Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020		Jun. 25, 2018
Class of Stock [Line Items]
(Benefit from) Provision for income taxes	$ (228)	$ (10)	[1]
Percent of tax benefits payable to continuing equity owners	85.00%			85.00%
Tax benefits retained (percent)				15.00%
Increase in net deferred tax assets	$ 96
Increase tax receivable agreement liability	$ 81
Period of payment to continuing equity owners	26 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	3,180
Class B Common Stock | Continuing Equity Owner
Class of Stock [Line Items]
Deferred tax asset recognized	41,104
Tax benefits due to continuing equity owners	$ 39,204
Common Stock | Class A Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	15,000	1,019,609
Common Stock | Class B Common Stock
Class of Stock [Line Items]
Redemption of common units in i3 Verticals, LLC (shares)	(15,000)	(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.