Derivative Financial Instruments - Counterparty Credit Quality with Respect to Fair Value of OTC Derivatives Assets (Detail) $ in Thousands	Aug. 31, 2015 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair value of OTC derivatives assets, Counterparty credit quality, A- or higher	$ 256,142
Fair value of OTC derivatives assets, Counterparty credit quality, BBB- to BBB+	124,498
Fair value of OTC derivatives assets, Counterparty credit quality, BB+ or lower	74,834
Fair value of OTC derivatives assets, Counterparty credit quality, Unrated	77,427
Total OTC derivative assets included in Financial instruments owned	$ 532,901