Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 137,695	$ 93,989
Current	14,236,582	14,331,715
Total Loans	14,374,277	14,425,704
90 Days Past Due & Accruing	1,160	856
Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	79,617	57,289
90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	58,078	36,700
Consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	6,862	7,108
Current	449,604	446,889
Total Loans	456,466	453,997
90 Days Past Due & Accruing	115	259
Consumer | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	5,406	5,732
Consumer | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,456	1,376
Consumer | Credit cards
Financing Receivable, Past Due [Line Items]
Total Past Due	1,191	1,489
Current	187,405	203,313
Total Loans	188,596	204,802
90 Days Past Due & Accruing	115	259
Consumer | Credit cards | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	866	848
Consumer | Credit cards | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	325	641
Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	5,671	5,619
Current	262,199	243,576
Total Loans	267,870	249,195
90 Days Past Due & Accruing	0	0
Consumer | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	4,540	4,884
Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,131	735
Real Estate
Financing Receivable, Past Due [Line Items]
Total Past Due	88,405	61,072
Current	10,745,360	10,960,868
Total Loans	10,833,765	11,021,940
90 Days Past Due & Accruing	322	597
Real Estate | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	57,473	39,755
Real Estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	30,932	21,317
Real Estate | Construction and development
Financing Receivable, Past Due [Line Items]
Total Past Due	7,726	6,870
Current	2,016,392	2,241,803
Total Loans	2,024,118	2,248,673
90 Days Past Due & Accruing	0	0
Real Estate | Construction and development | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,713	5,792
Real Estate | Construction and development | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	5,013	1,078
Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Total Past Due	46,482	40,107
Current	2,297,061	2,374,646
Total Loans	2,343,543	2,414,753
90 Days Past Due & Accruing	321	597
Real Estate | Single family residential | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	31,236	26,318
Real Estate | Single family residential | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	15,246	13,789
Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	34,197	14,095
Current	6,431,907	6,344,419
Total Loans	6,466,104	6,358,514
90 Days Past Due & Accruing	1	0
Real Estate | Other commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	23,524	7,645
Real Estate | Other commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	10,673	6,450
Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	42,428	25,809
Current	2,463,579	2,616,835
Total Loans	2,506,007	2,642,644
90 Days Past Due & Accruing	723	0
Commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	16,738	11,802
Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	25,690	14,007
Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	41,491	24,130
Current	2,272,981	2,426,989
Total Loans	2,314,472	2,451,119
90 Days Past Due & Accruing	723	0
Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	16,361	10,579
Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	25,130	13,551
Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	937	1,679
Current	190,598	189,846
Total Loans	191,535	191,525
90 Days Past Due & Accruing	0	0
Commercial | Agricultural | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	377	1,223
Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	560	456
Other
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	578,039	307,123
Total Loans	578,039	307,123
90 Days Past Due & Accruing	0	$ 0
Other | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0
Other | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0