Summary of Transactions Involving Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares under option, beginning of period, No. of Options	816	1,052
Granted, No. of Options
Exercised, No. of Options	(96)	(23)
Cancelled, No. of Options
Expired, No. of Options
Shares under option, end of period, No. of Options	720	1,029
Exercisable at end of period, No. of Options	720	1,029
Shares under option, beginning of period, Weighted Average Exercise Price	$ 19.61	$ 20.24
Granted, Weighted Average Exercise Price
Exercised, Weighted Average Exercise Price	$ 9.36	$ 29.92
Cancelled, Weighted Average Exercise Price
Expired, Weighted Average Exercise Price
Shares under option, end of period, Weighted Average Exercise Price	$ 20.96	$ 20.03
Exercisable at end of period, Weighted Average Exercise Price	$ 20.96	$ 20.03