Prosperity Bancshares (PB) 10-Q 8 Nov 13 2013 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2013	Nov. 01, 2013
Document And Entity Information [Abstract]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Trading Symbol	'PB	'
Entity Registrant Name	'PROSPERITY BANCSHARES INC	'
Entity Central Index Key	'0001068851	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	65,953,559

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
ASSETS	'	'
Cash and due from banks	$269,987	$325,952
Federal funds sold	1,121	352
Total cash and cash equivalents	271,108	326,304
Available for sale securities, at fair value	164,776	226,670
Held to maturity securities, at cost (fair value of $7,556,171 and $7,418,695, respectively)	7,606,569	7,215,395
Total securities	7,771,345	7,442,065
Loans held for sale	4,892	10,433
Loans held for investment	6,177,697	5,169,507
Total loans	6,182,589	5,179,940
Less: allowance for credit losses	-59,913	-52,564
Loans, net	6,122,676	5,127,376
Accrued interest receivable	38,183	42,337
Goodwill	1,351,782	1,217,162
Core deposit intangibles, net	25,233	26,159
Bank premises and equipment, net	232,240	205,268
Other real estate owned	7,432	7,234
Bank owned life insurance (BOLI)	122,123	109,108
Federal Home Loan Bank of Dallas stock	43,058	34,461
Other assets	69,099	46,099
TOTAL ASSETS	16,054,279	14,583,573
Deposits:	'	'
Noninterest-bearing	3,368,357	3,016,205
Interest-bearing	9,087,442	8,625,639
Total deposits	12,455,799	11,641,844
Other borrowings	605,951	256,753
Securities sold under repurchase agreements	431,969	454,502
Junior subordinated debentures	85,055	85,055
Accrued interest payable	2,267	1,904
Other liabilities	84,126	54,126
Total liabilities	13,665,167	12,494,184
COMMITMENTS AND CONTINGENCIES	'	'
SHAREHOLDERS' EQUITY:	'	'
Preferred stock, $1 par value; 20,000,000 shares authorized; none issued or outstanding	'	'
Common stock, $1 par value; 200,000,000 shares authorized; 60,419,980 and 56,484,234 shares issued at September 30, 2013 and December 31, 2012, respectively; 60,382,892 and 56,447,146 shares outstanding at September 30, 2013 and December 31, 2012, respectively	60,420	56,484
Capital surplus	1,453,263	1,274,290
Retained earnings	870,454	750,236
Accumulated other comprehensive income-net unrealized gain on available for sale securities, net of tax of $3,006 and $4,839, respectively	5,582	8,986
Less treasury stock, at cost, 37,088 shares	-607	-607
Total shareholders' equity	2,389,112	2,089,389
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$16,054,279	$14,583,573

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified
Statement Of Financial Position [Abstract]	'	'
Held to maturity securities, Fair value	$7,556,171	$7,418,695
Preferred stock, par value	$1	$1
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$1	$1
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	60,419,980	56,484,234
Common stock, shares outstanding	60,382,892	56,447,146
Accumulated other comprehensive income - unrealized gain on available for sale securities, tax	$3,006	$4,839
Treasury stock, shares	37,088	37,088

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
INTEREST INCOME:	'	'	'	'
Loans, including fees	$94,236	$80,587	$265,542	$188,597
Securities	41,961	37,025	117,893	113,418
Federal funds sold	16	21	111	108
Total interest income	136,213	117,633	383,546	302,123
INTEREST EXPENSE:	'	'	'	'
Deposits	8,314	9,395	26,174	26,269
Other borrowings	439	379	1,273	1,076
Securities sold under repurchase agreements	317	315	921	411
Junior subordinated debentures	610	651	1,821	1,962
Total interest expense	9,680	10,740	30,189	29,718
NET INTEREST INCOME	126,533	106,893	353,357	272,405
Provision for credit losses	4,025	1,800	9,375	2,550
NET INTEREST INCOME AFTER PROVISION FOR CREDIT LOSSES	122,508	105,093	343,982	269,855
NONINTEREST INCOME:	'	'	'	'
Nonsufficient funds (NSF) fees	8,649	9,265	25,504	19,050
Credit card, debit card and ATM card income	4,307	6,246	17,801	14,374
Service charges on deposit accounts	3,169	3,362	9,404	9,006
Trust income	901	831	2,814	831
Mortgage income	931	1,437	3,489	1,350
Other	3,597	2,687	11,257	6,818
Total noninterest income	21,554	23,828	70,269	51,429
NONINTEREST EXPENSE:	'	'	'	'
Salaries and employee benefits	37,135	36,701	107,861	83,525
Net occupancy and equipment	5,094	4,614	14,041	11,663
Debit card, data processing and software amortization	2,756	2,901	8,575	6,339
Regulatory assessments and FDIC insurance	2,516	2,107	7,490	5,314
Core deposit intangibles amortization	1,455	2,007	4,551	5,297
Depreciation	2,679	2,369	7,521	6,432
Communications (including telephone, courier and postage)	2,397	2,226	7,003	5,777
Other real estate expense	75	271	535	2,619
Other	7,430	7,046	21,027	14,523
Total noninterest expense	61,537	60,242	178,604	141,489
INCOME BEFORE INCOME TAXES	82,525	68,679	235,647	179,795
PROVISION FOR INCOME TAXES	27,247	22,503	77,220	60,160
NET INCOME	$55,278	$46,176	$158,427	$119,635
EARNINGS PER SHARE:	'	'	'	'
Basic	$0.92	$0.83	$2.68	$2.38
Diluted	$0.91	$0.82	$2.67	$2.37

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]	'	'	'	'
Net income	$55,278	$46,176	$158,427	$119,635
Securities available for sale:	'	'	'	'
Change in unrealized gain during period	-1,136	-718	-5,237	-3,736
Total other comprehensive loss	-1,136	-718	-5,237	-3,736
Deferred tax benefit related to other comprehensive income	398	251	1,833	1,308
Other comprehensive loss, net of tax	-738	-467	-3,404	-2,428
Comprehensive income	$54,540	$45,709	$155,023	$117,207

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS EQUITY (USD $)

Total

Texas Bankers, Inc [Member]

The Bank Arlington [Member]

American State Financial Corporation [Member]

East Texas Financial Services, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Common Stock [Member]

Capital Surplus [Member]

Capital Surplus [Member]

Capital Surplus [Member]

Capital Surplus [Member]

Capital Surplus [Member]

Capital Surplus [Member]

Retained Earnings [Member]

Accumulated Other Comprehensive Income [Member]

Treasury Stock [Member]

In Thousands, except Share data

Texas Bankers, Inc [Member]

The Bank Arlington [Member]

American State Financial Corporation [Member]

East Texas Financial Services, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Texas Bankers, Inc [Member]

The Bank Arlington [Member]

American State Financial Corporation [Member]

East Texas Financial Services, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

BALANCE at Dec. 31, 2011

$1,567,265

'

'

'

'

'

$46,947

'

'

'

'

'

$883,575

'

'

'

'

'

$623,878

$13,472

($607)

BALANCE, Shares at Dec. 31, 2011

'

'

'

'

'

'

46,947,415

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income

119,635

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

119,635

'

'

Other comprehensive loss

-2,428

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-2,428

'

Common stock issued in connection with the exercise of stock options and restricted stock awards

2,691

'

'

'

'

'

173

'

'

'

'

'

2,518

'

'

'

'

'

'

'

'

Common stock issued in connection with the exercise of stock options and restricted stock awards (in shares)

'

'

'

'

'

'

172,698

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock issued in connection with the acquisition

'

12,708

6,198

358,299

'

'

'

315

135

8,525

'

'

'

12,393

6,063

349,774

'

'

'

'

'

Common stock issued in connection with the acquisition (in shares)

'

'

'

'

'

'

'

314,953

135,347

8,524,835

'

'

'

'

'

'

'

'

'

'

'

Stock based compensation expense

3,218

'

'

'

'

'

'

'

'

'

'

'

3,218

'

'

'

'

'

'

'

'

Cash dividends declared

-29,410

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-29,410

'

'

BALANCE at Sep. 30, 2012

2,038,176

'

'

'

'

'

56,095

'

'

'

'

'

1,257,541

'

'

'

'

'

714,103

11,044

-607

BALANCE, Shares at Sep. 30, 2012

'

'

'

'

'

'

56,095,248

'

'

'

'

'

'

'

'

'

'

'

'

'

'

BALANCE at Dec. 31, 2012

2,089,389

'

'

'

'

'

56,484

'

'

'

'

'

1,274,290

'

'

'

'

'

750,236

8,986

-607

BALANCE, Shares at Dec. 31, 2012

'

'

'

'

'

'

56,484,234

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income

158,427

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

158,427

'

'

Other comprehensive loss

-3,404

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-3,404

'

Common stock issued in connection with the exercise of stock options and restricted stock awards

3,039

'

'

'

'

'

146

'

'

'

'

'

2,893

'

'

'

'

'

'

'

'

Common stock issued in connection with the exercise of stock options and restricted stock awards (in shares)

'

'

'

'

'

'

146,088

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock issued in connection with the acquisition

'

'

'

'

22,300

154,431

'

'

'

'

531

3,259

'

'

'

'

21,769

151,172

'

'

'

Common stock issued in connection with the acquisition (in shares)

'

'

'

'

'

'

'

'

'

'

530,940

3,258,718

'

'

'

'

'

'

'

'

'

Stock based compensation expense

3,139

'

'

'

'

'

'

'

'

'

'

'

3,139

'

'

'

'

'

'

'

'

Cash dividends declared

-38,209

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-38,209

'

'

BALANCE at Sep. 30, 2013

$2,389,112

'

'

'

'

'

$60,420

'

'

'

'

'

$1,453,263

'

'

'

'

'

$870,454

$5,582

($607)

BALANCE, Shares at Sep. 30, 2013

'

'

'

'

'

'

60,419,980

'

'

'

'

'

'

'

'

'

'

'

'

'

'

CONSOLIDATED_STATEMENTS_OF_CHA1

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS EQUITY (Parenthetical) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Statement Of Stockholders Equity [Abstract]	'	'
Cash dividends declared, per share	$0.65	$0.59

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:	'	'
Net income	$158,427	$119,635
Adjustments to reconcile net income to net cash provided by operating activities:	'	'
Depreciation and core deposit intangibles amortization	12,072	11,729
Provision for credit losses	9,375	2,550
Net amortization of premium on investments	56,825	42,897
Loss on sale or write down of premises, equipment and other real estate	785	331
Net accretion of discount on loans	-42,744	-11,988
Proceeds from sale of loans held for sale	143,745	9,438
Originations of loans held for sale	-140,715	'
Stock based compensation expense	3,139	3,218
Decrease (increase) in accrued interest receivable and other assets	25,058	-19,623
Increase in accrued interest payable and other liabilities	22,716	42,510
Net cash provided by operating activities	248,683	200,697
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Proceeds from maturities and principal paydowns of held to maturity securities	1,814,877	1,238,538
Purchase of held to maturity securities	-2,245,685	-2,499,561
Proceeds from maturities, sales and principal paydowns of available for sale securities	2,012,178	1,703,676
Purchase of available for sale securities	-1,954,999	-1,109,999
Net increase in loans held for investment	-47,466	-128,225
Purchase of bank premises and equipment	-20,937	-7,924
Proceeds from sale of bank premises, equipment and other real estate	11,232	12,004
Net cash used in investing activities	-138,534	-611,882
CASH FLOWS FROM FINANCING ACTIVITIES:	'	'
Net increase in noninterest-bearing deposits	43,221	193,360
Net (decrease) increase in interest-bearing deposits	-459,351	101,866
Net proceeds from other short-term borrowings	349,583	100,000
Repayments of other long-term borrowings	-41,095	-772
Net (decrease) increase in securities sold under repurchase agreements	-22,533	37,711
Proceeds from stock option exercises	3,039	2,691
Payments of cash dividends	-38,209	-29,410
Net cash (used in) provided by financing activities	-165,345	405,446
NET DECREASE IN CASH AND CASH EQUIVALENTS	-55,196	-5,739
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD	326,304	213,442
CASH AND CASH EQUIVALENTS, END OF PERIOD	271,108	207,703
NONCASH ACTIVITIES:	'	'
Acquisition of real estate through foreclosure of collateral	3,044	11,354
SUPPLEMENTAL INFORMATION:	'	'
Income taxes paid	69,659	53,737
Interest paid	29,674	30,434
Texas Bankers, Inc [Member]	'	'
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Net cash and cash equivalents acquired in the purchase of subsidiary	'	44,550
NONCASH ACTIVITIES:	'	'
Stock issued in connection with acquisition	'	12,708
The Bank Arlington [Member]	'	'
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Net cash and cash equivalents acquired in the purchase of subsidiary	'	12,037
NONCASH ACTIVITIES:	'	'
Stock issued in connection with acquisition	'	6,198
American State Financial Corporation [Member]	'	'
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Net cash and cash equivalents acquired in the purchase of subsidiary	'	123,022
NONCASH ACTIVITIES:	'	'
Stock issued in connection with acquisition	'	358,299
East Texas Financial Services, Inc [Member]	'	'
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Net cash and cash equivalents acquired in the purchase of subsidiary	3,471	'
NONCASH ACTIVITIES:	'	'
Stock issued in connection with acquisition	22,300	'
Coppermark Bancshares, Inc. [Member]	'	'
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Net cash and cash equivalents acquired in the purchase of subsidiary	288,795	'
NONCASH ACTIVITIES:	'	'
Stock issued in connection with acquisition	$154,431	'

BASIS_OF_PRESENTATION

BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
BASIS OF PRESENTATION	'
	1. BASIS OF PRESENTATION
	The interim consolidated financial statements include the accounts of Prosperity Bancshares, Inc.® (the “Company”) and its wholly-owned subsidiaries, Prosperity Bank® (the “Bank”) and Prosperity Holdings of Delaware, LLC. All intercompany transactions and balances have been eliminated.
	The accompanying unaudited interim consolidated financial statements have been prepared in accordance with generally accepted accounting principles for interim financial information and with the rules and regulations of the Securities and Exchange Commission. Accordingly, they do not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements. In the opinion of management, the statements reflect all adjustments necessary for a fair presentation of the financial position, results of operations and cash flows of the Company on a consolidated basis, and all such adjustments are of a normal recurring nature. These financial statements and the notes thereto should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2012. Operating results for the nine-month period ended September 30, 2013 are not necessarily indicative of the results that may be expected for the year ending December 31, 2013 or any other period.

INCOME_PER_COMMON_SHARE

INCOME PER COMMON SHARE	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
INCOME PER COMMON SHARE	'
	2. INCOME PER COMMON SHARE
	Outstanding stock options issued by the Company represent the only dilutive effect reflected in diluted weighted average shares. The following table illustrates the computation of basic and diluted earnings per share:
		Three Months Ended September 30,								Nine Months Ended September 30,
		2013				2012				2013				2012
		Amount		Per Share		Amount		Per Share		Amount		Per Share		Amount		Per Share
				Amount				Amount				Amount				Amount
		(In thousands, except per share data)
	Net income	$	55,278			$	46,176			$	158,427			$	119,635
	Basic:
	Weighted average shares outstanding		60,344	$	0.92		55,958	$	0.83		59,207	$	2.68		50,239	$	2.38
	Diluted:
	Add incremental shares for:
	Effect of dilutive securities—options		160				135				155				154
	Total		60,504	$	0.91		56,093	$	0.82		59,362	$	2.67		50,393	$	2.37
	There were no stock options exercisable during the three and nine months ended September 30, 2013 or 2012 that would have had an anti-dilutive effect on the above computation.

NEW_ACCOUNTING_STANDARDS

NEW ACCOUNTING STANDARDS	9 Months Ended
	Sep. 30, 2013
Accounting Changes And Error Corrections [Abstract]	'
NEW ACCOUNTING STANDARDS	'
	3. NEW ACCOUNTING STANDARDS
	Accounting Standards Updates (“ASU”)
	ASU 2012-02 “Intangibles—Goodwill and Other (Topic 350) — Testing Indefinite-Lived Intangible Assets for Impairment.” ASU 2012-02 gives entities the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that an indefinite-lived intangible asset is impaired. If, after assessing the totality of events or circumstances, an entity determines it is more likely than not that an indefinite-lived intangible asset is impaired, then the entity must perform the quantitative impairment test. If, under the quantitative impairment test, the carrying amount of the intangible asset exceeds its fair value, an entity should recognize an impairment loss in the amount of that excess permitting an entity to assess qualitative factors when testing indefinite-lived intangible assets for impairment results in guidance that is similar to the goodwill impairment testing guidance in ASU 2011-08. ASU 2012-02 became effective for the Company on January 1, 2013 and did not have a significant impact on the Company’s financial statements.
	ASU 2013-02 “Comprehensive Income (Topic 220) — Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income.” ASU 2013-02 amends recent guidance related to the reporting of comprehensive income to enhance the reporting of reclassifications out of accumulated other comprehensive income. ASU 2013-02 became effective for the Company on January 1, 2013 and did not have a significant impact on the Company’s financial statements. See Note 10 – Other Comprehensive (Loss) Income for applicable disclosures.

