Employee Benefit Plans (Supplemental Retirement Programs) (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) investment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Supplemental Employee Retirement Plan [Member]
Years since benefit was last offered to employees	8 years
Net periodic benefit cost SERP Restoration	$ 3.0	$ 3.9	$ 6.3
Benefit obligation SERP Restoration	$ 12.3	12.1
Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member]
Maximum deferral of base salary	50.00%
Maximum deferral of incentive compensation bonuses	100.00%
Number of permitted investment alternatives | investment	3
Expenses associated with deferred compensation plan	$ 1.4	1.0	$ 0.5
Deferred compensation liability	$ 21.0	$ 26.1
Supplemental Life Plan [Member]
Years since benefit was last offered to employees	7 years
Additional death benefits, minimum range	$ 0.4
Additional death benefits, maximum range	$ 2.0