Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 61,648	$ 59,005
Less: accumulated depreciation	(20,802)	(12,273)
Total property and equipment, net	40,846	46,732
Depreciation expense	8,531	7,991	$ 7,415
Lab equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	24,216	21,846
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	34,738	34,563
Computers equipment and purchased software
Property, Plant and Equipment [Line Items]
Total property and equipment	1,254	1,156
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 1,440	$ 1,440