Mesa Air (MESA) 10-Q 9 Feb 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2020	Jan. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	MESA
Title of 12(b) Security	Common Stock, no par value
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	NV
Entity File Number	001-38626
Entity Tax Identification Number	85-0302351
Entity Address, Address Line One	410 North 44th Street
Entity Address, Address Line Two	Suite 700
Entity Address, City or Town	Phoenix
Entity Address, Postal Zip Code	85008
City Area Code	602
Local Phone Number	685-4000
Entity Address, State or Province	AZ
Entity Registrant Name	MESA AIR GROUP, INC.
Entity Central Index Key	0000810332
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		35,568,290

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 181,300	$ 99,395
Restricted cash	3,634	3,446
Receivables, net	15,412	13,712
Expendable parts and supplies, net	22,760	22,971
Prepaid expenses and other current assets	12,897	16,067
Total current assets	236,003	155,591
Property and equipment, net	1,194,061	1,212,415
Intangibles, net	7,722	8,032
Lease and equipment deposits	1,851	1,899
Operating lease right-of-use assets	114,666	123,251
Other assets	514	742
Total assets	1,554,817	1,501,930
Current liabilities:
Current portion of long-term debt and financing leases	99,745	189,268
Current portion of deferred revenue	51,253	9,389
Current maturities of operating leases	44,712	43,932
Accounts payable	47,576	53,229
Accrued compensation	7,029	12,030
Other accrued expenses	37,581	45,478
Total current liabilities	287,896	353,326
Noncurrent liabilities:
Long-term debt and financing leases, excluding current portion	624,116	542,456
Noncurrent operating lease liabilities	53,570	62,531
Deferred credits	5,176	5,705
Deferred income taxes	69,111	64,275
Deferred revenue, net of current portion	26,504	14,369
Other noncurrent liabilities	4,147	1,409
Total noncurrent liabilities	782,624	690,745
Total liabilities	1,070,520	1,044,071
Commitments and contingencies (Note 14 and Note 15)
Stockholders' equity:
Preferred stock of no par value, 5,000,000 shares authorized; no shares issued and outstanding
Common stock of no par value and additional paid-in capital, 125,000,000 shares authorized; 35,532,162 (2021) and 35,526,918 (2020) shares issued and outstanding, 4,899,497 (2021) and 0 (2020) warrants issued and outstanding	255,092	242,772
Retained earnings	229,205	215,087
Total stockholders' equity	484,297	457,859
Total liabilities and stockholders' equity	$ 1,554,817	$ 1,501,930

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Sep. 30, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, no par value	$ 0	$ 0
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	35,532,162	35,526,918
Common stock, shares outstanding	35,532,162	35,526,918
Common stock, warrants issued	4,899,497	0
Common stock, warrants outstanding	4,899,497	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Operating revenues:
Total operating revenues	$ 150,371	$ 184,036
Operating expenses:
Flight operations	36,964	52,644
Fuel	390	169
Maintenance	52,864	58,095
Aircraft rent	10,048	11,329
Aircraft and traffic servicing	901	1,064
General and administrative	13,073	12,996
Depreciation and amortization	20,470	20,552
CARES Act grant recognition	(11,311)
Total operating expenses	123,399	156,849
Operating income	26,972	27,187
Other (expenses) income, net:
Interest expense	(9,082)	(12,628)
Interest income	126	58
Other (expense) income, net	923	(297)
Total other (expense), net	(8,033)	(12,867)
Income before taxes	18,939	14,320
Income tax expense	4,821	3,535
Net income and comprehensive income	$ 14,118	$ 10,785
Net income per share attributable to common shareholders
Basic	$ 0.40	$ 0.31
Diluted	$ 0.39	$ 0.31
Weighted-average common shares outstanding
Basic	35,531	35,023
Diluted	36,647	35,182
Contract Revenue [Member]
Operating revenues:
Total operating revenues	$ 127,158	$ 171,800
Pass Through and Other [Member]
Operating revenues:
Total operating revenues	$ 23,213	$ 12,236

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Revision of Prior Period Accounting Standards Update Adjustment [Member]	Common Stock [Member]	Number of Warrants [Member]	Common Stock and Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]Revision of Prior Period Accounting Standards Update Adjustment [Member]
Beginning balance at Sep. 30, 2019	$ 425,868				$ 238,504	$ 187,364
Beginning balance (ASU 2018-09 [Member]) at Sep. 30, 2019		$ 259					$ 259
Beginning balance, shares at Sep. 30, 2019			31,413,287	3,600,953
Stock compensation expense	1,320				1,320
Repurchased shares and warrants	(41)				(41)
Repurchased shares and warrants, shares			(5,558)
Warrants converted to common stock			1,612,481	(1,612,481)
Restricted shares issued, shares			18,916
Net income	10,785					10,785
Ending balance at Dec. 31, 2019	438,191				239,783	198,408
Ending balance, shares at Dec. 31, 2019			33,039,126	1,988,472
Beginning balance at Sep. 30, 2020	457,859				242,772	215,087
Beginning balance, shares at Sep. 30, 2020			35,526,918
Stock compensation expense	850				850
Repurchased shares and warrants	(19)		$ (20)		(19)
Repurchased shares and warrants, shares			(2,256)
Restricted shares issued, shares			7,500
Issuance of warrants, net of issuance costs	11,489				11,489
Issuance of warrants, net of issuance costs, shares				4,899,497
Net income	14,118					14,118
Ending balance at Dec. 31, 2020	$ 484,297				$ 255,092	$ 229,205
Ending balance, shares at Dec. 31, 2020			35,532,162	4,899,497

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net income	$ 14,118	$ 10,785
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	20,470	20,552
Stock compensation expense	850	1,320
Deferred income taxes	4,836	3,205
Amortization of deferred credits	(793)	(1,103)
Amortization of debt discount and issuance costs	1,860	1,054
Gain on extinguishment of debt	(950)
Loss on disposal of assets	24	407
Provision for obsolete expendable parts and supplies	(37)	97
Changes in assets and liabilities:
Receivables	(1,700)	(1,040)
Expendable parts and supplies	256	(1,158)
Prepaid expenses and other current assets	4,296	327
Accounts payable	(5,723)	(2,336)
Deferred revenue	53,999
Accrued liabilities	(12,637)	5,791
Change in operating lease right-of- use assets	404	329
Net cash provided by operating activities	79,273	38,230
Cash flows from investing activities:
Capital expenditures	(1,773)	(10,124)
Net returns (payments) on equipment & other deposits		(2,704)
Net cash used in investing activities	(1,773)	(12,828)
Cash flows from financing activities:
Proceeds from long-term debt	195,000
Principal payments on long-term debt and financing leases	(189,131)	(36,467)
Payments of debt and warrant issuance	(1,257)	(184)
Repurchase of stock	(19)	(41)
Net cash provided by financing activities	4,593	(36,692)
Net change in cash, cash equivalents and restricted cash	82,093	(11,290)
Cash, cash equivalents and restricted cash at beginning of period	102,841	72,501
Cash, cash equivalents and restricted cash at end of period	184,934	61,211
Supplemental cash flow information
Cash paid for interest	6,743	9,440
Cash paid for income taxes, net	1	15
Operating lease payments in operating cash flows	9,304	9,534
Supplemental non-cash operating activities
Right-of-use assets obtained in exchange of lease liabilities	69	142,165
Supplemental non-cash financing activities
Debt issuance cost related to loan agreement with US Department of Treasury	$ (1,887)
Accrued capital expenditures		$ 334

Organization and Operations

Organization and Operations	3 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Operations	1. Organization and Operations About Mesa Air Group, Inc. Headquartered in Phoenix, Arizona, Mesa Air Group, Inc. ("Mesa" or the "Company") is a holding company whose principal subsidiary, Mesa Airlines, Inc. ("Mesa Airlines"), operates as a regional air carrier providing scheduled flight service to 116 cities in 42 states, the District of Columbia, the Bahamas, and Mexico as well as Cargo services out of Cincinnati/Northern Kentucky International Airport. As of December 31, 2020, Mesa operated a fleet of 159 aircraft with approximately 420 daily departures and 3,200 employees. Mesa operates all of its flights as either American Eagle, United Express, or DHL Express The financial arrangements between the Company and its major airline partners involve a revenue-guarantee arrangement (i.e. a "capacity purchase agreement") whereby the major airline pays a monthly guaranteed amount for each aircraft under contract, a fixed fee for each block hour (the number of hours during which the aircraft is in revenue service, measured from the time of gate departure before take-off until the time of gate arrival at the destination) and flight flown and reimbursement of certain direct operating expenses in exchange for providing regional flying. The major airline partners also pay certain expenses directly to suppliers, such as fuel, ground operations and landing fees. Under the terms of these capacity purchase agreements, the major airline controls route selection, pricing and seat inventories, thereby reducing the Company's exposure to fluctuations in passenger traffic, fare levels, and fuel prices. American Capacity Purchase Agreement As of December 31, 2020, the Company operated 54 CRJ-900 aircraft for American under a Capacity Purchase Agreement. In exchange for providing flight services under our American Capacity Purchase Agreement, we receive a fixed monthly minimum amount per aircraft under contract plus certain additional amounts based upon the number of flights and block hours flown during each month. In addition, we may also receive incentives or incur penalties based upon our operational performance, including controllable on-time departures and controllable completion percentages. American also reimburses us for certain costs on an actual basis, including passenger liability and hull insurance and aircraft property taxes, all as set forth in our American Capacity Purchase Agreement. Other expenses, including fuel and certain landing fees, are directly paid to suppliers by American. In addition, American also provides, at no cost to us, certain ground handling and customer service functions, as well as airport-related facilities and gates at American hubs and cities where we operate. Our American Capacity Purchase Agreement establishes utilization credits which are required to be paid if the Company does not operate at minimum levels of flight operations. In prior periods, the FAA Qualification Standards (as defined below) have negatively impacted our ability to hire pilots at a rate sufficient to support required utilization levels, and, as a result, we have issued credits to American pursuant to the terms of our American Capacity Purchase Agreement. On November 19, 2020, we entered into an Amended and Restated American Capacity Purchase Agreement (the “Amended and Restated American Capacity Purchase Agreement”) with American which is effective as of January 1, 2021 and amends and restates the Code Share and Revenue Sharing Agreement, dated as of March 20, 2001 (as theretofore amended, supplemented and modified, the “Existing CPA”), between Mesa Airlines and American. The Amended and Restated American Purchase Agreement included the following amendments to the Existing CPA: ▪ A five-year term, commencing January 1, 2021 – December 31, 2025, covering 40 aircraft; ▪ Establishes new compensation payable to Mesa Airlines during the new term; ▪ Grants American the option in its sole discretion to withdraw up to: (a) 10 aircraft during calendar year 2021, provided that for the 6-month period ending June 30, 2021, American may only exercise this right if the number of mainline narrow body aircraft in American’s fleet has been reduced by a specified number of aircraft during such period, (b) 5 aircraft during each of calendar years 2022 and 2023, and (c) during the period from January 1, 2024 to July 31, 2024. American can remove the first 20 aircraft to the extent not otherwise removed in 2021 – 2023, and thereafter they have the right to remove the last 20 aircraft; ▪ Also grants American the right to withdraw a limited number of aircraft in connection with the failure to meet certain performance objectives for the fleet over consecutive monthly periods, or failure to satisfactorily complete established cabin interior program requirements by certain deadlines; and ▪ Provides American with additional termination rights, subject to certain cure periods, including the occurrence of a force majeure event (as defined in the American CPA) that lasts for a specified number of consecutive days (including but not limited to a future epidemic or pandemic), the occurrence of a labor dispute that affects Mesa’s ability to operate over a specified number of days, and operating in violation of any existing American collective bargaining agreement. Our ▪ If either American or the Company become insolvent, file for bankruptcy or fail to pay the debts as they become due , the non-defaulting party may terminate the agreement; ▪ Failure by the Company or American to perform the covenants, conditions or provisions of the American Capacity Purchase Agreement, subject to 15 days' notice and cure rights; ▪ If we are required by the FAA or the DOT to suspend operations and we have not resumed operations within three business days, except as a result of an emergency airworthiness directive from the FAA affecting all similarly equipped aircraft , American may terminate the agreement; ▪ If our controllable flight completion factor falls below certain levels for a specified period of time, subject to our right to cure, or; ▪ Upon the occurrence of a force majeure event (as defined in the Capacity Purchase Agreement) that lasts for a specified period of consecutive days and affects our ability to operate scheduled flights, including a future epidemic or pandemic; ▪ If a labor dispute affects our ability to operate over a specified number of days or we operate in violation of any existing American collective bargaining agreement; or ▪ Upon a change in our ownership or control without the written approval of American On December 22, 2020, we entered into Amendment No. 1 (“Amendment No. 1”) to the Amended and Restated American Capacity Purchase Agreement. The amendments in Amendment No. 1 reflect the following: ▪ The addition of CRJ-900 aircraft to the American CPA (collectively, the “Incremental Aircraft”) in accordance with the following schedule: (i) 3 aircraft, commencing January 5, 2021 to March 3, 2021, and (ii) increasing to a total of 5 aircraft, commencing March 4, 2021. The term of the Incremental Aircraft will be determined by American in its sole discretion; ▪ American’s right, exercisable in its sole discretion, to withdraw any Incremental Aircraft upon 60 days’ prior notice. American may specify one or more dates for the withdrawal of such Incremental Aircraft United Capacity Purchase Agreement As of December 31, 2020, we operated 20 CRJ-700, 60 E-175 and 12 E-175LL aircraft for United under our United Capacity Purchase Agreement. We expect to operate a total of 60 E175 and 20 E-175LL aircraft by mid-year in 2021 when we take delivery of the remaining 8 E-175LL aircraft by the end of June 2021. In exchange for providing the flight services under our United Capacity Purchase Agreement, we receive a fixed monthly minimum amount per aircraft under contract plus certain additional amounts based upon the number of flights and block hours flown and the results of passenger satisfaction surveys. United also reimburses us for certain costs on an actual basis, including property tax per aircraft and passenger liability insurance. Other expenses, including fuel and certain landing fees, are directly paid to suppliers by United. Under our United Capacity Purchase Agr eement, United owns of the 60 E - 175 and all of the new E 175 - LL aircraft (discussed below) and leases them to us at nominal amounts. United reimburses us on a pass-through basis for all costs related to heavy airframe and engine maintenance, landing gear, auxiliary power units ("APUs") and com ponent maintenance for the 42 E - 175 and all E - 175LL aircraft owned by United. Our United Capacity Purchase Agreement permits United, subject to certain conditions, including the payment of certain costs tied to aircraft type, to terminate the agreement in its discretion, or remove aircraft from service, by giving us notice of 90 days or more. If United elects to terminate our United Capacity Purchase Agreement in its entirety or permanently remove select aircraft from service, we are permitted to return any of the affected E-175 aircraft leased from United at no cost to us . On November 26, 2019, we amended and restated our United Capacity Purchase Agreement to, among other things, incorporate the terms of the 14 prior amendments to that Agreement and to extend the term thereof through the addition of 20 new Embraer E175LL aircraft to the scope of such Agreement. These new aircraft were to be financed and owned by us and operated for a period of twelve (12) years from the in-service date. Deliveries of the new E175LL aircraft were scheduled to begin in May 2020. In March 2020, the deliveries of the new E175LL aircraft were negotiated between United and Embraer to begin in September 2020 and be completed by the quarter ended June 30, 2021. Commencing five (5) years after the actual in-service date, United has the right to remove the E175LL aircraft from service by giving us notice of 90 days or more, subject to certain conditions, including the payment of certain wind-down expenses plus, if removed prior to the ten (10) year anniversary of the in-service date, certain accelerated margin payments. In addition to adding the 20 new E175LL aircraft to the amended and restated United Capacity Purchase Agreement, we extended the term of our 42 E-175 aircraft leased from United for an additional five (5) years, which now expire between 2024 and 2028. In addition, we own 18 E-175 aircraft that are operated for United and come out of service under the United Capacity Purchase Agreement in 2028. Under the amended and restated United Capacity Purchase Agreement, we agreed to lease our CRJ-700 aircraft to another United Express service provider for a term of seven (7) years. We will continue to operate such aircraft until they are transitioned to the new service provider. United has a right to purchase the CRJ-700 aircraft at the then fair market value. On November 4, 2020, we amended and restated our United Capacity Purchase Agreement to, among other things, ompany’s right-of-use assets and operating lease liabilities under ASC 842. We also agreed to a one-time provision for United to prepay $81.5 million under the United CPA for future performance by the Company (the “Prepayment”), and certain discounts on services provided under the capacity purchase agreement. We elected the practical expedient concerning the evaluation of a significant financing component for the Prepayment received in November 2020, and have accounted for the payment received within current deferred revenue. As of December 31, 2020, we have recognized $33.3 million of the Prepayment deferred revenue for flight services performed and expect to recognize the remaining balance to revenue as flight services are performed during the second quarter of 2021. DHL Flight Services On December 20, 2019, the Company entered into a Flight Services Agreement with DHL Network Operations (USA), Inc. Under the terms of this agreement, Mesa operates two Boeing 737-400F aircraft to provide air transportation services to DHL. The Company receives a fee per block hour with a minimum block hour guarantee. In addition, the costs for heavy maintenance including c-checks, off-wing engine maintenance and overhauls including LLPs, Landing Gear overhauls and LLPs, thrust reverser overhauls, and APU overhauls and LLPs are a direct pass through to DHL. Ground support including fueling and airport fees are paid directly by DHL. The Company is eligible for a monthly performance bonus or subject to a monthly penalty based on timeliness and completion performance. In connection with the Flight Services Agreement, the Company also entered into an Aircraft Sublease Agreement with DHL for the two Boeing 737-400F aircraft at no cost. The leases are not considered embedded leases within the contract and are excluded from the C ompany’s right-of-use assets and operating lease liabilities under ASC 842

