For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

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Costs of sales and operating expenses for the period incurred from transactions with related parties.

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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related Party Transactions (FY) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Related Party Transactions [Abstract]
Due from related parties	$ 0.2		$ 0.2		$ 0.1
Chief Executive Officer [Member]
Related Party Transactions [Abstract]
Payments and fees, related party	0.0	$ 0.2	0.3	$ 0.5
Affiliated Entities [Member]
Related Party Transactions [Abstract]
Purchase of inventories	14.6	1.3	34.1	16.2
Expenses incurred	0.6	0.5	1.6	1.6
Affiliated Entities and Individuals [Member]
Related Party Transactions [Abstract]
Fees received for goods and services	1.5	1.4	1.9	2.8
Payments and fees, related party	$ 0.0	$ 0.2	$ 0.4	$ 0.8
OneWater LLC [Member]
Related Party Transactions [Abstract]
Due from related parties					0.1	$ 0.9	$ 0.5
OneWater LLC [Member] \| Chief Executive Officer [Member]
Related Party Transactions [Abstract]
Payments and fees, related party					0.7	0.5	0.3
OneWater LLC [Member] \| Affiliated Entities [Member]
Related Party Transactions [Abstract]
Purchase of inventories					30.8	34.2	4.9
Expenses incurred					2.1	2.0	2.2
OneWater LLC [Member] \| Affiliated Entities and Individuals [Member]
Related Party Transactions [Abstract]
Fees received for goods and services					2.9	2.1	0.9
Payments and fees, related party					$ 1.0	$ 1.0	$ 0.7