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Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

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 condensed consolidated statements of operations as follows (in thousands):

		Three Months Ended September 30,								Nine Months Ended September 30,
		2019				2018				2019				2018
Research and development		$	633			$	229			$	1,409			$	955
General and administrative			569				400				1,399				1,257
Total stock-based compensation expense		$	1,202			$	629			$	2,808			$	2,212

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, 2018			1,350,582				1,122,677			$	11.63				9.22
Shares reserved for issuance			1,122,213
Options granted			(1,286,524	)			1,286,524				8.66
Options exercised			—				(7,029	)			0.79
Options cancelled			116,850				(116,850	)			10.25
Outstanding, September 30, 2019			1,303,121				2,285,322				10.05				9.05			$	1,360
Exercisable, September 30, 2019							373,574				11.40				8.33				387
Vested and expected to vest, September 30, 2019							2,285,322				8.63				9.05				1,360

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 September 30,						Nine Months Ended September 30,
		2019		2018				2019		2018
Employees and directors:
Fair value of common stock		$9.36 - $10.66		$9.03 - $13.94				$6.97 - $10.66		$8.57 - $15.45
Expected term (in years)		6.1		5.9 - 6.1				5.5 - 6.1		5.8 - 6.6
Expected volatility		92.4% - 92.6%		89.8% - 90.6%				92.4% - 104.8%		75.9% - 90.6%
Risk-free interest rate		1.4% - 1.8%		2.8% - 2.9%				1.4% - 2.6%		2.4% - 2.9%
Expected dividend yield		0.0%		0.0%				0.0%		0.0%
Non-employees:
Fair value of common stock		$8.84 - $10.26			—			$6.82 - $10.26		$15.45
Expected term (in years)		7.7 - 9.5			—			7.7 - 10.0			10.0
Expected volatility		89.7% - 90.8%			—			89.7% - 94.2%		77.9%
Risk-free interest rate		1.7% - 1.9%			—			1.7% - 2.6%		2.7%
Expected dividend yield		0.0%			—			0.0%		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, 2018			1,000
Vested			(1,000	)
Unvested shares — September 30, 2019			—

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, 2018			24,960
Granted			—
Vested			(7,800	)
Unvested shares — September 30, 2019			17,160

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Tabular disclosure of the changes in outstanding nonvested restricted stock shares.

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Tabular disclosure of cost recognized for award under share-based payment arrangement by plan. Includes, but is not limited to, related tax benefit.

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