Loans - Schedule of Loans Renegotiated in Troubled Debt Restructurings (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) note	Dec. 31, 2019 USD ($) note	Dec. 31, 2018 USD ($) note
Loans and Leases Receivable, Troubled Debt Restructuring
Loans renegotiated in troubled debt restructurings	$ 14,500,000	$ 24,900,000
Loans renegotiated in troubled debt restructurings, non-accrual loans	11,300,000	19,400,000
Loans renegotiated in troubled debt restructurings, accrual loans	$ 3,200,000	$ 5,500,000
Number of notes under troubled debt restructurings | note	3	11	5
Charge-offs directly related to modified loans	$ 0	$ 0	$ 0
Financing Receivable, Troubled Debt Restructuring, Postmodification	300,000	10,400,000	$ 4,100,000
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance		$ 300,000
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend	0
Balance of notes for which there was a payment default	0
Impaired Financing Receivable, Recorded Investment	63,500,000
Financing Receivable, Allowance for Credit Loss, Noncurrent	$ 2,900,000
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings | note	3	4	3
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 300,000	$ 3,300,000	$ 3,600,000
Impaired Financing Receivable, Recorded Investment		23,700,000	16,300,000
Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Financing Receivable, Troubled Debt Restructuring, Postmodification			200,000
Impaired Financing Receivable, Recorded Investment		8,200,000	12,700,000
Real Estate Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Impaired Financing Receivable, Recorded Investment		$ 41,100,000	$ 41,800,000
Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings | note		1	1
Concessions in troubled debt restructurings, amount		$ 0
Financing Receivable, Troubled Debt Restructuring, Postmodification		5,000,000.0
Impaired Financing Receivable, Recorded Investment		17,300,000	$ 19,900,000
Real Estate Construction Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Impaired Financing Receivable, Recorded Investment		$ 3,500,000	5,100,000
Agricultural Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings | note		6
Concessions in troubled debt restructurings, amount		$ 0
Financing Receivable, Troubled Debt Restructuring, Postmodification		2,100,000
Impaired Financing Receivable, Recorded Investment		6,300,000	$ 3,100,000
522291 Consumer Lending
Loans and Leases Receivable, Troubled Debt Restructuring
Number of notes under troubled debt restructurings | note			1
Concessions in troubled debt restructurings, amount			$ 0
Financing Receivable, Troubled Debt Restructuring, Postmodification			300,000
Interest Only Period Concession
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		200,000	3,600,000
Financing Receivable, Troubled Debt Restructuring, Postmodification	200,000
Interest Only Period Concession | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount		200,000	3,600,000
Financing Receivable, Troubled Debt Restructuring, Postmodification	200,000
Extension of terms or maturity
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification	0	200,000	0
Extension of terms or maturity | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification	0	200,000	0
Extension of terms or maturity | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification			0
Extension of terms or maturity | Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		0
Extension of terms or maturity | Agricultural Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		0
Extension of terms or maturity | 522291 Consumer Lending
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification			0
Interest rate adjustment
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Financing Receivable, Troubled Debt Restructuring, Postmodification	0	0
Interest rate adjustment | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Financing Receivable, Troubled Debt Restructuring, Postmodification	0	0
Interest rate adjustment | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Interest rate adjustment | Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		0
Interest rate adjustment | Agricultural Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		0
Interest rate adjustment | 522291 Consumer Lending
Loans and Leases Receivable, Troubled Debt Restructuring
Concessions in troubled debt restructurings, amount			0
Other
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification	100,000	10,000,000.0	500,000
Other | Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 100,000	2,900,000	0
Other | Agricultural Real Estate Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification			200,000
Other | Commercial Portfolio Segment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		5,000,000.0
Other | Agricultural Financing Receivable [Member]
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification		$ 2,100,000
Other | 522291 Consumer Lending
Loans and Leases Receivable, Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring, Postmodification			$ 300,000