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BORROWINGS - Narrative (Details) - USD ($)			3 Months Ended
BORROWINGS - Narrative (Details) - USD ($)	Mar. 15, 2022	Nov. 05, 2019	Sep. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Long-term borrowings			$ 371,251,000	$ 370,803,000
FHLB availability based on pledged collateral			3,000,000,000.0	3,100,000,000
FHLB advances			450,000,000.0	550,000,000.0
Unsecured lines of credit, correspondent banks
Debt Instrument [Line Items]
Maximum borrowing capacity			829,000,000.0	1,200,000,000
Federal Reserve Bank Term Funding Program
Debt Instrument [Line Items]
Repayments of debt			300,000,000
Federal Reserve and correspondent banks
Debt Instrument [Line Items]
Maximum borrowing capacity			771,800,000	651,300,000
Line of credit			0	0
Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Maximum borrowing capacity			3,400,000,000	3,600,000,000
Federal Home Loan Bank Advances \| Residential mortgage \| Asset pledged as collateral \| Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Maximum borrowing capacity			1,400,000,000	1,400,000,000
Federal Home Loan Bank Advances \| Commercial real estate loans \| Asset pledged as collateral \| Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Maximum borrowing capacity			3,900,000,000	4,000,000,000.0
Federal Home Loan Bank Advances \| Home equity lines of credit \| Asset pledged as collateral \| Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Maximum borrowing capacity			220,900,000	209,200,000
Federal Home Loan Bank Advances \| Multifamily loans \| Asset pledged as collateral \| Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 559,300,000	538,600,000
Subordinated Debt \| Fixed Floating Rate Subordinated Notes Due 2032
Debt Instrument [Line Items]
Aggregate principal amount	$ 200,000,000
Interest rate	3.875%		3.875%
Basis spread on variable rate	1.965%
Unamortized discount (premium) and debt issuance costs, net	$ 3,100,000
Subordinated Debt \| Fixed Floating Rate Subordinated Notes Due 2029
Debt Instrument [Line Items]
Interest rate		4.25%	4.25%
Basis spread on variable rate		2.88%
Unamortized discount (premium) and debt issuance costs, net		$ 2,900,000
Long-term borrowings		$ 175,000,000.0
Subordinated Debt \| Fixed Floating Rate Subordinated Notes Due 2029 \| Spread Adjustment
Debt Instrument [Line Items]
Basis spread on variable rate		0.26%
Retail Repurchase Agreements
Debt Instrument [Line Items]
Long-term debt			$ 70,800,000	70,800,000
Federal Funds Purchased
Debt Instrument [Line Items]
Long-term debt			$ 0	$ 0