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	Dec. 31, 2024	Sep. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	$ 9,929	$ 17,779
Derivative Liabilities, commodity contracts	(16,991)	(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	9,285	16,948
Derivative Liabilities, commodity contracts	(16,275)	(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	644	831
Derivative Liabilities, commodity contracts	(716)	(965)
Significant Other Observable Inputs Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets, commodity contracts	9,929	17,779
Derivative Liabilities, commodity contracts	(16,991)	(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	9,285	16,948
Derivative Liabilities, commodity contracts	(16,275)	(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	644	831
Derivative Liabilities, commodity contracts	$ (716)	$ (965)