Summary of Transactions Involving Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares under option, beginning of period, No. of Options	1,052	1,562
Granted, No. of Options
Exercised, No. of Options	(80)	(258)
Cancelled, No. of Options
Expired, No. of Options
Shares under option, end of period, No. of Options	972	1,304
Exercisable at end of period, No. of Options	972	1,304
Shares under option, beginning of period, Weighted Average Exercise Price	$ 20.24	$ 18.95
Granted, Weighted Average Exercise Price
Exercised, Weighted Average Exercise Price	$ 24.73	$ 13.17
Cancelled, Weighted Average Exercise Price
Expired, Weighted Average Exercise Price
Shares under option, end of period, Weighted Average Exercise Price	$ 19.87	$ 20.09
Exercisable at end of period, Weighted Average Exercise Price	$ 19.87	$ 20.09