Annual report pursuant to Section 13 and 15(d)

Equity - COPT and Subsidiaries (Details)

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Equity - COPT and Subsidiaries (Details) - USD ($)
 1 Months Ended 12 Months Ended
Nov. 02, 2017
Jun. 27, 2017
Jan. 21, 2017
Nov. 30, 2018
Sep. 30, 2016
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Preferred Stock                
Stock redeemed or called during period value               $ 172,500,000
Common Shares                
Number of common shares for each converted common unit (in shares)           1    
Number of operating partnerships units converted into common shares (in units)           105,039 1,904,615 339,513
Dividends declared per common share (in dollars per share)           $ 1.10 $ 1.10 $ 1.10
Preferred Shares                
Preferred Stock                
Number of preferred shares authorized           25,000,000.0    
Number of preferred shares of beneficial interest authorized (in dollars per share)           $ 0.01    
Series K Preferred Shares                
Preferred Stock                
Annual dividend yield     5.60%          
Series L                
Preferred Stock                
Annual dividend yield   7.375%            
Preferred stock redemption premium               $ 6,800,000
2016 ATM Program                
Common Shares                
Shares issued to the public             992,000 591,000
Issuance of stock, weighted average price per share (in dollars per share)             $ 30.46 $ 33.84
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses             $ 29,800,000 $ 19,700,000
Payments of stock issuance costs             $ 500,000 $ 300,000
2016 ATM Program | Common Shares                
Common Shares                
At-market-stock, offering program established, aggregate value         $ 200,000,000.0      
Shares issued to the public             992,000 591,000
Issuance of stock, weighted average price per share (in dollars per share)             $ 30.46 $ 33.84
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses             $ 29,800,000 $ 19,700,000
Payments of stock issuance costs             $ 500,000 $ 300,000
2018 ATM Program | Common Shares                
Common Shares                
At-market-stock, offering program established, aggregate value       $ 300,000,000        
Forward Equity Sale Agreement | Common Shares                
Common Shares                
Shares issued to the public           1,600,000 5,900,000 1,700,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses           $ 46,500,000 $ 172,500,000 $ 50,000,000.0
Forward equity sale agreement (in shares) 9,200,000              
Net proceeds from issuance of shares before underwriting discounts, commission and offering expenses $ 285,200,000              
Initial gross offering price per share (in dollars per share) $ 31.00              
Corporate Office Properties, L.P                
Preferred Stock                
Stock redeemed or called during period value               $ 172,500,000
Common Shares                
Number of common shares for each converted common unit (in shares)           1 1 1
Number of operating partnerships units converted into common shares (in units)           105,039 1,900,000 339,513
Dividends declared per common share (in dollars per share)           $ 1.10 $ 1.10 $ 1.10
Corporate Office Properties, L.P | Series K Preferred Shares                
Preferred Stock                
Annual dividend yield     5.60%          
Preferred stock, redemption price per share (in dollars per share)     $ 50.00          
Stock redeemed or called during period value     $ 26,600,000          
Corporate Office Properties, L.P | Series L                
Preferred Stock                
Annual dividend yield   7.375%            
Preferred stock, redemption price per share (in dollars per share)   $ 25.00            
Stock redeemed or called during period value   $ 172,500,000            
Preferred stock redemption premium               $ 6,800,000