LOANS, Amount of Business Lending Loans by Credit Quality Category (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Business Lending Loans by Credit Quality Category [Abstract]
Loans	$ 6,300,888	$ 6,256,757
Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	4,979,836	4,619,663
Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,321,052	1,637,094
Business Lending [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,403,624	2,424,223
Business Lending [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,582,807	1,376,599
Business Lending [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	820,817	1,047,624
Business Lending [Member] | Pass [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,134,619	2,134,137
Business Lending [Member] | Pass [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,394,290	1,170,156
Business Lending [Member] | Pass [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	740,329	963,981
Business Lending [Member] | Special Mention [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	160,550	166,397
Business Lending [Member] | Special Mention [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	112,777	129,076
Business Lending [Member] | Special Mention [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	47,773	37,321
Business Lending [Member] | Classified [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	101,025	111,995
Business Lending [Member] | Classified [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	75,740	77,367
Business Lending [Member] | Classified [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	25,285	34,628
Business Lending [Member] | Doubtful [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,579	1,579
Business Lending [Member] | Doubtful [Member] | Legacy Loans [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	1,579	1,579
Business Lending [Member] | Acquired Impaired [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	5,851	10,115
Business Lending [Member] | Acquired Impaired [Member] | Legacy Loans [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	5,851	10,115
All Other Loans [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,397,029	3,243,064
All Other Loans [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	500,235	589,470
All Other Loans [Member] | Performing [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,383,348	3,229,051
All Other Loans [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	496,384	584,874
All Other Loans [Member] | Nonperforming [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	13,681	14,013
All Other Loans [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,851	4,596
Consumer Mortgage [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,815,098	1,754,609
Consumer Mortgage [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	404,924	465,689
Consumer Mortgage [Member] | Performing [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,803,416	1,742,387
Consumer Mortgage [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	402,271	462,597
Consumer Mortgage [Member] | Nonperforming [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	11,682	12,222
Consumer Mortgage [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	2,653	3,092
Consumer Indirect [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,086,190	991,836
Consumer Indirect [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	12,753	20,142
Consumer Indirect [Member] | Performing [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,086,015	991,541
Consumer Indirect [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	12,719	20,134
Consumer Indirect [Member] | Nonperforming [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	175	295
Consumer Indirect [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	34	8
Consumer Direct [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	180,929	174,479
Consumer Direct [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,420	5,450
Consumer Direct [Member] | Performing [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	180,909	174,431
Consumer Direct [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	3,420	5,450
Consumer Direct [Member] | Nonperforming [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	20	48
Consumer Direct [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	0	0
Home Equity [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	314,812	322,140
Home Equity [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	79,138	98,189
Home Equity [Member] | Performing [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	313,008	320,692
Home Equity [Member] | Performing [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	77,974	96,693
Home Equity [Member] | Nonperforming [Member] | Legacy Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	1,804	1,448
Home Equity [Member] | Nonperforming [Member] | Acquired Loans [Member]
Business Lending Loans by Credit Quality Category [Abstract]
Loans	$ 1,164	$ 1,496