Annual report pursuant to Section 13 and 15(d)

Equity - COPT and Subsidiaries (Details)

v3.20.4
Equity - COPT and Subsidiaries (Details) - USD ($)
 1 Months Ended 12 Months Ended
Nov. 30, 2018
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Nov. 02, 2017
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)   14,009 105,039 1,904,615  
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      
2018 ATM Program | Common Shares          
Common Shares          
At-market-stock, offering program established, aggregate value $ 300,000,000.0        
Shares issued to the public (in shares)   0      
Forward Equity Sale Agreement | Common Shares          
Common Shares          
Shares issued to the public (in shares)     1,600,000 5,900,000  
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses     $ 46,500,000 $ 172,500,000  
Initial gross offering price per share (in dollars per share)         $ 31.00
2016 ATM Program | Common Shares          
Common Shares          
Shares issued to the public (in shares)       992,000  
Net proceeds from issuance of shares after underwriting discounts and commissions but before offering expenses       $ 29,800,000  
Issuance of stock, weighted average price per share (in dollars per share)       $ 30.46  
Payments of stock issuance costs       $ 500,000