Summary of Significant Accounting Policies - Schedule of Reclassifications Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Amortization of employee benefit plan items:
Income tax impact	$ 300	$ (1,000)
Amount reclassified out of accumulated other comprehensive loss	(1,102)	1,473
Amount reclassified out of accumulated other comprehensive loss
Amortization of employee benefit plan items:
Total before tax	(1,394)	2,492
Income tax impact	292	(1,019)
Amount reclassified out of accumulated other comprehensive loss	(1,102)	1,473
Prior service cost
Amortization of employee benefit plan items:
Total before tax	(25)	(25)
Settlement expense
Amortization of employee benefit plan items:
Total before tax	641	1,510
Actuarial loss
Amortization of employee benefit plan items:
Total before tax	$ (2,010)	$ 1,007