Cullen/Frost Bankers (CFR) 10-K 5 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Billions, except Share data, unless otherwise specified	Dec. 31, 2014	Jan. 23, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Entity Registrant Name	CULLEN/FROST BANKERS, INC.
Trading Symbol	CFR
Entity Central Index Key	39263
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		63,151,173
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$4.80

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Assets:
Cash and due from banks	$702,485	$885,121
Interest-bearing deposits	3,630,846	3,646,756
Federal funds sold and resell agreements	30,792	24,248
Total cash and cash equivalents	4,364,123	4,556,125
Securities held to maturity, at amortized cost	2,926,486	3,139,748
Securities available for sale, at estimated fair value	8,461,254	5,895,436
Trading account securities	15,426	16,398
Loans, net of unearned discounts	10,987,535	9,515,700
Less: Allowance for loan losses	-99,542	-92,438
Net loans	10,887,993	9,423,262
Premises and equipment, net	442,888	313,331
Goodwill	653,950	536,649
Other intangible assets, net	12,125	6,345
Cash surrender value of life insurance policies	172,050	141,108
Accrued interest receivable and other assets	341,480	284,537
Total assets	28,277,775	24,312,939
Liabilities:
Non-interest-bearing demand deposits	10,149,061	8,311,149
Interest-bearing deposits	13,986,869	12,377,637
Total deposits	24,135,930	20,688,786
Federal funds purchased and repurchase agreements	803,119	668,253
Junior subordinated deferrable interest debentures	137,115	123,712
Other long-term borrowings	100,000	100,000
Accrued interest payable and other liabilities	250,208	218,027
Total liabilities	25,426,372	21,798,778
Shareholders’ Equity:
Preferred stock, par value $0.01 per share; 10,000,000 shares authorized; 6,000,000 Series A shares ($25 liquidation preference) issued in both 2014 and 2013	144,486	144,486
Common stock, par value $0.01 per share; 210,000,000 shares authorized; 63,632,464 shares issued in 2014 and 61,632,464 shares issued in 2013	637	617
Additional paid-in capital	886,476	724,197
Retained earnings	1,710,324	1,575,282
Accumulated other comprehensive income, net of tax	141,814	140,434
Treasury stock, at cost; 483,041 shares in 2014 and 1,066,021 in 2013	-32,334	-70,855
Total shareholders’ equity	2,851,403	2,514,161
Total liabilities and shareholders’ equity	$28,277,775	$24,312,939

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Preferred stock, par value	$0.01	$0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	6,000,000	6,000,000
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	210,000,000	210,000,000
Common stock, shares issued	63,632,464	61,632,464
Treasury stock, shares	483,041	1,066,021
Series A Preferred Stock [Member]
Series A Preferred Stock, Liquidation preference value	$25	$25

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest income:
Loans, including fees	$440,958	$415,230	$401,364
Securities:
Taxable	93,087	97,873	132,432
Tax-exempt	156,618	122,031	93,412
Interest-bearing deposits	10,725	7,284	4,300
Federal funds sold and resell agreements	83	82	104
Total interest income	701,471	642,500	631,612
Interest expense:
Deposits	11,022	14,459	18,099
Federal funds purchased and repurchase agreements	134	121	140
Junior subordinated deferrable interest debentures	2,488	6,426	6,806
Other long-term borrowings	893	939	1,706
Total interest expense	14,537	21,945	26,751
Net interest income	686,934	620,555	604,861
Provision for loan losses	16,314	20,582	10,080
Net interest income after provision for loan losses	670,620	599,973	594,781
Non-interest income:
Trust and investment management fees	106,237	91,375	83,317
Service charges on deposit accounts	81,946	81,432	83,392
Insurance commissions and fees	45,115	43,140	39,948
Interchange and debit card transaction fees	18,372	16,979	16,933
Other charges, commissions and fees	36,180	34,185	30,180
Net gain (loss) on securities transactions	38	1,176	4,314
Other	32,256	34,531	30,703
Total non-interest income	320,144	302,818	288,787
Non-interest expense:
Salaries and wages	292,349	273,692	258,752
Employee benefits	60,151	62,407	57,635
Net occupancy	55,745	50,468	48,975
Furniture and equipment	62,087	58,443	55,279
Deposit insurance	13,232	11,682	11,087
Intangible amortization	3,520	3,141	3,896
Other	167,656	152,077	139,469
Total non-interest expense	654,740	611,910	575,093
Income before income taxes	336,024	290,881	308,475
Income taxes	58,047	53,015	70,523
Net income	277,977	237,866	237,952
Preferred stock dividends	8,063	6,719	0
Net income available to common shareholders	$269,914	$231,147	$237,952
Earnings per common share:
Basic (in dollars per share)	$4.32	$3.82	$3.87
Diluted (in dollars per share)	$4.29	$3.80	$3.86

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net income	$277,977	$237,866	$237,952
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	103,044	-115,245	33,412
Change in net unrealized gain on securities transferred to held-to-maturity	-35,441	-35,682	-657
Reclassification adjustment for net (gains) losses included in net income	-38	-1,176	-4,314
Total securities available for sale and transferred securities	67,565	-152,103	28,441
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	-34,837	35,293	-9,405
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	0	-49	-783
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	-30,604	-37,380	-37,380
Interest rate swap on junior subordinated deferrable interest debentures	0	4,064	4,224
Total derivatives	-30,604	-33,365	-33,939
Other comprehensive income (loss), before tax	2,124	-150,175	-14,903
Deferred tax expense (benefit) related to other comprehensive income	744	-52,561	-5,217
Other comprehensive income (loss), net of tax	1,380	-97,614	-9,686
Comprehensive income	$279,357	$140,252	$228,266

Consolidated_Statement_of_Chan

Consolidated Statement of Changes in Shareholders' Equity (USD $)	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2011	$2,283,537,000	$0	$613,000	$680,803,000	$1,354,759,000	$247,734,000	($372,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,952,000				237,952,000
Other comprehensive income, net of tax	-9,686,000					-9,686,000
Stock option exercises/deferred stock unit conversions	10,516,000		2,000	10,100,000	-6,000		420,000
Tax benefits from stock-based compensation	-384,000			-384,000
Stock-based compensation expense recognized in earnings	12,836,000			12,836,000
Non-vested stock awards and stock units	0			-387,000	-1,000		388,000
Purchase of treasury stock	-436,000						-436,000
Cash dividends – common stock	-116,853,000				-116,853,000
Balance at Dec. 31, 2012	2,417,482,000	0	615,000	702,968,000	1,475,851,000	238,048,000	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,866,000				237,866,000
Other comprehensive income, net of tax	-97,614,000					-97,614,000
Stock option exercises/deferred stock unit conversions	68,653,000		2,000	7,839,000	-12,097,000		72,909,000
Tax benefits from stock-based compensation	2,293,000			2,293,000
Stock-based compensation expense recognized in earnings	11,963,000			11,963,000
Non-vested stock awards and stock units	0			-866,000	0		866,000
Issuance of preferred stock	144,486,000	144,486,000
Purchase of treasury stock	-144,630,000						-144,630,000
Cash dividends – preferred stock	-6,719,000				-6,719,000
Cash dividends – common stock	-119,619,000				-119,619,000
Balance at Dec. 31, 2013	2,514,161,000	144,486,000	617,000	724,197,000	1,575,282,000	140,434,000	-70,855,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	277,977,000				277,977,000
Other comprehensive income, net of tax	1,380,000					1,380,000
Stock option exercises/deferred stock unit conversions	29,158,000			-2,620,000	-7,694,000		39,472,000
Tax benefits from stock-based compensation	3,202,000			3,202,000
Stock-based compensation expense recognized in earnings	12,503,000			12,503,000
Non-vested stock awards and stock units	0			-506,000			506,000
Common stock issued in acquisition of WNB Bancshares	149,720,000		20,000	149,700,000
Purchase of treasury stock	-1,457,000						-1,457,000
Cash dividends – preferred stock	-8,063,000				-8,063,000
Cash dividends – common stock	-127,178,000				-127,178,000
Balance at Dec. 31, 2014	$2,851,403,000	$144,486,000	$637,000	$886,476,000	$1,710,324,000	$141,814,000	($32,334,000)

Consolidated_Statement_of_Chan1

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock option exercises/deferred stock unit conversions, shares	594,231	1,319,786	206,366
Non-vested stock awards, shares	7,620	13,040	16,850
Non-vested stock units, shares	24,430	24,970	32,280
Stock Issued During Period, Shares, Acquisitions	2,000,000	0	0
Issuance of preferred stock, shares	0	6,000,000
Purchase of treasury stock, shares	18,871	2,245,572	7,960
Approximate cash dividends declared on preferred stock, per share	$1.34	$1.12
Cash dividends - common stock, per share	$2.03	$1.98	$1.90

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities:
Net income	$277,977	$237,866	$237,952
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	16,314	20,582	10,080
Deferred tax expense (benefit)	-4,130	3,279	-6,405
Accretion of loan discounts	-14,567	-12,654	-10,888
Securities premium amortization (discount accretion), net	61,268	41,921	21,701
Net (gain) loss on securities transactions	-38	-1,176	-4,314
Depreciation and amortization	39,694	38,471	37,776
Net loss on sale/write-down of assets/foreclosed assets	761	3,235	4,603
Stock-based compensation	12,503	11,963	12,836
Net tax benefit (deficiency) from stock-based compensation	19	-393	-555
Excess tax benefits from stock-based compensation	-3,183	-2,686	-171
Earnings on life insurance policies	-3,218	-3,103	-4,038
Net change in:
Trading account securities	972	14,686	-16,465
Accrued interest receivable and other assets	-73,184	-7,996	48,176
Accrued interest payable and other liabilities	-24,518	-170,389	-30,289
Net cash from operating activities	286,670	173,606	299,999
Investing Activities:
Securities held to maturity: Purchases	0	-257,571	-237,503
Securities held to maturity: Maturities, calls and principal repayments	153,523	14,891	2,100
Securities available for sale:
Purchases	-19,484,433	-11,178,144	-18,328,058
Sales	12,151,287	10,056,060	16,587,482
Maturities, calls and principal repayments	4,987,629	1,311,643	1,073,122
Net change in loans	-800,120	-317,987	-1,241,422
Net cash received (paid) in acquisitions	830,661	-1,896	-7,199
Proceeds from sales of premises and equipment	49	18,481	5,085
Purchases of premises and equipment	-131,970	-39,599	-24,891
Proceeds from sales of repossessed properties	11,281	8,200	15,816
Net cash from investing activities	-2,282,093	-385,922	-2,155,468
Financing Activities:
Net change in deposits	1,823,101	1,191,420	2,740,618
Net change in short-term borrowings	84,677	107,192	-161,141
Principal payments on long-term borrowings	0	-7	-19
Proceeds from stock option exercises	29,158	68,653	10,516
Excess tax benefits from stock-based compensation	3,183	2,686	171
Proceeds from issuance of preferred stock	0	144,486	0
Purchase of treasury stock	-1,457	-144,630	-436
Cash dividends paid on preferred stock	-8,063	-6,719	0
Cash dividends paid on common stock	-127,178	-119,619	-116,853
Net cash from financing activities	1,803,421	1,243,462	2,472,856
Net change in cash and cash equivalents	-192,002	1,031,146	617,387
Cash and cash equivalents at beginning of year	4,556,125	3,524,979	2,907,592
Cash and cash equivalents at end of year	$4,364,123	$4,556,125	$3,524,979

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies
	Nature of Operations. Cullen/Frost Bankers, Inc. (“Cullen/Frost”) is a financial holding company and a bank holding company headquartered in San Antonio, Texas that provides, through its subsidiaries, a broad array of products and services throughout numerous Texas markets. In addition to general commercial and consumer banking, other products and services offered include trust and investment management, investment banking, insurance, brokerage, leasing, treasury management and item processing.
	Basis of Presentation. The consolidated financial statements include the accounts of Cullen/Frost and all other entities in which Cullen/Frost has a controlling financial interest (collectively referred to as the “Corporation”). All significant intercompany balances and transactions have been eliminated in consolidation. The accounting and financial reporting policies the Corporation follows conform, in all material respects, to accounting principles generally accepted in the United States and to general practices within the financial services industry.
	The Corporation determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (“VIE”) under accounting principles generally accepted in the United States. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. The Corporation consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE. The Corporation’s wholly owned subsidiaries Cullen/Frost Capital Trust II and WNB Capital Trust I are VIEs for which the Corporation is not the primary beneficiary. Accordingly, the accounts of these trusts are not included in the Corporation’s consolidated financial statements.
	The Corporation has evaluated subsequent events for potential recognition and/or disclosure through the date these consolidated financial statements were issued. All acquisitions during the reported periods were accounted for using the purchase method. Accordingly, the operating results of the acquired companies are included with the Corporation’s results of operations since their respective dates of acquisition.
	Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses and the fair values of financial instruments and the status of contingencies are particularly subject to change.
	Cash Flow Reporting. Cash and cash equivalents include cash, deposits with other financial institutions that have an initial maturity of less than 90 days when acquired by the Corporation, federal funds sold and resell agreements. Net cash flows are reported for loans, deposit transactions and short-term borrowings. Additional cash flow information was as follows:
		Year Ended December 31,
		2014		2013		2012
	Cash paid for interest	$	14,705	$	22,449	$	29,378
	Cash paid for income tax	62,976		49,514		58,950
	Significant non-cash transactions:
	Transfer of securities from available for sale to held to maturity	—		—		2,266,195
	Unsettled purchases of securities	—		16,241		90,073
	Loans foreclosed and transferred to other real estate owned and foreclosed assets	4,363		6,870		7,817
	Premises and equipment transferred to other real estate owned and foreclosed assets	1,740		—		—
	Loans to facilitate the sale of other real estate owned	102		678		—
	Deferred gain on sale of building and parking garage	—		768		—
	Concentrations and Restrictions on Cash and Cash Equivalents. The Corporation maintains deposits with other financial institutions in amounts that exceed federal deposit insurance coverage. Furthermore, federal funds sold are essentially uncollateralized loans to other financial institutions. Management regularly evaluates the credit risk associated with the counterparties to these transactions and believes that the Corporation is not exposed to any significant credit risks on cash and cash equivalents.
	The Corporation was required to have $175.6 million and $116.6 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2014 and 2013. These deposits with the Federal Reserve Bank do not earn interest. Additionally, as of December 31, 2014, the Corporation had $12.1 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions.
	Repurchase/Resell Agreements. The Corporation purchases certain securities under agreements to resell. The amounts advanced under these agreements represent short-term loans and are reflected as assets in the accompanying consolidated balance sheets. The securities underlying these agreements are book-entry securities. The Corporation also sells certain securities under agreements to repurchase. The agreements are treated as collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying consolidated balance sheets. The dollar amount of the securities underlying the agreements remain in the asset accounts.
	Securities. Securities are classified as held to maturity and carried at amortized cost when management has the positive intent and ability to hold them until maturity. Securities to be held for indefinite periods of time are classified as available for sale and carried at fair value, with the unrealized holding gains and losses reported as a component of other comprehensive income, net of tax. Securities held for resale in anticipation of short-term market movements are classified as trading and are carried at fair value, with changes in unrealized holding gains and losses included in income. Management determines the appropriate classification of securities at the time of purchase. Securities with limited marketability, such as stock in the Federal Reserve Bank and the Federal Home Loan Bank, are carried at cost.
	Purchase premiums and discounts on securities are amortized or accreted to interest income over the expected lives of the securities using the interest method with a constant effective yield. Expectations related to prepayments are considered in the calculation of the constant effective yield necessary to apply the interest method for mortgage-backed securities and certain pools of municipal securities. Premium amortization and discount accretion for mortgage-backed securities and pools of municipal securities is adjusted for changes in prepayment estimates, as applicable.
	Realized gains and losses are derived from the amortized cost of the security sold. Declines in the fair value of held-to-maturity and available-for-sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses. In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer and (iii) the intent and ability of the Corporation to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value.
	Loans. Loans are reported at the principal balance outstanding net of unearned discounts. Interest income on loans is reported on the level-yield method and includes amortization of deferred loan fees and costs over the loan term. Net loan commitment fees or costs for commitment periods greater than one year are deferred and amortized into fee income or other expense on a straight-line basis over the commitment period. Income on direct financing leases is recognized on a basis that achieves a constant periodic rate of return on the outstanding investment. Further information regarding the Corporation’s accounting policies related to past due loans, non-accrual loans, impaired loans and troubled-debt restructurings is presented in Note 4 - Loans.
	Loans Acquired Through Transfer. Loans acquired through the completion of a transfer, including loans acquired in a business combination, are initially recorded at fair value.
	Acquired loans that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Corporation will be unable to collect all contractually required payments receivable are considered to be purchased credit-impaired. For purchased credit-impaired loans, the difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition (meaning the present value of all cash flows expected at acquisition that ultimately are not to be received).
	For acquired loans that are not deemed to be purchased credit-impaired at acquisition, the difference between the initial fair value and the unpaid principal balance is recognized as interest income on a level-yield basis over the lives of the related loans. Subsequent to acquisition, any valuation allowance on these loans reflects only the portion of probable losses that exceeds any unaccreted purchase discounts on these loans as of the measurement date.
	Allowance for Loan Losses. The allowance for loan losses is a reserve established through a provision for loan losses charged to expense, which represents management’s best estimate of probable losses that have been incurred within the existing portfolio of loans. The allowance, in the judgment of management, is necessary to reserve for estimated loan losses inherent in the loan portfolio. The allowance for loan losses includes allowance allocations calculated in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 310, “Receivables” and allowance allocations calculated in accordance with ASC Topic 450, “Contingencies.” Further information regarding the Corporation’s policies and methodology used to estimate the allowance for loan losses is presented in Note 4 - Loans.
	Premises and Equipment. Land is carried at cost. Building and improvements, and furniture and equipment are carried at cost, less accumulated depreciation, computed principally by the straight-line method based on the estimated useful lives of the related property. Leasehold improvements are generally depreciated over the lesser of the term of the respective leases or the estimated useful lives of the improvements.
	Foreclosed Assets. Assets acquired through or instead of loan foreclosure are held for sale and are initially recorded at fair value less estimated selling costs when acquired, establishing a new cost basis. Costs after acquisition are generally expensed. If the fair value of the asset declines, a write-down is recorded through expense. The valuation of foreclosed assets is subjective in nature and may be adjusted in the future because of changes in economic conditions. Foreclosed assets are included in other assets in the accompanying consolidated balance sheets and totaled $5.3 million and $11.9 million at December 31, 2014 and 2013.
	Goodwill. Goodwill represents the excess of the cost of businesses acquired over the fair value of the net assets acquired. Goodwill is assigned to reporting units and tested for impairment at least annually, or on an interim basis if an event occurs or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying value. See Note 6 - Goodwill and Other Intangible Assets.
	Intangibles and Other Long-Lived Assets. Intangible assets are acquired assets that lack physical substance but can be distinguished from goodwill because of contractual or other legal rights or because the asset is capable of being sold or exchanged either on its own or in combination with a related contract, asset, or liability. The Corporation’s intangible assets relate to core deposits, non-compete agreements and customer relationships. Intangible assets with definite useful lives are amortized on an accelerated basis over their estimated life. Intangible assets with indefinite useful lives are not amortized until their lives are determined to be definite. Intangible assets, premises and equipment and other long-lived assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows. If impaired, the assets are recorded at fair value. See Note 6 - Goodwill and Other Intangible Assets.
	Insurance Commissions and Fees. Commission revenue is recognized as of the effective date of the insurance policy. The Corporation also receives contingent commissions from insurance companies as additional incentive for achieving specified premium volume goals and/or the loss experience of the insurance placed by the Corporation. Contingent commissions from insurance companies are recognized when determinable, which is generally when such commissions are received or when the Corporation receives data from the insurance companies that allows the reasonable estimation of these amounts. The Corporation maintains a reserve for commission adjustments based on estimated policy cancellations. This reserve was not significant at December 31, 2014 or 2013.
	Stock-Based Compensation. Compensation expense for stock options, non-vested stock awards/stock units and deferred stock units is based on the fair value of the award on the measurement date, which, for the Corporation, is the date of the grant and is recognized ratably over the service period of the award. The fair value of stock options is estimated using a binomial lattice-based valuation model. The fair value of stock options granted prior to the fourth quarter of 2006 was estimated using the Black-Scholes option-pricing model. The fair value of non-vested stock awards/stock units and deferred stock units is generally the market price of the Corporation’s stock on the date of grant.
	Advertising Costs. Advertising costs are expensed as incurred.
	Income Taxes. Income tax expense is the total of the current year income tax due or refundable and the change in deferred tax assets and liabilities (excluding deferred tax assets and liabilities related to business combinations or components of other comprehensive income). Deferred tax assets and liabilities are the expected future tax amounts for the temporary differences between carrying amounts and tax bases of assets and liabilities, computed using enacted tax rates. A valuation allowance, if needed, reduces deferred tax assets to the expected amount most likely to be realized. Realization of deferred tax assets is dependent upon the generation of a sufficient level of future taxable income and recoverable taxes paid in prior years. Although realization is not assured, management believes it is more likely than not that all of the deferred tax assets will be realized. Interest and/or penalties related to income taxes are reported as a component of income tax expense.
	The Corporation files a consolidated income tax return with its subsidiaries. Federal income tax expense or benefit has been allocated to subsidiaries on a separate return basis.
	Basic and Diluted Earnings Per Common Share. Earnings per common share is computed using the two-class method prescribed under ASC Topic 260, “Earnings Per Share.” ASC Topic 260 provides that unvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are participating securities and shall be included in the computation of earnings per share pursuant to the two-class method. The Corporation has determined that its outstanding non-vested stock awards/stock units and deferred stock units are participating securities.
	Under the two-class method, basic earnings per common share is computed by dividing net earnings allocated to common stock by the weighted-average number of common shares outstanding during the applicable period, excluding outstanding participating securities. Diluted earnings per common share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation using the treasury stock method. A reconciliation of the weighted-average shares used in calculating basic earnings per common share and the weighted average common shares used in calculating diluted earnings per common share for the reported periods is provided in Note 11 - Earnings Per Common Share.
	Comprehensive Income. Comprehensive income includes all changes in shareholders’ equity during a period, except those resulting from transactions with shareholders. Besides net income, other components of the Corporation’s comprehensive income include the after tax effect of changes in the net unrealized gain/loss on securities available for sale, changes in the net unrealized gain on securities transferred to held to maturity, changes in the net actuarial gain/loss on defined benefit post-retirement benefit plans and changes in the accumulated gain/loss on effective cash flow hedging instruments. See Note 15 - Other Comprehensive Income (Loss).
	Derivative Financial Instruments. The Corporation’s hedging policies permit the use of various derivative financial instruments to manage interest rate risk or to hedge specified assets and liabilities. All derivatives are recorded at fair value on the Corporation’s balance sheet. Derivatives executed with the same counterparty are generally subject to master netting arrangements, however, fair value amounts recognized for derivatives and fair value amounts recognized for the right/obligation to reclaim/return cash collateral are not offset for financial reporting purposes. The Corporation may be required to recognize certain contracts and commitments as derivatives when the characteristics of those contracts and commitments meet the definition of a derivative.
	To qualify for hedge accounting, derivatives must be highly effective at reducing the risk associated with the exposure being hedged and must be designated as a hedge at the inception of the derivative contract. The Corporation considers a hedge to be highly effective if the change in fair value of the derivative hedging instrument is within 80% to 125% of the opposite change in the fair value of the hedged item attributable to the hedged risk. If derivative instruments are designated as hedges of fair values, and such hedges are highly effective, both the change in the fair value of the hedge and the hedged item are included in current earnings. Fair value adjustments related to cash flow hedges are recorded in other comprehensive income and are reclassified to earnings when the hedged transaction is reflected in earnings. Ineffective portions of hedges are reflected in earnings as they occur. Actual cash receipts and/or payments and related accruals on derivatives related to hedges are recorded as adjustments to the interest income or interest expense associated with the hedged item. During the life of the hedge, the Corporation formally assesses whether derivatives designated as hedging instruments continue to be highly effective in offsetting changes in the fair value or cash flows of hedged items. If it is determined that a hedge has ceased to be highly effective, the Corporation will discontinue hedge accounting prospectively. At such time, previous adjustments to the carrying value of the hedged item are reversed into current earnings and the derivative instrument is reclassified to a trading position recorded at fair value.
	Fair Value Measurements. In general, fair values of financial instruments are based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality and the Corporation’s creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time.
	Transfers of Financial Assets. Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (i) the assets have been isolated from the Corporation, (ii) the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (iii) the Corporation does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
	Loss Contingencies. Loss contingencies, including claims and legal actions arising in the ordinary course of business are recorded as liabilities when the likelihood of loss is probable and an amount or range of loss can be reasonably estimated.
	Trust Assets. Assets of the Corporation’s trust department, other than cash on deposit at Frost Bank, are not included in the accompanying financial statements because they are not assets of the Corporation.
	Reclassifications. Certain items in prior financial statements have been reclassified to conform to the current presentation.

Securities

Securities	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Securities	Securities
	Year-end securities held to maturity and available for sale consisted of the following:
		2014											2013
		Amortized			Gross			Gross			Estimated		Amortized		Gross		Gross		Estimated
		Cost			Unrealized			Unrealized			Fair Value		Cost		Unrealized		Unrealized		Fair Value
					Gains			Losses							Gains		Losses
	Held to Maturity:
	U.S. Treasury	$	249,009		$	14,604		$	—		$	263,613	$	248,592	$	20,139	$	—	$	268,731
	Residential mortgage-backed securities	8,012			92			—			8,104		9,674		89		143		9,620
	States and political subdivisions	2,668,115			34,243			9,035			2,693,323		2,880,482		7,691		137,861		2,750,312
	Other	1,350			—			—			1,350		1,000		—		—		1,000
	Total	$	2,926,486		$	48,939		$	9,035		$	2,966,390	$	3,139,748	$	27,919	$	138,004	$	3,029,663
	Available for Sale:
	U. S. Treasury	$	3,783,899		$	30,594		$	3,241		$	3,811,252	$	2,522,159	$	18,395	$	—	$	2,540,554
	U.S. government agencies/corporations	—			—			—			—		54,024		—		44		53,980
	Residential mortgage-backed securities	1,331,114			68,027			417			1,398,724		1,710,664		66,791		1,439		1,776,016
	States and political subdivisions	3,104,563			104,500			156			3,208,907		1,476,316		20,090		7,492		1,488,914
	Other	42,371			—			—			42,371		35,972		—		—		35,972
	Total	$	8,261,947		$	203,121		$	3,814		$	8,461,254	$	5,799,135	$	105,276	$	8,975	$	5,895,436
	All mortgage-backed securities included in the above table were issued by U.S. government agencies and corporations. At December 31, 2014, approximately 97.4% of the securities in the Corporation’s municipal bond portfolio were issued by political subdivisions or agencies within the State of Texas, of which approximately 64.9% are either guaranteed by the Texas Permanent School Fund, which has a “triple-A” insurer financial strength rating, or secured by U.S. Treasury securities via defeasance of the debt by the issuers. Securities with limited marketability, such as stock in the Federal Reserve Bank and the Federal Home Loan Bank, are carried at cost and are reported as other available for sale securities in the table above. The carrying value of securities pledged to secure public funds, trust deposits, repurchase agreements and for other purposes, as required or permitted by law was $3.0 billion at both December 31, 2014 and 2013.
	During the fourth quarter of 2012, the Corporation reclassified certain securities from available for sale to held to maturity. The securities had an aggregate fair value of $2.3 billion with an aggregate net unrealized gain of $165.7 million ($107.7 million, net of tax) on the date of the transfer. The net unamortized, unrealized gain on the transferred securities included in accumulated other comprehensive income in the accompanying balance sheet totaled $93.9 million ($61.0 million, net of tax) at December 31, 2014 and $129.3 million ($84.1 million, net of tax) at December 31, 2013. This amount will be amortized out of accumulated other comprehensive income over the remaining life of the underlying securities as an adjustment of the yield on those securities.
	Year-end securities with unrealized losses, segregated by length of impairment, were as follows:
		Less than 12 Months						More than 12 Months					Total
		Estimated			Unrealized			Estimated			Unrealized		Estimated		Unrealized
		Fair Value			Losses			Fair Value			Losses		Fair Value		Losses
	2014
	Held to Maturity:
	States and political subdivisions	$	68,024		$	144		$	683,251		$	8,891	$	751,275	$	9,035
	Total	$	68,024		$	144		$	683,251		$	8,891	$	751,275	$	9,035
	Available for Sale:
	U.S. Treasury	$	1,019,230		$	3,241		$	—		$	—	$	1,019,230	$	3,241
	Residential mortgage-backed securities	8,550			42			16,944			375		25,494		417
	States and political subdivisions	65,751			156			—			—		65,751		156
	Total	$	1,093,531		$	3,439		$	16,944		$	375	$	1,110,475	$	3,814
	2013
	Held to Maturity:
	Residential mortgage-backed securities	$	6,934		$	143		$	—		$	—	$	6,934	$	143
	States and political subdivisions	2,071,521			113,512			266,566			24,349		2,338,087		137,861
	Total	$	2,078,455		$	113,655		$	266,566		$	24,349	$	2,345,021	$	138,004
	Available for Sale:
	U.S. government agencies/ corporations	$	53,980		$	44		$	—		$	—	$	53,980	$	44
	Residential mortgage-backed securities	33,001			1,157			2,713			282		35,714		1,439
	States and political subdivisions	679,923			7,492			—			—		679,923		7,492
	Total	$	766,904		$	8,693		$	2,713		$	282	$	769,617	$	8,975
	Declines in the fair value of held-to-maturity and available-for-sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses to the extent the impairment is related to credit losses. The amount of the impairment related to other factors is recognized in other comprehensive income. In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer, and (iii) the intent and ability of the Corporation to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in cost.
	Management has the ability and intent to hold the securities classified as held to maturity in the table above until they mature, at which time the Corporation will receive full value for the securities. Furthermore, as of December 31, 2014, management does not have the intent to sell any of the securities classified as available for sale in the table above and believes that it is more likely than not that the Corporation will not have to sell any such securities before a recovery of cost. Any 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 bonds 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 December 31, 2014, management believes the impairments detailed in the table above are temporary and no impairment loss has been realized in the Corporation’s consolidated income statement.
	The amortized cost and estimated fair value of securities, excluding trading securities, at December 31, 2014 are presented below by contractual maturity. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. Residential mortgage-backed securities and equity securities are shown separately since they are not due at a single maturity date.
		Held to Maturity						Available for Sale
		Amortized			Estimated			Amortized			Estimated
		Cost			Fair Value			Cost			Fair Value
	Due in one year or less	$	153,701		$	155,505		$	515,567		$	517,482
	Due after one year through five years	533,990			564,854			2,474,795			2,486,488
	Due after five years through ten years	172,371			172,240			1,937,104			1,977,280
	Due after ten years	2,058,412			2,065,687			1,960,996			2,038,909
	Residential mortgage-backed securities	8,012			8,104			1,331,114			1,398,724
	Equity securities	—			—			42,371			42,371
	Total	$	2,926,486		$	2,966,390		$	8,261,947		$	8,461,254
	Sales of securities available for sale were as follows:
		2014			2013			2012
	Proceeds from sales	$	12,151,287		$	10,056,060		$	16,587,482
	Gross realized gains	39			1,206			6,943
	Gross realized losses	(1		)	(30		)	(2,629		)
	Tax (expense) benefit of securities gains/losses	(13		)	(412		)	(1,510		)
	Premium amortization and discount accretion included in interest income on securities was as follows:
	2014			2013			2012
Premium amortization	$	(68,070	)	$	(49,112	)	$	(28,364	)
Discount accretion	6,802			7,191			6,663
Net (premium amortization) discount accretion	$	(61,268	)	$	(41,921	)	$	(21,701	)
Year-end trading account securities, at estimated fair value, were as follows:
	2014			2013
U.S. Treasury	$	15,339		$	15,389
States and political subdivisions	87			1,009
Total	$	15,426		$	16,398
Net gains and losses on trading account securities were as follows:
	2014			2013			2012
Net gain on sales transactions	$	829		$	878		$	1,219
Net mark-to-market gains (losses)	—			(429		)	(161		)
Net gain on trading account securities	$	829		$	449		$	1,058

