Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Pension:
Pension and Retirement Plans
Interest cost	$ 137	$ 114	$ 350	$ 341
Expected return on plan assets	(156)	(149)	(400)	(445)
Amortization of past service costs	2	2	6	6
Amortization of net gain	(2)	(1)	(5)	(4)
Net periodic (benefit) cost	(19)	(34)	(49)	(102)
Pension: | United Kingdom
Pension and Retirement Plans
Interest cost	135	112	344	333
Expected return on plan assets	(156)	(149)	(400)	(445)
Amortization of past service costs	2	2	6	6
Amortization of net gain	0	0	0	0
Net periodic (benefit) cost	(19)	(35)	(50)	(106)
Pension: | U.S.
Pension and Retirement Plans
Interest cost	2	2	6	8
Expected return on plan assets	0	0	0	0
Amortization of past service costs	0	0	0	0
Amortization of net gain	(2)	(1)	(5)	(4)
Net periodic (benefit) cost	0	1	1	4
Post Retirement:
Pension and Retirement Plans
Service cost	7	5	20	17
Interest cost	14	16	44	48
Amortization of net gain	(29)	(43)	(89)	(129)
Net periodic (benefit) cost	(8)	(22)	(25)	(64)
Post Retirement: | United Kingdom
Pension and Retirement Plans
Service cost	0	0	0	0
Interest cost	0	0	0	0
Amortization of net gain	0	0	0	0
Net periodic (benefit) cost	0	0	0	0
Post Retirement: | U.S.
Pension and Retirement Plans
Service cost	7	5	20	17
Interest cost	14	16	44	48
Amortization of net gain	(29)	(43)	(89)	(129)
Net periodic (benefit) cost	$ (8)	$ (22)	$ (25)	$ (64)