(Loss)/Earnings Per Share - Calculations of Net (Loss)/Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2025	Mar. 31, 2024
Earnings Per Share And Equity [Abstract]
Net Income (Loss)	$ (58,631)	$ (114,558)	$ 11,660	$ (57,850)	$ (173,188)	$ (46,190)
Basic weighted average common shares outstanding	41,334		41,068		41,333	41,004
Diluted weighted average common shares outstanding	41,334		41,068		41,333	41,004
Net loss per common share attributable to Mesa Air Group:
Basic	$ (1.42)		$ 0.28		$ (4.19)	$ (1.13)
Diluted	$ (1.42)		$ 0.28		$ (4.19)	$ (1.13)