LOANS AND ALLOWANCE FOR CREDIT LOSSES - Amount of Business Lending Loans by Credit Quality Categories (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Term Loans Amortized Cost Basis by Origination Year
Total Loans	$ 8,982,335		$ 8,809,394
Current period gross charge-offs
Total Loans	3,230	$ 2,156
Legacy Loan
Term Loans Amortized Cost Basis by Origination Year
Total Loans	8,982,335		8,809,394
Business lending
Term Loans Amortized Cost Basis by Origination Year
Year One	130,505		752,160
Year Two	735,600		379,524
Year Three	366,460		237,510
Year Four	229,052		253,692
Year Five	244,174		195,296
Prior	843,712		688,510
Revolving Loans Amortized Cost Basis	705,080		686,761
Revolving Loans Converted to Term	493,359		452,212
Total Loans	3,747,942		3,645,665
Current period gross charge-offs
Year One	0
Year Two	47
Year Three	0
Year Four	0
Year Five	0
Prior	0
Revolving Loans Amortized Cost Basis	128
Revolving Loans Converted to Term	0
Total Loans	175
Business lending | Pass
Term Loans Amortized Cost Basis by Origination Year
Year One	129,658		747,573
Year Two	730,008		373,913
Year Three	361,349		232,591
Year Four	221,000		246,820
Year Five	237,879		168,468
Prior	753,972		604,745
Revolving Loans Amortized Cost Basis	667,589		646,771
Revolving Loans Converted to Term	442,133		401,531
Total Loans	3,543,588		3,422,412
Business lending | Special mention
Term Loans Amortized Cost Basis by Origination Year
Year One	623		2,787
Year Two	2,620		4,836
Year Three	4,712		3,781
Year Four	6,926		3,676
Year Five	3,261		14,593
Prior	56,953		45,627
Revolving Loans Amortized Cost Basis	30,721		29,403
Revolving Loans Converted to Term	31,774		29,975
Total Loans	137,590		134,678
Business lending | Classified
Term Loans Amortized Cost Basis by Origination Year
Year One	224		1,800
Year Two	2,972		775
Year Three	399		1,138
Year Four	1,126		3,196
Year Five	3,034		12,235
Prior	32,787		38,138
Revolving Loans Amortized Cost Basis	6,770		10,587
Revolving Loans Converted to Term	19,452		20,706
Total Loans	66,764		88,575
Business lending | Doubtful
Term Loans Amortized Cost Basis by Origination Year
Year One	0		0
Year Two	0		0
Year Three	0		0
Year Four	0		0
Year Five	0		0
Prior	0		0
Revolving Loans Amortized Cost Basis	0		0
Revolving Loans Converted to Term	0		0
Total Loans	0		0
Consumer mortgage
Term Loans Amortized Cost Basis by Origination Year
Year One	69,239		539,679
Year Two	531,692		672,042
Year Three	661,339		332,352
Year Four	325,447		255,089
Year Five	249,065		157,548
Prior	1,064,866		944,971
Revolving Loans Amortized Cost Basis	27,569		28,989
Revolving Loans Converted to Term	90,501		81,805
Total Loans	3,019,718		3,012,475
Current period gross charge-offs
Year One	0
Year Two	0
Year Three	0
Year Four	0
Year Five	0
Prior	19
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term	0
Total Loans	19
Consumer mortgage | FICO AB
Term Loans Amortized Cost Basis by Origination Year
Year One	51,091		379,171
Year Two	369,680		492,806
Year Three	483,541		218,462
Year Four	214,283		174,126
Year Five	169,477		100,560
Prior	681,572		608,605
Revolving Loans Amortized Cost Basis	369		954
Revolving Loans Converted to Term	66,009		59,088
Total Loans	2,036,022		2,033,772
Consumer mortgage | FICO AB | Performing
Term Loans Amortized Cost Basis by Origination Year
Year One	51,091		379,171
Year Two	369,653		492,731
Year Three	483,070		217,889
Year Four	213,716		173,942
Year Five	169,347		100,161
Prior	676,623		604,258
Revolving Loans Amortized Cost Basis	369		954
Revolving Loans Converted to Term	65,562		58,639
Total Loans	2,029,431		2,027,745
Consumer mortgage | FICO AB | Nonperforming
Term Loans Amortized Cost Basis by Origination Year
Year One	0		0
Year Two	27		75
Year Three	471		573
Year Four	567		184
Year Five	130		399
Prior	4,949		4,347
Revolving Loans Amortized Cost Basis	0		0
Revolving Loans Converted to Term	447		449
Total Loans	6,591		6,027
Consumer mortgage | FICO CDE
Term Loans Amortized Cost Basis by Origination Year
Year One	18,148		160,508
Year Two	162,012		179,236
Year Three	177,798		113,890
Year Four	111,164		80,963
Year Five	79,588		56,988
Prior	383,294		336,366
Revolving Loans Amortized Cost Basis	27,200		28,035
Revolving Loans Converted to Term	24,492		22,717
