Pension Plan (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Retirement Benefits [Abstract]
Service cost	$ 169	$ 151
Interest cost on projected benefit obligation	701	693
Expected return on plan assets	(1,354)	(1,325)
Net amortization and deferral	672	793
Net periodic pension cost	$ 188	$ 312