Leases, Commitments and Contingencies - Leases (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2019 USD ($)	Mar. 31, 2020 USD ($) aircraft	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | aircraft		103
Operating lease right-of-use assets		$ 326,698		$ 336,009
Current maturities of lease liabilities		88,649		94,806
Noncurrent operating leases		259,039		$ 259,237
Operating leases		$ 17,700
Weighted-average remaining lease term for operating leases		6 years 9 months 18 days
Weighted-average discount rate for operating leases		6.40%
Lease costs
Operating lease cost		$ 25,018	$ 27,221
Variable and short-term lease cost		1,344	1,475
Sublease income		(1,571)
Total lease cost		$ 24,791	$ 28,696
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