Warrant Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Series C Warrant [Member]

Fair Value of Convertible Preferred Stock Warrant Liability

The Company used the following inputs.

	December 31, 2019			December 31, 2018
Volatility		90	%		90	%
Contractual term (years)		0.17			1.17
Expected dividend yield		—	%		—	%
Risk-free rate		1.52	%		2.60	%

2017 PIPE Warrant Liability [Member]

Fair Value of Convertible Preferred Stock Warrant Liability

The following summarizes certain key assumptions used in estimating the fair values.

	December 31, 2019			December 31, 2018
Volatility		99	%		75	%
Contractual term (years)		1.0			2.0
Expected dividend yield		—	%		—	%
Risk-free rate		1.60	%		2.51	%

2018 PIPE Warrant Liability [Member]

Fair Value of Convertible Preferred Stock Warrant Liability

The following summarizes certain key assumptions used in estimating the fair values.

	December 31, 2019			December 31, 2018
Volatility		99	%		75	%
Contractual term (years)		4.0			5.0
Expected dividend yield		—	%		—	%
Risk-free rate		1.56	%		2.51	%