Employee Benefits Deferred Compensation Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	$ 7.1	$ 6.1
Deferred Compensation Arrangement with Individual, Compensation Expense	0.9	0.6	$ (0.1)
Deferred Compensation Plan Assets	7.1	6.1
Deferred Compensation Plan Assets, Income	$ 0.9	$ 0.6	$ (0.1)