BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES (Details)	1 Months Ended	12 Months Ended
	Nov. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) item segment subsidiary	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Property, Plant and Equipment
Number of investment subsidiaries (subsidiary) | subsidiary		2
Number of subsidiaries | subsidiary		4
Number of branches entity operates (branches)		78
Number of loan production offices		5
Transfer to other real estate | $		$ 570,000	$ 43,000	$ 567,000
Impairment of goodwill | $	$ 0
Repayment of deferred fees and interest in years		10 years
Expenses for deferred compensation | $		$ 78,000	117,000	111,000
Allowance for credit losses on unfunded commitments | $		2,100,000	3,000,000.0
Retained earnings | $		614,829,000	559,139,000
Compensation expense | $		0	0	0
Deferred compensation liability, current | $		$ 1,200,000	1,300,000
Incentive award, payment period		15 years
Compensation liability | $		$ 4,800,000	6,000,000.0
Share Based Compensation, Short Term Portion, Payment Period		75 days
Vesting period		3 years
Share Based Compensation, Long-Term Portion, Payment Period		75 days
Officers' compensation expense | $		$ 2,000,000.0	2,300,000	2,200,000
Deferred compensation liability incentive plan | $		$ 1,600,000	1,800,000
Likelihood of unfavorable settlement (percent)		50.00%
Number of reportable segments | segment		1
Minimum
Property, Plant and Equipment
Finite-lived intangible asset, useful life		10 years
Maximum
Property, Plant and Equipment
Finite-lived intangible asset, useful life		12 years
Furniture and Fixtures | Minimum
Property, Plant and Equipment
Property, plant and equipment, estimated useful lives		3
Furniture and Fixtures | Maximum
Property, Plant and Equipment
Property, plant and equipment, estimated useful lives		5 years
Buildings And Leasehold Improvements | Minimum
Property, Plant and Equipment
Property, plant and equipment, estimated useful lives		33
Buildings And Leasehold Improvements | Maximum
Property, Plant and Equipment
Property, plant and equipment, estimated useful lives		39 years
Vigo County
Property, Plant and Equipment
Number of branches entity operates (branches)		9
Daviess County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Clay County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Greene County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Knox County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Parke County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Putnam County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Sullivan County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Vanderburgh County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Vermillion County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Champaign County, Illinois
Property, Plant and Equipment
Number of loan production offices		4
Clark County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Coles County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Crawford County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Franklin County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Jasper County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Lawrence County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Livingston County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Marion County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		2
McLean County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Richland County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Vermilion County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		6
Wayne County, Illinois
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Calloway County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Breckinridge County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Christian County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Fulton County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Hancock County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Hopkins County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Marshall County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Todd County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Trigg County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Warren County, Kentucky
Property, Plant and Equipment
Number of branches entity operates (branches)		2
Cheatham County, Tennessee
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Houston County, Tennessee
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Montgomery County, Tennessee
Property, Plant and Equipment
Number of branches entity operates (branches)		3
Hamilton County, Indiana
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Rutherford County, Tennessee
Property, Plant and Equipment
Number of branches entity operates (branches)		1
Williamson County, Tennessee
Property, Plant and Equipment
Number of branches entity operates (branches)		1
First Financial Bank
Property, Plant and Equipment
Investments in subsidiaries | $		$ 1,000,000.0
Service fees
Property, Plant and Equipment
Revenue within scope of ASC 606 | $		$ 1,400,000	$ 1,300,000	$ 1,300,000