Loans and Allowance for Credit Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 14,606,900	$ 14,425,704
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	398,372	453,997
Consumer | Credit cards
Loans and Leases Receivable Disclosure [Line Items]
Loans	184,348	204,802
Consumer | Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	214,024	249,195
Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	10,533,787	11,021,940
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,010,256	2,248,673
Real Estate | Single family residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,207,087	2,414,753
Real Estate | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	6,316,444	6,358,514
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,255,931	2,642,644
Commercial | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	3,038,216	2,451,119
Commercial | Agricultural
Loans and Leases Receivable Disclosure [Line Items]
Loans	217,715	191,525
Other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 418,810	$ 307,123