Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
May 31, 2013	May 31, 2012	May 31, 2013	May 31, 2012	Aug. 31, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate	7.70%	13.80%	12.50%	19.80%
Discrete period income tax benefits related to changes in tax law and the reinstatement of the U.S federal research and development tax credit	$ 0.7
Reversal of tax reserves established in prior years	9.3
Gross liability for unrecognized tax benefits, excluding interest and penalties	18.2		18.2		24.6
Liabilities for payment of interest and penalties related to its unrecognized tax benefits	$ 2.8		$ 2.8		$ 4.5

A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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This element represents the total of accruals as of the date of the statement of financial position for interest recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity and the amount of statutory penalties for a tax position claimed or expected to be claimed by the entity, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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