SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
	Jul. 15, 2021 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2023 USD ($) segment shares	Jun. 30, 2022 USD ($) shares	Mar. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares	Mar. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares
Lessee, Lease, Description [Line Items]
Stock price per share (in usd per share) | $ / shares	$ 10
Gross offering proceeds	$ 277,700
Charitable contribution in cash	$ 1,500
Shares in ESOP (in shares) | shares	2,281,800	2,281,800	2,281,800
Loans receivable, allowance		$ 14,413	$ 14,413	$ 14,050	$ 14,153	$ 13,400	$ 13,465	$ 14,425
Reversal in reserve for commitments and letters of credit		636	$ 636			1,700
Number of operating segments | segment			1
Shareholders' equity		$ (366,534)	$ (366,534)	$ (412,293)	(385,693)	$ (393,718)	(420,214)	(429,471)
ESOP shares committed to be released (in shares) | shares		22,818	45,636	22,818
Common stock, outstanding (in shares) | shares		25,493,422	25,493,422			27,523,219
Unallocated Common Stock Held by ESOP
Lessee, Lease, Description [Line Items]
Shareholders' equity		$ 20,536	$ 20,536	$ 21,449	20,764	$ 20,993	21,677	21,905
Retained Earnings
Lessee, Lease, Description [Line Items]
Shareholders' equity		(168,703)	(168,703)	(170,050)	(170,528)	(171,763)	(170,010)	(169,457)
Common Stock
Lessee, Lease, Description [Line Items]
Shareholders' equity		$ (285)	$ (285)	$ (285)	$ (285)	$ (285)	$ (285)	$ (285)
Common stock, outstanding (in shares) | shares		25,493,422	25,493,422	28,522,500	27,385,482	27,523,219	28,522,500	28,522,500
Additional Paid-In Capital
Lessee, Lease, Description [Line Items]
Shareholders' equity		$ (272,267)	$ (272,267)	$ (282,154)	$ (271,507)	$ (279,454)	$ (282,100)	$ (282,006)
Treasury Stock
Lessee, Lease, Description [Line Items]
Shareholders' equity		31,060	31,060	0	12,737	12,072	0	0
Accumulated Other Comprehensive Income (Loss)
Lessee, Lease, Description [Line Items]
Shareholders' equity		$ 23,125	$ 23,125	$ 18,747	23,126	24,719	10,504	372
Cumulative Effect, Period of Adoption, Adjustment
Lessee, Lease, Description [Line Items]
Allowance for credit losses						18
Loans receivable, allowance					$ 0	668	$ 0	$ 0
Held-to-maturities securities allowance						170
Reversal in reserve for commitments and letters of credit						(811)
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						8
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2022-02 | Unallocated Common Stock Held by ESOP
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Loans receivable, allowance						660
Shareholders' equity						18
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13 | Unallocated Common Stock Held by ESOP
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						8
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Shareholders' equity						18
Cumulative Effect, Period of Adoption, Adjustment | Common Stock | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						$ 0
Common stock, outstanding (in shares) | shares						0
Cumulative Effect, Period of Adoption, Adjustment | Common Stock | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Shareholders' equity						$ 0
Common stock, outstanding (in shares) | shares						0
Cumulative Effect, Period of Adoption, Adjustment | Additional Paid-In Capital | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						$ 0
Cumulative Effect, Period of Adoption, Adjustment | Additional Paid-In Capital | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Treasury Stock | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Treasury Stock | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2022-02
Lessee, Lease, Description [Line Items]
Shareholders' equity						0
Cumulative Effect, Period of Adoption, Adjustment | Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2016-13
Lessee, Lease, Description [Line Items]
Shareholders' equity						$ 0
Public stock offering
Lessee, Lease, Description [Line Items]
Shares of common stock sold (in shares) | shares	27,772,500
Donation of shares to Blue Foundry Charitable Foundation
Lessee, Lease, Description [Line Items]
Shares of common stock sold (in shares) | shares	750,000
Blue Foundry Bancorp - NJ
Lessee, Lease, Description [Line Items]
Ownership interest percentage		100.00%	100.00%