Document and Entity Information - shares
9 Months Ended
Jun. 30, 2019
Jul. 31, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q3  
Trading Symbol MESA  
Entity File Number 001-38626  
Entity Tax Identification Number 850302351  
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 Arizona  
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 Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Current Reporting Status Yes  
Entity Common Stock, Shares Outstanding   31,413,287