GOODWILL, CORE DEPOSIT PREMIUM AND OTHER INTANGIBLE ASSETS (Book value, fair value of commercial serving rights and impairment) (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Impairment	$ 1,600,000	$ 58,000
15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,511,000	3,880,000
Fair Value	1,267,000	6,301,000
Impairment	244,000	20,000
30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	5,140,000	25,541,000
Fair Value	3,755,000	42,379,000
Impairment	1,385,000	38,000
Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	179,000	295,000
Fair Value	348,000	491,000
Impairment	7,000	0
More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,077,000	1,414,000
Fair Value	1,478,000	1,643,000
Impairment	0	0
Dubuque Bank and Trust Company | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	0	2,195,000
Fair Value	0	4,636,000
Impairment	0	0
Dubuque Bank and Trust Company | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	0	20,025,000
Fair Value	0	36,901,000
Impairment	0	0
First Bank & Trust | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,511,000	1,685,000
Fair Value	1,267,000	1,665,000
Impairment	244,000	20,000
First Bank & Trust | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	5,140,000	5,516,000
Fair Value	3,755,000	5,478,000
Impairment	1,385,000	38,000
Citywide Banks | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	0	1,000
Fair Value	0	6,000
Impairment	0	0
Citywide Banks | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	0	18,000
Fair Value	0	20,000
Impairment	0	0
Premier Valley Bank | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	24,000	45,000
Fair Value	17,000	74,000
Impairment	7,000	0
Premier Valley Bank | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	149,000	178,000
Fair Value	167,000	184,000
Impairment	0	0
Wisconsin Bank & Trust | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	155,000	249,000
Fair Value	331,000	411,000
Impairment	0	0
Wisconsin Bank & Trust | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	928,000	1,218,000
Fair Value	1,311,000	1,439,000
Impairment	$ 0	$ 0