Consolidated Statements of Equity - USD ($)  $ in Thousands  | 
Total  | 
Preferred Shares  | 
Common Shares  | 
Additional Paid-in Capital  | 
Cumulative Distributions in Excess of Net Income  | 
Accumulated Other Comprehensive Income (Loss)  | 
Noncontrolling Interests  | 
Corporate Office Properties, L.P.  | 
 Corporate Office Properties, L.P.  
Common Shares 
 | 
 Corporate Office Properties, L.P.  
Accumulated Other Comprehensive Income (Loss) 
 | 
 Corporate Office Properties, L.P.  
Noncontrolling Interests 
 | 
 Corporate Office Properties, L.P.  
Limited Partner 
 | 
 Corporate Office Properties, L.P.  
Limited Partner  
Preferred Shares 
 | 
 Corporate Office Properties, L.P.  
General Partner 
 | 
 Corporate Office Properties, L.P.  
General Partner  
Preferred Shares 
 | 
| Balance (COPT: 93,255,284 shares and 94,531,512 shares as of December 31, 2014 and 2015, respectively) at Dec. 31, 2014 | 
$ 1,520,884
 | 
$ 199,083
 | 
$ 933
 | 
$ 1,969,968
 | 
$ (717,264)
 | 
$ (1,297)
 | 
$ 69,461
 | 
$ 1,520,884
 | 
$ 1,305,219
 | 
$ (1,381)
 | 
$ 9,163
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 199,083
 | 
| Balance (preferred units) at Dec. 31, 2014 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
 
 | 
7,431,667
 | 
| Balance (in units/ shares) at Dec. 31, 2014 | 
93,255,284
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
97,092,835
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Increase (Decrease) in Shareholders' Equity | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Conversion of common units to common shares (COPT: 160,160 and 87,000 shares for the nine months ended September 30, 2015 and 2016, respectively) | 
$ 0
 | 
 
 | 
2
 | 
2,149
 | 
 
 | 
 
 | 
(2,151)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (in units) | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
890,241
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Issuance of common units resulting from common shares issued under at-the-market program (COPT: 890,241 shares for the nine months ended September 30, 2015) | 
$ 26,535
 | 
 
 | 
9
 | 
26,526
 | 
 
 | 
 
 | 
 
 | 
26,535
 | 
$ 26,535
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (in units/shares) | 
76,474
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
76,474
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Exercise of share options (COPT: 76,474 shares for the nine months ended September 30, 2015) | 
$ 2,008
 | 
 
 | 
0
 | 
2,008
 | 
 
 | 
 
 | 
 
 | 
2,008
 | 
$ 2,008
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation issuance, net of redemptions (in units/shares) | 
151,511
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
151,511
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation issuance, net of redemptions (COPT: 151,511 and 146,274 shares issued, net of redemptions for the nine months ended September 30, 2015 and 2016, respectively) | 
$ 5,600
 | 
 
 | 
1
 | 
5,599
 | 
 
 | 
 
 | 
 
 | 
5,600
 | 
$ 5,600
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of vested equity awards | 
(2,330)
 | 
 
 | 
 
 | 
(2,330)
 | 
 
 | 
 
 | 
 
 | 
(2,330)
 | 
(2,330)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustments to noncontrolling interests resulting from changes in ownership of COPLP | 
0
 | 
 
 | 
 
 | 
(591)
 | 
 
 | 
 
 | 
591
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Comprehensive income (loss) | 
120,044
 | 
 
 | 
 
 | 
 
 | 
118,936
 | 
(4,526)
 | 
5,634
 | 
120,044
 | 
112,507
 | 
(4,705)
 | 
1,090
 | 
 
 | 
$ 495
 | 
 
 | 
$ 10,657
 | 
| Dividends / Distributions to owners of common and preferred units | 
(88,658)
 | 
 
 | 
 
 | 
 
 | 
(88,658)
 | 
 
 | 
 
 | 
(92,188)
 | 
(81,036)
 | 
 
 | 
 
 | 
 
 | 
$ (495)
 | 
 
 | 
$ (10,657)
 | 
| Distributions to owners of common and preferred units in COPLP | 
(3,530)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(3,530)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Distributions to noncontrolling interests in subsidiaries | 
(47)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(47)
 | 
(47)
 | 
 
 | 
 
 | 
(47)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustment to arrive at fair value of redeemable noncontrolling interest | 
$ (599)
 | 
 
