Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	$ 15,240,000		$ 15,445,000
Past Due 90 Days or More	1,869,000	[1]	3,298,000	[1]
Total Past Due	17,109,000		18,743,000
Nonaccrual	63,998,000		65,238,000
Current Loans	5,842,659,000		5,714,900,000
Total LHFI	5,923,766,000		5,798,881,000
LHFI past due 90 days or more	1,900,000		3,300,000
LHFS past due 90 days or more	20,100,000		21,500,000
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	2,530,000		923,000
Past Due 90 Days or More	154,000	[1]	0	[1]
Total Past Due	2,684,000		923,000
Nonaccrual	11,259,000		13,327,000
Current Loans	578,715,000		582,639,000
Total LHFI	592,658,000		596,889,000
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	7,969,000		9,437,000
Past Due 90 Days or More	1,431,000	[1]	2,996,000	[1]
Total Past Due	9,400,000		12,433,000
Nonaccrual	24,585,000		21,603,000
Current Loans	1,499,796,000		1,451,528,000
Total LHFI	1,533,781,000		1,485,564,000
Loans Secured by Real Estate [Member] | Secured by Nonfarm, Nonresidential Properties [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	1,418,000		2,044,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	1,418,000		2,044,000
Nonaccrual	20,701,000		21,809,000
Current Loans	1,439,828,000		1,391,286,000
Total LHFI	1,461,947,000		1,415,139,000
Loans Secured by Real Estate [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	63,000		5,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	63,000		5,000
Nonaccrual	1,307,000		1,327,000
Current Loans	191,851,000		188,030,000
Total LHFI	193,221,000		189,362,000
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	1,874,000		1,007,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	1,874,000		1,007,000
Nonaccrual	5,451,000		6,286,000
Current Loans	1,200,042,000		1,150,321,000
Total LHFI	1,207,367,000		1,157,614,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	1,382,000		2,012,000
Past Due 90 Days or More	284,000	[1]	302,000	[1]
Total Past Due	1,666,000		2,314,000
Nonaccrual	134,000		151,000
Current Loans	158,353,000		162,843,000
Total LHFI	160,153,000		165,308,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days	4,000		17,000
Past Due 90 Days or More	0	[1]	0	[1]
Total Past Due	4,000		17,000
Nonaccrual	561,000		735,000
Current Loans	774,074,000		788,253,000
Total LHFI	$ 774,639,000		$ 789,005,000

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