Pension Plan (Details) - Components of net periodic pension cost - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of net periodic pension cost [Abstract]
Interest cost	$ 113	$ 116
Expected return on plan assets	(203)	(179)
Amortization of net actuarial loss	56	54
Net periodic pension benefit	$ (34)	$ (9)