Common Stock - Schedule of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Mar. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	61,057	63,284
2019 Plan
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	26,936	29,048
Options
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	21,269	21,191
Outstanding and unsettled restricted stock units (RSUs)
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	6,982	7,175
ESPP
Class of Stock [Line Items]
Shares of common stock reserved (in shares)	5,870	5,870