Loans and Allowance for Loan Losses - Average Recorded Investment and Interest Income Recognized (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Loans
Average recorded investment in impaired loans	$ 4,338	$ 2,394	$ 273
Interest income recognized	183	39
Residential real estate
Impaired Loans
Average recorded investment in impaired loans	156	155	68
Interest income recognized	1
Commercial and commercial real estate
Impaired Loans
Average recorded investment in impaired loans	3,703	2,222	$ 205
Interest income recognized	182	39
Agricultural production and real estate
Impaired Loans
Average recorded investment in impaired loans	282	$ 17
Consumer and margin loans
Impaired Loans
Average recorded investment in impaired loans	$ 197

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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