Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Thousands	Total	Class A	Class B	Common Stock Class A	Common Stock Class B	Additional Paid-in Capital	Retained Earnings	Noncontrolling Interest
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized	951					951
Forfeitures of restricted Class A common stock (shares)				4,010
Net loss attributable to non-controlling interests								2,173
Net loss (income)	2,351
Net income (loss) attributable to i3 Verticals, Inc.							178
Distributions to Non-controlling Interest Holders	(934)							(934)
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
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
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
Stockholders' Equity, ending at Mar. 31, 2019	114,735			$ 1	$ 2	41,284	(188)	73,636
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	1,345						705	640
Stockholders' Equity, beginning at Sep. 30, 2019	142,441			$ 1	$ 1	82,380	(2,309)	62,368
Common Stock, Shares, Outstanding, beginning at Sep. 30, 2019		14,444,115	12,921,637	14,444,115	12,921,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized	2,124					2,124
Net loss attributable to non-controlling interests								2,083
Net loss (income)	1,934
Net income (loss) attributable to i3 Verticals, Inc.							(149)
Common Stock, Shares, Outstanding, ending at Dec. 31, 2019				14,497,777	12,921,637
Stockholders' Equity, ending at Dec. 31, 2019	148,195			$ 1	$ 1	84,855	(1,753)	65,091
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercised (shares)				53,662
Stock Issued During Period, Value, Stock Options Exercised	351					351
Stockholders' Equity, beginning at Sep. 30, 2019	142,441			$ 1	$ 1	82,380	(2,309)	62,368
Common Stock, Shares, Outstanding, beginning at Sep. 30, 2019		14,444,115	12,921,637	14,444,115	12,921,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to non-controlling interests	(3,265)	$ (3,265)
Net loss (income)	3,853	3,853
Net income (loss) attributable to i3 Verticals, Inc.	588	$ 588
Purchases of exchangeable note hedges	(28,676)					(28,676)
Common Stock, Shares, Outstanding, ending at Mar. 31, 2020		15,038,918	12,411,621	15,038,918	12,411,621
Stockholders' Equity, ending at Mar. 31, 2020	$ 166,781			$ 1	$ 1	104,122	(1,016)	63,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercised (shares)	166,709
Stockholders' Equity, beginning at Dec. 31, 2019	$ 148,195			$ 1	$ 1	84,855	(1,753)	65,091
Common Stock, Shares, Outstanding, beginning at Dec. 31, 2019				14,497,777	12,921,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity based compensation recognized	2,510					2,510
Forfeitures of restricted Class A common stock (shares)				0
Net loss attributable to non-controlling interests	(1,182)	$ (1,182)						1,182
Net loss (income)	1,919	1,919
Net income (loss) attributable to i3 Verticals, Inc.	737	$ 737					737
Distributions to Non-controlling Interest Holders	(3)							(3)
Redemption of common units in i3 Verticals, LLC (shares)				510,016	(510,016)
Redemption of common units in i3 Verticals, LLC						2,597		(2,597)
Establishment of liabilities under a tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	596					596
Equity component of exchangeable notes, net of issuance costs and deferred taxes	27,569					27,569
Common Stock, Shares, Outstanding, ending at Mar. 31, 2020		15,038,918	12,411,621	15,038,918	12,411,621
Stockholders' Equity, ending at Mar. 31, 2020	166,781			$ 1	$ 1	104,122	$ (1,016)	$ 63,673
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercised (shares)				31,125
Stock Issued During Period, Value, Stock Options Exercised	2					2
Adjustments to Additional Paid in Capital, Warrant Issued	$ 14,669					$ 14,669