Stock Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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,
	2019		2018
	(in thousands)
Research and development	$	4,164	$	1,117
General and administrative		3,471		1,506
	$	7,635	$	2,623

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,
	2019	2018
Expected volatility	62.4% — 64.7%	52.80% — 60.12%
Weighted-average risk-free interest rate	1.36% — 2.60%	2.33% — 3.08%
Expected dividend yield	— %	— %
Expected term (in years)	6.25	5.5 — 7.6
Underlying common stock fair value	$12.73 — $30.34	$6.63 — $24.28

Summary of Option Activity under Plans

A summary of option activity under the Plans during the year ended December 31, 2019 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 as of January 1, 2019		3,203,122		$	10.47		8.9	$	39,018
Granted		1,898,215		$	21.60
Exercised		(114,277	)	$	3.07
Cancelled/Forfeited		(144,042	)	$	18.06
Outstanding at December 31, 2019		4,843,018		$	14.78		8.5	$	33,809
Vested and expected to vest at    December 31, 2019		4,843,018		$	14.78		8.5	$	33,809
Exercisable at December 31, 2019		1,593,532		$	8.72		7.6	$	20,021

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, 2019		151,289
Vested		(94,816	)
Issued		—
Repurchased		(34,807	)
Unvested shares—December 31, 2019		21,666