Earnings Per Share, Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Numerator
Net income (loss) attributable to i3 Verticals, Inc.	$ 737	$ (1,102)	$ 588	$ (924)
Denominator
Weighted average shares of Class A common stock outstanding (shares)	14,456,970	8,887,050	14,344,768	8,849,431
Weighted average shares of Class A common stock outstanding - diluted (shares)	16,106,757	8,887,050	15,778,077	8,849,431
Diluted net income per share (in USD per share)	$ 0.05	$ (0.12)	$ 0.04	$ (0.10)
Class A Common Stock
Numerator
Net income (loss) attributable to i3 Verticals, Inc.	$ 737	$ (1,102)	$ 588	$ (924)
Denominator
Weighted average shares of Class A common stock outstanding (shares)	14,456,970	8,887,050	14,344,768	8,849,431
Weighted average effect of dilutive securities (shares)	1,649,787		1,433,309
Weighted average shares of Class A common stock outstanding - diluted (shares)	16,106,757		15,778,077