Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Aug. 31, 2017 USD ($) $ / shares shares
Number of Stock Option Outstanding
Beginning Balance | shares	3,478,062
Granted | shares	307,390
Exercised | shares	(461,355)
Forfeited | shares	(132,467)
Ending Balance | shares	3,191,630
Options exercisable at end of Period | shares	2,340,204
Weighted Average Exercise Price
Beginning Balance | $ / shares	$ 23.96
Granted | $ / shares	26.95
Exercised | $ / shares	21.65
Forfeited | $ / shares	28.34
Ending Balance | $ / shares	24.40
Options exercisable at end of Period | $ / shares	$ 24.22
Option Outstanding weighted average remaining term	4 years 9 months 6 days
Option exercisable weighted average remaining term	3 years 7 months 2 days
Stock option, aggregate intrinsic Value | $	$ 5.6
Stock option, aggregate intrinsic Value | $	$ 5.0