Employee Benefit Plans - Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Net gains or losses recognized in other comprehensive income
Net gains (losses)	$ (6,294)	$ (55,918)	$ 24,411
Prior service (costs) gains	(1,728)	0	0
Net gains or losses and prior service costs or credits reclassified from other comprehensive income
Pension settlement loss	8,787	0	0
Amortization of losses	10,244	11,648	11,651
Amortization of prior service (credit) cost	846	572	761
Postretirement
Net gains or losses recognized in other comprehensive income
Net gains (losses)	(97)	2,640	1,639
Prior service (costs) gains	0	0	0
Net gains or losses and prior service costs or credits reclassified from other comprehensive income
Pension settlement loss	0	0	0
Amortization of losses	81	229	333
Amortization of prior service (credit) cost	$ (153)	$ (153)	$ (151)