Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Summary of LHFI Evaluated for Impairment (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	$ 54,410	$ 55,312
LHFI, Collectively Evaluated For Impairment	7,444,794	7,036,073
Total LHFI	7,499,204	7,091,385
Commercial and Industrial Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	16,525	7,622
LHFI, Collectively Evaluated For Impairment	1,404,857	1,335,589
Total LHFI	1,421,382	1,343,211
Consumer Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	189	31
LHFI, Collectively Evaluated For Impairment	169,884	169,104
Total LHFI	170,073	169,135
State and Other Political Subdivision Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	0	0
LHFI, Collectively Evaluated For Impairment	875,973	734,615
Total LHFI	875,973	734,615
Other Loans [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	821	512
LHFI, Collectively Evaluated For Impairment	437,984	421,984
Total LHFI	438,805	422,496
Loans Secured by Real Estate [Member] \| Construction, Land Development and Other Land [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	4,724	6,123
LHFI, Collectively Evaluated For Impairment	761,961	818,600
Total LHFI	766,685	824,723
Loans Secured by Real Estate [Member] \| Secured by 1-4 Family Residential Properties [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	20,107	23,079
LHFI, Collectively Evaluated For Impairment	1,572,346	1,626,422
Total LHFI	1,592,453	1,649,501
Loans Secured by Real Estate [Member] \| Secured by Nonfarm, Nonresidential Properties [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	10,313	17,800
LHFI, Collectively Evaluated For Impairment	1,905,840	1,718,676
Total LHFI	1,916,153	1,736,476
Loans Secured by Real Estate [Member] \| Other Real Estate Secured [Member]
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	1,731	145
LHFI, Collectively Evaluated For Impairment	315,949	211,083
Total LHFI	$ 317,680	$ 211,228

The balance of financing receivables that were collectively evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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The balance of financing receivables that were individually evaluated for impairment.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

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