Loans and Allowance for Loan Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	$ 13,002,952	$ 11,723,171
Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	12,761,764	11,523,787
Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	95,017	80,394
Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	146,039	118,407
Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	132	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	9,643,365	8,430,388
Loans, Excluding Acquired Loans | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,108,572	1,939,423
Loans, Excluding Acquired Loans | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,050,446	1,904,826
Loans, Excluding Acquired Loans | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,489	8,432
Loans, Excluding Acquired Loans | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	47,637	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	1,894,819	1,774,909
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,837,374	1,742,002
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,420	8,357
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	47,025	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	213,753	164,514
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	213,072	162,824
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	69	75
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	612	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	6,792,021	5,966,453
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,699,168	5,910,329
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	37,732	20,707
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	55,117	35,182
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4	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	1,712,858	1,300,723
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,705,376	1,296,988
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,456	1,910
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,026	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	1,448,455	1,440,443
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,422,086	1,420,052
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,246	1,628
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	23,119	18,528
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	4	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	3,630,708	3,225,287
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,571,706	3,193,289
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	33,030	17,169
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	25,972	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	403,726	405,470
Loans, Excluding Acquired Loans | Consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	401,080	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	2,646	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	195,083	204,173
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	194,433	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	650	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	208,643	201,297
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	206,647	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	1,996	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	339,046	119,042
Loans, Excluding Acquired Loans | Other | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	339,046	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	3,359,587	3,292,783
Loans Acquired | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	3,272,024	3,187,083
Loans Acquired | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	46,796	51,255
Loans Acquired | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	40,639	54,097
Loans Acquired | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	350,693	432,653
Loans Acquired | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	342,189	402,942
Loans Acquired | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,491	12,416
Loans Acquired | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,013	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	349,821	430,914
Loans Acquired | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	341,385	401,300
Loans Acquired | Commercial | Commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,491	12,416
Loans Acquired | Commercial | Commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	6,945	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	872	1,739
Loans Acquired | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	804	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	68	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	3,001,463	2,844,472
Loans Acquired | Real Estate | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,922,550	2,768,761
Loans Acquired | Real Estate | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	45,305	38,839
Loans Acquired | Real Estate | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	33,480	36,524
Loans Acquired | Real Estate | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	362,000	429,605
Loans Acquired | Real Estate | Construction | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	344,075	393,122
Loans Acquired | Real Estate | Construction | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	17,874	27,621
Loans Acquired | Real Estate | Construction | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	51	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	504,490	566,188
Loans Acquired | Real Estate | Single family residential | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	492,826	553,460
Loans Acquired | Real Estate | Single family residential | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	1,224	2,081
Loans Acquired | Real Estate | Single family residential | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	10,312	10,299
Loans Acquired | Real Estate | Single family residential | Risk Rate 7
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	128	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	2,134,973	1,848,679
Loans Acquired | Real Estate | Other commercial | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	2,085,649	1,822,179
Loans Acquired | Real Estate | Other commercial | Risk Rate 5
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	26,207	9,137
Loans Acquired | Real Estate | Other commercial | Risk Rate 6
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	23,117	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	7,431	15,658
Loans Acquired | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Credit Quality Indicator [Line Items]
Loans	7,285	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	146	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