Business Segments and Major Customers - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 Segment Customer Partner	Mar. 31, 2018 Customer Partner	Dec. 31, 2018
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
Revenue [Member] | Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage of benchmark	15.00%	15.00%
Revenue [Member] | Customer Concentration Risk [Member] | Delta Airline and American Airlines [Member]
Segment Reporting Information [Line Items]
Percentage of benchmark	29.00%	20.00%
Revenue [Member] | Customer Concentration Risk [Member] | American Airlines [Member]
Segment Reporting Information [Line Items]
Percentage of benchmark	10.00%	36.00%
Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Number of customers meeting concentration risk threshold	1
Number of airline partners meeting concentration risk threshold | Partner	1	1
Accounts Receivable [Member] | Credit Concentration Risk [Member] | American Airlines [Member]
Segment Reporting Information [Line Items]
Percentage of benchmark			11.00%
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Delta Air Lines [Member]
Segment Reporting Information [Line Items]
Percentage of benchmark	11.00%		11.00%