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	$ 120,756	$ 69,357	$ 24,100
General and administrative	39,407	25,293	9,710
Total operating expenses	160,163	94,650	33,810
Loss from operations	(160,163)	(94,650)	(33,810)
Interest income, net	1,211	178	8
Other expense, net	(35)	(23)	(9)
Net loss	(158,987)	(94,495)	(33,811)
Accretion of redeemable convertible preferred stock to redemption value			(2,294)
Net loss attributable to common stockholders	$ (158,987)	$ (94,495)	$ (36,105)
Net loss per share attributable to common stockholders—basic and diluted	$ (4.75)	$ (3.40)	$ (1.67)
Weighted average number of common shares used in net loss per share attributable to common stockholders—basic and diluted	33,492,795	27,778,288	21,574,347
Comprehensive loss:
Net loss	$ (158,987)	$ (94,495)	$ (33,811)
Other comprehensive items:
Unrealized loss on marketable securities	(102)
Total other comprehensive loss	(102)
Total comprehensive loss	$ (159,089)	$ (94,495)	$ (33,811)