| Document and Entity Information | Dec. 08, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 8, 2020 |
| Entity Registrant Name | Mesa Air Group, Inc. |
| Entity Central Index Key | 0000810332 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity File Number | 001-38626 |
| Entity Incorporation, State or Country Code | NV |
| 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, State or Province | AZ |
| Entity Address, Postal Zip Code | 85008 |
| City Area Code | 602 |
| Local Phone Number | 685-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, no par value |
| Trading Symbol | MESA |
| Security Exchange Name | NASDAQ |
| Current Fiscal Year End Date | --09-30 |
