Document and Entity Information	3 Months Ended
Document and Entity Information	Dec. 31, 2019 shares
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2020
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	33,039,126

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Current assets:
Cash and cash equivalents	$ 57,763	$ 68,855
Restricted cash	3,448	3,646
Receivables, net	24,121	23,080
Expendable parts and supplies, net	22,400	21,337
Prepaid expenses and other current assets	4,502	40,923
Total current assets	112,234	157,841
Property and equipment, net	1,261,267	1,273,585
Intangibles, net	9,157	9,532
Lease and equipment deposits	4,872	2,167
Operating lease right-of-use assets	146,071
Other assets	8,400	8,792
Total assets	1,542,001	1,451,917
Current liabilities:
Current portion of long-term debt and financing leases	166,089	165,900
Current maturities of operating leases	37,674
Accounts payable	47,750	49,930
Accrued compensation	10,048	11,988
Other accrued expenses	34,350	28,888
Total current liabilities	295,911	256,706
Noncurrent liabilities:
Long-term debt and financing leases, excluding current portion	641,017	677,423
Noncurrent operating lease liabilities	95,992
Deferred credits	11,032	12,134
Deferred income taxes	58,506	55,303
Other noncurrent liabilities	1,352	24,483
Total noncurrent liabilities	807,899	769,343
Total liabilities	1,103,810	1,026,049
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; 33,039,126 (2020) and 31,413,287 (2019) shares issued and outstanding, 1,988,472 (2020) and 3,600,953 (2019) warrants issued and outstanding	239,783	238,504
Retained earnings	198,408	187,364
Total stockholders' equity	438,191	425,868
Total liabilities and stockholders' equity	$ 1,542,001	$ 1,451,917

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Sep. 30, 2019
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	33,039,126	31,413,287
Common stock, shares outstanding	33,039,126	31,413,287
Common stock, warrants issued	1,988,472	3,600,953
Common stock, warrants outstanding	1,988,472	3,600,953

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating revenues:
Total operating revenues	$ 184,036	$ 178,156
Operating expenses:
Flight operations	52,644	53,245
Fuel	169	121
Maintenance	58,095	39,802
Aircraft rent	11,329	14,119
Aircraft and traffic servicing	1,064	934
General and administrative	12,996	12,214
Depreciation and amortization	20,552	18,491
Total operating expenses	156,849	138,926
Operating income	27,187	39,230
Other (expenses) income, net:
Interest expense	(12,628)	(14,842)
Interest income	58	156
Other (expense) income, net	(297)	486
Total other (expense), net	(12,867)	(14,200)
Income before taxes	14,320	25,030
Income tax expense	3,535	5,949
Net income	$ 10,785	$ 19,081
Net income per share attributable to common shareholders
Basic	$ 0.31	$ 0.55
Diluted	$ 0.31	$ 0.54
Weighted-average common shares outstanding
Basic	35,023	34,518
Diluted	35,182	35,113
Contract Revenue [Member]
Operating revenues:
Total operating revenues	$ 171,800	$ 170,449
Pass Through and Other [Member]
Operating revenues:
Total operating revenues	$ 12,236	$ 7,707

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Number of Warrants [Member]	Common Stock and Additional Paid-In Capital [Member]	Retained Earnings [Member]
Beginning balance at Sep. 30, 2018	$ 374,467			$ 234,683	$ 139,784
Beginning balance, shares at Sep. 30, 2018		23,902,903	10,614,990
Stock compensation expense	1,454			1,454
Stock issuance costs	157			157
Net income	19,081				19,081
Ending balance at Dec. 31, 2018	395,159			236,294	158,865
Ending balance, shares at Dec. 31, 2018		23,902,903	10,614,990
Beginning balance at Sep. 30, 2019	425,868			238,504	187,364
Beginning balance, shares at Sep. 30, 2019		31,413,287	3,600,953
Adoption ASU 2018-09 Stock compensation-income taxes \| ASU 2018-09 [Member]	259				259
Stock compensation expense	1,320			1,320
Repurchased shares and warrants	(41)	$ (40)		(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

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 10,785	$ 19,081
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	20,552	18,491
Stock compensation expense	1,320	1,454
Deferred income taxes	3,205	5,953
Amortization of deferred credits	(1,103)	(1,188)
Unfavorable lease liabilities		(1,548)
Amortization of debt financing costs and accretion of interest on non-interest-bearing subordinated notes	1,054	1,042
Loss (Gain) on disposal of assets	407	(1)
Provision for obsolete expendable parts and supplies	97	122
Changes in assets and liabilities:
Receivables	(1,040)	8,275
Expendable parts and supplies	(1,158)	(1,866)
Prepaid expenses and other current assets	327	(2,042)
Accounts payable	(2,336)	(2,829)
Accrued liabilities	5,791	(799)
Change in operating lease right-of- use assets	329
Net cash provided by operating activities	38,230	44,145
Cash flows from investing activities:
Capital expenditures	(10,124)	(26,036)
Sales of investment securities		4,947
Lease and equipment deposits	(2,795)
Returns of lease and equipment deposits	91	760
Net cash used in investing activities	(12,828)	(20,329)
Cash flows from financing activities:
Principal payments on long-term debt and financing leases	(36,467)	(38,605)
Debt financing costs	(184)	(258)
Stock issuance costs		157
Repurchase of stock	(41)
Net cash used in financing activities	(36,692)	(38,706)
Net change in cash, cash equivalents and restricted cash	(11,290)	(14,890)
Cash, cash equivalents and restricted cash at beginning of period	72,501	107,134
Cash, cash equivalents and restricted cash at end of period	61,211	92,244
Supplemental cash flow information
Cash paid for interest	9,440	12,266
Cash paid for income taxes, net	15
Operating lease payments in operating cash flows	9,534
Supplemental non-cash operating activities
Right-of-use assets obtained in exchange of lease liabilities	142,165
Supplemental non-cash investing activities
Accrued capital expenditures	$ 334	$ 5,635

Organization and Operations

3 Months Ended

Dec. 31, 2019

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 144 cities in 41 states, the District of Columbia, Canada, Mexico, Cuba, and the Bahamas. As of December 31, 2019, Mesa operated a fleet of 145 aircraft with approximately 742 daily departures and 3,600 employees. Mesa operates all of its flights as either American Eagle or United Express flights pursuant to the terms of the capacity purchase agreements entered into with American Airlines, Inc. (“American”) and United Airlines, Inc. (“United”).

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, 2019, the Company operated 60 CRJ-900 aircraft for American under our American 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 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.

Our American Capacity Purchase Agreement will terminate with respect to different tranches of aircraft between 2021 and 2025, unless otherwise extended or amended. As of the date of this filing, we remain in discussions with American regarding the terms of extending the 32 aircraft that are due to expire in 2021 and the 20 aircraft that are due to expire in 2022 and the 7 that expire in 2025. Our American Capacity Purchase Agreement is subject to termination prior to that date, subject to our right to cure, in various circumstances including:

▪

If either American or we become insolvent, file for bankruptcy or fail to pay our debts as they become due, the non-defaulting party may terminate the agreement;

▪

Failure by us or American to perform the covenants, conditions or provisions of our 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 a change in our ownership or control without the written approval of American.

