Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2024	Dec. 31, 2023
Commitments to Extend Credit [Member]
Loss Contingencies [Line Items]
Outstanding commitments	$ 96,480,000	$ 87,337,000
Commitments to Extend Credit [Member] \| Accounting Standards Update 2016-13 [Member]
Loss Contingencies [Line Items]
Outstanding commitments	42,600,000
Establishment of allowance for credit losses unfunded loan commitment	979,000
Mortgage Partnership Finance Program [Member]
Loss Contingencies [Line Items]
Commitments	1,400,000
Other commitments	$ 0	$ 0

Establishment of allowance for credit losses unfunded loan commitments.

No definition available.

Name:	bcow_EstablishmentOfAllowanceForCreditLossesUnfundedLoanCommitments
Namespace Prefix:	bcow_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of contractual obligation, including, but not limited to, long-term debt, lease obligation, purchase obligation, and other commitments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Publisher FASB
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+ Details

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Period Type:	instant

- Definition

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org/1943274/2147482907/825-10-50-10

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Period Type:

- Details

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Namespace Prefix:
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Balance Type:
Period Type: