Financial Instruments and Fair Values - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreement liability	$ 4,887		$ 4,887		$ 8,849
Net unrealized gain (loss)			8,500	$ (13,400)
Interest rate swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreement liability	4,900		4,900
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		265,000		265,000
Net unrealized gain (loss)	2,800	$ 2,900
Net loss to be reclassified into interest expense within the next 12 months			(11,000)
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 agreement liability	$ 4,900		$ 4,900		$ 8,800