INCOME TAXES - Additional Information (Details) - USD ($)	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Jun. 25, 2018
Class of Stock [Line Items]
Valuation allowance	$ 15,026,000	$ 17,631,000
Component of tax expense	26,000	0	$ 0
Accrued interest and penalties related to income taxes and potential income tax penalties	26,000	0	0
Unrecognized tax benefits	427,000	456,000	238,000	$ 83,000
Percent of tax benefits payable to continuing equity owners					85.00%
Tax benefits retained (percent)					15.00%
Increase (decrease) in net deferred tax assets	(805,000)	(1,187,000)	$ (932,000)
Deferred tax asset recognized	70,679,000	72,613,000
Accrued expenses and other current liabilities	24,525,000	88,252,000
Long-term tax receivable agreement obligations	$ 32,191,000	$ 29,347,000
Period of payment to continuing equity owners	22 years
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	$ 5,364,000
Class A Common Stock | Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (in shares)	1,281,739	60,718	24,748
Class B Common Stock | Continuing Equity Owner
Class of Stock [Line Items]
Increase (decrease) in net deferred tax assets	$ 9,398,000	$ 426,000	$ 208,000
Increase tax receivable agreement liability			$ 177,000
Increase tax receivable agreement liability	6,211,000	$ 362,000
Deferred tax asset recognized	37,872,000
Accrued expenses and other current liabilities	2,720,000
Long-term tax receivable agreement obligations	32,191,000
Class B Common Stock | Continuing Equity Owners
Class of Stock [Line Items]
Tax benefits due to continuing equity owners	$ 34,911,000
Class B Common Stock | Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (in shares)	(1,281,739)	(60,718)	(24,748)
Federal
Class of Stock [Line Items]
Net operating loss carryforwards	$ 213,000
Tax credit carryforward	181,000
State
Class of Stock [Line Items]
Net operating loss carryforwards	15,217,000
Deferred tax assets	$ 947,000