Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 114,856	$ 122,879
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,313	1,520
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	397	301
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	916	1,219
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	68,902	55,842
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	2,296	3,625
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	24,395	28,062
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	42,211	24,155
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	44,641	65,517
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	44,159	65,244
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 482	$ 273