Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (1) (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) Region	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	$ 83,500		$ 96,365
Total LHFI With No Related Allowance Recorded	14,364		23,135
Total LHFI With an Allowance Recorded	54,074		56,208
Total LHFI Carrying Amount	68,438		79,343
Related Allowance	14,220		12,764
Average Recorded Investment	$ 73,891		72,291
Maximum concentration of loan as a percentage of total LHFI (in hundredths)	10.00%
Key market regions | Region	5
Carrying amounts of nonaccrual LHFI considered for impairment analysis	$ 68,400		79,300
Minimum loan amount for loan to be individually assessed for impairment	500
Nonaccrual financing receivable, specifically evaluated for impairment	37,900		47,100
Nonaccrual financing receivable, allowance for credit losses, specifically evaluated for impairment	12,400		11,300
Nonaccrual financing receivable, allowance for credit losses, charge-offs, specifically evaluated for impairment	1,300	$ 55
Nonaccrual financing receivable specifically evaluated for impairment allowance for credit losses provisions	1,900	1,400
Nonaccrual financing receivable, not specifically evaluated for impairment	30,500		32,200
Nonaccrual financing receivable, allowance for credit losses, not specifically evaluated for impairment	1,800		1,500
Amount held by company of foreclosure or in substance repossession of consumer mortgage LHFI classified as TDRs	736
TDRs Classified as Consumer mortgage LHFI in the process of formal disclosure	149
Classified as Troubled Debt Restructuring LHFI	12,100	12,600
TDRs comprised of credits with interest only payments	8,300	8,400
Financing receivable, related allowance	1,900	1,500
Financing receivable, related charge-offs	806	$ 55
Construction, Land Development And Other Land Properties [Member] | Loans Secured by Real Estate [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	17,580		20,849
Total LHFI With No Related Allowance Recorded	4,918		7,411
Total LHFI With an Allowance Recorded	5,970		6,456
Total LHFI Carrying Amount	10,888		13,867
Related Allowance	3,007		2,767
Average Recorded Investment	12,378		13,597
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	30,483		31,151
Total LHFI With No Related Allowance Recorded	1,291		1,650
Total LHFI With an Allowance Recorded	23,591		23,971
Total LHFI Carrying Amount	24,882		25,621
Related Allowance	469		450
Average Recorded Investment	25,251		23,612
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	20,663		27,969
Total LHFI With No Related Allowance Recorded	6,727		12,868
Total LHFI With an Allowance Recorded	12,303		12,849
Total LHFI Carrying Amount	19,030		25,717
Related Allowance	3,295		2,787
Average Recorded Investment	22,373		23,763
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	704		1,594
Total LHFI With No Related Allowance Recorded	0		0
Total LHFI With an Allowance Recorded	610		1,318
Total LHFI Carrying Amount	610		1,318
Related Allowance	46		52
Average Recorded Investment	964		1,322
Commercial and Industrial Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	13,290		13,916
Total LHFI With No Related Allowance Recorded	1,428		1,206
Total LHFI With an Allowance Recorded	10,983		10,898
Total LHFI Carrying Amount	12,411		12,104
Related Allowance	7,196		6,449
Average Recorded Investment	12,258		9,195
Consumer Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	86		152
Total LHFI With No Related Allowance Recorded	0		0
Total LHFI With an Allowance Recorded	44		88
Total LHFI Carrying Amount	44		88
Related Allowance	0		0
Average Recorded Investment	66		120
State and Other Political Subdivision Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	0		0
Total LHFI With No Related Allowance Recorded	0		0
Total LHFI With an Allowance Recorded	0		0
Total LHFI Carrying Amount	0		0
Related Allowance	0		0
Average Recorded Investment	0		0
Other Loans [Member]
Loan and Lease Receivables, Impaired [Abstract]
Total LHFI Unpaid Principal Balance	694		734
Total LHFI With No Related Allowance Recorded	0		0
Total LHFI With an Allowance Recorded	573		628
Total LHFI Carrying Amount	573		628
Related Allowance	207		259
Average Recorded Investment	$ 601		$ 682