Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2012	May 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 129,132	$ 117,732
Available-for-Sale Securities, Gross Unrealized Gains	6,780	5,475
Available-for-Sale Securities, Gross Unrealized Losses	(743)	(3,078)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	135,169	120,129
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	92,304	82,131
Available-for-Sale Securities, Gross Unrealized Gains	6,020	4,490
Available-for-Sale Securities, Gross Unrealized Losses	(708)	(3,059)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	97,616	83,562
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,321	1,016
Available-for-Sale Securities, Gross Unrealized Gains	235	79
Available-for-Sale Securities, Gross Unrealized Losses	(12)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,544	1,095
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	27,639	24,380
Available-for-Sale Securities, Gross Unrealized Gains	2,385	2,776
Available-for-Sale Securities, Gross Unrealized Losses	(691)	(1,046)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	29,333	26,110
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,072	17,489
Available-for-Sale Securities, Gross Unrealized Gains	2,550	521
Available-for-Sale Securities, Gross Unrealized Losses		(936)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,622	17,074
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	43,272	39,246
Available-for-Sale Securities, Gross Unrealized Gains	850	1,114
Available-for-Sale Securities, Gross Unrealized Losses	(5)	(1,077)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	44,117	39,283
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	36,828	35,601
Available-for-Sale Securities, Gross Unrealized Gains	760	985
Available-for-Sale Securities, Gross Unrealized Losses	(35)	(19)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	37,553	36,567
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,565	19,347
Available-for-Sale Securities, Gross Unrealized Gains	405	530
Available-for-Sale Securities, Gross Unrealized Losses	(32)	(12)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,938	19,865
Fixed maturity \| Kemrock convertible bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	14,273	13,670
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	14,273	13,670
Fixed maturity \| Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,824	2,305
Available-for-Sale Securities, Gross Unrealized Gains	286	349
Available-for-Sale Securities, Gross Unrealized Losses	(1)	(5)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	2,109	2,649
Fixed maturity \| Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38	38
Available-for-Sale Securities, Gross Unrealized Gains	4	1
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	42	39
Fixed maturity \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	128	241
Available-for-Sale Securities, Gross Unrealized Gains	65	105
Available-for-Sale Securities, Gross Unrealized Losses	(2)	(2)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 191	$ 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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