Summary of Marketable Securities by Asset Type (Detail) - USD ($) $ in Thousands	Nov. 30, 2015	May. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 150,581	$ 149,864
Available-for-Sale Securities, Gross Unrealized Gains	5,723	8,721
Available-for-Sale Securities, Gross Unrealized Losses	(7,889)	(3,815)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	148,415	154,770
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	127,781	127,189
Available-for-Sale Securities, Gross Unrealized Gains	5,478	8,330
Available-for-Sale Securities, Gross Unrealized Losses	(7,631)	(3,653)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	125,628	131,866
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	4,282	3,722
Available-for-Sale Securities, Gross Unrealized Gains	415	339
Available-for-Sale Securities, Gross Unrealized Losses	(248)	(85)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	4,449	3,976
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	32,032	34,368
Available-for-Sale Securities, Gross Unrealized Gains	3,991	5,649
Available-for-Sale Securities, Gross Unrealized Losses	(955)	(559)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	35,068	39,458
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	33,605	32,657
Available-for-Sale Securities, Gross Unrealized Gains	948	2,114
Available-for-Sale Securities, Gross Unrealized Losses	(2,398)	(230)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,155	34,541
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	57,862	56,442
Available-for-Sale Securities, Gross Unrealized Gains	124	228
Available-for-Sale Securities, Gross Unrealized Losses	(4,030)	(2,779)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	53,956	53,891
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,800	22,675
Available-for-Sale Securities, Gross Unrealized Gains	245	391
Available-for-Sale Securities, Gross Unrealized Losses	(258)	(162)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,787	22,904
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	21,714	21,340
Available-for-Sale Securities, Gross Unrealized Gains	85	171
Available-for-Sale Securities, Gross Unrealized Losses	(258)	(162)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	21,541	21,349
Fixed maturity \| Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	36	36
Available-for-Sale Securities, Gross Unrealized Gains	2	2
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	38	38
Fixed maturity \| Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	18	81
Available-for-Sale Securities, Gross Unrealized Gains	23	47
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	41	128
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,032	1,218
Available-for-Sale Securities, Gross Unrealized Gains	135	171
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 1,167	$ 1,389

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)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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