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, 2025	Mar. 31, 2024	Dec. 31, 2024
Allowance for credit losses
Beginning balance	$ 195,281	$ 186,126	$ 186,126
Charge-offs	(27,101)	(11,859)
Recoveries	2,551	3,224
Provision (release)	16,784	15,138
Ending balance	187,515	192,629	195,281
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	6,814
Loans evaluated on a collective basis	187,515	185,815
Period-end loan balances:
Loans evaluated on an individual basis	114,782	69,568
Loans evaluated on a collective basis	12,991,459	12,910,713
Ending balance	13,106,241	12,980,281	13,187,874
Reverse mortgage, fair value	4,100	2,500	3,600
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	57,131	49,394	49,394
Charge-offs	(19,871)	(476)	(15,490)
Recoveries	579	1,766
Provision (release)	12,897	5,218
Ending balance	50,736	55,902	57,131
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	6,814
Loans evaluated on a collective basis	50,736	49,088
Period-end loan balances:
Loans evaluated on an individual basis	44,449	27,229
Loans evaluated on a collective basis	2,620,951	2,564,632
Ending balance	2,665,400	2,591,861	2,656,174
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	9,139	10,719	10,719
Charge-offs	0	0	(177)
Recoveries	7	201
Provision (release)	(736)	(351)
Ending balance	8,410	10,569	9,139
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	8,410	10,569
Period-end loan balances:
Loans evaluated on an individual basis	6,273	5,866
Loans evaluated on a collective basis	1,948,255	1,877,010
Ending balance	1,954,528	1,882,876	1,973,645
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	48,962	36,055	36,055
Charge-offs	0	(25)	(5,749)
Recoveries	525	2
Provision (release)	305	765
Ending balance	49,792	36,797	48,962
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	49,792	36,797
Period-end loan balances:
Loans evaluated on an individual basis	29,407	21,536
Loans evaluated on a collective basis	3,952,666	3,855,320
Ending balance	3,982,073	3,876,856	4,030,627
Commercial | Construction
Allowance for credit losses
Beginning balance	9,185	10,762	10,762
Charge-offs	0	0	0
Recoveries	0	0
Provision (release)	506	197
Ending balance	9,691	10,959	9,185
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	9,691	10,959
Period-end loan balances:
Loans evaluated on an individual basis	23,180	3,962
Loans evaluated on a collective basis	845,488	1,052,387
Ending balance	868,668	1,056,349	832,093
Commercial | Commercial Small Business Leases
Allowance for credit losses
Beginning balance	15,965	15,170	15,170
Charge-offs	(2,967)	(4,852)	(20,033)
Recoveries	619	591
Provision (release)	3,492	4,550
Ending balance	17,109	15,459	15,965
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	17,109	15,459
Period-end loan balances:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	636,460	633,803
Ending balance	636,460	633,803	647,516
Residential
Allowance for credit losses
Beginning balance	5,566	5,483	5,483
Charge-offs	0	(50)	(125)
Recoveries	47	89
Provision (release)	84	(115)
Ending balance	5,697	5,407	5,566
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	5,697	5,407
Period-end loan balances:
Loans evaluated on an individual basis	8,105	8,311
Loans evaluated on a collective basis	958,466	864,354
Ending balance	966,571	872,665	961,426
Consumer
Allowance for credit losses
Beginning balance	49,333	58,543	58,543
Charge-offs	(4,263)	(6,456)	(23,549)
Recoveries	774	575
Provision (release)	236	4,874
Ending balance	46,080	57,536	49,333
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	46,080	57,536
Period-end loan balances:
Loans evaluated on an individual basis	3,368	2,664
Loans evaluated on a collective basis	2,029,173	2,063,207
Ending balance	$ 2,032,541	$ 2,065,871	$ 2,086,393