ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for credit losses
Beginning balance	$ 186,126	$ 151,861	$ 151,861
Charge-offs	(11,859)	(13,666)
Recoveries	3,224	1,955
Provision	15,138	29,012
Ending balance	192,629	169,162	186,126
Period-end allowance allocated to:
Loans evaluated on an individual basis	6,814	4,653
Loans evaluated on a collective basis	185,815	164,509
Period-end loan balances:
Loans evaluated on an individual basis	69,568	40,891
Loans evaluated on a collective basis	12,910,713	12,102,377
Gross loans	12,980,281	12,143,268	12,766,518
Reverse mortgage, fair value	2,500	2,700	2,800
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	49,394	49,526	49,526
Charge-offs	(476)	(6,563)	(26,653)
Recoveries	1,766	701
Provision	5,218	9,809
Ending balance	55,902	53,473	49,394
Period-end allowance allocated to:
Loans evaluated on an individual basis	6,814	4,562
Loans evaluated on a collective basis	49,088	48,911
Period-end loan balances:
Loans evaluated on an individual basis	27,229	22,443
Loans evaluated on a collective basis	2,564,632	2,546,299
Gross loans	2,591,861	2,568,742	2,540,070
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	10,719	6,019	6,019
Charge-offs	0	0	(184)
Recoveries	201	5
Provision	(351)	32
Ending balance	10,569	6,056	10,719
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	91
Loans evaluated on a collective basis	10,569	5,965
Period-end loan balances:
Loans evaluated on an individual basis	5,866	1,907
Loans evaluated on a collective basis	1,877,010	1,844,754
Gross loans	1,882,876	1,846,661	1,886,087
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	36,055	21,473	21,473
Charge-offs	(25)	0	(300)
Recoveries	2	2
Provision	765	8,639
Ending balance	36,797	30,114	36,055
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	36,797	30,114
Period-end loan balances:
Loans evaluated on an individual basis	21,536	7,343
Loans evaluated on a collective basis	3,855,320	3,465,740
Gross loans	3,876,856	3,473,083	3,801,180
Commercial | Construction
Allowance for credit losses
Beginning balance	10,762	6,987	6,987
Charge-offs	0	0	(794)
Recoveries	0	530
Provision	197	2,155
Ending balance	10,959	9,672	10,762
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	10,959	9,672
Period-end loan balances:
Loans evaluated on an individual basis	3,962	760
Loans evaluated on a collective basis	1,052,387	1,022,951
Gross loans	1,056,349	1,023,711	1,035,530
Commercial | Commercial Small Business Leases
Allowance for credit losses
Beginning balance	15,170	9,868	9,868
Charge-offs	(4,852)	(2,899)	(15,641)
Recoveries	591	515
Provision	4,550	1,752
Ending balance	15,459	9,236	15,170
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	15,459	9,236
Period-end loan balances:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	633,803	576,584
Gross loans	633,803	576,584	623,622
Residential
Allowance for credit losses
Beginning balance	5,483	4,668	4,668
Charge-offs	(50)	0	(41)
Recoveries	89	43
Provision	(115)	616
Ending balance	5,407	5,327	5,483
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	5,407	5,327
Period-end loan balances:
Loans evaluated on an individual basis	8,311	6,522
Loans evaluated on a collective basis	864,354	779,538
Gross loans	872,665	786,060	867,895
Consumer
Allowance for credit losses
Beginning balance	58,543	53,320	53,320
Charge-offs	(6,456)	(4,204)	(22,394)
Recoveries	575	159
Provision	4,874	6,009
Ending balance	57,536	55,284	58,543
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	57,536	55,284
Period-end loan balances:
Loans evaluated on an individual basis	2,664	1,916
Loans evaluated on a collective basis	2,063,207	1,866,511
Gross loans	$ 2,065,871	$ 1,868,427	$ 2,012,134