Summary of Significant Accounting Policies - (Policies)	6 Months Ended
Jun. 30, 2026
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements include the accounts of Allegiant Travel Company (the “Company” or "Allegiant") and its majority-owned operating subsidiaries, including Allegiant Air, LLC ("Allegiant Air") and Sun Country, Inc., whose parent company, Sun Country Airlines Holdings, Inc. ("Sun Country"), was acquired on May 13, 2026. Purchase accounting impacts resulting from the acquisition of Sun Country are included as of that date. Financial results for periods prior to May 13, 2026, do not include Sun Country results. The Company's investments in unconsolidated affiliates, which are 50 percent or less owned, are accounted for under the equity or cost method, and are insignificant to the consolidated financial statements. All intercompany balances and transactions have been eliminated. These unaudited consolidated financial statements reflect all normal recurring adjustments which management believes are necessary to present fairly the financial position, results of operations, and cash flows of the Company for the respective periods presented. Certain information and footnote disclosures normally included in the annual consolidated financial statements prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") have been omitted pursuant to the rules and regulations of the Securities and Exchange Commission for Form 10-Q. These unaudited interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements of the Company and notes thereto included in the annual report of the Company on Form 10-K for the year ended December 31, 2025 and filed with the Securities and Exchange Commission. The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from these estimates. Operating results for the three and six months ended June 30, 2026 are not necessarily indicative of operating results for the entire year due to the seasonal nature of leisure travel, the volatility of aircraft fuel prices, other macroeconomic factors as well as the acquisition of Sun Country during second quarter 2026. The Company has reclassified certain prior period amounts to conform to the current period presentation. Significant Accounting Policies Except as described below, there have been no material changes to the Company's significant accounting policies described in Note 2 to the audited financial statements included in the Company's Annual Report on Form 10‑K for the year ended December 31, 2025. As a result of the completion of the acquisition of Sun Country on May 13, 2026, the Company adopted the following accounting policies related to Sun Country's business. Revenue Recognition Cargo In June 2024, Sun Country entered into the Amended and Restated Air Transportation Services Agreement ("ATSA") with Amazon.com Services, LLC ("Amazon"). Under this agreement, the Company operates a fleet of 737-800 cargo aircraft on behalf of Amazon. The ATSA includes an initial six-year term, which expires in October 2030. The agreement includes two additional, two-year renewal terms exercisable at Amazon's option, and a subsequent three-year renewal term subject to mutual written agreement, which, if not agreed to, will trigger a final two-year wind-down term. The ATSA has annual rate escalations. The cargo fleet of 22 aircraft is subleased directly from Amazon and the Company operates them pursuant to the ATSA. The sublease arrangement does not qualify as a lease because the Company does not control the use of the aircraft. As such, no right-of use asset or lease liability is recognized in the consolidated financial statements for the Amazon arrangement. The ATSA contains three performance obligations: Flight Services, Heavy Maintenance and Fuel. As Sun Country is the principal in providing Flight Services, revenue and related costs are recognized gross on the Statement of Income. Flight Services revenue is recognized when transportation services are provided. The Company acts as the agent in providing the Heavy Maintenance and Fuel performance obligations, which are reimbursed by Amazon based on the actual costs incurred. Reimbursements for heavy maintenance and fuel consumption are recognized in revenue, net of the actual amount of costs for heavy maintenance and fuel which are incurred to fulfill the performance obligations. The ATSA with Amazon consists of three main components of consideration: a fixed amount is received each month per aircraft, a fixed amount is received each month per flight, and an amount per block hour is received each month. The ATSA contains a Service Level Agreement ("SLA") which provides for penalties for certain delays and cancellations. The SLA can result in a bonus or penalty for each month depending on the Company's performance. Each reporting period, the Company updates its estimate of variable consideration over the contract term and treats the adjustment as an adjustment to the total transaction price. When updating the estimate, the Company considers whether there are any changes in expected usage, performance-based bonuses or penalties, and changes in reimbursable costs. The transaction price is allocated to the performance obligations based on their relative standalone selling price. In connection with the ATSA, Sun Country issued warrants to Amazon which allowed for