Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2022

Equity [Abstract]

Schedule of Shares of Common Stock Reserved for Issuance

As of March 31, 2022 and December 31, 2021, the Company had reserved shares of common stock for issuance as follows (in thousands):

	March 31, 2022	December 31, 2021
Reserve balance for Sales Agreement	14,183	14,183
Common stock options outstanding	13,240	10,485
Common stock options available for grant	6,937	6,698
ESPP shares available for purchase	507	507
401(k) Matching Plan (1)	200	18
Total	35,067	31,891

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(1)The Company sponsors a 401(k) defined contribution plan for its employees. Employee contributions are voluntary. In December 2011, the Company adopted the 401(k) Matching Plan, under which the Company made matching contributions in the form of common stock at a rate of $1.00 for each $2.00 of employee contributions up to a maximum $750 of common stock per employee per year. Effective January 1, 2022, the Company increased its matching contributions to a rate of $1.00 for each $2.00 of employee contributions up to a maximum $3,500 of common stock per employee per year. Effective January 1, 2022, the Company increased shares of common stock reserved pursuant to the 401(k) Matching Plan to 200,000 shares from 17,813 shares of common stock as of December 31, 2021.

Summary of Activity under 2008 Plan and 2018 Plan

A summary of the activity under the 2008 Plan and the 2018 Plan is as follows:

	Outstanding Options			Weighted Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (In Thousands)
	Number of Options (In Thousands)	Weighted Average Exercise Price
Balances at December 31, 2021	10,485	$	15.79	6.68	$	52,349
Options granted	3,007	15.26
Options exercised	(125)	5.36
Options cancelled	(127)	21.57
Balances at March 31, 2022	13,240	$	15.71	7.22	$	35,840
Vested and expected to vest at March 31, 2022	12,727	$	15.56	7.14	$	35,799
Exercisable at March 31, 2022	8,603	$	13.13	6.00	$	35,691

Summary of Stock Based Compensation Expense

Employee and director stock-based compensation expense was allocated as follows (in thousands):

	Three Months Ended March 31,
	2022		2021
Research and development	$	4,138	$	3,504
General and administrative	3,609		3,011
Total stock-based compensation expense	$	7,747	$	6,515