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP") and include the accounts of the Company and its wholly owned operating subsidiaries. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB"). All intercompany accounts and transactions have been eliminated in consolidation. Reclassifications of certain immaterial prior period amounts have been made to conform to the current period presentation. These condensed consolidated financial statements should be read in conjunction with, the Company's audited consolidated financial statements and notes thereto as of and for the year ended September 30, 2020 included in the Company's Annual Report on Form 10-K for the year ended September 30, 2020 on file with the U.S. Securities and Exchange Commission (the "SEC"). Information and footnote disclosures normally included in financial statements have been condensed or omitted in these condensed consolidated financial statements pursuant to the rules and regulations of the SEC and GAAP. These condensed consolidated financial statements reflect all adjustments that, in the opinion of management, are necessary to present fairly the results of operations for the interim periods presented. The Company is an "emerging growth company," as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act,") and may remain an emerging growth company until the last day of its fiscal year following the fifth anniversary of the Company’s initial public offer (“IPO”), subject to specified conditions. The JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to "opt out" of such extended transition period, which means that when a standard is issued or revised and it has different application dates for public or private companies, the Company will be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies. Contract revenue and Pass- through and other The Company recognizes contract revenue when the service is provided under its capacity purchase agreements. Under the capacity purchase agreements, our major airline partners generally pay for each departure, flight hour (measured from takeoff to landing, excluding taxi time) or block hour (measured from takeoff to landing, including taxi time) incurred, and an amount per aircraft in service each month with additional incentives based on flight completion and on-time performance. The major airline partners also directly pay for or reimburses the Company for certain direct expenses incurred under the capacity purchase agreement, such as fuel and airport landing fees. The Company’s performance obligation is met when each flight is completed, and revenue is recognized and reflected in contract revenue. The directly reimbursed expenses, earned as flights are completed over the agreement term, are recognized and reflected in pass-through revenue. The Company records deferred revenue when cash payments are received or are due from our airline partners in advance of the Company’s performance, including amounts that are refundable. We received an $81.5 million prepayment under the amended and restated United Capacity Purchase Agreement , we recognized $33.3 million of the prepayment and The deferred revenue balance as of December 31, 2020 represents our aggregate remaining performance obligations that will be recognized as revenue over the period in which the performance obligations are satisfied, and is expected to be recognized as revenue as follows (In thousands): Periods Ending December 31, Total Maturities Remainder of 2021 $ 48,420 2022 9,714 2023 9,563 2024 8,503 2025 1,338 Thereafter 219 Total $ 77,757 A portion of the Company's compensation under its capacity purchase agreements with American and United is designed to reimburse the Company for certain aircraft ownership costs. The Company has concluded that a component of its revenue under these agreements is deemed to be lease revenue, as such agreements identify the "right of use" of a specific type and number of aircraft over a stated period-of-time. The lease revenue associated with the Company's capacity purchase agreements is accounted for as an operating lease and is reflected as contract revenue on the Company's consolidated statements of operations. The Company recognized $49.5 million and $53.3 million of lease revenue for the three months ended December 31, 2020 and 2019, respectively. The Company has not separately stated aircraft rental income and aircraft rental expense in the consolidated statements of operations because the use of the aircraft is not a separate activity of the total service provided under our capacity purchase agreements. Aircraft Lease In addition to the aircraft we receive from United as nominal leases under our United Capacity Purchase Agreement, approximately 11% of our aircraft are leased from third parties. All of our aircraft leases have been classified as operating leases, which results in rental payments being charged to expense over the term of the related leases. In the event that we or one of our major airline partners decide to exit an activity involving leased aircraft, losses may be incurred. In the event that we exit an activity that results in exit losses, these losses are accrued as each aircraft is removed from operations for early termination penalties, lease settle up and other charges. Additionally, any remaining ROU assets and lease liabilities will be written off. The majority of the Company's leased aircraft are leased through trusts that have a sole purpose to purchase, finance, and lease these aircraft to the Company; therefore, they meet the criteria of a variable interest entity. However, since these are single-owner trusts in which the Company does not participate, the Company is not at risk for losses and is not considered the primary beneficiary. Management believes that the Company's maximum exposure under these leases is the remaining lease payments. Contract Liabilities Contract liabilities consist of deferred credits for cost reimbursements from major airline partners related to aircraft modifications associated with capacity purchase agreements and pilot training. The deferred credits are recognized over time depicting the pattern of transfer of control of services resulting in ratable recognition of revenue over the remaining term of the capacity purchase agreements. Current and non-current deferred credits are recorded to other accrued expenses and non-current deferred credits in the condensed consolidated balance sheets. The Company's total current and non-current deferred credit balances at December 31, 2020 and September 30, 2020 are $7.7 million and $8.5 million, respectively. The Company recognized $0.8 million and $1.1 million of the deferred credits to revenue during the three months ended December 31, 2020 and 2019. Contract Assets The Company recognizes assets from the costs incurred to fulfill a contract including aircraft painting and reconfiguration and flight service personnel training costs. These costs are amortized based on the pattern of transfer of the services in relation to flight hours over the term of the contract. Contract assets are recorded as other assets in the condensed consolidated balance sheets. The Company's contract assets balances at December 31, 2020 and September 30, 2020 are $1.6 million and $2.0 million, respectively. Contract cost amortization was $0.4 million and $0.6 million for the three months ended December 31, 2020 and 2019, respectively. Use of Estimates The preparation of the Company's condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, and expenses and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements. Actual results could differ from those estimates. Maintenance Expense The Company operates under a Federal Aviation Administration ("FAA") approved continuous inspection and maintenance program. The Company uses the direct expense method of accounting for its maintenance of regional jet engine overhauls, airframe, landing gear, and normal recurring maintenance wherein the Company recognizes the expense when the maintenance work is completed, or over the repair period, if materially different. Our maintenance policy is determined by fleet when major maintenance is incurred. For leased aircraft, the Company is subject to lease return provisions that require a minimum portion of the "life" of an overhaul be remaining on the engine at the lease return date. The Company estimates the cost of maintenance lease return obligations and accrues such costs over the remaining lease term when the expense is probable and can be reasonably estimated. Under the Company ' s aircraft operating lease agreements and FAA operating regulations, it is obligated to perform all required maintenance activities on its fleet, including component repairs, scheduled air frame checks and major engine restoration events. The Company estimate s the timing of the next major maintenance event based on assumptions including estimated usage, FAA-mandated maintenance intervals and average removal times as recommended by the manufacturer. The timing and the cost of maintenance are based on estimates, which can be impacted by changes in utilization of its aircraft, changes in government regulations and suggested manufacturer maintenance intervals. Major maintenance events consist of overhauls to major components. Engine overhaul expense totaled $14.4 million and $10.6 million for the three months ended December 31, 2020, and 2019, respectively, of which $9.6 million and $1.9 million, respectively, was pass-through expense. Airframe C-check expense totaled $10.1 million and $7.3 million for the three months ended December 31, 2020, and 2019, respectively, of which $7.1 million and $1.2 million, respectively, was pass-through expense.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Dec. 31, 2020
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	3. Recent Accounting Pronouncements In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848) (“ASU 2020-04”). This ASU provides optional expedients and exceptions for a limited period of time for accounting for contracts, hedging relationships, and other transactions affected by the London Interbank Offered Rate (LIBOR) or another reference rate expected to be discontinued. Optional expedients can be applied from March 12, 2020 through December 31, 2022. We are currently evaluating the impact that the new guidance will have on our consolidated financial statements. In June 2016, the FASB issued new guidance requiring all expected credit losses for financial instruments held at the reporting date to be measured based on historical experience, current conditions and reasonable supportable forecasts. This replaces the existing incurred loss model and is applicable to the measurement of credit losses on financial instruments measured at amortized cost and also applies to some off-balance sheet credit exposures. Our adoption of this guidance on a modified retrospective basis on October 1, 2020 did not have a material impact as credit losses have not been, and are not expected to be, significant based on historical collection trends, the financial condition of our airline partners and external market factors. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) ("ASU 2016-02"), which provides guidance requiring lessees to recognize a right-of-use asset and a lease liability on the balance sheet for substantially all leases, with the exception of short-term leases. Leases will be classified as either financing or operating, with classification affecting the pattern of expense recognition in the statement of income. The Company adopted Topic 842 effective October 1, 2019 and elected the package of transition practical expedients for expired or existing contracts, which does not require reassessment of: (1) whether any of the Company’s contracts are or contain leases, (2) lease classification and (3) initial direct costs. In July 2018, the FASB issued ASU No. 2018-11, "Targeted Improvements - Leases (Topic 842)." The Company did not elect the hindsight practical expedient. This update provides an optional transition method that allows entities to elect to apply the standard using the modified retrospective approach at its effective date, versus recasting the prior years presented. If this adoption method is elected, an entity would recognize a cumulative-effect adjustment to the opening balance of retained earnings in the year of adoption. The Company elected this adoption method on October 1, 2019.There was no adjustment to retained earnings. Additionally, the Company’s adoption of Topic 842 did not have a significant impact on the recognition, measurement or presentation of lease revenue and lease expenses within the consolidated statements of operations or the consolidated statements of cash flows. The Company’s adoption of Topic 842 did not have a material impact on the timing or amount of the Company’s lease revenue as a lessor. The Company’s prepaid aircraft rents, accrued aircraft rents and deferred rent credits that were separately stated in the Company’s September 30, 2019 balance sheet have been classified as a component of the Company’s right-of-use assets effective October 1, 2019. The consolidated financial statements for the year ended September 30, 2020 are presented under the new standard, while comparative years presented are not adjusted and continue to be reported in accordance with the Company’s historical accounting policy. See Note 14 and 15, "Leases and Commitments” and “Contingencies," for more information. We determine if an arrangement is a lease at inception. Our current lease activities are recorded in operating lease right-of-use (“ROU”) assets, current maturities of operating lease and noncurrent operating lease liabilities in the consolidated balance sheets. Finance leases are included in property and equipment, net, current portion of long-term debt and financing leases, long-term debt and financing leases, excluding current portion. ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Variable lease payments are not included in the calculation of the right-of-use assets and lease liability due to uncertainty of the payment amount and are recorded as lease expense in the period incurred. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. We use the implicit rate when readily determinable. Our lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for lease payments is recognized on a straight-line basis over the lease term. As a lessee, we elected a short-term lease exception policy on all classes of underlying assets, permitting us to not apply the recognition requirements of this standard to short-term leases (i.e. leases with terms of 12 months or less). As a lessor, our capacity purchase agreements identify the "right of use" of a specific type and number of aircraft over a stated period-of-time. A portion of the compensation in the capacity purchase agreements are designed to reimburse the Company for certain aircraft ownership costs of these aircraft. We account for the non-lease component under ASC 606 and account for the lease component under ASC 842. We allocate the consideration in the contract between the lease and non-lease components based on their stated contract prices, which is based on a cost basis approach representing our estimate of the stand-alone selling prices.

