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Additional Information with Respect to Non-vested Options (Detail) (Employee Stock Option, USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Year
Employee Stock Option
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Aggregate intrinsic value $ 3.3
Weighted-average remaining contractual term 8.56
Weighted-average remaining expected term 3.45
Weighted-average remaining vesting period 1.52
Unrecognized compensation cost $ 6.7