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
6 Months Ended 12 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Income Tax Disclosure [Abstract]      
Increase in unrecognized tax benefits $ 0 $ 0.3  
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
Reduction of reserve     0.4
Valuation allowance to offset deferred tax asset $ 2.9