Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2016

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				For the nine months
	ended September 30,				ended September 30,
(in thousands)	2016		2015		2016		2015
Research and development	$	505	$	264	$	1,398	$	874
General and administrative		1,514		1,213		4,696		5,180
Stock-based compensation expense	$	2,019	$	1,477	$	6,094	$	6,054

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

For the three months ended September 30, 2016 and 2015, 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 nine months ended September 30,
	2016	2015
Risk-free interest rate	1.27 - 1.37%	1.66 - 1.93%
Expected life in years	6	6
Expected volatility	79.26 - 79.34%	80.01 - 81.7%
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, 2016 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, 2015		3,481,469		$	4.96
Granted		157,300			7.76
Exercised		(169,000	)		4.81
Cancelled		(21,699	)		6.18
Outstanding, September 30, 2016		3,448,070		$	5.08		6.52	$	4,319
Vested and unvested expected to vest at September 30, 2016		3,357,976		$	4.25		5.57	$	4,206
Options exercisable, September 30, 2016		2,317,935		$	4.25		5.57	$	3,755
Options exercisable, December 31, 2015		2,120,834		$	4.24		5.84	$	8,622
Options available for future grant		2,632,629

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 2016 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2015		1,586,388		$	9.00
Granted		—			—
Vested		(350,000	)		9.35
Cancelled		—			—
Non-vested, September 30, 2016		1,236,388		$	9.00