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

Properties, Net (Details 6) ft² in Thousands, $ in Millions	3 Months Ended
Properties, Net (Details 6) ft² in Thousands, $ in Millions	Mar. 31, 2016 USD ($) ft² Property
Construction and Redevelopment Activities
Sale price of land \| $	$ 5.7
Newly constructed properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service	149
Number of real estate properties \| Property	1
Newly redeveloped properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service	51
Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties \| Property	8
Square footage of real estate properties (in square feet)	1,200
Properties under or approved for redevelopment
Construction and Redevelopment Activities
Number of real estate properties \| Property	3
Square footage of real estate properties (in square feet)	104