Impact of the COVID-19 Pandemic - Narrative (Details)			1 Months Ended	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 25, 2020 USD ($) borrowing aircraft engine $ / shares shares	Apr. 22, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) transaction	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) aircraft reportingUnit	Sep. 30, 2019 USD ($)	Oct. 23, 2020 USD ($) shares	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Reduction in workforce, percent				32.00%
Long-term borrowings									$ 602,264,000	$ 227,889,000
Number of reporting units | reportingUnit									1
Goodwill impairment				$ 0			$ 0		$ 106,662,000	0
Long-lived assets				2,121,218,000				$ 2,121,218,000	2,121,218,000				$ 2,316,772,000
Long lived asset impairment				0			$ 0		34,014,000	$ 0
Long-term debt				$ 1,172,399,000				$ 1,172,399,000	$ 1,172,399,000
COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Reduction in capacity, percent				(86.50%)					(60.20%)
Percentage of fleet parked				29.00%				29.00%	29.00%
Capital expenditures				$ 7,800,000					$ 101,800,000
Reduction in workforce, percent				32.00%
Cash, cash equivalents, and short-term investments				$ 979,100,000				$ 979,100,000	979,100,000
Grants received								240,600,000
CARES act funding								60,300,000
Economic Relief Program, maximum financial assistance				420,000,000.0				420,000,000.0	420,000,000.0
Economic Relief Program, amount borrowed				$ 45,000,000				45,000,000	$ 45,000,000
Number of sale leaseback transactions | transaction				2
Aircraft used to secure financing | aircraft									12
Fair value of aircraft used to secure financing				$ 242,700,000				242,700,000	$ 242,700,000
Goodwill impairment						$ 106,700,000
Indefinite-lived intangible assets				13,500,000				13,500,000	13,500,000
Long-lived assets				2,100,000,000				2,100,000,000	2,100,000,000
Maximum financial assistance		$ 300,900,000
COVID-19 | Payroll support program warrants
Unusual or Infrequent Item, or Both [Line Items]
Warrants issued (in shares) | shares		509,964
Exercise price of warrants (in dollars per share) | $ / shares		$ 11.82
Warrants expiration term		5 years
COVID-19 | Economic Relief Program Warrants
Unusual or Infrequent Item, or Both [Line Items]
Warrants issued (in shares) | shares	3,553,299
Exercise price of warrants (in dollars per share) | $ / shares	$ 11.82
Warrants expiration term	5 years
Shares per warrant (in shares) | shares	380,711
Percent of borrowing to be issued as warrants	10.00%
COVID-19 | Economic Relief Program Warrants | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Warrants issued (in shares) | shares											5,262,267
ATR-42 And ATR-72 fleets | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Long lived asset impairment					$ 34,000,000.0
Line of credit | Revolving credit facility
Unusual or Infrequent Item, or Both [Line Items]
Draw down of revolving loans			$ 235,000,000.0
Long-term debt				235,000,000				$ 235,000,000	$ 235,000,000				0
Line of credit | Revolving credit facility | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Draw down of revolving loans						$ 235,000,000.0
Financings Secured By Aircraft | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Long-term borrowings				$ 376,000,000.0
Payroll Support Program Facility
Unusual or Infrequent Item, or Both [Line Items]
Total principal sum of note												$ 60,300,000
Interest rate				1.00%				1.00%	1.00%
Long-term debt				$ 60,278,000				$ 60,278,000	$ 60,278,000				0
Payroll Support Program Facility | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Total principal sum of note												$ 60,300,000
Term of debt instrument									10 years
Interest rate		1.00%
Economic Relief Program Facility
Unusual or Infrequent Item, or Both [Line Items]
Maximum borrowing capacity	$ 420,000,000.0			420,000,000				420,000,000	$ 420,000,000
Long-term debt	$ 45,000,000.0			$ 45,000,000				$ 45,000,000	$ 45,000,000				$ 0
Economic Relief Program Facility | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Maximum borrowing capacity											$ 622,000,000
Economic Relief Program Facility | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Aircraft used to secure financing | aircraft	14
Interest rate	2.73%
Number of subsequent borrowings | borrowing	2
Collateral coverage ratio	2.0
Number of engines to secure financing | engine	28
Minimum debt service covenant ratio	1.75
Secured overnight financing rate | Payroll Support Program Facility
Unusual or Infrequent Item, or Both [Line Items]
Margin									2.00%
Secured overnight financing rate | Payroll Support Program Facility | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Margin		2.00%
London interbank offer rate | Line of credit | Revolving credit facility
Unusual or Infrequent Item, or Both [Line Items]
Margin			2.25%						2.25%
London interbank offer rate | Economic Relief Program Facility
Unusual or Infrequent Item, or Both [Line Items]
Margin									2.50%
London interbank offer rate | Economic Relief Program Facility | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Margin	2.50%
Minimum | Officer | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Reduction of salary, percent				10.00%				10.00%	10.00%
Maximum | Officer | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Reduction of salary, percent				50.00%				50.00%	50.00%