LOANS AND ALLOWANCE - Narrative (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) loan_segment	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for sale	$ 15,118,000		$ 18,934,000
Loans	12,465,582,000		12,486,027,000
Interest income recognized on non-accrual loans	$ 0	$ 0
Number of loan segments | loan_segment	10
Allowance for credit losses increase (decrease)	$ 253,000	(225,000)
Net charge-offs	2,300,000
Provision expense	$ 2,000,000	0
Standby letters of credit usual term	2 years
Increase (decrease) in provision	$ 0	0	3,800,000
Off-balance sheet commitments	19,500,000	$ 23,300,000	19,500,000	$ 23,300,000
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,722,365,000		3,670,948,000
Commercial real estate, non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,368,360,000		2,400,839,000
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,316,490,000		2,288,921,000
Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	68,900,000		79,200,000
Increase in past due loans	10,300,000
30-59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,406,000		34,075,000
Increase in past due loans	16,700,000
30-59 Days Past Due | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,279,000		5,021,000
Increase in past due loans	1,700,000
30-59 Days Past Due | Commercial real estate, non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	746,000		12,995,000
Increase in past due loans	12,200,000
30-59 Days Past Due | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,741,000		11,810,000
Increase in past due loans	3,100,000
60-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,491,000		11,189,000
Increase in past due loans	1,700,000
60-89 Days Past Due | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	267,000		1,622,000
60-89 Days Past Due | Commercial real estate, non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,988,000		195,000
60-89 Days Past Due | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,197,000		5,472,000
90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	41,978,000		33,980,000
Increase in past due loans	8,000,000
90 Days or More Past Due | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,407,000		6,858,000
90 Days or More Past Due | Commercial real estate, non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	22,781,000		11,465,000
Increase in past due loans	11,300,000
90 Days or More Past Due | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,848,000		$ 12,143,000
Increase in past due loans	$ 2,300,000