Stockholders' and Members' Equity, Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Mar. 30, 2022	Sep. 30, 2021
Stockholders' and Members' Equity [Abstract]
Share repurchase program authorized amount					$ 50,000
Share repurchase under program (in shares)			0
Numerator [Abstract]
Net income attributable to OneWater Inc.	$ 36,297	$ 20,475	$ 56,316	$ 28,263
Common Class A [Member]
Earnings (loss) per unit attributable to common interest holders [Abstract]
Common stock, shares outstanding (in shares)	13,879,290		13,879,290			13,276,538
Denominator [Abstract]
Weighted-average number of unrestricted outstanding common shares used to calculate basic net income per share (in shares)	13,864,000	10,901,000	13,619,000	10,838,000
Effect of dilutive securities [Abstract]
Restricted stock units (in shares)	408,000	270,000	398,000	245,000
Diluted weighted-average shares of Class A common stock outstanding used to calculate diluted earnings per share (in shares)	14,272,000	11,171,000	14,017,000	11,083,000
Earnings per share of Class A common stock - basic (in dollars per share)	$ 2.62	$ 1.88	$ 4.14	$ 2.61
Earnings per share of Class A common stock - diluted (in dollars per share)	$ 2.54	$ 1.83	$ 4.02	$ 2.55
Common Class B [Member]
Earnings (loss) per unit attributable to common interest holders [Abstract]
Common stock, shares outstanding (in shares)	1,429,940		1,429,940			1,819,112