COPT Defense Properties (CDP) 10-Q 1 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 18, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'CORPORATE OFFICE PROPERTIES TRUST	'
Entity Central Index Key	'0000860546	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	87,607,331
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Corporate Office Properties, L.P.	'	'
Entity Information [Line Items]	'	'
Entity Registrant Name	'CORPORATE OFFICE PROPERTIES, L.P.	'
Entity Central Index Key	'0001577966	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Amendment Flag	'false	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Properties, net:	'	'
Operating properties, net	$2,729,003	$2,702,693
Projects in development or held for future development	495,625	511,608
Total properties, net	3,224,628	3,214,301
Cash and cash equivalents	18,374	54,373
Restricted cash and marketable securities	10,965	11,448
Accounts receivable (net of allowance for doubtful accounts of $2,353 and $2,976, respectively)	30,152	27,000
Deferred rent receivable (net of allowance of $1,495 and $2,126, respectively)	91,082	89,456
Intangible assets on real estate acquisitions, net	55,678	59,258
Deferred leasing and financing costs, net	65,855	66,267
Mortgage and other investing receivables	55,231	53,663
Prepaid expenses and other assets	53,932	54,186
Total assets	3,605,897	3,629,952
Liabilities:	'	'
Debt, net	1,931,831	1,927,703
Accounts payable and accrued expenses	97,451	98,785
Rents received in advance and security deposits	28,267	31,492
Dividends and distributions payable	29,122	29,080
Deferred revenue associated with operating leases	12,281	10,369
Interest rate derivatives	3,196	3,309
Other liabilities	13,060	14,207
Total liabilities	2,115,208	2,114,945
Commitments and contingencies (Note 17)	'	'
Redeemable noncontrolling interest	17,654	17,758
Corporate Office Properties Trust’s shareholders’ equity:	'	'
Preferred Shares of beneficial interest at liquidation preference ($0.01 par value; 25,000,000 shares authorized; 9,431,667 shares issued and outstanding)	249,083	249,083
Common Shares of beneficial interest	876	874
Additional paid-in capital	1,816,467	1,814,015
Cumulative distributions in excess of net income	-665,708	-641,868
Accumulated other comprehensive income	2,072	3,480
Total Corporate Office Properties Trust’s shareholders’ equity	1,402,790	1,425,584
Noncontrolling interests in subsidiaries:	'	'
Common units in COPLP	51,757	53,468
Preferred units in COPLP	8,800	8,800
Other consolidated entities	9,688	9,397
Noncontrolling interests in subsidiaries	70,245	71,665
Total equity	1,473,035	1,497,249
Total liabilities, redeemable noncontrolling interest and equity	3,605,897	3,629,952
Corporate Office Properties, L.P.	'	'
Properties, net:	'	'
Operating properties, net	2,729,003	2,702,693
Projects in development or held for future development	495,625	511,608
Total properties, net	3,224,628	3,214,301
Cash and cash equivalents	18,374	54,373
Restricted cash and marketable securities	3,400	3,981
Accounts receivable (net of allowance for doubtful accounts of $2,353 and $2,976, respectively)	30,152	27,000
Deferred rent receivable (net of allowance of $1,495 and $2,126, respectively)	91,082	89,456
Intangible assets on real estate acquisitions, net	55,678	59,258
Deferred leasing and financing costs, net	65,855	66,267
Mortgage and other investing receivables	55,231	53,663
Prepaid expenses and other assets	53,932	54,186
Total assets	3,598,332	3,622,485
Liabilities:	'	'
Debt, net	1,931,831	1,927,703
Accounts payable and accrued expenses	97,451	98,785
Rents received in advance and security deposits	28,267	31,492
Dividends and distributions payable	29,122	29,080
Deferred revenue associated with operating leases	12,281	10,369
Interest rate derivatives	3,196	3,309
Other liabilities	5,495	6,740
Total liabilities	2,107,643	2,107,478
Commitments and contingencies (Note 17)	'	'
Redeemable noncontrolling interest	17,654	17,758
Corporate Office Properties Trust’s shareholders’ equity:	'	'
Common Shares of beneficial interest	1,203,297	1,226,318
Accumulated other comprehensive income	2,133	3,605
Total Corporate Office Properties Trust’s shareholders’ equity	1,463,313	1,487,806
Noncontrolling interests in subsidiaries:	'	'
Noncontrolling interests in subsidiaries	9,722	9,443
Total equity	1,473,035	1,497,249
Total liabilities, redeemable noncontrolling interest and equity	3,598,332	3,622,485
Corporate Office Properties, L.P. | General Partner	'	'
Corporate Office Properties Trust’s shareholders’ equity:	'	'
Preferred partners' capital accounts	249,083	249,083
Corporate Office Properties, L.P. | Limited Partner	'	'
Corporate Office Properties Trust’s shareholders’ equity:	'	'
Preferred partners' capital accounts	$8,800	$8,800

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Allowance for doubtful accounts - AR	$2,353	$2,976
Allowance - Deferred rent receivable	$1,495	$2,126
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	9,431,667	9,431,667
Preferred Shares of beneficial interest, shares outstanding	9,431,667	9,431,667
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 Shares of beneficial interest, shares issued	87,594,931	87,394,512
Common Shares of beneficial interest, shares outstanding	87,594,931	87,394,512

Consolidated_Balance_Sheets_Pa1

Consolidated Balance Sheets (Parenthetical 2) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Allowance for doubtful accounts - AR	$2,353	$2,976
Allowance - Deferred rent receivable	1,495	2,126
Common Shares of beneficial interest, shares outstanding	87,594,931	87,394,512
Corporate Office Properties, L.P.	'	'
Allowance for doubtful accounts - AR	2,353	2,976
Allowance - Deferred rent receivable	$1,495	$2,226
Corporate Office Properties, L.P. | General Partner	'	'
Preferred Units, Outstanding	9,431,667	9,431,667
Common Shares of beneficial interest, shares outstanding	87,594,931	87,394,512
Corporate Office Properties, L.P. | Limited Partner	'	'
Preferred Units, Outstanding	352,000	352,000
Common Shares of beneficial interest, shares outstanding	3,929,202	3,977,700

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Revenues	'		'
Rental revenue	$98,035		$91,849
Tenant recoveries and other real estate operations revenue	26,842		20,108
Construction contract and other service revenues	21,790		14,262
Total revenues	146,667		126,219
Expenses	'		'
Property operating expenses	49,772		40,388
Depreciation and amortization associated with real estate operations	43,596		27,010
Construction contract and other service expenses	18,624		13,477
General, administrative and leasing expenses	8,143		7,820
Business development expenses and land carry costs	1,326		1,359
Total operating expenses	121,461		90,054
Operating income	25,206		36,165
Interest expense	-20,827		-20,290
Interest and other income	1,285		946
Loss on early extinguishment of debt	0		-5,184
Income from continuing operations before equity in income of unconsolidated entities and income taxes	5,664		11,637
Equity in income of unconsolidated entities	60		41
Income tax expense	-64		-16
Income from continuing operations	5,660		11,662
Discontinued operations	11		1,261
Income before gain on sales of real estate	5,671		12,923
Gain on sales of real estate	0		2,354
Net income	5,671		15,277
Net (income) loss attributable to noncontrolling interests:	'		'
Common units in COPLP	-16		-429
Preferred units in COPLP	-165		-165
Other consolidated entities	-749		337
Net income attributable to COPT	4,741		15,020
Preferred share/unit dividends/distributions	-4,490		-6,106
Net income attributable to COPT common shareholders	251		8,914
Net income attributable to COPT:	'		'
Income from continuing operations	4,728		13,849
Discontinued operations, net	13		1,171
Net income attributable to COPT	4,741		15,020
Basic earnings per common share (1)	'		'
Income from continuing operations (in dollars per share/unit)	$0	[1]	$0.09	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.02	[1]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[1]	$0.11	[1]
Diluted earnings per common share (1)	'		'
Income from continuing operations (in dollars per share/unit)	$0	[1]	$0.09	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.02	[1]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[1]	$0.11	[1]
Dividends/distributions declared per common share/unit	$0.28		$0.28
Corporate Office Properties, L.P.	'		'
Revenues	'		'
Rental revenue	98,035		91,849
Tenant recoveries and other real estate operations revenue	26,842		20,108
Construction contract and other service revenues	21,790		14,262
Total revenues	146,667		126,219
Expenses	'		'
Property operating expenses	49,772		40,388
Depreciation and amortization associated with real estate operations	43,596		27,010
Construction contract and other service expenses	18,624		13,477
General, administrative and leasing expenses	8,143		7,820
Business development expenses and land carry costs	1,326		1,359
Total operating expenses	121,461		90,054
Operating income	25,206		36,165
Interest expense	-20,827		-20,290
Interest and other income	1,285		946
Loss on early extinguishment of debt	0		-5,184
Income from continuing operations before equity in income of unconsolidated entities and income taxes	5,664		11,637
Equity in income of unconsolidated entities	60		41
Income tax expense	-64		-16
Income from continuing operations	5,660		11,662
Discontinued operations	11		1,261
Income before gain on sales of real estate	5,671		12,923
Gain on sales of real estate	0		2,354
Net income	5,671		15,277
Net (income) loss attributable to noncontrolling interests:	'		'
Net (income) loss attributable to noncontrolling interests in consolidated entities	-737		336
Net income attributable to COPT	4,934		15,613
Preferred share/unit dividends/distributions	-4,655		-6,271
Net income attributable to COPT common shareholders	279		9,342
Net income attributable to COPT:	'		'
Income from continuing operations	4,921		14,385
Discontinued operations, net	13		1,228
Net income attributable to COPT	$4,934		$15,613
Basic earnings per common share (1)	'		'
Income from continuing operations (in dollars per share/unit)	$0	[2]	$0.09	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.02	[2]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[2]	$0.11	[2]
Diluted earnings per common share (1)	'		'
Income from continuing operations (in dollars per share/unit)	$0	[2]	$0.09	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.02	[2]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[2]	$0.11	[2]
Dividends/distributions declared per common share/unit	$0.28		$0.28
[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_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net income	$5,671	$15,277
Other comprehensive income	'	'
Unrealized (losses) gains on interest rate derivatives	-2,123	462
Losses on interest rate derivatives included in interest expense	695	658
Other comprehensive (loss) income	-1,428	1,120
Comprehensive income	4,243	16,397
Comprehensive (income) loss attributable to noncontrolling interests	-911	-352
Comprehensive income attributable to COPT	3,332	16,045
Corporate Office Properties, L.P.	'	'
Net income	5,671	15,277
Other comprehensive income	'	'
Unrealized (losses) gains on interest rate derivatives	-2,123	462
Losses on interest rate derivatives included in interest expense	695	658
Other comprehensive (loss) income	-1,428	1,120
Comprehensive income	4,243	16,397
Comprehensive (income) loss attributable to noncontrolling interests	-782	290
Comprehensive income attributable to COPT	$3,461	$16,687

Consolidated_Statements_of_Equ

Consolidated Statements of Equity (USD $)

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.

Corporate Office Properties, L.P.

Corporate Office Properties, L.P.

Corporate Office Properties, L.P.

Corporate Office Properties, L.P.

Corporate Office Properties, L.P.

Corporate Office Properties, L.P.

In Thousands, except Share data, unless otherwise specified

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Common Shares

Accumulated Other Comprehensive Income (Loss)

Noncontrolling Interests

Limited Partner

Limited Partner

General Partner

General Partner

USD ($)

USD ($)

USD ($)

Preferred Shares

Preferred Shares

USD ($)

USD ($)

Balance at Dec. 31, 2012

$1,436,499

$333,833

$809

$1,653,672

($617,455)

($5,435)

$71,075

$1,436,499

$1,089,391

($5,708)

$10,183

'

$8,800

'

$333,833

Balance (in units/ shares) at Dec. 31, 2012

80,952,986

'

'

'

'

'

'

'

85,020,528

'

'

'

'

'

'

Balance (preferred units) at Dec. 31, 2012

'

'

'

'

'

'

'

'

'

'

'

'

352,000

'

12,821,667

Increase (Decrease) in Shareholders' Equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion of common units to common shares (248,644 and 48,498 for the three months ended March 31, 2013 and 2014, respectively)

'

'

3

3,172

'

'

-3,175

'

'

'

'

'

'

'

'

Shares issued to the public (in dollars)

117,913

'

45

117,868

'

'

'

-117,913

117,913

'

'

'

'

'

'

Shares issued to the public (in units/ shares)

'

'

'

'

'

'

'

'

4,485,000

'

'

'

'

'

'

Exercise of share options (in units/shares)

16,453

'

'

'

'

'

'

'

16,453

'

'

'

'

'

'

Exercise of share options (in dollars)

301

'

'

301

'

'

'

301

301

'

'

'

'

'

'

Share-based compensation (in units/shares)

'

'

'

'

'

'

'

'

116,315

'

'

'

'

'

'

Share-based compensation

'

'

1

'

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation

'

'

'

1,999

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation

2,000

'

'

'

'

'

'

2,000

2,000

'

'

'

'

'

'

Restricted common units/shares redemptions

-60,960

'

'

'

'

'

'

'

-60,960

'

'

'

'

'

'

Restricted common units/shares redemptions (in dollars)

-1,576

'

'

-1,576

'

'

'

-1,576

-1,576

'

'

'

'

'

'

Adjustments to noncontrolling interests resulting from changes in ownership of COPLP

'

'

'

-2,229

'

'

2,229

'

'

'

'

'

'

'

'

Comprehensive income (loss)

17,187

'

'

'

15,020

1,025

1,142

17,187

9,342

1,074

500

'

165

'

6,106

Dividends/Distributions

-29,699

'

'

'

-29,699

'

'

-30,914

-24,643

'

'

'

-165

'

-6,106

Distributions to owners of common and preferred units in COPLP

-1,215

'

'

'

'

'

-1,215

'

'

'

'

'

'

'

'

Contributions from noncontrolling interests in other consolidated entities

85

'

'

0

'

'

