Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (1) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Region	Dec. 31, 2013	Dec. 31, 2012
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	$ 96,365,000	$ 86,982,000
Total LHFI With No Related Allowance Recorded	23,135,000	25,643,000
Total LHFI With an Allowance Recorded	56,208,000	39,595,000
Total Carrying Amount	79,343,000	65,238,000
Related Allowance	12,764,000	5,181,000
Average Recorded Investment	72,291,000	73,800,000
Maximum Concentration Of Loan as a Percentage of Total LHFI (in hundredths)	10.00%
Key market regions	5
Loans and Leases Receivable, Related Parties	95,200,000	89,000,000
New loan advances to related party	643,100,000
Loan repayment by related party	636,500,000
Loan decreases from changes in executive officers and directors	372,000
Carrying amounts of nonaccrual LHFI considered for impairment analysis	79,300,000	65,200,000
Minimum loan amount for loan to be individually assessed for impairment	500,000
Nonaccrual Financing Receivable, Specifically Evaluated For Impairment	47,100,000	31,600,000
Nonaccrual Financing Receivable, Allowance for Credit Losses, Specifically Evaluated For Impairment	11,300,000	2,200,000
Nonaccrual Financing Receivable, Allowance For Credit Losses, Charge-offs, Specifically Evaluated For Impairment	137,000	2,500,000	13,100,000
Nonaccrual Financing Receivable Specifically Evaluated For Impairment Allowance For Credit Losses Provisions	3,500,000	2,900,000	1,100,000
Nonaccrual Financing Receivable, Not Specifically Evaluated for Impairment	32,200,000	33,700,000
Nonaccrual Financing Receivable, Allowance for Credit Losses, Not Specifically Evaluated for Impairment	1,500,000	3,000,000
Classified as Troubled Debt Restructuring LHFI	11,300,000	14,800,000	24,300,000
TDRs comprised of credits with interest only payments	7,400,000	11,100,000	21,600,000
Financing Receivable, Related Allowance	1,700,000	1,600,000	4,300,000
Financing Receivable, Related Charge-offs	75,000	816,000	6,000,000
Loans Secured by Real Estate [Member] | Construction, Land Development and Other Land [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	20,849,000	24,350,000
Total LHFI With No Related Allowance Recorded	7,411,000	9,817,000
Total LHFI With an Allowance Recorded	6,456,000	3,510,000
Total Carrying Amount	13,867,000	13,327,000
Related Allowance	2,767,000	989,000
Average Recorded Investment	13,597,000	20,216,000
Loans Secured by Real Estate [Member] | Secured by 1-4 Family Residential Properties [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	31,151,000	26,541,000
Total LHFI With No Related Allowance Recorded	1,650,000	3,095,000
Total LHFI With an Allowance Recorded	23,971,000	18,508,000
Total Carrying Amount	25,621,000	21,603,000
Related Allowance	450,000	191,000
Average Recorded Investment	23,612,000	24,359,000
Loans Secured by Real Estate [Member] | Nonfarm, Nonresidential Properties [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	27,969,000	24,879,000
Total LHFI With No Related Allowance Recorded	12,868,000	10,225,000
Total LHFI With an Allowance Recorded	12,849,000	11,584,000
Total Carrying Amount	25,717,000	21,809,000
Related Allowance	2,787,000	2,307,000
Average Recorded Investment	23,763,000	20,049,000
Loans Secured by Real Estate [Member] | Other Real Estate Secured Financing Receivable [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	1,594,000	1,375,000
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	1,318,000	1,327,000
Total Carrying Amount	1,318,000	1,327,000
Related Allowance	52,000	122,000
Average Recorded Investment	1,322,000	2,641,000
Commercial and Industrial Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	13,916,000	8,702,000
Total LHFI With No Related Allowance Recorded	1,206,000	2,506,000
Total LHFI With an Allowance Recorded	10,898,000	3,780,000
Total Carrying Amount	12,104,000	6,286,000
Related Allowance	6,449,000	1,253,000
Average Recorded Investment	9,195,000	5,513,000
Consumer Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	152,000	286,000
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	88,000	151,000
Total Carrying Amount	88,000	151,000
Related Allowance	0	2,000
Average Recorded Investment	120,000	255,000
Other Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Unpaid Principal Balance	734,000	849,000
Total LHFI With No Related Allowance Recorded	0	0
Total LHFI With an Allowance Recorded	628,000	735,000
Total Carrying Amount	628,000	735,000
Related Allowance	259,000	317,000
Average Recorded Investment	$ 682,000	$ 767,000