Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2022

Equity [Abstract]

Summary of Stock Option Activity

Stock option activity for employee and nonemployee awards and related information is as follows (in thousands, except per share data):

	Number of Options			Weighted- Average Exercise Price Per Share
Outstanding at December 31, 2021		5,778		$	14.49
Granted		2,655			14.95
Exercised		(7	)		1.48
Forfeited/expired		(142	)		22.26
Outstanding at March 31, 2022		8,284		$	14.51

Schedule of Assumptions Used in Black-Scholes Model Pricing Model to to Determine Fair Value of Stock Option and Shares Purchasable Under ESPP

The assumptions used in the Black-Scholes model to determine the fair value of stock option grants and shares purchasable under the ESPP were as follows:

	Three Months Ended March 31,
Stock Option Grants	2022	2021
Risk-free interest rate	1.5% - 1.9%	0.5% - 1.1%
Expected volatility	85%	88%
Expected term (in years)	6.0 - 6.1	5.8 - 6.1
Expected dividend yield	—%	—%

	Three Months Ended March 31,
ESPP	2022	2021
Risk-free interest rate	N/A	N/A
Expected volatility	N/A	N/A
Expected term (in years)	N/A	N/A
Expected dividend yield	N/A	N/A

Schedule of Allocated Stock-based Compensation Expense

The allocation of stock-based compensation expense was as follows (in thousands):

	Three Months Ended March 31,
	2022		2021
Research and development expense	$	3,266	$	2,010
General and administrative expense		2,972		1,691
Total stock-based compensation expense	$	6,238	$	3,701