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

Annual report pursuant to Section 13 and 15(d)

Properties, Net (Narrative) (Details)

Properties, Net (Narrative) (Details) ft² in Thousands	3 Months Ended	12 Months Ended
Properties, Net (Narrative) (Details) ft² in Thousands	Dec. 31, 2018 USD ($) ft² property	Dec. 31, 2019 USD ($) ft² property	Dec. 31, 2018 USD ($) ft² property	Dec. 31, 2017 USD ($) ft² property	Dec. 05, 2019 property	Jun. 20, 2019 property	Oct. 27, 2017 USD ($) ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges		$ 329,000	$ 2,367,000	$ 15,116,000
Newly-developed properties placed in service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property	6	9	6	8
Area of real estate property (in sqft or acres) \| ft²	666	1,100	666	1,100
Redeveloped Property Placed in Service, Partially-Operational
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property		1
Area of real estate property (in sqft or acres) \| ft²		85
Properties under development or Contractually Commited for Construction
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property		13
Area of real estate property (in sqft or acres) \| ft²		2,300
Properties Under Or Approved For Redevelopment, Partially-Operational
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property		1
Area of real estate property (in sqft or acres) \| ft²		106
Newly-developed properties placed in service, partially operational
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property	2		2
Newly redeveloped properties placed In service
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property	1		1	3
Area of real estate property (in sqft or acres) \| ft²	22		22	94
Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties \| property				12
Transaction Value				$ 125,829,000
Gain (loss) on disposal				$ 5,636,000
Area of real estate property (in sqft or acres) \| ft²				799
Proceeds from sale of land held-for-investment				$ 14,300,000
Gains on sale of other land				$ 4,200,000
Fort Meade/BW Corridor sub-segment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges	$ 2,400,000
BREIT COPT DC JV LLC \| Variable Interest Entity, Not Primary Beneficiary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage		10.00%
Data Center Shells in Northern Virginia \| Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage sold		90.00%
Number of real estate properties \| property		9			2	7
Transaction Value		$ 345,100,000
Proceeds from divestiture of businesses		310,600,000
Gain (loss) on disposal		$ 105,200,000
Data Center Shells in Chester, Virginia \| Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transaction Value							$ 44,000,000.0
Gain (loss) on disposal	$ 1,500,000
Area of real estate property (in sqft or acres) \| ft²							193
Maximum exposure							$ 20,000,000