Concentrations

Concentrations	3 Months Ended
	Dec. 31, 2020
Risks And Uncertainties [Abstract]
Concentrations	4 . Concentrations At December 31, 2020, the Company had capacity purchase agreements with American and United and a Flight Services Agreement with DHL Network Operations (USA). All of the Company's condensed consolidated revenue for the three months ended December 31, 2020 and 2019 and accounts receivable at December 31, 2020 and September 30, 2019 was derived from these agreements. Amounts billed by the Company under capacity purchase agreements are subject to the Company's interpretation of the applicable capacity purchase agreement and are subject to audit by the Company's major airline partners. Periodically, the Company's major airline partners dispute amounts billed and pay amounts less than the amount billed. Ultimate collection of the remaining amounts not only depends upon the Company prevailing under the applicable audit, but also upon the financial well-being of the major airline partner. As such, the Company periodically reviews amounts due based on historical collection trends, the financial condition of airline partners and external market factors and records a reserve for amounts estimated to be uncollectible. The allowance for doubtful accounts was $0.9 million and $0.8 million at December 31, 2020 and September 30, 2020, respectively. If the Company's ability to collect these receivables and the financial viability of its partners is materially different than estimated, the Company's estimate of the allowance could be materially impacted. American accounted for approximately 46% and 51% of the Company's total revenue for the three months ended December 31, 2020 and 2019, respectively. United accounted for approximately

Intangible Assets

Intangible Assets	3 Months Ended
	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible Assets	5 . Intangible Assets Information about the intangible assets of the Company as of December 31, 2020 and September 30, 2020, is as follows (in thousands): December 31, September 30, 2020 2020 Customer relationship $ 43,800 $ 43,800 Accumulated amortization (36,078 ) (35,768 ) $ 7,722 $ 8,032 Total amortization expense recognized was approximately $0.3 million and $0.4 million for the three months ended December 31, 2020 and 2019, respectively. The Company expects to record amortization expense of $0.9 million for the remainder of 2021, and $1.0 million, $0.9 million, $0.8 million, $0.7 million for fiscal years 2022, 2023, 2024 and 2025, respectively.

Balance Sheet Information

Balance Sheet Information	3 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Information	6 . Balance Sheet Information Certain significant amounts included in the Company's condensed consolidated balance sheet as of December 31, 2020 and September 30, 2020, consisted of the following (in thousands): December 31, September 30, 2020 2020 Expendable parts and supplies, net: Expendable parts and supplies $ 27,347 $ 27,431 Less: obsolescence and other (4,587 ) (4,460 ) $ 22,760 $ 22,971 Prepaid expenses and other current assets: Deferred offering and reimbursed costs $ 1,129 $ 1,261 Other 11,768 14,806 $ 12,897 $ 16,067 Property and equipment, net: Aircraft and other flight equipment substantially pledged $ 1,597,394 $ 1,596,174 Other equipment 5,176 5,147 Leasehold improvements 2,763 2,763 Vehicles 995 1,032 Building 699 699 Furniture and fixtures 302 302 Total property and equipment 1,607,329 1,606,117 Less: accumulated depreciation (413,268 ) (393,702 ) $ 1,194,061 $ 1,212,415 Other accrued expenses: Accrued property taxes $ 12,690 $ 11,354 Accrued interest 5,149 3,268 Accrued vacation 6,143 5,975 Other 13,599 24,881 $ 37,581 $ 45,478 The Company records impairment charges on long-lived assets used in operations when events and circumstances indicate that the assets may be impaired, the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets, and the net book value of the assets exceeds their estimated fair value. The Company has assessed whether any impairment of its long-lived assets existed and has determined that no charges were deemed necessary under applicable accounting standards as of December 31, 2020. The Company’s assumptions about future conditions important to its assessment of potential impairment of its long-lived assets, including the impact of the COVID-19 pandemic to its business, are subject to uncertainty, and the Company will continue to monitor these conditions in future periods as new information becomes available, and will update its analyses accordingly. Depreciation expense totaled approximately $20.2 million and $20.2 million for the three months ended December 31, 2020 and 2019, respectively.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	7 . Fair Value Measurements The carrying values reported in the condensed consolidated balance sheets for cash and cash equivalents, accounts receivable, and accounts payable approximate fair value because of the immediate or short-term maturity of these financial instruments. The Company ' s debt agreements are not traded on an active market. The Company has determined the estimated fair value of its debt to be Level 3, as certain inputs used to determine the fair value of these agreements are unobservable and, therefore, could be sensitive to changes in inputs. The Company utilizes the discounted cash flow method to estimate the fair value of Level 3 debt. The carrying value and estimated fair value of the Company's long-term debt, including current maturities, were as follows (in millions): December 31, 2020 September 30, 2020 Carrying Fair Carrying Fair Value Value Value Value Long-term debt and financing leases, including current maturities(1) $ 746.4 $ 777.3 $ 743.3 $ 768.7 (1) Current and prior period long-term debts' carrying and fair values exclude net debt issuance costs.

