Loans & Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	$ 2,221,250	$ 2,183,265
Less: Unearned Income	5,955	5,664
Total Loans & Leases	2,215,295	2,177,601
Less: Allowance for Credit Losses	50,342	47,919	$ 41,523
Loans & Leases, Net	2,164,953	2,129,682
Collateral on borrowing lines	618,400
Federal Home Loan Bank [Member]
Loans and Leases Receivable Disclosure [Line Items]
Collateral on borrowing lines	618,400
Maximum borrowing capacity	521,200
Federal Reserve Bank [Member]
Loans and Leases Receivable Disclosure [Line Items]
Collateral on borrowing lines	568,600
Maximum borrowing capacity	381,400
Commercial Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	691,639	674,445
Total Loans & Leases	684,961	668,046
Less: Allowance for Credit Losses	10,922	11,110	10,063
Agricultural Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	499,231	467,685
Total Loans & Leases	499,231	467,685
Less: Allowance for Credit Losses	12,085	9,450	6,881
Real Estate Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	100,206	176,462
Total Loans & Leases	100,206	176,462
Less: Allowance for Credit Losses	1,846	3,223	2,485
Residential 1st Mortgages [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	260,751	242,247
Total Loans & Leases	260,751	242,247
Less: Allowance for Credit Losses	815	865	789
Home Equity Lines and Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	34,525	31,625
Total Loans & Leases	34,525	31,625
Less: Allowance for Credit Losses	2,324	2,140	2,146
Agricultural [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	273,582	295,325
Total Loans & Leases	273,582	295,325
Less: Allowance for Credit Losses	8,159	7,381	6,308
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	265,703	217,577
Total Loans & Leases	265,703	217,577
Less: Allowance for Credit Losses	9,197	8,515	7,836
Consumer & Other [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	6,656	6,913
Total Loans & Leases	6,656	6,913
Less: Allowance for Credit Losses	209	200	175
Leases [Member]
Loans and Leases Receivable Disclosure [Line Items]
Total Gross Loans & Leases	88,957	70,986
Total Loans & Leases	89,680	71,721
Less: Allowance for Credit Losses	$ 3,363	$ 3,586	$ 3,294