Pension and Retirement Plans - Components of net periodic benefit costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Decrease in minimum liability included in other comprehensive income (loss)	$ 1,063	$ (475)
International
Defined Benefit Plan Disclosure [Line Items]
Decrease in minimum liability included in other comprehensive income (loss)	914	(462)
U.S.
Defined Benefit Plan Disclosure [Line Items]
Decrease in minimum liability included in other comprehensive income (loss)	149	(13)
Pension
Defined Benefit Plan Disclosure [Line Items]
Interest cost	386	395
Expected return on plan assets	(327)	(312)
Amortization of net gain (loss)	146	169
Net periodic benefit cost from continuing operations	205	252
Decrease in minimum liability included in other comprehensive income (loss)	932	(469)
Pension | International
Defined Benefit Plan Disclosure [Line Items]
Interest cost	362	370
Expected return on plan assets	(327)	(312)
Amortization of net gain (loss)	149	170
Net periodic benefit cost from continuing operations	184	228
Decrease in minimum liability included in other comprehensive income (loss)	914	(462)
Pension | U.S.
Defined Benefit Plan Disclosure [Line Items]
Interest cost	24	25
Amortization of net gain (loss)	(3)	(1)
Net periodic benefit cost from continuing operations	21	24
Decrease in minimum liability included in other comprehensive income (loss)	18	(7)
Post Retirement
Defined Benefit Plan Disclosure [Line Items]
Service cost	34	40
Interest cost	53	47
Amortization of net gain (loss)	(20)	(18)
Net periodic benefit cost from continuing operations	67	69
Decrease in minimum liability included in other comprehensive income (loss)	131	(6)
Post Retirement | U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost	34	40
Interest cost	53	47
Amortization of net gain (loss)	(20)	(18)
Net periodic benefit cost from continuing operations	67	69
Decrease in minimum liability included in other comprehensive income (loss)	$ 131	$ (6)