Consolidated Statements of Cash Flows - USD ($)  $ in Thousands  | 
9 Months Ended | 
Sep. 30, 2016  | 
Sep. 30, 2015  | 
| Cash flows from operating activities | 
 
 | 
 
 | 
| Revenues from real estate operations received | 
$ 391,511
 | 
$ 373,607
 | 
| Construction contract and other service revenues received | 
54,399
 | 
104,817
 | 
| Property operating expenses paid | 
(154,203)
 | 
(146,274)
 | 
| Construction contract and other service expenses paid | 
(33,169)
 | 
(112,614)
 | 
| General, administrative, leasing, business development and land carry costs paid | 
(27,879)
 | 
(29,620)
 | 
| Interest expense paid | 
(61,662)
 | 
(46,278)
 | 
| Interest and other income received | 
472
 | 
4,130
 | 
| Other | 
504
 | 
(26)
 | 
| Net cash provided by operating activities | 
169,973
 | 
147,742
 | 
| Cash flows from investing activities | 
 
 | 
 
 | 
| Construction, development and redevelopment | 
(121,297)
 | 
(174,434)
 | 
| Acquisitions of operating properties and related intangible assets | 
0
 | 
(202,866)
 | 
| Tenant improvements on operating properties | 
(26,055)
 | 
(18,129)
 | 
| Other capital improvements on operating properties | 
(22,063)
 | 
(12,610)
 | 
| Proceeds from dispositions of properties | 
210,661
 | 
45,066
 | 
| Proceeds from partial sale of properties, net of related debt | 
43,686
 | 
0
 | 
| Investing receivables payments received | 
0
 | 
5,114
 | 
| Leasing costs paid | 
(6,024)
 | 
(8,603)
 | 
| Other | 
(991)
 | 
(4,827)
 | 
| Net cash provided by (used in) investing activities | 
77,917
 | 
(371,289)
 | 
| Proceeds from debt | 
 
 | 
 
 | 
| Revolving Credit Facility | 
362,500
 | 
422,000
 | 
| Unsecured senior notes | 
0
 | 
296,580
 | 
| Other debt proceeds | 
105,000
 | 
50,000
 | 
| Repayments of debt | 
 
 | 
 
 | 
| Revolving Credit Facility | 
(406,000)
 | 
(418,000)
 | 
| Scheduled principal amortization | 
(4,454)
 | 
(5,011)
 | 
| Other debt repayments | 
(203,056)
 | 
(50,681)
 | 
| Deferred financing costs paid | 
(825)
 | 
(5,377)
 | 
| Net proceeds from issuance of common shares/units | 
(46)
 | 
28,567
 | 
| Common share/unit dividends/distributions paid | 
(78,072)
 | 
(77,641)
 | 
| Preferred share/unit dividends/distributions paid | 
(10,657)
 | 
(10,657)
 | 
| Distributions paid to noncontrolling interests in COPLP | 
(3,476)
 | 
(3,581)
 | 
| Distributions paid to redeemable noncontrolling interests | 
(14,329)
 | 
0
 | 
| Redemption of vested equity awards | 
(2,179)
 | 
(2,330)
 | 
| Other | 
(5,032)
 | 
(2,559)
 | 
| Net cash (used in) provided by financing activities | 
(260,626)
 | 
221,310
 | 
| Net decrease in cash and cash equivalents | 
(12,736)
 | 
(2,237)
 | 
| Cash and cash equivalents | 
 
 | 
 
 | 
| Beginning of period | 
60,310
 | 
6,077
 | 
| End of period | 
47,574
 | 
3,840
 | 
| Reconciliation of net (loss) income to net cash provided by operating activities: | 
 
 | 
 
 | 
| Net (loss) income | 
(10,948)
 | 
126,261
 | 
| Adjustments to reconcile net (loss) income to net cash provided by operating activities: | 
 
 | 
 
 | 
| Depreciation and other amortization | 
101,429
 | 
105,397
 | 
| Impairment losses | 
99,797
 | 
3,779
 | 
| Losses on interest rate derivatives | 
347
 | 
0
 | 
| Amortization of deferred financing costs and net debt discounts | 
4,456
 | 
4,144
 | 
| Increase in deferred rent receivable | 
(930)
 | 
(11,939)
 | 
| Gain on sales of real estate | 
(34,101)
 | 
(4,000)
 | 
| Share-based compensation | 
5,637
 | 
4,949
 | 
| Loss (gain) on early extinguishment of debt | 
34
 | 
(86,075)
 | 
| Other | 
(2,761)
 | 
1,922
 | 
| Operating changes in assets and liabilities: | 
 
