Effect of Derivative Instruments on Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	$ (3,308)		$ 1,910		$ (4,661)		$ 6,428
Open Position
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts	(3,308)		1,910		(4,661)		6,428
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	2,718	[1]	2,531	[1]	11,245	[1]	15,951	[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	(82)	[1]	(67)	[1]	(177)	[1]	(401)	[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	$ (5)	[1]	$ (43)	[1]	$ (119)	[1]	$ (246)	[1]

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