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

Properties, Net (Details 4) ft² in Thousands	Mar. 31, 2018 ft² Property
Newly constructed properties placed in service
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) \| ft²	74
Number of real estate properties \| Property	1
Newly redeveloped properties placed in service
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) \| ft²	11
Number of real estate properties \| Property	1
Properties under construction or contractually committed for construction
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) \| ft²	597
Number of real estate properties \| Property	6
Properties under or approved for redevelopment
Construction, Redevelopment and Dispositions
Square footage of real estate properties (in square feet) \| ft²	22
Number of real estate properties \| Property	1