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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Alliance revenue	$ 30	$ 7	$ 71	$ 43
Operating expenses:
Research and development	6,678	2,510	19,248	6,835
General and administrative	2,873	2,179	7,646	5,305
Total operating expenses	9,551	4,689	26,894	12,140
Loss from operations	(9,521)	(4,682)	(26,823)	(12,097)
Other income (expense):
Investment income, net	14	2	45	6
Foreign currency exchange gain (loss)	52	(58)	54	(45)
Net loss	(9,455)	(4,738)	(26,724)	(12,136)
Loss on extinguishment of convertible preferred stock and preferred stock dividends	119	278	422	2,587
Net loss applicable to common stockholders	(9,574)	(5,016)	(27,146)	(14,723)
Basic and diluted net loss per common share applicable to common stockholders (Note 13)	$ (0.11)	$ (0.11)	$ (0.33)	$ (0.40)
Shares used in computing basic and diluted net loss per common share applicable to common stockholders	84,527	45,720	81,200	37,203
Net loss	(9,455)	(4,738)	(26,724)	(12,136)
Other comprehensive (loss) gain:
Unrealized (loss) gain on available-for-sale securities	(5)		5
Comprehensive loss	$ (9,460)	$ (4,738)	$ (26,719)	$ (12,136)