85

85

'

'

85

'

'

'

'

Adjustment to arrive at fair value of redeemable noncontrolling interest

-848

'

'

-848

'

'

'

-848

-848

'

'

'

'

'

'

Tax loss from share-based compensation

-104

'

'

-104

'

'

'

-104

-104

'

'

'

'

'

'

Balance at Mar. 31, 2013

1,540,543

333,833

858

1,772,255

-632,134

-4,410

70,141

1,540,543

1,191,776

-4,634

10,768

'

8,800

'

333,833

Balance (in units/ shares) at Mar. 31, 2013

85,758,438

'

'

'

'

'

'

'

89,577,336

'

'

'

'

'

'

Balance (preferred units) at Mar. 31, 2013

'

'

'

'

'

'

'

'

'

'

'

'

352,000

'

12,821,667

Balance 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 (in units/ shares) at Dec. 31, 2013

87,394,512

'

'

'

'

'

'

'

91,372,212

'

'

3,977,700

'

87,394,512

'

Balance (preferred units) at Dec. 31, 2013

'

'

'

'

'

'

'

'

'

'

'

352,000

352,000

9,431,667

9,431,667

Increase (Decrease) in Shareholders' Equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Conversion of common units to common shares (248,644 and 48,498 for the three months ended March 31, 2013 and 2014, respectively)

'

'

'

651

'

'

-651

'

'

'

'

'

'

'

'

Exercise of share options (in units/shares)

26,614

'

'

'

'

'

'

'

26,614

'

'

'

'

'

'

Exercise of share options (in dollars)

568

'

'

568

'

'

'

568

568

'

'

'

'

'

'

Share-based compensation (in units/shares)

'

'

'

'

'

'

'

'

166,272

'

'

'

'

'

'

Share-based compensation

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation

'

'

'

1,854

'

'

'

'

'

'

'

'

'

'

'

Share-based compensation

1,856

'

'

'

'

'

'

1,856

1,856

'

'

'

'

'

'

Restricted common units/shares redemptions

-40,965

'

'

'

'

'

'

'

-40,965

'

'

'

'

'

'

Restricted common units/shares redemptions (in dollars)

-1,092

'

'

-1,092

'

'

'

-1,092

-1,092

'

'

'

'

'

'

Adjustments to noncontrolling interests resulting from changes in ownership of COPLP

'

'

'

-69

'

'

69

'

'

'

'

'

'

'

'

Comprehensive income (loss)

3,741

'

'

'

4,741

-1,408

408

3,741

279

-1,472

279

'

165

'

4,490

Dividends/Distributions

-28,581

'

'

'

-28,581

'

'

-29,827

-25,172

'

'

'

-165

'

-4,490

Distributions to owners of common and preferred units in COPLP

-1,246

'

'

'

'

'

-1,246

'

'

'

'

'

'

'

'

Adjustment to arrive at fair value of redeemable noncontrolling interest

540

'

'

540

'

'

'

540

540

'

'

'

'

'

'

Balance at Mar. 31, 2014

$1,473,035

$249,083

$876

$1,816,467

($665,708)

$2,072

$70,245

$1,473,035

$1,203,297

$2,133

$9,722

'

$8,800

'

$249,083

Balance (in units/ shares) at Mar. 31, 2014

87,594,931

'

'

'

'

'

'

'

91,524,133

'

'

3,929,202

'

87,594,931

'

Balance (preferred units) at Mar. 31, 2014

'

'

'

'

'

'

'

'

'

'

'

352,000

352,000

9,431,667

9,431,667

Consolidated_Statements_of_Equ1

Consolidated Statements of Equity (Parenthetical)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Balance (in units/ shares)	87,594,931	85,758,438
Conversion of common units to common shares	48,498	248,644
Exercise of share options (in units/shares)	26,614	16,453
Restricted common units/shares redemptions	40,965	60,960
Common Shares	'	'
Shares issued to the public (in units/ shares)	0	4,485,000

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities	'	'
Revenues from real estate operations received	$116,386	$119,348
Construction contract and other service revenues received	17,289	15,695
Property operating expenses paid	-42,739	-38,865
Construction contract and other service expenses paid	-11,397	-15,588
General, administrative, leasing, business development and land carry costs paid	-9,906	-8,521
Interest expense paid	-18,403	-18,018
Previously accreted interest expense paid	0	-2,263
Payments in connection with early extinguishment of debt	-101	-4,803
Interest and other income received	217	320
Income taxes refund	192	6
Net cash provided by operating activities	51,538	47,311
Cash flows from investing activities	'	'
Construction, development and redevelopment	-42,625	-44,361
Tenant improvements on operating properties	-4,357	-5,263
Other capital improvements on operating properties	-9,115	-9,327
Mortgage and other loan receivables funded	-395	-2,231
Leasing costs paid	-4,422	-3,436
Other	59	4,442
Net cash used in investing activities	-60,855	-60,176
Proceeds from debt	'	'
Revolving Credit Facility	0	99,000
Other debt proceeds	5,700	68,132
Repayments of debt	'	'
Revolving Credit Facility	0	-99,000
Scheduled principal amortization	-1,855	-2,512
Other debt repayments	-50	-125,877
Deferred financing costs paid	-9	-1,109
Net proceeds from issuance of common shares/units	568	118,389
Common share/unit dividends/distributions paid	-24,036	-22,276
Preferred share/unit dividends/distributions paid	-4,490	-6,106
Distributions paid to noncontrolling interests in COPLP	-1,253	-1,370
Restricted share redemptions	-1,092	-1,576
Other	-165	85
Net cash (used in) provided by financing activities	-26,682	25,780
Net (decrease) increase in cash and cash equivalents	-35,999	12,915
Cash and cash equivalents	'	'
Beginning of period	54,373	10,594
End of period	18,374	23,509
Reconciliation of net income to net cash provided by operating activities:	'	'
Net income	5,671	15,277
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and other amortization	44,101	28,782
Impairment losses	1	1,857
Settlement of previously accreted interest expense	0	-2,263
Amortization of deferred financing costs	1,167	1,528
Decrease (increase) in deferred rent receivable	398	-4,236
Amortization of net debt discounts	171	710
Loss (gain) on sales of real estate	4	-2,354
Share-based compensation	1,555	1,649
Loss on early extinguishment of debt	-78	381
Other	-1,032	-580
Changes in operating assets and liabilities:	'	'
(Increase) decrease in accounts receivable	-1,769	6,342
Decrease in restricted cash and marketable securities	283	201
(Increase) decrease in prepaid expenses and other assets	-494	4,180
Increase (decrease) in accounts payable, accrued expenses and other liabilities	4,785	-2,555
Decrease in rents received in advance and security deposits	-3,225	-1,608
Net cash provided by operating activities	51,538	47,311
Supplemental schedule of non-cash investing and financing activities:	'	'
Decrease in accrued capital improvements, leasing and other investing activity costs	-7,985	-5,353
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests	-1,443	1,105
Dividends and distributions payable	29,122	29,947
Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares	651	3,175
Adjustments to noncontrolling interests resulting from changes in COPLP ownership	69	2,229
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in shareholders’ equity to carry redeemable noncontrolling interest at fair value	-540	848
Corporate Office Properties, L.P.	'	'
Cash flows from operating activities	'	'
Revenues from real estate operations received	116,386	119,348
Construction contract and other service revenues received	17,289	15,695
Property operating expenses paid	-42,739	-38,865
Construction contract and other service expenses paid	-11,397	-15,588
General, administrative, leasing, business development and land carry costs paid	-9,906	-8,521
Interest expense paid	-18,403	-18,018
Previously accreted interest expense paid	0	-2,263
Payments in connection with early extinguishment of debt	-101	-4,803
Interest and other income received	217	320
Income taxes refund	192	6
Net cash provided by operating activities	51,538	47,311
Cash flows from investing activities	'	'
Construction, development and redevelopment	-42,625	-44,361
Tenant improvements on operating properties	-4,357	-5,263
Other capital improvements on operating properties	-9,115	-9,327
Mortgage and other loan receivables funded	-395	-2,231
Leasing costs paid	-4,422	-3,436
Other	59	4,442
Net cash used in investing activities	-60,855	-60,176
Proceeds from debt	'	'
Revolving Credit Facility	0	99,000
Other debt proceeds	5,700	68,132
Repayments of debt	'	'
Revolving Credit Facility	0	-99,000
Scheduled principal amortization	-1,855	-2,512
Other debt repayments	-50	-125,877
Deferred financing costs paid	-9	-1,109
Net proceeds from issuance of common shares/units	568	118,389
Common share/unit dividends/distributions paid	-25,124	-23,481
Preferred share/unit dividends/distributions paid	-4,655	-6,271
Restricted share redemptions	-1,092	-1,576
Other	-165	85
Net cash (used in) provided by financing activities	-26,682	25,780
Net (decrease) increase in cash and cash equivalents	-35,999	12,915
Cash and cash equivalents	'	'
Beginning of period	54,373	10,594
End of period	18,374	23,509
Reconciliation of net income to net cash provided by operating activities:	'	'
Net income	5,671	15,277
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and other amortization	44,101	28,782
Impairment losses	1	1,857
Settlement of previously accreted interest expense	0	-2,263
Amortization of deferred financing costs	1,167	1,528
Decrease (increase) in deferred rent receivable	398	-4,236
Amortization of net debt discounts	171	710
Loss (gain) on sales of real estate	4	-2,354
Share-based compensation	1,555	1,649
Loss on early extinguishment of debt	-78	381
Other	-1,032	-580
Changes in operating assets and liabilities:	'	'
(Increase) decrease in accounts receivable	-1,769	6,342
Decrease in restricted cash and marketable securities	381	483
(Increase) decrease in prepaid expenses and other assets	-494	4,180
Increase (decrease) in accounts payable, accrued expenses and other liabilities	4,687	-2,837
Decrease in rents received in advance and security deposits	-3,225	-1,608
Net cash provided by operating activities	51,538	47,311
Supplemental schedule of non-cash investing and financing activities:	'	'
Decrease in accrued capital improvements, leasing and other investing activity costs	-7,985	-5,353
(Decrease) increase in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests	-1,443	1,105
Dividends and distributions payable	29,122	29,947
(Decrease) increase in redeemable noncontrolling interest and (increase) decrease in shareholders’ equity to carry redeemable noncontrolling interest at fair value	($540)	$848

Organization

Organization	3 Months Ended
	Mar. 31, 2014
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 defense contractors, most of whom are engaged in defense information technology and national security 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 March 31, 2014, our properties included the following:
	•	183 operating office properties totaling 17.5 million square feet;
	•	12 office properties under, or contractually committed for, construction or redevelopment that we estimate will total approximately 1.6 million square feet upon completion, including two partially operational properties included above;
	•	land held or under pre-construction totaling 1,716 acres (including 56 acres controlled but not owned) that we believe are potentially developable into approximately 19.7 million square feet; and
	•	a partially operational, wholesale data center which upon completion and stabilization is expected to have a critical load of 18 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”).
	Interests in COPLP are in the form of common and preferred units. As of March 31, 2014, COPT owned 95.7% of the outstanding COPLP common units (“common units”) and 96.4% of the outstanding COPLP preferred units (“preferred units”); the remaining common and preferred units in COPLP were owned by third parties. Three of COPT’s trustees controlled, either directly or through ownership by other entities or family members, 3.4% of COPLP’s common units as of March 31, 2014. 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 are 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_Account

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2014
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 they 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 the entity’s operations 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, 2013 included in our 2013 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 2013 Annual Report on Form 10-K.
	Reclassifications
	We reclassified certain amounts from prior periods to conform to the current period presentation of our consolidated financial statements with no effect on previously reported net income or equity.  These reclassifications occurred in conjunction with the transfer of properties to, and from, discontinued operations during 2013.
	Recent Accounting Pronouncement
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued guidance related to the reporting of discontinued operation and disclosures of disposals of components of an entity. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale and represents a strategic shift that has (or will have) a major effect on an entity’s operations and final result; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity. The guidance also provides for additional disclosure requirements in connection with both discontinued operations and other dispositions not qualifying as discontinued operations. The guidance will be effective for annual and interim periods beginning on or after December 15, 2014. The guidance applies prospectively to new disposals and new classifications of disposal groups as held for sale after the effective date. All entities may early adopt the guidance for new disposals (or new classifications as held for sale) that have not been reported in financial statements previously issued or available for issuance. We are in the process of evaluating this guidance.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
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 2013 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 March 31, 2014, we used a discount rate of 15.5%. The discount rate 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.
	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 6, we estimated the fair values of our mortgage and other 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 8, 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 6 for mortgage loans receivable, Note 8 for debt and Note 9 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 March 31, 2014 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds	$	7,249	$	—		$	—	$	7,249
	Common stocks	115		—			—		115
	Other	201		—			—		201
	Interest rate derivatives (2)	—		5,038			—		5,038
	Warrants to purchase common stock (2)	—		537			—		537
	Total Assets	$	7,565	$	5,575		$	—	$	13,140
	Liabilities:
	Deferred compensation plan liability (3)	$	—	$	7,565		$	—	$	7,565
	Interest rate derivatives	—		3,196			—		3,196
	Total Liabilities	$	—	$	10,761		$	—	$	10,761
	Redeemable noncontrolling interest	$	—	$	—		$	17,654	$	17,654
	(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 March 31, 2014 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	Assets:
	Interest rate derivatives (1)	$	—	$	5,038		$	—	$	5,038
	Warrants to purchase common stock (1)	—		537			—		537
	Total Assets	$	—	$	5,575		$	—	$	5,575
	Liabilities:
	Interest rate derivatives	$	—	$	3,196		$	—	$	3,196
	Redeemable noncontrolling interest	$	—	$	—		$	17,654	$	17,654
	(1) Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet.
	Nonrecurring Fair Value Measurements
	During the three months ended March 31, 2013, we recognized a non-cash impairment loss of $1.9 million for the amount by which the carrying values of certain properties exceeded their estimated fair values. The table below sets forth the fair value hierarchy of the valuation techniques used by us in determining the fair value of the property (dollars in thousands):
		Fair Value of Property Held as of March 31, 2013									Impairment Losses
		Quoted Prices in					Significant				Recognized in
		Active Markets for		Significant Other			Unobservable				Three Months
		Identical Assets		Observable Inputs			Inputs				Ended
	Description	(Level 1)		(Level 2)			(Level 3)		Total		31-Mar-13
	Assets:
	Properties, net	$	—	$	—		$	7,250	$	7,250	$	1,857
	The table below sets forth quantitative information about significant unobservable inputs used for the Level 3 fair value measurements reported above as of March 31, 2013 (dollars in thousands):
	Valuation Technique	Fair Value on		Unobservable Input		Range (Weighted Average)
		Measurement Date
	Bids for property indicative of value	$	7,250	Indicative bid		-1
	(1) This fair value measurement was developed as a result of negotiations between us and a purchaser of a property.

