Organization and Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 15, 2020	Jun. 10, 2019	Jun. 25, 2018	Sep. 30, 2021	Sep. 30, 2020
i3Verticals, LLC
Subsidiary, Sale of Stock [Line Items]
Non-controlling interest, ownership interest (percent)				68.30%	61.30%
Continuing Equity Owner
Subsidiary, Sale of Stock [Line Items]
Shareholders ownership interest (percent)				32.30%
Class A Common Stock | Continuing Equity Owner
Subsidiary, Sale of Stock [Line Items]
Shareholders ownership interest (percent)				0.60%
Class B Common Stock | Continuing Equity Owner
Subsidiary, Sale of Stock [Line Items]
Shareholders ownership interest (percent)				31.70%
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued (shares)			7,647,500
Public offering price (in USD per share)			$ 13
Net proceeds from IPO			$ 92,500
Secondary Public Offering | i3Verticals, LLC
Subsidiary, Sale of Stock [Line Items]
Net proceeds from IPO		$ 20,870
Common units, purchased (in units)		1,000,000
Secondary Public Offering | Continuing Equity Owner
Subsidiary, Sale of Stock [Line Items]
Common units, purchased (in units)		4,165,527
Secondary Public Offering | Class A Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued (shares)		5,165,527
Public offering price (in USD per share)		$ 22.75
Net proceeds from IPO		$ 111,640
Underwriters exercised option to purchase additional shares (shares)		673,764
Primary Public Offering | i3Verticals, LLC
Subsidiary, Sale of Stock [Line Items]
Net proceeds from IPO	$ 72,018
Common units, purchased (in units)	3,250,000
Primary Public Offering | Continuing Equity Owner
Subsidiary, Sale of Stock [Line Items]
Common units, purchased (in units)	487,500
Primary Public Offering | Class A Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued (shares)	3,737,500
Public offering price (in USD per share)	$ 23.5
Net proceeds from IPO	$ 83,400
Underwriters exercised option to purchase additional shares (shares)	487,500