Schedule of Net Periodic Pension Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan [Abstract]
Service cost	$ 968	$ 924	$ 2,017	$ 1,852
Interest cost	591	535	1,200	1,060
Expected return on plan assets	(169)	(147)	(350)	(293)
Amortization of actuarial net loss	392	403	795	794
Amortization of unrecognized prior service costs	17	15	34	30
Net periodic benefit cost	$ 1,799	$ 1,730	$ 3,696	$ 3,443