Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in minimum liability included in other comprehensive income (loss)	$ (244)	$ (4,096)
U.K..
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in minimum liability included in other comprehensive income (loss)	(313)	(3,509)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Increase (decrease) in minimum liability included in other comprehensive income (loss)	69	(587)
Pension:
Defined Benefit Plan Disclosure [Line Items]
Interest cost	442	279
Expected return on plan assets	(575)	(449)
Amortization of past service costs	7	7
Amortization of net (gain) loss	(4)	98
Net periodic benefit cost	(130)	(65)
Increase (decrease) in minimum liability included in other comprehensive income (loss)	(314)	(3,529)
Pension: | International
Defined Benefit Plan Disclosure [Line Items]
Interest cost	429	268
Pension: | U.K..
Defined Benefit Plan Disclosure [Line Items]
Interest cost	429	268
Expected return on plan assets	(575)	(449)
Amortization of past service costs	7	7
Amortization of net (gain) loss	0	97
Net periodic benefit cost	(139)	(77)
Increase (decrease) in minimum liability included in other comprehensive income (loss)	(313)	(3,509)
Pension: | U.S.
Defined Benefit Plan Disclosure [Line Items]
Interest cost	13	11
Expected return on plan assets	0	0
Amortization of past service costs	0	0
Amortization of net (gain) loss	(4)	1
Net periodic benefit cost	9	12
Increase (decrease) in minimum liability included in other comprehensive income (loss)	(1)	(20)
Post Retirement:
Defined Benefit Plan Disclosure [Line Items]
Service cost	24	44
Interest cost	62	46
Amortization of net (gain) loss	(196)	(7)
Net periodic benefit cost	(110)	83
Increase (decrease) in minimum liability included in other comprehensive income (loss)	70	(567)
Post Retirement: | International
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	0
Post Retirement: | U.K..
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	0
Amortization of net (gain) loss	0	0
Net periodic benefit cost	0	0
Increase (decrease) in minimum liability included in other comprehensive income (loss)	0	0
Post Retirement: | U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	24	44
Interest cost	62	46
Amortization of net (gain) loss	(196)	(7)
Net periodic benefit cost	(110)	83
Increase (decrease) in minimum liability included in other comprehensive income (loss)	$ 70	$ (567)