Leases, Commitments and Contingencies (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) aircraft	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | aircraft			43
Retained earnings	$ 2,149,900		$ 2,149,900		$ 2,052,006
Operating lease right-of-use assets	262,172		262,172		282,362
Current maturities of lease liabilities	78,289		78,289		82,641
Noncurrent operating leases	$ 187,860		187,860		$ 205,845
Operating leases			$ 40,800
Weighted-average remaining lease term for operating leases	6 years 3 months 18 days		6 years 3 months 18 days
Weighted-average discount rate for operating leases	6.10%		6.10%
Lease costs
Operating lease cost	$ 22,085	$ 24,140	$ 44,211	$ 49,158
Variable and short-term lease cost	1,056	1,207	2,280	2,551
Sublease income	(1,493)	(1,560)	(2,829)	(3,131)
Total lease cost	$ 21,648	$ 23,787	$ 43,662	$ 48,578
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	3 years		3 years
Aircraft | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	9 years		9 years
Airport Facilities | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 month		1 month
Airport Facilities | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	35 years		35 years