In the event that American has the right to terminate our American Capacity Purchase Agreement, American may, in lieu of termination, withdraw up to an aggregate of 14 aircraft from service under our American Capacity Purchase Agreement. Upon any such withdrawal, American's payments to us would be correspondingly reduced by the number of withdrawn aircraft.

On January 31, 2019, the Company entered into an amendment to the American Capacity Purchase Agreement, the terms of which provide for new and revised operational performance metrics, the Company's right to earn additional incentive compensation based on the achievement of such metrics, and the right of American to permanently withdraw up to six (6) aircraft in the event the Company fails to meet such new/revised performance metrics. Under the terms of such amendment the Company agreed, effective April 2, 2019, to convert two (2) aircraft to be utilized by the Company as operational spares in the Company's sole discretion throughout its system. In July 2019, American exercised its right to permanently withdraw two (2) aircraft from the American Capacity Purchase Agreement due to the Company's failure to meet certain performance metrics. The aircraft were removed on November 2, 2019. On November 25, 2019, the Company amended its agreement with American Airlines. The Company did not meet certain performance metrics during the most recent measurement period, which allows American to remove two additional aircraft from the capacity purchase agreement. American has agreed to defer the right to remove these two aircraft but has elected to remove one of two previously deferred aircraft, effective January 2, 2020. As of January 2, 2020 American has removed three (3) of the six (6) aircraft under this amendment and retains the right to permanently withdraw the remaining three (3) aircraft at any time.

United Capacity Purchase Agreement

As of December 31, 2019, the Company operated 20 CRJ-700 and 60 E-175 aircraft for United under our United Capacity Purchase Agreement. 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. We also receive a minimum profit margin based upon our operational performance. Under our United Capacity Purchase Agreement, United owns 42 of the 60 E-175 aircraft 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 component maintenance for the 42 E-175 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. In addition, if United removes any of our 18 owned E-175 aircraft from service at its direction, United would remain obligated to assume the aircraft ownership and associated debt with respect to such aircraft through the end of the term of the agreement.

On November 26, 2019, we amended and restated our United Capacity Purchase Agreement to, among other things, incorporate the terms of the 11 prior amendments to that Agreement and to extend the term thereof through the addition of twenty (20) new Embraer E175LL aircraft to the scope of such Agreement. These new aircraft will 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 are scheduled to begin in May 2020 and be completed by December 31, 2020. 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. As part of the amended and restated United Capacity Purchase Agreement, we agreed to lease our twenty (20) 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 over the period between May 2020 and December 2020. United has a right to purchase the CRJ 700 aircraft at the then fair market value. In addition, we own 18 E-175 aircraft that expire in 2028.

Our United Capacity Purchase Agreement is subject to early termination under various circumstances noted above and including:

▪

By United if certain operational performance factors fall below a specified percentage for a specified time, subject to notice under certain circumstances;

▪

By United if we fail to perform the material covenants, agreements, terms or conditions of our United Capacity Purchase Agreement or similar agreements with United, subject to thirty (30) days' notice and cure rights;

▪

If either United or we become insolvent, file bankruptcy or fail to pay debts when due, the non-defaulting party may terminate the agreement; or

▪

By United if we merge with, or if control of us is acquired by another air carrier or a corporation directly or indirectly owning or controlling another air carrier.

Summary of Significant Accounting Policies

3 Months Ended

Dec. 31, 2019

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.

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, 2019 included in the Company's Annual Report on Form 10-K for the year ended September 30, 2019 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 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.

Adoption of New Lease Standard

Effective October 1, 2019, we have adopted 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. 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 condensed 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 lessor, for our aircraft operated under our capacity purchase agreements, we have historically accounted for the non-lease component under ASC 606 and have historically accounted for the lease component under ASC 840. Under the available practical expedient, we have elected to account for the lease and non-lease components as a single component for all classes of underlying assets. As the predominant component of the combined components are the flights services, the leases are being accounted for entirely under ASC 606. 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).

Aircraft Lease

In addition to the aircraft we receive from United under our United Capacity Purchase Agreement, approximately 12% 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.

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 estimates 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 $10.6 million and $4.1 million for the three months ended December 31, 2019, and 2018, respectively, of which $1.9 million and $1.5 million, respectively, was pass-through expense. Airframe C-check expense totaled $7.3 million and $1.5 million for the three months ended December 31, 2019, and 2018, respectively, of which $1.2 million and $0.0 million, respectively, was pass-through expense

Recent Accounting Pronouncements

3 Months Ended

Dec. 31, 2019

Accounting Changes And Error Corrections [Abstract]

Recent Accounting Pronouncements

3.	Recent Accounting Pronouncements

In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). This ASU introduces a new accounting model known as Credit Expected Credit Losses (“CECL”). CECL requires earlier recognition of credit losses, while also providing additional transparency about credit risk. The CECL model utilizes a lifetime expected credit loss measurement objective for the recognition of credit losses for receivables at the time the financial asset is originated or acquired. The expected credit losses are adjusted each period for changes in expected lifetime credit losses. This model replaces the multiple existing impairment models in current GAAP, which generally require that a loss be incurred before it is recognized. The new standard will also apply to receivables arising from revenue transactions such as contract assets and accounts receivables. There are other provisions within the standard affecting how impairments of other financial assets may be recorded and presented, as well as expanded disclosures. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years, with early adoption permitted. The Company is currently evaluating the impact on its consolidated financial statements.

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 not 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 three months ended December 31, 2019 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, "Leases, Commitments and Contingencies," for more information.

In July 2018, the FASB issued ASU 2018-09, Codification Improvements, which contains amendments that affect a wide variety of Topics in the Codification, including amendment to Subtopic 718-40, Compensation-Stock Compensation-Income Taxes, that clarifies the timing of when an entity should recognize excess tax benefits. We adopted this standard on October 1, 2019 and it did not have a material impact on our condensed consolidated financial statements.

Concentrations

3 Months Ended

Dec. 31, 2019

Risks And Uncertainties [Abstract]

Concentrations

4.	Concentrations

At December 31, 2019, the Company had capacity purchase agreements with American and United. All of the Company's condensed consolidated revenue for the three months ended December 31, 2019 and 2018 and accounts receivable at December 31, 2019 and September 30, 2018 was derived from these agreements. The terms of both the American and United capacity purchase agreements are not aligned with the lease obligations on the aircraft performing services under such 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 past due and records a reserve for amounts estimated to be uncollectible. The allowance for doubtful accounts was $1.8 million and $1.0 million at December 31, 2019 and September 30, 2019, 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 51% and 53% of the Company's total revenue for the three months ended December 31, 2019 and 2018, respectively. United accounted for approximately 49% and 47% of the Company's revenue for the three months ended December 31, 2019 and 2018, respectively. A termination of either the American or the United capacity purchase agreement would have a material adverse effect on the Company's business prospects, financial condition, results of operations, and cash flows.

