Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)		$ 87.0
Company's effective tax rate	18.60%		28.00%
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 0.1
Increase In Unrecognized Tax Benefits That Would Impact Effective Tax Rate	0.4
Recognized interest expense related to unrecognized tax benefits	0.4
Interest and penalty related to unrecognized tax benefits recorded	6.9	$ 6.5
Reasonable possible increase in unrecognized tax benefits during the next twelve months	$ (13.2)