Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2013	May 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 112,474	$ 117,732
Available-for-Sale Securities, Gross Unrealized Gains	8,757	5,475
Available-for-Sale Securities, Gross Unrealized Losses	(3,562)	(3,078)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	117,669	120,129
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	75,499	82,131
Available-for-Sale Securities, Gross Unrealized Gains	8,137	4,490
Available-for-Sale Securities, Gross Unrealized Losses	(828)	(3,059)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	82,808	83,562
Equity securities | Stocks | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,090	1,016
Available-for-Sale Securities, Gross Unrealized Gains	290	79
Available-for-Sale Securities, Gross Unrealized Losses	(5)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,375	1,095
Equity securities | Stocks | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	28,594	24,380
Available-for-Sale Securities, Gross Unrealized Gains	4,128	2,776
Available-for-Sale Securities, Gross Unrealized Losses	(625)	(1,046)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,097	26,110
Equity securities | Mutual funds | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	21,304	17,489
Available-for-Sale Securities, Gross Unrealized Gains	3,623	521
Available-for-Sale Securities, Gross Unrealized Losses		(936)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	24,927	17,074
Equity securities | Mutual funds | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	24,511	39,246
Available-for-Sale Securities, Gross Unrealized Gains	96	1,114
Available-for-Sale Securities, Gross Unrealized Losses	(198)	(1,077)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	24,409	39,283
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	36,975	35,601
Available-for-Sale Securities, Gross Unrealized Gains	620	985
Available-for-Sale Securities, Gross Unrealized Losses	(2,734)	(19)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	34,861	36,567
Fixed maturity | U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,822	19,347
Available-for-Sale Securities, Gross Unrealized Gains	285	530
Available-for-Sale Securities, Gross Unrealized Losses	(69)	(12)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	21,038	19,865
Fixed maturity | Kemrock convertible bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	14,273	13,670
Available-for-Sale Securities, Gross Unrealized Losses	(2,662)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	11,611	13,670
Fixed maturity | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,728	2,305
Available-for-Sale Securities, Gross Unrealized Gains	268	349
Available-for-Sale Securities, Gross Unrealized Losses		(5)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,996	2,649
Fixed maturity | Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38	38
Available-for-Sale Securities, Gross Unrealized Gains	4	1
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	42	39
Fixed maturity | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	114	241
Available-for-Sale Securities, Gross Unrealized Gains	63	105
Available-for-Sale Securities, Gross Unrealized Losses	(3)	(2)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 174	$ 344