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

Annual report pursuant to Section 13 and 15(d)

Debt, Net (Details 4)

Debt, Net (Details 4)				1 Months Ended		12 Months Ended
Debt, Net (Details 4)	Oct. 10, 2018 USD ($) extension	Dec. 28, 2016 USD ($)	Dec. 17, 2015 USD ($)	Nov. 30, 2018 USD ($)	May 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Term Loan Facilities Maturing 2020 [Member]
Debt Instrument [Line Items]
Repayments of term loan				$ 100,000,000	$ 200,000,000
Term Credit Facility Effective August 2012 [Member]
Debt Instrument [Line Items]
Repayments of term loan								$ 120,000,000
Term Loan Facilities [Member]
Debt Instrument [Line Items]
Stated interest rate (as a percent)						3.60%
Minimum [Member] \| Term Loan Facilities [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)						0.85%
Maximum [Member] \| Term Loan Facilities [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)						1.65%
Revolving Credit Facility [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Weighted average borrowings						$ 188,100,000	$ 97,800,000
Weighted average interest rate (as a percent)						3.08%	2.44%
Line of Credit [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum availability	$ 800,000,000					$ 800,000,000
Aggregate maximum borrowing capacity	$ 1,250,000,000
Number of extensions \| extension	2
Extension option period (in years)	6 months
Line of credit facility, extension fee percentage	0.075%
Remaining borrowing capacity						587,000,000
Line of Credit [Member] \| Revolving Credit Facility [Member] \| Minimum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)	0.775%
Commitment fee percentage	0.125%
Line of Credit [Member] \| Revolving Credit Facility [Member] \| Maximum [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)	1.45%
Commitment fee percentage	0.30%
Unsecured Debt [Member] \| Term Credit Facility Effective December 2015 [Member]
Debt Instrument [Line Items]
Maximum availability			$ 250,000,000
Remaining borrowing capacity						$ 150,000,000
Initial amount borrowed			$ 100,000,000
Unsecured Debt [Member] \| Term Credit Facility Effective December 2016 [Member]
Debt Instrument [Line Items]
Initial amount borrowed		$ 150,000,000
Unsecured Debt [Member] \| Term Loan Facilities [Member]
Debt Instrument [Line Items]
Maximum availability	$ 500,000,000
Unsecured Debt [Member] \| Minimum [Member] \| Term Credit Facility Effective December 2015 [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)			0.85%
Unsecured Debt [Member] \| Maximum [Member] \| Term Credit Facility Effective December 2015 [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Variable rate, spread (as a percent)			1.65%
Senior Notes [Member]
Debt Instrument [Line Items]
Redemption price (percent)						100.00%
Senior Notes [Member] \| 5.0% Senior Notes [Member]
Debt Instrument [Line Items]
Loan amount						$ 300,000,000
Stated interest rate (as a percent)						5.00%
Unamortized discount included in carrying value						$ 2,400,000	$ 2,700,000
Interest rate on debt (as a percent)						5.15%
Senior Notes [Member] \| 5.0% Senior Notes [Member] \| Adjusted Treasury [Member]
Debt Instrument [Line Items]
Basis points used in determining redemption price prior to maturity						0.45%
Senior Notes [Member] \| 3.70% Senior Notes [Member]
Debt Instrument [Line Items]
Loan amount						$ 300,000,000
Stated interest rate (as a percent)						3.70%
Unamortized discount included in carrying value						$ 900,000	1,300,000
Interest rate on debt (as a percent)						3.85%
Senior Notes [Member] \| 3.70% Senior Notes [Member] \| Adjusted Treasury [Member]
Debt Instrument [Line Items]
Basis points used in determining redemption price prior to maturity						0.25%
Senior Notes [Member] \| 3.60% Senior Notes [Member]
Debt Instrument [Line Items]
Loan amount						$ 350,000,000
Stated interest rate (as a percent)						3.60%
Unamortized discount included in carrying value						$ 1,400,000	1,700,000
Interest rate on debt (as a percent)						3.70%
Senior Notes [Member] \| 3.60% Senior Notes [Member] \| Adjusted Treasury [Member]
Debt Instrument [Line Items]
Basis points used in determining redemption price prior to maturity						0.30%
Senior Notes [Member] \| 5.250% Senior Notes [Member]
Debt Instrument [Line Items]
Loan amount						$ 250,000,000
Stated interest rate (as a percent)						5.25%
Unamortized discount included in carrying value						$ 2,600,000	$ 3,000,000
Interest rate on debt (as a percent)						5.49%
Senior Notes [Member] \| 5.250% Senior Notes [Member] \| Adjusted Treasury [Member]
Debt Instrument [Line Items]
Basis points used in determining redemption price prior to maturity						0.40%