate) plus 0.900% to 1.850% , as determined by the credit ratings assigned to COPLP by the Ratings Agencies; and • certain changes to the financial covenants of the facility. On June 29, 2015, we issued a $300.0 million aggregate principal amount of 5.00% Senior Notes at an initial offering price of 99.510% of their face value. The proceeds from this issuance, after deducting underwriting discounts, but before other offering expenses, were $296.6 million . The notes mature on July 1, 2025. We may redeem the notes, in whole at any time or in part from time to time, at our option, at a redemption price equal to the greater of (1) the aggregate principal amount of the notes being redeemed and (2) the sum of the present values of the remaining scheduled payments of principal and interest thereon (not including any portion of such payments of interest accrued as of the date of redemption) discounted to its present value, on a semi-annual basis at an adjusted treasury rate plus 45 basis points, plus accrued and unpaid interest thereon to the date of redemption. The notes are unconditionally guaranteed by COPT. However, if this redemption occurs on or after three months prior to the maturity date, the redemption price will be equal to 100% of the principal amount of the notes being redeemed, plus accrued and unpaid interest thereon to, but not including, the redemption date. The carrying value of these notes reflects an unamortized discount totaling $3.4 million at September 30, 2015 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.15% . We capitalized interest costs of $1.5 million in the three months ended September 30, 2015 , $1.3 million in the three months ended September 30, 2014 , $5.6 million in the nine months ended September 30, 2015 and $4.3 million in the nine months ended September 30, 2014 . The following table sets forth information pertaining to the fair value of our debt (in thousands): September 30, 2015 December 31, 2014 Carrying Estimated Carrying Estimated Amount Fair Value Amount Fair Value Fixed-rate debt Unsecured Senior Notes $ 1,188,241 $ 1,212,120 $ 890,862 $ 901,599 Other fixed-rate debt 289,750 298,198 389,318 356,377 Variable-rate debt 643,249 644,243 639,877 642,091 $ 2,121,240 $ 2,154,561 $ 1,920,057 $ 1,900,067

Interest Rate Derivatives

Interest Rate Derivatives	9 Months Ended
	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Interest Rate Derivatives	Interest Rate Derivatives The following table sets forth the key terms and fair values of our interest rate swap derivatives (dollars in thousands): Fair Value at Notional Amount Fixed Rate Floating Rate Index Effective Date Expiration Date September 30, December 31, $ 36,249 (1) 3.8300% One-Month LIBOR + 2.25% 11/2/2010 11/2/2015 $ (44 ) $ (400 ) 100,000 0.8055% One-Month LIBOR 9/2/2014 9/1/2016 (396 ) (317 ) 100,000 0.8100% One-Month LIBOR 9/2/2014 9/1/2016 (401 ) (324 ) 100,000 1.6730% One-Month LIBOR 9/1/2015 8/1/2019 (2,386 ) 239 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 (2,617 ) 35 100,000 0.8320% One-Month LIBOR 1/3/2012 9/1/2015 — (407 ) 100,000 0.8320% One-Month LIBOR 1/3/2012 9/1/2015 — (407 ) $ (5,844 ) $ (1,581 ) (1) The notional amount of this instrument is scheduled to amortize to $36.2 million . Each of the one-month LIBOR interest rate swaps set forth in the table above was designated as a cash flow hedge of interest rate risk. The table below sets forth the fair value of our interest rate derivatives as well as their classification on our consolidated balance sheets (in thousands): September 30, 2015 December 31, 2014 Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets $ — Prepaid expenses and other assets $ 274 Interest rate swaps designated as cash flow hedges Interest rate derivatives (5,844 ) Interest rate derivatives (1,855 ) The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Amount of (loss) gain recognized in accumulated other comprehensive loss (“AOCL”) (effective portion) $ (3,638 ) $ 1,015 $ (6,720 ) $ (4,738 ) Amount of losses reclassified from AOCL into interest expense (effective portion) 915 756 2,457 2,170 Over the next 12 months, we estimate that approximately $3.5 million of losses will be reclassified from AOCL as an increase to interest expense. We have agreements with each of our interest rate derivative counterparties that contain provisions under which, if we default or are capable of being declared in default on defined levels of our indebtedness, we could also be declared in default on our derivative obligations. These agreements also incorporate the loan covenant provisions of our indebtedness with a lender affiliate of the derivative counterparties. Failure to comply with the loan covenant provisions could result in our being declared in default on any derivative instrument obligations covered by the agreements. As of September 30, 2015 , the fair value of interest rate derivatives in a liability position related to these agreements was $5.9 million , excluding the effects of accrued interest and credit valuation adjustments. As of September 30, 2015 , we had not posted any collateral related to these agreements. We are not in default with any of these provisions. If we breached any of these provisions, we could be required to settle our obligations under the agreements at their termination value of $6.3 million .

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest	9 Months Ended
	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest	Redeemable Noncontrolling Interest The table below sets forth the activity for a redeemable noncontrolling interest in a consolidated real estate joint venture (in thousands): For the Nine Months Ended September 30, 2015 2014 Beginning balance $ 18,417 $ 17,758 Distributions to noncontrolling interest, net (1,098 ) (976 ) Net income attributable to noncontrolling interest 1,690 1,647 Adjustment to arrive at fair value of interest 599 7 Ending balance $ 19,608 $ 18,436

Equity

Equity	9 Months Ended
	Sep. 30, 2015
Equity [Abstract]
Equity	Equity During the nine months ended September 30, 2015 , COPT issued 890,241 common shares at a weighted average price of $30.29 per share under its at-the-market (“ATM”) stock offering program established in October 2012. Net proceeds from the shares issued totaled $26.6 million , after payment of $0.4 million in commissions to sales agents. These net proceeds were contributed to COPLP in exchange for 890,241 common units. COPT’s remaining capacity under the ATM Plan is an aggregate gross sales price of $84.0 million in common share sales. During the nine months ended September 30, 2015 , certain COPLP limited partners redeemed 160,160 common units in COPLP for an equal number of common shares in COPT. See Note 14 for disclosure of COPT common share and COPLP common unit activity pertaining to our share-based compensation plans.

Information by Business Segment

Information by Business Segment	9 Months Ended
	Sep. 30, 2015
Segment Reporting [Abstract]
Information by Business Segment	Information by Business Segment We have ten reportable operating office property segments (comprised of: the Baltimore/Washington Corridor; Northern Virginia; San Antonio; Huntsville; Washington, DC — Capitol Riverfront; St. Mary’s and King George Counties; Greater Baltimore; Greater Philadelphia; Colorado Springs; and Other). In our 2015 quarterly reports on Form 10-Q, our Colorado Springs segment is, and will be, included in our Other segment as it is insignificant in the 2014 and 2015 reporting periods. We also have an operating wholesale data center segment. The table below reports segment financial information for our reportable segments (in thousands). We measure the performance of our segments through the measure we define as NOI from real estate operations, which is derived by subtracting property operating expenses from revenues from real estate operations. Operating Office Property Segments Baltimore/ Washington Corridor Northern Virginia San Antonio Huntsville Washington, DC - Capitol Riverfront St. Mary’s & King George Counties Greater Baltimore Greater Other Operating Wholesale Data Center Total Three Months Ended September 30, 2015 Revenues from real estate operations $ 62,009 $ 23,332 $ 9,492 $ 3,061 $ 3,336 $ 3,550 $ 16,134 $ 4,126 $ 2,568 $ 6,078 $ 133,686 Property operating expenses 20,169 7,785 4,808 888 1,962 1,325 6,461 1,249 242 4,008 48,897 NOI from real estate operations $ 41,840 $ 15,547 $ 4,684 $ 2,173 $ 1,374 $ 2,225 $ 9,673 $ 2,877 $ 2,326 $ 2,070 $ 84,789 Additions to long-lived assets $ 7,943 $ 1,749 $ — $ 175 $ 1,098 $ 986 $ 128,933 $ 246 $ (93 ) $ — $ 141,037 Transfers from non-operating properties $ 25,184 $ 34,195 $ 591 $ 1,207 $ — $ 1,408 $ 315 $ 5,506 $ — $ 73,804 $ 142,210 Three Months Ended September 30, 2014 — Revenues from real estate operations $ 58,883 $ 21,369 $ 9,031 $ 2,471 $ 3,524 $ 4,158 $ 10,436 $ 2,951 $ 2,541 $ 2,876 $ 118,240 Property operating expenses 19,457 7,500 5,100 763 1,824 1,277 3,810 837 260 2,053 42,881 NOI from real estate operations $ 39,426 $ 13,869 $ 3,931 $ 1,708 $ 1,700 $ 2,881 $ 6,626 $ 2,114 $ 2,281 $ 823 $ 75,359 Additions to long-lived assets $ 7,248 $ 5,898 $ — $ 455 $ 458 $ 5,189 $ 3,021 $ 625 $ (125 ) $ 24 $ 22,793 Transfers from non-operating properties $ 22,680 $ 15,403 $ — $ 1,496 $ — $ — $ 495 $ 2,506 $ — $ 222 $ 42,802 Nine Months Ended September 30, 2015 Revenues from real estate operations $ 184,412 $ 69,474 $ 28,867 $ 8,165 $ 10,091 $ 11,246 $ 40,508 $ 11,236 $ 7,659 $ 12,933 $ 384,591 Property operating expenses 63,291 25,593 15,398 2,605 5,837 4,238 16,367 3,565 655 8,441 145,990 NOI from real estate operations $ 121,121 $ 43,881 $ 13,469 $ 5,560 $ 4,254 $ 7,008 $ 24,141 $ 7,671 $ 7,004 $ 4,492 $ 238,601 Additions to long-lived assets $ 16,529 $ 89,152 $ 21 $ 466 $ 2,297 $ 3,149 $ 195,013 $ 824 $ 164 $ 108 $ 307,723 Transfers from non-operating properties $ 44,212 $ 101,412 $ 32,150 $ 13,184 $ — $ 1,408 $ 327 $ 22,222 $ 8 $ 89,183 $ 304,106 Segment assets at September 30, 2015 $ 1,297,431 $ 697,406 $ 148,336 $ 108,541 $ 94,120 $ 101,985 $ 455,469 $ 128,409 $ 76,259 $ 246,806 $ 3,354,762 Nine Months Ended September 30, 2014 Revenues from real estate operations $ 177,452 $ 67,235 $ 26,268 $ 7,430 $ 10,989 $ 12,676 $ 32,956 $ 8,657 $ 7,668 $ 7,769 $ 359,100 Property operating expenses 62,402 24,124 14,391 2,275 5,343 4,070 13,786 3,281 1,195 5,622 136,489 NOI from real estate operations $ 115,050 $ 43,111 $ 11,877 $ 5,155 $ 5,646 $ 8,606 $ 19,170 $ 5,376 $ 6,473 $ 2,147 $ 222,611 Additions to long-lived assets $ 19,278 $ 14,198 $ (6 ) $ 3,296 $ 999 $ 6,971 $ 5,275 $ 724 $ (163 ) $ 46 $ 50,618 Transfers from non-operating properties $ 50,303 $ 42,674 $ — $ 21,821 $ — $ — $ 3,522 $ 15,880 $ 30 $ 897 $ 135,127 Segment assets at September 30, 2014 $ 1,278,713 $ 648,248 $ 116,837 $ 98,334 $ 96,131 $ 100,009 $ 274,931 $ 107,051 $ 78,240 $ 164,192 $ 2,962,686 The following table reconciles our segment revenues to total revenues as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Segment revenues from real estate operations $ 133,686 $ 118,240 $ 384,591 $ 359,100 Construction contract and other service revenues 17,058 34,739 97,554 80,390 Less: Revenues from discontinued operations — 36 (4 ) 12 Total revenues $ 150,744 $ 153,015 $ 482,141 $ 439,502 The following table reconciles our segment property operating expenses to property operating expenses as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Segment property operating expenses $ 48,897 $ 42,881 $ 145,990 $ 136,489 Less: Property operating expenses from discontinued operations — 175 6 111 Total property operating expenses $ 48,897 $ 43,056 $ 145,996 $ 136,600 As previously discussed, we provide real estate services such as property management and construction and development services primarily for our properties but also for third parties. The primary manner in which we evaluate the operating performance of our service activities is through a measure we define as net operating income from service operations (“NOI from service operations”), which is based on the net of revenues and expenses from these activities. Construction contract and other service revenues and expenses consist primarily of subcontracted costs that are reimbursed to us by the customer along with a management fee. The operating margins from these activities are small relative to the revenue. We believe NOI from service operations is a useful measure in assessing both our level of activity and our profitability in conducting such operations. The table below sets forth the computation of our NOI from service operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Construction contract and other service revenues $ 17,058 $ 34,739 $ 97,554 $ 80,390 Construction contract and other service expenses (16,132 ) (33,593 ) (94,923 ) (75,353 ) NOI from service operations $ 926 $ 1,146 $ 2,631 $ 5,037 The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from continuing operations as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 NOI from real estate operations $ 84,789 $ 75,359 $ 238,601 $ 222,611 NOI from service operations 926 1,146 2,631 5,037 Interest and other income 692 1,191 3,217 3,775 Equity in income of unconsolidated entities 18 193 52 206 Income tax expense (48 ) (101 ) (153 ) (257 ) Other adjustments: — — Depreciation and other amortization associated with real estate operations (38,403 ) (30,237 ) (103,788 ) (104,728 ) Impairment losses (2,307 ) (66 ) (3,545 ) (1,368 ) General, administrative and leasing expenses (7,439 ) (7,211 ) (22,864 ) (22,882 ) Business development expenses and land carry costs (5,573 ) (1,430 ) (10,986 ) (4,107 ) Interest expense (24,121 ) (24,802 ) (66,727 ) (69,107 ) Less: NOI from discontinued operations — (139 ) (10 ) (99 ) Gain (loss) on early extinguishment of debt 85,745 (176 ) 85,677 (446 ) Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635 The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): September 30, September 30, Segment assets $ 3,354,762 $ 2,962,686 Non-operating property assets 416,540 518,951 Other assets 147,171 198,551 Total COPT consolidated assets $ 3,918,473 $ 3,680,188 The accounting policies of the segments are the same as those used to prepare our consolidated financial statements, except that discontinued operations are not presented separately for segment purposes. In the segment reporting presented above, we did not allocate interest expense, depreciation and amortization, impairment losses, loss on early extinguishment of debt and gain on sales of real estate to our real estate segments since they are not included in the measure of segment profit reviewed by management. We also did not allocate general and administrative expenses, business development expenses and land carry costs, interest and other income, equity in income of unconsolidated entities, income taxes and noncontrolling interests because these items represent general corporate or non-operating property items not attributable to segments.

