Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	$ 14,430,000	$ 11,720,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	396,748	405,470
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	191,946	201,297
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	6,884,422	5,966,453
Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,760,894	1,300,723
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,444,620	1,440,443
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	3,678,908	3,225,287
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	2,073,192	1,939,423
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,909,796	1,774,909
Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	163,396	164,514
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	275,714	119,042
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	32,737	28,076
Current	4,762,447	3,264,707
Loans and leases receivable, gross	4,795,184	3,292,783
90 Days Past Due & Accruing	597	2
Loans acquired | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	23,240	14,827
Loans acquired | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,497	13,249
Loans acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	967	386
Current	56,781	15,272
Loans and leases receivable, gross	57,748	15,658
90 Days Past Due & Accruing	0	2
Loans acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	827	337
Loans acquired | Consumer | Other consumer | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	140	49
Loans acquired | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	25,045	16,810
Current	3,974,613	2,827,662
Loans and leases receivable, gross	3,999,658	2,844,472
90 Days Past Due & Accruing	597	0
Loans acquired | Real Estate | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17,071	13,157
Loans acquired | Real Estate | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,974	3,653
Loans acquired | Real Estate | Construction and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,297	8,310
Current	474,670	421,295
Loans and leases receivable, gross	475,967	429,605
90 Days Past Due & Accruing	0	0
Loans acquired | Real Estate | Construction and development | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	824	8,283
Loans acquired | Real Estate | Construction and development | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	473	27
Loans acquired | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	17,924	7,755
Current	979,520	558,433
Loans and leases receivable, gross	997,444	566,188
90 Days Past Due & Accruing	597	0
Loans acquired | Real Estate | Single family residential | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	12,904	4,706
Loans acquired | Real Estate | Single family residential | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,020	3,049
Loans acquired | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,824	745
Current	2,520,423	1,847,934
Loans and leases receivable, gross	2,526,247	1,848,679
90 Days Past Due & Accruing	0	0
Loans acquired | Real Estate | Other commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,343	168
Loans acquired | Real Estate | Other commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	2,481	577
Loans acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	6,725	10,880
Current	731,053	421,773
Loans and leases receivable, gross	737,778	432,653
90 Days Past Due & Accruing	0	0
Loans acquired | Commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,342	1,333
Loans acquired | Commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,383	9,547
Loans acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	5,703	10,844
Current	580,017	420,070
Loans and leases receivable, gross	585,720	430,914
90 Days Past Due & Accruing	0	0
Loans acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,326	1,302
Loans acquired | Commercial | Commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,377	9,542
Loans acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,022	36
Current	151,036	1,703
Loans and leases receivable, gross	152,058	1,739
90 Days Past Due & Accruing	0	0
Loans acquired | Commercial | Agricultural | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,016	31
Loans acquired | Commercial | Agricultural | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 6	$ 5