Leases, Commitments and Contingencies (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) aircraft	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of aircraft leased | aircraft			107
Retained earnings	$ 2,098,456		$ 2,098,456		$ 2,079,179
Operating lease right-of-use assets	296,439		296,439		336,009
Current maturities of lease liabilities	83,291		83,291		94,806
Noncurrent operating leases	$ 221,839		221,839		$ 259,237
Operating leases			$ 68,000
Weighted-average remaining lease term for operating leases	6 years 7 months 6 days		6 years 7 months 6 days
Weighted-average discount rate for operating leases	6.10%		6.10%
Lease costs
Operating lease cost	$ 23,538	$ 25,173	$ 72,696	$ 80,041
Variable and short-term lease cost	950	1,343	3,501	4,164
Sublease income	(1,587)	(357)	(4,718)	(357)
Total lease cost	$ 22,901	$ 26,159	$ 71,479	$ 83,848
Aircraft
Lessee, Lease, Description [Line Items]
Retained earnings						$ 13,100
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 year		1 year
Aircraft | Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	10 years		10 years
Aircraft | CRJ 200
Lessee, Lease, Description [Line Items]
Impairment charges			$ 0
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	36 years		36 years