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INVESTMENT SECURITIES - Unrealized Losses and Fair Value of Securities (Details) $ in Thousands | Sep. 30, 2025 USD ($) security | Sep. 30, 2024 USD ($) security
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Number of debt securities with unrealized loss | security | 213 | 209
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | $ (1,446) | $ (429)
12 months or more, unrealized gross losses | (48,788) | (54,270)
Total, unrealized gross losses | (50,234) | (54,699)
Less than 12 months, fair value | 279,282 | 239,441
12 months or more, fair value | 941,676 | 1,125,962
Total, fair value | 1,220,958 | 1,365,403
Held-to-maturity securities |  |
Less than 12 months, unrealized gross losses | 0 | 0
12 months or more, unrealized gross losses | (37,136) | (36,839)
Total unrealized gross losses | (37,136) | (36,839)
Less than 12 months, fair value | 0 | 0
12 months or more, fair value | 310,597 | 348,573
Total, fair value | 310,597 | 348,573
Less than 12 months, unrealized gross losses | (1,446) | (429)
12 months or more, unrealized gross losses | (85,924) | (91,109)
Total unrealized gross losses | (87,370) | (91,538)
Less than 12 months, fair value | 279,282 | 239,441
12 months or more, fair value | 1,252,273 | 1,474,535
Total fair value | 1,531,555 | 1,713,976
Corporate debt securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (119) | 0
12 months or more, unrealized gross losses | (8,495) | (10,993)
Total, unrealized gross losses | (8,614) | (10,993)
Less than 12 months, fair value | 19,881 | 0
12 months or more, fair value | 102,342 | 146,060
Total, fair value | 122,223 | 146,060
Municipal bonds |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | 0 | (15)
12 months or more, unrealized gross losses | (405) | (394)
Total, unrealized gross losses | (405) | (409)
Less than 12 months, fair value | 0 | 19,985
12 months or more, fair value | 15,008 | 15,088
Total, fair value | 15,008 | 35,073
U.S. government and agency securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (483) |
12 months or more, unrealized gross losses | (127) |
Total, unrealized gross losses | (610) |
Less than 12 months, fair value | 143,444 |
12 months or more, fair value | 35,211 |
Total, fair value | 178,655 |
Asset-backed securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (62) | (249)
12 months or more, unrealized gross losses | (1,424) | (2,373)
Total, unrealized gross losses | (1,486) | (2,622)
Less than 12 months, fair value | 34,932 | 116,173
12 months or more, fair value | 135,315 | 235,846
Total, fair value | 170,247 | 352,019
Mortgage-backed securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (782) | (165)
12 months or more, unrealized gross losses | (38,337) | (40,510)
Total, unrealized gross losses | (39,119) | (40,675)
Less than 12 months, fair value | 81,025 | 103,283
12 months or more, fair value | 653,800 | 728,968
Total, fair value | $ 734,825 | $ 832,251

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