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Fair Value Measurement of Assets and Liabilities - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Fair Value Disclosures [Abstract]      
Financial instruments measured at fair value $ 0    
Foreign currency exchange forward contracts outstanding 0 $ 0  
Net foreign currency transaction gains (losses) $ 200,000 $ 3,600,000 $ 1,100,000