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Loans and ALLL (Summary of information pertaining to TDRs) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 USD ($) loan	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 USD ($) loan
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	$ 13,500	$ 14,746	$ 14,417	$ 14,627
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 132	$ 176	$ 371	$ 547
Number of Loans | loan	8	5	34	19
Pre-Modification Recorded Investment	$ 1,426	$ 1,564	$ 7,671	$ 7,585
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1,426	$ 1,564	$ 7,647	$ 7,585
Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	6	0	15	5
Pre-Modification Recorded Investment	$ 575	$ 0	$ 2,674	$ 1,357
Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	5	19	14
Pre-Modification Recorded Investment	$ 851	$ 1,564	$ 4,997	$ 6,228
Commercial other [Member]
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	778	1,669	1,263	1,363
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 16	$ 28	$ 55	$ 75
Number of Loans | loan	0	3	4	6
Pre-Modification Recorded Investment	$ 0	$ 1,385	$ 1,360	$ 1,698
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 1,385	$ 1,360	$ 1,698
Commercial other [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	1	0
Pre-Modification Recorded Investment	$ 0	$ 0	$ 174	$ 0
Commercial other [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	3	3	6
Pre-Modification Recorded Investment	$ 0	$ 1,385	$ 1,186	$ 1,698
Agricultural other [Member]
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	324	0	108	22
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 45	$ 0	$ 45	$ 0
Number of Loans | loan	7	0	22	7
Pre-Modification Recorded Investment	$ 1,327	$ 0	$ 5,718	$ 5,445
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1,327	$ 0	$ 5,694	$ 5,445
Agricultural other [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	5	0	12	4
Pre-Modification Recorded Investment	$ 476	$ 0	$ 2,345	$ 1,349
Agricultural other [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	2	0	10	3
Pre-Modification Recorded Investment	$ 851	$ 0	$ 3,373	$ 4,096
Residential real estate senior liens [Member]
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	7,512	8,333	7,694	8,379
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 17	$ 79	$ 107	$ 245
Number of Loans | loan	1	2	8	5
Pre-Modification Recorded Investment	$ 99	$ 179	$ 593	$ 434
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 99	$ 179	$ 593	$ 434
Residential real estate senior liens [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	0	2	0
Pre-Modification Recorded Investment	$ 99	$ 0	$ 155	$ 0
Residential real estate senior liens [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	2	6	5
Pre-Modification Recorded Investment	$ 0	$ 179	$ 438	$ 434
Residential real estate junior liens [Member]
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	18	73	29	75
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 0	$ 1	$ 0	$ 2
Number of Loans | loan	0	0	0	1
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 8
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 8
Residential real estate junior liens [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	0	1
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 8
Residential real estate junior liens [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	0	0
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Residential, Home Equity Line Of Credit, Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0	35	0	23
Impaired Financing Receivable, with Related Allowance, Interest Income, Accrual Method	$ 0	$ 0	$ 0	$ 0
Total residential real estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	2	8	6
Pre-Modification Recorded Investment	$ 99	$ 179	$ 593	$ 442
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 99	$ 179	$ 593	$ 442
Total residential real estate [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	1	0	2	1
Pre-Modification Recorded Investment	$ 99	$ 0	$ 155	$ 8
Total residential real estate [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	2	6	5
Pre-Modification Recorded Investment	$ 0	$ 179	$ 438	$ 434
Consumer Unsecured Financing Receivable [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	0	0
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Consumer Unsecured Financing Receivable [Member] | Interest Rate Below Market Reduction [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	0	0
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0
Consumer Unsecured Financing Receivable [Member] | Below Market Interest Rate and Extension of Amortization Period [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | loan	0	0	0	0
Pre-Modification Recorded Investment	$ 0	$ 0	$ 0	$ 0

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