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Allowance for Losses on Loans - Credit Risk Profile Based on Payment Activity (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Sep. 30, 2023
--- | --- | ---
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 20,996,836 | $ 17,653,757
Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 11,717,725 | 10,507,610
Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 4,089,719 | 2,886,594
Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 3,544,884 | 3,310,101
Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 2,283,922 | 2,315,318
Commercial loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 1,623,496 | 1,838,936
Commercial loans | Land - acquisition & development |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 175,704 | 156,661
Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 9,279,111 | 7,146,147
Consumer loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 223,377 | 324,451
Consumer loans | Single-family residential |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 8,619,916 | 6,388,990
Consumer loans | Land - consumer lot loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 114,256 | 124,842
Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 247,305 | 237,754
Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 74,257 | 70,110
Performing Loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 20,936,030 | $ 17,603,335
% of Total Loans | 99.70% | 99.70%
Performing Loans | Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 11,677,778 | $ 10,472,966
% of Total Loans | 99.70% | 99.70%
Performing Loans | Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 4,081,342 | $ 2,881,467
% of Total Loans | 99.80% | 99.80%
Performing Loans | Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 3,517,862 | $ 3,286,666
% of Total Loans | 99.20% | 99.30%
Performing Loans | Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 2,279,486 | $ 2,309,236
% of Total Loans | 99.80% | 99.70%
Performing Loans | Commercial loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 1,623,496 | $ 1,838,936
% of Total Loans | 100.00% | 100.00%
Performing Loans | Commercial loans | Land - acquisition & development |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 175,592 | $ 156,661
% of Total Loans | 99.90% | 100.00%
Performing Loans | Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 9,258,252 | $ 7,130,369
% of Total Loans | 99.80% | 99.80%
Performing Loans | Consumer loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 223,289 | $ 324,363
% of Total Loans | 100.00% | 100.00%
Performing Loans | Consumer loans | Single-family residential |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 8,599,900 | $ 6,374,072
% of Total Loans | 99.80% | 99.80%
Performing Loans | Consumer loans | Land - consumer lot loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 114,256 | $ 124,833
% of Total Loans | 100.00% | 100.00%
Performing Loans | Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 246,814 | $ 237,018
% of Total Loans | 99.80% | 99.70%
Performing Loans | Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 73,993 | $ 70,083
% of Total Loans | 99.60% | 100.00%
Non-Performing Loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 60,806 | $ 50,422
% of Total Loans | 0.30% | 0.30%
Non-Performing Loans | Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 39,947 | $ 34,644
% of Total Loans | 0.30% | 0.30%
Non-Performing Loans | Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 8,377 | $ 5,127
% of Total Loans | 0.20% | 0.20%
Non-Performing Loans | Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 27,022 | $ 23,435
% of Total Loans | 0.80% | 0.70%
Non-Performing Loans | Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 4,436 | $ 6,082
% of Total Loans | 0.20% | 0.30%
Non-Performing Loans | Commercial loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 0 | $ 0
% of Total Loans | 0.00% | 0.00%
Non-Performing Loans | Commercial loans | Land - acquisition & development |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 112 | $ 0
% of Total Loans | 0.10% | 0.00%
Non-Performing Loans | Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 20,859 | $ 15,778
% of Total Loans | 0.20% | 0.20%
Non-Performing Loans | Consumer loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 88 | $ 88
% of Total Loans | 0.00% | 0.00%
Non-Performing Loans | Consumer loans | Single-family residential |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 20,016 | $ 14,918
% of Total Loans | 0.20% | 0.20%
Non-Performing Loans | Consumer loans | Land - consumer lot loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 0 | $ 9
% of Total Loans | 0.00% | 0.00%
Non-Performing Loans | Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 491 | $ 736
% of Total Loans | 0.20% | 0.30%
Non-Performing Loans | Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 264 | $ 27
% of Total Loans | 0.40% | 0.00%

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