Summary of Marketable Securities by Asset Type (Detail) - USD ($) $ in Thousands	Feb. 28, 2017	May 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 158,781	$ 151,616
Available-for-Sale Securities, Gross Unrealized Gains	6,016	5,522
Available-for-Sale Securities, Gross Unrealized Losses	(5,602)	(10,182)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	159,195	146,956
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	135,567	129,025
Available-for-Sale Securities, Gross Unrealized Gains	5,843	5,171
Available-for-Sale Securities, Gross Unrealized Losses	(5,311)	(10,102)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	136,099	124,094
Equity securities \| Stocks \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	5,700	5,051
Available-for-Sale Securities, Gross Unrealized Gains	231	439
Available-for-Sale Securities, Gross Unrealized Losses	(155)	(247)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	5,776	5,243
Equity securities \| Stocks \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,690	27,717
Available-for-Sale Securities, Gross Unrealized Gains	3,054	3,831
Available-for-Sale Securities, Gross Unrealized Losses	(975)	(911)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,769	30,637
Equity securities \| Mutual funds \| Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	35,144	35,903
Available-for-Sale Securities, Gross Unrealized Gains	1,001	802
Available-for-Sale Securities, Gross Unrealized Losses	(1,765)	(4,357)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	34,380	32,348
Equity securities \| Mutual funds \| Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	64,033	60,354
Available-for-Sale Securities, Gross Unrealized Gains	1,557	99
Available-for-Sale Securities, Gross Unrealized Losses	(2,416)	(4,587)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	63,174	55,866
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	23,214	22,591
Available-for-Sale Securities, Gross Unrealized Gains	173	351
Available-for-Sale Securities, Gross Unrealized Losses	(291)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	23,096	22,862
Fixed maturity \| U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,499	21,704
Available-for-Sale Securities, Gross Unrealized Gains	76	214
Available-for-Sale Securities, Gross Unrealized Losses	(283)	(80)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,292	21,838
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	715	887
Available-for-Sale Securities, Gross Unrealized Gains	97	137
Available-for-Sale Securities, Gross Unrealized Losses	(8)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 804	$ 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)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-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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