Loans and Allowance for Loan Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,723,171	$ 10,779,685
Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,523,787	10,438,375
Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	80,394	165,736
Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	118,407	175,064
Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	583	376
Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,430,388	5,705,609
Loans, Excluding Acquired Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	405,470	465,516
Loans, Excluding Acquired Loans | Consumer | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	402,507	460,080
Loans, Excluding Acquired Loans | Consumer | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,963	5,436
Loans, Excluding Acquired Loans | Consumer | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	204,173	185,422
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	203,667	184,920
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	506	502
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	201,297	280,094
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	198,840	275,160
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,457	4,934
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,966,453	4,239,612
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,910,329	4,150,321
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	20,707	29,330
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	35,182	59,658
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	235	303
Loans, Excluding Acquired Loans | Real Estate | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,300,723	614,155
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,296,988	603,126
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,910	5,795
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,825	5,218
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	16
Loans, Excluding Acquired Loans | Real Estate | Construction | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,440,443	1,094,633
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,420,052	1,066,902
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,628	3,954
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	18,528	23,490
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	235	287
Loans, Excluding Acquired Loans | Real Estate | Single family residential | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,225,287	2,530,824
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,193,289	2,480,293
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,169	19,581
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	14,829	30,950
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real Estate | Other commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,939,423	973,519
Loans, Excluding Acquired Loans | Commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,904,826	882,442
Loans, Excluding Acquired Loans | Commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,432	74,278
Loans, Excluding Acquired Loans | Commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	26,165	16,592
Loans, Excluding Acquired Loans | Commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	73
Loans, Excluding Acquired Loans | Commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,774,909	825,217
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,742,002	736,377
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,357	74,254
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	24,550	14,402
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	50
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	164,514	148,302
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	162,824	146,065
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	75	24
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,615	2,190
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	23
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	119,042	26,962
Loans, Excluding Acquired Loans | Other | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	119,042	26,962
Loans, Excluding Acquired Loans | Other | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,292,783	5,074,076
Loans acquired | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,187,083	4,918,570
Loans acquired | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	51,255	62,128
Loans acquired | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	54,097	93,378
Loans acquired | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Loans acquired | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,658	51,467
Loans acquired | Consumer | Other consumer | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,380	50,625
Loans acquired | Consumer | Other consumer | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	21
Loans acquired | Consumer | Other consumer | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	278	821
Loans acquired | Consumer | Other consumer | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Consumer | Other consumer | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,844,472	3,818,037
Loans acquired | Real Estate | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,768,761	3,712,847
Loans acquired | Real Estate | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	38,839	48,206
Loans acquired | Real Estate | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	36,524	56,984
Loans acquired | Real Estate | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Loans acquired | Real Estate | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	429,605	637,032
Loans acquired | Real Estate | Construction | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	393,122	604,796
Loans acquired | Real Estate | Construction | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	27,621	30,524
Loans acquired | Real Estate | Construction | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,862	1,712
Loans acquired | Real Estate | Construction | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate | Construction | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	566,188	793,228
Loans acquired | Real Estate | Single family residential | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	553,460	770,954
Loans acquired | Real Estate | Single family residential | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,081	2,618
Loans acquired | Real Estate | Single family residential | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,299	19,656
Loans acquired | Real Estate | Single family residential | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	348	0
Loans acquired | Real Estate | Single family residential | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,848,679	2,387,777
Loans acquired | Real Estate | Other commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,822,179	2,337,097
Loans acquired | Real Estate | Other commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,137	15,064
Loans acquired | Real Estate | Other commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,363	35,616
Loans acquired | Real Estate | Other commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Real Estate | Other commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	432,653	1,062,163
Loans acquired | Commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	402,942	1,012,689
Loans acquired | Commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,416	13,901
Loans acquired | Commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,295	35,573
Loans acquired | Commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	430,914	995,587
Loans acquired | Commercial | Commercial | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	401,300	946,322
Loans acquired | Commercial | Commercial | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,416	13,901
Loans acquired | Commercial | Commercial | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,198	35,364
Loans acquired | Commercial | Commercial | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Commercial | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,739	66,576
Loans acquired | Commercial | Agricultural | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,642	66,367
Loans acquired | Commercial | Agricultural | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Agricultural | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	97	209
Loans acquired | Commercial | Agricultural | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Commercial | Agricultural | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Loans acquired | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 0	142,409
Loans acquired | Other | Risk Rate 1-4
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		142,409
Loans acquired | Other | Risk Rate 5
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Loans acquired | Other | Risk Rate 6
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Loans acquired | Other | Risk Rate 7
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		0
Loans acquired | Other | Risk Rate 8
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 0