Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																4 Months Ended	8 Months Ended	12 Months Ended
	Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Feb. 11, 2020	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Data (Unaudited) [Abstract]
Revenue	$ 271,036		$ 408,273		$ 189,963		$ 153,698		$ 208,751		$ 274,824		$ 180,771		$ 103,278				$ 1,022,970
Gross profit	64,066		94,685		44,584		32,189		46,351		62,731		39,725		23,319
Income from operations	16,517	[1]	50,678	[1]	8,722	[1]	2,552	[1]	12,777	[1]	26,927	[1]	12,803	[1]	785	[1]			78,469
Net (loss) income	5,974		40,622		2,979		(1,067)		5,024		32,680		(2,951)		2,510		$ (1,044)	$ 49,552	48,508	$ 37,263	$ 1,946
Net income attributable to OneWater Marine Inc	$ 1,973		$ 14,367		$ 1,085		$ 0		$ 0		$ 0		$ 0		$ 0				$ 17,425
Earnings per share of Class A common stock - basic (in dollars per share)	$ 0.30	[2]	$ 2.36	[2]	$ 0.18	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]			$ 2.79
Earnings per share of Class A common stock - diluted (in dollars per share)	$ 0.30	[2]	$ 2.36	[2]	$ 0.18	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]	$ 0	[2]			$ 2.77

[1] Transaction costs reported as other expenses for the three months ended December 31, 2019 and 2018 have been reclassified as operating expenses to conform to the presentation of the other quarters.

[2] 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 the Organizational Transactions and Offering. See Note 1.