COPT Defense Properties Annual report pursuant to Section 13 and 15(d)

Properties, net (Details 3)

Properties, net (Details 3) (USD $)	12 Months Ended			0 Months Ended
Properties, net (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 23, 2013
Dispositions
Gain on early extinguishment of debt	$ (9,552,000)	$ (27,030,000)	$ (943,000)
Non-operating Properties
Dispositions
Gain on Disposition	5,600,000
Sale price of non-operating properties	28,300,000	3,500,000
Secured Debt \| December 2013 Portfolio Conveyance
Dispositions
Debt settled through the surrender of real estate assets				146,500,000
Gain on early extinguishment of debt				67,800,000
Secured Debt \| Fair value measurement on a nonrecurring basis \| December 2013 Portfolio Conveyance
Dispositions
Fair value of real estate disposed in settlement of debt				74,000,000
Operating properties
Dispositions
Number of Buildings Disposed	8	31
Total Rentable Square Feet	302,958	2,345,000
Transaction Value of Operating Property Dispositions	28,835,000	293,301,000
Gain on Disposition	5,093,000	2,671,000
Operating properties \| 4969 and 4979 Mercantile Rd
Dispositions
Number of Buildings Disposed	2
Total Rentable Square Feet	96,721
Transaction Value of Operating Property Dispositions	5,960,000
Gain on Disposition	2,124,000
Operating properties \| 9930 and 9940 Franklin Square
Dispositions
Number of Buildings Disposed	2
Total Rentable Square Feet	71,992
Transaction Value of Operating Property Dispositions	10,475,000
Gain on Disposition	2,303,000
Operating properties \| 5020, 5022, 5024 and 5026 Campbell Boulevard
Dispositions
Number of Buildings Disposed	4
Total Rentable Square Feet	134,245
Transaction Value of Operating Property Dispositions	12,400,000
Gain on Disposition	666,000
Operating properties \| 920 Elkridge Landing Road
Dispositions
Number of Buildings Disposed		1
Total Rentable Square Feet		103,000
Transaction Value of Operating Property Dispositions		6,900,000
Gain on Disposition		0
Operating properties \| 4230 Forbes Boulevard
Dispositions
Number of Buildings Disposed		1
Total Rentable Square Feet		56,000
Transaction Value of Operating Property Dispositions		5,600,000
Gain on Disposition		1,507,000
Operating properties \| December 2013 Colorado Springs Portfolio Disposition
Dispositions
Number of Buildings Disposed		15
Total Rentable Square Feet		1,165,000
Transaction Value of Operating Property Dispositions		133,925,000
Gain on Disposition		1,164,000
Operating properties \| December 2013 Portfolio Conveyance
Dispositions
Number of Buildings Disposed		14
Total Rentable Square Feet		1,021,000
Transaction Value of Operating Property Dispositions		146,876,000
Gain on Disposition		$ 0