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

Properties, Net (Details 6) ft² in Thousands, $ in Millions	6 Months Ended
Properties, Net (Details 6) ft² in Thousands, $ in Millions	Jun. 30, 2016 USD ($) ft² Property
Construction and Redevelopment Activities
Sale price of land \| $	$ 5.7
Office properties under, or contractually committed for, construction or approved for redevelopment
Construction and Redevelopment Activities
Number of real estate properties	12
Square footage of real estate properties (in square feet) \| ft²	1,500
Newly constructed properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service \| ft²	298
Number of real estate properties	2
Newly redeveloped properties placed in service
Construction and Redevelopment Activities
Square feet of properties placed in service \| ft²	55
Number of real estate properties	2
Properties under construction or contractually committed for construction
Construction and Redevelopment Activities
Number of real estate properties	9
Square footage of real estate properties (in square feet) \| ft²	1,400
Properties completed Held-for-future lease \| Office properties under, or contractually committed for, construction or approved for redevelopment
Construction and Redevelopment Activities
Number of real estate properties	2
Properties under or approved for redevelopment
Construction and Redevelopment Activities
Number of real estate properties	3
Square footage of real estate properties (in square feet) \| ft²	104