Summary of Marketable Securities by Asset Type (Detail) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2014	May 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 129,416	$ 129,660
Available-for-Sale Securities, Gross Unrealized Gains	13,059	14,645
Available-for-Sale Securities, Gross Unrealized Losses	(1,411)	(1,425)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	141,064	142,880
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	107,326	106,838
Available-for-Sale Securities, Gross Unrealized Gains	12,659	14,223
Available-for-Sale Securities, Gross Unrealized Losses	(1,179)	(1,261)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	118,806	119,800
Equity securities | Stocks | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	2,315	984
Available-for-Sale Securities, Gross Unrealized Gains	887	669
Available-for-Sale Securities, Gross Unrealized Losses	(25)	(20)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	3,177	1,633
Equity securities | Stocks | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,867	31,071
Available-for-Sale Securities, Gross Unrealized Gains	7,704	8,965
Available-for-Sale Securities, Gross Unrealized Losses	(153)	(132)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	38,418	39,904
Equity securities | Mutual funds | Foreign
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	30,443	30,541
Available-for-Sale Securities, Gross Unrealized Gains	2,285	2,799
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	32,728	33,340
Equity securities | Mutual funds | Domestic
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	43,701	44,242
Available-for-Sale Securities, Gross Unrealized Gains	1,783	1,790
Available-for-Sale Securities, Gross Unrealized Losses	(1,001)	(1,109)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	44,483	44,923
Fixed maturity
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	22,090	22,822
Available-for-Sale Securities, Gross Unrealized Gains	400	422
Available-for-Sale Securities, Gross Unrealized Losses	(232)	(164)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	22,258	23,080
Fixed maturity | U.S. Treasury and other government
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	20,494	21,156
Available-for-Sale Securities, Gross Unrealized Gains	127	152
Available-for-Sale Securities, Gross Unrealized Losses	(228)	(164)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	20,393	21,144
Fixed maturity | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	1,474	1,544
Available-for-Sale Securities, Gross Unrealized Gains	219	212
Available-for-Sale Securities, Gross Unrealized Losses	(4)
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	1,689	1,756
Fixed maturity | Foreign bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38	37
Available-for-Sale Securities, Gross Unrealized Gains	1	3
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	39	40
Fixed maturity | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	84	85
Available-for-Sale Securities, Gross Unrealized Gains	53	55
Available-for-Sale Securities, Fair Value (Net Carrying Amount)	$ 137	$ 140