Financial Instruments and Fair Values - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	$ 6,176,000		$ 6,176,000		$ 8,849,000
Net unrealized gain (loss)			5,700,000	$ (16,300,000)
Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	6,200,000		6,200,000
Interest rate swap | Designated as hedging instrument | Cash flow hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate notional value	265,000,000.0		265,000,000.0		265,000,000.0
Net unrealized gain (loss)	2,800,000	$ 600,000
Net loss to be reclassified into interest expense within the next 12 months			(11,500,000)
Interest rate swap | Designated as hedging instrument | Cash flow hedging | Accounts payable and accrued expenses
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	$ 6,200,000		$ 6,200,000		$ 8,800,000