Loans and Allowance for Loan Losses - Age Analysis of Past Due Loans, Excluding Loans Acquired, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,002,952	$ 11,723,171
Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	54,422	36,687
Current	9,588,943	8,393,701
Total Loans	9,643,365	8,430,388
90 Days Past Due & Accruing	155	224
Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	31,346	21,917
90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	23,076	14,770
Consumer | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	5,685	6,699
Current	398,041	398,771
Total Loans	403,726	405,470
90 Days Past Due & Accruing	144	213
Consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,341	5,297
Consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	1,344	1,402
Consumer | Credit cards | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	1,608	1,539
Current	193,475	202,634
Total Loans	195,083	204,173
90 Days Past Due & Accruing	130	209
Consumer | Credit cards | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	958	1,033
Consumer | Credit cards | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	650	506
Consumer | Other consumer | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,077	5,160
Current	204,566	196,137
Total Loans	208,643	201,297
90 Days Past Due & Accruing	14	4
Consumer | Other consumer | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	3,383	4,264
Consumer | Other consumer | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	694	896
Real Estate | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	32,114	18,889
Current	6,759,907	5,947,564
Total Loans	6,792,021	5,966,453
90 Days Past Due & Accruing	0	0
Real Estate | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	21,721	11,681
Real Estate | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	10,393	7,208
Real Estate | Construction | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,303	841
Current	1,708,555	1,299,882
Total Loans	1,712,858	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	3,690	533
Real Estate | Construction | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	613	308
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	16,417	11,896
Current	1,432,038	1,428,547
Total Loans	1,448,455	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
Financing Receivable, Past Due [Line Items]
Total Past Due	10,022	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	6,395	4,127
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	11,394	6,152
Current	3,619,314	3,219,135
Total Loans	3,630,708	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	8,009	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	3,385	2,773
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	16,623	11,099
Current	2,091,949	1,928,324
Total Loans	2,108,572	1,939,423
90 Days Past Due & Accruing	11	11
Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	5,284	4,939
Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	11,339	6,160
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	15,989	9,577
Current	1,878,830	1,765,332
Total Loans	1,894,819	1,774,909
90 Days Past Due & Accruing	11	11
Commercial | Commercial | Gross 30-89 Days Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	4,999	4,472
Commercial | Commercial | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	10,990	5,105
Commercial | Agricultural | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	634	1,522
Current	213,119	162,992
Total Loans	213,753	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	285	467
Commercial | Agricultural | 90 Days or More Past Due | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	349	1,055
Other | Loans, Excluding Acquired Loans
Financing Receivable, Past Due [Line Items]
Total Past Due	0	0
Current	339,046	119,042
Total Loans	339,046	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