Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax [Line Items]
Effective income tax rate	18.50%	14.10%	15.20%	19.70%
Income tax provision	$ (21.3)	$ (15.8)	$ (73.8)	$ (91.0)
Income tax examination, increase (decrease) in liability from prior year		$ 2.6		$ 2.6
Unrecognized tax benefits related to federal, state and foreign taxes	21.3		21.3		$ 21.5
Unrecognized tax benefits that would impact effective tax rate	18.3		18.3
Accrued interest	3.6		3.6		$ 2.6
Decrease in unrecognized tax benefits within the next 12 months	5.1		$ 5.1
Number of months unrecognized tax benefits may decrease			12 months
Accounting Standards Update 2016-09
Income Tax [Line Items]
Income tax provision	$ 12.8		$ 50.3