Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2012

Activity under Stock-Based Compensation Plans

Activity under our stock plans is set forth below:


	Shares Underlying Outstanding Options (in thousands)			Weighted-Average Exercise Price Per Share (in thousands)		Weighted-Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Balance at December 31, 2011		10,987		$	3.10
Options granted		4,534			3.68
Options exercised		(1,166	)		1.79
Options cancelled:
Options forfeited (unvested)		(505	)		3.32
Options cancelled (vested)		(44	)		5.53

Balance at December 31, 2012		13,806		$	3.38		7.26	$	4,015

Vested and expected to vest at December 31, 2012		12,886		$	3.37		7.13	$	3,955

Exercisable at December 31, 2012		7,226		$	3.49		5.91	$	2,825

Summary of Restricted Stock Units Activity

A summary of the status of non-vested restricted stock units as of December 31, 2012, and activities during 2012 is summarized as follows:


	Number of Shares (In thousands)			Weighted-Average Grant-Date Fair Value
Non-vested as of December 31, 2011		115		$	1.98
Granted		1,815		$	4.23
Vested		(115	)	$	1.98
Forfeited or expired		(60	)	$	4.22

Non-vested as of December 31, 2012		1,755		$	4.23

Black-Scholes Valuation Model and Weighted-Average Assumptions

The fair value of each option is estimated on the date of grant using the Black-Scholes option valuation model and the following weighted-average assumptions:


	Stock Options									Employee Stock Purchase Plan
	Years Ended December 31,									Years Ended December 31,
	2012			2011			2010			2012			2011			2010
Weighted-average fair value	$	3.30		$	2.76		$	1.49		$	3.53		$	2.09		$	1.47
Risk-free interest rate		0.5	%		1.3	%		1.7	%		0.2	%		0.3	%		0.4	%
Expected life (in years)		4.2			4.0			4.0			1.1			1.2			0.9
Volatility		1.6			1.6			1.6			1.6			1.6			1.6

Stock-Based Compensation Expense

We recognized the following amounts of stock-based compensation expense (in thousands):


	Years Ended December 31,
	2012		2011		2010
Employees and directors stock-based compensation expense	$	10,439	$	5,185	$	2,378
Non-employees stock-based compensation expense		—		4		32

Total	$	10,439	$	5,189	$	2,410


	Years Ended December 31,
	2012		2011		2010
Research and development	$	3,514	$	2,103	$	632
General and administrative		6,925		3,086		1,778

Total	$	10,439	$	5,189	$	2,410