Loans

Loans	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Loans	Loans
	Year-end loans consisted of the following:
		2014				2013
	Commercial and industrial:
	Commercial	$	5,429,206			$	4,587,499
	Leases	338,537				319,577
	Total commercial and industrial	5,767,743				4,907,076
	Commercial real estate:
	Commercial mortgages	3,080,202				2,800,760
	Construction	629,988				426,639
	Land	291,907				239,937
	Total commercial real estate	4,002,097				3,467,336
	Consumer real estate:
	Home equity loans	342,725				329,853
	Home equity lines of credit	220,128				195,132
	Other	286,198				283,219
	Total consumer real estate	849,051				808,204
	Total real estate	4,851,148				4,275,540
	Consumer and other:
	Consumer installment	385,479				350,827
	Other	8,122				7,289
	Total consumer and other	393,601				358,116
	Unearned discounts	(24,957		)		(25,032		)
	Total loans	$	10,987,535			$	9,515,700
	Loan Origination/Risk Management. The Corporation has certain lending policies and procedures in place that are designed to maximize loan income within an acceptable level of risk. Management reviews and approves these policies and procedures on a regular basis. A reporting system supplements the review process by providing management with frequent reports related to loan production, loan quality, concentrations of credit, loan delinquencies and non-performing and potential problem loans. Diversification in the loan portfolio is a means of managing risk associated with fluctuations in economic conditions.
	Commercial and industrial loans are underwritten after evaluating and understanding the borrower’s ability to operate profitably and prudently expand its business. Underwriting standards are designed to promote relationship banking rather than transactional banking. Once it is determined that the borrower’s management possesses sound ethics and solid business acumen, the Corporation’s management examines current and projected cash flows to determine the ability of the borrower to repay their obligations as agreed. Commercial and industrial loans are primarily made based on the identified cash flows of the borrower and secondarily on the underlying collateral provided by the borrower. The cash flows of borrowers, however, may not be as expected and the collateral securing these loans may fluctuate in value. Most commercial and industrial loans are secured by the assets being financed or other business assets such as accounts receivable or inventory and may incorporate a personal guarantee; however, some short-term loans may be made on an unsecured basis. In the case of loans secured by accounts receivable, the availability of funds for the repayment of these loans may be substantially dependent on the ability of the borrower to collect amounts due from its customers.
	Commercial real estate loans are subject to underwriting standards and processes similar to commercial and industrial loans, in addition to those of real estate loans. These loans are viewed primarily as cash flow loans and secondarily as loans secured by real estate. Commercial real estate lending typically involves higher loan principal amounts and the repayment of these loans is generally largely dependent on the successful operation of the property securing the loan or the business conducted on the property securing the loan. Commercial real estate loans may be more adversely affected by conditions in the real estate markets or in the general economy. The properties securing the Corporation’s commercial real estate portfolio are diverse in terms of type and geographic location. This diversity helps reduce the Corporation’s exposure to adverse economic events that affect any single market or industry. Management monitors and evaluates commercial real estate loans based on collateral, geography and risk grade criteria. As a general rule, the Corporation avoids financing single-purpose projects unless other underwriting factors are present to help mitigate risk. The Corporation also utilizes third-party experts to provide insight and guidance about economic conditions and trends affecting market areas it serves. In addition, management tracks the level of owner-occupied commercial real estate loans versus non-owner occupied loans. At December 31, 2014, approximately 55% of the outstanding principal balance of the Corporation’s commercial real estate loans were secured by owner-occupied properties.
	With respect to loans to developers and builders that are secured by non-owner occupied properties that the Corporation may originate from time to time, the Corporation generally requires the borrower to have had an existing relationship with the Corporation and have a proven record of success. Construction loans are underwritten utilizing feasibility studies, independent appraisal reviews, sensitivity analysis of absorption and lease rates and financial analysis of the developers and property owners. Construction loans are generally based upon estimates of costs and value associated with the completed project. These estimates may be inaccurate. Construction loans often involve the disbursement of substantial funds with repayment substantially dependent on the success of the ultimate project. Sources of repayment for these types of loans may be pre-committed permanent loans from approved long-term lenders, sales of developed property or an interim loan commitment from the Corporation until permanent financing is obtained. These loans are closely monitored by on-site inspections and are considered to have higher risks than other real estate loans due to their ultimate repayment being sensitive to interest rate changes, governmental regulation of real property, general economic conditions and the availability of long-term financing.
	The Corporation originates consumer loans utilizing a computer-based credit scoring analysis to supplement the underwriting process. To monitor and manage consumer loan risk, policies and procedures are developed and modified, as needed, jointly by line and staff personnel. This activity, coupled with relatively small loan amounts that are spread across many individual borrowers, minimizes risk. Additionally, trend and outlook reports are reviewed by management on a regular basis. Underwriting standards for home equity loans are heavily influenced by statutory requirements, which include, but are not limited to, a maximum loan-to-value percentage of 80%, collection remedies, the number of such loans a borrower can have at one time and documentation requirements.
	The Corporation 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 Corporation’s policies and procedures.
	Concentrations of Credit. Most of the Corporation’s lending activity occurs within the State of Texas, including the four largest metropolitan areas of Austin, Dallas/Ft. Worth, Houston and San Antonio, as well as other markets. The majority of the Corporation’s loan portfolio consists of commercial and industrial and commercial real estate loans. As of December 31, 2014 and 2013, there were no concentrations of loans related to any single industry in excess of 10% of total loans other than energy loans, which totaled 16.1% and 11.7% of total loans, respectively.
	Foreign Loans. The Corporation 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 December 31, 2014 or 2013.
	Overdrafts. Deposit account overdrafts reported as loans totaled $7.7 million and $6.8 million at December 31, 2014 and 2013.
	Related Party Loans. In the ordinary course of business, the Corporation has granted loans to certain directors, executive officers and their affiliates (collectively referred to as “related parties”). These loans were made on substantially the same terms, including interest rates and collateral, as those prevailing at the time for comparable transactions with other unaffiliated persons and do not involve more than normal risk of collectibility. Activity in related party loans during 2014 is presented in the following table. Other changes were primarily related to changes in related-party status.
	Balance outstanding at December 31, 2013	$	76,672
	Principal additions	127,347
	Principal reductions	(165,963		)
	Other changes	644
	Balance outstanding at December 31, 2014	$	38,700
	Non-Accrual and Past Due Loans. Loans are considered past due if the required principal and interest payments have not been received as of the date such payments were due. Loans are placed on non-accrual status when, in management’s opinion, the borrower may be unable to meet payment obligations as they become due, as well as when required by regulatory provisions. In determining whether or not a borrower may be unable to meet payment obligations for each class of loans, the Corporation considers the borrower’s debt service capacity through the analysis of current financial information, if available, and/or current information with regards to the Corporation’s collateral position. Regulatory provisions would typically require the placement of a loan on non-accrual status if (i) principal or interest has been in default for a period of 90 days or more unless the loan is both well secured and in the process of collection or (ii) full payment of principal and interest is not expected. Loans may be placed on non-accrual status regardless of whether or not such loans are considered past due. When interest accrual is discontinued, all unpaid accrued interest is reversed. Interest income on non-accrual loans is recognized only to the extent that cash payments are received in excess of principal due. A loan may be returned to accrual status when all the principal and interest amounts contractually due are brought current and future principal and interest amounts contractually due are reasonably assured, which is typically evidenced by a sustained period (at least six months) of repayment performance by the borrower.
	Year-end non-accrual loans, segregated by class of loans, were as follows:
		2014				2013
	Commercial and industrial:
	Energy	$	636			$	590
	Other commercial	34,108				26,143
	Commercial real estate:
	Buildings, land and other	19,639				27,035
	Construction	2,792				—
	Consumer real estate	2,212				2,207
	Consumer and other	538				745
	Total	$	59,925			$	56,720
	As of December 31, 2014 and 2013, non-accrual loans reported in the table above included $8.3 million and $10.1 million related to loans that were restructured as “troubled debt restructurings” during 2014 and 2013, respectively. See the section captioned “Troubled Debt Restructurings” elsewhere in this note.
	Had non-accrual loans performed in accordance with their original contract terms, the Corporation would have recognized additional interest income, net of tax, of approximately $1.5 million in 2014, $2.2 million in 2013 and $2.6 million in 2012.
	An age analysis of past due loans (including both accruing and non-accruing loans), segregated by class of loans, as of December 31, 2014 was as follows:
		Loans				Loans				Total Past				Current			Total Loans			Accruing
		30-89 Days				90 or More				Due Loans				Loans						Loans 90 or
		Past Due				Days														More Days
						Past Due														Past Due
	Commercial and industrial:
	Energy	$	7,278			$	—			$	7,278			$	1,766,667		$	1,773,945		$	—
	Other commercial	16,350				33,998				50,348				3,943,450			3,993,798			14,254
	Commercial real estate:
	Buildings, land and other	6,535				11,308				17,843				3,354,266			3,372,109			3,333
	Construction	5,081				1,327				6,408				623,580			629,988			1,042
Consumer real estate	4,560				2,148				6,708				842,343			849,051			1,910
Consumer and other	5,706				476				6,182				387,419			393,601			402
Unearned discounts	—				—				—				(24,957		)	(24,957		)	—
Total	$	45,510			$	49,257			$	94,767			$	10,892,768		$	10,987,535		$	20,941
Impaired Loans. Loans are considered impaired when, based on current information and events, it is probable the Corporation 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 collectibility 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.
Regulatory guidelines require the Corporation to reevaluate the fair value of collateral supporting impaired collateral dependent loans on at least an annual basis. While the Corporation’s policy is to comply with the regulatory guidelines, the Corporation’s general practice is to reevaluate the fair value of collateral supporting impaired collateral dependent loans on a quarterly basis. Thus, appraisals are never considered to be outdated, and the Corporation does not need to make any adjustments to the appraised values. The fair value of collateral supporting impaired collateral dependent loans is evaluated by the Corporation’s internal appraisal services using a methodology that is consistent with the Uniform Standards of Professional Appraisal Practice. The fair value of collateral supporting impaired collateral dependent construction loans is based on an “as is” valuation.
Year-end impaired loans are set forth in the following table. No interest income was recognized on impaired loans subsequent to their classification as impaired.
	Unpaid				Recorded				Recorded				Total			Related			Average
	Contractual				Investment				Investment				Recorded			Allowance			Recorded
	Principal				With No				With				Investment						Investment
	Balance				Allowance				Allowance
2014
Commercial and industrial:
Energy	$	706			$	636			$	—			$	636		$	—		$	571
Other commercial	42,212				29,007				2,853				31,860			1,613			27,154
Commercial real estate:
Buildings, land and other	22,919				17,441				265				17,706			67			20,339
Construction	3,007				2,793				—				2,793			—			739
Consumer real estate	812				596				—				596			—			674
Consumer and other	—				—				—				—			—			159
Total	$	69,656			$	50,473			$	3,118			$	53,591		$	1,680		$	49,636
2013
Commercial and industrial:
Energy	$	545			$	531			$	—			$	531		$	—		$	428
Other commercial	31,429				15,337				7,004				22,341			4,140			34,894
Commercial real estate:
Buildings, land and other	27,792				15,697				8,870				24,567			2,786			34,633
Construction	—				—				—				—			—			634
Consumer real estate	907				745				—				745			—			804
Consumer and other	334				278				—				278			—			348
Total	$	61,007			$	32,588			$	15,874			$	48,462		$	6,926		$	71,741
2012
Commercial and industrial:
Energy	$	1,255			$	—			$	1,069			$	1,069		$	900		$	214
Other commercial	56,784				21,709				19,096				40,805			4,200			42,630
Commercial real estate:
Buildings, land and other	44,652				19,010				17,149				36,159			3,137			40,258
Construction	1,497				1,100				—				1,100			—			1,392
Consumer real estate	961				864				—				864			—			1,617
Consumer and other	428				400				—				400			—			469
Total	$	105,577			$	43,083			$	37,314			$	80,397		$	8,237		$	86,580
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, reductions in collateral and other actions intended to minimize potential losses. Troubled debt restructurings during 2014, 2013 and 2012 are set forth in the following table.
	2014								2013							2012
	Balance at				Balance at				Balance at				Balance at			Balance at			Balance at
	Restructure				Year-end				Restructure				Year-end			Restructure			Year-end
Commercial and industrial:
Energy	$	—			$	—			$	528			$	531		$	—		$	—
Other commercial	5,795				5,391				6,334				4,937			1,602			1,478
Commercial real estate:
Buildings, land and other	3,121				2,948				7,964				5,747			714			710
Consumer real estate	—				—				—				—			—			—
Consumer	—				—				7				—			—			—
	$	8,916			$	8,339			$	14,833			$	11,215		$	2,316		$	2,188
The modifications during the reported periods primarily related to extending the amortization periods, converting the loans to interest only for a limited period of time, consolidating notes and/or reducing collateral or interest rates. The modifications did not significantly impact the Corporation's determination of the allowance for loan losses. Approximately $2.7 million of commercial and industrial loans and $2.9 million of the commercial real estate loans restructured during 2014 were related to a single relationship that was previously restructured during 2013. As of December 31, 2014, there were no loans restructured during 2014 that were in excess of 90 days past due. During 2014, the Corporation charged off $627 thousand of commercial and industrial loans that were related to loans restructured during 2013. During 2014, the Corporation also foreclosed upon certain commercial real estate loans that were restructured during 2013. The Corporation recognized $500 thousand of other real estate owned and no charge-offs in connection with these foreclosures. The aforementioned charge-offs and foreclosures did not significantly impact the Corporation's determination of the allowance for loan losses. As of December 31, 2014, $8.3 million of the loans restructured in 2014 were on non-accrual status, while as of December 31, 2013, $10.1 million of the loans restructured in 2013 were on non-accrual status. See the section captioned “Non-accrual Loans” elsewhere in this note.
Credit Quality Indicators. As part of the on-going monitoring of the credit quality of the Corporation’s loan portfolio, management tracks certain credit quality indicators including trends related to (i) the weighted-average risk grade of commercial loans, (ii) the level of classified commercial loans, (iii) the delinquency status of consumer loans (see details above) (iv) net charge-offs, (v) non-performing loans (see details above) and (vi) the general economic conditions in the State of Texas.
The Corporation utilizes a risk grading matrix to assign a risk grade to each of its commercial loans. Loans are graded on a scale of 1 to 14. A description of the general characteristics of the 14 risk grades is as follows:
•	Grades 1, 2 and 3 - These grades include loans to very high credit quality borrowers of investment or near investment grade. These borrowers are generally publicly traded (grades 1 and 2), have significant capital strength, moderate leverage, stable earnings and growth, and readily available financing alternatives. Smaller entities, regardless of strength, would generally not fit in these grades.
•	Grades 4 and 5 - These grades include loans to borrowers of solid credit quality with moderate risk. Borrowers in these grades are differentiated from higher grades on the basis of size (capital and/or revenue), leverage, asset quality and the stability of the industry or market area.
•	Grades 6, 7 and 8 - These grades include “pass grade” loans to borrowers of acceptable credit quality and risk. Such borrowers are differentiated from Grades 4 and 5 in terms of size, secondary sources of repayment or they are of lesser stature in other key credit metrics in that they may be over-leveraged, under capitalized, inconsistent in performance or in an industry or an economic area that is known to have a higher level of risk, volatility, or susceptibility to weaknesses in the economy.
•	Grade 9 - This grade includes loans on management’s “watch list” and is intended to be utilized on a temporary basis for pass grade borrowers where a significant risk-modifying action is anticipated in the near term.
•	Grade 10 - This grade is for “Other Assets Especially Mentioned” in accordance with regulatory guidelines. This grade is intended to be temporary and includes loans to borrowers whose credit quality has clearly deteriorated and are at risk of further decline unless active measures are taken to correct the situation.
•	Grade 11 - This grade includes “Substandard” loans, in accordance with regulatory guidelines, for which the accrual of interest has not been stopped. By definition under regulatory guidelines, a “Substandard” loan has defined weaknesses which make payment default or principal exposure likely, but not yet certain. Such loans are apt to be dependent upon collateral liquidation, a secondary source of repayment or an event outside of the normal course of business.
•	Grade 12 - This grade includes “Substandard” loans, in accordance with regulatory guidelines, for which the accrual of interest has been stopped. This grade includes loans where interest is more than 120 days past due and not fully secured and loans where a specific valuation allowance may be necessary, but generally does not exceed 30% of the principal balance.
•	Grade 13 - This grade includes “Doubtful” loans in accordance with regulatory guidelines. Such loans are placed on non-accrual status and may be dependent upon collateral having a value that is difficult to determine or upon some near-term event which lacks certainty. Additionally, these loans generally have a specific valuation allowance in excess of 30% of the principal balance.
•	Grade 14 - This grade includes “Loss” loans in accordance with regulatory guidelines. Such loans are to be charged-off or charged-down when payment is acknowledged to be uncertain or when the timing or value of payments cannot be determined. “Loss” is not intended to imply that the loan or some portion of it will never be paid, nor does it in any way imply that there has been a forgiveness of debt.
In monitoring credit quality trends in the context of assessing the appropriate level of the allowance for loan losses, the Corporation monitors portfolio credit quality by the weighted-average risk grade of each class of commercial loan. Individual relationship managers review updated financial information for all pass grade loans to recalculate the risk grade on at least an annual basis. When a loan has a calculated risk grade of 9, it is still considered a pass grade loan; however, it is considered to be on management’s “watch list,” where a significant risk-modifying action is anticipated in the near term. When a loan has a calculated risk grade of 10 or higher, a special assets officer monitors the loan on an on-going basis. The following table presents weighted average risk grades for all commercial loans by class.
	December 31, 2014							December 31, 2013
	Weighted			Loans				Weighted			Loans
	Average							Average
	Risk Grade							Risk Grade
Commercial and industrial:
Energy
Risk grades 1-8	5.37			$	1,740,455			5.37			$	1,106,348
Risk grade 9	9			27,313				9			7,726
Risk grade 10	10			161				10			245
Risk grade 11	11			5,380				11			500
Risk grade 12	12			636				12			590
Risk grade 13	13			—				13			—
Total energy	5.45			$	1,773,945			5.4			$	1,115,409
Other commercial
Risk grades 1-8	5.93			$	3,785,171			5.95			$	3,507,963
Risk grade 9	9			65,166				9			74,766
Risk grade 10	10			54,519				10			89,878
Risk grade 11	11			55,034				11			92,917
Risk grade 12	12			31,683				12			21,389
Risk grade 13	13			2,225				13			4,754
Total other commercial	6.16			$	3,993,798			6.27			$	3,791,667
Commercial real estate:
Buildings, land and other
Risk grades 1-8	6.53			$	3,148,339			6.59			$	2,844,665
Risk grade 9	9			72,906				9			65,770
Risk grade 10	10			87,889				10			49,881
Risk grade 11	11			43,336				11			53,208
Risk grade 12	12			19,501				12			24,387
Risk grade 13	13			138				13			2,786
Total commercial real estate	6.76			$	3,372,109			6.83			$	3,040,697
Construction
Risk grades 1-8	6.91			$	617,805			7.05			$	418,999
Risk grade 9	9			8,003				9			1,301
Risk grade 10	10			1,323				10			5,931
Risk grade 11	11			64				11			408
Risk grade 12	12			2,793				12			—
Risk grade 13	13			—				13			—
Total construction	6.97			$	629,988			7.1			$	426,639
The Corporation has established maximum loan to value standards to be applied during the origination process of commercial and consumer real estate loans. The Corporation does not subsequently monitor loan-to-value ratios (either individually or on a weighted-average basis) for loans that are subsequently considered to be of a pass grade (grades 9 or better) and/or current with respect to principal and interest payments. As stated above, when an individual commercial real estate loan has a calculated risk grade of 10 or higher, a special assets officer analyzes the loan to determine whether the loan is impaired. At that time, the Corporation reassesses the loan to value position in the loan. If the loan is determined to be collateral dependent, specific allocations of the allowance for loan losses are made for the amount of any collateral deficiency. If a collateral deficiency is ultimately deemed to be uncollectible, the amount is charged-off. These loans and related assessments of collateral position are monitored on an individual, case-by-case basis. The Corporation does not monitor loan-to-value ratios on a weighted-average basis for commercial real estate loans having a calculated risk grade of 10 or higher. Nonetheless, there were six commercial real estate loans having a calculated risk grade of 10 or higher in excess of $5 million as of December 31, 2014, which totaled $44.4 million and had a weighted-average loan-to-value ratio of 53.7%. When an individual consumer real estate loan becomes past due by more than 10 days, the assigned relationship manager will begin collection efforts. The Corporation only reassesses the loan to value position in a consumer real estate loan if, during the course of the collections process, it is determined that the loan has become collateral dependent, and any collateral deficiency is recognized as a charge-off to the allowance for loan losses. Accordingly, the Corporation does not monitor loan-to-value ratios on a weighted-average basis for collateral dependent consumer real estate loans.
Generally, a commercial loan, or a portion thereof, is charged-off immediately when it is determined, through the analysis of any available current financial information with regards to the borrower, that the borrower is incapable of servicing unsecured debt, there is little or no prospect for near term improvement and no realistic strengthening action of significance is pending or, in the case of secured debt, when it is determined, through analysis of current information with regards to the Corporation’s collateral position, that amounts due from the borrower are in excess of the calculated current fair value of the collateral. Notwithstanding the foregoing, generally, commercial loans that become past due 180 cumulative days are charged-off. Generally, a consumer loan, or a portion thereof, is charged-off in accordance with regulatory guidelines which provide that such loans be charged-off when the Corporation becomes aware of the loss, such as from a triggering event that may include new information about a borrower’s intent/ability to repay the loan, bankruptcy, fraud or death, among other things, but in no case should the charge-off exceed specified delinquency time frames. Such delinquency time frames state that closed-end retail loans (loans with pre-defined maturity dates, such as real estate mortgages, home equity loans and consumer installment loans) that become past due 120 cumulative days and open-end retail loans (loans that roll-over at the end of each term, such as home equity lines of credit) that become past due 180 cumulative days should be classified as a loss and charged-off.
Net (charge-offs)/recoveries, segregated by class of loan, were as follows:
	2014				2013				2012
Commercial and industrial:
Energy	$	(1,237	)		$	(913	)		$	4
Other commercial	(2,911		)		(28,431		)		(13,627		)
Commercial real estate:
Buildings, land and other	(2,348		)		(381		)		698
Construction	348				256				78
Consumer real estate	(733		)		(719		)		(638		)
Consumer and other	(2,329		)		(2,409		)		(2,289		)
Total	$	(9,210	)		$	(32,597	)		$	(15,774	)
In assessing the general economic conditions in the State of Texas, management monitors and tracks the Texas Leading Index (“TLI”), which is produced by the Federal Reserve Bank of Dallas. The TLI is a single summary statistic that is designed to signal the likelihood of the Texas economy’s transition from expansion to recession and vice versa. Management believes this index provides a reliable indication of the direction of overall credit quality. The TLI is a composite of the following eight leading indicators: (i) Texas Value of the Dollar, (ii) U.S. Leading Index, (iii) real oil prices (iv) well permits, (v) initial claims for unemployment insurance, (vi) Texas Stock Index, (vii) Help-Wanted Index and (viii) average weekly hours worked in manufacturing. The TLI totaled 131.4 at November 30, 2014 (most recent date available) and 129.1 at December 31, 2013. A higher TLI value implies more favorable economic conditions.
Allowance for Loan Losses. The allowance for loan losses is a reserve established through a provision for loan losses charged to expense, which represents management’s best estimate of probable losses that have been incurred within the existing portfolio of loans. The allowance, in the judgment of management, is necessary to reserve for estimated loan losses and risks inherent in the loan portfolio. The Corporation’s allowance for loan loss methodology follows the accounting guidance set forth in U.S. generally accepted accounting principles and the Interagency Policy Statement on the Allowance for Loan and Lease Losses, which was jointly issued by U.S. bank regulatory agencies. In that regard, the Corporation’s allowance for loan losses includes allowance allocations calculated in accordance with ASC Topic 310, “Receivables” and allowance allocations calculated in accordance with ASC Topic 450, “Contingencies.” Accordingly, the methodology is based on historical loss experience by type of credit and internal risk grade, specific homogeneous risk pools and specific loss allocations, with adjustments for current events and conditions. The Corporation’s process for determining the appropriate level of the allowance for loan losses is designed to account for credit deterioration as it occurs. The provision for loan losses reflects loan quality trends, including the levels of and trends related to non-accrual loans, past due loans, potential problem loans, criticized loans and net charge-offs or recoveries, among other factors. The provision for loan losses also reflects the totality of actions taken on all loans for a particular period. In other words, the amount of the provision reflects not only the necessary increases in the allowance for loan losses related to newly identified criticized loans, but it also reflects actions taken related to other loans including, among other things, any necessary increases or decreases in required allowances for specific loans or loan pools.
The level of the allowance reflects management’s continuing evaluation of industry concentrations, specific credit risks, loan loss and recovery experience, current loan portfolio quality, present economic, political and regulatory conditions and unidentified losses inherent in the current loan portfolio. Portions of the allowance may be allocated for specific credits; however, the entire allowance is available for any credit that, in management’s judgment, should be charged off. While management utilizes its best judgment and information available, the ultimate determination of the appropriate level of the allowance is dependent upon a variety of factors beyond the Corporation’s control, including, among other things, the performance of the Corporation’s loan portfolio, the economy, changes in interest rates and the view of the regulatory authorities toward loan classifications. The Corporation monitors whether or not the allowance for loan loss allocation model, as a whole, calculates an appropriate level of allowance for loan losses that moves in direct correlation to the general macroeconomic and loan portfolio conditions the Corporation experiences over time.
The Corporation’s allowance for loan losses consists of three elements: (i) specific valuation allowances determined in accordance with ASC Topic 310 based on probable losses on specific loans; (ii) historical valuation allowances determined in accordance with ASC Topic 450 based on historical loan loss experience for similar loans with similar characteristics and trends, adjusted, as necessary, to reflect the impact of current conditions; and (iii) general valuation allowances determined in accordance with ASC Topic 450 based on general economic conditions and other risk factors both internal and external to the Corporation.
The allowances established for probable losses on specific loans are based on a regular analysis and evaluation of problem loans. Loans are classified based on an internal credit risk grading process that evaluates, among other things: (i) the obligor’s ability to repay; (ii) the underlying collateral, if any; and (iii) the economic environment and industry in which the borrower operates. This analysis is performed at the relationship manager level for all commercial loans. When a loan has a calculated grade of 10 or higher, a special assets officer analyzes the loan to determine whether the loan is impaired and, if impaired, the need to specifically allocate a portion of the allowance for loan losses to the loan. Specific valuation allowances are determined by analyzing the borrower’s ability to repay amounts owed, collateral deficiencies, the relative risk grade of the loan and economic conditions affecting the borrower’s industry, among other things.
Historical valuation allowances are calculated based on the historical gross loss experience of specific types of loans and the internal risk grade of such loans at the time they were charged-off. The Corporation calculates historical gross loss ratios for pools of similar loans with similar characteristics based on the proportion of actual charge-offs experienced to the total population of loans in the pool. The historical gross loss ratios are periodically (no less than annually) updated based on actual charge-off experience. A historical valuation allowance is established for each pool of similar loans based upon the product of the historical gross loss ratio and the total dollar amount of the loans in the pool. The Corporation’s pools of similar loans include similarly risk-graded groups of commercial and industrial loans, commercial real estate loans, consumer real estate loans and consumer and other loans.
The components of the general valuation allowance include (i) the additional reserves allocated as a result of applying an environmental risk adjustment factor to the base historical loss allocation, (ii) the additional reserves allocated for loans to borrowers in distressed industries and (iii) the additional reserves allocated for groups of similar loans with risk characteristics that exceed certain concentration limits established by management.
The environmental adjustment factor is based upon a more qualitative analysis of risk and is calculated through a survey of senior officers who are involved in credit making decisions at a corporate-wide and/or regional level. On a quarterly basis, survey participants rate the degree of various risks utilizing a numeric scale that translates to varying grades of high, moderate or low levels of risk. The results are then input into a risk-weighting matrix to determine an appropriate environmental risk adjustment factor. The various risks that may be considered in the determination of the environmental adjustment factor include, among other things, (i) the experience, ability and effectiveness of the bank’s lending management and staff; (ii) the effectiveness of the Corporation’s loan policies, procedures and internal controls; (iii) changes in asset quality; (iv) the impact of legislative and governmental influences affecting industry sectors; (v) the effectiveness of the internal loan review function; (vi) the impact of competition on loan structuring and pricing; and (vii) the impact of rising interest rates on portfolio risk. In periods where the surveyed risks are perceived to be higher, the risk-weighting matrix will generally result in a higher environmental adjustment factor, which, in turn will result in higher levels of general valuation allowance allocations. The opposite holds true in periods where the surveyed risks are perceived to be lower.
General valuation allowances also include amounts allocated for loans to borrowers in distressed industries. To determine the amount of the allocation for each loan portfolio segment, management calculates the weighted-average risk grade for all loans to borrowers in distressed industries by loan portfolio segment. A multiple is then applied to the amount by which the weighted-average risk grade for loans to borrowers in distressed industries exceeds the weighted-average risk grade for all pass-grade loans within the loan portfolio segment to derive an allocation factor for loans to borrowers in distressed industries. The amount of the allocation for each loan portfolio segment is the product of this allocation factor and the outstanding balance of pass-grade loans within the identified distressed industries that have a risk grade of 6 or higher. Management identifies potential distressed industries by analyzing industry trends related to delinquencies, classifications and charge-offs. At December 31, 2014 and 2013, certain segments of contractors were considered to be a distressed industry based on elevated levels of delinquencies, classifications and charge-offs relative to other industries within the Corporation’s loan portfolio. Furthermore, the Corporation determined, through a review of borrower financial information that, as a whole, contractors have experienced, among other things, decreased revenues, reduced backlog of work, compressed margins and little, if any, net income.
General valuation allowances also include allocations for groups of loans with similar risk characteristics that exceed certain concentration limits established by management and/or the Corporation’s board of directors. Concentration risk limits have been established, among other things, for certain industry concentrations, large balance and highly leveraged credit relationships that exceed specified risk grades, and loans originated with policy, credit and/or collateral exceptions that exceed specified risk grades. Additionally, general valuation allowances are provided for loans that did not undergo a separate, independent concurrence review during the underwriting process (generally those loans under $1.0 million at origination). The Corporation’s allowance methodology for general valuation allowances also includes a reduction factor for recoveries of prior charge-offs to compensate for the fact that historical loss allocations are based upon gross charge-offs rather than net. The adjustment for recoveries is based on the lower of annualized, year-to-date gross recoveries or the total gross recoveries for the preceding four quarters, adjusted, when necessary, for expected future trends in recoveries. General valuation allowances are also allocated for general macroeconomic risk related to current economic trends and other quantitative and qualitative factors that could impact the Corporation’s loan portfolio segments.
The following table presents details of the allowance for loan losses, segregated by loan portfolio segment.
	Commercial				Commercial				Consumer				Consumer			Unallocated			Total
	and				Real Estate				Real Estate				and Other
	Industrial
31-Dec-14
Historical valuation allowances	$	32,421			$	14,684			$	2,017			$	10,482		$	—		$	59,604
Specific valuation allowances	1,613				67				—				—			—			1,680
General valuation allowances:
Environmental risk adjustment	6,773				3,547				474				2,683			—			13,477
Distressed industries	3,090				3				—				—			—			3,093
Excessive industry concentrations	2,114				378				—				—			—			2,492
Large relationship concentrations	2,248				1,559				—				—			—			3,807
Highly-leveraged credit relationships	3,958				1,347				—				—			—			5,305
Policy exceptions	1,907				875				—				—			—			2,782
Credit and collateral exceptions	1,483				681				—				—			—			2,164
Loans not reviewed by concurrence	2,110				2,284				2,336				1,176			—			7,906
Adjustment for recoveries	(6,234		)		(1,800		)		(364		)		(7,439		)	—			(15,837		)
General macroeconomic risk	7,709				3,538				715				1,107			—			13,069
Total	$	59,192			$	27,163			$	5,178			$	8,009		$	—		$	99,542
31-Dec-13
Historical valuation allowances	$	29,357			$	13,042			$	2,644			$	8,695		$	—		$	53,738
Specific valuation allowances	4,140				2,786				—				—			—			6,926
General valuation allowances:
Environmental risk adjustment	5,497				3,314				664				2,331			—			11,806
Distressed industries	7,812				384				—				—			—			8,196
Excessive industry concentrations	1,499				367				—				—			—			1,866
Large relationship concentrations	1,529				1,081				—				—			—			2,610
Highly-leveraged credit relationships	4,535				619				—				—			—			5,154
Policy exceptions	—				—				—				—			2,492			2,492
Credit and collateral exceptions	—				—				—				—			1,398			1,398
Loans not reviewed by concurrence	2,009				2,201				2,250				1,064			—			7,524
Adjustment for recoveries	(3,588		)		(1,204		)		(328		)		(7,080		)	—			(12,200		)
General macroeconomic risk	—				—				—				—			2,928			2,928
Total	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
The Corporation monitors whether or not the allowance for loan loss allocation model, as a whole, calculates an appropriate level of allowance for loan losses that moves in direct correlation to the general macroeconomic and loan portfolio conditions the Corporation experiences over time. In assessing the general macroeconomic trends/conditions, the Corporation analyzes trends in the components of the TLI, as well as any available information related to regional, national and international economic conditions and events and the impact such conditions and events may have on the Corporation and its customers. With regard to assessing loan portfolio conditions, the Corporation analyzes trends in weighted-average portfolio risk-grades, classified and non-performing loans and charge-off activity. In periods where general macroeconomic and loan portfolio conditions are in a deteriorating trend or remain at deteriorated levels, based on historical trends, the Corporation would expect to see the allowance for loan loss allocation model, as a whole, calculate higher levels of required allowances than in periods where general macroeconomic and loan portfolio conditions are in an improving trend or remain at an elevated level, based on historical trends.
The following table details activity in the allowance for loan losses by portfolio segment for 2014, 2013 and 2012. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
	Commercial				Commercial				Consumer				Consumer			Unallocated			Total
	and				Real Estate				Real Estate				and Other
	Industrial
2014
Beginning balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
Provision for loan losses	10,550				6,573				681				5,328			(6,818		)	16,314
Charge-offs	(13,820		)		(3,800		)		(1,097		)		(9,768		)	—			(28,485		)
Recoveries	9,672				1,800				364				7,439			—			19,275
Net charge-offs	(4,148		)		(2,000		)		(733		)		(2,329		)	—			(9,210		)
Ending balance	$	59,192			$	27,163			$	5,178			8,009			$	—		$	99,542
Period-end amount allocated to:
Loans individually evaluated for impairment	$	11,836			$	1,164			$	—			$	—		$	—		$	13,000
Loans collectively evaluated for impairment	47,356				25,999				5,178				8,009			—			86,542
Ending balance	$	59,192			$	27,163			$	5,178			$	8,009		$	—		$	99,542
2013
Beginning balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
Provision for loan losses	27,970				(6,631		)		697				3,912			(5,366		)	20,582
Charge-offs	(32,932		)		(1,329		)		(1,047		)		(9,489		)	—			(44,797		)
Recoveries	3,588				1,204				328				7,080			—			12,200
Net charge-offs	(29,344		)		(125		)		(719		)		(2,409		)	—			(32,597		)
Ending balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
Period-end amount allocated to:
Loans individually evaluated for impairment	$	16,682			$	3,914			$	—			$	—		$	—		$	20,596
Loans collectively evaluated for impairment	36,108				18,676				5,230				5,010			6,818			71,842
Ending balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
2012
Beginning balance	$	42,774			$	20,912			$	3,540			$	12,635		$	30,286		$	110,147
Provision for loan losses	25,013				7,658				2,350				(6,839		)	(18,102		)	10,080
Charge-offs	(18,493		)		(3,951		)		(1,495		)		(9,101		)	—			(33,040		)
Recoveries	4,870				4,727				857				6,812			—			17,266
Net charge-offs	(13,623		)		776				(638		)		(2,289		)	—			(15,774		)
Ending balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
Period-end amount allocated to:
Loans individually evaluated for impairment	$	13,171			$	4,366			$	—			$	—		$	—		$	17,537
Loans collectively evaluated for impairment	40,993				24,980				5,252				3,507			12,184			86,916
Ending balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
The Corporation’s recorded investment in loans as of December 31, 2014 and 2013 related to each balance in the allowance for loan losses by portfolio segment and detailed on the basis of the impairment methodology used by the Corporation was as follows:
	Commercial				Commercial				Consumer				Consumer			Unearned			Total
	and				Real Estate				Real Estate				and Other			Discounts
	Industrial
2014
Loans individually evaluated for impairment	$	149,638			$	155,044			$	596			$	—		$	—		$	305,278
Loans collectively evaluated for impairment	5,618,105				3,847,053				848,455				393,601			(24,957		)	10,682,257
Ending balance	$	5,767,743			$	4,002,097			$	849,051			$	393,601		$	(24,957	)	$	10,987,535
2013
Loans individually evaluated for impairment	$	210,273			$	136,601			$	745			$	278		$	—		$	347,897
Loans collectively evaluated for impairment	4,696,803				3,330,735				807,459				357,838			(25,032		)	9,167,803
Ending balance	$	4,907,076			$	3,467,336			$	808,204			$	358,116		$	(25,032	)	$	9,515,700

Premises_and_Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment
	Year-end premises and equipment were as follows:
		2014			2013
	Land	$	102,334		$	97,095
	Buildings	240,430			231,066
	Furniture and equipment	103,603			212,169
	Leasehold improvements	60,902			61,221
	Construction in progress	118,367			10,074
		625,636			611,625
	Less accumulated depreciation and amortization	(182,748		)	(298,294		)
	Total premises and equipment, net	$	442,888		$	313,331
	Depreciation and amortization of premises and equipment totaled $23.5 million in 2014, $22.5 million in 2013 and $21.8 million in 2012.

Goodwill_and_Other_Intangible_

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets
	Goodwill and other intangible assets are presented in the table below. During 2014, the Corporation preliminarily recorded goodwill totaling $117.3 million and a core deposit intangible asset totaling $9.3 million in connection with the acquisition of WNB. See Note 2 - Mergers and Acquisitions.
	Goodwill. Year-end goodwill was as follows:
		2014		2013
	Goodwill	$	653,950	$	536,649
	Other Intangible Assets. Year-end other intangible assets were as follows:
		Gross		Accumulated			Net
		Intangible		Amortization			Intangible
		Assets					Assets
	2014
	Core deposits	$	44,266	$	(34,591	)	$	9,675
	Customer relationships	5,771		(3,643		)	2,128
	Non-compete agreements	725		(403		)	322
		$	50,762	$	(38,637	)	$	12,125
	2013
	Core deposits	$	34,966	$	(31,961	)	$	3,005
	Customer relationships	7,870		(5,042		)	2,828
	Non-compete agreements	1,135		(623		)	512
		$	43,971	$	(37,626	)	$	6,345
	Other intangible assets are amortized on an accelerated basis over their estimated lives, which range from 5 to 10 years. Amortization expense related to intangible assets totaled $3.5 million in 2014, $3.1 million in 2013, and $3.9 million in 2012. The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2014 is as follows:
	2015	$	3,324
	2016	2,413
	2017	1,619
	2018	1,346
	2019	1,102
	Thereafter	2,321
		$	12,125

Deposits

Deposits	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Deposits	Deposits
	Year-end deposits were as follows:
		2014		2013
	Non-interest-bearing demand deposits:
	Commercial and individual	$	9,256,045	$	7,445,656
	Correspondent banks	429,000		427,134
	Public funds	464,016		438,359
	Total non-interest-bearing demand deposits	10,149,061		8,311,149
	Interest-bearing deposits:
	Private accounts:
	Savings and interest checking	4,743,963		4,020,313
	Money market accounts	7,860,403		6,883,869
	Time accounts of $100,000 or more	490,209		508,441
	Time accounts under $100,000	454,220		438,800
	Total private accounts	13,548,795		11,851,423
	Public funds:
	Savings and interest checking	326,090		305,976
	Money market accounts	57,145		56,015
	Time accounts of $100,000 or more	53,684		160,637
	Time accounts under $100,000	1,155		3,586
	Total public funds	438,074		526,214
	Total interest-bearing deposits	13,986,869		12,377,637
	Total deposits	$	24,135,930	$	20,688,786
	The following table presents additional information about the Corporation’s year-end deposits:
		2014		2013
	Deposits from the Certificate of Deposit Account Registry Service (CDARS)	$	22	$	200
	Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB)	149		—
	Deposits from foreign sources (primarily Mexico)	744,295		769,970
	Deposits from certain directors, executive officers and their affiliates	176,821		144,216
	Scheduled maturities of time deposits, including both private and public funds, at December 31, 2014 were as follows:
	2015	$	857,857
	2016	140,882
	2017	379
	2018	92
	2019	58
		$	999,268
	Scheduled maturities of time deposits in amounts of $100,000 or more, including both private and public funds, at December 31, 2014, were as follows:
	Due within 3 months or less	$	228,010
	Due after 3 months and within 6 months	97,194
	Due after 6 months and within 12 months	142,973
	Due after 12 months	75,716
		$	543,893

Borrowed_Funds

Borrowed Funds	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Borrowed Funds	Borrowed Funds
	Federal Funds Purchased and Securities Sold Under Agreements to Repurchase. Federal funds purchased are short-term borrowings that typically mature within one to ninety days. Federal funds purchased totaled $12.0 million and $200 thousand at December 31, 2014 and 2013. Securities sold under agreements to repurchase are secured short-term borrowings that typically mature within thirty to ninety days. Securities sold under agreements to repurchase are stated at the amount of cash received in connection with the transaction. The Corporation may be required to provide additional collateral based on the fair value of the underlying securities. Securities sold under agreements to repurchase totaled $791.1 million and $668.1 million at December 31, 2014 and 2013.
	Subordinated Notes Payable. In February 2007, the Corporation issued $100 million of 5.75% fixed-to-floating rate subordinated notes that mature on February 15, 2017. The notes, which qualify as Tier 2 capital for Cullen/Frost under the capital rules in effect at December 31, 2014 (see Note 10 - Capital and Regulatory Matters), had an interest rate of 5.75% per annum, payable semi-annually on each February 15 and August 15, commencing on August 15, 2007 until February 15, 2012. From February 15, 2012, to but excluding the maturity date or date of earlier redemption and commencing on May 15, 2012, the notes bear interest at a rate per annum equal to three-month LIBOR for the related interest period plus 0.53% (0.76% and 0.77% at December 31, 2014 and 2013), payable quarterly on each February 15, May 15, August 15 and November 15. The notes are subordinated in right of payment to all of the Corporation's senior indebtedness and effectively subordinated to all existing and future debt and all other liabilities of the Corporation's subsidiaries. The notes cannot be accelerated except in the event of bankruptcy or the occurrence of certain other events of bankruptcy, insolvency or reorganization. The notes mature on February 15, 2017. The Corporation may elect to redeem the notes (subject to regulatory approval), in whole or in part, on any interest payment date on or after February 15, 2012 at a redemption price equal to 100% of the principal amount plus any accrued and unpaid interest. Unamortized debt issuance costs related to these notes, which are included in other assets, totaled $250 thousand and $370 thousand at December 31, 2014 and 2013. Proceeds from sale of the notes were used to fund a portion of the redemption of certain junior subordinated deferrable interest debentures.
	Junior Subordinated Deferrable Interest Debentures. At December 31, 2014 and 2013, the Corporation had $123.7 million of junior subordinated deferrable interest debentures issued to Cullen/Frost Capital Trust II (“Trust II”), a wholly owned Delaware statutory business trust. Unamortized debt issuance costs related to Trust II, which are included in other assets, totaled $1.1 million and $1.2 million at December 31, 2014 and 2013. At December 31, 2014, the Corporation also had $13.4 million of junior subordinated deferrable interest debentures issued to WNB Capital Trust I (“WNB Trust”), a wholly owned Delaware statutory business trust acquired in connection with the acquisition of WNB during the second quarter of 2014. Trust II and WNB Trust are variable interest entities for which the Corporation is not the primary beneficiary. As such, the accounts of Trust II and WNB Trust are not included in the Corporation’s consolidated financial statements. See Note 1 - Summary of Significant Accounting Policies for additional information about the Corporation’s consolidation policy. Details of the Corporation’s transactions with the capital trust are presented below.
	Trust II was formed in 2004 for the purpose of issuing $120 million of floating rate (three-month LIBOR plus a margin of 1.55%) trust preferred securities, which represent beneficial interests in the assets of the trust. The trust preferred securities will mature on March 1, 2034 and are redeemable with the approval of the Federal Reserve Board in whole or in part at the option of the Corporation at any time after March 1, 2009 and in whole at any time upon the occurrence of certain events affecting their tax or regulatory capital treatment. Distributions on the trust preferred securities are payable quarterly in arrears on March 1, June 1, September 1 and December 1 of each year. Trust II also issued $3.7 million of common equity securities to Cullen/Frost. The proceeds of the offering of the trust preferred securities and common equity securities were used to purchase $123.7 million of floating rate (three-month LIBOR plus a margin of 1.55%, which was equal to 1.78% and 1.79% at December 31, 2014 and 2013) junior subordinated deferrable interest debentures issued by the Corporation, which have terms substantially similar to the trust preferred securities. In October 2008, the Corporation entered into an interest rate swap contract on the junior subordinated deferrable interest debentures that effectively fixed the interest rate on the debentures for a period of five years, terminating in October 2013. See Note 16 - Derivative Financial Instruments.
	WNB Trust was formed in 2004 by WNB for the purpose of issuing $13.0 million of floating rate (three-month LIBOR plus a margin of 2.35%) trust preferred securities, which represent beneficial interests in the assets of the trust. The trust preferred securities will mature on July 23, 2034 and are redeemable with the approval of the Federal Reserve Board in whole or in part at the option of the Corporation at any time after July 23, 2009 and in whole at any time upon the occurrence of certain events affecting their tax or regulatory capital treatment. Distributions on the trust preferred securities are payable quarterly in arrears on January 23, April 23, July 23 and October 23 of each year. WNB Trust also issued $403 thousand of common equity securities to WNB. The proceeds of the offering of the trust preferred securities and common equity securities were used to purchase $13.4 million of floating rate (three-month LIBOR plus a margin of 2.35%, which was equal to 2.58% at December 31, 2014) junior subordinated deferrable interest debentures issued by WNB, which have terms substantially similar to the trust preferred securities.
	The Corporation has the right at any time during the term of the debentures issued to Trust II and WNB Trust to defer payments of interest at any time or from time to time for an extension period not exceeding 20 consecutive quarterly periods with respect to each extension period. Under the terms of the debentures, in the event that under certain circumstances there is an event of default under the debentures or the Corporation has elected to defer interest on the debentures, the Corporation may not, with certain exceptions, declare or pay any dividends or distributions on its capital stock or purchase or acquire any of its capital stock.
	Payments of distributions on the trust preferred securities and payments on redemption of the trust preferred securities are guaranteed by the Corporation on a limited basis. The Corporation is obligated by agreement to pay any costs, expenses or liabilities of Trust II and WNB Trust other than those arising under the trust preferred securities. The obligations of the Corporation under the junior subordinated debentures, the related indentures, the trust agreements establishing the trusts, the guarantees and the agreements as to expenses and liabilities, in the aggregate, constitute a full and unconditional guarantee by the Corporation of Trust II’s and WNB Trust's obligations under the trust preferred securities.
	Although the accounts of Trust II and WNB Trust are not included in the Corporation’s consolidated financial statements, the $120.0 million in trust preferred securities issued by Trust II and the $13.0 million in trust preferred securities issued by WNB Trust are included in the Tier 1 capital of Cullen/Frost for regulatory capital purposes as of December 31, 2014 and, in the case of Trust II, December 31, 2013. Federal Reserve Board rules applicable as of December 31, 2014 limit the aggregate amount of restricted core capital elements (which includes trust preferred securities, among other things) that may be included in the Tier 1 capital of most bank holding companies to 25% of all core capital elements, including restricted core capital elements, net of goodwill less any associated deferred tax liability. Amounts of restricted core capital elements in excess of these limits generally may be included in Tier 2 capital. This quantitative limit did not preclude the Corporation from including the aggregate $133.0 million in trust preferred securities outstanding in Tier 1 capital as of December 31, 2014. As more fully discussed in Note 10 - Capital and Regulatory Matters, new rules related to the implementation of the Basel III capital framework will require the phase-out of certain hybrid securities, such as trust preferred securities, as Tier 1 capital of bank holding companies beginning January 1, 2015.