 | 
 
 | 
| Decrease in accounts receivable | 
3,658
 | 
6,526
 | 
| Decrease (increase) in restricted cash and marketable securities | 
18
 | 
(1,102)
 | 
| Increase in prepaid expenses and other assets, net | 
(19,778)
 | 
(5,228)
 | 
| Increase (decrease) in accounts payable, accrued expenses and other liabilities | 
31,523
 | 
(655)
 | 
| (Decrease) increase in rents received in advance and security deposits | 
(8,408)
 | 
3,763
 | 
| Net cash provided by operating activities | 
169,973
 | 
147,742
 | 
| Supplemental schedule of non-cash investing and financing activities: | 
 
 | 
 
 | 
| Increase (decrease) in accrued capital improvements, leasing and other investing activity costs | 
9,963
 | 
(11,722)
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contributed in a joint venture | 
22,600
 | 
0
 | 
| Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interest | 
6,683
 | 
0
 | 
| Decrease in properties, net | 
(114,597)
 | 
0
 | 
| Increase in investment in unconsolidated real estate joint venture | 
25,680
 | 
0
 | 
| Decrease in debt | 
59,534
 | 
0
 | 
| Other net decreases in assets and liabilities | 
3,619
 | 
0
 | 
| Debt assumed on acquisition of operating property | 
0
 | 
55,490
 | 
| Other liabilities assumed on acquisition of operating properties | 
0
 | 
5,265
 | 
| Decrease in property in connection with surrender of property in settlement of debt | 
0
 | 
(82,738)
 | 
| Decrease in debt in connection with surrender of property in settlement of debt | 
0
 | 
(150,000)
 | 
| Decrease in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests | 
(13,817)
 | 
(4,263)
 | 
| Equity in other comprehensive loss of an equity method investee | 
(184)
 | 
(264)
 | 
| Dividends/distributions payable | 
30,225
 | 
30,182
 | 
| Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares | 
1,167
 | 
2,151
 | 
| Adjustments to noncontrolling interests resulting from changes in COPLP ownership | 
42
 | 
591
 | 
| Increase in redeemable noncontrolling interest and decrease in equity to carry redeemable noncontrolling interest at fair value | 
516
 | 
599
 | 
| Corporate Office Properties, L.P. | 
 
 | 
 
 | 
| Cash flows from operating activities | 
 
 | 
 
 | 
| Revenues from real estate operations received | 
391,511
 | 
373,607
 | 
| Construction contract and other service revenues received | 
54,399
 | 
104,817
 | 
| Property operating expenses paid | 
(154,203)
 | 
(146,274)
 | 
| Construction contract and other service expenses paid | 
(33,169)
 | 
(112,614)
 | 
| General, administrative, leasing, business development and land carry costs paid | 
(27,879)
 | 
(29,620)
 | 
| Interest expense paid | 
(61,662)
 | 
(46,278)
 | 
| Interest and other income received | 
472
 | 
4,130
 | 
| Other | 
504
 | 
(26)
 | 
| Net cash provided by operating activities | 
169,973
 | 
147,742
 | 
| Cash flows from investing activities | 
 
 | 
 
 | 
| Construction, development and redevelopment | 
(121,297)
 | 
(174,434)
 | 
| Acquisitions of operating properties and related intangible assets | 
0
 | 
(202,866)
 | 
| Tenant improvements on operating properties | 
(26,055)
 | 
(18,129)
 | 
| Other capital improvements on operating properties | 
(22,063)
 | 
(12,610)
 | 
| Proceeds from dispositions of properties | 
210,661
 | 
45,066
 | 
| Proceeds from partial sale of properties, net of related debt | 
43,686
 | 
0
 | 
| Investing receivables payments received | 
0
 | 
5,114
 | 
| Leasing costs paid | 
(6,024)
 | 
(8,603)
 | 
| Other | 
(991)
 | 
(4,827)
 | 
| Net cash provided by (used in) investing activities | 
77,917
 | 
(371,289)
 | 
| Proceeds from debt | 
 
 | 
 
 | 
| Revolving Credit Facility | 
362,500
 | 
422,000
 | 
| Unsecured senior notes | 
0
 | 
296,580
 | 
| Other debt proceeds | 
105,000
 | 
50,000
 | 
| Repayments of debt | 
 
