Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies (Details)

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Summary of Significant Accounting Policies (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
 3 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Misapplication Of Accounting Guidance Related To Recognition Of Deferred Tax Asset
Scenario, Previously Reported
Mar. 31, 2012
Misapplication Of Accounting Guidance Related To Recognition Of Deferred Tax Asset
Scenario, Adjustment
Sep. 30, 2012
Misapplication Of Accounting Guidance Related To Recognition Of Deferred Tax Asset
Scenario, Adjustment
Dec. 31, 2011
Over accrual Of Incentive Compensation Cost
Scenario, Previously Reported
Mar. 31, 2012
Over accrual Of Incentive Compensation Cost
Scenario, Adjustment
Sep. 30, 2012
Over accrual Of Incentive Compensation Cost
Scenario, Adjustment
Dec. 31, 2011
Misapplication of Accounting Guidance Related to Recognition of Deferred Tax Asset and Over Accrual of Incentive Compensation Cost [Member]
Scenario, Previously Reported
Mar. 31, 2012
Misapplication of Accounting Guidance Related to Recognition of Deferred Tax Asset and Over Accrual of Incentive Compensation Cost [Member]
Scenario, Adjustment
Sep. 30, 2012
Misapplication of Accounting Guidance Related to Recognition of Deferred Tax Asset and Over Accrual of Incentive Compensation Cost [Member]
Scenario, Adjustment
Quantifying Misstatement in Current Year Financial Statements [Line Items]                          
Net (loss) income $ (20,765) $ 7,470 $ (1,927) $ (37,103) $ 4,000     $ (700)     $ 3,300 $ (3,300) $ (3,300)
Income tax (expense) benefit 106 (457) 4,296 (6,043) (4,000) 4,000 4,000            
General and administrative expenses $ 5,061 $ 6,154 $ 19,820 $ 19,251       $ 700 $ (700) $ (700)      
Earnings per share, basic $ (0.39) [1] $ 0.03 [1] $ (0.27) [1] $ (0.70) [1] $ 0.05 $ (0.05) $ (0.05) $ (0.01) $ 0.01 $ 0.01 $ 0.04 $ (0.04) $ (0.04)
Earnings per share, diluted $ (0.39) [1] $ 0.03 [1] $ (0.27) [1] $ (0.70) [1] $ 0.05 $ (0.05) $ (0.05) $ (0.01) $ 0.01 $ 0.01 $ 0.04 $ (0.04) $ (0.04)
[1] Basic and diluted earnings per common share are calculated based on amounts attributable to common shareholders of Corporate Office Properties Trust.