ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Allowance for Loan Losses and Loan Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Allowance for credit losses
Beginning balance	$ 151,861	$ 94,507	$ 228,804
Initial allowance on acquired PCD loans		26,103
Charge-offs	(66,007)	(27,470)	(28,315)
Recoveries	12,199	10,638	11,105
(Credit) provision	88,073	48,083	(117,087)
Ending balance	186,126	151,861	94,507
Loans evaluated on an individual basis	1,591	2,428	8
Loans evaluated on a collective basis	184,535	149,433	94,499
Loans evaluated on an individual basis	67,496	40,740	21,138
Loans evaluated on a collective basis	12,699,022	11,868,696	7,860,917
Ending balance	12,766,518	11,909,436	7,882,055
Reverse mortgage, fair value	2,800	2,400	3,900
BMBC
Allowance for credit losses
Loans purchased with no credit deterioration		23,500
Commercial | Commercial and industrial
Allowance for credit losses
Beginning balance	59,394	49,967	150,875
Initial allowance on acquired PCD loans		22,614
Charge-offs	(42,294)	(19,004)	(23,592)
Recoveries	9,721	6,112	8,756
(Credit) provision	37,743	(295)	(86,072)
Ending balance	64,564	59,394	49,967
Loans evaluated on an individual basis	1,591	2,428	1
Loans evaluated on a collective basis	62,973	56,966	49,966
Loans evaluated on an individual basis	19,221	17,572	8,363
Loans evaluated on a collective basis	3,144,471	3,116,754	2,261,956
Ending balance	3,163,692	3,134,326	2,270,319
Commercial | Owner-occupied commercial
Allowance for credit losses
Beginning balance	6,019	4,574	9,615
Initial allowance on acquired PCD loans		595
Charge-offs	(184)	(179)	(83)
Recoveries	54	278	160
(Credit) provision	4,830	751	(5,118)
Ending balance	10,719	6,019	4,574
Loans evaluated on an individual basis	0	0	0
Loans evaluated on a collective basis	10,719	6,019	4,574
Loans evaluated on an individual basis	5,200	1,929	1,690
Loans evaluated on a collective basis	1,880,887	1,807,653	1,340,017
Ending balance	1,886,087	1,809,582	1,341,707
Commercial | Commercial mortgages
Allowance for credit losses
Beginning balance	21,473	11,623	31,071
Initial allowance on acquired PCD loans		2,684
Charge-offs	(300)	(581)	(73)
Recoveries	7	223	269
(Credit) provision	14,875	7,524	(19,644)
Ending balance	36,055	21,473	11,623
Loans evaluated on an individual basis	0	0	7
Loans evaluated on a collective basis	36,055	21,473	11,616
Loans evaluated on an individual basis	22,295	6,369	3,764
Loans evaluated on a collective basis	3,778,885	3,344,715	1,877,746
Ending balance	3,801,180	3,351,084	1,881,510
Commercial | Construction
Allowance for credit losses
Beginning balance	6,987	1,903	12,190
Initial allowance on acquired PCD loans		71
Charge-offs	(794)	0	(2,473)
Recoveries	532	2,567	0
(Credit) provision	4,037	2,446	(7,814)
Ending balance	10,762	6,987	1,903
Loans evaluated on an individual basis	0	0	0
Loans evaluated on a collective basis	10,762	6,987	1,903
Loans evaluated on an individual basis	12,617	5,143	0
Loans evaluated on a collective basis	1,022,913	1,038,906	687,213
Ending balance	1,035,530	1,044,049	687,213
Residential
Allowance for credit losses
Beginning balance	4,668	3,352	6,893
Initial allowance on acquired PCD loans		61
Charge-offs	(41)	(186)	0
Recoveries	260	665	789
(Credit) provision	596	776	(4,330)
Ending balance	5,483	4,668	3,352
Loans evaluated on an individual basis	0	0	0
Loans evaluated on a collective basis	5,483	4,668	3,352
Loans evaluated on an individual basis	5,876	7,680	5,000
Loans evaluated on a collective basis	862,019	751,785	537,733
Ending balance	867,895	759,465	542,733
Consumer
Allowance for credit losses
Beginning balance	53,320	23,088	18,160
Initial allowance on acquired PCD loans		78
Charge-offs	(22,394)	(7,520)	(2,094)
Recoveries	1,625	793	1,131
(Credit) provision	25,992	36,881	5,891
Ending balance	58,543	53,320	23,088
Loans evaluated on an individual basis	0	0	0
Loans evaluated on a collective basis	58,543	53,320	23,088
Loans evaluated on an individual basis	2,287	2,047	2,321
Loans evaluated on a collective basis	2,009,847	1,808,883	1,156,252
Ending balance	$ 2,012,134	$ 1,810,930	$ 1,158,573