Other Employee Benefit Plans (Schedule of Long-Term Disability Plan) (Details) - Long-Term Disability - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Benefit cost	$ 2,058	$ 1,936	$ 2,383
Discount rate (as a percent)	3.43%	3.71%	3.18%