Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Loan Portfolio [Abstract]
Total LHFI	$ 6,413,876	$ 6,449,469
Less allowance for loan losses, LHFI	71,321	69,616
Net LHFI	6,342,555	6,379,853
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	77,008	79,343
LHFI, Collectively Evaluated For Impairment	6,336,868	6,370,126
Total LHFI	6,413,876	6,449,469
Loans Secured by Real Estate [Member] \| Construction Land Development and Other Land [Member]
Loan Portfolio [Abstract]
Total LHFI	691,657	619,877
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	20,134	13,867
LHFI, Collectively Evaluated For Impairment	671,523	606,010
Total LHFI	691,657	619,877
Loans Secured by Real Estate [Member] \| Secured by 1-4 Family Residential Properties [Member]
Loan Portfolio [Abstract]
Total LHFI	1,613,993	1,634,397
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	23,620	25,621
LHFI, Collectively Evaluated For Impairment	1,590,373	1,608,776
Total LHFI	1,613,993	1,634,397
Loans Secured by Real Estate [Member] \| Secured by Nonfarm, Nonresidential Properties [Member]
Loan Portfolio [Abstract]
Total LHFI	1,516,895	1,553,193
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	17,887	25,717
LHFI, Collectively Evaluated For Impairment	1,499,008	1,527,476
Total LHFI	1,516,895	1,553,193
Loans Secured by Real Estate [Member] \| Other Real Estate Secured [Member]
Loan Portfolio [Abstract]
Total LHFI	233,322	253,787
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	723	1,318
LHFI, Collectively Evaluated For Impairment	232,599	252,469
Total LHFI	233,322	253,787
Commercial and Industrial Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	1,228,788	1,270,350
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	14,057	12,104
LHFI, Collectively Evaluated For Impairment	1,214,731	1,258,246
Total LHFI	1,228,788	1,270,350
Consumer Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	161,535	167,964
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	96	88
LHFI, Collectively Evaluated For Impairment	161,439	167,876
Total LHFI	161,535	167,964
State and Other Political Subdivision Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	614,330	602,727
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	0	0
LHFI, Collectively Evaluated For Impairment	614,330	602,727
Total LHFI	614,330	602,727
Other Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	353,356	347,174
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	491	628
LHFI, Collectively Evaluated For Impairment	352,865	346,546
Total LHFI	$ 353,356	$ 347,174

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)

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

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for 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 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(d))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Regulation S-X (SX)

-Number 210

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-Paragraph 7

-Subparagraph d

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

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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.

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-URI http://asc.fasb.org/extlink&oid=28368275&loc=d3e5074-111524

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Amount after allowance and 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 and loans held for sale.

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