Retirement Plans - Reconciliation of Level 3 Fixed Annuity Contracts Within Fair Value Hierarchy (Details 13) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Level 3 fund assets
Beginning Balance	$ 290,795
Benefits paid	(165)	$ (172)
Ending Balance	293,567	290,795
Significant Unobservable Inputs (Level 3)
Reconciliation of Level 3 fund assets
Beginning Balance	13,360
Ending Balance	12,862	13,360
Significant Unobservable Inputs (Level 3) | Annuitization Benefit
Reconciliation of Level 3 fund assets
Beginning Balance	0	12,475
Purchases	0	0
Benefits paid		(12,475)
Assets transferred due to termination of plan	0
Net loss	0	0
Ending Balance	$ 0	$ 0