SECURITIES

SECURITIES	9 Months Ended
	Sep. 30, 2013
Investments Debt And Equity Securities [Abstract]	'
SECURITIES	'
	4. SECURITIES
	The amortized cost and fair value of investment securities were as follows:
		September 30, 2013
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			Losses
		(Dollars in thousands)
	Available for Sale
	States and political subdivisions	$	29,130	$	1,002		$	—		$	30,132
	Collateralized mortgage obligations		512		3			(1	)		514
	Mortgage-backed securities		119,259		7,602			(24	)		126,837
	Other securities		7,288		5			—			7,293
	Total	$	156,189	$	8,612		$	(25	)	$	164,776
	Held to Maturity
	U.S. Treasury securities and obligations of U.S. Government agencies	$	3,252	$	23		$	—		$	3,275
	States and political subdivisions		333,380		1,640			(2,175	)		332,845
	Corporate debt securities		518		7			—			525
	Collateralized mortgage obligations		59,724		1,327			(48	)		61,003
	Mortgage-backed securities		7,186,737		98,915			(151,079	)		7,134,573
	Qualified School Construction Bonds (QSCB)		22,958		1,270			(278	)		23,950
	Total	$	7,606,569	$	103,182		$	(153,580	)	$	7,556,171
		31-Dec-12
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			Losses
		(Dollars in thousands)
	Available for Sale
	States and political subdivisions	$	34,743	$	1,691		$	—		$	36,434
	Collateralized mortgage obligations		616		—			(12	)		604
	Mortgage-backed securities		168,701		11,742			(27	)		180,416
	Other securities		8,786		430			—			9,216
	Total	$	212,846	$	13,863		$	(39	)	$	226,670
	Held to Maturity
	U.S. Treasury securities and obligations of U.S. Government agencies	$	7,061	$	160		$	—		$	7,221
	States and political subdivisions		391,510		7,074			(354	)		398,230
	Corporate debt securities		1,500		28			—			1,528
	Collateralized mortgage obligations		125,912		2,304			(50	)		128,166
	Mortgage-backed securities		6,676,512		196,206			(4,517	)		6,868,201
	Qualified School Construction Bonds (QSCB)		12,900		2,449			—			15,349
	Total	$	7,215,395	$	208,221		$	(4,921	)	$	7,418,695
	Management evaluates securities for other-than-temporary impairment (“OTTI”) at least on a quarterly basis, and more frequently when economic or market conditions warrant such an evaluation. The investment securities portfolio is evaluated for OTTI by segregating the portfolio into two general segments and applying the appropriate OTTI model.
	In determining OTTI, management considers many factors, including: (1) the length of time and the extent to which the fair value has been less than cost, (2) the financial condition and near-term prospects of the issuer, (3) whether the market decline was affected by macroeconomic conditions, and (4) whether the entity has the intent to sell the debt security or more likely than not will be required to sell the debt security before its anticipated recovery. The assessment of whether an other-than-temporary decline exists involves a high degree of subjectivity and judgment and is based on the information available to management at a point in time.
	When OTTI occurs, the amount of the other-than-temporary impairment recognized in earnings depends on whether an entity intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss. If an entity intends to sell or more likely than not will be required to sell the security before recovery of its amortized cost basis less any current-period credit loss, the OTTI shall be recognized in earnings equal to the entire difference between the investment’s amortized cost basis and its fair value at the balance sheet date. If an entity does not intend to sell the security and it is not more likely than not that the entity will be required to sell the security before recovery of its amortized cost basis less any current-period loss, the OTTI shall be separated into the amount representing the credit-related portion of the impairment loss (“credit loss”) and the noncredit portion of the impairment loss (“noncredit portion”). The amount of the total OTTI related to the credit loss is determined based on the difference between the present value of cash flows expected to be collected and the amortized cost basis and such difference is recognized in earnings. The amount of the total OTTI related to the noncredit portion is recognized in other comprehensive income, net of applicable taxes. The previous amortized cost basis less the OTTI recognized in earnings shall become the new amortized cost basis of the investment.
	As of September 30, 2013, the Company does not intend to sell any debt securities and management believes that the Company more likely than not will not be required to sell any debt securities before their anticipated recovery, at which time the Company will receive full value for the securities. Furthermore, as of September 30, 2013, management does not have the intent to sell any of its securities and believes that it is more likely than not that the Company will not have to sell any such securities before a recovery of cost. The unrealized losses are largely due to increases in market interest rates over the yields available at the time the underlying securities were purchased. The fair value is expected to recover as the securities approach their maturity date or repricing date or if market yields for such investments decline. Management does not believe any of the securities are impaired due to reasons of credit quality. Accordingly, as of September 30, 2013, management believes any impairment in the Company’s securities is temporary and no impairment loss has been realized in the Company’s consolidated statements of income.
	Securities, with unrealized losses segregated by length of time, that have been in a continuous loss position at September 30, 2013 and December 31, 2012 were as follows:
		September 30, 2013
		Less than 12 Months					More than 12 Months						Total
		Estimated		Unrealized			Estimated			Unrealized			Estimated		Unrealized
		Fair Value		Losses			Fair Value			Losses			Fair Value		Losses
		(Dollars in thousands)
	Available for Sale
	Collateralized mortgage obligations	$	15	$	—		$	53		$	(1	)	$	68	$	(1	)
	Mortgage-backed securities		409		—			3,539			(24	)		3,948		(24	)
	Other securities		—		—			—			—			—		—
	Total	$	424	$	—		$	3,592		$	(25	)	$	4,016	$	(25	)
	Held to Maturity
	States and political subdivisions	$	164,268	$	(2,222	)	$	10,264		$	(231	)	$	174,532	$	(2,453	)
	Collateralized mortgage obligations		1,391		(42	)		437			(6	)		1,828		(48	)
	Mortgage-backed securities		3,507,024		(145,835	)		102,028			(5,244	)		3,609,052		(151,079	)
	Total	$	3,672,683	$	(148,099	)	$	112,729		$	(5,481	)	$	3,785,412	$	(153,580	)
		31-Dec-12
		Less than 12 Months					More than 12 Months						Total
		Estimated		Unrealized			Estimated			Unrealized			Estimated		Unrealized
Fair Value		Losses		Fair Value			Losses			Fair Value			Losses
	(Dollars in thousands)
Available for Sale
Collateralized mortgage obligations	$	—	$	—		$	603		$	(12	)	$	603	$	(12	)
Mortgage-backed securities		224		—			3,964			(27	)		4,188		(27	)
Total	$	224	$	—		$	4,567		$	(39	)	$	4,791	$	(39	)
Held to Maturity
States and political subdivisions	$	37,322	$	(335	)	$	1,140		$	(19	)	$	38,462	$	(354	)
Collateralized mortgage obligations		2,366		(50	)		—			—			2,366		(50	)
Mortgage-backed securities		1,081,414		(4,516	)		234			(1	)		1,081,648		(4,517	)
Total	$	1,121,102	$	(4,901	)	$	1,374		$	(20	)	$	1,122,476	$	(4,921	)
At September 30, 2013, approximately 18.6% of securities were in an unrealized loss position for more than 12 months.
The amortized cost and fair value of investment securities at September 30, 2013, by contractual maturity, are shown below. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations at any time with or without call or prepayment penalties.
	Held to Maturity					Available for Sale
	Amortized		Fair			Amortized			Fair
	Cost		Value			Cost			Value
	(Dollars in thousands)
Due in one year or less	$	26,450	$	26,523		$	7,383		$	7,392
Due after one year through five years		120,137		120,135			4,990			5,175
Due after five years through ten years		138,529		138,049			20,997			21,721
Due after ten years		74,992		75,888			3,048			3,137
Subtotal		360,108		360,595			36,418			37,425
Mortgage-backed securities and collateralized mortgage obligations		7,246,461		7,195,576			119,771			127,351
Total	$	7,606,569	$	7,556,171		$	156,189		$	164,776
The Company had no gain or loss on sale of securities for the three and nine months ended September 30, 2013 and 2012. As of September 30, 2013, the Company had eight non-agency CMO’s remaining with a total book value of $1.8 million and total market value of $1.8 million.
At September 30, 2013 and December 31, 2012, the Company did not own securities of any one issuer (other than the U.S. government and its agencies) for which aggregate adjusted cost exceeded 10% of the consolidated shareholders’ equity at such respective dates.
Securities with an amortized cost of $4.22 billion and $4.13 billion and a fair value of $4.20 billion and $4.27 billion at September 30, 2013 and December 31, 2012, respectively, were pledged to collateralize public deposits and for other purposes required or permitted by law.

LOANS_AND_ALLOWANCE_FOR_CREDIT

LOANS AND ALLOWANCE FOR CREDIT LOSSES	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
LOANS AND ALLOWANCE FOR CREDIT LOSSES	'
	5. LOANS AND ALLOWANCE FOR CREDIT LOSSES
	The loan portfolio consists of various types of loans made principally to borrowers located in Texas and Oklahoma and is classified by major type as follows:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Residential mortgage loans held for sale		$	4,892		$	10,433
	Commercial and industrial			1,028,799			771,114
	Real estate:
	Construction and land development			703,193			550,768
	1-4 family residential (including home equity)			1,710,621			1,432,133
	Commercial real estate (including multi-family residential)			2,304,862			1,990,642
	Farmland			235,049			211,156
	Agriculture			86,469			74,481
	Consumer and other (net of unearned discount)			108,704			139,213
	Total loans held for investment			6,177,697			5,169,507
	Total		$	6,182,589		$	5,179,940
	(i) Commercial and Industrial Loans. In nearly all cases, the Company’s commercial loans are made in the Company’s market areas and are underwritten on the basis of the borrower’s ability to service the debt from income. As a general practice, the Company takes as collateral a lien on any available real estate, equipment or other assets owned by the borrower and obtains a personal guaranty of the borrower or principal. Working capital loans are primarily collateralized by short-term assets whereas term loans are primarily collateralized by long-term assets. In general, commercial loans involve more credit risk than residential mortgage loans and commercial mortgage loans and, therefore, usually yield a higher return. The increased risk in commercial loans is due to the type of collateral securing these loans. The increased risk also derives from the expectation that commercial loans generally will be serviced principally from the operations of the business, and those operations may not be successful. Historical trends have shown these types of loans to have higher delinquencies than mortgage loans. As a result of these additional complexities, variables and risks, commercial loans require more thorough underwriting and servicing than other types of loans.
	(ii) Commercial Real Estate. The Company makes commercial real estate related loans collateralized by owner-occupied and non-owner-occupied real estate to finance the purchase of real estate. The Company’s commercial real estate related loans are collateralized by first liens on real estate, typically have variable interest rates (or five year or less fixed rates) and amortize over a 15 to 20 year period. Payments on loans secured by such properties are often dependent on the successful operation or management of the properties. Accordingly, repayment of these loans may be subject to adverse conditions in the real estate market or the economy to a greater extent than other types of loans. The Company seeks to minimize these risks in a variety of ways, including giving careful consideration to the property’s operating history, future operating projections, current and projected occupancy, location and physical condition in connection with underwriting these loans. The underwriting analysis also includes credit verification, analysis of global cash flow, appraisals and a review of the financial condition of the borrower. At September 30, 2013, approximately 38.0% of the outstanding principal balance of the Company’s commercial real estate related loans was secured by owner-occupied properties.
	(iii) 1-4 Family Residential Loans. The Company originates 1-4 family residential mortgage loans and home equity loans collateralized by owner-occupied residential properties located in the Company’s market areas. The Company offers a variety of mortgage loan products which generally are amortized over five to 25 years. Loans collateralized by 1-4 family residential real estate generally have been originated in amounts of no more than 89% of appraised value or have mortgage insurance. The Company requires mortgage title insurance and hazard insurance. The Company has elected to keep all 1-4 family residential loans for its own account rather than selling such loans into the secondary market. By doing so, the Company is able to realize a higher yield on these loans; however, the Company also incurs interest rate risk as well as the risks associated with nonpayments on such loans.
	(iv) Construction and Land Development Loans. The Company makes loans to finance the construction of residential and, to a lesser extent, nonresidential properties. Construction loans generally are collateralized by first liens on real estate and have floating interest rates. The Company conducts periodic inspections, either directly or through an agent, prior to approval of periodic draws on these loans. Underwriting guidelines similar to those described above are also used in the Company’s construction lending activities. Construction loans involve additional risks attributable to the fact that loan funds are advanced upon the security of a project under construction, and the project is of uncertain value prior to its completion. Because of uncertainties inherent in estimating construction costs, the market value of the completed project and the effects of governmental regulation on real property, it can be difficult to accurately evaluate the total funds required to complete a project and the related loan to value ratio. As a result of these uncertainties, construction lending often involves the disbursement of substantial funds with repayment dependent, in part, on the success of the ultimate project rather than the ability of a borrower or guarantor to repay the loan. If the Company is forced to foreclose on a project prior to completion, there is no assurance that the Company will be able to recover all of the unpaid portion of the loan. In addition, the Company may be required to fund additional amounts to complete a project and may have to hold the property for an indeterminate period of time. While the Company has underwriting procedures designed to identify what it believes to be acceptable levels of risks in construction lending, no assurance can be given that these procedures will prevent losses from the risks described above.
	(v) Agriculture Loans. The Company provides agriculture loans for short-term crop production, including rice, cotton, milo and corn, farm equipment financing and agriculture real estate financing. The Company evaluates agriculture borrowers primarily based on their historical profitability, level of experience in their particular agriculture industry, overall financial capacity and the availability of secondary collateral to withstand economic and natural variations common to the industry. Because agriculture loans present a higher level of risk associated with events caused by nature, the Company routinely makes on-site visits and inspections in order to identify and monitor such risks.
	(vi) Consumer Loans. Consumer loans made by the Company include direct credit automobile loans, recreational vehicle loans, boat loans, home improvement loans, personal loans (collateralized and uncollateralized) and deposit account collateralized loans. The terms of these loans typically range from 12 to 120 months and vary based upon the nature of collateral and size of loan. Generally, consumer loans entail greater risk than do real estate secured loans, particularly in the case of consumer loans that are unsecured or collateralized by rapidly depreciating assets such as automobiles. In such cases, any repossessed collateral for a defaulted consumer loan may not provide an adequate source of repayment for the outstanding loan balance. The remaining deficiency often does not warrant further substantial collection efforts against the borrower beyond obtaining a deficiency judgment. In addition, consumer loan collections are dependent on the borrower’s continuing financial stability, and thus are more likely to be adversely affected by job loss, divorce, illness or personal bankruptcy. Furthermore, the application of various federal and state laws may limit the amount which can be recovered on such loans.
	The Company maintains an independent loan review department that reviews and validates the credit risk program on a periodic basis. Results of these reviews are presented to management. The loan review process complements and reinforces the risk identification and assessment decisions made by lenders and credit personnel, as well as the Company’s policies and procedures.
	Concentrations of Credit. Most of the Company’s lending activity occurs within the states of Texas and Oklahoma. The majority of the Company’s loan portfolio consists of commercial and industrial, commercial real estate and 1-4 family residential loans. As of September 30, 2013 and December 31, 2012, there were no concentrations of loans related to any single industry in excess of 10% of total loans.
	Foreign Loans. The Company has U.S. dollar denominated loans and commitments to borrowers in Mexico. The outstanding balance of these loans and the unfunded amounts available under these commitments were not significant at September 30, 2013 or December 31, 2012.
	Related Party Loans. As of September 30, 2013 and December 31, 2012, loans outstanding to directors, officers and their affiliates totaled $6.3 million and $6.7 million, respectively. All transactions entered into between the Company and such related parties are done in the ordinary course of business, made on the same terms and conditions as similar transactions with unaffiliated persons.
	An analysis of activity with respect to these related party loans is as follows:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Beginning balance on January 1		$	6,682		$	9,809
	New loans and reclassified related loans			306			967
	Repayments			(676	)		(4,094	)
	Ending balance		$	6,312		$	6,682
	Nonaccrual and Past Due Loans. The Company has several procedures in place to assist it in maintaining the overall quality of its loan portfolio. The Company has established underwriting guidelines to be followed by its officers and the Company also monitors its delinquency levels for any negative or adverse trends. There can be no assurance, however, that the Company’s loan portfolio will not become subject to increasing pressures from deteriorating borrower credit due to general economic conditions.
	The Company generally places a loan on nonaccrual status and ceases accruing interest when the payment of principal or interest is delinquent for 90 days, or earlier in some cases, unless the loan is in the process of collection and the underlying collateral fully supports the carrying value of the loan.
	The Company requires appraisals on loans collateralized by real estate. With respect to potential problem loans, an evaluation of the borrower’s overall financial condition is made to determine the need, if any, for possible writedowns or appropriate additions to the allowance for credit losses.
	An aging analysis of past due loans, segregated by class of loans, is as follows:
			September 30, 2013
			Loans Past Due and Still Accruing
			30-89 Days			90 or More			Total Past			Nonaccrual			Current			Total
						Days			Due Loans			Loans			Loans			Loans
			(Dollars in thousands)
	Construction and land development		$	3,465		$	—		$	3,465		$	469		$	699,259		$	703,193
	Agriculture and agriculture real estate (includes farmland)			557			—			557			23			320,938			321,518
	1-4 family (includes home equity) (1)			5,655			90			5,745			1,037			1,708,731			1,715,513
	Commercial real estate (includes multi-family residential)			7,065			34			7,099			2,223			2,295,540			2,304,862
	Commercial and industrial			9,230			148			9,378			1,069			1,018,352			1,028,799
	Consumer and other			391			11			402			133			108,169			108,704
	Total		$	26,363		$	283		$	26,646		$	4,954		$	6,150,989		$	6,182,589
			December 31, 2012
			Loans Past Due and Still Accruing
			30-89 Days			90 or More			Total Past			Nonaccrual			Current			Total
						Days			Due Loans			Loans			Loans			Loans
			(Dollars in thousands)
	Construction and land development		$	3,863		$	—		$	3,863		$	1,170		$	545,735		$	550,768
	Agriculture and agriculture real estate (includes farmland)			310			21			331			396			284,910			285,637
	1-4 family (includes home equity) (1)			2,307			310			2,617			1,598			1,438,351			1,442,566
	Commercial real estate (includes multi-family residential)			9,163			—			9,163			—			1,981,479			1,990,642
	Commercial and industrial			4,843			—			4,843			1,469			764,802			771,114
	Consumer and other			856			—			856			749			137,608			139,213
	Total		$	21,342		$	331		$	21,673		$	5,382		$	5,152,885		$	5,179,940
	-1	Includes $4.9 million and $10.4 million of residential mortgage loans held for sale at September 30, 2013 and December 31, 2012, respectively.
The following table presents information regarding past due loans and nonperforming assets as of the dates indicated:
		September 30,			December 31,
		2013			2012
		(Dollars in thousands)
Nonaccrual loans		$	4,954		$	5,382
Accruing loans 90 or more days past due			283			331
Total nonperforming loans			5,237			5,713
Repossessed assets			18			68
Other real estate			7,432			7,234
Total nonperforming assets		$	12,687		$	13,015
Nonperforming assets to total loans and other real estate			0.2	%		0.25	%
The Company believes its conservative lending approach has resulted in sound asset quality. The Company had $12.7 million in nonperforming assets at September 30, 2013 compared with $13.0 million at December 31, 2012. If interest on nonaccrual loans had been accrued under the original loan terms, approximately $341,000 and $252,000 would have been recorded as income for the nine months ended September 30, 2013 and 2012, respectively.
Purchased Credit-Impaired (PCI) Loans. In connection with the acquisition of American State Financial Corporation (ASB) on July 1, 2012, Community National Bank on October 1, 2012, East Texas Financial Services, Inc. on January 1, 2013 and Coppermark Bancshares, Inc. on April 1, 2013, the Company acquired loans both with and without evidence of credit quality deterioration since origination. The acquired loans were initially recorded at fair value with no carryover of any allowance for loan losses.
Loans acquired with evidence of credit quality deterioration at acquisition for which it was probable that the Company would not be able to collect all contractual amounts due were accounted for as PCI.
The carrying amount of acquired PCI loans included in the consolidated balance sheet and the related outstanding balance at September 30, 2013 and December 31, 2012 were as follows:
		September 30,			December 31,
		2013			2012
		(Dollars in thousands)
Acquired PCI loans:
Carrying amount		$	36,204		$	22,880
Outstanding balance			77,303			46,914
The outstanding balance represents the total amount owed as of September 30, 2013 and December 31, 2012, including accrued but unpaid interest and any amounts previously charged off. No allowance for loan losses was required on the acquired PCI loans at both September 30, 2013 and December 31, 2012.
Changes in the accretable yield for acquired PCI loans for the three and nine month periods ended September 30, 2013 and 2012 were as follows:
		Three Month Periods Ended September 30,						Nine Month Periods Ended September 30,
		2013			2012			2013			2012
		(Dollars in thousands)
Balance at beginning of period		$	13,011		$	—		$	7,459		$	—
Additions			349			8,157			7,877			8,157
Reclassifications from nonaccretable			3,088			—			4,343			—
Accretion			(5,840	)		(1,160	)		(9,071	)		(1,160	)
Balance at September 30		$	10,608		$	6,997		$	10,608		$	6,997
Impaired Loans. Loans are considered impaired when, based on current information and events, it is probable the Company will be unable to collect all amounts due in accordance with the original contractual terms of the loan agreement, including scheduled principal and interest payments. Impairment is evaluated in total for smaller-balance loans of a similar nature and on an individual loan basis for other loans. If a loan is impaired, a specific valuation allowance is allocated, if necessary, so that the loan is reported net, at the present value of estimated future cash flows using the loan’s existing rate or at the fair value of collateral if repayment is expected solely from the collateral. Interest payments on impaired loans are typically applied to principal unless collectability of the principal amount is reasonably assured, in which case interest is recognized on a cash basis. Impaired loans, or portions thereof, are charged off when deemed uncollectible.
Impaired loans as of September 30, 2013 are set forth in the following table. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment presented in the table below is reported on a year-to-date basis.
		September 30, 2013
		Recorded			Unpaid			Related			Average
		Investment			Principal			Allowance			Recorded
					Balance						Investment
		(Dollars in thousands)
With no related allowance recorded:
Construction and land development		$	257		$	265		$	—		$	701
Agriculture and agriculture real estate (includes farmland)			—			—			—			39
1-4 family (includes home equity)			310			279			—			401
Commercial real estate (includes multi-family residential)			1,213			1,237			—			832
Commercial and industrial			194			54			—			141
Consumer and other			—			—			—			5
Total			1,974			1,835			—			2,119
With an allowance recorded:
Construction and land development			—			—			—			—
Agriculture and agriculture real estate (includes farmland)			23			30			20			29
1-4 family (includes home equity)			71			96			53			535
Commercial real estate (includes multi-family residential)			17			18			17			1,234
Commercial and industrial			832			842			741			938
Consumer and other			80			87			69			73
Total			1,023			1,073			900			2,809
Total:
Construction and land development			257			265			—			701
Agriculture and agriculture real estate (includes farmland)			23			30			20			68
1-4 family (includes home equity)			381			375			53			936
Commercial real estate (includes multi-family residential)			1,230			1,255			17			2,066
Commercial and industrial			1,026			896			741			1,079
Consumer and other			80			87			69			78
		$	2,997		$	2,908		$	900		$	4,928
Impaired loans as of December 31, 2012 are set forth in the following tables. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment is reported on a year-to-date basis.
		December 31, 2012
		Recorded			Unpaid			Related			Average
		Investment			Principal			Allowance			Recorded
					Balance						Investment
		(Dollars in thousands)
With no related allowance recorded:
Construction and land development		$	1,144		$	1,175		$	—		$	368
Agriculture and agriculture real estate (includes farmland)			77			77			—			34
1-4 family (includes home equity)			491			522			—			381
Commercial real estate (includes multi-family residential)			450			476			—			676
Commercial and industrial			87			89			—			75
Consumer and other			10			10			—			3
Total			2,259			2,349			—			1,537
With an allowance recorded:
Construction and land development			—			—			—			451
Agriculture and agriculture real estate (includes farmland)			34			41			29			45
1-4 family (includes home equity)			999			1,017			273			720
Commercial real estate (includes multi-family residential)			2,450			2,451			610			2,725
Commercial and industrial			1,043			1,079			1,002			782
Consumer and other			66			81			67			21
Total			4,592			4,669			1,981			4,744
Total:
Construction and land development			1,144			1,175			—			819
Agriculture and agriculture real estate (includes farmland)			111			118			29			79
1-4 family (includes home equity)			1,490			1,539			273			1,101
Commercial real estate (includes multi-family residential)			2,900			2,927			610			3,401
Commercial and industrial			1,130			1,168			1,002			857
Consumer and other			76			91			67			24
		$	6,851		$	7,018		$	1,981		$	6,281
Credit Quality Indicators. As part of the ongoing monitoring of the credit quality of the Company’s loan portfolio and methodology for calculating the allowance for credit losses, management assigns and tracks loan grades to be used as credit quality indicators. The following is a general description of the loan grades used (1-7):
Grade 1 – Credits in this category are of the highest standards of credit quality with virtually no risk of loss. These borrowers would represent top rated companies and individuals with unquestionable financial standing with excellent global cash flow coverage, net worth, liquidity and collateral coverage and/or secured by CD/savings accounts.
Grade 2 – Credits in this category are not immune for risk but are well-protected by the collateral and paying capacity of the borrower. These loans may exhibit a minor unfavorable credit factor, but the overall credit is sufficiently strong to minimize the possibility of loss.
Grade 3 – Credits in this category constitute an undue and unwarranted credit risk, however the factors do not rise to a level of substandard. These credits have potential weaknesses and/or declining trends that, if not corrected, could expose the Company to risk at a future date. Credits graded 3 are monitored on the Company’s internally generated watch list and evaluated on a quarterly basis.
Grade 4 – Credits in this category are deemed “substandard” loans in accordance with regulatory guidelines. Loans in this category have well-defined weakness that, if not corrected, could make default of principal and interest possible, but it is not yet certain. Loans in this category are still accruing interest and may be dependent upon secondary sources of repayment and/or collateral liquidation.
Grade 5 – Credits in this category are deemed “substandard” and “impaired” pursuant to regulatory guidelines. As such, the Company has determined that it is probable that less than 100% of the principal and interest will be collected. Loans graded 5 are individually evaluated for a specific reserve valuation and will typically have the accrual of interest stopped.
Grade 6 – Credits in this category include “doubtful” loans in accordance with regulatory guidance. Such loans are on nonaccrual and factors have indicated a loss is imminent. These loans are also deemed “impaired.” While a specific reserve may be in place while the loan and collateral is being evaluated these loans are typically charged down to an amount the Company deems collectable.
Grade 7 – Credits in this category are deemed a “loss” in accordance with regulatory guidelines and charged off or charged down. The Company may continue collection efforts and may have partial recovery in the future.
The following table presents risk grades and classified loans by class of loan at September 30, 2013. Classified loans include loans in risk grades 5, 6 and 7.
		Construction			Agriculture and			1-4 Family			Commercial			Commercial			Consumer and			Total
		and Land			Agriculture Real			(includes			Real Estate			and Industrial			Other
		Development			Estate (includes			Home Equity) (1)			(includes Multi-
					Farmland)						Family Residential)
		(Dollars in thousands)
Grade 1		$	—		$	4,771		$	—		$	—		$	48,879		$	31,287		$	84,937
Grade 2			694,446			313,890			1,701,525			2,248,498			962,941			77,114			5,998,414
Grade 3			3,850			1,044			4,287			12,483			7,453			133			29,250
Grade 4			1,551			1,369			6,165			15,736			5,876			90			30,787
Grade 5			257			23			370			1,230			1,026			80			2,986
Grade 6			—			—			11			—			—			—			11
Grade 7			—			—			—			—			—			—			—
PCI Loans (2)			3,089			421			3,155			26,915			2,624			—			36,204
Total		$	703,193		$	321,518		$	1,715,513		$	2,304,862		$	1,028,799		$	108,704		$	6,182,589
-1	Includes $4.9 million of residential mortgage loans held for sale at September 30, 2013.
-2	Of the total PCI loans, $24.9 million were classified as substandard at September 30, 2013.
The following table presents risk grades and classified loans by class of loan at December 31, 2012. Classified loans include loans in risk grades 5, 6 and 7.
		Construction			Agriculture and			1-4 Family			Commercial			Commercial			Consumer and			Total
		and Land			Agriculture Real			(includes			Real Estate			and Industrial			Other
		Development			Estate (includes			Home Equity) (1)			(includes Multi-
					Farmland)						Family Residential)
		(Dollars in thousands)
Grade 1		$	476		$	4,195		$	515		$	—		$	53,965		$	38,789		$	97,940
Grade 2			537,340			277,333			1,431,095			1,945,319			702,587			100,163			4,993,837
Grade 3			7,250			2,024			4,947			11,760			8,926			—			34,907
Grade 4			4,256			1,694			4,303			11,711			1,385			176			23,525
Grade 5			1,144			111			1,477			2,900			1,130			76			6,838
Grade 6			—			—			13			—			—			—			13
Grade 7			—			—			—			—			—			—			—
PCI Loans			302			280			216			18,952			3,121			9			22,880
Total		$	550,768		$	285,637		$	1,442,566		$	1,990,642		$	771,114		$	139,213		$	5,179,940
-1	Includes $10.4 million of residential mortgage loans held for sale at December 31, 2012.
Allowance for Credit Losses. The allowance for credit losses is a valuation established through charges to earnings in the form of a provision for credit losses. Management has established an allowance for credit losses which it believes is adequate for estimated losses in the Company’s loan portfolio. The amount of the allowance for credit losses is affected by the following: (i) charge-offs of loans that occur when loans are deemed uncollectible and decrease the allowance, (ii) recoveries on loans previously charged off that increase the allowance and (iii) provisions for credit losses charged to earnings that increase the allowance. Based on an evaluation of the loan portfolio and consideration of the factors listed below, management presents a quarterly review of the allowance for credit losses to the Bank’s Board of Directors, indicating any change in the allowance since the last review and any recommendations as to adjustments in the allowance.
The Company’s allowance for credit losses consists of two components: a specific valuation allowance based on probable losses on specifically identified loans and a general valuation allowance based on historical loan loss experience, general economic conditions and other qualitative risk factors both internal and external to the Company.
In setting the specific valuation allowance, the Company follows a loan review program to evaluate the credit risk in the loan portfolio. Through this loan review process, the Company maintains an internal list of impaired loans which, along with the delinquency list of loans, helps management assess the overall quality of the loan portfolio and the adequacy of the allowance for credit losses. All loans that have been identified as impaired are reviewed on a quarterly basis in order to determine whether a specific reserve is required. For each impaired loan, the Company allocates a specific loan loss reserve primarily based on the value of the collateral securing the impaired loan requiring a reserve. The specific reserves are determined on an individual loan basis. Impaired loans are excluded from the general valuation allowance described below.
In determining the amount of the general valuation allowance, management considers factors such as historical loan loss experience, industry diversification of the Company’s commercial loan portfolio, concentration risk of specific loan types, the volume, growth and composition of the Company’s loan portfolio, current economic conditions that may affect the borrower’s ability to pay and the value of collateral, the evaluation of the Company’s loan portfolio through its internal loan review process, general economic conditions and other qualitative risk factors both internal and external to the Company and other relevant factors.
Based on a review of these factors for each loan type, the Company applies an estimated percentage to the outstanding balance of each loan type, excluding any impaired loan. The Company uses this information to establish the amount of the general valuation allowance.
In connection with its review of the loan portfolio, the Company considers risk elements attributable to particular loan types or categories in assessing the quality of individual loans. Some of the risk elements include:
	•		for 1-4 family residential mortgage loans, the borrower’s ability to repay the loan, including a consideration of the debt to income ratio and employment and income stability, the loan to value ratio, and the age, condition and marketability of collateral;
	•		for commercial real estate loans and multifamily residential loans, the debt service coverage ratio (income from the property in excess of operating expenses compared to loan payment requirements), operating results of the owner in the case of owner-occupied properties, the loan to value ratio, the age and condition of the collateral and the volatility of income, property value and future operating results typical of properties of that type;
	•		for construction and land development loans, the perceived feasibility of the project including the ability to sell developed lots or improvements constructed for resale or the ability to lease property constructed for lease, the quality and nature of contracts for presale or prelease, if any, experience and ability of the developer and loan to value ratio;
	•		for commercial and industrial loans, the operating results of the commercial, industrial or professional enterprise, the borrower’s business, professional and financial ability and expertise, the specific risks and volatility of income and operating results typical for businesses in that category and the value, nature and marketability of collateral;
	•		for agriculture real estate loans, the experience and financial capability of the borrower, projected debt service coverage of the operations of the borrower and loan to value ratio; and
	•		for non-real estate agriculture loans, the operating results, experience and financial capability of the borrower, historical and expected market conditions and the value, nature and marketability of collateral.
In addition, for each category, the Company considers secondary sources of income and the financial strength and credit history of the borrower and any guarantors.
At September 30, 2013, the allowance for credit losses totaled $59.9 million or 0.97% of total loans. At December 31, 2012, the allowance aggregated $52.6 million or 1.01% of total loans.
The following table details the recorded investment in loans and activity in the allowance for credit losses by portfolio segment for the three and nine months ended September 30, 2013. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
		Construction			Agriculture			1-4 Family			Commercial			Commercial			Consumer			Total
		and Land			and			(includes			Real Estate			and			and Other
		Development			Agriculture			Home			(includes			Industrial
					Real Estate			Equity)			Multi-Family
					(includes						Residential)
					Farmland)
		(Dollars in thousands)
Allowance for credit losses:
Three Months Ended
Balance June 30, 2013		$	11,991		$	982		$	13,435		$	22,831		$	6,293		$	644		$	56,176
Provision for credit losses			1,024			129			1,262			(658	)		1,356			912			4,025
Charge-offs			(14	)		(23	)		(20	)		—			(188	)		(897	)		(1,142	)
Recoveries			44			10			5			471			69			255			854
Net charge-offs			30			(13	)		(15	)		471			(119	)		(642	)		(288	)
Balance September 30, 2013		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
Nine Months Ended
Balance January 1, 2013		$	11,909		$	764		$	13,942		$	19,607		$	5,777		$	565		$	52,564
Provision for credit losses			1,173			352			892			3,309			2,070			1,579			9,375
Charge-offs			(270	)		(36	)		(182	)		(894	)		(592	)		(2,100	)		(4,074	)
Recoveries			233			18			30			622			275			870			2,048
Net charge-offs			(37	)		(18	)		(152	)		(272	)		(317	)		(1,230	)		(2,026	)
Balance September 30, 2013		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
Allowance for credit losses related to:
September 30, 2013
Individually evaluated for impairment		$	—		$	20		$	53		$	17		$	741		$	69		$	900
Collectively evaluated for impairment			13,045			1,078			14,629			22,627			6,789			845			59,013
PCI loans			—			—			—			—			—			—			—
Total allowance for credit losses		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
Recorded investment in loans:
September 30, 2013
Individually evaluated for impairment		$	257		$	23		$	381		$	1,230		$	1,026		$	80		$	2,997
Collectively evaluated for impairment			699,847			321,074			1,711,977			2,276,717			1,025,149			108,624			6,143,388
PCI loans			3,089			421			3,155			26,915			2,624			—			36,204
Total loans evaluated for impairment		$	703,193		$	321,518		$	1,715,513		$	2,304,862		$	1,028,799		$	108,704		$	6,182,589
The following table details the recorded investment in loans and activity in the allowance for credit losses by portfolio segment for the three and nine months ended September 30, 2012. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
		Construction			Agriculture			1-4 Family			Commercial			Commercial			Consumer			Total
		and Land			and			(includes			Real Estate			and			and Other
		Development			Agriculture			Home			(includes			Industrial
					Real Estate			Equity)			Multi-Family
					(includes						Residential)
					Farmland)
		(Dollars in thousands)
Allowance for credit losses:
Three Months Ended
Balance June 30, 2012		$	10,065		$	742		$	13,326		$	21,406		$	4,238		$	605		$	50,382
Provision for credit losses			359			(2	)		299			(509	)		660			993			1,800
Charge-offs			(159	)		—			(327	)		(909	)		(55	)		(1,663	)		(3,113	)
Recoveries			4			30			76			109			565			1,074			1,858
Net charge-offs			(155	)		30			(251	)		(800	)		510			(589	)		(1,255	)
Balance September 30, 2012		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
Nine Months Ended
Balance January 1, 2012		$	12,094		$	511		$	12,645		$	21,460		$	3,826		$	1,058		$	51,594
Provision for credit losses			(469	)		226			1,121			(250	)		1,237			685			2,550
Charge-offs			(1,368	)		—			(478	)		(1,278	)		(376	)		(2,101	)		(5,601	)
Recoveries			12			33			86			165			721			1,367			2,384
Net charge-offs			(1,356	)		33			(392	)		(1,113	)		345			(734	)		(3,217	)
Balance September 30, 2012		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
Allowance for credit losses related to:
September 30, 2012
Individually evaluated for impairment		$	26		$	61		$	336		$	567		$	1,180		$	20		$	2,190
Collectively evaluated for impairment			10,243			709			13,038			19,530			4,228			989			48,737
PCI loans			—			—			—			—			—			—			—
Total allowance for credit losses		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
Recorded investment in loans:
September 30, 2012
Individually evaluated for impairment		$	86		$	143		$	1,448		$	3,170		$	1,395		$	20		$	6,262
Collectively evaluated for impairment			495,005			303,913			1,396,114			1,950,488			751,379			148,361			5,045,260
PCI loans			1,326			78			155			22,454			3,568			—			27,581
Total loans evaluated for impairment		$	496,417		$	304,134		$	1,397,717		$	1,976,112		$	756,342		$	148,381		$	5,079,103
Troubled Debt Restructurings. The restructuring of a loan is considered a “troubled debt restructuring” if both (i) the borrower is experiencing financial difficulties and (ii) the creditor has granted a concession. Concessions may include interest rate reductions or below market interest rates, principal forgiveness, restructuring amortization schedules and other actions intended to minimize potential losses.
During the nine months ended September 30, 2013, a $249,000 loan was restructured. Default is determined at 90 or more days past due. The restructured loans from prior periods are performing and accruing loans.

