Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Nov. 30, 2012	Nov. 30, 2011	Nov. 30, 2012	Nov. 30, 2011
Income Tax [Line Items]
Effective income tax rate	35.10%	29.20%	41.30%	29.60%
Unrecognized tax benefits	$ 7.4		$ 7.4
Unrecognized tax benefits that would impact effective tax rate, if recognized	6.5		6.5
Accrued interest and penalties related to unrecognized tax benefits	5.7		5.7
Reserve for uncertain tax positions, current	$ 1.5		$ 1.5

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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