Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2014

Option Activity under Stock-Based Compensation Plans

Option activity under our stock-based compensation plans during the six months ended June 30, 2014 was as follows (in thousands except per share amounts):

	Shares Underlying Outstanding Options (in thousands)			Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (in thousands)
Balance at December 31, 2013		15,765		$	3.17
Options granted		5,455			1.69
Options exercised		(25	)		0.54
Options cancelled:
Options forfeited (unvested)		(454	)		2.70
Options cancelled (vested)		(587	)		3.64
Balance at June 30, 2014		20,154			2.77		6.14	$	647
Vested and expected to vest at June 30, 2014		20,154			2.77		6.14	$	647
Exercisable at June 30, 2014		11,588			3.27		3.88	$	548

Summary of Restricted Stock Units Activity

Restricted stock unit activity under our stock-based compensation plans during the six months ended June 30, 2014 was as follows (in thousands except per share amounts):

	Number of Shares (In thousands)			Weighted-Average Grant-Date Fair Value
Non-vested as of December 31, 2013		1,275		$	3.93
Granted		1,555		$	1.79
Vested		-		$	-
Forfeited or expired		(1,025	)	$	4.24
Non-vested as of June 30, 2014		1,805		$	1.71

Fair Value-Based Measurements and Weighted-Average Assumptions

The fair value-based measurements and weighted-average assumptions used in the calculations of these measurements are as follows:

	Stock Options						Stock Options						Employee Stock Purchase Plan
	Three Months Ended						Six Months Ended						Six Months Ended
	June 30,						June 30,						June 30,
	2014			2013			2014			2013			2014			2013
Weighted-average fair value	$	1.36		$	2.05		$	1.55		$	2.46		$	0.92		$	1.46
Risk-free interest rate		1.9	%		0.9	%		1.8	%		1.0	%		0.2	%		0.2	%
Expected life (in years)		5.8			6.0			5.9			5.9			1.1			1.3
Volatility		1.3			1.4			1.4			1.4			0.9			0.7

Stock-Based Compensation Expense

The components of stock-based compensation expense were (in thousands):

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2014		2013		2014		2013
Research and development	$	738	$	1,027	$	1,430	$	2,350
General and administrative		938		2,709		1,516		5,652
Total	$	1,676	$	3,736	$	2,946	$	8,002