Long-Term Debt, Financing Lease

Long-Term Debt, Financing Leases and Other Borrowings	3 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-Term Debt, Financing Leases and Other Borrowings	8 . Long-Term Debt, Financing Leases and Other Borrowings Long-term debt as of December 31, 2020 and September 30, 2020, consisted of the following (in thousands): December 31, September 30, 2020 2020 Notes payable to financial institution, collateralized by the underlying aircraft, due 2022 (1)(2) $ — $ 41,472 Notes payable to financial institution, collateralized by the underlying aircraft, due 2024 (3) — 55,674 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2027 (4) 105,989 105,887 Notes payable to secured parties, collateralized by the underlying aircraft, due 2028 (5) 172,137 172,137 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2028 (6) 134,325 138,114 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2022 (7) — 47,319 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2022 (8) — 29,682 Notes payable to financial institution due 2020 (10) 1,523 1,523 Notes payable to financial institution, collateralized by the underlying equipment, due 2020 (11) — 4,182 Other obligations due to financial institution, collateralized by the underlying equipment, due 2023 (12) 6,185 6,864 Notes payable to financial institution, collateralized by the underlying equipment, due 2024 (13) 58,988 63,341 Notes payable to financial institution, collateralized by the underlying aircraft, due 2023 (14) 43,750 48,125 Notes payable to financial institution due 2023 (15) 5,500 6,000 Revolving Credit Facility (16) 22,296 22,930 Notes payable to financial institution due 2025 (17) 195,705 — Gross long-term debt, including current maturities 746,398 743,250 Less unamortized debt issuance costs (11,174 ) — Less Notes payable warrants (11,363 ) (11,526 ) Net long-term debt, including current maturities 723,861 731,724 Less current portion (99,745 ) (189,268 ) Net long-term debt $ 624,116 $ 542,456 (1 ) In fiscal 2007, the Company financed three CRJ-900 and three CRJ-700 aircraft for $120.3 million. The debt bears interest at the monthly LIBOR plus 2.25% and requires monthly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020. (2 ) In fiscal 2014, the Company financed ten CRJ-900 aircraft for $88.4 million. The debt bears interest at the monthly LIBOR plus 1.95% and requires monthly principal and interest payments. In fiscal 2018, the Company repaid $40.0 million related to four CRJ-900 aircraft. During quarter ended December 31, 2020 (3 ) In fiscal 2014, the Company financed eight CRJ-900 aircraft with $114.5 million in debt. The debt bears interest at 5.00% and requires monthly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020 (4 ) In fiscal 2015, the Company financed seven CRJ-900 aircraft with $170.2 million in debt. The senior notes payable of $151.0 million bear interest at monthly LIBOR plus 2.71% and require monthly principal and interest payments. The subordinated notes payable are noninterest-bearing and become payable in full on the last day of the term of the notes. The Company has imputed an interest rate of 6.25% on the subordinated notes payable and recorded a related discount of $8.1 million, which is being accreted to interest expense over the term of the notes. (5 ) In fiscal 2016, the Company financed ten E-175 aircraft with $246.0 million in debt under an EETC financing arrangement (see discussion below). The debt bears interest ranging from 4.75% to 6.25% and requires semi-annual principal and interest payments. (6 ) In fiscal 2016, the Company financed eight E-175 aircraft with $195.3 million in debt. The senior notes payable of $172.0 million bear interest at the three-month LIBOR plus a spread ranging from 2.20% to 2.32% and require quarterly principal and interest payments. The subordinated notes payable bear interest at 4.50% and require quarterly principal and interest payments. (7) In June 2018, the Company refinanced six CRJ-900 aircraft with $27.5 million in debt and financed nine CRJ-900 aircraft, which were previously leased, with $69.6 million in debt. The senior notes payable of $65.8 million bear interest at the three-month LIBOR plus 3.50% and require quarterly principal and interest payments. The subordinated notes payable of $29.8 million bear interest at three month LIBOR plus 7.50% and require quarterly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020 (8) In during quarter ended December 31, 2020. ( 1 0) In fiscal 2015 and 2016, the Company financed certain flight equipment maintenance costs with $10.2 million in debt. The debt bears interest at the three-month LIBOR plus 3.07% (11 ) In fiscal 2016-2019, the Company financed certain flight equipment maintenance costs with $26.1 million in debt. The debt bears interest at the three-month LIBOR plus a spread ranging from 2.93% to 3.21%and requires quarterly principal and interest payments. The debt is subject to a fixed charge ratio covenant. The loan was paid in full during quarter ended December 31, 2020 12 ) In February 2018, the Company leased two spare engines. The leases were determined to be capital as the leases contain a bargain purchase option at the end of the term. Imputed interest is 9.128% and the leases requires monthly payments. (13) In January 2019, the Company financed certain flight equipment with $91.2 million in debt. The debt bears interest at the monthly LIBOR plus 3.10% and requires monthly principal and interest payments. (14) In June 2019, the Company financed ten CRJ-700 aircraft with $70.0 million in debt, which were previously leased. The debt bears interest at the monthly LIBOR plus 5.00% and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1 st (15 ) On September 27,2019, the Company financed certain flight equipment for $8.0 million. The debt bears interest at the monthly LIBOR plus 5.00% and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1 st (16) On September 25, 2019, the Company extended the term on their $35.0 million working capital draw loan by three years, which now terminates in September 2022. Interest is assessed on drawn amounts at one-month LIBOR plus 3.75%. During quarter ended June 30, 2020, $23.0 million was drawn to cover operational needs. (17) Principal maturities of long-term debt as of December 31, 2020, and for each of the next five years are as follows (in thousands): Periods Ending December 31, Total Principal Remainder of 2021 $ 82,535 2022 113,048 2023 89,462 2024 61,209 2025 56,526 Thereafter 343,618 $ 746,398 The net book value of collateralized aircraft and equipment as of December 31, 2020 was $1,077.0 million. Enhanced Equipment Trust Certificate ("EETC") In December 2015, an Enhanced Equipment Trust Certificate ("EETC") pass-through trust was created to issue pass-through certificates to obtain financing for new E-175 aircraft. At December 31, 2020 Mesa has $172.1 million of equipment notes outstanding issued under the EETC financing included in long-term debt on the condensed consolidated balance sheets. The structure of the EETC financing consists of a pass-through trust created by Mesa to issue pass-through certificates, which represent fractional undivided interests in the pass-through trust and are not obligations of Mesa. The proceeds of the issuance of the pass-through certificates were used to purchase equipment notes which were issued by Mesa and secured by its aircraft. The payment obligations under the equipment notes are those of Mesa. Proceeds received from the sale of pass-through certificates were initially held by a depositary in escrow for the benefit of the certificate holders until Mesa issued equipment notes to the trust, which purchased such notes with a portion of the escrowed funds. Mesa evaluated whether the pass-through trust formed for its EETC financing is a Variable Interest Entity ("VIE") and required to be consolidated. The pass-through trust was determined to be a VIE, however, the Company has determined that it does not have a variable interest in the pass-through trust, and therefore, has not consolidated the pass-through trust with its financial statements. CIT Revolving Credit Facility On September 25, 2019, the Company extended the term on their $35.0 million working capital draw loan by three years, which now terminates in September 2022. Interest is assessed on drawn amounts at one-month LIBOR plus 3.75%. During quarter ended June 30, 2020, $23.0 million was drawn to cover operational needs. Loan agreement with United States Department of Treasury On October 30, 2020, the Company entered into a Loan and Guarantee Agreement with United States Department of Treasury (the “U.S. Treasury”) for a secured loan facility of up to $200.0 million that matures in October 2025 (“the Treasury Loan Agreement”). On October 30, 2020, the Company borrowed $43.0 million (“the $43M Treasury Loan”) and on November 13, 2020, the Company borrowed an additional $152.0 million (“the $152M Treasury Loan”), collectively referred to as the “Treasury Term Loan Facility”. No further borrowings are available under the Treasury Loan Agreement. The Company also issued warrants to purchase shares of common stock to the U.S. Treasury. The Loan and Guarantee Agreement bear interest at a variable rate equal to (a)(i) the LIBOR rate divided by (ii) one minus the Eurodollar Reserve Percentage plus (b) 3.50%. Accrued interest on the loans will be payable in arrears on the first business day following the 14 th All principal amounts outstanding under the Loan and Guarantee Agreement are due and payable in a single installment on October 30, 2025 (the “ Maturity Date ”). Interest will be paid by increasing the principal amount of the loan by the amount of such interest due on an interest payment date for the first 12 months. Mesa's obligations under the Treasury Loan Agreement are secured by certain aircraft, aircraft engines, accounts receivable, ground service equipment and tooling (collectively, the “Collateral”). extent permitted by the CARES Act. Voluntary prepayments of loans under the Loan Agreement may be made, in whole or in part, by Mesa Airlines, without premium or penalty, at any time and from time to time. Amounts prepaid may not be reborrowed. Mandatory prepayments of loans under the Loan Agreement are required, without premium or penalty, to the extent necessary to comply with the covenants discussed below, certain dispositions of the Collateral, certain debt issuances secured by liens on the Collateral and certain insurance payments related to the Collateral. In addition, if a “change of control” (as defined in the Loan Agreement) occurs with respect to Mesa Airlines, Mesa Airlines will be required to repay the loans outstanding under the Loan Agreement. The Loan Agreement contains two financial covenants, a minimum collateral coverage ratio and a minimum liquidity level. The Loan Agreement also contains customary negative and affirmative covenants for credit facilities of this type, including, among others: (a) limitations on dividends and distributions; (b) limitations on the creation of certain liens; (c) restrictions on certain dispositions, investments and acquisitions; (d) limitations on transactions with affiliates; (e) restrictions on fundamental changes to the business, and (f) restrictions on lobbying activities. Additionally, the Company is required to comply with the relevant provisions of the CARES Act, including limits on employment level reductions after September 30, 2020, restrictions on dividends and stock buybacks, limitations on executive compensation, and requirements to maintain certain levels of scheduled service. In connection with the Loan and Guarantee Agreement and as partial compensation to Treasury for the provision of financial assistance under the Loan and Guarantee Agreement, the Company issued to Treasury warrants to purchase an aggregate of 4,899,497 shares of the Company’s common stock at an exercise price of $3.98 per share, which was the closing price of the Common Stock on The Nasdaq Stock Market on April 9, 2020. The exercise price and number of shares of common stock issuable under the Warrants are subject to adjustment as a result of anti-dilution provisions contained in the Warrants for certain stock issuances, dividends, and other corporate actions. The warrants expire on the fifth anniversary of the date of issuance and are exercisable either through net share settlement or net cash settlement, at the Company’s option. For accounting purposes, the fair value for the Treasury Loan Warrant Shares is estimated using a Black-Scholes option pricing model and recorded in stockholders' equity with an offsetting debt discount to the Treasury Term Loan Facility in the condensed consolidated balance sheet. The Company incurred $3.1 million in debt issuance costs relating to the Loan and Guarantee Agreement. In accordance with the applicable guidance, Mesa allocated the debt issuance costs between the Treasury Loan and related warrants. At funding on October 30, 2020, the $43M Treasury Loan was recorded net of $0.7 million in capitalized debt issuance costs. At funding on November 13, 2020, the $152M Treasury Loan was recorded net of $2.3 million in capitalized debt issuance costs. The remaining $0.1 million in debt issuance costs was allocated to the warrants as a reduction to the warrant value within additional paid-in capital. Debt issuance costs allocated to the debt are amortized into interest expense using the effective interest method over the term of the related loan. Debt Repayment Prior to the November 13, 2020 funding of the $152M Treasury Loan, the Company repaid $167.7 million in existing aircraft debt covering 44 aircraft, including indebtedness under its (a) Senior Loan Agreements, dated June 27, 2018, (b) Junior Loan Agreements, also dated June 27, 2018, (c) Credit Agreements, dated January 31, 2007, April 16, 2014, and May 23, 2014, (d) Senior Loan Agreements, dated December 27, 2017, and (e) Junior Loan Agreements, also dated December 27, 2017 (collectively, “the EDC Loans”). The Company made payments totaling $164.1 million to repay the EDC Loans, consisting of principal of $167.7 million, and a $3.6 million discount on the balance owed. Additionally, in connection with the repayment, $2.5 million of unamortized original issue discount and deferred financing costs were recorded as a loss on debt extinguishment, resulting in a net gain on extinguishment of $1.0 million recorded within other income. As of December 31, 2020, the Company is in compliance will all debt covenants.

Earnings Per Share and Equity

Earnings Per Share and Equity	3 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share and Equity	9 . Earnings Per Share and Equity Calculations of net income per common share attributable to Mesa Air Group were as follows (in thousands, except per share data): Three Months Ended December 31, 2020 2019 Net income attributable to Mesa Air Group $ 14,118 $ 10,785 Basic weighted average common shares outstanding 35,531 35,023 Add: Incremental shares for: Dilutive share adjustment - UST Warrant 800 — Dilutive share adjustment - Restricted Shares 316 159 Diluted weighted average common shares outstanding 36,647 35,182 Net income per common share attributable to Mesa Air Group: Basic $ 0.40 $ 0.31 Diluted $ 0.39 $ 0.31 Basic income per common share is computed by dividing net income attributable to Mesa Air Group by the weighted average number of common shares outstanding during the period. The number of incremental shares from the assumed issuance of shares relating to restricted stock and exercise of warrants (excluding warrants with a nominal conversion price) is calculated by applying the treasury stock method. Share-based awards and warrants whose impact is considered to be anti-dilutive under the treasury stock method were excluded from the diluted net income or loss per share calculation. In loss periods, these incremental shares are excluded from the calculation of diluted loss per share, as the inclusion of unvested restricted stock and warrants would have an anti-dilutive effect. There were no anti-dilutive shares relating to restricted stock and exercise of warrants that were excluded from the calculation of diluted loss per share for the three months ended December 31, 2020 and 2019.

Common Stock

Common Stock	3 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Common Stock	1 0 . Common Stock The Company previously issued warrants to third parties, which had a five-year In July 2018, the Company's Board of Directors and Compensation Committee approved the issuance of shares of restricted common stock under its 2018 Equity Incentive Plan (the "2018 Plan") immediately following completion of the Company's IPO to certain of its employees and directors in exchange for the cancellation of existing restricted phantom stock units, unvested restricted shares and SARs. The shares of restricted common stock issued under the 2018 Plan in exchange for the cancellation of restricted phantom stock units, unvested restricted shares and SARs are subject to vesting on the same terms set forth in the prior vesting schedules and are not subject to acceleration in connection with the 2018 Plan issuances. On April 9, 2019, and pursuant to Section 4.4 of the 2018 Plan in connection with the 2.5-for-1 stock split effected on August 8, 2018, the board of directors approved an increase in the number of shares authorized for issuance under the 2018 Plan by 1,000,000 shares of common stock. On October 30, 2020 and November 13, 2020, the Company entered into the Loan and Guarantee Agreement with the United States Department of the Treasury (the “Treasury”) and the Bank of New York Mellon, as Administrative and Collateral Agent, under the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”). In connection with the Loan and Guarantee Agreement and as partial compensation to the Treasury for the provision of financial assistance under the Loan and Guarantee Agreement, the Company issued warrants to the Treasury to purchase shares of the Company’s common stock, no par value, at an exercise price of $3.98 per share (the “Exercise Price”), which was the closing price of the Common Stock on The Nasdaq Stock Market on April 9, 2020. The Warrants were issued pursuant to the terms of a Treasury Warrant Agreement entered into by the Company and the Treasury. The exercise price and number of Warrant Shares issuable under the Warrants are subject to adjustment as a result of anti- dilution provisions contained in the Warrants for certain stock issuances, dividends, and other corporate actions. The warrants expire on the fifth anniversary of the date of issuance and are exercisable either through net share settlement or net cash settlement, at the Company’s option. The warrants will be accounted for within equity at a grant date fair value determined under the Black Scholes Option Pricing Model . As of December 31, 2020, 4,899,497 warrants were issued and outstanding. The Company has not historically paid dividends on shares of its common stock. Additionally, the Loan and Guarantee Agreement and the Company's aircraft lease facility (the "RASPRO" Lease Facility) with RASPRO Trust 2005, a pass-through trust, contain restrictions that limit the Company's ability to or prohibit it from paying dividends to holders of its common stock.

Income Taxes

Income Taxes	3 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	1 1 . Income Taxes The Company’s effective tax rate (ETR) from continuing operations was 25.5% for the three months ended December 31, 2020 and 24.7% for the three months ended December 31, 2019, respectively. The Company's ETR during the three months ended December 31, 2020 was different from the federal statutory rate of 21% primarily due to permanent book and tax deductible expense differences, state taxes, The Company's current year effective tax rate increased compared to the prior year tax rate as a result of a decrease to the forecast for the current fiscal year, As of September 30, 2020, the Company had aggregate federal and state net operating loss carryovers of approximately $512.4 million and $223.9 million, respectively, which expire in fiscal years 2027-2038 and 2021-2040, respectively. Approximately $3.1 million of state net operating loss carryforwards are expected to expire in the current fiscal year.

