Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of the net periodic pension cost:
Interest cost	$ 939	$ 991	$ 1,232
Expected return on plan assets	(1,717)	(1,665)	(1,566)
Amortization of actuarial losses	826	1,045	726
Net periodic pension cost	$ 48	$ 371	$ 392