Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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)	2017		2016		2017		2016
Research and development	$	615	$	505	$	1,772	$	1,398
General and administrative		1,467		1,514		4,393		4,696
Stock-based compensation expense	$	2,082	$	2,019	$	6,165	$	6,094

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

For the three months ended September 30, 2017 and 2016, 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,
	2017	2016
Risk-free interest rate	1.88 - 2.01%	1.27 - 1.37%
Expected life in years	6	6
Expected volatility	80.82 - 80.95%	79.26 - 79.34%
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, 2017 is as follows:

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding, December 31, 2016		3,465,335		$	5.07
Granted		359,000			6.28
Exercised		(80,000	)		4.85
Cancelled		(122,000	)		6.64
Outstanding, September 30, 2017		3,622,335		$	5.14		6.22	$	5,657
Options exercisable, September 30, 2017		2,696,835		$	4.62		5.39	$	5,215
Options exercisable, December 31, 2016		2,671,835		$	4.40		5.88	$	3,383
Options available for future grant		1,540,760

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 2017 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2016		1,680,492		$	7.49
Granted		—			—
Vested		(350,000	)		9.35
Cancelled		—			—
Non-vested, September 30, 2017		1,330,492		$	9.46