Pension and Other Postretirement Benefit Plans - Summary of Reconciliation of Changes in Plans Benefit Obligations Fair Value of Assets and Funded Status (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Fair value of assets, beginning balance	$ 312,455
Fair value of assets, ending balance	338,264	$ 312,455
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning balance	(428,216)	(459,439)
Interest cost	(18,324)	(17,090)	$ (18,731)
Actuarial (loss) gain, net	(47,632)	18,529
Benefits paid	30,736	29,784
Benefit obligation at ending balance	(463,436)	(428,216)	(459,439)
Change in plan assets:
Fair value of assets, beginning balance	312,455	347,773
Actual return on plan assets	54,945	(25,333)
Employer contributions	1,600	19,800
Benefits paid	(30,736)	(29,785)
Fair value of assets, ending balance	338,264	312,455	$ 347,773
Unfunded status at December 31	$ (125,172)	$ (115,761)