Nature of Operations and Summary of Significant Accounting Policies - Flying Agreements and Airport Customer Service and Other Revenues (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($) aircraft	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) aircraft	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($) item
Agreements with other airlines
Percentage of ASMs flown under fixed-fee arrangements									84.30%
Percentage of ASMs flown under pro-rate arrangements									15.70%
Revenues [Abstract]
Operating revenues | $	$ 803,489	$ 829,275	$ 805,515	$ 783,400	$ 771,241	$ 812,673	$ 791,512	$ 747,166	$ 3,221,679	$ 3,122,592	[1]	$ 3,063,702	[1]
Number of seats on aircraft | item												50
Alaska Capacity Purchase Agreement
Revenues [Abstract]
Number of aircraft									32
Sky West Airlines Inc | Delta Connection Agreement
Revenues [Abstract]
Term of agreement									4 years 1 month 6 days
Sky West Airlines Inc | Delta Connection Prorate Agreement
Revenues [Abstract]
Number of aircraft									29
Notice period for termination of agreement									30 days
Sky West Airlines Inc | United Express Agreements
Revenues [Abstract]
Term of agreement									7 years
Sky West Airlines Inc | United Express Prorate Agreement
Revenues [Abstract]
Number of aircraft									25
Notice period for termination of agreement									120 days
Sky West Airlines Inc | American Capacity Purchase Agreement
Revenues [Abstract]
Number of aircraft									58
Sky West Airlines Inc | American Prorate Agreement
Revenues [Abstract]
Notice period for termination of agreement									120 days
ExpressJet
Revenues [Abstract]
Lease term (in years)	5 years								5 years
Number of aircrafts to be leased									16
CRJ 200 | Sky West Airlines Inc | Delta Connection Agreement
Revenues [Abstract]
Number of aircraft									58
CRJ 200 | Sky West Airlines Inc | United Express Agreements
Revenues [Abstract]
Number of aircraft									65
CRJ 200 | Sky West Airlines Inc | American Prorate Agreement
Revenues [Abstract]
Number of aircraft									7
CRJ 200 | ExpressJet
Revenues [Abstract]
Number of aircraft ownership retained	16								16
CRJ 200 | ExpressJet | United Express Agreements
Revenues [Abstract]
Number of aircraft									16
CRJ 700 | Sky West Airlines Inc | Delta Connection Agreement
Revenues [Abstract]
Number of aircraft									22
CRJ 700 | Sky West Airlines Inc | United Express Agreements
Revenues [Abstract]
Number of aircraft									19
CRJ 700 | ExpressJet
Revenues [Abstract]
Number of aircraft ownership retained	10								10
CRJ 700 | ExpressJet | American Capacity Purchase Agreement
Revenues [Abstract]
Number of aircraft									10
CRJ 900 | Sky West Airlines Inc | Delta Connection Agreement
Revenues [Abstract]
Number of aircraft									41
E 175 | Sky West Airlines Inc | Delta Connection Agreement
Revenues [Abstract]
Number of aircraft									49
Number of aircrafts anticipated to place in service	9								9
E 175 | Sky West Airlines Inc | United Express Agreements
Revenues [Abstract]
Number of aircraft									65
E 175 | Sky West Airlines Inc | Alaska Capacity Purchase Agreement
Revenues [Abstract]
Number of aircrafts anticipated to place in service	3								3
ERJ 145 | ExpressJet | United Express Agreements
Revenues [Abstract]
Number of aircraft									100
Flying agreements
Revenues [Abstract]
Operating revenues | $									$ 3,169,520	3,078,297	[1]	$ 3,010,738	[1]
Flight operations
Revenues [Abstract]
Operating revenues | $									1,856,253	1,805,510		1,792,868
Aircraft lease
Revenues [Abstract]
Operating revenues | $									814,518	834,366		763,406
Prorate agreements
Revenues [Abstract]
Operating revenues | $									$ 498,749	$ 438,421		$ 454,464

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606). See Note 1 to the financial statements of this report for additional information.