Note 9 - Fair Value Disclosure - Estimated Fair Value of the Company's Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available-for-sale, fair value	$ 115,889	$ 106,208
Reported Value Measurement [Member]
Securities available-for-sale, fair value	115,889	106,208
Estimate of Fair Value Measurement [Member]
Securities available-for-sale, fair value	115,889	106,208
Fair Value, Inputs, Level 1 [Member] \| Reported Value Measurement [Member]
Interest Bearing	31,979	7,699
Non-Interest Bearing	11,766	6,583
Fair Value, Inputs, Level 1 [Member] \| Estimate of Fair Value Measurement [Member]
Interest Bearing	31,979	7,699
Non-Interest Bearing	11,766	6,583
Fair Value, Inputs, Level 3 [Member] \| Reported Value Measurement [Member]
Loans, Net	695,718	674,094
Fair Value, Inputs, Level 3 [Member] \| Estimate of Fair Value Measurement [Member]
Loans, Net	706,433	684,777
Fair Value, Inputs, Level 2 [Member] \| Reported Value Measurement [Member]
Restricted Stock	3,712	3,665
Bank-Owned Life Insurance	19,035	18,687
Accrued Interest Receivable	2,572	2,441
Deposits	762,374	698,218
Short-term Borrowings	24,662	27,027
Other Borrowed Funds	24,500	28,000
Accrued Interest Payable	413	334
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member]
Restricted Stock	3,712	3,665
Bank-Owned Life Insurance	19,035	18,687
Accrued Interest Receivable	2,572	2,441
Deposits	738,836	697,806
Short-term Borrowings	24,662	27,027
Other Borrowed Funds	24,671	28,098
Accrued Interest Payable	$ 413	$ 334

Represents fair value of accrued interest payable.

No definition available.

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Namespace Prefix:	cbfv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents fair value of accrued interest receivable.

+ References

No definition available.

+ Details

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Namespace Prefix:	cbfv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents fair value of bank-owned life insurance.

+ References

No definition available.

+ Details

Name:	cbfv_BankOwnedLifeInsuranceFairValue
Namespace Prefix:	cbfv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents fair value of interest bearing deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	cbfv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents fair value of non-interest bearing deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	cbfv_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

+ Details

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

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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

- Definition

Fair value portion of other liabilities.

+ References

No definition available.

+ Details

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

- Definition

The aggregate value of all restricted investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-12C.9(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.6(c))
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Details

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