Consolidated Statements of Cash Flows  $ in Thousands  | 
12 Months Ended | 
| 
 Dec. 31, 2017  
USD ($) 
 | 
 Dec. 31, 2016  
USD ($) 
 | 
 Dec. 31, 2015  
USD ($) 
 | 
| Cash flows from operating activities | 
 
 | 
 
 | 
 
 | 
| Revenues from real estate operations received | 
$ 510,985
 | 
$ 514,098
 | 
$ 503,503
 | 
| Construction contract and other service revenues received | 
102,531
 | 
76,824
 | 
117,107
 | 
| Property operating expenses paid | 
(186,478)
 | 
(197,254)
 | 
(190,281)
 | 
| Construction contract and other service expenses paid | 
(82,707)
 | 
(46,318)
 | 
(124,481)
 | 
| General, administrative, leasing, business development and land carry costs paid | 
(32,673)
 | 
(34,877)
 | 
(38,113)
 | 
| Interest expense paid | 
(73,079)
 | 
(78,158)
 | 
(65,816)
 | 
| Lease incentives paid | 
(9,725)
 | 
(2,760)
 | 
(1,724)
 | 
| Income taxes paid | 
(31)
 | 
(5)
 | 
(8)
 | 
| Other | 
1,831
 | 
988
 | 
3,821
 | 
| Net cash provided by operating activities | 
230,654
 | 
232,538
 | 
204,008
 | 
| Cash flows from investing activities | 
 
 | 
 
 | 
 
 | 
| Construction, development and redevelopment | 
(200,504)
 | 
(161,519)
 | 
(234,346)
 | 
| Acquisitions of operating properties and related intangible assets | 
0
 | 
0
 | 
(202,866)
 | 
| Tenant improvements on operating properties | 
(33,409)
 | 
(34,275)
 | 
(29,413)
 | 
| Other capital improvements on operating properties | 
(22,882)
 | 
(26,345)
 | 
(23,147)
 | 
| Proceeds from dispositions of properties | 
180,839
 | 
262,866
 | 
193,735
 | 
| Proceeds from partial sales of properties, net of related debt | 
0
 | 
43,681
 | 
0
 | 
| Leasing costs paid | 
(14,581)
 | 
(10,296)
 | 
(13,710)
 | 
| Other | 
827
 | 
(2,663)
 | 
2,215
 | 
| Net cash (used in) provided by investing activities | 
(89,710)
 | 
71,449
 | 
(307,532)
 | 
| Proceeds from debt | 
 
 | 
 
 | 
 
 | 
| Revolving Credit Facility | 
352,000
 | 
495,500
 | 
522,000
 | 
| Unsecured senior notes | 
0
 | 
0
 | 
296,580
 | 
| Other debt proceeds | 
0
 | 
255,000
 | 
164,000
 | 
| Repayments of debt | 
 
 | 
 
 | 
 
 | 
| Revolving Credit Facility | 
(226,000)
 | 
(539,000)
 | 
(561,500)
 | 
| Scheduled principal amortization | 
(3,862)
 | 
(5,395)
 | 
(6,728)
 | 
| Other debt repayments | 
(200,200)
 | 
(323,107)
 | 
(155,307)
 | 
| Deferred financing costs paid | 
(500)
 | 
(825)
 | 
(7,522)
 | 
| Net proceeds from issuance of common shares | 
69,534
 | 
109,069
 | 
28,567
 | 
| Redemption of preferred shares | 
(199,083)
 | 
0
 | 
0
 | 
| Common share/unit dividends/distributions paid | 
(109,174)
 | 
(104,135)
 | 
(103,638)
 | 
| Preferred share/unit dividends/distributions paid | 
(9,305)
 | 
(14,210)
 | 
(14,210)
 | 
| Distributions paid to noncontrolling interests in COPLP | 
(4,426)
 | 
(4,619)
 | 
(4,752)
 | 
| Distributions paid to redeemable noncontrolling interests | 
(8,215)
 | 
(15,206)
 | 
(2,993)
 | 
| Redemption of vested equity awards | 
(1,973)
 | 
(2,466)
 | 
(2,462)
 | 
| Other | 
2,658
 | 
(5,040)
 | 
5,722
 | 
| Net cash (used in) provided by financing activities | 
(338,546)
 | 
(154,434)
 | 
157,757
 | 
| Net (decrease) increase in cash and cash equivalents | 
(197,602)
 | 
149,553
 | 
54,233
 | 
| Cash and cash equivalents | 
 
