Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating expenses:
Research and development	$ 9,115	$ 4,738	$ 15,751	$ 10,034
General and administrative	3,831	1,874	7,808	3,315
Total operating expenses	12,946	6,612	23,559	13,349
Loss from operations	(12,946)	(6,612)	(23,559)	(13,349)
Other income (expense), net:
Change in fair value of preferred stock warrants		(8,630)		(9,956)
Other income (expense)	88	(6)	171	19
Total other income (expense), net	88	(8,636)	171	(9,937)
Loss before provision for income taxes	(12,858)	(15,248)	(23,388)	(23,286)
Provision for income taxes	14	1	22	11
Net loss	(12,872)	(15,249)	(23,410)	(23,297)
Adjustment to redemption value on redeemable convertible preferred stock		(140,880)		(151,885)
Net loss attributable to common stockholders	$ (12,872)	$ (156,129)	$ (23,410)	$ (175,182)
Net loss per share attributable to common stockholders, basic and diluted (Note 3)	$ (0.43)	$ (104.10)	$ (0.78)	$ (117.35)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (Note 3)	30,191,093	1,499,840	30,130,660	1,492,764