Leases, Commitments and Contingencies (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($) aircraft	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | aircraft	42
Retained earnings	$ 2,087,906		$ 2,052,006
Operating lease right-of-use assets	274,025		282,362
Current maturities of lease liabilities	82,671		82,641
Noncurrent operating leases	200,598		$ 205,845
Operating leases	$ 16,600
Weighted-average remaining lease term for operating leases	6 years 4 months 24 days
Weighted-average discount rate for operating leases	6.10%
Lease costs
Operating lease cost	$ 22,127	$ 25,018
Variable and short-term lease cost	1,224	1,344
Sublease income	(1,335)	(1,571)
Total lease cost	$ 22,016	$ 24,791
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	3 years
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