Allowance for Credit Losses, Aging Analysis of Loan & Lease Portfolio Including Unearned Income by the Time Past Due (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	$ 0	$ 0
Nonaccrual	495,000	0
Total Past Due	506,000	352,000
Current	3,099,086,000	2,672,675,000
Total Loans & Leases	3,099,592,000	2,673,027,000
Interest income forgone on nonaccrual loans	22,000	0	$ 0
30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	11,000	352,000
60-89 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	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	0	0
Current	958,980,000	838,570,000
Total Loans & Leases	958,980,000	838,570,000
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	0
Agricultural Real Estate [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
90 Days and Still Accruing	0	0
Nonaccrual	495,000	0
Total Past Due	495,000	0
Current	642,519,000	625,767,000
Total Loans & Leases	643,014,000	625,767,000
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	0	240,000
Current	185,741,000	115,404,000
Total Loans & Leases	185,741,000	115,644,000
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	240,000
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	0
Current	299,379,000	255,253,000
Total Loans & Leases	299,379,000	255,253,000
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	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
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	34,239,000	39,270,000
Total Loans & Leases	34,239,000	39,270,000
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	264,372,000	292,904,000
Total Loans & Leases	264,372,000	292,904,000
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	77,000
Current	374,816,000	384,718,000
Total Loans & Leases	374,816,000	384,795,000
Commercial [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	0	77,000
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	11,000	35,000
Current	235,518,000	15,387,000
Total Loans & Leases	235,529,000	15,422,000
Consumer & Other [Member] \| 30-59 Days Past Due [Member]
Aging Analysis of Loan & Lease Portfolio by Time Past Due [Abstract]
Total Past Due	11,000	35,000
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	103,522,000	105,402,000
Total Loans & Leases	103,522,000	105,402,000
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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Amount of financing receivable not past due.

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Amount of financing receivable on nonaccrual status.

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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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