Retirement Plans - Reconciliation of Level 3 Fixed Annuity Contracts Within Fair Value Hierarchy (Details 13) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Level 3 fund assets
Beginning Balance	$ 286,539
Benefits paid	(157)	$ (165)
Ending Balance	259,752	286,539
Significant Unobservable Inputs (Level 3)
Reconciliation of Level 3 fund assets
Beginning Balance	10,787
Ending Balance	$ 9,172	$ 10,787