Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Activity Under Stock Option Plans

Activity under the Company’s stock option plans during the year ended December 31, 2022 was as follows:

				Weighted-		Weighted-		Aggregate
				Average		Average		Intrinsic
	Options			Exercise		Remaining		Value
	Outstanding			Price		Term		(000’s)
Balance at December 31, 2021		6,553,594		$	16.07
Granted		4,139,204		$	19.54
Exercised		(524,774	)	$	9.00
Forfeited and expired		(410,695	)	$	19.28
Balance at December 31, 2022		9,757,329		$	17.79		8.0	$	23,149
Vested and expected to vest at December 31, 2022		9,757,329		$	17.79		8.0	$	23,149
Exercisable at December 31, 2022		4,122,612		$	15.90		6.6	$	18,493

Weighted Average Assumptions Used to Estimate Fair Value of Stock Options Granted to Employees

The following table summarizes the weighted average assumptions used to estimate the fair value of stock options granted under the Company’s stock option plans and the shares purchasable under the ESPP during the periods presented:

	Year ended December 31,
Stock Option Awards	2022			2021			2020
Expected term	6.1 years			6.0 years			6.0 years
Expected volatility		88	%		86	%		78	%
Risk free interest rate		2.8	%		1.0	%		0.8	%
Expected dividend yield		—	%		—	%		—	%

	Year ended December 31,
ESPP	2022			2021			2020
Expected term	1.3 years			1.6 years			1.4 years
Expected volatility		87	%		91	%		84	%
Risk free interest rate		4.1	%		0.3	%		0.2	%
Expected dividend yield		—	%		—	%		—	%

Summary of Stock-based Compensation Expense for the Equity Awards Issued to Employees and Non-Employees

Stock-based compensation expense for the equity awards issued by the Company to employees and non-employees for the periods presented below was as follows (in thousands):

	Year ended December 31,
	2022		2021		2020
Included in research and development	$	15,078	$	9,654	$	5,218
Included in general and administrative		13,190		7,698		5,209
Total stock-based compensation expense	$	28,268	$	17,352	$	10,427