Properties_net

Properties, net	3 Months Ended
	Mar. 31, 2014
Real Estate [Abstract]	'
Properties, net	'
	Properties, net
	Operating properties, net consisted of the following (in thousands):
		March 31,			December 31,
		2014			2013
	Land	$	436,381		$	430,472
	Buildings and improvements	2,927,800			2,869,870
	Less: accumulated depreciation	(635,178		)	(597,649		)
	Operating properties, net	$	2,729,003		$	2,702,693
	During the three months ended March 31, 2014, we recognized $12.9 million in additional depreciation expense resulting from our revision of the useful life of a property in Greater Philadelphia that was removed from service for redevelopment.
	Projects we had in development or held for future development consisted of the following (in thousands):
		March 31,			December 31,
		2014			2013
	Land	$	238,904		$	245,676
	Construction in progress, excluding land	256,721			265,932
	Projects in development or held for future development	$	495,625		$	511,608
	2014 Construction Activities
	During the three months ended March 31, 2014, we placed into service an aggregate of 355,000 square feet in two newly constructed office properties located in Northern Virginia and Huntsville, Alabama. As of March 31, 2014, we had eight office properties under construction, or for which we were contractually committed to construct, that we estimate will total 1.2 million square feet upon completion, including four in the Baltimore/Washington Corridor, three in Northern Virginia and one in San Antonio. We also had four office properties under redevelopment that we estimate will total 403,000 square feet upon completion, including two in Greater Philadelphia, one in the Baltimore/Washington Corridor and one in St. Mary’s County, Maryland.

Real_Estate_Joint_Ventures

Real Estate Joint Ventures	3 Months Ended
	Mar. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]	'
Real Estate Joint Ventures	'
	Real Estate Joint Ventures
	The table below sets forth information pertaining to our investments in consolidated real estate joint ventures as of March 31, 2014 (dollars in thousands):
				Nominal
				Ownership		March 31, 2014				-1
			Date	% as of		Total		Encumbered		Total
			Acquired	3/31/14	Nature of Activity	Assets		Assets		Liabilities
	LW Redstone Company, LLC		3/23/10	85%	Operates four buildings and developing others (2)	$	135,231	$	68,360	$	36,272
	M Square Associates, LLC		6/26/07	50%	Operates two buildings and developing others (3)	60,728		48,358		40,536
	COPT-FD Indian Head, LLC		10/23/06	75%	Holding land parcel (4)	6,436		—		—
						$	202,395	$	116,718	$	76,808
	-1	Excludes amounts eliminated in consolidation.
	-2	This joint venture’s property is in Huntsville, Alabama.
	-3	This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).
	-4	This joint venture’s property is in Charles County, Maryland. In 2012, the joint venture exercised its option under a development agreement to require Charles County to repurchase the land parcel at its original acquisition cost. Under the terms of the agreement with Charles County, the repurchase is expected to occur by August 2014.
	Our commitments and contingencies pertaining to our real estate joint ventures are disclosed in Note 17.

Mortgage_and_Other_Investing_R

Mortgage and Other Investing Receivables	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Mortgage and Other Investing Receivables	'
	Mortgage and Other Investing Receivables
	Mortgage and other investing receivables, including accrued interest thereon, consisted of the following (in thousands):
		March 31,		December 31,
		2014		2013
	Notes receivable from City of Huntsville	$	45,381	$	44,055
	Mortgage loan receivable	9,850		9,608
		$	55,231	$	53,663
	Our notes receivable from the City of Huntsville funded infrastructure costs in connection with our LW Redstone Company, LLC joint venture (see Note 5).  The mortgage loan receivable reflected above consisted of one loan secured by a property in Greater Baltimore. We did not have an allowance for credit losses in connection with our mortgage and other investing receivables as of March 31, 2014 or December 31, 2013.  The fair value of these receivables approximated their carrying amounts as of March 31, 2014 and December 31, 2013.

Prepaid_Expenses_and_Other_Ass

Prepaid Expenses and Other Assets	3 Months Ended
	Mar. 31, 2014
Prepaid Expense and Other Assets [Abstract]	'
Prepaid Expenses and Other Assets	'
	Prepaid Expenses and Other Assets
	Prepaid expenses and other assets consisted of the following (in thousands):
		March 31,		December 31,
		2014		2013
	Prepaid expenses	$	13,813	$	19,308
	Lease incentives	11,900		8,435
	Furniture, fixtures and equipment, net	7,068		6,556
	Interest rate derivatives	5,038		6,594
	Construction contract costs incurred in excess of billings	4,990		2,462
	Deferred tax asset, net (1)	4,241		4,305
	Other equity method investments	2,266		2,258
	Other assets	4,616		4,268
	Prepaid expenses and other assets	$	53,932	$	54,186
	(1) Includes a valuation allowance of $2.1 million.
	Other assets, as reported above, include operating notes receivable due from tenants with terms exceeding one year totaling $1.7 million as of March 31, 2014 and December 31, 2013; we carried allowances for estimated losses for $124,000 of the March 31, 2014 balance and $87,000 of the December 31, 2013 balance.

Debt

Debt	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	Our debt consisted of the following (dollars in thousands):
		Maximum
		Availability at			Carrying Value at							Scheduled Maturity
		March 31,			March 31,			December 31,		Stated Interest Rates as of		as of
		2014			2014			2013		March 31, 2014		March 31, 2014
	Mortgage and Other Secured Loans:
	Fixed rate mortgage loans (1)	-2			$	679,260		$	675,060	3.96% - 7.87% (3)		2014-2024
	Variable rate secured loan				37,491			37,691		LIBOR + 2.25% (4)		Nov-15
	Total mortgage and other secured loans				716,751			712,751
	Revolving Credit Facility (5)	$	800,000		—			—		LIBOR + 0.975% to 1.75%		Jul-17
	Term Loan Facilities	-6			620,000			620,000		LIBOR + 1.10% to 2.60% (7)		2015-2019
	Unsecured Senior Notes
	3.600% Senior Notes (8)				347,306			347,244		3.60%		May-23
	5.250% Senior Notes (9)				245,532			245,445		5.25%		Feb-24
	Unsecured notes payable				1,677			1,700		0% (10)		2026
	4.25% Exchangeable Senior Notes (11)				565			563		4.25%		Apr-30
	Total debt, net				$	1,931,831		$	1,927,703
	(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 $62,000 as of March 31, 2014 and $69,000 as of December 31, 2013.
	-2	Includes $19.8 million balance on construction loans with maximum available borrowings of $26.2 million.
	-3	The weighted average interest rate on these loans was 6.12% as of March 31, 2014.
	(4)	The interest rate on the loan outstanding was 2.41% as of March 31, 2014.
	-5	No borrowings were outstanding on this facility during the three months ended March 31, 2014.
	(6)	We have the ability to borrow an aggregate of an additional $180.0 million under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders.
	(7)	The weighted average interest rate on these loans was 1.78% as of March 31, 2014.
	-8	The carrying value of these notes included a principal amount of $350.0 million and an unamortized discount totaling $2.7 million as of March 31, 2014 and $2.8 million as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%.
	-9	The carrying value of these notes included a principal amount of $250.0 million and an unamortized discount totaling $4.5 million as of March 31, 2014 and $4.6 million as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%.
	(10)	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 $734,000 as of March 31, 2014 and $761,000 as of December 31, 2013.
	(11)	As described further in our 2013 Annual Report on Form 10-K, these notes have an exchange settlement feature that provides that the notes may, under certain circumstances, be exchangeable for cash and, at COPLP’s discretion, COPT common shares at an exchange rate (subject to adjustment) of 20.8513 shares per one thousand dollar principal amount of the notes (exchange rate is as of March 31, 2014 and is equivalent to an exchange price of $47.96 per common share).  The carrying value of these notes included a principal amount of $575,000 and an unamortized discount totaling $10,000 as of March 31, 2014 and $12,000 as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 6.05%.  Because the closing price of our common shares as of March 31, 2014 and December 31, 2013 was less than the exchange price per common share applicable to these notes, the if-converted value of the notes did not exceed the principal amount.  The table below sets forth interest expense recognized on these notes before deductions for amounts capitalized (in thousands):
			For the Three Months Ended March 31,
			2014			2013
	Interest expense at stated interest rate		$	6		$	2,304
	Interest expense associated with amortization of discount		3			864
	Total		$	9		$	3,168
	All debt is owed by the Operating Partnership. While COPT is not directly obligated by any debt, it has guaranteed our Revolving Credit Facility, Term Loan Facilities, Unsecured Senior Notes and 4.25% Exchangeable Senior Notes.
	In April 2014, a wholly owned subsidiary of ours defaulted on the payment terms of a $150.0 million nonrecourse mortgage loan secured by two operating properties in Northern Virginia with an aggregate estimated fair value that was less than the loan balance. This loan has an interest rate of 5.65% and is scheduled to mature in 2017.
	We capitalized interest costs of $1.6 million in the three months ended March 31, 2014 and $2.4 million in the three months ended March 31, 2013.
	The following table sets forth information pertaining to the fair value of our debt (in thousands):
		March 31, 2014						December 31, 2013
		Carrying			Estimated			Carrying		Estimated
		Amount			Fair Value			Amount		Fair Value
	Fixed-rate debt
	Unsecured Senior Notes	$	592,838		$	584,178		$	592,689	$	575,374
	4.25% Exchangeable Senior Notes	565			575			563		575
	Other fixed-rate debt	680,937			668,949			676,760		650,997
	Variable-rate debt	657,491			657,420			657,691		657,527
		$	1,931,831		$	1,911,122		$	1,927,703	$	1,884,473

Interest_Rate_Derivatives

Interest Rate Derivatives	3 Months Ended
	Mar. 31, 2014
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		March 31,			December 31,
											2014			2013
	$	100,000			0.61%		One-Month LIBOR	1/3/12	9/1/14		$	(195	)	$	(279	)
	100,000				0.61%		One-Month LIBOR	1/3/12	9/1/14		(194		)	(277		)
	100,000				0.83%		One-Month LIBOR	1/3/12	9/1/15		(807		)	(861		)
	100,000				0.83%		One-Month LIBOR	1/3/12	9/1/15		(807		)	(861		)
	37,491			-1	3.83%		One-Month LIBOR + 2.25%	11/2/10	11/2/15		(742		)	(832		)
	100,000				0.81%		One-Month LIBOR	9/2/14	9/1/16		(220		)	(94		)
	100,000				0.81%		One-Month LIBOR	9/2/14	9/1/16		(231		)	(105		)
	100,000				1.67%		One-Month LIBOR	9/1/15	8/1/19		2,604			3,377
	100,000				1.73%		One-Month LIBOR	9/1/15	8/1/19		2,434			3,217
											$	1,842		$	3,285
	-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 cash flow hedges 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 sheet (in thousands):
			March 31, 2014					31-Dec-13
	Derivatives		Balance Sheet Location		Fair Value			Balance Sheet Location	Fair Value
	Interest rate swaps designated as cash flow hedges		Prepaid expenses and other assets		$	5,038		Prepaid expenses and other assets	$	6,594
	Interest rate swaps designated as cash flow hedges		Interest rate derivatives		(3,196		)	Interest rate derivatives	(3,309		)
	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 March 31,
		2014				2013
	Amount of (losses) gains recognized in accumulated other comprehensive income (loss) (“AOCI”) (effective portion)	$	(2,123	)		$	462
	Amount of losses reclassified from AOCI into interest expense (effective portion)	695				658
	Over the next 12 months, we estimate that approximately $3.0 million of losses will be reclassified from AOCI 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 any 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 March 31, 2014, the fair value of interest rate derivatives in a liability position related to these agreements was $3.2 million, excluding the effects of accrued interest. As of March 31, 2014, 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 $3.4 million.

Redeemable_Noncontrolling_Inte

Redeemable Noncontrolling Interest	3 Months Ended
	Mar. 31, 2014
Noncontrolling Interest [Abstract]	'
Redeemable Noncontrolling Interest	'
	Redeemable Noncontrolling Interest
	The table below sets forth activity in a redeemable noncontrolling interest in a consolidated real estate joint venture (in thousands):
		Three Months Ended March 31,
		2014			2013
	Beginning balance	$	17,758		$	10,298
	Distribution to noncontrolling interest	(68		)	—
	Net income (loss) attributable to noncontrolling interest	504			(790		)
	Adjustment to arrive at fair value of interest	(540		)	848
	Ending balance	$	17,654		$	10,356

Equity

Equity	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Equity	'
	Equity
	During the three months ended March 31, 2014, certain COPLP limited partners redeemed 48,498 common units in COPLP for common shares in COPT on the basis of one common share for each common unit.
	See Note 13 for disclosure of COPT common share and COPLP common unit activity pertaining to our share-based compensation plans.

