INVESTMENT AND MORTGAGE-BACKED SECURITIES - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Securities available-for-sale:
Acquired securities available-for-sale on the Merger Date	$ 652,000,000.0
Securities held-to-maturity	177,354,000	$ 0
Securities pledged as collateral, carrying amount	$ 726,400,000	$ 99,400,000
Number of holdings of securities of any one issuer in an amount greater than 10% of stockholders equity	0	0
Threshold for disclosure percentage	10.00%	10.00%
Available for sale debt securities, unrealized loss position due to credit	$ 0
Accrued interest receivable on securities	4,400,000
Agency collateralized mortgage obligations ("CMOs")
Securities available-for-sale:
Securities held-to-maturity	60,054,000
Pass-through mortgage-backed securities ("MBS") issued by government sponsored entities ("GSEs")
Securities available-for-sale:
Securities held-to-maturity	117,300,000
Available for sale debt securities, unrealized loss position due to credit	$ 427,382,000	$ 5,007,000

Represents the carrying amount of securities pledged as collateral.

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Represents the holdings of securities of any one issuer, other than the U.S. Government and its agencies, in an amount greater than 10% of stockholders equity.

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Threshold percentage which the entity uses for disclosure.

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Fair value at acquisition of acquired loans accounted for as available-for-sale debt securities with evidence of deterioration of credit quality.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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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.

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