Leases - Leases (Details) $ in Thousands		3 Months Ended		12 Months Ended
	Jan. 01, 2019 USD ($)	Sep. 30, 2019 USD ($) aircraft	Mar. 31, 2019 USD ($) aircraft	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | item				94
Operating lease right-of-use assets				$ 336,009
Current maturities of lease liabilities				94,806
Noncurrent operating leases				259,237
Operating leases				$ 75,400
Weighted-average remaining lease term: Operating leases				6 years 10 months 2 days
Weighted-average discount rate: Operating leases				6.40%
Lease costs
Operating lease cost				$ 104,011	$ 185,337
Variable and short-term lease cost				5,232	5,143
Sublease income				(1,436)
Total lease cost				$ 107,807	$ 190,480
Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft acquired | aircraft		4	52
Payments for acquired aircraft		$ 30,000	$ 111,700
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				37 years