Loans Acquired - Age Analysis of Past Due Acquired Loans, Excluding Loans Covered by Loss Share (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	$ 11,720,000	$ 10,780,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	405,470	465,516
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	201,297	280,094
Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	5,966,453	4,239,612
Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,300,723	614,155
Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,440,443	1,094,633
Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	3,225,287	2,530,824
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,939,423	973,519
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	1,774,909	825,217
Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	164,514	148,302
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, gross	119,042	26,962
Loans acquired
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	28,076	47,684
Current	3,264,707	5,026,392
Loans and leases receivable, gross	3,292,783	5,074,076
90 Days Past Due & Accruing	2	3,145
Loans acquired | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	14,827	35,988
Loans acquired | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,249	11,696
Loans acquired | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	386	1,149
Current	15,272	50,318
Loans and leases receivable, gross	15,658	51,467
90 Days Past Due & Accruing	2	108
Loans acquired | Consumer | Other consumer | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	337	889
Loans acquired | Consumer | Other consumer | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	49	260
Loans acquired | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	16,810	43,086
Current	2,827,662	3,774,951
Loans and leases receivable, gross	2,844,472	3,818,037
90 Days Past Due & Accruing	0	2,970
Loans acquired | Real Estate | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	13,157	32,689
Loans acquired | Real Estate | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,653	10,397
Loans acquired | Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,310	4,025
Current	421,295	633,007
Loans and leases receivable, gross	429,605	637,032
90 Days Past Due & Accruing	0	279
Loans acquired | Real Estate | Construction | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	8,283	2,577
Loans acquired | Real Estate | Construction | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	27	1,448
Loans acquired | Real Estate | Single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	7,755	16,238
Current	558,433	776,990
Loans and leases receivable, gross	566,188	793,228
90 Days Past Due & Accruing	0	126
Loans acquired | Real Estate | Single family residential | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	4,706	12,936
Loans acquired | Real Estate | Single family residential | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	3,049	3,302
Loans acquired | Real Estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	745	22,823
Current	1,847,934	2,364,954
Loans and leases receivable, gross	1,848,679	2,387,777
90 Days Past Due & Accruing	0	2,565
Loans acquired | Real Estate | Other commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	168	17,176
Loans acquired | Real Estate | Other commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	577	5,647
Loans acquired | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	10,880	3,434
Current	421,773	1,058,729
Loans and leases receivable, gross	432,653	1,062,163
90 Days Past Due & Accruing	0	67
Loans acquired | Commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,333	2,395
Loans acquired | Commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,547	1,039
Loans acquired | Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	10,844	3,383
Current	420,070	992,204
Loans and leases receivable, gross	430,914	995,587
90 Days Past Due & Accruing	0	67
Loans acquired | Commercial | Commercial | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	1,302	2,344
Loans acquired | Commercial | Commercial | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	9,542	1,039
Loans acquired | Commercial | Agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	36	51
Current	1,703	66,525
Loans and leases receivable, gross	1,739	66,576
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	31	51
Loans acquired | Commercial | Agricultural | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due	$ 5	0
Loans acquired | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		15
Current		142,394
Loans and leases receivable, gross		142,409
90 Days Past Due & Accruing		0
Loans acquired | Other | Gross 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		15
Loans acquired | Other | 90 Days or More Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Past Due		$ 0