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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 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 172 $ 145 $ 516 $ 435
Interest cost 880 851 2,640 2,553
Expected return on plan assets (580) (752) (1,739) (2,256)
Net amortization and deferral 605 782 1,815 2,346
Net periodic benefit 1,077 1,026 3,232 3,078
Other Postretirement Benefit Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 21 52 64 156
Expected return on plan assets 0 0 (1) 0
Net accretion and deferral (138) (65) (413) (195)
Net periodic benefit $ (117) $ (13) $ (350) $ (39)