Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Class A	Class B	Redeemable Class A	Common Stock	Common Stock Class A	Common Stock Class B	Common Stock Class P	Additional Paid-in Capital	Retained Earnings	Retained Earnings Class A	Retained Earnings Redeemable Class A	Noncontrolling Interest
Members' Equity, beginning at Sep. 30, 2017	$ 3,146				$ 1,240	$ 34,924		$ 0		$ (33,018)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss (income)	(332)									(332)
Preferred return on Class A Units and Redeemable Class A Units	(168)					774					$ (774)	$ (168)
Issuance of common stock	104				104
Members' Equity, ending at Dec. 31, 2017	2,750				1,344	35,698		0		(34,292)
Members' Equity, beginning at Sep. 30, 2017	3,146				1,240	34,924		0		(33,018)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to non-controlling interests	0
Net loss (income)	(7,168)
Net income (loss) attributable to i3 Verticals, Inc.	(7,168)
Preferred return on Class A Units and Redeemable Class A Units		$ (1,672)		$ (377)
Members' Equity, ending at Mar. 31, 2018	(4,295)				1,344	36,596		0		(42,235)
Members' Equity, beginning at Dec. 31, 2017	2,750				1,344	$ 35,698		0		(34,292)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized	951
Forfeitures of restricted Class A common stock (shares)						4,010
Net loss attributable to non-controlling interests	0												$ 2,173
Net loss (income)	(6,836)									(6,836)
Net income (loss) attributable to i3 Verticals, Inc.	(6,836)									178
Distributions to Non-controlling Interest Holders	(934)												(934)
Preferred return on Class A Units and Redeemable Class A Units	(209)					$ 898				898		$ (209)
Members' Equity, ending at Mar. 31, 2018	(4,295)				$ 1,344	36,596		$ 0		(42,235)
Stockholders' Equity, beginning at Sep. 30, 2018	112,198					$ 1	$ 2		$ 38,562	736			72,897
Common Stock, Shares, Outstanding, beginning at Sep. 30, 2018		9,112,042	17,213,806			9,112,042	17,213,806
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized									951
Net loss (income)	2,351
Common Stock, Shares, Outstanding, ending at Dec. 31, 2018						9,108,032	17,213,806
Stockholders' Equity, ending at Dec. 31, 2018	114,566					$ 1	$ 2		39,513	914			74,136
Stockholders' Equity, beginning at Sep. 30, 2018	112,198					$ 1	$ 2		38,562	736			72,897
Common Stock, Shares, Outstanding, beginning at Sep. 30, 2018		9,112,042	17,213,806			9,112,042	17,213,806
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to non-controlling interests	(2,053)	$ (2,053)
Net loss (income)	1,129	1,129
Net income (loss) attributable to i3 Verticals, Inc.	(924)	$ (924)
Common Stock, Shares, Outstanding, ending at Mar. 31, 2019		9,192,030	17,112,164			9,192,030	17,112,164
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred return on Class A Units and Redeemable Class A Units		$ 0		$ 0
Stockholders' Equity, ending at Mar. 31, 2019	114,735					$ 1	$ 2		41,284	(188)			73,636
Stockholders' Equity, beginning at Dec. 31, 2018	114,566					$ 1	$ 2		39,513	914			74,136
Common Stock, Shares, Outstanding, beginning at Dec. 31, 2018						9,108,032	17,213,806
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized	1,363								1,363
Forfeitures of restricted Class A common stock (shares)						(17,644)
Net loss attributable to non-controlling interests	120	120											(120)
Net loss (income)	(1,222)	(1,222)
Net income (loss) attributable to i3 Verticals, Inc.	(1,102)	$ (1,102)								(1,102)
Distributions to Non-controlling Interest Holders	(89)												(89)
Redemption of common units in i3 Verticals, LLC (shares)						101,642	(101,642)
Redemption of common units in i3 Verticals, LLC									291				(291)
Establishment of liabilities under a tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	117								117
Common Stock, Shares, Outstanding, ending at Mar. 31, 2019		9,192,030	17,112,164			9,192,030	17,112,164
Stockholders' Equity, ending at Mar. 31, 2019	$ 114,735					$ 1	$ 2		$ 41,284	$ (188)			$ 73,636