Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2014	May 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 101,043	$ 105,483
Available-for-Sale Securities, Gross Unrealized Gains	12,839	8,644
Available-for-Sale Securities, Gross Unrealized Losses	(1,768)	(1,034)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	112,114	113,093
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	80,812	83,094
Available-for-Sale Securities, Gross Unrealized Gains	12,438	8,089
Available-for-Sale Securities, Gross Unrealized Losses	(1,450)	(891)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	91,800	90,292
Equity securities | Stocks | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	984	1,090
Available-for-Sale Securities, Gross Unrealized Gains	533	244
Available-for-Sale Securities, Gross Unrealized Losses	(32)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,485	1,334
Equity securities | Stocks | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,929	24,492
Available-for-Sale Securities, Gross Unrealized Gains	8,307	5,265
Available-for-Sale Securities, Gross Unrealized Losses	(244)	(392)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	38,992	29,365
Equity securities | Mutual funds | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	6,329	18,328
Available-for-Sale Securities, Gross Unrealized Gains	1,798	1,901
Available-for-Sale Securities, Gross Unrealized Losses	(8)	(7)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	8,119	20,222
Equity securities | Mutual funds | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	42,570	39,184
Available-for-Sale Securities, Gross Unrealized Gains	1,800	679
Available-for-Sale Securities, Gross Unrealized Losses	(1,166)	(492)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	43,204	39,371
Fixed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,231	22,389
Available-for-Sale Securities, Gross Unrealized Gains	401	555
Available-for-Sale Securities, Gross Unrealized Losses	(318)	(143)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,314	22,801
Fixed securities | U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	18,424	20,528
Available-for-Sale Securities, Gross Unrealized Gains	142	247
Available-for-Sale Securities, Gross Unrealized Losses	(318)	(139)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	18,248	20,636
Fixed securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,683	1,724
Available-for-Sale Securities, Gross Unrealized Gains	200	244
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,883	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	56	60
Available-for-Sale Securities, Gross Unrealized Losses		(4)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 143	$ 156