Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Income Taxes [Line Items]
Effective tax rate as applied to pre-tax income	38.00%	(130.00%)	6.00%	49.00%
Unrecognized tax benefits	$ 13.9		$ 13.9		$ 14.1
Unrecognized tax benefits, affect effective tax rate if recognized	7.4		7.4		7.4
Estimated overall decrease in unrecognized tax benefits in the next twelve months due to the expiration of various statutes of limitations	13.1		13.1
Interest on income taxes accrued related to uncertain tax positions	2.4		2.4		2.1
Income tax penalties accrued related to uncertain tax positions	$ 0.1		$ 0.1		$ 0.1

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 amount of statutory penalties accrued as of the date of the statement of financial position 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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- Definition

This element represents the amount of interest expense accrued as of the date of the statement of financial position 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.

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