v3.19.1
Document and Entity Information - shares
6 Months Ended
Mar. 31, 2019
Apr. 30, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
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 Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   28,785,577