Stock-Based Compensation (Tables)

9 Months Ended

Sep. 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 September 30,				For the nine months ended September 30,
(in thousands)	2019		2018		2019		2018
Research and development	$	339	$	552	$	1,068	$	1,765
General and administrative		1,147		928		3,673		5,085
Stock-based compensation expense	$	1,486	$	1,480	$	4,741	$	6,850

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

For the three months ended September 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 September 30,
	2019	2018
Risk-free interest rate	1.39 - 1.92%	2.82 - 2.98%
Expected life in years	6.25	6
Expected volatility	72.87 - 78.34%	82.27 - 83.08%
Expected dividend yield	0	0

Stock Option Activity under Stock Option Plan

Stock option activity under the Company’s stock option plan for the nine months ended September 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		1,835,755			2.69
Exercised		(482,500	)		3.48
Cancelled		(1,634,791	)		4.11
Outstanding, September 30, 2019		4,995,549		$	3.78		7.84	$	6,025
Options exercisable, September 30, 2019		2,581,327		$	4.59		6.60	$	2,425
Options exercisable, December 31, 2018		3,099,935		$	5.15		4.93	$	88
Options available for future grant		3,971,940

Summary of Unvested Restricted Stock

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

 

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2018		682,070		$	3.47
Granted		1,408,536			2.26
Vested		(446,428	)		2.24
Cancelled		(74,599	)		3.41
Non-vested, September 30, 2019		1,569,579		$	2.91