Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2013
Tax Credit Carryforward [Line Items]
Tax cuts and jobs act, change in tax rate, deferred tax liability, income tax benefit	$ 66.9
Adjustment to additional paid in capital, income tax effect from share-based compensation, net		$ 2.3
Liability for uncertainty in income taxes				$ 10.1
Increase (decrease) in unrecognized tax benefits	(2.0)
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Operating loss carryforwards, valuation allowance	$ 6.7		$ 4.0