Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recorded related to the 2010 Plan, 2018 Plan, and ESPP was recorded in the condensed statements of operations and allocated as follows (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	1,047	$	109	$	1,713	$	214
General and administrative		908		32		1,565		66
Total stock-based compensation expense	$	1,955	$	141	$	3,278	$	280

Summary of Stock Option

The following table summarizes stock option activity:

	Number of Shares			Weighted- Average Exercise		Weighted- Average Remaining Contractual Term (Years)
Balance—December 31, 2019		2,289,209		$	3.36		8.1
Granted		804,975		$	42.64
Exercised		(94,303	)	$	1.31
Cancelled		(25,334	)	$	15.96
Balance—June 30, 2020		2,974,547		$	13.95		8.2
Exercisable—June 30, 2020		1,180,003		$	2.90		6.7

Summary of Fair Value of Employee Stock Options Estimated Weighted-average Assumptions

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Three Months Ended					Six Months Ended
	June 30,					June 30,
	2020			2019		2020			2019
Expected term in years		6.1			—		6.0			6.0
Expected volatility		86.5	%		—		83.9	%		79.3	%
Risk-free interest rate		0.5	%		—		1.1	%		2.5	%
Dividend yield		—			—		—			—
Weighted average fair value of share-based awards granted	$	41.1		$	—	$	30.1		$	1.0

Summary of Fair Value of Employee Stock Purchase Plan Estimated Weighted-average Assumptions

The fair value of ESPP was estimated using the following weighted-average assumptions:

	Three Months Ended					Six Months Ended
	June 30,					June 30,
	2020			2019		2020			2019
Expected term in years		0.5			—		0.5			—
Expected volatility		100.1	%		—		100.1	%		—
Risk-free interest rate		0.2	%		—		0.2	%		—
Dividend yield		—			—		—			—