WARRANTS - Summary of Assumptions to Use Option Pricing Model (Detail)	Sep. 30, 2021	Dec. 31, 2020	Mar. 31, 2018
Common Stock Warrants | 2018 Direct Registered Offering | Expected term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs			7.0
Common Stock Warrants | 2018 Direct Registered Offering | Expected volatility (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs			0.625
Common Stock Warrants | 2018 Direct Registered Offering | Risk-free interest rate (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs			0.028
Common Stock Warrants | 2018 Direct Registered Offering | Expected dividend yield (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs			0
2017 Placement Warrants | Expected term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	2.3	3.0
2017 Placement Warrants | Expected volatility (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0.871	0.869
2017 Placement Warrants | Risk-free interest rate (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0.004	0.002
2017 Placement Warrants | Expected dividend yield (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0	0
2016 Placement Warrants | Expected term (in years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	1.9	2.6
2016 Placement Warrants | Expected volatility (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0.866	0.863
2016 Placement Warrants | Risk-free interest rate (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0.003	0.002
2016 Placement Warrants | Expected dividend yield (%)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants, fair value measurement inputs	0	0