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Number of additional shares authorized for issuance under share-based payment arrangement.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Stockholders' Equity - Additional Information (Details) - USD ($)		1 Months Ended					3 Months Ended			4 Months Ended	9 Months Ended		12 Months Ended
	Oct. 29, 2019	Jul. 31, 2020	Nov. 30, 2019	Oct. 31, 2019	May 31, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	May 06, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jan. 01, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from Initial Public Offering (IPO)												$ (1,299,000)
Preferred stock, shares authorized							40,000,000				40,000,000
Preferred stock, shares issued							0				0		0
Preferred stock, shares outstanding							0				0		0
Stock options, granted											1,134,977
Stock-based compensation cost							$ 2,070,000	$ 37,000			$ 3,461,000	$ 66,000
Common stock initially reserved for issuance							13,423,199				13,423,199
Unrecognized stock-based compensation expense							$ 24,700,000				$ 24,700,000
Unrecognized stock-based compensation expense, weighted-average period for recognition											3 years 9 months 18 days
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				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]
Stock options, granted											1,134,977
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. The Company initially had 2,700,000 shares of common stock available for issuance under the 2019 Plan, of which, 1,134,977 stock options were granted and 204,750 performance-based units were granted during the nine months ended September 30, 2020. As of September 30, 2020, 2,518,853 shares remain available for issuance, which includes the annual increase of 1,158,580 shares that were authorized on January 1, 2020.
Number of shares remain available for issuance, annual increase														1,158,580
Common stock initially reserved for issuance							2,518,853				2,518,853
2019 Incentive Award Plan \| Performance-Based Stock Units (PSU)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock awards, granted		204,750									204,750
Stock-based compensation cost											$ 0
Unrecognized stock-based compensation expense							$ 6,600,000				$ 6,600,000
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for issuance							559,645				559,645
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, 2020, 559,645 shares of common stock remain available for issuance, which includes the annual increase of 289,645 shares that were authorized on January 1, 2020.
Number of shares remain available for issuance, annual increase														289,645
Stock-based compensation cost							$ 100,000				$ 100,000
Common stock initially reserved for issuance				270,000			559,645				559,645
Estimated weighted-average fair value											$ 13.66
Unrecognized stock-based compensation expense							$ 400,000				$ 400,000
Unrecognized stock-based compensation expense, weighted-average period for recognition											1 year
Dividend yield											0.00%
Employee and Nonemployee Director
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated weighted-average fair value											$ 18.68
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 common stock										$ 1,000,000
Repurchase right lapse each month after first anniversary, shares										0.000208
Repurchases of shares			17,560
Shares aggregate repurchase price			$ 5.20
Common Stock \| 2019 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares authorized for issuance				2,700,000
Number of shares available for issuance							2,518,853				2,518,853
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]
Shares issued											0
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	$ 19.00
Proceeds from Initial Public Offering (IPO)	$ 191,500,000
Common Stock \| Underwriters
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							1,467,128				1,467,128
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				1,084,000
Common Stock \| Founders
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining number of shares to be repurchased							1,581,285				1,581,285
Common Stock \| Frazier
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued						1,491,072