Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2012

Stock-Based Compensation [Abstract]

Stock-based compensation

	Three months ended June  30,				Six months ended June  30,
	2012		2011		2012		2011
Stock-based compensation expense by type of award:
Employee stock options	$	206	$	132	$	401	$	266
Non-employee stock options		17		—		34		—
Total stock-based compensation expense	$	223	$	132	$	435	$	266

Stock-based compensation expenses

	Three months ended June  30,				Six months ended June  30,
	2012		2011		2012		2011
Research and development	$	67	$	24	$	129	$	56
General and administrative		156		108		306		210
	$	223	$	132	$	435	$	266

Weighted-average fair value assumptions of stock options

	Three months ended June  30,						Six months ended June  30,
Stock Options	2012			2011			2012			2011
Risk-free interest rate		0.9	%		1.6	%		0.8	%		2.0	%
Expected term (years)		5			5			5			5
Expected dividends		0.0	%		0.0	%		0.0	%		0.0	%
Volatility		91.2	%		90.5	%		90.7	%		89.2	%

Summary of stock option activity

	Number of shares			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2011		11,003,963		$	0.41
Granted		2,197,500			0.48
Exercised		—			0.00
Forfeited		(37,500	)		0.40
Expired		(180,000	)		0.40
Outstanding at June 30, 2012		12,983,963		$	0.42		8.06	$	228
Options vested and expected to vest at June 30, 2012		12,321,673		$	0.42		8.00	$	227
Options exercisable at June 30, 2012		5,846,575		$	0.42		7.08	$	190

Summary of nonvested option activity

	Number of shares			Weighted-Average Grant-Date Fair Value
Outstanding at December 31, 2011		6,285,949		$	0.27
Granted		2,197,500			0.34
Vested		(1,308,561	)		0.24
Forfeited		(37,500	)		0.28
Outstanding at June 30, 2012		7,137,388		$	0.27