Stock Option Plan (Tables)

12 Months Ended

Dec. 31, 2018

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,
	2018		2017
	(in thousands)
Research and development	$	1,117	$	115
General and administrative		1,506		141
	$	2,623	$	256

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,
	2018	2017
Expected volatility	52.80% - 60.12%	52.73% - 59.40%
Weighted-average risk-free interest rate	2.33% - 3.08%	2.04% - 2.37%
Expected dividend yield	— %	— %
Expected term (in years)	5.5 - 7.6	5.9 - 8.6
Underlying common stock fair value	$6.63 - $24.28	$0.63 - $6.63

Summary of Option Activity under Plans

A summary of option activity under the Plans during the year ended December 31, 2018 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, 2018		1,971,711		$	3.61		9.3	$	5,977
Granted		1,392,259		$	19.05
Exercised		(89,050	)	$	1.70
Cancelled/Forfeited		(71,798	)	$	2.72
Outstanding at December 31, 2018		3,203,122		$	10.47		8.9	$	39,018
Vested and expected to vest at    December 31, 2018		3,203,122		$	10.47		8.9	$	39,018
Exercisable at December 31, 2018		716,531		$	3.82		8.1	$	13,287

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, 2018		265,098
Vested		(129,959	)
Issued		16,150
Repurchased		—
Unvested shares—December 31, 2018		151,289