Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

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Stock-Based Compensation Expense on All Employee and Non-Employee Awards

The Company recognized stock-based compensation expense on all employee and non-employee awards as follows:

	For the three months ended September 30,				For the nine months ended September 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	522	$	339	$	1,587	$	1,068
General and administrative		1,270		1,147		3,806		3,673
Stock-based compensation expense	$	1,792	$	1,486	$	5,393	$	4,741

Fair Value of Stock Options Assumptions Using Black-Scholes Option Valuation Model

For the three months ended September 30, 2020 and 2019, the fair value of stock options was estimated on the date of grant using a Black-Scholes option valuation model with the following assumptions:

	For the three months ended September 30,
	2020	2019
Risk-free interest rate	0.36 - 0.39%	1.39 - 1.92%
Expected life in years	5.75 - 6.25	6.25
Expected volatility	73.59 - 74.18%	72.87 - 78.34%
Expected dividend yield	0%	0%

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plans for the nine months ended September 30, 2020 is as follows:

(in thousands, except share and per share data)	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2019		5,842,879		$	3.21
Granted		1,252,178			3.89
Exercised		(22,916	)		1.87
Cancelled		(499,950	)		3.84
Outstanding, September 30, 2020		6,572,191		$	3.93		7.82	$	978
Options exercisable, September 30, 2020		3,711,684		$	4.10		6.96	$	704
Options exercisable, December 31, 2019		2,765,357		$	4.39		6.70	$	3,603
Options available for future grant		6,986,610

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 2020 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2019		939,636		$	2.93
Granted		555,900			4.21
Vested		(64,917	)		3.42
Cancelled		(141,230	)		3.15
Non-vested, September 30, 2020		1,289,389		$	3.43