Retirement Plans - Reconciliation of Level 3 Partnership Assets Within Fair Value Hierarchy (Details 12) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Level 3 fund assets
Beginning Balance	$ 286,539
Ending Balance	259,752	$ 286,539
Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	10,787
Ending Balance	9,172	10,787
Significant Unobservable Inputs (Level 3) [Member]
Reconciliation of Level 3 fund assets
Beginning Balance	10,787
Ending Balance	9,172	10,787
Significant Unobservable Inputs (Level 3) [Member] | Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	10,787	12,862
Capital contributions	78	343
Realized and unrealized gain	1,154	2,107
Capital distributions	(2,847)	(4,525)
Ending Balance	$ 9,172	$ 10,787