Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,740,737	$ 11,723,171
Loans Acquired
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	38,449	28,076
Current	3,017,738	3,264,707
Total Loans	3,056,187	3,292,783
90 Days Past Due & Accruing	24	2
Loans Acquired | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,727	14,827
Loans Acquired | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	25,722	13,249
Loans Acquired | Consumer | Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	171	386
Current	11,808	15,272
Total Loans	11,979	15,658
90 Days Past Due & Accruing	0	2
Loans Acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	94	337
Loans Acquired | Consumer | Other consumer | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	77	49
Loans Acquired | Real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	24,340	16,810
Current	2,644,561	2,827,662
Total Loans	2,668,901	2,844,472
90 Days Past Due & Accruing	24	0
Loans Acquired | Real estate | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,368	13,157
Loans Acquired | Real estate | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	18,972	3,653
Loans Acquired | Real estate | Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,127	8,310
Current	396,385	421,295
Total Loans	404,512	429,605
90 Days Past Due & Accruing	0	0
Loans Acquired | Real estate | Construction | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5	8,283
Loans Acquired | Real estate | Construction | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,122	27
Loans Acquired | Real estate | Single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,641	7,755
Current	526,276	558,433
Total Loans	533,917	566,188
90 Days Past Due & Accruing	24	0
Loans Acquired | Real estate | Single family residential | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,058	4,706
Loans Acquired | Real estate | Single family residential | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,583	3,049
Loans Acquired | Real estate | Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,572	745
Current	1,721,900	1,847,934
Total Loans	1,730,472	1,848,679
90 Days Past Due & Accruing	0	0
Loans Acquired | Real estate | Other commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	305	168
Loans Acquired | Real estate | Other commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,267	577
Loans Acquired | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,938	10,880
Current	361,369	421,773
Total Loans	375,307	432,653
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,265	1,333
Loans Acquired | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,673	9,547
Loans Acquired | Commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,938	10,844
Current	360,095	420,070
Total Loans	374,033	430,914
90 Days Past Due & Accruing	0	0
Loans Acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,265	1,302
Loans Acquired | Commercial | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,673	9,542
Loans Acquired | Commercial | Agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	0	36
Current	1,274	1,703
Total Loans	1,274	1,739
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	0	31
Loans Acquired | Commercial | Agricultural | 90 Days or More Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 0	$ 5