Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2012

Black-Scholes Valuation Model and Weighted-Average Assumptions

The fair value-based measurement of each option is estimated on the date of grant using the Black-Scholes option valuation model. The fair value-based measurements and weighted-average assumptions used in the calculations of these measurements are as follows:


	Employee Stock Options												Employee Stock Purchase Plan
	Three Months Ended September 30,						Nine Months Ended September 30,						Nine Months Ended September 30,
	2012			2011			2012			2011			2012			2011
Weighted-average fair value per share	$	3.42		$	2.36		$	3.30		$	2.76		$	2.85		$	2.19
Risk-free interest rate		0.5	%		1.0	%		0.5	%		1.6	%		0.2	%		0.3	%
Expected life (in years)		4.0			4.0			4.0			4.0			1.2			1.2
Volatility		1.5			1.6			1.6			1.6			1.5			1.6
Expected dividends		—			—			—			—			—			—

Stock-Based Compensation Expense

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
Research and development expense	$	824	$	528	$	2,565	$	1,571
General and administrative expense		1,079		759		3,729		2,363

Total	$	1,903	$	1,287	$	6,294	$	3,934

Activity under Stock-Based Compensation Plans

Activity under the stock-based compensation plans during the nine months ended September 30, 2012, was as follows (in thousands except per share amounts):


	Options and Awards Available for Grant			Number of Options and Awards Outstanding			Weighted- Average Price Per Share
Balance at December 31, 2011		11,524			11,101		$	3.10
Options granted		(4,094	)		4,094		$	3.69
Awards granted		(1,815	)		1,815		$	4.23
Options exercised		—			(1,049	)	$	1.80
Awards vested		—			(115	)	$	1.98
Options cancelled:
Options forfeited (unvested)		412			(412	)	$	3.27
Options expired (vested)		36			(36	)	$	6.26
Awards cancelled (unvested)		—			(60	)	$	4.22

Balance at September 30, 2012		6,063			15,338		$	3.46

Summary of Outstanding Options Net of Expected Forfeitures (Vested and Expected to Vest) and Options Exercisable under Stock Option Plans

The following table summarizes outstanding options that are net of expected forfeitures (vested and expected to vest) and options exercisable under our stock option plans as of September 30, 2012 (in thousands, except per share amounts and years):


	Number of Shares		Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding options (vested and expected to vest)		12,561	$	3.35		7.27	$	20,857
Options exercisable		6,729	$	3.55		5.99	$	11,002