OffBalanceSheet_Arrangements_C

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies	Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies
	Financial Instruments with Off-Balance-Sheet Risk. In the normal course of business, the Corporation enters into various transactions, which, in accordance with generally accepted accounting principles are not included in its consolidated balance sheets. The Corporation 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 Corporation minimizes its exposure to loss under these commitments by subjecting them to credit approval and monitoring procedures.
	The Corporation enters into contractual commitments to extend credit, normally with fixed expiration dates or termination clauses, at specified rates and for specific purposes. Substantially all of the Corporation’s commitments to extend credit are contingent upon customers maintaining specific credit standards at the time of loan funding. Standby letters of credit are written conditional commitments issued by the Corporation to guarantee the performance of a customer to a third party. In the event the customer does not perform in accordance with the terms of the agreement with the third party, the Corporation would be required to fund the commitment. The maximum potential amount of future payments the Corporation could be required to make is represented by the contractual amount of the commitment. If the commitment were funded, the Corporation would be entitled to seek recovery from the customer. The Corporation’s policies generally require that standby letter of credit arrangements contain security and debt covenants similar to those contained in loan agreements.
	The Corporation considers the fees collected in connection with the issuance of standby letters of credit to be representative of the fair value of its obligation undertaken in issuing the guarantee. In accordance with applicable accounting standards related to guarantees, the Corporation defers fees collected in connection with the issuance of standby letters of credit. The fees are then recognized in income proportionately over the life of the standby letter of credit agreement. The deferred standby letter of credit fees represent the fair value of the Corporation’s potential obligations under the standby letter of credit guarantees.
	Year-end financial instruments with off-balance-sheet risk were as follows:
		2014		2013
	Commitments to extend credit	$	7,955,779	$	6,919,942
	Standby letters of credit	248,360		186,857
	Deferred standby letter of credit fees	1,942		1,450
	Credit Card Guarantees. The Corporation guarantees the credit card debt of certain customers to the merchant bank that issues the cards. At December 31, 2014 and 2013, the guarantees totaled approximately $8.9 million and $8.4 million, of which amounts, $1.5 million and $1.2 million were fully collateralized.
	Securities Lending. The Corporation lends certain customer securities to creditworthy brokers on behalf of those customers. If the borrower fails to return these securities, the Corporation indemnifies its customers based on the then current net realizable fair value of the securities. The Corporation holds collateral received in securities lending transactions as an agent. Accordingly, such collateral assets are not assets of the Corporation. The Corporation requires borrowers to provide collateral equal to or in excess of 100% of the fair value of the securities borrowed. The collateral is valued daily and additional collateral is requested as necessary. The maximum future payments guaranteed by the Corporation under these contractual agreements (representing the fair value of securities lent to brokers) totaled $2.5 billion at December 31, 2014. At December 31, 2014, the Corporation held pledged liquid assets with a fair value of $2.5 billion as collateral for these agreements.
	Lease Commitments. The Corporation leases certain office facilities and office equipment under operating leases. Rent expense for all operating leases totaled $28.2 million in 2014, $24.6 million in 2013 and $22.7 million in 2012. Future minimum lease payments due under non-cancelable operating leases at December 31, 2014 were as follows:
	2015	$	21,373
	2016	19,834
	2017	18,503
	2018	17,067
	2019	13,269
	Thereafter	77,000
		$	167,046
	It is expected that certain leases will be renewed, or equipment replaced with new leased equipment, as these leases expire. Aggregate future minimum rentals to be received under non-cancelable subleases greater than one year at December 31, 2014, were $209 thousand.
	The Corporation leases a branch facility from a partnership interest of a director. Payments related to this lease totaled $925 thousand in 2014, $871 thousand in 2013, and $902 thousand in 2012. The terms of the lease are substantially the same as those offered for comparable transactions with non-related parties at the time the lease transaction was consummated.
	Change in Control Agreements. The Corporation has change-in-control agreements with certain executive officers. Under these agreements, each covered person could receive, upon the effectiveness of a change-in-control, two to three times (depending on the person) his or her base compensation plus the target bonus established for the year, and any unpaid base salary and pro rata target bonus for the year in which the termination occurs, including vacation pay. Additionally, the executive’s insurance benefits will continue for two to three full years after the termination and all long-term incentive awards will immediately vest.
	Litigation. The Corporation is subject to various claims and legal actions that have arisen in the course of conducting business. Management does not expect the ultimate disposition of these matters to have a material adverse impact on the Corporation’s financial statements.

Capital_and_Regulatory_Matters

Capital and Regulatory Matters	12 Months Ended
	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Capital and Regulatory Matters	Capital and Regulatory Matters
	Regulatory Capital Requirements in Effect as of December 31, 2014. Banks and bank holding companies are subject to various regulatory capital requirements administered by state and federal banking agencies. Capital adequacy guidelines and, additionally for banks, prompt corrective action regulations, involve quantitative measures of assets, liabilities, and certain off-balance-sheet items calculated under regulatory accounting practices. Capital amounts and classifications are also subject to qualitative judgments by regulators about components, risk weighting and other factors.
	Quantitative measures established by regulations to ensure capital adequacy require the maintenance of minimum amounts and ratios (set forth in the table below) of total and Tier 1 capital (as defined in the regulations) to risk-weighted assets (as defined), and of Tier 1 capital to adjusted quarterly average assets (as defined).
	Cullen/Frost’s and Frost Bank’s Tier 1 capital consists of shareholders’ equity excluding unrealized gains and losses on securities available for sale, the accumulated gain or loss on effective cash flow hedging derivatives, the net actuarial gain/loss on the Corporation’s defined benefit post-retirement benefit plans, goodwill and other intangible assets. Tier 1 capital for Cullen/Frost also includes $144.5 million of 5.375% non-cumulative perpetual preferred stock and $133 million of trust preferred securities issued by its unconsolidated subsidiary trusts. Cullen/Frost’s and Frost Bank’s total capital is comprised of Tier 1 capital for each entity plus a permissible portion of the allowance for loan losses and outstanding subordinated debt. The Corporation’s aggregate $100 million of floating rate subordinated notes are not included in Tier 1 capital but the permissible portion (which decreases 20% per year during the final five years of the term of the notes) totaling $40 million at December 31, 2014 and $60 million at December 31, 2013, is included in total capital of Cullen/Frost.
	The Tier 1 and total capital ratios are calculated by dividing the respective capital amounts by risk-weighted assets. Risk-weighted assets are calculated based on regulatory requirements and include total assets, excluding goodwill and other intangible assets, allocated by risk weight category, and certain off-balance-sheet items (primarily loan commitments). The leverage ratio is calculated by dividing Tier 1 capital by adjusted quarterly average total assets, which exclude goodwill and other intangible assets.
	As further discussed below, in July 2013, Cullen/Frost’s and Frost Bank’s primary federal regulator, the Federal Reserve, published final rules establishing a new comprehensive capital framework for U.S. banking organizations which will become effective on January 1, 2015 (subject to a phase-in period for certain provisions).
	Year-end actual and required capital ratios for Cullen/Frost and Frost Bank were as follows:
		Actual				Minimum Required				Required to be
						for Capital Adequacy				Considered Well
						Purposes				Capitalized
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
	2014
	Total Capital to Risk-Weighted Assets
	Cullen/Frost	$	2,325,818	14.55	%	$	1,278,797	8	%	$	1,598,496	10	%
	Frost Bank	2,071,012		12.99		1,275,858		8		1,594,823		10
	Tier 1 Capital to Risk-Weighted Assets
	Cullen/Frost	2,186,276		13.68		639,398		4		959,098		6
	Frost Bank	1,979,415		12.41		637,929		4		956,894		6
	Leverage Ratio
	Cullen/Frost	2,186,276		8.16		1,072,035		4		1,340,043		5
	Frost Bank	1,979,415		7.4		1,070,109		4		1,337,636		5
	2013
	Total Capital to Risk-Weighted Assets
	Cullen/Frost	$	2,110,774	15.52	%	$	1,088,349	8	%	$	1,360,437	10	%
	Frost Bank	1,780,313		13.12		1,085,447		8		1,356,809		10
	Tier 1 Capital to Risk-Weighted Assets
	Cullen/Frost	1,958,336		14.39		544,175		4		816,262		6
	Frost Bank	1,707,307		12.58		542,724		4		814,085		6
	Leverage Ratio
	Cullen/Frost	1,958,336		8.49		922,728		4		1,153,410		5
	Frost Bank	1,707,307		7.42		920,107		4		1,150,134		5
	Management believes that, as of December 31, 2014, Cullen/Frost and its bank subsidiary, Frost Bank, were “well capitalized” based on the ratios presented above.
	Cullen/Frost and Frost Bank are subject to the regulatory capital requirements administered by the Federal Reserve and, for Frost Bank, the Federal Deposit Insurance Corporation (“FDIC”). Regulatory authorities can initiate certain mandatory actions if Cullen/Frost or Frost Bank fail to meet the minimum capital requirements, which could have a direct material effect on the Corporation’s financial statements. Management believes, as of December 31, 2014, that Cullen/Frost and Frost Bank meet all capital adequacy requirements to which they are subject.
	Trust Preferred Securities. In accordance with the applicable accounting standard related to variable interest entities, the accounts of the Corporation’s wholly owned subsidiary trust, Cullen/Frost Capital Trust II and WNB Capital Trust I, have not been included in the Corporation’s consolidated financial statements. However, the $133.0 million in trust preferred securities issued by these subsidiary trusts have been included in the Tier 1 capital of Cullen/Frost for regulatory capital purposes pursuant to guidance from the Federal Reserve. As more fully discussed below, new rules related to the implementation of the Basel III capital framework will require the phase-out of certain hybrid securities, such as trust preferred securities, as Tier 1 capital of bank holding companies beginning January 1, 2015.
	Preferred Stock. On February 15, 2013, the Corporation issued and sold 6,000,000 shares, or $150.0 million in aggregate liquidation preference, of it’s 5.375% Non-Cumulative Perpetual Preferred Stock, Series A, par value $0.01 and liquidation preference $25 per share (“Series A Preferred Stock”). Dividends on the Series A Preferred stock, if declared, accrue and are payable quarterly, in arrears, at a rate of 5.375%. The Series A Preferred Stock qualifies as Tier 1 capital for the purposes of the regulatory capital calculations. The net proceeds from the issuance and sale of the Series A Preferred Stock, after deducting underwriting discount and commissions, and the payment of expenses, were approximately $144.5 million. The net proceeds from the offering were used to fund the accelerated share repurchase further discussed below.
	Stock Repurchase Plans. From time to time, the Corporation’s board of directors has authorized stock repurchase plans. In general, stock repurchase plans allow the Corporation to proactively manage its capital position and return excess capital to shareholders. Shares purchased under such plans also provide the Corporation with shares of common stock necessary to satisfy obligations related to stock compensation awards. The accelerated share repurchase discussed below was part of a stock repurchase program that was authorized by the Corporation’s board of directors in December 2012 to buy up to $150.0 million of the Corporation’s common stock. As of December 31, 2014, the Corporation did not have any active stock repurchase plans.
	Accelerated Share Repurchase. Concurrent with the issuance and sale of the Series A Preferred Stock, on February 12, 2013, the Corporation entered into an accelerated share repurchase agreement (the “ASR agreement”) with Goldman, Sachs & Co. (“Goldman Sachs”). Under the ASR agreement, the Corporation paid $144.0 million to Goldman Sachs and received from Goldman Sachs 1,905,077 shares of the Corporation’s common stock, representing approximately 80% of the estimated total number of shares to be repurchased. Goldman Sachs borrowed such shares delivered to the Corporation from stock lenders, and during the term of the ASR agreement, purchased shares in the open market to return to those stock lenders. Final settlement of the ASR agreement occurred on August 13, 2013 and the Corporation received an additional 331,671 shares. The total number of shares that the Corporation repurchased was based on the volume-weighted-average price per share of the Corporation’s common stock during the repurchase period as adjusted pursuant to the terms and conditions of the ASR agreement.
	Dividend Restrictions. In the ordinary course of business, Cullen/Frost is dependent upon dividends from Frost Bank to provide funds for the payment of dividends to shareholders and to provide for other cash requirements. Banking regulations may limit the amount of dividends that may be paid. Approval by regulatory authorities is required if the effect of dividends declared would cause the regulatory capital of Frost Bank to fall below specified minimum levels. Approval is also required if dividends declared exceed the net profits for that year combined with the retained net profits for the preceding two years. Under the foregoing dividend restrictions and while maintaining its “well capitalized” status, at December 31, 2014, Frost Bank could pay aggregate dividends of up to $363.9 million to Cullen/Frost without prior regulatory approval.
	Under the terms of the junior subordinated deferrable interest debentures that Cullen/Frost has issued to Cullen/Frost Capital Trust II and WNB Capital Trust I, Cullen/Frost has the right at any time during the term of the debentures to defer the payment of interest at any time or from time to time for an extension period not exceeding 20 consecutive quarterly periods with respect to each extension period. In the event that the Corporation has elected to defer interest on the debentures, the Corporation may not, with certain exceptions, declare or pay any dividends or distributions on its capital stock or purchase or acquire any of its capital stock.
	Under the terms of the Series A Preferred Stock, in the event that the Corporation does not declare and pay dividends on the Series A Preferred Stock for the most recent dividend period, the Corporation may not, with certain exceptions, declare or pay dividends on, or purchase, redeem or otherwise acquire, shares of its common stock or any securities of the Corporation that rank junior to the Series A Preferred Stock.
	Basel III Capital Rules Effective January 1, 2015. In July 2013, Cullen/Frost’s and Frost Bank’s primary federal regulator, the Federal Reserve, published final rules (the “Basel III Capital Rules”) establishing a new comprehensive capital framework for U.S. banking organizations. The rules implement the Basel Committee’s December 2010 framework known as “Basel III” for strengthening international capital standards as well as certain provisions of the Dodd-Frank Act. The Basel III Capital Rules substantially revise the risk-based capital requirements applicable to bank holding companies and depository institutions, including Cullen/Frost and Frost Bank, compared to the current U.S. risk-based capital rules. The Basel III Capital Rules define the components of capital and address other issues affecting the numerator in banking institutions’ regulatory capital ratios. The Basel III Capital Rules also address risk weights and other issues affecting the denominator in banking institutions’ regulatory capital ratios and replace the existing risk-weighting approach, which was derived from the Basel I capital accords of the Basel Committee, with a more risk-sensitive approach based, in part, on the standardized approach in the Basel Committee’s 2004 “Basel II” capital accords. The Basel III Capital Rules also implement the requirements of Section 939A of the Dodd-Frank Act to remove references to credit ratings from the federal banking agencies’ rules. The Basel III Capital Rules are effective for Cullen/Frost and Frost Bank on January 1, 2015 (subject to a phase-in period for certain provisions).

Earnings_Per_Common_Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share
	Earnings Per Common Share. Earnings per common share is computed using the two-class method. Basic earnings per common share is computed by dividing net earnings allocated to common stock by the weighted-average number of common shares outstanding during the applicable period, excluding outstanding participating securities. Participating securities include non-vested stock awards/stock units and deferred stock units, though no actual shares of common stock related to non-vested stock units and deferred stock units have been issued. Non-vested stock awards/stock units and deferred stock units are considered participating securities because holders of these securities receive non-forfeitable dividends at the same rate as holders of the Corporation’s common stock. Diluted earnings per common share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation using the treasury stock method.
	The following table presents a reconciliation of net income available to common shareholders, net earnings allocated to common stock and the number of shares used in the calculation of basic and diluted earnings per common share.
		2014		2013		2012
	Net Income	$	277,977	$	237,866	$	237,952
	Less: Preferred stock dividends	8,063		6,719		—
	Net income available to common shareholders	269,914		231,147		237,952
	Less: Earnings allocated to participating securities	1,001		850		773
	Net earnings allocated to common stock	$	268,913	$	230,297	$	237,179
	Distributed earnings allocated to common stock	$	126,709	$	119,177	$	116,472
	Undistributed earnings allocated to common stock	142,204		111,120		120,707
	Net earnings allocated to common stock	$	268,913	$	230,297	$	237,179
	Weighted-average shares outstanding for basic earnings per common share	62,072,080		60,350,552		61,298,041
	Dilutive effect of stock compensation	901,448		765,858		345,341
	Weighted-average shares outstanding for diluted earnings per common share	62,973,528		61,116,410		61,643,382

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	Employee Benefit Plans
	Retirement Plans
	Profit Sharing Plans. The profit-sharing plan is a defined contribution retirement plan that covers employees who have completed at least one year of service and are age 21 or older. All contributions to the plan are made at the discretion of the Corporation and may be made without regard to current or accumulated profits. Contributions are allocated to eligible participants pro rata, based upon compensation, age and other factors. Plan participants self-direct the investment of allocated contributions by choosing from a menu of investment options. Account assets are subject to withdrawal restrictions and participants vest in their accounts after three years of service. The Corporation also maintains a separate non-qualified profit sharing plan for certain employees whose participation in the qualified profit sharing plan is limited. The plan offers such employees an alternative means of receiving comparable benefits. Expense related to these plans totaled $10.8 million in 2014, $11.4 million in 2013 and $9.2 million in 2012.
	Retirement Plan and Restoration Plan. The Corporation maintains a non-contributory defined benefit plan (the “Retirement Plan”) that was frozen as of December 31, 2001. The plan provides pension and death benefits to substantially all employees who were at least 21 years of age and had completed at least one year of service prior to December 31, 2001. Defined benefits are provided based on an employee’s final average compensation and years of service at the time the plan was frozen and age at retirement. The freezing of the plan provides that future salary increases will not be considered. The Corporation’s funding policy is to contribute yearly, at least the amount necessary to satisfy the funding standards of the Employee Retirement Income Security Act (“ERISA”).
	The Corporation’s Restoration of Retirement Income Plan (the “Restoration Plan”) provides benefits for eligible employees that are in excess of the limits under Section 415 of the Internal Revenue Code of 1986, as amended, that apply to the Retirement Plan. The Restoration Plan is designed to comply with the requirements of ERISA. The entire cost of the plan, which was also frozen as of December 31, 2001, is supported by contributions from the Corporation.
	The Corporation uses a December 31 measurement date for its defined benefit plans. Combined activity in the Corporation’s defined benefit pension plans was as follows:
		2014				2013				2012
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	163,876			$	178,158			$	157,855
	Interest cost	8,002				7,341				7,801
	Actuarial (gain) loss	34,438				(15,333		)		18,436
	Benefits paid	(6,679		)		(6,290		)		(5,934		)
	Benefit obligation at end of year	199,637				163,876				178,158
	Change in plan assets:
	Fair value of plan assets at beginning of year	164,769				145,901				137,253
	Actual return on plan assets	9,428				24,489				13,931
	Employer contributions	667				669				651
	Benefits paid	(6,679		)		(6,290		)		(5,934		)
	Fair value of plan assets at end of year	168,185				164,769				145,901
	Funded status of the plan at end of year and accrued (benefit) liability recognized	$	31,452			$	(893	)		$	32,257
	Accumulated benefit obligation at end of year	$	199,637			$	163,876			$	178,158
	Certain disaggregated information related to the Corporation’s defined benefit pension plans as of year-end was as follows:
		Retirement Plan								Restoration Plan
		2014				2013				2014			2013
	Projected benefit obligation	$	179,970			$	147,403			$	19,667		$	16,473
	Accumulated benefit obligation	179,970				147,403				19,667			16,473
	Fair value of plan assets	168,185				164,769				—			—
	Funded status of the plan at end of year and accrued (benefit) liability recognized	11,785				(17,366		)		19,667			16,473
	The components of the combined net periodic cost (benefit) for the Corporation’s defined benefit pension plans were as follows:
		2014				2013				2012
	Expected return on plan assets, net of expenses	$	(12,514	)		$	(11,087	)		$	(10,412	)
	Interest cost on projected benefit obligation	8,002				7,341				7,801
	Net amortization and deferral	2,687				6,558				5,709
	Net periodic cost (benefit)	$	(1,825	)		$	2,812			$	3,098
	Amounts related to the Corporation’s defined benefit pension plans recognized as a component of other comprehensive income were as follows:
		2014				2013				2012
	Net actuarial gain (loss)	$	(34,837	)		$	35,293			$	(9,405	)
	Deferred tax (expense) benefit	12,193				(12,353		)		3,292
	Other comprehensive income (loss), net of tax	$	(22,644	)		$	22,940			$	(6,113	)
	Amounts recognized as a component of accumulated other comprehensive loss as of year-end that have not been recognized as a component of the combined net period benefit cost of the Corporation’s defined benefit pension plans are presented in the following table. The Corporation expects to recognize approximately $7.0 million of the net actuarial loss reported in the following table as of December 31, 2014 as a component of net periodic benefit cost during 2015.
		2014				2013
	Net actuarial loss	$	(75,038	)		$	(40,201	)
	Deferred tax benefit	26,263				14,070
	Amounts included in accumulated other comprehensive loss, net of tax	$	(48,775	)		$	(26,131	)
	The weighted-average assumptions used to determine the benefit obligations as of the end of the years indicated and the net periodic benefit cost for the years indicated are presented in the table below. Because the plans were frozen, increases in compensation are not considered after 2001.
		2014			2013			2012
	Benefit obligations:
	Discount rate	4.2	%		5	%		4.2	%
	Net periodic benefit cost:
	Discount rate	5	%		4.2	%		5.05	%
	Expected return on plan assets	7.75			7.75			7.75
	Management uses an asset allocation optimization model to analyze the potential risks and rewards associated with various asset allocation strategies on a quarterly basis. As of December 31, 2014, management’s investment objective for the Corporation’s defined benefit plans is to achieve long-term growth. This strategy provides for a target asset allocation of approximately 65% invested in equity securities, approximately 32% invested in fixed income debt securities with any remainder invested in cash or short-term cash equivalents. The modeling process calculates, with a 90% confidence ratio, the potential risk associated with a given asset allocation and helps achieve adequate diversification of investment assets. The plan assets are reviewed annually to determine if the obligations can be met with the current investment mix and funding strategy.
	The major categories of assets in the Corporation’s Retirement Plan as of year-end are presented in the following table. Assets are segregated by the level of the valuation inputs within the fair value hierarchy established by ASC Topic 820 “Fair Value Measurements and Disclosures,” utilized to measure fair value (see Note 18 - Fair Value Measurements). The Corporation’s Restoration Plan is unfunded.
		2014				2013
	Level 1:
	Mutual funds	$	165,429			$	163,046
	Cash and cash equivalents	1,447				91
	Level 2:
	Corporate bonds and notes	653				893
	U.S. government agency securities	394				473
	States and political subdivisions	262				266
	Total fair value of plan assets	$	168,185			$	164,769
	Mutual funds include various equity, fixed-income and blended funds with varying investment strategies. Approximately 71% of mutual fund investments consist of equity investments as of December 31, 2014. The investment objective of equity funds is long-term capital appreciation with current income. The remaining mutual fund investments consist of U.S. fixed-income securities, including investment-grade U.S. Treasury securities, U.S. government agency securities and mortgage-backed securities, corporate bonds and notes and collateralized mortgage obligations. The investment objective of fixed-income funds is to maximize investment return while preserving investment principal. Corporate bonds and notes include investment-grade bonds and notes of U.S. companies from diversified industries. U.S. government agency securities include obligations of Ginnie Mae. States and political subdivisions include fixed income municipal securities. The Corporation’s investment strategies prohibit selling assets short and the use of derivatives. Additionally, the Corporation’s defined benefit plans do not directly invest in real estate, commodities, or private investments.
	The asset allocation optimization model is used to estimate the expected long-term rate of return for a given asset allocation strategy. Expectations of returns for each asset class are based on comprehensive reviews of historical data and economic/financial market theory. During periods with volatile interest rates and equity security prices, the model may call for changes in the allocation of plan investments to achieve desired returns. Management assumed a long-term rate of return of 7.75% in the determination of the net periodic benefit cost for 2014. The expected long-term rate of return on assets was selected from within the reasonable range of rates determined by historical real returns, net of inflation, for the asset classes covered by the plan’s investment policy and projections of inflation over the long-term period during which benefits are payable to plan participants.
As of December 31, 2014, expected future benefit payments related to the Corporation’s defined benefit plans were as follows:
2015	$	8,429
2016	11,991
2017	9,532
2018	9,988
2019	10,413
2020 through 2024	57,255
	$	107,608
The Corporation expects to contribute $1.1 million to the defined benefit plans during 2015.
Supplemental Executive Retirement Plan. The Corporation maintains a supplemental executive retirement plan (“SERP”) for one active key executive. The plan provides for target retirement benefits, as a percentage of pay, beginning at age 55. The target percentage is 45 percent of pay at age 55, increasing to 60 percent at age 60 and later. Benefits under the SERP are reduced, dollar-for-dollar, by benefits received under the profit sharing, non-qualified profit sharing, defined benefit retirement and restoration plans, described above, and any social security benefits. Expense related to this plan was not significant during 2014, 2013 and 2012.
Savings Plans
401(k) Plan and Thrift Incentive Plan. The Corporation maintains a 401(k) stock purchase plan that permits each participant to make before- or after-tax contributions in an amount not less than 2% and not exceeding 50% of eligible compensation and subject to dollar limits from Internal Revenue Service regulations. The Corporation matches 100% of the employee’s contributions to the plan based on the amount of each participant’s contributions up to a maximum of 6% of eligible compensation. Eligible employees must complete 90 days of service in order to enroll and vest in the Corporation’s matching contributions immediately. Expense related to the plan totaled $12.3 million in 2014, $11.5 million in 2013, and $10.8 million in 2012. The Corporation’s matching contribution is initially invested in the Cullen/Frost common stock fund. However, employees may immediately reallocate the Corporation’s matching portion, as well as invest their individual contribution, to any of a variety of investment alternatives offered under the 401(k) Plan.
The Corporation maintains a thrift incentive stock purchase plan to offer certain employees whose participation in the 401(k) plan is limited an alternative means of receiving comparable benefits. Expense related to this plan was not significant during 2014, 2013 and 2012.
Stock Compensation Plans
The Corporation has one active executive stock plan (the 2005 Omnibus Incentive Plan) and one active outside director stock plan (the 2007 Outside Directors Incentive Plan). The executive stock plan was established to help the Corporation retain and motivate key employees, while the outside director stock plan was established as a means to compensate outside directors for their service to the Corporation. Both of the plans have been approved by the Corporation’s shareholders. The Compensation and Benefits Committee (“Committee”) of the Corporation’s Board of Directors has sole authority to select the employees, establish the awards to be issued, and approve the terms and conditions of each award contract under the executive stock plans.
During 2005, the 2005 Omnibus Incentive Plan (“2005 Plan”) was established to replace all other previously approved executive stock plans and the remaining shares authorized for grant under the previous plan were canceled. Under the 2005 Plan, the Corporation may grant, among other things, nonqualified stock options, incentive stock options, stock awards, stock award units, stock appreciation rights, or any combination thereof to certain employees.
During 2007, the 2007 Outside Directors Incentive Plan (the “2007 Directors Plan”) was established to replace the previous plan. The 2007 Directors Plan allows the Corporation to grant nonqualified stock options, stock awards and stock award units to outside directors. Subject to the terms of the plan, stock options, stock awards and/or stock award units may be awarded in such number, and upon such terms, and at any time and from time to time as determined by the Committee.
Options awarded under the 2005 Plan during the periods presented have a ten-year life and generally vest in equal annual installments over a four-year period. Non-vested stock awards/stock units awarded under the 2005 Plan generally have a four-year-cliff vesting period. No options were awarded under the 2007 Directors Plan during the reported periods. Director deferred stock units awarded under the 2007 Directors Plan have immediate vesting. Upon retirement from the Corporation’s board of directors, non-employee directors will receive one share of the Corporation’s common stock for each deferred stock unit held. Outstanding non-vested stock units and director deferred stock units receive equivalent dividend payments as such dividends are declared on the Corporation’s common stock.
Each award from both plans is evidenced by an award agreement that specifies the option price, the duration of the option, the number of shares to which the option pertains, and such other provisions as the Committee determines. The option price for each grant is at least equal to the fair market value of a share of Cullen/Frost’s common stock on the date of grant. Options granted expire at such time as the Committee determines at the date of grant and in no event does the exercise period exceed a maximum of ten years. Upon a change-in-control of Cullen/Frost, as defined in the plans, all outstanding options and non-vested stock awards/units immediately vest.
A combined summary of activity in the Corporation’s active stock plans is presented in the following table.
							Non-Vested Stock						Stock Options
							Awards/Stock Units						Outstanding
							Outstanding
	Shares			Director			Number			Weighted-			Number		Weighted-
	Available			Deferred			of Shares			Average			of Shares		Average
	for Grant			Stock Units						Grant-Date					Exercise
				Outstanding						Fair Value					Price
Balance, January 1, 2012	1,963,455			22,092			169,530			$	50.33		4,968,822		$	51.49
Granted	(825,542	)		5,632			49,130			54.56			770,780		54.56
Stock options exercised	—			—			—			—			(206,336	)	50.96
Stock awards vested	—			—			(30,100	)		52.44			—		—
Forfeited	19,750			—			—			—			(19,750	)	50.49
Canceled/expired	(250	)		—			—			—			—		—
Balance, December 31, 2012	1,157,413			27,724			188,560			51.67			5,513,516		51.94
Authorized	2,293,660			—			—			—			—		—
Granted	(635,360	)		5,500			38,010			71.39			591,850		71.38
Stock options exercised	—			—			—			—			(1,319,786	)	52.02
Stock awards vested	—			—			(26,830	)		50.64			—		—
Forfeited	46,890			—			—			—			(46,890	)	46.05
Canceled/expired	—			—			—			—			—		—
Balance, December 31, 2013	2,862,603			33,224			199,740			55.32			4,738,690		54.35
Authorized	—			—			—			—			—		—
Granted	(955,443	)		5,643			32,050			78.92			917,750		78.93
Stock options exercised	—			—			—			—			(560,291	)	52.04
Stock awards/units vested	—			—			(56,300	)		52.46			—		—
Forfeited	66,267			—			—			—			(66,267	)	62.21
Canceled/expired	—			—			—			—			—		—
Balance, December 31, 2014	1,973,427			38,867			175,490			$	60.55		5,029,882		$	58.99
Of the shares available for grant included in the above table as of December 31, 2014, a total of 281,840 shares may be granted as full value awards, meaning awards other than in the form of stock options or stock appreciation rights, and which are settled by the issuance of shares.
Other information regarding options outstanding and exercisable as of December 31, 2014 is as follows:
										Options Outstanding							Options Exercisable
Range of										Number		Weighted-			Weighted-		Number	Weighted-
Exercise Prices										of Shares		Average			Average		of Shares	Average
												Exercise Price			Remaining			Exercise
															Contractual Life			Price
															in Years
$	45.01			to		$	50			946,265		$	48.26		5.58		760,240	$	49.91
50.01				to		55				2,273,190		52.61			5.58		1,907,700	52.24
55.01				to		60				334,075		57.63			1.88		334,075	57.63
70.01				to		75				576,602		71.38			8.84		140,613	71.38
75.01				to		80				899,750		78.94			9.8		—	—
						Total				5,029,882		58.99			6.46		3,142,628	53.11
The total intrinsic value of outstanding in-the-money stock options and outstanding in-the-money exercisable stock options was $66.5 million and $56.4 million at December 31, 2014.
Shares issued in connection with stock compensation awards are issued from available treasury shares. If no treasury shares are available, new shares are issued from available authorized shares. Shares issued in connection with stock compensation awards along with other related information were as follows:
	2014				2013				2012
New shares issued from available authorized shares	—				153,275				207,586
Issued from available treasury stock	601,851				1,179,551				15,600
Total	601,851				1,332,826				223,186
Proceeds from stock option exercises	$	29,158			$	68,653			$	10,516
Intrinsic value of stock options exercised	13,714				20,506				1,538
Fair value of stock awards/units vested	4,346				1,918				1,649
Stock-based Compensation Expense. Stock-based compensation expense is recognized ratably over the requisite service period for all awards. The service period generally matches the vesting period for most awards; however, the service period for certain executive officers does not extend past the date they reach 65 years of age. Stock-based compensation expense and the related income tax benefit was as follows:
	2014				2013				2012
Stock options	$	9,142			$	8,814			$	9,663
Non-vested stock awards/stock units	2,920				2,819				2,843
Deferred stock-units	441				330				330
Total	$	12,503			$	11,963			$	12,836
Income tax benefit	$	4,376			$	4,187			$	4,493
Unrecognized stock-based compensation expense at December 31, 2014 was as follows:
Stock options	$	22,066
Non-vested stock awards/stock units	2,437
Total	$	24,503
The weighted-average period over which the remaining unrecognized stock-based compensation expense related to stock options is expected to be recognized was 3.1 years as of December 31, 2014. The weighted-average period over which the remaining unrecognized stock-based compensation expense related to non-vested stock awards/stock units is expected to be recognized was 2.5 years as of December 31, 2014 .
Valuation of Stock-Based Compensation. The fair value of the Corporation’s employee stock options granted is estimated on the measurement date, which, for the Corporation, is the date of grant. The fair value of stock options is estimated using a binomial lattice-based valuation model that takes into account employee exercise patterns based on changes in the Corporation’s stock price and other variables, and allows for the use of dynamic assumptions about interest rates and expected volatility. The fair value of stock options granted prior to the fourth quarter of 2006 was estimated using the Black-Scholes option-pricing model.
The weighted-average fair value of stock options granted during 2014, 2013 and 2012 estimated using a binomial lattice-based valuation model, was $16.97, $13.74, and $11.07. The assumptions used to determine the fair value of options granted are detailed in the table below.
	2014			2013			2012
Weighted-average risk-free interest rate	2.33	%		2.65	%		1.85	%
Dividend yield	2.71			2.92			3.28
Weighted-average expected market price volatility	26.66			24.2			28.06
Weighted-average expected term	7.1 years			6.7 years			6.2 years
Expected volatility is based on the short-term historical volatility (estimated over the most recent two years) and the long-term historical volatility (estimated over a period at least equal to the contractual term of the options) of the Corporation’s stock, and other factors. A variance targeting methodology is utilized to estimate the convergence, or mean reversion, from short-term to long-term volatility within the model. In estimating the fair value of stock options under the binomial lattice-based valuation model, separate groups of employees that have similar historical exercise behavior are considered separately. The expected term of options granted is derived using a regression model and represents the period of time that options granted are expected to be outstanding. Certain groups of employees exhibit different behavior.
The fair value of non-vested stock awards/stock units and deferred stock units for the purposes of recognizing stock-based compensation expense is the market price of the stock on the measurement date, which, for the Corporation, is the date of the award.

