Derivatives and Hedging-Disclosures and Fair Value Measurements - Effect of Derivative Instruments on Statement of Operations (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2025	Mar. 31, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	[1]	$ (6,101)	$ (11,752)	$ (11,359)	$ 7,278
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]	$ 6,863	$ 13,386	$ 13,754	$ 18,109
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost and expenses	Cost and expenses	Cost and expenses	Cost and expenses
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]	$ 44	$ (55)	$ 131	$ (41)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Cost and expenses	Cost and expenses	Cost and expenses	Cost and expenses
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]	$ 245	$ (517)	$ 656	$ (909)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Delivery and branch expenses	Delivery and branch expenses	Delivery and branch expenses	Delivery and branch 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.