Loans (Troubled Debt Restructuring) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Number of Modifications	5	4
Pre-Modification Investment	$ 1,014	$ 572
Post- Modification Investment	$ 1,014	$ 572
Residential Real Estate and Consumer [Member] \| One-to-Four Family Owner-occupied [Member]
Number of Modifications	3	2
Pre-Modification Investment	$ 285	$ 302
Post- Modification Investment	$ 285	$ 302
Residential Real Estate and Consumer [Member] \| One-to-Four Family Investor-owned [Member]
Number of Modifications		1
Pre-Modification Investment		$ 250
Post- Modification Investment		$ 250
Residential Real Estate and Consumer [Member] \| Consumer [Member]
Number of Modifications		1
Pre-Modification Investment		$ 20
Post- Modification Investment		$ 20
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member]
Number of Modifications	2
Pre-Modification Investment	$ 729
Post- Modification Investment	$ 729

Number of financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffbw_ResidentialRealEstateAndConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ffbw_OneToFourFamilyOwnerOccupiedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ffbw_OneToFourFamilyInvestorOwnedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ffbw_ConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ffbw_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: