Derivative Financial Instruments - Counterparty Credit Quality with Respect to Fair Value of OTC Derivatives Assets (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2014
Offsetting [Abstract]
Fair value of OTC derivatives assets, Counterparty credit quality, A- or higher	$ 179,090
Fair value of OTC derivatives assets, Counterparty credit quality, BBB- to BBB+	52,347
Fair value of OTC derivatives assets, Counterparty credit quality, BB+ or lower	82,789
Fair value of OTC derivatives assets, Counterparty credit quality, Unrated	69,972
Fair value of Over the Counter Derivatives Assets Counterparty credit quality	$ 384,198