Pension and Other Postretirement Benefits - Benefits Expected to be Paid in Subsequent Years from Our Pension and Other Postretirement as Well as Medicare Subsidy Receipts (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Pension Benefits
Pension And Other Employee Benefit Plans [Line Items]
2019	$ 21,667
2020	22,965
2021	22,199
2022	23,157
2023	22,081
2024-2028	111,338
Total	223,407
Other Benefits
Pension And Other Employee Benefit Plans [Line Items]
2019	1,432
2020	1,436
2021	1,438
2022	1,438
2023	1,432
2024-2028	7,196
Total	$ 14,372