Pension and Other Postretirement Benefits - Amounts Recognized in Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in the balance sheets:
Accrued benefit liability, noncurrent	$ (136,227)	$ (127,748)
Pension Benefits
Amounts recognized in the balance sheets:
Prepaid benefit cost	5,542	4,801
Accrued benefit liability, current	(3,000)	(3,162)
Accrued benefit liability, noncurrent	(108,168)	(103,010)
Net funded status	(105,626)	(101,371)
Other Benefits
Amounts recognized in the balance sheets:
Prepaid benefit cost	0	0
Accrued benefit liability, current	(1,411)	(1,405)
Accrued benefit liability, noncurrent	(28,059)	(24,738)
Net funded status	$ (29,470)	$ (26,143)