Share-Based Compensation - Summary of Transactions Involving Stock Options (Detail) - $ / shares shares in Thousands	6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares under option, beginning of period, No. of Options	490	816
Granted, No. of Options	0	0
Exercised, No. of Options	(109)	(124)
Cancelled, No. of Options	0	0
Expired, No. of Options	0	0
Shares under option, end of period, No. of Options	381	692
Exercisable at end of period, No. of Options	381	692
Shares under option, beginning of period, Weighted Average Exercise Price	$ 24.80	$ 19.61
Granted, Weighted Average Exercise Price	0	0
Exercised, Weighted Average Exercise Price	21.41	10.40
Cancelled, Weighted Average Exercise Price	0	0
Expired, Weighted Average Exercise Price	0	0
Shares under option, end of period, Weighted Average Exercise Price	25.77	21.26
Exercisable at end of period, Weighted Average Exercise Price	$ 25.77	$ 21.26