Intangible Assets

3 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible Assets

5.	Intangible Assets

Information about the intangible assets of the Company at December 31, 2019 and September 30, 2019, were as follows (in thousands):

	December 31,			September 30,
	2019			2019
Customer relationship	$	43,800		$	43,800
Accumulated amortization		(34,643	)		(34,268	)
	$	9,157		$	9,532

Total amortization expense recognized was approximately $0.4 million and $0.5 million for the three months ended December 31, 2019 and 2018, respectively. The Company expects to record amortization expense of $1.1 million for the remainder of 2020, and $1.2 million, $1.0 million, $0.9 million, $0.8 million for fiscal years 2021, 2022, 2023, and 2024 respectively.

Balance Sheet Information

3 Months Ended

Dec. 31, 2019

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, 2019 and September 30, 2019, consisted of the following (in thousands):

	December 31,			September 30,
	2019			2019
Expendable parts and supplies, net:
Expendable parts and supplies	$	26,455		$	25,336
Less: obsolescence and other		(4,055	)		(3,999	)
	$	22,400		$	21,337

Prepaid expenses and other current assets:
Prepaid aircraft rent	$	-		$	35,786
Deferred offering and reimbursed costs		1,664			2,092
Other		2,838			3,045
	$	4,502		$	40,923
Property and equipment, net:
Aircraft and other flight equipment substantially pledged	$	1,588,368		$	1,582,199
Other equipment		5,122			5,122
Leasehold improvements		2,797			2,797
Vehicles		945			924
Building		699			699
Furniture and fixtures		302			302
Total property and equipment		1,598,233			1,592,043
Less: accumulated depreciation		(336,966	)		(318,458	)
	$	1,261,267		$	1,273,585

Other accrued expenses:
Accrued property taxes	$	11,018		$	9,186
Accrued interest		6,715			4,497
Accrued vacation		6,149			6,128
Accrued wheels, brakes and tires		3,072			1,513
Other		7,396			7,564
	$	34,350		$	28,888

Depreciation expense totaled approximately $20.2 million and $18.0 million for the three months ended December 31, 2019 and 2018, respectively.

Prior to the Company’s adoption of Topic 842 on October 1, 2019, the Company recorded amortization of the unfavorable lease liability of approximately $1.5 million for the three months ended December 31, 2018 as a reduction to lease expense. Upon the Company’s adoption of Topic 842, the unfavorable lease liability is now included in its ROU asset balance and amortized therein.

Fair Value Measurements

3 Months Ended

Dec. 31, 2019

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, 2019				September 30, 2019
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
Long-term debt and financing leases, including current maturities(1)	$	821.8	$	846.9	$	858.1	$	882.7

⁽¹⁾	Current and prior period long-term debts' carrying and fair values exclude net debt issuance costs.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Long-Term Debt, Financing Leases and Other Borrowings

3 Months Ended

Dec. 31, 2019

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, 2019 and September 30, 2019, consisted of the following (in thousands):

	December 31,			September 30,
	2019			2019
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2022⁽¹⁾⁽²⁾	$	45,019		$	49,795
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2024⁽³⁾		57,867			60,761
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2027⁽⁴⁾		107,940			110,912
Notes payable to secured parties, collateralized by the underlying
aircraft, due 2028⁽⁵⁾		191,168			191,168
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2028⁽⁶⁾		149,283			152,945
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2022⁽⁷⁾		65,984			71,998
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2022⁽⁸⁾		43,136			47,309
Notes payable to financial institution, collateralized by the underlying
equipment, due 2020⁽⁹⁾		1,244			1,659
Notes payable to financial institution due 2020⁽¹⁰⁾		1,822			2,329
Notes payable to financial institution, collateralized by the underlying
equipment, due 2020⁽¹¹⁾		5,358			6,962
Other obligations due to financial institution, collateralized by the underlying
equipment, due 2023⁽¹²⁾		8,162			8,530
Notes payable to financial institution, collateralized by the underlying
equipment, due 2024⁽¹³⁾		76,037			80,153
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2023⁽¹⁴⁾		61,250			65,625
Notes payable to financial institution due 2023 ⁽¹⁵⁾		7,503			8,000
Revolving Credit Facility ⁽¹⁶⁾		—			—
Gross long-term debt, including current maturities		821,773			858,145
Less unamortized debt issuance costs		(14,667	)		(14,822	)
Net long-term debt, including current maturities		807,106			843,323
Less current portion		(166,089	)		(165,900	)
Net long-term debt	$	641,017		$	677,423

⁽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% (4.16% at December 31, 2019) and requires monthly principal and interest payments.

⁽²⁾

In fiscal 2014, the Company financed ten CRJ-900 aircraft for $88.4 million. The debt bears interest at the monthly LIBOR plus a spread ranging from 1.95% to 7.25% (3.86% to 9.16% at December 31, 2019) and requires monthly principal and interest payments. In fiscal 2018, the Company repaid $40.0 million related to four CRJ-900 aircraft.

⁽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.

⁽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% (4.62% at December 31, 2019) 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% (3.96% to 4.08% at December 31, 2019) 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% (5.26 % at December 31, 2019) and require quarterly principal and interest payments. The subordinated notes payable of $29.8 million bear interest at three month LIBOR plus 7.50% (9.26% at December 31, 2019) and require quarterly principal and interest payments.

⁽⁸⁾

InDecember 2017, the Company refinanced nine CRJ-900 aircraft with $74.9 million in debt. The senior notes payable of $46.9 million bear interest at the three-month LIBOR plus 3.50% (5.26% at December 31, 2019) and require quarterly principal and interest payments. The subordinated notes payable bear interest at the three-month LIBOR plus 4.50% (6.26% at December 31, 2019) and require quarterly principal and interest payments.

⁽⁹⁾	In fiscal 2015, the Company financed certain flight equipment with $8.3 million in debt. The debt bears interest at 5.163% and requires monthly principal and interest payments.

⁽¹⁰⁾	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 monthly LIBOR plus 3.07% (4.98% at December 31, 2019) and requires quarterly principal and interest payments.

⁽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% (4.69% to 4.97% at December 31, 2019) and requires quarterly principal and interest payments. The debt is subject to a fixed charge ratio covenant. As of December 31, 2019, the Company was in compliance with this covenant.

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% (5.01% at December 31, 2019) 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% (6.91% at December 31, 2019) and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1^st quarter, 2020 due to United Airlines extension of CRJ-700.

⁽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% (6.91% at December 31, 2019) and requires monthly principal and interest payments. The interest rate reduced from 5.25% to 5.00% in 1^st quarter, 2020 due to United Airlines extension of CRJ-700.

⁽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%.

Principal maturities of long-term debt as of December 31, 2019, and for each of the next five years are as follows (in thousands):

Periods Ending December 31,	Total Principal
Remainder of 2020	$	166,089
2021		160,084
2022		140,139
2023		96,722
2024		62,605
Thereafter		196,134
	$	821,773

The net book value of collateralized aircraft and equipment as of December 31, 2019 was $1,081.0 million.

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, 2019 Mesa has $191.2 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.

On January 28, 2019, the Company entered into a Term Loan Agreement (the "Term Loan") pursuant to which the lenders thereunder committed to lend to the Company term loans in the aggregate principal amount of $91.2 million. Borrowings under the Term Loan bear interest at LIBOR plus 3.10%. This interest rate is significantly lower than the interest rate under the Company's Spare Engine Facility (defined below), which the Term Loan refinanced and replaced. The Spare Engine Facility accrued interest at LIBOR plus 7.25%. The Term Loan has a term of five years, with principal and interest payments due monthly over the term of the loan in accordance with an amortization schedule. The Company recorded a loss on extinguishment of debt of $3.6 million, due to a $1.9 million write-off of financing fees and $1.7 million in prepayment penalties, in connection with the repayment of the Spare Engine Facility.

