SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Premises and Equipment) (Details) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2023 USD ($) loan branch machine	Dec. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)	Jan. 31, 2020
Accounting Policies [Line Items]
Investments in unconsolidated subsidiaries accounted for under the equity methods	$ 0.1			$ 0.1		$ 0.1
Proceeds from sale of equity method in investment securities					$ 1.7
Proportional amortization investments	37.8			37.8		40.9
Investments in unconsolidated subsidiaries accounted for under the cost methods	$ 3.6			$ 3.6		$ 5.6
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued interest receivable			Accrued interest receivable		Accrued interest receivable
Available for sale accrued interest receivable	$ 3.2			$ 3.2		$ 3.1
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued interest receivable			Accrued interest receivable		Accrued interest receivable
Held-to-maturity accrued interest receivable	$ 1.2			$ 1.2		$ 1.3
Number of types of loans held for sale | loan				2
Accrued interest receivable on loans	$ 17.1			$ 17.1		$ 16.0
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued interest receivable			Accrued interest receivable		Accrued interest receivable
Maximum | Office buildings and improvements
Accounting Policies [Line Items]
Useful life	39 years			39 years
Maximum | Equipment
Accounting Policies [Line Items]
Useful life	7 years			7 years
Minimum | Office buildings and improvements
Accounting Policies [Line Items]
Useful life	5 years			5 years
Minimum | Equipment
Accounting Policies [Line Items]
Useful life	1 year			1 year
Swell Financial, Inc.
Accounting Policies [Line Items]
Proceeds from intellectual property rights and platform usage fees from products				$ 1.5
Swell Financial, Inc. | Maximum
Accounting Policies [Line Items]
Proceeds from sale of equity method in investment securities	$ 0.5	$ 0.5
Proceeds from intellectual property rights and platform usage fees from products		$ 1.5
Oahu HomeLoans, LLC
Accounting Policies [Line Items]
Ownership interest							50.00%
Gentry Home Loans LLC
Accounting Policies [Line Items]
Ownership interest	50.00%			50.00%
Island Pacific HomeLoans, LLC
Accounting Policies [Line Items]
Ownership interest	50.00%			50.00%
Haseko Home Loans LLC
Accounting Policies [Line Items]
Ownership interest	50.00%			50.00%
JAM FINTOP Banktech Fund, L.P.
Accounting Policies [Line Items]
Investments in unconsolidated subsidiaries accounted for under the equity methods					$ 2.0
Swell Financial, Inc.
Accounting Policies [Line Items]
Investments in unconsolidated subsidiaries accounted for under the equity methods			$ 2.0
Other intangible assets and services provided for common stock			1.5
Payments for repurchase of convertible preferred stock			$ 0.5
Central Bank
Accounting Policies [Line Items]
Number of branches | branch				27
Number of ATMs | machine				58