Stockholders' Equity, Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Feb. 10, 2020
Numerator [Abstract]
Net income attributable to OneWater Inc		$ 79,059	$ 17,425
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)		4,163,000	8,544,000
Restricted Stock Units [Member]
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)		232,000	220,000
Common Class A [Member]
Per Share Data [Abstract]
Common stock, shares outstanding (in shares)		13,276,538	10,391,661	0
Denominator [Abstract]
Weighted-average number of unrestricted outstanding common shares used to calculate basic net income per share (in shares)	[1]	11,087,000	6,243,000
Effect of dilutive securities:
Restricted stock units (in shares)		272,000	44,000
Diluted weighted-average shares of Class A common stock outstanding used to calculate diluted earnings per share (in shares)	[1]	11,359,000	6,287,000
Earnings per share of Class A common stock - basic (in dollars per share)	[1]	$ 7.13	$ 2.79
Earnings per share of Class A common stock - diluted (in dollars per share)	[1]	$ 6.96	$ 2.77
Common Class B [Member]
Per Share Data [Abstract]
Common stock, shares outstanding (in shares)		1,819,112	4,583,637	0
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)		3,931,000	8,324,000

[1] For the fiscal year ended September 30, 2020, represents earnings per share of Class A common stock and weighted-average shares of Class A common stock outstanding for the period from February 11, 2020 through September 30, 2020, the period following OneWater Marine Inc.’s initial public offering. See Note 1.