Loans and Allowance for Credit Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 12,900,897	$ 14,425,704
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	391,224	454,496
Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	180,354	204,802
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	210,870	249,694
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,223,791	10,884,524
Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,596,255	2,236,861
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,880,673	2,442,064
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,746,863	6,205,599
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,750,291	2,810,970
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	2,574,386	2,495,516
Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	175,905	315,454
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 535,591	$ 275,714