Loans Held for Investment - Schedule of Contractual Aging of Loans by Portfolio (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Nonaccrual, Interest Income	$ 0	$ 0
Impaired Financing Receivable, Interest Income, Accrual Method	0		$ 0	$ 0	$ 0
Accrued interest reversal				0
Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	7,900,000			7,900,000		$ 2,700,000
Nonaccrual loans	29,700,000			29,700,000		8,000,000.0
Total Loans	7,857,700,000			7,857,700,000		3,971,500,000
Land acquisition & development
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	800,000			800,000		200,000
Nonaccrual loans	4,100,000			4,100,000		700,000
Total Loans	355,700,000			355,700,000		247,800,000
Residential construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,400,000			1,400,000		4,200,000
Nonaccrual loans	0			0		0
Total Loans	444,800,000			444,800,000		262,000,000.0
Commercial construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	10,700,000			10,700,000		0
Nonaccrual loans	0			0		0
Total Loans	959,000,000.0			959,000,000.0		498,000,000.0
Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	12,900,000			12,900,000		4,400,000
Nonaccrual loans	4,100,000			4,100,000		700,000
Total Loans	1,759,500,000			1,759,500,000		1,007,800,000
Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5,700,000			5,700,000		3,900,000
Nonaccrual loans	5,000,000.0			5,000,000.0		2,900,000
Total Loans	2,060,400,000			2,060,400,000		1,538,200,000
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,400,000			2,400,000		2,100,000
Nonaccrual loans	37,900,000			37,900,000		4,900,000
Total Loans	821,500,000			821,500,000		213,900,000
Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	28,900,000			28,900,000		13,100,000
Nonaccrual loans	76,700,000			76,700,000		16,500,000
Total Loans	12,499,100,000			12,499,100,000		6,731,400,000
Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6,900,000			6,900,000		6,900,000
Nonaccrual loans	1,800,000			1,800,000		1,700,000
Total Loans	733,900,000			733,900,000		737,600,000
Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	800,000			800,000		800,000
Nonaccrual loans	200,000			200,000		100,000
Total Loans	157,300,000			157,300,000		129,200,000
Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,100,000			1,100,000		1,300,000
Nonaccrual loans	0			0		0
Total Loans	74,800,000			74,800,000		64,900,000
Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8,800,000			8,800,000		9,000,000.0
Nonaccrual loans	2,000,000.0			2,000,000.0		1,800,000
Total Loans	966,000,000.0			966,000,000.0		931,700,000
Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	11,500,000			11,500,000		6,700,000
Nonaccrual loans	13,900,000			13,900,000		5,000,000.0
Total Loans	3,036,000,000			3,036,000,000		1,475,500,000
Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	10,100,000			10,100,000		700,000
Nonaccrual loans	14,400,000			14,400,000		1,600,000
Total Loans	672,000,000.0			672,000,000.0		203,900,000
Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process						0
Nonaccrual loans						0
Total Loans	0			0		1,500,000
Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	59,300,000			59,300,000		29,500,000
Nonaccrual loans	107,000,000.0			107,000,000.0		24,900,000
Total Loans	17,173,100,000			17,173,100,000		9,344,000,000
30 to 59 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5,100,000			5,100,000		1,100,000
30 to 59 Days Past Due | Land acquisition & development
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	700,000			700,000		200,000
30 to 59 Days Past Due | Residential construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,000,000.0			1,000,000.0		4,200,000
30 to 59 Days Past Due | Commercial construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	10,700,000			10,700,000		0
30 to 59 Days Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	12,400,000			12,400,000		4,400,000
30 to 59 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	3,200,000			3,200,000		3,000,000.0
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,100,000			2,100,000		1,900,000
30 to 59 Days Past Due | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	22,800,000			22,800,000		10,400,000
30 to 59 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	5,300,000			5,300,000		5,100,000
30 to 59 Days Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	600,000			600,000		500,000
30 to 59 Days Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	600,000			600,000		600,000
30 to 59 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	6,500,000			6,500,000		6,200,000
30 to 59 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8,400,000			8,400,000		4,900,000
30 to 59 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	10,000,000.0			10,000,000.0		700,000
30 to 59 Days Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process						0
30 to 59 Days Past Due | Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	47,700,000			47,700,000		22,200,000
60 to 89 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,100,000			2,100,000		1,000,000.0
60 to 89 Days Past Due | Land acquisition & development
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	100,000			100,000		0
60 to 89 Days Past Due | Residential construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	400,000			400,000		0
