ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Allowance for credit losses
Beginning balance	$ 94,507	$ 94,507	$ 228,804	$ 47,576
Initial allowance on acquired PCD loans		26,103
Charge-offs		(27,470)	(28,315)	(13,521)
Recoveries		10,638	11,105	5,714
(Credit) provision		48,083	(117,087)	153,180
Ending balance		151,861	94,507	228,804
Loans evaluated on an individual basis		2,428	8	14
Loans evaluated on a collective basis		149,433	94,499	228,790
Loans evaluated on an individual basis		40,740	21,138	49,224
Loans evaluated on a collective basis		11,868,696	7,860,917	8,965,453
Ending balance		11,909,436	7,882,055	9,014,677
Reverse mortgage, fair value		2,400	3,900	10,100
Total purchase credit deteriorated (PCD) loans acquired				100
BMBC
Allowance for credit losses
Initial allowance on acquired PCD loans		26,100
Loans purchased with no credit deterioration		23,500
Total purchase credit deteriorated (PCD) loans acquired	208,267
Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				35,855
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	49,967	49,967	150,875	22,849
Initial allowance on acquired PCD loans		22,614
Charge-offs		(19,004)	(23,592)	(10,388)
Recoveries		6,112	8,756	4,255
(Credit) provision		(295)	(86,072)	114,412
Ending balance		59,394	49,967	150,875
Loans evaluated on an individual basis		2,428	1	1
Loans evaluated on a collective basis		56,966	49,966	150,874
Loans evaluated on an individual basis		17,572	8,363	14,048
Loans evaluated on a collective basis		3,116,754	2,261,956	2,935,255
Ending balance		3,134,326	2,270,319	2,949,303
Commercial | Commercial and industrial | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				19,747
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	4,574	4,574	9,615	4,616
Initial allowance on acquired PCD loans		595
Charge-offs		(179)	(83)	(336)
Recoveries		278	160	142
(Credit) provision		751	(5,118)	6,665
Ending balance		6,019	4,574	9,615
Loans evaluated on an individual basis		0	0	0
Loans evaluated on a collective basis		6,019	4,574	9,615
Loans evaluated on an individual basis		1,929	1,690	6,496
Loans evaluated on a collective basis		1,807,653	1,340,017	1,326,231
Ending balance		1,809,582	1,341,707	1,332,727
Commercial | Owner-occupied commercial | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				(1,472)
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	11,623	11,623	31,071	7,452
Initial allowance on acquired PCD loans		2,684
Charge-offs		(581)	(73)	(104)
Recoveries		223	269	158
(Credit) provision		7,524	(19,644)	21,903
Ending balance		21,473	11,623	31,071
Loans evaluated on an individual basis		0	7	13
Loans evaluated on a collective basis		21,473	11,616	31,058
Loans evaluated on an individual basis		6,369	3,764	20,309
Loans evaluated on a collective basis		3,344,715	1,877,746	2,065,753
Ending balance		3,351,084	1,881,510	2,086,062
Commercial | Commercial mortgages | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				1,662
Commercial | Construction
Allowance for credit losses
Beginning balance	1,903	1,903	12,190	3,891
Initial allowance on acquired PCD loans		71
Charge-offs		0	(2,473)	0
Recoveries		2,567	0	36
(Credit) provision		2,446	(7,814)	7,582
Ending balance		6,987	1,903	12,190
Loans evaluated on an individual basis		0	0	0
Loans evaluated on a collective basis		6,987	1,903	12,190
Loans evaluated on an individual basis		5,143	0	79
Loans evaluated on a collective basis		1,038,906	687,213	716,196
Ending balance		1,044,049	687,213	716,275
Commercial | Construction | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				681
Residential
Allowance for credit losses
Beginning balance	3,352	3,352	6,893	1,381
Initial allowance on acquired PCD loans		61
Charge-offs		(186)	0	(229)
Recoveries		665	789	230
(Credit) provision		776	(4,330)	(2,011)
Ending balance		4,668	3,352	6,893
Loans evaluated on an individual basis		0	0	0
Loans evaluated on a collective basis		4,668	3,352	6,893
Loans evaluated on an individual basis		7,680	5,000	5,921
Loans evaluated on a collective basis		751,785	537,733	758,472
Ending balance		759,465	542,733	764,393
Residential | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				7,522
Consumer
Allowance for credit losses
Beginning balance	$ 23,088	23,088	18,160	7,387
Initial allowance on acquired PCD loans		78
Charge-offs		(7,520)	(2,094)	(2,464)
Recoveries		793	1,131	893
(Credit) provision		36,881	5,891	4,629
Ending balance		53,320	23,088	18,160
Loans evaluated on an individual basis		0	0	0
Loans evaluated on a collective basis		53,320	23,088	18,160
Loans evaluated on an individual basis		2,047	2,321	2,371
Loans evaluated on a collective basis		1,808,883	1,156,252	1,163,546
Ending balance		$ 1,810,930	$ 1,158,573	1,165,917
Consumer | Impact of adoption ASC 326
Allowance for credit losses
Beginning balance				$ 7,715