Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Collaboration revenue:
Revenues	$ 39,752	$ 27,666	$ 44,096	$ 30,447
Costs and expenses:
Research and development	38,251	34,765	75,917	67,536
Selling, general and administrative	20,414	14,037	38,663	24,851
Total costs and expenses	58,665	48,802	114,580	92,387
Loss from operations	(18,913)	(21,136)	(70,484)	(61,940)
Other income, net	466	3,230	1,113	6,003
Loss before income taxes	(18,447)	(17,906)	(69,371)	(55,937)
Income tax (provision) benefit	(4)	44	(20)	24
Net loss	(18,451)	(17,862)	(69,391)	(55,913)
Other comprehensive (loss) income:
Net unrealized holding gains (losses) on short-term and long-term investments during the period, net of tax	161	452	(106)	721
Comprehensive loss	$ (18,290)	$ (17,410)	$ (69,497)	$ (55,192)
Net loss per share- basic and diluted (in dollars per share)	$ (0.34)	$ (0.34)	$ (1.29)	$ (1.08)
Weighted-average number of common shares used in computing net loss per share- basic and diluted (in shares)	53,860	52,689	53,610	51,912
Milestone
Collaboration revenue:
Revenues	$ 25,000	$ 25,000	$ 25,000	$ 25,000
Cost-sharing, net
Collaboration revenue:
Revenues	3,678	2,666	6,502	5,447
Royalty
Collaboration revenue:
Revenues	$ 11,074	$ 0	$ 12,594	$ 0