Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,858,195	$ 10,779,685
Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans		26,962
Loans Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	21,329	47,684
Current	3,713,592	5,026,392
Total Loans	3,734,921	5,074,076
90 Days Past Due & Accruing	1	3,145
Loans Acquired | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,778	35,988
Loans Acquired | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14,551	11,696
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	427	1,149
Current	20,851	50,318
Total Loans	21,278	51,467
90 Days Past Due & Accruing	0	108
Loans Acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	213	889
Loans Acquired | Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	214	260
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,379	43,086
Current	3,099,571	3,774,951
Total Loans	3,114,950	3,818,037
90 Days Past Due & Accruing	1	2,970
Loans Acquired | Real estate | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,067	32,689
Loans Acquired | Real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,312	10,397
Loans Acquired | Real estate | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,648	22,823
Current	2,033,541	2,364,954
Total Loans	2,040,189	2,387,777
90 Days Past Due & Accruing	0	2,565
Loans Acquired | Real estate | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,491	17,176
Loans Acquired | Real estate | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,157	5,647
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	324	4,025
Current	467,571	633,007
Total Loans	467,895	637,032
90 Days Past Due & Accruing	0	279
Loans Acquired | Real estate | Construction | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	117	2,577
Loans Acquired | Real estate | Construction | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	207	1,448
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,407	16,238
Current	598,459	776,990
Total Loans	606,866	793,228
90 Days Past Due & Accruing	1	126
Loans Acquired | Real estate | Single family residential | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,459	12,936
Loans Acquired | Real estate | Single family residential | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,948	3,302
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,523	3,434
Current	593,170	1,058,729
Total Loans	598,693	1,062,163
90 Days Past Due & Accruing	0	67
Loans Acquired | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,498	2,395
Loans Acquired | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,025	1,039
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,491	3,383
Current	591,150	992,204
Total Loans	596,641	995,587
90 Days Past Due & Accruing	0	67
Loans Acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,471	2,344
Loans Acquired | Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,020	1,039
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	32	51
Current	2,020	66,525
Total Loans	2,052	66,576
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Agricultural | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27	51
Loans Acquired | Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5	0
Loans Acquired | Other
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		15
Current		142,394
Total Loans	$ 0	142,409
90 Days Past Due & Accruing		0
Loans Acquired | Other | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		15
Loans Acquired | Other | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		$ 0