Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	$ 2,151	$ 6,267	$ 9,405	$ 14,284
Operating expenses:
Research and development	15,180	11,412	40,098	32,145
General and administrative	4,380	2,905	12,181	7,406
Total operating expenses	19,560	14,317	52,279	39,551
Other income:
Interest income	340	318	1,049	527
Total other income	340	318	1,049	527
Net loss	(17,069)	(7,732)	(41,825)	(24,740)
Other comprehensive loss:
Unrealized gain (loss) on marketable securities	48	(6)	107	(15)
Comprehensive loss	(17,021)	(7,738)	(41,718)	(24,755)
Net loss attributable to common stockholders - basic	(17,069)	(7,732)	(41,825)	(24,740)
Net loss attributable to common stockholders - diluted	$ (17,069)	$ (7,732)	$ (41,825)	$ (24,740)
Net loss per share attributable to common stockholders — basic and diluted	$ (0.74)	$ (0.35)	$ (1.82)	$ (2.94)
Weighted-average number of common shares used in net loss per share attributable to common stockholders — basic and diluted	23,152,019	22,242,129	22,979,516	8,407,541