Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 29, 2012	May 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 109,541	$ 127,753
Available-for-Sale Securities, Gross Unrealized Gains	8,433	23,408
Available-for-Sale Securities, Gross Unrealized Losses	(1,388)	(1,518)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	116,586	149,643
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	87,816	98,676
Available-for-Sale Securities, Gross Unrealized Gains	7,596	22,363
Available-for-Sale Securities, Gross Unrealized Losses	(1,310)	(1,437)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	94,102	119,602
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,016	25,387
Available-for-Sale Securities, Gross Unrealized Gains	267	12,162
Available-for-Sale Securities, Gross Unrealized Losses	(2)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,281	37,549
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	25,049	28,044
Available-for-Sale Securities, Gross Unrealized Gains	3,470	4,222
Available-for-Sale Securities, Gross Unrealized Losses	(931)	(417)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	27,588	31,849
Equity securities \| Kemrock global depository receipts
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	7,200
Available-for-Sale Securities, Gross Unrealized Losses	(114)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	7,086
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	16,030	14,680
Available-for-Sale Securities, Gross Unrealized Gains	1,846	3,733
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	17,876	18,413
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38,521	30,565
Available-for-Sale Securities, Gross Unrealized Gains	2,013	2,246
Available-for-Sale Securities, Gross Unrealized Losses	(263)	(1,020)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	40,271	31,791
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	21,725	29,077
Available-for-Sale Securities, Gross Unrealized Gains	837	1,045
Available-for-Sale Securities, Gross Unrealized Losses	(78)	(81)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,484	30,041
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	19,082	25,916
Available-for-Sale Securities, Gross Unrealized Gains	394	643
Available-for-Sale Securities, Gross Unrealized Losses	(73)	(79)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	19,403	26,480
Fixed maturity \| Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	2,365	2,729
Available-for-Sale Securities, Gross Unrealized Gains	333	301
Available-for-Sale Securities, Gross Unrealized Losses	(5)	(1)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	2,693	3,029
Fixed maturity \| Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38
Available-for-Sale Securities, Gross Unrealized Gains	1
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	39
Fixed maturity \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	240	432
Available-for-Sale Securities, Gross Unrealized Gains	109	101
Available-for-Sale Securities, Gross Unrealized Losses		(1)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 349	$ 532

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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