Share-Based Compensation and St

Share-Based Compensation and Stock Repurchases	3 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-Based Compensation and Stock Repurchases	1 2 . Share-Based Compensation and Stock Repurchases Restricted Stock The restricted share activity for the three months ended December 31, 2020 were summarized as follows: Weighted- Average Number Grant Date of Shares Fair Value Restricted shares unvested at September 30, 2020 1,195,548 $ 5.47 Granted 5,000 7.71 Vested (7,500 ) 7.37 Forfeited (17,500 ) 4.59 Restricted shares unvested at December 31, 2020 1,175,548 $ 5.48 As of December 31, 2020, there was $4.2 million, of total unrecognized compensation cost related to unvested share-based compensation arrangements. That cost is expected to be recognized over a weighted-average period of 2.0 years. Compensation cost for share-based awards are recognized on a straight-line basis over the vesting period. Share-based compensation expense for the three months ended December 31, 2020 and 2019 was $0.9 million and $1.3 million, respectively. The Company repurchased 2,256 shares of its common stock for $0.02 million to cover the income tax obligation on vested employee equity awards and warrant conversions during the three months ended December 31, 2020. The Company has granted restricted stock units (“RSUs”) as part of its long-term incentive compensation to employees and non-employee members of the Board of Directors. RSAs and RSUs generally vest over a period of 3 to 5 years employees and over one year for members of the Board of Directors. The restricted common stock underlying RSAs are deemed issued and outstanding upon grant, and carry the same voting rights of unrestricted outstanding common stock. The restricted common stock underlying RSUs are not deemed issued or outstanding upon grant, and do not carry any voting rights.

Employee Stock Purchase Plan

Employee Stock Purchase Plan	3 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Employee Stock Purchase Plan	13. 2019 ESPP The Mesa Air Group, Inc. 2019 Employee Stock Purchase Plan (the " 2019 ESPP A maximum of 500,000 Mesa Air Group, Inc. ordinary shares may be issued under the 2019 ESPP. As of December 31, 2020, eligible employees purchased and the Company issued 99,644 Mesa Air Group, Inc. ordinary shares under the 2019 ESPP.

Leases and Commitments

Leases and Commitments	3 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Leases and Commitments	1 4 . Leases and Commitments Effective As of December 31, 2020, the Company leased 18 aircraft, airport facilities, office space, and other property and equipment under non-cancelable operating leases. The leases require the Company to pay all taxes, maintenance, insurance, and other operating expenses. Rental expense is recognized on a straight-line basis over the lease term, net of lessor rebates and other incentives. The Company expects that, in the normal course of business, such operating leases that expire will be renewed or replaced by other leases, or the property may be purchased rather than leased. Aggregate rental expense under all operating aircraft, equipment and facility leases totaled approximately $13.8 million and $16.8 million for the three months ended December 31, 2020 and 2019, respectively. As of December 31, 2020, the Company’s operating lease right-of-use assets were $114.7 million, the Company’s current maturities of operating lease liabilities were $44.7 million, and the Company’s noncurrent lease liabilities were $53.6 million. The Company’s operating lease payments in operating cash flows for the three months ended December 31, 2020 and 2019 are $9.3 million and $9.5 million, respectively. The table below presents lease related terms and discount rates as of December 31, 2020: As of December 31,2020 Weighted average remaining lease term Operating leases 3.3 years Weighted average discount rate Operating leases 4.2 % The Table below represents lease expense recorded during three months ended December 31, 2020 and 2019. Three Months Ended December 31, 2020 2019 $ Change % Change Operating lease cost $ 13,839 $ 16,784 $ (2,945 ) (17.5 )% The following table summarizes future minimum rental payments primarily related to leased aircraft required under operating leases that had initial or remaining non-cancelable lease terms as of December 31, 2020 (in thousands): Periods Ending December 31, Total Maturities Remainder of 2021 $ 38,095 2022 33,242 2023 15,973 2024 14,682 2025 1,494 Thereafter 160 Less: Interest $ (5,364 ) Amounts recorded in the Consolidated Balance Sheet $ 98,282 The following represents future minimum lease obligations under non-cancelable operating leases as of September 30, 2019 (in thousands): Periods Ending September 30, Total Payments 2020 47,814 2021 46,007 2022 31,090 2023 13,726 2024 13,185 Thereafter 1,368 Total $ 153,190 Engine Purchase Commitments On October 8, 2020, the Company and General Electric Company (“GE”), acting through its GE-Aviation business unit, entered into an Amended and Restated Letter Agreement No. 13, which deferred the initial delivery and payment dates of the 20 new spare CF34-8C5 engines that were subject to previously disclosed letter agreements between the Company and GE. Under the terms of the Amended and Restated Letter Agreement, the Company agreed to purchase and take delivery of the 20 new space CF34-8C5 engines commencing in May 2021, with the final spare engine to be delivered in December 2021. Payments are now due in five (5) separate tranches commencing in December 2020, and in February, April, May and June 2021. The total purchase commitment related to these engines is approximately $118.9 million. However, the parties continue to discuss modifying the number of spare engines to be purchased by the Company and timing of deliveries under the Amended and restated Letter Agreement No. 13. If the Company fails to accept delivery of the spare engines when duly tendered, the Company may be assessed a minimum cancellation charge based on the engine price determined as of the date of scheduled engine delivery to the Company.

Contingencies

Contingencies	3 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Contingencies	1 5 . Contingencies The Company is involved in various legal proceedings (including, but not limited to, insured claims) and FAA civil action proceedings that the Company does not believe will have a material adverse effect upon its business, financial condition, or results of operations, although no assurance can be given to the ultimate outcome of any such proceedings.

Subsequent Events

Subsequent Events	3 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	1 6 . Subsequent Events In February 2021, the Company was granted $48.6 million in financial assistance by the Department of the Treasury under the Payroll Support Program Extension (“PSP2”) under the Consolidated Appropriations Act of 2021. The Company received the first installment of $24.3 million on February 8, 2021. The relief payments are conditioned on our agreement to refrain from conducting involuntary employee layoffs or furloughs through March 31, 2021. Other conditions include prohibitions on share repurchases and dividends through March 31, 2022, continuing essential air service as directed by the U.S. Department of Transportation and certain limitations on executive compensation.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America ("GAAP") and include the accounts of the Company and its wholly owned operating subsidiaries. Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB"). All intercompany accounts and transactions have been eliminated in consolidation. Reclassifications of certain immaterial prior period amounts have been made to conform to the current period presentation. These condensed consolidated financial statements should be read in conjunction with, the Company's audited consolidated financial statements and notes thereto as of and for the year ended September 30, 2020 included in the Company's Annual Report on Form 10-K for the year ended September 30, 2020 on file with the U.S. Securities and Exchange Commission (the "SEC"). Information and footnote disclosures normally included in financial statements have been condensed or omitted in these condensed consolidated financial statements pursuant to the rules and regulations of the SEC and GAAP. These condensed consolidated financial statements reflect all adjustments that, in the opinion of management, are necessary to present fairly the results of operations for the interim periods presented. The Company is an "emerging growth company," as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act,") and may remain an emerging growth company until the last day of its fiscal year following the fifth anniversary of the Company’s initial public offer (“IPO”), subject to specified conditions. The JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to "opt out" of such extended transition period, which means that when a standard is issued or revised and it has different application dates for public or private companies, the Company will be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies.
Contract revenue and Pass- through and other	Contract revenue and Pass- through and other The Company recognizes contract revenue when the service is provided under its capacity purchase agreements. Under the capacity purchase agreements, our major airline partners generally pay for each departure, flight hour (measured from takeoff to landing, excluding taxi time) or block hour (measured from takeoff to landing, including taxi time) incurred, and an amount per aircraft in service each month with additional incentives based on flight completion and on-time performance. The major airline partners also directly pay for or reimburses the Company for certain direct expenses incurred under the capacity purchase agreement, such as fuel and airport landing fees. The Company’s performance obligation is met when each flight is completed, and revenue is recognized and reflected in contract revenue. The directly reimbursed expenses, earned as flights are completed over the agreement term, are recognized and reflected in pass-through revenue. The Company records deferred revenue when cash payments are received or are due from our airline partners in advance of the Company’s performance, including amounts that are refundable. We received an $81.5 million prepayment under the amended and restated United Capacity Purchase Agreement , we recognized $33.3 million of the prepayment and The deferred revenue balance as of December 31, 2020 represents our aggregate remaining performance obligations that will be recognized as revenue over the period in which the performance obligations are satisfied, and is expected to be recognized as revenue as follows (In thousands): Periods Ending December 31, Total Maturities Remainder of 2021 $ 48,420 2022 9,714 2023 9,563 2024 8,503 2025 1,338 Thereafter 219 Total $ 77,757 A portion of the Company's compensation under its capacity purchase agreements with American and United is designed to reimburse the Company for certain aircraft ownership costs. The Company has concluded that a component of its revenue under these agreements is deemed to be lease revenue, as such agreements identify the "right of use" of a specific type and number of aircraft over a stated period-of-time. The lease revenue associated with the Company's capacity purchase agreements is accounted for as an operating lease and is reflected as contract revenue on the Company's consolidated statements of operations. The Company recognized $49.5 million and $53.3 million of lease revenue for the three months ended December 31, 2020 and 2019, respectively. The Company has not separately stated aircraft rental income and aircraft rental expense in the consolidated statements of operations because the use of the aircraft is not a separate activity of the total service provided under our capacity purchase agreements.
Aircraft Lease	Aircraft Lease In addition to the aircraft we receive from United as nominal leases under our United Capacity Purchase Agreement, approximately 11% of our aircraft are leased from third parties. All of our aircraft leases have been classified as operating leases, which results in rental payments being charged to expense over the term of the related leases. In the event that we or one of our major airline partners decide to exit an activity involving leased aircraft, losses may be incurred. In the event that we exit an activity that results in exit losses, these losses are accrued as each aircraft is removed from operations for early termination penalties, lease settle up and other charges. Additionally, any remaining ROU assets and lease liabilities will be written off. The majority of the Company's leased aircraft are leased through trusts that have a sole purpose to purchase, finance, and lease these aircraft to the Company; therefore, they meet the criteria of a variable interest entity. However, since these are single-owner trusts in which the Company does not participate, the Company is not at risk for losses and is not considered the primary beneficiary. Management believes that the Company's maximum exposure under these leases is the remaining lease payments.
Contract Liabilities	Contract Liabilities Contract liabilities consist of deferred credits for cost reimbursements from major airline partners related to aircraft modifications associated with capacity purchase agreements and pilot training. The deferred credits are recognized over time depicting the pattern of transfer of control of services resulting in ratable recognition of revenue over the remaining term of the capacity purchase agreements. Current and non-current deferred credits are recorded to other accrued expenses and non-current deferred credits in the condensed consolidated balance sheets. The Company's total current and non-current deferred credit balances at December 31, 2020 and September 30, 2020 are $7.7 million and $8.5 million, respectively. The Company recognized $0.8 million and $1.1 million of the deferred credits to revenue during the three months ended December 31, 2020 and 2019.
Contract Assets	Contract Assets The Company recognizes assets from the costs incurred to fulfill a contract including aircraft painting and reconfiguration and flight service personnel training costs. These costs are amortized based on the pattern of transfer of the services in relation to flight hours over the term of the contract. Contract assets are recorded as other assets in the condensed consolidated balance sheets. The Company's contract assets balances at December 31, 2020 and September 30, 2020 are $1.6 million and $2.0 million, respectively. Contract cost amortization was $0.4 million and $0.6 million for the three months ended December 31, 2020 and 2019, respectively.
Use of Estimates	Use of Estimates The preparation of the Company's condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, and expenses and the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements. Actual results could differ from those estimates.
Maintenance Expense	Maintenance Expense The Company operates under a Federal Aviation Administration ("FAA") approved continuous inspection and maintenance program. The Company uses the direct expense method of accounting for its maintenance of regional jet engine overhauls, airframe, landing gear, and normal recurring maintenance wherein the Company recognizes the expense when the maintenance work is completed, or over the repair period, if materially different. Our maintenance policy is determined by fleet when major maintenance is incurred. For leased aircraft, the Company is subject to lease return provisions that require a minimum portion of the "life" of an overhaul be remaining on the engine at the lease return date. The Company estimates the cost of maintenance lease return obligations and accrues such costs over the remaining lease term when the expense is probable and can be reasonably estimated. Under the Company ' s aircraft operating lease agreements and FAA operating regulations, it is obligated to perform all required maintenance activities on its fleet, including component repairs, scheduled air frame checks and major engine restoration events. The Company estimate s the timing of the next major maintenance event based on assumptions including estimated usage, FAA-mandated maintenance intervals and average removal times as recommended by the manufacturer. The timing and the cost of maintenance are based on estimates, which can be impacted by changes in utilization of its aircraft, changes in government regulations and suggested manufacturer maintenance intervals. Major maintenance events consist of overhauls to major components. Engine overhaul expense totaled $14.4 million and $10.6 million for the three months ended December 31, 2020, and 2019, respectively, of which $9.6 million and $1.9 million, respectively, was pass-through expense. Airframe C-check expense totaled $10.1 million and $7.3 million for the three months ended December 31, 2020, and 2019, respectively, of which $7.1 million and $1.2 million, respectively, was pass-through expense.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of Deferred Revenue Remaining Performance Obligations	The deferred revenue balance as of December 31, 2020 represents our aggregate remaining performance obligations that will be recognized as revenue over the period in which the performance obligations are satisfied, and is expected to be recognized as revenue as follows (In thousands): Periods Ending December 31, Total Maturities Remainder of 2021 $ 48,420 2022 9,714 2023 9,563 2024 8,503 2025 1,338 Thereafter 219 Total $ 77,757

