Fair Value Measurements and Derivative Instruments - Reconciliation of Gross Fair Value of Assets and Liabilities Subject to Offsetting Arrangements (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2014	Aug. 31, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amounts of Recognized Assets	$ 48	$ 413
Gross Liabilities Offset in the Balance Sheets	(1,726)	(2,200)
Commodity Contract [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gross Amounts of Recognized Assets	48	413
Gross Liabilities Offset in the Balance Sheets	(1,726)	(2,200)
Net Amount of Assets (Liabilities)	(1,678)	(1,787)
Cash Collateral on Deposit with Counterparty	3,192	3,490
Net Fair Value as Recorded in Balance Sheets	$ 1,514	$ 1,703