Leases (Details) $ in Thousands		12 Months Ended
	Jan. 01, 2019 USD ($)	Dec. 31, 2020 USD ($) aircraft	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Retained earnings		$ 2,052,006	$ 2,079,179
Operating lease right-of-use assets		282,362	336,009
Current maturities of lease liabilities		82,641	94,806
Noncurrent operating leases		205,845	259,237
Operating leases		$ 90,300
Weighted-average remaining lease term for operating leases		6 years 6 months
Weighted-average discount rate for operating leases		6.10%
Lease costs
Operating lease cost		$ 94,915	104,011
Variable and short-term lease cost		4,619	5,232
Sublease income		(6,304)	(1,436)
Total lease cost		$ 93,230	$ 107,807
Aircraft
Lessee, Lease, Description [Line Items]
Number of aircraft acquired | aircraft		41
Impairment charges	$ 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