Effect of Derivative Instruments on Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	$ 6,566		$ 6,775		$ (8,549)
Open Position
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	6,566		6,775		(8,549)
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Cost of product | Closed Positions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	11,781	[1]	17,769	[1]	18,636	[1]
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Cost of installations and service | Closed Positions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	(202)	[1]	(440)	[1]	(284)	[1]
Fair Value, Measurements, Recurring | Derivatives Not Designated as Hedging Instruments under FASB ASC 815-10 | Commodity Contract | Delivery and branch expenses | Closed Positions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Recognized, commodity contracts	$ (104)	[1]	$ (286)	[1]	$ (82)	[1]

[1] Represents realized closed positions and includes the cost of options as they expire.