FAIR_VALUE

FAIR VALUE	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
FAIR VALUE	'
	6. FAIR VALUE
	The Company uses fair value measurements to record fair value adjustments to certain assets and to determine fair value disclosures. Fair values represent the estimated price that would be received from selling an asset or paid to transfer a liability, otherwise known as an “exit price.” Securities available for sale are recorded at fair value on a recurring basis. Additionally, from time to time, the Company may be required to record at fair value other assets on a nonrecurring basis such as certain loans including loans held-for-sale, goodwill and other intangible assets and other real estate owned. These nonrecurring fair value adjustments typically involve application of lower-of-cost-or-market accounting or write downs of individual assets.
	Fair Value Hierarchy
	The Company groups financial assets and financial liabilities measured at fair value in three levels, based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. These levels are:
		•		Level 1—Quoted prices in active markets for identical assets or liabilities.
		•		Level 2—Other significant observable inputs (including quoted prices in active markets for similar assets or liabilities) or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
		•		Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
	The fair value of an asset or liability is the price that would be received to sell that asset or paid to transfer that liability in an orderly transaction occurring in the principal market (or most advantageous market in the absence of a principal market) for such asset or liability. In estimating fair value, the Company utilizes valuation techniques that are consistent with the market approach, the income approach and/or the cost approach. Such valuation techniques are consistently applied. Inputs to valuation techniques include the assumptions that market participants would use in pricing an asset or liability. FASB Accounting Standards Codification (“ASC”) Topic 820 establishes a fair value hierarchy for valuation inputs that gives the highest priority to quoted prices in active markets for identical assets and liabilities and the lowest priority to unobservable inputs.
	The fair value disclosures below represent the Company’s estimates based on relevant market information and information about the financial instruments. Fair value estimates are based on judgments regarding future expected loss experience, current economic conditions, risk characteristics of the various instruments, and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and therefore cannot be determined with precision. Changes in the above methodologies and assumptions could significantly affect the estimates.
	The following tables present fair values for assets measured at fair value on a recurring basis:
			As of September 30, 2013
			Level 1		Level 2		Level 3		Total
			(Dollars in thousands)
	Available for sale securities:
	States and political subdivisions		$	—	$	30,132	$	—	$	30,132
	Collateralized mortgage obligations			—		514		—		514
	Mortgage-backed securities			—		126,837		—		126,837
	Other securities			7,293		—		—		7,293
	Total		$	7,293	$	157,483	$	—	$	164,776
			As of December 31, 2012
			Level 1		Level 2		Level 3		Total
			(Dollars in thousands)
	Available for sale securities:
	States and political subdivisions		$	—	$	36,434	$	—	$	36,434
	Collateralized mortgage obligations			—		604		—		604
	Mortgage-backed securities			—		180,416		—		180,416
	Other securities			7,688		1,528		—		9,216
	Total		$	7,688	$	218,982	$	—	$	226,670
	Certain financial assets and financial liabilities are measured at fair value on a nonrecurring basis; that is, the instruments are not measured at fair value on an ongoing basis but are subject to fair value adjustments in certain circumstances (for example, when there is evidence of impairment). Financial assets measured at fair value on a non-recurring basis during the reported periods include certain impaired loans reported at the fair value of the underlying collateral if repayment is expected solely from the collateral. Collateral values are estimated using Level 2 inputs based on observable market data, typically in the case of real estate collateral. For the nine months ended September 30, 2013, the Company had additions to impaired loans of $5.5 million, of which $1.4 million were outstanding at September 30, 2013.
	Financial assets measured at fair value on a nonrecurring basis during the reported periods also include other real estate owned and repossessed assets. For the three and nine months ended September 30, 2013, the Company had additions to other real estate owned of $305,000 and $2.7 million, of which $305,000 and $1.1 million were outstanding at September 30, 2013, respectively. The remaining financial assets and financial liabilities measured at fair value on a non-recurring basis that were recorded in 2013 and remained outstanding at September 30, 2013 were not significant. During the reported periods, all fair value measurements for other real estate owned and repossessed assets utilized Level 2 inputs based on observable market data. There were no transfers between Level 1 and Level 2 assets during the nine months ended September 30, 2013.
	The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate that value:
	Cash and due from banks—For these short-term instruments, the carrying amount is a reasonable estimate of fair value. The Company classifies the estimated fair value of these instruments as Level 1.
	Federal funds sold—For these short-term instruments, the carrying amount is a reasonable estimate of fair value. The Company classifies the estimated fair value of these instruments as Level 1.
	Securities—Fair value measurements based upon quoted prices are considered Level 1 inputs. Level 1 securities consist of U.S. Treasury securities and certain equity securities which are included in the available for sale portfolio. For all other available for sale and held to maturity securities, if quoted prices are not available, fair values are measured using Level 2 inputs. For these securities, the Company generally obtains fair value measurements from an independent pricing service. The fair value measurements consider observable data that may include dealer quotes, market spreads, cash flows, the U.S. Treasury yield curve, live trading levels, trade execution data, market consensus prepayment speeds, credit information and the bond’s terms and conditions, among other things. The Company reviews the prices supplied by the independent pricing service, as well as their underlying pricing methodologies, for reasonableness.
	Securities available for sale are recorded at fair value on a recurring basis.
	Loans held for investment—The Company does not record loans at fair value on a recurring basis. As such, valuation techniques discussed herein for loans are primarily for estimating fair value disclosures. However, from time to time, the Company records nonrecurring fair value adjustments to impaired loans to reflect (1) partial write downs that are based on the observable market price or current appraised value of the collateral, or (2) the full charge-off of the loan carrying value. Where appraisals are not available, estimated cash flows are discounted using a rate commensurate with the credit risk associated with those cash flows. Assumptions regarding credit risk, cash flows and discount rates are judgmentally determined using available market information and specific borrower information.
	The estimated fair value approximates carrying value for variable-rate loans that reprice frequently and with no significant change in credit risk. The fair value of fixed-rate loans and variable-rate loans which reprice on an infrequent basis is estimated by discounting future cash flows using the current interest rates at which similar loans with similar terms would be made to borrowers of similar credit quality. An overall valuation adjustment is made for specific credit risks as well as general portfolio credit risk. The Company classifies the estimated fair value of loans held for investment as Level 3.
	Loans held for sale— Loans held for sale are carried at the lower of cost or estimated fair value. Fair value for consumer mortgages held for sale is based on commitments on hand from investors or prevailing market prices. As such, the Company classifies loans subjected to nonrecurring fair value adjustments as Level 1.
	Federal Home Loan Bank of Dallas Stock—The fair value of FHLB stock is estimated to be equal to its carrying amount as reported in the accompanying Consolidated Balance Sheets, given it is not a publicly traded equity security, it has an adjustable dividend rate, and all transactions in the stock are executed at the stated par value. FHLB stock is considered a Level 1 fair value.
	Other real estate owned—Other real estate owned is primarily foreclosed properties securing residential loans and commercial real estate. Foreclosed assets are adjusted to fair value less estimated costs to sell upon transfer of the loans to other real estate owned. Subsequently, these assets are carried at the lower of carrying value or fair value less estimated costs to sell. Other real estate carried at fair value based on an observable market price or a current appraised value is classified by the Company as Level 2. When management determines that the fair value of other real estate requires additional adjustments, either as a result of a non-current appraisal or when there is no observable market price, the Company classifies the other real estate as Level 3.
	Deposits—The fair value of demand deposits, savings accounts and certain money market deposits is the amount payable on demand at the reporting date. The fair value of fixed-maturity certificates of deposit is estimated using the rates currently offered for deposits of similar remaining maturities. Deposits fair value measurements utilize Level 2 inputs.
	Junior subordinated debentures—The fair value of the junior subordinated debentures was calculated using the quoted market prices, if available. If quoted market prices are not available, fair value is estimated using quoted market prices for similar subordinated debentures. Junior subordinated debentures fair value measurements utilize Level 2 inputs.
	Other borrowings—Rates currently available to the Company for debt with similar terms and remaining maturities are used to estimate the fair value of other borrowings using a discounted cash flows methodology and are measured utilizing Level 2 inputs.
	Securities sold under repurchase agreements—The fair value of securities sold under repurchase agreements is the amount payable on demand at the reporting date and are measured utilizing Level 2 inputs.
	Off-balance sheet financial instruments—The fair value of commitments to extend credit and standby letters of credit is estimated using the fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreement and the present creditworthiness of the counterparties. The Company has reviewed the unfunded portion of commitments to extend credit as well as standby and other letters of credit, and has determined that the fair value of such financial instruments is not material. The Company classifies the estimated fair value of credit-related financial instruments as Level 3.
	The following table summarizes the carrying values and estimated fair values of certain financial instruments not recorded at fair value on a regular basis:
			As of September 30, 2013
			Carrying		Estimated Fair Value
			Amount		Level 1		Level 2		Level 3		Total
			(Dollars in thousands)
	Assets
	Cash and due from banks		$	269,987	$	269,987	$	—	$	—	$	269,987
	Federal funds sold			1,121		1,121		—		—		1,121
	Held to maturity securities			7,606,569		—		7,556,171		—		7,556,171
	Loans held for sale			4,892		4,892		—		—		4,892
	Loans held for investment, net of allowance			6,117,784		—		—		6,143,355		6,143,355
	Federal Home Loan Bank of Dallas stock			43,058		43,058		—		—		43,058
	Liabilities
	Deposits:
	Noninterest-bearing		$	3,368,357	$	—	$	3,368,687	$	—	$	3,368,687
	Interest-bearing			9,087,442		—		8,286,130		—		8,286,130
	Other borrowings			605,951		—		607,471		—		607,471
	Securities sold under repurchase agreements			431,969		—		431,692		—		431,692
Junior subordinated debentures			85,055		—		81,696		—		81,696
		As of December 31, 2012
		Carrying		Estimated Fair Value
		Amount		Level 1		Level 2		Level 3		Total
		(Dollars in thousands)
Assets
Cash and due from banks		$	325,952	$	325,952	$	—	$	—	$	325,952
Federal funds sold			352		352		—		—		352
Held to maturity securities			7,215,395		—		7,418,695		—		7,418,695
Loans held for sale			10,433		10,433		—		—		10,433
Loans held for investment, net of allowance			5,116,943		—		—		5,186,779		5,186,779
Federal Home Loan Bank of Dallas stock			34,461		34,461		—		—		34,461
Liabilities
Deposits:
Noninterest-bearing		$	3,016,205	$	—	$	3,016,205	$	—	$	3,016,205
Interest-bearing			8,625,639		—		8,640,625		—		8,640,625
Other borrowings			256,753		—		258,819		—		258,819
Securities sold under repurchase agreements			454,502		—		454,596		—		454,596
Junior subordinated debentures			85,055		—		72,705		—		72,705
The Company’s off-balance sheet commitments including letters of credit, which totaled $1.19 billion at September 30, 2013, are funded at current market rates at the date they are drawn upon. It is management’s opinion that the fair value of these commitments would approximate their carrying value, if drawn upon.
The fair value estimates presented herein are based on pertinent information available to management at September 30, 2013. Although management is not aware of any factors that would significantly affect the estimated fair value amounts, such amounts have not been comprehensively revalued for purposes of these financial statements since those dates and, therefore, current estimates of fair value may differ significantly from the amounts presented herein.

