Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Total revenues	$ 18	$ 30	$ 18	$ 2,350
Cost of revenue				464
Gross profit	18	30	18	1,886
Operating expenses:
Research and development	19,475	16,046	39,856	29,396
General and administrative	5,371	6,138	10,488	12,329
Total operating expenses	24,846	22,184	50,344	41,725
Loss from operations	(24,828)	(22,154)	(50,326)	(39,839)
Interest expense	(1,451)	(692)	(2,885)	(692)
Other income (expense), net	812	557	1,602	1,227
Loss before provision for income taxes	(25,467)	(22,289)	(51,609)	(39,304)
Provision for income taxes		2	2	6
Net loss	$ (25,467)	$ (22,291)	$ (51,611)	$ (39,310)
Net loss per common share, basic and diluted	$ (0.41)	$ (0.42)	$ (0.82)	$ (0.78)
Shares used in computing net loss per share - basic and diluted	62,651,863	52,824,483	62,599,371	50,206,470
Comprehensive loss:
Net loss	$ (25,467)	$ (22,291)	$ (51,611)	$ (39,310)
Unrealized gain on available-for-sale securities, net of tax	4	55	54	11
Comprehensive loss	(25,463)	(22,236)	(51,557)	(39,299)
Licensing
Revenues:
Total revenues				2,320
Other
Revenues:
Total revenue	$ 18	$ 30	$ 18	$ 30