CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue
Total revenue	$ 12,926,000	$ 0	$ 0
Expenses
Research and development	93,872,000	58,085,000	68,487,000
General and administrative	21,681,000	13,450,000	15,292,000
Total operating expenses	115,553,000	71,535,000	83,779,000
Loss from operations	(102,627,000)	(71,535,000)	(83,779,000)
Other income, net	4,209,000	1,105,000	661,000
Net loss	(98,418,000)	(70,430,000)	(83,118,000)
Unrealized gain (loss) on available-for-sale investments	0	54,000	25,000
Comprehensive loss	$ (98,418,000)	$ (70,484,000)	$ (83,143,000)
Basic and diluted net loss per share (USD per share)	$ (3.19)	$ (2.78)	$ (4.20)
Weighted average number of shares used in computing net loss per share, basic and diluted (in shares)	30,897,717	25,290,222	19,787,349