Employee Stock Ownership Plan - Additional Information (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESOP Purchased \| shares	175,528
Compensation Expense \| $	$ 71
Fair Value of Unallocated Shares Of ESOP Share Price \| $ / shares	$ 10.78
Share-based Compensation Award, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested Percentage	20.00%
Vested Years Of Service	1 year
Share-based Compensation Award, Tranche Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested Percentage	40.00%
Vested Years Of Service	2 years
Share-based Compensation Award, Tranche Three [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested Percentage	60.00%
Vested Years Of Service	3 years
Share-based Compensation Award Tranche Four [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested Percentage	80.00%
Vested Years Of Service	4 years
Share-based Compensation Award Tranche Five [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vested Percentage	100.00%
Vested Years Of Service	5 years

Represents Fair Value of Unallocated Shares Of ESOP Share Price.

No definition available.

Name:	bcow_FairValueOfUnallocatedSharesOfEsopSharePrice
Namespace Prefix:	bcow_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of plan compensation cost recognized during the period.

+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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

- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

+ 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 (a)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPSharesContributedToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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

No definition available.

+ Details

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

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bcow_SharebasedCompensationAwardTrancheFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=bcow_SharebasedCompensationAwardTrancheFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: