Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015
Stock Options
Outstanding, beginning of year	3,306	4,044	4,752
Granted	111	154	97
Exercised	(1,076)	(874)	(758)
Forfeited	(34)	(18)	(47)
Outstanding, end of year	2,307	3,306	4,044
Exercisable at end of year	2,067	3,059	3,276
Weighted Average Exercise Price
Outstanding, beginning of year	$ 19.01	$ 18.25	$ 17.58
Granted	42.30	30.92	42.95
Exercised	16.90	17.22	17.24
Forfeited	29.95	32.25	17.00
Outstanding, end of year	20.99	19.01	18.25
Exercisable at end of year	$ 19.17	$ 17.85	$ 17.63
Weighted Average Remaining Contractual Life (in years)
Outstanding	3 years 11 months 12 days	4 years 3 months 29 days	4 years 9 months 25 days
Exercisable	3 years 5 months 20 days	4 years 4 days	4 years 5 months 1 day
Aggregate intrinsic value
Outstanding	$ 48,509	$ 61,178	$ 38,277
Exercisable	$ 47,488	$ 60,082	$ 31,625