Condensed Consolidated Statement of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 46	$ 2,362	$ 324	$ 3,242
Operating expenses:
Research and development	25,847	21,848	75,368	66,968
General and administrative	16,739	14,155	43,245	40,505
Total operating expenses	42,586	36,003	118,613	107,473
Loss from operations	(42,540)	(33,641)	(118,289)	(104,231)
Interest income	1,329	996	4,495	3,099
Interest expense	0	0	0	(44)
Change in fair value of derivative liability associated with the Medicis settlement	(68)	(45)	(139)	(150)
Other expense, net	(130)	(144)	(170)	(626)
Net loss	(41,409)	(32,834)	(114,103)	(101,952)
Unrealized gain (loss) and adjustment on securities included in net loss	(74)	90	50	(133)
Comprehensive loss	(41,483)	(32,744)	(114,053)	(102,085)
Basic and diluted net loss	$ (41,409)	$ (32,834)	$ (114,103)	$ (101,952)
Basic and diluted net loss (in dollar per share)	$ (0.96)	$ (0.91)	$ (2.67)	$ (2.82)
Basic and diluted weighted-average number of shares used in computing net loss per share (in shares)	43,314,831	36,272,445	42,730,983	36,116,745