Information_by_Business_Segmen

Information by Business Segment	3 Months Ended
	Mar. 31, 2014
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). 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/			Northern			San			Huntsville		Washington,		St. Mary’s &		Greater		Greater		Colorado			Other		Operating		Total
		Washington			Virginia			Antonio					DC - Capitol		King George		Baltimore		Philadelphia		Springs					Wholesale
		Corridor											Riverfront		Counties											Data Center
	Three Months Ended March 31, 2014
	Revenues from real estate operations	$	61,113		$	24,968		$	8,479		$	2,555	$	3,634	$	4,316	$	11,496	$	3,340	$	18		$	2,576	$	2,401	$	124,896
	Property operating expenses	23,597			8,973			4,474			653		1,765		1,504		5,476		1,300		(9		)	331		1,688		49,752
	NOI from real estate operations	$	37,516		$	15,995		$	4,005		$	1,902	$	1,869	$	2,812	$	6,020	$	2,040	$	27		$	2,245	$	713	$	75,144
	Additions to long-lived assets	$	5,741		$	3,495		$	(6	)	$	2,507	$	63	$	839	$	1,012	$	11	$	—		$	55	$	12	$	13,729
	Transfers from non-operating properties	$	(169	)	$	26,588		$	—		$	20,102	$	—	$	—	$	7,154	$	3,176	$	11		$	—	$	78	$	56,940
	Segment assets at March 31, 2014	$	1,237,796		$	636,895		$	117,812		$	99,378	$	97,843	$	95,645	$	307,699	$	94,428	$	7		$	79,535	$	165,711	$	2,932,749
	Three Months Ended March 31, 2013
	Revenues from real estate operations	$	58,660		$	22,942		$	7,757		$	740	$	4,244	$	3,992	$	10,719	$	2,487	$	6,682		$	2,501	$	1,353	$	122,077
	Property operating expenses	20,053			7,817			3,888			182		1,949		1,193		4,168		838		2,437			225		1,316		44,066
	NOI from real estate operations	$	38,607		$	15,125		$	3,869		$	558	$	2,295	$	2,799	$	6,551	$	1,649	$	4,245		$	2,276	$	37	$	78,011
	Additions to long-lived assets	$	2,760		$	1,544		$	10		$	—	$	157	$	275	$	702	$	—	$	315		$	91	$	—	$	5,854
	Transfers from non-operating properties	$	22,997		$	9,839		$	—		$	24,240	$	—	$	6	$	113	$	7,050	$	1,783		$	—	$	65,568	$	131,596
	Segment assets at March 31, 2013	$	1,279,794		$	574,970		$	119,145		$	52,361	$	102,928	$	97,346	$	317,953	$	85,017	$	177,728		$	81,714	$	166,920	$	3,055,876
	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 March 31,
		2014			2013
	Segment revenues from real estate operations	$	124,896		$	122,077
	Construction contract and other service revenues	21,790			14,262
	Less: Revenues from discontinued operations (Note 15)	(19		)	(10,120		)
	Total revenues	$	146,667		$	126,219
	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 March 31,
		2014			2013
	Segment property operating expenses	$	49,752		$	44,066
	Less: Property operating expenses from discontinued operations (Note 15)	20			(3,678		)
	Total property operating expenses	$	49,772		$	40,388
	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 March 31,
		2014			2013
	Construction contract and other service revenues	$	21,790		$	14,262
	Construction contract and other service expenses	(18,624		)	(13,477		)
	NOI from service operations	$	3,166		$	785
	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 March 31,
		2014			2013
	NOI from real estate operations	$	75,144		$	78,011
	NOI from service operations	3,166			785
	Interest and other income	1,285			946
	Equity in income of unconsolidated entities	60			41
	Income tax expense	(64		)	(16		)
	Other adjustments:	—
	Depreciation and other amortization associated with real estate operations	(43,596		)	(27,010		)
	General, administrative and leasing expenses	(8,143		)	(7,820		)
	Business development expenses and land carry costs	(1,326		)	(1,359		)
	Interest expense on continuing operations	(20,827		)	(20,290		)
	NOI from discontinued operations	(39		)	(6,442		)
	Loss on early extinguishment of debt	—			(5,184		)
	Income from continuing operations	$	5,660		$	11,662
	The following table reconciles our segment assets to the consolidated total assets of COPT and subsidiaries (in thousands):
		March 31,			March 31,
		2014			2013
	Segment assets	$	2,932,749		$	3,055,876
	Non-operating property assets	503,030			490,083
	Other assets	170,118			139,140
	Total COPT consolidated assets	$	3,605,897		$	3,685,099
	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 and loss on early extinguishment of debt 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.

ShareBased_Compensation

Share-Based Compensation	3 Months Ended
	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	Performance Share Units (“PSUs”)
	On March 6, 2014, our Board of Trustees granted 49,103 PSUs with an aggregate grant date fair value of $1.7 million to executives.  The PSUs have a performance period beginning on January 1, 2014 and concluding on the earlier of December 31, 2016 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 performance period ends due to a sale event or qualified termination, the number of earned PSUs is prorated based on the portion of the three-year performance 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 $35.09 per PSU using a Monte Carlo model, which included assumptions of, among other things, the following: baseline common share value of $26.52; expected volatility for COPT common shares of 28.6%; and a risk-free interest rate of 0.66%.  We are recognizing the grant date fair value in connection with these PSU awards over the period commencing on March 6, 2014 and ending on December 31, 2016.
	With regard to the PSUs granted to our executives in prior years that were outstanding as of December 31, 2013 as described in our 2013 Annual Report on Form 10-K:
	•	the performance period for the PSUs granted to executives on March 3, 2011 ended on March 2, 2014. Based on COPT’s total shareholder return during the performance period relative to its peer group of companies, there was no payout value in connection with the termination of the PSUs; and
	•	the PSUs granted to executives on March 1, 2012 and March 1, 2013 were outstanding as of March 31, 2014.
	Restricted Shares
	During the three months ended March 31, 2014, certain employees, as well as a nonemployee member of our Board of Trustees, were granted a total of 177,356 restricted shares with an aggregate grant date fair value of $4.7 million (weighted average of $26.63 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.  The grants of restricted shares to nonemployee Trustees vest on the first anniversary of the grant date provided that the Trustee remains in his or her position. During the three months ended March 31, 2014, forfeiture restrictions lapsed on 110,356 previously issued common shares; these shares had a weighted average grant date fair value of $29.52 per share, and the aggregate intrinsic value of the shares on the vesting dates was $2.9 million.
	Options
	During the three months ended March 31, 2014, 26,614 options to purchase common shares (“options”) were exercised.  The weighted average exercise price of these options was $21.34 per share, and the aggregate intrinsic value of the options exercised was $126,000.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2014
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 March 31,
		2014			2013
	Deferred
	Federal	$	(53	)	$	(13	)
	State	(11		)	(3		)
	Total income tax expense	$	(64	)	$	(16	)
	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 38.1% for the three months ended March 31, 2014 and 36.0% for the three months ended March 31, 2013.

Discontinued_Operations

Discontinued Operations	3 Months Ended
	Mar. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Discontinued Operations	'
	Discontinued Operations
	Income from discontinued operations primarily includes revenues and expenses associated with the following:
	•	920 Elkridge Landing Road in the Baltimore/Washington Corridor that was sold on June 25, 2013;
	•	4230 Forbes Boulevard in the Baltimore/Washington Corridor that was sold on December 11, 2013;
	•	15 operating properties in Colorado Springs that were sold on December 12, 2013; and
	•	nine operating properties the Baltimore/Washington Corridor and five operating properties in Colorado Springs for which the title to the properties was transferred to the mortgage lender on December 23, 2013.
	The table below sets forth the components of discontinued operations reported on our consolidated statements of operations (in thousands):
		For the Three Months Ended March 31,
		2014			2013
	Revenue from real estate operations	$	19		$	10,120
	Property operating expenses	20			(3,678		)
	Depreciation and amortization	—			(1,242		)
	Impairment losses	(1		)	(1,857		)
	General, administrative and leasing expenses	—			(1		)
	Interest expense	—			(2,081		)
	Loss on sales of real estate	(4		)	—
	Loss on early extinguishment of debt	(23		)	—
	Discontinued operations	$	11		$	1,261

Earnings_Per_Share_EPS_and_Ear

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU")	3 Months Ended
	Mar. 31, 2014
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 March 31,
		2014				2013
	Numerator:
	Income from continuing operations	$	5,660			$	11,662
	Gain on sales of real estate, net	—				2,354
	Preferred share dividends	(4,490		)		(6,106		)
	Income from continuing operations attributable to noncontrolling interests	(932		)		(167		)
	Income from continuing operations attributable to restricted shares	(121		)		(118		)
	Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders	$	117			$	7,625
	Discontinued operations	11				1,261
	Discontinued operations attributable to noncontrolling interests	2				(90		)
	Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	$	130			$	8,796
	Denominator (all weighted averages):
	Denominator for basic EPS (common shares)	87,080				81,397
	Dilutive effect of share-based compensation awards	112				52
	Denominator for diluted EPS (common shares)	87,192				81,449
	Basic EPS:
	Income from continuing operations attributable to COPT common shareholders	$	0			$	0.09
	Discontinued operations attributable to COPT common shareholders	0				0.02
	Net income attributable to COPT common shareholders	$	0			$	0.11
	Diluted EPS:
	Income from continuing operations attributable to COPT common shareholders	$	0			$	0.09
	Discontinued operations attributable to COPT common shareholders	0				0.02
	Net income attributable to COPT common shareholders	$	0			$	0.11
	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 March 31,
			2014			2013
	Conversion of common units		3,958			3,893
	Conversion of Series I Preferred Units		176			176
	Conversion of Series K Preferred Shares		434			434
	The following share-based compensation securities were excluded from the computation of diluted EPS because their effect was antidilutive:
	•	weighted average restricted shares for the three months ended March 31, 2014 and 2013 of 390,000 and 409,000, respectively, and
	•	weighted average options for the three months ended March 31, 2014 and 2013 of 588,000 and 621,000, respectively.
	As discussed in Note 8, we have outstanding senior notes that have 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 March 31,
			2014				2013
	Numerator:
	Income from continuing operations		$	5,660			$	11,662
	Gain on sales of real estate, net		—				2,354
	Preferred unit distributions		(4,655		)		(6,271		)
	(Income) loss from continuing operations attributable to noncontrolling interests		(739		)		369
	Income from continuing operations attributable to restricted units		(121		)		(118		)
	Numerator for basic and diluted EPU from continuing operations attributable to COPLP common unitholders		$	145			$	7,996
	Discontinued operations		11				1,261
	Discontinued operations attributable to noncontrolling interests		2				(33		)
	Numerator for basic and diluted EPU on net income attributable to COPLP common unitholders		$	158			$	9,224
	Denominator (all weighted averages):
	Denominator for basic EPU (common units)		91,038				85,290
	Dilutive effect of share-based compensation awards		112				52
	Denominator for basic and diluted EPU (common units)		91,150				85,342
	Basic EPU:
Income from continuing operations attributable to COPLP common unitholders		$	0			$	0.09
Discontinued operations attributable to COPLP common unitholders		0				0.02
Net income attributable to COPLP common unitholders		$	0			$	0.11
Diluted EPU:
Income from continuing operations attributable to COPLP common unitholders		$	0			$	0.09
Discontinued operations attributable to COPLP common unitholders		0				0.02
Net income attributable to COPLP common unitholders		$	0			$	0.11
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 March 31,
		2014			2013
Conversion of Series I preferred units		176			176
Conversion of Series K preferred units		434			434
The following share-based compensation securities were excluded from the computation of diluted EPU because their effect was antidilutive:
•	weighted average restricted units for the three months ended March 31, 2014 and 2013 of 390,000 and 409,000, respectively; and
•	weighted average options for the three months ended March 31, 2014 and 2013 of 588,000 and 621,000, respectively.
As discussed in Note 8, we have outstanding senior notes that have 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	3 Months Ended
	Mar. 31, 2014
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.
	Joint Ventures
	In connection with our 2005 contribution of properties to an unconsolidated partnership in which we hold a joint venture interest, we entered into standard nonrecourse loan guarantees (environmental indemnifications and guarantees against fraud and misrepresentation, and springing guarantees of partnership debt in the event of a voluntary bankruptcy of the partnership).  On December 6, 2013, the holder of mortgage debt encumbering all of the joint venture’s properties foreclosed on the properties. As a result, title to the properties was transferred to the mortgage lender and the joint venture was relieved of the debt obligation plus accrued interest and penalties. The joint venture still had $5.6 million in nonrecourse mezzanine debt as of March 31, 2014; however, the joint venture no longer holds any property and has ceased all business operations. Management estimates there to be no fair value to the guarantees as of March 31, 2014 because the actions that would trigger performance are all within our control.
	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 $1.9 million liability through March 31, 2014 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.
	Environmental Indemnity Agreement
	We agreed to provide certain environmental indemnifications in connection with a lease and subsequent sale of three New Jersey properties. 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.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2014
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 they 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 the entity’s operations 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, 2013 included in our 2013 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 2013 Annual Report on Form 10-K.
Reclassifications	'
	Reclassifications
	We reclassified certain amounts from prior periods to conform to the current period presentation of our consolidated financial statements with no effect on previously reported net income or equity.  These reclassifications occurred in conjunction with the transfer of properties to, and from, discontinued operations during 2013.
Recent Accounting Pronouncement	'
	Recent Accounting Pronouncement
	In April 2014, the Financial Accounting Standards Board (“FASB”) issued guidance related to the reporting of discontinued operation and disclosures of disposals of components of an entity. This guidance defines a discontinued operation as a component or group of components disposed or classified as held for sale and represents a strategic shift that has (or will have) a major effect on an entity’s operations and final result; the guidance states that a strategic shift could include a disposal of a major geographical area of operations, a major line of business, a major equity method investment or other major parts of an entity. The guidance also provides for additional disclosure requirements in connection with both discontinued operations and other dispositions not qualifying as discontinued operations. The guidance will be effective for annual and interim periods beginning on or after December 15, 2014. The guidance applies prospectively to new disposals and new classifications of disposal groups as held for sale after the effective date. All entities may early adopt the guidance for new disposals (or new classifications as held for sale) that have not been reported in financial statements previously issued or available for issuance. We are in the process of evaluating this guidance.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
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 COPT and its subsidiaries that are accounted for at fair value on a recurring basis as of March 31, 2014 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	Assets:
	Marketable securities in deferred compensation plan (1)
	Mutual funds	$	7,249	$	—		$	—	$	7,249
	Common stocks	115		—			—		115
	Other	201		—			—		201
	Interest rate derivatives (2)	—		5,038			—		5,038
	Warrants to purchase common stock (2)	—		537			—		537
	Total Assets	$	7,565	$	5,575		$	—	$	13,140
	Liabilities:
	Deferred compensation plan liability (3)	$	—	$	7,565		$	—	$	7,565
	Interest rate derivatives	—		3,196			—		3,196
	Total Liabilities	$	—	$	10,761		$	—	$	10,761
	Redeemable noncontrolling interest	$	—	$	—		$	17,654	$	17,654
	(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.
	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 March 31, 2014 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
		Active Markets for		Observable Inputs(Level 2)			Unobservable Inputs(Level 3)
		Identical Assets(Level 1)
	Assets:
	Interest rate derivatives (1)	$	—	$	5,038		$	—	$	5,038
	Warrants to purchase common stock (1)	—		537			—		537
	Total Assets	$	—	$	5,575		$	—	$	5,575
	Liabilities:
	Interest rate derivatives	$	—	$	3,196		$	—	$	3,196
	Redeemable noncontrolling interest	$	—	$	—		$	17,654	$	17,654
	(1) Included in the line entitled “prepaid expenses and other assets” on COPLP’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 techniques used by us in determining the fair value of the property (dollars in thousands):
		Fair Value of Property Held as of March 31, 2013									Impairment Losses
		Quoted Prices in					Significant				Recognized in
		Active Markets for		Significant Other			Unobservable				Three Months
		Identical Assets		Observable Inputs			Inputs				Ended
	Description	(Level 1)		(Level 2)			(Level 3)		Total		31-Mar-13
	Assets:
	Properties, net	$	—	$	—		$	7,250	$	7,250	$	1,857
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 March 31, 2013 (dollars in thousands):
	Valuation Technique	Fair Value on		Unobservable Input		Range (Weighted Average)
		Measurement Date
	Bids for property indicative of value	$	7,250	Indicative bid		-1
	(1) This fair value measurement was developed as a result of negotiations between us and a purchaser of a property.

