Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 14,425,260	$ 11,723,171
Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	61,252	36,687
Current	9,568,824	8,393,701
Total Loans	9,630,076	8,430,388
90 Days Past Due & Accruing	259	224
Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	34,049	21,917
90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27,203	14,770
Consumer | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,141	6,699
Current	390,607	398,771
Total Loans	396,748	405,470
90 Days Past Due & Accruing	259	213
Consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,905	5,297
Consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,236	1,402
Consumer | Credit cards | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,489	1,539
Current	203,313	202,634
Total Loans	204,802	204,173
90 Days Past Due & Accruing	259	209
Consumer | Credit cards | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	848	1,033
Consumer | Credit cards | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	641	506
Consumer | Other consumer | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,652	5,160
Current	187,294	196,137
Total Loans	191,946	201,297
90 Days Past Due & Accruing	0	4
Consumer | Other consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,057	4,264
Consumer | Other consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	595	896
Real Estate | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	36,027	18,889
Current	6,848,395	5,947,564
Total Loans	6,884,422	5,966,453
90 Days Past Due & Accruing	0	0
Real Estate | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	22,684	11,681
Real Estate | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,343	7,208
Real Estate | Construction and development | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,573	841
Current	1,755,321	1,299,882
Total Loans	1,760,894	1,300,723
90 Days Past Due & Accruing	0	0
Real Estate | Construction and development | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,968	533
Real Estate | Construction and development | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	605	308
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	22,183	11,896
Current	1,422,437	1,428,547
Total Loans	1,444,620	1,440,443
90 Days Past Due & Accruing	0	0
Real Estate | Single family residential | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,414	7,769
Real Estate | Single family residential | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,769	4,127
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,271	6,152
Current	3,670,637	3,219,135
Total Loans	3,678,908	3,225,287
90 Days Past Due & Accruing	0	0
Real Estate | Other commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,302	3,379
Real Estate | Other commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,969	2,773
Commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	19,084	11,099
Current	2,054,108	1,928,324
Total Loans	2,073,192	1,939,423
90 Days Past Due & Accruing	0	11
Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,460	4,939
Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,624	6,160
Commercial | Commercial | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	18,427	9,577
Current	1,891,369	1,765,332
Total Loans	1,909,796	1,774,909
90 Days Past Due & Accruing	0	11
Commercial | Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,253	4,472
Commercial | Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,174	5,105
Commercial | Agricultural | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	657	1,522
Current	162,739	162,992
Total Loans	163,396	164,514
90 Days Past Due & Accruing	0	0
Commercial | Agricultural | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	207	467
Commercial | Agricultural | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	450	1,055
Other | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0	0
Current	275,714	119,042
Total Loans	275,714	119,042
90 Days Past Due & Accruing	0	$ 0
Other | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	0
Other | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 0