Summary of Non-Vested Stock Option Awards (Detail) - $ / shares shares in Thousands	12 Months Ended
	May 31, 2017	May 31, 2016	May 31, 2015
Number of Stock Options
Non-vested, beginning of year	247
Granted	111	154	97
Vested	(84)
Forfeited	(34)
Non-vested, end of year	240	247
Weighted Average Grant Date Fair Value Per Share
Non-vested, beginning of year	$ 10.91
Granted	10.32
Vested	11.57
Forfeited	13.84
Non-vested, end of year	$ 9.99	$ 10.91