Consolidated Statements of Equity - USD ($)  $ in Thousands  | 
Total  | 
Preferred Shares [Member]  | 
Common Shares [Member]  | 
Additional Paid-in Capital [Member]  | 
Cumulative Distributions in Excess of Net Income [Member]  | 
Accumulated Other Comprehensive Income (Loss) [Member]  | 
Noncontrolling Interests [Member]  | 
Corporate Office Properties, L.P. [Member]  | 
 Corporate Office Properties, L.P. [Member]  
Common Shares [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
Accumulated Other Comprehensive Income (Loss) [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
Noncontrolling Interests [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
Limited Partner [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
Limited Partner [Member]  
Preferred Shares [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
General Partner [Member] 
 | 
 Corporate Office Properties, L.P. [Member]  
General Partner [Member]  
Preferred Shares [Member] 
 | 
| 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
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (preferred units) at Dec. 31, 2013 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
 
 | 
9,431,667
 | 
| Increase (Decrease) in Shareholders' Equity | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of preferred shares/units | 
 
 | 
(2,000,000)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(2,000,000)
 | 
| Redemption of preferred shares/units (2,000,000 shares in 2014 and 531,667 shares in 2016, respectively) | 
$ (50,000)
 | 
$ (50,000)
 | 
 
 | 
1,769
 | 
(1,769)
 | 
 
 | 
 
 | 
(50,000)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
$ (50,000)
 | 
| Conversion of common units to common shares (140,149, 160,160 and 87,000 shares in 2014, 2015 and 2016 respectively) | 
0
 | 
 
 | 
2
 | 
1,841
 | 
 
 | 
 
 | 
(1,843)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Shares issued to the public (5,520,000 common shares in 2014, respectively) | 
$ 148,666
 | 
 
 | 
$ 55
 | 
148,611
 | 
 
 | 
 
 | 
 
 | 
148,666
 | 
$ 148,666
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Shares issued to the public (in units/shares) | 
 
 | 
 
 | 
5,520,000
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
5,520,000
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (in units/shares) | 
62,888
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
62,888
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (62,888, 76,474 and shares in 2014 and 2015 respectively) | 
$ 1,489
 | 
 
 | 
 
 | 
1,489
 | 
 
 | 
 
 | 
 
 | 
1,489
 | 
$ 1,489
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (137,735, 149,353 and 158,912 shares issued, net of redemptions in 2014, 2015 and 2016 respectively) | 
$ 7,050
 | 
 
 | 
$ 2
 | 
7,048
 | 
 
 | 
 
 | 
 
 | 
7,050
 | 
$ 7,050
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (in shares/units) | 
137,735
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
137,735
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of vested equity awards | 
$ (1,554)
 | 
 
 | 
 
 | 
(1,554)
 | 
 
 | 
 
 | 
 
 | 
(1,554)
 | 
$ (1,554)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustments to noncontrolling interests resulting from changes in ownership of COPLP | 
0
 | 
 
 | 
 
 | 
(3,382)
 | 
 
 | 
 
 | 
3,382
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Comprehensive income | 
38,274
 | 
 
 | 
 
 | 
 
 | 
40,255
 | 
(4,777)
 | 
2,796
 | 
38,274
 | 
25,331
 | 
(4,986)
 | 
1,330
 | 
 
 | 
$ 660
 | 
 
 | 
15,939
 | 
| Dividends/Distributions | 
(113,882)
 | 
 
 | 
 
 | 
 
 | 
(113,882)
 | 
 
 | 
 
 | 
(118,811)
 | 
(102,212)
 | 
 
 | 
 
 | 
 
 | 
$ (660)
 | 
 
 | 
$ (15,939)
 | 
| Distributions to owners of common and preferred units in COPLP | 
(4,929)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(4,929)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Contributions from noncontrolling interests in other consolidated entities | 
3
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
3
 | 
3
 | 
 
 | 
 
 | 
3
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Distributions to noncontrolling interests in other consolidated entities | 
(1,613)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(1,613)
 | 
(1,613)
 | 
 
 | 
 
 | 
(1,613)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustment to arrive at fair value of redeemable noncontrolling interests | 
134
 | 
 