On June 14, 2019, the Company completed the purchase of ten CRJ-700 aircraft, which were previously leased under the aircraft lease facility with Wells Fargo Bank Northwest, National Association, as owner trustee and lessor (the “GECAS Lease Facility”), for $70.0 million. The Company financed the aircraft purchase with $70.0 million in new debt. The notes payable of $70.0 million require monthly payments of principal and interest through fiscal 2023 bearing interest at LIBOR plus 5.0%. The Company recorded non-cash lease termination expense of $9.5 million in connection with the lease buyout ⁽¹⁴⁾.

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%.

On September 27, 2019, the company financed certain flight equipment with $8.0 million in new debt. The debt of $8.0 million require monthly payments of principal and interest through fiscal 2023 bearing interest at Libor plus 5.0%⁽¹⁵⁾^.

Earnings Per Share and Equity

3 Months Ended

Dec. 31, 2019

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,
	2019		2018
Net income attributable to Mesa Air Group	$	10,785	$	19,081
Basic weighted average common shares outstanding		35,023		34,518
Add: Incremental shares for:
Dilutive effect of restricted stock		159		595
Diluted weighted average common shares outstanding		35,182		35,113
Net income per common share attributable to Mesa Air Group:
Basic	$	0.31	$	0.55
Diluted	$	0.31	$	0.54

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, 2019 and 2018.

Restatement

Basic and Diluted Net Income per Common Share Available to Common Shareholders for the Three Months Ended December 31, 2018

Subsequent to the issuance of the Company’s condensed consolidated financial statements for the three months ended December 31, 2018, we determined our previously issued condensed consolidated financial statements included warrants with a nominal conversion price in diluted income per common share available to common shareholders, however, they should have been included in basic income per common share available to common shareholders. Since diluted shares are under the treasury stock method, diluted income per common share available to common shareholders was impacted by this change. As a result, basic and diluted income per common share available to common shareholders for the periods ended December 31, 2018 have been restated to appropriately include the warrants with a nominal conversion price in basic income per common share available to common shareholders.

The restatement adjustment did not impact our previously reported consolidated balance sheet, consolidated statements of stockholders’ equity, consolidated statements of cash flows, or net income (in thousands, except per share data).

	Three Months Ended December 31, 2018
	As Previously Reported		As Restated
Net income per common share available to common shareholders - Basic	$	0.80	$	0.55
Shares used in computing net income per common share available to common shareholders - Basic		23,903		34,518
Net income per common share available to common shareholders - Diluted	$	0.55	$	0.54
Shares used in computing net income per common share available to common shareholders - Diluted		34,821		35,113

Common Stock

3 Months Ended

Dec. 31, 2019

Stockholders Equity Note [Abstract]

Common Stock

10.	Common Stock

The Company previously issued warrants to third parties, which had a five-year term to be converted to common stock at an exercise price of $0.004 per share. Certain persons who are not U.S. citizens currently hold outstanding warrants to purchase shares of the Company's common stock. The warrants are exercisable if consistent with federal law, which requires that no more than 24.9% of the Company's stock be voted, directly or indirectly, or controlled by persons who are not U.S. citizens. The warrants can be converted to common stock upon warrant holders demonstrating U.S. citizenship or if consistent with above described federal law ownership limitations. In June 2018, the Company and holders agreed to extend the term of outstanding warrants set to expire by five years (through fiscal year 2023).

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 August 8, 2018, the Company filed its Second Amended and Restated Articles of Incorporation, which, among other things: (i) effected a 2.5-for-1 stock split of its common stock; and (ii) increased the authorized number of shares of its common and preferred stock to 125,000,000 and 5,000,000, respectively. All references to share and per share amounts in the Company's condensed consolidated financial statements have been retrospectively revised to reflect the stock split and increase in authorized shares.

The Company's shares of common stock were listed on The NASDAQ Global Select Market under the symbol "MESA" effective August 10, 2018. On August 14, 2018, the Company completed its IPO, in which it issued and sold 9,630,000 shares of common stock, no par value, at a public offering price of $12.00 per share (the "Firm Shares"). Additionally, in connection with the IPO, the Company granted the underwriters an option to purchase up to an additional 1,444,500 shares of common stock at the same price. On September 11, 2018, the Company closed the sale of 1,344,500 shares ("Option Shares") of its common stock, in connection with the partial exercise of the overallotment option granted to the underwriters in its IPO. Of the 1,344,500 Option Shares sold, 723,985 were purchased directly from the Company and the remaining 620,515 shares were purchased directly from the selling shareholders. The Firm Shares and Option Shares were sold to the public for a price of $12.00 per share. The aggregate gross proceeds to us from the IPO were approximately $124.2 million. The Company received $111.7 million in net proceeds after deducting $8.7 million of underwriting discounts and commissions and $3.6 million in offering costs.

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.

The Company has not historically paid dividends on shares of its common stock. Additionally, the Company's aircraft lease facility (the "RASPRO" Lease Facility) with RASPRO Trust 2005, a pass-through trust contains restrictions that limit the Company's ability to or prohibit it from paying dividends to holders of its common stock.

Share-Based Compensation and Stock Repurchases

3 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation and Stock Repurchases

12.	Share-Based Compensation and Stock Repurchases

Restricted Stock

The restricted share activity for the three months ended December 31, 2019 were summarized as follows:

				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Restricted shares unvested at September 30, 2019		847,974		$	9.56
Granted		31,000			7.03
Vested		(18,916	)		9.83
Forfeited		—			—
Restricted shares unvested at December 31, 2019		860,058		$	9.46

As of December 31, 2019, there was $4.8 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 1.7 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, 2019 and 2018 was $1.3 million and $1.5 million, respectively.

The Company repurchased 5,403 shares of its common stock for $0.04 million to cover the income tax obligation on vested employee equity awards and warrant conversions during the three months ended December 31, 2019.

The Company has granted restricted stock awards (“RSAs”) and 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 for 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.

Leases and Commitments

3 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Leases and Commitments

14.	Leases and Commitments

Effective October 1, 2019, the Company adopted Topic 842 and recorded ROU assets and lease liabilities of $154.6 million and $141.9 million, respectively. As part of the adoption, prepaid aircraft rent, deferred rent credits and accrued aircraft rents of $35.8 million, $21.3 million and $1.8 million, respectively, were classified as a component of the Company’s ROU assets.

At December 31, 2019, 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 $16.8 million and $19.1 million for the three months ended December 31, 2019 and 2018, respectively.

As of December 31, 2019, the Company’s operating lease right-of-use assets were $146.1 million, the Company’s current maturities of operating lease liabilities were $37.7 million, and the Company’s noncurrent lease liabilities were $96.0 million.

