Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,365,895	$ 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	48,671	47,684
Current	4,183,763	5,026,392
Total Loans	4,232,434	5,074,076
90 Days Past Due & Accruing	1,927	3,145
Loans Acquired | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,079	35,988
Loans Acquired | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	35,592	11,696
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	596	1,149
Current	31,055	50,318
Total Loans	31,651	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	347	889
Loans Acquired | Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	249	260
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	36,399	43,086
Current	3,397,102	3,774,951
Total Loans	3,433,501	3,818,037
90 Days Past Due & Accruing	1,165	2,970
Loans Acquired | Real estate | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	9,022	32,689
Loans Acquired | Real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27,377	10,397
Loans Acquired | Real estate | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	23,748	22,823
Current	2,216,830	2,364,954
Total Loans	2,240,578	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	4,801	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	18,947	5,647
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,665	4,025
Current	519,656	633,007
Total Loans	521,321	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	645	2,577
Loans Acquired | Real estate | Construction | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,020	1,448
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,986	16,238
Current	660,616	776,990
Total Loans	671,602	793,228
90 Days Past Due & Accruing	1,165	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	3,576	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	7,410	3,302
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,676	3,434
Current	755,606	1,058,729
Total Loans	767,282	1,062,163
90 Days Past Due & Accruing	762	67
Loans Acquired | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,710	2,395
Loans Acquired | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,966	1,039
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,641	3,383
Current	752,832	992,204
Total Loans	764,473	995,587
90 Days Past Due & Accruing	762	67
Loans Acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	3,675	2,344
Loans Acquired | Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,966	1,039
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	35	51
Current	2,774	66,525
Total Loans	2,809	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	35	51
Loans Acquired | Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	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