LOANS, Credit Quality By Past Due Status (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Aged analysis of the company's loans [Abstract]
Total loans		$ 6,281,121	$ 6,256,757
Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,106	2,508
Nonaccrual		16,182	16,020
Total past due		53,387	51,563
Current		4,974,597	4,568,100
Total loans		5,027,984	4,619,663
Legacy Loan [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		35,099	33,035
Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		349	204
Nonaccrual		6,362	8,720
Total past due		9,332	17,167
Acquired impaired	[1]	5,446	10,115
Current		1,238,359	1,609,812
Total loans		1,253,137	1,637,094
Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		2,621	8,243
Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,396,977	2,424,223
Business Lending [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,618,827	1,376,599
Business Lending [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		778,150	1,047,624
Consumer Mortgage [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,848,450	1,754,609
Consumer Mortgage [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		386,958	465,689
Consumer Indirect [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,072,392	991,836
Consumer Indirect [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		10,815	20,142
Consumer Direct [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		175,774	174,479
Consumer Direct [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		3,046	5,450
Home Equity [Member] | Legacy Loan [Member]
Aged analysis of the company's loans [Abstract]
Total loans		312,541	322,140
Home Equity [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		74,168	98,189
Commercial Portfolio Segment [Member] | Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,396,977	2,424,223
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		179	571
Nonaccrual		4,872	3,944
Total past due		10,312	6,798
Current		1,608,515	1,369,801
Total loans		1,618,827	1,376,599
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		5,261	2,283
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		0	0
Nonaccrual		3,498	4,328
Total past due		4,472	8,989
Acquired impaired	[1]	5,446	10,115
Current		768,232	1,028,520
Total loans		778,150	1,047,624
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		974	4,661
Residential Portfolio Segment [Member] | Consumer Mortgage [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,235,408	2,220,298
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		1,393	1,500
Nonaccrual		9,872	10,722
Total past due		23,733	25,786
Current		1,824,717	1,728,823
Total loans		1,848,450	1,754,609
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		12,468	13,564
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		232	26
Nonaccrual		2,390	3,066
Total past due		3,463	5,695
Acquired impaired	[1]	0	0
Current		383,495	459,994
Total loans		386,958	465,689
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		841	2,603
Consumer Portfolio Segment [Member] | Consumer Indirect [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,083,207	1,011,978
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		258	295
Nonaccrual		0	0
Total past due		14,867	14,492
Current		1,057,525	977,344
Total loans		1,072,392	991,836
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		14,609	14,197
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		34	8
Nonaccrual		0	0
Total past due		112	253
Acquired impaired	[1]	0	0
Current		10,703	19,889
Total loans		10,815	20,142
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		78	245
Consumer Portfolio Segment [Member] | Consumer Direct [Member]
Aged analysis of the company's loans [Abstract]
Total loans		178,820	179,929
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		48	48
Nonaccrual		0	0
Total past due		1,826	1,923
Current		173,948	172,556
Total loans		175,774	174,479
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		1,778	1,875
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		4	0
Nonaccrual		0	0
Total past due		119	100
Acquired impaired	[1]	0	0
Current		2,927	5,350
Total loans		3,046	5,450
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		115	100
Consumer Portfolio Segment [Member] | Home Equity [Member]
Aged analysis of the company's loans [Abstract]
Total loans		386,709	420,329
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		228	94
Nonaccrual		1,438	1,354
Total past due		2,649	2,564
Current		309,892	319,576
Total loans		312,541	322,140
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		983	1,116
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		79	170
Nonaccrual		474	1,326
Total past due		1,166	2,130
Acquired impaired	[1]	0	0
Current		73,002	96,059
Total loans		74,168	98,189
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		$ 613	$ 634

[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.