Retirement Plans - Reconciliation of Level 3 Partnership Assets Within Fair Value Hierarchy (Details 12) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Level 3 fund assets
Beginning Balance	$ 259,752
Ending Balance	282,696	$ 259,752
Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	9,172
Ending Balance	7,539	9,172
Significant Unobservable Inputs (Level 3) [Member]
Reconciliation of Level 3 fund assets
Beginning Balance	9,172
Ending Balance	7,539	9,172
Significant Unobservable Inputs (Level 3) [Member] | Partnership
Reconciliation of Level 3 fund assets
Beginning Balance	9,172	10,787
Capital contributions	120	78
Realized and unrealized gain	(139)	1,154
Capital distributions	(1,614)	(2,847)
Ending Balance	$ 7,539	$ 9,172