Notes Payable - Floor Plan (Q3) (Details) - Inventory Financing Facility [Member] - USD ($) $ in Millions	9 Months Ended
Jun. 30, 2020	Sep. 30, 2019
Line of Credit Facility [Abstract]
Outstanding balance of facility	$ 176.1	$ 225.4
Credit facility, available borrowing capacity	$ 216.4	$ 67.1
New Inventory [Member] \| Minimum [Member]
Line of Credit Facility [Abstract]
Credit facility, interest rate	2.91%	4.77%
New Inventory [Member] \| Maximum [Member]
Line of Credit Facility [Abstract]
Credit facility, interest rate	5.16%	7.02%
Pre-owned Inventory [Member] \| Minimum [Member]
Line of Credit Facility [Abstract]
Credit facility, interest rate	3.16%	5.02%
Pre-owned Inventory [Member] \| Maximum [Member]
Line of Credit Facility [Abstract]
Credit facility, interest rate	5.41%	7.27%
LIBOR [Member]
Line of Credit Facility [Abstract]
Debt instrument, term of variable rate	1 month
LIBOR [Member] \| New Boats [Member] \| Minimum [Member]
Line of Credit Facility [Abstract]
Debt instrument, variable interest rate	2.75%
LIBOR [Member] \| New Boats [Member] \| Maximum [Member]
Line of Credit Facility [Abstract]
Debt instrument, variable interest rate	5.00%
Boat Rate [Member] \| New Boats [Member]
Line of Credit Facility [Abstract]
Debt instrument, variable interest rate	0.25%
Wells Fargo [Member]
Line of Credit Facility [Abstract]
Percentage of finance provided of vendor invoice price	100.00%

Term of the interest rate that fluctuates over time as a result of an underlying benchmark interest rate or index.

No definition available.

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- Definition

The percentage of finance provided of vendor invoice price for new boats, engines and trailers.

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(19))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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