Loans and Allowance for Credit Losses - Nonaccrual Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 131,383	$ 93,330
Consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	2,135	2,087
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	223	382
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	1,912	1,705
Real Estate
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	75,000	49,566
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	6,501	5,289
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	32,244	27,695
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	36,255	16,582
Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	54,248	41,677
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	53,538	40,924
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Loans in nonaccrual status	$ 710	$ 753