Document and Entity Information - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2019
Nov. 30, 2019
Jun. 28, 2019
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2019    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Trading Symbol MESA    
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 Well-known Seasoned Issuer No    
Entity Current Reporting Status No    
Entity Voluntary Filers No    
Entity Interactive Data Current Yes    
Entity Shell Company false    
Entity Small Business false    
Entity Emerging Growth Company true    
Entity Ex Transition Period true    
Entity Public Float     $ 277,501,075
Entity Common Stock, Shares Outstanding   32,362,483  
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    
Document Annual Report true    
Document Transition Report false    
Title of 12(b) Security Common Stock, no par value    
Documents Incorporated by Reference

Portions of the Registrant's definitive proxy statement relating to its 2020 annual meeting of shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. The 2020 Proxy Statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates