INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	[1]	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2022	Jun. 30, 2021	[1]	Jun. 25, 2018
Class of Stock [Line Items]
(Benefit from) Provision for income taxes	$ (1,810)			$ 662				$ (1,154)	$ 516
Percent of tax benefits payable to continuing equity owners	85.00%							85.00%			85.00%
Tax benefits retained (percent)											15.00%
Increase in net deferred tax assets								$ 875
Increase tax receivable agreement liability								$ 744
Period of payment to continuing equity owners								28 years
Minimum
Class of Stock [Line Items]
Expected payments for repurchase of redeemable noncontrolling interest	$ 0							$ 0
Maximum
Class of Stock [Line Items]
Expected payments for repurchase of redeemable noncontrolling interest	3,225							3,225
Class B Common Stock | Continuing Equity Owner
Class of Stock [Line Items]
Deferred tax asset recognized	40,617							40,617
Tax benefits due to continuing equity owners	$ 39,866							$ 39,866
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	56,000	40,000	15,000			651,870	1,019,609	111,000
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	56,000	40,000	15,000			651,870	1,019,609

[1] Effective October 1, 2020, the Company's financial statements are presented in accordance with ASU 2021-08, Accounting Standards Codification Topic 805, Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. See Note 2 to the interim consolidated financial statements for a description of the recently adopted accounting pronouncement and the impacts of adoption on the condensed consolidated statements of operations.