Benefit Plans (Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Components of Net Periodic Benefit Cost
Service cost	$ 1,001	$ 995
Interest cost	1,228	1,155
Net loss	291	213
Net periodic pension cost	$ 2,520	$ 2,363
Weighted Average Assumptions for Expense
Discount Rate	3.80%	4.50%
Rate of Compensation Increase	4.40%	4.40%