Pension Plans and Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,000	$ 2,600
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,819	2,456
Interest cost	9,302	11,592
Expected return on plan assets	(19,364)	(17,436)
Amortization of prior service cost (credit)	825	725
Net periodic benefit (income) cost	(6,418)	(2,663)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	166	145
Interest cost	410	585
Expected return on plan assets	(672)	(627)
Amortization of prior service cost (credit)	(48)	(78)
Net periodic benefit (income) cost	$ (144)	$ 25