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, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	[1]	$ (11,752)	$ 3,022	$ 7,278	$ 20,658
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]	$ 13,386	$ 13,954	$ 18,109	$ 5,012
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]	$ (55)	$ 39	$ (41)	$ 79
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]	$ (517)	$ 349	$ (909)	$ 149
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.