Goodwill, Core Deposit Intangibles and Other Intangible Assets (Book Value, Fair Value, and Valuation Allowance of Mortgage and Commercial Servicing Rights) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Impairment		$ 0
Mortgage Servicing Rights 30-year Tranche
Finite-Lived Intangible Assets [Line Items]
Book Value	$ 25,541,000	20,390,000
Fair Value	42,379,000	32,093,000
Impairment	38,000	0
Mortgage Servicing Rights 30-year Tranche | First Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	5,516,000
Fair Value	5,478,000
Impairment	38,000
Mortgage Servicing Rights 30-year Tranche | Dubuque Bank and Trust Company
Finite-Lived Intangible Assets [Line Items]
Book Value	20,025,000	20,390,000
Fair Value	36,901,000	32,093,000
Impairment	0	0
Mortgage Servicing Rights 15-year Tranche
Finite-Lived Intangible Assets [Line Items]
Book Value	3,880,000	2,858,000
Fair Value	6,301,000	4,988,000
Impairment	20,000	0
Mortgage Servicing Rights 15-year Tranche | First Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	1,685,000
Fair Value	1,665,000
Impairment	20,000
Mortgage Servicing Rights 15-year Tranche | Dubuque Bank and Trust Company
Finite-Lived Intangible Assets [Line Items]
Book Value	2,195,000	2,858,000
Fair Value	4,636,000	4,988,000
Impairment	0	0
Commercial Servicing Rights more than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	1,414,000	2,084,000
Fair Value	1,643,000	2,481,000
Impairment	0	12,000
Commercial Servicing Rights more than 20 Years | Premier Valley Bank
Finite-Lived Intangible Assets [Line Items]
Book Value	178,000	303,000
Fair Value	184,000	291,000
Impairment	0
Commercial Servicing Rights more than 20 Years | Citywide Banks of Colorado, Inc.
Finite-Lived Intangible Assets [Line Items]
Book Value	18,000	34,000
Fair Value	20,000	37,000
Impairment	0	0
Commercial Servicing Rights more than 20 Years | Wisconsin Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	1,218,000	1,747,000
Fair Value	1,439,000	2,153,000
Impairment	0	0
Commercial Servicing Rights less than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	295,000	537,000
Fair Value	491,000	740,000
Impairment	0	0
Commercial Servicing Rights less than 20 Years | Premier Valley Bank
Finite-Lived Intangible Assets [Line Items]
Book Value	45,000	83,000
Fair Value	74,000	110,000
Impairment	0	0
Commercial Servicing Rights less than 20 Years | Citywide Banks of Colorado, Inc.
Finite-Lived Intangible Assets [Line Items]
Book Value	1,000	8,000
Fair Value	6,000	11,000
Impairment	0	0
Commercial Servicing Rights less than 20 Years | Wisconsin Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	249,000	446,000
Fair Value	411,000	619,000
Impairment	$ 0	$ 0