Summary of Significant Accounting Policies (Details) $ in Thousands		3 Months Ended			6 Months Ended				12 Months Ended
	Oct. 01, 2019 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)		Mar. 31, 2020 USD ($) business	Mar. 31, 2019 USD ($)		Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2019 USD ($)
Concentration Risk [Line Items]
Inventories		$ 1,662			$ 1,662					$ 1,294
Notes Receivable, Fair Value Disclosure		1,195			$ 1,195					$ 195
Number of Businesses Acquired | business					0
Capitalized Contract Cost, Gross		2,830			$ 2,830
(Benefit from) provision for income taxes		(2,062)	$ (136)		(1,913)	$ 129
Net income (loss) attributable to i3 Verticals, Inc.		737	(1,102)		588	(924)
Amortization expense of intangible assets					3,088	3,019		$ 6,282	$ 5,821
Equity-based compensation expense					640
Interchange and network fees		0	54,685	[1]	0	$ 110,514	[1]
Operating Expenses
Concentration Risk [Line Items]
Interchange and network fees			$ 54,685		110,514
Intangible Assets, Amortization Period
Concentration Risk [Line Items]
Amortization expense of intangible assets					184
Change in Approach for Estimating the Realizability of a Deferred Tax Asset
Concentration Risk [Line Items]
Change in valuation allowance for deferred tax assets		(2,668)
(Benefit from) provision for income taxes		(2,668)
Net income (loss) attributable to i3 Verticals, Inc.		2,668			2,668
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Concentration Risk [Line Items]
Interchange and network fees		$ 63,199			$ 132,301
Accounting Standards Update 2014-09 [Member]
Concentration Risk [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax	$ 705

[1] Effective October 1, 2019, the Company's revenues are presented net of interchange and network fees in accordance with Accounting Standards Codification Topic 606, Revenue from Contracts with Customers. See Note 2 to our condensed consolidated financial statements for a description of the recently adopted accounting pronouncement.