Loans & Leases and Allowance for Credit Losses, Aging Analysis of Loan & Lease Portfolio by the Time Past Due (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	$ 0	$ 0	$ 0
Nonaccrual	0	0	4
Total Past Due	355	645	23
Current	2,416,247	2,214,650	2,216,756
Total Loans & Leases	2,416,602	2,215,295	2,216,779
30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	355	645	16
60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	3
Commercial Real Estate [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	767,410	684,961	683,037
Total Loans & Leases	767,410	684,961	683,037
Commercial Real Estate [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Agricultural Real Estate [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	553,608	499,231	470,738
Total Loans & Leases	553,608	499,231	470,738
Agricultural Real Estate [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Agricultural Real Estate [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Real Estate Construction [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	0	0
Current	92,521	100,206	162,167
Total Loans & Leases	92,521	100,206	162,167
Real Estate Construction [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Real Estate Construction [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Residential 1st Mortgages [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	167	448	0
Current	263,382	260,303	257,920
Total Loans & Leases	263,549	260,751	257,920
Residential 1st Mortgages [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	167	448	0
Residential 1st Mortgages [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Home Equity Lines & Loans [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	0	10	0
Current	38,490	34,515	33,350
Total Loans & Leases	38,490	34,525	33,350
Home Equity Lines & Loans [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	10	0
Home Equity Lines & Loans [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Agricultural [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	150	0	0
Current	287,671	273,582	259,127
Total Loans & Leases	287,821	273,582	259,127
Agricultural [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	150	0	0
Agricultural [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Commercial [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual	0	0	0
Total Past Due	21	180	3
Current	304,312	265,523	257,948
Total Loans & Leases	304,333	265,703	257,951
Commercial [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	21	180	0
Commercial [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	3
Consumer & Other [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual		0	4
Total Past Due	17	7	20
Current	7,706	6,649	7,292
Total Loans & Leases	7,723	6,656	7,312
Consumer & Other [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	17	7	16
Consumer & Other [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Leases [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0	0
Nonaccrual		0	0
Total Past Due	0	0	0
Current	101,147	89,680	85,177
Total Loans & Leases	101,147	89,680	85,177
Leases [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0	0
Leases [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	$ 0	$ 0	$ 0