Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 48,770	$ 20,235	$ 9,280
General and administrative	11,276	6,491	1,670
Total operating expenses	60,046	26,726	10,950
Loss from operations	(60,046)	(26,726)	(10,950)
Interest income	472	245	6
Other (expense) income, net	(94)	23	125
Net loss	(59,668)	(26,458)	(10,819)
Unrealized losses on short-term investments	(19)		(10)
Net loss and comprehensive loss	$ (59,687)	$ (26,458)	$ (10,829)
Net loss per share, basic and diluted	$ (5.59)	$ (23.03)	$ (21.56)
Weighted-average number of shares used in computing net loss per share, basic and diluted	10,673,559	1,148,827	501,707