 | 
 
 | 
134
 | 
 
 | 
 
 | 
 
 | 
134
 | 
134
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Tax loss from share-based compensation | 
$ (3)
 | 
 
 | 
 
 | 
(3)
 | 
 
 | 
 
 | 
 
 | 
(3)
 | 
$ (3)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (preferred units) at Dec. 31, 2014 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
 
 | 
7,431,667
 | 
| Balance (in units/ shares) at Dec. 31, 2014 | 
93,255,284
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
97,092,835
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance at Dec. 31, 2014 | 
$ 1,520,884
 | 
$ 199,083
 | 
933
 | 
1,969,968
 | 
(717,264)
 | 
(1,297)
 | 
69,461
 | 
1,520,884
 | 
$ 1,305,219
 | 
(1,381)
 | 
9,163
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 199,083
 | 
| Increase (Decrease) in Shareholders' Equity | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of preferred shares/units | 
 
 | 
0
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Conversion of common units to common shares (140,149, 160,160 and 87,000 shares in 2014, 2015 and 2016 respectively) | 
0
 | 
 
 | 
$ 2
 | 
2,149
 | 
 
 | 
 
 | 
(2,151)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Shares issued to the public (in units/shares) | 
 
 | 
 
 | 
0
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (in units) | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
890,241
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (890,241 shares in 2015 and 3,721,227 shares in 2016) | 
$ 26,535
 | 
 
 | 
$ 9
 | 
26,526
 | 
 
 | 
 
 | 
 
 | 
26,535
 | 
$ 26,535
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (in units/shares) | 
76,474
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
76,474
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (62,888, 76,474 and shares in 2014 and 2015 respectively) | 
$ 2,008
 | 
 
 | 
 
 | 
2,008
 | 
 
 | 
 
 | 
 
 | 
2,008
 | 
$ 2,008
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (137,735, 149,353 and 158,912 shares issued, net of redemptions in 2014, 2015 and 2016 respectively) | 
$ 7,398
 | 
 
 | 
1
 | 
7,397
 | 
 
 | 
 
 | 
 
 | 
7,398
 | 
$ 7,398
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (in shares/units) | 
149,353
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
149,353
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of vested equity awards | 
$ (2,462)
 | 
 
 | 
 
 | 
(2,462)
 | 
 
 | 
 
 | 
 
 | 
(2,462)
 | 
$ (2,462)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustments to noncontrolling interests resulting from changes in ownership of COPLP | 
0
 | 
 
 | 
 
 | 
(682)
 | 
 
 | 
 
 | 
682
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Comprehensive income | 
185,247
 | 
 
 | 
 
 | 
 
 | 
178,300
 | 
(1,541)
 | 
8,488
 | 
185,247
 | 
170,488
 | 
(1,604)
 | 
1,493
 | 
 
 | 
660
 | 
 
 | 
14,210
 | 
| Dividends/Distributions | 
(118,208)
 | 
 
 | 
 
 | 
 
 | 
(118,208)
 | 
 
 | 
 
 | 
(122,914)
 | 
(108,044)
 | 
 
 | 
 
 | 
 
 | 
$ (660)
 | 
 
 | 
$ (14,210)
 | 
| Distributions to owners of common and preferred units in COPLP | 
(4,706)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(4,706)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Contributions from noncontrolling interests in other consolidated entities | 
300
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
300
 | 
300
 | 
 
 | 
 
 | 
300
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Distributions to noncontrolling interests in other consolidated entities | 
(35)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(35)
 | 
(35)
 | 
 
 | 
 
 | 
(35)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustment to arrive at fair value of redeemable noncontrolling interests | 
116
 | 
 
 | 
 
 | 
116
 | 
 
 | 
 
 | 
 
 | 
116
 | 
116
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Tax loss from share-based compensation | 
$ (513)
 | 
 
 | 
 
 | 
(513)
 | 
 
 | 
 
 | 
 
 | 
(513)
 | 
$ (513)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (preferred units) at Dec. 31, 2015 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
352,000
 | 
7,431,667
 | 
7,431,667
 | 
| Balance (in units/ shares) at Dec. 31, 2015 | 
94,531,512
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
98,208,903
 | 
 
