Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board of Directors

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the board of directors were as follows, presented on a weighted-average basis:

	Six Months Ended June 30,
	2020			2019
Expected option life (years)		6.00			6.03
Risk-free interest rate		0.88	%		2.54	%
Expected volatility		75.72	%		80.86	%
Expected dividend yield		—	%		—	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the six months ended June 30, 2020:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2019		3,414,445		$	12.08		8.43	$	29,353
Granted		2,249,713		$	20.08
Exercised		(31,980	)	$	3.04
Cancelled or forfeited		(45,384	)	$	20.10
Outstanding as of June 30, 2020		5,586,794		$	15.29		8.68	$	22,733
Exercisable as of June 30, 2020		1,533,008		$	8.34		7.38	$	15,102

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s restricted common stock activity for the six months ended June 30, 2020:

	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2019		32,552		$	1.50
Granted		—
Vested		(20,982	)	$	1.01
Forfeited, canceled or expired		—
Issued and unvested as of June 30, 2020		11,570		$	2.38

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was allocated as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2020		2019		2020		2019
Research and development	$	1,966	$	901	$	3,409	$	1,761
General and administrative		1,933		762		3,312		1,357
Total stock-based compensation expense	$	3,899	$	1,663	$	6,721	$	3,118