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Segment Information - Additional Information (Detail) - Customer
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]      
Number of customers 1 1 1
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]      
Segment Reporting Information [Line Items]      
Percentage of total net revenues 13.00% 16.40% 16.20%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | China [Member]      
Segment Reporting Information [Line Items]      
Percentage of total net revenues 35.80% 32.10% 34.20%