 | 
 
 | 
| Revolving Credit Facility | 
(406,000)
 | 
(418,000)
 | 
| Scheduled principal amortization | 
(4,454)
 | 
(5,011)
 | 
| Other debt repayments | 
(203,056)
 | 
(50,681)
 | 
| Deferred financing costs paid | 
(825)
 | 
(5,377)
 | 
| Net proceeds from issuance of common shares/units | 
(46)
 | 
28,567
 | 
| Common share/unit dividends/distributions paid | 
(81,053)
 | 
(80,727)
 | 
| Preferred share/unit dividends/distributions paid | 
(11,152)
 | 
(11,152)
 | 
| Distributions paid to redeemable noncontrolling interests | 
(14,329)
 | 
0
 | 
| Redemption of vested equity awards | 
(2,179)
 | 
(2,330)
 | 
| Other | 
(5,032)
 | 
(2,559)
 | 
| Net cash (used in) provided by financing activities | 
(260,626)
 | 
221,310
 | 
| Net decrease in cash and cash equivalents | 
(12,736)
 | 
(2,237)
 | 
| Cash and cash equivalents | 
 
 | 
 
 | 
| Beginning of period | 
60,310
 | 
6,077
 | 
| End of period | 
47,574
 | 
3,840
 | 
| Reconciliation of net (loss) income to net cash provided by operating activities: | 
 
 | 
 
 | 
| Net (loss) income | 
(10,948)
 | 
126,261
 | 
| Adjustments to reconcile net (loss) income to net cash provided by operating activities: | 
 
 | 
 
 | 
| Depreciation and other amortization | 
101,429
 | 
105,397
 | 
| Impairment losses | 
99,797
 | 
3,779
 | 
| Losses on interest rate derivatives | 
347
 | 
0
 | 
| Amortization of deferred financing costs and net debt discounts | 
4,456
 | 
4,144
 | 
| Increase in deferred rent receivable | 
(930)
 | 
(11,939)
 | 
| Gain on sales of real estate | 
(34,101)
 | 
(4,000)
 | 
| Share-based compensation | 
5,637
 | 
4,949
 | 
| Loss (gain) on early extinguishment of debt | 
34
 | 
(86,075)
 | 
| Other | 
(2,761)
 | 
1,922
 | 
| Operating changes in assets and liabilities: | 
 
 | 
 
 | 
| Decrease in accounts receivable | 
3,658
 | 
6,526
 | 
| Decrease (increase) in restricted cash and marketable securities | 
(495)
 | 
(1,485)
 | 
| Increase in prepaid expenses and other assets, net | 
(19,778)
 | 
(5,228)
 | 
| Increase (decrease) in accounts payable, accrued expenses and other liabilities | 
32,036
 | 
(272)
 | 
| (Decrease) increase in rents received in advance and security deposits | 
(8,408)
 | 
3,763
 | 
| Net cash provided by operating activities | 
169,973
 | 
147,742
 | 
| Supplemental schedule of non-cash investing and financing activities: | 
 
 | 
 
 | 
| Increase (decrease) in accrued capital improvements, leasing and other investing activity costs | 
9,963
 | 
(11,722)
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contributed in a joint venture | 
22,600
 | 
0
 | 
| Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interest | 
6,683
 | 
0
 | 
| Decrease in properties, net | 
(114,597)
 | 
0
 | 
| Increase in investment in unconsolidated real estate joint venture | 
25,680
 | 
0
 | 
| Decrease in debt | 
59,534
 | 
0
 | 
| Other net decreases in assets and liabilities | 
3,619
 | 
0
 | 
| Debt assumed on acquisition of operating property | 
0
 | 
55,490
 | 
| Other liabilities assumed on acquisition of operating properties | 
0
 | 
5,265
 | 
| Decrease in property in connection with surrender of property in settlement of debt | 
0
 | 
(82,738)
 | 
| Decrease in debt in connection with surrender of property in settlement of debt | 
0
 | 
(150,000)
 | 
| Decrease in fair value of derivatives applied to accumulated other comprehensive loss and noncontrolling interests | 
(13,817)
 | 
(4,263)
 | 
| Equity in other comprehensive loss of an equity method investee | 
(184)
 | 
(264)
 | 
| Dividends/distributions payable | 
30,225
 | 
30,182
 | 
| Increase in redeemable noncontrolling interest and decrease in equity to carry redeemable noncontrolling interest at fair value | 
$ 516
 | 
$ 599
 |