ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Allowance for credit losses
Beginning balance	$ 186,304	$ 198,253	$ 195,281	$ 186,126	$ 186,126
Charge-offs		23,101		52,532
Charge-offs	(12,353)		(48,020)
Recoveries	3,267	3,916	13,272	10,521
Charge-offs arising from transfer of loans to held for sale	(826)		(9,481)
Provision (release)	6,838	18,422	32,178	53,375
Ending balance	183,230	197,490	183,230	197,490	195,281
Period-end allowance allocated to:
Loans evaluated on an individual basis	6,069	8,529	6,069	8,529
Loans evaluated on a collective basis	177,161	188,961	177,161	188,961
Period-end loan balances:
Loans evaluated on an individual basis	65,357	93,617	65,357	93,617
Loans evaluated on a collective basis	12,889,896	13,225,371	12,889,896	13,225,371
Ending balance	12,955,253	13,318,988	12,955,253	13,318,988	13,187,874
Reverse mortgage, fair value	5,300	3,200	5,300	3,200	3,600
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	52,121	56,516	57,131	49,394	49,394
Charge-offs		11,277	29,066	13,659	15,490
Charge-offs	(7,363)		(28,514)
Recoveries	1,541	2,481	3,985	5,983
Charge-offs arising from transfer of loans to held for sale	0		(552)
Provision (release)	3,330	9,075	17,579	15,077
Ending balance	49,629	56,795	49,629	56,795	57,131
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	8,529	0	8,529
Loans evaluated on a collective basis	49,629	48,266	49,629	48,266
Period-end loan balances:
Loans evaluated on an individual basis	14,986	64,972	14,986	64,972
Loans evaluated on a collective basis	2,610,166	2,574,294	2,610,166	2,574,294
Ending balance	2,625,152	2,639,266	2,625,152	2,639,266	2,656,174
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	8,584	9,668	9,139	10,719	10,719
Charge-offs		177	4	177	177
Charge-offs	(4)		(4)
Recoveries	4	4	16	209
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	(273)	292	(840)	(964)
Ending balance	8,311	9,787	8,311	9,787	9,139
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	8,311	9,787	8,311	9,787
Period-end loan balances:
Loans evaluated on an individual basis	6,672	6,465	6,672	6,465
Loans evaluated on a collective basis	1,916,095	1,997,257	1,916,095	1,997,257
Ending balance	1,922,767	2,003,722	1,922,767	2,003,722	1,973,645
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	54,775	46,831	48,962	36,055	36,055
Charge-offs		205	240	5,137	5,749
Charge-offs	(43)		(240)
Recoveries	0	79	527	183
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	(6,122)	2,284	(639)	17,888
Ending balance	48,610	48,989	48,610	48,989	48,962
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	48,610	48,989	48,610	48,989
Period-end loan balances:
Loans evaluated on an individual basis	3,145	7,449	3,145	7,449
Loans evaluated on a collective basis	3,852,826	4,141,600	3,852,826	4,141,600
Ending balance	3,855,971	4,149,049	3,855,971	4,149,049	4,030,627
Commercial | Construction
Allowance for credit losses
Beginning balance	10,696	9,198	9,185	10,762	10,762
Charge-offs		0	0	0	0
Charge-offs	0		0
Recoveries	0	0	0	0
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	6,478	(850)	7,989	(2,414)
Ending balance	17,174	8,348	17,174	8,348	9,185
Period-end allowance allocated to:
Loans evaluated on an individual basis	6,069	0	6,069	0
Loans evaluated on a collective basis	11,105	8,348	11,105	8,348
Period-end loan balances:
Loans evaluated on an individual basis	29,381	3,308	29,381	3,308
Loans evaluated on a collective basis	974,605	802,549	974,605	802,549
Ending balance	1,003,986	805,857	1,003,986	805,857	832,093
Commercial | Commercial Small Business Leases
Allowance for credit losses
Beginning balance	18,301	16,218	15,965	15,170	15,170
Charge-offs		5,451	11,203	15,191	20,033
Charge-offs	(3,860)		(11,203)
Recoveries	932	664	2,265	2,086
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	1,892	3,943	10,238	13,309
Ending balance	17,265	15,374	17,265	15,374	15,965
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	17,265	15,374	17,265	15,374
Period-end loan balances:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	617,256	645,421	617,256	645,421
Ending balance	617,256	645,421	617,256	645,421	647,516
Residential
Allowance for credit losses
Beginning balance	5,815	5,057	5,566	5,483	5,483
Charge-offs		8	0	109	125
Charge-offs	0		0
Recoveries	43	44	140	176
Charge-offs arising from transfer of loans to held for sale	0		0
Provision (release)	594	370	746	(87)
Ending balance	6,452	5,463	6,452	5,463	5,566
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	6,452	5,463	6,452	5,463
Period-end loan balances:
Loans evaluated on an individual basis	8,149	8,442	8,149	8,442
Loans evaluated on a collective basis	1,025,194	929,152	1,025,194	929,152
Ending balance	1,033,343	937,594	1,033,343	937,594	961,426
Consumer
Allowance for credit losses
Beginning balance	36,012	54,765	49,333	58,543	58,543
Charge-offs		5,983	16,988	18,259	23,549
Charge-offs	(1,083)		(8,059)
Recoveries	747	644	6,339	1,884
Charge-offs arising from transfer of loans to held for sale	(826)		(8,929)
Provision (release)	939	3,308	(2,895)	10,566
Ending balance	35,789	52,734	35,789	52,734	49,333
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	35,789	52,734	35,789	52,734
Period-end loan balances:
Loans evaluated on an individual basis	3,024	2,981	3,024	2,981
Loans evaluated on a collective basis	1,893,754	2,135,098	1,893,754	2,135,098
Ending balance	$ 1,896,778	$ 2,138,079	$ 1,896,778	$ 2,138,079	$ 2,086,393