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Derivatives and Hedging-Disclosures and Fair Value Measurements - Effect of Derivative Instruments on Statement of Operations (Detail) - USD ($)
$ in Thousands
3 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of (Gain) or Loss Unrealized, commodity contracts [1] $ 13,403 $ (17,395)
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] (9,975) 11,578
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] (127) 93
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] $ (284) $ 201
[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.