Allowance for Credit Losses, Aging Analysis of Loan Portfolio by the Time Past Due (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	$ 0	$ 0
Nonaccrual	0	0
Total Past Due	1,438	645
Current	2,569,803	2,214,650
Total Loans & Leases	2,571,241	2,215,295
Interest income forgone on nonaccrual loans	0	0	$ 127
30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	707	645
60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	731	0
Commercial Real Estate [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	731	0
Current	825,818	684,961
Total Loans & Leases	826,549	684,961
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
Commercial Real Estate [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	731	0
Agricultural Real Estate [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	584,625	499,231
Total Loans & Leases	584,625	499,231
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
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
Real Estate Construction [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	327	0
Current	98,241	100,206
Total Loans & Leases	98,568	100,206
Real Estate Construction [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	327	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
Residential 1st Mortgages [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	367	448
Current	259,369	260,303
Total Loans & Leases	259,736	260,751
Residential 1st Mortgages [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	367	448
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
Home Equity Lines and Loans [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	10
Current	40,789	34,515
Total Loans & Leases	40,789	34,525
Home Equity Lines and Loans [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	10
Home Equity Lines and Loans [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0
Agricultural [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	290,463	273,582
Total Loans & Leases	290,463	273,582
Agricultural [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	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
Commercial [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	180
Current	343,834	265,523
Total Loans & Leases	343,834	265,703
Commercial [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	180
Commercial [Member] | 60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	0
Consumer & Other [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	13	7
Current	19,399	6,649
Total Loans & Leases	19,412	6,656
Consumer & Other [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	13	7
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
Leases [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	0	0
Total Past Due	0	0
Current	107,265	89,680
Total Loans & Leases	107,265	89,680
Leases [Member] | 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	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