LOANS - Loans Evaluated for Impairment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans receivable: balance at end of period
Total	$ 2,485,613	$ 1,129,064
Commercial real estate
Loans receivable: balance at end of period
Total	826,746	418,119
Commercial and industrial
Loans receivable: balance at end of period
Total	379,423	151,240
Residential real estate
Loans receivable: balance at end of period
Total	1,155,682	506,612
Consumer
Loans receivable: balance at end of period
Total	123,762	53,093
Business Activities Loans
Loans receivable: balance at end of period
Individually evaluated for impairment	9,647	6,709
Collectively evaluated	1,442,983	1,122,355
Total	1,452,630	1,129,064
Business Activities Loans | Commercial real estate
Loans receivable: balance at end of period
Individually evaluated for impairment	7,604	4,481
Collectively evaluated	526,407	413,638
Total	534,011	418,119
Business Activities Loans | Commercial and industrial
Loans receivable: balance at end of period
Individually evaluated for impairment	626	486
Collectively evaluated	267,378	150,754
Total	268,004	151,240
Business Activities Loans | Residential real estate
Loans receivable: balance at end of period
Individually evaluated for impairment	1,404	1,709
Collectively evaluated	590,007	504,903
Total	591,411	506,612
Business Activities Loans | Consumer
Loans receivable: balance at end of period
Individually evaluated for impairment	13	33
Collectively evaluated	59,191	53,060
Total	59,204	53,093
Acquired Loans
Loans receivable: balance at end of period
Individually evaluated for impairment	1,146
Purchased Credit Impaired	12,587
Collectively evaluated	1,019,250
Total	1,032,983	0
Acquired Loans | Commercial real estate
Loans receivable: balance at end of period
Individually evaluated for impairment	241
Purchased Credit Impaired	8,655
Collectively evaluated	283,839
Total	292,735	0
Acquired Loans | Commercial and industrial
Loans receivable: balance at end of period
Individually evaluated for impairment	571
Purchased Credit Impaired	632
Collectively evaluated	110,216
Total	111,419	0
Acquired Loans | Residential real estate
Loans receivable: balance at end of period
Individually evaluated for impairment	271
Purchased Credit Impaired	3,259
Collectively evaluated	560,741
Total	564,271	0
Acquired Loans | Consumer
Loans receivable: balance at end of period
Individually evaluated for impairment	63
Purchased Credit Impaired	41
Collectively evaluated	64,454
Total	$ 64,558	$ 0