Loans - Schedule of Recorded Investment in Impaired Loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Dec. 31, 2018
Impaired Financing Receivable, Unpaid Principal Balance
Total Recorded Investment	$ 43,500,000
Related Allowance	0
Average Recorded Investment		$ 64,700,000
Accounts Receivable, Allowance for Credit Loss	122,300,000	144,300,000	$ 73,000,000.0	$ 144,300,000	$ 73,000,000.0
Provision charged (credited) to operating expense	(14,600,000)	56,900,000	13,900,000
Less loans charged-off			(23,600,000)
Add back recoveries of loans previously charged-off			9,700,000
Loans and Leases Receivable, Collateral for Secured Borrowings	11,700,000	17,500,000
Individually evaluated for impairment			3,600,000
Collectively evaluated for impairment			69,400,000
Loans and Leases Receivable, Allowance	122,300,000	144,300,000	73,000,000.0
Individually evaluated for impairment			64,700,000
Collectively evaluated for impairment			8,871,500,000
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			8,936,200,000
Impaired Financing Receivable, Interest Income, Accrual Method	0	300,000
Loans and Leases Receivable, Allowance	9,331,700,000	9,807,500,000
Accounts and Financing Receivable, after Allowance for Credit Loss, Noncurrent	100,000
Business Assets Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	3,000,000.0	7,400,000
Real Property Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	8,700,000	8,600,000
Other Property
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	0	1,500,000
Real Estate
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			28,900,000		31,000,000.0
Provision charged (credited) to operating expense			(1,300,000)
Less loans charged-off			(3,500,000)
Add back recoveries of loans previously charged-off			2,700,000
Individually evaluated for impairment			1,700,000
Collectively evaluated for impairment			27,200,000
Loans and Leases Receivable, Allowance			28,900,000
Individually evaluated for impairment			41,100,000
Collectively evaluated for impairment			5,897,100,000
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			5,938,200,000
Total consumer loans
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			9,900,000		8,700,000
Provision charged (credited) to operating expense			10,600,000
Less loans charged-off			(13,000,000.0)
Add back recoveries of loans previously charged-off			3,600,000
Individually evaluated for impairment			0
Collectively evaluated for impairment			9,900,000
Loans and Leases Receivable, Allowance			9,900,000
Individually evaluated for impairment			0
Collectively evaluated for impairment			1,045,200,000
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			1,045,200,000
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			32,600,000		31,300,000
Provision charged (credited) to operating expense			4,500,000
Less loans charged-off			(6,600,000)
Add back recoveries of loans previously charged-off			3,400,000
Individually evaluated for impairment			1,700,000
Collectively evaluated for impairment			30,900,000
Loans and Leases Receivable, Allowance			32,600,000
Individually evaluated for impairment			17,300,000
Collectively evaluated for impairment			1,656,400,000
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			1,673,700,000
Agriculture
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			1,600,000		2,000,000.0
Provision charged (credited) to operating expense			100,000
Less loans charged-off			(500,000)
Add back recoveries of loans previously charged-off			0
Individually evaluated for impairment			200,000
Collectively evaluated for impairment			1,400,000
Loans and Leases Receivable, Allowance			1,600,000
Individually evaluated for impairment			6,300,000
Collectively evaluated for impairment			272,800,000
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			279,100,000
Other Segments
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			0		$ 0
Provision charged (credited) to operating expense			0
Less loans charged-off			0
Add back recoveries of loans previously charged-off			0
Other
Impaired Financing Receivable, Unpaid Principal Balance
Individually evaluated for impairment			0
Collectively evaluated for impairment			0
Loans and Leases Receivable, Allowance			0
Individually evaluated for impairment			0
Collectively evaluated for impairment			0
Loans And Leases Receivable Held For Investment, Evaluated for Impairment			0
Commercial Real Estate Portfolio Segment [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		12,900,000
Recorded Investment With Allowance		10,800,000
Total Recorded Investment		23,700,000
Related Allowance		700,000
Accounts Receivable, Allowance for Credit Loss			19,500,000	54,800,000
Unpaid Total Principal Balance		29,200,000
Land Acquisition And Development Construction Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		400,000
Recorded Investment With Allowance		2,600,000
Total Recorded Investment		3,000,000.0
Related Allowance		500,000
Accounts Receivable, Allowance for Credit Loss			1,900,000	1,300,000
Unpaid Total Principal Balance		9,200,000
Financing Receivable, Originated in Current Fiscal Year	113,800,000	105,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	41,800,000	58,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	34,200,000	27,600,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	15,400,000	31,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	20,200,000	7,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	21,200,000	27,700,000
Financing Receivable, Revolving	1,200,000	6,400,000
Loans and Leases Receivable, Allowance	247,800,000	265,000,000.0
Residential Real Estate Construction Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		0
Recorded Investment With Allowance		0
