Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				For the six months ended June 30,
(in thousands)	2017		2016		2017		2016
Research and development	$	596	$	476	$	1,156	$	893
General and administrative		1,462		1,590		2,926		3,182
Stock-based compensation expense	$	2,058	$	2,066	$	4,082	$	4,075

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

For the three months ended June 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 June 30,
	2017	2016
Risk-free interest rate	1.85 - 2.05%	1.38 - 1.54%
Expected life in years	6	6
Expected volatility	80.93 - 81.03%	80.70 - 80.81%
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, 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		265,500			6.39
Exercised		(80,000	)		4.85
Cancelled		(113,000	)		6.66
Outstanding, June 30, 2017		3,537,835		$	5.13		6.51	$	5,876
Options exercisable, June 30, 2017		2,624,335		$	4.42		5.57	$	5,400
Options exercisable, December 31, 2016		2,671,835		$	4.40		5.88	$	3,383
Options available for future grant		1,625,260

Summary of Unvested Restricted Stock

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)	2017		2016		2017		2016
Research and development	$	596	$	476	$	1,156	$	893
General and administrative		1,462		1,590		2,926		3,182
Stock-based compensation expense	$	2,058	$	2,066	$	4,082	$	4,075