Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s consolidated statements of operations as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development	$	101	$	43	$	726	$	105
General and administrative		301		42		857		105
Total stock-based compensation expense	$	402	$	85	$	1,583	$	210

Summary of Stock Option Activity

The following table summarizes stock option activity under the Plans:

	Shares Available for Grant			Number of Options Outstanding		Weighted- Average Exercise Price per Option		Weighted- Average Remaining Contract Term		Aggregate Intrinsic Value
										(In thousands)
Outstanding, December 31, 2017		1,670,341			195,668	$	4.49		9.67
Shares reserved for issuance		641,239
Options granted(1)		(557,182	)		557,182		13.72
Restricted stock granted		(2,000	)
Restricted stock units granted		(24,960	)
Outstanding, June 30, 2018		1,727,438			752,850		11.32		9.50	$	966
Exercisable, June 30, 2018					—		—
Vested and expected to vest, June 30, 2018					752,850		11.32		9.50	$	966

(1) The Company granted 7,200 stock options to non-employees during the six months ended June 30, 2018.

Schedule of Assumptions to Estimate Fair Value of Stock Options for Employees and Non-Employees Using Black-Scholes Option Pricing Model

The fair value of stock options for employees and non-employees was estimated using a Black-Scholes option pricing model with the following assumptions:

	Three Months Ended June 30, 2018		Six Months Ended June 30, 2018
Employees:
Fair value of common stock	$8.57 - $9.91		$8.57 - $15.45
Expected term (in years)		6.6	5.8 - 6.6
Expected volatility	77.4% - 77.7%		76.1% - 77.7%
Risk-free interest rate	2.6% - 2.8%		2.4% - 2.8%
Expected dividend yield	0.0%		0.0%
Non-employees:
Fair value of common stock		—	$	15.45
Expected term (in years)		—		10.0
Expected volatility		—	77.9%
Risk-free interest rate		—	2.7%
Expected dividend yield		—	0.0%

Summary of Restricted Stock Activity

The summary of restricted stock activity and related information follows:

	Number of Restricted Shares Outstanding
Unvested shares — December 31, 2017		1,096,449
Granted		2,000
Vested		(1,096,449	)
Unvested shares — June 30, 2018		2,000

Summary of Restricted Stock Units Activity

The summary of restricted stock unit activity and related information follows:

	Number of Restricted Stock Units Outstanding
Unvested shares — December 31, 2017		—
Granted		24,960
Unvested shares — June 30, 2018		24,960