Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				For the six months ended June 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	535	$	297	$	1,065	$	729
General and administrative		1,126		1,502		2,536		2,526
Stock-based compensation expense	$	1,661	$	1,799	$	3,601	$	3,255

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

For the three months ended June 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 June 30,
	2020			2019
Risk-free interest rate		0.43 - 0.60	%		1.89 - 2.42	%
Expected life in years		6 - 6.25			5.75 - 6.25
Expected volatility		73.10 - 73.90	%		72.68 - 78.85	%
Expected dividend yield		0	%		0	%

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plans for the six months ended June 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		1,049,000			4.01
Exercised		(8,166	)		1.87
Cancelled		(322,200	)		3.49
Outstanding, June 30, 2020		6,561,513		$	3.96		7.90	$	2,900
Options exercisable, June 30, 2020		3,453,006		$	3.83		6.68	$	1,700
Options exercisable, December 31, 2019		2,765,357		$	4.39		6.70	$	3,603
Options available for future grant		6,032,404

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the six months ended June 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		—		—
Cancelled		141,230		3.15
Non-vested, June 30, 2020		1,354,306	$	3.43