Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6405-128476

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_BusinessCombinationDescriptionAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount recognized for assets, including goodwill, in excess of (less than) the aggregate liabilities assumed.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121647850&loc=d3e4845-128472

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of stores.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStores
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquireBusinessesGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=onew_TheSlalomShopLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableToBanksMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableOtherPayablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=onew_OceanBlueYachtSalesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=onew_RayClepperIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=onew_CaribeeBoatSalesAndMarinaIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=onew_CentralMarineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=onew_NotesPayableOtherPayablesOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions, 2019 (FY) (Details) $ in Thousands					9 Months Ended	12 Months Ended
Acquisitions, 2019 (FY) (Details) $ in Thousands	Aug. 01, 2019 USD ($) Store	May 01, 2019 USD ($)	Feb. 01, 2019 USD ($) Store	Dec. 01, 2018 USD ($) Store	Jun. 30, 2020 Store	Sep. 30, 2019 USD ($) Store	Jun. 30, 2019 USD ($)
Acquisition [Abstract]
Number of stores \| Store					63
OneWater LLC [Member]
Acquisition [Abstract]
Number of stores \| Store						63
Slalom Shop [Member]
Acquisition [Abstract]
Number of stores \| Store				2
Total purchase price				$ 7,900
Cash paid for acquisition				$ 1,600
Interest rate				5.00%
Notes payable term					3 years
Slalom Shop [Member] \| Notes Payable to Seller [Member]
Acquisition [Abstract]
Note payable to seller						$ 5,100
Slalom Shop [Member] \| Notes Payable to Seller at 5% [Member]
Acquisition [Abstract]
Note payable to seller				$ 1,300
Slalom Shop [Member] \| OneWater LLC [Member]
Acquisition [Abstract]
Number of stores \| Store				2
Total purchase price				$ 7,900
Cash paid for acquisition				$ 1,600
Interest rate				5.00%
Notes payable term						3 years
Slalom Shop [Member] \| OneWater LLC [Member] \| Notes Payable to Seller [Member]
Acquisition [Abstract]
Note payable to seller						$ 5,100
Slalom Shop [Member] \| OneWater LLC [Member] \| Notes Payable to Seller at 5% [Member]
Acquisition [Abstract]
Note payable to seller				$ 1,300
Ocean Blue [Member]
Acquisition [Abstract]
Number of stores \| Store			3
Total purchase price			$ 10,700
Cash paid for acquisition			$ 8,700
Interest rate			5.00%
Notes payable term					3 years
Ocean Blue [Member] \| Notes Payable to Seller at 5% [Member]
Acquisition [Abstract]
Note payable to seller			$ 1,900
Ocean Blue [Member] \| Long-term Debt [Member]
Acquisition [Abstract]
Note payable to seller			$ 8,500
Ocean Blue [Member] \| OneWater LLC [Member]
Acquisition [Abstract]
Number of stores \| Store			3
Total purchase price			$ 10,700
Cash paid for acquisition			$ 8,700
Interest rate			5.00%
Notes payable term						3 years
Ocean Blue [Member] \| OneWater LLC [Member] \| Notes Payable to Seller at 5% [Member]
Acquisition [Abstract]
Note payable to seller			$ 1,900
Ocean Blue [Member] \| OneWater LLC [Member] \| Long-term Debt [Member]
Acquisition [Abstract]
Note payable to seller			8,500
Ray Clepper [Member]
Acquisition [Abstract]
Total purchase price			300
Ray Clepper [Member] \| OneWater LLC [Member]
Acquisition [Abstract]
Total purchase price			$ 300
Caribee [Member]
Acquisition [Abstract]
Total purchase price		$ 10,300					$ 10,333
Caribee [Member] \| Long-term Debt [Member]
Acquisition [Abstract]
Note payable to seller		10,300
Caribee [Member] \| OneWater LLC [Member]
Acquisition [Abstract]
Total purchase price		10,300
Caribee [Member] \| OneWater LLC [Member] \| Long-term Debt [Member]
Acquisition [Abstract]
Note payable to seller		$ 10,300
Central Marine [Member] \| OneWater LLC [Member]
Acquisition [Abstract]
Number of stores \| Store	3
Total purchase price	$ 19,400
Cash paid for acquisition	$ 17,300
Interest rate	5.50%
Notes payable term						30 months
Central Marine [Member] \| OneWater LLC [Member] \| Notes Payable to Seller at 5.5% [Member]
Acquisition [Abstract]
Note payable to seller	$ 2,200