Summary of Notional Amounts of Outstanding Foreign Exchange Forwards (Detail) € in Millions, ¥ in Millions, £ in Millions, SGD in Millions, CAD in Millions, $ in Millions	Dec. 31, 2017 CAD	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 JPY (¥)	Dec. 31, 2017 SGD	Dec. 31, 2017 USD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 GBP (£)	Dec. 31, 2016 SGD
Contracts to Sell USD for GBP [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						$ 484.7
Contracts to Sell USD for GBP [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | £			£ 362.3
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 US Dollars for CAD [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						51.7
Contracts to Sell US Dollars for CAD [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | CAD	CAD 64.0
Contracts to Purchase Euros with Singapore Dollars [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount | SGD									SGD 55.5
Contracts to Purchase Euros with Singapore Dollars [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						39.2
Contracts to Sell USD for Singapore Dollars [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | SGD					SGD 53.0
Contracts to Sell USD for EUR [Member] | Sell [Member]
Derivative [Line Items]
Derivative Notional Amount						$ 465.2
Contracts to Sell USD for EUR [Member] | Buy [Member]
Derivative [Line Items]
Derivative Notional Amount | €		€ 390.0