Stock-Based Compensation Expense (Tables)

6 Months Ended

Jun. 30, 2013

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

Summary of Stock-Based Compensation Expense Related to Employee Stock Options

The following table summarizes stock-based compensation expense related to employee stock options for the three-month and six-month periods ended June 30, 2013 and June 30, 2012, which was allocated as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2013		2012		2013		2012
	(in thousands)				(in thousands)
Research and development	$	201	$	205	$	420	$	428
General and administrative		104		103		206		210
	$	305	$	308	$	626	$	638

Weighted-Average Assumptions Used in Valuation of Stock Option

The estimated fair value of employee stock options granted during the six months ended June 30, 2013 and 2012 was calculated using the Black-Scholes model with the following weighted-average assumptions:

	For the Six			For the Six
	Months Ended			Months Ended
	June 30, 2013			June 30, 2012
Risk-free interest rate		1.00	%		1.19	%
Expected dividend yield		0.00	%		0.00	%
Expected volatility		98.09	%		97.97	%
Expected life (years)		6.08			6.18
Weighted-average fair value of options granted	$	1.24		$	2.01

Stock Option Activity

The following table summarizes the stock option activity for the six months ended June 30, 2013:  

			Weighted		Weighted
			average		average		Aggregate
	Number		exercise		contractual		intrinsic
(in thousands,	of shares		price		life (years)		value
except exercise price and contractual term data)
Stock options outstanding, December 31, 2012		1,409	$	7.06
Granted		626		1.59
Forfeited		(207)		2.61
Expired		(14)		11.82
Stock options outstanding at June 30, 2013		1,814	$	5.65		7.47	$	-
Vested or expected to vest at June 30, 2013		1,665	$	5.97		7.31	$	-
Exercisable at June 30, 2013		874	$	9.28		5.65	$	-

Summary of Stock Options Outstanding

The following table summarizes information about our stock options outstanding as of June 30, 2013:

	Outstanding						Exercisable
			Weighted
			average		Weighted				Weighted
			remaining		average				average
Range of exercise	Number		contractual		exercise		Number		exercise
prices	of shares		life (in years)		price		of shares		price
	(number of shares in thousands)
$0.00 - $10.00		1,502		8.40	$	2.55		569	$	3.30
$10.01 - $20.00		161		2.87		16.16		161		16.15
$20.01 - $30.00		128		3.61		23.61		121		23.71
$30.01 - $41.25		23		0.82		33.32		23		33.32
		1,814		7.47	$	5.65		874	$	9.28