Other_NonInterest_Income_and_E

Other Non-Interest Income and Expense	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Other Non-Interest Income and Expense	Other Non-Interest Income and Expense
	Other non-interest income and expense totals are presented in the following tables. Components of these totals exceeding 1% of the aggregate of total net interest income and total non-interest income for any of the years presented are stated separately.
		2014		2013		2012
	Other non-interest income:
	Other	$	32,256	$	34,531	$	30,703
	Total	$	32,256	$	34,531	$	30,703
	Other non-interest expense:
	Advertising, promotions and public relations	$	28,998	$	26,232	$	27,194
	Legal and other professional fees	27,365		26,132		22,341
	Check card expense	15,970		11,787		10,227
	Travel/meals and entertainment	14,813		13,571		13,049
	Other	80,510		74,355		66,658
	Total	$	167,656	$	152,077	$	139,469

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	Income tax expense was as follows:
		2014			2013			2012
	Current income tax expense	$	62,177		$	49,736		$	76,928
	Deferred income tax expense (benefit)	(4,130		)	3,279			(6,405		)
	Income tax expense, as reported	$	58,047		$	53,015		$	70,523
	Reported income tax expense differed from the amounts computed by applying the U.S. federal statutory income tax rate of 35% to income before income taxes as follows:
		2014			2013			2012
	Income tax expense computed at the statutory rate	$	117,608		$	101,808		$	107,966
	Effect of tax-exempt interest	(58,761		)	(46,535		)	(36,543		)
	Bank owned life insurance income	(1,116		)	(1,086		)	(1,413		)
	Other	316			(1,172		)	513
	Income tax expense, as reported	$	58,047		$	53,015		$	70,523
	Year-end deferred taxes were as follows:
		2014			2013
	Deferred tax assets:
	Allowance for loan losses	$	34,840		$	32,353
	Net actuarial loss on defined benefit post-retirement benefit plans	26,263			14,070
	Stock-based compensation	18,839			17,746
	Bonus accrual	6,118			5,301
	Gain on sale of assets	2,139			2,234
	Partnerships	1,911			2,208
	Transaction costs	1,794			565
	Other	5,272			4,489
	Total gross deferred tax assets	97,176			78,966
	Deferred tax liabilities:
	Net unrealized gain on securities available for sale and effective cash flow hedging derivatives	(102,626		)	(89,689		)
	Premises and equipment	(20,039		)	(21,192		)
	Defined benefit post-retirement benefit plans	(15,010		)	(14,137		)
	Intangible assets	(6,143		)	(7,253		)
	Leases	(4,952		)	(4,237		)
	Reserve for medical insurance	(3,017		)	(2,171		)
	Prepaid expenses	(1,639		)	(1,618		)
	Other	(341		)	(1,456		)
	Total gross deferred tax liabilities	(153,767		)	(141,753		)
	Net deferred tax asset (liability)	$	(56,591	)	$	(62,787	)
	No valuation allowance for deferred tax assets was recorded at December 31, 2014 and 2013 as management believes it is more likely than not that all of the deferred tax assets will be realized because they were supported by recoverable taxes paid in prior years. There were no unrecognized tax benefits during any of the reported periods.
	The Corporation files income tax returns in the U.S. federal jurisdiction. The Company is no longer subject to U.S. federal income tax examinations by tax authorities for years before 2011.

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss)
	The tax effects allocated to each component of other comprehensive income (loss) were as follows:
		Before Tax			Tax Expense,			Net of Tax
		Amount			(Benefit)			Amount
	2014
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	103,044		$	36,065		$	66,979
	Change in net unrealized gain on securities transferred to held to maturity	(35,441		)	(12,404		)	(23,037		)
	Reclassification adjustment for net (gains) losses included in net income	(38		)	(13		)	(25		)
	Total securities available for sale and transferred securities	67,565			23,648			43,917
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	(34,837		)	(12,193		)	(22,644		)
	Derivatives:
	Reclassification adjustment for gains on interest rate swaps on variable-rate loans included in net income	(30,604		)	(10,711		)	(19,893		)
	Total other comprehensive income (loss)	$	2,124		$	744		$	1,380
	2013
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	(115,245	)	$	(40,335	)	$	(74,910	)
	Change in net unrealized gain on securities transferred to held to maturity	(35,682		)	(12,489		)	(23,193		)
	Reclassification adjustment for net (gains) losses included in net income	(1,176		)	(412		)	(764		)
	Total securities available for sale and transferred securities	(152,103		)	(53,236		)	(98,867		)
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	35,293			12,353			22,940
	Derivatives:
	Change in the accumulated gain/loss on effective cash flow hedge derivatives	(49		)	(17		)	(32		)
	Reclassification adjustments for (gains) losses included in net income:
	Interest rate swaps on variable-rate loans	(37,380		)	(13,083		)	(24,297		)
	Interest rate swap on junior subordinated deferrable interest debentures	4,064			1,422			2,642
	Total derivatives	(33,365		)	(11,678		)	(21,687		)
	Total other comprehensive income (loss)	$	(150,175	)	$	(52,561	)	$	(97,614	)
	2012
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	33,412		$	11,694		$	21,718
	Change in net unrealized gain on securities transferred to held to maturity	(657		)	(230		)	(427		)
	Reclassification adjustment for net (gains) losses included in net income	(4,314		)	(1,510		)	(2,804		)
	Total securities available for sale and transferred securities	28,441			9,954			18,487
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	(9,405		)	(3,292		)	(6,113		)
	Derivatives:
	Change in the accumulated gain/loss on effective cash flow hedge derivatives	(783		)	(274		)	(509		)
	Reclassification adjustments for (gains) losses included in net income:
	Interest rate swaps on variable-rate loans	(37,380		)	(13,083		)	(24,297		)
	Interest rate swap on junior subordinated deferrable interest debentures	4,224			1,478			2,746
	Total derivatives	(33,939		)	(11,879		)	(22,060		)
	Total other comprehensive income (loss)	$	(14,903	)	$	(5,217	)	$	(9,686	)
	Activity in accumulated other comprehensive income, net of tax, was as follows:
		Securities			Defined			Derivatives			Accumulated
		Available			Benefit						Other
		For Sale			Plans						Comprehensive
											Income
	Balance January 1, 2014	$	146,672		$	(26,131	)	$	19,893		$	140,434
	Other comprehensive income (loss) before reclassification	43,942			(22,644		)	—			21,298
	Amounts reclassified from accumulated other comprehensive income (loss)	(25		)	—			(19,893		)	(19,918		)
	Net other comprehensive income (loss) during period	43,917			(22,644		)	(19,893		)	1,380
	Balance December 31, 2014	$	190,589		$	(48,775	)	$	—		$	141,814
	Balance January 1, 2013	$	245,539		$	(49,071	)	$	41,580		$	238,048
	Other comprehensive income (loss) before reclassification	(98,103		)	22,940			(32		)	(75,195		)
	Amounts reclassified from accumulated other comprehensive income (loss)	(764		)	—			(21,655		)	(22,419		)
	Net other comprehensive income (loss) during period	(98,867		)	22,940			(21,687		)	(97,614		)
	Balance December 31, 2013	$	146,672		$	(26,131	)	$	19,893		$	140,434
	Balance January 1, 2012	$	227,052		$	(42,958	)	$	63,640		$	247,734
	Other comprehensive income (loss) before reclassification	21,291			(6,113		)	(509		)	14,669
	Amounts reclassified from accumulated other comprehensive income (loss)	(2,804		)	—			(21,551		)	(24,355		)
	Net other comprehensive income (loss) during period	18,487			(6,113		)	(22,060		)	(9,686		)
Balance December 31, 2012	$	245,539		$	(49,071	)	$	41,580		$	238,048

Derivative_Financial_Instrumen

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments
	The fair value of derivative positions outstanding is included in accrued interest receivable and other assets and accrued interest payable and other liabilities in the accompanying consolidated balance sheets and in the net change in each of these financial statement line items in the accompanying consolidated statements of cash flows.
	Interest Rate Derivatives. The Corporation utilizes interest rate swaps, caps and floors to mitigate exposure to interest rate risk and to facilitate the needs of its customers. The Corporation’s objectives for utilizing these derivative instruments are described below:
	The Corporation has entered into certain interest rate swap contracts that are matched to specific fixed-rate commercial loans or leases that the Corporation has entered into with its customers. These contracts have been designated as hedging instruments to hedge the risk of changes in the fair value of the underlying commercial loan/lease due to changes in interest rates. The related contracts are structured so that the notional amounts reduce over time to generally match the expected amortization of the underlying loan/lease.
	During 2007, the Corporation entered into three interest rate swap contracts on variable-rate loans with a total notional amount of $1.2 billion. The interest rate swap contracts were designated as hedging instruments in cash flow hedges with the objective of protecting the overall cash flows from the Corporation’s monthly interest receipts on a rolling portfolio of $1.2 billion of variable-rate loans outstanding throughout the 84-month period beginning in October 2007 and ending in October 2014 from the risk of variability of those cash flows such that the yield on the underlying loans would remain constant. The Corporation terminated portions of the hedges and settled portions of the interest rate swap contracts during November 2009 and terminated the remaining portions of the hedges and settled the remaining portions of the interest rate swap contracts during November 2010. The accumulated gain on the interest rate swaps upon settlement was deferred and amortized over the original lives of the underlying swap contracts. The amortization of the deferred accumulated gain ended in October 2014. As of December 31, 2013, the deferred accumulated gain applicable to the settled interest rate swap contracts included in accumulated other comprehensive income totaled $30.6 million ($19.9 million on an after-tax basis), all of which was recognized in interest income during 2014.
	In October 2008, the Corporation entered into an interest rate swap contract on junior subordinated deferrable interest debentures with a total notional amount of $120.0 million. The interest rate swap contract was designated as a hedging instrument in a cash flow hedge with the objective of protecting the quarterly interest payments on the Corporation’s $120.0 million of junior subordinated deferrable interest debentures issued to Cullen/Frost Capital Trust II throughout the five-year period beginning in December 2008 and ending in December 2013 from the risk of variability of those payments resulting from changes in the three-month LIBOR interest rate. Under the swap, the Corporation paid a fixed interest rate of 5.47% and received a variable interest rate of three-month LIBOR plus a margin of 1.55% on a total notional amount of $120.0 million, with quarterly settlements. The swap terminated in December 2013.
	The Corporation has entered into certain interest rate swap, cap and floor contracts that are not designated as hedging instruments. These derivative contracts relate to transactions in which the Corporation enters into an interest rate swap, cap and/or floor with a customer while at the same time entering into an offsetting interest rate swap, cap and/or floor with another financial institution. In connection with each swap transaction, the Corporation agrees to pay interest to the customer on a notional amount at a variable interest rate and receive interest from the customer on a similar notional amount at a fixed interest rate. At the same time, the Corporation agrees to pay another financial institution the same fixed interest rate on the same notional amount and receive the same variable interest rate on the same notional amount. The transaction allows the Corporation’s customer to effectively convert a variable rate loan to a fixed rate. Because the Corporation acts as an intermediary for its customer, changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact the Corporation’s results of operations.
	The notional amounts and estimated fair values of interest rate derivative contracts outstanding at December 31, 2014 and 2013 are presented in the following table. The Corporation obtains dealer quotations to value its interest rate derivative contracts designated as hedges of cash flows, while the fair values of other interest rate derivative contracts are estimated utilizing internal valuation models with observable market data inputs.
		December 31, 2014								December 31, 2013
		Notional				Estimated				Notional			Estimated
		Amount				Fair Value				Amount			Fair Value
	Derivatives designated as hedges of fair value:
	Financial institution counterparties:
	Loan/lease interest rate swaps - assets	$	31,614			$	469			$	50,965		$	1,386
	Loan/lease interest rate swaps - liabilities	37,672				(3,179		)		43,631			(4,191		)
	Non-hedging interest rate derivatives:
	Financial institution counterparties:
	Loan/lease interest rate swaps - assets	69,842				719				195,234			9,573
	Loan/lease interest rate swaps - liabilities	765,979				(38,952		)		626,980			(32,469		)
	Loan/lease interest rate caps - assets	73,058				1,003				53,058			1,309
	Customer counterparties:
	Loan/lease interest rate swaps - assets	765,979				38,910				626,980			32,426
	Loan/lease interest rate swaps - liabilities	69,842				(719		)		195,234			(9,573		)
	Loan/lease interest rate caps - liabilities	73,058				(1,003		)		53,058			(1,309		)
	The weighted-average rates paid and received for interest rate swaps outstanding at December 31, 2014 were as follows:
		Weighted-Average
		Interest			Interest
		Rate			Rate
		Paid			Received
	Interest rate swaps:
	Fair value hedge loan/lease interest rate swaps	2.8	%		0.16	%
	Non-hedging interest rate swaps - financial institution counterparties	4.05			1.67
	Non-hedging interest rate swap - customer counterparties	1.67			4.05
	The weighted-average strike rate for outstanding interest rate caps was 2.99% at December 31, 2014.
	Commodity Derivatives. The Corporation enters into commodity swaps and option contracts that are not designated as hedging instruments primarily to accommodate the business needs of its customers. Upon the origination of a commodity swap or option contract with a customer, the Corporation simultaneously enters into an offsetting contract with a third party financial institution to mitigate the exposure to fluctuations in commodity prices.
	The notional amounts and estimated fair values of non-hedging commodity swap and option derivative positions outstanding are presented in the following table. The Corporation obtains dealer quotations and uses internal valuation models with observable market data inputs to value its commodity derivative positions.
				December 31, 2014							December 31, 2013
		Notional		Notional			Estimated				Notional		Estimated
		Units		Amount			Fair Value				Amount		Fair Value
	Financial institution counterparties:
	Oil - assets	Barrels		470			$	14,357			356		$	1,004
	Oil - liabilities	Barrels		197			(1,670		)		1,574		(2,704		)
	Natural gas - assets	MMBTUs		12,235			12,707				14,240		2,903
	Natural gas - liabilities	MMBTUs		16,755			(4,095		)		22,510		(3,212		)
	Customer counterparties:
	Oil - assets	Barrels		197			1,670				1,574		2,818
	Oil - liabilities	Barrels		470			(14,318		)		356		(991		)
	Natural gas - assets	MMBTUs		16,755			4,095				22,850		3,301
	Natural gas - liabilities	MMBTUs		12,235			(12,646		)		13,900		(2,805		)
	Foreign Currency Derivatives. The Corporation enters into foreign currency forward contracts that are not designated as hedging instruments primarily to accommodate the business needs of its customers. Upon the origination of a foreign currency denominated transaction with a customer, the Corporation simultaneously enters into an offsetting contract with a third party to negate the exposure to fluctuations in foreign currency exchange rates. The Corporation also utilizes foreign currency forward contracts that are not designated as hedging instruments to mitigate the economic effect of fluctuations in foreign currency exchange rates on foreign currency holdings and certain short-term, non-U.S. dollar denominated loans. The notional amounts and fair values of open foreign currency forward contracts were as follows:
				31-Dec-14							31-Dec-13
		Notional		Notional			Estimated				Notional		Estimated
		Currency		Amount			Fair Value				Amount		Fair Value
	Financial institution counterparties:
	Forward contracts – assets	EUR		936			$	7			1,175		$	5
	Forward contracts - assets	CAD		24,724			659				18,886		85
	Forward contracts – liabilities	GBP		544			(2		)		—		—
	Forward contracts - liabilities	EUR		—			—				494		(4		)
	Forward contracts - liabilities	CAD		—			—				14,078		(23		)
	Customer counterparties:
	Forward contracts – assets	CAD		—			—				14,055		45
	Forward contracts – liabilities	CAD		24,680			(615		)		18,859		(58		)
	Gains, Losses and Derivative Cash Flows. For fair value hedges, the changes in the fair value of both the derivative hedging instrument and the hedged item are included in other non-interest income or other non-interest expense. The extent that such changes in fair value do not offset represents hedge ineffectiveness. Net cash flows from interest rate swaps on commercial loans/leases designated as hedging instruments in effective hedges of fair value are included in interest income on loans. For cash flow hedges, the effective portion of the gain or loss due to changes in the fair value of the derivative hedging instrument is included in other comprehensive income, while the ineffective portion (indicated by the excess of the cumulative change in the fair value of the derivative over that which is necessary to offset the cumulative change in expected future cash flows on the hedge transaction) is included in other non-interest income or other non-interest expense. Net cash flows from interest rate swaps on variable-rate loans designated as hedging instruments in effective hedges of cash flows and the reclassification from other comprehensive income of deferred gains associated with the termination of those hedges are included in interest income on loans. Net cash flows from the interest rate swap on junior subordinated deferrable interest debentures designated as a hedging instrument in an effective hedge of cash flows were included in interest expense on junior subordinated deferrable interest debentures during 2013 and 2012. For non-hedging derivative instruments, gains and losses due to changes in fair value and all cash flows are included in other non-interest income and other non-interest expense.
	Amounts included in the consolidated statements of income related to interest rate derivatives designated as hedges of fair value were as follows:
	2014				2013				2012
Commercial loan/lease interest rate swaps:
Amount of gain (loss) included in interest income on loans	$	(2,014	)		$	(2,437	)		$	(2,587	)
Amount of (gain) loss included in other non-interest expense	3				4				46
Amounts included in the consolidated statements of income and in other comprehensive income for the period related to interest rate derivatives designated as hedges of cash flows were as follows:
	2014				2013				2012
Interest rate swaps/caps/floors on variable-rate loans:
Amount reclassified from accumulated other comprehensive income to interest income on loans	$	30,604			$	37,380			$	37,380
Interest rate swaps on junior subordinated deferrable interest debentures:
Amount reclassified from accumulated other comprehensive income to interest expense on junior subordinated deferrable interest debentures	—				4,064				4,224
Amount of gain (loss) recognized in other comprehensive income	—				(49		)		(783		)
No ineffectiveness related to interest rate derivatives designated as hedges of cash flows was recognized in the consolidated statements of income during the reported periods. The amortization of the deferred accumulated gain applicable to the settled interest rate swap contracts ended in October 2014. As of December 31, 2013, the deferred accumulated gain applicable to the settled interest rate swap contracts included in accumulated other comprehensive income totaled $30.6 million ($19.9 million on an after-tax basis), all of which was recognized in interest income during 2014.
As stated above, the Corporation enters into non-hedge related derivative positions primarily to accommodate the business needs of its customers. Upon the origination of a derivative contract with a customer, the Corporation simultaneously enters into an offsetting derivative contract with a third party. The Corporation recognizes immediate income based upon the difference in the bid/ask spread of the underlying transactions with its customers and the third party. Because the Corporation acts only as an intermediary for its customer, subsequent changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact the Corporation’s results of operations.
Amounts included in the consolidated statements of income related to non-hedging interest rate, commodity and foreign currency derivative instruments are presented in the table below.
	2014				2013				2012
Non-hedging interest rate derivatives:
Other non-interest income	$	1,786			$	1,441			$	4,722
Other non-interest expense	(2		)		(96		)		(116		)
Non-hedging commodity derivatives:
Other non-interest income	118				496				124
Non-hedging foreign currency derivatives:
Other non-interest income	162				175				—
Counterparty Credit Risk. Derivative contracts involve the risk of dealing with both bank customers and institutional derivative counterparties and their ability to meet contractual terms. Institutional counterparties must have an investment grade credit rating and be approved by the Corporation’s Asset/Liability Management Committee. The Corporation’s credit exposure on interest rate swaps is limited to the net favorable value and interest payments of all swaps by each counterparty, while the Corporation’s credit exposure on commodity swaps/options and foreign currency forward contracts is limited to the net favorable value of all contracts by each counterparty. Credit exposure may be reduced by the amount of collateral pledged by the counterparty. There are no credit-risk-related contingent features associated with any of the Corporation’s derivative contracts. Certain derivative contracts with upstream financial institution counterparties may be terminated with respect to a party in the transaction, if such party does not have at least a minimum level rating assigned to either its senior unsecured long-term debt or its deposit obligations by certain third-party rating agencies.
The Corporation’s credit exposure relating to interest rate swaps, commodity swaps/options and foreign currency forward contracts with bank customers was approximately $39.0 million at December 31, 2014. This credit exposure is partly mitigated as transactions with customers are generally secured by the collateral, if any, securing the underlying transaction being hedged. The Corporation’s credit exposure, net of collateral pledged, relating to interest rate swaps, commodity swaps/options and foreign currency forward contracts with upstream financial institution counterparties was approximately $8.5 million at December 31, 2014. This amount was primarily related to excess collateral posted by the Corporation to counterparties and under-collateralized derivative assets held by the Corporation. Collateral levels for upstream financial institution counterparties are monitored and adjusted as necessary. See Note 17 – Balance Sheet Offsetting for additional information regarding the Corporation’s credit exposure with upstream financial institution counterparties.
The aggregate fair value of securities posted as collateral by the Corporation related to derivative contracts totaled $19.3 million at December 31, 2014. At such date, the Corporation also had $12.1 million in cash collateral on deposit with other financial institution counterparties.

Balance_Sheet_Offsetting

Balance Sheet Offsetting	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Balance Sheet Offsetting	Balance Sheet Offsetting
	Certain financial instruments, including resell and repurchase agreements, securities lending arrangements and derivatives, may be eligible for offset in the consolidated balance sheet and/or subject to master netting arrangements or similar agreements. The Corporation’s derivative transactions with upstream financial institution counterparties are generally executed under International Swaps and Derivative Association (“ISDA”) master agreements which include “right of set-off” provisions. In such cases there is generally a legally enforceable right to offset recognized amounts and there may be an intention to settle such amounts on a net basis. Nonetheless, the Corporation does not generally offset such financial instruments for financial reporting purposes.
	Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2014 is presented in the following tables.
		Gross Amount		Gross Amount			Net Amount
		Recognized		Offset			Recognized
	31-Dec-14
	Financial assets:
	Derivatives:
	Loan/lease interest rate swaps and caps	$	2,191	$	—		$	2,191
	Commodity swaps and options	27,064		—			27,064
	Foreign currency forward contracts	666		—			666
	Total derivatives	29,921		—			29,921
	Resell agreements	9,642		—			9,642
	Total	$	39,563	$	—		$	39,563
	Financial liabilities:
	Derivatives:
	Loan/lease interest rate swaps	$	42,131	$	—		$	42,131
	Commodity swaps and options	5,765		—			5,765
	Foreign currency forward contracts	2		—			2
	Total derivatives	47,898		—			47,898
	Repurchase agreements	791,119		—			791,119
	Total	$	839,017	$	—		$	839,017
				Gross Amounts Not Offset
		Net Amount		Financial			Collateral			Net
		Recognized		Instruments						Amount
	31-Dec-14
	Financial assets:
	Derivatives:
	Counterparty A	$	627	$	(627	)	$	—		$	—
	Counterparty B	17,308		(9,506		)	(4,925		)	2,877
	Counterparty C	7,991		(7,539		)	—			452
	Other counterparties	3,995		(2,764		)	(1,110		)	121
	Total derivatives	29,921		(20,436		)	(6,035		)	3,450
	Resell agreements	9,642		—			(9,642		)	—
	Total	$	39,563	$	(20,436	)	$	(15,677	)	$	3,450
	Financial liabilities:
	Derivatives:
	Counterparty A	$	18,653	$	(627	)	$	(17,626	)	$	400
	Counterparty B	9,506		(9,506		)	—			—
	Counterparty C	7,539		(7,539		)	—			—
	Other counterparties	12,200		(2,764		)	(8,681		)	755
	Total derivatives	47,898		(20,436		)	(26,307		)	1,155
	Repurchase agreements	791,119		—			(791,119		)	—
	Total	$	839,017	$	(20,436	)	$	(817,426	)	$	1,155
	Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2013 is presented in the following tables.
		Gross Amount		Gross Amount			Net Amount
		Recognized		Offset			Recognized
	31-Dec-13
	Financial assets:
	Derivatives:
	Loan/lease interest rate swaps and caps	$	12,268	$	—		$	12,268
	Commodity swaps and options	3,907		—			3,907
	Foreign currency forward contracts	90		—			90
	Total derivatives	16,265		—			16,265
	Resell agreements	7,898		—			7,898
	Total	$	24,163	$	—		$	24,163
	Financial liabilities:
	Derivatives:
	Loan/lease interest rate swaps	$	36,660	$	—		$	36,660
	Commodity swaps and options	5,916		—			5,916
	Foreign currency forward contracts	27		—			27
	Total derivatives	42,603		—			42,603
	Repurchase agreements	668,053		—			668,053
	Total	$	710,656	$	—		$	710,656
			Gross Amounts Not Offset
	Net Amount		Financial			Collateral			Net
	Recognized		Instruments						Amount
31-Dec-13
Financial assets:
Derivatives:
Counterparty A	$	3,342	$	(3,342	)	$	—		$	—
Counterparty B	8,196		(8,196		)	—			—
Counterparty C	1,187		(1,187		)	—			—
Other counterparties	3,540		(2,099		)	(1,360		)	81
Total derivatives	16,265		(14,824		)	(1,360		)	81
Resell agreements	7,898		—			(7,898		)	—
Total	$	24,163	$	(14,824	)	$	(9,258	)	$	81
Financial liabilities:
Derivatives:
Counterparty A	$	18,615	$	(3,342	)	$	(15,167	)	$	106
Counterparty B	9,054		(8,196		)	(613		)	245
Counterparty C	10,870		(1,187		)	(9,683		)	—
Other counterparties	4,064		(2,099		)	(1,549		)	416
Total derivatives	42,603		(14,824		)	(27,012		)	767
Repurchase agreements	668,053		—			(668,053		)	—
Total	$	710,656	$	(14,824	)	$	(695,065	)	$	767

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	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 Corporation 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. 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 or liabilities and the lowest priority to unobservable inputs. The fair value hierarchy is as follows:
	•	Level 1 Inputs - Unadjusted quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.
	•	Level 2 Inputs - Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. These might include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (such as interest rates, volatilities, prepayment speeds, credit risks, etc.) or inputs that are derived principally from or corroborated by market data by correlation or other means.
	•	Level 3 Inputs - Unobservable inputs for determining the fair values of assets or liabilities that reflect an entity’s own assumptions about the assumptions that market participants would use in pricing the assets or liabilities.
	In general, fair value is based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality and the Corporation’s creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. The Corporation’s valuation methodologies may produce a fair value calculation that may not be indicative of net realizable value or reflective of future fair values. While management believes the Corporation’s valuation methodologies are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. Furthermore, the reported fair value amounts have not been comprehensively revalued since the presentation dates, and therefore, estimates of fair value after the balance sheet date may differ significantly from the amounts presented herein. A more detailed description of the valuation methodologies used for assets and liabilities measured at fair value is set forth below. Transfers between levels of the fair value hierarchy are recognized on the actual date of the event or circumstances that caused the transfer, which generally coincides with the Corporation’s monthly and/or quarterly valuation process.
	Financial Assets and Financial Liabilities: Financial assets and financial liabilities measured at fair value on a recurring basis include the following:
	Securities Available for Sale. U.S. Treasury securities are reported at fair value utilizing Level 1 inputs. Other securities classified as available for sale are reported at fair value utilizing Level 2 inputs. For these securities, the Corporation 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 Corporation reviews the prices supplied by the independent pricing service, as well as their underlying pricing methodologies, for reasonableness and to ensure such prices are aligned with traditional pricing matrices. In general, the Corporation does not purchase investment portfolio securities that are esoteric or that have a complicated structure. The Corporation’s entire portfolio consists of traditional investments, nearly all of which are U.S. Treasury obligations, federal agency bullet or mortgage pass-through securities, or general obligation or revenue based municipal bonds. Pricing for such instruments is fairly generic and is easily obtained. From time to time, the Corporation will validate prices supplied by the independent pricing service by comparison to prices obtained from third-party sources or derived using internal models.
	Trading Securities. U.S. Treasury securities and exchange-listed common stock are reported at fair value utilizing Level 1 inputs. Other securities classified as trading are reported at fair value utilizing Level 2 inputs in the same manner as described above for securities available for sale.
	Derivatives. Derivatives are generally reported at fair value utilizing Level 2 inputs, except for foreign currency contracts, which are reported at fair value utilizing Level 1 inputs. The Corporation obtains dealer quotations and utilizes internally developed valuation models to value commodity swaps/options. The Corporation utilizes internally developed valuation models and/or third-party models with observable market data inputs to validate the valuations provided by the dealers. Though there has never been a significant discrepancy in the valuations, should such a significant discrepancy arise, the Corporation would obtain price verification from a third-party dealer. The Corporation utilizes internal valuation models with observable market data inputs to estimate fair values of customer interest rate swaps, caps and floors. The Corporation also obtains dealer quotations for these derivatives for comparative purposes to assess the reasonableness of the model valuations. In cases where significant credit valuation adjustments are incorporated into the estimation of fair value, reported amounts are considered to have been derived utilizing Level 3 inputs.
	For purposes of potential valuation adjustments to its derivative positions, the Corporation evaluates the credit risk of its counterparties as well as that of the Corporation. Accordingly, the Corporation has considered factors such as the likelihood of default by the Corporation and its counterparties, its net exposures, and remaining contractual life, among other things, in determining if any fair value adjustments related to credit risk are required. Counterparty exposure is evaluated by netting positions that are subject to master netting arrangements, as well as considering the amount of collateral securing the position. The Corporation reviews its counterparty exposure on a regular basis, and, when necessary, appropriate business actions are taken to adjust the exposure. The Corporation also utilizes this approach to estimate its own credit risk on derivative liability positions. To date, the Corporation has not realized any significant losses due to a counterparty’s inability to pay any net uncollateralized position. The change in value of derivative assets and derivative liabilities attributable to credit risk was not significant during the reported periods.
	The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value:
		Level 1			Level 2			Level 3			Total
		Inputs			Inputs			Inputs			Fair Value
	2014
	Securities available for sale:
	U.S. Treasury	$	3,811,252		$	—		$	—		$	3,811,252
	Residential mortgage-backed securities	—			1,398,724			—			1,398,724
	States and political subdivisions	—			3,208,907			—			3,208,907
	Other	—			42,371			—			42,371
	Trading account securities:
	U.S. Treasury	15,339			—			—			15,339
	States and political subdivisions	—			87			—			87
	Derivative assets:
	Interest rate swaps, caps and floors	—			40,931			170			41,101
	Commodity swaps and options	—			32,829			—			32,829
	Foreign currency forward contracts	666			—			—			666
	Derivative liabilities:
	Interest rate swaps, caps and floors	—			43,853			—			43,853
	Commodity swaps and options	—			32,729			—			32,729
	Foreign currency forward contracts	617			—			—			617
	2013
	Securities available for sale:
	U.S. Treasury	$	2,540,554		$	—		$	—		$	2,540,554
	U.S. government agencies/corporations	—			53,980			—			53,980
	Residential mortgage-backed securities	—			1,776,016			—			1,776,016
	States and political subdivisions	—			1,488,914			—			1,488,914
	Other	—			35,972			—			35,972
	Trading account securities:
	U.S. Treasury	15,389			—			—			15,389
	States and political subdivisions	—			1,009			—			1,009
	Derivative assets:
	Interest rate swaps, caps and floors	—			44,520			174			44,694
	Commodity swaps and options	—			10,026			—			10,026
	Foreign currency forward contracts	135			—			—			135
	Derivative liabilities:
	Interest rate swaps, caps and floors	—			47,542			—			47,542
	Commodity swaps and options	—			9,712			—			9,712
	Foreign currency forward contracts	85			—			—			85
	Derivative assets, measured at fair value on a recurring basis using significant unobservable (Level 3) inputs during the reported periods consist of interest rate swaps sold to loan customers. The significant unobservable (Level 3) inputs used in the fair value measurement of these interest rate swaps sold to loan customers primarily relate to the probability of default and loss severity in the event of default. The probability of default is determined by the underlying risk grade of the loan (see Note 4 – Loans) underlying the interest rate swap in that the probability of default increases as a loan’s risk grade deteriorates, while the loss severity is estimated through an analysis of the collateral supporting both the underlying loan and interest rate swap. Generally, a change in the assumption used for the probability of default is accompanied by a directionally similar change in the assumption used for the loss severity. As of December 31, 2014, the weighted-average risk grade of loans underlying interest rate swaps measured at fair value using significant unobservable (Level 3) inputs was 11.0. The weighted-average loss severity in the event of default on the interest rate swaps was 20.0%. A reconciliation of the beginning and ending balances of derivative assets measured at fair value on a recurring basis using significant unobservable (Level 3) inputs is not presented as such amounts were not significant during the reported periods.
	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, or Level 3 inputs based on customized discounting criteria, typically in the case of non-real estate collateral such as inventory, accounts receivable, equipment or other business assets.
	The following table presents impaired loans that were remeasured and reported at fair value through a specific valuation allowance allocation of the allowance for loan losses based upon the fair value of the underlying collateral:
		2014						2013					2012
		Level 2			Level 3			Level 2			Level 3		Level 2			Level 3
	Carrying value of impaired loans before allocations	$	—		$	2,715		$	9,374		$	—	$	18,319		$	15,754
	Specific valuation allowance allocations	—			(1,475		)	(2,785		)	—		(3,634		)	(2,911		)
	Fair value	$	—		$	1,240		$	6,589		$	—	$	14,685		$	12,843
	Non-Financial Assets and Non-Financial Liabilities: The Corporation has no non-financial assets or non-financial liabilities measured at fair value on a recurring basis. Certain non-financial assets measured at fair value on a non-recurring basis include foreclosed assets (upon initial recognition or subsequent impairment), non-financial assets and non-financial liabilities measured at fair value in the second step of a goodwill impairment test, and intangible assets and other non-financial long-lived assets measured at fair value for impairment assessment. Non-financial assets measured at fair value on a non-recurring basis during the reported periods include certain foreclosed assets which, upon initial recognition, were remeasured and reported at fair value through a charge-off to the allowance for loan losses and certain foreclosed assets which, subsequent to their initial recognition, were remeasured at fair value through a write-down included in other non-interest expense. The fair value of a foreclosed asset is estimated using Level 2 inputs based on observable market data or Level 3 inputs based on customized discounting criteria. During the reported periods, all fair value measurements for foreclosed assets utilized Level 2 inputs.
	The following table presents foreclosed assets that were remeasured and reported at fair value:
		2014			2013			2012
	Foreclosed assets remeasured at initial recognition:
	Carrying value of foreclosed assets prior to remeasurement	$	6,388		$	7,580		$	9,428
	Charge-offs recognized in the allowance for loan losses	(285		)	(710		)	(1,611		)
Fair value	$	6,103		$	6,870		$	7,817
Foreclosed assets remeasured subsequent to initial recognition:
Carrying value of foreclosed assets prior to remeasurement	$	5,026		$	4,979		$	12,126
Write-downs included in other non-interest expense	(1,289		)	(895		)	(2,093		)
Fair value	$	3,737		$	4,084		$	10,033
Charge-offs recognized upon loan foreclosures are generally offset by general or specific allocations of the allowance for loan losses and generally do not, and did not during the reported periods, significantly impact the Corporation’s provision for loan losses. Regulatory guidelines require the Corporation to reevaluate the fair value of other real estate owned on at least an annual basis. The Corporation’s policy is to comply with the regulatory guidelines. Accordingly, appraisals are never considered to be outdated, and the Corporation does not make any adjustments to the appraised values.
FASB ASC Topic 825, “Financial Instruments,” requires disclosure of the fair value of financial assets and financial liabilities, including those financial assets and financial liabilities that are not measured and reported at fair value on a recurring basis or non-recurring basis. The estimated fair value approximates carrying value for cash and cash equivalents, accrued interest and the cash surrender value of life insurance policies. The methodologies for other financial assets and financial liabilities that are not measured and reported at fair value on a recurring basis or non-recurring basis are discussed below:
Loans. 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.
Deposits. The estimated fair value approximates carrying value for demand deposits. The fair value of fixed-rate deposit liabilities with defined maturities is estimated by discounting future cash flows using the interest rates currently offered for deposits of similar remaining maturities. The estimated fair value of deposits does not take into account the value of the Corporation’s long-term relationships with depositors, commonly known as core deposit intangibles, which are separate intangible assets, and not considered financial instruments. Nonetheless, the Corporation would likely realize a core deposit premium if its deposit portfolio were sold in the principal market for such deposits.
Borrowed Funds. The estimated fair value approximates carrying value for short-term borrowings. The fair value of long-term fixed-rate borrowings is estimated using quoted market prices, if available, or by discounting future cash flows using current interest rates for similar financial instruments. The estimated fair value approximates carrying value for variable-rate junior subordinated deferrable interest debentures that reprice quarterly.
Loan Commitments, Standby and Commercial Letters of Credit. The Corporation’s lending commitments have variable interest rates and “escape” clauses if the customer’s credit quality deteriorates. Therefore, the fair values of these items are not significant and are not included in the following table.
The estimated fair values of financial instruments that are reported at amortized cost in the Corporation’s consolidated balance sheets, segregated by the level of valuation inputs within the fair value hierarchy utilized to measure fair value, were as follows:
	December 31, 2014						December 31, 2013
	Carrying			Estimated			Carrying			Estimated
	Amount			Fair Value			Amount			Fair Value
Financial assets:
Level 2 inputs:
Cash and cash equivalents	$	4,364,123		$	4,364,123		$	4,556,125		$	4,556,125
Securities held to maturity	2,926,486			2,966,390			3,139,748			3,029,663
Cash surrender value of life insurance policies	172,050			172,050			141,108			141,108
Accrued interest receivable	128,436			128,436			99,281			99,281
Level 3 inputs:
Loans, net	10,887,993			10,939,684			9,423,262			9,582,734
Financial liabilities:
Level 2 inputs:
Deposits	24,135,930			24,136,402			20,688,786			20,689,323
Federal funds purchased and repurchase agreements	803,119			803,119			668,253			668,253
Junior subordinated deferrable interest debentures	137,115			137,115			123,712			123,712
Subordinated notes payable and other borrowings	100,000			95,591			100,000			92,552
Accrued interest payable	1,132			1,132			1,300			1,300
Under ASC Topic 825, entities may choose to measure eligible financial instruments at fair value at specified election dates. The fair value measurement option (i) may be applied instrument by instrument, with certain exceptions, (ii) is generally irrevocable and (iii) is applied only to entire instruments and not to portions of instruments. Unrealized gains and losses on items for which the fair value measurement option has been elected must be reported in earnings at each subsequent reporting date. During the reported periods, the Corporation had no financial instruments measured at fair value under the fair value measurement option.

