Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2013	Jun. 30, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days		$ 22,379,000		$ 15,445,000
Past Due 90 Days or More		1,935,000	[1]	3,298,000	[1]
Total Past Due		24,314,000		18,743,000
Nonaccrual		71,118,000		65,238,000
Current Loans		6,091,568,000		5,714,900,000
Total LHFI		6,187,000,000		5,798,881,000
LHFI past due 90 days or more		1,900,000		3,300,000
LHFS past due 90 days or more		21,800,000		21,500,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program (in hundredths)		100.00%
Amount of delinquent loans repurchased	57,400,000
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		1,797,000		923,000
Past Due 90 Days or More		53,000	[1]	0	[1]
Total Past Due		1,850,000		923,000
Nonaccrual		21,142,000		13,327,000
Current Loans		508,659,000		582,639,000
Total LHFI		531,651,000		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		13,151,000		9,437,000
Past Due 90 Days or More		1,729,000	[1]	2,996,000	[1]
Total Past Due		14,880,000		12,433,000
Nonaccrual		23,403,000		21,603,000
Current Loans		1,543,576,000		1,451,528,000
Total LHFI		1,581,859,000		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		2,990,000		2,044,000
Past Due 90 Days or More		1,000	[1]	0	[1]
Total Past Due		2,991,000		2,044,000
Nonaccrual		18,659,000		21,809,000
Current Loans		1,522,866,000		1,391,286,000
Total LHFI		1,544,516,000		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		129,000		5,000
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		129,000		5,000
Nonaccrual		1,233,000		1,327,000
Current Loans		249,021,000		188,030,000
Total LHFI		250,383,000		189,362,000
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days		2,781,000		1,007,000
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		2,781,000		1,007,000
Nonaccrual		5,762,000		6,286,000
Current Loans		1,241,603,000		1,150,321,000
Total LHFI		1,250,146,000		1,157,614,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days		1,456,000		2,012,000
Past Due 90 Days or More		152,000	[1]	302,000	[1]
Total Past Due		1,608,000		2,314,000
Nonaccrual		107,000		151,000
Current Loans		163,657,000		162,843,000
Total LHFI		165,372,000		165,308,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 89 Days		75,000		17,000
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		75,000		17,000
Nonaccrual		812,000		735,000
Current Loans		862,186,000		788,253,000
Total LHFI		$ 863,073,000		$ 789,005,000

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