Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Details 5)

v3.10.0.1
Summary of Significant Accounting Policies (Details 5) - USD ($)
$ in Thousands
 12 Months Ended
Jan. 01, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Deferred non-incremental lease cost   $ 1,200 $ 1,100 $ 1,100  
Cumulative Distributions in Excess of Net Income [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance     (276)    
Cumulative Distributions in Excess of Net Income [Member] | Accounting Standards Update 2017-12 [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance         $ (276)
Accumulated Other Comprehensive Income (Loss) [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance     276    
Accumulated Other Comprehensive Income (Loss) [Member] | Accounting Standards Update 2017-12 [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance         276
Accumulated Other Comprehensive Income (Loss) [Member] | Corporate Office Properties, L.P. [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance     276    
Accumulated Other Comprehensive Income (Loss) [Member] | Corporate Office Properties, L.P. [Member] | Accounting Standards Update 2017-12 [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance         276
Common Shares [Member] | Corporate Office Properties, L.P. [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance     $ (276)    
Common Shares [Member] | Corporate Office Properties, L.P. [Member] | Accounting Standards Update 2017-12 [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of accounting change for adoption of hedge accounting guidance         $ (276)
Scenario, Forecast [Member] | Right-of-use Assets [Member] | Accounting Standards Update 2016-02 [Member] | Minimum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Effect of new accounting principle $ 14,000        
Scenario, Forecast [Member] | Right-of-use Assets [Member] | Accounting Standards Update 2016-02 [Member] | Maximum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Effect of new accounting principle 19,000        
Scenario, Forecast [Member] | Lease Liability [Member] | Accounting Standards Update 2016-02 [Member] | Minimum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Effect of new accounting principle 14,000        
Scenario, Forecast [Member] | Lease Liability [Member] | Accounting Standards Update 2016-02 [Member] | Maximum [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Effect of new accounting principle $ 19,000