Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 51,421,000	$ 39,995,000	$ 140,759,000	$ 95,172,000
General and administrative	16,619,000	15,016,000	48,122,000	42,261,000
Total operating expenses	68,040,000	55,011,000	188,881,000	137,433,000
Loss from operations	(68,040,000)	(55,011,000)	(188,881,000)	(137,433,000)
Other income (expense), net:
Interest and other income, net	2,005,000	4,309,000	7,606,000	13,693,000
Other expenses	(162,000)	0	(376,000)	0
Total other income (expense), net	1,843,000	4,309,000	7,230,000	13,693,000
Loss before income taxes	(66,197,000)	(50,702,000)	(181,651,000)	(123,740,000)
Benefit (expense) from income taxes	0	(33,000)	0	176,000
Net loss	(66,197,000)	(50,735,000)	(181,651,000)	(123,564,000)
Other comprehensive income:
Net unrealized gain (loss) on available-for-sale investments	(877,000)	(295,000)	(192,000)	1,560,000
Net comprehensive loss	$ (67,074,000)	$ (51,030,000)	$ (181,843,000)	$ (122,004,000)
Net loss per share, basic and diluted (in dollars per share)	$ (0.52)	$ (0.50)	$ (1.55)	$ (1.24)
Weighted-average number of shares used in computing net loss per share, basic and diluted (in shares)	127,140,755	102,186,644	117,227,079	99,801,001