Loans and Allowance for Probable Loan Losses - Allowance for Loan Losses, Loan Portfolio, by Impairment Method (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		$ 24,349	$ 9,022
Loans collectively evaluated for impairment		2,135,223	2,150,765	[1]
Total ending loan balance	[2]	2,179,863	2,181,133
Construction
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		2,342	2,461
Loans collectively evaluated for impairment		293,061	264,584	[1]
Total ending loan balance		295,633	267,830
1-4 Family Residential
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		1,793	2,936
Loans collectively evaluated for impairment		675,039	680,658	[1]
Total ending loan balance		683,944	690,895
Other
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		4,099	1,605
Loans collectively evaluated for impairment		493,344	463,564	[1]
Total ending loan balance		500,906	468,171
Commercial Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		14,987	1,011
Loans collectively evaluated for impairment		204,826	216,272	[1]
Total ending loan balance		228,789	226,460
Municipal Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		949	699
Loans collectively evaluated for impairment		255,543	256,793	[1]
Total ending loan balance		256,492	257,492
Loans to Individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Loans individually evaluated for impairment		179	310
Loans collectively evaluated for impairment		213,410	268,894	[1]
Total ending loan balance		214,099	270,285
Receivables Acquired with Deteriorated Credit Quality [Member]
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		20,291	21,346	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		230	785	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | 1-4 Family Residential
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		7,112	7,301	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | Other
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		3,463	3,002	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		8,976	9,177	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | Municipal Loans
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		0	0	[3]
Receivables Acquired with Deteriorated Credit Quality [Member] | Loans to Individuals
Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items]
Purchased credit impaired loans		$ 510	$ 1,081	[3]

[1] Includes purchased non impaired loans which were measured at fair value at acquisition and did not have an associated allowance for loan loss as of December 31, 2014.

[2] Includes approximately $679.7 million and $763.3 million of loans acquired with the Omni acquisition as of June 30, 2015 and December 31, 2014, respectively. These loans were measured at fair value at the acquisition date with no carryover of allowance for loan loss.

[3] PCI loans were measured at fair value at acquisition and did not have an associated allowance for loan loss as of December 31, 2014.