Debt Instrument, Prepayment Penalty

No definition available.

Name:	bcbp_DebtInstrumentPrepaymentPenalty
Namespace Prefix:	bcbp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Federal Home Loan Bank Advances, Unamortized Prepayment Penalties

+ References

No definition available.

+ Details

Name:	bcbp_FederalHomeLoanBankAdvancesUnamortizedPrepaymentPenalties
Namespace Prefix:	bcbp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Increase (Decrease) In Weighted Average Interest Rate

+ References

No definition available.

+ Details

Name:	bcbp_IncreaseDecreaseInWeightedAverageInterestRate
Namespace Prefix:	bcbp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum ratio of debt to total assets under debt covenant.

+ References

No definition available.

+ Details

Name:	bcbp_MaximumRatioOfDebtToTotalAssetsUnderDebtCovenant
Namespace Prefix:	bcbp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum total debt under debt covenant.

+ References

No definition available.

+ Details

Name:	bcbp_MaximumTotalDebtUnderDebtCovenant
Namespace Prefix:	bcbp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of restricted investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5086-111524

+ Details

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

- Definition

Amount of cash inflow from Federal Home Loan Bank (FHLBank) borrowing, classified as financing activity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3255-108585

+ Details

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

- Definition

Amount of cash outflow for repayment of Federal Home Loan Bank (FHLBank) borrowing, classified as financing activity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=bcbp_FederalHomeLoanBankOfNewYorkAdvanceDueSeptember2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bcbp_FederalHomeLoanBankOfNewYorkAdvanceIssuedOctober2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bcbp_FederalHomeLoanBankOfNewYorkAdvanceDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bcbp_FederalHomeLoanBankOfNewYorkAdvanceIssuedNovember2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=bcbp_FederalHomeLoanBankOfNewYorkAdvancesDueIn2021And2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Short-Term Debt and Long-term Debt (Narrative) (Details) - USD ($)	1 Months Ended		12 Months Ended
	Nov. 30, 2020	Oct. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Loans pledged as collateral			$ 814,600,000	$ 772,800,000
Securities pledged as collateral			0	0
Unamortized prepayment penalties			$ 2,600,000	0
Maximum ratio of debt to total assets under debt covenant			50.00%
Maximum total debt under debt covenant			$ 1,412,000,000
Repayments of Federal Home Loan Bank of New York Advances			142,800,000	50,000,000
Net proceeds from Federal Home Loan Bank of New York Advances			88,161,000	$ 50,000,000
FHLB Of New York Advance Due September 2022 [Member]
Debt Instrument [Line Items]
Repayments of Federal Home Loan Bank of New York Advances		$ 20,800,000
Fixed interest rate		3.10%
FHLB Of New York Advance Issued October 2020 [Member]
Debt Instrument [Line Items]
Fixed interest rate		0.59%
Net proceeds from Federal Home Loan Bank of New York Advances		$ 20,800,000
Debt term		5 years
Prepayment penalty		1.15%
FHLB Of New York Advance Due 2023 [Member]
Debt Instrument [Line Items]
Repayments of Federal Home Loan Bank of New York Advances	$ 25,000,000.0
Fixed interest rate	2.90%
FHLB Of New York Advance Issued November 2020 [Member]
Debt Instrument [Line Items]
Fixed interest rate	0.68%
Net proceeds from Federal Home Loan Bank of New York Advances	$ 25,000,000.0
Debt term	5 years
Prepayment penalty	1.25%
FHLB Of New York Advances Due In 2021 And 2022 [Member]
Debt Instrument [Line Items]
Debt extinguished			$ 47,000,000.0
Weigted average interest rate			2.24%
Increase (decrease) in weighted average interest rate			(0.12%)