Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Income Tax Contingency [Line Items]
Effective tax rate attributable to continuing operations	26.70%	30.40%	30.40%	32.20%
Increase in unrecognized tax benefits			$ 3.6
Gross accrued interest and penalties on unrecognized tax benefits	0.9		0.9		0.6
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates	9.2		9.2		5.4
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates , interest and penalties	$ 0.7		$ 0.7		$ 0.5

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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