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Commitments and Contingencies (Details)
$ in Thousands
3 Months Ended
Mar. 31, 2018
USD ($)
aircraft
Future minimum rental payments required under operating leases  
March through December 2018 $ 85,825
2019 85,563
2020 101,523
2021 93,118
2022 75,178
Thereafter 159,347
Total future lease obligations $ 600,554
E 175  
Future minimum rental payments required under operating leases  
Number of aircraft under firm purchase commitment | aircraft 37
E 175 | Alaska  
Future minimum rental payments required under operating leases  
Number of additional aircraft placed into service, deferred | aircraft 3