LOANS, Credit Quality By Past Due Status (Details) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Aged analysis of the company's loans [Abstract]
Total loans		$ 6,266,086	$ 6,281,121
Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		2,593	2,106
Nonaccrual		15,524	16,182
Total past due		44,910	53,387
Current		5,018,644	4,974,597
Total loans		5,063,554	5,027,984
Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		26,793	35,099
Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		426	349
Nonaccrual		5,728	6,362
Total past due		10,186	9,332
Acquired impaired	[1]	5,342	5,446
Current		1,187,004	1,238,359
Total loans		1,202,532	1,253,137
Acquired Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		4,032	2,621
Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,410,477	2,396,977
Business Lending [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,663,207	1,618,827
Business Lending [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		747,270	778,150
Consumer Mortgage [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,864,445	1,848,450
Consumer Mortgage [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		372,985	386,958
Consumer Indirect [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,061,518	1,072,392
Consumer Indirect [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		9,322	10,815
Consumer Direct [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		170,360	175,774
Consumer Direct [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,682	3,046
Home Equity [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		304,024	312,541
Home Equity [Member] | Acquired Loans [Member]
Aged analysis of the company's loans [Abstract]
Total loans		70,273	74,168
Commercial Portfolio Segment [Member] | Business Lending [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,410,477	2,396,977
Commercial Portfolio Segment [Member] | Business Lending [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		68	179
Nonaccrual		4,147	4,872
Total past due		10,257	10,312
Current		1,652,950	1,608,515
Total loans		1,663,207	1,618,827
Commercial Portfolio Segment [Member] | Business Lending [Member] | Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		6,042	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		66	0
Nonaccrual		3,254	3,498
Total past due		5,846	4,472
Acquired impaired	[1]	5,342	5,446
Current		736,082	768,232
Total loans		747,270	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		2,526	974
Residential Portfolio Segment [Member] | Consumer Mortgage [Member]
Aged analysis of the company's loans [Abstract]
Total loans		2,237,430	2,235,408
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		1,960	1,393
Nonaccrual		9,794	9,872
Total past due		20,691	23,733
Current		1,843,754	1,824,717
Total loans		1,864,445	1,848,450
Residential Portfolio Segment [Member] | Consumer Mortgage [Member] | Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		8,937	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		287	232
Nonaccrual		1,954	2,390
Total past due		3,124	3,463
Acquired impaired	[1]	0	0
Current		369,861	383,495
Total loans		372,985	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		883	841
Consumer Portfolio Segment [Member] | Consumer Indirect [Member]
Aged analysis of the company's loans [Abstract]
Total loans		1,070,840	1,083,207
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		201	258
Nonaccrual		0	0
Total past due		10,025	14,867
Current		1,051,493	1,057,525
Total loans		1,061,518	1,072,392
Consumer Portfolio Segment [Member] | Consumer Indirect [Member] | Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		9,824	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		33	34
Nonaccrual		0	0
Total past due		65	112
Acquired impaired	[1]	0	0
Current		9,257	10,703
Total loans		9,322	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		32	78
Consumer Portfolio Segment [Member] | Consumer Direct [Member]
Aged analysis of the company's loans [Abstract]
Total loans		173,042	178,820
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		41	48
Nonaccrual		0	0
Total past due		1,026	1,826
Current		169,334	173,948
Total loans		170,360	175,774
Consumer Portfolio Segment [Member] | Consumer Direct [Member] | Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		985	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		25	4
Nonaccrual		0	0
Total past due		58	119
Acquired impaired	[1]	0	0
Current		2,624	2,927
Total loans		2,682	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		33	115
Consumer Portfolio Segment [Member] | Home Equity [Member]
Aged analysis of the company's loans [Abstract]
Total loans		374,297	386,709
Consumer Portfolio Segment [Member] | Home Equity [Member] | Legacy Loans [Member]
Aged analysis of the company's loans [Abstract]
90 + days past due and still accruing		323	228
Nonaccrual		1,583	1,438
Total past due		2,911	2,649
Current		301,113	309,892
Total loans		304,024	312,541
Consumer Portfolio Segment [Member] | Home Equity [Member] | Legacy Loans [Member] | Past Due 30 - 89 Days [Member]
Aged analysis of the company's loans [Abstract]
Total past due		1,005	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		15	79
Nonaccrual		520	474
Total past due		1,093	1,166
Acquired impaired	[1]	0	0
Current		69,180	73,002
Total loans		70,273	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		$ 558	$ 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.