Annual report pursuant to Section 13 and 15(d)

Real Estate Joint Ventures (Unconsolidated Real Estate Joint Ventures) (Details)

v3.20.4
Real Estate Joint Ventures (Unconsolidated Real Estate Joint Ventures) (Details)
$ in Thousands
Dec. 31, 2020
USD ($)
property
Dec. 22, 2020
Dec. 21, 2020
Oct. 30, 2020
Dec. 31, 2019
USD ($)
Unconsolidated Real Estate Joint Ventures          
Schedule of Equity Method Investments [Line Items]          
Number of real estate properties | property 17        
Real estate equity method investments $ 29,303       $ 51,949
B RE COPT DC JV II LLC          
Schedule of Equity Method Investments [Line Items]          
Ownership percentage 10.00% 10.00%   10.00%  
Number of real estate properties | property 8        
Real estate equity method investments $ 15,988       $ 0
Difference between the joint venture's cost basis and the entity's share of B RE COPT’s underlying equity in the net assets acquired from GI-COPT $ 7,400        
BREIT COPT DC JV LLC          
Schedule of Equity Method Investments [Line Items]          
Ownership percentage 10.00%       10.00%
Number of real estate properties | property 9        
Real estate equity method investments $ 13,315       $ 14,133
GI-COPT DC Partnership LLC          
Schedule of Equity Method Investments [Line Items]          
Ownership percentage     50.00%   50.00%
Real estate equity method investments $ 0       $ 37,816