LOANS, Amount of Business Lending Loans by Credit Quality Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Business Lending Loans by Credit Quality Category [Abstract]
Loans	$ 6,890,543	$ 6,281,121
Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	5,450,592	5,027,984
Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,439,951	1,253,137
Business Lending [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,775,876	2,396,977
Business Lending [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,856,585	1,618,827
Business Lending [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	919,291	778,150
Business Lending [Member] | Pass [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,487,973	2,141,830
Business Lending [Member] | Pass [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,655,280	1,439,337
Business Lending [Member] | Pass [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	832,693	702,493
Business Lending [Member] | Special Mention [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	144,277	145,172
Business Lending [Member] | Special Mention [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	98,953	105,065
Business Lending [Member] | Special Mention [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	45,324	40,107
Business Lending [Member] | Classified [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	131,829	102,950
Business Lending [Member] | Classified [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	102,352	74,425
Business Lending [Member] | Classified [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	29,477	28,525
Business Lending [Member] | Doubtful [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	0	1,579
Business Lending [Member] | Doubtful [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	0	0
Business Lending [Member] | Doubtful [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	0	1,579
Business Lending [Member] | Acquired Impaired [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	11,797	5,446
Business Lending [Member] | Acquired Impaired [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	0	0
Business Lending [Member] | Acquired Impaired [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	11,797	5,446
All Other Loans [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,594,007	3,409,157
All Other Loans [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	520,660	474,987
All Other Loans [Member] | Performing [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,579,851	3,395,920
All Other Loans [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	517,264	471,774
All Other Loans [Member] | Nonperforming [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	14,156	13,237
All Other Loans [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,396	3,213
Consumer Mortgage [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,996,716	1,848,450
Consumer Mortgage [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	434,186	386,958
Consumer Mortgage [Member] | Performing [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,984,533	1,837,185
Consumer Mortgage [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	431,523	384,336
Consumer Mortgage [Member] | Nonperforming [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	12,183	11,265
Consumer Mortgage [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,663	2,622
Consumer Indirect [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,107,308	1,072,392
Consumer Indirect [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	5,754	10,815
Consumer Indirect [Member] | Performing [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,107,183	1,072,134
Consumer Indirect [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	5,723	10,781
Consumer Indirect [Member] | Nonperforming [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	125	258
Consumer Indirect [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	31	34
Consumer Direct [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	175,976	175,774
Consumer Direct [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	8,402	3,046
Consumer Direct [Member] | Performing [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	175,900	175,726
Consumer Direct [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	8,350	3,042
Consumer Direct [Member] | Nonperforming [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	76	48
Consumer Direct [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	52	4
Home Equity [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	314,007	312,541
Home Equity [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	72,318	74,168
Home Equity [Member] | Performing [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	312,235	310,875
Home Equity [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	71,668	73,615
Home Equity [Member] | Nonperforming [Member] | Legacy Loan [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,772	1,666
Home Equity [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	$ 650	$ 553