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Share-based compensation arrangement by share-based payment award award vesting description.

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Stock options repriced during period.

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Stock options repriced during period exercise price per share.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Aggregate number of common shares reserved for future issuance.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Description of service or performance condition required to be met for earning right to award under share-based payment arrangement. Includes, but is not limited to, combination of market, performance or service condition.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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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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An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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Percentage of vesting of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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Stock-Based Compensation - Additional Information (Details) - USD ($)					1 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended		12 Months Ended	43 Months Ended
	Jul. 24, 2019	Jul. 02, 2019	Apr. 03, 2019	Jun. 08, 2016	Jun. 30, 2020	Jan. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Apr. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for future issuance							14,280,326			14,280,326		13,781,623	13,781,623
Share-based awards, vesting conditions										As of September 30, 2020, the Company has granted service-based awards, which vest over a defined period of service, and performance-based and market-based awards, which vest upon the achievement of defined conditions. Service-based awards generally vest over a four-year period, with the first 25% vesting following twelve months of continued employment or service, and the remainder vesting in twelve quarterly installments over the following three years. In 2016, 2018 and 2019, the Company granted stock option awards to certain employees with terms that allow for vesting upon the achievement of performance conditions specific to the Company’s corporate goals, including but not limited to certain research, business development and liquidity milestones. Also in 2018, the Company granted a stock option award to a non-employee with service conditions that provide for accelerated vesting upon the consummation of an initial public offering. Additionally, in 2016 the Company granted stock option awards to an executive with terms that provide for vesting upon the achievement of both performance and market conditions, as the awards vest upon the occurrence of certain events, including the consummation of an initial public offering, and market conditions subject to a specified return to certain of the Company’s investors. This award was modified in July 2019 to a service-based award.
Share-based awards, vesting period										4 years
Stock option, expiration period										10 years
Treasury stock, shares							0			0
Weighted average grant date fair value per share of options granted							$ 9.67	$ 6.38		$ 8.52	$ 9.35
Aggregate intrinsic value of stock options exercised							$ 100,000	$ 100,000		$ 1,000,000	$ 100,000
Shares granted										623,935
Fair value per share of common stock		$ 10.25	$ 24.32
Stock options repriced during period exercise price per share	$ 10.25
Stock options repriced during period									1,089,147
Stock-based compensation expense							1,820,000	$ 2,349,000		$ 4,961,000	$ 4,883,000
Total unrecognized compensation expense related to option awards							$ 16,000,000			$ 16,000,000
Weighted-average period of unrecognized compensation expense related to option awards										2 years 8 months 12 days
Performance-Based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares granted							0	63,963		0	63,963
Fair value per share of common stock								$ 10.25			$ 10.25
Stock-based compensation expense							$ 0	$ 0		$ 0	$ 0
Market-Based Awards \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share of options granted												$ 2.12
Award Repricing
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value per share of common stock										$ 10.25
Incremental expense	$ 1,200,000
Tranche 1
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based awards, vesting period										12 months
Share-based awards, vesting percentage										25.00%
Tranche 2
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based awards, vesting period										3 years
Share-based awards, vesting description										twelve quarterly installments
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price per share of stock option to fair market value of common stock				100.00%
Term of stock option granted				10 years
Shares of common stock reserved for future issuance				1,074,581			4,925,159			4,925,159		4,413,455	4,413,455
Increase in number of shares reserved for issuance					319,815	191,889							3,338,874
Number of shares available for future issuance							274,057			274,057		72,781	72,781