Warrants - Summary of Assumptions to Use Option Pricing Model (Detail)	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2018
Common Stock | 2018 Direct Registered Offering | Expected Term
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Expected term (in years)			7 years
Common Stock | 2018 Direct Registered Offering | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs			0.625
Common Stock | 2018 Direct Registered Offering | Risk-free Interest Rate
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs			0.028
Common Stock | 2018 Direct Registered Offering | Expected Dividend Yield
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs			0.00
2017 Placement Warrants | Expected Term
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Expected term (in years)	3 years 9 months 18 days	4 years
2017 Placement Warrants | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.729	0.680
2017 Placement Warrants | Risk-free Interest Rate
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.003	0.017
2017 Placement Warrants | Expected Dividend Yield
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.000	0.000
2016 Placement Warrants | Expected Term
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Expected term (in years)	3 years 4 months 24 days	3 years 7 months 6 days
2016 Placement Warrants | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.719	0.675
2016 Placement Warrants | Risk-free Interest Rate
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.003	0.016
2016 Placement Warrants | Expected Dividend Yield
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.000	0.000