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation Performance Share Units (“PSUs”) On March 5, 2015, our Board of Trustees granted 45,656 PSUs with an aggregate grant date fair value of $1.7 million to executives. The PSUs have a performance period beginning on January 1, 2015 and concluding on the earlier of December 31, 2017 or the date of: (1) termination by us without cause, death or disability of the executive or constructive discharge of the executive (collectively, “qualified termination”); or (2) a sale event. The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned PSUs Payout % 75th or greater 200% of PSUs granted 50th or greater 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted If the percentile rank exceeds the 25th percentile and is between two of the percentile ranks set forth in the table above, then the percentage of the earned PSUs will be interpolated between the ranges set forth in the table above to reflect any performance between the listed percentiles. At the end of the performance period, we, in settlement of the award, will issue a number of fully-vested COPT common shares equal to the sum of: • the number of earned PSUs in settlement of the award plan; plus • the aggregate dividends that would have been paid with respect to the common shares issued in settlement of the earned PSUs through the date of settlement had such shares been issued on the grant date, divided by the share price on such settlement date, as defined under the terms of the agreement. If a service period ends due to a sale event or qualified termination, the number of earned PSUs is prorated based on the portion of the service period that has elapsed. If employment is terminated by the employee or by us for cause, all PSUs are forfeited. PSUs do not carry voting rights. We computed a grant date fair value of $36.76 per PSU using a Monte Carlo model, which included assumptions of, among other things, the following: baseline common share value of $29.28 ; expected volatility for COPT common shares of 19.9% ; and a risk-free interest rate of 0.99% . We are recognizing the grant date fair value in connection with these PSU awards over the period commencing on March 6, 2015 and ending on December 31, 2017. With regard to the PSUs granted to our executives in prior years that were outstanding as of December 31, 2014 as described in our 2014 Annual Report on Form 10-K: • the performance period for the PSUs granted to executives on March 1, 2012 ended on December 31, 2014. Based on COPT’s total shareholder return during the performance period relative to its peer group of companies, we issued 40,309 common shares in settlement of the PSUs on March 5, 2015; and • we issued 15,289 common shares on March 5, 2015 to Mr. Stephen E. Riffee, our former Chief Financial Officer, upon his departure on February 3, 2015, in settlement of PSUs granted on March 1, 2013 and March 6, 2014. Restricted Shares During the nine months ended September 30, 2015 , certain employees were granted a total of 193,499 restricted common shares with an aggregate grant date fair value of $5.6 million (weighted average of $28.93 per share). Restricted shares granted to employees vest based on increments and over periods of time set forth under the terms of the respective awards provided that the employees remain employed by us. During the nine months ended September 30, 2015 , forfeiture restrictions lapsed on 163,145 previously issued common shares; these shares had a weighted average grant date fair value of $26.15 per share, and the aggregate intrinsic value of the shares on the vesting dates was $4.6 million . Deferred Share Awards During the nine months ended September 30, 2015 , nonemployee members of our Board of Trustees were granted a total of 24,056 deferred share awards with an aggregate grant date fair value of $642,000 ( $26.70 per share). Deferred share awards vest on the first anniversary of the grant date, provided that the Trustee remains in his or her position. We settle deferred share awards by issuing an equivalent number of common shares upon vesting of the awards or a later date elected by the Trustee (generally upon cessation of being a Trustee). During the nine months ended September 30, 2015 , we issued 15,485 common shares in settlement of deferred share awards granted in 2014; these shares had a grant date fair value of $26.77 per share, and the aggregate intrinsic value of the shares on the settlement date was $413,000 . Options During the nine months ended September 30, 2015 , 76,474 options to purchase common shares (“options”) were exercised. The weighted average exercise price of these options was $26.27 per share, and the aggregate intrinsic value of the options exercised was $300,000 .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes We own a TRS that is subject to Federal and state income taxes. Our TRS’s provision for income taxes consisted of the following (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Deferred Federal $ 39 $ 83 $ 125 $ 215 State 9 18 28 42 Total income tax expense $ 48 $ 101 $ 153 $ 257 Items in our TRS contributing to temporary differences that lead to deferred taxes include depreciation and amortization, share-based compensation, certain accrued compensation, compensation paid in the form of contributions to a deferred nonqualified compensation plan and net operating losses that are not deductible until future periods. Our TRS’s combined Federal and state effective tax rate was 37.7% for the three and nine months ended September 30, 2015 and 2014.

Earnings Per Share ("EPS") and

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU")	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”)	Earnings Per Share (“EPS”) and Earnings Per Unit (“EPU”) COPT and Subsidiaries EPS We present both basic and diluted EPS. We compute basic EPS by dividing net income available to common shareholders allocable to unrestricted common shares under the two-class method by the weighted average number of unrestricted common shares outstanding during the period. Our computation of diluted EPS is similar except that: • the denominator is increased to include: (1) the weighted average number of potential additional common shares that would have been outstanding if securities that are convertible into COPT common shares were converted; and (2) the effect of dilutive potential common shares outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and • the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common shares that we added to the denominator. Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Numerator: Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635 Gain on sales of real estate, net 15 10,630 4,000 10,630 Preferred share dividends (3,552 ) (3,553 ) (10,657 ) (12,387 ) Issuance costs associated with redeemed preferred shares — — — (1,769 ) Income from continuing operations attributable to noncontrolling interests (4,494 ) (1,820 ) (7,322 ) (3,923 ) Income from continuing operations attributable to share-based compensation awards (369 ) (103 ) (475 ) (332 ) Numerator for basic EPS from continuing operations attributable to COPT common shareholders 85,879 18,881 107,651 20,854 Convertible preferred shares 372 — — — Dilutive effect of common units in COPLP on diluted EPS from continuing operations — — 4,225 — Numerator for diluted EPS from continuing operations attributable to COPT common shareholders $ 86,251 $ 18,881 $ 111,876 $ 20,854 Numerator for basic EPS from continuing operations attributable to COPT common shareholders $ 85,879 $ 18,881 $ 107,651 $ 20,854 Discontinued operations — 191 156 4 Discontinued operations attributable to noncontrolling interests — (8 ) (3 ) 5 Numerator for basic EPS on net income attributable to COPT common shareholders 85,879 19,064 107,804 20,863 Convertible preferred shares 372 — — — Dilutive effect of common units in COPLP — — 4,231 — Numerator for diluted EPS on net income attributable to COPT common shareholders $ 86,251 $ 19,064 $ 112,035 $ 20,863 Denominator (all weighted averages): Denominator for basic EPS (common shares) 94,153 87,290 93,830 87,196 Convertible preferred shares 434 — — — Dilutive effect of common units — — 3,697 — Dilutive effect of share-based compensation awards 21 195 82 169 Denominator for diluted EPS (common shares) 94,608 87,485 97,609 87,365 Basic EPS: Income from continuing operations attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPT common shareholders 0.00 0.00 0.00 0.00 Net income attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Diluted EPS: Income from continuing operations attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPT common shareholders 0.00 0.00 0.00 0.00 Net income attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Our diluted EPS computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPS for the respective periods (in thousands): Weighted Average Shares Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Conversion of common units 3,679 3,876 — 3,915 Conversion of Series I Preferred Units 176 176 176 176 Conversion of Series K Preferred Shares — 434 434 434 The following share-based compensation securities were excluded from the computation of diluted EPS because their effects were antidilutive: • weighted average restricted shares and deferred share awards for the three months ended September 30, 2015 and 2014 of 411,000 and 401,000 , respectively, and for the nine months ended September 30, 2015 and 2014 of 412,000 and 404,000 , respectively; and • weighted average options for the three months ended September 30, 2015 and 2014 of 440,000 and 490,000 , respectively, and for the nine months ended September 30, 2015 and 2014 of 480,000 and 495,000 , respectively. As discussed in Note 9, we had outstanding senior notes, which we redeemed in April 2015, with an exchange settlement feature, but such notes did not affect our diluted EPS reported above since the weighted average closing price of COPT’s common shares during each of the periods was less than the exchange prices per common share applicable for such periods. COPLP and Subsidiaries EPU We present both basic and diluted EPU. We compute basic EPU by dividing net income available to common unitholders allocable to unrestricted common units under the two-class method by the weighted average number of unrestricted common units outstanding during the period. Our computation of diluted EPU is similar except that: • the denominator is increased to include: (1) the weighted average number of potential additional common units that would have been outstanding if securities that are convertible into our common units were converted; and (2) the effect of dilutive potential common units outstanding during the period attributable to share-based compensation using the treasury stock or if-converted methods; and • the numerator is adjusted to add back any changes in income or loss that would result from the assumed conversion into common units that we added to the denominator. Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Numerator: Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635 Gain on sales of real estate, net 15 10,630 4,000 10,630 Preferred unit distributions (3,717 ) (3,718 ) (11,152 ) (12,882 ) Issuance costs associated with redeemed preferred units — — — (1,769 ) Income from continuing operations attributable to noncontrolling interests (972 ) (897 ) (2,605 ) (2,476 ) Income from continuing operations attributable to share-based compensation awards (369 ) (103 ) (475 ) (332 ) Numerator for basic EPU from continuing operations attributable to COPLP common unitholders 89,236 19,639 111,873 21,806 Convertible preferred units 372 — — — Numerator for diluted EPU from continuing operations attributable to COPLP common unitholders $ 89,608 $ 19,639 $ 111,873 $ 21,806 Numerator for basic EPU from continuing operations attributable to COPLP common unitholders $ 89,236 $ 19,639 $ 111,873 $ 21,806 Discontinued operations — 191 156 4 Discontinued operations attributable to noncontrolling interests — — 3 5 Numerator for basic EPU on net income attributable to COPLP common unitholders 89,236 19,830 112,032 21,815 Convertible preferred units 372 — — — Numerator for diluted EPU on net income attributable to COPLP common unitholders $ 89,608 $ 19,830 $ 112,032 $ 21,815 Denominator (all weighted averages): Denominator for basic EPU (common units) 97,832 91,166 97,527 91,111 Convertible preferred shares 434 — — — Dilutive effect of share-based compensation awards 21 195 82 169 Denominator for basic and diluted EPU (common units) 98,287 91,361 97,609 91,280 Basic EPU: Income from continuing operations attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPLP common unitholders 0.00 0.00 0.00 0.00 Net income attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Diluted EPU: Income from continuing operations attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPLP common unitholders 0.00 0.00 0.00 0.00 Net income attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Conversion of Series I preferred units 176 176 176 176 Conversion of Series K preferred units — 434 434 434 The following share-based compensation securities were excluded from the computation of diluted EPU because their effects were antidilutive: • weighted average restricted units and deferred share awards for the three months ended September 30, 2015 and 2014 of 411,000 and 401,000 , respectively, and for the nine months ended September 30, 2015 and 2014 of 412,000 and 404,000 , respectively; and • weighted average options for the three months ended September 30, 2015 and 2014 of 440,000 and 490,000 , respectively, and for the nine months ended September 30, 2015 and 2014 of 480,000 and 495,000 , respectively. As discussed in Note 9, we had outstanding senior notes, which we redeemed in April 2015, with an exchange settlement feature, but such notes did not affect our diluted EPU reported above since the weighted average closing price of COPT’s common shares during each of the periods was less than the exchange prices per common share applicable for such periods.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Litigation In the normal course of business, we are involved in legal actions arising from our ownership and administration of properties. We establish reserves for specific legal proceedings when we determine that the likelihood of an unfavorable outcome is probable and the amount of loss can be reasonably estimated. Management does not anticipate that any liabilities that may result from such proceedings will have a materially adverse effect on our financial position, operations or liquidity. Our assessment of the potential outcomes of these matters involves significant judgment and is subject to change based on future developments. Environmental We are subject to various Federal, state and local environmental regulations related to our property ownership and operation. We have performed environmental assessments of our properties, the results of which have not revealed any environmental liability that we believe would have a materially adverse effect on our financial position, operations or liquidity. Tax Incremental Financing Obligation In August 2010, Anne Arundel County, Maryland issued $30 million in tax incremental financing bonds to third-party investors in order to finance public improvements needed in connection with our project known as National Business Park North. The real estate taxes on increases in assessed value of a development district encompassing National Business Park North are to be transferred to a special fund pledged to the repayment of the bonds. We recognized a $2.2 million liability through September 30, 2015 representing our estimated obligation to fund through a special tax any future shortfalls between debt service on the bonds and real estate taxes available to repay the bonds. Operating Leases We are obligated as lessee under operating leases (mostly ground leases) with various expiration dates extending to the year 2100. Future minimum rental payments due under the terms of these operating leases as of September 30, 2015 follow (in thousands): Year Ending December 31, 2015 (1) $ 289 2016 1,171 2017 1,096 2018 1,052 2019 1,036 Thereafter 86,999 $ 91,643 (1) Represents three months ending December 31, 2015. Contractual Obligations We had amounts remaining to be incurred under various contractual obligations as of September 30, 2015 that included the following: • new development and redevelopment obligations of $97.9 million (including acquisitions of land); • capital expenditures for operating properties of $41.9 million ; • third party construction and development of $8.1 million ; and • other purchase obligations of $4.0 million . Environmental Indemnity Agreement In connection with a lease and subsequent sale in 2008 and 2010 of three properties in Dayton, New Jersey, we agreed to provide certain environmental indemnifications. The prior owner of the properties, a Fortune 100 company that is responsible for groundwater contamination at such properties, previously agreed to indemnify us for (1) direct losses incurred in connection with the contamination and (2) its failure to perform remediation activities required by the State of New Jersey, up to the point that the state declares the remediation to be complete. Under the environmental indemnification agreement, we agreed to the following: • to indemnify the tenant against losses covered under the prior owner’s indemnity agreement if the prior owner fails to indemnify the tenant for such losses. This indemnification is capped at $5.0 million in perpetuity after the State of New Jersey declares the remediation to be complete; • to indemnify the tenant for consequential damages (e.g., business interruption) at one of the buildings in perpetuity and another of the buildings through 2025. This indemnification is limited to $12.5 million ; and • to pay 50% of additional costs related to construction and environmental regulatory activities incurred by the tenant as a result of the indemnified environmental condition of the properties. This indemnification is limited to $300,000 annually and $1.5 million in the aggregate.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2015
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On October 27, 2015, we sold 13200 Woodland Park Road, a 397,000 square foot office property in Herndon, Virginia (in the Northern Virginia region) for $84.0 million , resulting in a gain on sale of approximately $42 million .

