Loans Receivable and Allowance for Loan Losses - Troubled Debt Restructuring (Details) $ in Thousands	9 Months Ended
Sep. 30, 2019 USD ($) loan	Sep. 30, 2018 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
No. of Loans \| loan	1	5
Pre-modification Recorded Investment	$ 4,095	$ 1,050
Post-modification Recorded Investment	$ 4,095	$ 1,050
Real estate loans \| One-to-four family
Financing Receivable, Troubled Debt Restructuring [Line Items]
No. of Loans \| loan	0	4
Pre-modification Recorded Investment	$ 0	$ 462
Post-modification Recorded Investment	$ 0	$ 462
Real estate loans \| Multifamily and commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
No. of Loans \| loan	1	0
Pre-modification Recorded Investment	$ 4,095	$ 0
Post-modification Recorded Investment	$ 4,095	$ 0
Consumer loans \| Home equity loans and advances
Financing Receivable, Troubled Debt Restructuring [Line Items]
No. of Loans \| loan	0	1
Pre-modification Recorded Investment	$ 0	$ 588
Post-modification Recorded Investment	$ 0	$ 588

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.

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ 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

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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