GOODWILL_AND_CORE_DEPOSIT_INTA

GOODWILL AND CORE DEPOSIT INTANGIBLES	9 Months Ended
	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
GOODWILL AND CORE DEPOSIT INTANGIBLES	'
	7. GOODWILL AND CORE DEPOSIT INTANGIBLES
	Changes in the carrying amount of the Company’s goodwill and core deposit intangibles (“CDI”) for nine months ended September 30, 2013 and the year ended December 31, 2012 were as follows:
		Goodwill			Core Deposit
					Intangibles
		(Dollars in thousands)
	Balance as of December 31, 2011	$	924,537		$	20,996
	Less:
	Amortization		—			(7,229	)
	Add:
	Acquisition of Texas Bankers, Inc.		6,077			—
	Acquisition of The Bank Arlington		2,102			—
	Acquisition of ASB		274,119			12,392
	Acquisition of Community National Bank		10,327			—
	Balance as of December 31, 2012		1,217,162			26,159
	Less:
	Amortization		—			(4,551	)
	Add:
	Measurement period adjustment of The Bank Arlington		(130	)		—
	Measurement period adjustment of ASB		(3,094	)		2,110
	Measurement period adjustment of Community National Bank		1,999			—
	Acquisition of East Texas Financial Services, Inc.		16,658			—
	Acquisition of Coppermark Bancshares, Inc.		119,187			1,515
	Balance as of September 30, 2013	$	1,351,782		$	25,233
	Goodwill is recorded on the acquisition date of each entity. The Company may record subsequent adjustments to goodwill for amounts undeterminable at acquisition date, such as deferred taxes and real estate valuations, and therefore the goodwill amounts reflected in the table above may change accordingly. The Company initially records the total premium paid on acquisitions as goodwill. After finalizing the valuation, core deposit intangibles are identified and reclassified from goodwill to core deposit intangibles on the balance sheet. This reclassification has no effect on total assets, liabilities, shareholders’ equity, net income or cash flows. Management performs an evaluation annually, and more frequently if a triggering event occurs, of whether any impairment of the goodwill and other intangibles has occurred. If any such impairment is determined, a write-down is recorded. As of September 30, 2013, there were no impairments recorded on goodwill.
	The measurement period for the Company to determine the fair value of acquired identifiable assets and assumed liabilities will be at the end of the earlier of (i) twelve months from the date of acquisition or (ii) as soon as the Company receives the information it
	was seeking about facts and circumstances that existed as of the date of acquisition. As such, certain acquisitions completed during 2012 and 2013 may be subject to adjustment.
	Core deposit intangibles are amortized on an accelerated basis over their estimated lives, which the Company believes is between 8 and 15 years. Amortization expense related to intangible assets totaled $1.5 million and $2.0 million for the three months ended September 30, 2013 and 2012, respectively, and $4.6 million and $5.3 million for the nine months ended September 30, 2013 and 2012, respectively. The estimated aggregate future amortization expense for intangible assets remaining as of September 30, 2013 was as follows (dollars in thousands):
	Remaining 2013	$	1,483
	2014		4,841
	2015		4,201
	2016		3,761
	2017		2,076
	Thereafter		8,871
	Total	$	25,233

STOCK_BASED_COMPENSATION

STOCK BASED COMPENSATION	9 Months Ended
	Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]	'
STOCK BASED COMPENSATION	'
	8. STOCK BASED COMPENSATION
	At September 30, 2013, the Company had four stock-based employee compensation plans and one stock option plan assumed in connection with an acquisition under which no additional options will be granted. Two of the four plans adopted by the Company have expired and therefore no additional awards may be issued under those plans.
	During 2004, the Company’s Board of Directors adopted the Prosperity Bancshares, Inc. 2004 Stock Incentive Plan (the “2004 Plan”) which authorizes the issuance of up to 1,250,000 shares of common stock pursuant to the exercise or grant, as the case may be, of awards under such plan and the shareholders approved the 2004 Plan in 2005. The Company has granted shares with forfeiture restrictions (“restricted stock”) to certain directors, officers and associates under the 2004 Plan. The awardee is not entitled to the shares until they vest, which is generally over a one to five year period, but the awardee is entitled to receive dividends on and vote the shares prior to vesting. The shares granted do not have a cost to the awardee and the only requirement of vesting is continued service to the Company. Compensation cost related to restricted stock is calculated based on the fair value of the shares at the date of grant. If the awardee leaves the Company before the shares vest, the unvested shares are forfeited.
	On February 22, 2012, the Company’s Board of Directors adopted the Prosperity Bancshares, Inc. 2012 Stock Incentive Plan (the “2012 Plan”), subject to approval by the Company’s shareholders. The Company’s shareholders approved the 2012 Plan at the annual meeting of shareholders on April 17, 2012. The 2012 Plan authorizes the issuance of up to 1,250,000 shares of common stock upon the exercise of options granted under the 2012 Plan or pursuant to the grant or exercise, as the case may be, of other awards granted under the 2012 Plan, including restricted stock, stock appreciation rights, phantom stock awards and performance awards. As of September 30, 2013, no options or other awards have been granted under the 2012 Plan.
	The Company received $1.2 million and $300,000 in cash from the exercise of stock options during the three-month periods ended September 30, 2013 and 2012, respectively, and $3.0 million and $2.7 million during the nine-month periods ended September 30, 2013 and 2012, respectively. There was no tax benefit realized from option exercises of the share-based payment arrangements during the three and nine month periods ended September 30, 2013 and 2012.
	As of September 30, 2013, there was $7.0 million of total unrecognized compensation expense related to stock-based compensation arrangements. That cost is expected to be recognized over a weighted average period of 2.5 years.

CONTRACTUAL_OBLIGATIONS_AND_OF

CONTRACTUAL OBLIGATIONS AND OFF-BALANCE SHEET ITEMS	9 Months Ended
	Sep. 30, 2013
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
CONTRACTUAL OBLIGATIONS AND OFF-BALANCE SHEET ITEMS	'
	9. CONTRACTUAL OBLIGATIONS AND OFF-BALANCE SHEET ITEMS
	Contractual Obligations
	The following table summarizes the Company’s contractual obligations and other commitments to make future payments as of September 30, 2013 (other than deposit obligations). The payments do not include pre-payment options that may be available to the Company. The Company’s future cash payments associated with its contractual obligations pursuant to its junior subordinated debentures, FHLB borrowings and operating leases as of September 30, 2013 are summarized below. Payments for junior subordinated debentures include interest of $46.2 million that will be paid over the future periods. The future interest payments were calculated using the current rate in effect at September 30, 2013. The current principal balance of the junior subordinated debentures at September 30, 2013 was $85.1 million. Payments for FHLB borrowings include interest of $2.5 million that will be paid over the future periods. Payments related to leases are based on actual payments specified in underlying contracts.
		1 year or less		More than 1		3 years or		5 years		Total
				year but less		more but less		or more
				than 3 years		than 5 years
		(Dollars in thousands)
	Junior subordinated debentures	$	578	$	4,624	$	4,623	$	121,438	$	131,263
	Federal Home Loan Bank notes payable and other borrowings		595,407		3,836		2,312		6,899		608,454
	Operating leases		1,247		7,785		3,264		380		12,676
	Total	$	597,232	$	16,245	$	10,199	$	128,717	$	752,393
	Off-Balance Sheet Items
	In the normal course of business, the Company enters into various transactions, which, in accordance with accounting principles generally accepted in the United States, are not included in its consolidated balance sheets. The Company enters into these transactions to meet the financing needs of its customers. These transactions include commitments to extend credit and standby letters of credit, which involve, to varying degrees, elements of credit risk and interest rate risk in excess of the amounts recognized in the consolidated balance sheets.
	The Company’s commitments associated with outstanding standby letters of credit and commitments to extend credit as of September 30, 2013 are summarized below. Since commitments associated with letters of credit and commitments to extend credit may expire unused, the amounts shown do not necessarily reflect the actual future cash funding requirements.
		1 year or less		More than 1		3 years or		5 years		Total
				year but less		more but less		or more
				than 3 years		than 5 years
		(Dollars in thousands)
	Standby letters of credit	$	37,537	$	5,291	$	30	$	—	$	42,858
	Commitments to extend credit		159,906		609,923		49,941		323,938		1,143,708
	Total	$	197,443	$	615,214	$	49,971	$	323,938	$	1,186,566

OTHER_COMPREHENSIVE_LOSS_INCOM

OTHER COMPREHENSIVE (LOSS) INCOME	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
OTHER COMPREHENSIVE (LOSS) INCOME	'
	10. OTHER COMPREHENSIVE (LOSS) INCOME
	The tax effects allocated to each component of other comprehensive (loss) income were as follows:
		Three Months Ended September 30,
		2013									2012
		Before Tax			Tax Benefit			Net of Tax			Before Tax			Tax Benefit		Net of Tax
		Amount						Amount			Amount					Amount
		(Dollars in thousands)
	Other comprehensive loss:
	Securities available for sale:
	Change in unrealized gain during period	$	(1,136	)	$	398		$	(738	)	$	(718	)	$	251	$	(467	)
	Total securities available for sale		(1,136	)		398			(738	)		(718	)		251		(467	)
	Total other comprehensive loss	$	(1,136	)	$	398		$	(738	)	$	(718	)	$	251	$	(467	)
		Nine Months Ended September 30,
		2013									2012
		Before Tax			Tax Benefit			Net of Tax			Before Tax			Tax Benefit		Net of Tax
		Amount						Amount			Amount					Amount
		(Dollars in thousands)
	Other comprehensive loss:
	Securities available for sale:
	Change in unrealized gain during period	$	(5,237	)	$	1,833		$	(3,404	)	$	(3,736	)	$	1,308	$	(2,428	)
	Total securities available for sale		(5,237	)		1,833			(3,404	)		(3,736	)		1,308		(2,428	)
	Total other comprehensive loss	$	(5,237	)	$	1,833		$	(3,404	)	$	(3,736	)	$	1,308	$	(2,428	)
	Activity in accumulated other comprehensive income, net of tax, was as follows:
		Securities			Accumulated
		Available for			Other
		Sale			Comprehensive
					Income
		(Dollars in thousands)
	Balance at January 1, 2013	$	8,986		$	8,986
	Other comprehensive loss		(3,404	)		(3,404	)
	Balance at September 30, 2013	$	5,582		$	5,582
	Balance at January 1, 2012	$	13,472		$	13,472
	Other comprehensive loss		(2,428	)		(2,428	)
	Balance at September 30, 2012	$	11,044		$	11,044

ACQUISITIONS

ACQUISITIONS	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
ACQUISITIONS	'
	11. ACQUISITIONS
	Pending Acquisition of F&M Bancorporation Inc.—On August 29, 2013, the Company announced the signing of a definitive merger agreement to acquire F&M Bancorporation Inc. (“FMBC”) and its wholly-owned subsidiary The F&M Bank & Trust Company (“F&M Bank”) headquartered in Tulsa, Oklahoma. F&M Bank operates 13 banking locations; 10 in Tulsa, Oklahoma and surrounding areas and 3 in Dallas, Texas. As of September 30, 2013, FMBC on a consolidated basis, reported total assets of $2.47 billion, total loans of $1.88 billion and total deposits of $2.26 billion. Under the terms of the definitive agreement, the Company will issue approximately 3,298,246 shares of Company common stock plus $47.0 million in cash for all outstanding shares of FMBC capital stock, subject to certain conditions and potential adjustments. The transaction is subject to customary closing conditions, including the receipt of customary regulatory approvals and approval by FMBC’s shareholders.
	Acquisition of FVNB Corp.— On November 1, 2013, the Company completed the acquisition of FVNB Corp. and its wholly owned subsidiary, First Victoria National Bank (collectively, “FVNB”) headquartered in Victoria, Texas. The acquisition was not considered significant to the Company’s financial statements and therefore pro forma financial data and related disclosures are not included. Refer to Note 12 – Subsequent Events for further information regarding the FVNB acquisition.
	Acquisition of Coppermark Bancshares, Inc.—On April 1, 2013, the Company completed the acquisition of Coppermark Bancshares, Inc. and its wholly-owned subsidiary, Coppermark Bank (collectively, “Coppermark”). Coppermark operated 9 full-service banking offices: 6 in Oklahoma City, Oklahoma and surrounding areas and 3 in the Dallas, Texas area. The Company acquired Coppermark to expand its market into Oklahoma. The acquisition was not considered significant to the Company’s financial statements and therefore pro forma financial data and related disclosures are not included.
	As of March 31, 2013, Coppermark reported, on a consolidated basis, total assets of $1.25 billion, total loans of $847.6 million and total deposits of $1.11 billion. Under the terms of the acquisition agreement, the Company issued 3,258,718 shares of Company common stock plus $60.0 million in cash for all outstanding shares of Coppermark Bancshares, Inc. capital stock, for total merger consideration of $214.4 million based on the Company’s closing stock price of $47.39. The Company recognized initial goodwill of $91.7 million which does not include subsequent fair value adjustments that are still being finalized. Goodwill is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes. Additionally, the Company recognized $1.5 million of core deposit intangibles. For the nine months ended September 30, 2013, the Company incurred approximately $787,000 of pre-tax merger related expenses related to the Coppermark acquisition.
	Acquisition of East Texas Financial Services, Inc.—On January 1, 2013, the Company completed the acquisition of East Texas Financial Services, Inc. (OTC BB: FFBT) and its wholly-owned subsidiary, First Federal Bank Texas (collectively, “East Texas Financial Services”). East Texas Financial Services operated 4 banking offices in the Tyler MSA, including three locations in Tyler, Texas and one location in Gilmer, Texas. The Company acquired East Texas Financial Services to increase its market share in the East Texas area. The acquisition was not considered significant to the Company’s financial statements and therefore pro forma financial data and related disclosures are not included.
	As of December 31, 2012, East Texas Financial Services reported, on a consolidated basis, total assets of $165.0 million, total loans of $129.3 million and total deposits of $112.3 million. Under the terms of the acquisition agreement, the Company issued 530,940 shares of Company common stock for all outstanding shares of East Texas Financial Services capital stock, for total merger consideration of $22.3 million based on the Company’s closing stock price of $42.00. The Company recognized initial goodwill of $7.0 million which does not include subsequent fair value adjustments that are still being finalized. Goodwill is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes.
	Acquisition of Community National Bank—On October 1, 2012, the Company completed the acquisition of Community National Bank, Bellaire, Texas. Community National Bank operated 1 banking office in Bellaire, Texas, in the Houston Metropolitan Area. The Company acquired Community National Bank to increase its market share in the Houston area. The acquisition is not considered significant to the Company’s financial statements and therefore pro forma financial data is not included.
	As of September 30, 2012, Community National Bank reported total assets of $182.0 million, total loans of $68.0 million and total deposits of $164.6 million. Under the terms of the acquisition agreement, the Company issued 372,282 shares of Company common stock plus $11.4 million in cash for all outstanding shares of Community National Bank capital stock, for total merger consideration of $27.3 million, based on the Company’s closing stock price of $42.62. The Company recognized initial goodwill of $10.6 million which does not include subsequent fair value adjustments that are still being finalized. Goodwill is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes.
	Acquisition of American State Financial Corporation—On July 1, 2012, the Company completed the acquisition of American State Financial Corporation and its wholly owned subsidiary American State Bank (collectively referred to as “ASB”). ASB operated 37 full service banking offices in 18 counties across West Texas. The Company acquired ASB to increase its market share in the West Texas area.
	Under the terms of the acquisition agreement, the Company issued 8,524,835 shares of Company common stock plus $178.5 million in cash for all outstanding shares of American State Financial Corporation capital stock, for total merger consideration of $536.8 million based on the Company’s closing stock price of $42.03. The Company recognized goodwill of $271.0 million which is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired. Goodwill resulted from a combination of expected operational synergies, an enhanced branching network, and cross-selling opportunities. Goodwill is not expected to be deductible for tax purposes. Additionally, the Company recognized $14.5 million of core deposit intangibles.
	Acquisition of The Bank Arlington—On April 1, 2012, the Company completed the acquisition of The Bank Arlington. The Bank Arlington operated one banking office in Arlington, Texas, in the Dallas/Fort Worth CMSA. The Company acquired The Bank Arlington to increase its market share in the Dallas/Fort Worth area. The acquisition is not considered significant to the Company’s financial statements and therefore pro forma financial data and related disclosures are not included.
	As of March 31, 2012, The Bank Arlington reported total assets of $37.3 million, total loans of $22.9 million and total deposits of $33.2 million. Under the terms of the acquisition agreement, the Company issued 135,347 shares of Company common stock for all outstanding shares of The Bank Arlington capital stock, for total merger consideration of $6.2 million, based on the Company’s closing stock price of $45.80. The Company recognized goodwill of $2.0 million which is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes.
	Acquisition of Texas Bankers, Inc.—On January 1, 2012, the Company completed the acquisition of Texas Bankers, Inc. and its wholly-owned subsidiary, Bank of Texas, Austin, Texas. The three Bank of Texas banking offices in the Austin, Texas CMSA consisted of a location in Rollingwood, which was consolidated with the Company’s Westlake location and remains in Bank of Texas’ Rollingwood banking office; one banking center in downtown Austin, which was consolidated into the Company’s downtown Austin location; and another banking center in Thorndale. The Company acquired Texas Bankers, Inc. to increase is its market share in the Central Texas area. The acquisition is not considered significant to the Company’s financial statements and therefore pro forma financial data and related disclosures are not included.
	Texas Bankers, Inc. on a consolidated basis, reported total assets of $77.0 million, total loans of $27.6 million and total deposits of $70.4 million as of December 31, 2011. Under the terms of the acquisition agreement, the Company issued 314,953 shares of Company common stock for all outstanding shares of Texas Bankers capital stock, for total merger consideration of $12.7 million, based on the Company’s closing stock price of $40.35. The Company recognized goodwill of $6.1 million which is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes.
	The following pro forma information presents the results of operations for the three and nine months ended September 30, 2013 and 2012, as if the Coppermark, East Texas Financial Services, Community National Bank, ASB and The Bank Arlington acquisitions had occurred on January 1, 2012.
			Three months ended September 30,				Nine months ended September 30,
			2013		2012 (1)		2013		2012 (1)
			(Dollars in thousands, except per				(Dollars in thousands, except per
			share data)				share data)
	Net interest income		$	126,533	$	127,501	$	375,699	$	403,983
	Net income			55,278		53,266		165,090		184,368
	Basic earnings per share			0.92		0.89		2.64		2.92
	Diluted earnings per share			0.91		0.88		2.64		2.92
	-1	Includes a nonrecurring gain on sale of securities of $23.4 million, or $0.37 earnings per share, by ASB during the second quarter of 2012.

