Foreclosed Assets - Schedule of no valuation allowance foreclosed assets (Detail)	12 Months Ended
Dec. 31, 2019 USD ($)
Foreclosed Asset [Abstract]
Foreclosed assets, beginning of period	$ 0
Loans receivable transferred	134,000
Gain on sales	103,000
Proceeds from sales	(237,000)
Write downs	0
Other	0
Foreclosed assets, end of period	$ 0

Foreclosed asset

No definition available.

Name:	bcow_ForeclosedAssetAbstract
Namespace Prefix:	bcow_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

It represents foreclosed assets writedowns

+ References

No definition available.

+ Details

Name:	bcow_ForeclosedAssetsWriteDowns
Namespace Prefix:	bcow_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

It represents Gain loss on sales

+ References

No definition available.

+ Details

Name:	bcow_GainLossOnSalesOfForeclosedAssets
Namespace Prefix:	bcow_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loans Receivable Transferred To Foreclosed Assets.

+ References

No definition available.

+ Details

Name:	bcow_LoansReceivableTransferredToForeclosedAssets
Namespace Prefix:	bcow_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5162-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4437-111522

+ Details

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

- Definition

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

+ References

+ Details

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

- Definition

The cash inflow from the sale assets received in full or partial satisfaction of a receivable including real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts. Foreclosed assets also include loans that are treated as if the underlying collateral had been foreclosed because the institution has taken possession of the collateral, even though legal foreclosure or repossession proceedings have not taken place.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration