Pension and Other Postretirement Benefits - Summary of Accumulated Other Comprehensive Loss That Have Not Been Recognized as Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 80,671	$ 56,746
Net prior service cost	2,798	2,661
Total	83,469
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(436)	(600)
Net prior service cost	0	$ 0
Total	$ (436)