Pension and Other Postretirement Benefit Plans - Summary of Net Period Benefit Costs (Details) - Pension Benefits - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan And Other Postretirement Benefit Plan Table Text Block [Line Items]
Interest cost	$ 18,324	$ 17,090	$ 18,731
Expected return on plan assets	(18,510)	(18,790)	(20,934)
Amortization of prior service credit	(1,432)	(1,432)	(1,432)
Amortization of actuarial loss	6,516	7,362	6,517
Net cost	$ 4,898	$ 4,230	$ 2,882
Weighted-average discount rate used to measure benefit obligations	3.53%	4.41%	3.81%
Weighted average assumptions used to determine net benefit cost:
Discount rate	4.41%	3.81%	4.36%
Expected return on plan assets	5.75%	5.75%	6.50%