Derivative Financial Instruments - Counterparty Credit Quality with Respect to Fair Value of OTC Derivatives Assets (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2013
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Fair value of OTC derivatives assets, Counterparty credit quality, A- or higher	$ 232,256
Fair value of OTC derivatives assets, Counterparty credit quality, BBB- to BBB+	34,697
Fair value of OTC derivatives assets, Counterparty credit quality, BB+ or lower	54,576
Fair value of OTC derivatives assets, Counterparty credit quality, Unrated	19,412
Fair value of Over the Counter Derivatives Assets Counterparty credit quality	$ 340,941

Fair value of over counter derivatives assets counterparty credit quality A- or higher.

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Fair value of OTC derivatives assets, counterparty credit quality BBB- to BBB.

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Fair value of OTC derivatives assets, counterparty credit quality BB or lower.

No definition available.

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Fair value of OTC derivatives assets, counterparty credit quality unrated.

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OTC Derivative Assets Included In Financial Instruments Owned.

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