LOANS - Summary of Information Pertaining to Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Impaired Loans Excluding Purchased Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 14,420	$ 18,281	$ 14,202
Troubled debt restructurings not included above	11,375	13,659	13,599
Total impaired loans	25,795	31,940	27,801
Interest income recognized on impaired loans	239	240	1,010
Foregone interest income on impaired loans	190	274	197
Purchased Impaired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	15,940	23,606	15,428
Troubled debt restructurings not included above	20,649	20,448	20,472
Total impaired loans	36,589	44,054	35,900
Interest income recognized on impaired loans	696	379	379
Foregone interest income on impaired loans	$ 245	$ 337	$ 281