Quarterly report pursuant to Section 13 or 15(d)

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Income Taxes [Line Items]      
Increase in unrecognized tax benefits $ 0 $ 0.03  
Liabilities for unrecognized tax benefits     1.3
Unrecognized tax benefit, interest accrued net of federal income tax benefits     0.02
Unrecognized tax benefits, penalty     0.02
Additional reduction of reserve     0.4
Valuation allowance to offset deferred tax asset $ 2.9