Annual report pursuant to Section 13 and 15(d)

Equity - COPT and Subsidiaries (Details)

v3.10.0.1
Equity - COPT and Subsidiaries (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Nov. 02, 2017
Jun. 27, 2017
Jan. 21, 2017
Nov. 30, 2018
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Preferred Stock                  
Stock redeemed or called during period value               $ 172,500,000 $ 26,583,000
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)             1,904,615 339,513 87,000
Dividends declared per common share (in dollars per share)             $ 1.1 $ 1.10 $ 1.10
Preferred Shares [Member]                  
Preferred Stock                  
Number of preferred shares authorized             25,000,000    
Number of preferred shares of beneficial interest authorized (in dollars per share)             $ 0.01    
Series K Preferred Shares [Member]                  
Preferred Stock                  
Annual dividend yield     5.60%            
Issuance costs associated with redeemed preferred shares           $ 17,000      
Series L [Member]                  
Preferred Stock                  
Annual dividend yield   7.375%              
Issuance costs associated with redeemed preferred shares               $ 6,800,000  
2016 ATM Program [Member]                  
Common Shares                  
Shares issued to the public             992,000 591,000 3,700,000
Issuance of stock, weighted average price per share (in dollars per share)           $ 29.56 $ 30.46 $ 33.84 $ 29.56
Payments of stock issuance costs             $ 500,000 $ 300,000 $ 900,000
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses             $ 29,800,000 $ 19,700,000 $ 109,100,000
2016 ATM Program [Member] | Common Shares [Member]                  
Common Shares                  
At-market-stock, offering program established, aggregate value         $ 200,000,000        
Shares issued to the public           3,700,000 992,000 591,000  
Issuance of stock, weighted average price per share (in dollars per share)           $ 29.56 $ 30.46 $ 33.84 $ 29.56
Payments of stock issuance costs           $ 900,000 $ 500,000 $ 300,000  
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses           109,100,000 $ 29,800,000 $ 19,700,000  
2018 ATM Program [Member] | Common Shares [Member]                  
Common Shares                  
At-market-stock, offering program established, aggregate value       $ 300,000,000          
Forward Equity Sale Agreement [Member] | Common Shares [Member]                  
Common Shares                  
Forward Equity Sale Agreement, Offering Program Established, Aggregate Shares 9,200,000                
Shares issued to the public             5,900,000 1,700,000  
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                
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses             $ 172,500,000 $ 50,000,000  
Remaining shares under agreements             1,600,000    
Settlement value of remaining capacity             $ 46,400,000    
Corporate Office Properties, L.P. [Member]                  
Preferred Stock                  
Stock redeemed or called during period value               $ 172,500,000 $ 26,583,000
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)             1,900,000 339,513.000 87,000
Dividends declared per common share (in dollars per share)             $ 1.1 $ 1.10 $ 1.10
Corporate Office Properties, L.P. [Member] | Series K Preferred Shares [Member]                  
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            
Issuance costs associated with redeemed preferred shares           $ 17,000      
Corporate Office Properties, L.P. [Member] | Series L [Member]                  
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              
Issuance costs associated with redeemed preferred shares               $ 6,800,000