Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2012

Significant Accounting Policies

Schedule of weighted-average assumptions used for valuation of Employee Stock Options

	Nine Months Ended September 30,
	2012		2011
Risk-free interest rate	1.0	%	2.3	%
Dividend yield	0.0	%	0.0	%
Volatility	50.65	%	52.4	%
Expected life	5.1 years		5.3 years

Schedule of weighted-average assumptions used for valuation of Board of Director Stock Options

	Nine Months EndedSeptember 30,
	2012		2011
Risk-free interest rate	1.3	%	2.9	%
Dividend yield	0.0	%	0.0	%
Volatility	51.3	%	52.8	%
Expected Life	7.6 years		7.8 years

Schedule of weighted-average assumptions used for valuation of ESPP

	Nine Months Ended September 30,
	2012		2011
Risk-free interest rate	0.2	%	0.1	%
Dividend yield	0.0	%	0.0	%
Volatility	49.6	%	34.9	%
Expected life	6 months		6 months

Schedule of stock-based compensation expense

The following table summarizes stock-based compensation expense for the three and nine months ended September 30, 2012 and 2011 (in thousands), which was allocated as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2012		2011		2012		2011
Research and development	$	1,720	$	2,017	$	5,728	$	6,594
General and administrative	314		347		1,033		1,002
Total	$	2,034	$	2,364	$	6,761	$	7,596