Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013	Aug. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate	29.00%	15.70%	17.60%	16.00%
Discrete item, changes in foreign statutory tax rates	$ 0.7
Discrete item, change in tax law and reinstatement of US Federal research and development tax credit		1.2
Reversal of tax reserves		2.4
Gross liability for unrecognized tax benefits, excluding interest and penalties	19.2		19.2		18.0
Liabilities for payment of interest and penalties related to its unrecognized tax benefits	$ 3.4		$ 3.4		$ 2.9