Quarterly report pursuant to Section 13 or 15(d)

Customer Concentration (Details)

v3.8.0.1
Customer Concentration (Details) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Concentration Risk [Line Items]        
Cash and cash equivalents $ 58,037 $ 56,155 $ 50,686 $ 223,552
Sales Revenue Segment | Customer Concentration Risk        
Concentration Risk [Line Items]        
Southwest Airlines, concentration risk, percent 19.00% 22.00%    
Sales Revenue Segment | Customer Concentration Risk | Connectivity        
Concentration Risk [Line Items]        
Southwest Airlines, concentration risk, percent 36.00% 63.00%    
Accounts Receivable | Customer Concentration Risk        
Concentration Risk [Line Items]        
Southwest Airlines, concentration risk, percent 13.00% 12.00%    
Foreign subsidiaries        
Concentration Risk [Line Items]        
Cash and cash equivalents $ 21,900