Equity - COPT and Subsidiaries (Details) (USD $)	1 Months Ended			12 Months Ended			0 Months Ended
	Nov. 30, 2014	Mar. 31, 2013	Oct. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jul. 16, 2013	Jun. 16, 2014	Apr. 22, 2013
Preferred Stock
Number of shares issued				7,431,667
Aggregate liquidation preference				$ 199,083,000	$ 249,083,000
Stock redeemed or called during period value				50,000,000	84,750,000	55,000,000
Common Shares
Shares issued to the public	5,520,000	4,485,000
Per share value of common and preferred shares issued to the public (in dollars per share)	$ 27.30	$ 26.34
Net proceeds from issue of shares after underwriter discounts but before offering expenses	148,900,000	118,100,000		148,666,000	117,961,000
At-market-stock, offering program established, aggregate value			150,000,000.0
Number of common shares for each converted common unit (in shares)				1
Number of operating partnerships units converted into common shares (in units)				140,149	311,343	234,246
Dividends declared per common share				$ 1.1000	$ 1.10	$ 1.10
Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public					1,500,000		1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses							38,500,000
Issuance of stock, weighted average price per share							$ 26.05
Payments of stock issuance costs							586,000
At-market stock, offering program established, remaining capacity				110,900,000
Preferred Shares
Preferred Stock
Number of preferred shares authorized				25,000,000
Number of preferred shares of beneficial interest authorized (in dollars per share)				$ 0.01
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses						165,652,000
Series H
Preferred Stock
Annual dividend yield								7.50%
Preferred stock, redemption price per share								$ 25.00
Stock redeemed or called during period value								50,000,000
Issuance costs associated with redeemed preferred shares								1,800,000
Series K
Preferred Stock
Number of shares issued				531,667
Aggregate liquidation preference				26,583,000
Annual dividend yield				5.60%
Annual dividend per share (in dollars per share)				$ 2.80000
Number of common shares to be issued on conversion of each preferred share				0.8163
Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued				6,900,000
Aggregate liquidation preference				172,500,000
Annual dividend yield				7.375%
Annual dividend per share (in dollars per share)				$ 1.84375
Series J
Preferred Stock
Annual dividend yield									7.625%
Preferred stock, redemption price per share									$ 25.00
Stock redeemed or called during period value									84,800,000
Issuance costs associated with redeemed preferred shares									2,900,000
Corporate Office Properties, L.P.
Preferred Stock
Number of shares issued				7,431,667
Aggregate liquidation preference				199,083,000
Stock redeemed or called during period value				50,000,000	84,750,000	55,000,000
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses				148,666,000	117,961,000
Number of common shares for each converted common unit (in shares)				1
Number of operating partnerships units converted into common shares (in units)				140,149.000	311,343.000
Dividends declared per common share				$ 1.1	$ 1.10	$ 1.10
Corporate Office Properties, L.P. | Common Stock Issued to Public Under At-the-Market Program
Common Shares
Shares issued to the public							1,500,000
Net proceeds from issue of shares after underwriter discounts but before offering expenses							38,500,000
Issuance of stock, weighted average price per share							$ 26.05
Payments of stock issuance costs							586,000
Corporate Office Properties, L.P. | Preferred Shares
Common Shares
Net proceeds from issue of shares after underwriter discounts but before offering expenses						165,652,000
Corporate Office Properties, L.P. | Series H
Preferred Stock
Annual dividend yield								7.50%
Preferred stock, redemption price per share								$ 25.00
Stock redeemed or called during period value								50,000,000
Issuance costs associated with redeemed preferred shares								1,800,000
Corporate Office Properties, L.P. | Series K
Preferred Stock
Number of shares issued				531,667
Aggregate liquidation preference				26,583,000
Annual dividend yield				5.60%
Annual dividend per share (in dollars per share)				$ 2.80000
Number of common shares to be issued on conversion of each preferred share				0.8163
Corporate Office Properties, L.P. | Series L Cumulative Preferred Stock
Preferred Stock
Number of shares issued				6,900,000
Aggregate liquidation preference				172,500,000
Annual dividend yield				7.375%
Annual dividend per share (in dollars per share)				$ 1.84375
Corporate Office Properties, L.P. | Series J
Preferred Stock
Annual dividend yield									7.625%
Preferred stock, redemption price per share									$ 25.00
Stock redeemed or called during period value									84,800,000
Issuance costs associated with redeemed preferred shares									$ 2,900,000