Loans and Allowance for Credit Losses - Loan Portfolio by Categories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 10,825,227	$ 12,900,897
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	358,376	391,224
Consumer | Credit cards
Loans and Leases Receivable Disclosure [Line Items]
Loans	175,884	188,845
Consumer | Other consumer
Loans and Leases Receivable Disclosure [Line Items]
Loans	182,492	202,379
Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Loans	8,079,343	9,223,791
Real Estate | Construction and development
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,229,740	1,596,255
Real Estate | Single family residential
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,540,701	1,880,673
Real Estate | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	5,308,902	5,746,863
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	2,038,640	2,750,291
Commercial | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Loans	1,821,905	2,574,386
Commercial | Agricultural
Loans and Leases Receivable Disclosure [Line Items]
Loans	216,735	175,905
Other
Loans and Leases Receivable Disclosure [Line Items]
Loans	$ 348,868	$ 535,591