Properties_net_Tables

Properties, net (Tables)	3 Months Ended
	Mar. 31, 2014
Real Estate [Abstract]	'
Schedule of operating properties, net	'
	Operating properties, net consisted of the following (in thousands):
		March 31,			December 31,
		2014			2013
	Land	$	436,381		$	430,472
	Buildings and improvements	2,927,800			2,869,870
	Less: accumulated depreciation	(635,178		)	(597,649		)
	Operating properties, net	$	2,729,003		$	2,702,693
Schedule of projects in development or held for future development	'
	Projects we had in development or held for future development consisted of the following (in thousands):
		March 31,			December 31,
		2014			2013
	Land	$	238,904		$	245,676
	Construction in progress, excluding land	256,721			265,932
	Projects in development or held for future development	$	495,625		$	511,608

Real_Estate_Joint_Ventures_Tab

Real Estate Joint Ventures (Tables)	3 Months Ended
	Mar. 31, 2014
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 investments in consolidated real estate joint ventures as of March 31, 2014 (dollars in thousands):
				Nominal
				Ownership		March 31, 2014				-1
			Date	% as of		Total		Encumbered		Total
			Acquired	3/31/14	Nature of Activity	Assets		Assets		Liabilities
	LW Redstone Company, LLC		3/23/10	85%	Operates four buildings and developing others (2)	$	135,231	$	68,360	$	36,272
	M Square Associates, LLC		6/26/07	50%	Operates two buildings and developing others (3)	60,728		48,358		40,536
	COPT-FD Indian Head, LLC		10/23/06	75%	Holding land parcel (4)	6,436		—		—
						$	202,395	$	116,718	$	76,808
	-1	Excludes amounts eliminated in consolidation.
	-2	This joint venture’s property is in Huntsville, Alabama.
	-3	This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).
	-4	This joint venture’s property is in Charles County, Maryland. In 2012, the joint venture exercised its option under a development agreement to require Charles County to repurchase the land parcel at its original acquisition cost. Under the terms of the agreement with Charles County, the repurchase is expected to occur by August 2014.

Mortgage_and_Other_Investing_R1

Mortgage and Other Investing Receivables (Tables)	3 Months Ended
	Mar. 31, 2014
Receivables [Abstract]	'
Mortgage and other investing receivables	'
	Mortgage and other investing receivables, including accrued interest thereon, consisted of the following (in thousands):
		March 31,		December 31,
		2014		2013
	Notes receivable from City of Huntsville	$	45,381	$	44,055
	Mortgage loan receivable	9,850		9,608
		$	55,231	$	53,663

Prepaid_Expenses_and_Other_Ass1

Prepaid Expenses and Other Assets (Tables)	3 Months Ended
	Mar. 31, 2014
Prepaid Expense and Other Assets [Abstract]	'
Schedule of prepaid expenses and other assets	'
	Prepaid expenses and other assets consisted of the following (in thousands):
		March 31,		December 31,
		2014		2013
	Prepaid expenses	$	13,813	$	19,308
	Lease incentives	11,900		8,435
	Furniture, fixtures and equipment, net	7,068		6,556
	Interest rate derivatives	5,038		6,594
	Construction contract costs incurred in excess of billings	4,990		2,462
	Deferred tax asset, net (1)	4,241		4,305
	Other equity method investments	2,266		2,258
	Other assets	4,616		4,268
	Prepaid expenses and other assets	$	53,932	$	54,186
	(1) Includes a valuation allowance of $2.1 million.

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Schedule of debt	'
	Our debt consisted of the following (dollars in thousands):
		Maximum
		Availability at			Carrying Value at							Scheduled Maturity
		March 31,			March 31,			December 31,		Stated Interest Rates as of		as of
		2014			2014			2013		March 31, 2014		March 31, 2014
	Mortgage and Other Secured Loans:
	Fixed rate mortgage loans (1)	-2			$	679,260		$	675,060	3.96% - 7.87% (3)		2014-2024
	Variable rate secured loan				37,491			37,691		LIBOR + 2.25% (4)		Nov-15
	Total mortgage and other secured loans				716,751			712,751
	Revolving Credit Facility (5)	$	800,000		—			—		LIBOR + 0.975% to 1.75%		Jul-17
	Term Loan Facilities	-6			620,000			620,000		LIBOR + 1.10% to 2.60% (7)		2015-2019
	Unsecured Senior Notes
	3.600% Senior Notes (8)				347,306			347,244		3.60%		May-23
	5.250% Senior Notes (9)				245,532			245,445		5.25%		Feb-24
	Unsecured notes payable				1,677			1,700		0% (10)		2026
	4.25% Exchangeable Senior Notes (11)				565			563		4.25%		Apr-30
	Total debt, net				$	1,931,831		$	1,927,703
	(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 $62,000 as of March 31, 2014 and $69,000 as of December 31, 2013.
	-2	Includes $19.8 million balance on construction loans with maximum available borrowings of $26.2 million.
	-3	The weighted average interest rate on these loans was 6.12% as of March 31, 2014.
	(4)	The interest rate on the loan outstanding was 2.41% as of March 31, 2014.
	-5	No borrowings were outstanding on this facility during the three months ended March 31, 2014.
	(6)	We have the ability to borrow an aggregate of an additional $180.0 million under these term loan facilities, provided that there is no default under the facilities and subject to the approval of the lenders.
	(7)	The weighted average interest rate on these loans was 1.78% as of March 31, 2014.
	-8	The carrying value of these notes included a principal amount of $350.0 million and an unamortized discount totaling $2.7 million as of March 31, 2014 and $2.8 million as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%.
	-9	The carrying value of these notes included a principal amount of $250.0 million and an unamortized discount totaling $4.5 million as of March 31, 2014 and $4.6 million as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%.
	(10)	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 $734,000 as of March 31, 2014 and $761,000 as of December 31, 2013.
	(11)	As described further in our 2013 Annual Report on Form 10-K, these notes have an exchange settlement feature that provides that the notes may, under certain circumstances, be exchangeable for cash and, at COPLP’s discretion, COPT common shares at an exchange rate (subject to adjustment) of 20.8513 shares per one thousand dollar principal amount of the notes (exchange rate is as of March 31, 2014 and is equivalent to an exchange price of $47.96 per common share).  The carrying value of these notes included a principal amount of $575,000 and an unamortized discount totaling $10,000 as of March 31, 2014 and $12,000 as of December 31, 2013.  The effective interest rate under the notes, including amortization of the issuance costs, was 6.05%.  Because the closing price of our common shares as of March 31, 2014 and December 31, 2013 was less than the exchange price per common share applicable to these notes, the if-converted value of the notes did not exceed the principal amount.  The table below sets forth interest expense recognized on these notes before deductions for amounts capitalized (in thousands):
			For the Three Months Ended March 31,
			2014			2013
	Interest expense at stated interest rate		$	6		$	2,304
	Interest expense associated with amortization of discount		3			864
	Total		$	9		$	3,168
Schedule of the fair value of debt	'
	The following table sets forth information pertaining to the fair value of our debt (in thousands):
		March 31, 2014						December 31, 2013
		Carrying			Estimated			Carrying		Estimated
		Amount			Fair Value			Amount		Fair Value
	Fixed-rate debt
	Unsecured Senior Notes	$	592,838		$	584,178		$	592,689	$	575,374
	4.25% Exchangeable Senior Notes	565			575			563		575
	Other fixed-rate debt	680,937			668,949			676,760		650,997
	Variable-rate debt	657,491			657,420			657,691		657,527
		$	1,931,831		$	1,911,122		$	1,927,703	$	1,884,473

Interest_Rate_Derivatives_Tabl

Interest Rate Derivatives (Tables)	3 Months Ended
	Mar. 31, 2014
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		March 31,			December 31,
											2014			2013
	$	100,000			0.61%		One-Month LIBOR	1/3/12	9/1/14		$	(195	)	$	(279	)
	100,000				0.61%		One-Month LIBOR	1/3/12	9/1/14		(194		)	(277		)
	100,000				0.83%		One-Month LIBOR	1/3/12	9/1/15		(807		)	(861		)
	100,000				0.83%		One-Month LIBOR	1/3/12	9/1/15		(807		)	(861		)
	37,491			-1	3.83%		One-Month LIBOR + 2.25%	11/2/10	11/2/15		(742		)	(832		)
	100,000				0.81%		One-Month LIBOR	9/2/14	9/1/16		(220		)	(94		)
	100,000				0.81%		One-Month LIBOR	9/2/14	9/1/16		(231		)	(105		)
	100,000				1.67%		One-Month LIBOR	9/1/15	8/1/19		2,604			3,377
	100,000				1.73%		One-Month LIBOR	9/1/15	8/1/19		2,434			3,217
											$	1,842		$	3,285
	-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 sheet (in thousands):
			March 31, 2014					31-Dec-13
	Derivatives		Balance Sheet Location		Fair Value			Balance Sheet Location	Fair Value
	Interest rate swaps designated as cash flow hedges		Prepaid expenses and other assets		$	5,038		Prepaid expenses and other assets	$	6,594
	Interest rate swaps designated as cash flow hedges		Interest rate derivatives		(3,196		)	Interest rate derivatives	(3,309		)
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 March 31,
		2014				2013
	Amount of (losses) gains recognized in accumulated other comprehensive income (loss) (“AOCI”) (effective portion)	$	(2,123	)		$	462
	Amount of losses reclassified from AOCI into interest expense (effective portion)	695				658

Redeemable_Noncontrolling_Inte1

Redeemable Noncontrolling Interest (Tables)	3 Months Ended
	Mar. 31, 2014
Noncontrolling Interest [Abstract]	'
Schedule of activity for redeemable noncontrolling interest	'
	The table below sets forth activity in a redeemable noncontrolling interest in a consolidated real estate joint venture (in thousands):
		Three Months Ended March 31,
		2014			2013
	Beginning balance	$	17,758		$	10,298
	Distribution to noncontrolling interest	(68		)	—
	Net income (loss) attributable to noncontrolling interest	504			(790		)
	Adjustment to arrive at fair value of interest	(540		)	848
	Ending balance	$	17,654		$	10,356

