Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 59,054	$ 122,879
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	781	1,520
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	390	301
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	391	1,219
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	41,236	55,842
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	2,330	3,625
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	21,068	28,062
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	17,838	24,155
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	17,037	65,517
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	16,532	65,244
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 505	$ 273