Retirement Plans, Amounts Recognized in Accumulated Other Comprehensive Income Table (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Retirement Account Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	$ (342)	$ 122
Net actuarial loss	35,443	32,879
Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss	35,101	33,001
Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service cost	(580)	0
Net actuarial loss	79	73
Amount not yet recognized in net periodic benefit cost, but recognized in accumulated other comprehensive loss	$ (501)	$ 73