Pension and Retirement Plans - Amounts recognized in the consolidated balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	$ (6,792)	$ (7,239)
Deferred tax	24	56
Accumulated other comprehensive income	6,120	6,302
Net amount recognized	(648)	(881)
Accumulated benefit obligation	(16,532)	(15,477)
Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(5,089)	(5,723)
Deferred tax	14	15
Accumulated other comprehensive income	5,960	6,189
Net amount recognized	885	481
Accumulated benefit obligation	(14,829)	(13,961)
Post Retirement
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(1,703)	(1,516)
Deferred tax	10	41
Accumulated other comprehensive income	160	113
Net amount recognized	(1,533)	(1,362)
Accumulated benefit obligation	(1,703)	(1,516)
International
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(4,663)	(5,209)
Accumulated other comprehensive income	5,934	6,165
Net amount recognized	1,271	956
Accumulated benefit obligation	(14,403)	(13,447)
International | Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(4,663)	(5,209)
Accumulated other comprehensive income	5,934	6,165
Net amount recognized	1,271	956
Accumulated benefit obligation	(14,403)	(13,447)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(2,129)	(2,030)
Deferred tax	24	56
Accumulated other comprehensive income	186	137
Net amount recognized	(1,919)	(1,837)
Accumulated benefit obligation	(2,129)	(2,030)
U.S. | Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(426)	(514)
Deferred tax	14	15
Accumulated other comprehensive income	26	24
Net amount recognized	(386)	(475)
Accumulated benefit obligation	(426)	(514)
U.S. | Post Retirement
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(1,703)	(1,516)
Deferred tax	10	41
Accumulated other comprehensive income	160	113
Net amount recognized	(1,533)	(1,362)
Accumulated benefit obligation	$ (1,703)	$ (1,516)