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Business Segments and Major Customers - Additional Information (Detail)
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Customer
Sep. 30, 2016
Customer
Sep. 30, 2017
Segment
Partner
Customer
Sep. 30, 2016
Customer
Dec. 31, 2016
Partner
Customer
Segment Reporting Information [Line Items]          
Number of operating segments | Segment     3    
Revenue [Member]          
Segment Reporting Information [Line Items]          
Number of customers meeting concentration risk threshold 0 0 0 0  
Revenue [Member] | Customer Concentration Risk [Member]          
Segment Reporting Information [Line Items]          
Percentage of benchmark 10.00% 10.00% 10.00% 10.00%  
Revenue [Member] | Customer Concentration Risk [Member] | Delta Airline and American Airlines [Member]          
Segment Reporting Information [Line Items]          
Percentage of benchmark 47.00% 50.00% 47.00% 50.00%  
Accounts Receivable [Member]          
Segment Reporting Information [Line Items]          
Number of customers meeting concentration risk threshold     2   0
Number of airline partners meeting concentration risk threshold | Partner     1   1
Accounts Receivable [Member] | Customer Concentration Risk [Member]          
Segment Reporting Information [Line Items]          
Percentage of benchmark     22.00%   10.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member]          
Segment Reporting Information [Line Items]          
Percentage of benchmark     19.00%   18.00%