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Investment Securities: Held-to-Maturity Investment Securities by Risk (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Sep. 30, 2024
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Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | $ 140,954 | $ 172,097
U.S. Treasury and U.S. government agency securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 69,475 | 92,312
U.S. government agencies |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 47,017 | 49,481
Private label residential |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 22,744 | 28,479
Municipal securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 1,220 | 1,330
Bank issued trust preferred securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 498 | 495
AAA/AA/A |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 132,257 | 159,300
AAA/AA/A | U.S. Treasury and U.S. government agency securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 69,475 | 92,312
AAA/AA/A | U.S. government agencies |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 47,017 | 49,481
AAA/AA/A | Private label residential |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 14,545 | 16,277
AAA/AA/A | Municipal securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 1,220 | 1,230
AAA/AA/A | Bank issued trust preferred securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B | U.S. Treasury and U.S. government agency securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B | U.S. government agencies |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B | Private label residential |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B | Municipal securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
BBB/BB/B | Bank issued trust preferred securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
Unrated |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 8,697 | 12,797
Unrated | U.S. Treasury and U.S. government agency securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
Unrated | U.S. government agencies |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 0
Unrated | Private label residential |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 8,199 | 12,202
Unrated | Municipal securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | 0 | 100
Unrated | Bank issued trust preferred securities |  |
Debt Securities, Held-to-Maturity, Credit Quality Indicator [Line Items] |  |
Total held to maturity | $ 498 | $ 495

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