Information_by_Business_Segmen1

Information by Business Segment (Tables)	3 Months Ended
	Mar. 31, 2014
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/			Northern			San			Huntsville		Washington,		St. Mary’s &		Greater		Greater		Colorado			Other		Operating		Total
		Washington			Virginia			Antonio					DC - Capitol		King George		Baltimore		Philadelphia		Springs					Wholesale
		Corridor											Riverfront		Counties											Data Center
	Three Months Ended March 31, 2014
	Revenues from real estate operations	$	61,113		$	24,968		$	8,479		$	2,555	$	3,634	$	4,316	$	11,496	$	3,340	$	18		$	2,576	$	2,401	$	124,896
	Property operating expenses	23,597			8,973			4,474			653		1,765		1,504		5,476		1,300		(9		)	331		1,688		49,752
	NOI from real estate operations	$	37,516		$	15,995		$	4,005		$	1,902	$	1,869	$	2,812	$	6,020	$	2,040	$	27		$	2,245	$	713	$	75,144
	Additions to long-lived assets	$	5,741		$	3,495		$	(6	)	$	2,507	$	63	$	839	$	1,012	$	11	$	—		$	55	$	12	$	13,729
	Transfers from non-operating properties	$	(169	)	$	26,588		$	—		$	20,102	$	—	$	—	$	7,154	$	3,176	$	11		$	—	$	78	$	56,940
	Segment assets at March 31, 2014	$	1,237,796		$	636,895		$	117,812		$	99,378	$	97,843	$	95,645	$	307,699	$	94,428	$	7		$	79,535	$	165,711	$	2,932,749
	Three Months Ended March 31, 2013
	Revenues from real estate operations	$	58,660		$	22,942		$	7,757		$	740	$	4,244	$	3,992	$	10,719	$	2,487	$	6,682		$	2,501	$	1,353	$	122,077
	Property operating expenses	20,053			7,817			3,888			182		1,949		1,193		4,168		838		2,437			225		1,316		44,066
	NOI from real estate operations	$	38,607		$	15,125		$	3,869		$	558	$	2,295	$	2,799	$	6,551	$	1,649	$	4,245		$	2,276	$	37	$	78,011
	Additions to long-lived assets	$	2,760		$	1,544		$	10		$	—	$	157	$	275	$	702	$	—	$	315		$	91	$	—	$	5,854
	Transfers from non-operating properties	$	22,997		$	9,839		$	—		$	24,240	$	—	$	6	$	113	$	7,050	$	1,783		$	—	$	65,568	$	131,596
	Segment assets at March 31, 2013	$	1,279,794		$	574,970		$	119,145		$	52,361	$	102,928	$	97,346	$	317,953	$	85,017	$	177,728		$	81,714	$	166,920	$	3,055,876
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 March 31,
		2014			2013
	Segment revenues from real estate operations	$	124,896		$	122,077
	Construction contract and other service revenues	21,790			14,262
	Less: Revenues from discontinued operations (Note 15)	(19		)	(10,120		)
	Total revenues	$	146,667		$	126,219
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 March 31,
		2014			2013
	Segment property operating expenses	$	49,752		$	44,066
	Less: Property operating expenses from discontinued operations (Note 15)	20			(3,678		)
	Total property operating expenses	$	49,772		$	40,388
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 March 31,
		2014			2013
	Construction contract and other service revenues	$	21,790		$	14,262
	Construction contract and other service expenses	(18,624		)	(13,477		)
	NOI from service operations	$	3,166		$	785
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 March 31,
		2014			2013
	NOI from real estate operations	$	75,144		$	78,011
	NOI from service operations	3,166			785
	Interest and other income	1,285			946
	Equity in income of unconsolidated entities	60			41
	Income tax expense	(64		)	(16		)
	Other adjustments:	—
	Depreciation and other amortization associated with real estate operations	(43,596		)	(27,010		)
	General, administrative and leasing expenses	(8,143		)	(7,820		)
	Business development expenses and land carry costs	(1,326		)	(1,359		)
	Interest expense on continuing operations	(20,827		)	(20,290		)
	NOI from discontinued operations	(39		)	(6,442		)
	Loss on early extinguishment of debt	—			(5,184		)
	Income from continuing operations	$	5,660		$	11,662
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):
		March 31,			March 31,
		2014			2013
	Segment assets	$	2,932,749		$	3,055,876
	Non-operating property assets	503,030			490,083
	Other assets	170,118			139,140
	Total COPT consolidated assets	$	3,605,897		$	3,685,099

ShareBased_Compensation_Tables

Share-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2014
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)	3 Months Ended
	Mar. 31, 2014
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 March 31,
		2014			2013
	Deferred
	Federal	$	(53	)	$	(13	)
	State	(11		)	(3		)
	Total income tax expense	$	(64	)	$	(16	)

Discontinued_Operations_Tables

Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Components of discontinued operations	'
	The table below sets forth the components of discontinued operations reported on our consolidated statements of operations (in thousands):
		For the Three Months Ended March 31,
		2014			2013
	Revenue from real estate operations	$	19		$	10,120
	Property operating expenses	20			(3,678		)
	Depreciation and amortization	—			(1,242		)
	Impairment losses	(1		)	(1,857		)
	General, administrative and leasing expenses	—			(1		)
	Interest expense	—			(2,081		)
	Loss on sales of real estate	(4		)	—
	Loss on early extinguishment of debt	(23		)	—
	Discontinued operations	$	11		$	1,261

Earnings_Per_Share_EPS_and_Ear1

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Tables)	3 Months Ended
	Mar. 31, 2014
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 March 31,
		2014				2013
	Numerator:
	Income from continuing operations	$	5,660			$	11,662
	Gain on sales of real estate, net	—				2,354
	Preferred share dividends	(4,490		)		(6,106		)
	Income from continuing operations attributable to noncontrolling interests	(932		)		(167		)
	Income from continuing operations attributable to restricted shares	(121		)		(118		)
	Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders	$	117			$	7,625
	Discontinued operations	11				1,261
	Discontinued operations attributable to noncontrolling interests	2				(90		)
	Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	$	130			$	8,796
	Denominator (all weighted averages):
	Denominator for basic EPS (common shares)	87,080				81,397
	Dilutive effect of share-based compensation awards	112				52
	Denominator for diluted EPS (common shares)	87,192				81,449
	Basic EPS:
	Income from continuing operations attributable to COPT common shareholders	$	0			$	0.09
	Discontinued operations attributable to COPT common shareholders	0				0.02
	Net income attributable to COPT common shareholders	$	0			$	0.11
	Diluted EPS:
	Income from continuing operations attributable to COPT common shareholders	$	0			$	0.09
	Discontinued operations attributable to COPT common shareholders	0				0.02
	Net income attributable to COPT common shareholders	$	0			$	0.11
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 March 31,
			2014			2013
	Conversion of common units		3,958			3,893
	Conversion of Series I Preferred Units		176			176
	Conversion of Series K Preferred Shares		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 March 31,
			2014				2013
	Numerator:
	Income from continuing operations		$	5,660			$	11,662
	Gain on sales of real estate, net		—				2,354
	Preferred unit distributions		(4,655		)		(6,271		)
	(Income) loss from continuing operations attributable to noncontrolling interests		(739		)		369
	Income from continuing operations attributable to restricted units		(121		)		(118		)
	Numerator for basic and diluted EPU from continuing operations attributable to COPLP common unitholders		$	145			$	7,996
	Discontinued operations		11				1,261
	Discontinued operations attributable to noncontrolling interests		2				(33		)
	Numerator for basic and diluted EPU on net income attributable to COPLP common unitholders		$	158			$	9,224
	Denominator (all weighted averages):
	Denominator for basic EPU (common units)		91,038				85,290
	Dilutive effect of share-based compensation awards		112				52
	Denominator for basic and diluted EPU (common units)		91,150				85,342
	Basic EPU:
	Income from continuing operations attributable to COPLP common unitholders		$	0			$	0.09
	Discontinued operations attributable to COPLP common unitholders		0				0.02
	Net income attributable to COPLP common unitholders		$	0			$	0.11
	Diluted EPU:
	Income from continuing operations attributable to COPLP common unitholders		$	0			$	0.09
	Discontinued operations attributable to COPLP common unitholders		0				0.02
	Net income attributable to COPLP common unitholders		$	0			$	0.11
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 March 31,
			2014			2013
	Conversion of Series I preferred units		176			176
	Conversion of Series K preferred units		434			434

Organization_Details

Organization (Details)	3 Months Ended
	Mar. 31, 2014
	sqft
	acre
Operating office properties	'
Investments in real estate	'
Number of real estate properties	183
Square footage of real estate properties (in square feet)	17,500,000
Office properties under, or contractually committed for, construction or approved for redevelopment	'
Investments in real estate	'
Number of real estate properties	12
Square footage of real estate properties (in square feet)	1,600,000
Office properties under construction or redevelopment which are partially operational	'
Investments in real estate	'
Number of real estate properties	2
Land held or under pre-construction	'
Investments in real estate	'
Area of land held or under pre-construction (in acres)	1,716
Area of land parcels controlled but not owned (in acres)	56
Developable square footage of real estate properties (in square feet)	19,700,000
Partially operational, wholesale data center	'
Investments in real estate	'
The expected stabilization critical load after completion of development (in megawatts)	18

Organization_Details_2

Organization (Details 2) (Corporate Office Properties, L.P.)	3 Months Ended
	Mar. 31, 2014
	Trustee
Common Units	'
Forms of ownership in Operating Partnership and ownership percentage by the entity	'
Percentage ownership in operating partnership	95.70%
Number of trustees controlling additional common units	3
Additional percentage of common units controlled by trustees (as a percent)	3.40%
Preferred Units	'
Forms of ownership in Operating Partnership and ownership percentage by the entity	'
Percentage ownership in operating partnership	96.40%

Fair_Value_Measurements_Detail

Fair Value Measurements (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Liabilities:	'		'	'	'
Interest rate derivatives	$3,196		$3,309	'	'
Redeemable noncontrolling interest	17,654		17,758	10,356	10,298
Corporate Office Properties, L.P.	'		'	'	'
Liabilities:	'		'	'	'
Interest rate derivatives	3,196		3,309	'	'
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1)	'		'	'	'
Assets:	'		'	'	'
Assets	7,565		'	'	'
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	7,249	[1]	'	'	'
Fair value measurement on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Shares	'		'	'	'
Assets:	'		'	'	'
Marketable securities in deferred compensation plan	115	[1]	'	'	'
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	201	[1]	'	'	'
Fair value measurement on a recurring basis | Significant Other Observable Inputs (Level 2)	'		'	'	'
Assets:	'		'	'	'
Interest rate derivatives	5,038	[2]	'	'	'
Warrants to purchase common stock	537	[2]	'	'	'
Assets	5,575		'	'	'
Liabilities:	'		'	'	'
Deferred compensation plan liability	7,565		'	'	'
Interest rate derivatives	3,196		'	'	'
Liabilities	10,761		'	'	'
Fair value measurement on a recurring basis | Significant Unobservable Inputs (Level 3)	'		'	'	'
Liabilities:	'		'	'	'
Redeemable noncontrolling interest	17,654		'	'	'
Fair value measurement on a recurring basis | Total Estimated Fair Value	'		'	'	'
Assets:	'		'	'	'
Interest rate derivatives	5,038	[2]	'	'	'
Warrants to purchase common stock	537	[2]	'	'	'
Assets	13,140		'	'	'
Liabilities:	'		'	'	'
Deferred compensation plan liability	7,565	[3]	'	'	'
Interest rate derivatives	3,196		'	'	'
Liabilities	10,761		'	'	'
Redeemable noncontrolling interest	17,654		'	'	'
Fair value measurement on a recurring basis | Total Estimated Fair Value | Mutual funds	'		'	'	'
Assets:	'		'	'	'
Marketable securities in deferred compensation plan	7,249	[1]	'	'	'
Fair value measurement on a recurring basis | Total Estimated Fair Value | Common Shares	'		'	'	'
Assets:	'		'	'	'
Marketable securities in deferred compensation plan	115	[1]	'	'	'
Fair value measurement on a recurring basis | Total Estimated Fair Value | Other	'		'	'	'
Assets:	'		'	'	'
Marketable securities in deferred compensation plan	201	[1]	'	'	'
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Significant Other Observable Inputs (Level 2)	'		'	'	'
Assets:	'		'	'	'
Interest rate derivatives	5,038	[4]	'	'	'
Warrants to purchase common stock	537	[4]	'	'	'
Assets	5,575		'	'	'
Liabilities:	'		'	'	'
Interest rate derivatives	3,196		'	'	'
Fair value measurement on a recurring basis | Corporate Office Properties, L.P. | Total Estimated Fair Value	'		'	'	'
Assets:	'		'	'	'
Interest rate derivatives	5,038	[4]	'	'	'
Warrants to purchase common stock	537	[4]	'	'	'
Assets	5,575		'	'	'
Liabilities:	'		'	'	'
Interest rate derivatives	3,196		'	'	'
Redeemable noncontrolling interest	$17,654		'	'	'
[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.
[4]	Included in the line entitled “prepaid expenses and other assets” on COPLP’s consolidated balance sheet.

Fair_Value_Measurements_Detail1

Fair Value Measurements (Details 2) (Fair value measurement on a nonrecurring basis, Properties,net, USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2013
Assets and liabilities measured at fair value on a non-recurring basis	'
Impairment losses (recoveries)	$1,857
Significant Unobservable Inputs (Level 3)	'
Assets and liabilities measured at fair value on a non-recurring basis	'
Assets	7,250
Total Estimated Fair Value	'
Assets and liabilities measured at fair value on a non-recurring basis	'
Assets	$7,250

Fair_Value_Measurements_Detail2

Fair Value Measurements (Details 3) (Significant Unobservable Inputs (Level 3), USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2013
	Fair value measurement on a recurring basis	Properties,net	Properties,net
	Redeemable Non-Controlling Interest	Fair value measurement on a nonrecurring basis	Fair value measurement on a nonrecurring basis
			Bids for property indicative of value
Quantitative information for significant unobservable inputs used for Level 3 fair value measurements	'	'	'
Fair value inputs, discount rate	15.50%	'	'
Fair value on measurement date	'	$7,250	$7,250

Properties_net_Details

Properties, net (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Dec. 31, 2013
			Greater Philadelphia	Operating properties, net	Operating properties, net	Operating properties, net	Operating properties, net	Operating properties, net	Operating properties, net
						Land	Land	Buildings and improvements	Buildings and improvements
Properties	'	'	'	'	'	'	'	'	'
Gross	'	'	'	'	'	$436,381,000	$430,472,000	$2,927,800,000	$2,869,870,000
Less: accumulated depreciation	'	'	'	-635,178,000	-597,649,000	'	'	'	'
Operating properties, net	2,729,003,000	2,702,693,000	'	'	'	'	'	'	'
Depreciation Expense on Reclassified Assets	'	'	$12,900,000	'	'	'	'	'	'

Properties_net_Details_2

Properties, net (Details 2) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Properties	'	'
Projects in development or held for future development	$495,625	$511,608
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	238,904	245,676
Projects in development or held for future development | Construction in progress, excluding land	'	'
Properties	'	'
Projects in development or held for future development	$256,721	$265,932

