Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 2,607	$ 42,000
Cost of revenue	466	8,400
Gross profit	2,141	33,600
Operating expenses:
Research and development	69,373	75,484	$ 94,161
General and administrative	23,715	23,231	18,734
Total operating expenses	93,088	98,715	112,895
Loss from operations	(90,947)	(65,115)	(112,895)
Interest expense	(3,534)
Other income (expense), net	3,187	1,955	508
Loss before provision for income taxes	(91,294)	(63,160)	(112,387)
Provision for income taxes	4	1,179
Net loss	$ (91,298)	$ (64,339)	$ (112,387)
Net loss per common share, basic and diluted	$ (1.62)	$ (1.36)	$ (2.80)
Shares used in computing net loss per share - basic and diluted	56,219,919	47,435,331	40,118,522
Comprehensive loss:
Net loss	$ (91,298)	$ (64,339)	$ (112,387)
Unrealized gain (loss) on available-for-sale securities, net of tax	9	24	(71)
Comprehensive loss	(91,289)	(64,315)	$ (112,458)
Licensing
Revenues:
Total revenues	2,320	$ 42,000
Other
Revenues:
Total revenues	$ 287