Derivatives and Hedging-Disclosures and Fair Value Measurements - Effect of Derivative Instruments on Statement of Operations (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	[1]	$ (603)	$ 984	$ (11,962)	$ 8,262
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]	$ 2,248	$ 2,323	$ 16,002	$ 20,432
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]	$ 40	$ (133)	$ 171	$ (174)
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]	$ 234	$ (20)	$ 890	$ (929)
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.