Intangible Assets (Tables)

Intangible Assets (Tables)	3 Months Ended
	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Information About Intangible Assets	Information about the intangible assets of the Company as of December 31, 2020 and September 30, 2020, is as follows (in thousands): December 31, September 30, 2020 2020 Customer relationship $ 43,800 $ 43,800 Accumulated amortization (36,078 ) (35,768 ) $ 7,722 $ 8,032

Balance Sheet Information (Tabl

Balance Sheet Information (Tables)	3 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet	Certain significant amounts included in the Company's condensed consolidated balance sheet as of December 31, 2020 and September 30, 2020, consisted of the following (in thousands): December 31, September 30, 2020 2020 Expendable parts and supplies, net: Expendable parts and supplies $ 27,347 $ 27,431 Less: obsolescence and other (4,587 ) (4,460 ) $ 22,760 $ 22,971 Prepaid expenses and other current assets: Deferred offering and reimbursed costs $ 1,129 $ 1,261 Other 11,768 14,806 $ 12,897 $ 16,067 Property and equipment, net: Aircraft and other flight equipment substantially pledged $ 1,597,394 $ 1,596,174 Other equipment 5,176 5,147 Leasehold improvements 2,763 2,763 Vehicles 995 1,032 Building 699 699 Furniture and fixtures 302 302 Total property and equipment 1,607,329 1,606,117 Less: accumulated depreciation (413,268 ) (393,702 ) $ 1,194,061 $ 1,212,415 Other accrued expenses: Accrued property taxes $ 12,690 $ 11,354 Accrued interest 5,149 3,268 Accrued vacation 6,143 5,975 Other 13,599 24,881 $ 37,581 $ 45,478

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Carrying Value and Estimated Fair Value of Long-term Debt, Including Current Maturities	The carrying value and estimated fair value of the Company's long-term debt, including current maturities, were as follows (in millions): December 31, 2020 September 30, 2020 Carrying Fair Carrying Fair Value Value Value Value Long-term debt and financing leases, including current maturities(1) $ 746.4 $ 777.3 $ 743.3 $ 768.7 (1) Current and prior period long-term debts' carrying and fair values exclude net debt issuance costs.

Long-Term Debt, Financing Lea_2

Long-Term Debt, Financing Leases and Other Borrowings (Tables)	3 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Long-term Debt	Long-term debt as of December 31, 2020 and September 30, 2020, consisted of the following (in thousands): December 31, September 30, 2020 2020 Notes payable to financial institution, collateralized by the underlying aircraft, due 2022 (1)(2) $ — $ 41,472 Notes payable to financial institution, collateralized by the underlying aircraft, due 2024 (3) — 55,674 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2027 (4) 105,989 105,887 Notes payable to secured parties, collateralized by the underlying aircraft, due 2028 (5) 172,137 172,137 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2028 (6) 134,325 138,114 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2022 (7) — 47,319 Senior and subordinated notes payable to secured parties, collateralized by the underlying aircraft, due 2022 (8) — 29,682 Notes payable to financial institution due 2020 (10) 1,523 1,523 Notes payable to financial institution, collateralized by the underlying equipment, due 2020 (11) — 4,182 Other obligations due to financial institution, collateralized by the underlying equipment, due 2023 (12) 6,185 6,864 Notes payable to financial institution, collateralized by the underlying equipment, due 2024 (13) 58,988 63,341 Notes payable to financial institution, collateralized by the underlying aircraft, due 2023 (14) 43,750 48,125 Notes payable to financial institution due 2023 (15) 5,500 6,000 Revolving Credit Facility (16) 22,296 22,930 Notes payable to financial institution due 2025 (17) 195,705 — Gross long-term debt, including current maturities 746,398 743,250 Less unamortized debt issuance costs (11,174 ) — Less Notes payable warrants (11,363 ) (11,526 ) Net long-term debt, including current maturities 723,861 731,724 Less current portion (99,745 ) (189,268 ) Net long-term debt $ 624,116 $ 542,456 (1 ) In fiscal 2007, the Company financed three CRJ-900 and three CRJ-700 aircraft for $120.3 million. The debt bears interest at the monthly LIBOR plus 2.25% and requires monthly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020. (2 ) In fiscal 2014, the Company financed ten CRJ-900 aircraft for $88.4 million. The debt bears interest at the monthly LIBOR plus 1.95% and requires monthly principal and interest payments. In fiscal 2018, the Company repaid $40.0 million related to four CRJ-900 aircraft. During quarter ended December 31, 2020 (3 ) In fiscal 2014, the Company financed eight CRJ-900 aircraft with $114.5 million in debt. The debt bears interest at 5.00% and requires monthly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020 (4 ) In fiscal 2015, the Company financed seven CRJ-900 aircraft with $170.2 million in debt. The senior notes payable of $151.0 million bear interest at monthly LIBOR plus 2.71% and require monthly principal and interest payments. The subordinated notes payable are noninterest-bearing and become payable in full on the last day of the term of the notes. The Company has imputed an interest rate of 6.25% on the subordinated notes payable and recorded a related discount of $8.1 million, which is being accreted to interest expense over the term of the notes. (5 ) In fiscal 2016, the Company financed ten E-175 aircraft with $246.0 million in debt under an EETC financing arrangement (see discussion below). The debt bears interest ranging from 4.75% to 6.25% and requires semi-annual principal and interest payments. (6 ) In fiscal 2016, the Company financed eight E-175 aircraft with $195.3 million in debt. The senior notes payable of $172.0 million bear interest at the three-month LIBOR plus a spread ranging from 2.20% to 2.32% and require quarterly principal and interest payments. The subordinated notes payable bear interest at 4.50% and require quarterly principal and interest payments. (7) In June 2018, the Company refinanced six CRJ-900 aircraft with $27.5 million in debt and financed nine CRJ-900 aircraft, which were previously leased, with $69.6 million in debt. The senior notes payable of $65.8 million bear interest at the three-month LIBOR plus 3.50% and require quarterly principal and interest payments. The subordinated notes payable of $29.8 million bear interest at three month LIBOR plus 7.50% and require quarterly principal and interest payments. The loan was paid in full during quarter ended December 31, 2020 (8) In during quarter ended December 31, 2020. ( 1 0) In fiscal 2015 and 2016, the Company financed certain flight equipment maintenance costs with $10.2 million in debt. The debt bears interest at the three-month LIBOR plus 3.07% (11 ) In fiscal 2016-2019, the Company financed certain flight equipment maintenance costs with $26.1 million in debt. The debt bears interest at the three-month LIBOR plus a spread ranging from 2.93% to 3.21%and requires quarterly principal and interest payments. The debt is subject to a fixed charge ratio covenant. The loan was paid in full during quarter ended December 31, 2020 12 ) In February 2018, the Company leased two spare engines. The leases were determined to be capital as the leases contain a bargain purchase option at the end of the term. Imputed interest is 9.128% and the leases requires monthly payments. (13) In January 2019, the Company financed certain flight equipment with $91.2 million in debt. The debt bears interest at the monthly LIBOR plus 3.10% and requires monthly principal and interest payments. (14) In June 2019, the Company financed ten CRJ-700 aircraft with $70.0 million in debt, which were previously leased. The debt bears interest at the monthly LIBOR plus 5.00% and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1 st (15 ) On September 27,2019, the Company financed certain flight equipment for $8.0 million. The debt bears interest at the monthly LIBOR plus 5.00% and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1 st (16) On September 25, 2019, the Company extended the term on their $35.0 million working capital draw loan by three years, which now terminates in September 2022. Interest is assessed on drawn amounts at one-month LIBOR plus 3.75%. During quarter ended June 30, 2020, $23.0 million was drawn to cover operational needs. (17)
Schedule of Principal Maturities of Long-term Debt	Principal maturities of long-term debt as of December 31, 2020, and for each of the next five years are as follows (in thousands): Periods Ending December 31, Total Principal Remainder of 2021 $ 82,535 2022 113,048 2023 89,462 2024 61,209 2025 56,526 Thereafter 343,618 $ 746,398

Earnings Per Share and Equity (

Earnings Per Share and Equity (Tables)	3 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Calculations of Net Income Per Common Share	Calculations of net income per common share attributable to Mesa Air Group were as follows (in thousands, except per share data): Three Months Ended December 31, 2020 2019 Net income attributable to Mesa Air Group $ 14,118 $ 10,785 Basic weighted average common shares outstanding 35,531 35,023 Add: Incremental shares for: Dilutive share adjustment - UST Warrant 800 — Dilutive share adjustment - Restricted Shares 316 159 Diluted weighted average common shares outstanding 36,647 35,182 Net income per common share attributable to Mesa Air Group: Basic $ 0.40 $ 0.31 Diluted $ 0.39 $ 0.31

Share-Based Compensation and _2

Share-Based Compensation and Stock Repurchases (Tables)	3 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Restricted Share Activity	The restricted share activity for the three months ended December 31, 2020 were summarized as follows: Weighted- Average Number Grant Date of Shares Fair Value Restricted shares unvested at September 30, 2020 1,195,548 $ 5.47 Granted 5,000 7.71 Vested (7,500 ) 7.37 Forfeited (17,500 ) 4.59 Restricted shares unvested at December 31, 2020 1,175,548 $ 5.48

Leases and Commitments (Tables)

Leases and Commitments (Tables)	3 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Lease Related Terms and Discount Rates	The table below presents lease related terms and discount rates as of December 31, 2020: As of December 31,2020 Weighted average remaining lease term Operating leases 3.3 years Weighted average discount rate Operating leases 4.2 %
Schedule of Lease Expense	The Table below represents lease expense recorded during three months ended December 31, 2020 and 2019. Three Months Ended December 31, 2020 2019 $ Change % Change Operating lease cost $ 13,839 $ 16,784 $ (2,945 ) (17.5 )%
Schedule of Future Minimum Rental Payments under Operating Leases of Initial or Remaining Non-cancelable Lease Terms	The following table summarizes future minimum rental payments primarily related to leased aircraft required under operating leases that had initial or remaining non-cancelable lease terms as of December 31, 2020 (in thousands): Periods Ending December 31, Total Maturities Remainder of 2021 $ 38,095 2022 33,242 2023 15,973 2024 14,682 2025 1,494 Thereafter 160 Less: Interest $ (5,364 ) Amounts recorded in the Consolidated Balance Sheet $ 98,282
Schedule of Future Minimum Lease Obligations under Non-cancelable Operating Leases	The following represents future minimum lease obligations under non-cancelable operating leases as of September 30, 2019 (in thousands): Periods Ending September 30, Total Payments 2020 47,814 2021 46,007 2022 31,090 2023 13,726 2024 13,185 Thereafter 1,368 Total $ 153,190

Organization and Operations - A

Organization and Operations - Additional Information (Detail) $ in Thousands	Mar. 04, 2021Air-craft	Nov. 19, 2020USD ($)Air-craft	Nov. 04, 2020USD ($)Air-craft	Dec. 20, 2019Air-craft	Nov. 26, 2019Air-craft	Mar. 03, 2021Air-craft	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)Daily_DepartureStateAir-craftCityEmployee
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of states in which entity operates | State								42
Number of aircrafts operated								159
Number of cities in which entity operates | City								116
Number of daily departures | Daily_Departure								420
Number of employees | Employee								3,200
Maximum number of aircraft withdraw in twenty twenty one		10
Maximum number of aircraft withdraw in twenty twenty two		5
Maximum number of aircraft withdraw in twenty twenty three		5
Number of aircraft removed due to failure to meet certain performance objectives		20
Number of aircraft removed due to failure to meet certain performance objectives thereafter		20
Notice period for termination of agreement								Our United Capacity Purchase Agreement permits United, subject to certain conditions, including the payment of certain costs tied to aircraft type, to terminate the agreement in its discretion, or remove aircraft from service, by giving us notice of 90 days or more.
American Capacity Purchase Agreement [Member] | American Airlines Inc. [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Amendment Term | $		$ 5
Number of aircraft financed		40
CRJ-900 Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated								54
CRJ-900 Aircraft [Member] | American Capacity Purchase Agreement [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Notice period for termination of agreement								American’s right, exercisable in its sole discretion, to withdraw any Incremental Aircraft upon 60 days’ prior notice.  American may specify one or more dates for the withdrawal of such Incremental Aircraft
CRJ-900 Aircraft [Member] | American Capacity Purchase Agreement [Member] | Scenario Forecast [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts expected to operate	5					3
CRJ-700 Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated								20
CRJ-700 Aircraft [Member] | United [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Aircraft lease term					7 years
E-175 Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated								60
Number of aircrafts expected to operate								60
Lease expiration year					2028
E-175 Aircraft [Member] | United [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated					42			42
Number of additional aircrafts					18
Aircraft lease extension period					5 years
E-175 Aircraft [Member] | United [Member] | Minimum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Lease expiration year					2024
E-175 Aircraft [Member] | United [Member] | Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Lease expiration year					2028
E175LL Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated								12
Number of aircrafts expected to operate								20
Number of aircraft expected to delivered			8					8
Number of additional aircrafts					20
Number of years in operation					12 years
Air drafts delivery month and year description.								deliveries of the new E175LL aircraft were negotiated between United and Embraer to begin in September 2020 and be completed by the quarter ended June 30, 2021
Termination of aircraft operation, description								Commencing five (5) years after the actual in-service date, United has the right to remove the E175LL aircraft from service by giving us notice of 90 days or more, subject to certain conditions, including the payment of certain wind-down expenses plus, if removed prior to the ten (10) year anniversary of the in-service date, certain accelerated margin payments.
Aircraft lease term			12 years
Number of aircraft leased			20
Number of aircraft delivered			12
Prepayment | $			$ 81,500					$ 81,500
Deferred revenue, revenue recognized | $								$ 33,300
Prepayment Terms Description								The terms of the Prepayment also include affirmative and negative covenants and events of default customary for transactions of this type. Proceeds from the Prepayment were used to retire debt on certain airframes and engines that serve as collateral under the term loan facility provided to the Company by the U.S. Treasury. See Note 8.
E175LL Aircraft [Member] | Scenario Forecast [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Deferred revenue, revenue recognized | $							$ 48,200
Boeing 737400F [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated				2

