Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (4) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2014 KeyRatios LoanPool CreditRiskGrade	Dec. 31, 2013
Financing Receivable Aging [Abstract]
Current	$ 6,091,568	$ 5,714,900
Past Due 30 - 89 Days	22,379	15,445
Nonaccrual	71,118	65,238
Total LHFI	6,187,000	5,798,881
Number of days used as baseline in evaluating collateral documentation exceptions for loan policy	90 days
Loan amount used as baseline in credit quality review for loan policy	100
Number of key quality ratios	6
Number of individual credit risk grades	10
Number of primary commercial loan groups	9
Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable Aging [Abstract]
Current	508,659	582,639
Past Due 30 - 89 Days	1,797	923
Nonaccrual	21,142	13,327
Total LHFI	531,651	596,889
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,543,576	1,451,528
Past Due 30 - 89 Days	13,151	9,437
Nonaccrual	23,403	21,603
Total LHFI	1,581,859	1,485,564
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,522,866	1,391,286
Past Due 30 - 89 Days	2,990	2,044
Nonaccrual	18,659	21,809
Total LHFI	1,544,516	1,415,139
Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Current	249,021	188,030
Past Due 30 - 89 Days	129	5
Nonaccrual	1,233	1,327
Total LHFI	250,383	189,362
Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	163,657	162,843
Past Due 30 - 89 Days	1,456	2,012
Nonaccrual	107	151
Total LHFI	165,372	165,308
Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	862,186	788,253
Past Due 30 - 89 Days	75	17
Nonaccrual	812	735
Total LHFI	863,073	789,005
Commercial Portfolio Segment [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,507,078	4,213,735
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,289,098	3,982,761
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	41,198	36,313
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	174,105	190,743
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	2,677	3,918
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	474,403	545,691
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	426,213	493,380
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	3,321	4,383
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	44,726	47,610
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	143	318
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	134,263	128,068
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	125,513	119,640
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,500	479
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	7,069	7,839
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	181	110
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,543,536	1,413,692
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,459,068	1,313,470
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	5,988	12,620
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	78,187	87,203
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	293	399
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable [Abstract]
Financing receivable commercial	247,538	185,942
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	240,816	178,951
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	6,722	6,756
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	235
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,250,136	1,157,596
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,195,331	1,099,429
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	22,591	18,771
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	30,694	37,209
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,520	2,187
Commercial Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	297	496
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	297	496
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Commercial Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	856,905	782,250
Commercial Portfolio Segment [Member] | Other Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	841,860	777,395
Commercial Portfolio Segment [Member] | Other Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	7,798	60
Commercial Portfolio Segment [Member] | Other Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	6,707	4,126
Commercial Portfolio Segment [Member] | Other Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	540	669
Consumer Portfolio Segment [Member]
Financing Receivable Aging [Abstract]
Current	1,643,474	1,552,447
Past Due 30 - 89 Days	14,137	11,095
Past Due 90 Days or More	1,936	3,298
Nonaccrual	20,375	18,306
Subtotal	1,679,922	1,585,146
Total LHFI	6,187,000	5,798,881
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable Aging [Abstract]
Current	56,804	50,850
Past Due 30 - 89 Days	258	131
Past Due 90 Days or More	54	0
Nonaccrual	132	217
Subtotal	57,248	51,198
Total LHFI	531,651	596,889
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,413,308	1,327,624
Past Due 30 - 89 Days	12,423	8,937
Past Due 90 Days or More	1,728	2,996
Nonaccrual	20,137	17,939
Subtotal	1,447,596	1,357,496
Total LHFI	1,581,859	1,485,564
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	980	1,439
Past Due 30 - 89 Days	0	8
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	980	1,447
Total LHFI	1,544,516	1,415,139
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Current	2,845	3,418
Past Due 30 - 89 Days	0	2
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	2,845	3,420
Total LHFI	250,383	189,362
Consumer Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Aging [Abstract]
Current	9	13
Past Due 30 - 89 Days	0	5
Past Due 90 Days or More	1	0
Nonaccrual	0	0
Subtotal	10	18
Total LHFI	1,250,146	1,157,614
Consumer Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	163,360	162,348
Past Due 30 - 89 Days	1,456	2,012
Past Due 90 Days or More	153	302
Nonaccrual	106	150
Subtotal	165,075	164,812
Total LHFI	165,372	165,308
Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	6,168	6,755
Past Due 30 - 89 Days	0	0
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	6,168	6,755
Total LHFI	$ 863,073	$ 789,005