Earnings Per Share, Basic (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Numerator
Net loss (income)	$ 1,919	$ 1,934	$ (1,222)	$ 2,351	$ 3,853	$ 1,129
Less: Net income (loss) attributable to non-controlling interests	1,182		(120)		3,265	2,053
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
Basic net income (loss) per share (in USD per share)	$ 0.05		$ (0.12)		$ 0.04	$ (0.10)
Class A Common Stock
Numerator
Net loss (income)	$ 1,919		$ (1,222)		$ 3,853	$ 1,129
Less: Net income (loss) attributable to non-controlling interests	1,182		(120)		3,265	2,053
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