Total Loans	983,696		978,703
Consumer mortgage | FICO CDE | Performing
Term Loans Amortized Cost Basis by Origination Year
Year One	18,148		160,388
Year Two	161,398		178,262
Year Three	176,898		112,640
Year Four	109,853		79,357
Year Five	78,092		54,861
Prior	368,417		323,189
Revolving Loans Amortized Cost Basis	27,200		27,884
Revolving Loans Converted to Term	23,477		22,056
Total Loans	963,483		958,637
Consumer mortgage | FICO CDE | Nonperforming
Term Loans Amortized Cost Basis by Origination Year
Year One	0		120
Year Two	614		974
Year Three	900		1,250
Year Four	1,311		1,606
Year Five	1,496		2,127
Prior	14,877		13,177
Revolving Loans Amortized Cost Basis	0		151
Revolving Loans Converted to Term	1,015		661
Total Loans	20,213		20,066
Consumer indirect
Term Loans Amortized Cost Basis by Origination Year
Year One	203,427		777,531
Year Two	731,829		422,595
Year Three	381,878		129,502
Year Four	112,803		99,660
Year Five	82,525		52,313
Prior	93,197		58,052
Revolving Loans Amortized Cost Basis	0		0
Revolving Loans Converted to Term	0		0
Total Loans	1,605,659		1,539,653
Current period gross charge-offs
Year One	0
Year Two	913
Year Three	621
Year Four	382
Year Five	189
Prior	426
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term	0
Total Loans	2,531
Consumer indirect | Performing
Term Loans Amortized Cost Basis by Origination Year
Year One	203,427		777,513
Year Two	731,811		422,594
Year Three	381,847		129,449
Year Four	112,730		99,593
Year Five	82,525		52,298
Prior	93,168		58,028
Revolving Loans Amortized Cost Basis	0		0
Revolving Loans Converted to Term	0		0
Total Loans	1,605,508		1,539,475
Consumer indirect | Nonperforming
Term Loans Amortized Cost Basis by Origination Year
Year One	0		18
Year Two	18		1
Year Three	31		53
Year Four	73		67
Year Five	0		15
Prior	29		24
Revolving Loans Amortized Cost Basis	0		0
Revolving Loans Converted to Term	0		0
Total Loans	151		178
Consumer direct
Term Loans Amortized Cost Basis by Origination Year
Year One	22,565		84,117
Year Two	73,660		46,432
Year Three	40,886		17,067
Year Four	14,585		12,730
Year Five	10,188		5,602
Prior	8,691		5,070
Revolving Loans Amortized Cost Basis	6,414		6,585
Revolving Loans Converted to Term	0		2
Total Loans	176,989		177,605
Current period gross charge-offs
Year One	0
Year Two	172
Year Three	151
Year Four	15
Year Five	21
Prior	95
Revolving Loans Amortized Cost Basis	51
Revolving Loans Converted to Term	0
Total Loans	505
Consumer direct | Performing
Term Loans Amortized Cost Basis by Origination Year
Year One	22,565		84,111
Year Two	73,630		46,381
Year Three	40,886		17,066
Year Four	14,585		12,729
Year Five	10,188		5,573
Prior	8,622		5,020
Revolving Loans Amortized Cost Basis	6,406		6,563
Revolving Loans Converted to Term	0		2
Total Loans	176,882		177,445
Consumer direct | Nonperforming
Term Loans Amortized Cost Basis by Origination Year
Year One	0		6
Year Two	30		51
Year Three	0		1
Year Four	0		1
Year Five	0		29
Prior	69		50
Revolving Loans Amortized Cost Basis	8		22
Revolving Loans Converted to Term	0		0
Total Loans	107		160
Home equity
Term Loans Amortized Cost Basis by Origination Year
Year One	11,531		69,575
Year Two	68,635		72,280
Year Three	70,173		38,078
Year Four	36,635		31,675
Year Five	30,285		16,173
Prior	54,463		41,703
Revolving Loans Amortized Cost Basis	129,950		133,266
Revolving Loans Converted to Term	30,355		31,246
Total Loans	432,027		433,996
Current period gross charge-offs
Year One	0
Year Two	0
Year Three	0
Year Four	0
Year Five	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term	0
Total Loans	0
Home equity | Performing
Term Loans Amortized Cost Basis by Origination Year
Year One	11,531		69,575
Year Two	68,635		72,270
Year Three	70,163		37,964
Year Four	36,328		31,506
Year Five	30,112		16,068
Prior	53,840		41,097
Revolving Loans Amortized Cost Basis	129,361		132,703
Revolving Loans Converted to Term	29,739		30,569
Total Loans	429,709		431,752
Home equity | Nonperforming
Term Loans Amortized Cost Basis by Origination Year
Year One	0		0
Year Two	0		10
Year Three	10		114
Year Four	307		169
Year Five	173		105
Prior	623		606
Revolving Loans Amortized Cost Basis	589		563
Revolving Loans Converted to Term	616		677
Total Loans	$ 2,318		$ 2,244