Loans & Leases and Allowance for Credit Losses, Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 2,235,083	$ 2,215,295	$ 2,146,032
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,188,179	2,170,292	2,108,941
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	38,708	36,123	32,518
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	8,196	8,880	4,573
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	698,349	684,961	676,527
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	691,537	677,636	668,243
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,812	6,843	6,768
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	482	1,516
Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	508,400	499,231	463,645
Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	495,936	488,672	461,318
Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	8,537	6,529	1,351
Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	3,927	4,030	976
Real Estate Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	96,315	100,206	164,791
Real Estate Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	86,779	90,728	156,426
Real Estate Construction [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	9,536	9,478	8,365
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	264,137	260,751	249,628
Residential 1st Mortgages [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	263,101	259,795	249,238
Residential 1st Mortgages [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	0	41	45
Residential 1st Mortgages [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	1,036	915	345
Home Equity Lines & Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	34,691	34,525	31,817
Home Equity Lines & Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	34,643	34,476	31,752
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	48	49	65
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	261,427	273,582	266,010
Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	252,553	264,425	255,390
Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,286	6,439	9,857
Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,588	2,718	763
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	274,682	265,703	209,184
Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	268,745	260,565	204,792
Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	5,460	4,610	3,638
Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	477	528	754
Consumer & Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,685	6,656	7,119
Consumer & Other [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	6,565	6,498	6,965
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	120	158	154
Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	90,397	89,680	77,311
Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	88,320	87,497	74,817
Leases [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	2,077	2,183	2,494
Leases [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans & leases	$ 0	$ 0	$ 0