Loans & Leases and Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Risk Ratings (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 2,146,032	$ 2,177,601	$ 1,993,071
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,108,941	2,144,650	1,961,069
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	32,518	26,588	25,670
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	4,573	6,363	6,332
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	676,527	668,046	611,511
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	668,243	659,694	602,242
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,768	6,817	8,573
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,516	1,535	696
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	463,645	467,685	432,281
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	461,318	464,997	429,785
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,351	1,384	2,496
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	976	1,304	0
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	164,791	176,462	166,455
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	156,426	176,462	164,895
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	8,365	0	1,560
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	249,628	242,247	212,205
Residential 1st Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	249,238	241,816	210,884
Residential 1st Mortgages [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	45	47	410
Residential 1st Mortgages [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	345	384	911
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	31,817	31,625	31,639
Home Equity Lines & Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	31,752	31,558	30,701
Home Equity Lines & Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	72
Home Equity Lines & Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	65	67	866
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	266,010	295,325	253,655
Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	255,390	283,525	252,387
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	9,857	11,366	638
Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	763	434	630
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	209,184	217,577	213,479
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	204,792	208,172	202,878
Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	3,638	6,974	7,582
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	754	2,431	3,019
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	7,119	6,913	7,066
Consumer & Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,965	6,705	6,856
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	154	208	210
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	77,311	71,721	64,780
Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	74,817	71,721	60,441
Leases [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,494	0	4,339
Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 0	$ 0	$ 0