Consolidated Statements of Operations - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Collaboration and license revenue	$ 50,593,000	$ 71,689,000	$ 13,038,000
Grant revenue	88,000	1,290,000	351,000
Total revenue	50,681,000	72,979,000	13,389,000
Operating expenses:
Research and development	87,718,000	58,649,000	23,513,000
General and administrative	34,277,000	27,805,000	8,994,000
Amortization of intangible assets	549,000	89,000	0
Total operating expenses	122,544,000	86,543,000	32,507,000
Loss from operations	(71,863,000)	(13,564,000)	(19,118,000)
Loss from remeasurement of fair value of warrants		(26,077,000)	(566,000)
Gain on extinguishment of convertible promissory notes			3,553,000
Interest income (expense), net	2,219,000	494,000	(2,395,000)
Other (expense) income, net	(40,000)	(161,000)	1,512,000
Loss before income tax	(69,684,000)	(39,308,000)	(17,014,000)
Income tax (provision) benefit	(21,464,000)	99,000
Net loss	$ (91,148,000)	$ (39,209,000)	$ (17,014,000)
Net loss per common share, basic and diluted	$ (1.40)	$ (0.88)	$ (53.06)
Shares used in computing net loss per common share, basic and diluted	65,200,762	44,706,393	320,686