Investment Securities - Investment securities with gross unrealized losses (Details) $ in Thousands	Jun. 30, 2024 USD ($) position	Sep. 30, 2023 USD ($) position
Fair Value
Continuous loss position less than twelve months	$ 25,557	$ 53,662
Continuous loss position more than twelve months	180,582	163,211
Total debt securities available for sale	$ 206,139	$ 216,873
Number of Investment Positions
Continuous loss position less than twelve months | position	27	53
Continuous loss position more than twelve months | position	153	150
Total debt securities available for sale | position	180	203
Continuous loss position more than twelve months, held to maturity | position		1
Total debt securities held to maturity | position		1
Gross Unrealized Losses
Continuous loss position less than twelve months	$ 256	$ 4,144
Continuous loss position more than twelve months	22,098	33,360
Total debt securities available for sale	22,354	37,504
Fair Value
Continuous loss position more than twelve months, held to maturity		19
Total debt securities held to maturity		19
Gross Unrealized Losses
Continuous loss position more than twelve months, held to maturity		1
U.S. Treasury notes
Fair Value
Continuous loss position less than twelve months	1,225	1,576
Continuous loss position more than twelve months	$ 25,225	$ 24,373
Number of Investment Positions
Continuous loss position less than twelve months | position	4	5
Continuous loss position more than twelve months | position	1	1
Gross Unrealized Losses
Continuous loss position less than twelve months	$ 17	$ 49
Continuous loss position more than twelve months	3,832	4,600
Agency mortgage-backed
Fair Value
Continuous loss position less than twelve months		163
Continuous loss position more than twelve months	$ 23,530	$ 23,859
Number of Investment Positions
Continuous loss position less than twelve months | position		2
Continuous loss position more than twelve months | position	15	15
Continuous loss position more than twelve months, held to maturity | position		1
Gross Unrealized Losses
Continuous loss position less than twelve months		$ 8
Continuous loss position more than twelve months	$ 3,385	4,266
Fair Value
Continuous loss position more than twelve months, held to maturity		19
Gross Unrealized Losses
Continuous loss position more than twelve months, held to maturity		1
Agency CMO
Fair Value
Continuous loss position more than twelve months	$ 12,312	$ 8,493
Number of Investment Positions
Continuous loss position more than twelve months | position	15	14
Gross Unrealized Losses
Continuous loss position more than twelve months	$ 1,089	$ 860
Privately-issued CMO
Fair Value
Continuous loss position more than twelve months	$ 239	$ 375
Number of Investment Positions
Continuous loss position more than twelve months | position	1	2
Gross Unrealized Losses
Continuous loss position more than twelve months	$ 2	$ 30
Privately-issued ABS
Fair Value
Continuous loss position more than twelve months	$ 147	$ 212
Number of Investment Positions
Continuous loss position more than twelve months | position	1	1
Gross Unrealized Losses
Continuous loss position more than twelve months	$ 1	$ 3
Agency CMO
Fair Value
Continuous loss position less than twelve months		$ 4,249
Number of Investment Positions
Continuous loss position less than twelve months | position		1
Gross Unrealized Losses
Continuous loss position less than twelve months		$ 462
SBA certificates
Fair Value
Continuous loss position less than twelve months		31
Continuous loss position more than twelve months	$ 10,800	$ 10,714
Number of Investment Positions
Continuous loss position less than twelve months | position		1
Continuous loss position more than twelve months | position	3	2
Gross Unrealized Losses
Continuous loss position less than twelve months		$ 3
Continuous loss position more than twelve months	$ 424	839
Municipal bonds
Fair Value
Continuous loss position less than twelve months	24,332	45,931
Continuous loss position more than twelve months	$ 106,450	$ 95,185
Number of Investment Positions
Continuous loss position less than twelve months | position	23	43
Continuous loss position more than twelve months | position	116	115
Gross Unrealized Losses
Continuous loss position less than twelve months	$ 239	$ 3,334
Continuous loss position more than twelve months	13,244	22,762
Other
Fair Value
Continuous loss position less than twelve months		$ 1,712
Continuous loss position more than twelve months	$ 1,879
Number of Investment Positions
Continuous loss position less than twelve months | position		1
Continuous loss position more than twelve months | position	1
Gross Unrealized Losses
Continuous loss position less than twelve months		$ 288
Continuous loss position more than twelve months	$ 121