Total Recorded Investment		0
Related Allowance		0
Accounts Receivable, Allowance for Credit Loss			1,500,000	1,600,000
Unpaid Total Principal Balance		100,000
Financing Receivable, Originated in Current Fiscal Year	112,400,000	80,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	7,400,000	64,700,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	13,700,000	16,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	900,000	5,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	400,000	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	100,000
Financing Receivable, Revolving	127,200,000	83,200,000
Loans and Leases Receivable, Allowance	262,000,000.0	250,900,000
Commercial Real Estate Construction [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		500,000
Recorded Investment With Allowance		0
Total Recorded Investment		500,000
Related Allowance		100,000
Accounts Receivable, Allowance for Credit Loss			2,700,000	7,300,000
Unpaid Total Principal Balance		1,000,000.0
Financing Receivable, Originated in Current Fiscal Year	209,700,000	236,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	141,400,000	195,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	118,800,000	62,700,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	27,600,000	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	6,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	500,000	200,000
Financing Receivable, Revolving	0	11,600,000
Loans and Leases Receivable, Allowance	498,000,000.0	523,500,000
Real Estate Construction Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		900,000
Recorded Investment With Allowance		2,600,000
Total Recorded Investment		3,500,000
Related Allowance		600,000
Unpaid Total Principal Balance		10,300,000
Agricultural Real Estate Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		5,200,000
Recorded Investment With Allowance		3,000,000.0
Total Recorded Investment		8,200,000
Related Allowance		200,000
Accounts Receivable, Allowance for Credit Loss			500,000	2,700,000
Unpaid Total Principal Balance		8,600,000
Financing Receivable, Originated in Current Fiscal Year	62,400,000	54,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	38,600,000	58,200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	37,300,000	32,600,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	23,300,000	19,600,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	13,200,000	17,000,000.0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	33,300,000	32,600,000
Financing Receivable, Revolving	5,800,000	6,400,000
Loans and Leases Receivable, Allowance	213,900,000	220,600,000
Real Estate Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		22,900,000
Recorded Investment With Allowance		18,200,000
Total Recorded Investment		41,100,000
Related Allowance		1,700,000
Average Recorded Investment		41,400,000
Accounts Receivable, Allowance for Credit Loss			28,900,000	80,500,000
Loans and Leases Receivable, Collateral for Secured Borrowings	8,200,000	8,900,000
Unpaid Total Principal Balance		55,000,000.0
Impaired Financing Receivable, Interest Income, Accrual Method		100,000
Real Estate Financing Receivable [Member] | Business Assets Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	1,200,000	1,300,000
Real Estate Financing Receivable [Member] | Real Property Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	7,000,000.0	6,500,000
Real Estate Financing Receivable [Member] | Other Property
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	0	1,100,000
Agricultural Financing Receivable [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		2,300,000
Recorded Investment With Allowance		4,000,000.0
Total Recorded Investment		6,300,000
Related Allowance		200,000
Accounts Receivable, Allowance for Credit Loss			1,600,000	700,000
Loans and Leases Receivable, Collateral for Secured Borrowings	700,000	800,000
Unpaid Total Principal Balance		6,900,000
Agricultural Financing Receivable [Member] | Business Assets Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	0	0
Agricultural Financing Receivable [Member] | Real Property Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	700,000	800,000
Agricultural Financing Receivable [Member] | Other Property
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	0	0
Residential Real Estate
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		3,900,000
Recorded Investment With Allowance		1,800,000
Total Recorded Investment		5,700,000
Related Allowance		200,000
Accounts Receivable, Allowance for Credit Loss			2,800,000	12,800,000
Unpaid Total Principal Balance		6,900,000
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		12,000,000.0
Recorded Investment With Allowance		5,300,000
Total Recorded Investment		17,300,000
Related Allowance		1,700,000
Average Recorded Investment		18,700,000
Accounts Receivable, Allowance for Credit Loss			32,600,000	39,200,000
Loans and Leases Receivable, Collateral for Secured Borrowings	2,800,000	7,800,000
Unpaid Total Principal Balance		25,500,000
Impaired Financing Receivable, Interest Income, Accrual Method		200,000
Commercial Portfolio Segment [Member] | Business Assets Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	1,800,000	6,100,000
Commercial Portfolio Segment [Member] | Real Property Pledged as Collateral
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	1,000,000.0	1,300,000
Commercial Portfolio Segment [Member] | Other Property
Impaired Financing Receivable, Unpaid Principal Balance
Loans and Leases Receivable, Collateral for Secured Borrowings	0	400,000
Loans held for investment
Impaired Financing Receivable, Unpaid Principal Balance
Recorded Investment With No Allowance		37,200,000
Recorded Investment With Allowance		27,500,000
