Nature of Operations and Summary of Significant Accounting Policies - Aircraft Fleet (Details)	12 Months Ended
	Dec. 31, 2018 item aircraft	Dec. 31, 2016 item
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of daily departures to different destinations | item	2,770
Number of aircraft held by entity	628
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	128
CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	41
ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	105
E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	146
United
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	290
Percentage of aggregate capacity operated	48.60%
United | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	106
United | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	19
United | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	100
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	199
Percentage of aggregate capacity operated	33.40%
Delta | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	87
Delta | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	22
Delta | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	41
Delta | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	49
American
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	75
Percentage of aggregate capacity operated	12.60%
American | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	7
American | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	68
Alaska
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	32
Percentage of aggregate capacity operated	5.40%
Alaska | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	32
Aircraft in scheduled service
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	596
Aircraft in scheduled service | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	200
Aircraft in scheduled service | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	109
Aircraft in scheduled service | CRJ 900
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	41
Aircraft in scheduled service | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	100
Aircraft in scheduled service | E 175
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	146
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	28
Other | CRJ 200
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	4
Other | CRJ 700
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	19
Other | ERJ 145
Nature of Operations and Summary of Significant Accounting Policies [Line Items]
Number of aircraft held by entity	5