Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	$ 7,619	$ 10,135	$ 14,220
Operating expenses:
Research and development	64,905	62,260	42,249
General and administrative	33,809	19,738	13,270
Total operating expenses	98,714	81,998	55,519
Operating loss	(91,095)	(71,863)	(41,299)
Other income (expense), net
Interest income, net	3,310	1,227	976
Other (expense) income, net	(683)	(62)	182
Total other income (expense), net	2,627	1,165	1,158
Loss before income taxes	(88,468)	(70,698)	(40,141)
Income tax provision	180		(52)
Net loss	(88,288)	(70,698)	(40,193)
Other comprehensive (loss) income
Net unrealized gain (loss) on available-for-sale-securities, net of tax expense of $128 for the year ended December 31, 2016	34	(235)	199
Total other comprehensive income (loss)	34	(235)	199
Comprehensive loss	$ (88,254)	$ (70,933)	$ (39,994)
Net loss per share, basic and diluted	$ (2.75)	$ (2.64)	$ (1.59)
Weighted-average common shares outstanding, basic and diluted	32,065,781	26,803,711	25,302,414