Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaboration revenue	$ 20,433	$ 2,094	$ 71,717	$ 5,611
Operating expenses:
Research and development	29,777	16,632	83,184	47,991
General and administrative	8,463	6,609	26,444	25,554
Total operating expenses	38,240	23,241	109,628	73,545
Operating loss	(17,807)	(21,147)	(37,911)	(67,934)
Other income:
Interest income	1,823	942	5,065	2,399
Other income (expense), net	978	(84)	1,823	(402)
Total other income	2,801	858	6,888	1,997
Loss before income taxes	(15,006)	(20,289)	(31,023)	(65,937)
Income tax benefit				180
Net loss	(15,006)	(20,289)	(31,023)	(65,757)
Other comprehensive (loss) income
Net unrealized (loss) gain on available-for-sale securities	(116)	(49)	118	(7)
Total other comprehensive (loss) income	(116)	(49)	118	113
Comprehensive loss	$ (15,122)	$ (20,338)	$ (30,905)	$ (65,644)
Net loss per share, basic and diluted	$ (0.41)	$ (0.63)	$ (0.87)	$ (2.06)
Weighted-average common shares outstanding, basic and diluted	36,742,993	32,191,475	35,581,408	31,977,670
ASU 2016-01
Other comprehensive (loss) income
Cumulative effect adjustment resulting from ASU No. 2016-01				$ 120