SUBSEQUENT_EVENT

SUBSEQUENT EVENT	9 Months Ended
	Sep. 30, 2013
Subsequent Events [Abstract]	'
SUBSEQUENT EVENT	'
	12. SUBSEQUENT EVENT
	Acquisition of FVNB Corp.—On November 1, 2013, the Company completed the acquisition of FVNB Corp. and its wholly owned subsidiary, First Victoria National Bank (collectively, “FVNB”) headquartered in Victoria, Texas. FVNB operated 33 banking locations; 4 in Victoria, Texas, 7 in the South Texas area including Corpus Christi; 6 in the Bryan/College Station area; 5 in the Central Texas area including New Braunfels; and 11 in the Houston area including The Woodlands and Huntsville.
	As of September 30, 2013, FVNB, on a consolidated basis, reported total assets of $2.47 billion, total loans of $1.65 billion and total deposits of $2.20 billion. Under the terms of the acquisition agreement, the Company issued 5,570,667 shares of Company common stock plus $91.3 million in cash for all outstanding shares of FVNB Corp. capital stock for total merger consideration of $439.1 million based on the Company’s closing stock price of $62.45. The Company recognized initial goodwill of $278.3 million which does not include subsequent fair value adjustments that are still being finalized. Goodwill is calculated as the excess of both the consideration exchanged and liabilities assumed as compared to the fair value of identifiable assets acquired, none of which is expected to be deductible for tax purposes. For the nine months ended September 30, 2013, the Company incurred approximately $121,000 of pre-tax merger related expenses related to the FVNB acquisition.

NEW_ACCOUNTING_STANDARDS_Polic

NEW ACCOUNTING STANDARDS (Policies)	9 Months Ended
	Sep. 30, 2013
Accounting Changes And Error Corrections [Abstract]	'
New Accounting Standards	'
	ASU 2012-02 “Intangibles—Goodwill and Other (Topic 350) — Testing Indefinite-Lived Intangible Assets for Impairment.” ASU 2012-02 gives entities the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that an indefinite-lived intangible asset is impaired. If, after assessing the totality of events or circumstances, an entity determines it is more likely than not that an indefinite-lived intangible asset is impaired, then the entity must perform the quantitative impairment test. If, under the quantitative impairment test, the carrying amount of the intangible asset exceeds its fair value, an entity should recognize an impairment loss in the amount of that excess permitting an entity to assess qualitative factors when testing indefinite-lived intangible assets for impairment results in guidance that is similar to the goodwill impairment testing guidance in ASU 2011-08. ASU 2012-02 became effective for the Company on January 1, 2013 and did not have a significant impact on the Company’s financial statements.
	ASU 2013-02 “Comprehensive Income (Topic 220) — Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income.” ASU 2013-02 amends recent guidance related to the reporting of comprehensive income to enhance the reporting of reclassifications out of accumulated other comprehensive income. ASU 2013-02 became effective for the Company on January 1, 2013 and did not have a significant impact on the Company’s financial statements. See Note 10 – Other Comprehensive (Loss) Income for applicable disclosures.

INCOME_PER_COMMON_SHARE_Tables

INCOME PER COMMON SHARE (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Computation of Basic and Diluted Earnings Per Share	'
	The following table illustrates the computation of basic and diluted earnings per share:
		Three Months Ended September 30,								Nine Months Ended September 30,
		2013				2012				2013				2012
		Amount		Per Share		Amount		Per Share		Amount		Per Share		Amount		Per Share
				Amount				Amount				Amount				Amount
		(In thousands, except per share data)
	Net income	$	55,278			$	46,176			$	158,427			$	119,635
	Basic:
	Weighted average shares outstanding		60,344	$	0.92		55,958	$	0.83		59,207	$	2.68		50,239	$	2.38
	Diluted:
	Add incremental shares for:
	Effect of dilutive securities—options		160				135				155				154
	Total		60,504	$	0.91		56,093	$	0.82		59,362	$	2.67		50,393	$	2.37

SECURITIES_Tables

SECURITIES (Tables)	9 Months Ended
	Sep. 30, 2013
Investments Debt And Equity Securities [Abstract]	'
Schedule of Investment Securities	'
	The amortized cost and fair value of investment securities were as follows:
		September 30, 2013
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			Losses
		(Dollars in thousands)
	Available for Sale
	States and political subdivisions	$	29,130	$	1,002		$	—		$	30,132
	Collateralized mortgage obligations		512		3			(1	)		514
	Mortgage-backed securities		119,259		7,602			(24	)		126,837
	Other securities		7,288		5			—			7,293
	Total	$	156,189	$	8,612		$	(25	)	$	164,776
	Held to Maturity
	U.S. Treasury securities and obligations of U.S. Government agencies	$	3,252	$	23		$	—		$	3,275
	States and political subdivisions		333,380		1,640			(2,175	)		332,845
	Corporate debt securities		518		7			—			525
	Collateralized mortgage obligations		59,724		1,327			(48	)		61,003
	Mortgage-backed securities		7,186,737		98,915			(151,079	)		7,134,573
	Qualified School Construction Bonds (QSCB)		22,958		1,270			(278	)		23,950
	Total	$	7,606,569	$	103,182		$	(153,580	)	$	7,556,171
		31-Dec-12
		Amortized		Gross			Gross			Fair
		Cost		Unrealized			Unrealized			Value
				Gains			Losses
		(Dollars in thousands)
	Available for Sale
	States and political subdivisions	$	34,743	$	1,691		$	—		$	36,434
	Collateralized mortgage obligations		616		—			(12	)		604
	Mortgage-backed securities		168,701		11,742			(27	)		180,416
	Other securities		8,786		430			—			9,216
	Total	$	212,846	$	13,863		$	(39	)	$	226,670
	Held to Maturity
	U.S. Treasury securities and obligations of U.S. Government agencies	$	7,061	$	160		$	—		$	7,221
	States and political subdivisions		391,510		7,074			(354	)		398,230
	Corporate debt securities		1,500		28			—			1,528
	Collateralized mortgage obligations		125,912		2,304			(50	)		128,166
	Mortgage-backed securities		6,676,512		196,206			(4,517	)		6,868,201
	Qualified School Construction Bonds (QSCB)		12,900		2,449			—			15,349
	Total	$	7,215,395	$	208,221		$	(4,921	)	$	7,418,695
Schedule of Securities with Unrealized Losses	'
	Securities, with unrealized losses segregated by length of time, that have been in a continuous loss position at September 30, 2013 and December 31, 2012 were as follows:
		September 30, 2013
		Less than 12 Months					More than 12 Months						Total
		Estimated		Unrealized			Estimated			Unrealized			Estimated		Unrealized
		Fair Value		Losses			Fair Value			Losses			Fair Value		Losses
		(Dollars in thousands)
	Available for Sale
	Collateralized mortgage obligations	$	15	$	—		$	53		$	(1	)	$	68	$	(1	)
	Mortgage-backed securities		409		—			3,539			(24	)		3,948		(24	)
	Other securities		—		—			—			—			—		—
	Total	$	424	$	—		$	3,592		$	(25	)	$	4,016	$	(25	)
	Held to Maturity
	States and political subdivisions	$	164,268	$	(2,222	)	$	10,264		$	(231	)	$	174,532	$	(2,453	)
	Collateralized mortgage obligations		1,391		(42	)		437			(6	)		1,828		(48	)
	Mortgage-backed securities		3,507,024		(145,835	)		102,028			(5,244	)		3,609,052		(151,079	)
	Total	$	3,672,683	$	(148,099	)	$	112,729		$	(5,481	)	$	3,785,412	$	(153,580	)
		31-Dec-12
		Less than 12 Months					More than 12 Months						Total
		Estimated		Unrealized			Estimated			Unrealized			Estimated		Unrealized
		Fair Value		Losses			Fair Value			Losses			Fair Value		Losses
		(Dollars in thousands)
	Available for Sale
	Collateralized mortgage obligations	$	—	$	—		$	603		$	(12	)	$	603	$	(12	)
	Mortgage-backed securities		224		—			3,964			(27	)		4,188		(27	)
	Total	$	224	$	—		$	4,567		$	(39	)	$	4,791	$	(39	)
	Held to Maturity
	States and political subdivisions	$	37,322	$	(335	)	$	1,140		$	(19	)	$	38,462	$	(354	)
	Collateralized mortgage obligations		2,366		(50	)		—			—			2,366		(50	)
	Mortgage-backed securities		1,081,414		(4,516	)		234			(1	)		1,081,648		(4,517	)
	Total	$	1,121,102	$	(4,901	)	$	1,374		$	(20	)	$	1,122,476	$	(4,921	)
Amortized Cost and Fair Value of Investment Securities by Contractual Maturity	'
	The amortized cost and fair value of investment securities at September 30, 2013, by contractual maturity, are shown below. Actual maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations at any time with or without call or prepayment penalties.
		Held to Maturity					Available for Sale
		Amortized		Fair			Amortized			Fair
		Cost		Value			Cost			Value
		(Dollars in thousands)
	Due in one year or less	$	26,450	$	26,523		$	7,383		$	7,392
	Due after one year through five years		120,137		120,135			4,990			5,175
	Due after five years through ten years		138,529		138,049			20,997			21,721
	Due after ten years		74,992		75,888			3,048			3,137
	Subtotal		360,108		360,595			36,418			37,425
	Mortgage-backed securities and collateralized mortgage obligations		7,246,461		7,195,576			119,771			127,351
	Total	$	7,606,569	$	7,556,171		$	156,189		$	164,776

LOANS_AND_ALLOWANCE_FOR_CREDIT1

LOANS AND ALLOWANCE FOR CREDIT LOSSES (Tables)	9 Months Ended
	Sep. 30, 2013
Text Block [Abstract]	'
Schedule of Types of Loans in Loan Portfolio	'
	The loan portfolio consists of various types of loans made principally to borrowers located in Texas and Oklahoma and is classified by major type as follows:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Residential mortgage loans held for sale		$	4,892		$	10,433
	Commercial and industrial			1,028,799			771,114
	Real estate:
	Construction and land development			703,193			550,768
	1-4 family residential (including home equity)			1,710,621			1,432,133
	Commercial real estate (including multi-family residential)			2,304,862			1,990,642
	Farmland			235,049			211,156
	Agriculture			86,469			74,481
	Consumer and other (net of unearned discount)			108,704			139,213
	Total loans held for investment			6,177,697			5,169,507
	Total		$	6,182,589		$	5,179,940
Schedule of Activity with Respect to Related-Party Loans	'
	An analysis of activity with respect to these related party loans is as follows:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Beginning balance on January 1		$	6,682		$	9,809
	New loans and reclassified related loans			306			967
	Repayments			(676	)		(4,094	)
	Ending balance		$	6,312		$	6,682
Schedule of Past Due Loans with Age Analysis, Segregated by Class of Loans	'
	An aging analysis of past due loans, segregated by class of loans, is as follows:
			September 30, 2013
			Loans Past Due and Still Accruing
			30-89 Days			90 or More			Total Past			Nonaccrual			Current			Total
						Days			Due Loans			Loans			Loans			Loans
			(Dollars in thousands)
	Construction and land development		$	3,465		$	—		$	3,465		$	469		$	699,259		$	703,193
	Agriculture and agriculture real estate (includes farmland)			557			—			557			23			320,938			321,518
	1-4 family (includes home equity) (1)			5,655			90			5,745			1,037			1,708,731			1,715,513
	Commercial real estate (includes multi-family residential)			7,065			34			7,099			2,223			2,295,540			2,304,862
	Commercial and industrial			9,230			148			9,378			1,069			1,018,352			1,028,799
	Consumer and other			391			11			402			133			108,169			108,704
	Total		$	26,363		$	283		$	26,646		$	4,954		$	6,150,989		$	6,182,589
			December 31, 2012
			Loans Past Due and Still Accruing
			30-89 Days			90 or More			Total Past			Nonaccrual			Current			Total
						Days			Due Loans			Loans			Loans			Loans
			(Dollars in thousands)
	Construction and land development		$	3,863		$	—		$	3,863		$	1,170		$	545,735		$	550,768
	Agriculture and agriculture real estate (includes farmland)			310			21			331			396			284,910			285,637
	1-4 family (includes home equity) (1)			2,307			310			2,617			1,598			1,438,351			1,442,566
	Commercial real estate (includes multi-family residential)			9,163			—			9,163			—			1,981,479			1,990,642
	Commercial and industrial			4,843			—			4,843			1,469			764,802			771,114
	Consumer and other			856			—			856			749			137,608			139,213
	Total		$	21,342		$	331		$	21,673		$	5,382		$	5,152,885		$	5,179,940
	-1	Includes $4.9 million and $10.4 million of residential mortgage loans held for sale at September 30, 2013 and December 31, 2012, respectively.
Schedule of Nonperforming Assets	'
	The following table presents information regarding past due loans and nonperforming assets as of the dates indicated:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Nonaccrual loans		$	4,954		$	5,382
	Accruing loans 90 or more days past due			283			331
	Total nonperforming loans			5,237			5,713
	Repossessed assets			18			68
	Other real estate			7,432			7,234
	Total nonperforming assets		$	12,687		$	13,015
	Nonperforming assets to total loans and other real estate			0.2	%		0.25	%
Summary of Carrying Value and Outstanding Balance for Purchased Credit Impaired Loans	'
	The carrying amount of acquired PCI loans included in the consolidated balance sheet and the related outstanding balance at September 30, 2013 and December 31, 2012 were as follows:
			September 30,			December 31,
			2013			2012
			(Dollars in thousands)
	Acquired PCI loans:
	Carrying amount		$	36,204		$	22,880
	Outstanding balance			77,303			46,914
Summary of Changes in Accretable Yield for Acquired PCI Loans	'
	Changes in the accretable yield for acquired PCI loans for the three and nine month periods ended September 30, 2013 and 2012 were as follows:
			Three Month Periods Ended September 30,						Nine Month Periods Ended September 30,
			2013			2012			2013			2012
			(Dollars in thousands)
	Balance at beginning of period		$	13,011		$	—		$	7,459		$	—
	Additions			349			8,157			7,877			8,157
	Reclassifications from nonaccretable			3,088			—			4,343			—
	Accretion			(5,840	)		(1,160	)		(9,071	)		(1,160	)
	Balance at September 30		$	10,608		$	6,997		$	10,608		$	6,997
Schedule of Impaired Loans	'
	Impaired loans as of September 30, 2013 are set forth in the following table. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment presented in the table below is reported on a year-to-date basis.
			September 30, 2013
			Recorded			Unpaid			Related			Average
			Investment			Principal			Allowance			Recorded
						Balance						Investment
			(Dollars in thousands)
	With no related allowance recorded:
	Construction and land development		$	257		$	265		$	—		$	701
	Agriculture and agriculture real estate (includes farmland)			—			—			—			39
	1-4 family (includes home equity)			310			279			—			401
	Commercial real estate (includes multi-family residential)			1,213			1,237			—			832
	Commercial and industrial			194			54			—			141
	Consumer and other			—			—			—			5
	Total			1,974			1,835			—			2,119
	With an allowance recorded:
	Construction and land development			—			—			—			—
	Agriculture and agriculture real estate (includes farmland)			23			30			20			29
	1-4 family (includes home equity)			71			96			53			535
	Commercial real estate (includes multi-family residential)			17			18			17			1,234
	Commercial and industrial			832			842			741			938
	Consumer and other			80			87			69			73
	Total			1,023			1,073			900			2,809
	Total:
	Construction and land development			257			265			—			701
	Agriculture and agriculture real estate (includes farmland)			23			30			20			68
	1-4 family (includes home equity)			381			375			53			936
	Commercial real estate (includes multi-family residential)			1,230			1,255			17			2,066
	Commercial and industrial			1,026			896			741			1,079
	Consumer and other			80			87			69			78
			$	2,997		$	2,908		$	900		$	4,928
	Impaired loans as of December 31, 2012 are set forth in the following tables. No interest income was recognized on impaired loans subsequent to their classification as impaired. The average recorded investment is reported on a year-to-date basis.
			December 31, 2012
			Recorded			Unpaid			Related			Average
			Investment			Principal			Allowance			Recorded
						Balance						Investment
			(Dollars in thousands)
	With no related allowance recorded:
	Construction and land development		$	1,144		$	1,175		$	—		$	368
	Agriculture and agriculture real estate (includes farmland)			77			77			—			34
	1-4 family (includes home equity)			491			522			—			381
	Commercial real estate (includes multi-family residential)			450			476			—			676
	Commercial and industrial			87			89			—			75
	Consumer and other			10			10			—			3
	Total			2,259			2,349			—			1,537
	With an allowance recorded:
	Construction and land development			—			—			—			451
	Agriculture and agriculture real estate (includes farmland)			34			41			29			45
	1-4 family (includes home equity)			999			1,017			273			720
	Commercial real estate (includes multi-family residential)			2,450			2,451			610			2,725
	Commercial and industrial			1,043			1,079			1,002			782
	Consumer and other			66			81			67			21
	Total			4,592			4,669			1,981			4,744
	Total:
	Construction and land development			1,144			1,175			—			819
	Agriculture and agriculture real estate (includes farmland)			111			118			29			79
	1-4 family (includes home equity)			1,490			1,539			273			1,101
	Commercial real estate (includes multi-family residential)			2,900			2,927			610			3,401
	Commercial and industrial			1,130			1,168			1,002			857
	Consumer and other			76			91			67			24
			$	6,851		$	7,018		$	1,981		$	6,281
Schedule Showing Risk Grades and Classified Loans by Class of Loan	'
	The following table presents risk grades and classified loans by class of loan at September 30, 2013. Classified loans include loans in risk grades 5, 6 and 7.
			Construction			Agriculture and			1-4 Family			Commercial			Commercial			Consumer and			Total
			and Land			Agriculture Real			(includes			Real Estate			and Industrial			Other
			Development			Estate (includes			Home Equity) (1)			(includes Multi-
						Farmland)						Family Residential)
			(Dollars in thousands)
	Grade 1		$	—		$	4,771		$	—		$	—		$	48,879		$	31,287		$	84,937
	Grade 2			694,446			313,890			1,701,525			2,248,498			962,941			77,114			5,998,414
	Grade 3			3,850			1,044			4,287			12,483			7,453			133			29,250
	Grade 4			1,551			1,369			6,165			15,736			5,876			90			30,787
	Grade 5			257			23			370			1,230			1,026			80			2,986
	Grade 6			—			—			11			—			—			—			11
	Grade 7			—			—			—			—			—			—			—
	PCI Loans (2)			3,089			421			3,155			26,915			2,624			—			36,204
	Total		$	703,193		$	321,518		$	1,715,513		$	2,304,862		$	1,028,799		$	108,704		$	6,182,589
	-1	Includes $4.9 million of residential mortgage loans held for sale at September 30, 2013.
	-2	Of the total PCI loans, $24.9 million were classified as substandard at September 30, 2013.
	The following table presents risk grades and classified loans by class of loan at December 31, 2012. Classified loans include loans in risk grades 5, 6 and 7.
			Construction			Agriculture and			1-4 Family			Commercial			Commercial			Consumer and			Total
			and Land			Agriculture Real			(includes			Real Estate			and Industrial			Other
			Development			Estate (includes			Home Equity) (1)			(includes Multi-
						Farmland)						Family Residential)
			(Dollars in thousands)
	Grade 1		$	476		$	4,195		$	515		$	—		$	53,965		$	38,789		$	97,940
	Grade 2			537,340			277,333			1,431,095			1,945,319			702,587			100,163			4,993,837
	Grade 3			7,250			2,024			4,947			11,760			8,926			—			34,907
	Grade 4			4,256			1,694			4,303			11,711			1,385			176			23,525
	Grade 5			1,144			111			1,477			2,900			1,130			76			6,838
	Grade 6			—			—			13			—			—			—			13
	Grade 7			—			—			—			—			—			—			—
	PCI Loans			302			280			216			18,952			3,121			9			22,880
	Total		$	550,768		$	285,637		$	1,442,566		$	1,990,642		$	771,114		$	139,213		$	5,179,940
	-1	Includes $10.4 million of residential mortgage loans held for sale at December 31, 2012.
Schedule of Recorded Investment in Loans and Activity in Allowance for Credit Losses by Portfolio Segment	'
	The following table details the recorded investment in loans and activity in the allowance for credit losses by portfolio segment for the three and nine months ended September 30, 2013. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
			Construction			Agriculture			1-4 Family			Commercial			Commercial			Consumer			Total
			and Land			and			(includes			Real Estate			and			and Other
			Development			Agriculture			Home			(includes			Industrial
						Real Estate			Equity)			Multi-Family
						(includes						Residential)
						Farmland)
			(Dollars in thousands)
	Allowance for credit losses:
	Three Months Ended
	Balance June 30, 2013		$	11,991		$	982		$	13,435		$	22,831		$	6,293		$	644		$	56,176
	Provision for credit losses			1,024			129			1,262			(658	)		1,356			912			4,025
	Charge-offs			(14	)		(23	)		(20	)		—			(188	)		(897	)		(1,142	)
	Recoveries			44			10			5			471			69			255			854
	Net charge-offs			30			(13	)		(15	)		471			(119	)		(642	)		(288	)
	Balance September 30, 2013		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
	Nine Months Ended
	Balance January 1, 2013		$	11,909		$	764		$	13,942		$	19,607		$	5,777		$	565		$	52,564
	Provision for credit losses			1,173			352			892			3,309			2,070			1,579			9,375
	Charge-offs			(270	)		(36	)		(182	)		(894	)		(592	)		(2,100	)		(4,074	)
	Recoveries			233			18			30			622			275			870			2,048
	Net charge-offs			(37	)		(18	)		(152	)		(272	)		(317	)		(1,230	)		(2,026	)
	Balance September 30, 2013		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
	Allowance for credit losses related to:
	September 30, 2013
	Individually evaluated for impairment		$	—		$	20		$	53		$	17		$	741		$	69		$	900
	Collectively evaluated for impairment			13,045			1,078			14,629			22,627			6,789			845			59,013
	PCI loans			—			—			—			—			—			—			—
	Total allowance for credit losses		$	13,045		$	1,098		$	14,682		$	22,644		$	7,530		$	914		$	59,913
	Recorded investment in loans:
	September 30, 2013
	Individually evaluated for impairment		$	257		$	23		$	381		$	1,230		$	1,026		$	80		$	2,997
	Collectively evaluated for impairment			699,847			321,074			1,711,977			2,276,717			1,025,149			108,624			6,143,388
	PCI loans			3,089			421			3,155			26,915			2,624			—			36,204
	Total loans evaluated for impairment		$	703,193		$	321,518		$	1,715,513		$	2,304,862		$	1,028,799		$	108,704		$	6,182,589
	The following table details the recorded investment in loans and activity in the allowance for credit losses by portfolio segment for the three and nine months ended September 30, 2012. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
			Construction			Agriculture			1-4 Family			Commercial			Commercial			Consumer			Total
			and Land			and			(includes			Real Estate			and			and Other
			Development			Agriculture			Home			(includes			Industrial
						Real Estate			Equity)			Multi-Family
						(includes						Residential)
						Farmland)
			(Dollars in thousands)
	Allowance for credit losses:
	Three Months Ended
	Balance June 30, 2012		$	10,065		$	742		$	13,326		$	21,406		$	4,238		$	605		$	50,382
	Provision for credit losses			359			(2	)		299			(509	)		660			993			1,800
	Charge-offs			(159	)		—			(327	)		(909	)		(55	)		(1,663	)		(3,113	)
	Recoveries			4			30			76			109			565			1,074			1,858
	Net charge-offs			(155	)		30			(251	)		(800	)		510			(589	)		(1,255	)
	Balance September 30, 2012		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
	Nine Months Ended
	Balance January 1, 2012		$	12,094		$	511		$	12,645		$	21,460		$	3,826		$	1,058		$	51,594
	Provision for credit losses			(469	)		226			1,121			(250	)		1,237			685			2,550
	Charge-offs			(1,368	)		—			(478	)		(1,278	)		(376	)		(2,101	)		(5,601	)
	Recoveries			12			33			86			165			721			1,367			2,384
	Net charge-offs			(1,356	)		33			(392	)		(1,113	)		345			(734	)		(3,217	)
	Balance September 30, 2012		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
	Allowance for credit losses related to:
	September 30, 2012
	Individually evaluated for impairment		$	26		$	61		$	336		$	567		$	1,180		$	20		$	2,190
	Collectively evaluated for impairment			10,243			709			13,038			19,530			4,228			989			48,737
	PCI loans			—			—			—			—			—			—			—
Total allowance for credit losses		$	10,269		$	770		$	13,374		$	20,097		$	5,408		$	1,009		$	50,927
Recorded investment in loans:
September 30, 2012
Individually evaluated for impairment		$	86		$	143		$	1,448		$	3,170		$	1,395		$	20		$	6,262
Collectively evaluated for impairment			495,005			303,913			1,396,114			1,950,488			751,379			148,361			5,045,260
PCI loans			1,326			78			155			22,454			3,568			—			27,581
Total loans evaluated for impairment		$	496,417		$	304,134		$	1,397,717		$	1,976,112		$	756,342		$	148,381		$	5,079,103

