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v3.20.4

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Mar. 31, 2021 | Jan. 15, 2021 | Dec. 24, 2020 | Sep. 30, 2020 | Apr. 20, 2020
Subsequent Event [Line Items] |  |  |  |  |
Proceeds Received From Payroll Support Program |  |  |  | $ 153.8 |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  |  |  | $ 83.33
Percent of Securities to be Issued Based on Amount of Note Issued |  | 10.00% |  |  |
Payroll Support Program Grant Extension [Member] |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Class of Warrant or Right, Exercise Price of Warrants or Rights |  |  | $ 179.23 |  |
Subsequent Event | Payroll Support Program Grant Extension [Member] |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Increase In Debt Instrument For Additional Installment |  | 30.00% |  |  |
Debt Instrument, Amount Need To Exceed To Disburse Note |  | $ 100.0 |  |  |
Subsequent Event | Payroll Support Program Grant Extension [Member] |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |
Proceeds Received From Payroll Support Program |  | $ 45.9 |  |  |
Proceeds Expected From Payroll Support Program | $ 91.8 |  |  |  |

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- Definition Debt Instrument, Amount Need To Exceed To Disburse Note + References No definition available. + Details
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Namespace Prefix: | algt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Increase In Debt Instrument For Additional Installment + References No definition available. + Details
Name: | algt_IncreaseInDebtInstrumentForAdditionalInstallment
Namespace Prefix: | algt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Percent of Securities to be Issued Based on Amount of Note Issued + References No definition available. + Details
Name: | algt_PercentOfSecuritiesToBeIssuedBasedOnAmountOfNoteIssued
Namespace Prefix: | algt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Proceeds Expected From Payroll Support Program + References No definition available. + Details
Name: | algt_ProceedsExpectedFromPayrollSupportProgram
Namespace Prefix: | algt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Proceeds Received From Payroll Support Program + References No definition available. + Details
Name: | algt_ProceedsReceivedFromPayrollSupportProgram
Namespace Prefix: | algt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 + Details
Name: | us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=algt_PayrollSupportProgramGrantExtensionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |