Employee Benefit Plans (Summary of Net Periodic Benefit Cost and Actuarial Assumptions Used to Determine Net Cost) (Details) - Employee Pension Plans [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of net periodic benefit cost
Interest cost	$ 3,919	$ 4,153	$ 4,055
Service cost	850	600
Return on plan assets	(4,358)	(4,803)	(5,021)
Recognized net actuarial losses	1,897	1,745	1,869
Net periodic benefit cost	$ 2,308	$ 1,695	$ 903
Actuarial Assumptions Used to Determine Net Cost
Discount rate (as a percent)	3.90%	4.10%	3.75%
Expected return on assets (as a percent)	6.00%	6.00%	6.50%