As of December 31, 2019, the Company’s operating lease payments in operating cash flows for the quarter ended December 31, 2019 is $9.5 million. The disclosure is not applicable for the quarter ended December 31, 2018 due to the method of adoption of the new leasing Standard ASC-842.⁽¹⁾

The table below presents lease related terms and discount rates as of December 31, 2019:

As of December 31,2019

Weighted average remaining lease term Operating

leases

4.3 years

Weighted average discount rate Operating leases

4.3

	Three Months Ended December 31,
	2019		2018		$ Change			% Change
Operating lease cost	$	16,784	$	19,089	$	(2,305	)		(12.1	)%

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, 2019 (in thousands):

Periods Ending December 31,	Total Maturities
2020	$	36,246
2021		44,529
2022		31,108
2023		13,772
2024		13,184
Thereafter		1,384
Less: Interest	$	(9,732	)
Amounts recorded in the Consolidated Balance Sheet	$	130,491

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

Supplemental Disclosure

3 Months Ended

Dec. 31, 2019

Supplemental Cash Flow Elements [Abstract]

Supplemental Disclosure

16.	Supplemental Disclosure

The Company adopted ASU 2016-18 on a retrospective basis during the quarter ended December 31, 2018. The following is a reconciliation of the captions in the Condensed Consolidated Balance Sheets to the Condensed Consolidated Statements of Cash Flows (in thousands):

	December 31,		September 30,		December 31,		September 30,
	2019		2019		2018		2018
Condensed Consolidated Balance Sheets
Cash and cash equivalents	$	57,763	$	68,855	$	88,600	$	103,311
Restricted cash		3,448		3,646		3,644		3,823
Cash, cash equivalents, and restricted cash in Condensed Consolidated Statement of Cash Flows	$	61,211	$	72,501	$	92,244	$	107,134

The restricted cash balance primarily includes deposits in trust accounts to collateralize letters of credit and to fund workers' compensation claims, landing fees, and other business needs.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2019
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. 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, 2019 included in the Company's Annual Report on Form 10-K for the year ended September 30, 2019 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 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.
Adoption of New Lease Standard	Adoption of New Lease Standard Effective October 1, 2019, we have adopted 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. 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 condensed 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 lessor, for our aircraft operated under our capacity purchase agreements, we have historically accounted for the non-lease component under ASC 606 and have historically accounted for the lease component under ASC 840. Under the available practical expedient, we have elected to account for the lease and non-lease components as a single component for all classes of underlying assets. As the predominant component of the combined components are the flights services, the leases are being accounted for entirely under ASC 606. 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).
Aircraft Lease	Aircraft Lease In addition to the aircraft we receive from United under our United Capacity Purchase Agreement, approximately 12% 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.
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 estimates 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 $10.6 million and $4.1 million for the three months ended December 31, 2019, and 2018, respectively, of which $1.9 million and $1.5 million, respectively, was pass-through expense. Airframe C-check expense totaled $7.3 million and $1.5 million for the three months ended December 31, 2019, and 2018, respectively, of which $1.2 million and $0.0 million, respectively, was pass-through expense

Intangible Assets (Tables)

3 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Information About Intangible Assets

Information about the intangible assets of the Company at December 31, 2019 and September 30, 2019, were as follows (in thousands):

	December 31,			September 30,
	2019			2019
Customer relationship	$	43,800		$	43,800
Accumulated amortization		(34,643	)		(34,268	)
	$	9,157		$	9,532

Balance Sheet Information (Tables)

3 Months Ended

Dec. 31, 2019

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, 2019 and September 30, 2019, consisted of the following (in thousands):

	December 31,			September 30,
	2019			2019
Expendable parts and supplies, net:
Expendable parts and supplies	$	26,455		$	25,336
Less: obsolescence and other		(4,055	)		(3,999	)
	$	22,400		$	21,337

Prepaid expenses and other current assets:
Prepaid aircraft rent	$	-		$	35,786
Deferred offering and reimbursed costs		1,664			2,092
Other		2,838			3,045
	$	4,502		$	40,923
Property and equipment, net:
Aircraft and other flight equipment substantially pledged	$	1,588,368		$	1,582,199
Other equipment		5,122			5,122
Leasehold improvements		2,797			2,797
Vehicles		945			924
Building		699			699
Furniture and fixtures		302			302
Total property and equipment		1,598,233			1,592,043
Less: accumulated depreciation		(336,966	)		(318,458	)
	$	1,261,267		$	1,273,585

Other accrued expenses:
Accrued property taxes	$	11,018		$	9,186
Accrued interest		6,715			4,497
Accrued vacation		6,149			6,128
Accrued wheels, brakes and tires		3,072			1,513
Other		7,396			7,564
	$	34,350		$	28,888

Fair Value Measurements (Tables)

3 Months Ended

Dec. 31, 2019

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, 2019				September 30, 2019
	Carrying		Fair		Carrying		Fair
	Value		Value		Value		Value
Long-term debt and financing leases, including current maturities(1)	$	821.8	$	846.9	$	858.1	$	882.7

⁽¹⁾	Current and prior period long-term debts' carrying and fair values exclude net debt issuance costs.

Long-Term Debt, Financing Leases and Other Borrowings (Tables)

3 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Schedule of Long-term Debt

Long-term debt as of December 31, 2019 and September 30, 2019, consisted of the following (in thousands):

	December 31,			September 30,
	2019			2019
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2022⁽¹⁾⁽²⁾	$	45,019		$	49,795
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2024⁽³⁾		57,867			60,761
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2027⁽⁴⁾		107,940			110,912
Notes payable to secured parties, collateralized by the underlying
aircraft, due 2028⁽⁵⁾		191,168			191,168
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2028⁽⁶⁾		149,283			152,945
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2022⁽⁷⁾		65,984			71,998
Senior and subordinated notes payable to secured parties, collateralized
by the underlying aircraft, due 2022⁽⁸⁾		43,136			47,309
Notes payable to financial institution, collateralized by the underlying
equipment, due 2020⁽⁹⁾		1,244			1,659
Notes payable to financial institution due 2020⁽¹⁰⁾		1,822			2,329
Notes payable to financial institution, collateralized by the underlying
equipment, due 2020⁽¹¹⁾		5,358			6,962
Other obligations due to financial institution, collateralized by the underlying
equipment, due 2023⁽¹²⁾		8,162			8,530
Notes payable to financial institution, collateralized by the underlying
equipment, due 2024⁽¹³⁾		76,037			80,153
Notes payable to financial institution, collateralized by the underlying
aircraft, due 2023⁽¹⁴⁾		61,250			65,625
Notes payable to financial institution due 2023 ⁽¹⁵⁾		7,503			8,000
Revolving Credit Facility ⁽¹⁶⁾		—			—
Gross long-term debt, including current maturities		821,773			858,145
Less unamortized debt issuance costs		(14,667	)		(14,822	)
Net long-term debt, including current maturities		807,106			843,323
Less current portion		(166,089	)		(165,900	)
Net long-term debt	$	641,017		$	677,423

⁽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% (4.16% at December 31, 2019) and requires monthly principal and interest payments.

⁽²⁾

⁽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.

⁽⁴⁾

⁽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⁾

⁽⁷⁾

⁽⁸⁾

⁽⁹⁾	In fiscal 2015, the Company financed certain flight equipment with $8.3 million in debt. The debt bears interest at 5.163% and requires monthly principal and interest payments.

