Stockholders' Equity (Deficit) (Tables)

12 Months Ended

Dec. 31, 2021

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 and contractual term data):

	Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		3,788		$	9.06
Granted		2,671			23.23
Exercised		(172	)		5.42
Forfeited/expired		(509	)		22.99
Outstanding at December 31, 2021		5,778		$	14.49		8.5	$	58,950
Vested and expected to vest at     December 31, 2021		5,778		$	14.49		8.5	$	58,950
Exercisable at December 31, 2021		1,885		$	8.91		7.8	$	29,226

Schedule of Assumptions used in Black-Scholes Model to Determine Fair Value of Stock/Unit Option Grants and Shares Purchasable under ESPP

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

	Year Ended December 31,
Stock/Unit Option Grants	2021	2020	2019
Risk-free interest rate	0.5% - 1.3%	0.3% - 1.5%	1.4% - 2.7%
Expected volatility	86% - 88%	88% - 92%	84% - 88%
Expected term (in years)	5.5 - 6.1	5.4 - 6.1	2.0 - 6.1
Expected dividend yield	—%	—%	—%

	Year Ended December 31,
ESPP	2021	2020	2019
Risk-free interest rate	0.1%	0.1% - 0.2%	N/A
Expected volatility	69% - 75%	75% - 96%	N/A
Expected term (in years)	0.5	0.5	N/A
Expected dividend yield	—%	—%	N/A

Schedule of Allocated Stock-based Compensation Expense

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

	Year Ended December 31,
	2021		2020		2019
Research and development expense	$	9,228	$	1,895	$	84
General and administrative expense		7,828		2,415		322
Total stock-based compensation expense	$	17,056	$	4,310	$	406

Schedule of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance consisted of the following (in thousands):

	December 31,
	2021		2020
Common stock options issued and outstanding		5,778		3,788
Equity awards available for future issuance    under equity plans		2,575		2,852
Common stock authorized under the ESPP		639		296
Total		8,992		6,936