Condensed 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	$ 2,094	$ 1,148	$ 5,611	$ 3,790
Operating expenses:
Research and development	16,632	19,561	47,991	48,933
General and administrative	6,609	4,942	25,554	14,372
Total operating expenses	23,241	24,503	73,545	63,305
Operating loss	(21,147)	(23,355)	(67,934)	(59,515)
Other income
Interest income, net	942	291	2,399	799
Other expense, net	(84)	(282)	(402)	(184)
Total other income	858	9	1,997	615
Loss before income taxes	(20,289)	(23,346)	(65,937)	(58,900)
Income tax benefit			180	31
Net loss	(20,289)	(23,346)	(65,757)	(58,869)
Other comprehensive (loss) income
Unrealized (loss) gain on available-for-sale-securities, net of income tax benefit of $53 for the three months ended September 30, 2017	(49)	(485)	108	(403)
Total other comprehensive (loss) income	(49)	(485)	108	(403)
Comprehensive loss	$ (20,338)	$ (23,831)	$ (65,649)	$ (59,272)
Net loss per share, basic and diluted	$ (0.63)	$ (0.89)	$ (2.06)	$ (2.27)
Weighted-average common shares outstanding, basic and diluted	32,191,475	26,164,527	31,977,670	25,968,849