LOANS, Amount of Business Lending Loans by Credit Quality Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 6,256,757	$ 4,948,562
Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,619,663	4,453,202
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,637,094	495,360
Business Lending [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,424,223	1,490,076
Business Lending [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,376,599	1,277,666
Business Lending [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,047,624	212,410
Business Lending [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,134,137	1,213,170
Business Lending [Member] | Pass [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,170,156	1,051,005
Business Lending [Member] | Pass [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	963,981	162,165
Business Lending [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	166,397	165,292
Business Lending [Member] | Special Mention [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	129,076	135,602
Business Lending [Member] | Special Mention [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	37,321	29,690
Business Lending [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	111,995	105,587
Business Lending [Member] | Classified [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	77,367	90,585
Business Lending [Member] | Classified [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	34,628	15,002
Business Lending [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,579	474
Business Lending [Member] | Doubtful [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	474
Business Lending [Member] | Doubtful [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,579	0
Business Lending [Member] | Acquired Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	10,115	5,553
Business Lending [Member] | Acquired Impaired [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Business Lending [Member] | Acquired Impaired [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	10,115	5,553
All Other Loans [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,243,064	3,175,536
All Other Loans [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	589,470	282,950
All Other Loans [Member] | Performing [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,229,051	3,160,929
All Other Loans [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	584,874	279,070
All Other Loans [Member] | Nonperforming [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	14,013	14,607
All Other Loans [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,596	3,880
Consumer Mortgage [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,754,609	1,659,760
Consumer Mortgage [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	465,689	159,941
Consumer Mortgage [Member] | Performing [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,742,387	1,647,228
Consumer Mortgage [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	462,597	157,404
Consumer Mortgage [Member] | Nonperforming [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	12,222	12,532
Consumer Mortgage [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,092	2,537
Consumer Indirect [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	991,836	1,014,825
Consumer Indirect [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	20,142	30,147
Consumer Indirect [Member] | Performing [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	991,541	1,014,659
Consumer Indirect [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	20,134	30,144
Consumer Indirect [Member] | Nonperforming [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	295	166
Consumer Indirect [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8	3
Consumer Direct [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	174,479	181,922
Consumer Direct [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,450	9,893
Consumer Direct [Member] | Performing [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	174,431	181,864
Consumer Direct [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,450	9,893
Consumer Direct [Member] | Nonperforming [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	48	58
Consumer Direct [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Home Equity [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	322,140	319,029
Home Equity [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	98,189	82,969
Home Equity [Member] | Performing [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	320,692	317,178
Home Equity [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	96,693	81,629
Home Equity [Member] | Nonperforming [Member] | Legacy Loan [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,448	1,851
Home Equity [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,496	$ 1,340