v3.26.1
Fair Value Measurements: Balances of assets and liabilities measured at estimated fair value on a recurring basis (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value $ 90,484 $ 78,240
MBS: U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 90,484 73,272
Recurring    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 91,342 79,104
Recurring | U.S. Treasury and U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   4,968
Recurring | MBS: U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 90,484 73,272
Recurring | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 858 864
Recurring | Fair Value, Inputs, Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 858 5,832
Recurring | Fair Value, Inputs, Level 1 | U.S. Treasury and U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   4,968
Recurring | Fair Value, Inputs, Level 1 | MBS: U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring | Fair Value, Inputs, Level 1 | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 858 864
Recurring | Fair Value, Inputs, Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 90,484 73,272
Recurring | Fair Value, Inputs, Level 2 | U.S. Treasury and U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   0
Recurring | Fair Value, Inputs, Level 2 | MBS: U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 90,484 73,272
Recurring | Fair Value, Inputs, Level 2 | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring | Fair Value, Inputs, Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring | Fair Value, Inputs, Level 3 | U.S. Treasury and U.S. government agency securities    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value   0
Recurring | Fair Value, Inputs, Level 3 | MBS: U.S. government agencies    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value 0 0
Recurring | Fair Value, Inputs, Level 3 | Mutual funds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Estimated Fair Value $ 0 $ 0