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
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Allowance for credit losses
Beginning balance	$ 171,869	$ 141,970	$ 151,861	$ 94,507
Initial allowance on acquired PCD loans				26,103
Charge-offs	(16,847)	(7,498)	(46,387)	(16,316)
Recoveries	2,552	4,273	7,257	7,214
Provision (credit)	18,414	7,450	63,257	34,687
Ending balance	175,988	146,195	175,988	146,195
Period-end allowance allocated to:
Loans evaluated on an individual basis	2,815	5,348	2,815	5,348
Loans evaluated on a collective basis	173,173	140,847	173,173	140,847
Period-end loan balances:
Loans evaluated on an individual basis	63,179	46,456	63,179	46,456
Loans evaluated on a collective basis	12,612,442	11,655,916	12,612,442	11,655,916
Gross loans	12,675,621	11,702,372	12,675,621	11,702,372	$ 11,909,436
Reverse mortgage, fair value	2,800	3,000	2,800	3,000	2,400
BMBC
Period-end loan balances:
Loans purchased with no credit deterioration				23,500
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	62,783	60,921	59,394	49,967
Initial allowance on acquired PCD loans				22,614
Charge-offs	(10,675)	(5,120)	(30,496)	(11,308)
Recoveries	2,124	3,194	5,554	4,667
Provision (credit)	7,438	889	27,218	(6,056)
Ending balance	61,670	59,884	61,670	59,884
Period-end allowance allocated to:
Loans evaluated on an individual basis	1,054	5,348	1,054	5,348
Loans evaluated on a collective basis	60,616	54,536	60,616	54,536
Period-end loan balances:
Loans evaluated on an individual basis	26,355	21,565	26,355	21,565
Loans evaluated on a collective basis	3,223,382	3,147,913	3,223,382	3,147,913
Gross loans	3,249,737	3,169,478	3,249,737	3,169,478	3,134,326
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	6,335	5,510	6,019	4,574
Initial allowance on acquired PCD loans				595
Charge-offs	0	0	(184)	(179)
Recoveries	14	4	50	271
Provision (credit)	1,501	489	1,965	742
Ending balance	7,850	6,003	7,850	6,003
Period-end allowance allocated to:
Loans evaluated on an individual basis	161	0	161	0
Loans evaluated on a collective basis	7,689	6,003	7,689	6,003
Period-end loan balances:
Loans evaluated on an individual basis	16,442	1,713	16,442	1,713
Loans evaluated on a collective basis	1,907,729	1,786,878	1,907,729	1,786,878
Gross loans	1,924,171	1,788,591	1,924,171	1,788,591	1,809,582
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	31,937	23,663	21,473	11,623
Initial allowance on acquired PCD loans				2,684
Charge-offs	(300)	(544)	(300)	(581)
Recoveries	1	101	4	223
Provision (credit)	1,549	(1,686)	12,010	7,585
Ending balance	33,187	21,534	33,187	21,534
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	33,187	21,534	33,187	21,534
Period-end loan balances:
Loans evaluated on an individual basis	7,918	9,483	7,918	9,483
Loans evaluated on a collective basis	3,637,805	3,270,896	3,637,805	3,270,896
Gross loans	3,645,723	3,280,379	3,645,723	3,280,379	3,351,084
Commercial | Construction
Allowance for credit losses
Beginning balance	9,228	5,058	6,987	1,903
Initial allowance on acquired PCD loans				71
Charge-offs	0	0	0	0
Recoveries	1	653	532	653
Provision (credit)	2,088	788	3,798	3,872
Ending balance	11,317	6,499	11,317	6,499
Period-end allowance allocated to:
Loans evaluated on an individual basis	1,600	0	1,600	0
Loans evaluated on a collective basis	9,717	6,499	9,717	6,499
Period-end loan balances:
Loans evaluated on an individual basis	4,828	5,360	4,828	5,360
Loans evaluated on a collective basis	1,038,740	1,022,843	1,038,740	1,022,843
Gross loans	1,043,568	1,028,203	1,043,568	1,028,203	1,044,049
Residential
Allowance for credit losses
Beginning balance	5,043	4,988	4,668	3,352
Initial allowance on acquired PCD loans				61
Charge-offs	0	0	(33)	(186)
Recoveries	55	207	211	737
Provision (credit)	253	(377)	505	854
Ending balance	5,351	4,818	5,351	4,818
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	5,351	4,818	5,351	4,818
Period-end loan balances:
Loans evaluated on an individual basis	5,838	6,451	5,838	6,451
Loans evaluated on a collective basis	849,502	752,142	849,502	752,142
Gross loans	855,340	758,593	855,340	758,593	759,465
Consumer
Allowance for credit losses
Beginning balance	56,543	41,830	53,320	23,088
Initial allowance on acquired PCD loans				78
Charge-offs	(5,872)	(1,834)	(15,374)	(4,062)
Recoveries	357	114	906	663
Provision (credit)	5,585	7,347	17,761	27,690
Ending balance	56,613	47,457	56,613	47,457
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	56,613	47,457	56,613	47,457
Period-end loan balances:
Loans evaluated on an individual basis	1,798	1,884	1,798	1,884
Loans evaluated on a collective basis	1,955,284	1,675,244	1,955,284	1,675,244
Gross loans	$ 1,957,082	$ 1,677,128	$ 1,957,082	$ 1,677,128	$ 1,810,930