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The COPT consolidated financial statements include the accounts of COPT, the Operating Partnership, their subsidiaries and other entities in which COPT has a majority voting interest and control. The COPLP consolidated financial statements include the accounts of COPLP, its subsidiaries and other entities in which COPLP has a majority voting interest and control. We also consolidate certain entities when control of such entities can be achieved through means other than voting rights (“variable interest entities” or “VIEs”) if we are deemed to be the primary beneficiary of such entities. We eliminate all significant intercompany balances and transactions in consolidation. We use the equity method of accounting when we own an interest in an entity and can exert significant influence over but cannot control the entity’s operations. We discontinue equity method accounting if our investment in an entity (and net advances) is reduced to zero unless we have guaranteed obligations of the entity or are otherwise committed to provide further financial support for the entity. These interim financial statements should be read together with the consolidated financial statements and notes thereto as of and for the year ended December 31, 2014 included in our 2014 Annual Report on Form 10-K. The unaudited consolidated financial statements include all adjustments that are necessary, in the opinion of management, to fairly present our financial position and results of operations. All adjustments are of a normal recurring nature. The consolidated financial statements have been prepared using the accounting policies described in our 2014 Annual Report on Form 10-K.
Recent Accounting Pronouncement	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued guidance regarding the recognition of revenue from contracts with customers. Under this guidance, an entity will recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Additionally, this guidance requires improved disclosures regarding the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. We are required to adopt this guidance for our annual and interim periods beginning January 1, 2018 using one of two methods: retrospective restatement for each reporting period presented at the time of adoption, or retrospectively with the cumulative effect of initially applying this guidance recognized at the date of initial application. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In January 2015, the FASB issued guidance regarding the presentation of extraordinary and unusual items in statements of operations. This guidance eliminates the concept of extraordinary items. However, the presentation and disclosure requirements for items that are either unusual in nature or infrequent in occurrence remain and will be expanded to include items that are both unusual in nature and infrequent in occurrence. This guidance is effective for periods beginning after December 15, 2015. We expect that the application of this guidance will have no effect on our reported consolidated financial statements. In February 2015, the FASB issued guidance regarding amendments to the consolidation analysis. This guidance amends the criteria for determining which entities are considered variable interest entities (“VIE”), amends the criteria for determining if a service provider possesses a variable interest in a VIE and ends the deferral granted to investment companies for application of the VIE consolidation model. This guidance is effective for annual periods, and interim periods therein, beginning after December 15, 2015. We are currently assessing the financial impact of this guidance on our consolidated financial statements. In April 2015, the FASB issued guidance that changes the presentation of debt issuance costs in financial statements. This guidance requires an entity to present such costs in the balance sheet as a direct deduction from the related debt liability rather than as an asset. Amortization of the costs will continue to be reported as interest expense. This guidance was further updated in August 2015 with respect to debt issuance costs of line-of-credit arrangements to note that it will be permissible for an entity to defer and present debt issuance costs as an asset and subsequently amortize the deferred debt issuance costs ratably over the term of a line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. This guidance is effective for annual reporting periods beginning after December 15, 2016. Early adoption is permitted. This guidance will be applied retrospectively to each prior period presented. We expect that the application of this guidance will not materially affect our consolidated financial statements. In September 2015, the FASB issued guidance that eliminates the requirement to restate prior period financial statements for measurement period adjustments following a business combination. The guidance requires that the cumulative impact of a measurement period adjustment (including the impact on prior periods) be recognized in the reporting period in which the adjustment is identified. The prior period impact of the adjustment should be either presented separately on the face of the statement of operations or disclosed in the notes. This guidance is effective for annual reporting periods beginning after December 15, 2015. This guidance will be applied prospectively for measurement period adjustments that occur after the effective date. We expect that the application of this guidance will not materially affect our consolidated financial statements.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Schedule of fair value assets and liabilities measured on recurring basis	The table below sets forth financial assets and liabilities of COPLP and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2015 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Warrants to purchase common stock (1) $ — $ 42 $ — $ 42 Liabilities: Interest rate derivatives $ — $ 5,844 $ — $ 5,844 Redeemable noncontrolling interest $ — $ — $ 19,608 $ 19,608 (1) Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet. The table below sets forth financial assets and liabilities of COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of September 30, 2015 and the hierarchy level of inputs used in measuring their respective fair values under applicable accounting standards (in thousands): Description Quoted Prices in Significant Other Significant Total Assets: Marketable securities in deferred compensation plan (1) Mutual funds $ 5,395 $ — $ — $ 5,395 Other 104 — — 104 Warrants to purchase common stock (2) — 42 — 42 Total assets $ 5,499 $ 42 $ — $ 5,541 Liabilities: Deferred compensation plan liability (3) $ — $ 5,499 $ — $ 5,499 Interest rate derivatives — 5,844 — 5,844 Total liabilities $ — $ 11,343 $ — $ 11,343 Redeemable noncontrolling interest $ — $ — $ 19,608 $ 19,608 (1) Included in the line entitled “restricted cash and marketable securities” on COPT’s consolidated balance sheet. (2) Included in the line entitled “prepaid expenses and other assets” on COPT’s consolidated balance sheet. (3) Included in the line entitled “other liabilities” on COPT’s consolidated balance sheet.
Schedule of fair value hierarchy of impaired properties and other assets associated with such properties	The table below sets forth the fair value hierarchy of the valuation technique we used to determine the fair values of these properties (dollars in thousands): Fair Values of Properties Held as of September 30, 2015 Quoted Prices in Significant Active Markets for Significant Other Unobservable Identical Assets Observable Inputs Inputs Description (Level 1) (Level 2) (Level 3) Total Assets: Assets held for sale, net (1) $ — $ — $ 7,225 $ 7,225 (1) Represents estimated fair values less costs to sell.
Schedule of quantitative information about significant unobservable inputs used for Level 3 fair value measurements	The table below sets forth quantitative information about significant unobservable inputs used for the Level 3 fair value measurements reported above as of September 30, 2015 (dollars in thousands): Valuation Technique Fair Values on Measurement Date Unobservable Input Range (Weighted Average) (1) Discounted cash flow $ 7,225 Discount rate 8.25% Terminal capitalization rate 7.75% Market rent growth rate 2.0% Expense growth rate 2.0% (1) Only one value applied for these unobservable inputs.

Properties, Net (Tables)

Properties, Net (Tables)	9 Months Ended
	Sep. 30, 2015
Real Estate [Abstract]
Schedule of operating properties, net	Operating properties, net consisted of the following (in thousands): September 30, December 31, Land $ 466,701 $ 439,355 Buildings and improvements 3,141,889 3,015,216 Less: Accumulated depreciation (675,747 ) (703,083 ) Operating properties, net $ 2,932,843 $ 2,751,488
Schedule of projects in development or held for future development	Projects in development or held for future development consisted of the following (in thousands): September 30, December 31, Land $ 207,748 $ 214,977 Development in progress, excluding land 207,009 330,449 Projects in development or held for future development $ 414,757 $ 545,426
Components of assets held for sale	The table below sets forth the components of assets held for sale on our consolidated balance sheet for these properties (in thousands): September 30, 2015 Properties, net $ 142,817 Deferred rent receivable 3,998 Intangible assets on real estate acquisitions, net 799 Deferred leasing costs, net 2,053 Lease incentives, net 905 Assets held for sale, net $ 150,572
Schedule of allocation of acquisition costs	The table below sets forth the allocation of the aggregate acquisition costs of these properties (in thousands): Land, operating properties $ 55,076 Building and improvements 139,520 Intangible assets on real estate acquisitions 75,846 Total assets 270,442 Below-market leases (6,820 ) Total acquisition cost $ 263,622
Schedule of intangible assets recorded in connection with acquisition	Intangible assets recorded in connection with these acquisitions included the following (dollars in thousands): Weighted Average Amortization Period (in Years) Tenant relationship value $ 31,208 12 In-place lease value 35,231 7 Above-market leases 6,720 4 Below-market cost arrangements 2,687 40 $ 75,846 10
Pro Forma Results	The pro forma financial information was prepared for comparative purposes only and is not necessarily indicative of what would have occurred had these acquisitions been made at that time or of results which may occur in the future (in thousands, except per shares amounts). For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 (Unaudited) (Unaudited) Pro forma total revenues $ 152,736 $ 162,085 $ 498,657 $ 467,224 Pro forma net income attributable to COPT common shareholders $ 88,836 $ 19,683 $ 112,941 $ 19,266 Pro forma EPS: Basic $ 0.94 $ 0.22 $ 1.20 $ 0.22 Diluted $ 0.94 $ 0.22 $ 1.20 $ 0.22

Real Estate Joint Ventures (Tab

Real Estate Joint Ventures (Tables)	9 Months Ended
	Sep. 30, 2015
Equity Method Investments and Joint Ventures [Abstract]
Schedule of information related to investments in consolidated real estate joint ventures	The table below sets forth information pertaining to our material investments in consolidated real estate joint ventures as of September 30, 2015 (dollars in thousands): Nominal Ownership September 30, 2015 (1) Date % as of Total Encumbered Total Acquired 9/30/2015 Nature of Activity Assets Assets Liabilities LW Redstone Company, LLC 3/23/2010 85% Development and operation of real estate (2) $ 144,906 $ 64,395 $ 39,093 M Square Associates, LLC 6/26/2007 50% Development and operation of real estate (3) 58,840 48,301 38,117 $ 203,746 $ 112,696 $ 77,210 (1) Excludes amounts eliminated in consolidation. (2) This joint venture’s properties are in Huntsville. (3) This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).

