Income Taxes - Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Unrecognized Tax Benefits [Line Items]
Unrecognized tax benefits - beginning of year	$ 58.2	$ 38.2	$ 31.0
Gross additions - current year tax positions	31.0	10.7	4.6
Gross additions - prior year tax positions	10.9	10.4	8.3
Gross additions (reductions) - purchase accounting adjustments	4.0	9.7	0.1
Gross reductions - prior year tax positions	(9.4)	(9.8)	(2.1)
Gross reductions - settlements with taxing authorities	(7.2)	(1.0)	(3.6)
Impact of change in foreign exchange rates	0.0	0.0	(0.1)
Unrecognized tax benefits - end of year	$ 87.5	$ 58.2	$ 38.2