Sale of Stock, Percentage of Common Stock to be Contributed to an Existing Charitable Foundation

No definition available.

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- 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

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- Definition

Specific incremental costs directly attributable to a proposed or actual offering of securities which are deferred at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.A)
-URI http://asc.fasb.org/extlink&oid=27011391&loc=d3e105025-122735

+ Details

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- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

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- Definition

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

+ References

No definition available.

+ Details

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- Details

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- Details

Name:	dei_LegalEntityAxis=clbk_ColumbiaBankFoundationMember
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- Details

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Plan of Stock Issuance - Narrative (Details) - USD ($) $ in Millions	Apr. 20, 2018	Sep. 27, 2017	Mar. 31, 2018
Class of Stock [Line Items]
Percentage of common stock to be contributed to an existing charitable foundation		3.00%
Total deferred costs			$ 1.7
Columbia Financial Inc \| Minority Owners
Class of Stock [Line Items]
Sale of stock, percentage of ownership interest		43.00%
Columbia Financial Inc \| Columbia Bank, MHC
Class of Stock [Line Items]
Sale of stock, percentage of ownership interest		54.00%
Subsequent event \| Columbia Bank, MHC
Class of Stock [Line Items]
Shares issued (shares)	62,580,155
Subsequent event \| Columbia Bank Foundation
Class of Stock [Line Items]
Shares issued (shares)	3,476,675
Employee Stock \| Subsequent event
Class of Stock [Line Items]
Shares issued (shares)	49,832,345