the purchase of Sun Country's common stock. On the acquisition date, all of these warrants vested pursuant to the warrant agreement and were exercised on a net settlement basis into Sun Country shares, for which the Company paid merger consideration to Amazon. In connection with these warrants, the Company recorded a contract asset in the opening post-acquisition balance sheet. This contract asset will be amortized against cargo revenue over the remaining term of the ATSA through a reduction to the transaction price for Flight Services. Lessor Maintenance Deposits Certain of the Company's aircraft lease agreements acquired from Sun Country provide that the Company pay maintenance reserves monthly to aircraft lessors to be held as collateral in advance of major maintenance activities required to be performed by the Company. Generally, maintenance reserve payments are variable based on actual flight hours or cycles. These lease agreements provide that maintenance reserves are reimbursable to the Company upon completion of the maintenance event in an amount equal to the lesser of (1) the amount of the maintenance reserve held by the lessor associated with the specific maintenance event or (2) the qualifying costs related to the specific maintenance event. Maintenance reserve payments that are expected to be recoverable via reimbursable expenses are reflected as Short-term lessor maintenance deposits and in deposits and other assets on the accompanying Consolidated Balance Sheets. These deposits are expected to be reimbursed to the Company upon performance of maintenance activities or used towards the purchase of the aircraft at the end of the lease. Lessor maintenance deposits deemed improbable of recovery are expensed as incurred and recorded within aircraft rent. The Company made certain assumptions at the inception of the lease and at each balance sheet date to determine the recoverability of maintenance deposits. These assumptions are based on various factors, such as the estimated time between the maintenance events, the estimated cost of such maintenance events, the date the aircraft is due to be returned to the lessor, and the estimated number of flight hours and cycles the aircraft is expected to fly before it is purchased or returned to the lessor. Changes in estimates are accounted for on a prospective basis. As of June 30, 2026, all maintenance deposits recorded in the consolidated balance sheet as of June 30, 2026, which include $37.6 million of short term deposits and $15.5 million of noncurrent deposits included in deposits and other assets, are estimated to be recoverable either through reimbursable maintenance events or through application towards the purchase of the aircraft. Goodwill and Other Intangible Assets Goodwill represents the excess purchase price over the estimated fair value of net assets acquired in the Sun Country acquisition. Other intangible assets with finite lives represent customer relationships in the co-brand credit card program and the trade name acquired in the Sun Country acquisition. Goodwill is tested for impairment at least annually, or more frequently if events or changes in circumstances indicate that it might be impaired. Goodwill is tested at the reporting unit level. The Company has two reporting units: Allegiant Air and Sun Country. All of the Company's Goodwill balance is associated with the Sun Country reporting unit. Other intangible assets with finite lives are amortized over an estimated useful life. The estimated useful life for the customer relationships and trade name acquired from Sun Country is two years. The value of Goodwill is assessed under either a qualitative or quantitative approach. Under a qualitative approach, the Company considers various market factors, including certain key assumptions, such as the market value of the airline and other airlines, fuel prices, the overall economy, passenger yields and changes to the regulatory environment. The Company analyzes these factors to determine if events and circumstances have affected the fair value of Goodwill. If it is determined that it is more likely than not that the asset may be impaired, the Company uses a quantitative approach to determine the reporting unit or intangible asset’s fair value incorporating the key assumptions listed below. An impairment charge is recorded for the amount of carrying value that exceeds the determined fair value as of the testing date. When the Company evaluates Goodwill for impairment using a quantitative approach, the Company utilizes market and income approach valuation techniques. These measurements include the following key assumptions, 1) forecasted revenues, expenses and cash flows, 2) current discount rates, 3) comparative market multiples, 4) observable market transactions, and 5) anticipated changes to the regulatory environment. These assumptions are consistent with those that hypothetical market participants would use. Because the Company is required to make estimates and assumptions when evaluating Goodwill for impairment, actual amounts may differ materially from these estimates. The Company has not identified any triggering events during the six months ended June 30, 2026. Refer to Note 2 for further discussion on the Sun Country acquisition, including certain impacts on our Consolidated Financial Statements.

