Loans & Leases and Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Risk Ratings (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 2,216,779	$ 2,177,601	$ 2,079,670
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,180,249	2,144,650	2,054,256
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	26,763	26,588	18,627
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	9,767	6,363	6,787
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	683,037	668,046	627,114
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	678,083	659,694	618,975
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	4,458	6,817	7,141
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	496	1,535	998
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	470,738	467,685	439,972
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	465,427	464,997	437,059
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,281	1,384	1,418
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	4,030	1,304	1,495
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	162,167	176,462	175,045
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	152,989	176,462	173,556
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	9,178	0	1,489
Real Estate Construction [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Residential 1st Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	257,920	242,247	238,376
Residential 1st Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	256,906	241,816	237,254
Residential 1st Mortgages [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	43	47	404
Residential 1st Mortgages [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	971	384	718
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	33,350	31,625	32,513
Home Equity Lines & Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	33,297	31,558	32,408
Home Equity Lines & Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Home Equity Lines & Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	53	67	105
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	259,127	295,325	274,704
Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	250,372	283,525	273,184
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	5,331	11,366	1,070
Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	3,424	434	450
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	257,951	217,577	214,086
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	253,144	208,172	204,119
Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	4,184	6,974	7,105
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	623	2,431	2,862
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	7,312	6,913	6,975
Consumer & Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	7,142	6,705	6,816
Consumer & Other [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Consumer & Other [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	170	208	159
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	85,177	71,721	70,885
Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	82,889	71,721	70,885
Leases [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,288	0	0
Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 0	$ 0	$ 0