Employee Benefit Plans - Reconciliation of Benefit Obligations, Plan Assets and Funded Status (Details) - Other postretirement benefits - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation at beginning of year	$ 6,075	$ 5,551
Service cost	103	103	$ 124
Interest cost	154	210	189
Actuarial gain	202	657
Plan participants' contributions	474	532
Benefits paid	(863)	(978)
Benefit obligation and funded status at end of year	$ 6,145	$ 6,075	$ 5,551