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, 2025	Sep. 30, 2024	Sep. 30, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	[1]	$ (13,390)	$ 19,018	$ 1,977
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]	$ 17,635	$ 20,268	$ 17,268
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost of Product and Service Sold	Cost of Product and Service Sold	Cost of Product and Service 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]	$ 219	$ (184)	$ 16
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost of Product and Service Sold	Cost of Product and Service Sold	Cost of Product and Service 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]	$ 934	$ (865)	$ 434
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.