The accompanying unaudited consolidated financial statements include the accounts of Allegiant Travel Company (the “Company” or "Allegiant") and its majority-owned operating subsidiaries, including Allegiant Air, LLC ("Allegiant Air") and Sun Country, Inc., whose parent company, Sun Country Airlines Holdings, Inc. ("Sun Country"), was acquired on May 13, 2026. Purchase accounting impacts resulting from the acquisition of Sun Country are included as of that date. Financial results for periods prior to May 13, 2026, do not include Sun Country results. The Company's investments in unconsolidated affiliates, which are 50 percent or less owned, are accounted for under the equity or cost method, and are insignificant to the consolidated financial statements. All intercompany balances and transactions have been eliminated.

These unaudited consolidated financial statements reflect all normal recurring adjustments which management believes are necessary to present fairly the financial position, results of operations, and cash flows of the Company for the respective periods presented. Certain information and footnote disclosures normally included in the annual consolidated financial statements prepared in accordance with U.S. generally accepted accounting principles ("U.S. GAAP") have been omitted pursuant to the rules and regulations of the Securities and Exchange Commission for Form 10-Q. These unaudited interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements of the Company and notes thereto included in the annual report of the Company on Form 10-K for the year ended December 31, 2025 and filed with the Securities and Exchange Commission.

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and disclosure of contingent assets and liabilities, at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from these estimates.

Operating results for the three and six months ended June 30, 2026 are not necessarily indicative of operating results for the entire year due to the seasonal nature of leisure travel, the volatility of aircraft fuel prices, other macroeconomic factors as well as the acquisition of Sun Country during second quarter 2026.

Except as described below, there have been no material changes to the Company's significant accounting policies described in Note 2 to the audited financial statements included in the Company's Annual Report on Form 10‑K for the year ended December 31, 2025. As a result of the completion of the acquisition of Sun Country on May 13, 2026, the Company adopted the following accounting policies related to Sun Country's business.

In June 2024, Sun Country entered into the Amended and Restated Air Transportation Services Agreement ("ATSA") with Amazon.com Services, LLC ("Amazon"). Under this agreement, the Company operates a fleet of 737-800 cargo aircraft on behalf of Amazon. The ATSA includes an initial six-year term, which expires in October 2030. The agreement includes two additional, two-year renewal terms exercisable at Amazon's option, and a subsequent three-year renewal term subject to mutual written agreement, which, if not agreed to, will trigger a final two-year wind-down term. The ATSA has annual rate escalations.

The cargo fleet of 22 aircraft is subleased directly from Amazon and the Company operates them pursuant to the ATSA. The sublease arrangement does not qualify as a lease because the Company does not control the use of the aircraft. As such, no right-of use asset or lease liability is recognized in the consolidated financial statements for the Amazon arrangement.

The ATSA contains three performance obligations: Flight Services, Heavy Maintenance and Fuel. As Sun Country is the principal in providing Flight Services, revenue and related costs are recognized gross on the Statement of Income. Flight Services revenue is recognized when transportation services are provided. The Company acts as the agent in providing the Heavy Maintenance and Fuel performance obligations, which are reimbursed by Amazon based on the actual costs incurred. Reimbursements for heavy maintenance and fuel consumption are recognized in revenue, net of the actual amount of costs for heavy maintenance and fuel which are incurred to fulfill the performance obligations.

The ATSA with Amazon consists of three main components of consideration: a fixed amount is received each month per aircraft, a fixed amount is received each month per flight, and an amount per block hour is received each month. The ATSA contains a Service Level Agreement ("SLA") which provides for penalties for certain delays and cancellations. The SLA can result in a bonus or penalty for each month depending on the Company's performance. Each reporting period, the Company updates its estimate of variable consideration over the contract term and treats the adjustment as an adjustment to the total transaction price. When updating the estimate, the Company considers whether there are any changes in expected usage, performance-based bonuses or penalties, and changes in reimbursable costs. The transaction price is allocated to the performance obligations based on their relative standalone selling price.

