Condensed Consolidated Statements of Operations (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues:
Collaboration agreements	$ 6,157	$ 3,812	$ 10,240	$ 5,475
Research grants	777	762	1,317	2,341
Total revenues	6,934	4,574	11,557	7,816
Operating expenses:
Research and development	9,278	7,574	17,498	14,857
General and administrative	3,124	2,744	6,432	5,986
Total operating expenses	12,402	10,318	23,930	20,843
Loss from operations	(5,468)	(5,744)	(12,373)	(13,027)
Interest and other income, net	18	16	38	31
Net loss	$ (5,450)	$ (5,728)	$ (12,335)	$ (12,996)
Basic and diluted net loss per share	$ (0.10)	$ (0.11)	$ (0.23)	$ (0.25)
Shares used in computing basic and diluted net loss per share	53,786	52,657	53,583	52,612