Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidated Statements of Operations
License and collaboration revenue - related party	$ 20,063
Operating expenses:
Research and development	46,181	$ 25,705	$ 11,831
General and administrative	11,779	6,961	2,963
Total operating expenses	57,960	32,666	14,794
Loss from operations	(37,897)	(32,666)	(14,794)
Interest income	940	242	19
Change in fair value of redeemable convertible preferred stock tranche and warrant liabilities		(4,719)	(83)
Other expense		(34)
Net loss	(36,957)	(37,177)	(14,858)
Net loss attributable to common stockholders	$ (36,957)	$ (37,735)	$ (14,933)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (2.09)	$ (5.80)	$ (59.32)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted	17,694,505	6,501,796	251,717