Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details 2)

v3.8.0.1
Fair Value Measurements (Details 2) - Fair value measurement on a recurring basis [Member] - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Assets:    
Interest rate derivatives $ 3,073 $ 158
Assets 7,689 5,595
Liabilities:    
Deferred compensation plan liability 4,616 5,437
Interest rate derivatives   1,572
Redeemable preferred shares of beneficial interest   26,583
Liabilities   33,592
Mutual funds [Member]    
Assets:    
Marketable securities in deferred compensation plan 4,547 5,346
Other [Member]    
Assets:    
Marketable securities in deferred compensation plan 69 91
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]    
Assets:    
Assets 4,616 5,437
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mutual funds [Member]    
Assets:    
Marketable securities in deferred compensation plan 4,547 5,346
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]    
Assets:    
Marketable securities in deferred compensation plan 69 91
Significant Other Observable Inputs (Level 2) [Member]    
Assets:    
Interest rate derivatives 3,073 158
Assets 3,073 158
Liabilities:    
Deferred compensation plan liability 4,616 5,437
Interest rate derivatives   1,572
Redeemable preferred shares of beneficial interest   26,583
Liabilities   33,592
Corporate Office Properties, L.P. [Member]    
Assets:    
Interest rate derivatives 3,073 158
Liabilities:    
Interest rate derivatives   1,572
Redeemable preferred shares of beneficial interest   26,583
Liabilities   28,155
Corporate Office Properties, L.P. [Member] | Significant Other Observable Inputs (Level 2) [Member]    
Assets:    
Interest rate derivatives $ 3,073 158
Liabilities:    
Interest rate derivatives   1,572
Redeemable preferred shares of beneficial interest   26,583
Liabilities   $ 28,155