Retirement Plans - Reconciliation of Level 3 Partnership Assets Within Fair Value Hierarchy (Details 12) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Level 3 fund assets
Beginning Balance	$ 290,795
Ending Balance	293,567	$ 290,795
Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	13,360
Ending Balance	12,862	13,360
Significant Unobservable Inputs (Level 3) [Member]
Reconciliation of Level 3 fund assets
Beginning Balance	13,360
Ending Balance	12,862	13,360
Significant Unobservable Inputs (Level 3) [Member] | Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	13,360	11,239
Net ordinary gain attributable to partnership assets	0	0
Capital contributions	1,419	2,808
Realized and unrealized gain	584	754
Capital distributions	(2,501)	(1,441)
Ending Balance	$ 12,862	$ 13,360