Financial Instruments and Fair Values - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Interest rate swap agreements liability	$ 8,849,000	$ 13,330,000
Interest rate swaps
Derivative [Line Items]
Interest rate swap agreements liability	8,900,000
Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Loss expected to be reclassified within twelve months	11,500,000
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Aggregate notional value	265,000,000.0	390,000,000.0
Unrealized loss on valuation of interest rate swap agreements	10,500,000	20,600,000
Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap, Three Month LIBOR, 2.9580% | LIBOR
Derivative [Line Items]
Notional amount	125,000,000.0
Payment of termination settlement fee	20,300,000
Accounts payable and accrued expenses | Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Interest rate swap agreements liability	$ 8,800,000	$ 13,300,000