Effect of Derivative Instruments on Statement of Operations (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts		$ (5,415)	$ (3,308)	$ (9,756)	$ (4,661)
Open Position
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amount of (Gain) or Loss Unrealized, commodity contracts		(5,415)	(3,308)	(9,756)	(4,661)
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	[1]	6,599	2,718	17,115	11,245
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	[1]	280	(82)	1,625	(177)
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	[1]	$ 251	$ (5)	$ 1,716	$ (119)

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