Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Stock Options
Outstanding, beginning of year	4,752	5,517	7,511
Granted	97	130	1,034
Exercised	(758)	(828)	(2,858)
Forfeited	(47)	(67)	(170)
Outstanding, end of year	4,044	4,752	5,517
Exercisable at end of year	3,276	2,996	2,682
Weighted Average Exercise Price
Outstanding, beginning of year	$ 17.58	$ 17.19	$ 16.65
Granted	42.95	32.21	20.83
Exercised	17.24	17.39	17.18
Forfeited	17.00	16.13	15.86
Outstanding, end of year	18.25	17.58	17.19
Exercisable at end of year	$ 17.63	$ 17.57	$ 17.70
Weighted Average Remaining Contractual Life (in years)
Outstanding	4 years 9 months 26 days	5 years 6 months	6 years 22 days
Exercisable	4 years 5 months 1 day	4 years 8 months 1 day	4 years 6 months
Aggregate intrinsic value
Outstanding	$ 38,277	$ 107,970	$ 94,860
Exercisable	$ 31,625	$ 68,108	$ 44,752