Leases, Commitments and Contingencies - Leases (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) aircraft	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | aircraft				107
Operating lease right-of-use assets		$ 310,016		$ 310,016		$ 336,009
Current maturities of lease liabilities		87,415		87,415		94,806
Noncurrent operating leases		$ 238,572		238,572		$ 259,237
Operating leases				$ 41,300
Weighted-average remaining lease term for operating leases		6 years 8 months 12 days		6 years 8 months 12 days
Weighted-average discount rate for operating leases		6.10%		6.10%
Lease costs
Operating lease cost		$ 24,140	$ 27,647	$ 49,158	$ 54,868
Variable and short-term lease cost		1,207	1,346	2,551	2,821
Sublease income		(1,560)		(3,131)
Total lease cost		$ 23,787	$ 28,993	$ 48,578	$ 57,689
Aircraft
Lessee, Lease, Description [Line Items]
Impairment adjustment on retained earnings	$ 13,100
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term				1 year
Aircraft | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term				10 years
Airport Facilities | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term				1 month
Airport Facilities | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term				36 years