Intangible Assets on Real Est31

Intangible Assets on Real Estate Acquisition, Net (Tables)	9 Months Ended
	Sep. 30, 2015
Intangible Assets on Real Estate Acquisitions [Abstract]
Schedule of intangible assets on real estate acquisitions	Intangible assets on real estate acquisitions consisted of the following, excluding amounts for properties held for sale (in thousands): September 30, 2015 December 31, 2014 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount In-place lease value $ 138,410 $ 87,667 $ 50,743 $ 123,759 $ 101,040 $ 22,719 Tenant relationship value 63,117 22,525 40,592 42,301 28,492 13,809 Below-market cost arrangements 15,102 6,505 8,597 12,415 5,984 6,431 Above-market leases 13,844 7,987 5,857 8,659 8,159 500 Market concentration premium 1,333 948 385 1,333 938 395 $ 231,806 $ 125,632 $ 106,174 $ 188,467 $ 144,613 $ 43,854

Investing Receivables (Tables)

Investing Receivables (Tables)	9 Months Ended
	Sep. 30, 2015
Receivables [Abstract]
Schedule of investing receivables	Investing receivables, including accrued interest thereon, consisted of the following (in thousands): September 30, December 31, Notes receivable from the City of Huntsville $ 43,821 $ 49,147 Other investing loans receivable 3,000 3,000 $ 46,821 $ 52,147

Prepaid Expenses and Other As33

Prepaid Expenses and Other Assets, Net (Tables)	9 Months Ended
	Sep. 30, 2015
Prepaid Expense and Other Assets [Abstract]
Schedule of prepaid expenses and other assets	Prepaid expenses and other assets consisted of the following (in thousands): September 30, December 31, Prepaid expenses $ 28,655 $ 20,570 Lease incentives, net 11,589 13,344 Furniture, fixtures and equipment, net 5,941 6,637 Construction contract costs incurred in excess of billings 4,722 6,656 Deferred tax asset, net (1) 4,015 4,002 Operating notes receivable 3,744 3,797 Equity method investments 1,626 2,368 Other assets 6,495 2,875 Prepaid expenses and other assets, net $ 66,787 $ 60,249 (1) Includes a valuation allowance of $2.1 million .

Debt, Net (Tables)

Debt, Net (Tables)	9 Months Ended
	Sep. 30, 2015
Debt Disclosure [Abstract]
Schedule of debt	Our debt consisted of the following (dollars in thousands): Maximum Availability at Carrying Value at Scheduled Maturity September 30, September 30, December 31, Stated Interest Rates as of as of September 30, 2015 September 30, 2015 Mortgage and Other Secured Loans: Fixed rate mortgage loans (1) $ 288,217 $ 387,139 3.96% - 7.87% (2) 2016-2024 Variable rate secured loan 36,249 36,877 LIBOR + 2.25% (3) November 2015 Total mortgage and other secured loans 324,466 424,016 Revolving Credit Facility $ 800,000 87,000 83,000 LIBOR + 0.875% to 1.60% (4) May 2019 Term Loan Facilities (5) 520,000 520,000 LIBOR + 0.90% to 2.60% (6) 2016-2020 Unsecured Senior Notes 3.600% Senior Notes (7) 347,691 347,496 3.60% May 2023 5.250% Senior Notes (8) 246,074 245,797 5.25% February 2024 3.700% Senior Notes (9) 297,830 297,569 3.70% June 2021 5.000% Senior Note (10) 296,646 — 5.00% July 2025 Unsecured notes payable 1,533 1,607 0% (11) 2026 4.25% Exchangeable Senior Notes (12) — 572 N/A (12) Total debt, net $ 2,121,240 $ 1,920,057 (1) Several of the fixed rate mortgages carry interest rates that were above or below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying values of these loans reflect net unamortized premiums totaling $24,000 as of September 30, 2015 and $42,000 as of December 31, 2014 . Please refer to Note 4 for disclosure pertaining to the removal of a $150.0 million nonrecourse mortgage loan from our balance sheet on August 28, 2015. (2) The weighted average interest rate on our fixed rate mortgage loans was 6.07% as of September 30, 2015 . (3) The interest rate on the loan outstanding was 2.45% as of September 30, 2015 . (4) The weighted average interest rate on the Revolving Credit Facility was 1.48% as of September 30, 2015 . (5) We have the ability to borrow an additional $380.0 million in the aggregate under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders. (6) The weighted average interest rate on these loans was 1.78% as of September 30, 2015 . (7) The carrying value of these notes included a principal amount of $350.0 million and an unamortized discount totaling $2.3 million as of September 30, 2015 and $2.5 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.70% . (8) The carrying value of these notes included a principal amount of $250.0 million and an unamortized discount totaling $3.9 million as of September 30, 2015 and $4.2 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 5.49% . (9) The carrying value of these notes included a principal amount of $300.0 million and an unamortized discount totaling $2.2 million as of September 30, 2015 and $2.4 million as of December 31, 2014 . The effective interest rate under the notes, including amortization of the issuance costs, was 3.85% . (10) Refer to the paragraph below for disclosure pertaining to these notes. (11) These notes carry interest rates that were below market rates upon assumption and therefore were recorded at their fair value based on applicable effective interest rates. The carrying value of these notes reflects an unamortized discount totaling $578,000 as of September 30, 2015 and $654,000 as of December 31, 2014 . (12) On April 20, 2015, we redeemed these notes at 100% of their principal amount.
Schedule of the fair value of debt	The following table sets forth information pertaining to the fair value of our debt (in thousands): September 30, 2015 December 31, 2014 Carrying Estimated Carrying Estimated Amount Fair Value Amount Fair Value Fixed-rate debt Unsecured Senior Notes $ 1,188,241 $ 1,212,120 $ 890,862 $ 901,599 Other fixed-rate debt 289,750 298,198 389,318 356,377 Variable-rate debt 643,249 644,243 639,877 642,091 $ 2,121,240 $ 2,154,561 $ 1,920,057 $ 1,900,067

Interest Rate Derivatives (Tabl

Interest Rate Derivatives (Tables)	9 Months Ended
	Sep. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of key terms and fair values of interest rate swap derivatives	The following table sets forth the key terms and fair values of our interest rate swap derivatives (dollars in thousands): Fair Value at Notional Amount Fixed Rate Floating Rate Index Effective Date Expiration Date September 30, December 31, $ 36,249 (1) 3.8300% One-Month LIBOR + 2.25% 11/2/2010 11/2/2015 $ (44 ) $ (400 ) 100,000 0.8055% One-Month LIBOR 9/2/2014 9/1/2016 (396 ) (317 ) 100,000 0.8100% One-Month LIBOR 9/2/2014 9/1/2016 (401 ) (324 ) 100,000 1.6730% One-Month LIBOR 9/1/2015 8/1/2019 (2,386 ) 239 100,000 1.7300% One-Month LIBOR 9/1/2015 8/1/2019 (2,617 ) 35 100,000 0.8320% One-Month LIBOR 1/3/2012 9/1/2015 — (407 ) 100,000 0.8320% One-Month LIBOR 1/3/2012 9/1/2015 — (407 ) $ (5,844 ) $ (1,581 ) (1) The notional amount of this instrument is scheduled to amortize to $36.2 million .
Schedule of fair value and balance sheet classification of interest rate derivatives	The table below sets forth the fair value of our interest rate derivatives as well as their classification on our consolidated balance sheets (in thousands): September 30, 2015 December 31, 2014 Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value Interest rate swaps designated as cash flow hedges Prepaid expenses and other assets $ — Prepaid expenses and other assets $ 274 Interest rate swaps designated as cash flow hedges Interest rate derivatives (5,844 ) Interest rate derivatives (1,855 )
Schedule of effect of interest rate derivatives on consolidated statements of operations and comprehensive income	The table below presents the effect of our interest rate derivatives on our consolidated statements of operations and comprehensive income (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Amount of (loss) gain recognized in accumulated other comprehensive loss (“AOCL”) (effective portion) $ (3,638 ) $ 1,015 $ (6,720 ) $ (4,738 ) Amount of losses reclassified from AOCL into interest expense (effective portion) 915 756 2,457 2,170

Redeemable Noncontrolling Int36

Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Schedule of activity for redeemable noncontrolling interest	The table below sets forth the activity for a redeemable noncontrolling interest in a consolidated real estate joint venture (in thousands): For the Nine Months Ended September 30, 2015 2014 Beginning balance $ 18,417 $ 17,758 Distributions to noncontrolling interest, net (1,098 ) (976 ) Net income attributable to noncontrolling interest 1,690 1,647 Adjustment to arrive at fair value of interest 599 7 Ending balance $ 19,608 $ 18,436

Information by Business Segme37

Information by Business Segment (Tables)	9 Months Ended
	Sep. 30, 2015
Segment Reporting [Abstract]
Schedule of segment financial information for real estate operations	The table below reports segment financial information for our reportable segments (in thousands). We measure the performance of our segments through the measure we define as NOI from real estate operations, which is derived by subtracting property operating expenses from revenues from real estate operations. Operating Office Property Segments Baltimore/ Washington Corridor Northern Virginia San Antonio Huntsville Washington, DC - Capitol Riverfront St. Mary’s & King George Counties Greater Baltimore Greater Other Operating Wholesale Data Center Total Three Months Ended September 30, 2015 Revenues from real estate operations $ 62,009 $ 23,332 $ 9,492 $ 3,061 $ 3,336 $ 3,550 $ 16,134 $ 4,126 $ 2,568 $ 6,078 $ 133,686 Property operating expenses 20,169 7,785 4,808 888 1,962 1,325 6,461 1,249 242 4,008 48,897 NOI from real estate operations $ 41,840 $ 15,547 $ 4,684 $ 2,173 $ 1,374 $ 2,225 $ 9,673 $ 2,877 $ 2,326 $ 2,070 $ 84,789 Additions to long-lived assets $ 7,943 $ 1,749 $ — $ 175 $ 1,098 $ 986 $ 128,933 $ 246 $ (93 ) $ — $ 141,037 Transfers from non-operating properties $ 25,184 $ 34,195 $ 591 $ 1,207 $ — $ 1,408 $ 315 $ 5,506 $ — $ 73,804 $ 142,210 Three Months Ended September 30, 2014 — Revenues from real estate operations $ 58,883 $ 21,369 $ 9,031 $ 2,471 $ 3,524 $ 4,158 $ 10,436 $ 2,951 $ 2,541 $ 2,876 $ 118,240 Property operating expenses 19,457 7,500 5,100 763 1,824 1,277 3,810 837 260 2,053 42,881 NOI from real estate operations $ 39,426 $ 13,869 $ 3,931 $ 1,708 $ 1,700 $ 2,881 $ 6,626 $ 2,114 $ 2,281 $ 823 $ 75,359 Additions to long-lived assets $ 7,248 $ 5,898 $ — $ 455 $ 458 $ 5,189 $ 3,021 $ 625 $ (125 ) $ 24 $ 22,793 Transfers from non-operating properties $ 22,680 $ 15,403 $ — $ 1,496 $ — $ — $ 495 $ 2,506 $ — $ 222 $ 42,802 Nine Months Ended September 30, 2015 Revenues from real estate operations $ 184,412 $ 69,474 $ 28,867 $ 8,165 $ 10,091 $ 11,246 $ 40,508 $ 11,236 $ 7,659 $ 12,933 $ 384,591 Property operating expenses 63,291 25,593 15,398 2,605 5,837 4,238 16,367 3,565 655 8,441 145,990 NOI from real estate operations $ 121,121 $ 43,881 $ 13,469 $ 5,560 $ 4,254 $ 7,008 $ 24,141 $ 7,671 $ 7,004 $ 4,492 $ 238,601 Additions to long-lived assets $ 16,529 $ 89,152 $ 21 $ 466 $ 2,297 $ 3,149 $ 195,013 $ 824 $ 164 $ 108 $ 307,723 Transfers from non-operating properties $ 44,212 $ 101,412 $ 32,150 $ 13,184 $ — $ 1,408 $ 327 $ 22,222 $ 8 $ 89,183 $ 304,106 Segment assets at September 30, 2015 $ 1,297,431 $ 697,406 $ 148,336 $ 108,541 $ 94,120 $ 101,985 $ 455,469 $ 128,409 $ 76,259 $ 246,806 $ 3,354,762 Nine Months Ended September 30, 2014 Revenues from real estate operations $ 177,452 $ 67,235 $ 26,268 $ 7,430 $ 10,989 $ 12,676 $ 32,956 $ 8,657 $ 7,668 $ 7,769 $ 359,100 Property operating expenses 62,402 24,124 14,391 2,275 5,343 4,070 13,786 3,281 1,195 5,622 136,489 NOI from real estate operations $ 115,050 $ 43,111 $ 11,877 $ 5,155 $ 5,646 $ 8,606 $ 19,170 $ 5,376 $ 6,473 $ 2,147 $ 222,611 Additions to long-lived assets $ 19,278 $ 14,198 $ (6 ) $ 3,296 $ 999 $ 6,971 $ 5,275 $ 724 $ (163 ) $ 46 $ 50,618 Transfers from non-operating properties $ 50,303 $ 42,674 $ — $ 21,821 $ — $ — $ 3,522 $ 15,880 $ 30 $ 897 $ 135,127 Segment assets at September 30, 2014 $ 1,278,713 $ 648,248 $ 116,837 $ 98,334 $ 96,131 $ 100,009 $ 274,931 $ 107,051 $ 78,240 $ 164,192 $ 2,962,686
Schedule of reconciliation of segment revenues to total revenues	The following table reconciles our segment revenues to total revenues as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Segment revenues from real estate operations $ 133,686 $ 118,240 $ 384,591 $ 359,100 Construction contract and other service revenues 17,058 34,739 97,554 80,390 Less: Revenues from discontinued operations — 36 (4 ) 12 Total revenues $ 150,744 $ 153,015 $ 482,141 $ 439,502
Schedule of reconciliation of segment property operating expenses to total property operating expenses	The following table reconciles our segment property operating expenses to property operating expenses as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Segment property operating expenses $ 48,897 $ 42,881 $ 145,990 $ 136,489 Less: Property operating expenses from discontinued operations — 175 6 111 Total property operating expenses $ 48,897 $ 43,056 $ 145,996 $ 136,600
Schedule of computation of net operating income from service operations	The table below sets forth the computation of our NOI from service operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Construction contract and other service revenues $ 17,058 $ 34,739 $ 97,554 $ 80,390 Construction contract and other service expenses (16,132 ) (33,593 ) (94,923 ) (75,353 ) NOI from service operations $ 926 $ 1,146 $ 2,631 $ 5,037
Schedule of reconciliation of net operating income from real estate operations and service operations to (loss) income from continuing operations	The following table reconciles our NOI from real estate operations for reportable segments and NOI from service operations to income from continuing operations as reported on our consolidated statements of operations (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 NOI from real estate operations $ 84,789 $ 75,359 $ 238,601 $ 222,611 NOI from service operations 926 1,146 2,631 5,037 Interest and other income 692 1,191 3,217 3,775 Equity in income of unconsolidated entities 18 193 52 206 Income tax expense (48 ) (101 ) (153 ) (257 ) Other adjustments: — — Depreciation and other amortization associated with real estate operations (38,403 ) (30,237 ) (103,788 ) (104,728 ) Impairment losses (2,307 ) (66 ) (3,545 ) (1,368 ) General, administrative and leasing expenses (7,439 ) (7,211 ) (22,864 ) (22,882 ) Business development expenses and land carry costs (5,573 ) (1,430 ) (10,986 ) (4,107 ) Interest expense (24,121 ) (24,802 ) (66,727 ) (69,107 ) Less: NOI from discontinued operations — (139 ) (10 ) (99 ) Gain (loss) on early extinguishment of debt 85,745 (176 ) 85,677 (446 ) Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635
Schedule of reconciliation of segment assets to total assets	The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands): September 30, September 30, Segment assets $ 3,354,762 $ 2,962,686 Non-operating property assets 416,540 518,951 Other assets 147,171 198,551 Total COPT consolidated assets $ 3,918,473 $ 3,680,188

