Loans and Allowance for Loan Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 14,374,277	$ 14,425,704
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	456,466	453,997
Consumer | Credit cards
Loans and Leases Receivable Disclosure [Line Items]
Loans	188,596	204,802
Consumer | Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	267,870	249,195
Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	10,833,765	11,021,940
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,024,118	2,248,673
Real Estate | Single family residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,343,543	2,414,753
Real Estate | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	6,466,104	6,358,514
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,506,007	2,642,644
Commercial | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,314,472	2,451,119
Commercial | Agricultural
Loans and Leases Receivable Disclosure [Line Items]
Loans	191,535	191,525
Other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 578,039	$ 307,123