Total Recorded Investment		64,700,000
Related Allowance		3,600,000
Unpaid Total Principal Balance		87,400,000
Home Equity Loan
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			1,000,000.0	1,400,000
Financing Receivable, Originated in Current Fiscal Year	11,400,000	12,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	7,000,000.0	7,300,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	4,000,000.0	7,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	4,800,000	9,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	4,200,000	4,800,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	12,500,000	14,800,000
Financing Receivable, Revolving	350,700,000	328,200,000
Loans and Leases Receivable, Allowance	394,600,000	384,000,000.0
Home Equity Loan | Performing Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	11,100,000	12,000,000.0
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	7,000,000.0	7,100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	3,700,000	7,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	4,800,000	9,700,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	3,600,000	4,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	12,000,000.0	14,400,000
Financing Receivable, Revolving	350,700,000	328,100,000
Loans and Leases Receivable, Allowance	392,900,000	383,100,000
Home Equity Loan | Nonperforming Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	300,000	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	300,000	0
Financing Receivable, Originated Three Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	600,000	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	500,000	400,000
Financing Receivable, Revolving	0	100,000
Loans and Leases Receivable, Allowance	1,700,000	900,000
Indirect consumer
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			4,500,000	16,700,000
Financing Receivable, Originated in Current Fiscal Year	273,100,000	334,600,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	209,100,000	188,100,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	108,700,000	118,000,000.0
Financing Receivable, Originated Three Years before Latest Fiscal Year	64,200,000	74,000,000.0
Financing Receivable, Originated Four Years before Latest Fiscal Year	37,100,000	47,700,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	45,400,000	42,700,000
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Allowance	737,600,000	805,100,000
Indirect consumer | Performing Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	272,600,000	334,500,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	208,600,000	187,900,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	108,300,000	117,900,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	64,000,000.0	73,800,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	37,000,000.0	47,600,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	45,000,000.0	42,600,000
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Allowance	735,500,000	804,300,000
Indirect consumer | Nonperforming Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	500,000	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	500,000	200,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	400,000	100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	200,000	200,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	100,000	100,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	400,000	100,000
Financing Receivable, Revolving	0	0
Loans and Leases Receivable, Allowance	2,100,000	800,000
Other consumer
Impaired Financing Receivable, Unpaid Principal Balance
Accounts Receivable, Allowance for Credit Loss			$ 2,900,000	$ 4,600,000
Financing Receivable, Originated in Current Fiscal Year	42,600,000	47,200,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	27,900,000	29,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	15,000,000.0	28,200,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	13,400,000	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,800,000	5,300,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	7,600,000	8,600,000
Financing Receivable, Revolving	16,900,000	20,000,000.0
Loans and Leases Receivable, Allowance	129,200,000	150,600,000
Other consumer | Performing Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	42,500,000	47,100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	27,900,000	29,400,000
Financing Receivable, Originated Two Years before Latest Fiscal Year	15,000,000.0	28,100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	13,300,000	11,900,000
Financing Receivable, Originated Four Years before Latest Fiscal Year	5,800,000	5,300,000
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	7,600,000	8,600,000
Financing Receivable, Revolving	16,900,000	19,900,000
Loans and Leases Receivable, Allowance	129,000,000.0	150,300,000
Other consumer | Nonperforming Financial Instruments
Impaired Financing Receivable, Unpaid Principal Balance
Financing Receivable, Originated in Current Fiscal Year	100,000	100,000
Financing Receivable, Originated in Fiscal Year before Latest Fiscal Year	0	0
Financing Receivable, Originated Two Years before Latest Fiscal Year	0	100,000
Financing Receivable, Originated Three Years before Latest Fiscal Year	100,000	0
Financing Receivable, Originated Four Years before Latest Fiscal Year	0	0
Financing Receivable, Originated Five or More Years before Latest Fiscal Year	0	0
Financing Receivable, Revolving	0	100,000
Loans and Leases Receivable, Allowance	$ 200,000	300,000
Agricultural Sector
Impaired Financing Receivable, Unpaid Principal Balance
Average Recorded Investment		4,600,000
Impaired Financing Receivable, Interest Income, Accrual Method		$ 0