Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2012

Stock-Based Compensation [Abstract]

Stock-Based Compensation Expense

	Years ended December 31,
	2012		2011		2010
Research and development	$	873	$	610	$	335
General and administrative		1,218		1,437		1,004
Total stock-based compensation expenses	$	2,091	$	2,047	$	1,339

Summary of Option Activity

	2005 Stock Incentive Plan					1995 Stock Option Plan
	Stock Options			Weighted- Average Exercise Price		Stock Options			Weighted- Average Exercise Price
Outstanding at January 1, 2012		7,412,746		$	2.22		474,650		$	4.38
Granted		3,483,000		$	1.29		-		$	-
Exercised		(90,534	)	$	0.61		-		$	-
Canceled		(1,661,387	)	$	2.27		(262,750	)	$	3.86
Outstanding at December 31, 2012		9,143,825		$	1.87		211,900		$	4.94
Vested and expected to vest at December 31, 2012		8,255,692		$	1.92		211,900		$	4.94
Shares exercisable at December 31, 2012		3,541,268		$	2.34		211,900		$	4.94
Shares available for grant at December 31, 2012		5,752,361

Assumptions used to Estimate Grant Date Fair Value of Stock Options granted using Black-Scholes Option-Pricing Model

	2012		2011		2010
Weighted average fair value of options granted		$0.71		$1.14		$1.47
Risk-free interest rate		0.55%-1.54%		0.48%-1.91%		0.93%-2.89%
Dividend yield		0%		0%		0%
Volatility		75.5%-78.6%		73.3%-81.0%		97.0%-108.0%
Expected term (in years)		3.34-7.09		3.26-4.47		3.06-6.26
Expected forfeiture rate		0%-23.15%		0%-23.15%		21.07%

Summary of Restricted Stock Awards Activity

	Number of Shares			Per Share Weighted- Average Grant-Date Fair Value
Outstanding at January 1, 2012		53,333		$	1.63
Restricted stock granted		-		$	-
Restricted stock vested		(19,999	)	$	2.03
Restricted stock forfeited		-		$	-
Outstanding at December 31, 2012		33,334		$	1.39