Summary of Significant Accounting Policies - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Amortization of employee benefit plan items:
Amounts reclassified from accumulated other comprehensive loss, tax	$ 5,100	$ 300
Amount reclassified out of accumulated other comprehensive income	13,657	(1,102)
Prior service cost
Amortization of employee benefit plan items:
Total before tax	(13)	(25)
Settlement expense
Amortization of employee benefit plan items:
Total before tax	19,900	641
Actuarial loss
Amortization of employee benefit plan items:
Total before tax	(1,103)	(2,010)
Amount reclassified out of accumulated other comprehensive loss
Amortization of employee benefit plan items:
Total before tax	18,784	(1,394)
Amounts reclassified from accumulated other comprehensive loss, tax	(5,127)	292
Amount reclassified out of accumulated other comprehensive income	$ 13,657	$ (1,102)