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Stock-Based Compensation - Schedule of Assumptions Used in Estimation of Fair Value of the Share-based Payment Awards on the Grant Date (Detail) - Options
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate 2.50% 2.20%
Volatility 128.40% 109.50%
Expected life (years)   4 years
Dividend yield 0.00% 0.00%
Minimum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected life (years) 3 years  
Maximum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected life (years) 5 years