Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2013	May 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 120,665	$ 105,483
Available-for-Sale Securities, Gross Unrealized Gains	16,140	8,644
Available-for-Sale Securities, Gross Unrealized Losses	(1,581)	(1,034)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	135,224	113,093
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	99,237	83,094
Available-for-Sale Securities, Gross Unrealized Gains	15,721	8,089
Available-for-Sale Securities, Gross Unrealized Losses	(1,295)	(891)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	113,663	90,292
Equity securities | Stocks | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	372	1,090
Available-for-Sale Securities, Gross Unrealized Gains	107	244
Available-for-Sale Securities, Gross Unrealized Losses	(39)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	440	1,334
Equity securities | Stocks | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	31,849	24,492
Available-for-Sale Securities, Gross Unrealized Gains	7,947	5,265
Available-for-Sale Securities, Gross Unrealized Losses	(239)	(392)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	39,557	29,365
Equity securities | Mutual funds | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	26,367	18,328
Available-for-Sale Securities, Gross Unrealized Gains	5,535	1,901
Available-for-Sale Securities, Gross Unrealized Losses		(7)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	31,902	20,222
Equity securities | Mutual funds | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	40,649	39,184
Available-for-Sale Securities, Gross Unrealized Gains	2,132	679
Available-for-Sale Securities, Gross Unrealized Losses	(1,017)	(492)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	41,764	39,371
Fixed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	21,428	22,389
Available-for-Sale Securities, Gross Unrealized Gains	419	555
Available-for-Sale Securities, Gross Unrealized Losses	(286)	(143)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	21,561	22,801
Fixed securities | U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	19,595	20,528
Available-for-Sale Securities, Gross Unrealized Gains	163	247
Available-for-Sale Securities, Gross Unrealized Losses	(286)	(139)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	19,472	20,636
Fixed securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,709	1,724
Available-for-Sale Securities, Gross Unrealized Gains	196	244
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	87	100
Available-for-Sale Securities, Gross Unrealized Gains	57	60
Available-for-Sale Securities, Gross Unrealized Losses		(4)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 144	$ 156