Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,002,952	$ 11,723,171
Loans Acquired
Financing Receivable, Past Due [Line Items]
Total Past Due	9,825	28,076
Current	3,349,762	3,264,707
Total Loans	3,359,587	3,292,783
90 Days Past Due & Accruing	21	2
Loans Acquired | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	6,320	14,827
Loans Acquired | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,505	13,249
Loans Acquired | Consumer | Other consumer
Financing Receivable, Past Due [Line Items]
Total Past Due	167	386
Current	7,264	15,272
Total Loans	7,431	15,658
90 Days Past Due & Accruing	4	2
Loans Acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	131	337
Loans Acquired | Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	36	49
Loans Acquired | Real Estate
Financing Receivable, Past Due [Line Items]
Total Past Due	8,327	16,810
Current	2,993,136	2,827,662
Total Loans	3,001,463	2,844,472
90 Days Past Due & Accruing	17	0
Loans Acquired | Real Estate | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	5,582	13,157
Loans Acquired | Real Estate | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	2,745	3,653
Loans Acquired | Real Estate | Construction
Financing Receivable, Past Due [Line Items]
Total Past Due	42	8,310
Current	361,958	421,295
Total Loans	362,000	429,605
90 Days Past Due & Accruing	0	0
Loans Acquired | Real Estate | Construction | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	30	8,283
Loans Acquired | Real Estate | Construction | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	12	27
Loans Acquired | Real Estate | Single family residential
Financing Receivable, Past Due [Line Items]
Total Past Due	5,454	7,755
Current	499,036	558,433
Total Loans	504,490	566,188
90 Days Past Due & Accruing	17	0
Loans Acquired | Real Estate | Single family residential | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	3,664	4,706
Loans Acquired | Real Estate | Single family residential | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,790	3,049
Loans Acquired | Real Estate | Other commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	2,831	745
Current	2,132,142	1,847,934
Total Loans	2,134,973	1,848,679
90 Days Past Due & Accruing	0	0
Loans Acquired | Real Estate | Other commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	1,888	168
Loans Acquired | Real Estate | Other commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	943	577
Loans Acquired | Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	1,331	10,880
Current	349,362	421,773
Total Loans	350,693	432,653
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	607	1,333
Loans Acquired | Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	724	9,547
Loans Acquired | Commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Past Due	1,331	10,844
Current	348,490	420,070
Total Loans	349,821	430,914
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	607	1,302
Loans Acquired | Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	724	9,542
Loans Acquired | Commercial | Agricultural
Financing Receivable, Past Due [Line Items]
Total Past Due	0	36
Current	872	1,703
Total Loans	872	1,739
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Agricultural | Gross 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	0	31
Loans Acquired | Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Past Due [Line Items]
Total Past Due	$ 0	$ 5