Employee Benefit Plans - Net Periodic Benefit Pension Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of net periodic benefit cost
Interest cost	$ 1,377	$ 1,841	$ 2,031
Expected return on plan assets	(3,763)	(4,642)	(3,820)
Recognized net actuarial loss	816	531	533
Amortization of prior service cost	0	0	0
Recognized settlement loss	2,931	1,781	2,703
Net periodic cost (income)	1,361	(489)	1,447
Other changes in plan assets and benefit obligations recognized as a charge to other comprehensive income (loss)
Net (loss) gain for the period	(8,584)	1,313	(7,086)
Amortization of net loss	3,747	2,311	3,236
Total unrealized (loss) gain	(4,837)	3,624	(3,850)
Total recognized in net periodic pension cost and other comprehensive income (loss)	$ (6,198)	$ 4,113	$ (5,297)
Weighted-average assumptions used to determine the net periodic cost
Discount rate	3.04%	4.10%	3.45%
Expected return on plan assets		5.75%	5.75%
Minimum
Weighted-average assumptions used to determine the net periodic cost
Expected return on plan assets	5.75%
Maximum
Weighted-average assumptions used to determine the net periodic cost
Expected return on plan assets	3.60%