 | 
 
 | 
 
 | 
| Beginning of year | 
209,863
 | 
60,310
 | 
6,077
 | 
| End of year | 
12,261
 | 
209,863
 | 
60,310
 | 
| Reconciliation of net income to net cash provided by operating activities: | 
 
 | 
 
 | 
 
 | 
| Net income | 
76,333
 | 
15,655
 | 
188,878
 | 
| Adjustments to reconcile net income to net cash provided by operating activities: | 
 
 | 
 
 | 
 
 | 
| Depreciation and other amortization | 
136,501
 | 
134,870
 | 
142,231
 | 
| Impairment losses | 
15,116
 | 
101,341
 | 
23,523
 | 
| Amortization of deferred financing costs and net debt discounts | 
4,307
 | 
5,885
 | 
5,588
 | 
| Increase in deferred rent receivable | 
(2,651)
 | 
(145)
 | 
(14,969)
 | 
| Gain on sales of real estate | 
(9,890)
 | 
(40,986)
 | 
(68,047)
 | 
| Share-based compensation | 
5,615
 | 
6,843
 | 
6,574
 | 
| Loss (gain) on early extinguishment of debt | 
513
 | 
456
 | 
(86,028)
 | 
| Other | 
(6,121)
 | 
(4,295)
 | 
528
 | 
| Changes in operating assets and liabilities: | 
 
 | 
 
 | 
 
 | 
| Decrease (increase) in accounts receivable | 
2,783
 | 
(5,262)
 | 
1,331
 | 
| Decrease (increase) in restricted cash and marketable securities | 
2,015
 | 
(365)
 | 
(1,241)
 | 
| Decrease (increase) in prepaid expenses and other assets, net | 
5,737
 | 
(17,272)
 | 
2,853
 | 
| Increase (decrease) in accounts payable, accrued expenses and other liabilities | 
4,309
 | 
43,163
 | 
(3,620)
 | 
| (Decrease) increase in rents received in advance and security deposits | 
(3,913)
 | 
(7,350)
 | 
6,407
 | 
| Net cash provided by operating activities | 
230,654
 | 
232,538
 | 
204,008
 | 
| Supplemental schedule of non-cash investing and financing activities: | 
 
 | 
 
 | 
 
 | 
| (Decrease) increase in accrued capital improvements, leasing and other investing activity costs | 
(10,654)
 | 
5,950
 | 
(14,797)
 | 
| Increase in property in connection with capital lease obligation | 
16,127
 | 
0
 | 
0
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture | 
0
 | 
22,600
 | 
0
 | 
| Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interests | 
0
 | 
6,675
 | 
0
 | 
| Decrease in properties, net | 
0
 | 
(114,597)
 | 
0
 | 
| Increase in investment in unconsolidated real estate joint venture | 
0
 | 
25,680
 | 
0
 | 
| Decrease in debt | 
0
 | 
59,534
 | 
0
 | 
| Other net decreases in assets and liabilities | 
0
 | 
3,619
 | 
0
 | 
| Debt assumed on acquisition of operating property | 
0
 | 
0
 | 
55,490
 | 
| Other liabilities assumed on acquisition of operating properties | 
0
 | 
0
 | 
5,179
 | 
| Decrease in property in connection with surrender of property in settlement of debt | 
0
 | 
0
 | 
(82,738)
 | 
| Decrease in debt in connection with surrender of property in settlement of debt | 
0
 | 
0
 | 
(150,000)
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture | 
0
 | 
0
 | 
1,415
 | 
| Increase (decrease) in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests | 
3,845
 | 
1,315
 | 
(1,140)
 | 
| Equity in other comprehensive income (loss) of an equity method investee | 
39
 | 
(184)
 | 
(264)
 | 
| Reclassification of preferred shares to be redeemed to liability | 
0
 | 
26,583
 | 
0
 | 
| Dividends/distribution payable | 
28,921
 | 
31,335
 | 
30,178
 | 
| Decrease in noncontrolling interests and increase in shareholders’ equity in connection with the conversion of common units into common shares | 
4,636
 | 
1,167
 | 
2,151
 | 
| Adjustments to noncontrolling interests resulting from changes in COPLP ownership | 
1,486
 | 
2,158
 | 
682
 | 
| (Decrease) increase in redeemable noncontrolling interests and (increase) decrease in equity to carry redeemable noncontrolling interests at fair value | 
(626)
 | 
621
 | 
(116)
 | 
| Corporate Office Properties, L.P. [Member] | 
 
