Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2011

Significant Accounting Policies

Components of Comprehensive loss

	Three Months Ended September 30,						Nine Months Ended September 30,
	2011			2010			2011			2010
Comprehensive loss:
Unrealized holding gains (losses)	$	(1,552	)	$	221		$	(2,102	)	$	(66	)
Reclassification adjustment for realized loss included in net loss	—			—			—			(925		)
Net loss	(26,882		)	(12,454		)	(64,765		)	(47,265		)
Comprehensive loss	$	(28,434	)	$	(12,233	)	$	(66,867	)	$	(48,256	)

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

	Nine Months Ended September 30,
	2011		2010
Risk-free interest rate	2.3	%	2.8	%
Dividend yield	0.0	%	0.0	%
Volatility	52.4	%	55.7	%
Expected Life	5.3 years		5.2 years

Board of Director Stock Options:

	Nine Months EndedSeptember 30,
	2011		2010
Risk-free interest rate	2.9	%	2.7	%
Dividend yield	0.0	%	0.0	%
Volatility	52.8	%	57.7	%
Expected Life	7.8 years		7.8 years

Schedule of weighted-average assumptions used for valuation of ESPP

	Nine Months Ended September 30,
	2011		2010
Risk-free interest rate	0.1	%	0.2	%
Dividend yield	0.0	%	0.0	%
Volatility	34.9	%	47.8	%
Expected Life	6 months		6 months

Schedule of stock-based compensation expense related to employee and non-employee stock options and the ESPP

	Three Months Ended September 30,				Nine Months Ended September 30,
	2011		2010		2011		2010
Research and development	$	2,017	$	2,476	$	6,594	$	7,912
General and administrative	347		484		1,002		1,535
Total	$	2,364	$	2,960	$	7,596	$	9,447