Summary of Non-Vested Stock Option Awards (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Number of Stock Options
Non-vested, beginning of year	2,835
Granted	130	1,034	600
Vested	(1,142)
Forfeited	(67)
Non-vested, end of year	1,756	2,835
Weighted Average Grant Date Fair Value Per Share
Non-vested, beginning of year	$ 5.96
Granted	$ 11.82
Vested	$ 6.02
Forfeited	$ 5.45
Non-vested, end of year	$ 6.38	$ 5.96