 | 
 
 | 
 
 | 
| Cash flows from operating activities | 
 
 | 
 
 | 
 
 | 
| Revenues from real estate operations received | 
510,985
 | 
514,098
 | 
503,503
 | 
| Construction contract and other service revenues received | 
102,531
 | 
76,824
 | 
117,107
 | 
| Property operating expenses paid | 
(186,478)
 | 
(197,254)
 | 
(190,281)
 | 
| Construction contract and other service expenses paid | 
(82,707)
 | 
(46,318)
 | 
(124,481)
 | 
| General, administrative, leasing, business development and land carry costs paid | 
(32,673)
 | 
(34,877)
 | 
(38,113)
 | 
| Interest expense paid | 
(73,079)
 | 
(78,158)
 | 
(65,816)
 | 
| Lease incentives paid | 
(9,725)
 | 
(2,760)
 | 
(1,724)
 | 
| Income taxes paid | 
(31)
 | 
(5)
 | 
(8)
 | 
| Other | 
1,831
 | 
988
 | 
3,821
 | 
| Net cash provided by operating activities | 
230,654
 | 
232,538
 | 
204,008
 | 
| Cash flows from investing activities | 
 
 | 
 
 | 
 
 | 
| Construction, development and redevelopment | 
(200,504)
 | 
(161,519)
 | 
(234,346)
 | 
| Acquisitions of operating properties and related intangible assets | 
0
 | 
0
 | 
(202,866)
 | 
| Tenant improvements on operating properties | 
(33,409)
 | 
(34,275)
 | 
(29,413)
 | 
| Other capital improvements on operating properties | 
(22,882)
 | 
(26,345)
 | 
(23,147)
 | 
| Proceeds from dispositions of properties | 
180,839
 | 
262,866
 | 
193,735
 | 
| Proceeds from partial sales of properties, net of related debt | 
0
 | 
43,681
 | 
0
 | 
| Leasing costs paid | 
(14,581)
 | 
(10,296)
 | 
(13,710)
 | 
| Other | 
827
 | 
(2,663)
 | 
2,215
 | 
| Net cash (used in) provided by investing activities | 
(89,710)
 | 
71,449
 | 
(307,532)
 | 
| Proceeds from debt | 
 
 | 
 
 | 
 
 | 
| Revolving Credit Facility | 
352,000
 | 
495,500
 | 
522,000
 | 
| Unsecured senior notes | 
0
 | 
0
 | 
296,580
 | 
| Other debt proceeds | 
0
 | 
255,000
 | 
164,000
 | 
| Repayments of debt | 
 
 | 
 
 | 
 
 | 
| Revolving Credit Facility | 
(226,000)
 | 
(539,000)
 | 
(561,500)
 | 
| Scheduled principal amortization | 
(3,862)
 | 
(5,395)
 | 
(6,728)
 | 
| Other debt repayments | 
(200,200)
 | 
(323,107)
 | 
(155,307)
 | 
| Deferred financing costs paid | 
(500)
 | 
(825)
 | 
(7,522)
 | 
| Net proceeds from issuance of common shares | 
69,534
 | 
109,069
 | 
28,567
 | 
| Redemption of preferred shares | 
(199,083)
 | 
0
 | 
0
 | 
| Common share/unit dividends/distributions paid | 
(112,940)
 | 
(108,094)
 | 
(107,730)
 | 
| Preferred share/unit dividends/distributions paid | 
(9,965)
 | 
(14,870)
 | 
(14,870)
 | 
| Distributions paid to redeemable noncontrolling interests | 
(8,215)
 | 
(15,206)
 | 
0
 | 
| Redemption of vested equity awards | 
(1,973)
 | 
(2,466)
 | 
(2,462)
 | 
| Other | 
2,658
 | 
(5,040)
 | 
2,729
 | 
| Net cash (used in) provided by financing activities | 
(338,546)
 | 
(154,434)
 | 
157,757
 | 
| Net (decrease) increase in cash and cash equivalents | 
(197,602)
 | 
149,553
 | 
54,233
 | 
| Cash and cash equivalents | 
 
