Loans and Allowance for Loan Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 13,127,013	$ 11,723,171
Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,863,999	11,523,787
Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	90,248	80,394
Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	172,215	118,407
Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	551	583
Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,262,497	8,430,388
Loans, Excluding Acquired Loans | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,063,617	1,939,423
Loans, Excluding Acquired Loans | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,011,472	1,904,826
Loans, Excluding Acquired Loans | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,423	8,432
Loans, Excluding Acquired Loans | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	42,722	26,165
Loans, Excluding Acquired Loans | Commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,871,695	1,774,909
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,821,027	1,742,002
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,349	8,357
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	41,319	24,550
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	191,922	164,514
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	190,445	162,824
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	74	75
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,403	1,615
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,516,150	5,966,453
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,444,730	5,910,329
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	24,294	20,707
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	46,899	35,182
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	227	235
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,540,352	1,300,723
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,536,632	1,296,988
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	477	1,910
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,243	1,825
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,444,525	1,440,443
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,420,143	1,420,052
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,674	1,628
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	21,481	18,528
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	227	235
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,531,273	3,225,287
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,487,955	3,193,289
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	21,143	17,169
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	22,175	14,829
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	395,364	405,470
Loans, Excluding Acquired Loans | Consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	392,779	402,507
Loans, Excluding Acquired Loans | Consumer | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,585	2,963
Loans, Excluding Acquired Loans | Consumer | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	187,919	204,173
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	187,363	203,667
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	556	506
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	207,445	201,297
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	205,416	198,840
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,029	2,457
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	287,366	119,042
Loans, Excluding Acquired Loans | Other | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	287,366	119,042
Loans, Excluding Acquired Loans | Other | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,864,516	3,292,783
Loans Acquired | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,727,652	3,187,083
Loans Acquired | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	56,531	51,255
Loans Acquired | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	80,009	54,097
Loans Acquired | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Loans Acquired | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	412,660	432,653
Loans Acquired | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	395,457	402,942
Loans Acquired | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,537	12,416
Loans Acquired | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	15,666	17,295
Loans Acquired | Commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	411,577	430,914
Loans Acquired | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	394,439	401,300
Loans Acquired | Commercial | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,537	12,416
Loans Acquired | Commercial | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	15,601	17,198
Loans Acquired | Commercial | Commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,083	1,739
Loans Acquired | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,018	1,642
Loans Acquired | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	65	97
Loans Acquired | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,442,152	2,844,472
Loans Acquired | Real Estate | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,322,663	2,768,761
Loans Acquired | Real Estate | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	54,994	38,839
Loans Acquired | Real Estate | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	64,171	36,524
Loans Acquired | Real Estate | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Loans Acquired | Real Estate | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	426,482	429,605
Loans Acquired | Real Estate | Construction | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	400,925	393,122
Loans Acquired | Real Estate | Construction | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	17,928	27,621
Loans Acquired | Real Estate | Construction | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,629	8,862
Loans Acquired | Real Estate | Construction | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate | Construction | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate | Single family residential
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	554,534	566,188
Loans Acquired | Real Estate | Single family residential | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	539,716	553,460
Loans Acquired | Real Estate | Single family residential | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,833	2,081
Loans Acquired | Real Estate | Single family residential | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,661	10,299
Loans Acquired | Real Estate | Single family residential | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	324	348
Loans Acquired | Real Estate | Single family residential | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,461,136	1,848,679
Loans Acquired | Real Estate | Other commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,382,022	1,822,179
Loans Acquired | Real Estate | Other commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	35,233	9,137
Loans Acquired | Real Estate | Other commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	43,881	17,363
Loans Acquired | Real Estate | Other commercial | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Real Estate | Other commercial | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,704	15,658
Loans Acquired | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	9,532	15,380
Loans Acquired | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	172	278
Loans Acquired | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 0	$ 0