ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Allowance for credit losses
Beginning balance	$ 187,515	$ 192,629	$ 195,281	$ 186,126	$ 186,126
Charge-offs	(8,566)		(35,667)
Charge-offs		17,572		29,431
Recoveries	7,454	3,381	10,005	6,605
Charge-offs arising from transfer of loans to held for sale	(8,655)		(8,655)
Provision (release)	8,556	19,815	25,340	34,953
Ending balance	186,304	198,253	186,304	198,253	195,281
Period-end allowance allocated to:
Loans evaluated on an individual basis	6,294	8,055	6,294	8,055
Loans evaluated on a collective basis	180,010	190,198	180,010	190,198
Period-end loan balances:
Loans evaluated on an individual basis	97,603	67,493	97,603	67,493
Loans evaluated on a collective basis	12,891,943	13,073,897	12,891,943	13,073,897
Ending balance	12,989,546	13,141,390	12,989,546	13,141,390	13,187,874
Reverse mortgage, fair value	4,700	2,800	4,700	2,800	3,600
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	50,736	55,902	57,131	49,394	49,394
Charge-offs	(1,280)		(21,151)
Charge-offs		1,906	21,703	2,382	15,490
Recoveries	1,865	1,736	2,444	3,502
Charge-offs arising from transfer of loans to held for sale	(552)		(552)
Provision (release)	1,352	784	14,249	6,002
Ending balance	52,121	56,516	52,121	56,516	57,131
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	8,055	0	8,055
Loans evaluated on a collective basis	52,121	48,461	52,121	48,461
Period-end loan balances:
Loans evaluated on an individual basis	27,551	39,217	27,551	39,217
Loans evaluated on a collective basis	2,716,841	2,599,935	2,716,841	2,599,935
Ending balance	2,744,392	2,639,152	2,744,392	2,639,152	2,656,174
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	8,410	10,569	9,139	10,719	10,719
Charge-offs	0		0
Charge-offs		0	0	0	177
Recoveries	5	4	12	205
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	169	(905)	(567)	(1,256)
Ending balance	8,584	9,668	8,584	9,668	9,139
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	8,584	9,668	8,584	9,668
Period-end loan balances:
Loans evaluated on an individual basis	6,311	4,260	6,311	4,260
Loans evaluated on a collective basis	1,941,283	1,936,417	1,941,283	1,936,417
Ending balance	1,947,594	1,940,677	1,947,594	1,940,677	1,973,645
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	49,792	36,797	48,962	36,055	36,055
Charge-offs	(197)		(197)
Charge-offs		4,907	197	4,932	5,749
Recoveries	2	102	527	104
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	5,178	14,839	5,483	15,604
Ending balance	54,775	46,831	54,775	46,831	48,962
Period-end allowance allocated to:
Loans evaluated on an individual basis	5,125	0	5,125	0
Loans evaluated on a collective basis	49,650	46,831	49,650	46,831
Period-end loan balances:
Loans evaluated on an individual basis	24,115	8,991	24,115	8,991
Loans evaluated on a collective basis	3,887,422	4,025,827	3,887,422	4,025,827
Ending balance	3,911,537	4,034,818	3,911,537	4,034,818	4,030,627
Commercial | Construction
Allowance for credit losses
Beginning balance	9,691	10,959	9,185	10,762	10,762
Charge-offs	0		0
Charge-offs		0	0	0	0
Recoveries	0	0	0	0
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	1,005	(1,761)	1,511	(1,564)
Ending balance	10,696	9,198	10,696	9,198	9,185
Period-end allowance allocated to:
Loans evaluated on an individual basis	1,169	0	1,169	0
Loans evaluated on a collective basis	9,527	9,198	9,527	9,198
Period-end loan balances:
Loans evaluated on an individual basis	28,505	3,887	28,505	3,887
Loans evaluated on a collective basis	829,126	875,330	829,126	875,330
Ending balance	857,631	879,217	857,631	879,217	832,093
Commercial | Commercial Small Business Leases
Allowance for credit losses
Beginning balance	17,109	15,459	15,965	15,170	15,170
Charge-offs	(4,376)		(7,343)
Charge-offs		4,888	7,343	9,740	20,033
Recoveries	714	831	1,333	1,422
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	4,854	4,816	8,346	9,366
Ending balance	18,301	16,218	18,301	16,218	15,965
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	18,301	16,218	18,301	16,218
Period-end loan balances:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	630,127	643,520	630,127	643,520
Ending balance	630,127	643,520	630,127	643,520	647,516
Residential
Allowance for credit losses
Beginning balance	5,697	5,407	5,566	5,483	5,483
Charge-offs	0		0
Charge-offs		51	0	101	125
Recoveries	50	43	97	132
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	68	(342)	152	(457)
Ending balance	5,815	5,057	5,815	5,057	5,566
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	5,815	5,057	5,815	5,057
Period-end loan balances:
Loans evaluated on an individual basis	7,665	8,300	7,665	8,300
Loans evaluated on a collective basis	968,797	889,273	968,797	889,273
Ending balance	976,462	897,573	976,462	897,573	961,426
Consumer
Allowance for credit losses
Beginning balance	46,080	57,536	49,333	58,543	58,543
Charge-offs	(2,713)		(6,976)
Charge-offs		5,820	15,079	12,276	23,549
Recoveries	4,818	665	5,592	1,240
Charge-offs arising from transfer of loans to held for sale	(8,103)		(8,103)
Provision (release)	(4,070)	2,384	(3,834)	7,258
Ending balance	36,012	54,765	36,012	54,765	49,333
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	36,012	54,765	36,012	54,765
Period-end loan balances:
Loans evaluated on an individual basis	3,456	2,838	3,456	2,838
Loans evaluated on a collective basis	1,918,347	2,103,595	1,918,347	2,103,595
Ending balance	$ 1,921,803	$ 2,106,433	$ 1,921,803	$ 2,106,433	$ 2,086,393