LOANS AND ALLOWANCE FOR LOAN LOSSES - Summary of Information Pertaining to Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Loans Excluding Purchased Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 14,202	$ 18,114	$ 16,860
Troubled debt restructurings not included above	13,599	14,209	14,418
Total impaired loans	27,801	32,323	31,278
Interest income recognized on impaired loans	1,867	1,033	909
Foregone interest income on impaired loans	950	977	1,204
Purchased Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	15,428	22,966	26,568
Troubled debt restructurings not included above	20,472	23,543	22,656
Total impaired loans	35,900	46,509	49,224
Interest income recognized on impaired loans	1,625	2,755	1,671
Foregone interest income on impaired loans	$ 1,239	$ 1,637	$ 2,961