Stock Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model

The assumptions used in the Black-Scholes option pricing model are as follows:

	Three months ended March 31,
	2021		2020
Expected volatility	66.8% — 67.1%		63.2% — 63.5%
Weighted-average risk-free interest rate	0.50% — 0.76%		0.74% — 1.73%
Expected dividend yield	— %		— %
Expected term (in years)		6.25		6.25
Underlying common stock fair value	$11.64 — $13.91		$17.00 — $21.75

Summary of Option Activity under Plans

The following table summarizes the Company’s stock option activity for the three months ended March 31, 2021:

	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at January 1, 2021		5,840,824		$	15.18		7.8	$	12,278
Granted		1,628,650		$	13.81
Exercised		(55,277	)	$	2.43
Cancelled/Forfeited		(72,839	)	$	19.40
Outstanding at March 31, 2021		7,341,358		$	14.93		8.1	$	8,684
Vested and expected to vest at    March 31, 2021		7,341,358		$	14.93		8.1	$	8,684
Exercisable at March 31, 2021		3,199,381		$	12.78		7.0	$	8,100

Summary of Unvested Common Stock from Early Exercises Subject to Repurchase

A summary of the Company’s unvested common stock from early exercises that is subject to repurchase by the Company is as follows:

	Shares
Unvested shares - January 1, 2021		3,091
Vested		(1,011	)
Issued		—
Repurchased		—
Unvested shares - March 31, 2021		2,080

Summary of Company's RSU Activity

The following table summarizes the Company’s RSU activity for the three months ended March 31, 2021:

	Number of Restricted Stock Units		Weighted- Average Grant Date Fair Value
Outstanding at January 1, 2021		-	$	—
Granted		277,400	$	13.85
Vested		—	$	—
Forfeited		—	$	—
Outstanding at March 31, 2021		277,400	$	13.85

Schedule of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options and restricted stock units as follows:

	Three months ended March 31,
	2021		2020
	(in thousands)
Research and development	$	1,857	$	1,313
General and administrative		2,026		1,570
	$	3,883	$	2,883