Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 6,200,000	$ 6,900,000
State and local net operating loss carryforwards of net of valuation allowance	3,600,000
Federal operating loss carryforwards, net of valuation allowances	600,000
Foreign operating loss carryforwards, net of valuation allowances	2,000,000
Foreign tax credits, net	0
Valuation allowance	15,000,000.0	12,400,000
Net change in total valuation allowance	2,600,000
Foreign tax credit carryforwards	2,000,000.0	2,400,000
Foreign earnings repatriated	300,600,000	$ 30,000,000
Gain Capital Holdings Inc
Operating Loss Carryforwards [Line Items]
Foreign tax credit carryforwards	$ 800,000