LOANS - Summary of Information Pertaining to Impaired Loans (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Loans Excluding Purchased Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 15,325	$ 16,570	$ 18,114
Troubled debt restructurings not included above	12,452	14,013	14,209
Total impaired loans	27,777	30,583	32,323
Loans Excluding Purchased Loan | Quater-to-date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable, interest income, accrual method	297	252	225
Loans and leases receivable, impaired, interest lost on nonaccrual loans	233	239	267
Loans Excluding Purchased Loan | Year-to-date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable, interest income, accrual method	857	808	1,033
Loans and leases receivable, impaired, interest lost on nonaccrual loans	753	710	977
Purchased Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	19,049	23,827	22,966
Troubled debt restructurings not included above	20,205	21,117	23,543
Total impaired loans	39,254	44,944	46,509
Purchased Loans | Quater-to-date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable, interest income, accrual method	493	1,493	377
Loans and leases receivable, impaired, interest lost on nonaccrual loans	356	346	354
Purchased Loans | Year-to-date
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired financing receivable, interest income, accrual method	1,246	2,378	2,755
Loans and leases receivable, impaired, interest lost on nonaccrual loans	$ 958	$ 1,283	$ 1,637