LOANS AND LEASES - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured Loans, Portion Determined to be Uncollectible	$ 700,000	$ 100,000		$ 200,000
Purchased impaired loans	105,022,000		$ 105,022,000			$ 104,960,000
Restructured Loans, Nonaccrual Status	4,700,000		4,700,000			6,400,000
Write-downs	455,000	134,000	717,000	415,000
Gain (loss) on sale of other real estate owned	(538,000)	(237,000)	(332,000)	(423,000)
Real Estate Acquired Through Foreclosure	1,918,000	3,116,000	1,918,000	3,116,000	$ 1,853,000	$ 2,781,000	$ 5,961,000	$ 6,284,000
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured Loans, Loan Relationships, Review Threshold Amount Minimum			250,000
Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured Loans, Loan Relationships, Review Threshold Amount Minimum			250,000
Write-downs	197,000	$ 32,000	362,000	$ 151,000
MainSource [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased impaired loans	$ 18,000,000.0		$ 18,000,000.0