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, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment	$ 0
15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	4,056,000
Fair Value	6,488,000
Impairment	0
30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	26,115,000
Fair Value	41,093,000
Impairment	0
Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	315,000	$ 537,000
Fair Value	607,000	740,000
Impairment	0	0
More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,553,000	2,084,000
Fair Value	1,922,000	2,481,000
Impairment	0	12,000
Dubuque Bank and Trust Company | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	2,371,000	2,858,000
Fair Value	4,747,000	4,988,000
Impairment	0	0
Dubuque Bank and Trust Company | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	20,632,000	20,390,000
Fair Value	35,610,000	32,093,000
Impairment	0	0
First Bank & Trust | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,685,000
Fair Value	1,741,000
Impairment	0
First Bank & Trust | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	5,483,000
Fair Value	5,483,000
Impairment	0
Citywide Banks | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	2,000	8,000
Fair Value	6,000	11,000
Impairment	0	0
Citywide Banks | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	30,000	34,000
Fair Value	33,000	37,000
Impairment	0	0
Premier Valley Bank | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	53,000	83,000
Fair Value	82,000	110,000
Impairment	0	0
Premier Valley Bank | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	188,000	303,000
Fair Value	203,000	291,000
Impairment	0	12,000
Wisconsin Bank & Trust | 15 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		2,858,000
Fair Value		4,988,000
Impairment		0
Wisconsin Bank & Trust | 30 Years
Finite-Lived Intangible Assets [Line Items]
Book Value		20,390,000
Fair Value		32,093,000
Impairment		0
Wisconsin Bank & Trust | Less Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	260,000	446,000
Fair Value	519,000	619,000
Impairment	0	0
Wisconsin Bank & Trust | More Than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,335,000	1,747,000
Fair Value	1,686,000	2,153,000
Impairment	$ 0	$ 0