Schedule of Recorded Investment in Criticized Loans by Class and Credit Quality Indicator (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 5,340,189	$ 5,193,321
Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,816,813	1,793,258
Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	218,650	224,066
Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	113,944	111,763
Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	117,643	94,890
Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	450,237	430,719
Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,030,593	1,032,851
Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	166,872	156,234
Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,464,515	3,413,062
Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	687,768	622,529
Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	153,185	153,717
Credit card consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	66,221	68,107
Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	907,174	844,353
Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	824,962	792,416
Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	139,892	142,151
Other Assets Especially Mentioned
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	142,560	127,270
Other Assets Especially Mentioned | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	73,383	61,787
Other Assets Especially Mentioned | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	12,843	16,593
Other Assets Especially Mentioned | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,835	1,640
Other Assets Especially Mentioned | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	166
Other Assets Especially Mentioned | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	14,678	18,399
Other Assets Especially Mentioned | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	6,885	4,453
Other Assets Especially Mentioned | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	6,459	6,114
Other Assets Especially Mentioned | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	101,405	90,753
Other Assets Especially Mentioned | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	760	644
Other Assets Especially Mentioned | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,006	651
Other Assets Especially Mentioned | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,766	1,295
Other Assets Especially Mentioned | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	33,934	32,975
Other Assets Especially Mentioned | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5,455	2,247
Substandard
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	176,021	162,785
Substandard | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	87,756	84,556
Substandard | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	9,462	12,482
Substandard | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	754	1,886
Substandard | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4,104	323
Substandard | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	14,320	14,691
Substandard | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	9,862	9,661
Substandard | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	21,756	16,529
Substandard | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	133,694	125,437
Substandard | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,159	1,131
Substandard | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	776	1,130
Substandard | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,935	2,261
Substandard | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	33,771	27,982
Substandard | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	6,621	7,105
Doubtful
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	41,344	30,350
Doubtful | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18,351	10,609
Doubtful | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,709	591
Doubtful | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	0
Doubtful | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,481	756
Doubtful | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	3,190	1,347
Doubtful | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	517	2,540
Doubtful | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	0	0
Doubtful | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	22,058	14,496
Doubtful | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	130	154
Doubtful | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	192	198
Doubtful | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	322	352
Doubtful | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	18,435	15,085
Doubtful | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	529	417
Total Criticized Loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	359,925	320,405
Total Criticized Loans | Commercial real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	179,490	156,952
Total Criticized Loans | Land acquisition & development construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	24,014	29,666
Total Criticized Loans | Residential construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,589	3,526
Total Criticized Loans | Commercial construction real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	5,585	1,245
Total Criticized Loans | Total construction loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	32,188	34,437
Total Criticized Loans | Residential real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	17,264	16,654
Total Criticized Loans | Agricultural real estate
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	28,215	22,643
Total Criticized Loans | Total real estate loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	257,157	230,686
Total Criticized Loans | Indirect consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	2,049	1,929
Total Criticized Loans | Other consumer
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	1,974	1,979
Total Criticized Loans | Total consumer loans
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	4,023	3,908
Total Criticized Loans | Commercial
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	86,140	76,042
Total Criticized Loans | Agricultural
Loans and Leases Receivable Recorded Investment, Criticized Loans [Line Items]
Loans held for investment	$ 12,605	$ 9,769