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Stock-Based Compensation - Additional Information (Detail) (USD $)
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2012
Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of RSUs and restricted stock granted       
Estimated forfeitures for stock options   1.60% 1.60%
Forfeitures rate for restricted stock units   0.00% 0.00%
Unamortized compensation cost $ 15.8 $ 15.8  
Recognition period of non-vested compensation cost   2 years 4 months 24 days  
Total pre-tax intrinsic value of options exercised $ 0.5 $ 4.1  
Restricted Stock Units (RSUs) [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of RSUs and restricted stock granted   0 0
Restricted Stock [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of RSUs and restricted stock granted   0 0