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, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	$ 48,466	$ 44,359
Net prior service cost	2,734	11
Total	51,200
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss (gain)	(3,047)	(1,545)
Net prior service cost	0	$ 0
Total	$ (3,047)