Stockholders' Equity - Additional Information (Details)			1 Months Ended							3 Months Ended			4 Months Ended	9 Months Ended		12 Months Ended
	Dec. 16, 2020 USD ($) $ / shares shares	Oct. 29, 2019 USD ($) $ / shares shares	Aug. 31, 2021 shares	Jan. 31, 2021 shares	Nov. 30, 2020 USD ($)	Nov. 30, 2019 $ / shares shares	Oct. 31, 2019 shares	May 31, 2019 shares	Mar. 31, 2019 shares	Sep. 30, 2021 USD ($) shares	Mar. 31, 2021 shares	Sep. 30, 2020 USD ($)	May 06, 2019 USD ($) shares	Sep. 30, 2021 USD ($) $ / shares shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 shares	Jan. 01, 2021 shares	Jan. 01, 2020 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Preferred stock, shares authorized										40,000,000				40,000,000		40,000,000
Preferred stock, shares issued										0				0		0
Preferred stock, shares outstanding										0				0		0
Stock options, granted														1,568,250
Stock-based compensation cost | $										$ 4,419,000		$ 2,070,000		$ 12,474,000	$ 3,461,000
Common stock initially reserved for issuance										14,887,549				14,887,549
Unrecognized stock-based compensation expense | $										$ 49,400,000				$ 49,400,000
Unrecognized stock-based compensation expense, weighted-average period for recognition														2 years 10 months 24 days
Defined contribution plan employer contribution expense | $										$ 100,000				$ 700,000		$ 300,000
Defined contribution plan, employer matching contribution, percentage										75.00%				75.00%		75.00%
Employer discretionary match number of shares settled			18,394	8,356
Dividend yield														0.00%
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield														0.00%
2019 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized for issuance																	2,231,739
Stock options, granted																	1,400,528
Number of shares available for issuance							0
2019 Equity Incentive Plan | Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards, granted																	16,260
2019 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized for issuance																1,158,580
Stock options, granted														1,568,250
Number of shares available for issuance										1,931,919				1,931,919
Annual increase to shares available for issuance percentage of outstanding common stock							5.00%
Equity plan, description							The number of shares initially available for issuance will be increased by (i) the number of shares subject to stock options or similar awards granted under the Existing Incentive Plan that expire or otherwise terminate without having been exercised in full after the effective date of the 2019 Plan and unvested shares issued pursuant to awards granted under the Existing Incentive Plan that are forfeited to or repurchased by the Company after the effective date of the 2019 Plan, with the maximum number of shares to be added to the 2019 Plan pursuant to clause (i) above equal to 1,416,788 shares, and (ii) an annual increase on January 1 of each calendar year beginning in 2020 and ending in 2029, equal to the lesser of (a) 5% of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (b) such smaller number of shares as determined by the board of directors. As of September 30, 2021, 1,931,919 shares of common stock remain available for issuance, which includes 1,568,250 stock options and 130,050 performance-based units granted during the nine months ended September 30, 2021 as well as the annual increases of 1,250,511 and 1,158,580 shares that were authorized on January 1, 2021 and 2020.
Number of shares remain available for issuance, annual increase																		1,250,511
Common stock initially reserved for issuance										1,931,919				1,931,919
2019 Incentive Award Plan | Performance-Based Stock Units (PSU)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards, granted														130,050		220,000
Stock-based compensation cost | $														$ 0
Unrecognized stock-based compensation expense | $										$ 10,900,000				$ 10,900,000
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance										842,036				842,036
Annual increase to shares available for issuance percentage of outstanding common stock							1.00%
Equity plan, description							In addition, the number of shares available for issuance under the ESPP will be annually increased on January 1 of each calendar year beginning in 2020 and ending in 2029, by an amount equal to the lesser of: (i) 1% of the shares outstanding on the final day of the immediately preceding calendar year and (ii) such smaller number of shares as is determined by the board of directors. As of September 30, 2021, 842,036 shares of common stock remain available for issuance, which includes the 30,237 shares sold to employees during the nine months ended September 30, 2021 as well as the annual increases of 312,628 and 289,645 shares that were authorized on January 1, 2021 and 2020 respectively.
Number of shares remain available for issuance, annual increase																		312,628	289,645
Stock-based compensation cost | $										$ 100,000				$ 300,000
Common stock initially reserved for issuance							270,000			842,036				842,036
Number of shares issued														30,237
Estimated weighted-average fair value | $ / shares														$ 14.66
Unrecognized stock-based compensation expense | $										$ 100,000				$ 100,000
Unrecognized stock-based compensation expense, weighted-average period for recognition														3 months 18 days
Dividend yield														0.00%
Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued	2,250,000
Common stock, price per share | $ / shares		$ 42.00
Proceeds from issuance initial public offering gross | $	$ 94,500,000
Purchase price per share after deducting underwriting discounts and commissions | $ / shares	$ 39.48
Net proceeds after deducting underwriters commission | $	$ 88,800,000
Purchase of additional offering expenses | $	$ 200,000
At-the-Market Offering Program
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued														0
Employee and Nonemployee Director
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated weighted-average fair value | $ / shares														$ 23.20
Open Market Sale Agreement with Jefferies LLC | At-the-Market Offering Program
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from issuance of shares | $					$ 125,000,000.0
Percentage of gross sales price per share sold					3.00%
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued													2,524,852
Number of shares authorized to repurchase									3,373,408
Stock repurchase program, number of shares right lapse									843,352
Remaining number of shares to be repurchased									2,530,056
Stock repurchase program, period in force									48 months
Stock repurchase program expiration date									Mar. 31, 2023
Proceeds from issuance of shares | $													$ 1,000
Repurchase right lapse each month after first anniversary, shares													0.000208
Repurchases of shares						17,560
Shares aggregate repurchase price | $ / shares						$ 5.20
Employer discretionary match number of shares settled										18,394	8,356
Common Stock | 2019 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional number of shares available for issuance							1,416,788
Common Stock | Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum percentage of eligible compensation contributed by participants							20.00%
Common Stock | IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		10,997,630
Common stock, price per share | $ / shares		$ 19.00
Proceeds from Initial Public Offering (IPO) | $		$ 191,500,000
Common Stock | Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued		1,434,473
Common Stock | Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining number of shares to be repurchased										893,014				893,014
Common Stock | First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase right lapse rate													25.00%
Common Stock | Takeda License
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued								1,084,000
Common Stock | Founders
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining number of shares to be repurchased										474,385				474,385
Common Stock | Frazier
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued									1,491,072