Derivatives and Hedging-Disclosures and Fair Value Measurements - Effect of Derivative Instruments on Statement of Operations (Detail) - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts		$ (12,500)	$ (1,100)
Amount of (Gain) or Loss Unrealized, commodity contracts	[1]	1,977	17,286	$ (36,138)
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Cost of product
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	[2]	$ 17,268	$ (34,523)	$ 2,395
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost of Goods and Services Sold	Cost of Goods and Services Sold	Cost of Goods and Services Sold
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Cost of installations and service
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	[2]	$ 16	$ (1,555)	$ (359)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost of Goods and Services Sold	Cost of Goods and Services Sold	Cost of Goods and Services Sold
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Delivery and branch expenses
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	[2]	$ 434	$ (3,423)	$ 183
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Operating Costs and Expenses	Operating Costs and Expenses	Operating Costs and Expenses

[1] Represents the change in value of unrealized open positions and expired options.

[2] Represents realized closed positions and includes the cost of options as they expire.