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of payouts for defined performance under performance-based awards of share-based compensation	The number of PSUs earned (“earned PSUs”) at the end of the performance period will be determined based on the percentile rank of COPT’s total shareholder return relative to a peer group of companies, as set forth in the following schedule: Percentile Rank Earned PSUs Payout % 75th or greater 200% of PSUs granted 50th or greater 100% of PSUs granted 25th 50% of PSUs granted Below 25th 0% of PSUs granted

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Components of provision for income tax	Our TRS’s provision for income taxes consisted of the following (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Deferred Federal $ 39 $ 83 $ 125 $ 215 State 9 18 28 42 Total income tax expense $ 48 $ 101 $ 153 $ 257

Earnings Per Share ("EPS") an40

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earnings per share	Summaries of the numerator and denominator for purposes of basic and diluted EPS calculations are set forth below (in thousands, except per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Numerator: Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635 Gain on sales of real estate, net 15 10,630 4,000 10,630 Preferred share dividends (3,552 ) (3,553 ) (10,657 ) (12,387 ) Issuance costs associated with redeemed preferred shares — — — (1,769 ) Income from continuing operations attributable to noncontrolling interests (4,494 ) (1,820 ) (7,322 ) (3,923 ) Income from continuing operations attributable to share-based compensation awards (369 ) (103 ) (475 ) (332 ) Numerator for basic EPS from continuing operations attributable to COPT common shareholders 85,879 18,881 107,651 20,854 Convertible preferred shares 372 — — — Dilutive effect of common units in COPLP on diluted EPS from continuing operations — — 4,225 — Numerator for diluted EPS from continuing operations attributable to COPT common shareholders $ 86,251 $ 18,881 $ 111,876 $ 20,854 Numerator for basic EPS from continuing operations attributable to COPT common shareholders $ 85,879 $ 18,881 $ 107,651 $ 20,854 Discontinued operations — 191 156 4 Discontinued operations attributable to noncontrolling interests — (8 ) (3 ) 5 Numerator for basic EPS on net income attributable to COPT common shareholders 85,879 19,064 107,804 20,863 Convertible preferred shares 372 — — — Dilutive effect of common units in COPLP — — 4,231 — Numerator for diluted EPS on net income attributable to COPT common shareholders $ 86,251 $ 19,064 $ 112,035 $ 20,863 Denominator (all weighted averages): Denominator for basic EPS (common shares) 94,153 87,290 93,830 87,196 Convertible preferred shares 434 — — — Dilutive effect of common units — — 3,697 — Dilutive effect of share-based compensation awards 21 195 82 169 Denominator for diluted EPS (common shares) 94,608 87,485 97,609 87,365 Basic EPS: Income from continuing operations attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPT common shareholders 0.00 0.00 0.00 0.00 Net income attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Diluted EPS: Income from continuing operations attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPT common shareholders 0.00 0.00 0.00 0.00 Net income attributable to COPT common shareholders $ 0.91 $ 0.22 $ 1.15 $ 0.24
Schedule of securities excluded from computation of diluted earnings per share	Our diluted EPS computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPS for the respective periods (in thousands): Weighted Average Shares Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Conversion of common units 3,679 3,876 — 3,915 Conversion of Series I Preferred Units 176 176 176 176 Conversion of Series K Preferred Shares — 434 434 434
Corporate Office Properties, L.P.
Earnings Per Share [Line Items]
Summary of calculation of numerator and denominator in basic and diluted earnings per share	Summaries of the numerator and denominator for purposes of basic and diluted EPU calculations are set forth below (in thousands, except per unit data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Numerator: Income from continuing operations $ 94,279 $ 13,727 $ 122,105 $ 28,635 Gain on sales of real estate, net 15 10,630 4,000 10,630 Preferred unit distributions (3,717 ) (3,718 ) (11,152 ) (12,882 ) Issuance costs associated with redeemed preferred units — — — (1,769 ) Income from continuing operations attributable to noncontrolling interests (972 ) (897 ) (2,605 ) (2,476 ) Income from continuing operations attributable to share-based compensation awards (369 ) (103 ) (475 ) (332 ) Numerator for basic EPU from continuing operations attributable to COPLP common unitholders 89,236 19,639 111,873 21,806 Convertible preferred units 372 — — — Numerator for diluted EPU from continuing operations attributable to COPLP common unitholders $ 89,608 $ 19,639 $ 111,873 $ 21,806 Numerator for basic EPU from continuing operations attributable to COPLP common unitholders $ 89,236 $ 19,639 $ 111,873 $ 21,806 Discontinued operations — 191 156 4 Discontinued operations attributable to noncontrolling interests — — 3 5 Numerator for basic EPU on net income attributable to COPLP common unitholders 89,236 19,830 112,032 21,815 Convertible preferred units 372 — — — Numerator for diluted EPU on net income attributable to COPLP common unitholders $ 89,608 $ 19,830 $ 112,032 $ 21,815 Denominator (all weighted averages): Denominator for basic EPU (common units) 97,832 91,166 97,527 91,111 Convertible preferred shares 434 — — — Dilutive effect of share-based compensation awards 21 195 82 169 Denominator for basic and diluted EPU (common units) 98,287 91,361 97,609 91,280 Basic EPU: Income from continuing operations attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPLP common unitholders 0.00 0.00 0.00 0.00 Net income attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Diluted EPU: Income from continuing operations attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24 Discontinued operations attributable to COPLP common unitholders 0.00 0.00 0.00 0.00 Net income attributable to COPLP common unitholders $ 0.91 $ 0.22 $ 1.15 $ 0.24
Schedule of securities excluded from computation of diluted earnings per share	Our diluted EPU computations do not include the effects of the following securities since the conversions of such securities would increase diluted EPU for the respective periods (in thousands): Weighted Average Units Excluded from Denominator For the Three Months Ended September 30, For the Nine Months Ended September 30, 2015 2014 2015 2014 Conversion of Series I preferred units 176 176 176 176 Conversion of Series K preferred units — 434 434 434

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Future minimum rental payments for operating leases	Future minimum rental payments due under the terms of these operating leases as of September 30, 2015 follow (in thousands): Year Ending December 31, 2015 (1) $ 289 2016 1,171 2017 1,096 2018 1,052 2019 1,036 Thereafter 86,999 $ 91,643 (1) Represents three months ending December 31, 2015

Organization (Details)

Organization (Details) ft² in Thousands	Sep. 30, 2015ft²aPropertyMW
Properties under or approved for redevelopment
Investments in real estate
Number of real estate properties	4
Area of real estate property | ft²	156
Operating office properties
Investments in real estate
Number of real estate properties	183
Area of real estate property | ft²	18,800
Office properties under, or contractually committed for, construction or approved for redevelopment
Investments in real estate
Number of real estate properties	10
Area of real estate property | ft²	1,200
Partially operational properties | Properties under or approved for redevelopment
Investments in real estate
Number of real estate properties	1
Land controlled for future development
Investments in real estate
Area of real estate property | a	1,450
Developable square feet | ft²	17,700
Wholesale Data Center
Investments in real estate
Represents the amount of the critical load of the property (in megawatts) | MW	19.25

Organization (Details 2)

Organization (Details 2) - Corporate Office Properties, L.P.	9 Months Ended
	Sep. 30, 2015
Common Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	96.30%
Preferred Units
Forms of ownership in Operating Partnership and ownership percentage by the entity
Percentage ownership in operating partnership	95.50%

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Liabilities:
Interest rate derivatives	$ 5,844	$ 1,855
Redeemable noncontrolling interest	19,608	18,417	$ 18,436	$ 17,758
Corporate Office Properties, L.P.
Liabilities:
Interest rate derivatives	5,844	$ 1,855
Fair value measurement on a recurring basis
Assets:
Warrants to purchase common stock	42
Assets	5,541
Liabilities:
Deferred compensation plan liability	5,499
Interest rate derivatives	5,844
Liabilities	11,343
Redeemable noncontrolling interest	19,608
Fair value measurement on a recurring basis | Mutual funds
Assets:
Marketable securities in deferred compensation plan	5,395
Fair value measurement on a recurring basis | Other
Assets:
Marketable securities in deferred compensation plan	104
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Assets	5,499
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mutual funds
Assets:
Marketable securities in deferred compensation plan	5,395
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Assets:
Marketable securities in deferred compensation plan	104
Fair value measurement on a recurring basis | Significant Other Observable Inputs (Level 2)
Assets:
Warrants to purchase common stock	42
Assets	42
Liabilities:
Deferred compensation plan liability	5,499
Interest rate derivatives	5,844
Liabilities	11,343
Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)
Liabilities:
Redeemable noncontrolling interest	19,608
Fair value measurement on a recurring basis | Corporate Office Properties, L.P.
Assets:
Warrants to purchase common stock	42
Liabilities:
Interest rate derivatives	5,844
Redeemable noncontrolling interest	19,608
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2)
Assets:
Warrants to purchase common stock	42
Liabilities:
Interest rate derivatives	5,844
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Unobservable Inputs (Level 3)
Liabilities:
Redeemable noncontrolling interest	$ 19,608

Fair Value Measurements (Deta45

Fair Value Measurements (Details 2) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)Property	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)
Assets and liabilities measured at fair value on a non-recurring basis
Impairment losses	$ 2,307	$ 66	$ 3,545	$ 1,368
Redeemable Non-Controlling Interest | Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)
Assets and liabilities measured at fair value on a non-recurring basis
Fair value inputs, discount rate			15.50%
Real Estate Investment Properties, Net | Fair value measurement on a nonrecurring basis
Assets and liabilities measured at fair value on a non-recurring basis
Impairment losses				$ 1,400
Northern Virginia | Real Estate Investment Properties, Net | Fair value measurement on a nonrecurring basis
Assets and liabilities measured at fair value on a non-recurring basis
Impairment losses			$ 1,300
Greater Baltimore | Real Estate Investment Properties, Net | Fair value measurement on a nonrecurring basis
Assets and liabilities measured at fair value on a non-recurring basis
Impairment losses	$ 2,300
Number of properties, impairment loss recognized | Property	3

