Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Details 3)

v3.10.0.1
Summary of Significant Accounting Policies (Details 3) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture $ 40,318 $ 42,263 $ 40,318 $ 42,263 $ 41,787 $ 43,661
Cumulative distributions in excess of net income (833,508) (783,848) (833,508) (783,848) (802,085) (747,825)
Noncontrolling interests in subsidiaries 41,557 44,716 41,557 44,716 66,165 72,267
Common units 1,088   1,088   1,013  
Equity in income of unconsolidated entities 374 371 1,120 1,118    
Net income 20,322 22,334 60,187 63,933    
Net income attributable to noncontrolling interests - Common units in COPLP (380) (693) (1,532) (1,576)    
Net income attributable to COPT/COPLP 18,697 20,579 55,281 59,124    
Net income attributable to COPT/COPLP common share/unit holders 18,697 $ 20,579 55,281 $ 46,058    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.21   $ 0.46    
Comprehensive income 21,440 $ 22,648 68,091 $ 64,835    
Comprehensive income attributable to COPT/ COPLP 19,793 20,883 62,946 59,996    
Corporate Office Properties, L.P.            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture 40,318 42,263 40,318 42,263 41,787 43,661
Noncontrolling interests in subsidiaries 13,277   13,277   12,312  
Common units 1,577,299 1,411,980 1,577,299 1,411,980 1,445,022 1,419,710
Equity in income of unconsolidated entities 374 371 1,120 1,118    
Net income 20,322 22,334 60,187 63,933    
Net income attributable to COPT/COPLP 19,242 21,437 57,308 61,195    
Net income attributable to COPT/COPLP common share/unit holders 19,077 $ 21,272 56,813 $ 47,634    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.21   $ 0.46    
Comprehensive income 21,440 $ 22,648 68,091 $ 64,835    
Comprehensive income attributable to COPT/ COPLP $ 20,360 21,751 $ 65,212 62,097    
As Previously Reported            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture   25,194   25,194 25,066 25,548
Cumulative distributions in excess of net income   (800,290)   (800,290) (818,190) (765,276)
Noncontrolling interests in subsidiaries   44,089   44,089 65,549 71,605
Equity in income of unconsolidated entities   719   2,162    
Net income   22,682   64,977    
Net income attributable to noncontrolling interests - Common units in COPLP   (704)   (1,611)    
Net income attributable to COPT/COPLP   20,916   60,133    
Net income attributable to COPT/COPLP common share/unit holders   $ 20,916   $ 47,067    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.21   $ 0.47    
Comprehensive income   $ 22,996   $ 65,879    
Comprehensive income attributable to COPT/ COPLP   21,220   61,005    
As Previously Reported | Corporate Office Properties, L.P.            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture   25,194   25,194 25,066 25,548
Common units   1,394,911   1,394,911 1,428,301 1,401,597
Equity in income of unconsolidated entities   719   2,162    
Net income   22,682   64,977    
Net income attributable to COPT/COPLP   21,785   62,239    
Net income attributable to COPT/COPLP common share/unit holders   $ 21,620   $ 48,678    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.21   $ 0.47    
Comprehensive income   $ 22,996   $ 65,879    
Comprehensive income attributable to COPT/ COPLP   22,099   63,141    
Accounting Standards Update 2017-05            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture   17,069   17,069 16,721 18,113
Cumulative distributions in excess of net income   16,442   16,442 16,105 17,451
Noncontrolling interests in subsidiaries   627   627 616 662
Equity in income of unconsolidated entities   (348)   (1,044)    
Net income   (348)   (1,044)    
Net income attributable to noncontrolling interests - Common units in COPLP   11   35    
Net income attributable to COPT/COPLP   (337)   (1,009)    
Net income attributable to COPT/COPLP common share/unit holders   $ (337)   $ (1,009)    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.00   $ (0.01)    
Comprehensive income   $ (348)   $ (1,044)    
Comprehensive income attributable to COPT/ COPLP   (337)   (1,009)    
Accounting Standards Update 2017-05 | Corporate Office Properties, L.P.            
New Accounting Pronouncements or Change in Accounting Principle [Line Items]            
Investment in unconsolidated real estate joint venture   17,069   17,069 16,721 18,113
Common units   17,069   17,069 $ 16,721 $ 18,113
Equity in income of unconsolidated entities   (348)   (1,044)    
Net income   (348)   (1,044)    
Net income attributable to COPT/COPLP   (348)   (1,044)    
Net income attributable to COPT/COPLP common share/unit holders   $ (348)   $ (1,044)    
Earnings per common share/unit - basic and diluted (in dollars per share)   $ 0.00   $ (0.01)    
Comprehensive income   $ (348)   $ (1,044)    
Comprehensive income attributable to COPT/ COPLP   $ (348)   $ (1,044)