LOANS, Credit Quality By Past Due Status (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
Aged analysis of the company's loans [Abstract]
Total loans		$ 6,890,543	$ 6,281,121
Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,707	2,106
Nonaccrual		15,415	16,182
Total past due		48,684	53,387
Current		5,401,908	4,974,597
Total loans		5,450,592	5,027,984
Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		30,562	35,099
Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,719	349
Nonaccrual		3,420	6,362
Total past due		16,429	9,332
Acquired impaired	[1]	11,797	5,446
Current		1,411,725	1,238,359
Total loans		1,439,951	1,253,137
Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		10,290	2,621
Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,775,876	2,396,977
Business Lending [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,856,585	1,618,827
Business Lending [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		919,291	778,150
Consumer Mortgage [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,996,716	1,848,450
Consumer Mortgage [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		434,186	386,958
Consumer Indirect [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,107,308	1,072,392
Consumer Indirect [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		5,754	10,815
Consumer Direct [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		175,976	175,774
Consumer Direct [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		8,402	3,046
Home Equity [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		314,007	312,541
Home Equity [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		72,318	74,168
Commercial Portfolio Segment [Member] | Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,775,876	2,396,977
Commercial Portfolio Segment [Member] | Business Lending [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		126	179
Nonaccrual		3,840	4,872
Total past due		7,902	10,312
Current		1,848,683	1,608,515
Total loans		1,856,585	1,618,827
Commercial Portfolio Segment [Member] | Business Lending [Member] | Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		3,936	5,261
Commercial Portfolio Segment [Member] | Business Lending [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,173	0
Nonaccrual		570	3,498
Total past due		11,261	4,472
Acquired impaired	[1]	11,797	5,446
Current		896,233	768,232
Total loans		919,291	778,150
Commercial Portfolio Segment [Member] | Business Lending [Member] | Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		8,518	974
Residential Portfolio Segment [Member] | Consumer Mortgage [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,430,902	2,235,408
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,052	1,393
Nonaccrual		10,131	9,872
Total past due		23,173	23,733
Current		1,973,543	1,824,717
Total loans		1,996,716	1,848,450
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		10,990	12,468
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		277	232
Nonaccrual		2,386	2,390
Total past due		3,553	3,463
Acquired impaired	[1]	0	0
Current		430,633	383,495
Total loans		434,186	386,958
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		890	841
Consumer Portfolio Segment [Member] | Consumer Indirect [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,113,062	1,083,207
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		125	258
Nonaccrual		0	0
Total past due		12,798	14,867
Current		1,094,510	1,057,525
Total loans		1,107,308	1,072,392
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		12,673	14,609
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		31	34
Nonaccrual		0	0
Total past due		110	112
Acquired impaired	[1]	0	0
Current		5,644	10,703
Total loans		5,754	10,815
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		79	78
Consumer Portfolio Segment [Member] | Consumer Direct [Member]
Aged analysis of the company's loans [Abstract]
Total loans		184,378	178,820
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		76	48
Nonaccrual		0	0
Total past due		1,531	1,826
Current		174,445	173,948
Total loans		175,976	175,774
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		1,455	1,778
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		0	4
Nonaccrual		52	0
Total past due		111	119
Acquired impaired	[1]	0	0
Current		8,291	2,927
Total loans		8,402	3,046
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		59	115
Consumer Portfolio Segment [Member] | Home Equity [Member]
Aged analysis of the company's loans [Abstract]
Total loans		386,325	386,709
Consumer Portfolio Segment [Member] | Home Equity [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		328	228
Nonaccrual		1,444	1,438
Total past due		3,280	2,649
Current		310,727	309,892
Total loans		314,007	312,541
Consumer Portfolio Segment [Member] | Home Equity [Member] | Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		1,508	983
Consumer Portfolio Segment [Member] | Home Equity [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		238	79
Nonaccrual		412	474
Total past due		1,394	1,166
Acquired impaired	[1]	0	0
Current		70,924	73,002
Total loans		72,318	74,168
Consumer Portfolio Segment [Member] | Home Equity [Member] | Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		$ 744	$ 613

[1] Acquired impaired loans were not classified as nonperforming assets as the loans are considered to be performing under ASC 310-30.  As a result interest income, through the accretion of the difference between the carrying amount of the loans and the expected cashflows, is being recognized on all acquired impaired loans.Acquired impaired loans were not classified as nonperforming assets as the loans are considered to be performing under ASC 310-30.  As a result interest income, through the accretion of the difference between the carrying amount of the loans and the expected cashflows, is being recognized on all acquired impaired loans.