Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Loan Portfolio [Abstract]
Total LHFI	$ 6,791,643	$ 6,449,469
Less allowance for loan losses, LHFI	65,607	69,616
Net LHFI	6,726,036	6,379,853
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	61,131	79,343
LHFI, Collectively Evaluated For Impairment	6,730,512	6,370,126
Total LHFI	6,791,643	6,449,469
Construction, Land Development and Other Land [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	785,472	619,877
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	8,748	13,867
LHFI, Collectively Evaluated For Impairment	776,724	606,010
Total LHFI	785,472	619,877
Secured by 1-4 Family Residential Properties [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,638,639	1,634,397
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	22,342	25,621
LHFI, Collectively Evaluated For Impairment	1,616,297	1,608,776
Total LHFI	1,638,639	1,634,397
Secured by Nonfarm, Nonresidential Properties [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	1,604,453	1,553,193
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	20,465	25,717
LHFI, Collectively Evaluated For Impairment	1,583,988	1,527,476
Total LHFI	1,604,453	1,553,193
Other Real Estate Secured [Member] \| Loans Secured by Real Estate [Member]
Loan Portfolio [Abstract]
Total LHFI	225,523	253,787
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	434	1,318
LHFI, Collectively Evaluated For Impairment	225,089	252,469
Total LHFI	225,523	253,787
Commercial and Industrial Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	1,270,277	1,270,350
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	8,571	12,104
LHFI, Collectively Evaluated For Impairment	1,261,706	1,258,246
Total LHFI	1,270,277	1,270,350
Consumer Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	169,509	167,964
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	45	88
LHFI, Collectively Evaluated For Impairment	169,464	167,876
Total LHFI	169,509	167,964
State and Other Political Subdivision Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	677,539	602,727
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	0	0
LHFI, Collectively Evaluated For Impairment	677,539	602,727
Total LHFI	677,539	602,727
Other Loans [Member]
Loan Portfolio [Abstract]
Total LHFI	420,231	347,174
Loans and Leases Receivable, Other Information [Abstract]
LHFI, Individually Evaluated For Impairment	526	628
LHFI, Collectively Evaluated For Impairment	419,705	346,546
Total LHFI	$ 420,231	$ 347,174

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

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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.

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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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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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