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Components of Net Periodic Benefit Cost (Details Textual) - USD ($)
$ in Thousands
 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year     $ 2,500
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year     858
Defined Contribution Plan Employer Accrued Discretionary Contribution Amount $ 1,300 $ 1,200  
Post Retirement Health Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefits Plan Estimated Future Employer Contributions In Next Fiscal Year     $ 260
Defined Benefit Plan, Plan Assets, Contributions by Employer 167    
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Contributions by Employer $ 1,900