Derivative Instruments (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Interest rate swaps classified as:
Gross derivative assets	$ 0		$ 0		$ 0
Gross derivative liabilities	(10,618,000)		(10,618,000)		(5,121,000)
Net derivative liability	(10,618,000)		(10,618,000)		$ (5,121,000)
Amount of loss recognized in OCI	(2,443,000)	$ (1,386,000)	(26,949,000)	$ (6,874,000)
Total amount of Interest Expense presented in the consolidated statements of income	(12,725,000)	(16,145,000)	(41,942,000)	(46,750,000)
Interest rate swaps
Interest rate swaps classified as:
Total amount of Interest Expense presented in the consolidated statements of income	(12,725,000)	(16,145,000)	(41,942,000)	(46,750,000)
Interest rate swaps | Interest Expense
Interest rate swaps classified as:
Amount of loss recognized in OCI	(2,443,000)	(1,386,000)	(26,949,000)	(6,874,000)
Amount of previously recorded gain/(loss) reclassified from OCI into Interest Expense	(810,000)	$ 427,000	(989,000)	$ 1,871,000
$250 Million Unsecured 2018 Term Loan | Unsecured Debt
Derivative [Line Items]
Face amount of debt instrument	$ 250,000,000		$ 250,000,000
$250 Million Unsecured 2018 Term Loan | Interest rate swaps
Derivative [Line Items]
Number of swap agreements | contract	2		2
Notional amount	$ 100,000,000		$ 100,000,000
$250 Million Unsecured 2018 Term Loan | Interest rate swaps | Unsecured Debt
Derivative [Line Items]
Face amount of debt instrument	$ 250,000,000		$ 250,000,000