Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (4) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable Aging [Abstract]
Current	$ 5,363,243,000	$ 5,468,820,000
Past Due 30 - 89 Days	25,058,000	35,193,000
Nonaccrual	83,322,000	82,363,000
Total LHFI	5,474,396,000	5,592,754,000
Number of days used as baseline in evaluating collateral documentation exceptions for loan policy (in days)	90 days
Credit amount used as baseline in evaluating residential real estate development and non-owner occupied commercial real estate for loan policy	1,000,000
Loan amount used as baseline in credit quality review for loan policy	100,000
Charge-off amount used as baseline in credit quality review for loan policy	25,000
Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable Aging [Abstract]
Current	456,799,000	436,475,000
Past Due 30 - 89 Days	3,700,000	4,957,000
Nonaccrual	24,443,000	27,105,000
Total LHFI	485,419,000	468,975,000
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,335,262,000	1,454,609,000
Past Due 30 - 89 Days	9,205,000	12,626,000
Nonaccrual	27,149,000	27,114,000
Total LHFI	1,372,901,000	1,497,480,000
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,359,873,000	1,382,515,000
Past Due 30 - 89 Days	7,666,000	9,460,000
Nonaccrual	17,880,000	18,289,000
Total LHFI	1,385,669,000	1,410,264,000
Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	173,093,000	185,821,000
Past Due 30 - 89 Days	546,000	172,000
Nonaccrual	1,040,000	3,956,000
Total LHFI	174,680,000	189,949,000
Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	157,565,000	167,536,000
Past Due 30 - 89 Days	2,184,000	3,480,000
Nonaccrual	277,000	360,000
Total LHFI	160,253,000	171,660,000
Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	684,644,000	683,934,000
Past Due 30 - 89 Days	499,000	181,000
Nonaccrual	3,480,000	798,000
Total LHFI	688,623,000	684,913,000
Commercial Portfolio Segment [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,010,208,000	3,990,846,000
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	3,724,726,000	3,691,500,000
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	79,220,000	74,475,000
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	203,288,000	222,178,000
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	2,974,000	2,693,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	442,775,000	422,966,000
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	360,197,000	335,179,000
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	23,060,000	23,812,000
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	59,289,000	63,832,000
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	229,000	143,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	123,916,000	125,080,000
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	110,110,000	110,333,000
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	2,288,000	1,012,000
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	11,387,000	13,303,000
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	131,000	432,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,384,701,000	1,409,058,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,279,133,000	1,298,820,000
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	12,323,000	12,156,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	92,932,000	98,082,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	313,000	0
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable [Abstract]
Financing receivable commercial	169,980,000	185,002,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	167,063,000	178,790,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	340,000	444,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	2,577,000	5,768,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,206,629,000	1,169,161,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,131,149,000	1,091,356,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	41,159,000	36,992,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	32,776,000	39,479,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,545,000	1,334,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	366,000	404,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	366,000	404,000
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	681,841,000	679,175,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	676,708,000	676,618,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	50,000	59,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,327,000	1,714,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	756,000	784,000
Consumer Portfolio Segment [Member]
Financing Receivable Aging [Abstract]
Current	1,428,984,000	1,562,265,000
Past Due 30 - 89 Days	11,472,000	15,101,000
Past Due Greater Than 90 Days	1,512,000	2,915,000
Nonaccrual	22,220,000	21,627,000
Subtotal	1,464,188,000	1,601,908,000
Total LHFI	5,474,396,000	5,592,754,000
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable Aging [Abstract]
Current	41,948,000	44,131,000
Past Due 30 - 89 Days	491,000	1,109,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	205,000	769,000
Subtotal	42,644,000	46,009,000
Total LHFI	485,419,000	468,975,000
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,217,358,000	1,339,000,000
Past Due 30 - 89 Days	8,634,000	10,332,000
Past Due Greater Than 90 Days	1,284,000	2,630,000
Nonaccrual	21,709,000	20,438,000
Subtotal	1,248,985,000	1,372,400,000
Total LHFI	1,372,901,000	1,497,480,000
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	968,000	1,206,000
Past Due 30 - 89 Days	0	0
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	968,000	1,206,000
Total LHFI	1,385,669,000	1,410,264,000
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	4,533,000	4,746,000
Past Due 30 - 89 Days	147,000	150,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	20,000	51,000
Subtotal	4,700,000	4,947,000
Total LHFI	174,680,000	189,949,000
Consumer Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Aging [Abstract]
Current	195,000	313,000
Past Due 30 - 89 Days	17,000	29,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	10,000	10,000
Subtotal	222,000	352,000
Total LHFI	1,206,851,000	1,169,513,000
Consumer Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	157,200,000	167,131,000
Past Due 30 - 89 Days	2,183,000	3,481,000
Past Due Greater Than 90 Days	228,000	285,000
Nonaccrual	276,000	359,000
Subtotal	159,887,000	171,256,000
Total LHFI	160,253,000	171,660,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	6,782,000	5,738,000
Past Due 30 - 89 Days	0	0
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	6,782,000	5,738,000
Total LHFI	$ 688,623,000	$ 684,913,000