Loans & Leases and Allowance for Credit Losses, Loan Portfolio Allocated by Management's Internal Risk Ratings (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 2,079,670	$ 1,996,359	$ 1,910,270
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,054,256	1,972,059	1,883,570
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	18,627	18,169	20,667
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,787	6,131	6,033
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	627,114	603,650	558,743
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	618,975	595,011	550,011
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	7,141	7,917	8,038
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	998	722	694
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	439,972	424,034	432,610
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	437,059	424,034	432,610
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,418	0	0
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,495	0	0
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	175,045	151,974	161,762
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	173,556	150,379	160,133
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,489	1,595	1,629
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	238,376	206,405	196,893
Residential 1st Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	237,254	205,135	195,477
Residential 1st Mortgages [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	404	413	733
Residential 1st Mortgages [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	718	857	683
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	32,513	33,056	31,833
Home Equity Lines & Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	32,408	32,419	31,149
Home Equity Lines & Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	75	78
Home Equity Lines & Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	105	562	606
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	274,704	293,966	249,783
Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	273,184	293,325	249,116
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,070	9	437
Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	450	632	230
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	214,086	210,804	210,491
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	204,119	199,467	197,193
Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	7,105	8,160	9,752
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,862	3,177	3,546
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,975	6,592	6,735
Consumer & Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,816	6,411	6,461
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	159	181	274
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	70,885	65,878	61,420
Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	70,885	65,878	61,420
Leases [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	0	0
Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 0	$ 0	$ 0