Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	$ 6,267	$ 3,262	$ 14,284	$ 13,175
Operating expenses:
Research and development	11,412	7,555	32,145	23,163
General and administrative	2,905	1,598	7,406	5,044
Total operating expenses	14,317	9,153	39,551	28,207
Other income:
Interest income	318	54	527	73
Total other income	318	54	527	73
Net loss	(7,732)	(5,837)	(24,740)	(14,959)
Other comprehensive loss:
Unrealized loss on marketable securities	(6)		(15)
Comprehensive loss	$ (7,738)	$ (5,837)	$ (24,755)	$ (14,959)
Net loss per share attributable to common stockholders — basic and diluted	$ (0.35)	$ (4.56)	$ (2.94)	$ (11.72)
Weighted-average number of common shares used in net loss per share attributable to common stockholders — basic and diluted	22,242,129	1,279,383	8,407,541	1,276,819