Stock-Based Compensation - Restricted Stock Plan and Performance Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restricted Stock | 2009 Restricted Stock Plan
Restricted stock plan activity, number of shares
Unvested and deferred at beginning of the period (in shares)			89,843
Granted (in shares)			38,675
Forfeited / Canceled (in shares)			(100)
Vested and deferred (in shares)			(42,283)
Unvested and deferred at end of the period (in shares)	86,135		86,135
Expected to vest (in shares)	86,135		86,135
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested and deferred at beginning of the period (in dollars per share)			$ 37.17
Granted (in dollars per share)			48.63
Forfeited / Canceled (in dollars per share)			46.46
Vested and deferred (in dollars per share)			26.56
Unvested and deferred at end of the period (in dollars per share)	$ 47.51		47.51
Expected to vest (in dollars per share)	$ 47.51		$ 47.51
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)			42,283
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)			$ 26.56
Restricted stock plan activity, other disclosures
Compensation expense	$ 401	$ 298	$ 1,278	$ 945
Remaining unrecognized compensation expense	$ 2,049		$ 2,049
Weighted average period for recognition			1 year 3 months 10 days
Restricted Stock | 2009 Restricted Stock Plan | Employee
Restricted stock plan activity, other disclosures
Repurchase of stock from employees (in shares)			32,675
Average purchase price (in dollars per share)	$ 47.18		$ 47.18
Restricted Stock | 2016 Restricted Stock Plan
Restricted stock plan activity, other disclosures
Compensation expense			$ 250	269
Deferred Restricted Stock | 2016 Restricted Stock Plan
Restricted stock plan activity, number of shares
Vested and deferred (in shares)			(30,325)
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)			$ 36.61
Deferred Restricted Stock plan activity, number of shares
Outstanding at beginning of period (in shares)			8,974
Granted (in shares)			5,575
Vested and deferred (in shares)			(8,974)
Outstanding at end of period (in shares)	5,575		5,575
Vested (in shares)			30,325
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Outstanding at beginning of period (in dollars per share)			$ 49.19
Granted (in dollars per share)			48.63
Vested and deferred (in dollars per share)			49.19
Outstanding at end of period (in dollars per share)	$ 48.63		48.63
Vested and deferred (in dollars per share)			$ 36.61
Restricted stock plan activity, other disclosures
Compensation expense	$ 68	110
Remaining unrecognized compensation expense	113		$ 113
Weighted average period for recognition			5 months 1 day
Performance Shares
Stock-Based Compensation
Remaining unrecognized compensation expense	$ 1,872		$ 1,872
Restricted stock plan activity, number of shares
Unvested and deferred at beginning of the period (in shares)			70,749
Granted (in shares)			24,375
Vested and deferred (in shares)			(31,804)
Unvested and deferred at end of the period (in shares)	63,320		63,320
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Unvested and deferred at beginning of the period (in dollars per share)			$ 48.60
Granted (in dollars per share)			60.40
Forfeited / Canceled (in dollars per share)			0.00
Vested and deferred (in dollars per share)			28.23
Unvested and deferred at end of the period (in dollars per share)	$ 63.37		$ 63.37
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)			31,804
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)			$ 28.23
Restricted stock plan activity, other disclosures
Compensation expense	$ 354	$ 309	$ 975	$ 915
Weighted average period for recognition			1 year 3 months 25 days
Repurchase of stock from employees (in shares)			17,481
Average purchase price (in dollars per share)	$ 45.16		$ 45.16
Performance Shares | Certain Employees
Restricted stock plan activity, number of shares
Vested and deferred (in shares)			(39,756)
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)			39,756