Common Stock and Employee Stock Plans - Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2019 shares
Options issued and outstanding under the 2008 Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	2,957,350
RSUs outstanding under the 2008 Plan, the 2018 Plan, and the 2019 Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	41,685,376
Remaining shares available for future issuance under the 2019 ESPP Plan and the 2019 Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	60,767,268