Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020	Jun. 25, 2018
Class of Stock [Line Items]
Valuation allowance	$ 27,555,000	$ 20,269,000
Investment in partnership	56,388,000	57,080,000
Accrued interest related to uncertain tax positions	0	0
Accrued penalties related to uncertain tax positions	0	0
Unrecognized tax benefits	83,000	108,000	$ 184,000
Percent of tax benefits payable to continuing equity owners				85.00%
Tax benefits retained (percent)				15.00%
Increase in net deferred tax assets			6,307,000
Increase tax receivable agreement liability			$ 5,361,000
Deferred tax asset recognized	$ 78,314,000	76,230,000
Period of payment to continuing equity owners	26 years
i3 Vericals, LLC
Class of Stock [Line Items]
Valuation allowance	$ 21,838,000
Change in valuation allowance for deferred tax assets	(6,391,000)
Investment in partnership	56,388,000
Minimum
Class of Stock [Line Items]
Expected payments for repurchase of redeemable noncontrolling interest	0
Maximum
Class of Stock [Line Items]
Expected payments for repurchase of redeemable noncontrolling interest	3,315,000
Continuing Equity Owner | Class B Common Stock
Class of Stock [Line Items]
Increase in deferred tax assets	898,000	13,990,000
Increase tax receivable agreement liability	763,000	$ 11,892,000
Deferred tax asset recognized	40,981,000
Tax benefits due to continuing equity owners	$ 40,832,000
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	(111,000)	(1,671,479)	1,021,016
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	111,000	1,671,479	1,021,016
Federal
Class of Stock [Line Items]
Net operating loss carryforwards	$ 43,233,000	$ 35,312,000
Tax credit carryforward	359,000	661,000
Provision for (Benefit from) deferred income taxes	9,438,000	$ 8,077,000
Valuation allowance	808,000
Change in valuation allowance for deferred tax assets	(15,000)
State
Class of Stock [Line Items]
Net operating loss carryforwards	108,992,000
Provision for (Benefit from) deferred income taxes	6,913,000
Valuation allowance	4,909,000
Change in valuation allowance for deferred tax assets	$ (880,000)