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
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Allowance for credit losses
Beginning balance	$ 169,162	$ 136,330	$ 151,861	$ 94,507
Initial allowance on acquired PCD loans				26,103
Charge-offs	(15,874)	(3,967)	(29,540)	(8,818)
Recoveries	2,750	1,339	4,705	2,939
Provision (credit)	15,831	8,268	44,843	27,239
Ending balance	171,869	141,970	171,869	141,970
Period-end allowance allocated to:
Loans evaluated on an individual basis	1,953	5,437	1,953	5,437
Loans evaluated on a collective basis	169,916	136,533	169,916	136,533
Period-end loan balances:
Loans evaluated on an individual basis	39,268	50,795	39,268	50,795
Loans evaluated on a collective basis	12,297,566	11,429,323	12,297,566	11,429,323
Gross loans	12,336,834	11,480,118	12,336,834	11,480,118	$ 11,909,436
Reverse mortgage, fair value	3,100	2,600	3,100	2,600	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	62,709	65,716	59,394	49,967
Initial allowance on acquired PCD loans				22,614
Charge-offs	(10,359)	(2,549)	(19,821)	(6,188)
Recoveries	2,214	870	3,430	1,471
Provision (credit)	8,219	(3,116)	19,780	(6,943)
Ending balance	62,783	60,921	62,783	60,921
Period-end allowance allocated to:
Loans evaluated on an individual basis	1,953	5,437	1,953	5,437
Loans evaluated on a collective basis	60,830	55,484	60,830	55,484
Period-end loan balances:
Loans evaluated on an individual basis	18,367	29,030	18,367	29,030
Loans evaluated on a collective basis	3,195,419	3,078,710	3,195,419	3,078,710
Gross loans	3,213,786	3,107,740	3,213,786	3,107,740	3,134,326
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	6,056	6,125	6,019	4,574
Initial allowance on acquired PCD loans				595
Charge-offs	(184)	0	(184)	(179)
Recoveries	31	141	36	267
Provision (credit)	432	(756)	464	253
Ending balance	6,335	5,510	6,335	5,510
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	6,335	5,510	6,335	5,510
Period-end loan balances:
Loans evaluated on an individual basis	3,979	787	3,979	787
Loans evaluated on a collective basis	1,879,076	1,822,442	1,879,076	1,822,442
Gross loans	1,883,055	1,823,229	1,883,055	1,823,229	1,809,582
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	30,114	23,105	21,473	11,623
Initial allowance on acquired PCD loans				2,684
Charge-offs	0	0	0	(37)
Recoveries	1	1	3	122
Provision (credit)	1,822	557	10,461	9,271
Ending balance	31,937	23,663	31,937	23,663
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	31,937	23,663	31,937	23,663
Period-end loan balances:
Loans evaluated on an individual basis	7,515	7,771	7,515	7,771
Loans evaluated on a collective basis	3,545,285	3,313,883	3,545,285	3,313,883
Gross loans	3,552,800	3,321,654	3,552,800	3,321,654	3,351,084
Commercial | Construction
Allowance for credit losses
Beginning balance	9,672	3,145	6,987	1,903
Initial allowance on acquired PCD loans				71
Charge-offs	0	0	0	0
Recoveries	1	0	531	0
Provision (credit)	(445)	1,913	1,710	3,084
Ending balance	9,228	5,058	9,228	5,058
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	9,228	5,058	9,228	5,058
Period-end loan balances:
Loans evaluated on an individual basis	741	5,392	741	5,392
Loans evaluated on a collective basis	954,483	928,932	954,483	928,932
Gross loans	955,224	934,324	955,224	934,324	1,044,049
Residential
Allowance for credit losses
Beginning balance	5,327	4,956	4,668	3,352
Initial allowance on acquired PCD loans				61
Charge-offs	(33)	0	(33)	(186)
Recoveries	113	144	156	530
Provision (credit)	(364)	(112)	252	1,231
Ending balance	5,043	4,988	5,043	4,988
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	5,043	4,988	5,043	4,988
Period-end loan balances:
Loans evaluated on an individual basis	6,491	5,803	6,491	5,803
Loans evaluated on a collective basis	820,259	764,772	820,259	764,772
Gross loans	826,750	770,575	826,750	770,575	759,465
Consumer
Allowance for credit losses
Beginning balance	55,284	33,283	53,320	23,088
Initial allowance on acquired PCD loans				78
Charge-offs	(5,298)	(1,418)	(9,502)	(2,228)
Recoveries	390	183	549	549
Provision (credit)	6,167	9,782	12,176	20,343
Ending balance	56,543	41,830	56,543	41,830
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0	0	0
Loans evaluated on a collective basis	56,543	41,830	56,543	41,830
Period-end loan balances:
Loans evaluated on an individual basis	2,175	2,012	2,175	2,012
Loans evaluated on a collective basis	1,903,044	1,520,584	1,903,044	1,520,584
Gross loans	$ 1,905,219	$ 1,522,596	$ 1,905,219	$ 1,522,596	$ 1,810,930