Fair Value Measurements (Deta46

Fair Value Measurements (Details 3) - Real Estate Investment Properties, Net - Fair value measurement on a nonrecurring basis $ in Thousands	Sep. 30, 2015USD ($)
Assets and liabilities measured at fair value on a non-recurring basis
Assets	$ 7,225
Significant Unobservable Inputs (Level 3)
Assets and liabilities measured at fair value on a non-recurring basis
Assets	$ 7,225

Fair Value Measurements (Deta47

Fair Value Measurements (Details 4) - Fair value measurement on a nonrecurring basis $ in Thousands	9 Months Ended
	Sep. 30, 2015USD ($)
Real Estate Investment Properties, Net
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets	$ 7,225
Discounted Cash Flow Valuation Technique
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Discount rate	8.25%
Terminal capitalization	7.75%
Market rent growth rate	2.00%
Expense growth rate	2.00%
Significant Unobservable Inputs (Level 3) | Real Estate Investment Properties, Net
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets	$ 7,225
Significant Unobservable Inputs (Level 3) | Discounted Cash Flow Valuation Technique | Real Estate Investment Properties, Net
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Assets	$ 7,225

Properties, Net (Details)

Properties, Net (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Investments in real estate
Operating properties, net		$ 2,932,843	$ 2,751,488
Greater Philadelphia
Investments in real estate
Depreciation expense on reclassified assets	$ 12,900
Operating properties, net
Investments in real estate
Less: accumulated depreciation		(675,747)	(703,083)
Operating properties, net | Land
Investments in real estate
Gross		466,701	439,355
Operating properties, net | Buildings and improvements
Investments in real estate
Gross		$ 3,141,889	$ 3,015,216

Properties, Net (Details 2)

Properties, Net (Details 2) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Properties
Projects in development or held for future development	$ 414,757	$ 545,426
Projects in development or held for future development | Land in development or held for future development
Properties
Projects in development or held for future development	207,748	214,977
Projects in development or held for future development | Construction in progress, excluding land
Properties
Projects in development or held for future development	$ 207,009	$ 330,449

Properties, Net (Details 3)

Properties, Net (Details 3) $ in Thousands	Sep. 30, 2015USD ($)Property	Dec. 31, 2014USD ($)Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, net	$ 150,572	$ 14,339
Greater Baltimore | Assets Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties, impairment loss recognized | Property		2
Assets held for sale, net		$ 14,300
2015 Assets Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Properties, net	142,817
Deferred rent receivable	3,998
Intangible assets on real estate acquisitions, net	799
Deferred leasing costs, net	2,053
Lease incentives, net	905
Assets held for sale, net	$ 150,572
2015 Assets Held For Sale | Greater Baltimore
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties, impairment loss recognized | Property	18
2015 Assets Held For Sale | Northern Virginia
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties, impairment loss recognized | Property	1

Properties, Net (Details 4)

Properties, Net (Details 4) ft² in Thousands, $ in Thousands	Aug. 07, 2015USD ($)ft²	Apr. 15, 2015USD ($)ft²	Mar. 19, 2015USD ($)ft²	Sep. 30, 2015USD ($)	Sep. 30, 2015USD ($)
Business Acquisition [Line Items]
Weighted average useful life					10 years
Tenant relationship value
Business Acquisition [Line Items]
Weighted average useful life					11 years
Below-market cost arrangements
Business Acquisition [Line Items]
Weighted average useful life					35 years
2015 Acquisitions
Business Acquisition [Line Items]
Land				$ 55,076	$ 55,076
Building and improvements				139,520	139,520
Intangible assets on real estate acquisitions				75,846	75,846
Total assets				270,442	270,442
Below-market leases				(6,820)	(6,820)
Total acquisition cost				263,622	263,622
Finite-lived intangible assets acquired					$ 75,846
Weighted average useful life					10 years
Revenues				6,900	$ 11,200
Contributions to net income from continuing operations				487	697
Operating property acquisition costs				$ 2,700	4,100
2015 Acquisitions | Tenant relationship value
Business Acquisition [Line Items]
Finite-lived intangible assets acquired					$ 31,208
Weighted average useful life					12 years
2015 Acquisitions | In-place lease value
Business Acquisition [Line Items]
Finite-lived intangible assets acquired					$ 35,231
Weighted average useful life					7 years
2015 Acquisitions | Above market leases
Business Acquisition [Line Items]
Finite-lived intangible assets acquired					$ 6,720
Weighted average useful life					4 years
2015 Acquisitions | Below-market cost arrangements
Business Acquisition [Line Items]
Finite-lived intangible assets acquired					$ 2,687
Weighted average useful life					40 years
250 W Pratt St | Baltimore, Maryland
Business Acquisition [Line Items]
Square footage of real estate properties (in square feet) | ft²			367
Acquired property percentage leased			96.20%
Total acquisition cost			$ 61,900
2600 Park Tower Drive | Northern Virginia
Business Acquisition [Line Items]
Square footage of real estate properties (in square feet) | ft²		237
Acquired property percentage leased		100.00%
Total acquisition cost		$ 80,500
100 and 30 Light Street | Baltimore, Maryland
Business Acquisition [Line Items]
Square footage of real estate properties (in square feet) | ft²	558
Acquired property percentage leased	93.50%
Total acquisition cost	$ 121,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	55,000
Estimated fair value	$ 55,500

Properties, Net (Details 5)

Properties, Net (Details 5) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Real Estate [Abstract]
Pro forma total revenues	$ 152,736	$ 162,085	$ 498,657	$ 467,224
Pro forma net income attributable to COPT common shareholders	$ 88,836	$ 19,683	$ 112,941	$ 19,266
Pro Forma EPS, Basic (in dollars per share)	$ 0.94	$ 0.22	$ 1.20	$ 0.22
Pro Forma EPS, Diluted (in dollars per share)	$ 0.94	$ 0.22	$ 1.20	$ 0.22

Properties, Net (Details 6)

Properties, Net (Details 6) ft² in Thousands, $ in Thousands	Aug. 28, 2015USD ($)ft²Property	Jul. 27, 2015USD ($)ft²	Sep. 30, 2015USD ($)ft²Property	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)ft²Property	Sep. 30, 2014USD ($)
Construction and Redevelopment Activities
Gain (loss) on early extinguishment of debt | $			$ 85,745	$ (176)	$ 85,677	$ (446)
Newly constructed properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service | ft²					897
Number of real estate properties			7		7
Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Square footage of real estate properties (in square feet) | ft²			1,000		1,000
Number of real estate properties			6		6
Number of partially operational real estate properties			1		1
Properties under or approved for redevelopment
Construction and Redevelopment Activities
Square footage of real estate properties (in square feet) | ft²			156		156
Number of real estate properties			4		4
Northern Virginia | Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties			4		4
Greater Philadelphia and St. Mary's County, Maryland | Newly redeveloped properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service | ft²					170
Number of real estate properties			2		2
Baltimore and Washington Corridor | Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties			2		2
Operating properties, net | 1550 Westbranch Drive | Northern Virginia
Construction and Redevelopment Activities
Square footage of real estate properties (in square feet) | ft²		160
Transaction value of operating property disposition | $		$ 27,800
Operating properties, net | 15000 and 15010 Conference Center Drive | Northern Virginia
Construction and Redevelopment Activities
Square footage of real estate properties (in square feet) | ft²	665
Number of properties disposed	2
Debt settled through the surrender of real estate assets | $	$ 150,000
Fair value of real estate disposed in settlement of debt | $	99,000
Gain (loss) on early extinguishment of debt | $	$ 84,800
Non-operating properties
Construction and Redevelopment Activities
Sale price of land | $					$ 18,100
Gain on sale | $					$ 4,000

Real Estate Joint Ventures (Det

Real Estate Joint Ventures (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015USD ($)
Consolidated real estate joint ventures
Investments in consolidated real estate joint ventures
Total Assets	$ 203,746
Encumbered Assets	112,696
Total Liabilities	$ 77,210
LW Redstone Company, LLC | Variable Interest Entity, Primary Beneficiary [Member]
Investments in consolidated real estate joint ventures
Ownership (as a percent)	85.00%
Total Assets	$ 144,906
Encumbered Assets	64,395
Total Liabilities	$ 39,093
M Square Associates, LLC | Variable Interest Entity, Primary Beneficiary [Member]
Investments in consolidated real estate joint ventures
Ownership (as a percent)	50.00%
Total Assets	$ 58,840
Encumbered Assets	48,301
Total Liabilities	$ 38,117

Intangible Assets on Real Est55

Intangible Assets on Real Estate Acquisition, Net (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 231,806		$ 188,467
Accumulated Amortization	125,632		144,613
Net Carrying Amount	106,174		43,854
Amortization of intangible assets	$ 11,900	$ 10,800
Weighted average useful life	10 years
Estimated future amortization expense associated with the intangible asset categories for the next five years
Remainder of fiscal year	$ 5,100
2,016	19,700
2,017	17,100
2,018	12,300
2,019	9,300
2,020	7,300
In-place lease value
Intangible assets on real estate acquisitions
Gross Carrying Amount	138,410		123,759
Accumulated Amortization	87,667		101,040
Net Carrying Amount	$ 50,743		22,719
Weighted average useful life	6 years
Tenant relationship value
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 63,117		42,301
Accumulated Amortization	22,525		28,492
Net Carrying Amount	$ 40,592		13,809
Weighted average useful life	11 years
Below-market cost arrangements
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 15,102		12,415
Accumulated Amortization	6,505		5,984
Net Carrying Amount	$ 8,597		6,431
Weighted average useful life	35 years
Above-market leases
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 13,844		8,659
Accumulated Amortization	7,987		8,159
Net Carrying Amount	$ 5,857		500
Weighted average useful life	4 years
Market concentration premium
Intangible assets on real estate acquisitions
Gross Carrying Amount	$ 1,333		1,333
Accumulated Amortization	948		938
Net Carrying Amount	$ 385		$ 395
Weighted average useful life	27 years

Investing Receivables (Details)

Investing Receivables (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 46,821	$ 52,147
Notes Receivable from City of Huntsville
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 43,821	49,147
Notes Receivable from City of Huntsville | LW Redstone Company, LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Stated interest rate (as a percent)	9.95%
Other investing loans receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investing receivables	$ 3,000	$ 3,000

Prepaid Expenses and Other As57

Prepaid Expenses and Other Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Prepaid Expense and Other Assets [Abstract]
Prepaid expenses	$ 28,655	$ 20,570
Lease incentives, net	11,589	13,344
Furniture, fixtures and equipment, net	5,941	6,637
Construction contract costs incurred in excess of billings	4,722	6,656
Deferred tax asset, net	4,015	4,002
Operating notes receivable	3,744	3,797
Equity method investments	1,626	2,368
Other assets	6,495	2,875
Prepaid expenses and other assets, net	66,787	60,249
Long-term Operating Notes Receivable
Mortgage and Other Investing Receivables [Line Items]
Operating notes receivable	3,700	3,600
Allowances for estimated losses	278	252
Taxable REIT Subsidiary
Mortgage and Other Investing Receivables [Line Items]
Deferred tax assets, valuation allowance	$ 2,100	$ 2,100

Debt, Net (Details)

