Stockholders' Equity and Stock Based Compensation - Shares of Common Stock Reserved for Future Issuance (Details) - shares shares in Thousands	Sep. 30, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	101,878	199,943
Redeemable convertible preferred stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	0	153,938
2011 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	0	9,981
2011 Stock Plan | Options and RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	60,319	36,024
2021 Equity Incentive Plan:
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	35,059	0
2021 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock reserved for issuance (in shares)	6,500	0