Note 4 - Loans Held for Investment, Net (Details Textual)	6 Months Ended
Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Nonaccrual	$ 3,590,539		$ 3,643,608
Impaired Financing Receivable, Interest Income, Nonaccrual	0	$ 4,000
Financing Receivable, Troubled Debt Restructuring	$ 51,000		$ 54,000
Veterans Administration Loan [Member]
Number of Receivable Commitments Outstanding	0		0
Real Estate [Member]
Financing Receivable, Nonaccrual	$ 2,700,000
Nonaccrual Loan Secure Percentage	76.40%
Small Business Administration [Member]
Financing Receivable, Nonaccrual	$ 2,300,000
Nonaccrual Loan Secure Percentage	64.20%
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Nonaccrual	$ 2,982,136		$ 2,993,923
Commercial Real Estate Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable, before Allowance for Credit Loss, Total	$ 17,700,000		$ 20,800,000

Amount of interest income recognized on loans while in nonaccrual status.

No definition available.

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Namespace Prefix:	bctf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

It represents the percentage of nonaccrual loans secured.

+ References

No definition available.

+ Details

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Namespace Prefix:	bctf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of receivable commitments outstanding.

+ References

No definition available.

+ Details

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Namespace Prefix:	bctf_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

+ Details

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

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919230-210447

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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- Details

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