Operating_Segments

Operating Segments	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Operating Segments	Operating Segments
	The Corporation is managed under a matrix organizational structure whereby its two primary operating segments, Banking and Frost Wealth Advisors, overlap a regional reporting structure. The regions are primarily based upon geographic location and include Austin, Corpus Christi, Dallas, Fort Worth, Houston, Permian Basin, Rio Grande Valley, San Antonio and Statewide. The Corporation is primarily managed based on the line of business structure. In that regard, all regions have the same lines of business, which have the same product and service offerings, have similar types and classes of customers and utilize similar service delivery methods. Pricing guidelines for products and services are the same across all regions. The regional reporting structure is primarily a means to scale the lines of business to provide a local, community focus for customer relations and business development.
	Banking and Frost Wealth Advisors are delineated by the products and services that each segment offers. The Banking operating segment includes both commercial and consumer banking services, Frost Securities, Inc. and Frost Insurance Agency. Commercial banking services are provided to corporations and other business clients and include a wide array of lending and cash management products. Consumer banking services include direct lending and depository services. Frost Insurance Agency provides insurance brokerage services to individuals and businesses covering corporate and personal property and casualty products, as well as group health and life insurance products and human resources consulting services. Frost Securities, Inc. provides advisory and private equity services to middle market companies. The Frost Wealth Advisors operating segment includes fee-based services within private trust, retirement services, and financial management services, including personal wealth management and brokerage services. A third operating segment, Non-Banks, is for the most part the parent holding company, as well as certain other insignificant non-bank subsidiaries of the parent that, for the most part, have little or no activity. The parent company’s principal activities include the direct and indirect ownership of the Corporation’s banking and non-banking subsidiaries and the issuance of debt and equity. Its principal source of revenue is dividends from its subsidiaries.
	The accounting policies of each reportable segment are the same as those of the Corporation except for the following items, which impact the Banking and Frost Wealth Advisors segments: (i) expenses for consolidated back-office operations and general overhead-type expenses such as executive administration, accounting and internal audit are allocated to operating segments based on estimated uses of those services, (ii) income tax expense for the individual segments is calculated essentially at the statutory rate, and (iii) the parent company records the tax expense or benefit necessary to reconcile to the consolidated total.
	The Corporation uses a match-funded transfer pricing process to assess operating segment performance. The process helps the Corporation to (i) identify the cost or opportunity value of funds within each business segment, (ii) measure the profitability of a particular business segment by relating appropriate costs to revenues, (iii) evaluate each business segment in a manner consistent with its economic impact on consolidated earnings, and (iv) enhance asset and liability pricing decisions.
	Financial results by operating segment are detailed below. Certain prior period amounts have been reclassified to conform to the current presentation.
		Banking		Frost			Non-Banks			Consolidated
				Wealth
				Advisors
	2014
	Net interest income (expense)	$	683,579	$	6,734		$	(3,379	)	$	686,934
	Provision for loan losses	16,312		2			—			16,314
	Non-interest income	193,883		122,261			4,000			320,144
	Non-interest expense	549,812		96,330			8,598			654,740
	Income (loss) before income taxes	311,338		32,663			(7,977		)	336,024
	Income tax expense (benefit)	51,881		11,431			(5,265		)	58,047
	Net income (loss)	259,457		21,232			(2,712		)	277,977
	Preferred stock dividends	—		—			8,063			8,063
	Net income (loss) available to common shareholders	$	259,457	$	21,232		$	(10,775	)	$	269,914
	Revenues from (expenses to) external customers	$	877,462	$	128,995		$	621		$	1,007,078
	Average assets (in millions)(1)	$	25,734	$	32		$	2		$	25,768
	2013
	Net interest income (expense)	$	621,333	$	6,586		$	(7,364	)	$	620,555
	Provision for loan losses	20,585		(3		)	—			20,582
	Non-interest income	190,767		107,759			4,292			302,818
	Non-interest expense	513,909		90,132			7,869			611,910
	Income (loss) before income taxes	277,606		24,216			(10,941		)	290,881
	Income tax expense (benefit)	50,823		8,563			(6,371		)	53,015
	Net income (loss)	226,783		15,653			(4,570		)	237,866
	Preferred stock dividends	—		—			6,719			6,719
	Net income (loss) available to common shareholders	$	226,783	$	15,653		$	(11,289	)	$	231,147
	Revenues from (expenses to) external customers	$	812,100	$	114,345		$	(3,072	)	$	923,373
	Average assets (in millions)(1)	$	22,709	$	31		$	12		$	22,752
	2012
	Net interest income (expense)	$	605,330	$	8,013		$	(8,482	)	$	604,861
	Provision for loan losses	10,078		2			—			10,080
	Non-interest income	188,440		96,577			3,770			288,787
	Non-interest expense	485,302		82,744			7,047			575,093
	Income (loss) before income taxes	298,390		21,844			(11,759		)	308,475
	Income tax expense (benefit)	69,078		7,646			(6,201		)	70,523
	Net income (loss)	$	229,312	$	14,198		$	(5,558	)	$	237,952
	Revenues from (expenses to) external customers	$	793,770	$	104,590		$	(4,712	)	$	893,648
	Average assets (in millions)(1)	$	20,783	$	29		$	15		$	20,827
	-1	Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.5 billion, $29.0 billion and $26.2 billion at December 31, 2014, 2013 and 2012.

Condensed_Financial_Statements

Condensed Financial Statements of Parent Company	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Statements of Parent Company	Condensed Financial Statements of Parent Company
	Condensed financial statements pertaining only to Cullen/Frost Bankers, Inc. are presented below. Investments in subsidiaries are stated using the equity method of accounting.
	Condensed Balance Sheets
		December 31,
		2014			2013
	Assets:
	Cash	$	7,335		$	7,477
	Resell agreements	286,660			320,200
	Total cash and cash equivalents	293,995			327,677
	Investment in subsidiaries	2,791,647			2,409,433
	Accrued interest receivable and other assets	29,705			19,038
	Total assets	$	3,115,347		$	2,756,148
	Liabilities:
	Junior subordinated deferrable interest debentures	$	137,115		$	123,712
	Subordinated notes payable	100,000			100,000
	Accrued interest payable and other liabilities	26,829			18,275
	Total liabilities	263,944			241,987
	Shareholders’ Equity	2,851,403			2,514,161
	Total liabilities and shareholders’ equity	$	3,115,347		$	2,756,148
	Condensed Statements of Income
		Year Ended December 31,
		2014			2013			2012
	Income:
	Dividend income paid by Frost Bank	$	114,439		$	144,642		$	143,623
	Dividend income paid by non-banks	4,323			2,819			3,077
	Interest and other income	69			79			308
	Total income	118,831			147,540			147,008
	Expenses:
	Interest expense	3,381			7,365			8,512
	Salaries and employee benefits	1,218			1,175			1,167
	Other	8,526			6,735			6,727
	Total expenses	13,125			15,275			16,406
	Income before income taxes and equity in undistributed earnings of subsidiaries	105,706			132,265			130,602
	Income tax benefit	6,702			7,845			7,463
	Equity in undistributed earnings of subsidiaries	165,569			97,756			99,887
	Net income	277,977			237,866			237,952
	Preferred stock dividends	8,063			6,719			—
	Net income available to common shareholders	$	269,914		$	231,147		$	237,952
	Condensed Statements of Cash Flows
		Year Ended December 31,
		2014			2013			2012
	Operating Activities:
	Net income	$	277,977		$	237,866		$	237,952
	Adjustments to reconcile net income to net cash provided by operating activities:
	Equity in undistributed earnings of subsidiaries	(165,569		)	(97,756		)	(99,887		)
	Stock-based compensation	441			330			330
	Excess tax benefits from stock-based compensation	(165		)	(155		)	(133		)
	Net change in other assets and other liabilities	(1,984		)	2,372			(2,256		)
	Net cash from operating activities	110,700			142,657			136,006
	Investing Activities:
	Net cash received in acquisitions	830,661			—			—
	Capital contribution to subsidiaries	(879,730		)	—			—
	Net cash from investing activities	(49,069		)	—			—
	Financing Activities:
	Proceeds from stock option exercises	29,158			68,653			10,516
	Proceeds from stock-based compensation activities of subsidiaries	12,062			11,633			12,506
	Excess tax benefits from stock-based compensation	165			155			133
	Proceeds from issuance of preferred stock	—			144,486			—
	Purchase of treasury stock	(1,457		)	(144,630		)	(436		)
	Cash dividends paid on preferred stock	(8,063		)	(6,719		)	—
	Cash dividends paid on common stock	(127,178		)	(119,619		)	(116,853		)
	Net cash from financing activities	(95,313		)	(46,041		)	(94,134		)
	Net change in cash and cash equivalents	(33,682		)	96,616			41,872
	Cash and cash equivalents at beginning of year	327,677			231,061			189,189
Cash and cash equivalents at end of year	$	293,995		$	327,677		$	231,061

Accounting_Standards_Updates

Accounting Standards Updates	12 Months Ended
	Dec. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Standards Updates	Accounting Standards Updates
	ASU No. 2011-03, “Transfers and Servicing (Topic 860) - Reconsideration of Effective Control for Repurchase Agreements.” ASU 2011-03 is intended to improve financial reporting of repurchase agreements and other agreements that both entitle and obligate a transferor to repurchase or redeem financial assets before their maturity. ASU 2011-03 removes from the assessment of effective control (i) the criterion requiring the transferor to have the ability to repurchase or redeem the financial assets on substantially the agreed terms, even in the event of default by the transferee, and (ii) the collateral maintenance guidance related to that criterion. ASU 2011-03 became effective for the Corporation on January 1, 2012 and did not have a significant impact on the Corporation’s financial statements.
	ASU 2011-04, “Fair Value Measurement (Topic 820) - Amendments to Achieve Common Fair Value Measurements and Disclosure Requirements in U.S. GAAP and IFRSs.” ASU 2011-04 amends Topic 820, “Fair Value Measurements and Disclosures,” to converge the fair value measurement guidance in U.S. generally accepted accounting principles and International Financial Reporting Standards. ASU 2011-04 clarifies the application of existing fair value measurement requirements, changes certain principles in Topic 820 and requires additional fair value disclosures. ASU 2011-04 became effective for the Corporation on January 1, 2012 and, aside from new disclosures included in Note 18 – Fair Value Measurements, did not have a significant impact on the Corporation’s financial statements.
	ASU 2011-05, “Comprehensive Income (Topic 220) - Presentation of Comprehensive Income.” ASU 2011-05 amends Topic 220, “Comprehensive Income,” to require that all non-owner changes in stockholders’ equity be presented in either a single continuous statement of comprehensive income or in two separate but consecutive statements. Additionally, ASU 2011-05 requires entities to present, on the face of the financial statements, reclassification adjustments for items that are reclassified from other comprehensive income to net income in the statement or statements where the components of net income and the components of other comprehensive income are presented. The option to present components of other comprehensive income as part of the statement of changes in stockholders’ equity was eliminated. ASU 2011-05 became effective for the Corporation on January 1, 2012; however, certain provisions related to the presentation of reclassification adjustments were deferred by ASU 2011-12 “Comprehensive Income (Topic 220) – Deferral of the Effective Date for Amendments to the Presentation of Reclassifications of Items Out of Accumulated Other Comprehensive Income in Accounting Standards Update No. 2011-05.” ASU 2013-02, “Comprehensive Income (Topic 220) – Reporting of Amounts Reclassified Out of Accumulated Other Comprehensive Income,” amended the guidance of ASU 2011-05 related to the reporting of reclassifications out of accumulated other comprehensive income. ASU 2013-02 became effective for the Corporation on January 1, 2013. As a result of the these accounting standards updates, the Corporation’s financial statements now include separate statements of comprehensive income and additional footnote disclosures (see Note 15 – Other Comprehensive Income (Loss)).
	ASU 2011-08, “Intangibles – Goodwill and Other (Topic 350) - Testing Goodwill for Impairment.” ASU 2011-08 amends Topic 350, “Intangibles – Goodwill and Other,” to give 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 the fair value of a reporting unit is less than its carrying amount. If, after assessing the totality of events or circumstances, an entity determines it is not more likely than not that the fair value of a reporting unit is less than its carrying amount, then performing the two-step impairment test is unnecessary. However, if an entity concludes otherwise, then it is required to perform the first step of the two-step impairment test by calculating the fair value of the reporting unit and comparing the fair value with the carrying amount of the reporting unit. ASU 2011-08 became effective for the Corporation on January 1, 2012 and did not have a significant impact on the Corporation’s financial statements.
	ASU 2011-11, “Balance Sheet (Topic 210) – Disclosures about Offsetting Assets and Liabilities.” ASU 2011-11 amends Topic 210, “Balance Sheet,” to require an entity to disclose both gross and net information about financial instruments, such as sales and repurchase agreements and reverse sale and repurchase agreements and securities borrowing/lending arrangements, and derivative instruments that are eligible for offset in the statement of financial position and/or subject to a master netting arrangement or similar agreement. ASU No. 2013-01, “Balance Sheet (Topic 210) – Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities,” clarifies that ordinary trade receivables are not within the scope of ASU 2011-11. ASU 2011-11, as amended by ASU 2013-01, became effective for the Corporation on January 1, 2013. See Note 17 – Balance Sheet Offsetting for applicable disclosures.
	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 Corporation on January 1, 2013 and did not have a significant impact on the Corporation’s financial statements.
	ASU 2012-06, “Business Combinations (Topic 805) - Subsequent Accounting for an Indemnification Asset Recognized at the Acquisition Date as a Result of a Government-Assisted Acquisition of a Financial Institution (a consensus of the FASB Emerging Issues Task Force).” ASU 2012-06 clarifies the applicable guidance for subsequently measuring an indemnification asset recognized as a result of a government-assisted acquisition of a financial institution. Under ASU 2012-06, when a reporting entity recognizes an indemnification asset as a result of a government-assisted acquisition of a financial institution and, subsequently, a change in the cash flows expected to be collected on the indemnification asset occurs (as a result of a change in cash flows expected to be collected on the assets subject to indemnification), the reporting entity should subsequently account for the change in the measurement of the indemnification asset on the same basis as the change in the assets subject to indemnification. Any amortization of changes in value should be limited to the contractual term of the indemnification agreement (that is, the lesser of the term of the indemnification agreement and the remaining life of the indemnified assets). ASU 2012-06 became effective for the Corporation on January 1, 2013 and did not have a significant impact on the Corporation’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 Corporation on January 1, 2013 and did not have a significant impact on the Corporation’s financial statements. See Note 15 – Other Comprehensive Income (Loss).
	ASU 2013-08, “Financial Services – Investment Companies (Topic 946) – Amendments to the Scope, Measurement and Disclosure Requirements.” ASU 2013-08 clarifies the characteristics of investment companies and sets forth a new approach for determining whether a company is an investment company. The fundamental characteristics of an investment company include (i) the company obtains funds from investors and provides the investors with investment management services; (ii) the company commits to its investors that its business purpose and only substantive activities are investing the funds for returns solely from capital appreciation, investment income, or both; and (iii) the company or its affiliates do not obtain or have the objective of obtaining returns or benefits from an investee or its affiliates that are not normally attributable to ownership interests or that are other than capital appreciation or investment income. ASU 2013-08 also sets forth the scope, measurement and disclosure requirements for investment companies. ASU 2013-08 became effective for the Corporation on January 1, 2014 and did not have a significant impact on the Corporation’s financial statements.
	ASU 2013-10, “Derivatives and Hedging (Topic 815) – Inclusion of the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) as a Benchmark Interest Rate for Hedge Accounting Purposes.” ASU 2013-10 permits the Fed Funds Effective Swap Rate (or Overnight Index Swap Rate) to be used as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815, in addition to interest rates on direct Treasury obligations of the U.S. government and the London Interbank Offered Rate (“LIBOR”). ASU 2013-10 became effective for qualifying new or redesignated hedging relationships entered into on or after July 17, 2013 and did not have a significant impact on the Corporation’s financial statements.
	ASU 2014-09, “Revenue from Contracts with Customers (Topic 606).” ASU 2014-09 implements a common revenue standard that clarifies the principles for recognizing revenue. The core principle of ASU 2014-09 is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that core principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract and (v) recognize revenue when (or as) the entity satisfies a performance obligation. ASU 2014-09 is effective for the Corporation on January 1, 2017. The Corporation is still evaluating the potential impact on the Corporation's financial statements.
	ASU 2014-11, “Transfers and Servicing (Topic 860).” ASU 2014-11 requires that repurchase-to-maturity transactions be accounted for as secured borrowings consistent with the accounting for other repurchase agreements. In addition, ASU 2014-11 requires separate accounting for repurchase financings, which entails the transfer of a financial asset executed contemporaneously with a repurchase agreement with the same counterparty. ASU 2014-11 requires entities to disclose certain information about transfers accounted for as sales in transactions that are economically similar to repurchase agreements. In addition, ASU 2014-11 requires disclosures related to collateral, remaining contractual tenor and of the potential risks associated with repurchase agreements, securities lending transactions and repurchase-to-maturity transactions. ASU 2014-11 is effective for the Corporation on January 1, 2015 and is not expected to have a significant impact on the Corporation's financial statements.
	ASU 2015-01, “Income Statement - Extraordinary and Unusual Items (Subtopic 225-20) – Simplifying Income Statement Presentation by Eliminating the Concept of Extraordinary Items.” ASU 2015-01 eliminates from U.S. GAAP the concept of extraordinary items, which, among other things, required an entity to segregate extraordinary items considered to be unusual and infrequent from the results of ordinary operations and show the item separately in the income statement, net of tax, after income from continuing operations. ASU 2015-01 is effective for the Corporation beginning January 1, 2016, though early adoption is permitted. ASU 2015-01 is not expected to have a significant impact on the Corporation's financial statements.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Acquisition	Mergers and Acquisition
	On May 30, 2014, the Corporation acquired WNB Bancshares, Inc. (“WNB”), including its subsidiary Western National Bank (“Western”), a privately-held bank holding company and bank located in the Permian Basin region of Texas. The Corporation purchased all of the outstanding shares of WNB for approximately $198.8 million. The total purchase price included $149.7 million of the Corporation’s common stock (2 million shares) and $49.1 million in cash. Western was integrated into Frost Bank as of the close of business on June 20, 2014.
	The acquisition of WNB was accounted for using the acquisition method with all cash consideration funded through internal sources. The operating results of WNB are included with the Corporation’s results of operations since the date of acquisition. The total purchase price paid for the acquisition of WNB was allocated based on the estimated fair values of the assets acquired and liabilities assumed as set forth below. The purchase price allocation is preliminary and is subject to final determination and valuation of the fair value of assets acquired and liabilities assumed.
	Cash and cash equivalents	$	879,740
	Securities available for sale	154,227
	Loans	670,619
	Premises and equipment	22,853
	Core deposit intangible asset	9,300
	Goodwill	117,301
	Other assets	33,644
	Deposits	(1,624,043		)
	Other borrowings	(63,592		)
	Other liabilities	(1,251		)
		$	198,798
	The loans acquired in this transaction were recorded at fair value with no carryover of any existing allowance for loan losses. Purchased credit-impaired loans, meaning those loans with evidence of credit quality deterioration at acquisition, were not significant. The core deposit intangible asset acquired in this transaction will be amortized using an accelerated method over a period of 10 years. Pro forma condensed consolidated results of operations assuming WNB had been acquired at the beginning of the reported periods are not presented because the effect of this acquisition was not considered significant based on the SEC significance tests.
	Expenditures related to the acquisition of WNB totaled $7.1 million and $1.4 million during 2014 and 2013, respectively, and are reported as a component of other non-interest expense in the accompanying consolidated income statements.
	As part of the approval process in connection with the acquisition of WNB, the Corporation agreed with the Federal Reserve that before bringing it any further expansionary proposals, the Corporation would enhance certain compliance programs, including those related to fair lending. The Corporation is currently working on these enhancements.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations. Cullen/Frost Bankers, Inc. (“Cullen/Frost”) is a financial holding company and a bank holding company headquartered in San Antonio, Texas that provides, through its subsidiaries, a broad array of products and services throughout numerous Texas markets. In addition to general commercial and consumer banking, other products and services offered include trust and investment management, investment banking, insurance, brokerage, leasing, treasury management and item processing.
Basis of Presentation	Basis of Presentation. The consolidated financial statements include the accounts of Cullen/Frost and all other entities in which Cullen/Frost has a controlling financial interest (collectively referred to as the “Corporation”). All significant intercompany balances and transactions have been eliminated in consolidation. The accounting and financial reporting policies the Corporation follows conform, in all material respects, to accounting principles generally accepted in the United States and to general practices within the financial services industry.
	The Corporation determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (“VIE”) under accounting principles generally accepted in the United States. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. The Corporation consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE. The Corporation’s wholly owned subsidiaries Cullen/Frost Capital Trust II and WNB Capital Trust I are VIEs for which the Corporation is not the primary beneficiary. Accordingly, the accounts of these trusts are not included in the Corporation’s consolidated financial statements.
	The Corporation has evaluated subsequent events for potential recognition and/or disclosure through the date these consolidated financial statements were issued. All acquisitions during the reported periods were accounted for using the purchase method. Accordingly, the operating results of the acquired companies are included with the Corporation’s results of operations since their respective dates of acquisition.
Use of Estimates	Use of Estimates. The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses and the fair values of financial instruments and the status of contingencies are particularly subject to change.
Concentrations and Restrictions on Cash and Cash Equivalents	Concentrations and Restrictions on Cash and Cash Equivalents. The Corporation maintains deposits with other financial institutions in amounts that exceed federal deposit insurance coverage. Furthermore, federal funds sold are essentially uncollateralized loans to other financial institutions. Management regularly evaluates the credit risk associated with the counterparties to these transactions and believes that the Corporation is not exposed to any significant credit risks on cash and cash equivalents.
	The Corporation was required to have $175.6 million and $116.6 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2014 and 2013. These deposits with the Federal Reserve Bank do not earn interest. Additionally, as of December 31, 2014, the Corporation had $12.1 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions.
Repurchase/Resell Agreements	Repurchase/Resell Agreements. The Corporation purchases certain securities under agreements to resell. The amounts advanced under these agreements represent short-term loans and are reflected as assets in the accompanying consolidated balance sheets. The securities underlying these agreements are book-entry securities. The Corporation also sells certain securities under agreements to repurchase. The agreements are treated as collateralized financing transactions and the obligations to repurchase securities sold are reflected as a liability in the accompanying consolidated balance sheets. The dollar amount of the securities underlying the agreements remain in the asset accounts.
Securities	Securities. Securities are classified as held to maturity and carried at amortized cost when management has the positive intent and ability to hold them until maturity. Securities to be held for indefinite periods of time are classified as available for sale and carried at fair value, with the unrealized holding gains and losses reported as a component of other comprehensive income, net of tax. Securities held for resale in anticipation of short-term market movements are classified as trading and are carried at fair value, with changes in unrealized holding gains and losses included in income. Management determines the appropriate classification of securities at the time of purchase. Securities with limited marketability, such as stock in the Federal Reserve Bank and the Federal Home Loan Bank, are carried at cost.
	Purchase premiums and discounts on securities are amortized or accreted to interest income over the expected lives of the securities using the interest method with a constant effective yield. Expectations related to prepayments are considered in the calculation of the constant effective yield necessary to apply the interest method for mortgage-backed securities and certain pools of municipal securities. Premium amortization and discount accretion for mortgage-backed securities and pools of municipal securities is adjusted for changes in prepayment estimates, as applicable.
	Realized gains and losses are derived from the amortized cost of the security sold. Declines in the fair value of held-to-maturity and available-for-sale securities below their cost that are deemed to be other than temporary are reflected in earnings as realized losses. In estimating other-than-temporary impairment losses, management considers, among other things, (i) the length of time and the extent to which the fair value has been less than cost, (ii) the financial condition and near-term prospects of the issuer and (iii) the intent and ability of the Corporation to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in fair value.
Loans	Loans. Loans are reported at the principal balance outstanding net of unearned discounts. Interest income on loans is reported on the level-yield method and includes amortization of deferred loan fees and costs over the loan term. Net loan commitment fees or costs for commitment periods greater than one year are deferred and amortized into fee income or other expense on a straight-line basis over the commitment period. Income on direct financing leases is recognized on a basis that achieves a constant periodic rate of return on the outstanding investment. Further information regarding the Corporation’s accounting policies related to past due loans, non-accrual loans, impaired loans and troubled-debt restructurings is presented in Note 4 - Loans.
Loans Acquired Through Transfer	Loans Acquired Through Transfer. Loans acquired through the completion of a transfer, including loans acquired in a business combination, are initially recorded at fair value.
	Acquired loans that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that the Corporation will be unable to collect all contractually required payments receivable are considered to be purchased credit-impaired. For purchased credit-impaired loans, the difference between the undiscounted cash flows expected at acquisition and the recorded fair value of the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition (meaning the present value of all cash flows expected at acquisition that ultimately are not to be received).
Allowance for Loan Losses	Allowance for Loan Losses. The allowance for loan losses is a reserve established through a provision for loan losses charged to expense, which represents management’s best estimate of probable losses that have been incurred within the existing portfolio of loans. The allowance, in the judgment of management, is necessary to reserve for estimated loan losses inherent in the loan portfolio. The allowance for loan losses includes allowance allocations calculated in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 310, “Receivables” and allowance allocations calculated in accordance with ASC Topic 450, “Contingencies.” Further information regarding the Corporation’s policies and methodology used to estimate the allowance for loan losses is presented in Note 4 - Loans.
Premises and Equipment	Premises and Equipment. Land is carried at cost. Building and improvements, and furniture and equipment are carried at cost, less accumulated depreciation, computed principally by the straight-line method based on the estimated useful lives of the related property. Leasehold improvements are generally depreciated over the lesser of the term of the respective leases or the estimated useful lives of the improvements.
Foreclosed Assets	Foreclosed Assets. Assets acquired through or instead of loan foreclosure are held for sale and are initially recorded at fair value less estimated selling costs when acquired, establishing a new cost basis. Costs after acquisition are generally expensed. If the fair value of the asset declines, a write-down is recorded through expense. The valuation of foreclosed assets is subjective in nature and may be adjusted in the future because of changes in economic conditions. Foreclosed assets are included in other assets in the accompanying consolidated balance sheets and totaled $5.3 million and $11.9 million at December 31, 2014 and 2013.
Goodwill	Goodwill. Goodwill represents the excess of the cost of businesses acquired over the fair value of the net assets acquired. Goodwill is assigned to reporting units and tested for impairment at least annually, or on an interim basis if an event occurs or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying value. See Note 6 - Goodwill and Other Intangible Assets.
Intangibles and Other Long Lived Assets	Intangibles and Other Long-Lived Assets. Intangible assets are acquired assets that lack physical substance but can be distinguished from goodwill because of contractual or other legal rights or because the asset is capable of being sold or exchanged either on its own or in combination with a related contract, asset, or liability. The Corporation’s intangible assets relate to core deposits, non-compete agreements and customer relationships. Intangible assets with definite useful lives are amortized on an accelerated basis over their estimated life. Intangible assets with indefinite useful lives are not amortized until their lives are determined to be definite. Intangible assets, premises and equipment and other long-lived assets are tested for impairment whenever events or changes in circumstances indicate the carrying amount of the assets may not be recoverable from future undiscounted cash flows. If impaired, the assets are recorded at fair value. See Note 6 - Goodwill and Other Intangible Assets.
Insurance Commissions and Fees	Insurance Commissions and Fees. Commission revenue is recognized as of the effective date of the insurance policy. The Corporation also receives contingent commissions from insurance companies as additional incentive for achieving specified premium volume goals and/or the loss experience of the insurance placed by the Corporation. Contingent commissions from insurance companies are recognized when determinable, which is generally when such commissions are received or when the Corporation receives data from the insurance companies that allows the reasonable estimation of these amounts. The Corporation maintains a reserve for commission adjustments based on estimated policy cancellations. This reserve was not significant at December 31, 2014 or 2013.
Stock Based Compensation	Stock-Based Compensation. Compensation expense for stock options, non-vested stock awards/stock units and deferred stock units is based on the fair value of the award on the measurement date, which, for the Corporation, is the date of the grant and is recognized ratably over the service period of the award. The fair value of stock options is estimated using a binomial lattice-based valuation model. The fair value of stock options granted prior to the fourth quarter of 2006 was estimated using the Black-Scholes option-pricing model. The fair value of non-vested stock awards/stock units and deferred stock units is generally the market price of the Corporation’s stock on the date of grant.
Advertising Costs	Advertising Costs. Advertising costs are expensed as incurred.
Income Taxes	Income Taxes. Income tax expense is the total of the current year income tax due or refundable and the change in deferred tax assets and liabilities (excluding deferred tax assets and liabilities related to business combinations or components of other comprehensive income). Deferred tax assets and liabilities are the expected future tax amounts for the temporary differences between carrying amounts and tax bases of assets and liabilities, computed using enacted tax rates. A valuation allowance, if needed, reduces deferred tax assets to the expected amount most likely to be realized. Realization of deferred tax assets is dependent upon the generation of a sufficient level of future taxable income and recoverable taxes paid in prior years. Although realization is not assured, management believes it is more likely than not that all of the deferred tax assets will be realized. Interest and/or penalties related to income taxes are reported as a component of income tax expense.
	The Corporation files a consolidated income tax return with its subsidiaries. Federal income tax expense or benefit has been allocated to subsidiaries on a separate return basis.
Basic and Diluted Earnings Per Common Share	Basic and Diluted Earnings Per Common Share. Earnings per common share is computed using the two-class method prescribed under ASC Topic 260, “Earnings Per Share.” ASC Topic 260 provides that unvested share-based payment awards that contain nonforfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are participating securities and shall be included in the computation of earnings per share pursuant to the two-class method. The Corporation has determined that its outstanding non-vested stock awards/stock units and deferred stock units are participating securities.
	Under the two-class method, basic earnings per common share is computed by dividing net earnings allocated to common stock by the weighted-average number of common shares outstanding during the applicable period, excluding outstanding participating securities. Diluted earnings per common share is computed using the weighted-average number of shares determined for the basic earnings per common share computation plus the dilutive effect of stock compensation using the treasury stock method. A reconciliation of the weighted-average shares used in calculating basic earnings per common share and the weighted average common shares used in calculating diluted earnings per common share for the reported periods is provided in Note 11 - Earnings Per Common Share.
Comprehensive Income	Comprehensive Income. Comprehensive income includes all changes in shareholders’ equity during a period, except those resulting from transactions with shareholders. Besides net income, other components of the Corporation’s comprehensive income include the after tax effect of changes in the net unrealized gain/loss on securities available for sale, changes in the net unrealized gain on securities transferred to held to maturity, changes in the net actuarial gain/loss on defined benefit post-retirement benefit plans and changes in the accumulated gain/loss on effective cash flow hedging instruments. See Note 15 - Other Comprehensive Income (Loss).
Derivative Financial Instruments	Derivative Financial Instruments. The Corporation’s hedging policies permit the use of various derivative financial instruments to manage interest rate risk or to hedge specified assets and liabilities. All derivatives are recorded at fair value on the Corporation’s balance sheet. Derivatives executed with the same counterparty are generally subject to master netting arrangements, however, fair value amounts recognized for derivatives and fair value amounts recognized for the right/obligation to reclaim/return cash collateral are not offset for financial reporting purposes. The Corporation may be required to recognize certain contracts and commitments as derivatives when the characteristics of those contracts and commitments meet the definition of a derivative.
	To qualify for hedge accounting, derivatives must be highly effective at reducing the risk associated with the exposure being hedged and must be designated as a hedge at the inception of the derivative contract. The Corporation considers a hedge to be highly effective if the change in fair value of the derivative hedging instrument is within 80% to 125% of the opposite change in the fair value of the hedged item attributable to the hedged risk. If derivative instruments are designated as hedges of fair values, and such hedges are highly effective, both the change in the fair value of the hedge and the hedged item are included in current earnings. Fair value adjustments related to cash flow hedges are recorded in other comprehensive income and are reclassified to earnings when the hedged transaction is reflected in earnings. Ineffective portions of hedges are reflected in earnings as they occur. Actual cash receipts and/or payments and related accruals on derivatives related to hedges are recorded as adjustments to the interest income or interest expense associated with the hedged item. During the life of the hedge, the Corporation formally assesses whether derivatives designated as hedging instruments continue to be highly effective in offsetting changes in the fair value or cash flows of hedged items. If it is determined that a hedge has ceased to be highly effective, the Corporation will discontinue hedge accounting prospectively. At such time, previous adjustments to the carrying value of the hedged item are reversed into current earnings and the derivative instrument is reclassified to a trading position recorded at fair value.
Fair Value Measurements	Fair Value Measurements. In general, fair values of financial instruments are based upon quoted market prices, where available. If such quoted market prices are not available, fair value is based upon internally developed models that primarily use, as inputs, observable market-based parameters. Valuation adjustments may be made to ensure that financial instruments are recorded at fair value. These adjustments may include amounts to reflect counterparty credit quality and the Corporation’s creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time.
Transfers of Financial Assets	Transfers of Financial Assets. Transfers of financial assets are accounted for as sales when control over the assets has been surrendered. Control over transferred assets is deemed to be surrendered when (i) the assets have been isolated from the Corporation, (ii) the transferee obtains the right (free of conditions that constrain it from taking advantage of that right) to pledge or exchange the transferred assets, and (iii) the Corporation does not maintain effective control over the transferred assets through an agreement to repurchase them before their maturity.
Loss Contingencies	Loss Contingencies. Loss contingencies, including claims and legal actions arising in the ordinary course of business are recorded as liabilities when the likelihood of loss is probable and an amount or range of loss can be reasonably estimated.
Trust Assets	Trust Assets. Assets of the Corporation’s trust department, other than cash on deposit at Frost Bank, are not included in the accompanying financial statements because they are not assets of the Corporation.
Reclassifications	Reclassifications. Certain items in prior financial statements have been reclassified to conform to the current presentation.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Additional Cash Flow Information	Additional cash flow information was as follows:
		Year Ended December 31,
		2014		2013		2012
	Cash paid for interest	$	14,705	$	22,449	$	29,378
	Cash paid for income tax	62,976		49,514		58,950
	Significant non-cash transactions:
	Transfer of securities from available for sale to held to maturity	—		—		2,266,195
	Unsettled purchases of securities	—		16,241		90,073
	Loans foreclosed and transferred to other real estate owned and foreclosed assets	4,363		6,870		7,817
	Premises and equipment transferred to other real estate owned and foreclosed assets	1,740		—		—
	Loans to facilitate the sale of other real estate owned	102		678		—
	Deferred gain on sale of building and parking garage	—		768		—

Securities_Tables

Securities (Tables)	12 Months Ended
	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Year End Securities Held To Maturity And Available For Sale	Year-end securities held to maturity and available for sale consisted of the following:
		2014											2013
		Amortized			Gross			Gross			Estimated		Amortized		Gross		Gross		Estimated
		Cost			Unrealized			Unrealized			Fair Value		Cost		Unrealized		Unrealized		Fair Value
					Gains			Losses							Gains		Losses
	Held to Maturity:
	U.S. Treasury	$	249,009		$	14,604		$	—		$	263,613	$	248,592	$	20,139	$	—	$	268,731
	Residential mortgage-backed securities	8,012			92			—			8,104		9,674		89		143		9,620
	States and political subdivisions	2,668,115			34,243			9,035			2,693,323		2,880,482		7,691		137,861		2,750,312
	Other	1,350			—			—			1,350		1,000		—		—		1,000
	Total	$	2,926,486		$	48,939		$	9,035		$	2,966,390	$	3,139,748	$	27,919	$	138,004	$	3,029,663
	Available for Sale:
	U. S. Treasury	$	3,783,899		$	30,594		$	3,241		$	3,811,252	$	2,522,159	$	18,395	$	—	$	2,540,554
	U.S. government agencies/corporations	—			—			—			—		54,024		—		44		53,980
	Residential mortgage-backed securities	1,331,114			68,027			417			1,398,724		1,710,664		66,791		1,439		1,776,016
	States and political subdivisions	3,104,563			104,500			156			3,208,907		1,476,316		20,090		7,492		1,488,914
	Other	42,371			—			—			42,371		35,972		—		—		35,972
	Total	$	8,261,947		$	203,121		$	3,814		$	8,461,254	$	5,799,135	$	105,276	$	8,975	$	5,895,436
Year End Securities with Unrealized Losses, Segregated by Length of Impairment	Year-end securities with unrealized losses, segregated by length of impairment, were as follows:
		Less than 12 Months						More than 12 Months					Total
		Estimated			Unrealized			Estimated			Unrealized		Estimated		Unrealized
		Fair Value			Losses			Fair Value			Losses		Fair Value		Losses
	2014
	Held to Maturity:
	States and political subdivisions	$	68,024		$	144		$	683,251		$	8,891	$	751,275	$	9,035
	Total	$	68,024		$	144		$	683,251		$	8,891	$	751,275	$	9,035
	Available for Sale:
	U.S. Treasury	$	1,019,230		$	3,241		$	—		$	—	$	1,019,230	$	3,241
	Residential mortgage-backed securities	8,550			42			16,944			375		25,494		417
	States and political subdivisions	65,751			156			—			—		65,751		156
	Total	$	1,093,531		$	3,439		$	16,944		$	375	$	1,110,475	$	3,814
	2013
	Held to Maturity:
	Residential mortgage-backed securities	$	6,934		$	143		$	—		$	—	$	6,934	$	143
	States and political subdivisions	2,071,521			113,512			266,566			24,349		2,338,087		137,861
	Total	$	2,078,455		$	113,655		$	266,566		$	24,349	$	2,345,021	$	138,004
	Available for Sale:
	U.S. government agencies/ corporations	$	53,980		$	44		$	—		$	—	$	53,980	$	44
	Residential mortgage-backed securities	33,001			1,157			2,713			282		35,714		1,439
	States and political subdivisions	679,923			7,492			—			—		679,923		7,492
	Total	$	766,904		$	8,693		$	2,713		$	282	$	769,617	$	8,975
Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity	The amortized cost and estimated fair value of securities, excluding trading securities, at December 31, 2014 are presented below by contractual maturity. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations. Residential mortgage-backed securities and equity securities are shown separately since they are not due at a single maturity date.
		Held to Maturity						Available for Sale
		Amortized			Estimated			Amortized			Estimated
		Cost			Fair Value			Cost			Fair Value
	Due in one year or less	$	153,701		$	155,505		$	515,567		$	517,482
	Due after one year through five years	533,990			564,854			2,474,795			2,486,488
	Due after five years through ten years	172,371			172,240			1,937,104			1,977,280
	Due after ten years	2,058,412			2,065,687			1,960,996			2,038,909
	Residential mortgage-backed securities	8,012			8,104			1,331,114			1,398,724
	Equity securities	—			—			42,371			42,371
	Total	$	2,926,486		$	2,966,390		$	8,261,947		$	8,461,254
Sales of Securities Available for Sale	Sales of securities available for sale were as follows:
		2014			2013			2012
	Proceeds from sales	$	12,151,287		$	10,056,060		$	16,587,482
	Gross realized gains	39			1,206			6,943
	Gross realized losses	(1		)	(30		)	(2,629		)
	Tax (expense) benefit of securities gains/losses	(13		)	(412		)	(1,510		)
Premium Amortization and Discount Accretion Included in Income on Securities [Table Text Block]	Premium amortization and discount accretion included in interest income on securities was as follows:
		2014			2013			2012
	Premium amortization	$	(68,070	)	$	(49,112	)	$	(28,364	)
	Discount accretion	6,802			7,191			6,663
	Net (premium amortization) discount accretion	$	(61,268	)	$	(41,921	)	$	(21,701	)
Year End Trading Account Securities, at Estimated Fair Value	Year-end trading account securities, at estimated fair value, were as follows:
		2014			2013
	U.S. Treasury	$	15,339		$	15,389
	States and political subdivisions	87			1,009
	Total	$	15,426		$	16,398
Net Gains and Losses on Trading Account Securities	Net gains and losses on trading account securities were as follows:
		2014			2013			2012
	Net gain on sales transactions	$	829		$	878		$	1,219
	Net mark-to-market gains (losses)	—			(429		)	(161		)
	Net gain on trading account securities	$	829		$	449		$	1,058

