COPT Defense Properties Quarterly report pursuant to Section 13 or 15(d)

Properties, net (Details 4)	6 Months Ended
Properties, net (Details 4)	Jun. 30, 2013 Property sqft
Newly constructed properties placed in service
Construction and Redevelopment Activities
Square Feet of Properties Placed in Service	236,000
Number of Real Estate Properties Placed In Service	3
Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties	11
Square footage of real estate properties (in square feet)	1,500,000
Properties under construction or contractually committed for construction \| Northern Virginia
Construction and Redevelopment Activities
Number of real estate properties	5
Properties under construction or contractually committed for construction \| Baltimore and Washington Corridor
Construction and Redevelopment Activities
Number of real estate properties	3
Properties under construction or contractually committed for construction \| Huntsville
Construction and Redevelopment Activities
Number of real estate properties	3
Properties under redevelopment \| Greater Philadelphia
Construction and Redevelopment Activities
Number of real estate properties	1
Square footage of real estate properties (in square feet)	183,000