Benefit Plans - Change in Projected Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in projected benefit obligation:
Projected benefit obligation at beginning of year	$ 175,405	$ 157,364
Interest cost	4,941	6,113	$ 5,542
Actuarial loss	18,813	20,001
Benefits paid	(8,310)	(8,073)
Projected benefit obligation at end of year	190,849	175,405	157,364
Change in fair value of plan assets:
Fair value of plan assets at beginning of year	236,621	210,508
Actual return on plan assets	30,987	32,835
Employer contributions	1,353	1,351
Benefits paid	(8,310)	(8,073)
Fair value of plan assets at end of year	260,651	236,621	$ 210,508
Funded status of the plan
Asset recognized	69,802	61,216
Accumulated benefit obligation	190,849	175,405
Accrued interest receivable	$ 623	$ 641