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Business Segment Information - Additional Information (Detail) - Segment
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Segment Reporting Information [Line Items]      
Number of operating segment 1    
Customer Concentration Risk [Member] | Revenue [Member] | Customer A [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage 24.00%    
Customer Concentration Risk [Member] | Revenue [Member] | Minimum [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage 10.00%    
Customer Concentration Risk [Member] | Revenue [Member] | Minimum [Member] | No Customer [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage   10.00% 10.00%
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Customer A [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage 16.00%    
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Customer B [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage 30.00%    
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Minimum [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage 10.00%    
Customer Concentration Risk [Member] | Accounts Receivable [Member] | Minimum [Member] | No Customer [Member]      
Segment Reporting Information [Line Items]      
Concentration risk percentage   10.00%