Components of Net Periodic Benefit Cost (Details Textual) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year			$ 2,300
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year			813
Defined Contribution Plan Employer Accrued Discretionary Contribution Amount	$ 837	$ 867
Post Retirement Health Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year			$ 264
Defined Benefit Plan, Plan Assets, Contributions by Employer	122
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 792