 | 
 
 | 
 
 | 
| Beginning of year | 
209,863
 | 
60,310
 | 
6,077
 | 
| End of year | 
12,261
 | 
209,863
 | 
60,310
 | 
| Reconciliation of net income to net cash provided by operating activities: | 
 
 | 
 
 | 
 
 | 
| Net income | 
76,333
 | 
15,655
 | 
188,878
 | 
| Adjustments to reconcile net income to net cash provided by operating activities: | 
 
 | 
 
 | 
 
 | 
| Depreciation and other amortization | 
136,501
 | 
134,870
 | 
142,231
 | 
| Impairment losses | 
15,116
 | 
101,341
 | 
23,523
 | 
| Amortization of deferred financing costs and net debt discounts | 
4,307
 | 
5,885
 | 
5,588
 | 
| Increase in deferred rent receivable | 
(2,651)
 | 
(145)
 | 
(14,969)
 | 
| Gain on sales of real estate | 
(9,890)
 | 
(40,986)
 | 
(68,047)
 | 
| Share-based compensation | 
5,615
 | 
6,843
 | 
6,574
 | 
| Loss (gain) on early extinguishment of debt | 
513
 | 
456
 | 
(86,028)
 | 
| Other | 
(6,121)
 | 
(4,295)
 | 
528
 | 
| Changes in operating assets and liabilities: | 
 
 | 
 
 | 
 
 | 
| Decrease (increase) in accounts receivable | 
2,783
 | 
(5,262)
 | 
1,331
 | 
| Decrease (increase) in restricted cash and marketable securities | 
1,194
 | 
(691)
 | 
(1,360)
 | 
| Decrease (increase) in prepaid expenses and other assets, net | 
5,737
 | 
(17,272)
 | 
2,853
 | 
| Increase (decrease) in accounts payable, accrued expenses and other liabilities | 
5,130
 | 
43,489
 | 
(3,501)
 | 
| (Decrease) increase in rents received in advance and security deposits | 
(3,913)
 | 
(7,350)
 | 
6,407
 | 
| Net cash provided by operating activities | 
230,654
 | 
232,538
 | 
204,008
 | 
| Supplemental schedule of non-cash investing and financing activities: | 
 
 | 
 
 | 
 
 | 
| (Decrease) increase in accrued capital improvements, leasing and other investing activity costs | 
(10,654)
 | 
5,950
 | 
(14,797)
 | 
| Increase in property in connection with capital lease obligation | 
16,127
 | 
0
 | 
0
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture | 
0
 | 
22,600
 | 
0
 | 
| Decrease in redeemable noncontrolling interests and increase in other liabilities in connection with distribution payable to redeemable noncontrolling interests | 
0
 | 
6,675
 | 
0
 | 
| Decrease in properties, net | 
0
 | 
(114,597)
 | 
0
 | 
| Increase in investment in unconsolidated real estate joint venture | 
0
 | 
25,680
 | 
0
 | 
| Decrease in debt | 
0
 | 
59,534
 | 
0
 | 
| Other net decreases in assets and liabilities | 
0
 | 
3,619
 | 
0
 | 
| Debt assumed on acquisition of operating property | 
0
 | 
0
 | 
55,490
 | 
| Other liabilities assumed on acquisition of operating properties | 
0
 | 
0
 | 
5,179
 | 
| Decrease in property in connection with surrender of property in settlement of debt | 
0
 | 
0
 | 
(82,738)
 | 
| Decrease in debt in connection with surrender of property in settlement of debt | 
0
 | 
0
 | 
(150,000)
 | 
| Increase in property and redeemable noncontrolling interests in connection with property contribution by redeemable noncontrolling interests in a joint venture | 
0
 | 
0
 | 
1,415
 | 
| Increase (decrease) in fair value of derivatives applied to accumulated other comprehensive income (loss) and noncontrolling interests | 
3,845
 | 
1,315
 | 
(1,140)
 | 
| Equity in other comprehensive income (loss) of an equity method investee | 
39
 | 
(184)
 | 
(264)
 | 
| Reclassification of preferred shares to be redeemed to liability | 
0
 | 
26,583
 | 
0
 | 
| Dividends/distribution payable | 
28,921
 | 
31,335
 | 
30,178
 | 
| (Decrease) increase in redeemable noncontrolling interests and (increase) decrease in equity to carry redeemable noncontrolling interests at fair value | 
$ (626)
 | 
$ 621
 | 
$ (116)
 |