Summary of Transactions Involving Stock Options (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares under option, beginning of period, No. of Options	1,562	1,856
Granted, No. of Options
Exercised, No. of Options	(508)	(217)
Cancelled, No. of Options		(2)
Expired, No. of Options		(10)
Shares under option, end of period, No. of Options	1,054	1,627
Exercisable at end of period, No. of Options	1,054	1,623
Shares under option, beginning of period, Weighted Average Exercise Price	$ 18.95	$ 17.81
Granted, Weighted Average Exercise Price
Exercised, Weighted Average Exercise Price	$ 16.23	$ 10.27
Cancelled, Weighted Average Exercise Price		$ 30.33
Expired, Weighted Average Exercise Price		$ 30.33
Shares under option, end of period, Weighted Average Exercise Price	$ 20.25	$ 18.73
Exercisable at end of period, Weighted Average Exercise Price	$ 20.25	$ 18.70