RELATED PARTY AND PARTY-IN-INTEREST TRANSACTIONS (Details) - Needham Bank 401(k) Plan - USD ($) |
12 Months Ended | |
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Dec. 31, 2025 |
Dec. 31, 2024 |
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| RELATED PARTY AND PARTY-IN-INTEREST TRANSACTIONS | ||
| Custodian fees | $ 81,440 | |
| Custodian | ||
| RELATED PARTY AND PARTY-IN-INTEREST TRANSACTIONS | ||
| Custodian fees | $ 81,440 | |
| NB Bancorp, Inc | Common stock | ||
| RELATED PARTY AND PARTY-IN-INTEREST TRANSACTIONS | ||
| Number of shares held | 600,002 | 633,201 |
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- Definition Amount of decrease in net asset available for benefit from administrative expense incurred by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Reference 1: http://www.xbrl.org/2003/role/exampleRef
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- Definition Number of shares or units of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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