LOANS, Amount of Business Lending Loans by Credit Quality Category (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 6,308,720	$ 4,948,562
Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,568,263	4,453,202
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,740,457	495,360
Business Lending [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,458,981	1,490,076
Business Lending [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,342,436	1,277,666
Business Lending [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,116,545	212,410
Business Lending [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,150,341	1,213,170
Business Lending [Member] | Pass [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,122,422	1,051,005
Business Lending [Member] | Pass [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,027,919	162,165
Business Lending [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	161,916	165,292
Business Lending [Member] | Special Mention [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	126,928	135,602
Business Lending [Member] | Special Mention [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	34,988	29,690
Business Lending [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	133,130	105,587
Business Lending [Member] | Classified [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	93,086	90,585
Business Lending [Member] | Classified [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	40,044	15,002
Business Lending [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	474
Business Lending [Member] | Doubtful [Member] | Legacy Loans [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	0	0
Business Lending [Member] | Acquired Impaired [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	13,594	5,553
Business Lending [Member] | Acquired Impaired [Member] | Legacy Loans [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	13,594	5,553
All Other Loans [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,225,827	3,175,536
All Other Loans [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	623,912	282,950
All Other Loans [Member] | Performing [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,212,401	3,160,929
All Other Loans [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	618,769	279,070
All Other Loans [Member] | Nonperforming [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	13,426	14,607
All Other Loans [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	5,143	3,880
Consumer Mortgage [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,718,875	1,659,760
Consumer Mortgage [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	487,652	159,941
Consumer Mortgage [Member] | Performing [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,707,146	1,647,228
Consumer Mortgage [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	483,896	157,404
Consumer Mortgage [Member] | Nonperforming [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	11,729	12,532
Consumer Mortgage [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,756	2,537
Consumer Indirect [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,011,298	1,014,825
Consumer Indirect [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	23,418	30,147
Consumer Indirect [Member] | Performing [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,011,131	1,014,659
Consumer Indirect [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	23,418	30,144
Consumer Indirect [Member] | Nonperforming [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	167	166
Consumer Indirect [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	0	3
Consumer Direct [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	177,396	181,922
Consumer Direct [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	6,502	9,893
Consumer Direct [Member] | Performing [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	177,329	181,864
Consumer Direct [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	6,500	9,893
Consumer Direct [Member] | Nonperforming [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	67	58
Consumer Direct [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2	0
Home Equity [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	318,258	319,029
Home Equity [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	106,340	82,969
Home Equity [Member] | Performing [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	316,795	317,178
Home Equity [Member] | Performing [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	104,955	81,629
Home Equity [Member] | Nonperforming [Member] | Legacy Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,463	1,851
Home Equity [Member] | Nonperforming [Member] | Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,385	$ 1,340