| Document and Entity Information | Dec. 29, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001348036 |
| Document Type | 8-K |
| Document Period End Date | Dec. 29, 2020 |
| Entity Registrant Name | AVALARA, INC. |
| Entity Incorporation State Country Code | WA |
| Entity File Number | 001-38525 |
| Entity Tax Identification Number | 91-1995935 |
| Entity Address, Address Line One | 255 South King Street |
| Entity Address, Address Line Two | Suite 1800 |
| Entity Address, City or Town | Seattle |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98104 |
| City Area Code | (206) |
| Local Phone Number | 826-4900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, Par Value $0.0001 Per Share |
| Trading Symbol | AVLR |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
