Leases - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025 USD ($) AirCraft	Mar. 31, 2024 USD ($)	Mar. 31, 2025 USD ($) AirCraft	Mar. 31, 2024 USD ($)
Lessee, Lease, Description [Line Items]
Number of leased aircraft | AirCraft	23		23
Aggregate rental expense under all operating aircraft, equipment and facility leases | $	$ 2,840	$ 4,595	$ 6,109	$ 12,565
Weighted average remaining lease term Operating leases	6 years 2 months 12 days		6 years 2 months 12 days
Weighted average discount rate Operating leases	5.40%		5.40%