GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Book value, fair value of commercial serving rights and impairment) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Valuation Allowance	$ 1,400,000
Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	80,000	$ 87,000
Fair Value	230,000	203,000
Valuation Allowance	0	0
More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	655,000	776,000
Fair Value	1,009,000	1,085,000
Valuation Allowance	0	0
First Bank & Trust | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,667,000	1,522,000
Fair Value	1,266,000	1,100,000
Valuation Allowance	401,000	422,000
First Bank & Trust | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	6,380,000	5,445,000
Fair Value	4,952,000	4,089,000
Valuation Allowance	$ 1,428,000	$ 1,356,000