Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,109	$ 956
Interest cost	3,781	4,840
Expected return on plan assets	(4,921)	(5,444)
Amortization of prior service cost (credit)	43	16
Recognized actuarial loss (gain)	2,359	1,833
Net periodic benefit cost (credit)	2,371	2,201
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	35	50
Amortization of prior service cost (credit)	(509)	(509)
Recognized actuarial loss (gain)	(19)	(96)
Net periodic benefit cost (credit)	$ (493)	$ (555)