Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Sep. 30, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	77,351	63,284
2019 Plan
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	25,165	29,048
Options
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	19,065	21,191
Outstanding and unsettled restricted stock units (RSUs)
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	7,700	7,175
Shares available for issuance under the ESPP
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	5,449	5,870
Convertible senior notes
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	19,972	0