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Loans Receivable - Narrative (Details) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2024 USD ($) agreement | Mar. 31, 2024 USD ($) portfolioSegment | Sep. 30, 2023 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Number of portfolio segments for loans held for investment | portfolioSegment |  | 2 |
Loans held for sale | $ 2,993,658,000 | $ 2,993,658,000 | $ 0
Accrued interest receivables for loans | 103,137,000 | 103,137,000 | 77,349,000
Loans pledged to secure borrowings from the Federal Home Loan Bank | $ 9,131,125,000 | 9,131,125,000 | 8,941,201,000
Number of pledge agreements | agreement | 2 |  |
Gross loans | $ 22,598,153,000 | 22,598,153,000 | 19,648,504,000
Nonaccrual interest income recognized |  | 435,000 |
Impaired, interest income on accrual accrual and performed loans |  | 1,347,000 |
Loan modified, subsequent default |  | 0 |
FRB Advances |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Short-term debt | 0 | 0 |
FRB Advances | Asset Pledged as Collateral |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Gross loans | 3,681,859,000 | 3,681,859,000 |
FHLB of San Francisco | FHLB Advances | Asset Pledged as Collateral |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Gross loans | 1,757,206,000 | 1,757,206,000 |
Commercial loans |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Gross loans | 12,882,231,000 | 12,882,231,000 | 12,094,294,000
Commercial loans | Commercial & industrial |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Gross loans | 2,290,452,000 | 2,290,452,000 | $ 2,321,717,000
Commercial loans | Commercial & industrial | 31 days past due |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Loan modified, accumulated amortized cost | $ 0 | $ 0 |

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