Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	$ 25,058,000		$ 35,193,000
Past Due Greater Than 90 Days	2,773,000	[1]	6,378,000	[1]
Total Past Due	27,831,000		41,571,000
Nonaccrual	83,322,000		82,363,000
Current Loans	5,363,243,000		5,468,820,000
Total LHFI	5,474,396,000		5,592,754,000
LHFI past due 90 days or more	2,800,000		6,400,000
LHFS past due 90 days or more	4,500,000		43,100,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program (in hundredths)	100.00%
Option to repurchase	58,000,000
Repurchase gain included in gain on sales of loans	542,000
Loans Secured by Real Estate [Member] | Construction Land Development and Other Land Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	3,700,000		4,957,000
Past Due Greater Than 90 Days	477,000	[1]	438,000	[1]
Total Past Due	4,177,000		5,395,000
Nonaccrual	24,443,000		27,105,000
Current Loans	456,799,000		436,475,000
Total LHFI	485,419,000		468,975,000
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	9,205,000		12,626,000
Past Due Greater Than 90 Days	1,285,000	[1]	3,131,000	[1]
Total Past Due	10,490,000		15,757,000
Nonaccrual	27,149,000		27,114,000
Current Loans	1,335,262,000		1,454,609,000
Total LHFI	1,372,901,000		1,497,480,000
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	7,666,000		9,460,000
Past Due Greater Than 90 Days	250,000	[1]	0	[1]
Total Past Due	7,916,000		9,460,000
Nonaccrual	17,880,000		18,289,000
Current Loans	1,359,873,000		1,382,515,000
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, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	546,000		172,000
Past Due Greater Than 90 Days	1,000	[1]	0	[1]
Total Past Due	547,000		172,000
Nonaccrual	1,040,000		3,956,000
Current Loans	173,093,000		185,821,000
Total LHFI	174,680,000		189,949,000
Commercial And Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	1,258,000		4,317,000
Past Due Greater Than 90 Days	533,000	[1]	2,525,000	[1]
Total Past Due	1,791,000		6,842,000
Nonaccrual	9,053,000		4,741,000
Current Loans	1,196,007,000		1,157,930,000
Total LHFI	1,206,851,000		1,169,513,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	2,184,000		3,480,000
Past Due Greater Than 90 Days	227,000	[1]	284,000	[1]
Total Past Due	2,411,000		3,764,000
Nonaccrual	277,000		360,000
Current Loans	157,565,000		167,536,000
Total LHFI	160,253,000		171,660,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	499,000		181,000
Past Due Greater Than 90 Days	0	[1]	0	[1]
Total Past Due	499,000		181,000
Nonaccrual	3,480,000		798,000
Current Loans	684,644,000		683,934,000
Total LHFI	$ 688,623,000		$ 684,913,000

[1] Past due greater than 90 days but still accruing interest.