ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Allowance for credit losses
Beginning balance	$ 151,861	$ 94,507
Initial allowance on acquired PCD loans		26,103
Charge-offs	(13,666)	(4,851)
Recoveries	1,955	1,600
Provision (credit)	29,012	18,971
Ending balance	169,162	136,330
Period-end allowance allocated to:
Loans evaluated on an individual basis	4,653	6,992
Loans evaluated on a collective basis	164,509	129,338
Period-end loan balances:
Loans evaluated on an individual basis	40,891	50,166
Loans evaluated on a collective basis	12,102,377	11,279,362
Gross loans	12,143,268	11,329,528	$ 11,909,436
Reverse mortgage, fair value	2,700	4,300	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	59,394	49,967
Initial allowance on acquired PCD loans		22,614
Charge-offs	(9,462)	(3,639)
Recoveries	1,216	601
Provision (credit)	11,561	(3,827)
Ending balance	62,709	65,716
Period-end allowance allocated to:
Loans evaluated on an individual basis	4,562	6,987
Loans evaluated on a collective basis	58,147	58,729
Period-end loan balances:
Loans evaluated on an individual basis	22,443	27,735
Loans evaluated on a collective basis	3,122,883	2,956,392
Gross loans	3,145,326	2,984,127	3,134,326
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	6,019	4,574
Initial allowance on acquired PCD loans		595
Charge-offs	0	(179)
Recoveries	5	126
Provision (credit)	32	1,009
Ending balance	6,056	6,125
Period-end allowance allocated to:
Loans evaluated on an individual basis	91	0
Loans evaluated on a collective basis	5,965	6,125
Period-end loan balances:
Loans evaluated on an individual basis	1,907	1,023
Loans evaluated on a collective basis	1,844,754	1,871,804
Gross loans	1,846,661	1,872,827	1,809,582
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	21,473	11,623
Initial allowance on acquired PCD loans		2,684
Charge-offs	0	(37)
Recoveries	2	121
Provision (credit)	8,639	8,714
Ending balance	30,114	23,105
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	5
Loans evaluated on a collective basis	30,114	23,100
Period-end loan balances:
Loans evaluated on an individual basis	7,343	7,106
Loans evaluated on a collective basis	3,465,740	3,354,136
Gross loans	3,473,083	3,361,242	3,351,084
Commercial | Construction
Allowance for credit losses
Beginning balance	6,987	1,903
Initial allowance on acquired PCD loans		71
Charge-offs	0	0
Recoveries	530	0
Provision (credit)	2,155	1,171
Ending balance	9,672	3,145
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	9,672	3,145
Period-end loan balances:
Loans evaluated on an individual basis	760	5,556
Loans evaluated on a collective basis	1,022,951	918,334
Gross loans	1,023,711	923,890	1,044,049
Residential
Allowance for credit losses
Beginning balance	4,668	3,352
Initial allowance on acquired PCD loans		61
Charge-offs	0	(186)
Recoveries	43	386
Provision (credit)	616	1,343
Ending balance	5,327	4,956
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	5,327	4,956
Period-end loan balances:
Loans evaluated on an individual basis	6,522	6,424
Loans evaluated on a collective basis	779,538	798,902
Gross loans	786,060	805,326	759,465
Consumer
Allowance for credit losses
Beginning balance	53,320	23,088
Initial allowance on acquired PCD loans		78
Charge-offs	(4,204)	(810)
Recoveries	159	366
Provision (credit)	6,009	10,561
Ending balance	55,284	33,283
Period-end allowance allocated to:
Loans evaluated on an individual basis	0	0
Loans evaluated on a collective basis	55,284	33,283
Period-end loan balances:
Loans evaluated on an individual basis	1,916	2,322
Loans evaluated on a collective basis	1,866,511	1,379,794
Gross loans	$ 1,868,427	$ 1,382,116	$ 1,810,930