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Nov. 04, 2020	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Summary Of Significant Accounting Policies [Line Items]
Current and non-current deferred credit balances			$ 7.7		$ 8.5
Recognized deferred credits to revenue			0.8	$ 1.1
Contract assets balances			1.6		$ 2
Contract cost amortization			0.4	0.6
Engine overhaul expense			14.4	10.6
Engine overhaul pass-through expense			9.6	1.9
Airframe check expense			10.1	7.3
Airframe check pass-through expense			$ 7.1	1.2
Aircraft [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage leased			11.00%
Contract Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Lease revenue			$ 49.5	$ 53.3
E175LL Aircraft [Member]
Summary Of Significant Accounting Policies [Line Items]
Prepayment	$ 81.5		81.5
Prepayment recognized			$ 33.3
E175LL Aircraft [Member] | Scenario Forecast [Member]
Summary Of Significant Accounting Policies [Line Items]
Prepayment recognized		$ 48.2

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Deferred Revenue Remaining Performance Obligations (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 77,757
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 48,420
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 9,714
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 9,563
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 8,503
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2025-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 1,338
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2026-01-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Total Maturities	$ 219
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Deferred Revenue Remaining Performance Obligations (Detail 1) $ in Thousands	Dec. 31, 2020USD ($)
Revenue Performance Obligation Satisfied Over Time [Abstract]
Total Maturities	$ 77,757

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Oct. 01, 2019	Sep. 30, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative-effect adjustment to retained earnings	$ 484,297,000	$ 457,859,000	$ 438,191,000		$ 425,868,000
Accounting Standards Update 2016-02 [Member] | Cumulative Effect Period Of Adoption Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative-effect adjustment to retained earnings				$ 0

Concentrations - Additional Inf

Concentrations - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Concentration Risk [Line Items]
Allowance for doubtful accounts	$ 0.9		$ 0.8
Sales Revenue, Net [Member] | American Airlines Inc. [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	46.00%	51.00%
Sales Revenue, Net [Member] | United [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	53.00%	49.00%
Sales Revenue, Net [Member] | DHL [Member] | Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	1.00%	0.00%

Intangible Assets - Information

Intangible Assets - Information About Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Intangible Assets Net Excluding Goodwill [Abstract]
Customer relationship	$ 43,800	$ 43,800
Accumulated amortization	(36,078)	(35,768)
Total	$ 7,722	$ 8,032

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Intangible Assets Net Excluding Goodwill [Abstract]
Amortization expense recognized	$ 0.3	$ 0.4
Amortization expense for remainder of 2021	0.9
Amortization expense for 2022	1
Amortization expense for 2023	0.9
Amortization expense for 2024	0.8
Amortization expense for 2025	$ 0.7

Balance Sheet Information - Sum

Balance Sheet Information - Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Expendable parts and supplies, net:
Expendable parts and supplies	$ 27,347	$ 27,431
Less: obsolescence and other	(4,587)	(4,460)
Expendable parts and supplies, net	22,760	22,971
Prepaid expenses and other current assets:
Deferred offering and reimbursed costs	1,129	1,261
Other	11,768	14,806
Prepaid expenses and other current assets	12,897	16,067
Property and equipment, net:
Property and equipment-gross	1,607,329	1,606,117
Less: accumulated depreciation	(413,268)	(393,702)
Property and equipment-net	1,194,061	1,212,415
Other accrued expenses:
Accrued property taxes	12,690	11,354
Accrued interest	5,149	3,268
Accrued vacation	6,143	5,975
Other	13,599	24,881
Other accrued expenses	37,581	45,478
Aircraft and Other Flight Equipment Substantially Pledged [Member]
Property and equipment, net:
Property and equipment-gross	1,597,394	1,596,174
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	5,176	5,147
Leasehold Improvements [Member]
Property and equipment, net:
Property and equipment-gross	2,763	2,763
Vehicles [Member]
Property and equipment, net:
Property and equipment-gross	995	1,032
Building [Member]
Property and equipment, net:
Property and equipment-gross	699	699
Furniture and Fixtures [Member]
Property and equipment, net:
Property and equipment-gross	$ 302	$ 302

Balance Sheet Information - Add

Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 20.2	$ 20.2

Fair Value Measurements - Carry

Fair Value Measurements - Carrying Value and Estimated Fair Value of Long-term Debt, Including Current Maturities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Long-term debt and finance leases, including current maturities, carrying value	$ 746,398	$ 743,250
Long-term debt and finance leases, including current maturities, fair value	$ 777,300	$ 768,700

Long-Term Debt, Financing Lea_3

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Long-term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 746,398	$ 743,250
Less unamortized debt issuance costs	(11,174)
Less Notes payable warrants	(11,363)	(11,526)
Net long-term debt, including current maturities	723,861	731,724
Less current portion	(99,745)	(189,268)
Net long-term debt	624,116	542,456
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	22,296	22,930
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities		41,472
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities		55,674
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	105,989	105,887
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	172,137	172,137
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	134,325	138,114
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities		47,319
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member] | CRJ-900 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities		29,682
Notes Payable to Financial Institution Due 2020 [Member] | Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	1,523	1,523
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] | Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities		4,182
Other Obligations Due to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	6,185	6,864
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	58,988	63,341
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	43,750	48,125
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	5,500	$ 6,000
Notes Payable to Financial Institution Due 2025 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 195,705

Long-Term Debt, Financing Lea_4

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail)

Nov. 12, 2020USD ($)Air-craft

Oct. 30, 2020USD ($)

Sep. 27, 2019USD ($)

Sep. 25, 2019USD ($)

Jun. 30, 2019USD ($)Airfleet

Jan. 31, 2019USD ($)

Jun. 30, 2018USD ($)Air-craft

Feb. 28, 2018Engine

Dec. 31, 2017USD ($)Air-craft

Dec. 31, 2020USD ($)

Jun. 30, 2020USD ($)

Dec. 31, 2019

Mar. 31, 2020

Sep. 30, 2020

Sep. 30, 2019USD ($)

Sep. 30, 2018USD ($)

Sep. 30, 2017USD ($)Airfleet

Sep. 30, 2016USD ($)Air-craft

Sep. 30, 2015USD ($)Air-craft

Nov. 14, 2020USD ($)

Nov. 13, 2020USD ($)

Sep. 30, 2014USD ($)Airfleet

Debt Instrument [Line Items]

Proceeds from long-term debt

$ 195,000,000

Loan Agreement [Member]

Debt Instrument [Line Items]

Number of aircraft financed | Air-craft

44

Repayments of long term debt

$ 167,700,000

Secured term loan facility, amount borrowed

$ 43,000,000

Secured term loan facility, additional amount borrowed

$ 152,000,000

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2022

2022

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Number of aircraft refinanced | Airfleet

3

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] | CRJ-700 [Member]

Debt Instrument [Line Items]

Number of aircraft refinanced | Airfleet

3

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] | Three C- R- J-900 and Three C- R- J-700 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 120,300,000

Long term debt interest rate description

monthly LIBOR plus 2.25%

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] | Three C- R- J-900 and Three C- R- J-700 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

2.25%

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] | Ten C- R- J-900 Aircraft [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 88,400,000

Long term debt interest rate description

monthly LIBOR plus 1.95%

Number of aircraft financed | Airfleet

10

Long term debt interest rate percentage

1.95%

Repayments of long term debt

$ 40,000,000

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2024

2024

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member] | Eight C- R- J-900 Aircraft [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 114,500,000

Number of aircraft financed | Airfleet

8

Long term debt interest rate percentage

5.00%

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2027

2027

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 170,200,000

Number of aircraft financed | Air-craft

7

Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2028

2028

Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] | Ten E-175 Aircraft [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 246,000,000

Number of aircraft financed | Air-craft

10

Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] | Ten E-175 Aircraft [Member] | Minimum [Member]

Debt Instrument [Line Items]

Long term debt interest rate percentage

4.75%

Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] | Ten E-175 Aircraft [Member] | Maximum [Member]

Debt Instrument [Line Items]

Long term debt interest rate percentage

6.25%

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2028

2028

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] | Eight E-175 Aircraft [Member] | Minimum [Member]

Debt Instrument [Line Items]

Number of aircraft refinanced | Air-craft

8

Debt instrument, face amount

$ 195,300,000

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2022

2022

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2022

2022

Number of aircraft refinanced | Air-craft

6

9

Debt instrument, face amount

$ 27,500,000

$ 74,900,000

Number of aircraft financed | Air-craft

9

Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member] | CRJ-900 [Member] | Capital Lease Obligations [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 69,600,000

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2020

2020

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 26,100,000

$ 26,100,000

$ 26,100,000

$ 26,100,000

Long term debt interest rate description

three-month LIBOR plus a spread ranging from 2.93% to 3.21%

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] | Flight Equipment Maintenance [Member] | LIBOR [Member] | Minimum [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

2.93%

2.93%

2.93%

2.93%

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] | Flight Equipment Maintenance [Member] | LIBOR [Member] | Maximum [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

3.21%

3.21%

3.21%

3.21%

Notes Payable to Financial Institution Due 2020 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2020

2020

Notes Payable to Financial Institution Due 2020 [Member] | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 10,200,000

$ 10,200,000

Long term debt interest rate description

three-month LIBOR plus 3.07%

Notes Payable to Financial Institution Due 2020 [Member] | Flight Equipment Maintenance [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt interest rate percentage

3.07%

3.07%

Notes Payable To Financial Institution Collateralized By Underlying Equipment Due Two Thousand Twenty Two | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2023

2023

Other Obligations Due to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2024

2024

Imputed interest

9.128%

Number of spare engines leased | Engine

2

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2023

2023

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member] | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 91,200,000

Long term debt interest rate description

monthly LIBOR plus 3.10%

Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member] | Flight Equipment Maintenance [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

3.10%

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]

Debt Instrument [Line Items]

Debt instrument maturity year

2023

2023

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] | CRJ-700 Aircraft [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 70,000,000

Long term debt interest rate description

monthly LIBOR plus 5.00%

Number of aircraft financed | Airfleet

10

Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] | CRJ-700 Aircraft [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

5.25%

5.00%

5.25%

Notes Payable To Financial Institution Collateralized By Underlying Equipment Due Two Thousand Twenty Three

Debt Instrument [Line Items]

Debt instrument maturity year

2025

2025

Senior Notes Due Two Thousand Twenty Seven [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 151,000,000

Long term debt interest rate description

monthly LIBOR plus 2.71%

Senior Notes Due Two Thousand Twenty Seven [Member] | CRJ-900 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

2.71%

Subordinated Notes Due Two Thousand Twenty Seven [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Imputed interest

6.25%

Debt discount

$ 8,100,000

Senior Notes Due 2008 [Member] | Eight E-175 Aircraft [Member]

Debt Instrument [Line Items]

Long term debt interest rate description

three-month LIBOR plus a spread ranging from 2.20% to 2.32%

Senior Notes Due 2008 [Member] | Eight E-175 Aircraft [Member] | Minimum [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 172,000,000

Senior Notes Due 2008 [Member] | Eight E-175 Aircraft [Member] | LIBOR [Member] | Minimum [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

2.20%

Senior Notes Due 2008 [Member] | Eight E-175 Aircraft [Member] | LIBOR [Member] | Maximum [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

2.32%

Subordinated Notes Due 2008 [Member] | Eight E-175 Aircraft [Member]

Debt Instrument [Line Items]

Long term debt interest rate percentage

4.50%

Senior Notes Due 2020 [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 65,800,000

