Condensed Statements of Operations and Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Alliance revenue	$ 7	$ 3	$ 43	$ 40
Operating expenses:
Research and development	2,510	3,278	6,835	10,595
General and administrative	2,179	1,477	5,305	5,014
Total operating expenses	4,689	4,755	12,140	15,609
Loss from operations	(4,682)	(4,752)	(12,097)	(15,569)
Other income (expense):
Decrease in fair value of warrant liability		109		106
Investment income, net	2	2	6	8
Foreign currency exchange (loss) gain	(58)	(28)	(45)	13
Net loss	(4,738)	(4,669)	(12,136)	(15,442)
Loss on extinguishment of convertible preferred stock and preferred stock dividends	278	160	2,587	480
Net loss applicable to common stockholders	(5,016)	(4,829)	(14,723)	(15,922)
Basic and diluted net loss per common share applicable to common stockholders (Note 11)	$ (0.11)	$ (0.17)	$ (0.40)	$ (0.58)
Shares used in computing basic and diluted net loss per common share applicable to common stockholders	45,720	27,640	37,203	27,639
Comprehensive loss	$ (4,738)	$ (4,669)	$ (12,136)	$ (15,442)