Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Credit Ratings (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 2,177,601	$ 1,996,359
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,144,650	1,972,059
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	26,588	18,169
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,363	6,131
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	668,046	603,650
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	659,694	595,011
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,817	7,917
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,535	722
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	467,685	424,034
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	464,997	424,034
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,384	0
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,304	0
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	176,462	151,974
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	176,462	150,379
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	1,595
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	242,247	206,405
Residential 1st Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	241,816	205,135
Residential 1st Mortgages [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	47	413
Residential 1st Mortgages [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	384	857
Home Equity Lines and Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	31,625	33,056
Home Equity Lines and Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	31,558	32,419
Home Equity Lines and Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	75
Home Equity Lines and Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	67	562
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	295,325	293,966
Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	283,525	293,325
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	11,366	9
Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	434	632
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	217,577	210,804
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	208,172	199,467
Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,974	8,160
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,431	3,177
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,913	6,592
Consumer & Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,705	6,411
Consumer & Other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0
Consumer & Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	208	181
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	71,721	65,878
Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	71,721	65,878
Leases [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0
Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 0	$ 0