Pension and Retirement Plans - Fair value of plan assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	$ 10,880	$ 10,034
Cash on deposit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	137	428
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	9,682	8,703
Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	1,061	903
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	8,571	7,945
Level 1 | Cash on deposit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	137	428
Level 1 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	8,142	7,251
Level 1 | Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	292	266
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	2,309	2,089
Level 2 | Cash on deposit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	0	0
Level 2 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	1,540	1,452
Level 2 | Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	769	637
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	0	0
Level 3 | Cash on deposit
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	0	0
Level 3 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	0	0
Level 3 | Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of the assets	$ 0	$ 0