Passenger and Ground Handling and Other Revenue (Details)	3 Months Ended	9 Months Ended
	Dec. 31, 2017 aircraft	Sep. 30, 2017 aircraft item
Agreements with other airlines
Percentage of ASMs flown under fixed-fee arrangements		87.80%
Percentage of ASMs flown under pro-rate arrangements		12.20%
Sky West Airlines Inc | Delta Connection Prorate Agreement
Agreements with other airlines
Term of agreement		30 days
Sky West Airlines Inc | United Express Prorate Agreement
Agreements with other airlines
Term of agreement		120 days
Sky West Airlines Inc | American Prorate Agreement
Agreements with other airlines
Term of agreement		120 days
CRJ 200 | Sky West Airlines Inc | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		63
CRJ 200 | Sky West Airlines Inc | Delta Connection Prorate Agreement
Agreements with other airlines
Number of aircraft under contract		24
CRJ 200 | Sky West Airlines Inc | United Express Agreements
Agreements with other airlines
Number of aircraft under contract		56
CRJ 200 | Sky West Airlines Inc | United Express Prorate Agreement
Agreements with other airlines
Number of aircraft under contract		22
CRJ 200 | Sky West Airlines Inc | American Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		10
CRJ 200 | Sky West Airlines Inc | American Prorate Agreement
Agreements with other airlines
Number of aircraft under contract		7
CRJ 200 | Sky West Airlines Inc | Alaska Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		7
CRJ 200 | ExpressJet | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		2
CRJ 700 | Sky West Airlines Inc | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		27
CRJ 700 | Sky West Airlines Inc | United Express Agreements
Agreements with other airlines
Number of aircraft under contract		20
CRJ 700 | Sky West Airlines Inc | American Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		37
CRJ 700 | Sky West Airlines Inc | Alaska Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		2
CRJ 700 | ExpressJet | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		33
CRJ 700 | ExpressJet | American Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		12
CRJ 900 | Sky West Airlines Inc | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		36
CRJ 900 | ExpressJet | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		24
E 175
Agreements with other airlines
Number of seats on aircraft | item		76
E 175 | Sky West Airlines Inc | Delta Connection Agreements
Agreements with other airlines
Number of aircraft under contract		18
E 175 | Sky West Airlines Inc | United Express Agreements
Agreements with other airlines
Number of aircraft under contract		65
E 175 | Sky West Airlines Inc | Alaska Capacity Purchase Agreement
Agreements with other airlines
Number of aircraft under contract		21
E 175 | Alaska | Forecast
Agreements with other airlines
Number of additional aircraft placed into service	14
E 175 | Delta | Forecast
Agreements with other airlines
Number of additional aircraft placed into service	31
E175 SC
Agreements with other airlines
Number of seats on aircraft | item		70
ERJ 145 | ExpressJet | United Express Agreements
Agreements with other airlines
Number of aircraft under contract		115
ERJ 135 | ExpressJet | United Express Agreements
Agreements with other airlines
Number of aircraft under contract		3