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Weighted Average Assumptions used in Determining Fair Value of Common Stock Options (Detail)
6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Expected volatility 55.00% 52.60%
Risk-free interest rate 1.15% 0.80%
Expected term 5 years 7 months 6 days 5 years 1 month 6 days
Dividend yield 0.00% 0.00%