Quarterly report pursuant to Section 13 or 15(d)

Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail)

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Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail)
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]        
Expected term 5 years 6 months 4 years 2 months 12 days 5 years 10 months 24 days 3 years 9 months 18 days
Volatility 87.70% 96.50% 91.01% 97.91%
Risk-free interest rate 1.54% 1.69% 1.65% 1.66%