 | 
 
 | 
3,677,391
 | 
 
 | 
94,531,512
 | 
 
 | 
| Balance at Dec. 31, 2015 | 
$ 1,616,564
 | 
$ 199,083
 | 
945
 | 
2,004,507
 | 
(657,172)
 | 
(2,838)
 | 
72,039
 | 
1,616,564
 | 
$ 1,400,745
 | 
(2,985)
 | 
10,921
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 199,083
 | 
| Increase (Decrease) in Shareholders' Equity | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of preferred shares/units | 
 
 | 
(531,667)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(531,667)
 | 
| Redemption of preferred shares/units (2,000,000 shares in 2014 and 531,667 shares in 2016, respectively) | 
(26,583)
 | 
$ (26,583)
 | 
 
 | 
17
 | 
(17)
 | 
 
 | 
 
 | 
26,583
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
$ (26,583)
 | 
| Conversion of common units to common shares (140,149, 160,160 and 87,000 shares in 2014, 2015 and 2016 respectively) | 
0
 | 
 
 | 
1
 | 
1,166
 | 
 
 | 
 
 | 
(1,167)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (in units) | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
3,721,227
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (890,241 shares in 2015 and 3,721,227 shares in 2016) | 
109,053
 | 
 
 | 
37
 | 
109,016
 | 
 
 | 
 
 | 
 
 | 
109,053
 | 
$ 109,053
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (137,735, 149,353 and 158,912 shares issued, net of redemptions in 2014, 2015 and 2016 respectively) | 
$ 7,453
 | 
 
 | 
2
 | 
7,451
 | 
 
 | 
 
 | 
 
 | 
7,453
 | 
$ 7,453
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation (in shares/units) | 
158,912
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
158,912
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of vested equity awards | 
$ (2,466)
 | 
 
 | 
 
 | 
(2,466)
 | 
 
 | 
 
 | 
 
 | 
(2,466)
 | 
$ (2,466)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustments to noncontrolling interests resulting from changes in ownership of COPLP | 
0
 | 
 
 | 
 
 | 
(2,158)
 | 
 
 | 
 
 | 
2,158
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Comprehensive income | 
14,543
 | 
 
 | 
 
 | 
 
 | 
11,439
 | 
1,107
 | 
1,997
 | 
14,543
 | 
(3,017)
 | 
1,131
 | 
1,472
 | 
 
 | 
660
 | 
 
 | 
14,297
 | 
| Dividends/Distributions | 
(119,526)
 | 
 
 | 
 
 | 
 
 | 
(119,526)
 | 
 
 | 
 
 | 
(124,176)
 | 
(109,219)
 | 
 
 | 
 
 | 
 
 | 
$ (660)
 | 
 
 | 
$ (14,297)
 | 
| Distributions to owners of common and preferred units in COPLP | 
(4,650)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(4,650)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Contributions from noncontrolling interests in other consolidated entities | 
1,244
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
1,244
 | 
1,244
 | 
 
 | 
 
 | 
1,244
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Distributions to noncontrolling interests in other consolidated entities | 
(16)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(16)
 | 
(16)
 | 
 
 | 
 
 | 
(16)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustment to arrive at fair value of redeemable noncontrolling interests | 
(621)
 | 
 
 | 
 
 | 
(621)
 | 
 
 | 
 
 | 
 
 | 
(621)
 | 
(621)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Tax loss from share-based compensation | 
$ (331)
 | 
 
 | 
 
 | 
(331)
 | 
 
 | 
 
 | 
 
 | 
(331)
 | 
$ (331)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (preferred units) at Dec. 31, 2016 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
352,000
 | 
6,900,000
 | 
6,900,000
 | 
| Balance (in units/ shares) at Dec. 31, 2016 | 
98,498,651
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
102,089,042.000
 | 
 
 | 
 
 | 
3,590,391
 | 
 
 | 
98,498,651
 | 
 
 | 
| Balance at Dec. 31, 2016 | 
$ 1,594,664
 | 
$ 172,500
 | 
$ 985
 | 
$ 2,116,581
 | 
$ (765,276)
 | 
$ (1,731)
 | 
$ 71,605
 | 
$ 1,594,664
 | 
$ 1,401,597
 | 
$ (1,854)
 | 
$ 13,621
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 172,500
 |