Summary of Non-Vested Stock Option Awards (Detail) - $ / shares shares in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Number of Stock Options
Non-vested, beginning of year	1,756
Granted	97	130	1,034
Vested	(1,038)
Forfeited	(47)
Non-vested, end of year	768	1,756
Weighted Average Grant Date Fair Value Per Share
Non-vested, beginning of year	$ 6.38
Granted	15.98
Vested	6.32
Forfeited	6.33
Non-vested, end of year	$ 7.66	$ 6.38