DISCONTINUED OPERATIONS - Income (Loss) From Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Operating expenses
Net (loss) income from discontinued operations attributable to non-controlling interest									$ 6,639	$ 66,980	$ 6,351
Net income from discontinued operations attributable to i3 Verticals, Inc.	$ 1,926	$ 13,292	$ (1,173)	$ 201	$ 111,448	$ 4,254	$ 3,860	$ 4,633	14,246	124,195	15,805
Gain on disposal									25,960	205,576	0
Discontinued Operations, Held-for-Sale or Disposed of by Sale | Healthcare RCM Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue									22,463	39,104	37,045
Operating expenses
Other costs of services (excluding depreciation and amortization)									14,553	24,125	22,387
Selling, general and administrative									7,317	9,949	9,910
Depreciation and amortization									1,940	3,243	3,118
Change in fair value of contingent consideration									1,302	(712)	788
Total operating expenses									25,112	36,605	36,203
(Loss) income from operations									(2,649)	2,499	842
Other expense (income) (including gain on disposal									(25,753)	0	0
(Loss) income become income taxes from discontinued operations									23,104	2,499	842
(Benefit from) provision for income taxes									3,782	(200)	(281)
Net (loss) income from discontinued operations									19,322	2,699	1,123
Net (loss) income from discontinued operations attributable to non-controlling interest									6,081	767	329
Net income from discontinued operations attributable to i3 Verticals, Inc.									13,241	1,932	794
Gain on disposal									25,960	0	0
Discontinued Operations, Held-for-Sale or Disposed of by Sale | Merchant Services Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue									0	145,907	143,517
Operating expenses
Other costs of services (excluding depreciation and amortization)									0	67,122	65,197
Selling, general and administrative									0	45,880	42,005
Depreciation and amortization									0	8,649	10,023
Change in fair value of contingent consideration									0	0	14
Total operating expenses									0	121,651	117,239
(Loss) income from operations									0	24,256	26,278
Interest expense, net									0	43	0
Other expense (income) (including gain on disposal									661	(205,576)	2,660
Total other expenses (income)									661	(205,533)	2,660
(Loss) income become income taxes from discontinued operations									(661)	229,789	23,618
(Benefit from) provision for income taxes									(2,224)	41,313	2,585
Net (loss) income from discontinued operations									1,563	188,476	21,033
Net (loss) income from discontinued operations attributable to non-controlling interest									558	66,213	6,022
Net income from discontinued operations attributable to i3 Verticals, Inc.									$ 1,005	122,263	15,011
Gain on disposal										$ 205,576	$ 0