Investments - Summary of Company's Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Aug. 31, 2012	May 31, 2012
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	$ 16.1	$ 16.2
Available-for-sale, Unrealized Gains	0.8
Available-for-sale, Unrealized Losses		(0.2)
Available-for-sale, Fair Value	16.9	16.0
Trading, Amortized Cost	0.8	0.4
Trading, Realized Gains
Trading, Realized Losses
Trading, Fair Value	0.8	0.4
Equity securities [Member]
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	0.2	0.4
Available-for-sale, Unrealized Gains	0.2
Available-for-sale, Unrealized Losses		(0.2)
Available-for-sale, Fair Value	0.4	0.2
Trading, Amortized Cost	0.8	0.4
Trading, Realized Gains
Trading, Realized Losses
Trading, Fair Value	0.8	0.4
Time deposit [Member]
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	9.5	9.5
Available-for-sale, Fair Value	9.5	9.5
Greek bonds [Member]
Summary of Investment Holdings [Line Items]
Available-for-sale, Amortized Cost	6.4	6.3
Available-for-sale, Unrealized Gains	0.6
Available-for-sale, Fair Value	$ 7.0	$ 6.3

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.

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