Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 26,356	$ 19,078	$ 2,843
General and administrative	9,472	3,500	1,162
Total operating expenses	35,828	22,578	4,005
Loss from operations	(35,828)	(22,578)	(4,005)
Other income (expense), net:
Change in fair value of preferred stock warrants	(17,443)	(1,380)	(202)
Interest expense			(2,719)
Other income	66	87	94
Total other income (expense), net	(17,377)	(1,293)	(2,827)
Loss before provision for income taxes	(53,205)	(23,871)	(6,832)
Provision for income taxes	55	2
Net loss	(53,260)	(23,873)	(6,832)
Adjustment to redemption value on redeemable convertible preferred stock	(374,015)	(49,849)	(5,713)
Net loss attributable to common stockholders	$ (453,184)	$ (73,722)	$ (12,545)
Net loss per share attributable to common stockholders, basic and diluted (Note 3)	$ (31.47)	$ (69.08)	$ (19.18)
Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted (Note 3)	14,399,506	1,067,259	653,914
Series B and B-1 [Member]
Other income (expense), net:
Redeemable convertible preferred stock dividend	$ (5,543)
Series C and D [Member]
Other income (expense), net:
Redeemable convertible preferred stock dividend	$ (20,366)