Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (2) (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable Aging [Abstract]
Current	$ 5,415,443,000	$ 5,708,531,000
Past Due 30 - 89 Days	26,163,000	34,265,000
Nonaccrual	80,658,000	110,458,000
Total LHFI	5,527,963,000	5,857,484,000
Number of Days used as Baseline in Evaluating Collateral Documentation Exceptions For Loan Policy (in days)	90 days
Loan Amount Used as Baseline in Credit Quality Review For Loan Policy	100,000
Credit Amount Used as Baseline in Evaluating Residential Real Estate Development and Non-owner Occupied Commercial Real Estate For Loan Policy	1,000,000
Charge-off Amount Used as Baseline in Credit Quality Review For Loan Policy	25,000
Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member]
Financing Receivable Aging [Abstract]
Current	432,760,000	430,228,000
Past Due 30 - 89 Days	1,762,000	1,784,000
Nonaccrual	26,077,000	40,413,000
Total LHFI	460,599,000	474,082,000
Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member]
Financing Receivable Aging [Abstract]
Current	1,471,739,000	1,725,521,000
Past Due 30 - 89 Days	12,672,000	9,755,000
Nonaccrual	24,260,000	24,348,000
Total LHFI	1,511,514,000	1,760,930,000
Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,375,208,000	1,391,868,000
Past Due 30 - 89 Days	3,364,000	9,925,000
Nonaccrual	18,873,000	23,981,000
Total LHFI	1,397,536,000	1,425,774,000
Real Estate Secured Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	180,720,000	198,099,000
Past Due 30 - 89 Days	184,000	879,000
Nonaccrual	3,900,000	5,871,000
Total LHFI	184,804,000	204,849,000
Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	177,006,000	235,261,000
Past Due 30 - 89 Days	4,246,000	7,172,000
Nonaccrual	411,000	825,000
Total LHFI	181,896,000	243,756,000
Other Loans Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	626,937,000	604,752,000
Past Due 30 - 89 Days	74,000	3,104,000
Nonaccrual	922,000	872,000
Total LHFI	627,933,000	608,728,000
Commercial Portfolio Segment [Member]
Financing Receivable [Abstract]
Financing receivable commercial	3,906,118,000	3,924,755,000
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	3,584,068,000	3,554,041,000
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	74,793,000	84,848,000
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	241,981,000	284,694,000
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	5,276,000	1,172,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	413,564,000	425,182,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	321,938,000	308,618,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	23,923,000	26,273,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	67,703,000	90,175,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	116,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member]
Financing Receivable [Abstract]
Financing receivable commercial	131,226,000	135,621,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	115,316,000	119,155,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,026,000	142,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	14,844,000	16,324,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	40,000	0
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,396,489,000	1,424,641,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,277,544,000	1,287,886,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	12,607,000	26,232,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	106,338,000	110,472,000
Commercial Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	51,000
Commercial Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,163,162,000	1,137,584,000
Commercial Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	1,075,124,000	1,048,556,000
Commercial Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	36,782,000	32,046,000
Commercial Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	46,845,000	56,577,000
Commercial Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,411,000	405,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable [Abstract]
Financing receivable commercial	343,000	668,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	343,000	643,000
Commercial Portfolio Segment [Member] | Consumer Loans [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	25,000
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 Financing Receivable [Member]
Financing Receivable [Abstract]
Financing receivable commercial	622,003,000	602,845,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	620,563,000	600,411,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	4,000	0
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	611,000	1,834,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	825,000	600,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable [Abstract]
Financing receivable commercial	179,331,000	198,214,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member] | Pass [Member]
Financing Receivable [Abstract]
Financing receivable commercial	173,240,000	188,772,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member] | Special Mention [Member]
Financing Receivable [Abstract]
Financing receivable commercial	451,000	130,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member] | Substandard [Member]
Financing Receivable [Abstract]
Financing receivable commercial	5,640,000	9,312,000
Commercial Portfolio Segment [Member] | Other Loans Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member] | Doubtful [Member]
Financing Receivable [Abstract]
Financing receivable commercial	0	0
Consumer Portfolio Segment [Member]
Financing Receivable Aging [Abstract]
Current	1,585,236,000	1,893,658,000
Past Due 30 - 89 Days	15,012,000	16,356,000
Past Due Greater Than 90 Days	2,917,000	1,804,000
Nonaccrual	18,680,000	20,911,000
Subtotal	1,621,845,000	1,932,729,000
Total LHFI	5,527,963,000	5,857,484,000
Consumer Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Construction Land Development And Other Land Properties [Member]
Financing Receivable Aging [Abstract]
Current	45,790,000	47,253,000
Past Due 30 - 89 Days	353,000	353,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	892,000	1,294,000
Subtotal	47,035,000	48,900,000
Total LHFI	460,599,000	474,082,000
Consumer Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by 1-4 Family Residential Properties[Member]
Financing Receivable Aging [Abstract]
Current	1,349,926,000	1,596,800,000
Past Due 30 - 89 Days	10,335,000	8,477,000
Past Due Greater Than 90 Days	2,683,000	1,306,000
Nonaccrual	17,344,000	18,726,000
Subtotal	1,380,288,000	1,625,309,000
Total LHFI	1,511,514,000	1,760,930,000
Consumer Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Secured by NonFarm, Nonresidential Properties [Member]
Financing Receivable Aging [Abstract]
Current	1,047,000	1,133,000
Past Due 30 - 89 Days	0	0
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	1,047,000	1,133,000
Total LHFI	1,397,536,000	1,425,774,000
Consumer Portfolio Segment [Member] | Real Estate Secured Financing Receivable [Member] | Other Real Estate Secured Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	5,416,000	6,405,000
Past Due 30 - 89 Days	33,000	201,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	24,000	29,000
Subtotal	5,473,000	6,635,000
Total LHFI	184,804,000	204,849,000
Consumer Portfolio Segment [Member] | Commercial And Industrial Loans Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	464,000	1,626,000
Past Due 30 - 89 Days	45,000	118,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	10,000	37,000
Subtotal	519,000	1,781,000
Total LHFI	1,163,681,000	1,139,365,000
Consumer Portfolio Segment [Member] | Consumer Loans [Member]
Financing Receivable Aging [Abstract]
Current	176,663,000	234,593,000
Past Due 30 - 89 Days	4,246,000	7,172,000
Past Due Greater Than 90 Days	234,000	498,000
Nonaccrual	410,000	825,000
Subtotal	181,553,000	243,088,000
Total LHFI	181,896,000	243,756,000
Consumer Portfolio Segment [Member] | Other Loans Financing Receivable [Member]
Financing Receivable Aging [Abstract]
Current	5,930,000	5,848,000
Past Due 30 - 89 Days	0	35,000
Past Due Greater Than 90 Days	0	0
Nonaccrual	0	0
Subtotal	5,930,000	5,883,000
Total LHFI	$ 627,933,000	$ 608,728,000