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Business Combination - Summary of Merger-Related Expenses (Details) - Luther Burbank - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023
Business Acquisition [Line Items] |  |
Merger-related expenses | $ 26,319 | $ 3,015
Severance and employee-related |  |
Business Acquisition [Line Items] |  |
Merger-related expenses | 18,846 | 0
Legal and Professional |  |
Business Acquisition [Line Items] |  |
Merger-related expenses | 5,573 | 2,773
Charitable contributions |  |
Business Acquisition [Line Items] |  |
Merger-related expenses | 1,000 | 0
System conversion and integration |  |
Business Acquisition [Line Items] |  |
Merger-related expenses | $ 900 | $ 242

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