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Estimated Fair Value of Options Granted using Black-Scholes Option-Pricing Model with Weighted-Average Assumptions (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected life (years) 10 years 5 years 183 days 9 years 40 days 5 years 183 days
Interest rate 1.60% 1.60% 1.50% 1.60%
Volatility 53.40% 50.80% 53.00% 50.80%
Dividend yield     0.00%