Loans Receivable Held for Investment, Average of Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income (Q3) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income [Abstract]
Average recorded investment	$ 4,882	$ 5,683	$ 5,055	$ 6,220	$ 6,024	$ 8,904
Cash basis interest income recognized	80	90	417	636	995	455
Foregone interest income	22	41	67	121	120	280
Loans delinquent amount	0		0
Real Estate [Member] \| Single Family [Member]
Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income [Abstract]
Average recorded investment	589	625	596	631
Cash basis interest income recognized	7	7	22	22
Real Estate [Member] \| Multi-Family [Member]
Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income [Abstract]
Average recorded investment	305	317	308	320
Cash basis interest income recognized	5	6	16	17
Real Estate [Member] \| Church [Member]
Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income [Abstract]
Average recorded investment	3,938	4,678	4,094	5,206	5,017	7,893
Cash basis interest income recognized	67	76	376	594	939	398
Commercial - Other [Member]
Loans Individually Evaluated for Impairment by Loan Type and Related Interest Income [Abstract]
Average recorded investment	50	63	57	63	63	64
Cash basis interest income recognized	$ 1	$ 1	$ 3	$ 3	$ 5	$ 4

No definition available.

Name:	byfc_LoansIndividuallyEvaluatedForImpairmentByLoanTypeAndRelatedInterestIncomeAbstract
Namespace Prefix:	byfc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This is the principal amount of loans (across all types of loans) that are overdue in payment by a set number of days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)(4)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeCashBasisMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=byfc_ChurchLoanMember
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: