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Fair Value Stock Options at Grant Date using Weighted-Average Assumption (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Weighted Average Fair Values [Line Items]      
Historical volatility 61.00% 60.00% 73.00%
Expected term (years) 6 years 5 years 7 months 6 days 5 years
Risk-free interest rate 1.10% 1.96% 2.18%
Expected dividend yield 0.86% 0.89% 0.00%