Debt, Net (Details)	Jun. 29, 2015USD ($)	May. 06, 2015USD ($)extensions	Apr. 20, 2015	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Aug. 28, 2015USD ($)	May. 05, 2015USD ($)	Dec. 31, 2014USD ($)
Debt
Carrying Value				$ 2,121,240,000		$ 2,121,240,000				$ 1,920,057,000
Interest costs capitalized				1,500,000	$ 1,300,000	5,600,000	$ 4,300,000
Line of Credit | Revolving Credit Facility
Debt
Number of extensions | extensions		2
Term of extension option		6 months
Line of Credit | Revolving Credit Facility | Minimum
Debt
Commitment fee (as a percent)		0.125%
Line of Credit | Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)		0.875%
Line of Credit | Revolving Credit Facility | Maximum
Debt
Commitment fee (as a percent)		0.30%
Line of Credit | Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)		1.60%
Line of Credit | Term Loan Facilities
Debt
Maximum availability		$ 300,000,000							$ 250,000,000
Increase to maximum borrowing capacity		200,000,000
Aggregate maximum borrowing capacity		500,000,000
Proceeds from issuance of debt		$ 50,000,000
Line of Credit | Term Loan Facilities | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)		0.90%
Line of Credit | Term Loan Facilities | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)		1.85%
Mortgage and Other Secured Loans:
Debt
Carrying Value				324,466,000		324,466,000				424,016,000
Fixed rate mortgage loans
Debt
Carrying Value				288,217,000		$ 288,217,000				387,139,000
Stated interest rates, low end of range (as a percent)						3.96%
Stated interest rates, high end of range (as a percent)						7.87%
Unamortized premium included in carrying value				$ 24,000		$ 24,000				42,000
Debt settled through the surrender of real estate assets								$ 150,000,000
Weighted-average interest rate excluding incremental rate on default rate				6.07%		6.07%
Variable rate secured loans
Debt
Carrying Value				$ 36,249,000		$ 36,249,000				36,877,000
Description of variable rate basis						LIBOR
Stated interest rate (as a percent)				2.45%		2.45%
Variable rate secured loans | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)						2.25%
Variable rate secured loans | Revolving Credit Facility
Debt
Weighted average interest rate (as a percent)				1.48%		1.48%
Revolving Credit Facility
Debt
Carrying Value				$ 87,000,000		$ 87,000,000				83,000,000
Description of variable rate basis						LIBOR
Revolving Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)						0.875%
Revolving Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)						1.60%
Revolving Credit Facility | Revolving Credit Facility
Debt
Maximum availability				800,000,000		$ 800,000,000
Term Loan Facilities
Debt
Carrying Value				$ 520,000,000		$ 520,000,000				520,000,000
Description of variable rate basis						LIBOR
Weighted average interest rate (as a percent)				1.78%		1.78%
Additional borrowing capacity available provided there is no default under the agreement				$ 380,000,000		$ 380,000,000
Term Loan Facilities | Minimum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)						0.90%
Term Loan Facilities | Maximum | London Interbank Offered Rate (LIBOR)
Debt
Variable rate, spread (as a percent)						2.60%
3.60% Senior Notes | Unsecured senior notes
Debt
Carrying Value				$ 347,691,000		$ 347,691,000				347,496,000
Stated interest rate (as a percent)				3.60%		3.60%
Debt instrument, face amount				$ 350,000,000		$ 350,000,000
Unamortized discount included in carrying value				$ 2,300,000		$ 2,300,000				2,500,000
Interest rate on debt (as a percent)				3.70%		3.70%
5.250% Senior Notes | Unsecured senior notes
Debt
Carrying Value				$ 246,074,000		$ 246,074,000				245,797,000
Stated interest rate (as a percent)				5.25%		5.25%
Debt instrument, face amount				$ 250,000,000		$ 250,000,000
Unamortized discount included in carrying value				$ 3,900,000		$ 3,900,000				4,200,000
Interest rate on debt (as a percent)				5.49%		5.49%
3.70% Senior Notes | Unsecured senior notes
Debt
Carrying Value				$ 297,830,000		$ 297,830,000				297,569,000
Stated interest rate (as a percent)				3.70%		3.70%
Debt instrument, face amount				$ 300,000,000		$ 300,000,000
Unamortized discount included in carrying value				$ 2,200,000		$ 2,200,000				2,400,000
Interest rate on debt (as a percent)				3.85%		3.85%
5.000% Senior Notes | Unsecured senior notes
Debt
Carrying Value				$ 296,646,000		$ 296,646,000				0
Stated interest rate (as a percent)	5.00%			5.00%		5.00%
Debt instrument, face amount	$ 300,000,000
Unamortized discount included in carrying value				$ 3,400,000		$ 3,400,000
Interest rate on debt (as a percent)				5.15%		5.15%
Debt issuance as a percentage of principal amount	99.51%
Proceeds from debt, net	$ 296,600,000
Redemption price ( as a percent)	100.00%
5.000% Senior Notes | Unsecured senior notes | Adjusted Treasury
Debt
Basis points used in determining redemption price prior to maturity	0.45%
Unsecured notes payable
Debt
Carrying Value				$ 1,533,000		$ 1,533,000				1,607,000
Stated interest rate (as a percent)				0.00%		0.00%
Unamortized discount included in carrying value				$ 578,000		$ 578,000				654,000
4.25% Exchangeable Senior Notes
Debt
Carrying Value				$ 0		$ 0				$ 572,000
Percentage of principal amount redeemed			100.00%

Debt, Net (Details 2)

Debt, Net (Details 2) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Carrying amount and estimated fair value of debt
Carrying Value	$ 2,121,240	$ 1,920,057
Carrying Amount
Carrying amount and estimated fair value of debt
Variable-rate debt	643,249	639,877
Carrying Value	2,121,240	1,920,057
Carrying Amount | Unsecured senior notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	1,188,241	890,862
Carrying Amount | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Fixed-rate debt	289,750	389,318
Total Estimated Fair Value
Carrying amount and estimated fair value of debt
Variable-rate debt	644,243	642,091
Carrying Value	2,154,561	1,900,067
Total Estimated Fair Value | Unsecured senior notes
Carrying amount and estimated fair value of debt
Fixed-rate debt	1,212,120	901,599
Total Estimated Fair Value | Other fixed-rate debt
Carrying amount and estimated fair value of debt
Fixed-rate debt	$ 298,198	$ 356,377

Interest Rate Derivatives (Deta

Interest Rate Derivatives (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Amount of (loss) gain recognized in accumulated other comprehensive loss (“AOCL”) (effective portion)	$ (3,638)	$ 1,015	$ (6,720)	$ (4,738)
Interest Expense
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Amount of losses reclassified from AOCL into interest expense (effective portion)	915	$ 756	2,457	$ 2,170
Interest rate swaps
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income
Approximate loss amount to be reclassified from AOCI to interest expense over the next 12 months	3,500		3,500
Interest rate derivatives in liability position, fair value	5,900		5,900
Termination value to settle obligations under interest rate derivative agreements	6,300		6,300
Interest rate swaps | Prepaid expenses and other current assets
Fair value of interest rate derivatives and balance sheet classification
Interest rate derivatives	0		0		$ 274
Interest rate swaps | Interest rate derivatives
Fair value of interest rate derivatives and balance sheet classification
Fair value of Interest rate swaps classified as interest rate derivatives	(5,844)		(5,844)		(1,855)
Designated
Fair values of interest rate swap derivatives
Fair value of interest rate swaps	(5,844)		(5,844)		(1,581)
Designated | Interest rate swap, effective date November 2, 2010
Fair values of interest rate swap derivatives
Notional Amount	$ 36,249		$ 36,249
Fixed rate (as a percent)	3.83%		3.83%
Fair value of interest rate swaps	$ (44)		$ (44)		(400)
Notional amount of interest rate derivatives after scheduled amortization	$ 36,200		$ 36,200
Designated | Interest rate swap, effective date November 2, 2010 | London Interbank Offered Rate (LIBOR)
Fair values of interest rate swap derivatives
Derivative, basis spread on variable rate	2.25%		2.25%
Designated | Interest rate swap, effective date September 2, 2014, swap one
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	0.8055%		0.8055%
Fair value of interest rate swaps	$ (396)		$ (396)		(317)
Designated | Interest rate swap, effective date September 2, 2014, swap two
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	0.81%		0.81%
Fair value of interest rate swaps	$ (401)		$ (401)		(324)
Designated | Interest rate swap, effective date September 1, 2015, swap one
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	1.673%		1.673%
Fair value of interest rate swaps	$ (2,386)		$ (2,386)		239
Designated | Interest rate swap, effective date September 1, 2015, swap two
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	1.73%		1.73%
Fair value of interest rate swaps	$ (2,617)		$ (2,617)		35
Designated | Interest rate swap, effective date January 3, 2012, swap three
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	0.832%		0.832%
Fair value of interest rate swaps	$ 0		$ 0		(407)
Designated | Interest rate swap, effective date January 3, 2012, swap four
Fair values of interest rate swap derivatives
Notional Amount	$ 100,000		$ 100,000
Fixed rate (as a percent)	0.832%		0.832%
Fair value of interest rate swaps	$ 0		$ 0		$ (407)

Redeemable Noncontrolling Int61

Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Redeemable Noncontrolling Interest [Roll Forward]
Beginning balance	$ 18,417	$ 17,758
Distributions to noncontrolling interest, net	(1,098)	(976)
Net income attributable to noncontrolling interest	1,690	1,647
Adjustment to arrive at fair value of interest	599	7
Ending balance	$ 19,608	$ 18,436

Equity (Details)

Equity (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Number of operating partnerships units converted into common shares (in units)	160,160	117,149
Common Stock Issued to Public Under At-the-Market Program
Class of Stock [Line Items]
Shares issued to the public (in units/ shares)	890,241
Weighted average price per share of stock issued	$ 30.29
Net proceeds of stock issuance	$ 26.6
Commission costs	0.4
Common Shares
Class of Stock [Line Items]
Remaining capacity under ATM Plan	$ 84
Corporate Office Properties, L.P. | Common Shares
Class of Stock [Line Items]
Shares issued to the public (in units/ shares)	890,241

Information by Business Segme63

Information by Business Segment (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)segment	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)segment	Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)
Segment Reporting [Abstract]
Number of primary office property segments | segment	10		10
Segment financial information for real estate operations
Revenues from real estate operations	$ 133,686	$ 118,240	$ 384,591	$ 359,100
Property operating expenses	48,897	42,881	145,990	136,489
NOI from real estate operations	84,789	75,359	238,601	222,611
Segment assets	3,918,473	3,680,188	3,918,473	3,680,188	$ 3,670,257
Operating Segment Total
Segment financial information for real estate operations
Revenues from real estate operations	133,686	118,240	384,591	359,100
Property operating expenses	48,897	42,881	145,990	136,489
NOI from real estate operations	84,789	75,359	238,601	222,611
Additions to long-lived assets	141,037	22,793	307,723	50,618
Transfers from non-operating properties	142,210	42,802	304,106	135,127
Segment assets	3,354,762	2,962,686	3,354,762	2,962,686
Baltimore and Washington Corridor
Segment financial information for real estate operations
Revenues from real estate operations	62,009	58,883	184,412	177,452
Property operating expenses	20,169	19,457	63,291	62,402
NOI from real estate operations	41,840	39,426	121,121	115,050
Additions to long-lived assets	7,943	7,248	16,529	19,278
Transfers from non-operating properties	25,184	22,680	44,212	50,303
Segment assets	1,297,431	1,278,713	1,297,431	1,278,713
Northern Virginia
Segment financial information for real estate operations
Revenues from real estate operations	23,332	21,369	69,474	67,235
Property operating expenses	7,785	7,500	25,593	24,124
NOI from real estate operations	15,547	13,869	43,881	43,111
Additions to long-lived assets	1,749	5,898	89,152	14,198
Transfers from non-operating properties	34,195	15,403	101,412	42,674
Segment assets	697,406	648,248	697,406	648,248
San Antonio
Segment financial information for real estate operations
Revenues from real estate operations	9,492	9,031	28,867	26,268
Property operating expenses	4,808	5,100	15,398	14,391
NOI from real estate operations	4,684	3,931	13,469	11,877
Additions to long-lived assets	0	0	21	(6)
Transfers from non-operating properties	591	0	32,150	0
Segment assets	148,336	116,837	148,336	116,837
Huntsville
Segment financial information for real estate operations
Revenues from real estate operations	3,061	2,471	8,165	7,430
Property operating expenses	888	763	2,605	2,275
NOI from real estate operations	2,173	1,708	5,560	5,155
Additions to long-lived assets	175	455	466	3,296
Transfers from non-operating properties	1,207	1,496	13,184	21,821
Segment assets	108,541	98,334	108,541	98,334
Washington, DC - Capitol Riverfront
Segment financial information for real estate operations
Revenues from real estate operations	3,336	3,524	10,091	10,989
Property operating expenses	1,962	1,824	5,837	5,343
NOI from real estate operations	1,374	1,700	4,254	5,646
Additions to long-lived assets	1,098	458	2,297	999
Transfers from non-operating properties	0	0	0	0
Segment assets	94,120	96,131	94,120	96,131
St. Mary's and King George Counties
Segment financial information for real estate operations
Revenues from real estate operations	3,550	4,158	11,246	12,676
Property operating expenses	1,325	1,277	4,238	4,070
NOI from real estate operations	2,225	2,881	7,008	8,606
Additions to long-lived assets	986	5,189	3,149	6,971
Transfers from non-operating properties	1,408	0	1,408	0
Segment assets	101,985	100,009	101,985	100,009
Greater Baltimore
Segment financial information for real estate operations
Revenues from real estate operations	16,134	10,436	40,508	32,956
Property operating expenses	6,461	3,810	16,367	13,786
NOI from real estate operations	9,673	6,626	24,141	19,170
Additions to long-lived assets	128,933	3,021	195,013	5,275
Transfers from non-operating properties	315	495	327	3,522
Segment assets	455,469	274,931	455,469	274,931
Greater Philadelphia
Segment financial information for real estate operations
Revenues from real estate operations	4,126	2,951	11,236	8,657
Property operating expenses	1,249	837	3,565	3,281
NOI from real estate operations	2,877	2,114	7,671	5,376
Additions to long-lived assets	246	625	824	724
Transfers from non-operating properties	5,506	2,506	22,222	15,880
Segment assets	128,409	107,051	128,409	107,051
Other
Segment financial information for real estate operations
Revenues from real estate operations	2,568	2,541	7,659	7,668
Property operating expenses	242	260	655	1,195
NOI from real estate operations	2,326	2,281	7,004	6,473
Additions to long-lived assets	(93)	(125)	164	(163)
Transfers from non-operating properties	0	0	8	30
Segment assets	76,259	78,240	76,259	78,240
Wholesale Data Center
Segment financial information for real estate operations
Revenues from real estate operations	6,078	2,876	12,933	7,769
Property operating expenses	4,008	2,053	8,441	5,622
NOI from real estate operations	2,070	823	4,492	2,147
Additions to long-lived assets	0	24	108	46
Transfers from non-operating properties	73,804	222	89,183	897
Segment assets	$ 246,806	$ 164,192	$ 246,806	$ 164,192

