Condensed Consolidated Statements of Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues:
Collaboration agreements	$ 3,812	$ 608	$ 5,475	$ 2,095
Research grants	762	906	2,341	1,619
Total revenues	4,574	1,514	7,816	3,714
Operating expenses:
Research and development	7,574	8,119	14,857	16,381
General and administrative	2,744	3,676	5,986	7,215
Total operating expenses	10,318	11,795	20,843	23,596
Loss from operations	(5,744)	(10,281)	(13,027)	(19,882)
Interest and other income, net	16	22	31	45
Net loss	(5,728)	(10,259)	(12,996)	(19,837)
Basic and diluted net loss per share	$ (0.11)	$ (0.20)	$ (0.25)	$ (0.41)
Shares used in computing basic and diluted net loss per share	52,657	51,500	52,612	48,514
Net loss	(5,728)	(10,259)	(12,996)	(19,837)
Changes in unrealized gain (loss) on available-for-sale securities	(4)	3	(19)	23
Comprehensive loss	$ (5,732)	$ (10,256)	$ (13,015)	$ (19,814)