Accounts Receivable - Movement in the allowance for credit losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ (4,057)	$ (4,906)	$ (4,199)
Charged to costs and expenses	(1,733)	(537)	(788)
Write-offs	780	1,277	39
Foreign currency and other	186	109	42
Balance at end of period	$ (4,824)	$ (4,057)	$ (4,906)