Impairment (Notes)	9 Months Ended
Impairment (Notes)	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Restructuring, Impairment, and Other Activities Disclosure [Text Block]	Impairment Accounting Standards Codification (ASC) 360 - Property, Plant, and Equipment (ASC 360) requires long-lived assets to be assessed for impairment when events and circumstances indicate that the assets may be impaired. As described in Note 2, in the first nine months of 2020, the Company's operations and liquidity were significantly impacted by decreased passenger demand and U.S. government travel restrictions and quarantine requirements due to COVID-19. As a result of these events and circumstances, the Company performed impairment tests on its long-lived assets in connection with the preparation of its financial statements. In accordance with ASC 360, an impairment of a long-lived asset or group of long-lived assets exists only when the sum of the estimated undiscounted future cash flows expected to be generated directly by the assets is less than the carrying value of the assets. Assets were grouped by operating segment when estimating future cash flows, and further grouped within each segment as applicable. Estimates of future cash flows were generally based on historical results, and management's best estimate of future market and operating conditions. Airline Segment Long-lived assets for the Airline segment consist primarily of owned and leased flight and ground equipment. To test the recoverability of the Company's airline operating fleet, undiscounted future cash flows for each aircraft under the Company's current expected operating fleet plan were assessed and it was determined that there was no impairment as of September 30, 2020. As the Company obtains greater clarity about the duration and extent of reduced demand and potentially executes further capacity adjustments, the Company will continue to evaluate its current fleet compared to network requirements and may decide to permanently retire additional aircraft. The Airline has an equity investment in a technology company. A $5.0 million charge was recorded to impair the investment in the second quarter 2020. As a result of the impairment, net book value of the investment is zero. This decision reflects management's best estimate of the fair value of this investment based on recent market trends. Sunseeker Resort Segment Long-lived assets for Sunseeker Resort and related Kingsway Golf Course consist primarily of the land, construction in process, building, and other various equipment. As a result of the impairment tests performed, the Company determined the sum of the undiscounted cash flows was less than the long-lived assets' carrying value. A $136.8 million impairment charge was recorded in the first quarter 2020 to reflect the difference between the carrying values of these assets and their fair values. Fair value reflects management's best estimate, including valuation inputs from third parties and recent market transactions. Based on an evaluation of impairment indicators in the second and third quarters 2020, no additional impairment was recognized. Other non-Airline Segment Long-lived assets for Allegiant Nonstop family entertainment centers consist primarily of leasehold improvements, arcade games, various equipment, and ROU assets. As a result of the impairment tests performed, the Company determined the sum of the undiscounted cash flows were less than the long-lived assets' carrying value. An $18.3 million impairment charge was recorded in the first quarter 2020 to reflect the difference between the carrying values of these assets and their fair values. Fair value reflects management's best estimate, including valuation inputs from third parties and recent market trends. Based on an evaluation of impairment indicators in the second and third quarters 2020, no additional impairment was recognized. Long-lived assets for Teesnap consist primarily of capitalized software and computer equipment. As a result of the impairment tests performed, the Company determined the sum of the undiscounted cash flows was less than the long-lived assets' carrying value. Management does not expect to recover any of the book value of the assets through operations, and an $8.3 million impairment charge was recorded in the first quarter 2020 to write down all long-lived assets to a net book value of zero. This reflects management's best estimate of the fair value of these assets based on recent market trends.