Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 17,258	$ 15,087	$ 17,239
Operating expenses:
Research and development	67,045	75,836	89,382
General and administrative	34,795	36,035	33,751
Loss on impairment of intangible assets	5,006	3,992
Amortization of intangible assets	554	584	559
Total operating expenses	107,400	116,447	123,692
Loss from operations	(90,142)	(101,360)	(106,453)
Interest income, net	5,451	5,284	3,444
Other expense, net	(93)	(64)	(218)
Loss before income tax	(84,784)	(96,140)	(103,227)
Income tax benefit	2,412	783	11,364
Net loss	$ (82,372)	$ (95,357)	$ (91,863)
Net loss per common share, basic and diluted	$ (1.03)	$ (1.21)	$ (1.26)
Shares used in computing net loss per common share, basic and diluted	80,110,711	78,812,407	72,901,215
Collaboration and license revenue
Revenue:
Total revenue	$ 17,258	$ 15,087	$ 17,109
Grant revenue
Revenue:
Total revenue			$ 130