Employee Benefit Plans - Change in Postretirement Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in Benefit Obligation
Benefit obligation at beginning of year	$ 29,777	$ 31,050	$ 37,482
Service cost	1,533	1,776	1,508
Interest cost	1,283	1,172	1,097
Actuarial (gain) loss	3,279	(3,165)	5,156
Benefits paid	(1,434)	(1,056)	(1,204)
Curtailments	0	0	(4,346)
Plan amendments	0	0	(8,643)
Benefit obligation at end of year	34,438	29,777	31,050
Change in Plan Assets
Fair value of plan assets at end of year	0	0	0
Funded status at end of year	$ (34,438)	$ (29,777)	$ (31,050)