Pension and Retirement Plans - Amounts recognized in the consolidated balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	$ (7,239)	$ (6,508)
Deferred tax	56	114
Accumulated other comprehensive income	6,302	5,298
Net amount recognized	(881)	(1,096)
Accumulated benefit obligation	(15,477)	(14,779)
Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(5,723)	(5,189)
Deferred tax	15	21
Accumulated other comprehensive income	6,189	5,264
Net amount recognized	481	96
Accumulated benefit obligation	(13,961)	(13,459)
Post Retirement
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(1,516)	(1,320)
Deferred tax	41	93
Accumulated other comprehensive income	113	34
Net amount recognized	(1,362)	(1,193)
Accumulated benefit obligation	(1,516)	(1,318)
International
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(5,209)	(4,604)
Deferred tax		(1)
Accumulated other comprehensive income	6,165	5,251
Net amount recognized	956	646
Accumulated benefit obligation	(13,447)	(12,874)
International | Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(5,209)	(4,604)
Deferred tax		(1)
Accumulated other comprehensive income	6,165	5,251
Net amount recognized	956	646
Accumulated benefit obligation	(13,447)	(12,874)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(2,030)	(1,904)
Deferred tax	56	115
Accumulated other comprehensive income	137	47
Net amount recognized	(1,837)	(1,742)
Accumulated benefit obligation	(2,030)	(1,905)
U.S. | Pension
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(514)	(585)
Deferred tax	15	22
Accumulated other comprehensive income	24	13
Net amount recognized	(475)	(550)
Accumulated benefit obligation	(514)	(585)
U.S. | Post Retirement
Defined Benefit Plan Disclosure [Line Items]
Accrued benefit liability	(1,516)	(1,320)
Deferred tax	41	93
Accumulated other comprehensive income	113	34
Net amount recognized	(1,362)	(1,193)
Accumulated benefit obligation	$ (1,516)	$ (1,318)