Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	$ 122,879	$ 93,330
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	1,520	2,087
Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	301	382
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	1,219	1,705
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	55,842	49,566
Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	3,625	5,289
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	28,062	27,695
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	24,155	16,582
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	65,517	41,677
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	65,244	40,924
Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans in nonaccrual status	$ 273	$ 753