Retirement Plans - Periodic Pension Cost (Benefit) (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 270	$ 272	$ 280
Expected return on assets	(319)	(332)	(371)
Amortization of net loss	82	88	45
Net periodic pension cost (benefit)	$ 33	$ 28	$ (46)