Allowance for Credit Losses, Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings (Details) - USD ($) $ in Thousands	Sep. 30, 2021		Dec. 31, 2020		Sep. 30, 2020
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	$ 3,139,801		$ 3,099,592		$ 3,111,931
Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	3,102,315	[1]	3,071,556	[2]	3,082,975	[3]
Watch [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	954,400		958,200		947,400
Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	20,671		9,405		8,080
Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	16,815		18,631		20,876
Doubtful [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Loss [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Commercial Real Estate [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	1,114,149		958,980		871,623
Commercial Real Estate [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	1,098,929	[1]	946,621	[2]	861,874	[3]
Commercial Real Estate [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	7,371		7,849		5,239
Commercial Real Estate [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	7,849		4,510		4,510
Agricultural Real Estate [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	656,337		643,014		639,172
Agricultural Real Estate [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	646,486	[1]	631,043	[2]	624,859	[3]
Agricultural Real Estate [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	3,312		400		1,525
Agricultural Real Estate [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	6,539		11,571		12,788
Real Estate Construction [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	178,451		185,741		186,623
Real Estate Construction [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	178,451	[1]	185,741	[2]	186,623	[3]
Real Estate Construction [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Real Estate Construction [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Residential 1st Mortgages [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	309,728		299,379		293,489
Residential 1st Mortgages [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	308,960	[1]	298,689	[2]	292,792	[3]
Residential 1st Mortgages [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Residential 1st Mortgages [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	768		690		697
Home Equity Lines & Loans [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	31,664		34,239		35,875
Home Equity Lines & Loans [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	31,490	[1]	34,058	[2]	35,691	[3]
Home Equity Lines & Loans [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Home Equity Lines & Loans [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	174		181		184
Agricultural [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	235,085		264,372		252,031
Agricultural [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	233,493	[1]	263,781	[2]	251,108	[3]
Agricultural [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	1,018		96		0
Agricultural [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	574		495		923
Commercial [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	394,326		374,816		367,052
Commercial [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	384,660	[1]	373,038	[2]	364,465	[3]
Commercial [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	8,970		1,060		1,316
Commercial [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	696		718		1,271
Consumer & Other [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	129,665		235,529		359,697
Consumer & Other [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	129,450	[1]	235,063	[2]	359,194	[3]
Consumer & Other [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Consumer & Other [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	215		466		503
Leases [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	90,396		103,522		106,369
Leases [Member] | Pass [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	90,396	[1]	103,522	[2]	106,369	[3]
Leases [Member] | Special Mention [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	0		0		0
Leases [Member] | Substandard [Member]
Loan & Lease Portfolio Allocated by Management's Internal Risk Ratings [Abstract]
Loans & Leases	$ 0		$ 0		$ 0

[1] Includes "Watch" loans of $954.4 million.

[2] Includes "Watch" loans of $958.2 million.

[3] Includes "Watch" loans of $947.4 million.