Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Fair Value Measurements - Assumption Used to Determine Fair Value of Warrant Liability (Detail)
Mar. 31, 2019
yr
Dec. 31, 2018
yr
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 0.42 0.67
Representative's Warrant [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 181.4 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 2.40 2.63
2016 Warrants [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 96.6 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 2.33 2.58
2016 Warrants [Member] | Risk-free Interest Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 2.27 2.46
2017 Warrants [Member] | Expected Volatility [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 93.9 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 3.33 3.58
2017 Warrants [Member] | Risk-free Interest Rate [Member]    
Fair Value Measurement Inputs and Valuation Techniques [Line Items]    
Fair value of warrant liability 2.21 2.49