Stock-Based Compensation - Restricted Stock Plan and Performance Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
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)			(35,692)
Unvested and deferred at end of the period (in shares)	90,493		90,493
Expected to vest (in shares)	90,493		90,493
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)			37.06
Unvested and deferred at end of the period (in dollars per share)	$ 37.07		37.07
Expected to vest (in dollars per share)	$ 37.07		$ 37.07
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)			35,692
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)			$ 37.06
Restricted stock plan activity, other disclosures
Compensation expense	$ 298	$ 375	$ 945	$ 1,120
Remaining unrecognized compensation expense	$ 1,764		$ 1,764
Weighted average period for recognition			1 year 5 months 1 day
Restricted Stock | 2009 Restricted Stock Plan | Employee
Restricted stock plan activity, other disclosures
Repurchase of stock from employees (in shares)			17,531
Average purchase price (in dollars per share)	$ 52.74		$ 52.74
Deferred Restricted Stock | 2016 Restricted Stock Plan
Restricted stock plan activity, number of shares
Vested and deferred (in shares)			(21,351)
Restricted stock plan activity, Weighted Average Fair Value at Grant Date
Vested and deferred (in dollars per share)			$ 31.32
Deferred Restricted Stock plan activity, number of shares
Outstanding at beginning of period (in shares)			3,801
Granted (in shares)			8,974
Vested and deferred (in shares)			(3,801)
Outstanding at end of period (in shares)	8,974		8,974
Vested (in shares)			21,351
Deferred Restricted Stock plan activity, Weighted Average Fair Value at Grant Date
Outstanding at beginning of period (in dollars per share)			$ 44.07
Granted (in dollars per share)			49.19
Vested and deferred (in dollars per share)			44.07
Outstanding at end of period (in dollars per share)	$ 49.19		49.19
Vested and deferred (in dollars per share)			$ 31.32
Restricted stock plan activity, other disclosures
Compensation expense	$ 110	42	$ 269	126
Remaining unrecognized compensation expense	202		$ 202
Weighted average period for recognition			5 months 15 days
Performance Shares
Stock-Based Compensation
Remaining unrecognized compensation expense	$ 1,684		$ 1,684
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		70,749
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		$ 48.60
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	$ 309	$ 284	$ 915	$ 737
Weighted average period for recognition			1 year 4 months 9 days
Repurchase of stock from employees (in shares)			5,474
Average purchase price (in dollars per share)	$ 52.41		$ 52.41
Performance Shares | Certain Employees
Restricted stock plan activity, number of shares
Vested and deferred (in shares)			(12,429)
Deferred Restricted Stock plan activity, number of shares
Vested (in shares)			12,429