Consolidated Statement of Changes in Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Class A	Class B	Class P	Common Stock	Common Stock Class A	Common Stock Class B	Additional Paid-In Capital	Accumulated Members' Deficit/Retained Earnings	Accumulated Members' Deficit/Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Non-Controlling Interest	Non-Controlling Interest Cumulative Effect, Period of Adoption, Adjustment
Members' Equity, beginning at Sep. 30, 2017	$ 3,146				$ 0	$ 1,240	$ 34,924			$ (33,018)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred return on Class A Units and Redeemable Class A Units			$ (2,522)
Purchase of common units in i3 Verticals, LLC from selling unitholder	0
Members' Equity, ending at Sep. 30, 2018					$ 0	$ 0	$ 0			0
Common Stock, Shares, Outstanding, beginning (in shares) at Sep. 30, 2017							0	0
Stockholders' Equity, beginning at Sep. 30, 2017							$ 0	$ 0	$ 0	0		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Distributions to non-controlling interest holders	0
Net (loss) income	(6,898)		736
Net (loss) income attributable to non-controlling interests	(1,937)		(1,937)
Net loss (income)	(4,961)		2,673
Common Stock, Shares, Outstanding, ending (in shares) at Sep. 30, 2018							9,112,042	17,213,806
Stockholders' Equity, ending at Sep. 30, 2018	112,198						$ 1	$ 2	38,562	736		72,897
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred return on Class A Units and Redeemable Class A Units			0
Issuance of common stock	21,660								21,660
Issuance of class A common stock (shares)							1,000,000
Purchase of common units in i3 Verticals, LLC from selling unitholder	(12,077)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	3,959								3,959
Equity based compensation recognized	6,124								6,124
Forfeitures of restricted Class A common stock (shares)							(36,113)
Forfeitures of restricted Class A common stock	0
Distributions to non-controlling interest holders	(2,060)											(2,060)
Redemption of common units in i3 Verticals, LLC (shares)							4,292,169	(4,292,169)
Redemption of common units in i3 Verticals, LLC	(1)							$ (1)	12,077			(12,077)
Capitalization of public offering costs	(899)								(899)
Issuance of restricted Class A common stock under Equity Plan (shares)							8,799
Issuance of restricted Class A common stock under Equity Plan	225								225
Exercise of equity-based awards (shares)							67,218
Exercise of equity-based awards	672								672
Net (loss) income	(3,045)		(3,045)							(3,045)
Net (loss) income attributable to non-controlling interests	(3,608)		(3,608)									3,608
Net loss (income)	563		$ 563
Common Stock, Shares, Outstanding, ending (in shares) at Sep. 30, 2019			14,444,115	12,921,637			14,444,115	12,921,637
Stockholders' Equity, ending at Sep. 30, 2019	142,441	$ 1,345					$ 1	$ 1	82,380	(2,309)	$ 705	62,368	$ 640
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred return on Class A Units and Redeemable Class A Units			$ 0
Issuance of common stock	72,557						$ 1		72,556
Issuance of class A common stock (shares)							3,250,000
Purchase of common units in i3 Verticals, LLC from selling unitholder	(5,080)
Deferred tax asset adjustment	(941)								(941)
Establishment of liabilities under tax receivable agreement and related changes to deferred tax assets associated with increases in tax basis	896								896
Equity based compensation recognized	10,452								10,452
Adjustment related to prior periods	0								(2,730)			2,730
Distributions to non-controlling interest holders	(3)											(3)
Redemption of common units in i3 Verticals, LLC (shares)							1,021,016	(1,021,016)
Redemption of common units in i3 Verticals, LLC	0								5,080			(5,080)
Capitalization of public offering costs	$ (697)								(697)
Exercise of equity-based awards (shares)	331,141						149,012
Exercise of equity-based awards	$ 254								254
Allocation of equity to non-controlling interests	0								(24,495)			24,495
Equity component of exchangeable notes, net of issuance costs and deferred taxes	27,578								27,578
Purchases of exchangeable note hedges	(28,676)								(28,676)
Issuance of warrants	14,669								14,669
Repurchases of exchangeable notes	1,272								1,272
Net (loss) income	(419)		(419)							(419)
Net (loss) income attributable to non-controlling interests	560		560									(560)
Net loss (income)	(979)		$ (979)
Common Stock, Shares, Outstanding, ending (in shares) at Sep. 30, 2020			18,864,143	11,900,621			18,864,143	11,900,621
Stockholders' Equity, ending at Sep. 30, 2020	$ 240,168						$ 2	$ 1	$ 157,598	$ (2,023)		$ 84,590