Information by Business Segme64

Information by Business Segment (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reconciliation of segment revenues to total revenues
Segment revenues from real estate operations	$ 133,686	$ 118,240	$ 384,591	$ 359,100
Construction contract and other service revenues	17,058	34,739	97,554	80,390
Less: Revenues from discontinued operations	0	36	(4)	12
Total revenues	150,744	153,015	482,141	439,502
Reconciliation of segment property operating expenses to property operating expenses
Segment property operating expenses	48,897	42,881	145,990	136,489
Less: Property operating expenses from discontinued operations	0	175	6	111
Total property operating expenses	48,897	43,056	145,996	136,600
Computation of net operating income from service operations
Construction contract and other service revenues	17,058	34,739	97,554	80,390
Construction contract and other service expenses	(16,132)	(33,593)	(94,923)	(75,353)
NOI from service operations	926	1,146	2,631	5,037
Reconciliation of NOI from real estate operations and NOI from service operations to (loss) income from continuing operations
NOI from real estate operations	84,789	75,359	238,601	222,611
NOI from service operations	926	1,146	2,631	5,037
Interest and other income	692	1,191	3,217	3,775
Equity in income of unconsolidated entities	18	193	52	206
Income tax expense	(48)	(101)	(153)	(257)
Other adjustments:
Depreciation and other amortization associated with real estate operations	(38,403)	(30,237)	(103,788)	(104,728)
Impairment losses	(2,307)	(66)	(3,545)	(1,368)
General, administrative and leasing expenses	(7,439)	(7,211)	(22,864)	(22,882)
Business development expenses and land carry costs	(5,573)	(1,430)	(10,986)	(4,107)
Interest expense	(24,121)	(24,802)	(66,727)	(69,107)
Less: NOI from discontinued operations	0	(139)	(10)	(99)
Gain (loss) on early extinguishment of debt	85,745	(176)	85,677	(446)
Income from continuing operations	$ 94,279	$ 13,727	$ 122,105	$ 28,635

Information by Business Segme65

Information by Business Segment (Details 3) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Reconciliation of segment assets to total assets
Assets	$ 3,918,473	$ 3,670,257	$ 3,680,188
Segment assets
Reconciliation of segment assets to total assets
Assets	3,354,762		2,962,686
Non-operating property assets
Reconciliation of segment assets to total assets
Assets	416,540		518,951
Other assets
Reconciliation of segment assets to total assets
Assets	$ 147,171		$ 198,551

Share-Based Compensation (Detai

Share-Based Compensation (Details) $ / shares in Units, $ in Thousands	Mar. 05, 2015USD ($)shares	Sep. 30, 2015USD ($)Percentile_Rank$ / sharesshares	Sep. 30, 2014shares
Options
Exercised (in shares)		76,474	57,888
Performance share units
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 36.76
Baseline value per common share (in dollars per share) | $ / shares		$ 29.28
Expected volatility of common shares (as a percent)		19.90%
Risk-free interest rate (as a percent)		0.99%
Restricted shares
Share-Based Compensation
Stock awards granted (in shares or units)		193,499
Aggregate grant date fair value | $		$ 5,600
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 28.93
Other Share-based Compensation Additional Disclosures
Shares vested (in shares)		163,145
Weighted average fair value of shares vested (in dollars per share) | $ / shares		$ 26.15
Aggregate intrinsic value of awards upon vesting | $		$ 4,600
Deferred shares
Share-Based Compensation
Stock awards granted (in shares or units)		24,056
Aggregate grant date fair value | $		$ 642
Assumptions used to value stock awards
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 26.70
Other Share-based Compensation Additional Disclosures
Shares vested (in shares)		15,485
Weighted average fair value of shares vested (in dollars per share) | $ / shares		$ 26.77
Aggregate intrinsic value of awards upon vesting | $		$ 413
Options
Options
Exercised (in shares)		76,474
Weighted average exercise price (in dollars per share) | $ / shares		$ 26.27
Aggregate intrinsic value of options exercised (in dollars) | $		$ 300
2014 PSU Grants | Performance share units
Share-Based Compensation
Stock awards granted (in shares or units)	45,656
Aggregate grant date fair value | $	$ 1,700
Potential earned PSUs payout for defined levels of performance under awards
Earned PSUs payout (as a percent of PSUs granted) on 75th or greater percentile rank		200.00%
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank		100.00%
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank		50.00%
Performance share units granted on percentile rank below 25th (as a percent)		0.00%
The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25% | Percentile_Rank		2
2012 PSU Grants | Performance share units
Assumptions used to value stock awards
Shares issued for awards vested in period	40,309
2013 PSU Grants | Performance share units | Former Chief Financial Officer
Assumptions used to value stock awards
Shares issued for awards vested in period	15,289

Income Taxes (Details)

Income Taxes (Details) - Taxable REIT Subsidiary - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Deferred
Federal	$ 39	$ 83	$ 125	$ 215
State	9	18	28	42
Total income tax expense	$ 48	$ 101	$ 153	$ 257
Effective tax rate (as a percent)	37.70%	37.70%	37.70%	37.70%

Earnings Per Share ("EPS") an68

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Income from continuing operations		$ 94,279	$ 13,727	$ 122,105	$ 28,635
Gain on sales of real estate, net		15	10,630	4,000	10,630
Preferred share/unit dividends/distributions		(3,552)	(3,553)	(10,657)	(12,387)
Issuance costs associated with redeemed preferred shares/unit		0	0	0	(1,769)
Income from continuing operations attributable to noncontrolling interests		(4,494)	(1,820)	(7,322)	(3,923)
Income from continuing operations attributable to share-based compensation awards		(369)	(103)	(475)	(332)
Numerator for basic EPS from continuing operations attributable to COPT common shareholders		85,879	18,881	107,651	20,854
Convertible preferred shares/units		372	0	0	0
Dilutive effect of common shares/units in COPT on diluted EPS from continuing operations		0	0	4,225	0
Numerator for diluted EPS from continuing operations attributable to COPT common shareholders		86,251	18,881	111,876	20,854
Discontinued operations		0	191	156	4
Discontinued operations attributable to noncontrolling interests		0	(8)	(3)	5
Numerator for basic EPS on net income attributable to COPT common shareholders		85,879	19,064	107,804	20,863
Dilutive effect of common shares/units in COPT		0		4,231	0
Numerator for diluted EPS on net income attributable to COPT common shareholders		$ 86,251	$ 19,064	$ 112,035	$ 20,863
Denominator (all weighted averages):
Denominator for basic EPS (common shares)		94,153	87,290	93,830	87,196
Convertible preferred shares (shares)		434	0	0	0
Dilutive effect of common units (shares)		0		3,697	0
Dilutive effect of share-based compensation awards (shares)		21	195	82	169
Denominator for diluted EPS (common shares)		94,608	87,485	97,609	87,365
Basic EPS:
Income from continuing operations (in dollars per share/unit)	[1]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
Discontinued operations (in dollars per share/unit)	[1]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[1]	0.91	0.22	1.15	0.24
Diluted EPS:
Income from continuing operations (in dollars per share/unit)	[1]	0.91	0.22	1.15	0.24
Discontinued operations (in dollars per share/unit)	[1]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[1]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
Corporate Office Properties, L.P.
Numerator:
Income from continuing operations		$ 94,279	$ 13,727	$ 122,105	$ 28,635
Gain on sales of real estate, net		15	10,630	4,000	10,630
Preferred share/unit dividends/distributions		(3,717)	(3,718)	(11,152)	(12,882)
Issuance costs associated with redeemed preferred shares/unit		0	0	0	(1,769)
Income from continuing operations attributable to noncontrolling interests		(972)	(897)	(2,605)	(2,476)
Income from continuing operations attributable to share-based compensation awards		(369)	(103)	(475)	(332)
Numerator for basic EPS from continuing operations attributable to COPT common shareholders		89,236	19,639	111,873	21,806
Convertible preferred shares/units		372	0	0	0
Numerator for diluted EPS from continuing operations attributable to COPT common shareholders		89,608	19,639	111,873	21,806
Discontinued operations		0	191	156	4
Discontinued operations attributable to noncontrolling interests		0	0	3	5
Numerator for basic EPS on net income attributable to COPT common shareholders		89,236	19,830	112,032	21,815
Numerator for diluted EPS on net income attributable to COPT common shareholders		$ 89,608	$ 19,830	$ 112,032	$ 21,815
Denominator (all weighted averages):
Denominator for basic EPS (common shares)		97,832	91,166	97,527	91,111
Convertible preferred shares (shares)		434	0	0	0
Dilutive effect of share-based compensation awards (shares)		21	195	82	169
Denominator for diluted EPS (common shares)		98,287	91,361	97,609	91,280
Basic EPS:
Income from continuing operations (in dollars per share/unit)	[2]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
Discontinued operations (in dollars per share/unit)	[2]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[2]	0.91	0.22	1.15	0.24
Diluted EPS:
Income from continuing operations (in dollars per share/unit)	[2]	0.91	0.22	1.15	0.24
Discontinued operations (in dollars per share/unit)	[2]	0	0	0	0
Net income attributable to COPT common shareholders (in dollars per share/unit)	[2]	$ 0.91	$ 0.22	$ 1.15	$ 0.24
[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.

Earnings Per Share ("EPS") an69

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details 2) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Conversion of common units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,679	3,876	0	3,915
Conversion of Series I Preferred Units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176	176	176
Conversion of Series K Preferred Shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	0	434	434	434
Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	411	401	412	404
Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	440	490	480	495
Corporate Office Properties, L.P. | Weighted average restricted stock and deferred shares
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	411	401	412	404
Corporate Office Properties, L.P. | Weighted average options
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	440	490	480	495
Corporate Office Properties, L.P. | Conversion of Series I preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176	176	176
Corporate Office Properties, L.P. | Conversion of Series K preferred units
Antidilutive securities
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	0	434	434	434

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details)	Sep. 30, 2015USD ($)Property	Aug. 31, 2010USD ($)
Tax incremental financing obligation
Liability recognized with regard to tax incremental financing obligation at end of current period	$ 2,200,000
Environmental Indemnity Agreement
Number of lease properties which were provided environmental indemnifications | Property	3
Environmental indemnification to the tenant against losses covered under prior owner's indemnity agreement	$ 5,000,000
Maximum environmental indemnification to the tenant against consequential damages after acquisition of property	$ 12,500,000
Additional costs agreed to be paid by the entity related to construction and environmental regulatory activities (as a percent)	50.00%
Maximum annual additional costs agreed to be paid by the entity related to construction and environmental regulatory activities	$ 300,000
Maximum additional costs agreed to be paid by the entity related to construction and environmental regulatory activities	1,500,000
New Development and Redevelopment Obligations
Loss Contingencies [Line Items]
Purchase obligations	97,900,000
Capital Expenditures For Operating Properties
Loss Contingencies [Line Items]
Purchase obligations	41,900,000
Third Party Construction and Development
Loss Contingencies [Line Items]
Purchase obligations	8,100,000
Other Purchase Obligations
Loss Contingencies [Line Items]
Purchase obligations	$ 4,000,000
Anne Arundel County, Maryland | Tax Incremental Financing Bond
Tax incremental financing obligation
Debt instrument, face amount		$ 30,000,000

Commitments and Contingencies71

Commitments and Contingencies - Future Minimum Payments (Details) $ in Thousands	Sep. 30, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,015	$ 289
2,016	1,171
2,017	1,096
2,018	1,052
2,019	1,036
Thereafter	86,999
Total	$ 91,643

Subsequent Event (Details)

Subsequent Event (Details) ft² in Thousands, $ in Thousands	Oct. 27, 2015USD ($)ft²	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)
Subsequent Event [Line Items]
Gain on sale		$ 4,000	$ 10,654
Subsequent Event | Northern Virginia | 13200 Woodland Park Rd
Subsequent Event [Line Items]
Square footage of real estate properties (in square feet) | ft²	397
Transaction value of operating property disposition	$ 84,000
Gain on sale	$ 42,000