Loans and Allowance for Loan Losses - Loans by Credit Risk Rating, Segregated by Class of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 11,365,895	$ 10,779,685
Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	11,114,152	10,438,375
Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	77,588	165,736
Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	173,525	175,064
Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	630	376
Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Other
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		26,962
Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans, Excluding Acquired Loans
Financing Receivable, Recorded Investment [Line Items]
Loans	7,133,461	5,705,609
Loans, Excluding Acquired Loans | Consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	457,682	465,516
Loans, Excluding Acquired Loans | Consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	453,314	460,080
Loans, Excluding Acquired Loans | Consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	4,368	5,436
Loans, Excluding Acquired Loans | Consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards
Financing Receivable, Recorded Investment [Line Items]
Loans	180,352	185,422
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	179,969	184,920
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	383	502
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Credit cards | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	277,330	280,094
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	273,345	275,160
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	3,985	4,934
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	5,098,927	4,239,612
Loans, Excluding Acquired Loans | Real estate | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	5,028,702	4,150,321
Loans, Excluding Acquired Loans | Real estate | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	12,645	29,330
Loans, Excluding Acquired Loans | Real estate | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	57,346	59,658
Loans, Excluding Acquired Loans | Real estate | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	234	303
Loans, Excluding Acquired Loans | Real estate | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	967,720	614,155
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	960,791	603,126
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	2,314	5,795
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	4,599	5,218
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	16	16
Loans, Excluding Acquired Loans | Real estate | Construction | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Single family residential
Financing Receivable, Recorded Investment [Line Items]
Loans	1,314,787	1,094,633
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,287,314	1,066,902
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	1,711	3,954
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	25,544	23,490
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	218	287
Loans, Excluding Acquired Loans | Real estate | Single family residential | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Other commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	2,816,420	2,530,824
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	2,780,597	2,480,293
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	8,620	19,581
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	27,203	30,950
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Real estate | Other commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,424,916	973,519
Loans, Excluding Acquired Loans | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,383,781	882,442
Loans, Excluding Acquired Loans | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	12,958	74,278
Loans, Excluding Acquired Loans | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	28,154	16,592
Loans, Excluding Acquired Loans | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	23	73
Loans, Excluding Acquired Loans | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,237,910	825,217
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	1,199,553	736,377
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	12,803	74,254
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	25,554	14,402
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	50
Loans, Excluding Acquired Loans | Commercial | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	134
Loans, Excluding Acquired Loans | Commercial | Agricultural
Financing Receivable, Recorded Investment [Line Items]
Loans	187,006	148,302
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	184,228	146,065
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	155	24
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	2,600	2,190
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	23	23
Loans, Excluding Acquired Loans | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans, Excluding Acquired Loans | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	151,936	26,962
Loans, Excluding Acquired Loans | Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	151,936
Loans, Excluding Acquired Loans | Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans, Excluding Acquired Loans | Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0
Loans Acquired
Financing Receivable, Recorded Investment [Line Items]
Loans	4,232,434	5,074,076
Loans Acquired | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	4,096,419	4,918,570
Loans Acquired | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	51,985	62,128
Loans Acquired | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	83,657	93,378
Loans Acquired | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	373	0
Loans Acquired | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	31,651	51,467
Loans Acquired | Consumer | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	30,912	50,625
Loans Acquired | Consumer | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	10	21
Loans Acquired | Consumer | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	729	821
Loans Acquired | Consumer | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Consumer | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate
Financing Receivable, Recorded Investment [Line Items]
Loans	3,433,501	3,818,037
Loans Acquired | Real estate | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	3,345,324	3,712,847
Loans Acquired | Real estate | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	32,931	48,206
Loans Acquired | Real estate | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	54,873	56,984
Loans Acquired | Real estate | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	373	0
Loans Acquired | Real estate | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Other consumer
Financing Receivable, Recorded Investment [Line Items]
Loans	2,240,578	2,387,777
Loans Acquired | Real estate | Other consumer | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	2,190,767	2,337,097
Loans Acquired | Real estate | Other consumer | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	11,345	15,064
Loans Acquired | Real estate | Other consumer | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	38,466	35,616
Loans Acquired | Real estate | Other consumer | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Other consumer | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans	521,321	637,032
Loans Acquired | Real estate | Construction | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	500,741	604,796
Loans Acquired | Real estate | Construction | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	19,624	30,524
Loans Acquired | Real estate | Construction | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	956	1,712
Loans Acquired | Real estate | Construction | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Construction | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment [Line Items]
Loans	671,602	793,228
Loans Acquired | Real estate | Single family residential | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	653,816	770,954
Loans Acquired | Real estate | Single family residential | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	1,962	2,618
Loans Acquired | Real estate | Single family residential | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	15,451	19,656
Loans Acquired | Real estate | Single family residential | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	373	0
Loans Acquired | Real estate | Single family residential | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Real estate | Other commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	2,240,578	2,387,777
Loans Acquired | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	767,282	1,062,163
Loans Acquired | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	720,183	1,012,689
Loans Acquired | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	19,044	13,901
Loans Acquired | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	28,055	35,573
Loans Acquired | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	764,473	995,587
Loans Acquired | Commercial | Commercial | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	717,441	946,322
Loans Acquired | Commercial | Commercial | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	19,044	13,901
Loans Acquired | Commercial | Commercial | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	27,988	35,364
Loans Acquired | Commercial | Commercial | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Commercial | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment [Line Items]
Loans	2,809	66,576
Loans Acquired | Commercial | Agricultural | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans	2,742	66,367
Loans Acquired | Commercial | Agricultural | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans	67	209
Loans Acquired | Commercial | Agricultural | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Commercial | Agricultural | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans	0	0
Loans Acquired | Other
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 0	142,409
Loans Acquired | Other | Risk Rate 1-4
Financing Receivable, Recorded Investment [Line Items]
Loans		142,409
Loans Acquired | Other | Risk Rate 5
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 6
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 7
Financing Receivable, Recorded Investment [Line Items]
Loans		0
Loans Acquired | Other | Risk Rate 8
Financing Receivable, Recorded Investment [Line Items]
Loans		$ 0