Retirement Plans - Periodic Pension Cost (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 56	$ 63	$ 168	$ 189
Expected return on assets	(79)	(74)	(237)	(222)
Amortization of net loss	21	24	63	72
Net periodic pension cost	$ (2)	$ 13	$ (6)	$ 39