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Stock-Based Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
9 Months Ended1 Months Ended9 Months Ended
Sep. 30, 2011
Restricted stock units
Year
Jun. 30, 2011
Restricted stock units
Non-employee Directors
Sep. 30, 2011
Performance Based Restricted Units
Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]   
Restricted stock units granted in shares37,9006,738120,000
Restricted stock units, vesting period (in years) 1 year3 years
Fair value of restricted stock units$ 1.4$ 0.3$ 4.4
Restricted stock units, period of amortization (in years)5 3