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Employee Benefit Plans Summary of Pension Plan and Postretirement Plan Net Periodic Benefit Cost (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Pension Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 0 $ 150
Interest cost 830 881
Expected return on plan assets (451) (726)
Net amortization and deferral 663 782
Net periodic benefit 1,042 1,087
Other Postretirement Benefit Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 17 38
Net accretion and deferral (141) (65)
Net periodic benefit $ (124) $ (27)