Retirement Plans - Net Periodic Pension Cost (Details) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 224	$ 253	$ 270
Expected return on assets	(317)	(295)	(319)
Amortization of net loss	84	96	82
Net periodic pension cost	$ (9)	$ 54	$ 33