Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Taxes [Line Items]
Foreign pretax earnings	$ 27,800	$ 33,000	$ 45,200
Current foreign tax expense related to foreign tax withholdings	4,600	6,500	$ 5,300
Foreign tax credit carryforward	$ 10,286	$ 14,590
Foreign tax credit carry forward year	10 years
U.S. federal statutory income tax rate	35.00%	35.00%	35.00%
Excess amount for financial reporting over tax basis of investments in foreign subsidiaries	$ 47,000
Unrecognized tax benefits	6,480	$ 6,799	$ 4,634	$ 4,554
Unrecognized tax benefits that would impact the effective tax rate if recognized	5,800
Unrecognized tax benefits, accrued interest	400
California Franchise Tax Board | Research Tax Credit Carryforward
Income Taxes [Line Items]
Excess state research credit	7,300
Valuation allowance	7,300
United States
Income Taxes [Line Items]
Foreign tax credit carryforward	9,600
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 17,100
Net operating loss carryforwards expiration dates	2020
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 300
Net operating loss carryforwards expiration dates	2021
Foreign NOL carryforwards
Income Taxes [Line Items]
Net operating loss carryforwards	$ 38,800
Foreign NOL carryforwards | China
Income Taxes [Line Items]
Net operating loss carryforwards	$ 24,200