FAIR_VALUE_Tables

FAIR VALUE (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis	'
	The following tables present fair values for assets measured at fair value on a recurring basis:
		As of September 30, 2013
		Level 1		Level 2		Level 3		Total
		(Dollars in thousands)
	Available for sale securities:
	States and political subdivisions	$	—	$	30,132	$	—	$	30,132
	Collateralized mortgage obligations		—		514		—		514
	Mortgage-backed securities		—		126,837		—		126,837
	Other securities		7,293		—		—		7,293
	Total	$	7,293	$	157,483	$	—	$	164,776
		As of December 31, 2012
		Level 1		Level 2		Level 3		Total
		(Dollars in thousands)
	Available for sale securities:
	States and political subdivisions	$	—	$	36,434	$	—	$	36,434
	Collateralized mortgage obligations		—		604		—		604
	Mortgage-backed securities		—		180,416		—		180,416
	Other securities		7,688		1,528		—		9,216
	Total	$	7,688	$	218,982	$	—	$	226,670
Summary of Financial Assets and Liabilities Measured on Recurring and Non-Recurring Basis	'
	The following table summarizes the carrying values and estimated fair values of certain financial instruments not recorded at fair value on a regular basis:
		As of September 30, 2013
		Carrying		Estimated Fair Value
		Amount		Level 1		Level 2		Level 3		Total
		(Dollars in thousands)
	Assets
	Cash and due from banks	$	269,987	$	269,987	$	—	$	—	$	269,987
	Federal funds sold		1,121		1,121		—		—		1,121
	Held to maturity securities		7,606,569		—		7,556,171		—		7,556,171
	Loans held for sale		4,892		4,892		—		—		4,892
	Loans held for investment, net of allowance		6,117,784		—		—		6,143,355		6,143,355
	Federal Home Loan Bank of Dallas stock		43,058		43,058		—		—		43,058
	Liabilities
	Deposits:
	Noninterest-bearing	$	3,368,357	$	—	$	3,368,687	$	—	$	3,368,687
	Interest-bearing		9,087,442		—		8,286,130		—		8,286,130
	Other borrowings		605,951		—		607,471		—		607,471
	Securities sold under repurchase agreements		431,969		—		431,692		—		431,692
	Junior subordinated debentures		85,055		—		81,696		—		81,696
		As of December 31, 2012
		Carrying		Estimated Fair Value
		Amount		Level 1		Level 2		Level 3		Total
		(Dollars in thousands)
	Assets
	Cash and due from banks	$	325,952	$	325,952	$	—	$	—	$	325,952
	Federal funds sold		352		352		—		—		352
	Held to maturity securities		7,215,395		—		7,418,695		—		7,418,695
	Loans held for sale		10,433		10,433		—		—		10,433
	Loans held for investment, net of allowance		5,116,943		—		—		5,186,779		5,186,779
	Federal Home Loan Bank of Dallas stock		34,461		34,461		—		—		34,461
	Liabilities
	Deposits:
	Noninterest-bearing	$	3,016,205	$	—	$	3,016,205	$	—	$	3,016,205
	Interest-bearing		8,625,639		—		8,640,625		—		8,640,625
	Other borrowings		256,753		—		258,819		—		258,819
	Securities sold under repurchase agreements		454,502		—		454,596		—		454,596
	Junior subordinated debentures		85,055		—		72,705		—		72,705

GOODWILL_AND_CORE_DEPOSIT_INTA1

GOODWILL AND CORE DEPOSIT INTANGIBLES (Tables)	9 Months Ended
	Sep. 30, 2013
Goodwill And Intangible Assets Disclosure [Abstract]	'
Schedule of Goodwill and Core Deposit Intangibles	'
	Changes in the carrying amount of the Company’s goodwill and core deposit intangibles (“CDI”) for nine months ended September 30, 2013 and the year ended December 31, 2012 were as follows:
		Goodwill			Core Deposit
					Intangibles
		(Dollars in thousands)
	Balance as of December 31, 2011	$	924,537		$	20,996
	Less:
	Amortization		—			(7,229	)
	Add:
	Acquisition of Texas Bankers, Inc.		6,077			—
	Acquisition of The Bank Arlington		2,102			—
	Acquisition of ASB		274,119			12,392
	Acquisition of Community National Bank		10,327			—
	Balance as of December 31, 2012		1,217,162			26,159
	Less:
	Amortization		—			(4,551	)
	Add:
	Measurement period adjustment of The Bank Arlington		(130	)		—
	Measurement period adjustment of ASB		(3,094	)		2,110
	Measurement period adjustment of Community National Bank		1,999			—
	Acquisition of East Texas Financial Services, Inc.		16,658			—
	Acquisition of Coppermark Bancshares, Inc.		119,187			1,515
	Balance as of September 30, 2013	$	1,351,782		$	25,233
Schedule of Estimated Aggregate Future Amortization Expense for Intangible Assets	'
	The estimated aggregate future amortization expense for intangible assets remaining as of September 30, 2013 was as follows (dollars in thousands):
	Remaining 2013	$	1,483
	2014		4,841
	2015		4,201
	2016		3,761
	2017		2,076
	Thereafter		8,871
	Total	$	25,233

CONTRACTUAL_OBLIGATIONS_AND_OF1

CONTRACTUAL OBLIGATIONS AND OFF-BALANCE SHEET ITEMS (Tables)	9 Months Ended
	Sep. 30, 2013
Organization Consolidation And Presentation Of Financial Statements [Abstract]	'
Contractual Obligations and Other Commitments	'
	Payments related to leases are based on actual payments specified in underlying contracts.
		1 year or less		More than 1		3 years or		5 years		Total
				year but less		more but less		or more
				than 3 years		than 5 years
		(Dollars in thousands)
	Junior subordinated debentures	$	578	$	4,624	$	4,623	$	121,438	$	131,263
	Federal Home Loan Bank notes payable and other borrowings		595,407		3,836		2,312		6,899		608,454
	Operating leases		1,247		7,785		3,264		380		12,676
	Total	$	597,232	$	16,245	$	10,199	$	128,717	$	752,393
Letters of Credit and Commitments	'
	The Company’s commitments associated with outstanding standby letters of credit and commitments to extend credit as of September 30, 2013 are summarized below. Since commitments associated with letters of credit and commitments to extend credit may expire unused, the amounts shown do not necessarily reflect the actual future cash funding requirements.
		1 year or less		More than 1		3 years or		5 years		Total
				year but less		more but less		or more
				than 3 years		than 5 years
		(Dollars in thousands)
	Standby letters of credit	$	37,537	$	5,291	$	30	$	—	$	42,858
	Commitments to extend credit		159,906		609,923		49,941		323,938		1,143,708
	Total	$	197,443	$	615,214	$	49,971	$	323,938	$	1,186,566

OTHER_COMPREHENSIVE_LOSS_INCOM1

OTHER COMPREHENSIVE (LOSS) INCOME (Tables)	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]	'
Schedule of Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss)	'
	The tax effects allocated to each component of other comprehensive (loss) income were as follows:
		Three Months Ended September 30,
		2013									2012
		Before Tax			Tax Benefit			Net of Tax			Before Tax			Tax Benefit		Net of Tax
		Amount						Amount			Amount					Amount
		(Dollars in thousands)
	Other comprehensive loss:
	Securities available for sale:
	Change in unrealized gain during period	$	(1,136	)	$	398		$	(738	)	$	(718	)	$	251	$	(467	)
	Total securities available for sale		(1,136	)		398			(738	)		(718	)		251		(467	)
	Total other comprehensive loss	$	(1,136	)	$	398		$	(738	)	$	(718	)	$	251	$	(467	)
		Nine Months Ended September 30,
		2013									2012
		Before Tax			Tax Benefit			Net of Tax			Before Tax			Tax Benefit		Net of Tax
		Amount						Amount			Amount					Amount
		(Dollars in thousands)
	Other comprehensive loss:
	Securities available for sale:
	Change in unrealized gain during period	$	(5,237	)	$	1,833		$	(3,404	)	$	(3,736	)	$	1,308	$	(2,428	)
	Total securities available for sale		(5,237	)		1,833			(3,404	)		(3,736	)		1,308		(2,428	)
	Total other comprehensive loss	$	(5,237	)	$	1,833		$	(3,404	)	$	(3,736	)	$	1,308	$	(2,428	)
Activity of Accumulated Other Comprehensive Income	'
	Activity in accumulated other comprehensive income, net of tax, was as follows:
		Securities			Accumulated
		Available for			Other
		Sale			Comprehensive
					Income
		(Dollars in thousands)
	Balance at January 1, 2013	$	8,986		$	8,986
	Other comprehensive loss		(3,404	)		(3,404	)
	Balance at September 30, 2013	$	5,582		$	5,582
	Balance at January 1, 2012	$	13,472		$	13,472
	Other comprehensive loss		(2,428	)		(2,428	)
	Balance at September 30, 2012	$	11,044		$	11,044

ACQUISITIONS_Tables

ACQUISITIONS (Tables)	9 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Information Regarding Results of Operations on Acquisition	'
	The following pro forma information presents the results of operations for the three and nine months ended September 30, 2013 and 2012, as if the Coppermark, East Texas Financial Services, Community National Bank, ASB and The Bank Arlington acquisitions had occurred on January 1, 2012.
			Three months ended September 30,				Nine months ended September 30,
			2013		2012 (1)		2013		2012 (1)
			(Dollars in thousands, except per				(Dollars in thousands, except per
			share data)				share data)
	Net interest income		$	126,533	$	127,501	$	375,699	$	403,983
	Net income			55,278		53,266		165,090		184,368
	Basic earnings per share			0.92		0.89		2.64		2.92
	Diluted earnings per share			0.91		0.88		2.64		2.92
	-1	Includes gain on sale of securities of $23.4 million by ASB during the second quarter of 2012.

Income_Per_Common_Share_Comput

Income Per Common Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'
Net income	$55,278	$46,176	$158,427	$119,635
Weighted average shares outstanding (basic)	60,344	55,958	59,207	50,239
Effect of dilutive securities-options	160	135	155	154
Total	60,504	56,093	59,362	50,393
Basic earnings per common share	$0.92	$0.83	$2.68	$2.38
Diluted earnings per common share	$0.91	$0.82	$2.67	$2.37

Income_Per_Common_Share_Additi

Income Per Common Share - Additional Information (Detail)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'
Stock options exercisable that would have had an anti-dilutive effect	0	0	0	0

Securities_Schedule_of_Investm

Securities - Schedule of Investment Securities (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Investment Securities [Line Items]	'	'
Amortized Cost	$156,189	$212,846
Gross Unrealized Gains	8,612	13,863
Gross Unrealized Losses	-25	-39
Fair Value	164,776	226,670
States and Political Subdivisions [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	29,130	34,743
Gross Unrealized Gains	1,002	1,691
Fair Value	30,132	36,434
Collateralized Mortgage Obligations [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	512	616
Gross Unrealized Gains	3	'
Gross Unrealized Losses	-1	-12
Fair Value	514	604
Mortgage-backed Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	119,259	168,701
Gross Unrealized Gains	7,602	11,742
Gross Unrealized Losses	-24	-27
Fair Value	126,837	180,416
Other Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	7,288	8,786
Gross Unrealized Gains	5	430
Fair Value	7,293	9,216
Held to Maturity Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	7,606,569	7,215,395
Gross Unrealized Gains	103,182	208,221
Gross Unrealized Losses	-153,580	-4,921
Fair Value	7,556,171	7,418,695
Held to Maturity Securities [Member] | States and Political Subdivisions [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	333,380	391,510
Gross Unrealized Gains	1,640	7,074
Gross Unrealized Losses	-2,175	-354
Fair Value	332,845	398,230
Held to Maturity Securities [Member] | Collateralized Mortgage Obligations [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	59,724	125,912
Gross Unrealized Gains	1,327	2,304
Gross Unrealized Losses	-48	-50
Fair Value	61,003	128,166
Held to Maturity Securities [Member] | Mortgage-backed Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	7,186,737	6,676,512
Gross Unrealized Gains	98,915	196,206
Gross Unrealized Losses	-151,079	-4,517
Fair Value	7,134,573	6,868,201
Held to Maturity Securities [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	3,252	7,061
Gross Unrealized Gains	23	160
Fair Value	3,275	7,221
Held to Maturity Securities [Member] | Corporate Debt Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	518	1,500
Gross Unrealized Gains	7	28
Fair Value	525	1,528
Held to Maturity Securities [Member] | Qualified School Construction Bonds (QSCB) [Member]	'	'
Investment Securities [Line Items]	'	'
Amortized Cost	22,958	12,900
Gross Unrealized Gains	1,270	2,449
Gross Unrealized Losses	-278	'
Fair Value	$23,950	$15,349

Securities_Schedule_of_Securit

Securities - Schedule of Securities with Unrealized Losses (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Investment Securities [Line Items]	'	'
Available for Sale, Estimated Fair Value, Less than 12 Months	$424	$224
Available for Sale, Unrealized Losses, Less than 12 Months	'	'
Available for Sale, Estimated Fair Value, More than 12 Months	3,592	4,567
Available for Sale, Unrealized Losses, More than 12 Months	-25	-39
Available for Sale, Estimated Fair Value, Total	4,016	4,791
Available for Sale, Unrealized Losses, Total	-25	-39
Collateralized Mortgage Obligations [Member]	'	'
Investment Securities [Line Items]	'	'
Available for Sale, Estimated Fair Value, Less than 12 Months	15	'
Available for Sale, Unrealized Losses, Less than 12 Months	'	'
Available for Sale, Estimated Fair Value, More than 12 Months	53	603
Available for Sale, Unrealized Losses, More than 12 Months	-1	-12
Available for Sale, Estimated Fair Value, Total	68	603
Available for Sale, Unrealized Losses, Total	-1	-12
Mortgage-backed Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Available for Sale, Estimated Fair Value, Less than 12 Months	409	224
Available for Sale, Unrealized Losses, Less than 12 Months	'	'
Available for Sale, Estimated Fair Value, More than 12 Months	3,539	3,964
Available for Sale, Unrealized Losses, More than 12 Months	-24	-27
Available for Sale, Estimated Fair Value, Total	3,948	4,188
Available for Sale, Unrealized Losses, Total	-24	-27
Other Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Available for Sale, Unrealized Losses, Less than 12 Months	'	'
Held to Maturity Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Held to Maturity, Estimated Fair Value, Less than 12 Months	3,672,683	1,121,102
Held to Maturity, Unrealized Losses, Less than 12 Months	-148,099	-4,901
Held to Maturity, Estimated Fair Value, More than 12 Months	112,729	1,374
Held to Maturity, Unrealized Losses, More than 12 Months	-5,481	-20
Held to Maturity, Estimated Fair Value, Total	3,785,412	1,122,476
Held to Maturity, Unrealized Losses, Total	-153,580	-4,921
Held to Maturity Securities [Member] | Collateralized Mortgage Obligations [Member]	'	'
Investment Securities [Line Items]	'	'
Held to Maturity, Estimated Fair Value, Less than 12 Months	1,391	2,366
Held to Maturity, Unrealized Losses, Less than 12 Months	-42	-50
Held to Maturity, Estimated Fair Value, More than 12 Months	437	'
Held to Maturity, Unrealized Losses, More than 12 Months	-6	'
Held to Maturity, Estimated Fair Value, Total	1,828	2,366
Held to Maturity, Unrealized Losses, Total	-48	-50
Held to Maturity Securities [Member] | Mortgage-backed Securities [Member]	'	'
Investment Securities [Line Items]	'	'
Held to Maturity, Estimated Fair Value, Less than 12 Months	3,507,024	1,081,414
Held to Maturity, Unrealized Losses, Less than 12 Months	-145,835	-4,516
Held to Maturity, Estimated Fair Value, More than 12 Months	102,028	234
Held to Maturity, Unrealized Losses, More than 12 Months	-5,244	-1
Held to Maturity, Estimated Fair Value, Total	3,609,052	1,081,648
Held to Maturity, Unrealized Losses, Total	-151,079	-4,517
Held to Maturity Securities [Member] | States and Political Subdivisions [Member]	'	'
Investment Securities [Line Items]	'	'
Held to Maturity, Estimated Fair Value, Less than 12 Months	164,268	37,322
Held to Maturity, Unrealized Losses, Less than 12 Months	-2,222	-335
Held to Maturity, Estimated Fair Value, More than 12 Months	10,264	1,140
Held to Maturity, Unrealized Losses, More than 12 Months	-231	-19
Held to Maturity, Estimated Fair Value, Total	174,532	38,462
Held to Maturity, Unrealized Losses, Total	($2,453)	($354)

Securities_Additional_Informat

Securities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012
	Investment		Investment
Investment Securities [Line Items]	'	'	'	'
Securities in unrealized loss position	'	'	18.60%	'
Loss on sale of securities	$0	$0	$0	'
Number of non-agency collateralized mortgage obligations	8	'	8	'
Book value of remaining non agency CMO's	1,800,000	'	1,800,000	'
Fair value of remaining non-agency CMO's	1,800,000	'	1,800,000	'
Aggregate adjusted cost exceeded consolidated shareholders' equity	'	'	10.00%	10.00%
Amortized Cost	156,189,000	'	156,189,000	212,846,000
Available for sale securities	164,776,000	'	164,776,000	226,670,000
Collateralized Securities [Member]	'	'	'	'
Investment Securities [Line Items]	'	'	'	'
Amortized Cost	4,220,000,000	'	4,220,000,000	4,130,000,000
Available for sale securities	$4,200,000,000	'	$4,200,000,000	$4,270,000,000

