Income Tax Expense - Additional information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Dec. 22, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Expense [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 0	$ 100,000	$ 100,000
Operating Loss Carryforwards, Valuation Allowance		600,000	600,000
Net operating loss carryforward - foreign		3,766,000	4,603,000
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration		16,000,000.0
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration		600,000
Deferred Tax Assets, Operating Loss Carryforwards, State and Local		600,000
Deferred Tax Assets, Tax Credit Carryforwards, Research		1,900,000
State Research And Other Credit Carryforwards, With Expiration Date		1,400,000
State Research And Other Credit Carry Forwards Without Expiration Date		500,000
Deferred Tax Assets, Valuation Allowance		4,520,000	7,144,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ 2,600,000	$ 2,700,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	24.50%	35.00%
Defined Benefit Plan, Plan Assets, Contributions by Employer		$ 2,700,000	$ 10,200,000
Accrued interest related to uncertain tax positions		0
Penalties have been accrued		0
Excess Foreign Tax Credits
Income Tax Expense [Line Items]
Tax Credit Carryforward, Amount		0	2,400,000
Foreign Valuation Allowance
Income Tax Expense [Line Items]
Operating Loss Carryforwards, Valuation Allowance		3,600,000	3,800,000
State and Local Jurisdiction
Income Tax Expense [Line Items]
Operating Loss Carryforwards, Valuation Allowance		400,000	$ 400,000
Net operating loss carryforward - foreign		$ 16,600,000
Tax Cuts And Jobs Act
Income Tax Expense [Line Items]
Effective Income Taxes Foreign Withholding Taxes	$ 0