Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Details)

v2.4.0.6
Summary of Significant Accounting Policies (Details) (USD $)
 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 12 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Sep. 30, 2012
Scenario, Previously Reported
Jun. 30, 2012
Scenario, Previously Reported
Mar. 31, 2012
Scenario, Previously Reported
Dec. 31, 2011
Scenario, Previously Reported
Sep. 30, 2011
Scenario, Previously Reported
Jun. 30, 2011
Scenario, Previously Reported
Mar. 31, 2011
Scenario, Previously Reported
Dec. 31, 2011
Scenario, Previously Reported
Dec. 31, 2011
Scenario, Adjustment
Dec. 31, 2011
Scenario, Revised
Dec. 31, 2011
Misapplication Of Accounting Guidance Related To Recognition Of Deferred Tax Asset
Scenario, Previously Reported
Dec. 31, 2011
Over accrual Of Incentive Compensation Cost
Scenario, Previously Reported
Sep. 30, 2012
Misapplication of Accounting Guidance Related to Recognization of Losses Related to Consolidated Real Estate Joint Ventures
Scenario, Previously Reported
Dec. 31, 2011
Misapplication of Accounting Guidance Related to Recognization of Losses Related to Consolidated Real Estate Joint Ventures
Scenario, Previously Reported
Dec. 31, 2011
Misapplication of Accounting Guidance Related to Reporting for a Noncontrolling Interest in a Consolidated Real Estate Joint Venture
Scenario, Previously Reported
Quantifying Misstatement in Current Year Financial Statements [Line Items]                                                    
Earnings per share, basic $ 0.16 $ (0.39) $ 0.10 $ 0.09 $ (1.26) $ 0.04 $ (0.40) $ (0.33) $ (0.03) [1] $ (1.97) [1] $ 0.43 [1]       $ (1.21) $ 0.03 $ (0.42) $ (0.33)                
Prepaid expenses and other assets $ 77,455,000       $ 83,650,000       $ 77,455,000 $ 83,650,000         $ 87,619,000       $ 87,619,000 $ (3,969,000) $ 83,650,000          
Accounts payable and accrued expenses 97,922,000       95,714,000       97,922,000 95,714,000         96,425,000       96,425,000 (711,000) 95,714,000          
Redeemable noncontrolling interest 10,298,000       8,908,000       10,298,000 8,908,000         0       0 8,908,000 8,908,000         8,900,000
Additional paid-in capital 1,653,672,000       1,451,078,000       1,653,672,000 1,451,078,000         1,452,393,000       1,452,393,000 (1,315,000) 1,451,078,000          
Cumulative distributions in excess of net income (617,455,000)       (534,041,000)       (617,455,000) (534,041,000)         (532,288,000)       (532,288,000) (1,753,000) (534,041,000)          
Common units in the Operating Partnership 52,122,000       55,183,000       52,122,000 55,183,000         55,281,000       55,281,000 (98,000) 55,183,000          
Other consolidated entities 10,153,000       9,559,000       10,153,000 9,559,000         18,559,000       18,559,000 (9,000,000) 9,559,000          
General, administrative and leasing expenses                   30,314,000                 31,025,000 (711,000)            
Income tax (expense) benefit                 (381,000) 6,710,000 (108,000)               10,679,000 (3,969,000)            
Net (loss) income 19,010,000 (20,765,000) 11,861,000 10,235,000 (91,102,000) 7,470,000 (25,378,000) (18,566,000) 20,341,000 (127,576,000) 45,504,000 (20,765,000) 11,861,000 6,977,000 (87,215,000) 7,470,000 (26,007,000) (18,566,000) (124,318,000) (3,258,000)   4,000,000 (700,000) 1,800,000 1,400,000  
Net loss attributable to noncontrolling interests in common units in the Operating Partnership                 87,000 8,439,000 (2,116,000)               8,341,000 98,000            
Net (income) loss attributable to noncontrolling interests in other consolidated entities                 1,209,000 369,000 32,000               (1,038,000) 1,407,000            
Net income (loss) attributable to Corporate Office Properties Trust 18,539,000 (19,162,000) 11,305,000 10,295,000 (85,496,000) 6,844,000 (23,414,000) (17,362,000) 20,977,000 (119,428,000) 42,760,000 (19,772,000) 10,754,000 6,677,000 (82,227,000) 6,566,000 (24,224,000) (17,790,000) (117,675,000) (1,753,000)            
Net loss attributable to Corporate Office Properties Trust common shareholders $ 12,433,000 $ (27,535,000) $ 7,138,000 $ 6,270,000 $ (89,522,000) $ 2,819,000 $ (27,440,000) $ (21,387,000) $ (1,694,000) $ (135,530,000) $ 26,658,000 $ (28,145,000) $ 6,587,000 $ 2,652,000 $ (86,253,000) $ 2,541,000 $ (28,250,000) $ (21,815,000) $ (133,777,000) $ (1,753,000)            
Basic and diluted earnings per common share:                                                    
Loss from continuing operations                   $ (1.31)                 $ (1.29) $ (0.02)            
Net loss attributable to COPT common shareholders   $ (0.39) $ 0.10 $ 0.09           $ (1.97)   $ (0.39) $ 0.09 $ 0.04         $ (1.94) $ (0.03)            
[1] Basic and diluted earnings per common share are calculated based on amounts attributable to common shareholders of Corporate Office Properties Trust.