Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 167,713	$ 93,330
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,624	2,087
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	253	382
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,371	1,705
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	115,313	49,566
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	3,806	5,289
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	31,080	27,695
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	80,427	16,582
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	50,776	41,677
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	50,239	40,924
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 537	$ 753