Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis:

	Year Ended December 31,
	2018			2017
Expected option life (years)		6.06			6.08
Risk-free interest rate		2.74	%		1.93	%
Expected volatility		81.60	%		84.54	%
Expected dividend yield		—	%		—	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2018:

	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2017		1,034,961		$	0.78		8.94	$	3,427
Granted		1,277,528		$	12.78
Exercised		(16,974	)	$	0.98
Cancelled or forfeited		(131,414	)	$	2.54
Outstanding as of December 31, 2018		2,164,101		$	7.75		8.77	$	23,083
Exercisable as of December 31, 2018		538,214		$	1.22		7.97	$	8,311
Unvested as of December 31, 2018		1,625,886		$	9.92		9.04	$	14,771

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s restricted common stock activity for the year ended December 31, 2018:

	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2017		276,301		$	0.42
Vested		(123,026	)	$	0.42
Forfeited, canceled or expired		—		$	—
Issued and unvested as of December 31, 2018		153,275		$	0.42

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was allocated as follows:

	Year Ended December 31,
	2018		2017
Research and development	$	920	$	80
General and administrative		1,276		97
Total stock-based compensation expense	$	2,196	$	177