 | 
 
 | 
(599)
 | 
 
 | 
 
 | 
 
 | 
(599)
 | 
$ (599)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (in units/ shares) at Sep. 30, 2015 | 
94,533,670
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
98,211,061
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (preferred units) at Sep. 30, 2015 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
 
 | 
7,431,667
 | 
| Balance (COPT: 94,533,670 shares and 94,764,786 shares as of September 30, 2015 and 2016, respectively) at Sep. 30, 2015 | 
$ 1,579,907
 | 
199,083
 | 
945
 | 
2,002,730
 | 
(686,986)
 | 
(5,823)
 | 
69,958
 | 
1,579,907
 | 
$ 1,367,904
 | 
(6,086)
 | 
10,206
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 199,083
 | 
| Balance (COPT: 93,255,284 shares and 94,531,512 shares as of December 31, 2014 and 2015, respectively) 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
 | 
| 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
 | 
 
 | 
| Increase (Decrease) in Shareholders' Equity | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Conversion of common units to common shares (COPT: 160,160 and 87,000 shares for the nine months ended September 30, 2015 and 2016, respectively) | 
$ 0
 | 
 
 | 
1
 | 
1,166
 | 
 
 | 
 
 | 
(1,167)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Costs associated with common shares issued to the public | 
$ (5)
 | 
 
 | 
 
 | 
(5)
 | 
 
 | 
 
 | 
 
 | 
(5)
 | 
$ (5)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation issuance, net of redemptions (in units/shares) | 
146,274
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
146,274
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Share-based compensation issuance, net of redemptions (COPT: 151,511 and 146,274 shares issued, net of redemptions for the nine months ended September 30, 2015 and 2016, respectively) | 
$ 6,177
 | 
 
 | 
2
 | 
6,175
 | 
 
 | 
 
 | 
 
 | 
6,177
 | 
$ 6,177
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Redemption of vested equity awards | 
(2,179)
 | 
 
 | 
 
 | 
(2,179)
 | 
 
 | 
 
 | 
 
 | 
(2,179)
 | 
(2,179)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustments to noncontrolling interests resulting from changes in ownership of COPLP | 
0
 | 
 
 | 
 
 | 
(42)
 | 
 
 | 
 
 | 
42
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Comprehensive income (loss) | 
(26,629)
 | 
 
 | 
 
 | 
 
 | 
(13,294)
 | 
(13,476)
 | 
141
 | 
(26,629)
 | 
(24,903)
 | 
(14,002)
 | 
1,124
 | 
 
 | 
$ 495
 | 
 
 | 
$ 10,657
 | 
| Dividends / Distributions to owners of common and preferred units | 
(88,796)
 | 
 
 | 
 
 | 
 
 | 
(88,796)
 | 
 
 | 
 
 | 
(92,294)
 | 
(81,142)
 | 
 
 | 
 
 | 
 
 | 
$ (495)
 | 
 
 | 
$ (10,657)
 | 
| Distributions to owners of common and preferred units in COPLP | 
(3,498)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(3,498)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Distributions to noncontrolling interests in subsidiaries | 
(12)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
(12)
 | 
(12)
 | 
 
 | 
 
 | 
(12)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Adjustment to arrive at fair value of redeemable noncontrolling interest | 
(516)
 | 
 
 | 
 
 | 
(516)
 | 
 
 | 
 
 | 
 
 | 
(516)
 | 
(516)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Tax loss from share-based compensation | 
$ (319)
 | 
 
 | 
 
 | 
(319)
 | 
 
 | 
 
 | 
 
 | 
(319)
 | 
$ (319)
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
| Balance (in units/ shares) at Sep. 30, 2016 | 
94,764,786
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
98,355,177.000
 | 
 
 | 
 
 | 
3,590,391
 | 
 
 | 
94,764,786
 | 
 
 | 
| Balance (preferred units) at Sep. 30, 2016 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
 
 | 
352,000
 | 
352,000
 | 
7,431,667
 | 
7,431,667
 | 
| Balance (COPT: 94,533,670 shares and 94,764,786 shares as of September 30, 2015 and 2016, respectively) at Sep. 30, 2016 | 
$ 1,500,787
 | 
$ 199,083
 | 
$ 948
 | 
$ 2,008,787
 | 
$ (759,262)
 | 
$ (16,314)
 | 
$ 67,545
 | 
$ 1,500,787
 | 
$ 1,297,858
 | 
$ (16,987)
 | 
$ 12,033
 | 
 
 | 
$ 8,800
 | 
 
 | 
$ 199,083
 |