Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (4) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Sep. 30, 2014 KeyRatios LoanPool CreditRiskGrade	Dec. 31, 2013
Financing Receivable Aging [Abstract]
Current	$ 6,213,544	$ 5,714,900
Nonaccrual	88,314	65,238
Total LHFI	6,333,651	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 [Member]
Financing Receivable Aging [Abstract]
Current	559,414	582,639
Nonaccrual	20,286	13,327
Total LHFI	580,794	596,889
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,586,040	1,451,528
Nonaccrual	27,017	21,603
Total LHFI	1,625,480	1,485,564
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,523,615	1,391,286
Nonaccrual	23,885	21,809
Total LHFI	1,560,901	1,415,139
Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Current	238,349	188,030
Nonaccrual	1,203	1,327
Total LHFI	239,819	189,362
Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	166,511	162,843
Nonaccrual	160	151
Total LHFI	168,813	165,308
Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	910,397	788,253
Nonaccrual	585	735
Total LHFI	911,091	789,005
Commercial Portfolio Segment [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,609,392	4,213,735
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,385,604	3,982,761
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	49,064	36,313
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	172,673	190,743
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	2,051	3,918
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [Member]
Financing Receivable [Abstract]
Financing receivable commercial	521,401	545,691
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	482,131	493,380
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,774	4,383
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	37,353	47,610
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [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	138,883	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	129,352	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	1,692	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	7,576	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	263	110
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,560,001	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	1,442,787	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	31,921	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	85,081	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	212	399
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable [Abstract]
Financing receivable commercial	237,304	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	230,604	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	6,700	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	1,246,752	1,157,596
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,210,480	1,099,429
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	6,007	18,771
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	29,418	37,209
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	847	2,187
Commercial Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	198	496
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	198	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	904,853	782,250
Commercial Portfolio Segment [Member] | Other Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	890,052	777,395
Commercial Portfolio Segment [Member] | Other Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	7,670	60
Commercial Portfolio Segment [Member] | Other Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	6,545	4,126
Commercial Portfolio Segment [Member] | Other Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	586	669
Consumer Portfolio Segment [Member]
Financing Receivable Aging [Abstract]
Current	1,686,007	1,552,447
Past Due 30-89 Days	11,705	11,095
Past Due 90 Days or More	3,118	3,298
Nonaccrual	23,429	18,306
Subtotal	1,724,259	1,585,146
Total LHFI	6,333,651	5,798,881
Consumer Portfolio Segment [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Past Due 30-89 Days	0
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land [Member]
Financing Receivable Aging [Abstract]
Current	58,866	50,850
Past Due 30-89 Days	424	131
Past Due 90 Days or More	0	0
Nonaccrual	103	217
Subtotal	59,393	51,198
Total LHFI	580,794	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	1,451,174	1,327,624
Past Due 30-89 Days	9,411	8,937
Past Due 90 Days or More	2,845	2,996
Nonaccrual	23,167	17,939
Subtotal	1,486,597	1,357,496
Total LHFI	1,625,480	1,485,564
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	900	1,439
Past Due 30-89 Days	0	8
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	900	1,447
Total LHFI	1,560,901	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	2,515	3,418
Past Due 30-89 Days	0	2
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	2,515	3,420
Total LHFI	239,819	189,362
Consumer Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Aging [Abstract]
Current	0	13
Past Due 30-89 Days	0	5
Past Due 90 Days or More	1	0
Nonaccrual	0	0
Subtotal	1	18
Total LHFI	1,246,753	1,157,614
Consumer Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	166,314	162,348
Past Due 30-89 Days	1,870	2,012
Past Due 90 Days or More	272	302
Nonaccrual	159	150
Subtotal	168,615	164,812
Total LHFI	168,813	165,308
Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	6,238	6,755
Past Due 30-89 Days		0
Past Due 90 Days or More	0	0
Nonaccrual	0	0
Subtotal	6,238	6,755
Total LHFI	$ 911,091	$ 789,005