Loans Receivable Held for Investment, Activity in Allowance for Loan Losses by Loan Type (FY) (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
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	$ 3,215	$ 2,771	$ 3,182	$ 2,929	$ 2,929	$ 4,069
Provision for (recapture of) loan losses	0	47	29	(301)	(7)	(1,254)
Recoveries	0	0	4	190	260	114
Loans charged off	0	0	0	0	0	0
Ending balance	3,215	2,818	3,215	2,818	3,182	2,929
Real Estate [Member] \| Single Family [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance			312	369	369	594
Provision for (recapture of) loan losses					(57)	(225)
Recoveries					0	0
Loans charged off					0	0
Ending balance					312	369
Real Estate [Member] \| Multi-Family [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance			2,319	1,880	1,880	2,300
Provision for (recapture of) loan losses					439	(420)
Recoveries					0	0
Loans charged off					0	0
Ending balance					2,319	1,880
Real Estate [Member] \| Commercial Real Estate [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	169	58	133	52	52	71
Provision for (recapture of) loan losses	17	0	53	6	81	(19)
Recoveries	0	0	0	0	0	0
Loans charged off	0	0	0	0	0	0
Ending balance	186	58	186	58	133	52
Real Estate [Member] \| Church [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	282	401	362	603	603	1,081
Provision for (recapture of) loan losses	(28)	(24)	(108)	(416)	(501)	(592)
Recoveries	0	0	0	190	260	114
Loans charged off	0	0	0	0	0	0
Ending balance	254	377	254	377	362	603
Real Estate [Member] \| Construction [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	22	44	48	19	19	17
Provision for (recapture of) loan losses	0	6	(26)	31	29	2
Recoveries	0	0	0	0	0	0
Loans charged off	0	0	0	0	0	0
Ending balance	22	50	22	50	48	19
Commercial - Other [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	6	5	7	6	6	6
Provision for (recapture of) loan losses	(1)	0	(2)	(1)	1	0
Recoveries	0	0	0	0	0	0
Loans charged off	0	0	0	0	0	0
Ending balance	5	5	5	5	7	6
Consumer [Member]
Allowance for Loan and Lease Losses by Loan Type [Roll Forward]
Beginning balance	0	3	1	0	0	0
Provision for (recapture of) loan losses	2	(1)	1	2	1	0
Recoveries	0	0	0	0	0	0
Loans charged off	0	0	0	0	0	0
Ending balance	$ 2	$ 2	$ 2	$ 2	$ 1	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

Name:	us-gaap_LoansAndLeasesReceivableAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

Name:	us-gaap_ProvisionForLoanAndLeaseLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
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_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: