Equity Incentive Plans and Stock-Based Compensation - Incentive Stock Options and Nonqualified Stock Options - Additional Information (Details) - Incentive Stock Options and Nonqualified Stock Options - $ / shares	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value of stock option			$ 5.14	$ 4.37
Non-employee Director | Third Rock Ventures
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option, vesting period	3 years
Option granted	26,573
Grant date fair value of stock option	$ 100,000
Vesting rights			The common shares subject to these options vest 1/12th on the last day of each calendar quarter over a three-year period and commenced vesting upon the Company’s IPO in June 2020.
2015 Equity and 2020 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option, vesting period			4 years
Stock option, expiration period			10 years
Option granted			1,567,198	1,220,104
Shares of Common Stock Available for Future Grants under the 2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted		292,001