Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2013	May 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 108,429	$ 105,483
Available-for-Sale Securities, Gross Unrealized Gains	7,786	8,644
Available-for-Sale Securities, Gross Unrealized Losses	(2,365)	(1,034)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	113,850	113,093
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	86,204	83,094
Available-for-Sale Securities, Gross Unrealized Gains	7,367	8,089
Available-for-Sale Securities, Gross Unrealized Losses	(2,023)	(891)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	91,548	90,292
Equity securities | Stocks | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,090	1,090
Available-for-Sale Securities, Gross Unrealized Gains	367	244
Available-for-Sale Securities, Gross Unrealized Losses	(47)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,410	1,334
Equity securities | Stocks | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,931	24,492
Available-for-Sale Securities, Gross Unrealized Gains	4,749	5,265
Available-for-Sale Securities, Gross Unrealized Losses	(488)	(392)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	35,192	29,365
Equity securities | Mutual funds | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	26,348	18,328
Available-for-Sale Securities, Gross Unrealized Gains	2,018	1,901
Available-for-Sale Securities, Gross Unrealized Losses	(148)	(7)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	28,218	20,222
Equity securities | Mutual funds | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	27,835	39,184
Available-for-Sale Securities, Gross Unrealized Gains	233	679
Available-for-Sale Securities, Gross Unrealized Losses	(1,340)	(492)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	26,728	39,371
Fixed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,225	22,389
Available-for-Sale Securities, Gross Unrealized Gains	419	555
Available-for-Sale Securities, Gross Unrealized Losses	(342)	(143)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,302	22,801
Fixed securities | U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,386	20,528
Available-for-Sale Securities, Gross Unrealized Gains	166	247
Available-for-Sale Securities, Gross Unrealized Losses	(341)	(139)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,211	20,636
Fixed securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,714	1,724
Available-for-Sale Securities, Gross Unrealized Gains	192	244
Available-for-Sale Securities, Gross Unrealized Losses	(1)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,905	1,968
Fixed securities | Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	37	37
Available-for-Sale Securities, Gross Unrealized Gains	3	4
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	40	41
Fixed securities | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	88	100
Available-for-Sale Securities, Gross Unrealized Gains	58	60
Available-for-Sale Securities, Gross Unrealized Losses		(4)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 146	$ 156