⁽¹⁰⁾	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 monthly LIBOR plus 3.07% (4.98% at December 31, 2019) and requires quarterly principal and interest payments.

⁽¹¹⁾

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% (5.01% at December 31, 2019) and requires monthly principal and interest payments.

⁽¹⁴⁾

⁽¹⁵⁾

⁽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%.

Schedule of Principal Maturities of Long-term Debt

Principal maturities of long-term debt as of December 31, 2019, and for each of the next five years are as follows (in thousands):

Periods Ending December 31,	Total Principal
Remainder of 2020	$	166,089
2021		160,084
2022		140,139
2023		96,722
2024		62,605
Thereafter		196,134
	$	821,773

Earnings Per Share and Equity (Tables)

3 Months Ended

Dec. 31, 2019

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,
	2019		2018
Net income attributable to Mesa Air Group	$	10,785	$	19,081
Basic weighted average common shares outstanding		35,023		34,518
Add: Incremental shares for:
Dilutive effect of restricted stock		159		595
Diluted weighted average common shares outstanding		35,182		35,113
Net income per common share attributable to Mesa Air Group:
Basic	$	0.31	$	0.55
Diluted	$	0.31	$	0.54

Summary of Basic and Diluted Net Income per Common Share Available to Common Shareholders

	Three Months Ended December 31, 2018
	As Previously Reported		As Restated
Net income per common share available to common shareholders - Basic	$	0.80	$	0.55
Shares used in computing net income per common share available to common shareholders - Basic		23,903		34,518
Net income per common share available to common shareholders - Diluted	$	0.55	$	0.54
Shares used in computing net income per common share available to common shareholders - Diluted		34,821		35,113

Share-Based Compensation and Stock Repurchases (Tables)

3 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Restricted Share Activity

The restricted share activity for the three months ended December 31, 2019 were summarized as follows:

				Weighted-
				Average
	Number			Grant Date
	of Shares			Fair Value
Restricted shares unvested at September 30, 2019		847,974		$	9.56
Granted		31,000			7.03
Vested		(18,916	)		9.83
Forfeited		—			—
Restricted shares unvested at December 31, 2019		860,058		$	9.46

Leases and Commitments (Tables)

3 Months Ended

Dec. 31, 2019

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, 2019:

As of December 31,2019

Weighted average remaining lease term Operating

leases

4.3 years

Weighted average discount rate Operating leases

4.3

Schedule of Operating Lease Cost

	Three Months Ended December 31,
	2019		2018		$ Change			% Change
Operating lease cost	$	16,784	$	19,089	$	(2,305	)		(12.1	)%

Schedule of Future Minimum Rental Payments under Operating Leases of Initial or Remaining Non-cancelable Lease Terms

Periods Ending December 31,	Total Maturities
2020	$	36,246
2021		44,529
2022		31,108
2023		13,772
2024		13,184
Thereafter		1,384
Less: Interest	$	(9,732	)
Amounts recorded in the Consolidated Balance Sheet	$	130,491

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

Supplemental Disclosure (Tables)

3 Months Ended

Dec. 31, 2019

Supplemental Cash Flow Elements [Abstract]

Reconciliation of Captions in Condensed Consolidated Balance Sheets to Condensed Consolidated Statements of Cash Flows

The following is a reconciliation of the captions in the Condensed Consolidated Balance Sheets to the Condensed Consolidated Statements of Cash Flows (in thousands):

	December 31,		September 30,		December 31,		September 30,
	2019		2019		2018		2018
Condensed Consolidated Balance Sheets
Cash and cash equivalents	$	57,763	$	68,855	$	88,600	$	103,311
Restricted cash		3,448		3,646		3,644		3,823
Cash, cash equivalents, and restricted cash in Condensed Consolidated Statement of Cash Flows	$	61,211	$	72,501	$	92,244	$	107,134

Organization and Operations - Additional Information (Detail)					1 Months Ended	3 Months Ended
	Jan. 02, 2020 Air-craft	Nov. 26, 2019 Air-craft	Nov. 25, 2019 Air-craft	Jan. 31, 2019 Air-craft	Jul. 31, 2019 Air-craft	Dec. 31, 2019 Daily_Departure State Air-craft City Employee	Apr. 02, 2019 Air-craft
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of states in which entity operates \| State						41
Number of aircrafts operated						145
Number of cities in which entity operates \| City						144
Number of daily departures \| Daily_Departure						742
Number of employees \| Employee						3,600
Maximum number of aircraft to permanently withdraw in the event company fails to meet new/ revise performance metrics				6
Number of aircraft converted to be utilized as operational spares							2
Number of aircraft permanently withdraw due to failure to meet new/revised performance metrics					2
American capacity purchase agreement termination notice period						15 days
Number of additional aircraft permanently withdrawn due to company's failure to meet certain performance metrics			2
Maximum number of aircraft to withdraw in the event company fails to meet new/ revise performance metrics						14
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.
Number of leased aircraft						18
United capacity purchase agreement termination notice period						30 days
Subsequent Event [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of deferred aircraft elected to remove	1
Number of aircraft removed due to failure to meet new/revised performance metrics	3
Number of aircraft that would be withdrawn at any time due to failure to meet new/revised performance metrics	3
Minimum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Capacity purchase agreement, expiration year						2021
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Capacity purchase agreement, expiration year						2025
CRJ-900 Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated						60
CRJ-900 Aircraft [Member] \| Aircraft Lease Expire In 2021 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operated aircrafts expired or set to expire						32
Lease expiration year						2021
CRJ-900 Aircraft [Member] \| Aircraft Lease Expire In 2021 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operated aircrafts expired or set to expire						20
Lease expiration year						2022
CRJ-900 Aircraft [Member] \| Aircraft Lease Expire In 2025 [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of operated aircrafts expired or set to expire						7
Lease expiration year						2025
CRJ-700 Aircraft [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated						20
Number of leased aircraft		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		18				60
Lease expiration year		2028
E-175 Aircraft [Member] \| Mesa [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated						18
E-175 Aircraft [Member] \| United [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Number of aircrafts operated		42				42
Aircraft lease extension period		5 years
E-175 Aircraft [Member] \| Minimum [Member] \| United [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Lease expiration year		2024
E-175 Aircraft [Member] \| Maximum [Member] \| United [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 additional aircrafts		20
Number of years in operation		12 years
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.

