Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI (6) (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Scale	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Loan Market Factor	Sep. 30, 2014 USD ($)
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		$ 69,616			$ 69,616
Provision for loan losses, LHFI	$ 2,514		$ 3,058		5,332	$ 2,604
Balance at end of period	65,607				65,607
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Total	65,607	$ 69,616			$ 69,616		$ 65,607
Number of loan types for commercial portfolio | Loan							9
Number of unique qualitative factors used to analyze consumer loans | Market							5
Number of risk rate factors for commercial loans | Factor							450
Length of loss emergence period in the quantitative portion of the allowance for loan loss methodology for commercial LHFI		1 year 6 months
Additional provision amount quantitative portion of the allowance for loan loss methodology for commercial LHFI		$ 2,300
Minimum score for qualitative risk factor | Scale					0
Maximum score for qualitative risk factor | Scale					100
Amount of provision recapture resulting from the elimination of cap and floors for criticized risk ratings in the qualitative portion of the allowance for loan loss methodology for commercial LHFI		1,800
Amount of provision recapture resulting from market region distribution related to qualitative portion of the allowance for loan loss methodology for commercial LHFI		2,100
Amount of provision recapture resulting from market region distribution related to quantitative portion of the allowance for loan loss methodology for commercial LHFI		785
Additional provision due to revision of methodology	2,200	1,100	822	$ 1,400
Maximum value of commercial LHFI which were subject to further refinement of allowance for loan loss methodology			500
Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		69,616			$ 69,616	66,448
Loans charged-off					(18,688)	(10,052)
Recoveries					9,347	11,134
Net (charge-offs) recoveries					(9,341)	1,082
Provision for loan losses, LHFI					5,332	2,604
Balance at end of period	65,607		70,134		65,607	70,134
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							$ 8,107	$ 10,725
Collectively							57,500	59,409
Total	65,607	69,616	70,134		69,616	66,448	65,607	70,134
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		13,073			13,073	13,165
Loans charged-off					(2,236)	(604)
Recoveries					1,274	3,413
Provision for loan losses, LHFI					395	(6,139)
Balance at end of period	12,506		9,835		12,506	9,835
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							2,054	2,607
Collectively							10,452	7,228
Total	12,506	13,073	9,835		13,073	13,165	12,506	9,835
Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		9,677			9,677	9,633
Loans charged-off					(2,013)	(2,306)
Recoveries					781	861
Provision for loan losses, LHFI					1,529	1,986
Balance at end of period	9,974		10,174		9,974	10,174
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							267	431
Collectively							9,707	9,743
Total	9,974	9,677	10,174		9,677	9,633	9,974	10,174
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		18,523			18,523	19,672
Loans charged-off					(1,282)	(240)
Recoveries					397	400
Provision for loan losses, LHFI					(1,517)	1,099
Balance at end of period	16,121		20,931		16,121	20,931
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							2,602	2,163
Collectively							13,519	18,768
Total	16,121	18,523	20,931		18,523	19,672	16,121	20,931
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		2,141			2,141	2,080
Loans charged-off					(24)	(277)
Recoveries					6	0
Provision for loan losses, LHFI					(382)	571
Balance at end of period	1,741		2,374		1,741	2,374
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							28	57
Collectively							1,713	2,317
Total	1,741	2,141	2,374		2,141	2,080	1,741	2,374
Commercial and Industrial Loans [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		19,917			19,917	15,522
Loans charged-off					(7,243)	(1,787)
Recoveries					1,553	1,321
Provision for loan losses, LHFI					5,109	4,490
Balance at end of period	19,336		19,546		19,336	19,546
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							2,956	5,203
Collectively							16,380	14,343
Total	19,336	19,917	19,546		19,917	15,522	19,336	19,546
Consumer Loans [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		2,149			2,149	2,405
Loans charged-off					(1,543)	(1,304)
Recoveries					2,639	2,760
Provision for loan losses, LHFI					(1,166)	(1,631)
Balance at end of period	2,079		2,230		2,079	2,230
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							0	1
Collectively							2,079	2,229
Total	2,079	2,149	2,230		2,149	2,405	2,079	2,230
State and Other Political Subdivision Loans [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		1,314			1,314	1,205
Loans charged-off					0	0
Recoveries					0	0
Provision for loan losses, LHFI					(624)	736
Balance at end of period	690		1,941		690	1,941
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							0	0
Collectively							690	1,941
Total	690	1,314	1,941		1,314	1,205	690	1,941
Other Loans [Member] | Allowance for Loan Loses, LHFI [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period		2,822			2,822	2,766
Loans charged-off					(4,347)	(3,534)
Recoveries					2,697	2,379
Provision for loan losses, LHFI					1,988	1,492
Balance at end of period	3,160		3,103		3,160	3,103
Financing Receivable, Allowance for Credit Loss, Additional Information [Abstract]
Individually							200	263
Collectively							2,960	2,840
Total	$ 3,160	$ 2,822	$ 3,103		$ 2,822	$ 2,766	$ 3,160	$ 3,103