Securities_Amortized_Cost_and_

Securities - Amortized Cost and Fair Value of Investment Securities by Contractual Maturity (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Amortized Cost And Fair Value Debt Securities [Abstract]	'	'
Due in one year or less, Held to Maturity, Amortized Cost	$26,450	'
Due after one year through five years, Held to Maturity, Amortized Cost	120,137	'
Due after five years through ten years, Held to Maturity, Amortized Cost	138,529	'
Due after ten years, Held to Maturity, Amortized Cost	74,992	'
Subtotal, Held to Maturity, Amortized Cost	360,108	'
Mortgage-backed securities and collateralized mortgage obligations, Held to Maturity, Amortized Cost	7,246,461	'
Total, Held to Maturity, Amortized Cost	7,606,569	7,215,395
Due in one year or less, Held to Maturity, Fair Value	26,523	'
Due after one year through five years, Held to Maturity, Fair Value	120,135	'
Due after five years through ten years, Held to Maturity, Fair Value	138,049	'
Due after ten years, Held to Maturity, Fair Value	75,888	'
Subtotal, Held to Maturity, Fair Value	360,595	'
Mortgage-backed securities and collateralized mortgage obligations, Held to Maturity, Fair Value	7,195,576	'
Total, Held to Maturity, Fair Value	7,556,171	7,418,695
Due in one year or less, Available for Sale, Amortized Cost	7,383	'
Due after one year through five years, Available for Sale, Amortized Cost	4,990	'
Due after five years through ten years, Available for Sale, Amortized Cost	20,997	'
Due after ten years, Available for Sale, Amortized Cost	3,048	'
Subtotal, Available for Sale, Amortized Cost	36,418	'
Mortgage-backed securities and collateralized mortgage obligations, Available for Sale, Amortized Cost	119,771	'
Total, Available for Sale, Amortized Cost	156,189	'
Due in one year or less, Available for Sale, Fair Value	7,392	'
Due after one year through five years, Available for Sale, Fair Value	5,175	'
Due after five years through ten years, Available for Sale, Fair Value	21,721	'
Due after ten years, Available for Sale, Fair Value	3,137	'
Subtotal, Available for Sale, Fair Value	37,425	'
Mortgage-backed securities and collateralized mortgage obligations, Available for Sale, Fair Value	127,351	'
Fair Value	$164,776	$226,670

Recovered_Sheet1

Loans and Allowance for Credit Losses - Schedule of Types of Loans in Loan Portfolio (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Commercial and industrial	$1,028,799	$771,114	'
Consumer and other (net of unearned discount)	108,704	139,213	'
Total loans held for investment	6,177,697	5,169,507	'
Total	6,182,589	5,179,940	5,079,103
Residential Mortgage [Member]	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Residential mortgage loans held for sale	4,892	10,433	'
Construction and Land Development [Member]	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Real estate	703,193	550,768	'
Total	703,193	550,768	496,417
1-4 Family (Includes Home Equity) [Member]	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Real estate	1,710,621	1,432,133	'
Total	1,715,513	1,442,566	1,397,717
Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Real estate	2,304,862	1,990,642	'
Total	2,304,862	1,990,642	1,976,112
Farmland [Member]	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'
Real estate	235,049	211,156	'
Agriculture	$86,469	$74,481	'

Recovered_Sheet2

Loans and Allowance for Credit Losses - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
	Y
	D
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Fixed rate, in years	5	'	'	'
Percentage of loans related to single industry on total loans, maximum	10.00%	'	10.00%	'
Loans outstanding to directors, officers and affiliates	$6,312,000	'	$6,682,000	$9,809,000
Minimum period for ceases accruing interest, in days	90	'	'	'
Total nonperforming assets	12,687,000	'	13,015,000	'
Interest on nonaccrual loans	341,000	252,000	'	'
Allowance for loan losses	0	'	0	'
Interest income recognized on impaired loans	0	'	'	'
Maximum principal and interest collectible on substandard impaired loans, percentage	100.00%	'	'	'
Allowance for credit losses totaled	59,900,000	'	52,600,000	'
Allowance for credit losses as a percentage of total loans	0.97%	'	1.01%	'
Determined period of default, minimum number of days past due	90	'	'	'
Loan Restructured	$249,000	'	'	'
Commercial Mortgages [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Percentage of outstanding principal balance, commercial real estate loans	38.00%	'	'	'
1-4 Family Residential Loans [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Originated loan maximum percentage of appraised value	89.00%	'	'	'
Minimum [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	12	'	'	'
Minimum [Member] | Commercial Mortgages [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	15	'	'	'
Minimum [Member] | 1-4 Family Residential Loans [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	5	'	'	'
Maximum [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	120	'	'	'
Maximum [Member] | Commercial Mortgages [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	20	'	'	'
Maximum [Member] | 1-4 Family Residential Loans [Member]	'	'	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'	'	'
Term of consumer loans	25	'	'	'

Loans_and_Allowance_for_Credit2

Loans and Allowance for Credit Losses - Schedule of Activity with Respect to Related-Party Loans (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Receivables [Abstract]	'	'
Beginning balance	$6,682	$9,809
New loans and reclassified related loans	306	967
Repayments	-676	-4,094
Ending balance	$6,312	$6,682

Loans_and_Allowance_for_Credit3

Loans and Allowance for Credit Losses - Schedule of Past Due Loans with Age Analysis, Segregated by Class of Loans (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	$26,363	$21,342	'
90 or More Days	283	331	'
Total Past Due Loans	26,646	21,673	'
Nonaccrual Loans	4,954	5,382	'
Current Loans	6,150,989	5,152,885	'
Total Loans	6,182,589	5,179,940	5,079,103
Construction and Land Development [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	3,465	3,863	'
Total Past Due Loans	3,465	3,863	'
Nonaccrual Loans	469	1,170	'
Current Loans	699,259	545,735	'
Total Loans	703,193	550,768	496,417
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	557	310	'
90 or More Days	'	21	'
Total Past Due Loans	557	331	'
Nonaccrual Loans	23	396	'
Current Loans	320,938	284,910	'
Total Loans	321,518	285,637	'
1-4 Family (Includes Home Equity) [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	5,655	2,307	'
90 or More Days	90	310	'
Total Past Due Loans	5,745	2,617	'
Nonaccrual Loans	1,037	1,598	'
Current Loans	1,708,731	1,438,351	'
Total Loans	1,715,513	1,442,566	1,397,717
Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	7,065	9,163	'
90 or More Days	34	'	'
Total Past Due Loans	7,099	9,163	'
Nonaccrual Loans	2,223	'	'
Current Loans	2,295,540	1,981,479	'
Total Loans	2,304,862	1,990,642	1,976,112
Commercial and Industrial [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	9,230	4,843	'
90 or More Days	148	'	'
Total Past Due Loans	9,378	4,843	'
Nonaccrual Loans	1,069	1,469	'
Current Loans	1,018,352	764,802	'
Total Loans	1,028,799	771,114	756,342
Consumer and Other [Member]	'	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'	'
30-89 Days	391	856	'
90 or More Days	11	'	'
Total Past Due Loans	402	856	'
Nonaccrual Loans	133	749	'
Current Loans	108,169	137,608	'
Total Loans	$108,704	$139,213	$148,381

Loans_and_Allowance_for_Credit4

Loans and Allowance for Credit Losses - Schedule of Past Due Loans with Age Analysis, Segregated by Class of Loans (Parenthetical) (Detail) (Residential Mortgage [Member], USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Residential Mortgage [Member]	'	'
Financing Receivable, Recorded Investment, Past Due [Line Items]	'	'
Residential mortgage loans held for sale	$4,892	$10,433

Loans_and_Allowance_for_Credit5

Loans and Allowance for Credit Losses - Schedule of Nonperforming Assets (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Receivables [Abstract]	'	'
Nonaccrual Loans	$4,954	$5,382
Accruing loans 90 or more days past due	283	331
Total nonperforming loans	5,237	5,713
Repossessed assets	18	68
Other real estate	7,432	7,234
Total nonperforming assets	$12,687	$13,015
Nonperforming assets to total loans and other real estate	0.20%	0.25%

Loans_and_Allowance_for_Credit6

Loans and Allowance for Credit Losses - Summary of Carrying Value and Outstanding Balance for Purchased Credit Impaired Loans (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Acquired PCI loans:	'	'
Carrying amount	$36,204	$22,880
Outstanding balance	$77,303	$46,914

Loans_and_Allowance_for_Credit7

Loans and Allowance for Credit Losses - Summary of Changes in Accretable Yield for Acquired PCI Loans (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Combinations [Abstract]	'	'	'	'
Balance at beginning of period	$13,011	'	$7,459	'
Additions	349	8,157	7,877	8,157
Reclassifications from nonaccretable	3,088	'	4,343	'
Accretion	-5,840	-1,160	-9,071	-1,160
Balance at ending of period	$10,608	$6,997	$10,608	$6,997

Loans_and_Allowances_for_Credi

Loans and Allowances for Credit Losses - Schedule of Impaired Loans (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	$2,997	$6,851
Unpaid Principal Balance	2,908	7,018
Related Allowance	900	1,981
Average Recorded Investment	4,928	6,281
Construction and Land Development [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	257	1,144
Unpaid Principal Balance	265	1,175
Average Recorded Investment	701	819
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	23	111
Unpaid Principal Balance	30	118
Related Allowance	20	29
Average Recorded Investment	68	79
1-4 Family (Includes Home Equity) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	381	1,490
Unpaid Principal Balance	375	1,539
Related Allowance	53	273
Average Recorded Investment	936	1,101
Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	1,230	2,900
Unpaid Principal Balance	1,255	2,927
Related Allowance	17	610
Average Recorded Investment	2,066	3,401
Commercial and Industrial [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	1,026	1,130
Unpaid Principal Balance	896	1,168
Related Allowance	741	1,002
Average Recorded Investment	1,079	857
Consumer and Other [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	80	76
Unpaid Principal Balance	87	91
Related Allowance	69	67
Average Recorded Investment	78	24
With No Related Allowance Recorded [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	1,974	2,259
Unpaid Principal Balance	1,835	2,349
Average Recorded Investment	2,119	1,537
With No Related Allowance Recorded [Member] | Construction and Land Development [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	257	1,144
Unpaid Principal Balance	265	1,175
Average Recorded Investment	701	368
With No Related Allowance Recorded [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	'	77
Unpaid Principal Balance	'	77
Average Recorded Investment	39	34
With No Related Allowance Recorded [Member] | 1-4 Family (Includes Home Equity) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	310	491
Unpaid Principal Balance	279	522
Average Recorded Investment	401	381
With No Related Allowance Recorded [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	1,213	450
Unpaid Principal Balance	1,237	476
Average Recorded Investment	832	676
With No Related Allowance Recorded [Member] | Commercial and Industrial [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	194	87
Unpaid Principal Balance	54	89
Average Recorded Investment	141	75
With No Related Allowance Recorded [Member] | Consumer and Other [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	'	10
Unpaid Principal Balance	'	10
Average Recorded Investment	5	3
With an Allowance Recorded [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	1,023	4,592
Unpaid Principal Balance	1,073	4,669
Related Allowance	900	1,981
Average Recorded Investment	2,809	4,744
With an Allowance Recorded [Member] | Construction and Land Development [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Average Recorded Investment	'	451
With an Allowance Recorded [Member] | Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	23	34
Unpaid Principal Balance	30	41
Related Allowance	20	29
Average Recorded Investment	29	45
With an Allowance Recorded [Member] | 1-4 Family (Includes Home Equity) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	71	999
Unpaid Principal Balance	96	1,017
Related Allowance	53	273
Average Recorded Investment	535	720
With an Allowance Recorded [Member] | Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	17	2,450
Unpaid Principal Balance	18	2,451
Related Allowance	17	610
Average Recorded Investment	1,234	2,725
With an Allowance Recorded [Member] | Commercial and Industrial [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	832	1,043
Unpaid Principal Balance	842	1,079
Related Allowance	741	1,002
Average Recorded Investment	938	782
With an Allowance Recorded [Member] | Consumer and Other [Member]	'	'
Financing Receivable, Impaired [Line Items]	'	'
Recorded Investment	80	66
Unpaid Principal Balance	87	81
Related Allowance	69	67
Average Recorded Investment	$73	$21

Loans_and_Allowance_for_Credit8

Loans and Allowance for Credit Losses - Schedule Showing Risk Grades and Classified Loans by Class of Loan (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	$6,182,589	$5,179,940	$5,079,103
Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	84,937	97,940	'
Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	5,998,414	4,993,837	'
Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	29,250	34,907	'
Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	30,787	23,525	'
Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	2,986	6,838	'
Grade 6 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	11	13	'
PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	36,204	22,880	'
Construction and Land Development [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	703,193	550,768	496,417
Construction and Land Development [Member] | Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	'	476	'
Construction and Land Development [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	694,446	537,340	'
Construction and Land Development [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	3,850	7,250	'
Construction and Land Development [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,551	4,256	'
Construction and Land Development [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	257	1,144	'
Construction and Land Development [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	3,089	302	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	321,518	285,637	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	4,771	4,195	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	313,890	277,333	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,044	2,024	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,369	1,694	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	23	111	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	421	280	'
1-4 Family (Includes Home Equity) [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,715,513	1,442,566	1,397,717
1-4 Family (Includes Home Equity) [Member] | Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	'	515	'
1-4 Family (Includes Home Equity) [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,701,525	1,431,095	'
1-4 Family (Includes Home Equity) [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	4,287	4,947	'
1-4 Family (Includes Home Equity) [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	6,165	4,303	'
1-4 Family (Includes Home Equity) [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	370	1,477	'
1-4 Family (Includes Home Equity) [Member] | Grade 6 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	11	13	'
1-4 Family (Includes Home Equity) [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	3,155	216	'
Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	2,304,862	1,990,642	1,976,112
Commercial Real Estate (Includes Multi-Family Residential) [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	2,248,498	1,945,319	'
Commercial Real Estate (Includes Multi-Family Residential) [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	12,483	11,760	'
Commercial Real Estate (Includes Multi-Family Residential) [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	15,736	11,711	'
Commercial Real Estate (Includes Multi-Family Residential) [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,230	2,900	'
Commercial Real Estate (Includes Multi-Family Residential) [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	26,915	18,952	'
Commercial and Industrial [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,028,799	771,114	756,342
Commercial and Industrial [Member] | Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	48,879	53,965	'
Commercial and Industrial [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	962,941	702,587	'
Commercial and Industrial [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	7,453	8,926	'
Commercial and Industrial [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	5,876	1,385	'
Commercial and Industrial [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	1,026	1,130	'
Commercial and Industrial [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	2,624	3,121	'
Consumer and Other [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	108,704	139,213	148,381
Consumer and Other [Member] | Grade 1 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	31,287	38,789	'
Consumer and Other [Member] | Grade 2 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	77,114	100,163	'
Consumer and Other [Member] | Grade 3 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	133	'	'
Consumer and Other [Member] | Grade 4 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	90	176	'
Consumer and Other [Member] | Grade 5 [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	80	76	'
Consumer and Other [Member] | PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Loans held for investment	'	$9	'

Loans_and_Allowance_for_Credit9

Loans and Allowance for Credit Losses - Schedule Showing Risk Grades and Classified Loans by Class of Loan (Parenthetical) (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Mortgage loans held for sale	$4,900	$10,400	'
Substandard loan	6,182,589	5,179,940	5,079,103
PCI Loans [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Substandard loan	36,204	22,880	'
PCI Loans [Member] | Substandard [Member]	'	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'	'
Substandard loan	$24,900	'	'

Recovered_Sheet3

Loans and Allowance for Credit Losses - Schedule of Recorded Investment in Loans and Activity in Allowance for Credit Losses by Portfolio Segment (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	$56,176	$50,382	$52,564	$51,594	'
Provision for credit losses	4,025	1,800	9,375	2,550	'
Charge-offs	-1,142	-3,113	-4,074	-5,601	'
Recoveries	854	1,858	2,048	2,384	'
Net charge-offs	-288	-1,255	-2,026	-3,217	'
Allowance for credit losses, Ending Balance	59,913	50,927	59,913	50,927	'
Individually evaluated for impairment	900	2,190	900	2,190	'
Collectively evaluated for impairment	59,013	48,737	59,013	48,737	'
PCI loans	-36,204	-27,581	-36,204	-27,581	'
Total allowance for credit losses	59,913	50,927	59,913	50,927	'
PCI loans	36,204	27,581	36,204	27,581	'
Total loans evaluated for impairment	6,182,589	5,079,103	6,182,589	5,079,103	5,179,940
Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	2,997	6,262	2,997	6,262	'
Collectively evaluated for impairment	6,143,388	5,045,260	6,143,388	5,045,260	'
Construction and Land Development [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	11,991	10,065	11,909	12,094	'
Provision for credit losses	1,024	359	1,173	-469	'
Charge-offs	-14	-159	-270	-1,368	'
Recoveries	44	4	233	12	'
Net charge-offs	30	-155	-37	-1,356	'
Allowance for credit losses, Ending Balance	13,045	10,269	13,045	10,269	'
Individually evaluated for impairment	'	26	'	26	'
Collectively evaluated for impairment	13,045	10,243	13,045	10,243	'
PCI loans	-3,089	-1,326	-3,089	-1,326	'
Total allowance for credit losses	13,045	10,269	13,045	10,269	'
PCI loans	3,089	1,326	3,089	1,326	'
Total loans evaluated for impairment	703,193	496,417	703,193	496,417	550,768
Construction and Land Development [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	257	86	257	86	'
Collectively evaluated for impairment	699,847	495,005	699,847	495,005	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	982	742	764	511	'
Provision for credit losses	129	-2	352	226	'
Charge-offs	-23	'	-36	'	'
Recoveries	10	30	18	33	'
Net charge-offs	-13	30	-18	33	'
Allowance for credit losses, Ending Balance	1,098	770	1,098	770	'
Individually evaluated for impairment	20	61	20	61	'
Collectively evaluated for impairment	1,078	709	1,078	709	'
PCI loans	-421	-78	-421	-78	'
Total allowance for credit losses	1,098	770	1,098	770	'
PCI loans	421	78	421	78	'
Total loans evaluated for impairment	321,518	304,134	321,518	304,134	'
Agriculture and Agriculture Real Estate (Includes Farmland) [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	23	143	23	143	'
Collectively evaluated for impairment	321,074	303,913	321,074	303,913	'
1-4 Family (Includes Home Equity) [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	13,435	13,326	13,942	12,645	'
Provision for credit losses	1,262	299	892	1,121	'
Charge-offs	-20	-327	-182	-478	'
Recoveries	5	76	30	86	'
Net charge-offs	-15	-251	-152	-392	'
Allowance for credit losses, Ending Balance	14,682	13,374	14,682	13,374	'
Individually evaluated for impairment	53	336	53	336	'
Collectively evaluated for impairment	14,629	13,038	14,629	13,038	'
PCI loans	-3,155	-155	-3,155	-155	'
Total allowance for credit losses	14,682	13,374	14,682	13,374	'
PCI loans	3,155	155	3,155	155	'
Total loans evaluated for impairment	1,715,513	1,397,717	1,715,513	1,397,717	1,442,566
1-4 Family (Includes Home Equity) [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	381	1,448	381	1,448	'
Collectively evaluated for impairment	1,711,977	1,396,114	1,711,977	1,396,114	'
Commercial Real Estate (Includes Multi-Family Residential) [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	22,831	21,406	19,607	21,460	'
Provision for credit losses	-658	-509	3,309	-250	'
Charge-offs	'	-909	-894	-1,278	'
Recoveries	471	109	622	165	'
Net charge-offs	471	-800	-272	-1,113	'
Allowance for credit losses, Ending Balance	22,644	20,097	22,644	20,097	'
Individually evaluated for impairment	17	567	17	567	'
Collectively evaluated for impairment	22,627	19,530	22,627	19,530	'
PCI loans	-26,915	-22,454	-26,915	-22,454	'
Total allowance for credit losses	22,644	20,097	22,644	20,097	'
PCI loans	26,915	22,454	26,915	22,454	'
Total loans evaluated for impairment	2,304,862	1,976,112	2,304,862	1,976,112	1,990,642
Commercial Real Estate (Includes Multi-Family Residential) [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	1,230	3,170	1,230	3,170	'
Collectively evaluated for impairment	2,276,717	1,950,488	2,276,717	1,950,488	'
Commercial and Industrial [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	6,293	4,238	5,777	3,826	'
Provision for credit losses	1,356	660	2,070	1,237	'
Charge-offs	-188	-55	-592	-376	'
Recoveries	69	565	275	721	'
Net charge-offs	-119	510	-317	345	'
Allowance for credit losses, Ending Balance	7,530	5,408	7,530	5,408	'
Individually evaluated for impairment	741	1,180	741	1,180	'
Collectively evaluated for impairment	6,789	4,228	6,789	4,228	'
PCI loans	-2,624	-3,568	-2,624	-3,568	'
Total allowance for credit losses	7,530	5,408	7,530	5,408	'
PCI loans	2,624	3,568	2,624	3,568	'
Total loans evaluated for impairment	1,028,799	756,342	1,028,799	756,342	771,114
Commercial and Industrial [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	1,026	1,395	1,026	1,395	'
Collectively evaluated for impairment	1,025,149	751,379	1,025,149	751,379	'
Consumer and Other [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Allowance for credit losses, Beginning Balance	644	605	565	1,058	'
Provision for credit losses	912	993	1,579	685	'
Charge-offs	-897	-1,663	-2,100	-2,101	'
Recoveries	255	1,074	870	1,367	'
Net charge-offs	-642	-589	-1,230	-734	'
Allowance for credit losses, Ending Balance	914	1,009	914	1,009	'
Individually evaluated for impairment	69	20	69	20	'
Collectively evaluated for impairment	845	989	845	989	'
PCI loans	'	'	'	'	'
Total allowance for credit losses	914	1,009	914	1,009	'
PCI loans	'	'	'	'	'
Total loans evaluated for impairment	108,704	148,381	108,704	148,381	139,213
Consumer and Other [Member] | Loans [Member]	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'
Individually evaluated for impairment	80	20	80	20	'
Collectively evaluated for impairment	$108,624	$148,361	$108,624	$148,361	'

