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FAIR VALUE OF FINANCIAL INSTRUMENTS - Assets Measured at Fair Value on Recurring Basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value $ 1,219,616 $ 1,327,843
Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Common equities and mutual funds 4,808 3,787
Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Common equities and mutual funds 0 0
Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Common equities and mutual funds 0 0
SBA securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 9,900 10,769
Obligations of states and political subdivisions    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 124 162
Non-bank qualified obligations of states and political subdivisions    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 171,786 187,040
Asset-backed securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 108,115 136,372
Mortgage-backed securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 906,566 972,250
Recurring    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 1,219,616 1,327,843
Common equities and mutual funds 4,808 3,787
Non-marketable equity securities 13,456 13,237
Recurring | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Common equities and mutual funds 4,808 3,787
Non-marketable equity securities 0 0
Recurring | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 1,219,616 1,327,843
Common equities and mutual funds 0 0
Non-marketable equity securities 0 0
Recurring | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Common equities and mutual funds 0 0
Non-marketable equity securities 0 0
Recurring | Corporate securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 23,125 21,250
Recurring | Corporate securities | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Corporate securities | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 23,125 21,250
Recurring | Corporate securities | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | SBA securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 9,900 10,769
Recurring | SBA securities | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | SBA securities | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 9,900 10,769
Recurring | SBA securities | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Obligations of states and political subdivisions    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 124 162
Recurring | Obligations of states and political subdivisions | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Obligations of states and political subdivisions | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 124 162
Recurring | Obligations of states and political subdivisions | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Non-bank qualified obligations of states and political subdivisions    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 171,786 187,040
Recurring | Non-bank qualified obligations of states and political subdivisions | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Non-bank qualified obligations of states and political subdivisions | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 171,786 187,040
Recurring | Non-bank qualified obligations of states and political subdivisions | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Asset-backed securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 108,115 136,372
Recurring | Asset-backed securities | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Asset-backed securities | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 108,115 136,372
Recurring | Asset-backed securities | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Mortgage-backed securities    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 906,566 972,250
Recurring | Mortgage-backed securities | Level 1    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 0 0
Recurring | Mortgage-backed securities | Level 2    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value 906,566 972,250
Recurring | Mortgage-backed securities | Level 3    
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value $ 0 $ 0