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Segments - Additional Information (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Segment Reporting Information [Line Items]      
Number of reportable segments   2  
Concentration Risk, Additional Characteristic International sales accounted for less than 10% in each of the last three years.    
Sales Revenue, Net      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 100.00% 100.00% 100.00%
Five Largest Customers | Sales Revenue, Net      
Segment Reporting Information [Line Items]      
Concentration Risk, Percentage 24.00% 24.00% 25.00%