Summary of Notional Amounts of Outstanding Foreign Exchange Forwards, Cash Flow Hedging (Detail) € in Millions, ¥ in Millions, £ in Millions, SGD in Millions, CAD in Millions, $ in Millions	Sep. 30, 2017 CAD	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 GBP (£)	Sep. 30, 2017 JPY (¥)	Sep. 30, 2017 SGD	Sep. 30, 2017 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 GBP (£)	Dec. 31, 2016 SGD
Contracts to Sell US Dollars for GBP [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						$ 471.0
Contracts to Sell US Dollars for GBP [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | £			£ 356.1
Contracts to Sell USD for JPY [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						24.3
Contracts to Sell USD for JPY [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | ¥				¥ 2,700.0
Contracts to Sell USD for CAD [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						51.9
Contracts to Sell USD for CAD [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | CAD	CAD 64.0
Contracts to Purchase Euros with SGD [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount | SGD									SGD 55.5
Contracts to Purchase Euros with SGD [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | €							€ 36.0
Contracts to Sell Euros for GBP [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount | €							€ 31.0
Contracts to Sell Euros for GBP [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | £								£ 25.9
Contracts to sell USD for Singapore dollars [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						38.9
Contracts to sell USD for Singapore dollars [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | SGD					SGD 53.0
Contracts to sell euros for USD [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount | €		€ 6.0
Contracts to sell euros for USD [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount						7.2
Contracts to sell USD for EUR [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						$ 54.3
Contracts to sell USD for EUR [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | €		€ 45.0