Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Licensing revenue	$ 42,000		$ 21,611
Collaborative development revenue			2,415
Total revenue	42,000		24,026
Cost of revenue	8,400
Gross profit	33,600		24,026
Operating expenses:
Research and development	75,484	$ 94,161	39,885
General and administrative	23,231	18,734	13,530
Total operating expenses	98,715	112,895	53,415
Loss from operations	(65,115)	(112,895)	(29,389)
Other income (expense), net	1,955	508	(261)
Loss before provision for income taxes	(63,160)	(112,387)	(29,650)
Provision for (benefit from) income taxes	1,179		(29)
Net loss	$ (64,339)	$ (112,387)	$ (29,621)
Net loss per common share, basic and diluted	$ (1.36)	$ (2.80)	$ (1.29)
Shares used in computing net loss per share - basic and diluted	47,435,331	40,118,522	22,892,640
Comprehensive Loss:
Net loss	$ (64,339)	$ (112,387)	$ (29,621)
Unrealized loss on available-for-sale securities, net of tax	24	(71)
Comprehensive loss	$ (64,315)	$ (112,458)	$ (29,621)