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

Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements (Details 3)

Fair Value Measurements (Details 3) $ in Thousands	3 Months Ended						12 Months Ended
Fair Value Measurements (Details 3) $ in Thousands	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($) Property	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Fair value of impaired properties and other assets
Assets held for sale, net	$ 42,226		$ 94,654				$ 42,226	$ 94,654
Impairment losses							15,123	101,391	$ 23,289
Held-for-sale [Member]
Fair value of impaired properties and other assets
Assets held for sale, net	42,226		94,654				42,226	94,654
Fort Meade/BW Corridor [Member]
Fair value of impaired properties and other assets
Number of properties \| Property						2
Fair value measurement on a nonrecurring basis [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Assets held for sale, net			94,700	$ 161,500	$ 300,600	$ 225,900		$ 94,700	96,800
Impairment losses				11,500		$ 2,400
Fair value measurement on a nonrecurring basis [Member] \| Disposed of by sale [Member]
Fair value of impaired properties and other assets
Impairment losses			300
Transaction value of operating property dispositions			54,100	210,700
Fair value measurement on a nonrecurring basis [Member] \| Operating properties, net [Member]
Fair value of impaired properties and other assets
Assets	3,850						3,850
Fair value measurement on a nonrecurring basis [Member] \| Operating properties, net [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of impaired properties and other assets
Assets	3,850						3,850
Fair value measurement on a nonrecurring basis [Member] \| Projects in development or held for future development [Member]
Fair value of impaired properties and other assets
Assets	1,755						1,755
Fair value measurement on a nonrecurring basis [Member] \| Projects in development or held for future development [Member] \| Fair Value, Inputs, Level 3 [Member]
Fair value of impaired properties and other assets
Assets	1,755						$ 1,755
Fair value measurement on a nonrecurring basis [Member] \| Northern Virginia Defense/IT and Fort Meade/Baltimore Washington Corridor [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment losses					14,100
Fair value measurement on a nonrecurring basis [Member] \| Defense/Information Technology Sector [Member] \| Northern Virginia Defense/IT [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment losses				13,300
Fair value measurement on a nonrecurring basis [Member] \| Aberdeen, Maryland [Member] \| Land in development or held for future development [Member]
Fair value of impaired properties and other assets
Impairment of Long-Lived Assets to be Disposed of	4,700
Impairment losses					4,400
Fair value measurement on a nonrecurring basis [Member] \| Aberdeen, Maryland [Member] \| Other Segments [Member]
Fair value of impaired properties and other assets
Impairment of Long-Lived Assets to be Disposed of	$ 9,000
Fair value measurement on a nonrecurring basis [Member] \| Frederick, Maryland [Member] \| Land in development or held for future development [Member]
Fair value of impaired properties and other assets
Impairment losses					8,200
Fair value measurement on a nonrecurring basis [Member] \| Greater Philadelphia [Member] \| Regional Office [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment losses					6,200
Fair value measurement on a nonrecurring basis [Member] \| Colorado Springs, Colorado and White Marsh, Maryland [Member] \| Regional Office [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment losses					2,400
Fair value measurement on a nonrecurring basis [Member] \| Colorado Springs [Member] \| Held-for-sale [Member] \| Land in development or held for future development [Member]
Fair value of impaired properties and other assets
Impairment losses									12,800
Fair value measurement on a nonrecurring basis [Member] \| White Marsh, Maryland [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment of Long-Lived Assets to be Disposed of		$ 1,600
Impairment losses			$ 1,300	10,000
Fair value measurement on a nonrecurring basis [Member] \| White Marsh, Maryland [Member] \| Held-for-sale [Member] \| Land in development or held for future development [Member]
Fair value of impaired properties and other assets
Impairment losses				$ 2,900
Fair value measurement on a nonrecurring basis [Member] \| White Marsh, Maryland [Member] \| Regional Office [Member] \| Held-for-sale [Member]
Fair value of impaired properties and other assets
Impairment losses									2,600
Operating properties, net [Member] \| Fair value measurement on a nonrecurring basis [Member] \| Aberdeen, Maryland [Member] \| Land in development or held for future development [Member]
Fair value of impaired properties and other assets
Impairment losses									6,600
Operating properties, net [Member] \| Fair value measurement on a nonrecurring basis [Member] \| Aberdeen, Maryland [Member] \| Other Segments [Member]
Fair value of impaired properties and other assets
Impairment losses					$ 34,400
Operating properties, net [Member] \| Fair value measurement on a nonrecurring basis [Member] \| Northern Virginia [Member] \| Regional Office [Member]
Fair value of impaired properties and other assets
Impairment losses									$ 1,300