Annual report pursuant to Section 13 and 15(d)

Properties, Net (Narrative) (Details)

v3.20.4
Properties, Net (Narrative) (Details)
ft² in Thousands
 3 Months Ended 12 Months Ended
Oct. 30, 2020
USD ($)
property
Sep. 30, 2020
USD ($)
Dec. 31, 2018
USD ($)
ft²
property
Dec. 31, 2019
USD ($)
ft²
property
Dec. 31, 2018
USD ($)
ft²
property
Dec. 31, 2020
ft²
property
Dec. 22, 2020
Dec. 05, 2019
property
Jun. 20, 2019
property
Oct. 27, 2017
USD ($)
ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Ownership percentage sold 90.00%     90.00%            
Number of properties sold 2     9            
B RE COPT DC JV II LLC                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Ownership percentage 10.00%         10.00% 10.00%      
Number of real estate properties           8        
BREIT COPT DC JV LLC                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Ownership percentage       10.00%   10.00%        
Number of real estate properties           9        
Baltimore, Maryland                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Impairment charges | $   $ 1,500,000                
Expansion of Fully-Operational Properties Placed in Service                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Area of real estate property (in sqft or acres) | ft²           42        
Number of real estate properties           3        
Properties Under Development, Partially-Operational                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Number of real estate properties           3        
Newly-developed properties placed in service                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Area of real estate property (in sqft or acres) | ft²     666 1,100 666 1,800        
Number of real estate properties     6 9 6 11        
Redeveloped Property Placed in Service                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Area of real estate property (in sqft or acres) | ft²           21        
Properties under development                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Area of real estate property (in sqft or acres) | ft²           1,500        
Number of real estate properties           11        
Newly redeveloped properties placed In service                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Area of real estate property (in sqft or acres) | ft²     22 85 22          
Number of real estate properties     1 1 1          
Fort Meade/BW Corridor sub-segment                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Impairment charges | $         $ 2,400,000          
Data Center Shells in Northern Virginia | Disposed of by sale                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Ownership percentage sold 90.00%     90.00%            
Number of properties sold 2     9       2 7  
Transaction value | $ $ 89,700,000     $ 345,100,000            
Proceeds from sale | $ 80,700,000     310,600,000            
Gain on disposal | $ $ 30,000,000.0     $ 105,200,000            
Data Center Shells in Chester, Virginia | Disposed of by sale                    
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]                    
Transaction value | $                   $ 44,000,000.0
Gain on disposal | $     $ 1,500,000              
Area of real estate property (in sqft or acres) | ft²                   193
Maximum exposure | $                   $ 20,000,000