| Document and Entity Information - USD ($) $ in Millions | 12 Months Ended | ||
| Dec. 31, 2019 | Feb. 21, 2020 | Jun. 28, 2019 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | true | ||
| Document Period End Date | Dec. 31, 2019 | ||
| Document Fiscal Year Focus | 2019 | ||
| Document Fiscal Period Focus | FY | ||
| Trading Symbol | AVLR | ||
| Entity Registrant Name | AVALARA, INC. | ||
| Entity Central Index Key | 0001348036 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity Filer Category | Large Accelerated Filer | ||
| Entity Small Business | false | ||
| Entity Emerging Growth Company | false | ||
| Entity Common Stock, Shares Outstanding | 78,010,310 | ||
| Entity Current Reporting Status | Yes | ||
| Entity Shell Company | false | ||
| 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 | ||
| Entity Interactive Data Current | Yes | ||
| Title of 12(b) Security | Common Stock, Par Value $0.0001 Per Share | ||
| Security Exchange Name | NYSE | ||
| Entity Incorporation, State or Country Code | WA | ||
| Document Transition Report | false | ||
| Document Annual Report | true | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Entity Public Float | $ 5,012 | ||
| Documents Incorporated by Reference | DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s Definitive Proxy Statement relating to the 2020 Annual Meeting of Shareholders, are incorporated by reference into Part III of this report. | ||
| Amendment Description | Avalara, Inc. (the “Company”) is filing this Amendment No. 1 (this “Amendment No. 1”) to its annual report on Form 10-K for the fiscal year ended December 31, 2019, as filed with the Securities and Exchange Commission on February 28, 2020 (the “Original Form 10-K”), in order to correct the inadvertent omission of certain language in paragraph 4 of the certification of its Chief Executive Officer filed as Exhibit 31.1 and the certification of its Chief Financial Officer filed as Exhibit 31.2 to the Original Form 10-K. This Amendment No. 1 should be read in conjunction with the Original Form 10-K, which continues to speak as of the date of the Original Form 10-K. Other than the filing of the corrected certifications mentioned above, this Amendment No. 1 does not modify or update the disclosures in the Original Form 10-K in any way. Accordingly, this Amendment No. 1 does not reflect events occurring after the filing of the Original Form 10-K or modify or update any related or other disclosures. |
