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Derivative Instruments and Hedging Activities - Interest Rate Swap Agreements (Details) - Interest Rate Swap Agreements - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jul. 31, 2019
Derivative [Line Items]
Notional amount	$ 350,000,000		$ 350,000,000		$ 350,000,000	$ 350,000,000
Unrealized (gains) losses associated with interest rate swap agreements	(1,185,000)	$ 3,468,000	14,445,000	$ 11,073,000
Cumulative net losses in AOCI	23,219,000		23,219,000
Other Long-Term Liabilities
Derivative [Line Items]
Derivative liability	$ 23,219,000		$ 23,219,000		$ 8,774,000