Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 80,282	$ 122,879
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	876	1,520
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	282	301
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	594	1,219
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	50,308	55,842
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,737	3,625
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	29,553	28,062
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	19,018	24,155
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	29,098	65,517
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	28,649	65,244
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 449	$ 273