| Cover - USD ($) | 12 Months Ended | |
| Sep. 30, 2024 | Jan. 24, 2025 |
| Document Information [Line Items] | | |
| Document Type | 10-K/A | |
| Amendment Flag | true | |
| Amendment Description | This Amendment No. 1 to the Annual Report on Form 10-K (this “Amendment”) amends the Annual Report on Form 10-K for the fiscal year ended September 30, 2024, originally filed on December 13, 2024 (the “Original Filing”) by ESSA Bancorp, Inc., a Pennsylvania corporation (“ESSA Bancorp” or the “Company”). ESSA Bancorp is filing this Amendment to present the information required by Part III of Form 10-K as the Company will not file its definitive annual proxy statement within 120 days of the end of its fiscal year ended September 30, 2024. Pursuant to Rule 12b-15 under the Securities Exchange Act of 1934, as amended, this Amendment also contains new certifications by the principal executive officer and the principal financial officer as required by Section 302 of the Sarbanes-Oxley Act of 2002. Accordingly, Item 15(a)(3) of Part IV is amended to include the currently dated certifications as exhibits. Because no financial statements have been included in this Amendment and this Amendment does not contain or amend any disclosure with respect to Items 307 and 308 of Regulation S-K, paragraphs 3, 4 and 5 of the certifications have been omitted. On January 9, 2025, the Company entered into a definitive merger agreement with CNB Financial Corporation, pursuant to which the companies will combine in an all-stock merger. The completion of the merger remains subject to receipt of the requisite stockholder and regulatory approvals and other customary closing conditions. As a result, the Company does not anticipate holding an annual meeting of stockholders prior to the closing of the proposed merger. Except as described above or as expressly noted in this Amendment, no other changes have been made to the Original Filing. The Original Filing continues to speak as of and for the periods covered in the Original Filing, and the Company has not updated the disclosures contained therein to reflect any subsequent events. | |
| Document Period End Date | Sep. 30, 2024 | |
| Document Fiscal Year Focus | 2024 | |
| Document Fiscal Period Focus | FY | |
| Trading Symbol | ESSA | |
| Entity Registrant Name | ESSA Bancorp, Inc. | |
| Entity Central Index Key | 0001382230 | |
| Current Fiscal Year End Date | --09-30 | |
| Entity Well-known Seasoned Issuer | No | |
| Entity Current Reporting Status | Yes | |
| Entity Voluntary Filers | No | |
| Entity Filer Category | Non-accelerated Filer | |
| Entity Small Business | true | |
| Entity Emerging Growth Company | false | |
| Entity Shell Company | false | |
| Entity Public Float | | $ 195,325,406 |
| Entity Common Stock, Shares Outstanding | | 18,133,095 |
| Entity File Number | 001-33384 | |
| Entity Tax Identification Number | 20-8023072 | |
| Entity Address, Address Line One | 200 Palmer Street | |
| Entity Address, City or Town | Stroudsburg | |
| Entity Address, State or Province | PA | |
| Entity Address, Postal Zip Code | 18360 | |
| City Area Code | 855 | |
| Local Phone Number | 713-8001 | |
| Entity Interactive Data Current | Yes | |
| Entity Incorporation, State or Country Code | PA | |
| Title of 12(b) Security | Common Stock, $0.01 par value | |
| Security Exchange Name | NASDAQ | |
| Document Annual Report | true | |
| ICFR Auditor Attestation Flag | false | |
| Document Transition Report | false | |
| Document Financial Statement Error Correction [Flag] | false | |
| Auditor Name | S.R. Snodgrass, P.C. | |
| Auditor Location | Conshohocken, Pennsylvania | |
| Auditor Firm ID | 74 | |
| Documents Incorporated by Reference | None | |
