Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 15,454	$ 7,620	$ 15,454	$ 7,620
Less: accumulated depreciation	(5,100)	(1,783)	(5,100)	(1,783)
Property and equipment, net	10,354	5,837	10,354	5,837
Depreciation and amortization expense			3,326	1,263	$ 364
Computer, equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment	2,218	652	2,218	652
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment	915	730	915	730
Capitalized internal-use software
Property, Plant and Equipment [Line Items]
Property and equipment	11,229	5,653	11,229	5,653
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	1,092	585	$ 1,092	$ 585
Property, Plant and Equipment
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 3,300	$ 1,300			$ 400