Balance Sheet Components - Property and Equipment, Net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 296,079,000
Less: Accumulated depreciation	(94,584,000)
Property and equipment, net	201,495,000
Property, plant and equipment, gross		$ 276,433,000
Less: Accumulated depreciation		(64,456,000)
Property and equipment, net		211,977,000		$ 209,494,000
Depreciation and amortization	31,021,000	24,862,000	$ 20,537,000
Building
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	0
Property, plant and equipment, gross		140,442,000
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	108,257,000
Property, plant and equipment, gross		96,907,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	152,426,000
Property, plant and equipment, gross		13,741,000
Furniture, fixtures and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,316,000
Property, plant and equipment, gross		2,122,000
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,985,000
Property, plant and equipment, gross		11,513,000
Internally developed software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,020,000
Property, plant and equipment, gross		7,020,000
Property and equipment, net		0
Right-of-use asset, financing
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,853,000
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 3,222,000
Property, plant and equipment, gross		$ 4,688,000