Loans_Tables

Loans (Tables)	12 Months Ended
	Dec. 31, 2014
Receivables [Abstract]
Loans	Year-end loans consisted of the following:
		2014				2013
	Commercial and industrial:
	Commercial	$	5,429,206			$	4,587,499
	Leases	338,537				319,577
	Total commercial and industrial	5,767,743				4,907,076
	Commercial real estate:
	Commercial mortgages	3,080,202				2,800,760
	Construction	629,988				426,639
	Land	291,907				239,937
	Total commercial real estate	4,002,097				3,467,336
	Consumer real estate:
	Home equity loans	342,725				329,853
	Home equity lines of credit	220,128				195,132
	Other	286,198				283,219
	Total consumer real estate	849,051				808,204
	Total real estate	4,851,148				4,275,540
	Consumer and other:
	Consumer installment	385,479				350,827
	Other	8,122				7,289
	Total consumer and other	393,601				358,116
	Unearned discounts	(24,957		)		(25,032		)
	Total loans	$	10,987,535			$	9,515,700
Activities in Related Party Loans	Activity in related party loans during 2014 is presented in the following table. Other changes were primarily related to changes in related-party status.
	Balance outstanding at December 31, 2013	$	76,672
	Principal additions	127,347
	Principal reductions	(165,963		)
	Other changes	644
	Balance outstanding at December 31, 2014	$	38,700
Non-Accrual Loans, Segregated by Class of Loans	Year-end non-accrual loans, segregated by class of loans, were as follows:
		2014				2013
	Commercial and industrial:
	Energy	$	636			$	590
	Other commercial	34,108				26,143
	Commercial real estate:
	Buildings, land and other	19,639				27,035
	Construction	2,792				—
	Consumer real estate	2,212				2,207
	Consumer and other	538				745
	Total	$	59,925			$	56,720
Age Analysis of Past Due Loans, Segregated by Class of Loans	An age analysis of past due loans (including both accruing and non-accruing loans), segregated by class of loans, as of December 31, 2014 was as follows:
		Loans				Loans				Total Past				Current			Total Loans			Accruing
		30-89 Days				90 or More				Due Loans				Loans						Loans 90 or
		Past Due				Days														More Days
						Past Due														Past Due
	Commercial and industrial:
	Energy	$	7,278			$	—			$	7,278			$	1,766,667		$	1,773,945		$	—
	Other commercial	16,350				33,998				50,348				3,943,450			3,993,798			14,254
	Commercial real estate:
	Buildings, land and other	6,535				11,308				17,843				3,354,266			3,372,109			3,333
	Construction	5,081				1,327				6,408				623,580			629,988			1,042
	Consumer real estate	4,560				2,148				6,708				842,343			849,051			1,910
	Consumer and other	5,706				476				6,182				387,419			393,601			402
	Unearned discounts	—				—				—				(24,957		)	(24,957		)	—
	Total	$	45,510			$	49,257			$	94,767			$	10,892,768		$	10,987,535		$	20,941
Impaired Loans	Year-end impaired loans are set forth in the following table. No interest income was recognized on impaired loans subsequent to their classification as impaired.
		Unpaid				Recorded				Recorded				Total			Related			Average
		Contractual				Investment				Investment				Recorded			Allowance			Recorded
		Principal				With No				With				Investment						Investment
		Balance				Allowance				Allowance
	2014
	Commercial and industrial:
	Energy	$	706			$	636			$	—			$	636		$	—		$	571
	Other commercial	42,212				29,007				2,853				31,860			1,613			27,154
	Commercial real estate:
	Buildings, land and other	22,919				17,441				265				17,706			67			20,339
	Construction	3,007				2,793				—				2,793			—			739
	Consumer real estate	812				596				—				596			—			674
	Consumer and other	—				—				—				—			—			159
	Total	$	69,656			$	50,473			$	3,118			$	53,591		$	1,680		$	49,636
	2013
	Commercial and industrial:
	Energy	$	545			$	531			$	—			$	531		$	—		$	428
	Other commercial	31,429				15,337				7,004				22,341			4,140			34,894
	Commercial real estate:
	Buildings, land and other	27,792				15,697				8,870				24,567			2,786			34,633
	Construction	—				—				—				—			—			634
	Consumer real estate	907				745				—				745			—			804
	Consumer and other	334				278				—				278			—			348
	Total	$	61,007			$	32,588			$	15,874			$	48,462		$	6,926		$	71,741
	2012
	Commercial and industrial:
	Energy	$	1,255			$	—			$	1,069			$	1,069		$	900		$	214
	Other commercial	56,784				21,709				19,096				40,805			4,200			42,630
	Commercial real estate:
	Buildings, land and other	44,652				19,010				17,149				36,159			3,137			40,258
	Construction	1,497				1,100				—				1,100			—			1,392
	Consumer real estate	961				864				—				864			—			1,617
	Consumer and other	428				400				—				400			—			469
	Total	$	105,577			$	43,083			$	37,314			$	80,397		$	8,237		$	86,580
Troubled Debt Restructurings	Troubled debt restructurings during 2014, 2013 and 2012 are set forth in the following table.
		2014								2013							2012
		Balance at				Balance at				Balance at				Balance at			Balance at			Balance at
		Restructure				Year-end				Restructure				Year-end			Restructure			Year-end
	Commercial and industrial:
	Energy	$	—			$	—			$	528			$	531		$	—		$	—
	Other commercial	5,795				5,391				6,334				4,937			1,602			1,478
	Commercial real estate:
	Buildings, land and other	3,121				2,948				7,964				5,747			714			710
	Consumer real estate	—				—				—				—			—			—
	Consumer	—				—				7				—			—			—
		$	8,916			$	8,339			$	14,833			$	11,215		$	2,316		$	2,188
Weighted Average Risk Grades for All Commercial Loans by Class	The following table presents weighted average risk grades for all commercial loans by class.
		December 31, 2014							December 31, 2013
		Weighted			Loans				Weighted			Loans
		Average							Average
		Risk Grade							Risk Grade
	Commercial and industrial:
	Energy
	Risk grades 1-8	5.37			$	1,740,455			5.37			$	1,106,348
	Risk grade 9	9			27,313				9			7,726
	Risk grade 10	10			161				10			245
	Risk grade 11	11			5,380				11			500
	Risk grade 12	12			636				12			590
	Risk grade 13	13			—				13			—
	Total energy	5.45			$	1,773,945			5.4			$	1,115,409
	Other commercial
	Risk grades 1-8	5.93			$	3,785,171			5.95			$	3,507,963
	Risk grade 9	9			65,166				9			74,766
	Risk grade 10	10			54,519				10			89,878
	Risk grade 11	11			55,034				11			92,917
	Risk grade 12	12			31,683				12			21,389
	Risk grade 13	13			2,225				13			4,754
	Total other commercial	6.16			$	3,993,798			6.27			$	3,791,667
	Commercial real estate:
	Buildings, land and other
	Risk grades 1-8	6.53			$	3,148,339			6.59			$	2,844,665
	Risk grade 9	9			72,906				9			65,770
	Risk grade 10	10			87,889				10			49,881
	Risk grade 11	11			43,336				11			53,208
	Risk grade 12	12			19,501				12			24,387
	Risk grade 13	13			138				13			2,786
	Total commercial real estate	6.76			$	3,372,109			6.83			$	3,040,697
	Construction
	Risk grades 1-8	6.91			$	617,805			7.05			$	418,999
	Risk grade 9	9			8,003				9			1,301
	Risk grade 10	10			1,323				10			5,931
	Risk grade 11	11			64				11			408
	Risk grade 12	12			2,793				12			—
	Risk grade 13	13			—				13			—
	Total construction	6.97			$	629,988			7.1			$	426,639
Net (Charge-Offs)/Recoveries, Segregated by Class of Loans	Net (charge-offs)/recoveries, segregated by class of loan, were as follows:
		2014				2013				2012
	Commercial and industrial:
	Energy	$	(1,237	)		$	(913	)		$	4
	Other commercial	(2,911		)		(28,431		)		(13,627		)
	Commercial real estate:
	Buildings, land and other	(2,348		)		(381		)		698
	Construction	348				256				78
	Consumer real estate	(733		)		(719		)		(638		)
	Consumer and other	(2,329		)		(2,409		)		(2,289		)
	Total	$	(9,210	)		$	(32,597	)		$	(15,774	)
Unallocated Portion of the Allowance for Loan Losses	The following table presents details of the allowance for loan losses, segregated by loan portfolio segment.
		Commercial				Commercial				Consumer				Consumer			Unallocated			Total
		and				Real Estate				Real Estate				and Other
		Industrial
	31-Dec-14
	Historical valuation allowances	$	32,421			$	14,684			$	2,017			$	10,482		$	—		$	59,604
	Specific valuation allowances	1,613				67				—				—			—			1,680
	General valuation allowances:
	Environmental risk adjustment	6,773				3,547				474				2,683			—			13,477
	Distressed industries	3,090				3				—				—			—			3,093
	Excessive industry concentrations	2,114				378				—				—			—			2,492
	Large relationship concentrations	2,248				1,559				—				—			—			3,807
	Highly-leveraged credit relationships	3,958				1,347				—				—			—			5,305
	Policy exceptions	1,907				875				—				—			—			2,782
	Credit and collateral exceptions	1,483				681				—				—			—			2,164
	Loans not reviewed by concurrence	2,110				2,284				2,336				1,176			—			7,906
	Adjustment for recoveries	(6,234		)		(1,800		)		(364		)		(7,439		)	—			(15,837		)
	General macroeconomic risk	7,709				3,538				715				1,107			—			13,069
	Total	$	59,192			$	27,163			$	5,178			$	8,009		$	—		$	99,542
	31-Dec-13
	Historical valuation allowances	$	29,357			$	13,042			$	2,644			$	8,695		$	—		$	53,738
	Specific valuation allowances	4,140				2,786				—				—			—			6,926
	General valuation allowances:
	Environmental risk adjustment	5,497				3,314				664				2,331			—			11,806
	Distressed industries	7,812				384				—				—			—			8,196
	Excessive industry concentrations	1,499				367				—				—			—			1,866
	Large relationship concentrations	1,529				1,081				—				—			—			2,610
	Highly-leveraged credit relationships	4,535				619				—				—			—			5,154
	Policy exceptions	—				—				—				—			2,492			2,492
	Credit and collateral exceptions	—				—				—				—			1,398			1,398
	Loans not reviewed by concurrence	2,009				2,201				2,250				1,064			—			7,524
	Adjustment for recoveries	(3,588		)		(1,204		)		(328		)		(7,080		)	—			(12,200		)
	General macroeconomic risk	—				—				—				—			2,928			2,928
	Total	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
Activity in Allowance for Loan Losses by Portfolio Segment	The following table details activity in the allowance for loan losses by portfolio segment for 2014, 2013 and 2012. Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories.
		Commercial				Commercial				Consumer				Consumer			Unallocated			Total
		and				Real Estate				Real Estate				and Other
		Industrial
	2014
	Beginning balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
	Provision for loan losses	10,550				6,573				681				5,328			(6,818		)	16,314
	Charge-offs	(13,820		)		(3,800		)		(1,097		)		(9,768		)	—			(28,485		)
	Recoveries	9,672				1,800				364				7,439			—			19,275
	Net charge-offs	(4,148		)		(2,000		)		(733		)		(2,329		)	—			(9,210		)
	Ending balance	$	59,192			$	27,163			$	5,178			8,009			$	—		$	99,542
	Period-end amount allocated to:
	Loans individually evaluated for impairment	$	11,836			$	1,164			$	—			$	—		$	—		$	13,000
	Loans collectively evaluated for impairment	47,356				25,999				5,178				8,009			—			86,542
	Ending balance	$	59,192			$	27,163			$	5,178			$	8,009		$	—		$	99,542
	2013
	Beginning balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
	Provision for loan losses	27,970				(6,631		)		697				3,912			(5,366		)	20,582
	Charge-offs	(32,932		)		(1,329		)		(1,047		)		(9,489		)	—			(44,797		)
	Recoveries	3,588				1,204				328				7,080			—			12,200
	Net charge-offs	(29,344		)		(125		)		(719		)		(2,409		)	—			(32,597		)
	Ending balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
	Period-end amount allocated to:
	Loans individually evaluated for impairment	$	16,682			$	3,914			$	—			$	—		$	—		$	20,596
	Loans collectively evaluated for impairment	36,108				18,676				5,230				5,010			6,818			71,842
	Ending balance	$	52,790			$	22,590			$	5,230			$	5,010		$	6,818		$	92,438
	2012
	Beginning balance	$	42,774			$	20,912			$	3,540			$	12,635		$	30,286		$	110,147
	Provision for loan losses	25,013				7,658				2,350				(6,839		)	(18,102		)	10,080
	Charge-offs	(18,493		)		(3,951		)		(1,495		)		(9,101		)	—			(33,040		)
	Recoveries	4,870				4,727				857				6,812			—			17,266
	Net charge-offs	(13,623		)		776				(638		)		(2,289		)	—			(15,774		)
	Ending balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
	Period-end amount allocated to:
	Loans individually evaluated for impairment	$	13,171			$	4,366			$	—			$	—		$	—		$	17,537
	Loans collectively evaluated for impairment	40,993				24,980				5,252				3,507			12,184			86,916
	Ending balance	$	54,164			$	29,346			$	5,252			$	3,507		$	12,184		$	104,453
Investment in Loans Related to the Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology	The Corporation’s recorded investment in loans as of December 31, 2014 and 2013 related to each balance in the allowance for loan losses by portfolio segment and detailed on the basis of the impairment methodology used by the Corporation was as follows:
		Commercial				Commercial				Consumer				Consumer			Unearned			Total
		and				Real Estate				Real Estate				and Other			Discounts
		Industrial
	2014
	Loans individually evaluated for impairment	$	149,638			$	155,044			$	596			$	—		$	—		$	305,278
	Loans collectively evaluated for impairment	5,618,105				3,847,053				848,455				393,601			(24,957		)	10,682,257
	Ending balance	$	5,767,743			$	4,002,097			$	849,051			$	393,601		$	(24,957	)	$	10,987,535
	2013
	Loans individually evaluated for impairment	$	210,273			$	136,601			$	745			$	278		$	—		$	347,897
	Loans collectively evaluated for impairment	4,696,803				3,330,735				807,459				357,838			(25,032		)	9,167,803
	Ending balance	$	4,907,076			$	3,467,336			$	808,204			$	358,116		$	(25,032	)	$	9,515,700

Premises_and_Equipment_Tables

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Premises and Equipment	Year-end premises and equipment were as follows:
		2014			2013
	Land	$	102,334		$	97,095
	Buildings	240,430			231,066
	Furniture and equipment	103,603			212,169
	Leasehold improvements	60,902			61,221
	Construction in progress	118,367			10,074
		625,636			611,625
	Less accumulated depreciation and amortization	(182,748		)	(298,294		)
	Total premises and equipment, net	$	442,888		$	313,331

Goodwill_and_Other_Intangible_1

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill. Year-end goodwill was as follows:
		2014		2013
	Goodwill	$	653,950	$	536,649
Schedule of Other Intangible Assets	Other Intangible Assets. Year-end other intangible assets were as follows:
		Gross		Accumulated			Net
		Intangible		Amortization			Intangible
		Assets					Assets
	2014
	Core deposits	$	44,266	$	(34,591	)	$	9,675
	Customer relationships	5,771		(3,643		)	2,128
	Non-compete agreements	725		(403		)	322
		$	50,762	$	(38,637	)	$	12,125
	2013
	Core deposits	$	34,966	$	(31,961	)	$	3,005
	Customer relationships	7,870		(5,042		)	2,828
	Non-compete agreements	1,135		(623		)	512
		$	43,971	$	(37,626	)	$	6,345
Estimated Aggregate Future Amortization Expense for Intangible Assets	The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2014 is as follows:
	2015	$	3,324
	2016	2,413
	2017	1,619
	2018	1,346
	2019	1,102
	Thereafter	2,321
		$	12,125

Deposits_Tables

Deposits (Tables)	12 Months Ended
	Dec. 31, 2014
Deposits [Abstract]
Schedule of Deposits	Year-end deposits were as follows:
		2014		2013
	Non-interest-bearing demand deposits:
	Commercial and individual	$	9,256,045	$	7,445,656
	Correspondent banks	429,000		427,134
	Public funds	464,016		438,359
	Total non-interest-bearing demand deposits	10,149,061		8,311,149
	Interest-bearing deposits:
	Private accounts:
	Savings and interest checking	4,743,963		4,020,313
	Money market accounts	7,860,403		6,883,869
	Time accounts of $100,000 or more	490,209		508,441
	Time accounts under $100,000	454,220		438,800
	Total private accounts	13,548,795		11,851,423
	Public funds:
	Savings and interest checking	326,090		305,976
	Money market accounts	57,145		56,015
	Time accounts of $100,000 or more	53,684		160,637
	Time accounts under $100,000	1,155		3,586
	Total public funds	438,074		526,214
	Total interest-bearing deposits	13,986,869		12,377,637
	Total deposits	$	24,135,930	$	20,688,786
Additional Information About Corporation's Deposits	The following table presents additional information about the Corporation’s year-end deposits:
		2014		2013
	Deposits from the Certificate of Deposit Account Registry Service (CDARS)	$	22	$	200
	Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB)	149		—
	Deposits from foreign sources (primarily Mexico)	744,295		769,970
	Deposits from certain directors, executive officers and their affiliates	176,821		144,216
Scheduled Maturities of Time Deposits	Scheduled maturities of time deposits, including both private and public funds, at December 31, 2014 were as follows:
	2015	$	857,857
	2016	140,882
	2017	379
	2018	92
	2019	58
		$	999,268
Scheduled Maturities of Time Deposits in Amounts of $100,000 or More	Scheduled maturities of time deposits in amounts of $100,000 or more, including both private and public funds, at December 31, 2014, were as follows:
	Due within 3 months or less	$	228,010
	Due after 3 months and within 6 months	97,194
	Due after 6 months and within 12 months	142,973
	Due after 12 months	75,716
		$	543,893

OffBalanceSheet_Arrangements_C1

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Financial Instruments With Off-Balance-Sheet Risk	Year-end financial instruments with off-balance-sheet risk were as follows:
		2014		2013
	Commitments to extend credit	$	7,955,779	$	6,919,942
	Standby letters of credit	248,360		186,857
	Deferred standby letter of credit fees	1,942		1,450
Future Minimum Lease Payments Due Under Non-Cancelable Operating Leases	Future minimum lease payments due under non-cancelable operating leases at December 31, 2014 were as follows:
	2015	$	21,373
	2016	19,834
	2017	18,503
	2018	17,067
	2019	13,269
	Thereafter	77,000
		$	167,046

Capital_and_Regulatory_Matters1

Capital and Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2014
Regulatory Capital Requirements [Abstract]
Actual and Required Capital Ratios	Year-end actual and required capital ratios for Cullen/Frost and Frost Bank were as follows:
		Actual				Minimum Required				Required to be
						for Capital Adequacy				Considered Well
						Purposes				Capitalized
		Capital		Ratio		Capital		Ratio		Capital		Ratio
		Amount				Amount				Amount
	2014
	Total Capital to Risk-Weighted Assets
	Cullen/Frost	$	2,325,818	14.55	%	$	1,278,797	8	%	$	1,598,496	10	%
	Frost Bank	2,071,012		12.99		1,275,858		8		1,594,823		10
	Tier 1 Capital to Risk-Weighted Assets
	Cullen/Frost	2,186,276		13.68		639,398		4		959,098		6
	Frost Bank	1,979,415		12.41		637,929		4		956,894		6
	Leverage Ratio
	Cullen/Frost	2,186,276		8.16		1,072,035		4		1,340,043		5
	Frost Bank	1,979,415		7.4		1,070,109		4		1,337,636		5
	2013
	Total Capital to Risk-Weighted Assets
	Cullen/Frost	$	2,110,774	15.52	%	$	1,088,349	8	%	$	1,360,437	10	%
	Frost Bank	1,780,313		13.12		1,085,447		8		1,356,809		10
	Tier 1 Capital to Risk-Weighted Assets
	Cullen/Frost	1,958,336		14.39		544,175		4		816,262		6
	Frost Bank	1,707,307		12.58		542,724		4		814,085		6
	Leverage Ratio
	Cullen/Frost	1,958,336		8.49		922,728		4		1,153,410		5
	Frost Bank	1,707,307		7.42		920,107		4		1,150,134		5

Earnings_Per_Common_Share_Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2014
Earnings Per Share [Abstract]
Basic and Diluted Earnings Per Common Share	The following table presents a reconciliation of net income available to common shareholders, net earnings allocated to common stock and the number of shares used in the calculation of basic and diluted earnings per common share.
		2014		2013		2012
	Net Income	$	277,977	$	237,866	$	237,952
	Less: Preferred stock dividends	8,063		6,719		—
	Net income available to common shareholders	269,914		231,147		237,952
	Less: Earnings allocated to participating securities	1,001		850		773
	Net earnings allocated to common stock	$	268,913	$	230,297	$	237,179
	Distributed earnings allocated to common stock	$	126,709	$	119,177	$	116,472
	Undistributed earnings allocated to common stock	142,204		111,120		120,707
	Net earnings allocated to common stock	$	268,913	$	230,297	$	237,179
	Weighted-average shares outstanding for basic earnings per common share	62,072,080		60,350,552		61,298,041
	Dilutive effect of stock compensation	901,448		765,858		345,341
	Weighted-average shares outstanding for diluted earnings per common share	62,973,528		61,116,410		61,643,382

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Combined Activity in Corporations Defined Benefit Pension Plans	The Corporation uses a December 31 measurement date for its defined benefit plans. Combined activity in the Corporation’s defined benefit pension plans was as follows:
		2014				2013				2012
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	163,876			$	178,158			$	157,855
	Interest cost	8,002				7,341				7,801
	Actuarial (gain) loss	34,438				(15,333		)		18,436
	Benefits paid	(6,679		)		(6,290		)		(5,934		)
	Benefit obligation at end of year	199,637				163,876				178,158
	Change in plan assets:
	Fair value of plan assets at beginning of year	164,769				145,901				137,253
	Actual return on plan assets	9,428				24,489				13,931
	Employer contributions	667				669				651
	Benefits paid	(6,679		)		(6,290		)		(5,934		)
	Fair value of plan assets at end of year	168,185				164,769				145,901
	Funded status of the plan at end of year and accrued (benefit) liability recognized	$	31,452			$	(893	)		$	32,257
	Accumulated benefit obligation at end of year	$	199,637			$	163,876			$	178,158
Disaggregated Information Related to Corporations Defined Benefit Pension Plans	Certain disaggregated information related to the Corporation’s defined benefit pension plans as of year-end was as follows:
		Retirement Plan								Restoration Plan
		2014				2013				2014			2013
	Projected benefit obligation	$	179,970			$	147,403			$	19,667		$	16,473
	Accumulated benefit obligation	179,970				147,403				19,667			16,473
	Fair value of plan assets	168,185				164,769				—			—
	Funded status of the plan at end of year and accrued (benefit) liability recognized	11,785				(17,366		)		19,667			16,473
Net Periodic Benefit Cost (Benefit)	The components of the combined net periodic cost (benefit) for the Corporation’s defined benefit pension plans were as follows:
		2014				2013				2012
	Expected return on plan assets, net of expenses	$	(12,514	)		$	(11,087	)		$	(10,412	)
	Interest cost on projected benefit obligation	8,002				7,341				7,801
	Net amortization and deferral	2,687				6,558				5,709
	Net periodic cost (benefit)	$	(1,825	)		$	2,812			$	3,098
Defined Benefit Pension Plans Recognized as Component of Other Comprehensive Income	Amounts related to the Corporation’s defined benefit pension plans recognized as a component of other comprehensive income were as follows:
		2014				2013				2012
	Net actuarial gain (loss)	$	(34,837	)		$	35,293			$	(9,405	)
	Deferred tax (expense) benefit	12,193				(12,353		)		3,292
	Other comprehensive income (loss), net of tax	$	(22,644	)		$	22,940			$	(6,113	)
Defined Benefit Pension Plans Not Recognized as Component of Combined Net Period Benefit Cost	The Corporation expects to recognize approximately $7.0 million of the net actuarial loss reported in the following table as of December 31, 2014 as a component of net periodic benefit cost during 2015.
		2014				2013
	Net actuarial loss	$	(75,038	)		$	(40,201	)
	Deferred tax benefit	26,263				14,070
	Amounts included in accumulated other comprehensive loss, net of tax	$	(48,775	)		$	(26,131	)
Weighted-Average Assumptions Used to Determine Benefit Obligations	The weighted-average assumptions used to determine the benefit obligations as of the end of the years indicated and the net periodic benefit cost for the years indicated are presented in the table below. Because the plans were frozen, increases in compensation are not considered after 2001.
		2014			2013			2012
	Benefit obligations:
	Discount rate	4.2	%		5	%		4.2	%
	Net periodic benefit cost:
	Discount rate	5	%		4.2	%		5.05	%
	Expected return on plan assets	7.75			7.75			7.75
Fair Value of Plan Assets	The major categories of assets in the Corporation’s Retirement Plan as of year-end are presented in the following table. Assets are segregated by the level of the valuation inputs within the fair value hierarchy established by ASC Topic 820 “Fair Value Measurements and Disclosures,” utilized to measure fair value (see Note 18 - Fair Value Measurements). The Corporation’s Restoration Plan is unfunded.
		2014				2013
	Level 1:
	Mutual funds	$	165,429			$	163,046
	Cash and cash equivalents	1,447				91
	Level 2:
	Corporate bonds and notes	653				893
	U.S. government agency securities	394				473
	States and political subdivisions	262				266
	Total fair value of plan assets	$	168,185			$	164,769
Expected Future Benefit Payments Related to Defined Benefit Plans	As of December 31, 2014, expected future benefit payments related to the Corporation’s defined benefit plans were as follows:
	2015	$	8,429
	2016	11,991
	2017	9,532
	2018	9,988
	2019	10,413
	2020 through 2024	57,255
		$	107,608
Summary of Activity in Corporation's Active Stock Plans	A combined summary of activity in the Corporation’s active stock plans is presented in the following table.
								Non-Vested Stock						Stock Options
								Awards/Stock Units						Outstanding
								Outstanding
		Shares			Director			Number			Weighted-			Number		Weighted-
		Available			Deferred			of Shares			Average			of Shares		Average
		for Grant			Stock Units						Grant-Date					Exercise
					Outstanding						Fair Value					Price
	Balance, January 1, 2012	1,963,455			22,092			169,530			$	50.33		4,968,822		$	51.49
	Granted	(825,542	)		5,632			49,130			54.56			770,780		54.56
	Stock options exercised	—			—			—			—			(206,336	)	50.96
	Stock awards vested	—			—			(30,100	)		52.44			—		—
	Forfeited	19,750			—			—			—			(19,750	)	50.49
	Canceled/expired	(250	)		—			—			—			—		—
	Balance, December 31, 2012	1,157,413			27,724			188,560			51.67			5,513,516		51.94
	Authorized	2,293,660			—			—			—			—		—
	Granted	(635,360	)		5,500			38,010			71.39			591,850		71.38
	Stock options exercised	—			—			—			—			(1,319,786	)	52.02
	Stock awards vested	—			—			(26,830	)		50.64			—		—
	Forfeited	46,890			—			—			—			(46,890	)	46.05
	Canceled/expired	—			—			—			—			—		—
	Balance, December 31, 2013	2,862,603			33,224			199,740			55.32			4,738,690		54.35
	Authorized	—			—			—			—			—		—
	Granted	(955,443	)		5,643			32,050			78.92			917,750		78.93
	Stock options exercised	—			—			—			—			(560,291	)	52.04
	Stock awards/units vested	—			—			(56,300	)		52.46			—		—
	Forfeited	66,267			—			—			—			(66,267	)	62.21
	Canceled/expired	—			—			—			—			—		—
	Balance, December 31, 2014	1,973,427			38,867			175,490			$	60.55		5,029,882		$	58.99
Options Outstanding and Exercisable	Other information regarding options outstanding and exercisable as of December 31, 2014 is as follows:
											Options Outstanding							Options Exercisable
	Range of										Number		Weighted-			Weighted-		Number	Weighted-
	Exercise Prices										of Shares		Average			Average		of Shares	Average
													Exercise Price			Remaining			Exercise
																Contractual Life			Price
																in Years
	$	45.01			to		$	50			946,265		$	48.26		5.58		760,240	$	49.91
	50.01				to		55				2,273,190		52.61			5.58		1,907,700	52.24
	55.01				to		60				334,075		57.63			1.88		334,075	57.63
	70.01				to		75				576,602		71.38			8.84		140,613	71.38
	75.01				to		80				899,750		78.94			9.8		—	—
							Total				5,029,882		58.99			6.46		3,142,628	53.11
Shares Issued in Connection With Stock Compensation Awards	Shares issued in connection with stock compensation awards are issued from available treasury shares. If no treasury shares are available, new shares are issued from available authorized shares. Shares issued in connection with stock compensation awards along with other related information were as follows:
		2014				2013				2012
	New shares issued from available authorized shares	—				153,275				207,586
	Issued from available treasury stock	601,851				1,179,551				15,600
	Total	601,851				1,332,826				223,186
	Proceeds from stock option exercises	$	29,158			$	68,653			$	10,516
	Intrinsic value of stock options exercised	13,714				20,506				1,538
	Fair value of stock awards/units vested	4,346				1,918				1,649
Stock-Based Compensation Expense	Stock-based compensation expense and the related income tax benefit was as follows:
		2014				2013				2012
	Stock options	$	9,142			$	8,814			$	9,663
	Non-vested stock awards/stock units	2,920				2,819				2,843
	Deferred stock-units	441				330				330
	Total	$	12,503			$	11,963			$	12,836
	Income tax benefit	$	4,376			$	4,187			$	4,493
Unrecognized Stock-Based Compensation Expense	Unrecognized stock-based compensation expense at December 31, 2014 was as follows:
	Stock options	$	22,066
	Non-vested stock awards/stock units	2,437
	Total	$	24,503
Assumptions Used to Determine The Fair Value of Options Granted	The assumptions used to determine the fair value of options granted are detailed in the table below.
		2014			2013			2012
	Weighted-average risk-free interest rate	2.33	%		2.65	%		1.85	%
	Dividend yield	2.71			2.92			3.28
	Weighted-average expected market price volatility	26.66			24.2			28.06
	Weighted-average expected term	7.1 years			6.7 years			6.2 years

Other_NonInterest_Income_and_E1

Other Non-Interest Income and Expense (Tables)	12 Months Ended
	Dec. 31, 2014
Other Income and Expenses [Abstract]
Other Non-Interest Income and Expense
		2014		2013		2012
	Other non-interest income:
	Other	$	32,256	$	34,531	$	30,703
	Total	$	32,256	$	34,531	$	30,703
	Other non-interest expense:
	Advertising, promotions and public relations	$	28,998	$	26,232	$	27,194
	Legal and other professional fees	27,365		26,132		22,341
	Check card expense	15,970		11,787		10,227
	Travel/meals and entertainment	14,813		13,571		13,049
	Other	80,510		74,355		66,658
	Total	$	167,656	$	152,077	$	139,469

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Tax Expense	Income tax expense was as follows:
		2014			2013			2012
	Current income tax expense	$	62,177		$	49,736		$	76,928
	Deferred income tax expense (benefit)	(4,130		)	3,279			(6,405		)
	Income tax expense, as reported	$	58,047		$	53,015		$	70,523
Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate	Reported income tax expense differed from the amounts computed by applying the U.S. federal statutory income tax rate of 35% to income before income taxes as follows:
		2014			2013			2012
	Income tax expense computed at the statutory rate	$	117,608		$	101,808		$	107,966
	Effect of tax-exempt interest	(58,761		)	(46,535		)	(36,543		)
	Bank owned life insurance income	(1,116		)	(1,086		)	(1,413		)
	Other	316			(1,172		)	513
	Income tax expense, as reported	$	58,047		$	53,015		$	70,523
Schedule of Deferred Tax Assets and Liabilities	Year-end deferred taxes were as follows:
		2014			2013
	Deferred tax assets:
	Allowance for loan losses	$	34,840		$	32,353
	Net actuarial loss on defined benefit post-retirement benefit plans	26,263			14,070
	Stock-based compensation	18,839			17,746
	Bonus accrual	6,118			5,301
	Gain on sale of assets	2,139			2,234
	Partnerships	1,911			2,208
	Transaction costs	1,794			565
	Other	5,272			4,489
	Total gross deferred tax assets	97,176			78,966
	Deferred tax liabilities:
	Net unrealized gain on securities available for sale and effective cash flow hedging derivatives	(102,626		)	(89,689		)
	Premises and equipment	(20,039		)	(21,192		)
	Defined benefit post-retirement benefit plans	(15,010		)	(14,137		)
	Intangible assets	(6,143		)	(7,253		)
	Leases	(4,952		)	(4,237		)
	Reserve for medical insurance	(3,017		)	(2,171		)
	Prepaid expenses	(1,639		)	(1,618		)
	Other	(341		)	(1,456		)
	Total gross deferred tax liabilities	(153,767		)	(141,753		)
	Net deferred tax asset (liability)	$	(56,591	)	$	(62,787	)

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Component of Other Comprehensive Income (Loss)	The tax effects allocated to each component of other comprehensive income (loss) were as follows:
		Before Tax			Tax Expense,			Net of Tax
		Amount			(Benefit)			Amount
	2014
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	103,044		$	36,065		$	66,979
	Change in net unrealized gain on securities transferred to held to maturity	(35,441		)	(12,404		)	(23,037		)
	Reclassification adjustment for net (gains) losses included in net income	(38		)	(13		)	(25		)
	Total securities available for sale and transferred securities	67,565			23,648			43,917
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	(34,837		)	(12,193		)	(22,644		)
	Derivatives:
	Reclassification adjustment for gains on interest rate swaps on variable-rate loans included in net income	(30,604		)	(10,711		)	(19,893		)
	Total other comprehensive income (loss)	$	2,124		$	744		$	1,380
	2013
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	(115,245	)	$	(40,335	)	$	(74,910	)
	Change in net unrealized gain on securities transferred to held to maturity	(35,682		)	(12,489		)	(23,193		)
	Reclassification adjustment for net (gains) losses included in net income	(1,176		)	(412		)	(764		)
	Total securities available for sale and transferred securities	(152,103		)	(53,236		)	(98,867		)
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	35,293			12,353			22,940
	Derivatives:
	Change in the accumulated gain/loss on effective cash flow hedge derivatives	(49		)	(17		)	(32		)
	Reclassification adjustments for (gains) losses included in net income:
	Interest rate swaps on variable-rate loans	(37,380		)	(13,083		)	(24,297		)
	Interest rate swap on junior subordinated deferrable interest debentures	4,064			1,422			2,642
	Total derivatives	(33,365		)	(11,678		)	(21,687		)
	Total other comprehensive income (loss)	$	(150,175	)	$	(52,561	)	$	(97,614	)
	2012
	Securities available for sale and transferred securities:
	Change in net unrealized gain/loss during the period	$	33,412		$	11,694		$	21,718
	Change in net unrealized gain on securities transferred to held to maturity	(657		)	(230		)	(427		)
	Reclassification adjustment for net (gains) losses included in net income	(4,314		)	(1,510		)	(2,804		)
	Total securities available for sale and transferred securities	28,441			9,954			18,487
	Defined-benefit post-retirement benefit plans:
	Change in the net actuarial gain/loss	(9,405		)	(3,292		)	(6,113		)
	Derivatives:
	Change in the accumulated gain/loss on effective cash flow hedge derivatives	(783		)	(274		)	(509		)
	Reclassification adjustments for (gains) losses included in net income:
	Interest rate swaps on variable-rate loans	(37,380		)	(13,083		)	(24,297		)
	Interest rate swap on junior subordinated deferrable interest debentures	4,224			1,478			2,746
	Total derivatives	(33,939		)	(11,879		)	(22,060		)
	Total other comprehensive income (loss)	$	(14,903	)	$	(5,217	)	$	(9,686	)
Schedule of Accumulated Other Comprehensive Income, Net of Tax	Activity in accumulated other comprehensive income, net of tax, was as follows:
		Securities			Defined			Derivatives			Accumulated
		Available			Benefit						Other
		For Sale			Plans						Comprehensive
											Income
	Balance January 1, 2014	$	146,672		$	(26,131	)	$	19,893		$	140,434
	Other comprehensive income (loss) before reclassification	43,942			(22,644		)	—			21,298
	Amounts reclassified from accumulated other comprehensive income (loss)	(25		)	—			(19,893		)	(19,918		)
	Net other comprehensive income (loss) during period	43,917			(22,644		)	(19,893		)	1,380
	Balance December 31, 2014	$	190,589		$	(48,775	)	$	—		$	141,814
	Balance January 1, 2013	$	245,539		$	(49,071	)	$	41,580		$	238,048
	Other comprehensive income (loss) before reclassification	(98,103		)	22,940			(32		)	(75,195		)
	Amounts reclassified from accumulated other comprehensive income (loss)	(764		)	—			(21,655		)	(22,419		)
	Net other comprehensive income (loss) during period	(98,867		)	22,940			(21,687		)	(97,614		)
	Balance December 31, 2013	$	146,672		$	(26,131	)	$	19,893		$	140,434
	Balance January 1, 2012	$	227,052		$	(42,958	)	$	63,640		$	247,734
	Other comprehensive income (loss) before reclassification	21,291			(6,113		)	(509		)	14,669
	Amounts reclassified from accumulated other comprehensive income (loss)	(2,804		)	—			(21,551		)	(24,355		)
	Net other comprehensive income (loss) during period	18,487			(6,113		)	(22,060		)	(9,686		)
	Balance December 31, 2012	$	245,539		$	(49,071	)	$	41,580		$	238,048

