Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Contingency [Line Items]
Impact on effective tax rates due to Tax Cut and Jobs Act	(4.60%)			(1.70%)
Remeaurement due to Tax Cut and Jobs Act	$ (5.0)			$ (5.0)
Toll tax related to Tax Cut and Jobs Act	$ 0.7			$ 0.7
Impact on effective tax rate related to toll tax	0.60%			0.20%
Impactoneffectivetaxraterelatedtoassertiontax				(0.10%)
Assertion tax related to Tax Cut and Jobs Act				$ (0.4)
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)		$ 87.0
Company's effective tax rate	17.60%		29.40%	19.70%	29.40%
Unrecognized Tax Benefits, Period Increase (Decrease)	$ 0.8
Increase In Unrecognized Tax Benefits That Would Impact Effective Tax Rate	1.4
Recognized interest expense related to unrecognized tax benefits	0.1			$ 1.1
Interest and penalty related to unrecognized tax benefits recorded	7.6	6.5		7.6
Reasonable possible increase in unrecognized tax benefits during the next twelve months	$ (11.5)			$ (11.5)
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense		75.0
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Liability		$ 12.0