Allowance for Credit Losses, Aging Analysis of Loan Portfolio by the Time Past Due (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	$ 0	$ 0
Nonaccrual	0	0
Total Past Due	352	1,438
Current	2,672,675	2,569,803
Total Loans & Leases	2,673,027	2,571,241
Interest income forgone on nonaccrual loans	0	0	$ 0
30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	352	707
60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	731
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	0	731
Current	838,570	825,818
Total Loans & Leases	838,570	826,549
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	0	731
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	625,767	584,625
Total Loans & Leases	625,767	584,625
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	240	327
Current	115,404	98,241
Total Loans & Leases	115,644	98,568
Real Estate Construction [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	240	327
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	0	367
Current	255,253	259,369
Total Loans & Leases	255,253	259,736
Residential 1st Mortgages [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	367
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	0
Current	39,270	40,789
Total Loans & Leases	39,270	40,789
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	0
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	292,904	290,463
Total Loans & Leases	292,904	290,463
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	77	0
Current	384,718	343,834
Total Loans & Leases	384,795	343,834
Commercial [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	77	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
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	35	13
Current	15,387	19,399
Total Loans & Leases	15,422	19,412
Consumer & Other [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	35	13
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	105,402	107,265
Total Loans & Leases	105,402	107,265
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

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Amount of financing receivable 90 days or more past due and still accruing.

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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