Stock-Based Compensation - Restricted Stock Plan and Performance Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Feb. 25, 2022	Jan. 24, 2020	Mar. 01, 2016
Restricted Stock | 2009 Restricted Stock Plan
Restricted stock plan activity, number of shares
Unvested and deferred at beginning of the period (in shares)	96,536
Granted (in shares)	30,159
Forfeited / Canceled (in shares)	(510)
Vested and deferred (in shares)	(36,342)
Unvested and deferred at end of the period (in shares)	89,843	96,536
Expected to vest (in shares)	89,843
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested and deferred at beginning of the period (in dollars per share)	$ 33.23
Granted (in dollars per share)	49.23
Forfeited / Canceled (in dollars per share)	30.11
Vested and deferred (in dollars per share)	36.82
Unvested and deferred at end of the period (in dollars per share)	37.17	$ 33.23
Expected to vest (in dollars per share)	$ 37.17
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)	36,342
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)	$ 36.82
Restricted stock plan activity, other disclosures
Compensation expense	$ 1,257	$ 1,474	$ 2,024
Remaining unrecognized compensation expense	$ 1,451
Weighted average period for recognition	1 year 2 months 1 day
Restricted Stock | 2009 Restricted Stock Plan | Employee
Restricted stock plan activity, other disclosures
Repurchase of stock from employees (in shares)	17,708
Average purchase price (in dollars per share)	$ 52.72
Restricted Stock | 2016 Restricted Stock Plan
Restricted stock plan activity, number of shares
Unvested and deferred at beginning of the period (in shares)	3,801
Granted (in shares)	8,974
Vested and deferred (in shares)	(3,801)
Unvested and deferred at end of the period (in shares)	8,974	3,801
Expected to vest (in shares)	21,351
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested and deferred at beginning of the period (in dollars per share)	$ 44.07
Granted (in dollars per share)	49.19
Vested and deferred (in dollars per share)	44.07
Unvested and deferred at end of the period (in dollars per share)	49.19	$ 44.07
Expected to vest (in dollars per share)	$ 31.32
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)	3,801
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)	$ 44.07
Restricted stock plan activity, other disclosures
Compensation expense	$ 378	$ 168	188
Remaining unrecognized compensation expense	$ 91
Weighted average period for recognition	2 months 15 days
Restricted Stock, Restricted Stock Units and Performance Shares
Stock-Based Compensation
Number of shares authorized under the plan						275,000
Restricted Stock, Restricted Stock Units and Performance Shares | 2020 Incentive Compensation Plan
Stock-Based Compensation
Number of shares authorized under the plan				575,000	250,000
Performance Shares
Stock-Based Compensation
Award vesting period	3 years
Performance Shares | Certain Employees
Restricted stock plan activity, number of shares
Unvested and deferred at beginning of the period (in shares)	76,420
Granted (in shares)	19,555
Vested and deferred (in shares)	(25,226)
Unvested and deferred at end of the period (in shares)	70,749	76,420
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested and deferred at beginning of the period (in dollars per share)	$ 41.37
Granted (in dollars per share)	69.39
Forfeited / Canceled (in dollars per share)	0.00
Vested and deferred (in dollars per share)	42.83
Unvested and deferred at end of the period (in dollars per share)	$ 48.60	$ 41.37
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)	25,226
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)	$ 42.83
Restricted stock plan activity, other disclosures
Compensation expense	$ 1,224	$ 1,021	$ 1,082
Remaining unrecognized compensation expense	$ 1,376
Weighted average period for recognition	1 year 6 months 10 days