EARNINGS PER SHARE, Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									9 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021		Mar. 31, 2021	[1]	Dec. 31, 2020	[1]	Jun. 30, 2022	Jun. 30, 2021
Numerator
Net loss	$ (4,688)	$ (10,438)	$ (3,681)	$ (4,201)	[1],[2]	$ 1,330		$ (3,022)		$ (18,807)	$ (5,894)	[2],[3],[4]
Less: Net loss attributable to non-controlling interests	(960)			(921)	[2]					(5,178)	(1,918)	[2]
Net loss attributable to i3 Verticals, Inc.	$ (3,728)			$ (3,280)	[2]					$ (13,629)	$ (3,976)	[2]
Denominator
Weighted average shares of Class A common stock outstanding - basic (in shares)	22,229,787			21,926,225	[2]					22,116,172	20,658,700	[2]
Weighted average shares of Class A common stock outstanding - diluted (in shares)	22,229,787			21,926,225	[2]					22,116,172	20,658,700	[2]
Basic net loss per share (in USD per share)	$ (0.17)			$ (0.15)	[2]					$ (0.62)	$ (0.19)	[2]
Diluted net loss per share (in USD per share)	$ (0.17)			$ (0.15)	[2]					$ (0.62)	$ (0.19)	[2]
Class A Common Stock
Numerator
Net loss	$ (4,688)			$ (4,201)						$ (18,807)	$ (5,894)
Less: Net loss attributable to non-controlling interests	(960)			(921)						(5,178)	(1,918)
Net loss attributable to i3 Verticals, Inc.	$ (3,728)			$ (3,280)						$ (13,629)	$ (3,976)
Denominator
Weighted average shares of Class A common stock outstanding - basic (in shares)	22,229,787			21,926,225						22,116,172	20,658,700
Weighted average shares of Class A common stock outstanding - diluted (in shares)	22,229,787			21,926,225						22,116,172	20,658,700

[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 statement of changes in equity.

[2] 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.

[3] 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 cash flows.

[4] The prior period amounts included in the statement of cash flows have been updated to correct settlement assets as restricted cash, which were previously reported as cash flows used in operating and investing activities. These adjustments reflect a decrease in prior year cash flows provided by operating activities of $2,046 and a decrease of $7,009 in cash outflows for acquisitions of businesses, net of cash and restricted cash acquired within cash flows used in investing activities, resulting in a combined increase of $4,963 in cash, cash equivalents, and restricted cash at the end of the period.