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Share-Based Compensation Plans - Fair Value of Options as of Grant Dates Using Weighted Average Assumptions (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average fair value   $ 6.98 $ 10.74
Expected volatility   41.85% 47.50%
Expected life (years)   6 years 6 months 6 years 6 months
Risk-free interest rate   2.58% 2.87%
Dividend yield 0.00% 0.00% 0.00%