STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Alliance revenue	$ 16,199	$ 249	$ 73
Operating expenses:
Research and development	39,824	33,699	27,493
General and administrative	15,132	15,396	11,332
Total operating expenses	54,956	49,095	38,825
Loss from operations	(38,757)	(48,846)	(38,752)
Other income (expense):
Interest income	415	357	66
Interest expense	(80)	(105)	(27)
Foreign currency exchange gain	33	39	71
Net loss	(38,389)	(48,555)	(38,642)
Loss on extinguishment of convertible preferred stock and preferred stock dividends			519
Net loss	$ (38,389)	$ (48,555)	$ (38,642)
Basic and diluted net loss per common share (Note 12)	$ (0.30)	$ (0.42)	$ (0.47)
Shares used in computing basic and diluted net loss per common share	127,597	115,092	82,827
Net loss	$ (38,389)	$ (48,555)	$ (39,161)
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale securities	117	(117)	(10)
Other comprehensive loss	117	(117)	(10)
Comprehensive loss	$ (38,272)	$ (48,672)	$ (38,652)