Accumulated Other Comprehensive Income - Schedule of Amounts Reclassified from Accumulated Other Comprehensive Income into Consolidated Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amortization of prior service cost
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Amortization of prior service cost	$ 709	$ 709	$ 2,733
Postretirement Benefits
Line items in income statement impacted by reclassifications out of accumulated other comprehensive income
Amortization of prior service cost	709	709	2,733
Income tax expense	(162)	(162)	(1,010)
Cumulative effect of adoption of ASU 2018-02 reclassified to retained earnings	0	(446)	0
Total reclassifications for the period	$ 547	$ 101	$ 1,723