Long term debt, basis spread on variable rate

3.50%

Senior Notes Due 2020 [Member] | CRJ-900 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt interest rate description

three-month LIBOR plus 3.50%

Subordinated Notes Due 2020 [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 29,800,000

Long term debt, basis spread on variable rate

7.50%

Subordinated Notes Due 2020 [Member] | CRJ-900 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt interest rate description

three month LIBOR plus 7.50%

Senior Notes due Two Thousand Twenty Two [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 46,900,000

Long term debt interest rate description

three-month LIBOR plus 3.50%

Senior Notes due Two Thousand Twenty Two [Member] | CRJ-900 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

3.50%

Subordinated Notes DueTwoThousandTwentyTwo [Member] | CRJ-900 [Member]

Debt Instrument [Line Items]

Long term debt interest rate description

three-month LIBOR plus 4.50%

Subordinated Notes DueTwoThousandTwentyTwo [Member] | CRJ-900 [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt interest rate percentage

4.50%

Notes Payable to Financial Institution Due 2023 [Member] | Flight Equipment Maintenance [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 8,000,000

Long term debt interest rate description

monthly LIBOR plus 5.00%

Notes Payable to Financial Institution Due 2023 [Member] | Flight Equipment Maintenance [Member] | LIBOR [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

5.25%

5.00%

5.25%

Working Capital Draw Loan [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Debt instrument, face amount

$ 35,000,000

Long term debt interest rate description

one-month LIBOR plus 3.75%

Term loan, term

3 years

Debt instrument, expiration year and month

2022-09

Proceeds from long-term debt

$ 23,000,000

Working Capital Draw Loan [Member] | LIBOR [Member] | Revolving Credit Facility [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

3.75%

Secured Term Loan Facility [Member] | Loan Agreement [Member]

Debt Instrument [Line Items]

Long term debt, basis spread on variable rate

3.50%

Long term debt interest rate description

three-month LIBOR plus 3.50%

Secured term loan facility, maximum borrowing capacity

$ 200,000,000

Secured term loan facility, amount borrowed

$ 43,000,000

Secured term loan facility, additional amount borrowed

$ 0

$ 152,000,000

Debt instrument, maturity date

Oct. 30, 2025

Oct. 30, 2025

Long-Term Debt, Financing Lea_5

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Principal Maturities of Long-term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Long Term Debt By Maturity [Abstract]
Remainder of 2021	$ 82,535
2022	113,048
2023	89,462
2024	61,209
2025	56,526
Thereafter	343,618
Long-term debt	$ 746,398	$ 743,250

Long-Term Debt, Financing Lea_6

Long-Term Debt, Financing Leases and Other Borrowings - Additional Information (Detail)	Nov. 13, 2020USD ($)	Nov. 12, 2020USD ($)Air-craft	Oct. 30, 2020USD ($)$ / sharesshares	Sep. 25, 2019USD ($)	Dec. 31, 2020USD ($)$ / shares	Jun. 30, 2020USD ($)	Nov. 14, 2020USD ($)	Sep. 30, 2020USD ($)	Apr. 09, 2020$ / shares
Debt Instrument [Line Items]
Property and equipment, net					$ 1,194,061,000			$ 1,212,415,000
Long-Term Debt					723,861,000			$ 731,724,000
Proceeds from long-term debt					$ 195,000,000
Warrants of common stock exercise price | $ / shares					$ 0.004				$ 3.98
Maximum [Member]
Debt Instrument [Line Items]
Calculated collateral coverage ratio			1.6
Minimum [Member]
Debt Instrument [Line Items]
Additional collateral coverage ratio			1.6
Loan Agreement [Member]
Debt Instrument [Line Items]
Secured term loan facility, amount borrowed			$ 43,000,000
Secured term loan facility, additional amount borrowed	$ 152,000,000
Warrants to purchase shares of common stock | shares			4,899,497
Warrants of common stock exercise price | $ / shares			$ 3.98
Debt issuance costs allocated to warrants					$ 100,000
Repayments of long term debt		$ 167,700,000
Number of aircraft financed | Air-craft		44
Loan Agreement [Member] | $43M Treasury Loan [Member]
Debt Instrument [Line Items]
Capitalized debt issuance costs, net			$ 700,000
Loan Agreement [Member] | $152M Treasury Loan [Member]
Debt Instrument [Line Items]
Capitalized debt issuance costs, net	2,300,000
Loan Agreement [Member] | EDC Loans [Member]
Debt Instrument [Line Items]
Debt issuance costs	3,100,000
Repayments of long term debt	1,000,000
Payment of loans		$ 164,100,000
Discount for balance amount of loans		$ 3,600,000
Debt discount	2,500,000
Equipment Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt					$ 172,100,000
Working Capital Draw Loan [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 35,000,000
Term loan, term				3 years
Debt instrument, expiration year and month				2022-09
Long term debt interest rate description					one-month LIBOR plus 3.75%
Proceeds from long-term debt						$ 23,000,000
Working Capital Draw Loan [Member] | Revolving Credit Facility [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate				3.75%
Secured Term Loan Facility [Member] | Loan Agreement [Member]
Debt Instrument [Line Items]
Long term debt interest rate description					three-month LIBOR plus 3.50%
Long term debt, basis spread on variable rate			3.50%
Secured term loan facility, maximum borrowing capacity			$ 200,000,000
Secured term loan facility, amount borrowed			$ 43,000,000
Secured term loan facility, additional amount borrowed	152,000,000						$ 0
Debt instrument, maturity date			Oct. 30, 2025		Oct. 30, 2025
Secured Term Loan Facility [Member] | Loan Agreement [Member] | $43M Treasury Loan [Member]
Debt Instrument [Line Items]
Secured term loan facility, amount borrowed			$ 43,000,000
Secured Term Loan Facility [Member] | Loan Agreement [Member] | $152M Treasury Loan [Member]
Debt Instrument [Line Items]
Secured term loan facility, additional amount borrowed	$ 152,000,000						$ 0
Aircraft and Equipment [Member] | Pledged as Collateral [Member]
Debt Instrument [Line Items]
Property and equipment, net					$ 1,077,000,000

Earnings Per Share and Equity -

Earnings Per Share and Equity - Calculations of Net Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share And Equity [Abstract]
Net income	$ 14,118	$ 10,785
Basic weighted average common shares outstanding	35,531	35,023
Add: Incremental shares for:
Dilutive share adjustment - UST Warrant	800
Dilutive share adjustment - Restricted Shares	316	159
Diluted weighted average common shares outstanding	36,647	35,182
Net income per common share attributable to Mesa Air Group:
Basic	$ 0.40	$ 0.31
Diluted	$ 0.39	$ 0.31

Earnings Per Share and Equity_2

Earnings Per Share and Equity - Additional Information (Detail) - shares	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restricted Stock [Member]
Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted loss per share	0	0
Number of Warrants [Member]
Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted loss per share	0	0

Common Stock - Additional Infor

Common Stock - Additional Information (Detail)	Apr. 09, 2019	Aug. 08, 2018shares	Dec. 31, 2020$ / sharesshares	Sep. 30, 2020shares	Apr. 09, 2020$ / shares
Class of Warrant or Right [Line Items]
Warrants term			5 years
Warrants of common stock exercise price | $ / shares			$ 0.004		$ 3.98
Maximum percentage of stock pertaining to restrictions			24.90%
Extended term of outstanding warrants expiration period			5 years
Warrants of common stock expiration date			Sep. 30, 2023
Common stock, warrants issued			4,899,497	0
Common stock, warrants outstanding			4,899,497	0
2018 Equity Incentive Plan [Member]
Class of Warrant or Right [Line Items]
Common stock, stock split			2.5-for-1 stock split effected
Stock split ratio	2.5
Increase in number of shares authorized for issuance		1,000,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Income Taxes [Line Items]
Effective tax rate (ETR) from continuing operations	25.50%	24.70%
Statutory federal tax rate	21.00%
State net operating loss carryforwards			$ 3.1
Domestic Tax Authority [Member] | 2027-2038 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards			512.4
State and Local Jurisdiction [Member] | 2021-2040 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards			$ 223.9
Minimum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2027
Minimum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2021
Maximum [Member] | Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2038
Maximum [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2040

Share-Based Compensation and _3

Share-Based Compensation and Stock Repurchases - Schedule of Restricted Share Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Dec. 31, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning Balance | shares	1,195,548
Number of Shares, Granted | shares	5,000
Number of Shares, Vested | shares	(7,500)
Number of Shares, Forfeited | shares	(17,500)
Number of Shares, Unvested, Ending Balance | shares	1,175,548
Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance | $ / shares	$ 5.47
Weighted-Average Grant Date Fair Value, Granted | $ / shares	7.71
Weighted-Average Grant Date Fair Value, Vested | $ / shares	7.37
Weighted-Average Grant Date Fair Value, Forfeited | $ / shares	4.59
Weighted-Average Grant Date Fair Value, Unvested, Ending Balance | $ / shares	$ 5.48

Share-Based Compensation and _4

Share-Based Compensation and Stock Repurchases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested share-based compensation arrangements	$ 4,200
Unrecognized compensation cost, period for recognition	2 years
Share-based compensation expense	$ 900	$ 1,300
Repurchased shares, value	$ 19	$ 41
Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period	1 year
Restricted Stock Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period	3 years
Restricted Stock Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period	5 years
Restricted Stock Award | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period	3 years
Restricted Stock Award | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period	5 years
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchased shares, shares	2,256
Repurchased shares, value	$ 20

Employee Stock Purchase Plan -

Employee Stock Purchase Plan - Additional Information (Detail) - 2019 ESPP [Member]	3 Months Ended
	Dec. 31, 2020shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ordinary shares, discount rate	10.00%
Number of ordinary shares issued	99,644
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible employees contribution from their eligible compensation during each semi annual	1.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible employees contribution from their eligible compensation during each semi annual	15.00%
Number of ordinary shares issued	500,000

Leases and Commitments - Additi

Leases and Commitments - Additional Information (Detail) $ in Thousands	3 Months Ended
	Dec. 31, 2020USD ($)Air-craftEngine	Dec. 31, 2019USD ($)	Sep. 30, 2020USD ($)	Oct. 01, 2019USD ($)
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets	$ 114,666		$ 123,251
Number of leased aircraft | Air-craft	18
Aggregate rental expense under all operating aircraft, equipment and facility leases	$ 13,800	$ 16,800
Operating lease current liabilities	44,712		43,932
Operating lease noncurrent liabilities	53,570		$ 62,531
Operating lease payments in operating cash flows	$ 9,304	$ 9,534
CF34-8C5 Engine [Member] | Letter Agreement No. 13-1 [Member]
Operating Leased Assets [Line Items]
Number of new spare engines to be acquired | Engine	20
New spare engines delivery month and year description	Under the terms of the Amended and Restated Letter Agreement, the Company agreed to purchase and take delivery of the 20 new space CF34-8C5 engines commencing in May 2021, with the final spare engine to be delivered in December 2021
New Spare engines payments commencing month and year description	Payments are now due in five (5) separate tranches commencing in December 2020, and in February, April, May and June 2021
Purchase commitment amount	$ 118,900
Accounting Standards Update 2016-02 [Member]
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets				$ 154,600
Operating lease, liability				141,900
Accounting Standards Update 2016-02 [Member] | Prepaid Aircraft Rent [Member]
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets				35,800
Accounting Standards Update 2016-02 [Member] | Deferred Rent Credits [Member]
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets				21,300
Accounting Standards Update 2016-02 [Member] | Accrued Aircraft Rents [Member]
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets				$ 1,800

Leases and Commitments - Schedu

Leases and Commitments - Schedule of Lease Related Terms and Discount Rates (Detail)	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term Operating leases	3 years 3 months 18 days
Weighted average discount rate Operating leases	4.20%

Leases and Commitments - Sche_2

Leases and Commitments - Schedule of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Operating lease cost	$ 13,839	$ 16,784
Change in operating lease cost	$ (2,945)
Percentage of change in operating lease cost	(17.50%)

Leases and Commitments - Sche_3

Leases and Commitments - Schedule of Future Minimum Rental Payments under Operating Leases of Initial or Remaining Non-cancelable Lease Terms (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
Remainder of 2021	$ 38,095
2022	33,242
2023	15,973
2024	14,682
2025	1,494
Thereafter	160
Less: Interest	(5,364)
Amounts recorded in the Consolidated Balance Sheet	$ 98,282

Leases and Commitments - Sche_4

Leases and Commitments - Schedule of Future Minimum Lease Obligations under Non-cancelable Operating Leases (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2020	$ 47,814
2021	46,007
2022	31,090
2023	13,726
2024	13,185
Thereafter	1,368
Total	$ 153,190

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - USD ($) $ in Millions	Feb. 08, 2021	Feb. 01, 2021
Subsequent Event [Line Items]
Payroll Support Program Extension, amount granted		$ 48.6
Payroll Support Program Extension, amount received	$ 24.3