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
Collaboration revenue:
Collaboration revenue from customers	$ 5,811	$ 4,098	$ 9,363	$ 8,209
Other collaboration revenue	36	99	88	193
Total collaboration revenue	5,847	4,197	9,451	8,402
Operating expenses:
Research and development	53,152	51,884	104,168	89,287
General and administrative	13,972	15,076	26,527	24,386
Total operating expenses	67,124	66,960	130,695	113,673
Loss from operations	(61,277)	(62,763)	(121,244)	(105,271)
Interest and other income, net	2,598	4,113	5,667	7,629
Loss before income taxes	(58,679)	(58,650)	(115,577)	(97,642)
Income tax benefit (provision)	(79)	313	56	313
Net loss	(58,758)	(58,337)	(115,521)	(97,329)
Other comprehensive income (loss):
Net unrealized gain (loss) on marketable securities, net of tax	(284)	547	201	1,528
Comprehensive loss	$ (59,042)	$ (57,790)	$ (115,320)	$ (95,801)
Net loss per share, basic and diluted (usd per share)	$ (0.56)	$ (0.61)	$ (1.11)	$ (1.02)
Weighted average number of shares outstanding, basic and diluted (in shares)	105,717,912	95,495,497	104,068,815	95,241,412