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Allowance for Losses on Loans - Credit Risk Profile Based on Payment Activity (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Sep. 30, 2023
--- | --- | ---
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 17,763,942 | $ 17,653,757
Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 10,563,949 | 10,507,610
Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 3,022,457 | 2,886,594
Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 3,332,293 | 3,310,101
Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 2,364,982 | 2,315,318
Commercial loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 1,695,506 | 1,838,936
Commercial loans | Land - acquisition & development |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 148,711 | 156,661
Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 7,199,993 | 7,146,147
Consumer loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 263,638 | 324,451
Consumer loans | Single-family residential |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 6,495,449 | 6,388,990
Consumer loans | Land - consumer lot loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 118,917 | 124,842
Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 247,145 | 237,754
Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | 74,844 | 70,110
Performing Loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 17,718,684 | $ 17,603,335
% of Total Loans | 99.70% | 99.70%
Performing Loans | Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 10,535,097 | $ 10,472,966
% of Total Loans | 99.70% | 99.70%
Performing Loans | Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 3,022,325 | $ 2,881,467
% of Total Loans | 100.00% | 99.80%
Performing Loans | Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 3,308,010 | $ 3,286,666
% of Total Loans | 99.30% | 99.30%
Performing Loans | Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 2,360,545 | $ 2,309,236
% of Total Loans | 99.80% | 99.70%
Performing Loans | Commercial loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 1,695,506 | $ 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 | $ 148,711 | $ 156,661
% of Total Loans | 100.00% | 100.00%
Performing Loans | Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 7,183,587 | $ 7,130,369
% of Total Loans | 99.80% | 99.80%
Performing Loans | Consumer loans | Construction |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 263,550 | $ 324,363
% of Total Loans | 100.00% | 100.00%
Performing Loans | Consumer loans | Single-family residential |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 6,480,053 | $ 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 | $ 118,860 | $ 124,833
% of Total Loans | 100.00% | 100.00%
Performing Loans | Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 246,542 | $ 237,018
% of Total Loans | 99.80% | 99.70%
Performing Loans | Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 74,582 | $ 70,083
% of Total Loans | 99.60% | 100.00%
Non-Performing Loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 45,258 | $ 50,422
% of Total Loans | 0.30% | 0.30%
Non-Performing Loans | Commercial loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 28,852 | $ 34,644
% of Total Loans | 0.30% | 0.30%
Non-Performing Loans | Commercial loans | Multi-family |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 132 | $ 5,127
% of Total Loans | 0.00% | 0.20%
Non-Performing Loans | Commercial loans | Commercial real estate |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 24,283 | $ 23,435
% of Total Loans | 0.70% | 0.70%
Non-Performing Loans | Commercial loans | Commercial & industrial |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 4,437 | $ 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 | $ 0 | $ 0
% of Total Loans | 0.00% | 0.00%
Non-Performing Loans | Consumer loans |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 16,406 | $ 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 | $ 15,396 | $ 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 | $ 57 | $ 9
% of Total Loans | 0.00% | 0.00%
Non-Performing Loans | Consumer loans | HELOC |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 603 | $ 736
% of Total Loans | 0.20% | 0.30%
Non-Performing Loans | Consumer loans | Consumer |  |
Financing Receivable, Credit Quality Indicator [Line Items] |  |
Amount | $ 262 | $ 27
% of Total Loans | 0.40% | 0.00%

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- Definition Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479344/326-20-45-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-3B Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-5 + Details
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