Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2019

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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)	2019		2018		2019		2018
Research and development	$	297	$	609	$	729	$	1,212
General and administrative		1,502		1,102		2,526		4,158
Stock-based compensation expense	$	1,799	$	1,711	$	3,255	$	5,370

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

For the three months ended June 30, 2019 and 2018, 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,
	2019	2018
Risk-free interest rate	1.89 - 2.42%	2.66 - 2.91%
Expected life in years	5.75 - 6.25	6
Expected volatility	72.68 - 78.85%	81.48 - 81.66%
Expected dividend yield	0	0

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plan for the six months ended June 30, 2019 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, 2018		5,277,085		$	4.24
Granted		1,695,755			2.54
Exercised		(332,416	)		2.95
Cancelled		(1,562,833	)		4.14
Outstanding, June 30, 2019		5,077,591		$	3.78		7.91	$	12,463
Options exercisable, June 30, 2019		2,378,158		$	4.90		5.93	$	4,220
Options exercisable, December 31, 2018		3,099,935		$	5.15		4.93	$	88
Options available for future grant		4,069,982

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the six months ended June 30, 2019 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2018		682,070		$	3.47
Granted		1,393,536			2.24
Vested		(446,428	)		2.24
Cancelled		(74,599	)		3.41
Non-vested, June 30, 2019		1,554,579		$	2.90