Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	6 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	$ 24,068,000		$ 35,193,000
Past Due Greater Than 90 Days	4,195,000	[1]	6,378,000	[1]
Total Past Due	28,263,000		41,571,000
Nonaccrual	74,318,000		82,363,000
Current Loans	5,474,801,000		5,468,820,000
Total LHFI	5,577,382,000		5,592,754,000
LHFI past due 90 days or more	4,200,000		6,400,000
LHFS past due 90 days or more	14,000,000		43,100,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program (in hundredths)	100.00%
Repurchase gain included in gain on sales of loans	534,000
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	2,935,000		4,957,000
Past Due Greater Than 90 Days	57,000	[1]	438,000	[1]
Total Past Due	2,992,000		5,395,000
Nonaccrual	16,259,000		27,105,000
Current Loans	500,012,000		436,475,000
Total LHFI	519,263,000		468,975,000
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	7,480,000		12,626,000
Past Due Greater Than 90 Days	3,936,000	[1]	3,131,000	[1]
Total Past Due	11,416,000		15,757,000
Nonaccrual	23,837,000		27,114,000
Current Loans	1,379,618,000		1,454,609,000
Total LHFI	1,414,871,000		1,497,480,000
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	4,406,000		9,460,000
Past Due Greater Than 90 Days	0	[1]	0	[1]
Total Past Due	4,406,000		9,460,000
Nonaccrual	18,418,000		18,289,000
Current Loans	1,384,106,000		1,382,515,000
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, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	61,000		172,000
Past Due Greater Than 90 Days	0	[1]	0	[1]
Total Past Due	61,000		172,000
Nonaccrual	511,000		3,956,000
Current Loans	191,996,000		185,821,000
Total LHFI	192,568,000		189,949,000
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	6,274,000		4,317,000
Past Due Greater Than 90 Days	0	[1]	2,525,000	[1]
Total Past Due	6,274,000		6,842,000
Nonaccrual	14,193,000		4,741,000
Current Loans	1,148,860,000		1,157,930,000
Total LHFI	1,169,327,000		1,169,513,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	2,493,000		3,480,000
Past Due Greater Than 90 Days	202,000	[1]	284,000	[1]
Total Past Due	2,695,000		3,764,000
Nonaccrual	267,000		360,000
Current Loans	157,356,000		167,536,000
Total LHFI	160,318,000		171,660,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	419,000		181,000
Past Due Greater Than 90 Days	0	[1]	0	[1]
Total Past Due	419,000		181,000
Nonaccrual	833,000		798,000
Current Loans	712,853,000		683,934,000
Total LHFI	$ 714,105,000		$ 684,913,000

[1] Past due 90 days or more but still accruing interest.