Properties_net_Details_3

Properties, net (Details 3)	3 Months Ended
	Mar. 31, 2014
	Property
	sqft
Newly constructed properties placed in service	'
Construction and Redevelopment Activities	'
Square Feet of Properties Placed in Service	355,000
Number of Real Estate Properties Placed In Service	2
Properties under construction or contractually committed for construction	'
Construction and Redevelopment Activities	'
Number of real estate properties	8
Square footage of real estate properties (in square feet)	1,200,000
Properties under construction or contractually committed for construction | Baltimore and Washington Corridor	'
Construction and Redevelopment Activities	'
Number of real estate properties	4
Properties under construction or contractually committed for construction | Northern Virginia	'
Construction and Redevelopment Activities	'
Number of real estate properties	3
Properties under construction or contractually committed for construction | San Antonio	'
Construction and Redevelopment Activities	'
Number of real estate properties	1
Properties under or approved for redevelopment	'
Construction and Redevelopment Activities	'
Number of real estate properties	4
Square footage of real estate properties (in square feet)	403,000
Properties under or approved for redevelopment | Baltimore and Washington Corridor	'
Construction and Redevelopment Activities	'
Number of real estate properties	1
Properties under or approved for redevelopment | Greater Philadelphia	'
Construction and Redevelopment Activities	'
Number of real estate properties	2
Properties under or approved for redevelopment | St. Mary's and King George Counties	'
Construction and Redevelopment Activities	'
Number of real estate properties	1

Real_Estate_Joint_Ventures_Det

Real Estate Joint Ventures (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014
	buillding
Consolidated real estate joint ventures	'
Investments in consolidated real estate joint ventures	'
Total Assets	$202,395	[1]
Pledged Assets	116,718	[1]
Total Liabilities	76,808	[1]
LW Redstone Company, LLC	'
Investments in consolidated real estate joint ventures	'
Ownership (as a percent)	85.00%
Total Assets	135,231	[1],[2]
Pledged Assets	68,360	[1],[2]
Total Liabilities	36,272	[1],[2]
Buildings Operated by Joint Ventures Number	4	[2]
M Square Associates, LLC	'
Investments in consolidated real estate joint ventures	'
Ownership (as a percent)	50.00%
Total Assets	60,728	[1],[3]
Pledged Assets	48,358	[1],[3]
Total Liabilities	40,536	[1],[3]
Buildings Operated by Joint Ventures Number	2	[3]
COPT-FD Indian Head, LLC	'
Investments in consolidated real estate joint ventures	'
Ownership (as a percent)	75.00%
Total Assets	$6,436	[1],[4]
[1]	Excludes amounts eliminated in consolidation.
[2]	This joint venture’s property is in Huntsville, Alabama.
[3]	This joint venture’s properties are in College Park, Maryland (in the Baltimore/Washington Corridor).
[4]	This joint venture’s property is in Charles County, Maryland. In 2012, the joint venture exercised its option under a development agreement to require Charles County to repurchase the land parcel at its original acquisition cost. Under the terms of the agreement with Charles County, the repurchase is expected to occur by August 2014.

Mortgage_and_Other_Investing_R2

Mortgage and Other Investing Receivables (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Mortgage and other investing receivables	$55,231	$53,663
Notes Receivable from City of Huntsville	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Mortgage and other investing receivables	45,381	44,055
Mortgage Receivable	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Mortgage and other investing receivables	$9,850	$9,608
Number of mortgage loans receivable	1	'

Prepaid_Expenses_and_Other_Ass2

Prepaid Expenses and Other Assets (Details) (USD $)	Mar. 31, 2014		Dec. 31, 2013
Prepaid Expense and Other Assets [Abstract]	'		'
Prepaid expenses	$13,813,000		$19,308,000
Lease incentives	11,900,000		8,435,000
Furniture, fixtures and equipment, net	7,068,000		6,556,000
Interest rate derivatives	5,038,000		6,594,000
Construction contract costs incurred in excess of billings	4,990,000		2,462,000
Deferred tax asset, net (1)	4,241,000	[1]	4,305,000	[1]
Other equity method investments	2,266,000		2,258,000
Other assets	4,616,000		4,268,000
Prepaid expenses and other assets	53,932,000		54,186,000
Long-term Operating Notes Receivable	'		'
Mortgage and Other Investing Receivables [Line Items]	'		'
Operating Notes Receivable Long-term	1,700,000		1,700,000
Allowance for Notes, Loans and Financing Receivable, Noncurrent	124,000		87,000
Taxable REIT Subsidiary	'		'
Mortgage and Other Investing Receivables [Line Items]	'		'
Deferred Tax Assets, Valuation Allowance	$2,100,000		$2,100,000
[1]	Includes a valuation allowance of $2.1 million.

Debt_Details

Debt (Details) (USD $)

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2013

Dec. 31, 2013

Apr. 01, 2014

Apr. 01, 2014

Mar. 31, 2014

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mortgage and Other Secured Loans:

Mortgage and Other Secured Loans:

Fixed rate mortgage loans

Fixed rate mortgage loans

Variable rate secured loans

Variable rate secured loans

Revolving Credit Facility

Revolving Credit Facility

Term Loan Facilities

Term Loan Facilities

Unsecured notes payable

Unsecured notes payable

4.25% Exchangeable Senior Notes

4.25% Exchangeable Senior Notes

4.25% Exchangeable Senior Notes

Debt in default of payment terms

Debt in default of payment terms

Construction loans

Unsecured senior notes

Unsecured senior notes

Unsecured senior notes

Unsecured senior notes

Revolving Credit Facility

Minimum

Minimum

Maximum

Maximum

Wholly owned subsidiary

Wholly owned subsidiary

Fixed rate mortgage loans

3.60% Senior Notes

3.60% Senior Notes

5.250% Senior Notes

5.250% Senior Notes

Revolving Credit Facility

Term Loan Facilities

Revolving Credit Facility

Term Loan Facilities

Subsequent Event

Subsequent Event

Northern Virginia

Property

Debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum Availability

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$800,000,000

[1]

'

'

'

'

Carrying Value

1,931,831,000

'

1,927,703,000

716,751,000

712,751,000

679,260,000

[2]

675,060,000

[2]

37,491,000

37,691,000

0

[1]

0

[1]

620,000,000

620,000,000

1,677,000

1,700,000

565,000

[3]

'

563,000

[3]

150,000,000

'

19,800,000

347,306,000

[4]

347,244,000

[4]

245,532,000

[5]

245,445,000

[5]

'

'

'

'

'

Stated Interest Rates, low end of range (as a percent)

'

'

'

'

'

3.96%

[6]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stated Interest Rates, high end of range (as a percent)

'

'

'

'

'

7.87%

[6]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Description of variable rate basis

'

'

'

'

'

'

'

'LIBOR

[7]

'

'LIBOR

[1]

'

'LIBOR

[8]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Variable rate, spread (as a percent)

'

'

'

'

'

'

'

2.25%

[7]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.98%

[1]

1.10%

[8]

1.75%

[1]

2.60%

[8]

Stated interest rate (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

0.00%

[9]

'

4.25%

'

'

5.65%

'

'

3.60%

'

5.25%

'

'

'

'

'

'

Unamortized premium included in carrying value

'

'

'

'

'

62,000

69,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Maximum Borrowing Capacity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

26,200,000

'

'

'

'

'

'

'

'

'

Weighted average interest rate (as a percent)

'

'

'

'

'

6.12%

'

'

'

'

'

1.78%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate on debt (as a percent)

'

'

'

'

'

'

'

2.41%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional borrowing capacity available provided there is no default under the agreement

'

'

'

'

'

'

'

'

'

'

'

180,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument, face amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

350,000,000

'

250,000,000

'

'

'

'

'

'

Unamortized discount included in carrying value

'

'

'

'

'

'

'

'

'

'

'

'

'

734,000

761,000

10,000

'

12,000

'

'

'

2,700,000

2,800,000

4,500,000

4,600,000

'

'

'

'

'

Effective interest rate, including amortization of issuance costs (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.05%

'

'

'

'

'

3.70%

'

5.49%

'

'

'

'

'

'

Exchange rate per $1000 principal amount (in common shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20.8513

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Convertible debt principal amount, basis for exchange

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exchange price per common share based on exchange rate (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$47.96

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal amount of debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

575,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense at stated interest rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,000

2,304,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense associated with amortization of discount

171,000

710,000

'

'

'

'

'

'

'

'

'

'

'

'

'

3,000

864,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Total interest expenses

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9,000

3,168,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of properties pledged as collateral on loan in default

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

Capitalized interest costs

$1,600,000

$2,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

No borrowings were outstanding on this facility during the three months ended March 31, 2014.

[2]

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 $62,000 as of March 31, 2014 and $69,000 as of December 31, 2013.

[3]

As described further in our 2013 Annual Report on Form 10-K, these notes have an exchange settlement feature that provides that the notes may, under certain circumstances, be exchangeable for cash and, at COPLP’s discretion, COPT common shares at an exchange rate (subject to adjustment) of 20.8513 shares per one thousand dollar principal amount of the notes (exchange rate is as of March 31, 2014 and is equivalent to an exchange price of $47.96 per common share). The carrying value of these notes included a principal amount of $575,000 and an unamortized discount totaling $10,000 as of March 31, 2014 and $12,000 as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 6.05%. Because the closing price of our common shares as of March 31, 2014 and December 31, 2013 was less than the exchange price per common share applicable to these notes, the if-converted value of the notes did not exceed the principal amount. The table below sets forth interest expense recognized on these notes before deductions for amounts capitalized (in thousands): For the Three Months Ended March 31, 2014 2013Interest expense at stated interest rate $6 $2,304Interest expense associated with amortization of discount 3 864Total $9 $3,168

[4]

The carrying value of these notes included a principal amount of $350.0 million and an unamortized discount totaling $2.7 million as of March 31, 2014 and $2.8 million as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 3.70%.

[5]

The carrying value of these notes included a principal amount of $250.0 million and an unamortized discount totaling $4.5 million as of March 31, 2014 and $4.6 million as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 5.49%.

[6]

The weighted average interest rate on these loans was 6.12% as of March 31, 2014.

[7]

The interest rate on the loan outstanding was 2.41% as of March 31, 2014.

[8]

The weighted average interest rate on these loans was 1.78% as of March 31, 2014.

[9]

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 $734,000 as of March 31, 2014 and $761,000 as of December 31, 2013.

Debt_Details_2

Debt (Details 2) (USD $)	Mar. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Carrying amount and estimated fair value of debt	'		'
Carrying Value	$1,931,831		$1,927,703
4.25% Exchangeable Senior Notes	'		'
Carrying amount and estimated fair value of debt	'		'
Carrying Value	565	[1]	563	[1]
Carrying Amount	'		'
Carrying amount and estimated fair value of debt	'		'
Variable-rate debt	657,491		657,691
Carrying Value	1,931,831		1,927,703
Carrying Amount | Unsecured senior notes	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	592,838		592,689
Carrying Amount | 4.25% Exchangeable Senior Notes	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	565		563
Carrying Amount | Other fixed-rate debt	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	680,937		676,760
Total Estimated Fair Value	'		'
Carrying amount and estimated fair value of debt	'		'
Variable-rate debt	657,420		657,527
Carrying Value	1,911,122		1,884,473
Total Estimated Fair Value | Unsecured senior notes	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	584,178		575,374
Total Estimated Fair Value | 4.25% Exchangeable Senior Notes	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	575		575
Total Estimated Fair Value | Other fixed-rate debt	'		'
Carrying amount and estimated fair value of debt	'		'
Fixed-rate debt	$668,949		$650,997
[1]	As described further in our 2013 Annual Report on Form 10-K, these notes have an exchange settlement feature that provides that the notes may, under certain circumstances, be exchangeable for cash and, at COPLP’s discretion, COPT common shares at an exchange rate (subject to adjustment) of 20.8513 shares per one thousand dollar principal amount of the notes (exchange rate is as of March 31, 2014 and is equivalent to an exchange price of $47.96 per common share). The carrying value of these notes included a principal amount of $575,000 and an unamortized discount totaling $10,000 as of March 31, 2014 and $12,000 as of December 31, 2013. The effective interest rate under the notes, including amortization of the issuance costs, was 6.05%. Because the closing price of our common shares as of March 31, 2014 and December 31, 2013 was less than the exchange price per common share applicable to these notes, the if-converted value of the notes did not exceed the principal amount. The table below sets forth interest expense recognized on these notes before deductions for amounts capitalized (in thousands): For the Three Months Ended March 31, 2014 2013Interest expense at stated interest rate $6 $2,304Interest expense associated with amortization of discount 3 864Total $9 $3,168

Interest_Rate_Derivatives_Deta

Interest Rate Derivatives (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Fair values of interest rate swap derivatives	'		'	'
Fair value of interest rate swaps	$1,842,000		'	$3,285,000
Fair value of interest rate derivatives and balance sheet classification	'		'	'
Interest rate derivatives	5,038,000		'	6,594,000
Effect of interest rate derivatives on consolidated statements of operations and comprehensive income	'		'	'
Amount of (losses) gains recognized in accumulated other comprehensive income (loss) (“AOCI”) (effective portion)	-2,123,000		462,000	'
Amount of losses reclassified from AOCI into interest expense (effective portion)	695,000		658,000	'
Interest rate swaps	'		'	'
Fair value of interest rate derivatives and balance sheet classification	'		'	'
Interest rate derivatives	5,038,000		'	6,594,000
Fair value of Interest rate swaps classified as interest rate derivatives	-3,196,000		'	-3,309,000
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	-3,000,000		'	'
Interest rate derivatives in liability position, fair value	3,200,000		'	'
Termination value to settle obligations under interest rate derivative agreements	3,400,000		'	'
Designated | Interest rate swap, effective date January 3, 2012, swap one	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.61%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-195,000		'	-279,000
Designated | Interest rate swap, effective date January 3, 2012, swap two	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.61%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-194,000		'	-277,000
Designated | Interest rate swap, effective date January 3, 2012, swap three	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.83%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-807,000		'	-861,000
Designated | Interest rate swap, effective date January 3, 2012, swap four	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.83%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-807,000		'	-861,000
Designated | Interest rate swap, effective date November 2, 2010	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	37,491,000	[1]	'	'
Fixed rate (as a percent)	3.83%		'	'
Floating rate index	'One-Month LIBOR + 2.25%		'	'
Derivative, Basis Spread on Variable Rate	2.25%		'	'
Fair value of interest rate swaps	-742,000		'	-832,000
Notional amount of interest rate derivatives after scheduled amortization	36,200,000		'	'
Designated | Interest rate swap, effective date September 2, 2014, swap one	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.81%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-220,000		'	-94,000
Designated | Interest rate swap, effective date September 2, 2014, swap two	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	0.81%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	-231,000		'	-105,000
Designated | Interest rate swap, effective date September 1, 2015, swap one	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	1.67%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	2,604,000		'	3,377,000
Designated | Interest rate swap, effective date September 1, 2015, swap two	'		'	'
Fair values of interest rate swap derivatives	'		'	'
Notional Amount	100,000,000		'	'
Fixed rate (as a percent)	1.73%		'	'
Floating rate index	'One-Month LIBOR		'	'
Fair value of interest rate swaps	$2,434,000		'	$3,217,000
[1]	The notional amount of this instrument is scheduled to amortize to $36.2 million.

