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Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Fair Value Measurements [Line Items]    
Maturity period limit of foreign currency exchange instruments (in months) 3 months  
Foreign Exchange Forward Contract    
Fair Value Measurements [Line Items]    
Notional amount of foreign exchange forward contracts not designated as hedging instruments $ 380.0 $ 514.0