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding	The notional amounts and estimated fair values of interest rate derivative contracts outstanding at December 31, 2014 and 2013 are presented in the following table. The Corporation obtains dealer quotations to value its interest rate derivative contracts designated as hedges of cash flows, while the fair values of other interest rate derivative contracts are estimated utilizing internal valuation models with observable market data inputs.
		December 31, 2014								December 31, 2013
		Notional				Estimated				Notional			Estimated
		Amount				Fair Value				Amount			Fair Value
	Derivatives designated as hedges of fair value:
	Financial institution counterparties:
	Loan/lease interest rate swaps - assets	$	31,614			$	469			$	50,965		$	1,386
	Loan/lease interest rate swaps - liabilities	37,672				(3,179		)		43,631			(4,191		)
	Non-hedging interest rate derivatives:
	Financial institution counterparties:
	Loan/lease interest rate swaps - assets	69,842				719				195,234			9,573
	Loan/lease interest rate swaps - liabilities	765,979				(38,952		)		626,980			(32,469		)
	Loan/lease interest rate caps - assets	73,058				1,003				53,058			1,309
	Customer counterparties:
	Loan/lease interest rate swaps - assets	765,979				38,910				626,980			32,426
	Loan/lease interest rate swaps - liabilities	69,842				(719		)		195,234			(9,573		)
	Loan/lease interest rate caps - liabilities	73,058				(1,003		)		53,058			(1,309		)
Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding	The weighted-average rates paid and received for interest rate swaps outstanding at December 31, 2014 were as follows:
		Weighted-Average
		Interest			Interest
		Rate			Rate
		Paid			Received
	Interest rate swaps:
	Fair value hedge loan/lease interest rate swaps	2.8	%		0.16	%
	Non-hedging interest rate swaps - financial institution counterparties	4.05			1.67
	Non-hedging interest rate swap - customer counterparties	1.67			4.05
Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions	The notional amounts and estimated fair values of non-hedging commodity swap and option derivative positions outstanding are presented in the following table. The Corporation obtains dealer quotations and uses internal valuation models with observable market data inputs to value its commodity derivative positions.
				December 31, 2014							December 31, 2013
		Notional		Notional			Estimated				Notional		Estimated
		Units		Amount			Fair Value				Amount		Fair Value
	Financial institution counterparties:
	Oil - assets	Barrels		470			$	14,357			356		$	1,004
	Oil - liabilities	Barrels		197			(1,670		)		1,574		(2,704		)
	Natural gas - assets	MMBTUs		12,235			12,707				14,240		2,903
	Natural gas - liabilities	MMBTUs		16,755			(4,095		)		22,510		(3,212		)
	Customer counterparties:
	Oil - assets	Barrels		197			1,670				1,574		2,818
	Oil - liabilities	Barrels		470			(14,318		)		356		(991		)
	Natural gas - assets	MMBTUs		16,755			4,095				22,850		3,301
	Natural gas - liabilities	MMBTUs		12,235			(12,646		)		13,900		(2,805		)
Schedule of Foreign Exchange Contracts, Statement of Financial Position	The notional amounts and fair values of open foreign currency forward contracts were as follows:
				31-Dec-14							31-Dec-13
		Notional		Notional			Estimated				Notional		Estimated
		Currency		Amount			Fair Value				Amount		Fair Value
	Financial institution counterparties:
	Forward contracts – assets	EUR		936			$	7			1,175		$	5
	Forward contracts - assets	CAD		24,724			659				18,886		85
	Forward contracts – liabilities	GBP		544			(2		)		—		—
	Forward contracts - liabilities	EUR		—			—				494		(4		)
	Forward contracts - liabilities	CAD		—			—				14,078		(23		)
	Customer counterparties:
	Forward contracts – assets	CAD		—			—				14,055		45
	Forward contracts – liabilities	CAD		24,680			(615		)		18,859		(58		)
Schedule of Amounts Related to Interest Rate Derivatives Designated as Hedges of Fair Value	Amounts included in the consolidated statements of income related to interest rate derivatives designated as hedges of fair value were as follows:
		2014				2013				2012
	Commercial loan/lease interest rate swaps:
	Amount of gain (loss) included in interest income on loans	$	(2,014	)		$	(2,437	)		$	(2,587	)
	Amount of (gain) loss included in other non-interest expense	3				4				46
Schedule of Amounts Related to Interest Rate Derivatives Included in Income Designated as Hedges of Cash Flows	Amounts included in the consolidated statements of income and in other comprehensive income for the period related to interest rate derivatives designated as hedges of cash flows were as follows:
		2014				2013				2012
	Interest rate swaps/caps/floors on variable-rate loans:
	Amount reclassified from accumulated other comprehensive income to interest income on loans	$	30,604			$	37,380			$	37,380
	Interest rate swaps on junior subordinated deferrable interest debentures:
	Amount reclassified from accumulated other comprehensive income to interest expense on junior subordinated deferrable interest debentures	—				4,064				4,224
	Amount of gain (loss) recognized in other comprehensive income	—				(49		)		(783		)
Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives	Amounts included in the consolidated statements of income related to non-hedging interest rate, commodity and foreign currency derivative instruments are presented in the table below.
		2014				2013				2012
	Non-hedging interest rate derivatives:
	Other non-interest income	$	1,786			$	1,441			$	4,722
	Other non-interest expense	(2		)		(96		)		(116		)
	Non-hedging commodity derivatives:
	Other non-interest income	118				496				124
	Non-hedging foreign currency derivatives:
	Other non-interest income	162				175				—

Balance_Sheet_Offsetting_Table

Balance Sheet Offsetting (Tables)	12 Months Ended
	Dec. 31, 2014											Dec. 31, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments Eligible for Offset Consolidated Balance Sheet	Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2014 is presented in the following tables.											Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2013 is presented in the following tables.
		Gross Amount		Gross Amount			Net Amount						Gross Amount		Gross Amount			Net Amount
		Recognized		Offset			Recognized						Recognized		Offset			Recognized
	31-Dec-14											31-Dec-13
	Financial assets:											Financial assets:
	Derivatives:											Derivatives:
	Loan/lease interest rate swaps and caps	$	2,191	$	—		$	2,191				Loan/lease interest rate swaps and caps	$	12,268	$	—		$	12,268
	Commodity swaps and options	27,064		—			27,064					Commodity swaps and options	3,907		—			3,907
	Foreign currency forward contracts	666		—			666					Foreign currency forward contracts	90		—			90
	Total derivatives	29,921		—			29,921					Total derivatives	16,265		—			16,265
	Resell agreements	9,642		—			9,642					Resell agreements	7,898		—			7,898
	Total	$	39,563	$	—		$	39,563				Total	$	24,163	$	—		$	24,163
	Financial liabilities:											Financial liabilities:
	Derivatives:											Derivatives:
	Loan/lease interest rate swaps	$	42,131	$	—		$	42,131				Loan/lease interest rate swaps	$	36,660	$	—		$	36,660
	Commodity swaps and options	5,765		—			5,765					Commodity swaps and options	5,916		—			5,916
	Foreign currency forward contracts	2		—			2					Foreign currency forward contracts	27		—			27
	Total derivatives	47,898		—			47,898					Total derivatives	42,603		—			42,603
	Repurchase agreements	791,119		—			791,119					Repurchase agreements	668,053		—			668,053
	Total	$	839,017	$	—		$	839,017				Total	$	710,656	$	—		$	710,656
Financial Instruments Derivative Assets Liabilities And Resell Agreements Net Of Amount Not Offset
				Gross Amounts Not Offset											Gross Amounts Not Offset
		Net Amount		Financial			Collateral			Net			Net Amount		Financial			Collateral			Net
		Recognized		Instruments						Amount			Recognized		Instruments						Amount
	31-Dec-14											31-Dec-13
	Financial assets:											Financial assets:
	Derivatives:											Derivatives:
	Counterparty A	$	627	$	(627	)	$	—		$	—	Counterparty A	$	3,342	$	(3,342	)	$	—		$	—
	Counterparty B	17,308		(9,506		)	(4,925		)	2,877		Counterparty B	8,196		(8,196		)	—			—
	Counterparty C	7,991		(7,539		)	—			452		Counterparty C	1,187		(1,187		)	—			—
	Other counterparties	3,995		(2,764		)	(1,110		)	121		Other counterparties	3,540		(2,099		)	(1,360		)	81
	Total derivatives	29,921		(20,436		)	(6,035		)	3,450		Total derivatives	16,265		(14,824		)	(1,360		)	81
	Resell agreements	9,642		—			(9,642		)	—		Resell agreements	7,898		—			(7,898		)	—
	Total	$	39,563	$	(20,436	)	$	(15,677	)	$	3,450	Total	$	24,163	$	(14,824	)	$	(9,258	)	$	81
	Financial liabilities:											Financial liabilities:
	Derivatives:											Derivatives:
	Counterparty A	$	18,653	$	(627	)	$	(17,626	)	$	400	Counterparty A	$	18,615	$	(3,342	)	$	(15,167	)	$	106
	Counterparty B	9,506		(9,506		)	—			—		Counterparty B	9,054		(8,196		)	(613		)	245
	Counterparty C	7,539		(7,539		)	—			—		Counterparty C	10,870		(1,187		)	(9,683		)	—
	Other counterparties	12,200		(2,764		)	(8,681		)	755		Other counterparties	4,064		(2,099		)	(1,549		)	416
	Total derivatives	47,898		(20,436		)	(26,307		)	1,155		Total derivatives	42,603		(14,824		)	(27,012		)	767
	Repurchase agreements	791,119		—			(791,119		)	—		Repurchase agreements	668,053		—			(668,053		)	—
	Total	$	839,017	$	(20,436	)	$	(817,426	)	$	1,155	Total	$	710,656	$	(14,824	)	$	(695,065	)	$	767

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	The following table summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2014 and 2013, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value:
		Level 1			Level 2			Level 3			Total
		Inputs			Inputs			Inputs			Fair Value
	2014
	Securities available for sale:
	U.S. Treasury	$	3,811,252		$	—		$	—		$	3,811,252
	Residential mortgage-backed securities	—			1,398,724			—			1,398,724
	States and political subdivisions	—			3,208,907			—			3,208,907
	Other	—			42,371			—			42,371
	Trading account securities:
	U.S. Treasury	15,339			—			—			15,339
	States and political subdivisions	—			87			—			87
	Derivative assets:
	Interest rate swaps, caps and floors	—			40,931			170			41,101
	Commodity swaps and options	—			32,829			—			32,829
	Foreign currency forward contracts	666			—			—			666
	Derivative liabilities:
	Interest rate swaps, caps and floors	—			43,853			—			43,853
	Commodity swaps and options	—			32,729			—			32,729
	Foreign currency forward contracts	617			—			—			617
	2013
	Securities available for sale:
	U.S. Treasury	$	2,540,554		$	—		$	—		$	2,540,554
	U.S. government agencies/corporations	—			53,980			—			53,980
	Residential mortgage-backed securities	—			1,776,016			—			1,776,016
	States and political subdivisions	—			1,488,914			—			1,488,914
	Other	—			35,972			—			35,972
	Trading account securities:
	U.S. Treasury	15,389			—			—			15,389
	States and political subdivisions	—			1,009			—			1,009
	Derivative assets:
	Interest rate swaps, caps and floors	—			44,520			174			44,694
	Commodity swaps and options	—			10,026			—			10,026
	Foreign currency forward contracts	135			—			—			135
	Derivative liabilities:
	Interest rate swaps, caps and floors	—			47,542			—			47,542
	Commodity swaps and options	—			9,712			—			9,712
	Foreign currency forward contracts	85			—			—			85
Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral	The following table presents impaired loans that were remeasured and reported at fair value through a specific valuation allowance allocation of the allowance for loan losses based upon the fair value of the underlying collateral:
		2014						2013					2012
		Level 2			Level 3			Level 2			Level 3		Level 2			Level 3
	Carrying value of impaired loans before allocations	$	—		$	2,715		$	9,374		$	—	$	18,319		$	15,754
	Specific valuation allowance allocations	—			(1,475		)	(2,785		)	—		(3,634		)	(2,911		)
	Fair value	$	—		$	1,240		$	6,589		$	—	$	14,685		$	12,843
Foreclosed Assets Remeasured and Reported at Fair Value	The following table presents foreclosed assets that were remeasured and reported at fair value:
		2014			2013			2012
	Foreclosed assets remeasured at initial recognition:
	Carrying value of foreclosed assets prior to remeasurement	$	6,388		$	7,580		$	9,428
	Charge-offs recognized in the allowance for loan losses	(285		)	(710		)	(1,611		)
	Fair value	$	6,103		$	6,870		$	7,817
	Foreclosed assets remeasured subsequent to initial recognition:
	Carrying value of foreclosed assets prior to remeasurement	$	5,026		$	4,979		$	12,126
	Write-downs included in other non-interest expense	(1,289		)	(895		)	(2,093		)
	Fair value	$	3,737		$	4,084		$	10,033
Estimated Fair Values of Financial Instruments	The estimated fair values of financial instruments that are reported at amortized cost in the Corporation’s consolidated balance sheets, segregated by the level of valuation inputs within the fair value hierarchy utilized to measure fair value, were as follows:
		December 31, 2014						December 31, 2013
		Carrying			Estimated			Carrying			Estimated
		Amount			Fair Value			Amount			Fair Value
	Financial assets:
	Level 2 inputs:
	Cash and cash equivalents	$	4,364,123		$	4,364,123		$	4,556,125		$	4,556,125
	Securities held to maturity	2,926,486			2,966,390			3,139,748			3,029,663
	Cash surrender value of life insurance policies	172,050			172,050			141,108			141,108
	Accrued interest receivable	128,436			128,436			99,281			99,281
	Level 3 inputs:
	Loans, net	10,887,993			10,939,684			9,423,262			9,582,734
	Financial liabilities:
	Level 2 inputs:
	Deposits	24,135,930			24,136,402			20,688,786			20,689,323
	Federal funds purchased and repurchase agreements	803,119			803,119			668,253			668,253
	Junior subordinated deferrable interest debentures	137,115			137,115			123,712			123,712
	Subordinated notes payable and other borrowings	100,000			95,591			100,000			92,552
	Accrued interest payable	1,132			1,132			1,300			1,300

Operating_Segments_Tables

Operating Segments (Tables)	12 Months Ended
	Dec. 31, 2014
Segment Reporting [Abstract]
Summary of Operating Results by Segment	Financial results by operating segment are detailed below. Certain prior period amounts have been reclassified to conform to the current presentation.
		Banking		Frost			Non-Banks			Consolidated
				Wealth
				Advisors
	2014
	Net interest income (expense)	$	683,579	$	6,734		$	(3,379	)	$	686,934
	Provision for loan losses	16,312		2			—			16,314
	Non-interest income	193,883		122,261			4,000			320,144
	Non-interest expense	549,812		96,330			8,598			654,740
	Income (loss) before income taxes	311,338		32,663			(7,977		)	336,024
	Income tax expense (benefit)	51,881		11,431			(5,265		)	58,047
	Net income (loss)	259,457		21,232			(2,712		)	277,977
	Preferred stock dividends	—		—			8,063			8,063
	Net income (loss) available to common shareholders	$	259,457	$	21,232		$	(10,775	)	$	269,914
	Revenues from (expenses to) external customers	$	877,462	$	128,995		$	621		$	1,007,078
	Average assets (in millions)(1)	$	25,734	$	32		$	2		$	25,768
	2013
	Net interest income (expense)	$	621,333	$	6,586		$	(7,364	)	$	620,555
	Provision for loan losses	20,585		(3		)	—			20,582
	Non-interest income	190,767		107,759			4,292			302,818
	Non-interest expense	513,909		90,132			7,869			611,910
	Income (loss) before income taxes	277,606		24,216			(10,941		)	290,881
	Income tax expense (benefit)	50,823		8,563			(6,371		)	53,015
	Net income (loss)	226,783		15,653			(4,570		)	237,866
	Preferred stock dividends	—		—			6,719			6,719
	Net income (loss) available to common shareholders	$	226,783	$	15,653		$	(11,289	)	$	231,147
	Revenues from (expenses to) external customers	$	812,100	$	114,345		$	(3,072	)	$	923,373
	Average assets (in millions)(1)	$	22,709	$	31		$	12		$	22,752
	2012
	Net interest income (expense)	$	605,330	$	8,013		$	(8,482	)	$	604,861
	Provision for loan losses	10,078		2			—			10,080
	Non-interest income	188,440		96,577			3,770			288,787
	Non-interest expense	485,302		82,744			7,047			575,093
	Income (loss) before income taxes	298,390		21,844			(11,759		)	308,475
	Income tax expense (benefit)	69,078		7,646			(6,201		)	70,523
	Net income (loss)	$	229,312	$	14,198		$	(5,558	)	$	237,952
	Revenues from (expenses to) external customers	$	793,770	$	104,590		$	(4,712	)	$	893,648
	Average assets (in millions)(1)	$	20,783	$	29		$	15		$	20,827
	-1	Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.5 billion, $29.0 billion and $26.2 billion at December 31, 2014, 2013 and 2012.

Condensed_Financial_Statements1

Condensed Financial Statements of Parent Company (Tables)	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of Condensed Balance Sheets	Condensed Balance Sheets
		December 31,
		2014			2013
	Assets:
	Cash	$	7,335		$	7,477
	Resell agreements	286,660			320,200
	Total cash and cash equivalents	293,995			327,677
	Investment in subsidiaries	2,791,647			2,409,433
	Accrued interest receivable and other assets	29,705			19,038
	Total assets	$	3,115,347		$	2,756,148
	Liabilities:
	Junior subordinated deferrable interest debentures	$	137,115		$	123,712
	Subordinated notes payable	100,000			100,000
	Accrued interest payable and other liabilities	26,829			18,275
	Total liabilities	263,944			241,987
	Shareholders’ Equity	2,851,403			2,514,161
	Total liabilities and shareholders’ equity	$	3,115,347		$	2,756,148
Schedule of Condensed Statements of Income	Condensed Statements of Income
		Year Ended December 31,
		2014			2013			2012
	Income:
	Dividend income paid by Frost Bank	$	114,439		$	144,642		$	143,623
	Dividend income paid by non-banks	4,323			2,819			3,077
	Interest and other income	69			79			308
	Total income	118,831			147,540			147,008
	Expenses:
	Interest expense	3,381			7,365			8,512
	Salaries and employee benefits	1,218			1,175			1,167
	Other	8,526			6,735			6,727
	Total expenses	13,125			15,275			16,406
	Income before income taxes and equity in undistributed earnings of subsidiaries	105,706			132,265			130,602
	Income tax benefit	6,702			7,845			7,463
	Equity in undistributed earnings of subsidiaries	165,569			97,756			99,887
	Net income	277,977			237,866			237,952
	Preferred stock dividends	8,063			6,719			—
	Net income available to common shareholders	$	269,914		$	231,147		$	237,952
Schedule of Condensed Statements of Cash Flows	Condensed Statements of Cash Flows
		Year Ended December 31,
		2014			2013			2012
	Operating Activities:
	Net income	$	277,977		$	237,866		$	237,952
	Adjustments to reconcile net income to net cash provided by operating activities:
	Equity in undistributed earnings of subsidiaries	(165,569		)	(97,756		)	(99,887		)
	Stock-based compensation	441			330			330
	Excess tax benefits from stock-based compensation	(165		)	(155		)	(133		)
	Net change in other assets and other liabilities	(1,984		)	2,372			(2,256		)
	Net cash from operating activities	110,700			142,657			136,006
	Investing Activities:
	Net cash received in acquisitions	830,661			—			—
	Capital contribution to subsidiaries	(879,730		)	—			—
	Net cash from investing activities	(49,069		)	—			—
	Financing Activities:
	Proceeds from stock option exercises	29,158			68,653			10,516
	Proceeds from stock-based compensation activities of subsidiaries	12,062			11,633			12,506
	Excess tax benefits from stock-based compensation	165			155			133
	Proceeds from issuance of preferred stock	—			144,486			—
	Purchase of treasury stock	(1,457		)	(144,630		)	(436		)
	Cash dividends paid on preferred stock	(8,063		)	(6,719		)	—
	Cash dividends paid on common stock	(127,178		)	(119,619		)	(116,853		)
	Net cash from financing activities	(95,313		)	(46,041		)	(94,134		)
	Net change in cash and cash equivalents	(33,682		)	96,616			41,872
	Cash and cash equivalents at beginning of year	327,677			231,061			189,189
	Cash and cash equivalents at end of year	$	293,995		$	327,677		$	231,061

Acquisition_Tables

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2014
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The total purchase price paid for the acquisition of WNB was allocated based on the estimated fair values of the assets acquired and liabilities assumed as set forth below. The purchase price allocation is preliminary and is subject to final determination and valuation of the fair value of assets acquired and liabilities assumed.
	Cash and cash equivalents	$	879,740
	Securities available for sale	154,227
	Loans	670,619
	Premises and equipment	22,853
	Core deposit intangible asset	9,300
	Goodwill	117,301
	Other assets	33,644
	Deposits	(1,624,043		)
	Other borrowings	(63,592		)
	Other liabilities	(1,251		)
		$	198,798

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Additional Cash Flow Information) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Abstract]
Cash paid for interest	$14,705	$22,449	$29,378
Cash paid for income tax	62,976	49,514	58,950
Transfer of securities from available for sale to held to maturity	0	0	2,266,195
Unsettled purchases of securities	0	16,241	90,073
Loans foreclosed and transferred to other real estate owned and foreclosed assets	4,363	6,870	7,817
Premises and equipment transferred to other real estate owned and foreclosed assets	1,740	0	0
Loans to facilitate the sale of other real estate owned	102	678	0
Deferred gain on sale of building and parking garage	$0	$768	$0

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash on hand or on deposit required	175,600,000	$116,600,000
Cash collateral on deposit	12,100,000
Foreclosed assets	5,300,000	$11,900,000
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	80.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Range of change in fair value of derivative hedging instrument to be considered highly effective	125.00%

Securities_Year_End_Securities

Securities (Year End Securities Held to Maturity and Available for Sale) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	$2,926,486	$3,139,748
Held to Maturity, Gross Unrealized Gains	48,939	27,919
Held to Maturity, Gross Unrealized Losses	9,035	138,004
Held to Maturity, Estimated Fair Value	2,966,390	3,029,663
Available for Sale, Amortized Cost	8,261,947	5,799,135
Available for Sale, Gross Unrealized Gains	203,121	105,276
Available for Sale, Gross Unrealized Losses	3,814	8,975
Available for Sale, Estimated Fair Value	8,461,254	5,895,436
US Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	249,009	248,592
Held to Maturity, Gross Unrealized Gains	14,604	20,139
Held to Maturity, Gross Unrealized Losses	0	0
Held to Maturity, Estimated Fair Value	263,613	268,731
Available for Sale, Amortized Cost	3,783,899	2,522,159
Available for Sale, Gross Unrealized Gains	30,594	18,395
Available for Sale, Gross Unrealized Losses	3,241	0
Available for Sale, Estimated Fair Value	3,811,252	2,540,554
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	8,012	9,674
Held to Maturity, Gross Unrealized Gains	92	89
Held to Maturity, Gross Unrealized Losses	0	143
Held to Maturity, Estimated Fair Value	8,104	9,620
Available for Sale, Amortized Cost	1,331,114	1,710,664
Available for Sale, Gross Unrealized Gains	68,027	66,791
Available for Sale, Gross Unrealized Losses	417	1,439
Available for Sale, Estimated Fair Value	1,398,724	1,776,016
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Amortized Cost	0	54,024
Available for Sale, Gross Unrealized Gains	0	0
Available for Sale, Gross Unrealized Losses	0	44
Available for Sale, Estimated Fair Value	0	53,980
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	2,668,115	2,880,482
Held to Maturity, Gross Unrealized Gains	34,243	7,691
Held to Maturity, Gross Unrealized Losses	9,035	137,861
Held to Maturity, Estimated Fair Value	2,693,323	2,750,312
Available for Sale, Amortized Cost	3,104,563	1,476,316
Available for Sale, Gross Unrealized Gains	104,500	20,090
Available for Sale, Gross Unrealized Losses	156	7,492
Available for Sale, Estimated Fair Value	3,208,907	1,488,914
Other [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,350	1,000
Held to Maturity, Gross Unrealized Gains	0	0
Held to Maturity, Gross Unrealized Losses	0	0
Held to Maturity, Estimated Fair Value	1,350	1,000
Available for Sale, Amortized Cost	42,371	35,972
Available for Sale, Gross Unrealized Gains	0	0
Available for Sale, Gross Unrealized Losses	0	0
Available for Sale, Estimated Fair Value	$42,371	$35,972

Securities_Narrative_Detail

Securities (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Marketable Securities [Line Items]
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas	97.40%
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas guaranteed by Texas permanent school fund	64.90%
Carrying value of pledged securities	$3,000,000,000	$3,000,000,000
Securities available for sale, at estimated fair value	8,461,254,000	5,895,436,000
Available for sale securities reclassified to held to maturity, unrealized gain			165,700,000
Available for sale securities reclassified to held to maturity, unrealized gain net of tax			107,700,000
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, pre tax	93,900,000	129,300,000
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	61,000,000	84,100,000
Reclassified To Held To Maturity [Member]
Schedule Of Marketable Securities [Line Items]
Securities available for sale, at estimated fair value			$2,300,000,000

Securities_Year_End_Securities1

Securities (Year End Securities with Unrealized Losses Segregated by Length of Impairment) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	$68,024	$2,078,455
Held to Maturity, Less than 12 Months, Unrealized Losses	144	113,655
Held to Maturity, More than 12 Months, Estimated Fair Value	683,251	266,566
Held to Maturity, More than 12 Months, Unrealized Losses	8,891	24,349
Held to Maturity, Total Estimated Fair Value	751,275	2,345,021
Held to Maturity, Total Unrealized Losses	9,035	138,004
Available for Sale, Less than 12 Months, Estimated Fair Value	1,093,531	766,904
Available for Sale, Less than 12 Months, Unrealized Losses	3,439	8,693
Available for Sale, More than 12 Months, Estimated Fair Value	16,944	2,713
Available for Sale, More than 12 Months, Unrealized Losses	375	282
Available for Sale, Total Estimated Fair Value	1,110,475	769,617
Available for Sale, Total Unrealized Losses	3,814	8,975
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	68,024	2,071,521
Held to Maturity, Less than 12 Months, Unrealized Losses	144	113,512
Held to Maturity, More than 12 Months, Estimated Fair Value	683,251	266,566
Held to Maturity, More than 12 Months, Unrealized Losses	8,891	24,349
Held to Maturity, Total Estimated Fair Value	751,275	2,338,087
Held to Maturity, Total Unrealized Losses	9,035	137,861
Available for Sale, Less than 12 Months, Estimated Fair Value	65,751	679,923
Available for Sale, Less than 12 Months, Unrealized Losses	156	7,492
Available for Sale, More than 12 Months, Estimated Fair Value	0
Available for Sale, More than 12 Months, Unrealized Losses	0
Available for Sale, Total Estimated Fair Value	65,751	679,923
Available for Sale, Total Unrealized Losses	156	7,492
US Treasury Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Less than 12 Months, Estimated Fair Value	1,019,230
Available for Sale, Less than 12 Months, Unrealized Losses	3,241
Available for Sale, More than 12 Months, Estimated Fair Value	0
Available for Sale, More than 12 Months, Unrealized Losses	0
Available for Sale, Total Estimated Fair Value	1,019,230
Available for Sale, Total Unrealized Losses	3,241
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Less than 12 Months, Estimated Fair Value		53,980
Available for Sale, Less than 12 Months, Unrealized Losses		44
Available for Sale, Total Estimated Fair Value		53,980
Available for Sale, Total Unrealized Losses		44
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value		6,934
Held to Maturity, Less than 12 Months, Unrealized Losses		143
Held to Maturity, Total Estimated Fair Value		6,934
Held to Maturity, Total Unrealized Losses		143
Available for Sale, Less than 12 Months, Estimated Fair Value	8,550	33,001
Available for Sale, Less than 12 Months, Unrealized Losses	42	1,157
Available for Sale, More than 12 Months, Estimated Fair Value	16,944	2,713
Available for Sale, More than 12 Months, Unrealized Losses	375	282
Available for Sale, Total Estimated Fair Value	25,494	35,714
Available for Sale, Total Unrealized Losses	$417	$1,439

Securities_Amortized_Cost_and_

Securities (Amortized Cost and Estimated Fair Value of Securities Excluding Trading Securities Presented by Contractual Maturity) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Investments, Debt and Equity Securities [Abstract]
Held to Maturity, Due in one year or less, Amortized Cost	$153,701
Held to Maturity, Due after one year through five years, Amortized Cost	533,990
Held to Maturity, Due after five years through ten years, Amortized Cost	172,371
Held to Maturity, Due after ten years, Amortized Cost	2,058,412
Held to Maturity, Residential mortgage-backed securities, Amortized Cost	8,012
Held-to-maturity, Equity Securities, Amortized Cost	0
Held to Maturity, Amortized Cost	2,926,486	3,139,748
Held to Maturity, Due in one year or less, Estimated Fair Value	155,505
Held to Maturity, Due after one year through five years, Estimated Fair Value	564,854
Held to Maturity, Due after five years through ten years, Estimated Fair Value	172,240
Held to Maturity, Due after ten years, Estimated Fair Value	2,065,687
Held to Maturity, Residential mortgage-backed securities, Estimated Fair Value	8,104
Held-to-maturity, Equity Securities, Estimated Fair Value	0
Held to Maturity, Estimated Fair Value	2,966,390	3,029,663
Available for Sale, Due in one year or less, Amortized Cost	515,567
Available for Sale, Due after one year through five years, Amortized Cost	2,474,795
Available for Sale, Due after five years through ten years, Amortized Cost	1,937,104
Available for Sale, Due after ten years, Amortized Cost	1,960,996
Available For Sale, Residential mortgage-backed securities, Amortized Cost	1,331,114
Available for Sale, Equity securities, Amortized Cost	42,371
Available for Sale, Amortized Cost	8,261,947	5,799,135
Available for Sale, Due in one year or less, Estimated Fair Value	517,482
Available for Sale, Due after one year through five years, Estimated Fair Value	2,486,488
Available for Sale, Due after five years through ten years, Estimated Fair Value	1,977,280
Available for Sale, Due after ten years, Estimated Fair Value	2,038,909
Available for Sale, Residential mortgage-backed securities, Estimated Fair Value	1,398,724
Available for Sale, Equity securities, Estimated Fair Value	42,371
Available for Sale, Estimated Fair Value	$8,461,254	$5,895,436

Securities_Sales_of_Securities

Securities (Sales of Securities Available for Sale) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$12,151,287	$10,056,060	$16,587,482
Gross realized gains	39	1,206	6,943
Gross realized losses	-1	-30	-2,629
Tax (expense) benefit of securities gains/losses	($13)	($412)	($1,510)

Securities_Securities_Premium_

Securities Securities - (Premium Amortization and Discount Accretion Included in Income on Securities) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Premium Amortization	($68,070)	($49,112)	($28,364)
Discount Accretion	6,802	7,191	6,663
Net (Premium Amortization) Discount Accretion	($61,268)	($41,921)	($21,701)

Securities_Year_End_Trading_Ac

Securities (Year End Trading Account Securities at Estimated Fair Value) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$15,426	$16,398
US Treasury [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	15,339	15,389
States and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$87	$1,009

Securities_Net_Gains_and_Losse

Securities (Net Gains and Losses on Trading Account Securities) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$829	$878	$1,219
Net mark-to-market gains (losses)	0	-429	-161
Net gain on trading account securities	$829	$449	$1,058

Loans_Loans_Detail

Loans (Loans) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$5,767,743	$4,907,076
Commercial mortgages	3,080,202	2,800,760
Construction	629,988	426,639
Land	291,907	239,937
Total commercial real estate	4,002,097	3,467,336
Home equity loans	342,725	329,853
Home equity lines of credit	220,128	195,132
Other	286,198	283,219
Total consumer real estate	849,051	808,204
Total real estate	4,851,148	4,275,540
Consumer installment	385,479	350,827
Other	8,122	7,289
Total consumer and other	393,601	358,116
Unearned discounts	-24,957	-25,032
Total loans	10,987,535	9,515,700
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	5,429,206	4,587,499
Leases [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$338,537	$319,577

Loans_Narrative_Detail

Loans (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2014
	Item
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration of loans in a single industry in excess of ten percent	0.00%	0.00%
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$8,916,000	$14,833,000	$2,316,000
Maximum loan-to-value percentage on home equity loans	80.00%
Maximum percentage loan related to single industry	10.00%	10.00%
Commercial and industrial loans related to overdraft for correspondent bank customer	7,700,000	6,800,000
Minimum number of days to be considered past due	90 days
Troubled debt restructurings	8,339,000	11,215,000	2,188,000
Previously restructured loans past due	0
Number of days past due for payment of interest on loans, minimum	120 days
Number of loans with calculated risk of 10 or higher greater than $5 million	6
Loan amount threshold	5,000,000
Loan value with weighted-average loan-to-value	44,400,000
Weighted-average loan-to-value ratio	53.70%
Texas Leading Index economic condition indicator		129.1		131.4
Maximum origination value of loans which were subject to further refinement of valuation methodology	1,000,000
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	528,000	0
Percentage of loans related to a single industry	16.10%	11.70%
Troubled debt restructurings	0	531,000	0
Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of owner-occupied commercial real estate loans	55.00%
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	8,300,000	10,100,000
Additional interest that would have been recognized on non-accrual loans, net of tax	1,500,000	2,200,000	2,600,000
Consumer Real Estate Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	0	0
Troubled debt restructurings	0	0	0
Grade 12 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
General percentage of valuation allowance in excess of principal balance, maximum	30.00%
Grade 13 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
General percentage of valuation allowance in excess of principal balance, minimum	30.00%
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	5,795,000	6,334,000	1,602,000
Troubled debt restructurings	5,391,000	4,937,000	1,478,000
Amount charged off related to loans restructured	627,000
Number of days past due for payment of interest on loans, minimum	180 days
Commercial and Industrial, Other Commercial [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	2,700,000
Commercial Real Estate Buildings Land And Other Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	3,121,000	7,964,000	714,000
Troubled debt restructurings	2,948,000	5,747,000	710,000
Amount charged off related to loans restructured	0
Previously Restructured Loans Moved to OREO	500,000
Commercial Real Estate Buildings Land And Other Financing Receivable [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$2,900,000

Loans_Activities_in_Related_Pa

Loans (Activities in Related Party Loans) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
Receivables [Abstract]
Balance outstanding at December 31, 2013	$76,672
Principal additions	127,347
Principal reductions	-165,963
Other Changes	644
Balance outstanding at December 31, 2014	$38,700

Loans_NonAccrual_Loans_Segrega

Loans (Non-Accrual Loans, Segregated by Class of Loans) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$59,925	$56,720
Commercial and Industrial, Energy [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	636	590
Commercial and Industrial, Other Commercial [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	34,108	26,143
Commercial Real Estate, Buildings, Land and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	19,639	27,035
Commercial Real Estate, Construction [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	2,792	0
Consumer Real Estate [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	2,212	2,207
Consumer and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$538	$745

Loans_Age_Analysis_of_Past_Due

Loans (Age Analysis of Past Due Loans, Segregated by Class of Loans) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	$45,510
Loans 90 or More Days Past Due	49,257
Total Past Due Loans	94,767
Current Loans	10,892,768
Total loans	10,987,535	9,515,700
Accruing Loans 90 or More Days Past Due	20,941
Commercial and Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	7,278
Loans 90 or More Days Past Due	0
Total Past Due Loans	7,278
Current Loans	1,766,667
Total loans	1,773,945
Accruing Loans 90 or More Days Past Due	0
Commercial and Industrial, Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	16,350
Loans 90 or More Days Past Due	33,998
Total Past Due Loans	50,348
Current Loans	3,943,450
Total loans	3,993,798
Accruing Loans 90 or More Days Past Due	14,254
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	6,535
Loans 90 or More Days Past Due	11,308
Total Past Due Loans	17,843
Current Loans	3,354,266
Total loans	3,372,109
Accruing Loans 90 or More Days Past Due	3,333
Commercial Real Estate, Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	5,081
Loans 90 or More Days Past Due	1,327
Total Past Due Loans	6,408
Current Loans	623,580
Total loans	629,988
Accruing Loans 90 or More Days Past Due	1,042
Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	4,560
Loans 90 or More Days Past Due	2,148
Total Past Due Loans	6,708
Current Loans	842,343
Total loans	849,051
Accruing Loans 90 or More Days Past Due	1,910
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	5,706
Loans 90 or More Days Past Due	476
Total Past Due Loans	6,182
Current Loans	387,419
Total loans	393,601
Accruing Loans 90 or More Days Past Due	402
Unearned Discounts [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans 30-89 Days Past Due	0
Loans 90 or More Days Past Due	0
Total Past Due Loans	0
Current Loans	-24,957
Total loans	-24,957
Accruing Loans 90 or More Days Past Due	$0

Loans_Impaired_Loans_Detail

Loans (Impaired Loans) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$69,656	$61,007	$105,577
Recorded Investment With No Allowance	50,473	32,588	43,083
Recorded Investment With Allowance	3,118	15,874	37,314
Total Recorded Investment	53,591	48,462	80,397
Related Allowance	1,680	6,926	8,237
Average Recorded Investment	49,636	71,741	86,580
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	706	545	1,255
Recorded Investment With No Allowance	636	531	0
Recorded Investment With Allowance	0	0	1,069
Total Recorded Investment	636	531	1,069
Related Allowance	0	0	900
Average Recorded Investment	571	428	214
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	42,212	31,429	56,784
Recorded Investment With No Allowance	29,007	15,337	21,709
Recorded Investment With Allowance	2,853	7,004	19,096
Total Recorded Investment	31,860	22,341	40,805
Related Allowance	1,613	4,140	4,200
Average Recorded Investment	27,154	34,894	42,630
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	22,919	27,792	44,652
Recorded Investment With No Allowance	17,441	15,697	19,010
Recorded Investment With Allowance	265	8,870	17,149
Total Recorded Investment	17,706	24,567	36,159
Related Allowance	67	2,786	3,137
Average Recorded Investment	20,339	34,633	40,258
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	3,007	0	1,497
Recorded Investment With No Allowance	2,793	0	1,100
Total Recorded Investment	2,793	0	1,100
Average Recorded Investment	739	634	1,392
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	812	907	961
Recorded Investment With No Allowance	596	745	864
Total Recorded Investment	596	745	864
Average Recorded Investment	674	804	1,617
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	334	428
Recorded Investment With No Allowance	0	278	400
Total Recorded Investment	0	278	400
Average Recorded Investment	$159	$348	$469

Loans_Troubled_Debt_Restructur

Loans (Troubled Debt Restructurings) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Balance at Restructure	$8,916	$14,833	$2,316
Balance at Year-end	8,339	11,215	2,188
Commercial and Industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	528	0
Balance at Year-end	0	531	0
Commercial and Industrial, Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	5,795	6,334	1,602
Balance at Year-end	5,391	4,937	1,478
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	3,121	7,964	714
Balance at Year-end	2,948	5,747	710
Consumer Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	0	0
Balance at Year-end	0	0	0
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	7	0
Balance at Year-end	$0	$0	$0

