Cover Page Cover Page |
Jul. 28, 2026 |
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| Cover [Abstract] | |
| Document Type | 8-K/A |
| Document Period End Date | Jul. 28, 2026 |
| Entity Registrant Name | Columbia Financial, Inc. |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 001-43410 |
| Entity Tax Identification Number | 42-1991301 |
| Entity Address, Address Line One | 19-01 Route 208 North |
| Entity Address, City or Town | Fair Lawn |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07410 |
| City Area Code | 800 |
| Local Phone Number | 522-4167 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $0.01 par value per share |
| Trading Symbol | CLBK |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0002115119 |
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- Definition For the EDGAR submission types of Form 8-K: the date of the report, the date of the earliest event reported; for the EDGAR submission types of Form N-1A: the filing date; for all other submission types: the end of the reporting or transition period. The format of the date is YYYY-MM-DD. No definition available.
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- Definition The type of document being provided (such as 10-K, 10-Q, 485BPOS, etc). The document type is limited to the same value as the supporting SEC submission type, or the word 'Other'. No definition available.
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- Definition Address Line 1 such as Attn, Building Name, Street Name No definition available.
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- Definition Indicate if registrant meets the emerging growth company criteria. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Two-character EDGAR code representing the state or country of incorporation. No definition available.
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- Definition The exact name of the entity filing the report as specified in its charter, which is required by forms filed with the SEC. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The Tax Identification Number (TIN), also known as an Employer Identification Number (EIN), is a unique 9-digit value assigned by the IRS. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Local phone number for entity. No definition available.
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- Definition Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Boolean flag that is true when the Form 8-K filing is intended to satisfy the filing obligation of the registrant as written communications pursuant to Rule 425 under the Securities Act. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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