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Impairment (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges |  |  | $ 161,600,000 | $ 0 | $ 0
Long-Lived Assets |  | $ 0 | 0 |  |
Allegiant Air |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges |  |  | 5,000,000.0 |  |
Sunseeker Resorts |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges | $ 128,900,000 | 0 |  |  |
Other |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges |  |  | 26,600,000 |  |
Other | Allegiant Nonstop |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges | 18,300,000 | $ 0 |  |  |
Other | Teesnap |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges | 8,300,000 |  |  |  |
Kingsway Golf |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges | $ 1,100,000 |  |  |  |
Airbus A320 Aircraft Series | Allegiant Air |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Special charges |  |  | $ 0 |  |

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- Definition Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228 + Details
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- Definition Long-lived assets other than financial instruments, long-term customer relationships of a financial institution, mortgage and other servicing rights, deferred policy acquisition costs, and deferred tax assets. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 41 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599 + Details
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