Investment Securities: Unrealized Gain (Loss) on Investments (Details) $ in Thousands	Sep. 30, 2023 USD ($) security	Sep. 30, 2022 USD ($) security
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 27,175	$ 189,351
Estimated Fair Value - 12 Months or Longer	224,179	47,652
Total Estimated Fair Value	251,354	237,003
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	(680)	(10,937)
Gross Unrealized Losses - 12 Months or Longer	(16,067)	(6,148)
Total Gross Unrealized Losses	$ (16,747)	$ (17,085)
Held-to-maturity, Qty, Less Than 12 Months | security	15	100
Held-to-maturity, Qty, 12 Months or Longer | security	111	20
Estimated Fair Value - Less Than 12 Months	$ 10,635	$ 25,170
Estimated Fair Value - 12 Months or Longer	30,809	15,705
Total Estimated Fair Value	41,444	40,875
Available-for-sale Securities, Gross Unrealized Losses:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Accumulated Loss	(308)	(292)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,053)	(602)
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,361)	$ (894)
Available-for-sale, Qty, Less than 12 Months | security	3	16
Available-for-sale, Qty, 12 Months or Longer | security	27	13
U.S. Treasury and U.S. government agency securities
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 9,455	$ 115,504
Estimated Fair Value - 12 Months or Longer	152,082	33,638
Total Estimated Fair Value	161,537	149,142
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	(129)	(7,224)
Gross Unrealized Losses - 12 Months or Longer	(9,959)	(4,885)
Total Gross Unrealized Losses	$ (10,088)	$ (12,109)
Held-to-maturity, Qty, Less Than 12 Months | security	1	17
Held-to-maturity, Qty, 12 Months or Longer | security	26	9
Mortgage-backed securities, U.S. government agencies
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 16,432	$ 35,896
Estimated Fair Value - 12 Months or Longer	31,703	5,306
Total Estimated Fair Value	48,135	41,202
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	(549)	(1,449)
Gross Unrealized Losses - 12 Months or Longer	(3,401)	(1,037)
Total Gross Unrealized Losses	$ (3,950)	$ (2,486)
Held-to-maturity, Qty, Less Than 12 Months | security	13	54
Held-to-maturity, Qty, 12 Months or Longer | security	51	5
Estimated Fair Value - Less Than 12 Months	$ 10,635	$ 25,170
Estimated Fair Value - 12 Months or Longer	30,809	15,705
Total Estimated Fair Value	41,444	40,875
Available-for-sale Securities, Gross Unrealized Losses:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Accumulated Loss	(308)	(292)
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,053)	(602)
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (1,361)	$ (894)
Available-for-sale, Qty, Less than 12 Months | security	3	16
Available-for-sale, Qty, 12 Months or Longer | security	27	13
Mortgage-backed securities, Private label residential
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 1,288	$ 35,447
Estimated Fair Value - 12 Months or Longer	38,205	8,708
Total Estimated Fair Value	39,493	44,155
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	(2)	(2,166)
Gross Unrealized Losses - 12 Months or Longer	(2,609)	(226)
Total Gross Unrealized Losses	$ (2,611)	$ (2,392)
Held-to-maturity, Qty, Less Than 12 Months | security	1	27
Held-to-maturity, Qty, 12 Months or Longer | security	32	6
Taxable municipal securities
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 0
Estimated Fair Value - 12 Months or Longer	1,740
Total Estimated Fair Value	1,740
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	0
Gross Unrealized Losses - 12 Months or Longer	(47)
Total Gross Unrealized Losses	$ (47)
Held-to-maturity, Qty, Less Than 12 Months | security	0
Held-to-maturity, Qty, 12 Months or Longer | security	1
Bank issued trust preferred securities
Held-to-maturity Securities, Fair Value:
Estimated Fair Value - Less Than 12 Months	$ 0	$ 469
Estimated Fair Value - 12 Months or Longer	449	0
Total Estimated Fair Value	449	469
Held-to-maturity Securities, Gross Unrealized Losses
Gross Unrealized Losses - Less Than 12 Months	0	(31)
Gross Unrealized Losses - 12 Months or Longer	(51)	0
Total Gross Unrealized Losses	$ (51)	$ (31)
Held-to-maturity, Qty, Less Than 12 Months | security	0	1
Held-to-maturity, Qty, 12 Months or Longer | security	1	0