Concentrations - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Concentration Risk [Line Items]
Allowance for doubtful accounts	$ 1.8		$ 1.0
Sales Revenue, Net [Member] \| American Airlines Inc. [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	51.00%	53.00%
Sales Revenue, Net [Member] \| United [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	49.00%	47.00%

Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Intangible Assets Net Excluding Goodwill [Abstract]
Amortization expense recognized	$ 0.4	$ 0.5
Amortization expense for remainder of 2020	1.1
Amortization expense for 2021	1.2
Amortization expense for 2022	1.0
Amortization expense for 2023	0.9
Amortization expense for 2024	$ 0.8

Balance Sheet Information - Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Expendable parts and supplies, net:
Expendable parts and supplies	$ 26,455	$ 25,336
Less: obsolescence and other	(4,055)	(3,999)
Expendable parts and supplies, net	22,400	21,337
Prepaid expenses and other current assets:
Prepaid aircraft rent		35,786
Deferred offering and reimbursed costs	1,664	2,092
Other	2,838	3,045
Prepaid expenses and other current assets	4,502	40,923
Property and equipment, net:
Property and equipment-gross	1,598,233	1,592,043
Less: accumulated depreciation	(336,966)	(318,458)
Property and equipment-net	1,261,267	1,273,585
Other accrued expenses:
Accrued property taxes	11,018	9,186
Accrued interest	6,715	4,497
Accrued vacation	6,149	6,128
Accrued wheels, brakes and tires	3,072	1,513
Other	7,396	7,564
Other accrued expenses	34,350	28,888
Aircraft and Other Flight Equipment Substantially Pledged [Member]
Property and equipment, net:
Property and equipment-gross	1,588,368	1,582,199
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	5,122	5,122
Leasehold Improvements [Member]
Property and equipment, net:
Property and equipment-gross	2,797	2,797
Vehicles [Member]
Property and equipment, net:
Property and equipment-gross	945	924
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

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Long-term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 821,773	$ 858,145
Less unamortized debt issuance costs	(14,667)	(14,822)
Net long-term debt, including current maturities	807,106	843,323
Less current portion	(166,089)	(165,900)
Net long-term debt	641,017	677,423
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	45,019	49,795
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	57,867	60,761
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	107,940	110,912
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	191,168	191,168
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	149,283	152,945
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	65,984	71,998
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	43,136	47,309
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	1,244	1,659
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	5,358	6,962
Notes Payable to Financial Institution Due 2020 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	1,822	2,329
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	8,162	8,530
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	76,037	80,153
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	61,250	65,625
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 7,503	$ 8,000

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail) $ in Millions				1 Months Ended					3 Months Ended	12 Months Ended
	Sep. 27, 2019 USD ($)	Sep. 25, 2019 USD ($)	Jun. 14, 2019 USD ($)	Jun. 30, 2019 USD ($) Airfleet	Jan. 31, 2019 USD ($)	Jun. 30, 2018 USD ($) Air-craft	Feb. 28, 2018 Engine	Dec. 31, 2017 USD ($) Air-craft	Dec. 31, 2019	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) Air-craft	Sep. 30, 2015 USD ($) Air-craft	Sep. 30, 2007 USD ($) Airfleet	Sep. 30, 2014 USD ($) Airfleet
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															$ 120.3
Long term debt interest rate percentage									4.16%
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																$ 88.4
Long term debt interest rate description									LIBOR plus a spread ranging from 1.95% to 7.25%
Number of aircraft financed \| Airfleet																10
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									3.86%							1.95%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									9.16%							7.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Four C- R- J-900 Aircraft [Member]
Debt Instrument [Line Items]
Repayments of long term debt											$ 40.0
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																$ 114.5
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														$ 170.2
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													$ 246.0
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													$ 195.3
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						$ 27.5		$ 74.9
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						$ 69.6
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument maturity year									2020	2020
Debt instrument, face amount														$ 8.3
Long term debt interest rate percentage														5.163%
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
Debt instrument, face amount										$ 26.1	$ 26.1	$ 26.1	$ 26.1
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] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									4.69%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									4.97%
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													$ 10.2	$ 10.2
Long term debt interest rate percentage									4.98%
Long term debt interest rate description									monthly 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%
Other Obligations Due to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year									2023	2023
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									2024	2024
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 91.2
Long term debt interest rate percentage									5.01%
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 [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			$ 70.0	$ 70.0
Long term debt interest rate percentage									6.91%
Long term debt interest rate description			LIBOR plus 5.0%.						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 Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year									2023	2023
Notes Payable to Financial Institution Due 2023 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 8.0
Long term debt interest rate percentage									6.91%
Long term debt interest rate description	Libor plus 5.0%								monthly LIBOR plus 5.00%
Notes Payable to Financial Institution Due 2023 [Member] \| Flight Equipment [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate	5.25%								5.00%	5.25%
Senior Notes Due Two Thousand Twenty Seven [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount														$ 151.0
Long term debt interest rate percentage									4.62%
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														$ 8.1
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													$ 172.0
Long term debt interest rate percentage									3.96%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									4.08%
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						$ 65.8
Long term debt interest rate percentage									5.26%
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						$ 29.8
Long term debt interest rate percentage									9.26%
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								$ 46.9
Long term debt interest rate percentage									5.26%
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 percentage									6.26%
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%
Working Capital Draw Loan [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 35.0
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
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%

Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Principal Maturities of Long-term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Long Term Debt By Maturity [Abstract]
Remainder of 2020	$ 166,089
2021	160,084
2022	140,139
2023	96,722
2024	62,605
Thereafter	196,134
Long-term debt	$ 821,773	$ 858,145

Long-Term Debt, Financing Leases and Other Borrowings - Additional Information (Detail) $ in Thousands					1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 27, 2019 USD ($)	Sep. 25, 2019 USD ($)	Jun. 14, 2019 USD ($) Air-craft	Jan. 28, 2019 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Property and equipment, net						$ 1,261,267	$ 1,273,585
Long-Term Debt						807,106	$ 843,323
Equipment Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt						$ 191,200
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 91,200
Long term debt interest rate description						LIBOR plus 3.10%
Term loan, term				5 years
Write-off of financing cost				$ 1,900
Payment for debt extinguishment prepayment penalties				1,700
Term Loan [Member] \| Spare Engine Facility [Member]
Debt Instrument [Line Items]
Long term debt interest rate description						LIBOR plus 7.25%
Loss on extinguishment of debt				$ 3,600
Term Loan [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate				3.10%
Term Loan [Member] \| LIBOR [Member] \| Spare Engine Facility [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate				7.25%
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		$ 70,000
Long term debt interest rate description			LIBOR plus 5.0%.			monthly LIBOR plus 5.00%
Number of aircraft purchased \| Air-craft			10
Payment for aircraft purchased			$ 70,000
Non-cash lease termination expense			$ 9,500
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] \| LIBOR [Member] \| CRJ-700 Aircraft [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
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
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%
Aircraft and Equipment [Member] \| Pledged as Collateral [Member]
Debt Instrument [Line Items]
Property and equipment, net						$ 1,081,000
Flight Equipment [Member] \| Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 8,000
Long term debt interest rate description	Libor plus 5.0%					monthly LIBOR plus 5.00%
Flight Equipment [Member] \| Notes Payable to Financial Institution Due 2023 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate	5.25%					5.00%	5.25%

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, 2019	Dec. 31, 2018
Earnings Per Share And Equity [Abstract]
Net income	$ 10,785	$ 19,081
Basic weighted average common shares outstanding	35,023	34,518
Add: Incremental shares for:
Dilutive effect of restricted stock	159	595
Diluted weighted average common shares outstanding	35,182	35,113
Net income per common share attributable to Mesa Air Group:
Basic	$ 0.31	$ 0.55
Diluted	$ 0.31	$ 0.54

