Warrant Liabilities - Fair Value of Convertible Preferred Stock Warrant Liability (Detail)	Sep. 30, 2020	Dec. 31, 2019
Expected Dividend Yield [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.00
Series C Warrant [Member] | Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input		0.90
Series C Warrant [Member] | Contractual Term [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement term		2 months 1 day
Series C Warrant [Member] | Risk-free Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input		0.0152
2017 PIPE Warrant Liability [Member] | Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.23	0.99
2017 PIPE Warrant Liability [Member] | Contractual Term [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement term	2 months 12 days	1 year
2017 PIPE Warrant Liability [Member] | Risk-free Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0010	0.0160
2018 PIPE Warrant Liability [Member] | Volatility [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.00	0.99
2018 PIPE Warrant Liability [Member] | Contractual Term [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement term	3 years 2 months 12 days	4 years
2018 PIPE Warrant Liability [Member] | Risk-free Rate [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.0017	0.0156