Stock Compensation

3 Months Ended

Mar. 31, 2012

Stock Compensation [Abstract]

Stock Compensation

7. STOCK COMPENSATION

Stock Options

In general, stock options granted prior to December 31, 2010 vest over a three year period, with one-third of the underlying shares vesting on each anniversary of grant, and have a ten year term. Beginning in January 2011, stock options granted generally vest over a four year period, with one-fourth of the underlying shares vesting on the first anniversary of the grant and 1/48^th of the underlying shares vesting monthly thereafter, such that the underlying shares will be fully vested on the fourth anniversary of the grant. As of March 31, 2012, 13,040,676 shares of common stock remain available for future grant.

A summary of the Company's stock option activity with respect to the three months ended March 31, 2012 follows:

Stock Options	Underlying Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at December 31, 2011		14,505,857		$	1.86
Granted		653,000			1.40
Exercised		(667	)		0.92
Canceled or expired		(1,409,138	)		1.42
Outstanding at March 31, 2012		13,749,052		$	1.89		7.39	$	2,626,000
Vested at March 31, 2012 and expected to vest		13,202,433		$	1.91		7.31	$	2,477,000
Exercisable at March 31, 2012		5,149,551		$	2.54		4.33	$	609,000

The weighted-average fair value per share of stock-based awards granted to employees during the three months ended March 31, 2012 and 2011 was $0.91 and $1.54, respectively. During the three months ended March 31, 2012 and 2011, the total intrinsic value of stock options exercised was $280 and $0 respectively, and the total grant date fair value of stock options that vested was $1,942,000 and $1,089,000, respectively.

Valuation Assumptions

Stock-based compensation costs are based on the fair value calculated from the Black-Scholes option-pricing model on the date of grant for stock options. The fair value of stock grants is amortized as compensation expense on a straight-line basis over the vesting period of the grants.

The fair values of stock options granted during the periods presented were measured on the date of grant using the Black-Scholes option-pricing model, with the following assumptions:

	Three Months Ended March 31,
	2012			2011
Risk-free interest rate		1.1	%		2.4	%
Expected dividend yield		0	%		0	%
Expected lives		5.3 years			5.4 years
Expected volatility		79.7	%		81.6	%

Stock-based Compensation Expense

A summary of the stock-based compensation expense recognized in the statements of operations is as follows:

	Three Months Ended March 31,
	2012		2011
	(in thousands)
Research and development	$	253	$	373
General and administrative		455		772
Total	$	708	$	1,145

As of March 31, 2012, there was $7,526,000 of unrecognized compensation cost related to non-vested share-based compensation arrangements granted, including stock options and restricted stock. These costs are expected to be recognized over a weighted-average period of 3.1 years.