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

Fair Value Measurements (Details 3)

Fair Value Measurements (Details 3) (USD $)	12 Months Ended
Fair Value Measurements (Details 3) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair value of impaired properties and other assets
Impairment losses	$ 1,416,000us-gaap_AssetImpairmentCharges	$ 5,857,000us-gaap_AssetImpairmentCharges	$ 43,678,000us-gaap_AssetImpairmentCharges
Exit costs included in impairment losses in connection with dispositions	0	979,000	4,146,000
Fair value measurement on a recurring basis
Fair value of impaired properties and other assets
Assets	6,320,000	14,660,000
Fair value measurement on a nonrecurring basis \| Projects in development or held for future development
Fair value of impaired properties and other assets
Impairment losses			1,900,000
Fair value measurement on a nonrecurring basis \| Property Conveyances
Fair value of impaired properties and other assets
Impairment losses		11,000,000
Exit costs included in impairment losses in connection with dispositions		560,000
Fair value measurement on a nonrecurring basis \| Other Properties with Shortened Holding Periods
Fair value of impaired properties and other assets
Number of properties, shortened holding period		2
Fair value measurement on a nonrecurring basis \| Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses			19,000,000
Exit costs included in impairment losses in connection with dispositions		419,000
Fair value measurement on a nonrecurring basis \| Properties, Net
Fair value of impaired properties and other assets
Impairment losses		31,068,000
Assets		4,459,000
Fair value measurement on a nonrecurring basis \| Additional Property Disposed [Member]
Fair value of impaired properties and other assets
Impairment losses			5,100,000
Fair value measurement on a nonrecurring basis \| Significant Unobservable Inputs (Level 3) \| Strategic Reallocation Plan
Fair value of impaired properties and other assets
Exit costs included in impairment losses in connection with dispositions			4,200,000
Fair value measurement on a nonrecurring basis \| Significant Unobservable Inputs (Level 3) \| Properties, Net
Fair value of impaired properties and other assets
Exit costs included in impairment losses in connection with dispositions		979,000
Assets		4,459,000
Fair value measurement on a nonrecurring basis \| Discounted Cash Flow
Fair value of impaired properties and other assets
Discount rate		10.00%
Terminal capitalization rate		9.50%
Market rent growth rate		3.00%
Expense growth rate		3.00%
Fair value measurement on a nonrecurring basis \| Discounted Cash Flow \| Significant Unobservable Inputs (Level 3) \| Properties, Net
Fair value of impaired properties and other assets
Assets		4,459,000
Fair value measurement on a nonrecurring basis \| Discontinued Operations \| Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses		15,200,000	23,200,000
Fair value measurement on a nonrecurring basis \| Greater Baltimore \| Other Properties with Shortened Holding Periods
Fair value of impaired properties and other assets
Impairment losses	1,371,000	5,900,000
Fair value measurement on a nonrecurring basis \| Greater Philadelphia
Fair value of impaired properties and other assets
Impairment losses			46,100,000
Future expenditures for redevelopment			25,000,000
Fair value measurement on a nonrecurring basis \| Colorado Springs \| Strategic Reallocation Plan
Fair value of impaired properties and other assets
Impairment losses			$ 6,900,000
Redeemable non-controlling interest \| Fair value measurement on a recurring basis \| Significant Unobservable Inputs (Level 3)
Fair value of impaired properties and other assets
Discount rate	15.50%	15.50%