Nature of Operations and Summary of Significant Accounting Policies - Aircraft Fleet (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2016 item	Dec. 31, 2017 item aircraft
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of daily departures to different destinations | item		2,980
Number of aircraft held by entity		623
Number of seats on aircraft | item	50
CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		208
CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		136
CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		117
E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		107
Number of seats on aircraft | item		76
E175 SC
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of seats on aircraft | item		70
Number of aircraft ordered		30
EMB 120
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft removed from service		11
Number of seats on aircraft | item		30
United
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		278
Percentage of aggregate capacity operated		46.70%
United | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		81
United | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		20
United | ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
United | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		109
United | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		65
Delta
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		225
Percentage of aggregate capacity operated		37.80%
Delta | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		94
Delta | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		60
Delta | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
Delta | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		19
American
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		65
Percentage of aggregate capacity operated		10.90%
American | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		16
American | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		49
Alaska
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		27
Percentage of aggregate capacity operated		4.60%
Alaska | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Alaska | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		23
Aircraft in scheduled service
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		595
Aircraft in scheduled service | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		195
Aircraft in scheduled service | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		129
Aircraft in scheduled service | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		52
Aircraft in scheduled service | ERJ 135
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		3
Aircraft in scheduled service | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		109
Aircraft in scheduled service | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		107
Subleased to an un-affiliated entity
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Subleased to an un-affiliated entity | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		4
Other
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		24
Other | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		9
Other | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		7
Other | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity		8