Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Assumption Used to Determine Fair Value of Warrant Liability (Detail)

v3.19.2
Fair Value Measurements - Assumption Used to Determine Fair Value of Warrant Liability (Detail)
Jun. 30, 2019
yr
Dec. 31, 2018
yr
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 0.17 0.67
Representative's Warrant [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 124.2 70.9
Representative's Warrant [Member] | Risk-free Interest Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 1.92 2.63
2016 Warrants [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 100.58 72.6
2016 Warrants [Member] | Remaining Contractual term (in years) [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 2.08 2.58
2016 Warrants [Member] | Risk-free Interest Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 1.75 2.46
2017 Warrants [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 97.1 87.3
2017 Warrants [Member] | Remaining Contractual term (in years) [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 3.08 3.58
2017 Warrants [Member] | Risk-free Interest Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 1.71 2.49