Parent Company - Condensed Statement of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
OPERATING ACTIVITIES
Net income	$ 14,416	$ 12,623
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for depreciation	1,077	1,084
(Increase) decrease in accrued interest receivable	(695)	415
Deferred federal income taxes	(134)	1,026
Other, net	2,856	(1,968)
Net cash provided by operating activities	19,749	18,190
FINANCING ACTIVITIES
Purchase of treasury stock shares	(6,567)	(7,797)
Dividends on common stock	(4,559)	(4,266)
Net cash provided by (used for) financing activities	68,493	(56,428)
Increase in cash and cash equivalents	103,675	8,703
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	52,242	43,539
CASH AND CASH EQUIVALENTS AT END OF YEAR	155,917	52,242
Parent Company [Member]
OPERATING ACTIVITIES
Net income	14,416	12,623
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net earnings of subsidiary	(4,357)	(2,518)
Provision for depreciation	10	10
Increase in accrued income taxes	(4)	(58)
(Increase) decrease in accrued interest receivable	67	(61)
Deferred federal income taxes		1
Other, net	684	707
Net cash provided by operating activities	10,816	10,704
FINANCING ACTIVITIES
Purchase of treasury stock shares	(6,567)	(7,797)
Dividends on common stock	(4,559)	(4,266)
Net cash provided by (used for) financing activities	(11,126)	(12,063)
Increase in cash and cash equivalents	(310)	(1,359)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	2,354	3,713
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 2,044	$ 2,354