Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (5) (Details) (USD $)	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2013	Sep. 30, 2014		Dec. 31, 2013
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 59 Days		$ 20,655,000		$ 12,606,000
Past Due 60 - 89 Days		7,299,000		2,839,000
Past Due 90 Days or More		3,839,000	[1]	3,298,000	[1]
Total Past Due		31,793,000		18,743,000
Nonaccrual		88,314,000		65,238,000
Current Loans		6,213,544,000		5,714,900,000
Total LHFI		6,333,651,000		5,798,881,000
LHFI past due 90 days or more		3,800,000		3,300,000
LHFS past due 90 days or more		25,000,000		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 [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 59 Days		466,000		656,000
Past Due 60 - 89 Days		360,000		267,000
Past Due 90 Days or More		268,000	[1]	0	[1]
Total Past Due		1,094,000		923,000
Nonaccrual		20,286,000		13,327,000
Current Loans		559,414,000		582,639,000
Total LHFI		580,794,000		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 - 59 Days		6,685,000		7,322,000
Past Due 60 - 89 Days		2,893,000		2,115,000
Past Due 90 Days or More		2,845,000	[1]	2,996,000	[1]
Total Past Due		12,423,000		12,433,000
Nonaccrual		27,017,000		21,603,000
Current Loans		1,586,040,000		1,451,528,000
Total LHFI		1,625,480,000		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 - 59 Days		9,787,000		1,934,000
Past Due 60 - 89 Days		3,614,000		110,000
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		13,401,000		2,044,000
Nonaccrual		23,885,000		21,809,000
Current Loans		1,523,615,000		1,391,286,000
Total LHFI		1,560,901,000		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 - 59 Days		202,000		2,000
Past Due 60 - 89 Days		65,000		3,000
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		267,000		5,000
Nonaccrual		1,203,000		1,327,000
Current Loans		238,349,000		188,030,000
Total LHFI		239,819,000		189,362,000
Commercial and Industrial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 59 Days		1,806,000		809,000
Past Due 60 - 89 Days		97,000		198,000
Past Due 90 Days or More		454,000	[1]	0	[1]
Total Past Due		2,357,000		1,007,000
Nonaccrual		15,178,000		6,286,000
Current Loans		1,229,218,000		1,150,321,000
Total LHFI		1,246,753,000		1,157,614,000
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 59 Days		1,627,000		1,866,000
Past Due 60 - 89 Days		243,000		146,000
Past Due 90 Days or More		272,000	[1]	302,000	[1]
Total Past Due		2,142,000		2,314,000
Nonaccrual		160,000		151,000
Current Loans		166,511,000		162,843,000
Total LHFI		168,813,000		165,308,000
Other Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due 30 - 59 Days		82,000		17,000
Past Due 60 - 89 Days		27,000		0
Past Due 90 Days or More		0	[1]	0	[1]
Total Past Due		109,000		17,000
Nonaccrual		585,000		735,000
Current Loans		910,397,000		788,253,000
Total LHFI		$ 911,091,000		$ 789,005,000

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