FAIR VALUE DISCLOSURES - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Financial assets
Investment securities held-to-maturity	$ 79,542	$ 80,321
Other investments	125,548	129,945
Loans held for sale	11,500	9,200
Interest Receivable	60,130	56,900
Deposits
Noninterest-bearing	3,175,876	3,317,960
Savings	4,467,894	4,331,228
Time	$ 2,896,860	$ 2,718,390
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Discount Rate	11.52%	11.50%
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed	5.91%	5.92%
Impaired Commercial And Commercial Real Estate Loans Member
Deposits
Principal Amount of Commercial and Commercial Real Estate Loans	$ 5,500	$ 19,700
Allowance for Loan and Lease Losses, Real Estate	900	4,400
Carrying value
Financial assets
Cash and short-term investments	950,697	1,006,019
Investment securities held-to-maturity	79,542	80,321
Other investments	11,324	20,554
Loans and leases	11,060,846	10,791,743
Interest Receivable	74,377	72,620
Deposits
Deposits	13,457,148	13,360,797
Short-term borrowings	862,145	937,814
Long-term debt	343,236	344,115
Interest Payable	48,171	51,454
Fair value
Financial assets
Cash and short-term investments	950,697	1,006,019
Investment securities held-to-maturity	70,850	71,688
Other investments	11,324	20,554
Loans and leases	10,759,097	10,468,144
Interest Receivable	74,377	72,620
Deposits
Deposits	13,440,989	13,347,319
Short-term borrowings	862,145	937,814
Long-term debt	296,116	350,426
Interest Payable	48,171	51,454
Fair Value, Inputs, Level 1 [Member] | Fair value
Financial assets
Cash and short-term investments	950,697	1,006,019
Investment securities held-to-maturity	0	0
Other investments	1,284	1,194
Loans and leases	0	0
Interest Receivable	0	0
Deposits
Deposits	0	0
Short-term borrowings	862,145	937,814
Long-term debt	0	0
Interest Payable	4,283	15,494
Fair Value, Inputs, Level 2 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	70,850	71,688
Other investments	10,040	10,040
Loans and leases	0	0
Interest Receivable	14,247	15,697
Deposits
Deposits	13,440,989	13,347,319
Short-term borrowings	0	0
Long-term debt	296,116	350,426
Interest Payable	43,888	35,960
Fair Value, Inputs, Level 3 [Member] | Fair value
Financial assets
Cash and short-term investments	0	0
Investment securities held-to-maturity	0	0
Other investments	0	9,320
Loans and leases	10,759,097	10,468,144
Interest Receivable		56,923
Deposits
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Interest Payable	$ 0	$ 0