Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue:
Collaboration revenue - related party	$ 2,710
Total revenue	2,710
Operating expenses:
Research and development expenses	15,416	$ 5,561
General and administrative expenses	7,210	2,606
Total operating expenses	22,626	8,167
Loss from operations	(19,916)	(8,167)
Other income (expense):
Interest income	268	49
Interest expense	(56)	(66)
Revaluation of preferred stock warrant liability		213
Total other income, net	212	196
Net loss	$ (19,704)	$ (7,971)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.50)	$ (1.15)
Weighted average common shares outstanding, basic and diluted	39,186,130	6,912,725
Other comprehensive income:
Unrealized gain on investments, net of tax of $0	$ 78	$ 31
Total other comprehensive income	78	31
Comprehensive loss	$ (19,626)	$ (7,940)