Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2013	May 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 105,483	$ 117,732
Available-for-Sale Securities, Gross Unrealized Gains	8,644	5,475
Available-for-Sale Securities, Gross Unrealized Losses	(1,034)	(3,078)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	113,093	120,129
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	83,094	82,131
Available-for-Sale Securities, Gross Unrealized Gains	8,089	4,490
Available-for-Sale Securities, Gross Unrealized Losses	(891)	(3,059)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	90,292	83,562
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,090	1,016
Available-for-Sale Securities, Gross Unrealized Gains	244	79
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,334	1,095
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	24,492	24,380
Available-for-Sale Securities, Gross Unrealized Gains	5,265	2,776
Available-for-Sale Securities, Gross Unrealized Losses	(392)	(1,046)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	29,365	26,110
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	18,328	17,489
Available-for-Sale Securities, Gross Unrealized Gains	1,901	521
Available-for-Sale Securities, Gross Unrealized Losses	(7)	(936)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,222	17,074
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	39,184	39,246
Available-for-Sale Securities, Gross Unrealized Gains	679	1,114
Available-for-Sale Securities, Gross Unrealized Losses	(492)	(1,077)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	39,371	39,283
Fixed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,389	35,601
Available-for-Sale Securities, Gross Unrealized Gains	555	985
Available-for-Sale Securities, Gross Unrealized Losses	(143)	(19)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,801	36,567
Fixed securities \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,528	19,347
Available-for-Sale Securities, Gross Unrealized Gains	247	530
Available-for-Sale Securities, Gross Unrealized Losses	(139)	(12)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,636	19,865
Fixed securities \| Kemrock convertible bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost		13,670
Available-for-Sale Securities, Fair Value (Net Carrying Amount)		13,670
Fixed securities \| Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,724	2,305
Available-for-Sale Securities, Gross Unrealized Gains	244	349
Available-for-Sale Securities, Gross Unrealized Losses		(5)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,968	2,649
Fixed securities \| Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	37	38
Available-for-Sale Securities, Gross Unrealized Gains	4	1
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	41	39
Fixed securities \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	100	241
Available-for-Sale Securities, Gross Unrealized Gains	60	105
Available-for-Sale Securities, Gross Unrealized Losses	(4)	(2)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 156	$ 344

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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