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Earnings Per Share and Equity - Summary of Basic and Diluted Net Income per Common Share Available to Common Shareholders (Detail) - $ / shares shares in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Line Items]
Net income per common share available to common shareholders - Basic	$ 0.31	$ 0.55
Shares used in computing net income per common share available to common shareholders - Basic	35,023	34,518
Net income per common share available to common shareholders - Diluted	$ 0.31	$ 0.54
Shares used in computing net income per common share available to common shareholders - Diluted	35,182	35,113
As Previously Reported
Earnings Per Share [Line Items]
Net income per common share available to common shareholders - Basic		$ 0.80
Shares used in computing net income per common share available to common shareholders - Basic		23,903
Net income per common share available to common shareholders - Diluted		$ 0.55
Shares used in computing net income per common share available to common shareholders - Diluted		34,821
As Restated
Earnings Per Share [Line Items]
Net income per common share available to common shareholders - Basic		$ 0.55
Shares used in computing net income per common share available to common shareholders - Basic		34,518
Net income per common share available to common shareholders - Diluted		$ 0.54
Shares used in computing net income per common share available to common shareholders - Diluted		35,113

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions					3 Months Ended
	Apr. 09, 2019	Sep. 11, 2018 $ / shares shares	Aug. 14, 2018 $ / shares shares	Aug. 08, 2018 shares	Dec. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 $ / shares shares
Class of Warrant or Right [Line Items]
Warrants term					5 years
Warrants of common stock exercise price \| $ / shares					$ 0.004
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, stock split					effected a 2.5-for-1 stock split
Stock split ratio				2.5
Common stock, shares authorized				125,000,000	125,000,000	125,000,000
Preferred stock, shares authorized				5,000,000	5,000,000	5,000,000
Stock issued during period, shares, new issues		1,344,500
Common stock, no par value \| $ / shares					$ 0	$ 0
Common stock, warrants issued					1,988,472	3,600,953
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
IPO [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues			9,630,000
Common stock, no par value \| $ / shares
Shares issued, price per share \| $ / shares			$ 12.00
Gross proceeds of initial public offering \| $					$ 124.2
Net proceeds from initial public offering \| $					111.7
Underwriting discounts and commissions \| $					8.7
Offering costs \| $					$ 3.6
Underwriter Options [Member]
Class of Warrant or Right [Line Items]
Common stock, warrants issued			1,444,500
Purchased Directly From Company [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues		723,985
Purchased Directly From Selling Shareholders [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues		620,515
Firm Shares and Option Shares [Member]
Class of Warrant or Right [Line Items]
Shares issued, price per share \| $ / shares		$ 12.00

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Income Taxes [Line Items]
Effective tax rate (ETR) from continuing operations	24.70%	23.80%
Statutory federal tax rate	21.00%
State net operating loss carryforwards			$ 2.7
Domestic Tax Authority [Member] \| 2027-2037 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards			$ 478.3
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2020
State and Local Jurisdiction [Member] \| 2020-2039 [Member]
Income Taxes [Line Items]
Net operating loss carryforwards			$ 228.3
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			2020
Maximum [Member] \| Domestic Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2037
Maximum [Member] \| State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards, expiration year			2039

Share-Based Compensation and Stock Repurchases - Schedule of Restricted Share Activity (Detail) - Restricted Stock [Member]	3 Months Ended
	Dec. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Unvested, Beginning Balance \| shares	847,974
Number of Shares, Granted \| shares	31,000
Number of Shares, Vested \| shares	(18,916)
Number of Shares, Forfeited \| shares	0
Number of Shares, Unvested, Ending Balance \| shares	860,058
Weighted-Average Grant Date Fair Value, Unvested, Beginning Balance \| $ / shares	$ 9.56
Weighted-Average Grant Date Fair Value, Granted \| $ / shares	7.03
Weighted-Average Grant Date Fair Value, Vested \| $ / shares	9.83
Weighted-Average Grant Date Fair Value, Forfeited \| $ / shares	0
Weighted-Average Grant Date Fair Value, Unvested, Ending Balance \| $ / shares	$ 9.46

Share-Based Compensation and Stock Repurchases - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested share-based compensation arrangements	$ 4,800
Unrecognized compensation cost, period for recognition	1 year 8 months 12 days
Share-based compensation expense	$ 1,300	$ 1,500
Repurchased shares, value	$ 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	5,403
Repurchased shares, value	$ 40

Employee Stock Purchase Plan - Additional Information (Detail) - 2019 ESPP [Member]	3 Months Ended
	Dec. 31, 2019 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ordinary shares, discount rate	10.00%
Number of ordinary shares issued	0
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 - Additional Information (Detail) $ in Thousands	3 Months Ended
	Dec. 31, 2019 USD ($) Air-craft	Dec. 31, 2018 USD ($)	Oct. 01, 2019 USD ($)
Operating Leased Assets [Line Items]
Operating lease, right-of-use assets	$ 146,071
Number of leased aircraft \| Air-craft	18
Aggregate rental expense under all operating aircraft, equipment and facility leases	$ 16,800	$ 19,100
Operating lease current liabilities	37,674
Operating lease noncurrent liabilities	95,992
Operating lease payments in operating cash flows	$ 9,534
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 - Schedule of Future Minimum Rental Payments under Operating Leases of Initial or Remaining Non-cancelable Lease Terms (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2020	$ 36,246
2021	44,529
2022	31,108
2023	13,772
2024	13,184
Thereafter	1,384
Less: Interest	(9,732)
Amounts recorded in the Consolidated Balance Sheet	$ 130,491

Leases and Commitments - Schedule of Future Minimum Lease Obligations under Non-cancelable Operating Leases (Detail) $ in Thousands	Sep. 30, 2019 USD ($)
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

Supplemental Disclosure - Reconciliation of Captions in Condensed Consolidated Balance Sheets to Condensed Consolidated Statements of Cash Flows (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 57,763	$ 68,855	$ 88,600	$ 103,311
Restricted cash	3,448	3,646	3,644	3,823
Cash, cash equivalents, and restricted cash in Condensed Consolidated Statement of Cash Flows	$ 61,211	$ 72,501	$ 92,244	$ 107,134

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Engine overhaul expense	$ 10.6	$ 4.1
Engine overhaul pass-through expense	1.9	1.5
Airframe check expense	7.3	1.5
Airframe check pass-through expense	$ 1.2	$ 0.0
Aircraft [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage leased	12.00%

Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 20,200	$ 18,000
Amortization of unfavorable lease liability		$ 1,548

Intangible Assets - Information About Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Intangible Assets Net Excluding Goodwill [Abstract]
Customer relationship	$ 43,800	$ 43,800
Accumulated amortization	(34,643)	(34,268)
Total	$ 9,157	$ 9,532

Fair Value Measurements - Carrying Value and Estimated Fair Value of Long-term Debt, Including Current Maturities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Long-term debt and finance leases, including current maturities, carrying value	$ 821,773	$ 858,145
Long-term debt and finance leases, including current maturities, fair value	$ 846,900	$ 882,700

Earnings Per Share and Equity - Additional Information (Detail) - shares	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
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

Leases and Commitments - Schedule of Lease Related Terms and Discount Rates (Detail)	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term Operating leases	4 years 3 months 18 days
Weighted average discount rate Operating leases	4.30%