Allowance for Loan Losses - Loans Evaluated for Impairment Individually and Collectively by Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 1,271	$ 1,157
Loans collectively evaluated for impairment	6,587	6,745
Purchased credit-impaired loans	0	0
Total allowance for loan losses	7,858	7,902	$ 7,923	$ 7,770
Loans individually evaluated for impairment	7,564	7,606
Loans collectively evaluated for impairment	906,115	889,416
Purchased credit-impaired loans	5,270	5,323
Total Loans	918,949	902,345
Mortgage Loans on Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	1,151	1,036
Loans collectively evaluated for impairment	4,108	3,931
Purchased credit-impaired loans	0	0
Total allowance for loan losses	5,259	4,967	4,190	3,864
Loans individually evaluated for impairment	7,444	7,485
Loans collectively evaluated for impairment	712,828	701,235
Purchased credit-impaired loans	5,222	5,277
Total Loans	725,494	713,997
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans collectively evaluated for impairment	1,406	1,374
Purchased credit-impaired loans	0	0
Total allowance for loan losses	1,406	1,374	1,043	878
Loans collectively evaluated for impairment	173,360	164,608
Total Loans	173,360	164,608
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	120	121
Loans collectively evaluated for impairment	1,073	1,440
Purchased credit-impaired loans	0	0
Total allowance for loan losses	1,193	1,561	$ 2,690	$ 3,028
Loans individually evaluated for impairment	120	121
Loans collectively evaluated for impairment	19,927	23,573
Purchased credit-impaired loans	48	46
Total Loans	$ 20,095	$ 23,740

Financing receivable allowance for credit losses related to purchased credit impaired loans.

No definition available.

Name:	bayk_FinancingReceivableAllowanceForCreditLossesRelatedToPurchasedCreditImpairedLoans
Namespace Prefix:	bayk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivable, purchased credit impaired loans.

+ References

No definition available.

+ Details

Name:	bayk_FinancingReceivablePurchasedCreditImpairedLoans
Namespace Prefix:	bayk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ 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 (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ 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=84173941&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ 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=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ 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 (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ 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 (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes 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 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

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

- Details

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

- Details

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

- Details

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