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, 2017	Dec. 31, 2016
Less than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	$ 896,000	$ 1,008,000
Fair Value	1,108,000	1,200,000
Impairment	0	0
Less than 20 Years | Centennial Bank and Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	17,000	19,000
Fair Value	18,000	23,000
Impairment	0	0
Less than 20 Years | Premier Valley Bank
Finite-Lived Intangible Assets [Line Items]
Book Value	131,000	156,000
Fair Value	161,000	180,000
Impairment	0	0
Less than 20 Years | Wisconsin Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	748,000	833,000
Fair Value	929,000	997,000
Impairment	0	0
More than 20 Years
Finite-Lived Intangible Assets [Line Items]
Book Value	2,614,000	2,715,000
Fair Value	2,932,000	2,927,000
Impairment	28,000	33,000
More than 20 Years | Centennial Bank and Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	103,000	107,000
Fair Value	114,000	114,000
Impairment	0	0
More than 20 Years | Premier Valley Bank
Finite-Lived Intangible Assets [Line Items]
Book Value	345,000	359,000
Fair Value	317,000	326,000
Impairment	28,000	33,000
More than 20 Years | Wisconsin Bank & Trust
Finite-Lived Intangible Assets [Line Items]
Book Value	2,166,000	2,249,000
Fair Value	2,501,000	2,487,000
Impairment	$ 0	$ 0