WARRANTS - Summary of Assumptions to Use Option Pricing Model (Detail)	Jun. 30, 2021	Dec. 31, 2020
Common Stock Warrants | 2018 Direct Registered Offering | Expected Term
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Expected term (in years)	7 years
Common Stock Warrants | 2018 Direct Registered Offering | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.625
Common Stock Warrants | 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 Warrants | 2018 Direct Registered Offering | Expected Dividend Yield
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0
2017 Placement Warrants | Expected Term
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Expected term (in years)	2 years 7 months 6 days	3 years
2017 Placement Warrants | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.887	0.869
2017 Placement Warrants | Risk-free Interest Rate
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.003	0.002
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)	2 years 1 month 6 days	2 years 7 months 6 days
2016 Placement Warrants | Expected Volatility
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.880	0.863
2016 Placement Warrants | Risk-free Interest Rate
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.002	0.002
2016 Placement Warrants | Expected Dividend Yield
Fair Value Inputs1 Liabilities Quantitative Information [Line Items]
Warrants, fair value measurement inputs	0.000	0.000