Document and Entity Information - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2018
Nov. 30, 2018
Mar. 31, 2018
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Sep. 30, 2018    
Document Fiscal Year Focus 2018    
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 Non-accelerated Filer    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status No    
Entity Voluntary Filers No    
Entity Shell Company false    
Entity Small Business false    
Entity Emerging Growth Company true    
Entity Ex Transition Period true    
Entity Public Float     $ 0
Entity Common Stock, Shares Outstanding   23,902,903