Stockholders' and Members' Equity, Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Feb. 10, 2020
Numerator [Abstract]
Net income attributable to OneWater Inc	$ 7,788
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)	4,405,000
Restricted Stock Units [Member]
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)	206,000
Common Class A [Member]
Earnings (loss) per unit attributable to common interest holders [Abstract]
Common stock, shares outstanding (in shares)	10,867,291	10,391,661	0
Denominator [Abstract]
Weighted-average number of unrestricted outstanding common shares used to calculate basic net income per share (in shares)	10,776,000
Effect of dilutive securities [Abstract]
Restricted stock units (in shares)	210,000
Diluted weighted-average shares of Class A common stock outstanding used to calculate diluted net income per share (in shares)	10,986,000
Earnings per share of Class A common stock - basic (in dollars per share)	$ 0.72
Earnings per share of Class A common stock - diluted (in dollars per share)	$ 0.71
Common Class B [Member]
Earnings (loss) per unit attributable to common interest holders [Abstract]
Common stock, shares outstanding (in shares)	4,108,007	4,583,637	0
Antidilutive Securities [Abstract]
Antidilutive securities excluded from computation of diluted weighted average shares (in shares)	4,199,000