Quarterly report pursuant to Section 13 or 15(d)

Stock Options - Summary of Assumptions Used Principally in Determining Fair Value of Options Granted (Detail)

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Stock Options - Summary of Assumptions Used Principally in Determining Fair Value of Options Granted (Detail) - Stock Options [Member]
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk free interest rate 1.98% 1.94%
Expected dividend yield 0.00% 0.00%
Expected term in years 8 years 7 months 2 days 6 years 3 months
Expected volatility 97.00% 91.59%
Estimated forfeiture rate 0.65% 20.00%