Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 47,296,000	$ 31,774,000	$ 89,337,000	$ 55,177,000
General and administrative	15,862,000	14,187,000	31,502,000	27,245,000
Total operating expenses	63,158,000	45,961,000	120,839,000	82,422,000
Loss from operations	(63,158,000)	(45,961,000)	(120,839,000)	(82,422,000)
Other income (expense), net:
Interest and other income, net	2,340,000	4,559,000	5,600,000	9,384,000
Other expenses	(156,000)	0	(215,000)	0
Total other income (expense), net	2,184,000	4,559,000	5,385,000	9,384,000
Loss before income taxes	(60,974,000)	(41,402,000)	(115,454,000)	(73,038,000)
Benefit from income taxes	0	159,000	0	209,000
Net loss	(60,974,000)	(41,243,000)	(115,454,000)	(72,829,000)
Other comprehensive income:
Net unrealized gain on available-for-sale investments	220,000	756,000	685,000	1,855,000
Net comprehensive loss	$ (60,754,000)	$ (40,487,000)	$ (114,769,000)	$ (70,974,000)
Net loss per share, basic and diluted (in dollars per share)	$ (0.53)	$ (0.41)	$ (1.03)	$ (0.74)
Weighted-average number of shares used in computing net loss per share, basic and diluted (in shares)	115,377,210	99,846,946	112,163,123	98,588,410