Annual report pursuant to Section 13 and 15(d)

Equity - COPT and Subsidiaries (Details)

v3.6.0.2
Equity - COPT and Subsidiaries (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Jan. 21, 2017
Jun. 16, 2014
Sep. 30, 2016
Nov. 30, 2014
Oct. 31, 2012
Dec. 31, 2016
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Preferred Stock                  
Number of shares issued           7,431,667 7,431,667    
Aggregate liquidation preference           $ 172,500,000 $ 172,500,000 $ 199,083,000  
Aggregate liquidation preference           $ 199,083,000 199,083,000    
Stock redeemed or called during period value             $ 26,583,000   $ 50,000,000
Common Shares                  
Shares issued to the public       5,520,000          
Per share value of common and preferred shares issued to the public (in dollars per share)       $ 27.30          
Net proceeds from issue of shares after underwriter discounts but before offering expenses       $ 148,900,000         $ 148,666,000
Number of common shares for each converted common unit (in shares)             1    
Number of operating partnerships units converted into common shares (in units)             87,000 160,160 140,149
Dividends declared per common share (in dollars per share)             $ 1.1 $ 1.10 $ 1.10
Common Stock Issued to Public Under At-the-Market Program [Member]                  
Common Shares                  
Shares issued to the public           3,721,227 3,721,227 890,241 0
At-market-stock, offering program established, aggregate value     $ 200,000,000   $ 150,000,000.0        
Issuance of stock, weighted average price per share (in dollars per share)           $ 29.56   $ 30.29  
Net proceeds from shares issued           $ 109,100,000   $ 26,600,000  
Payments of stock issuance costs           900,000   $ 400,000  
At-market stock, offering program established, remaining capacity           $ 90,000,000 $ 90,000,000    
Preferred Shares [Member]                  
Preferred Stock                  
Number of preferred shares authorized           25,000,000 25,000,000    
Number of preferred shares of beneficial interest authorized (in dollars per share)           $ 0.01 $ 0.01    
Series K [Member]                  
Preferred Stock                  
Number of shares issued           531,667 531,667    
Number of common shares to be issued on conversion of each preferred share           0.8163 0.8163    
Aggregate liquidation preference           $ 26,583,000 $ 26,583,000    
Annual dividend yield             5.60%    
Annual dividend per share (in dollars per share)             $ 2.80000    
Issuance costs associated with redeemed preferred shares             $ 17,000    
Series K [Member] | Subsequent Event [Member]                  
Preferred Stock                  
Preferred stock, redemption price per share (in dollars per share) $ 50                
Series K [Member] | Subsequent Event [Member] | Significant Other Observable Inputs (Level 2) [Member]                  
Preferred Stock                  
Stock redeemed or called during period value $ 26,600,000                
Series L [Member]                  
Preferred Stock                  
Number of shares issued           6,900,000 6,900,000    
Aggregate liquidation preference           $ 172,500,000 $ 172,500,000    
Annual dividend yield             7.375%    
Annual dividend per share (in dollars per share)             $ 1.84375    
Series H [Member]                  
Preferred Stock                  
Annual dividend yield   7.50%              
Preferred stock, redemption price per share (in dollars per share)   $ 25              
Stock redeemed or called during period value   $ 50,000,000              
Issuance costs associated with redeemed preferred shares   $ 1,800,000