Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (4) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable Aging [Abstract]
Current	$ 5,474,801,000	$ 5,468,820,000
Past Due 30 - 89 Days	24,068,000	35,193,000
Nonaccrual	74,318,000	82,363,000
Total LHFI	5,577,382,000	5,592,754,000
Number of days used as baseline in evaluating collateral documentation exceptions for loan policy	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	500,012,000	436,475,000
Past Due 30 - 89 Days	2,935,000	4,957,000
Nonaccrual	16,259,000	27,105,000
Total LHFI	519,263,000	468,975,000
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,379,618,000	1,454,609,000
Past Due 30 - 89 Days	7,480,000	12,626,000
Nonaccrual	23,837,000	27,114,000
Total LHFI	1,414,871,000	1,497,480,000
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,384,106,000	1,382,515,000
Past Due 30 - 89 Days	4,406,000	9,460,000
Nonaccrual	18,418,000	18,289,000
Total LHFI	1,406,930,000	1,410,264,000
Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Current	191,996,000	185,821,000
Past Due 30 - 89 Days	61,000	172,000
Nonaccrual	511,000	3,956,000
Total LHFI	192,568,000	189,949,000
Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	157,356,000	167,536,000
Past Due 30 - 89 Days	2,493,000	3,480,000
Nonaccrual	267,000	360,000
Total LHFI	160,318,000	171,660,000
Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	712,853,000	683,934,000
Past Due 30 - 89 Days	419,000	181,000
Nonaccrual	833,000	798,000
Total LHFI	714,105,000	684,913,000
Commercial Portfolio Segment [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,068,741,000	3,990,846,000
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	3,807,782,000	3,691,500,000
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	47,054,000	74,475,000
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	204,482,000	222,178,000
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	9,423,000	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	476,708,000	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	399,494,000	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	21,168,000	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	55,903,000	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	143,000	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	119,992,000	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	109,948,000	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	476,000	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	9,452,000	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	116,000	432,000
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,405,945,000	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	1,293,456,000	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	17,063,000	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	94,952,000	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	474,000	0
Commercial Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable [Abstract]
Financing receivable commercial	188,225,000	185,002,000
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	180,281,000	178,790,000
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	6,551,000	444,000
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	1,393,000	5,768,000
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	0
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,169,221,000	1,169,161,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,118,523,000	1,091,356,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,796,000	36,992,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	40,961,000	39,479,000
Commercial Portfolio Segment [Member] | Commercial and Industrial Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	7,941,000	1,334,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	340,000	404,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	340,000	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	708,310,000	679,175,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	705,740,000	676,618,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	59,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,821,000	1,714,000
Commercial Portfolio Segment [Member] | Other Loans [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	749,000	784,000
Consumer Portfolio Segment [Member]
Financing Receivable Aging [Abstract]
Current	1,476,217,000	1,562,265,000
Past Due 30 - 89 Days	9,031,000	15,101,000
Past Due Greater Than 90 Days	4,195,000	2,915,000
Nonaccrual	19,198,000	21,627,000
Subtotal	1,508,641,000	1,601,908,000
Total LHFI	5,577,382,000	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	42,197,000	44,131,000
Past Due 30 - 89 Days	110,000	1,109,000
Past Due Greater Than 90 Days	57,000	0
Nonaccrual	191,000	769,000
Subtotal	42,555,000	46,009,000
Total LHFI	519,263,000	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	1,265,822,000	1,339,000,000
Past Due 30 - 89 Days	6,380,000	10,332,000
Past Due Greater Than 90 Days	3,936,000	2,630,000
Nonaccrual	18,741,000	20,438,000
Subtotal	1,294,879,000	1,372,400,000
Total LHFI	1,414,871,000	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	949,000	1,206,000
Past Due 30 - 89 Days	36,000	0
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	985,000	1,206,000
Total LHFI	1,406,930,000	1,410,264,000
Consumer Portfolio Segment [Member] | Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Aging [Abstract]
Current	4,343,000	4,746,000
Past Due 30 - 89 Days	0	150,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	51,000
Subtotal	4,343,000	4,947,000
Total LHFI	192,568,000	189,949,000
Consumer Portfolio Segment [Member] | Commercial and Industrial Loans [Member]
Financing Receivable Aging [Abstract]
Current	94,000	313,000
Past Due 30 - 89 Days	12,000	29,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	10,000
Subtotal	106,000	352,000
Total LHFI	1,169,327,000	1,169,513,000
Consumer Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	157,017,000	167,131,000
Past Due 30 - 89 Days	2,493,000	3,481,000
Past Due Greater Than 90 Days	202,000	285,000
Nonaccrual	266,000	359,000
Subtotal	159,978,000	171,256,000
Total LHFI	160,318,000	171,660,000
Consumer Portfolio Segment [Member] | Other Loans [Member]
Financing Receivable Aging [Abstract]
Current	5,795,000	5,738,000
Past Due 30 - 89 Days	0	0
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	5,795,000	5,738,000
Total LHFI	$ 714,105,000	$ 684,913,000