STOCK-BASED COMPENSATION - Schedule of share-based compensation expense (Details) - Blue Foundry Bancorp 2022 Equity Incentive Plan (Equity Plan) - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2025 |
Dec. 31, 2024 |
|
| Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] | ||
| Total share-based compensation expense | $ 3,121 | $ 3,165 |
| Stock option expense | ||
| Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] | ||
| Total share-based compensation expense | 1,406 | 1,461 |
| Restricted stock expense | ||
| Employee Stock Ownership Plan (ESOP) Disclosures [Line Items] | ||
| Total share-based compensation expense | $ 1,715 | $ 1,704 |