SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Millions		3 Months Ended
Jul. 15, 2021 USD ($) $ / shares shares	Mar. 31, 2022 segment shares
Lessee, Lease, Description [Line Items]
Stock price per share \| $ / shares	$ 10
Gross offering proceeds \| $	$ 277.7
Charitable contribution in cash \| $	$ 1.5
Shares in ESOP	2,281,800	2,281,800
Number of operating segments \| segment		1
Public stock offering
Lessee, Lease, Description [Line Items]
Shares of common stock sold	27,772,500
Donation of shares to Blue Foundry Charitable Foundation
Lessee, Lease, Description [Line Items]
Shares of common stock sold	750,000
Blue Foundry Bancorp - NJ
Lessee, Lease, Description [Line Items]
Ownership interest percentage		100.00%

Payments For Charitable Contributions

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- Definition

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

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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

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8672-108599

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Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

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

+ References

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

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