Schedule of Net Periodic Pension Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plan [Abstract]
Service cost	$ 1,049	$ 928
Interest cost	609	525
Expected return on plan assets	(181)	(146)
Amortization of actuarial net loss	403	391
Amortization of unrecognized prior service costs	17	15
Net periodic benefit cost	$ 1,897	$ 1,713