Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Consolidated Statements of Operations and Comprehensive Loss
Collaboration revenue	$ 28,681	$ 46,087	$ 46,748	$ 51,284
Operating expenses:
Research and development	29,423	28,576	61,718	53,407
General and administrative	8,239	8,322	18,444	17,981
Total operating expenses	37,662	36,898	80,162	71,388
Operating (loss) income	(8,981)	9,189	(33,414)	(20,104)
Other income, net:
Interest income	346	2,097	1,324	3,242
Other (expense) income	(46)	(133)	(854)	845
Total other income, net	300	1,964	470	4,087
Net (loss) income	(8,681)	11,153	(32,944)	(16,017)
Other comprehensive (loss) income
Net unrealized (loss) gain on available-for-sale-securities	(276)	176	249	234
Total other comprehensive (loss) income	(276)	176	249	234
Comprehensive (loss) income	$ (8,957)	$ 11,329	$ (32,695)	$ (15,783)
Net (loss) income per share, basic	$ (0.23)	$ 0.30	$ (0.89)	$ (0.46)
Net (loss) income per share, diluted	$ (0.23)	$ 0.29	$ (0.89)	$ (0.46)
Weighted-average common shares outstanding, basic	37,029,524	36,610,918	36,996,390	34,990,989
Weighted-average common shares outstanding, diluted	37,029,524	37,941,257	36,996,390	34,990,989