Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2013

Stock-based Compensation [Abstract]

Weighted average assumptions

The fair value of the stock options granted was estimated based on the following weighted average assumptions for three and six months ended June 30, 2013 and 2012:

	Three Months Ended June 30,						Six Months Ended June 30,
	2013			2012			2013			2012
Dividend yield		0	%		0	%		0	%		0	%
Expected volatility		92	%		92	%		92	%		92	%
Risk-free interest rate		1.44	%		0.72	%		0.84	%		1.05	%
Expected term	5.6 years			5.6 years			5.6 years			5.6 years

Stock option activity

Stock option activity for the six months ended June 30, 2013 was as follows:

	Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2012		6,788,383		$	8.99		7.36	$	1,531
Granted		1,088,703			3.02
Exercised		(129,317	)		1.69
Forfeited, expired or cancelled		(75,829	)		27.68
Options outstanding at June 30, 2013		7,671,940		$	8.08		7.31	$	4,868
Options exercisable at June 30, 2013		4,647,726		$	11.36		6.23	$	2,506

Unvested RSU activity

Unvested RSU activity for the six months ended June 30, 2013 is summarized below:

	Number of Shares			Weighted-Average Grant-Date Fair Value
Unvested balance at December 31, 2012		1,459,853		$	2.75
Granted		949,310			3.84
Vested		(164,998	)		2.50
Forfeited		(16,260	)		2.22
Unvested balance at June 30, 2013		2,227,905		$	2.59

Stock-based compensation expense

The following table shows total stock-based compensation expense included in the condensed consolidated statements of comprehensive loss for the three and six months ended June 30, 2013 and 2012 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2013		2012		2013		2012
Research and development	$	432	$	295	$	1,429	$	680
Selling, general and administrative		667		277		1,290		566
Total stock-based compensation expense	$	1,099	$	572	$	2,719	$	1,246