Employee Stock Ownership Plan - Employee Stock Ownership Plan (ESOP) Disclosures (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Shares committed to be released	1,755	7,021
Total allocated shares	14,042	7,021
Total unallocated shares	159,731	161,486
Total ESOP shares	175,528	175,528
Fair value of unallocated shares (based on $14.24 and $9.96 share price as of March 31, 2021 and December 31, 2020, respectively)	$ 2,275	$ 1,608

Represents number of shares for which compensation cost not allocated.

No definition available.

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Namespace Prefix:	bcow_
Data Type:	xbrli:sharesItemType
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Period Type:	instant

- Definition

Shares committed to be released.

+ References

No definition available.

+ Details

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- Definition

Fair value of unearned shares held by the employee stock ownership plan (ESOP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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

- Definition

The shares or units in an ESOP trust that have been assigned to individual participant accounts based on a known formula. IRS rules require allocations to be nondiscriminatory generally based on compensation, length of service, or a combination of both. For any particular participant such shares or units may be vested, unvested, or partially vested.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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Period Type:	instant

- Definition

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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