In connection with the ATSA, Sun Country issued warrants to Amazon which allowed for the purchase of Sun Country's common stock. On the acquisition date, all of these warrants vested pursuant to the warrant agreement and were exercised on a net settlement basis into Sun Country shares, for which the Company paid merger consideration to Amazon. In connection with these warrants, the Company recorded a contract asset in the opening post-acquisition balance sheet. This contract asset will be amortized against cargo revenue over the remaining term of the ATSA through a reduction to the transaction price for Flight Services.

Certain of the Company's aircraft lease agreements acquired from Sun Country provide that the Company pay maintenance reserves monthly to aircraft lessors to be held as collateral in advance of major maintenance activities required to be performed by the Company. Generally, maintenance reserve payments are variable based on actual flight hours or cycles. These lease agreements provide that maintenance reserves are reimbursable to the Company upon completion of the maintenance event in an amount equal to the lesser of (1) the amount of the maintenance reserve held by the lessor associated with the specific maintenance event or (2) the qualifying costs related to the specific maintenance event.

Maintenance reserve payments that are expected to be recoverable via reimbursable expenses are reflected as Short-term lessor maintenance deposits and in deposits and other assets on the accompanying Consolidated Balance Sheets. These deposits are expected to be reimbursed to the Company upon performance of maintenance activities or used towards the purchase of the aircraft at the end of the lease. Lessor maintenance deposits deemed improbable of recovery are expensed as incurred and recorded within aircraft rent.

The Company made certain assumptions at the inception of the lease and at each balance sheet date to determine the recoverability of maintenance deposits. These assumptions are based on various factors, such as the estimated time between the maintenance events, the estimated cost of such maintenance events, the date the aircraft is due to be returned to the lessor, and the estimated number of flight hours and cycles the aircraft is expected to fly before it is purchased or returned to the lessor. Changes in estimates are accounted for on a prospective basis. As of June 30, 2026, all maintenance deposits recorded in the consolidated balance sheet as of June 30, 2026, which include $37.6 million of short term deposits and $15.5 million of noncurrent deposits included in deposits and other assets, are estimated to be recoverable either through reimbursable maintenance events or through application towards the purchase of the aircraft.

Goodwill represents the excess purchase price over the estimated fair value of net assets acquired in the Sun Country acquisition. Other intangible assets with finite lives represent customer relationships in the co-brand credit card program and the trade name acquired in the Sun Country acquisition. Goodwill is tested for impairment at least annually, or more frequently if events or changes in circumstances indicate that it might be impaired. Goodwill is tested at the reporting unit level. The Company has two reporting units: Allegiant Air and Sun Country. All of the Company's Goodwill balance is associated with the Sun Country reporting unit.

Other intangible assets with finite lives are amortized over an estimated useful life. The estimated useful life for the customer relationships and trade name acquired from Sun Country is two years.

The value of Goodwill is assessed under either a qualitative or quantitative approach. Under a qualitative approach, the Company considers various market factors, including certain key assumptions, such as the market value of the airline and other airlines, fuel prices, the overall economy, passenger yields and changes to the regulatory environment. The Company analyzes these factors to determine if events and circumstances have affected the fair value of Goodwill. If it is determined that it is more likely than not that the asset may be impaired, the Company uses a quantitative approach to determine the reporting unit or intangible asset’s fair value incorporating the key assumptions listed below. An impairment charge is recorded for the amount of carrying value that exceeds the determined fair value as of the testing date.

When the Company evaluates Goodwill for impairment using a quantitative approach, the Company utilizes market and income approach valuation techniques. These measurements include the following key assumptions, 1) forecasted revenues, expenses and cash flows, 2) current discount rates, 3) comparative market multiples, 4) observable market transactions, and 5) anticipated changes to the regulatory environment. These assumptions are consistent with those that hypothetical market participants would use. Because the Company is required to make estimates and assumptions when evaluating Goodwill for impairment, actual amounts may differ materially from these estimates.