Redeemable_Noncontrolling_Inte2

Redeemable Noncontrolling Interests (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Redeemable Noncontrolling Interest [Roll Forward]	'	'
Beginning balance	$17,758	$10,298
Distribution to noncontrolling interest	-68	0
Net income (loss) attributable to noncontrolling interest	504	-790
Adjustment to arrive at fair value of interest	-540	848
Ending balance	$17,654	$10,356

Equity_Details

Equity (Details)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Equity [Abstract]	'	'
Number of operating partnerships units converted into common shares (in units)	48,498	248,644
Number of common shares for each converted common unit (in shares)	1	'

Information_by_Business_Segmen2

Information by Business Segment (Details) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
	segment
Segment Reporting [Abstract]	'	'	'
Number of primary office property segments	10	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	$124,896	$122,077	'
Property operating expenses	49,752	44,066	'
NOI from real estate operations	75,144	78,011	'
Segment assets	3,605,897	3,685,099	3,629,952
Operating Segment Total	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	124,896	122,077	'
Property operating expenses	49,752	44,066	'
NOI from real estate operations	75,144	78,011	'
Additions to long-lived assets	13,729	5,854	'
Transfers from non-operating properties	56,940	131,596	'
Segment assets	2,932,749	3,055,876	'
Baltimore and Washington Corridor	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	61,113	58,660	'
Property operating expenses	23,597	20,053	'
NOI from real estate operations	37,516	38,607	'
Additions to long-lived assets	5,741	2,760	'
Transfers from non-operating properties	-169	22,997	'
Segment assets	1,237,796	1,279,794	'
Northern Virginia	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	24,968	22,942	'
Property operating expenses	8,973	7,817	'
NOI from real estate operations	15,995	15,125	'
Additions to long-lived assets	3,495	1,544	'
Transfers from non-operating properties	26,588	9,839	'
Segment assets	636,895	574,970	'
San Antonio	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	8,479	7,757	'
Property operating expenses	4,474	3,888	'
NOI from real estate operations	4,005	3,869	'
Additions to long-lived assets	-6	10	'
Transfers from non-operating properties	0	0	'
Segment assets	117,812	119,145	'
Huntsville	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	2,555	740	'
Property operating expenses	653	182	'
NOI from real estate operations	1,902	558	'
Additions to long-lived assets	2,507	0	'
Transfers from non-operating properties	20,102	24,240	'
Segment assets	99,378	52,361	'
Washington, DC - Capitol Riverfront	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	3,634	4,244	'
Property operating expenses	1,765	1,949	'
NOI from real estate operations	1,869	2,295	'
Additions to long-lived assets	63	157	'
Transfers from non-operating properties	0	0	'
Segment assets	97,843	102,928	'
St. Mary's and King George Counties	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	4,316	3,992	'
Property operating expenses	1,504	1,193	'
NOI from real estate operations	2,812	2,799	'
Additions to long-lived assets	839	275	'
Transfers from non-operating properties	0	6	'
Segment assets	95,645	97,346	'
Greater Baltimore	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	11,496	10,719	'
Property operating expenses	5,476	4,168	'
NOI from real estate operations	6,020	6,551	'
Additions to long-lived assets	1,012	702	'
Transfers from non-operating properties	7,154	113	'
Segment assets	307,699	317,953	'
Greater Philadelphia	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	3,340	2,487	'
Property operating expenses	1,300	838	'
NOI from real estate operations	2,040	1,649	'
Additions to long-lived assets	11	0	'
Transfers from non-operating properties	3,176	7,050	'
Segment assets	94,428	85,017	'
Colorado Springs	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	18	6,682	'
Property operating expenses	-9	2,437	'
NOI from real estate operations	27	4,245	'
Additions to long-lived assets	0	315	'
Transfers from non-operating properties	11	1,783	'
Segment assets	7	177,728	'
Other	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	2,576	2,501	'
Property operating expenses	331	225	'
NOI from real estate operations	2,245	2,276	'
Additions to long-lived assets	55	91	'
Transfers from non-operating properties	0	0	'
Segment assets	79,535	81,714	'
Wholesale Data Center	'	'	'
Segment financial information for real estate operations	'	'	'
Revenues from real estate operations	2,401	1,353	'
Property operating expenses	1,688	1,316	'
NOI from real estate operations	713	37	'
Additions to long-lived assets	12	0	'
Transfers from non-operating properties	78	65,568	'
Segment assets	$165,711	$166,920	'

Information_by_Business_Segmen3

Information by Business Segment (Details 2) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Reconciliation of segment revenues to total revenues	'	'
Segment revenues from real estate operations	$124,896	$122,077
Construction contract and other service revenues	21,790	14,262
Less: Revenues from discontinued operations (Note 15)	-19	-10,120
Total revenues	146,667	126,219
Reconciliation of segment property operating expenses to property operating expenses	'	'
Segment property operating expenses	49,752	44,066
Less: Property operating expenses from discontinued operations (Note 15)	20	-3,678
Total property operating expenses	49,772	40,388
Computation of net operating income from service operations	'	'
Construction contract and other service revenues	21,790	14,262
Construction contract and other service expenses	-18,624	-13,477
NOI from service operations	3,166	785
Reconciliation of NOI from real estate operations and NOI from service operations to (loss) income from continuing operations	'	'
NOI from real estate operations	75,144	78,011
NOI from service operations	3,166	785
Interest and other income	1,285	946
Equity in income of unconsolidated entities	60	41
Income tax expense	-64	-16
Other adjustments:	'	'
Depreciation and other amortization associated with real estate operations	-43,596	-27,010
General, administrative and leasing expenses	-8,143	-7,820
Business development expenses and land carry costs	-1,326	-1,359
Interest expense on continuing operations	-20,827	-20,290
NOI from discontinued operations	-39	-6,442
Loss on early extinguishment of debt	0	-5,184
Income from continuing operations	$5,660	$11,662

Information_by_Business_Segmen4

Information by Business Segment (Details 3) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
In Thousands, unless otherwise specified
Reconciliation of segment assets to total assets	'	'	'
Assets	$3,605,897	$3,629,952	$3,685,099
Segment assets	'	'	'
Reconciliation of segment assets to total assets	'	'	'
Assets	2,932,749	'	3,055,876
Non-operating property assets	'	'	'
Reconciliation of segment assets to total assets	'	'	'
Assets	503,030	'	490,083
Other assets	'	'	'
Reconciliation of segment assets to total assets	'	'	'
Assets	$170,118	'	$139,140

ShareBased_Compensation_Detail

Share-Based Compensation (Details) (USD $)	3 Months Ended				0 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2014	Mar. 06, 2014	Mar. 31, 2014
			Restricted shares	Options	2014 PSU Grants	2014 PSU Grants
					Performance share units	Performance share units
						Percentile_Rank
Share-Based Compensation	'	'	'	'	'	'
Stock awards granted (in shares or units)	'	'	177,356	'	49,103	'
Aggregate grant date fair value	'	'	$4,700,000	'	$1,700,000	'
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%	'	'	'	'	'	2
Performance period of the award (in years)	'	'	'	'	'	'3 years
Assumptions used to value stock awards	'	'	'	'	'	'
Weighted average grant date fair value (in dollars per share)	'	'	$26.63	'	'	$35.09
Baseline value per common share (in dollars per share)	'	'	'	'	'	$26.52
Expected volatility of common shares (as a percent)	'	'	'	'	'	28.60%
Risk-free interest rate (as a percent)	'	'	'	'	'	0.66%
Other Share-based Compensation Additional Disclosures	'	'	'	'	'	'
Shares vested (in shares)	'	'	110,356	'	'	'
Weighted average fair value of shares vested (in dollars per share)	'	'	$29.52	'	'	'
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed	'	'	2,900,000	'	'	'
Options	'	'	'	'	'	'
Exercised (in shares)	26,614	16,453	'	26,614	'	'
Weighted average exercise price (in dollars per share)	'	'	'	$21.34	'	'
Aggregate intrinsic value of options exercised (in dollars)	'	'	'	$126,000	'	'

Income_Taxes_Details

Income Taxes (Details) (Taxable REIT Subsidiary, USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Taxable REIT Subsidiary	'	'
Deferred income tax (expense) benefit	'	'
Federal	($53)	($13)
State	-11	-3
Total income tax expense	($64)	($16)
Effective tax rate (as a percent)	38.10%	36.00%

Discontinued_Operations_Detail

Discontinued Operations (Details) (USD $)	3 Months Ended		0 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 12, 2013	Dec. 23, 2013	Dec. 23, 2013
			December 2013 Colorado Springs Portfolio Disposition	Baltimore and Washington Corridor	Colorado Springs
			Property	Property	Property
Properties	'	'	'	'	'
Number of properties sold	'	'	15	'	'
Number of properties transferred	'	'	'	9	5
Revenue from real estate operations	$19	$10,120	'	'	'
Property operating expenses	20	-3,678	'	'	'
Depreciation and amortization	0	-1,242	'	'	'
Impairment losses	-1	-1,857	'	'	'
General, administrative and leasing expenses	0	-1	'	'	'
Interest expense	0	-2,081	'	'	'
Loss on sales of real estate	-4	0	'	'	'
Loss on early extinguishment of debt	-23	0	'	'	'
Discontinued operations	$11	$1,261	'	'	'

Earnings_Per_Share_EPS_and_Ear2

Earnings Per Share ("EPS") and Earnings Per Unit ("EPU") (Details) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Numerator:	'		'
Income from continuing operations	$5,660		$11,662
Gain on sales of real estate, net	0		2,354
Preferred share/unit dividends/distributions	-4,490		-6,106
(Income) loss from continuing operations attributable to noncontrolling interests	-932		-167
Income from continuing operations attributable to restricted shares	-121		-118
Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders	117		7,625
Discontinued operations	11		1,261
Discontinued operations attributable to noncontrolling interests	2		-90
Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	130		8,796
Denominator (all weighted averages):	'		'
Denominator for basic EPS (common shares)	87,080		81,397
Dilutive effect of share-based compensation awards	112		52
Denominator for diluted EPS (common shares)	87,192		81,449
Basic EPS:	'		'
Income from continuing operations (in dollars per share/unit)	$0	[1]	$0.09	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.02	[1]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[1]	$0.11	[1]
Diluted EPS:	'		'
Income from continuing operations (in dollars per share/unit)	$0	[1]	$0.09	[1]
Discontinued operations (in dollars per share/unit)	$0	[1]	$0.02	[1]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[1]	$0.11	[1]
Corporate Office Properties, L.P.	'		'
Numerator:	'		'
Income from continuing operations	5,660		11,662
Gain on sales of real estate, net	0		2,354
Preferred share/unit dividends/distributions	-4,655		-6,271
(Income) loss from continuing operations attributable to noncontrolling interests	-739		369
Income from continuing operations attributable to restricted shares	-121		-118
Numerator for basic and diluted EPS from continuing operations attributable to COPT common shareholders	145		7,996
Discontinued operations	11		1,261
Discontinued operations attributable to noncontrolling interests	2		-33
Numerator for basic and diluted EPS on net income attributable to COPT common shareholders	$158		$9,224
Denominator (all weighted averages):	'		'
Denominator for basic EPS (common shares)	91,038		85,290
Dilutive effect of share-based compensation awards	112		52
Denominator for diluted EPS (common shares)	91,150		85,342
Basic EPS:	'		'
Income from continuing operations (in dollars per share/unit)	$0	[2]	$0.09	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.02	[2]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[2]	$0.11	[2]
Diluted EPS:	'		'
Income from continuing operations (in dollars per share/unit)	$0	[2]	$0.09	[2]
Discontinued operations (in dollars per share/unit)	$0	[2]	$0.02	[2]
Net income attributable to COPT common shareholders (in dollars per share/unit)	$0	[2]	$0.11	[2]
[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_Details

Earnings Per Share ("EPS") (Details 2)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Conversion of common units	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	3,958	3,893
Conversion of Series I Preferred Units	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	176	176
Conversion of Series K Preferred Shares	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	434	434
Weighted average restricted shares	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	390	409
Weighted average options	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	588	621
Corporate Office Properties, L.P. | Weighted average restricted shares	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	390	409
Corporate Office Properties, L.P. | Weighted average options	'	'
Antidilutive securities	'	'
Antidilutive securities excluded from computation of diluted earnings per share (in shares)	588	621
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
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)	434	434

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (USD $)	1 Months Ended
	Aug. 31, 2010	Mar. 31, 2014
		Property
Tax incremental financing obligation	'	'
The amount of tax incremental financing bonds issued by Anne Arundel County, Maryland	$30,000,000	'
Liability recognized with regard to tax incremental financing obligation at end of current period	'	1,900,000
Environmental Indemnity Agreement	'	'
Number of lease properties which were provided environmental indemnifications	'	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
Nonrecourse loan guarantees of unconsolidated partnership	'	'
Joint Ventures	'	'
Maximum approximate amount required to be paid under the guarantees for outstanding debt, excluding interest and penalties	'	$5,600,000