Employee Benefit Plans - Amounts recognized in consolidated balance sheets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Long-term pension liabilities	$ (33,080,000)	$ (39,254,000)
Cash contribution made	4,450,000
Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Funded status of the Retirement Income Plan	(2,052,000)	(8,377,000)
SERP liability	(31,028,000)	(30,877,000)
Long-term pension liabilities	$ (33,080,000)	$ (39,254,000)