Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Pension and Retirement Plans
(Decrease) increase in minimum liability included in other comprehensive income (loss)	$ 2,714	$ 60
United Kingdom
Pension and Retirement Plans
(Decrease) increase in minimum liability included in other comprehensive income (loss)	2,736	(106)
U.S.
Pension and Retirement Plans
(Decrease) increase in minimum liability included in other comprehensive income (loss)	(22)	166
Pension
Pension and Retirement Plans
Interest cost	439	451
Expected return on plan assets	(519)	(515)
Amortization of past service costs	8	8
Amortization of net gain	(2)	(5)
Net periodic (benefit) cost	(74)	(61)
(Decrease) increase in minimum liability included in other comprehensive income (loss)	2,736	(100)
Pension | Foreign
Pension and Retirement Plans
Interest cost	431	440
Pension | United Kingdom
Pension and Retirement Plans
Interest cost	431	440
Expected return on plan assets	(519)	(515)
Amortization of past service costs	8	8
Amortization of net gain	0	0
Net periodic (benefit) cost	(80)	(67)
(Decrease) increase in minimum liability included in other comprehensive income (loss)	2,736	(106)
Pension | U.S.
Pension and Retirement Plans
Interest cost	8	11
Expected return on plan assets	0	0
Amortization of past service costs	0	0
Amortization of net gain	(2)	(5)
Net periodic (benefit) cost	6	6
(Decrease) increase in minimum liability included in other comprehensive income (loss)		6
Post Retirement:
Pension and Retirement Plans
Service cost	26	23
Interest cost	58	64
Amortization of net gain	(119)	(172)
Net periodic (benefit) cost	(35)	(85)
(Decrease) increase in minimum liability included in other comprehensive income (loss)	(22)	160
Post Retirement: | Foreign
Pension and Retirement Plans
Service cost	0	0
Interest cost	0	0
Post Retirement: | United Kingdom
Pension and Retirement Plans
Service cost	0	0
Interest cost	0	0
Amortization of net gain	0	0
Net periodic (benefit) cost	0	0
(Decrease) increase in minimum liability included in other comprehensive income (loss)	0	0
Post Retirement: | U.S.
Pension and Retirement Plans
Service cost	26	23
Interest cost	58	64
Amortization of net gain	(119)	(172)
Net periodic (benefit) cost	(35)	(85)
(Decrease) increase in minimum liability included in other comprehensive income (loss)	$ (22)	$ 160