CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses
Research and development	$ 31,988	$ 35,254	$ 63,304	$ 68,700
General and administrative	31,200	18,559	54,912	35,232
Total operating expenses	63,188	53,813	118,216	103,932
Loss from operations	(63,188)	(53,813)	(118,216)	(103,932)
Interest income, net	358	1,294	1,149	1,930
Loss before provision for income taxes	(62,830)	(52,519)	(117,067)	(102,002)
Provision for income taxes	48	33	77	50
Net loss	(62,878)	(52,552)	(117,144)	(102,052)
Other comprehensive loss, net of tax:
Unrealized gains (losses) on investments	174	2	345	(15)
Comprehensive loss	$ (62,704)	$ (52,550)	$ (116,799)	$ (102,067)
Net loss per common share, basic and diluted	$ (1.01)	$ (0.91)	$ (1.88)	$ (1.83)
Weighted average shares used in computing net loss per common share, basic and diluted	62,332	57,903	62,178	55,752