Note 5 - Loans Held for Investment, Net - Impaired Loans (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Impaired loans, with no related allowance recorded, recorded investment	$ 3,505,288	$ 3,643,608
Impaired loans, with no related allowance recorded, principal net of charge-offs,	3,505,288	3,643,608
Impaired loans, with no related allowance recorded, average recorded investment	3,530,021	3,663,931
Impaired loans, with related allowance recorded, recorded investment	0	0
Impaired loans, with an allowance recorded, principal net of charge-offs	0	0
Impaired loans, related allowance	0	0
Impaired loans, with an allowance recorded, average recorded investment	0	0
Impaired loans, fair value disclosure	3,505,288	3,643,608
Impaired loans, principal net of charge-offs	3,505,288	3,643,608
Impaired loans, average recorded investment	3,530,021	3,663,931
Impaired loans, fair value disclosure	3,505,288	3,643,608
Commercial Real Estate Portfolio Segment [Member]
Impaired loans, with no related allowance recorded, recorded investment	2,718,731	2,993,923
Impaired loans, with no related allowance recorded, principal net of charge-offs,	2,718,731	2,993,923
Impaired loans, with no related allowance recorded, average recorded investment	2,738,545	3,007,495
Impaired loans, related allowance	0
Impaired loans, fair value disclosure	2,718,731	2,993,923
Impaired loans, principal net of charge-offs	2,718,731	2,993,923
Impaired loans, average recorded investment	2,738,545	3,007,495
Impaired loans, fair value disclosure	2,718,731	2,993,923
One-to-four Family Residential Real Estate Portfolio Segment [Member]
Impaired loans, with no related allowance recorded, recorded investment	786,557	649,685
Impaired loans, with no related allowance recorded, principal net of charge-offs,	786,557	649,685
Impaired loans, with no related allowance recorded, average recorded investment	791,476	656,436
Impaired loans, related allowance	0
Impaired loans, fair value disclosure	786,557	649,685
Impaired loans, principal net of charge-offs	786,557	649,685
Impaired loans, average recorded investment	791,476	656,436
Impaired loans, fair value disclosure	786,557	649,685
Commercial and Industrial Portfolio Segment [Member]
Impaired loans, with no related allowance recorded, recorded investment
Impaired loans, with no related allowance recorded, principal net of charge-offs,
Impaired loans, with no related allowance recorded, average recorded investment
Impaired loans, related allowance
Impaired loans, fair value disclosure
Impaired loans, principal net of charge-offs
Impaired loans, average recorded investment
Impaired loans, fair value disclosure
Consumer and Other Portfolio Segment [Member]
Impaired loans, with no related allowance recorded, recorded investment
Impaired loans, with no related allowance recorded, principal net of charge-offs,
Impaired loans, with no related allowance recorded, average recorded investment
Impaired loans, related allowance
Impaired loans, fair value disclosure
Impaired loans, principal net of charge-offs
Impaired loans, average recorded investment
Impaired loans, fair value disclosure

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

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=118936363&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=118936363&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 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 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no 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 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

Reference 2: 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=118936363&loc=d3e5212-111524

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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