Condensed Financial Information - Parent Company Only: Condensed Statements of Cash Flows, Parent Company (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities
Net income	$ 8,447	$ 7,100	$ 6,755	$ 6,859	$ 6,355	$ 5,924	$ 5,708	$ 6,296	$ 29,161	$ 24,283	$ 27,118
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense									537	390	320
Net cash provided by operating activities									30,158	23,020	30,997
Cash flows from investing activities
Net cash used in investing activities									(8,246)	(45,797)	(170,223)
Cash flows from financing activities
Proceeds from exercise of stock options									1,665	659	698
Repurchase of common stock, net of tax									(5,759)	(5,958)	(4,998)
Payment of dividends									(8,085)	(7,650)	(8,267)
Net cash provided by (used in) financing activities									56,788	58,784	(48,808)
Net increase (decrease) in cash and cash equivalents									78,700	36,007	(188,034)
Cash and cash equivalents:
Beginning of year				164,728					164,728
End of year	243,428				164,728				243,428	164,728
Parent Company
Cash flows from operating activities
Net income									29,161	24,283	27,118
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed income of Bank									(17,401)	(10,442)	(15,897)
Stock-based compensation expense									537	390	320
Other, net									22	(50)	100
Net cash provided by operating activities									12,319	14,181	11,641
Cash flows from investing activities
Investment in Bank									(415)	(319)	(267)
Net cash used in investing activities									(415)	(319)	(267)
Cash flows from financing activities
Proceeds from exercise of stock options									1,665	659	698
Repurchase of common stock, net of tax									(5,759)	(5,958)	(4,998)
Payment of dividends									(8,085)	(7,650)	(8,267)
Net cash provided by (used in) financing activities									(12,179)	(12,949)	(12,567)
Net increase (decrease) in cash and cash equivalents									(275)	913	(1,193)
Cash and cash equivalents:
Beginning of year				$ 1,430				$ 517	1,430	517	1,710
End of year	$ 1,155				$ 1,430				$ 1,155	$ 1,430	$ 517