Fair_Value_Schedule_of_Fair_Va

Fair Value - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	$164,776	$226,670
States and Political Subdivisions [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	30,132	36,434
Collateralized Mortgage Obligations [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	514	604
Mortgage - Backed Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	126,837	180,416
Other Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	7,293	9,216
Level 1 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	7,293	7,688
Level 1 [Member] | States and Political Subdivisions [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 1 [Member] | Collateralized Mortgage Obligations [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 1 [Member] | Mortgage - Backed Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 1 [Member] | Other Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	7,293	7,688
Level 2 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	157,483	218,982
Level 2 [Member] | States and Political Subdivisions [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	30,132	36,434
Level 2 [Member] | Collateralized Mortgage Obligations [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	514	604
Level 2 [Member] | Mortgage - Backed Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	126,837	180,416
Level 2 [Member] | Other Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	1,528
Level 3 [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 3 [Member] | States and Political Subdivisions [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 3 [Member] | Collateralized Mortgage Obligations [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 3 [Member] | Mortgage - Backed Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'
Level 3 [Member] | Other Securities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available for sale securities	'	'

Fair_Value_Additional_Informat

Fair Value - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'	'
Additions to impaired loans	'	$5,500,000
Impaired loans, outstanding	'	1,400,000
Additions to other real estate	305,000	2,700,000
Real estate owned outstanding	305,000	1,100,000
Off balance sheet commitments	$1,190,000,000	$1,190,000,000

Fair_Value_Summary_of_Financia

Fair Value - Summary of Financial Assets and Liabilities Measured on Recurring and Non-Recurring Basis (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 30, 2012	Sep. 30, 2013	Dec. 30, 2012	Sep. 30, 2013	Dec. 30, 2012	Sep. 30, 2013	Dec. 30, 2012	Sep. 30, 2013	Dec. 30, 2012
In Thousands, unless otherwise specified			Carrying Amount [Member]	Carrying Amount [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]	Estimated Fair Value [Member]
							Level 1 [Member]	Level 1 [Member]	Level 2 [Member]	Level 2 [Member]	Level 3 [Member]	Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]	'	'	'	'	'	'	'	'	'	'	'	'
Cash and due from banks	$269,987	$325,952	$269,987	$325,952	$269,987	$325,952	$269,987	$325,952	'	'	'	'
Federal funds sold	1,121	352	1,121	352	1,121	352	1,121	352	'	'	'	'
Held to maturity securities	7,556,171	7,418,695	7,606,569	7,215,395	7,556,171	7,418,695	'	'	7,556,171	7,418,695	'	'
Loans held for sale	'	'	4,892	10,433	4,892	10,433	4,892	10,433	'	'	'	'
Loans held for investment, net of allowance	'	'	6,117,784	5,116,943	6,143,355	5,186,779	'	'	'	'	6,143,355	5,186,779
Federal Home Loan Bank of Dallas stock	43,058	34,461	43,058	34,461	43,058	34,461	43,058	34,461	'	'	'	'
Noninterest-bearing	3,368,357	3,016,205	3,368,357	3,016,205	3,368,687	3,016,205	'	'	3,368,687	3,016,205	'	'
Interest-bearing	9,087,442	8,625,639	9,087,442	8,625,639	8,286,130	8,640,625	'	'	8,286,130	8,640,625	'	'
Other borrowings	605,951	256,753	605,951	256,753	607,471	258,819	'	'	607,471	258,819	'	'
Securities sold under repurchase agreements	431,969	454,502	431,969	454,502	431,692	454,596	'	'	431,692	454,596	'	'
Junior subordinated debentures	$85,055	$85,055	$85,055	$85,055	$81,696	$72,705	'	'	$81,696	$72,705	'	'

Recovered_Sheet4

Goodwill and Core Deposit Intangibles - Schedule of Goodwill and Core Deposit Intangibles (Detail) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

In Thousands, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Jun. 30, 2012

Jul. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Sep. 30, 2012

Sep. 30, 2013

Mar. 31, 2013

Sep. 30, 2013

Texas Bankers, Inc [Member]

The Bank Arlington [Member]

The Bank Arlington [Member]

The Bank Arlington [Member]

American State Financial Corporation [Member]

American State Financial Corporation [Member]

American State Financial Corporation [Member]

Community National Bank [Member]

Community National Bank [Member]

Community National Bank [Member]

East Texas Financial Services, Inc [Member]

Coppermark Bancshares, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Goodwill And Intangible Assets [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill, Beginning Balance

'

'

$1,217,162

$924,537

$924,537

'

'

'

$2,000

'

'

'

'

'

$10,600

$7,000

'

'

Goodwill, Amortization

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Goodwill, Measurement period adjustment

'

'

'

'

'

'

-130

'

'

'

-3,094

'

1,999

'

'

'

'

'

Goodwill, Acquisition

'

'

'

'

'

6,077

'

2,102

'

'

'

274,119

'

10,327

'

16,658

'

119,187

Goodwill, Ending Balance

1,351,782

'

1,351,782

'

1,217,162

'

'

'

2,000

271,000

'

'

'

'

10,600

'

91,700

'

Core Deposit Intangibles, Beginning Balance

'

'

26,159

20,996

20,996

'

'

'

'

'

'

'

'

'

'

'

'

'

Core Deposit Intangibles, Measurement period adjustment

'

'

'

'

'

'

'

'

'

'

2,110

'

'

'

'

'

'

'

Core Deposit Intangibles, Amortization

-1,455

-2,007

-4,551

-5,297

-7,229

'

'

'

'

'

'

'

'

'

'

'

'

'

Core Deposit Intangibles, Acquisition

'

'

'

'

'

'

'

'

'

14,500

'

12,392

'

'

'

'

1,500

1,515

Core Deposit Intangibles, Ending Balance

$25,233

'

$25,233

'

$26,159

'

'

'

'

'

'

'

'

'

'

'

'

'

Recovered_Sheet5

Goodwill and Core Deposit Intangibles - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Goodwill And Intangible Assets [Line Items]	'	'	'	'	'
Impairments recorded on goodwill	$0	'	$0	'	'
Amortization expense related to intangible assets	$1,455,000	$2,007,000	$4,551,000	$5,297,000	$7,229,000
Minimum [Member]	'	'	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'	'	'
Intangible assets, estimated life in years	'	'	'8 years	'	'
Maximum [Member]	'	'	'	'	'
Goodwill And Intangible Assets [Line Items]	'	'	'	'	'
Intangible assets, estimated life in years	'	'	'15 years	'	'

Goodwill_and_Core_Deposit_Inta2

Goodwill and Core Deposit Intangibles - Schedule of Estimated Aggregate Future Amortization Expense for Intangible Assets (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Goodwill And Intangible Assets Disclosure [Abstract]	'	'	'
Remaining 2013	$1,483	'	'
2014	4,841	'	'
2015	4,201	'	'
2016	3,761	'	'
2017	2,076	'	'
Thereafter	8,871	'	'
Total	$25,233	$26,159	$20,996

Stock_Based_Compensation_Addit

Stock Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
	OptionPlan		OptionPlan
Compensation Related Costs Share Based Payments Disclosure [Line Items]	'	'	'	'
Number of stock-based employee compensation plans	4	'	4	'
Number of stock option plans	1	'	1	'
Number of stock-based employee compensation plans expired	2	'	2	'
Proceeds from stock options exercised	$1,200,000	$300,000	$3,039,000	$2,691,000
Tax benefit from option exercises	0	0	0	0
Unrecognized compensation expense	$7,000,000	'	$7,000,000	'
Expected weighted average period of unrecognized compensation expense recognized, in years	'	'	'2 years 6 months	'
2004 Stock Option Plan [Member] | Maximum [Member]	'	'	'	'
Compensation Related Costs Share Based Payments Disclosure [Line Items]	'	'	'	'
Number of shares authorizes the issuance	1,250,000	'	1,250,000	'
Share based compensation arrangement by share based payment award award vesting period in years	'	'	'5 years	'
2004 Stock Option Plan [Member] | Minimum [Member]	'	'	'	'
Compensation Related Costs Share Based Payments Disclosure [Line Items]	'	'	'	'
Share based compensation arrangement by share based payment award award vesting period in years	'	'	'1 year	'
2012 Stock Incentive Plan [Member]	'	'	'	'
Compensation Related Costs Share Based Payments Disclosure [Line Items]	'	'	'	'
Options or other awards granted	0	'	'	'
2012 Stock Incentive Plan [Member] | Maximum [Member]	'	'	'	'
Compensation Related Costs Share Based Payments Disclosure [Line Items]	'	'	'	'
Number of shares authorizes the issuance	1,250,000	'	1,250,000	'

Recovered_Sheet6

Contractual Obligations and Off-Balance Sheet Items - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Commitments And Guarantee Obligations [Line Items]	'	'	'	'	'
Interest portion junior subordinated debentures	$610,000	$651,000	$1,821,000	$1,962,000	'
Current principal balance of the junior subordinated debentures	85,055,000	'	85,055,000	'	85,055,000
Interest to be paid over future periods included in FHLB payments	'	'	2,500,000	'	'
Contractual Obligations [Member]	'	'	'	'	'
Commitments And Guarantee Obligations [Line Items]	'	'	'	'	'
Interest portion junior subordinated debentures	'	'	46,200,000	'	'
Current principal balance of the junior subordinated debentures	$85,055,000	'	$85,055,000	'	'

Recovered_Sheet7

Contractual Obligations and Off-Balance Sheet Items - Contractual Obligations and Other Commitments (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Commitments And Guarantee Obligations [Line Items]	'
1 year or less	$597,232
More than 1 year but less than 3 years	16,245
3 years or more but less than 5 years	10,199
5 years or more	128,717
Total	752,393
Junior Subordinated Debentures [Member]	'
Commitments And Guarantee Obligations [Line Items]	'
1 year or less	578
More than 1 year but less than 3 years	4,624
3 years or more but less than 5 years	4,623
5 years or more	121,438
Total	131,263
Federal Home Loan Bank Notes Payable and Other Borrowings [Member]	'
Commitments And Guarantee Obligations [Line Items]	'
1 year or less	595,407
More than 1 year but less than 3 years	3,836
3 years or more but less than 5 years	2,312
5 years or more	6,899
Total	608,454
Operating Leases [Member]	'
Commitments And Guarantee Obligations [Line Items]	'
1 year or less	1,247
More than 1 year but less than 3 years	7,785
3 years or more but less than 5 years	3,264
5 years or more	380
Total	$12,676

Contractual_Obligations_and_Of2

Contractual Obligations and Off-Balance Sheet Items - Letters of Credit and Commitments (Detail) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Contractual Obligation Fiscal Year Maturity [Line Items]	'
1 year or less	$597,232
More than 1 year but less than 3 years	16,245
3 years or more but less than 5 years	10,199
5 years or more	128,717
Total	752,393
Off Balance Sheet Activities [Member]	'
Contractual Obligation Fiscal Year Maturity [Line Items]	'
1 year or less	197,443
More than 1 year but less than 3 years	615,214
3 years or more but less than 5 years	49,971
5 years or more	323,938
Total	1,186,566
Off Balance Sheet Activities [Member] | Standby Letters of Credit [Member]	'
Contractual Obligation Fiscal Year Maturity [Line Items]	'
1 year or less	37,537
More than 1 year but less than 3 years	5,291
3 years or more but less than 5 years	30
5 years or more	'
Total	42,858
Off Balance Sheet Activities [Member] | Commitments to Extend Credit [Member]	'
Contractual Obligation Fiscal Year Maturity [Line Items]	'
1 year or less	159,906
More than 1 year but less than 3 years	609,923
3 years or more but less than 5 years	49,941
5 years or more	323,938
Total	$1,143,708

Recovered_Sheet8

Other Comprehensive (Loss) Income - Schedule of Tax Effects Allocated to Each Component of Other Comprehensive Income (Loss) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Comprehensive Income Loss Tax [Abstract]	'	'	'	'
Change in unrealized gain during period, Before Tax Amount	($1,136)	($718)	($5,237)	($3,736)
Total securities available for sale, Before Tax Amount	-1,136	-718	-5,237	-3,736
Total other comprehensive loss, Before Tax Amount	-1,136	-718	-5,237	-3,736
Change in unrealized gain during period, Tax Benefit	398	251	1,833	1,308
Total securities available for sale, Tax Benefit	398	251	1,833	1,308
Total other comprehensive loss, Tax Benefit	398	251	1,833	1,308
Change in unrealized gain during period, Net of Tax Amount	-738	-467	-3,404	-2,428
Total securities available for sale, Net of Tax Amount	-738	-467	-3,404	-2,428
Total other comprehensive loss, Net of Tax Amount	($738)	($467)	($3,404)	($2,428)

Recovered_Sheet9

Other Comprehensive (Loss) Income - Activity of Accumulated Other Comprehensive Income (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Comprehensive Income Loss Tax [Abstract]	'	'	'	'
Beginning Balance, Securities Available for Sale	'	'	$8,986	$13,472
Other comprehensive loss, Securities Available for Sale	-738	-467	-3,404	-2,428
Ending Balance, Securities Available for Sale	5,582	11,044	5,582	11,044
Beginning Balance, Accumulated Other Comprehensive Income	'	'	8,986	13,472
Other comprehensive loss, Accumulated Other Comprehensive Income	-738	-467	-3,404	-2,428
Ending Balance, Accumulated Other Comprehensive Income	$5,582	$11,044	$5,582	$11,044

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Detail) (USD $)

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Jun. 30, 2012

Dec. 31, 2012

Apr. 01, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Mar. 31, 2013

Jun. 30, 2013

Sep. 30, 2013

Jun. 30, 2013

Jun. 30, 2013

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2012

Oct. 01, 2012

Jul. 31, 2012

Dec. 31, 2012

Jul. 31, 2012

Texas Bankers, Inc [Member]

Texas Bankers, Inc [Member]

The Bank Arlington [Member]

The Bank Arlington [Member]

The Bank Arlington [Member]

F&M Bancorporation Inc. [Member]

F&M Bancorporation Inc. [Member]

F&M Bancorporation Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

Coppermark Bancshares, Inc. [Member]

East Texas Financial Services, Inc [Member]

East Texas Financial Services, Inc [Member]

East Texas Financial Services, Inc [Member]

Community National Bank [Member]

Community National Bank [Member]

Community National Bank [Member]

American State Financial Corporation [Member]

American State Financial Corporation [Member]

American State Financial Corporation [Member]

TEXAS [Member]

Branch_office

BankingCenters

Tulsa, Oklahoma [Member]

Dallas, Texas [Member]

Bank

Dallas, Texas [Member]

Oklahoma City, Oklahoma [Member]

TEXAS [Member]

TEXAS [Member]

Country

TEXAS [Member]

Branch_office

BankingCenters

BankingCenters

Bank

Bank

Branch_office

Branch_office

Branch_office

Loans At Acquisition Date [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of Banking Offices

'

'

'

'

'

'

'

'

13

10

3

'

9

'

3

6

'

'

'

'

'

'

'

'

37

Total assets

$16,054,279,000

$14,583,573,000

'

'

'

'

'

'

$2,470,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total loans

'

'

'

'

'

'

'

'

1,880,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total deposits

12,455,799,000

11,641,844,000

'

'

'

'

'

'

2,260,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock shares issued

'

'

'

314,953

'

135,347

'

'

3,298,246

'

'

3,258,718

3,258,718

'

'

'

'

530,940

'

372,282

'

'

8,524,835

'

'

Cash paid for outstanding shares

'

'

'

'

'

'

'

'

47,000,000

'

'

60,000,000

'

'

'

'

'

'

'

11,400,000

'

'

178,500,000

'

'

Total assets

'

'

'

77,000,000

'

37,300,000

'

'

'

'

'

1,250,000,000

'

'

'

'

'

165,000,000

'

182,000,000

'

'

'

'

'

Total loans

'

'

'

27,600,000

'

22,900,000

'

'

'

'

'

847,600,000

'

'

'

'

'

129,300,000

'

68,000,000

'

'

'

'

'

Total deposits

'

'

'

70,400,000

'

33,200,000

'

'

'

'

'

1,110,000,000

'

'

'

'

'

112,300,000

'

164,600,000

'

'

'

'

'

Closing common stock price

'

'

'

$40.35

'

$45.80

'

'

'

'

'

$47.39

'

'

'

'

'

$42

'

$42.62

'

'

$42.03

'

'

Goodwill recognized on business acquisition

1,351,782,000

1,217,162,000

924,537,000

6,100,000

'

2,000,000

'

'

'

'

'

91,700,000

'

'

'

'

'

7,000,000

'

10,600,000

'

'

271,000,000

'

'

Core deposit intangibles recognized

'

'

'

'

'

'

'

'

'

'

'

1,500,000

'

1,515,000

'

'

'

'

'

'

'

'

14,500,000

12,392,000

'

Merger related expense

'

'

'

'

'

'

'

'

'

'

'

'

787,000

'

'

'

'

'

'

'

'

'

'

'

'

Total merger consideration

'

'

'

12,700,000

'

6,200,000

'

'

'

'

'

'

214,400,000

'

'

'

'

22,300,000

'

'

'

'

'

'

'

Number of Banking Offices operated

'

'

'

'

3

'

'

1

'

'

'

'

'

'

'

'

'

'

4

'

'

1

'

'

'

Total merger consideration

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

27,300,000

'

'

'

'

'

Merger consideration

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$536,800,000

'

'

Number of counties bank operates

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

18

'

'

Acquisitions_Information_Regar

Acquisitions - Information Regarding Results of Operations on Acquisition (Detail) (USD $)	3 Months Ended		9 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Combinations [Abstract]	'	'	'	'
Net interest income	$126,533	$127,501	$375,699	$403,983
Net income	$55,278	$53,266	$165,090	$184,368
Basic earnings per share	$0.92	$0.89	$2.64	$2.92
Diluted earnings per share	$0.91	$0.88	$2.64	$2.92

Acquisitions_Information_Regar1

Acquisitions - Information Regarding Results of Operations on Acquisition (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended		6 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2012
					American State Financial Corporation [Member]
					Non Recurring [Member]
Business Acquisition Pro Forma Information [Line Items]	'	'	'	'	'
Gain on sale of securities	$0	$0	$0	'	$23,400
Earning per share	$0.92	$0.89	$2.64	$2.92	$0.37

Subsequent_Event_Additional_In

Subsequent Event - Additional Information (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011	Nov. 01, 2013	Sep. 30, 2013	Nov. 01, 2013	Nov. 01, 2013	Nov. 01, 2013	Nov. 01, 2013	Nov. 01, 2013
				FVNB [Member]	FVNB [Member]	Victoria [Member]	South Texas [Member]	Bryan/College Station [Member]	Central Texas [Member]	Houston [Member]
				Subsequent Event [Member]	Subsequent Event [Member]	FVNB [Member]	FVNB [Member]	FVNB [Member]	FVNB [Member]	FVNB [Member]
				Branch_office		Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]	Subsequent Event [Member]
						Branch_office	Branch_office	Branch_office	Branch_office	Branch_office
Subsequent Event [Line Items]	'	'	'	'	'	'	'	'	'	'
Number of banking offices	'	'	'	33	'	4	7	6	5	11
Total assets	$16,054,279,000	$14,583,573,000	'	'	$2,470,000,000	'	'	'	'	'
Total loans	'	'	'	'	1,650,000,000	'	'	'	'	'
Total deposits	12,455,799,000	11,641,844,000	'	'	2,200,000,000	'	'	'	'	'
Shares issued as consideration for business acquisition	'	'	'	5,570,667	'	'	'	'	'	'
Cash paid to shareholders of acquired company	'	'	'	91,300,000	'	'	'	'	'	'
Total merger consideration	'	'	'	439,100,000	'	'	'	'	'	'
Closing common stock price	'	'	'	$62.45	'	'	'	'	'	'
Goodwill recognized on business acquisition	1,351,782,000	1,217,162,000	924,537,000	278,300,000	'	'	'	'	'	'
Merger related expense	'	'	'	'	$121,000	'	'	'	'	'