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Stock Incentive Plan - Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Estimate Fair Value of Stock Options (Details) - Stock Options - Employees and Directors
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate, minimum 1.90% 1.90%
Risk-free interest rate, maximum 2.30% 2.60%
Expected volatility, minimum 82.00% 82.00%
Expected volatility, maximum 83.00% 83.00%
Minimum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term (in years) 5 years 6 months 5 years 6 months
Maximum    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term (in years) 6 years 1 month 6 days 6 years 9 months 18 days