GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Book value, fair value of commercial serving rights and impairment) (Details) - USD ($)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Impairment		$ 2,000,000.0
15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		1,533,000	$ 1,482,000
Fair Value		1,017,000	1,368,000
Impairment	$ 114,000	516,000
30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		5,478,000	5,050,000
Fair Value		3,469,000	4,253,000
Impairment	797,000	2,009,000
Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		100,000	129,000
Fair Value		247,000	285,000
Impairment	0	0	0
More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		884,000	986,000
Fair Value		1,170,000	1,309,000
Impairment	0	0	0
First Bank & Trust | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		1,533,000	1,482,000
Fair Value		1,017,000	1,368,000
Impairment	114,000	516,000
First Bank & Trust | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		5,478,000	5,050,000
Fair Value		3,469,000	4,253,000
Impairment	797,000	2,009,000
Premier Valley Bank | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		1,000	1,000
Fair Value		11,000	13,000
Impairment	0	0
Premier Valley Bank | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		111,000	135,000
Fair Value		140,000	161,000
Impairment	0	0
Wisconsin Bank & Trust | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		99,000	128,000
Fair Value		236,000	272,000
Impairment	0	0
Wisconsin Bank & Trust | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		773,000	851,000
Fair Value		1,030,000	$ 1,148,000
Impairment	$ 0	$ 0