Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2012	May 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 126,763	$ 127,753
Available-for-Sale Securities, Gross Unrealized Gains	5,475	23,408
Available-for-Sale Securities, Gross Unrealized Losses	(3,078)	(1,518)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	129,160	149,643
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	82,131	98,676
Available-for-Sale Securities, Gross Unrealized Gains	4,490	22,363
Available-for-Sale Securities, Gross Unrealized Losses	(3,059)	(1,437)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	83,562	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	79	12,162
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,095	37,549
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	24,380	28,044
Available-for-Sale Securities, Gross Unrealized Gains	2,776	4,222
Available-for-Sale Securities, Gross Unrealized Losses	(1,046)	(417)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	26,110	31,849
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	17,489	14,680
Available-for-Sale Securities, Gross Unrealized Gains	521	3,733
Available-for-Sale Securities, Gross Unrealized Losses	(936)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	17,074	18,413
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	39,246	30,565
Available-for-Sale Securities, Gross Unrealized Gains	1,114	2,246
Available-for-Sale Securities, Gross Unrealized Losses	(1,077)	(1,020)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	39,283	31,791
Fixed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	44,632	29,077
Available-for-Sale Securities, Gross Unrealized Gains	985	1,045
Available-for-Sale Securities, Gross Unrealized Losses	(19)	(81)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	45,598	30,041
Fixed securities \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	19,347	25,916
Available-for-Sale Securities, Gross Unrealized Gains	530	643
Available-for-Sale Securities, Gross Unrealized Losses	(12)	(79)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	19,865	26,480
Fixed securities \| Investment in Kemrock convertible debt
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,701
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,701
Fixed securities \| Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	2,305	2,729
Available-for-Sale Securities, Gross Unrealized Gains	349	301
Available-for-Sale Securities, Gross Unrealized Losses	(5)	(1)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	2,649	3,029
Fixed securities \| 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 securities \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	241	432
Available-for-Sale Securities, Gross Unrealized Gains	105	101
Available-for-Sale Securities, Gross Unrealized Losses	(2)	(1)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 344	$ 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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