| Quarterly Data (Unaudited) | 
Quarterly Data (Unaudited) 
The tables below set forth selected quarterly information for the years ended December 31, 2017 and 2016 (in thousands, except per share/unit data). 
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|   | For the Year Ended December 31, 2017 |   | For the Year Ended December 31, 2016 |  
|   | First Quarter |   | Second Quarter |   | Third Quarter |   | Fourth Quarter |   | First Quarter |   | Second Quarter |   | Third Quarter |   | Fourth Quarter |  
| COPT and Subsidiaries |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  
| Revenues | $ | 139,801 | 
 |   | $ | 151,435 | 
 |   | $ | 157,017 | 
 |   | $ | 164,567 | 
 |   | $ | 144,307 | 
 |   | $ | 145,927 | 
 |   | $ | 142,103 | 
 |   | $ | 141,991 | 
 |  
| Operating income | $ | 35,433 | 
 |   | $ | 36,618 | 
 |   | $ | 38,939 | 
 |   | $ | 24,847 | 
 |   | $ | 30,464 | 
 |   | $ | (27,021 | ) |   | $ | 11,525 | 
 |   | $ | 37,442 | 
 |  
| Income (loss) from continuing operations | $ | 18,850 | 
 |   | $ | 19,195 | 
 |   | $ | 21,494 | 
 |   | $ | 6,904 | 
 |   | $ | 8,096 | 
 |   | $ | (48,316 | ) |   | $ | (4,829 | ) |   | $ | 19,718 | 
 |  
| Net income (loss) | $ | 23,088 | 
 |   | $ | 19,207 | 
 |   | $ | 22,682 | 
 |   | $ | 11,356 | 
 |   | $ | 8,096 | 
 |   | $ | (48,316 | ) |   | $ | 29,272 | 
 |   | $ | 26,603 | 
 |  
| Net (income) loss attributable to noncontrolling interests | (1,733 | ) |   | (1,345 | ) |   | (1,766 | ) |   | (1,398 | ) |   | (1,270 | ) |   | 897 | 
 |   | (1,973 | ) |   | (1,870 | ) |  
| Net income (loss) attributable to COPT | 21,355 | 
 |   | 17,862 | 
 |   | 20,916 | 
 |   | 9,958 | 
 |   | 6,826 | 
 |   | (47,419 | ) |   | 27,299 | 
 |   | 24,733 | 
 |  
| Preferred share dividends | (3,180 | ) |   | (3,039 | ) |   | — | 
 |   | — | 
 |   | (3,552 | ) |   | (3,553 | ) |   | (3,552 | ) |   | (3,640 | ) |  
| Issuance costs associated with redeemed preferred shares | — | 
 |   | (6,847 | ) |   | — | 
 |   | — | 
 |   | — | 
 |   | — | 
 |   | — | 
 |   | (17 | ) |  
| Net income (loss) attributable to COPT common shareholders | $ | 18,175 | 
 |   | $ | 7,976 | 
 |   | $ | 20,916 | 
 |   | $ | 9,958 | 
 |   | $ | 3,274 | 
 |   | $ | (50,972 | ) |   | $ | 23,747 | 
 |   | $ | 21,076 | 
 |  
|   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  
| Basic EPS | $ | 0.18 | 
 |   | $ | 0.08 | 
 |   | $ | 0.21 | 
 |   | $ | 0.10 | 
 |   | $ | 0.03 | 
 |   | $ | (0.54 | ) |   | $ | 0.25 | 
 |   | $ | 0.22 | 
 |  
| Diluted EPS | $ | 0.18 | 
 |   | $ | 0.08 | 
 |   | $ | 0.21 | 
 |   | $ | 0.10 | 
 |   | $ | 0.03 | 
 |   | $ | (0.54 | ) |   | $ | 0.25 | 
 |   | $ | 0.22 | 
 | 
 
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|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| COPLP and Subsidiaries |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  
| Revenues | $ | 139,801 | 
 |   | $ | 151,435 | 
 |   | $ | 157,017 | 
 |   | $ | 164,567 | 
 |   | $ | 144,307 | 
 |   | $ | 145,927 | 
 |   | $ | 142,103 | 
 |   | $ | 141,991 | 
 |  
| Operating income | $ | 35,433 | 
 |   | $ | 36,618 | 
 |   | $ | 38,939 | 
 |   | $ | 24,847 | 
 |   | $ | 30,464 | 
 |   | $ | (27,021 | ) |   | $ | 11,525 | 
 |   | $ | 37,442 | 
 |  
| Income (loss) from continuing operations | $ | 18,850 | 
 |   | $ | 19,195 | 
 |   | $ | 21,494 | 
 |   | $ | 6,904 | 
 |   | $ | 8,096 | 
 |   | $ | (48,316 | ) |   | $ | (4,829 | ) |   | $ | 19,718 | 
 |  
| Net income (loss) | $ | 23,088 | 
 |   | $ | 19,207 | 
 |   | $ | 22,682 | 
 |   | $ | 11,356 | 
 |   | $ | 8,096 | 
 |   | $ | (48,316 | ) |   | $ | 29,272 | 
 |   | $ | 26,603 | 
 |  
| Net income attributable to noncontrolling interests | (934 | ) |   | (907 | ) |   | (897 | ) |   | (908 | ) |   | (979 | ) |   | (911 | ) |   | (913 | ) |   | (912 | ) |  
| Net income (loss) attributable to COPLP | 22,154 | 
 |   | 18,300 | 
 |   | 21,785 | 
 |   | 10,448 | 
 |   | 7,117 | 
 |   | (49,227 | ) |   | 28,359 | 
 |   | 25,691 | 
 |  
| Preferred unit distributions | (3,345 | ) |   | (3,204 | ) |   | (165 | ) |   | (165 | ) |   | (3,717 | ) |   | (3,718 | ) |   | (3,717 | ) |   | (3,805 | ) |  
| Issuance costs associated with redeemed preferred units | — | 
 |   | (6,847 | ) |   | — | 
 |   | — | 
 |   | — | 
 |   | — | 
 |   | — | 
 |   | (17 | ) |  
| Net income (loss) attributable to COPLP common unitholders | $ | 18,809 | 
 |   | $ | 8,249 | 
 |   | $ | 21,620 | 
 |   | $ | 10,283 | 
 |   | $ | 3,400 | 
 |   | $ | (52,945 | ) |   | $ | 24,642 | 
 |   | $ | 21,869 | 
 |  
|   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |  
| Basic EPU | $ | 0.18 | 
 |   | $ | 0.08 | 
 |   | $ | 0.21 | 
 |   | $ | 0.10 | 
 |   | $ | 0.03 | 
 |   | $ | (0.54 | ) |   | $ | 0.25 | 
 |   | $ | 0.22 | 
 |  
| Diluted EPU | $ | 0.18 | 
 |   | $ | 0.08 | 
 |   | $ | 0.21 | 
 |   | $ | 0.10 | 
 |   | $ | 0.03 | 
 |   | $ | (0.54 | ) |   | $ | 0.25 | 
 |   | $ | 0.22 | 
 |  |