| Cover Page - shares | 3 Months Ended | |
| Mar. 31, 2021 | May 07, 2021 | |
| Cover [Abstract] | ||
| Document Type | 10-Q/A | |
| Amendment Flag | true | |
| Document Period End Date | Mar. 31, 2021 | |
| Document Fiscal Year Focus | 2021 | |
| Document Fiscal Period Focus | Q1 | |
| Trading Symbol | ALNA | |
| Entity Registrant Name | Allena Pharmaceuticals, Inc. | |
| Entity Central Index Key | 0001624658 | |
| Entity Current Reporting Status | Yes | |
| Entity Interactive Data Current | Yes | |
| Current Fiscal Year End Date | --12-31 | |
| Entity Filer Category | Non-accelerated Filer | |
| Entity Shell Company | false | |
| Entity Small Business | true | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | true | |
| Entity Common Stock, Shares Outstanding | 57,690,060 | |
| Entity File Number | 001-38268 | |
| Entity Tax Identification Number | 45-2729920 | |
| Entity Address, Address Line One | One Newton Executive Park | |
| Entity Address, Address Line Two | Suite 202 | |
| Entity Address, City or Town | Newton | |
| Entity Address, State or Province | MA | |
| Entity Address, Postal Zip Code | 02462 | |
| City Area Code | 617 | |
| Local Phone Number | 467-4577 | |
| Title of 12(b) Security | Common Stock, par value $0.001 per share | |
| Security Exchange Name | NASDAQ | |
| Document Quarterly Report | true | |
| Document Transition Report | false | |
| Entity Incorporation, State or Country Code | DE | |
| Amendment Description | Allena Pharmaceuticals, Inc. (the “Company”) is filing this Amendment No. 1 (the “Amendment”) on Form 10-Q/A to amend its Quarterly Report on Form 10-Q for the quarter ended March 31, 2021, filed with the Securities and Exchange Commission on May 13, 2021 (the “Original 10-Q”), for the purpose of filing revised versions of Exhibits 31.1 and 31.2 filed with the Original 10-Q. The Company is filing revised exhibits solely in order to include in the certifications set forth in the Exhibits the language added to the introductory portion of paragraph 4 and the language of revised paragraph 4(b), which language was inadvertently omitted from the certifications when originally filed. The Amendment does not reflect events occurring after the date of the filing of the Original 10-Q or modify or update any of the other disclosures contained therein in any way. Accordingly, the Amendment should be read in conjunction with the Original 10-Q. The Amendment consists solely of the preceding cover page, this explanatory note, the signature page and paragraphs 1, 2, 4 and 5 of each of the revised certifications filed as exhibits to the Amendment. Because no financial statements have been included in this Amendment, paragraph 3 of each of the certifications set forth in the Exhibits has been omitted. |
