Cover |
Jun. 23, 2026 |
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| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 23, 2026 |
| Registrant Name | Columbia Financial, Inc. |
| Entity Incorporation, State or Country Code | MD |
| Entity File Number | 333-294103 |
| 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, 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 |
| Entity Address, State or Province | NJ |
| false | false |
| 0002115119 | 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 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 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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