Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
Foreign pretax earnings	$ 36,000	$ 10,800	$ 43,300
Current foreign tax expense related to foreign tax withholdings	6,500	6,000	4,600
Unrecognized tax benefits	5,834	$ 6,113	$ 6,480	$ 6,799
Unrecognized tax benefits that would impact the effective tax rate if recognized	5,700
Unrecognized tax benefits, accrued interest	$ 300
Effective income tax rate	21.00%	24.50%	35.00%
Unremitted earnings of foreign subsidiaries	$ 95,600
California Franchise Tax Board | Research Tax Credit Carryforward
Income Taxes [Line Items]
Excess state research credit	14,100
Valuation allowance	14,100
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 10,600
Net operating loss carryforwards expiration dates	2020
U.S. Federal | Research Tax Credit Carryforward
Income Taxes [Line Items]
Excess state research credit	$ 3,800
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 200
Net operating loss carryforwards expiration dates	2021
Foreign NOL carryforwards
Income Taxes [Line Items]
Net operating loss carryforwards	$ 25,000
Foreign NOL carryforwards | China
Income Taxes [Line Items]
Net operating loss carryforwards	3,500
Foreign NOL carryforwards | GERMANY
Income Taxes [Line Items]
Net operating loss carryforwards	$ 12,700