Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Taxes [Line Items]
Foreign pretax earnings	$ 42,200	$ 36,000	$ 10,800
Current foreign tax expense related to foreign tax withholdings	6,400	6,500	6,000
Unrecognized tax benefits	7,994	$ 5,834	$ 6,113	$ 6,480
Unrecognized tax benefits that would impact the effective tax rate if recognized	7,800
Unrecognized tax benefits, accrued interest	$ 400
Effective income tax rate	21.00%	21.00%	24.50%
Unremitted earnings of foreign subsidiaries	$ 111,700
California Franchise Tax Board | Research Tax Credit Carryforward
Income Taxes [Line Items]
Excess state research credit	16,600
Valuation allowance	16,600
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 7,600
Net operating loss carryforwards expiration dates	2024
U.S. Federal | Research Tax Credit Carryforward
Income Taxes [Line Items]
Excess state research credit	$ 4,700
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 100
Net operating loss carryforwards expiration dates	2021
Foreign NOL carryforwards
Income Taxes [Line Items]
Net operating loss carryforwards	$ 31,300
Foreign NOL carryforwards | China
Income Taxes [Line Items]
Net operating loss carryforwards	5,500
Foreign NOL carryforwards | GERMANY
Income Taxes [Line Items]
Net operating loss carryforwards	$ 19,500