Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate			16.9708%	47.20%
Total gross liability for unrecognized tax benefits	$ 52.8	$ 12.0	$ 52.8
Provisional income tax expense		2.2
Decrease to provisional income tax expense	$ 3.6
Decrease of income tax expense related to remeasurement of certain deferred tax assets and liabilities due to lower tax rate		28.0
Transition tax expense		$ 26.6