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Stock-Based Compensation Arrangements - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized stock-based compensation cost, pre-tax $ 19.5
Weighted average remaining vesting period for unrecognized pre-tax stock-based compensation expense, in years 1 year 7 months 6 days
Employees And Non-Employee Directors
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Shares tendered to satisfy tax withholding requirements on vesting of restricted stock 70,117
Average price per share on which shares are tendered to satisfy tax withholding requirements on vesting of restricted stock $ 30.47