Financial Instruments and Fair Value Measurements - Foreign Currency Contracts Activity (Parenthetical) (Detail) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2017
USD ($)
Contracts
|
Dec. 31, 2016
USD ($)
Contracts
|
Dec. 31, 2015
USD ($)
Contracts
|
|
| Derivative Instruments And Hedging Activities Disclosure [Abstract] | |||
| Number of option contracts exercised | Contracts | 44 | 49 | 32 |
| Gains (losses) from option contracts exercised | $ | $ 12.6 | $ 3.0 | $ 14.6 |