Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	9 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	$ 34,380,000		$ 35,193,000
Past Due 90 Days or More	2,344,000	[1]	6,378,000	[1]
Total Past Due	36,724,000		41,571,000
Nonaccrual	73,381,000		82,363,000
Current Loans	5,586,536,000		5,468,820,000
Total LHFI	5,696,641,000		5,592,754,000
LHFI past due 90 days or more	2,300,000		6,400,000
LHFS past due 90 days or more	18,400,000		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	12,401,000		4,957,000
Past Due 90 Days or More	1,000	[1]	438,000	[1]
Total Past Due	12,402,000		5,395,000
Nonaccrual	14,454,000		27,105,000
Current Loans	545,201,000		436,475,000
Total LHFI	572,057,000		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	10,925,000		12,626,000
Past Due 90 Days or More	1,996,000	[1]	3,131,000	[1]
Total Past Due	12,921,000		15,757,000
Nonaccrual	23,715,000		27,114,000
Current Loans	1,446,327,000		1,454,609,000
Total LHFI	1,482,963,000		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	6,163,000		9,460,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	6,163,000		9,460,000
Nonaccrual	21,290,000		18,289,000
Current Loans	1,380,889,000		1,382,515,000
Total LHFI	1,408,342,000		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	120,000		172,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	120,000		172,000
Nonaccrual	503,000		3,956,000
Current Loans	195,705,000		185,821,000
Total LHFI	196,328,000		189,949,000
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	2,665,000		4,317,000
Past Due 90 Days or More	41,000	[1]	2,525,000	[1]
Total Past Due	2,706,000		6,842,000
Nonaccrual	12,196,000		4,741,000
Current Loans	1,117,961,000		1,157,930,000
Total LHFI	1,132,863,000		1,169,513,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	2,018,000		3,480,000
Past Due 90 Days or More	306,000	[1]	284,000	[1]
Total Past Due	2,324,000		3,764,000
Nonaccrual	203,000		360,000
Current Loans	162,085,000		167,536,000
Total LHFI	164,612,000		171,660,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	88,000		181,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	88,000		181,000
Nonaccrual	1,020,000		798,000
Current Loans	738,368,000		683,934,000
Total LHFI	$ 739,476,000		$ 684,913,000

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