Employee Benefits - Benefit Obligation Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Benefit Obligation
Benefit obligation at the beginning of the period	$ 19,214	$ 18,927	$ 20,793
Service cost	392	335	367
Interest cost	485	658	600
Payments	(1,913)	(1,913)	(1,913)
Actuarial (gain) loss	1,568	1,207	(920)
Benefit obligation at the end of the period	$ 19,746	$ 19,214	$ 18,927