GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Roll Forward]
Goodwill, beginning of period	$ 373,121	$ 373,121
Goodwill, end of period	373,121	373,121
Finite-lived Intangible Assets [Roll Forward]
Intangible Assets, Net (Including Goodwill)	378,082	378,805	$ 382,561
Amortization	(723)	(3,756)
Core Deposit Intangibles [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite-Lived Intangible Assets, Net	4,961	5,684	$ 9,440
Amortization	$ (723)	$ (3,756)

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

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