Common Stock and Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

Common Stock Reserved for Future Issuance

The following shares of common stock were reserved for future issuance as of December 31, 2019 (in thousands):

Class A-1 convertible preferred stock outstanding (as-converted)	4,159
Class A-2 convertible preferred stock outstanding (as-converted)	32,884
Initial Closing warrants	13,890
Milestone Closing warrants	32,884
Common stock options outstanding	3,098
RSUs outstanding	129
Common stock available for future grant under the 2019 Equity Incentive Plan	404
Employee Stock Purchase Plan	192
Total common shares reserved for future issuance	87,640

Stock Option Activity

The following table summarizes our stock option activity under all equity incentive plans for the year ended December 31, 2019 (shares and aggregate intrinsic value in thousands):

	Number of options		Weighted average exercise price		Weighted average remaining contractual term	Aggregate intrinsic value
Options outstanding at December 31, 2018	59		$	45.60
Granted	3,224		$	0.68
Exercised	(3	)	$	0.95
Canceled/forfeited/expired	(182	)	$	6.81
Options outstanding at December 31, 2019	3,098		$	1.17	9.6	$	703
Exercisable at December 31, 2019	237		$	6.78	8.5	$	35

Schedule of Restricted Stock Units Activity

The following table summarizes our RSU activity under all equity incentive plans for the year ended December 31, 2019 (shares and aggregate intrinsic value in thousands): 

	Number of options		Weighted average grant date fair value		Weighted average remaining contractual term	Aggregate intrinsic value
RSUs outstanding at December 31, 2018	601		$	1.50
Granted	287		$	0.95
Vested	(559	)	$	1.27
Canceled/forfeited/expired	(200	)	$	1.34
RSUs outstanding at December 31, 2019	129		$	1.50	0.8	$	115

Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan

The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2012 Equity Incentive Plan, 2015 Inducement Plan, 2019 Equity Incentive Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented:

	Year ended December 31,
	2019		2018
Stock options
Risk-free interest rate	1.7	%	2.7	%
Volatility	94.6	%	87.8	%
Dividend yield	—		—
Expected term (years)	6.1		6.1
Performance stock options
Risk-free interest rate	2.6	%	2.7	%
Volatility	93.8	%	87.4	%
Dividend yield	—		—
Expected term (years)	6.1		5.7
Employee stock purchase plan shares
Risk-free interest rate	2.3	%	1.9	%
Volatility	110.5	%	100.6	%
Dividend yield	—		—
Expected term (years)	0.5		0.5

Stock-Based Compensation

The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands):

	Year ended December 31,
	2019		2018
Research and development	$	309	$	2,256
General and administrative	1,979		3,184
Total	$	2,288	$	5,440