LOANS - Amount of Business Lending Loans by Credit Quality Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Term Loans Amortized Cost Basis by Origination Year
Loans	$ 7,282,582	$ 7,415,952
Legacy Loan [Member]
Term Loans Amortized Cost Basis by Origination Year
Total past due		111,610
Loans		7,415,952
Acquired Loans [Member]
Term Loans Amortized Cost Basis by Origination Year
Total past due	93,056
Loans	7,282,582
Business Lending [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	424,374
2020	380,124	881,201
2019	371,881	391,969
2018	349,559	373,807
2017	239,364	263,820
2016		275,730
Prior	762,700	660,921
Revolving Loans Amortized Cost Basis	564,175	592,629
Total past due	3,092,177	3,440,077
Business Lending [Member] | Pass [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	418,709
2020	365,951	860,178
2019	339,050	351,350
2018	261,444	312,087
2017	179,753	217,138
2016		231,453
Prior	624,089	543,999
Revolving Loans Amortized Cost Basis	501,995	483,018
Total past due	2,690,991	2,999,223
Business Lending [Member] | Special Mention [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	4,877
2020	12,376	14,687
2019	11,965	36,041
2018	39,450	28,410
2017	34,331	21,875
2016		29,386
Prior	64,406	51,657
Revolving Loans Amortized Cost Basis	26,468	52,732
Total past due	193,873	234,788
Business Lending [Member] | Classified [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	788
2020	1,797	6,336
2019	20,851	4,560
2018	47,749	30,422
2017	25,280	24,807
2016		14,891
Prior	74,205	65,157
Revolving Loans Amortized Cost Basis	34,856	56,000
Total past due	205,526	202,173
Business Lending [Member] | Doubtful [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	0
2020	0	0
2019	15	18
2018	916	2,888
2017	0	0
2016		0
Prior	0	108
Revolving Loans Amortized Cost Basis	856	879
Total past due	1,787	3,893
Consumer Mortgage [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	470,060
2020	363,905	375,637
2019	287,375	330,825
2018	194,688	248,468
2017	185,933	240,217
2016		246,256
Prior	949,807	942,393
Revolving Loans Amortized Cost Basis	19,206	17,703
Total past due	2,470,974	2,401,499
Consumer Mortgage [Member] | FICO AB [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	360,580
2020	237,931	260,588
2019	195,086	227,027
2018	128,042	166,913
2017	126,311	164,051
2016		161,256
Prior	615,271	617,685
Revolving Loans Amortized Cost Basis	0	321
Total past due	1,663,221	1,597,841
Consumer Mortgage [Member] | FICO AB [Member] | Performing [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	360,580
2020	237,931	260,588
2019	195,086	227,027
2018	127,786	166,638
2017	125,836	163,653
2016		160,911
Prior	612,420	614,976
Revolving Loans Amortized Cost Basis	0	321
Total past due	1,659,639	1,594,114
Consumer Mortgage [Member] | FICO AB [Member] | Nonperforming Financial Instruments [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	0
2020	0	0
2019	0	0
2018	256	275
2017	475	398
2016		345
Prior	2,851	2,709
Revolving Loans Amortized Cost Basis	0	0
Total past due	3,582	3,727
Consumer Mortgage [Member] | FICO CDE [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	109,480
2020	125,974	115,049
2019	92,289	103,798
2018	66,646	81,555
2017	59,622	76,166
2016		85,000
Prior	334,536	324,708
Revolving Loans Amortized Cost Basis	19,206	17,382
Total past due	807,753	803,658
Consumer Mortgage [Member] | FICO CDE [Member] | Performing [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	109,400
2020	125,742	115,049
2019	91,312	102,788
2018	65,967	80,973
2017	58,841	75,289
2016		83,214
Prior	323,974	314,668
Revolving Loans Amortized Cost Basis	19,206	17,382
Total past due	794,442	789,363
Consumer Mortgage [Member] | FICO CDE [Member] | Nonperforming Financial Instruments [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	80
2020	232	0
2019	977	1,010
2018	679	582
2017	781	877
2016		1,786
Prior	10,562	10,040
Revolving Loans Amortized Cost Basis	0	0
Total past due	13,311	14,295
Consumer Indirect [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	480,254
2020	229,407	303,522
2019	209,968	305,953
2018	126,137	202,455
2017	48,633	86,514
2016		61,465
Prior	73,979	61,976
Revolving Loans Amortized Cost Basis	0	0
Total past due	1,168,378	1,021,885
Consumer Indirect [Member] | Performing [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	480,254
2020	229,368	303,471
2019	209,894	305,901
2018	126,128	202,373
2017	48,624	86,497
2016		61,449
Prior	73,979	61,975
Revolving Loans Amortized Cost Basis	0	0
Total past due	1,168,247	1,021,666
Consumer Indirect [Member] | Nonperforming Financial Instruments [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	0
2020	39	51
2019	74	52
2018	9	82
2017	9	17
2016		16
Prior	0	1
Revolving Loans Amortized Cost Basis	0	0
Total past due	131	219
Consumer Direct [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	61,119
2020	32,913	49,182
2019	29,380	47,011
2018	15,122	27,874
2017	5,668	12,331
2016		5,232
Prior	5,273	4,149
Revolving Loans Amortized Cost Basis	6,127	6,878
Total past due	155,602	152,657
Consumer Direct [Member] | Performing [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	61,119
2020	32,913	49,181
2019	29,379	46,992
2018	15,118	27,872
2017	5,668	12,326
2016		5,232
Prior	5,259	4,146
Revolving Loans Amortized Cost Basis	6,126	6,878
Total past due	155,582	152,627
Consumer Direct [Member] | Nonperforming Financial Instruments [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	0
2020	0	1
2019	1	19
2018	4	2
2017	0	5
2016		0
Prior	14	3
Revolving Loans Amortized Cost Basis	1	0
Total past due	20	30
Home Equity [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	56,317
2020	45,432	48,145
2019	39,046	48,804
2018	21,396	28,147
2017	17,233	23,628
2016		18,011
Prior	39,845	36,390
Revolving Loans Amortized Cost Basis	176,182	196,709
Total past due	395,451	399,834
Home Equity [Member] | Performing [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	56,317
2020	45,314	48,145
2019	39,025	48,780
2018	21,292	28,074
2017	17,137	23,524
2016		17,828
Prior	39,052	35,900
Revolving Loans Amortized Cost Basis	174,485	194,773
Total past due	392,622	397,024
Home Equity [Member] | Nonperforming Financial Instruments [Member]
Term Loans Amortized Cost Basis by Origination Year
2021	0
2020	118	0
2019	21	24
2018	104	73
2017	96	104
2016		183
Prior	793	490
Revolving Loans Amortized Cost Basis	1,697	1,936
Total past due	$ 2,829	$ 2,810