Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2013

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)	2013			2012		2013		2012
Research and development	$	(145	)	$	426	$	392	$	942
General and administrative		277			652		1,281		1,348
Stock-based employee compensation expense	$	132		$	1,078	$	1,673	$	2,290

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

For the six months ended June 30, 2013 and 2012, 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,
	2013			2012
Risk-free interest rate		1.65	%	0.93 - 1.10%
Expected life in years		6		6
Expected volatility		95.45	%	83.36 - 83.52%
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, 2013 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, 2012		7,147,303		$	4.11
Granted		1,426,400			2.49
Exercised		(455,168	)		1.87
Cancelled		(1,580,116	)		4.73
Outstanding, June 30, 2013		6,538,419		$	3.76		7.11	$	956
Vested and unvested expected to vest at June 30, 2013		6,481,884		$	3.85		5.03	$	948
Options exercisable, June 30, 2013		3,406,985		$	3.85		5.03	$	956
Options exercisable, December 31, 2012		3,683,786		$	3.56		5.28	$	3,972
Options available for future grant		1,430,403

Summary of Unvested Restricted Stock

A summary of the status of unvested restricted stock for the six months ended June 30, 2013 is as follows:

	Number of Shares			Weighted-Average Grant Date Fair  Value
Non-vested, December 31, 2012		733,739		$	4.37
Granted		—			—
Vested		(138,814	)		4.26
Cancelled		(140,600	)		4.42
Non-vested, June 30, 2013		454,325		$	4.38