Earnings Per Share - Calculations of Net (Loss) Income Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share And Equity [Abstract]
Net (loss)/income	$ (120,116)	$ (182,678)	$ 16,588
Basic weighted average common shares outstanding	39,465	36,133	35,713
Add: Incremental shares for:
Dilutive effect of warrants			2,543
Dilutive effect of restricted stock			587
Diluted weighted average common shares outstanding	39,465	36,133	38,843
Net (loss)/income per common share attributable to Mesa Air Group:
Basic	$ (3.04)	$ (5.06)	$ 0.46
Diluted	$ (3.04)	$ (5.06)	$ 0.43