Derivatives and Hedging-Disclosures and Fair Value Measurements - Company's Commodity Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 - Commodity Contract - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	$ 7,728	$ 17,779
Derivative Liabilities, commodity contracts	(9,255)	(31,884)
Fair liability and fair asset value of derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	7,165	16,948
Derivative Liabilities, commodity contracts	(8,769)	(30,919)
Deferred charges and other assets, net and other long-term liabilities, net balances
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts		831
Derivative Liabilities, commodity contracts		(965)
Deferred Charges And Other Assets Net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	563
Derivative Liabilities, commodity contracts	(486)
Significant Other Observable Inputs Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	7,728	17,779
Derivative Liabilities, commodity contracts	(9,255)	(31,884)
Significant Other Observable Inputs Level 2 | Fair liability and fair asset value of derivative instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	7,165	16,948
Derivative Liabilities, commodity contracts	(8,769)	(30,919)
Significant Other Observable Inputs Level 2 | Deferred charges and other assets, net and other long-term liabilities, net balances
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts		831
Derivative Liabilities, commodity contracts		$ (965)
Significant Other Observable Inputs Level 2 | Deferred Charges And Other Assets Net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	563
Derivative Liabilities, commodity contracts	$ (486)