LOANS AND LEASES - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Apr. 01, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased impaired loans	$ 117,155,000		$ 117,155,000				$ 104,960,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield					$ 1,200,000
Certain Loans Acquired in Transfer, Nonaccretable Difference					2,700,000
Restructured Loans, Nonaccrual Status	5,900,000		5,900,000				6,400,000
Write-downs	139,000	$ 172,000	262,000	$ 281,000
Gain (loss) on sale of other real estate owned	283,000	(162,000)	206,000	(186,000)
Real Estate Acquired Through Foreclosure	1,853,000	5,961,000	1,853,000	5,961,000		$ 1,065,000	$ 2,781,000	$ 5,300,000	$ 6,284,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value					2,700,000,000
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition					$ 2,900,000,000
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	139,000	$ 56,000	165,000	$ 119,000
MainSource [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchased impaired loans	$ 24,100,000		$ 24,100,000