Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2014

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)	2014		2013		2014		2013
Research and development	$	340	$	119	$	1,126	$	511
General and administrative		808		690		2,457		1,971
Stock-based employee compensation expense	$	1,148	$	809	$	3,583	$	2,482

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

For the three months ended September 30, 2014 and 2013, 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,
	2014			2013
Risk-free interest rate		2.03	%	1.61 - 1.74%
Expected life in years		6		6
Expected volatility		92.36	%	94.96 - 95.64%
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, 2014 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, 2013		6,747,302		$	3.81
Granted		114,300			4.11
Exercised		(585,638	)		2.26
Cancelled		(483,536	)		4.28
Outstanding, September 30, 2014		5,792,428		$	3.94		6.91	$	1,457
Vested and unvested expected to vest at June 30, 2014		5,731,490		$	4.12		5.41	$	1,441
Options exercisable, September 30, 2014		3,257,661		$	4.12		5.41	$	498
Options exercisable, December 31, 2013		3,471,935		$	4.01		5.03	$	2,654
Options available for future grant		5,555,864

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the nine months ended September 30, 2014 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair Value
Non-vested, December 31, 2013		352,865		$	4.38
Granted		—			—
Vested		(48,433	)		4.51
Cancelled		(20,999	)		4.41
Non-vested, September 30, 2014		283,433		$	4.35