Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenue:
Collaboration revenue - related party	$ 3,004		$ 5,714
Total revenue	3,004		5,714
Operating expenses:
Research and development expenses	22,174	$ 8,784	37,590	$ 14,345
General and administrative expenses	8,970	3,556	16,180	6,162
Total operating expenses	31,144	12,340	53,770	20,507
Loss from operations	(28,140)	(12,340)	(48,056)	(20,507)
Other income (expense):
Interest income	495	151	763	199
Interest expense	(268)	(146)	(324)	(211)
Revaluation of preferred stock warrant liability		(220)		(7)
Total other income (expense), net	227	(215)	439	(19)
Net loss	$ (27,913)	$ (12,555)	$ (47,617)	$ (20,526)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.70)	$ (1.45)	$ (1.21)	$ (2.64)
Weighted average common shares outstanding, basic and diluted	39,600,344	8,640,218	39,393,238	7,777,679
Other comprehensive income:
Unrealized gain/(loss) on investments, net of tax of $0	$ (25)	$ (8)	$ 53	$ 23
Total other comprehensive income	(25)	(8)	53	23
Comprehensive loss	$ (27,938)	$ (12,563)	$ (47,564)	$ (20,503)