Financial Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Parenthetical) (Detail) - Not Designated as Hedging Instrument - Foreign Exchange Swaps - Fair Value, Measurements, Nonrecurring - Less Than Six Months - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives Fair Value [Line Items]
Derivative notional volume, amount after offsetting swaps	$ 468.2	$ 226.5
Derivative asset, amount after offsetting swaps	2.4	1.1
Derivative liability, amount after offsetting swaps	$ 0.3	$ 0.0