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Employee Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Lump-sum settlement cost   $ (15,606)  
Pension Benefits [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Service cost  
Interest cost 1,786 2,329 $ 2,319
Expected return on plan assets (2,569) (2,745) (3,046)
Amortization of unrecognized net loss (gain) 475 499 440
Contractual benefit charge 270 131  
Total net periodic benefit cost (38) 214 (287)
Postretirement Benefit Plan [Member]      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Service cost 48 60 70
Interest cost 199 934 2,970
Amortization of unrecognized prior service cost 14 18 42
Amortization of unrecognized net loss (gain) (317) (97) 647
Lump-sum settlement cost   (15,606)  
Curtailment recognition   6  
Contractual benefit charge 150 16  
Total net periodic benefit cost $ 94 $ (14,669) $ 3,729