Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,127,013	$ 11,723,171
Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	49,750	36,687
Current	9,212,747	8,393,701
Total Loans	9,262,497	8,430,388
90 Days Past Due & Accruing	267	224
Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	27,089	21,917
90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	22,661	14,770
Consumer | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,639	6,699
Current	390,725	398,771
Total Loans	395,364	405,470
90 Days Past Due & Accruing	232	213
Consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	3,504	5,297
Consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	1,135	1,402
Consumer | Credit cards | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	1,260	1,539
Current	186,659	202,634
Total Loans	187,919	204,173
90 Days Past Due & Accruing	230	209
Consumer | Credit cards | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	704	1,033
Consumer | Credit cards | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	556	506
Consumer | Other consumer | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	3,379	5,160
Current	204,066	196,137
Total Loans	207,445	201,297
90 Days Past Due & Accruing	2	4
Consumer | Other consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	2,800	4,264
Consumer | Other consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	579	896
Real Estate | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	29,829	18,889
Current	6,486,321	5,947,564
Total Loans	6,516,150	5,966,453
90 Days Past Due & Accruing	17	0
Real Estate | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	16,979	11,681
Real Estate | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	12,850	7,208
Real Estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	5,020	841
Current	1,535,332	1,299,882
Total Loans	1,540,352	1,300,723
90 Days Past Due & Accruing	0	0
Real Estate | Construction | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,031	533
Real Estate | Construction | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	989	308
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	15,730	11,896
Current	1,428,795	1,428,547
Total Loans	1,444,525	1,440,443
90 Days Past Due & Accruing	17	0
Real Estate | Single family residential | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	8,976	7,769
Real Estate | Single family residential | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	6,754	4,127
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	9,079	6,152
Current	3,522,194	3,219,135
Total Loans	3,531,273	3,225,287
90 Days Past Due & Accruing	0	0
Real Estate | Other commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	3,972	3,379
Real Estate | Other commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	5,107	2,773
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	15,282	11,099
Current	2,048,335	1,928,324
Total Loans	2,063,617	1,939,423
90 Days Past Due & Accruing	18	11
Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	6,606	4,939
Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	8,676	6,160
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	14,142	9,577
Current	1,857,553	1,765,332
Total Loans	1,871,695	1,774,909
90 Days Past Due & Accruing	18	11
Commercial | Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	6,364	4,472
Commercial | Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	7,778	5,105
Commercial | Agricultural | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	1,140	1,522
Current	190,782	162,992
Total Loans	191,922	164,514
90 Days Past Due & Accruing	0	0
Commercial | Agricultural | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	242	467
Commercial | Agricultural | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	898	1,055
Other | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	287,366	119,042
Total Loans	287,366	119,042
90 Days Past Due & Accruing	0	$ 0
Other | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	0
Other | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0