Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Collaboration revenue:
Revenue	$ 73,993	$ 13,991	$ 13,481
Costs and expenses:
Research and development	153,953	103,902	89,726
Selling, general and administrative	56,485	34,503	33,738
Total costs and expenses	210,438	138,405	123,464
Loss from operations	(136,445)	(124,414)	(109,983)
Other income (expense), net	819	(52)	(992)
Interest income	10,706	5,568	2,553
Other income, net	11,525	5,516	1,561
Loss before income taxes	(124,920)	(118,898)	(108,422)
Income tax benefit (provision)	62	27	(32)
Net loss	(124,858)	(118,871)	(108,454)
Other comprehensive income (loss):
Net unrealized holding gains (losses) on short- and long-term investments during the period, net of tax	583	335	(470)
Comprehensive loss	$ (124,275)	$ (118,536)	$ (108,924)
Net loss per share- basic and diluted (in dollars per share)	$ (2.38)	$ (2.59)	$ (2.68)
Weighted-average number of common shares used in computing net loss per share-basic and diluted (in shares)	52,453	45,898	40,420
License and milestone
Collaboration revenue:
Revenue	$ 60,000	$ 0	$ 541
Cost Sharing
Collaboration revenue:
Revenue	$ 13,993	$ 13,991	$ 12,940