Stockholders' Equity - Narrative (Details) - USD ($)		3 Months Ended				9 Months Ended
	Jan. 01, 2025	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024	Dec. 31, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock, voting rights						one
Total intrinsic value of options exercised		$ 700,000			$ 100,000	$ 700,000	$ 400,000
Nonvested award, cost not yet recognized		$ 100,000				$ 100,000
Stock compensation not yet recognized, vesting period						5 years 1 month 6 days
PSU vested in 2022 and released (in shares)		391,950
General and administrative expense
Class of Stock [Line Items]
Share-based payment arrangement expense		$ 1,700,000			1,800,000	$ 5,200,000	5,900,000
Research and development expense
Class of Stock [Line Items]
Share-based payment arrangement expense		$ 500,000			700,000	$ 1,600,000	1,800,000
Stock Plans
Class of Stock [Line Items]
Stock option plan, exercisable period						4 years
Stock Plans | Share-based payment arrangement, nonemployee
Class of Stock [Line Items]
Stock option plan, exercisable period						10 years
Stock Plans | One year from the vesting commencement date
Class of Stock [Line Items]
Stock option plan, vesting percentage						25.00%
Vesting period						1 year
Stock Plans | More than one year from vesting commencement date
Class of Stock [Line Items]
Stock option plan, vesting percentage						2.778%
Employee Stock | Employee Stock Purchase Plan
Class of Stock [Line Items]
Purchase price of common stock						85.00%
Number of shares authorized (in shares)								5,639,944		1,846,710
Evergreen shares reserve feature period						10 years
Percentage of fully diluted shares of common stock						1.00%
Increase in number of shares of authorized common stock (in shares)						3,693,420
Employee Stock | Stock Plans
Class of Stock [Line Items]
Common stock, shares reserved (in shares)	30,752,349							30,040,212
Stock options available for grant (in shares)		5,617,675				5,617,675
Employee Stock | 2021 Equity Incentive Plan
Class of Stock [Line Items]
Number of shares authorized (in shares)									18,467,109
Evergreen shares reserve feature period						10 years
Percentage of fully diluted shares of common stock						5.00%
Maximum percentage of share reserve, outstanding diluted stock						15.00%
Number of additional shares authorized (in shares)	712,137
RSU awards
Class of Stock [Line Items]
Vesting period						1 year 2 months 12 days
Fair value of options vested		$ 100,000			$ 1,000,000.0	$ 1,000,000.0	$ 2,400,000
Release period		60 days				60 days
Vested (in shares)		91,592	392,794	407,548
RSU awards | Stock Plans
Class of Stock [Line Items]
Vesting period						3 years
Requisite service period						3 years
RSU awards | Stock Plans | Tranche one
Class of Stock [Line Items]
Stock option plan, vesting percentage						33.30%
RSU awards | Stock Plans | Tranche two
Class of Stock [Line Items]
Stock option plan, vesting percentage						33.30%
RSU awards | Stock Plans | Tranche three
Class of Stock [Line Items]
Stock option plan, vesting percentage						33.30%
RSU awards | 2021 Equity Incentive Plan
Class of Stock [Line Items]
Stock compensation not yet recognized, vesting period						3 years
Cost not yet recognized, excluding options		$ 8,900,000				$ 8,900,000
Performance-based stock awards
Class of Stock [Line Items]
Share-based payment arrangement expense						$ 6,000,000
Performance-based stock awards | Stock Plans | Minimum
Class of Stock [Line Items]
Stock option plan, vesting percentage						0.00%
Performance-based stock awards | Stock Plans | Maximum
Class of Stock [Line Items]
Stock option plan, vesting percentage						300.00%
Performance-based stock awards | 2021 Equity Incentive Plan
Class of Stock [Line Items]
Vested (in shares)		57,600			25,200	157,300	79,200
Share-based payment arrangement expense		$ 0			$ 0	$ 0	$ 0