60 to 89 Days Past Due | Commercial construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
60 to 89 Days Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	500,000			500,000		0
60 to 89 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,100,000			2,100,000		800,000
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		200,000
60 to 89 Days Past Due | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	4,700,000			4,700,000		2,000,000.0
60 to 89 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,400,000			1,400,000		1,400,000
60 to 89 Days Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	200,000			200,000		200,000
60 to 89 Days Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	200,000			200,000		200,000
60 to 89 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,800,000			1,800,000		1,800,000
60 to 89 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,100,000			2,100,000		700,000
60 to 89 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	100,000			100,000		0
60 to 89 Days Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process						0
60 to 89 Days Past Due | Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	8,700,000			8,700,000		4,500,000
Equal to or Greater than 90 Days Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	700,000			700,000		600,000
Equal to or Greater than 90 Days Past Due | Land acquisition & development
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
Equal to or Greater than 90 Days Past Due | Residential construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
Equal to or Greater than 90 Days Past Due | Commercial construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
Equal to or Greater than 90 Days Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
Equal to or Greater than 90 Days Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	400,000			400,000		100,000
Equal to or Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	300,000			300,000		0
Equal to or Greater than 90 Days Past Due | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,400,000			1,400,000		700,000
Equal to or Greater than 90 Days Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	200,000			200,000		400,000
Equal to or Greater than 90 Days Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		100,000
Equal to or Greater than 90 Days Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	300,000			300,000		500,000
Equal to or Greater than 90 Days Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	500,000			500,000		1,000,000.0
Equal to or Greater than 90 Days Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,000,000.0			1,000,000.0		1,100,000
Equal to or Greater than 90 Days Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	0			0		0
Equal to or Greater than 90 Days Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process						0
Equal to or Greater than 90 Days Past Due | Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,900,000			2,900,000		2,800,000
Financial Asset, Not Past Due | Commercial real estate
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	7,820,100,000			7,820,100,000		3,960,800,000
Financial Asset, Not Past Due | Land acquisition & development
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	350,800,000			350,800,000		246,900,000
Financial Asset, Not Past Due | Residential construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	443,400,000			443,400,000		257,800,000
Financial Asset, Not Past Due | Commercial construction
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	948,300,000			948,300,000		498,000,000.0
Financial Asset, Not Past Due | Total construction loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	1,742,500,000			1,742,500,000		1,002,700,000
Financial Asset, Not Past Due | Residential
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	2,049,700,000			2,049,700,000		1,531,400,000
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	781,200,000			781,200,000		206,900,000
Financial Asset, Not Past Due | Total real estate loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	12,393,500,000			12,393,500,000		6,701,800,000
Financial Asset, Not Past Due | Indirect consumer
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	725,200,000			725,200,000		729,000,000.0
Financial Asset, Not Past Due | Direct and advance lines
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	156,300,000			156,300,000		128,300,000
Financial Asset, Not Past Due | Credit card
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	73,700,000			73,700,000		63,600,000
Financial Asset, Not Past Due | Total consumer loans
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	955,200,000			955,200,000		920,900,000
Financial Asset, Not Past Due | Commercial
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	3,010,600,000			3,010,600,000		1,463,800,000
Financial Asset, Not Past Due | Agricultural
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	647,500,000			647,500,000		201,600,000
Financial Asset, Not Past Due | Other, including overdrafts
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process						1,500,000
Financial Asset, Not Past Due | Loans And Leases Held For Investment [Member]
Loans and Leases Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Loan in Process	$ 17,006,800,000			$ 17,006,800,000		$ 9,289,600,000