Stock Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2020

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:

	For the Years Ended December 31,
	2020	2019
Expected volatility	63.2% — 66.3%	62.4% — 64.7%
Weighted-average risk-free interest rate	0.31% — 1.73%	1.36% — 2.60%
Expected dividend yield	— %	— %
Expected term (in years)	5.5 - 6.25	6.25
Underlying common stock fair value	$9.82 - $21.75	$12.73 — $30.34

Schedule of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options and shares purchased under the 2018 ESPP as follows:

	For the Years Ended December 31,
	2020		2019
	(in thousands)
Research and development	$	6,390	$	4,164
General and administrative		6,858		3,471
	$	13,248	$	7,635

Summary of Option Activity under Plans

A summary of option activity under the Plans during the year ended December 31, 2020 is as follows:

	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, 2020		4,843,018		$	14.78		8.5	$	33,809
Granted		1,311,200		$	17.82
Exercised		(46,410	)	$	3.79
Cancelled/Forfeited		(266,984	)	$	22.75
Outstanding at December 31, 2020		5,840,824		$	15.18		7.8	$	12,278
Vested and expected to vest at    December 31, 2020		5,840,824		$	15.18		7.8	$	12,278
Exercisable at December 31, 2020		2,869,589		$	12.18		7.0	$	10,803

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, 2020		21,666
Vested		(18,575	)
Issued		—
Repurchased		—
Unvested shares—December 31, 2020		3,091