Employee Benefit Plans - Net Periodic Benefit Cost Not yet Recognized (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ (2,842)	$ (1,681)
Net losses	(160,058)	(172,484)
Deferred income tax benefit	37,050	39,299
Accumulated other comprehensive income (loss)	(125,850)	(134,866)
Postretirement
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	1,185	1,338
Net losses	(2,266)	(2,280)
Deferred income tax benefit	293	218
Accumulated other comprehensive income (loss)	$ (788)	$ (724)