Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Unearned  Shares Issued to Employee Stock Ownership Plan ("ESOP")	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Sep. 30, 2017	$ 111,000	$ 13,286	$ (397)	$ 98,235	$ (124)
Beginning Balance (in shares) at Sep. 30, 2017		7,361,077
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,721			16,721
Other comprehensive loss	(5)				(5)
Exercise of stock options	$ 318	$ 318
Exercise of stock options (in shares)	40,100	40,100
Common stock dividends	$ (4,431)			(4,431)
Earned ESOP shares, net of income taxes	882	$ 618	264
Stock option compensation expense	172	172
Ending Balance at Sep. 30, 2018	124,657	$ 14,394	(133)	110,525	(129)
Ending Balance (in shares) at Sep. 30, 2018		7,401,177
Beginning Balance at Sep. 30, 2018	124,657	$ 14,394	(133)	110,525	(129)
Beginning Balance (in shares) at Sep. 30, 2018		7,401,177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,020			24,020
Other comprehensive loss	$ 116				116
Repurchase of common stock		$ (499)
Repurchase of common stock (in shares)	(499,000)	(20,440)
Common stock issued for business combination (shares)		904,826
Common stock issued for business combination	$ 28,267	$ 28,267
Exercise of stock options	$ 401	$ 401
Exercise of stock options (in shares)	43,856	43,856
Common stock dividends	$ (6,495)			(6,495)
Earned ESOP shares, net of income taxes	441	$ 308	133
Stock option compensation expense	159	159
Ending Balance at Sep. 30, 2019	171,067	$ 43,030	$ 0	127,987	50
Ending Balance (in shares) at Sep. 30, 2019		8,329,419
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update ("ASU") 2016-01				(63)	63
Net income	24,269			24,269
Other comprehensive loss	11				11
Repurchase of common stock	(1,238)	$ (1,238)
Repurchase of common stock (in shares)		(56,601)
Exercise of stock options	$ 391	$ 391
Exercise of stock options (in shares)	37,975	37,975
Common stock dividends	$ (7,083)			(7,083)
Earned ESOP shares, net of income taxes	31	$ 31
Stock option compensation expense	182	182
Ending Balance at Sep. 30, 2020	$ 187,630	$ 42,396		$ 145,173	$ 61
Ending Balance (in shares) at Sep. 30, 2020		8,310,793