Summary of Marketable Securities by Asset Type (Detail) - USD ($) $ in Thousands	Nov. 30, 2016	May 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 156,749	$ 151,616
Available-for-Sale Securities, Gross Unrealized Gains	4,808	5,522
Available-for-Sale Securities, Gross Unrealized Losses	(8,093)	(10,182)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	153,464	146,956
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	133,740	129,025
Available-for-Sale Securities, Gross Unrealized Gains	4,628	5,171
Available-for-Sale Securities, Gross Unrealized Losses	(7,790)	(10,102)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	130,578	124,094
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	5,699	5,051
Available-for-Sale Securities, Gross Unrealized Gains	229	439
Available-for-Sale Securities, Gross Unrealized Losses	(323)	(247)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	5,605	5,243
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	31,050	27,717
Available-for-Sale Securities, Gross Unrealized Gains	2,086	3,831
Available-for-Sale Securities, Gross Unrealized Losses	(1,325)	(911)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	31,811	30,637
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	34,419	35,903
Available-for-Sale Securities, Gross Unrealized Gains	920	802
Available-for-Sale Securities, Gross Unrealized Losses	(3,204)	(4,357)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,135	32,348
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	62,572	60,354
Available-for-Sale Securities, Gross Unrealized Gains	1,393	99
Available-for-Sale Securities, Gross Unrealized Losses	(2,938)	(4,587)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	61,027	55,866
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	23,009	22,591
Available-for-Sale Securities, Gross Unrealized Gains	180	351
Available-for-Sale Securities, Gross Unrealized Losses	(303)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,886	22,862
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,235	21,704
Available-for-Sale Securities, Gross Unrealized Gains	76	214
Available-for-Sale Securities, Gross Unrealized Losses	(295)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,016	21,838
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	774	887
Available-for-Sale Securities, Gross Unrealized Gains	104	137
Available-for-Sale Securities, Gross Unrealized Losses	(8)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 870	$ 1,024

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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