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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands | Sep. 30, 2025 USD ($) branch shares | Sep. 02, 2025 | Dec. 31, 2024 USD ($)
--- | --- | --- | ---
Business Combination [Line Items] |  |  |
Number of banking branches | branch | 166 |  |
Intangible assets amortization period (in years) | 8 years |  |
Accrued contingent liability | $ | $ 4,200 |  | $ 3,100
Mechanics Bancorp | Legacy Mechanics Bank Shareholders |  |  |
Business Combination [Line Items] |  |  |
Economic equity interest after merger |  | 91.70% |
Voting equity interest after merger |  | 91.34% |
Mechanics Bancorp | Legacy Homestreet, Inc. Shareholders |  |  |
Business Combination [Line Items] |  |  |
Economic equity interest after merger |  | 8.30% |
Voting equity interest after merger |  | 8.66% |
Mechanics Bancorp 2025 Equity Incentive Plan |  |  |
Business Combination [Line Items] |  |  |
Equity incentive plan shares (in shares) | shares | 7,750,000 |  |
Mechanics Bank Acquisition | Mechanics Bancorp |  |  |
Business Combination [Line Items] |  |  |
Voting equity interest after merger |  | 100.00% |
Minimum | Core Deposits |  |  |
Business Combination [Line Items] |  |  |
Intangible assets amortization period (in years) | 6 years |  |
Maximum | Core Deposits |  |  |
Business Combination [Line Items] |  |  |
Intangible assets amortization period (in years) | 10 years |  |

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