Effect of Derivative Instruments on Consolidated Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Oct. 31, 2014	Oct. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) Loss Recognized In Income on Derivative	$ 0	$ (16,976)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) Loss Recognized In Income on Derivative	(10)	(17,005)
Not Designated as Hedging Instrument | Commodity Contracts | Cost of Sales
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) Loss Recognized In Income on Derivative	(10)	(29)
Not Designated as Hedging Instrument | Warrant | Gain Loss On Warrant Liability
Derivative Instruments, Gain (Loss) [Line Items]
Amount of (Gain) Loss Recognized In Income on Derivative	$ 0	$ (16,976)