Loans_Weighted_Average_Risk_Gr

Loans (Weighted Average Risk Grades for All Commercial Loans b Class) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	Grade	Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$5,767,743	$4,907,076
Loans	4,002,097	3,467,336
Loans	629,988	426,639
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.45	5.4
Loans	1,773,945	1,115,409
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.16	6.27
Loans	3,993,798	3,791,667
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.76	6.83
Loans	3,372,109	3,040,697
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.97	7.1
Loans	629,988	426,639
Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.37	5.37
Loans	1,740,455	1,106,348
Risk Grade One To Eight [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	5.93	5.95
Loans	3,785,171	3,507,963
Risk Grade One To Eight [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.53	6.59
Loans	3,148,339	2,844,665
Risk Grade One To Eight [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	6.91	7.05
Loans	617,805	418,999
Risk Grade Nine [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9	9
Loans	27,313	7,726
Risk Grade Nine [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9	9
Loans	65,166	74,766
Risk Grade Nine [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9	9
Loans	72,906	65,770
Risk Grade Nine [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	9	9
Loans	8,003	1,301
Risk Grade Ten [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10	10
Loans	161	245
Risk Grade Ten [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10	10
Loans	54,519	89,878
Risk Grade Ten [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10	10
Loans	87,889	49,881
Risk Grade Ten [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	10	10
Loans	1,323	5,931
Risk Grade Eleven [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11	11
Loans	5,380	500
Risk Grade Eleven [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11	11
Loans	55,034	92,917
Risk Grade Eleven [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11	11
Loans	43,336	53,208
Risk Grade Eleven [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	11	11
Loans	64	408
Risk Grade Twelve [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12	12
Loans	636	590
Risk Grade Twelve [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12	12
Loans	31,683	21,389
Risk Grade Twelve [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12	12
Loans	19,501	24,387
Risk Grade Twelve [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	12	12
Loans	2,793	0
Risk Grade Thirteen [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13	13
Loans	0	0
Risk Grade Thirteen [Member] | Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13	13
Loans	2,225	4,754
Risk Grade Thirteen [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13	13
Loans	138	2,786
Risk Grade Thirteen [Member] | Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	13	13
Loans	$0	$0
Minimum [Member] | Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	1	1
Maximum [Member] | Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade	8	8

Loans_Net_ChargeOffsRecoveries

Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	($9,210)	($32,597)	($15,774)
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	-1,237	-913	4
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	-2,911	-28,431	-13,627
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	-2,348	-381	698
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	348	256	78
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	-733	-719	-638
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	($2,329)	($2,409)	($2,289)

Loans_Unallocated_Portion_of_A

Loans (Unallocated Portion of Allowance for Loan Losses) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$99,542	$92,438	$104,453	$110,147
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	59,604	53,738
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,680	6,926
Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	13,477	11,806
Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,093	8,196
Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,492	1,866
Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,807	2,610
Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,305	5,154
Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,782	2,492
Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,164	1,398
Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,906	7,524
Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	-15,837	-12,200
General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	13,069	2,928
Commercial and Industrial [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	59,192	52,790	54,164	42,774
Commercial and Industrial [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	32,421	29,357
Commercial and Industrial [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,613	4,140
Commercial and Industrial [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	6,773	5,497
Commercial and Industrial [Member] | Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,090	7,812
Commercial and Industrial [Member] | Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,114	1,499
Commercial and Industrial [Member] | Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,248	1,529
Commercial and Industrial [Member] | Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,958	4,535
Commercial and Industrial [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,907	0
Commercial and Industrial [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,483	0
Commercial and Industrial [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,110	2,009
Commercial and Industrial [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	-6,234	-3,588
Commercial and Industrial [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,709	0
Commercial Real Estate [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	27,163	22,590	29,346	20,912
Commercial Real Estate [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	14,684	13,042
Commercial Real Estate [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	67	2,786
Commercial Real Estate [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,547	3,314
Commercial Real Estate [Member] | Distressed Industries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3	384
Commercial Real Estate [Member] | Excessive Industry Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	378	367
Commercial Real Estate [Member] | Large Relationship Concentrations [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,559	1,081
Commercial Real Estate [Member] | Highly-Leveraged Credit Relationships [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,347	619
Commercial Real Estate [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	875	0
Commercial Real Estate [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	681	0
Commercial Real Estate [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,284	2,201
Commercial Real Estate [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	-1,800	-1,204
Commercial Real Estate [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	3,538	0
Consumer Real Estate [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,178	5,230	5,252	3,540
Consumer Real Estate [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,017	2,644
Consumer Real Estate [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	474	664
Consumer Real Estate [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,336	2,250
Consumer Real Estate [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	-364	-328
Consumer Real Estate [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	715	0
Consumer and Other [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	8,009	5,010	3,507	12,635
Consumer and Other [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	10,482	8,695
Consumer and Other [Member] | Environmental Risk Adjustment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,683	2,331
Consumer and Other [Member] | Loans Not Reviewed by Concurrence [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,176	1,064
Consumer and Other [Member] | Adjustment for Recoveries [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	-7,439	-7,080
Consumer and Other [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,107	0
Unallocated [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	6,818	12,184	30,286
Unallocated [Member] | Policy Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	2,492
Unallocated [Member] | Credit and Collateral Exceptions [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	1,398
Unallocated [Member] | General Macroeconomic Risk [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$0	$2,928

Loans_Activity_in_Allowance_fo

Loans (Activity in Allowance for Loan Losses by Portfolio Segment) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$92,438	$104,453	$110,147
Provision for loan losses	16,314	20,582	10,080
Charge-offs	-28,485	-44,797	-33,040
Recoveries	19,275	12,200	17,266
Net charge-offs	-9,210	-32,597	-15,774
Ending balance	99,542	92,438	104,453
Loans individually evaluated for impairment	13,000	20,596	17,537
Loans collectively evaluated for impairment	86,542	71,842	86,916
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	52,790	54,164	42,774
Provision for loan losses	10,550	27,970	25,013
Charge-offs	-13,820	-32,932	-18,493
Recoveries	9,672	3,588	4,870
Net charge-offs	-4,148	-29,344	-13,623
Ending balance	59,192	52,790	54,164
Loans individually evaluated for impairment	11,836	16,682	13,171
Loans collectively evaluated for impairment	47,356	36,108	40,993
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	22,590	29,346	20,912
Provision for loan losses	6,573	-6,631	7,658
Charge-offs	-3,800	-1,329	-3,951
Recoveries	1,800	1,204	4,727
Net charge-offs	-2,000	-125	776
Ending balance	27,163	22,590	29,346
Loans individually evaluated for impairment	1,164	3,914	4,366
Loans collectively evaluated for impairment	25,999	18,676	24,980
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,230	5,252	3,540
Provision for loan losses	681	697	2,350
Charge-offs	-1,097	-1,047	-1,495
Recoveries	364	328	857
Net charge-offs	-733	-719	-638
Ending balance	5,178	5,230	5,252
Loans individually evaluated for impairment	0	0	0
Loans collectively evaluated for impairment	5,178	5,230	5,252
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,010	3,507	12,635
Provision for loan losses	5,328	3,912	-6,839
Charge-offs	-9,768	-9,489	-9,101
Recoveries	7,439	7,080	6,812
Net charge-offs	-2,329	-2,409	-2,289
Ending balance	8,009	5,010	3,507
Loans individually evaluated for impairment	0	0	0
Loans collectively evaluated for impairment	8,009	5,010	3,507
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,818	12,184	30,286
Provision for loan losses	-6,818	-5,366	-18,102
Charge-offs	0	0	0
Recoveries	0	0	0
Net charge-offs	0	0	0
Ending balance	0	6,818	12,184
Loans individually evaluated for impairment	0	0	0
Loans collectively evaluated for impairment	$0	$6,818	$12,184

Loans_Investment_in_Loans_Rela

Loans (Investment in Loans Related to Allowance for Loan Loss by Portfolio Segment Disaggregated Based on Impairment Methodology) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	$5,767,743	$4,907,076
Commercial Real Estate	4,002,097	3,467,336
Consumer Real Estate	849,051	808,204
Consumer and Other	393,601	358,116
Unearned discounts	-24,957	-25,032
Total loans	10,987,535	9,515,700
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	149,638	210,273
Commercial Real Estate	155,044	136,601
Consumer Real Estate	596	745
Consumer and Other	0	278
Unearned discounts	0	0
Total loans	305,278	347,897
Loans Collectively Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial:	5,618,105	4,696,803
Commercial Real Estate	3,847,053	3,330,735
Consumer Real Estate	848,455	807,459
Consumer and Other	393,601	357,838
Unearned discounts	-24,957	-25,032
Total loans	$10,682,257	$9,167,803

Premises_and_Equipment_Premise

Premises and Equipment (Premises and Equipment) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Abstract]
Land	$102,334	$97,095
Buildings	240,430	231,066
Furniture and equipment	103,603	212,169
Leasehold improvements	60,902	61,221
Construction in progress	118,367	10,074
Premises and equipment, Gross	625,636	611,625
Less accumulated depreciation and amortization	-182,748	-298,294
Total premises and equipment, net	$442,888	$313,331

Premises_and_Equipment_Narrati

Premises and Equipment (Narrative) (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation and amortization of premises and equipment, year to date	$23.50	$22.50	$21.80

Goodwill_and_Other_Intangible_2

Goodwill and Other Intangible Assets (Schedule of Goodwill) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$653,950	$536,649

Goodwill_and_Other_Intangible_3

Goodwill and Other Intangible Assets (Schedule of Other Intangible Assets) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$50,762	$43,971
Accumulated Amortization	-38,637	-37,626
Net Intangible Assets	12,125	6,345
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	44,266	34,966
Accumulated Amortization	-34,591	-31,961
Net Intangible Assets	9,675	3,005
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	5,771	7,870
Accumulated Amortization	-3,643	-5,042
Net Intangible Assets	2,128	2,828
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	725	1,135
Accumulated Amortization	-403	-623
Net Intangible Assets	$322	$512

Goodwill_and_Other_Intangible_4

Goodwill and Other Intangible Assets (Narrative) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization expense related to intangible assets	$3,520	$3,141	$3,896
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	5 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	10 years

Goodwill_and_Other_Intangible_5

Goodwill and Other Intangible Assets (Estimated Aggregate Future Amortization Expense for Intangible Assets) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]
2015	$3,324
2016	2,413
2017	1,619
2018	1,346
2019	1,102
Thereafter	2,321
Net Intangible Assets	$12,125	$6,345

Deposits_Schedule_of_Deposits_

Deposits (Schedule of Deposits) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deposit [Line Items]
Non-interest-bearing demand deposits:	$10,149,061	$8,311,149
Total Interest-bearing deposits	13,986,869	12,377,637
Total deposits	24,135,930	20,688,786
Commercial and Individual [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	9,256,045	7,445,656
Correspondent Banks [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	429,000	427,134
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	4,743,963	4,020,313
Money market accounts	7,860,403	6,883,869
Time accounts of $100,000 or more	490,209	508,441
Time accounts under $100,000	454,220	438,800
Total private accounts	13,548,795	11,851,423
Public Funds [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	464,016	438,359
Savings and interest checking	326,090	305,976
Money market accounts	57,145	56,015
Time accounts of $100,000 or more	53,684	160,637
Time accounts under $100,000	1,155	3,586
Total public funds	$438,074	$526,214

Deposits_Additional_Informatio

Deposits (Additional Information About Corporation's Deposits) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deposits [Abstract]
Deposits from the Certificate of Deposit Account Registry Service (CDARS)	$22	$200
Promontory Interfinancial Network Insured Cash Sweep Service	149	0
Deposits from foreign sources (primarily Mexico)	744,295	769,970
Deposits from certain directors, executive officers and their affiliates	$176,821	$144,216

Deposits_Scheduled_Maturities_

Deposits (Scheduled Maturities of Time Deposits) (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Deposits [Abstract]
2015	$857,857
2016	140,882
2017	379
2018	92
2019	58
Time deposits, Total	$999,268

Deposits_Scheduled_Maturities_1

Deposits (Scheduled Maturities of Time Deposits in Amounts of $100,000 or More) (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Deposits [Abstract]
Due within 3 months or less	$228,010
Due after 3 months and within 6 months	97,194
Due after 6 months and within 12 months	142,973
Due after 12 months	75,716
Time deposits, $100,000 or more, total	$543,893

Borrowed_Funds_Narrative_Detai

Borrowed Funds (Narrative) (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2004	Feb. 28, 2007
	quarter
Borrowed Funds [Line Items]
Federal funds purchased	$12,000,000	$200,000
Securities sold under agreements to repurchase	791,100,000	668,100,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures	20
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Common equity securities		144,486,000
Maximum allowable percentage of core capital included in Tier 1 Capital by Most Bank Holding Companies	25.00%
Proceeds from Issuance of Trust Preferred Securities	133,000,000	120,000,000
Trust II [Member]
Borrowed Funds [Line Items]
Advances, variable-rate	1.78%	1.79%	1.55%
LIBOR plus margin			Three-month LIBOR plus a margin of 1.55%
Trust preferred securities, issued			120,000,000
Maturity date of trust preferred securities	1-Mar-34
WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Advances, variable-rate	2.58%		2.35%
Trust preferred securities, issued			13,000,000
Maturity date of trust preferred securities	23-Jul-34
Federal Funds Purchased [Member] | Minimum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period	1 day
Federal Funds Purchased [Member] | Maximum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period	90 days
Securities Sold under Agreements to Repurchase [Member] | Minimum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period	30 days
Securities Sold under Agreements to Repurchase [Member] | Maximum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period	90 days
Subordinated Notes Payable [Member]
Borrowed Funds [Line Items]
Subordinated Notes				100,000,000
Subordinated Notes interest rate				5.75%
Maturity date				15-Feb-17
Advances, variable-rate	0.76%	0.77%		0.53%
LIBOR plus margin				Three-month LIBOR for the related interest period plus 0.53%
Percentage of redemption price	100.00%
Unamortized debt issuance cost related to note	250,000	370,000
Junior Subordinated Deferrable Interest Debenture [Member] | Trust II [Member]
Borrowed Funds [Line Items]
Unamortized debt issuance cost related to note	1,100,000	1,200,000
Junior subordinated deferrable interest debentures	123,712,000	123,712,000
Common equity securities	3,700,000
Junior Subordinated Deferrable Interest Debenture [Member] | WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Junior subordinated deferrable interest debentures	13,403,000
Common equity securities	$403,000

OffBalanceSheet_Arrangements_C2

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Financial Instruments With Off-Balance-Sheet Risk) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$248,360	$186,857
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	7,955,779	6,919,942
Deferred Standby Letter of Credit Fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$1,942	$1,450

OffBalance_Sheet_Arrangements_

Off-Balance Sheet Arrangements Commitments Guarantees and Contingencies (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments And Guarantees [Line Items]
Credit card guarantees	$8,900,000	$8,400,000
Fully collateralized credit card guarantees	1,500,000	1,200,000
Minimum percentage of collateral required for securities borrowed	100.00%
Maximum future payments guaranteed	2,500,000,000
Held in trust liquid assets as collateral	2,500,000,000
Rent expense for operating leases	28,200,000	24,600,000	22,700,000
Aggregate future minimum rentals to be received under non-cancelable subleases greater than one year	209,000
Partnership Interest of a Director [Member]
Commitments And Guarantees [Line Items]
Rent expense for operating leases	$925,000	$871,000	$902,000

OffBalanceSheet_Arrangements_C3

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Future Minimum Lease Payments Due Under Non-Cancelable Operating Leases) (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]
2015	$21,373
2016	19,834
2017	18,503
2018	17,067
2019	13,269
Thereafter	77,000
Future minimum lease payments due, total	$167,046

Capital_and_Regulatory_Matters2

Capital and Regulatory Matters (Narrative) (Detail) (USD $)	0 Months Ended		12 Months Ended		0 Months Ended
	Aug. 13, 2013	Feb. 12, 2013	Dec. 31, 2014	Dec. 31, 2013	Feb. 15, 2013
			quarter
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock			$144,500,000	$144,500,000
Non-cumulative perpetual preferred stock, dividend rate percentage			5.38%	5.38%
Trust preferred securities			133,000,000	120,000,000
Corporation's aggregate subordinated notes			137,115,000	123,712,000
Preferred stock, shares issued			6,000,000	6,000,000
Preferred stock, par value			$0.01	$0.01
Issuance of preferred stock				144,486,000
Accelerated share repurchase authorized amount			150,000,000
Amount paid under accelerated share repurchase agreement		144,000,000
Shares repurchased under accelerated share repurchase program	331,671	1,905,077
Accelerated Share Repurchase Program Repurchase Share Percent		80.00%
Aggregate dividends available for payment without prior regulatory approval			363,900,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures			20
Non Cumulative Perpetual Preferred Stock And Seriesa Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, shares issued					6,000,000
Series A Preferred Stock, Liquidation preference value					150,000,000
Issuance of preferred stock					144,500,000
Non Cumulative Perpetual Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock, dividend rate percentage					5.38%
Preferred stock, par value					$0.01
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Series A Preferred Stock, Liquidation preference value			25	25
Liquidation preference per share					$25
Floating Rate Subordinated Notes [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Corporation's aggregate subordinated notes			100,000,000
Per year percentage of decreases in permissible portion of Subordinate Note included in Total Capital			20.00%
Final years of the term of the notes			5 years
Permissible portion of subordinated note included in total capital			$40,000,000	$60,000,000

Regulatory_Matters_Actual_and_

Regulatory Matters (Actual and Required Capital Ratios) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cullen/Frost [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	$2,325,818	$2,110,774
Total Capital to Risk-Weighted Assets, Actual, Ratio	14.55%	15.52%
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount	1,278,797	1,088,349
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	1,598,496	1,360,437
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	2,186,276	1,958,336
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	13.68%	14.39%
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount	639,398	544,175
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	959,098	816,262
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	6.00%	6.00%
Leverage Ratio, Actual, Capital Amount	2,186,276	1,958,336
Leverage Ratio, Actual, Ratio	8.16%	8.49%
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Capital Amount	1,072,035	922,728
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	1,340,043	1,153,410
Leverage Ratio, Required to be Considered Well Capitalized, Ratio	5.00%	5.00%
Frost Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	2,071,012	1,780,313
Total Capital to Risk-Weighted Assets, Actual, Ratio	12.99%	13.12%
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount	1,275,858	1,085,447
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio	8.00%	8.00%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	1,594,823	1,356,809
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	1,979,415	1,707,307
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.41%	12.58%
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount	637,929	542,724
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	956,894	814,085
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	6.00%	6.00%
Leverage Ratio, Actual, Capital Amount	1,979,415	1,707,307
Leverage Ratio, Actual, Ratio	7.40%	7.42%
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Capital Amount	1,070,109	920,107
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$1,337,636	$1,150,134
Leverage Ratio, Required to be Considered Well Capitalized, Ratio	5.00%	5.00%

Earnings_Per_Common_Share_Basi

Earnings Per Common Share (Basic and Diluted Earnings Per Common Share) (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income	$277,977	$237,866	$237,952
Less: Preferred stock dividends	8,063	6,719	0
Net income available to common shareholders	269,914	231,147	237,952
Less: Earnings allocated to participating securities	1,001	850	773
Net earnings allocated to common stock	268,913	230,297	237,179
Distributed earnings allocated to common stock	126,709	119,177	116,472
Undistributed earnings allocated to common stock	142,204	111,120	120,707
Net earnings allocated to common stock	$268,913	$230,297	$237,179
Weighted-average shares outstanding for basic earnings per common share	62,072,080	60,350,552	61,298,041
Dilutive effect of stock compensation	901,448	765,858	345,341
Weighted-average shares outstanding for diluted earnings per common share	62,973,528	61,116,410	61,643,382

Employee_Benefit_Plans_Narrati

Employee Benefit Plans (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expense related to benefit plans	$10,800,000	$11,400,000	$9,200,000
Net actuarial loss expected to be recognized	7,000,000
Modeling process confidence ratio	90.00%
Percentage of equity investments in mutual fund	71.00%
Assumed long-term rate of return	7.75%
Expected defined benefit plans contribution within a year	1,100,000
Target percentage of pay at age 55	45.00%
Target percentage of pay at age 60	60.00%
Stock purchase plan expense	9,142,000	8,814,000	9,663,000
Maximum exercise period of options granted, years	10 years
Awards other than in the form of stock options	281,840
Intrinsic value of outstanding in-the-money stock options	66,500,000
Outstanding in-the-money exercisable stock options	56,400,000
Weighted-average period, unrecognized expense related to stock options, years	3 years 1 month 6 days
Weighted-average period, unrecognized expense related to non-vested stock awards, years	2 years 6 months
Weighted-average fair value of stock options granted	$16.97	$13.74	$11.07
401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution match by employer	100.00%
Participants contribution eligible for match	6.00%
Stock purchase plan expense	$12,300,000	$11,500,000	$10,800,000
Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	65.00%
Fixed Income Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	32.00%
2005 Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years	10 years	10 years
Vesting period of options awarded, years	4 years	4 years	4 years
2005 Plan [Member] | Non Vested Stock Awards and Stock Units [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years	10 years	10 years
Cliff vesting period, years	4 years	4 years	4 years
2007 Directors Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Options awarded during period	0	0	0
Minimum [Member] | 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution percentage of eligible compensation	2.00%
Maximum [Member] | 401(k) Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Contribution percentage of eligible compensation	50.00%

Employee_Benefit_Plans_Combine

Employee Benefit Plans (Combined Activity in Corporations Defined Benefit Pension Plans) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Benefit obligation at beginning of year	$163,876	$178,158	$157,855
Interest cost	8,002	7,341	7,801
Actuarial (gain) loss	34,438	-15,333	18,436
Benefits paid	-6,679	-6,290	-5,934
Benefit obligation at end of year	199,637	163,876	178,158
Fair value of plan assets at beginning of year	164,769	145,901	137,253
Actual return on plan assets	9,428	24,489	13,931
Employer contributions	667	669	651
Benefits paid	-6,679	-6,290	-5,934
Fair value of plan assets at end of year	168,185	164,769	145,901
Funded status of the plan at end of year and accrued (benefit) liability recognized	31,452	-893	32,257
Accumulated benefit obligation at end of year	$199,637	$163,876	$178,158

Employee_Benefit_Plans_Disaggr

Employee Benefit Plans (Disaggregated Information Related to Corporations Defined Benefit Pension Plans) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$199,637	$163,876	$178,158	$157,855
Accumulated benefit obligation	199,637	163,876	178,158
Fair value of plan assets	168,185	164,769	145,901	137,253
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	179,970	147,403
Accumulated benefit obligation	179,970	147,403
Fair value of plan assets	168,185	164,769
Funded status of the plan at end of year and accrued (benefit) liability recognized	11,785	-17,366
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	19,667	16,473
Accumulated benefit obligation	19,667	16,473
Fair value of plan assets	0	0
Funded status of the plan at end of year and accrued (benefit) liability recognized	$19,667	$16,473

Employee_Benefit_Plans_Net_Per

Employee Benefit Plans (Net Periodic Benefit Cost (Benefit)) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	($12,514)	($11,087)	($10,412)
Interest cost on projected benefit obligation	8,002	7,341	7,801
Net amortization and deferral	2,687	6,558	5,709
Net periodic cost (benefit)	($1,825)	$2,812	$3,098

Employee_Benefit_Plans_Defined

Employee Benefit Plans (Defined Benefit Pension Plans Recognized as Component of Other Comprehensive Income) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$34,837	($35,293)	$9,405
Deferred tax (expense) benefit	-12,193	12,353	-3,292
Defined Benefit Pension Plans Recognized As Component Of Other Comprehensive Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	-34,837	35,293	-9,405
Deferred tax (expense) benefit	12,193	-12,353	3,292
Other comprehensive income (loss), net of tax	($22,644)	$22,940	($6,113)

Employee_Benefit_Plans_Defined1

Employee Benefit Plans (Defined Benefit Pension Plans not Recognized as Component of Combined Net Period Benefit Cost) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Amounts included in accumulated other comprehensive loss, net of tax	$22,644	($22,940)	$6,113
Not Recognized As Combined Net Period Benefit Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	-75,038	-40,201
Deferred tax benefit	26,263	14,070
Amounts included in accumulated other comprehensive loss, net of tax	($48,775)	($26,131)

Employee_Benefit_Plans_Weighte

Employee Benefit Plans (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Benefit obligations, Discount rate	4.20%	5.00%	4.20%
Net periodic benefit cost, Discount rate	5.00%	4.20%	5.05%
Net periodic benefit cost, Expected return on plan assets	7.75%	7.75%	7.75%

Employee_Benefit_Plans_Fair_Va

Employee Benefit Plans (Fair Value of Plan Assets) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$168,185	$164,769	$145,901	$137,253
Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165,429	163,046
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,447	91
Corporate Bonds And Notes [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	653	893
US Government Agency Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	394	473
States and Political Subdivisions [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$262	$266

Employee_Benefit_Plans_Expecte

Employee Benefit Plans (Expected Future Benefit Payments Related to Defined Benefit Plans) (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Compensation and Retirement Disclosure [Abstract]
2015	$8,429
2016	11,991
2017	9,532
2018	9,988
2019	10,413
2020 through 2024	57,255
Total defined benefit plan expected future benefit payments	$107,608

Employee_Benefit_Plans_Summary

Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Shares Available for Grant	2,862,603	1,157,413	1,963,455
Authorized, Shares Available for Grant	0	2,293,660
Granted, Shares Available for Grant	-955,443	-635,360	-825,542
Forfeited, Shares Available for Grant	66,267	46,890	19,750
Cancelled/expired, Shares Available for Grant	0	0	-250
Ending Balance, Shares Available for Grant	1,973,427	2,862,603	1,157,413
Beginning Balance, Director Deferred Stock Units Outstanding	33,224	27,724	22,092
Granted, Director Deferred Stock Units Outstanding	5,643	5,500	5,632
Ending Balance, Director Deferred Stock Units Outstanding	38,867	33,224	27,724
Stock options exercised, Number of Shares	-594,231	-1,319,786	-206,366
Beginning Balance, Weighted-Average Grant-Date Fair Value	$13.74	$11.07
Ending Balance, Weighted-Average Grant-Date Fair Value	$16.97	$13.74	$11.07
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	199,740	188,560	169,530
Granted, Number of Shares	32,050	38,010	49,130
Stock awards vested, Number of Shares	-56,300	-26,830	-30,100
Ending Balance, Number of Shares	175,490	199,740	188,560
Beginning Balance, Weighted-Average Grant-Date Fair Value	$55.32	$51.67	$50.33
Granted, Weighted-Average Grant-Date Fair Value	$78.92	$71.39	$54.56
Stock awards vested, Weighted-Average Grant-Date Fair Value	$52.46	$50.64	$52.44
Ending Balance, Weighted-Average Grant-Date Fair Value	$60.55	$55.32	$51.67
Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	4,738,690	5,513,516	4,968,822
Granted, Number of Shares	917,750	591,850	770,780
Stock options exercised, Number of Shares	-560,291	-1,319,786	-206,336
Forfeited, Number of Shares	-66,267	-46,890	-19,750
Ending Balance, Number of Shares	5,029,882	4,738,690	5,513,516
Beginning Balance, Weighted-Average Exercise Price	$54.35	$51.94	$51.49
Granted, Weighted-Average Exercise Price	$78.93	$71.38	$54.56
Stock options exercised, Weighted-Average Exercise Price	$52.04	$52.02	$50.96
Forfeited, Weighted-Average Exercise Price	$62.21	$46.05	$50.49
Ending Balance, Weighted-Average Exercise Price	$58.99	$54.35	$51.94

Employee_Benefit_Plans_Options

Employee Benefit Plans (Options Outstanding and Exercisable) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted- Average Remaining Contractual Life in Years	3 years 1 month 6 days
$ 45.01 - $ 50.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	45.01
Range of Exercise Prices, Maximum	50
50.01 - 55.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	50.01
Range of Exercise Prices, Maximum	55
55.01 - 60.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	55.01
Range of Exercise Prices, Maximum	60
70.01 - 75.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	70.01
Range of Exercise Prices, Maximum	75
75.01 - 80.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	75.01
Range of Exercise Prices, Maximum	80
Options Outstanding [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	5,029,882
Weighted-Average Exercise Price, Options Outstanding	58.99
Weighted- Average Remaining Contractual Life in Years	6 years 5 months 16 days
Options Outstanding [Member] | $ 45.01 - $ 50.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	946,265
Weighted-Average Exercise Price, Options Outstanding	48.26
Weighted- Average Remaining Contractual Life in Years	5 years 6 months 29 days
Options Outstanding [Member] | 50.01 - 55.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	2,273,190
Weighted-Average Exercise Price, Options Outstanding	52.61
Weighted- Average Remaining Contractual Life in Years	5 years 6 months 29 days
Options Outstanding [Member] | 55.01 - 60.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	334,075
Weighted-Average Exercise Price, Options Outstanding	57.63
Weighted- Average Remaining Contractual Life in Years	1 year 10 months 17 days
Options Outstanding [Member] | 70.01 - 75.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	576,602
Weighted-Average Exercise Price, Options Outstanding	71.38
Weighted- Average Remaining Contractual Life in Years	8 years 10 months 2 days
Options Outstanding [Member] | 75.01 - 80.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding	899,750
Weighted-Average Exercise Price, Options Outstanding	78.94
Weighted- Average Remaining Contractual Life in Years	9 years 9 months 18 days
Options Exercisable [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	3,142,628
Weighted-Average Exercise Price, Option Exercisable	53.11
Options Exercisable [Member] | $ 45.01 - $ 50.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	760,240
Weighted-Average Exercise Price, Option Exercisable	49.91
Options Exercisable [Member] | 50.01 - 55.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	1,907,700
Weighted-Average Exercise Price, Option Exercisable	52.24
Options Exercisable [Member] | 55.01 - 60.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	334,075
Weighted-Average Exercise Price, Option Exercisable	57.63
Options Exercisable [Member] | 70.01 - 75.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	140,613
Weighted-Average Exercise Price, Option Exercisable	71.38
Options Exercisable [Member] | 75.01 - 80.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable	0
Weighted-Average Exercise Price, Option Exercisable	0

Employee_Benefit_Plans_Shares_

Employee Benefit Plans (Shares Issued in Connection with Stock Compensation Awards) (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
New shares issued from available authorized shares	0	153,275	207,586
Issued from available treasury stock	601,851	1,179,551	15,600
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	601,851	1,332,826	223,186
Proceeds from stock option exercises	$29,158	$68,653	$10,516
Intrinsic value of stock options exercised	13,714	20,506	1,538
Fair value of stock awards/units vested	$4,346	$1,918	$1,649

Employee_Benefit_Plans_StockBa

Employee Benefit Plans (Stock-Based Compensation Expense) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Stock options	$9,142	$8,814	$9,663
Non-vested stock awards/stock units	2,920	2,819	2,843
Deferred stock-units	441	330	330
Total	12,503	11,963	12,836
Income tax benefit	$4,376	$4,187	$4,493

Employee_Benefit_Plans_Unrecog

Employee Benefit Plans (Unrecognized Stock-Based Compensation Expense) (Detail) (USD $)	Dec. 31, 2014
In Thousands, unless otherwise specified
Compensation and Retirement Disclosure [Abstract]
Stock options	$22,066
Non-vested stock awards/stock units	2,437
Total	$24,503

Employee_Benefit_Plans_Assumpt

Employee Benefit Plans (Assumptions to Determine Fair Value of Options Granted) (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Weighted-average risk-free interest rate	2.33%	2.65%	1.85%
Dividend yield	2.71%	2.92%	3.28%
Weighted-average expected market price volatility	26.66%	24.20%	28.06%
Weighted-average expected term	7 years 1 month 6 days	6 years 8 months 12 days	6 years 2 months 12 days

Other_NonInterest_Income_and_E2

Other Non-Interest Income and Expense (Narrative) (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income and Expenses [Abstract]
Minimum percentage of the aggregate total net interest income and total non interest income required for amounts to be stated separately	1.00%	1.00%	1.00%

Other_NonInterest_Income_and_E3

Other Non-Interest Income and Expense (Other Non-Interest Income and Expense) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income and Expenses [Abstract]
Other	$32,256	$34,531	$30,703
Total other non-interest income	32,256	34,531	30,703
Advertising, promotions and public relations	28,998	26,232	27,194
Legal and other professional fees	27,365	26,132	22,341
Check card expense	15,970	11,787	10,227
Travel/meals and entertainment	14,813	13,571	13,049
Other	80,510	74,355	66,658
Total other non-interest expense	$167,656	$152,077	$139,469

Income_Taxes_Income_Tax_Expens

Income Taxes (Income Tax Expense) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Current income tax expense	$62,177	$49,736	$76,928
Deferred income tax expense (benefit)	-4,130	3,279	-6,405
Income tax expense, as reported	$58,047	$53,015	$70,523

Income_Taxes_Narrative_Detail

Income Taxes (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	35.00%
Valuation allowance	$0	$0
Unrecognized tax benefits	$0	$0

Income_Taxes_Income_Tax_Comput

Income Taxes (Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Income tax expense computed at the statutory rate	$117,608	$101,808	$107,966
Effect of tax-exempt interest	-58,761	-46,535	-36,543
Bank owned life insurance income	-1,116	-1,086	-1,413
Other	316	-1,172	513
Income tax expense, as reported	$58,047	$53,015	$70,523

Income_Taxes_Schedule_of_Defer

Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]
Allowance for loan losses	$34,840	$32,353
Net actuarial loss on defined benefit post-retirement benefit plans	26,263	14,070
Stock-based compensation	18,839	17,746
Bonus accrual	6,118	5,301
Gain on sale of assets	2,139	2,234
Partnerships	1,911	2,208
Transaction costs	1,794	565
Other	5,272	4,489
Total gross deferred tax assets	97,176	78,966
Net unrealized gain on securities available for sale and effective cash flow hedging derivatives	-102,626	-89,689
Premises and equipment	-20,039	-21,192
Defined benefit post-retirement benefit plans	-15,010	-14,137
Intangible assets	-6,143	-7,253
Leases	-4,952	-4,237
Reserve for medical insurance	-3,017	-2,171
Prepaid expenses	-1,639	-1,618
Other	-341	-1,456
Total gross deferred tax liabilities	-153,767	-141,753
Net deferred tax asset (liability)	($56,591)	($62,787)

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$103,044	($115,245)	$33,412
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	-35,441	-35,682	-657
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	-38	-1,176	-4,314
Total securities available for sale and transferred securities	67,565	-152,103	28,441
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	-34,837	35,293	-9,405
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	0	-49	-783
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	-30,604	-37,380	-37,380
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Before Tax Amount	0	4,064	4,224
Total derivatives	-30,604	-33,365	-33,939
Other comprehensive income (loss), before tax	2,124	-150,175	-14,903
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	36,065	-40,335	11,694
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	-12,404	-12,489	-230
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	-13	-412	-1,510
Total securities available for sale and transferred securities, Tax Expense (Benefit)	23,648	-53,236	9,954
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	-12,193	12,353	-3,292
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)		-17	-274
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)	-10,711	-13,083	-13,083
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Tax Expense (Benefit)		1,422	1,478
Derivatives, Total derivatives, Tax Expense, (Benefit)		-11,678	-11,879
Total other comprehensive income, Tax Expense (Benefit)	744	-52,561	-5,217
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax	66,979	-74,910	21,718
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, net of tax	-23,037	-23,193	-427
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax	-25	-764	-2,804
Total securities available for sale and transferred securities, net of tax	43,917	-98,867	18,487
Defined-benefit post-retirement plans, Change in the net actuarial gain/loss, net of tax	-22,644	22,940	-6,113
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, net of tax		-32	-509
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swaps on variable-rate loans, net of tax	-19,893	-24,297	-24,297
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swap on junior subordinated deferrable interest debentures, net of tax		2,642	2,746
Derivatives, Total derivatives, net of tax		-21,687	-22,060
Other comprehensive income (loss), net of tax	$1,380	($97,614)	($9,686)

Other_Comprehensive_Income_Sch

Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$140,434	$238,048	$247,734
Other comprehensive income (loss) before reclassification	21,298	-75,195	14,669
Amounts reclassified from accumulated other comprehensive income (loss)	-19,918	-22,419	-24,355
Net other comprehensive income (loss) during period	1,380	-97,614	-9,686
Ending Balance	141,814	140,434	238,048
Securities Available For Sale [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	146,672	245,539	227,052
Other comprehensive income (loss) before reclassification	43,942	-98,103	21,291
Amounts reclassified from accumulated other comprehensive income (loss)	-25	-764	-2,804
Net other comprehensive income (loss) during period	43,917	-98,867	18,487
Ending Balance	190,589	146,672	245,539
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	-26,131	-49,071	-42,958
Other comprehensive income (loss) before reclassification	-22,644	22,940	-6,113
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Net other comprehensive income (loss) during period	-22,644	22,940	-6,113
Ending Balance	-48,775	-26,131	-49,071
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	19,893	41,580	63,640
Other comprehensive income (loss) before reclassification	0	-32	-509
Amounts reclassified from accumulated other comprehensive income (loss)	-19,893	-21,655	-21,551
Net other comprehensive income (loss) during period	-19,893	-21,687	-22,060
Ending Balance	$0	$19,893	$41,580

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Narrative) (Detail) (USD $)	12 Months Ended		1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2007	Dec. 31, 2007	Oct. 31, 2008
Derivative [Line Items]
Deferred accumulated gain		$30,600,000
Deferred accumulated after-tax gain		19,900,000
Weighted-average strike rate for outstanding interest rate caps	2.99%
Approximate credit exposure related to swaps with bank customers	39,000,000
Aggregate fair value of securities posted as collateral for derivative contracts	19,300,000
Cash collateral on deposit with other financial institutions	12,100,000
Interest Rate Swaps With Upstream Financial Institution Counterparties [Member]
Derivative [Line Items]
Approximate credit exposure related to swaps with bank customers	8,500,000
Variable-Rate Loans Outstanding [Member]
Derivative [Line Items]
Notional amount of interest rate swap contracts				1,200,000,000
Principal amount outstanding of variable-rate loans			1,200,000,000
Period for which cash flow hedges were used to hedge monthly interest receipts			84 months
Junior Subordinated Deferred Interest Debentures [Member]
Derivative [Line Items]
Notional amount of interest rate swap contracts					$120,000,000
Period for which cash flow hedges were used to hedge quarterly interest payments		5 years
Swap fixed interest rate to be paid		5.47%
Variable interest rate of three-month LIBOR plus a margin		1.55%

Derivative_Financial_Instrumen3

Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	$31,614	$50,965
Estimated Fair Value	469	1,386
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	37,672	43,631
Estimated Fair Value	-3,179	-4,191
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	69,842	195,234
Estimated Fair Value	719	9,573
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	765,979	626,980
Estimated Fair Value	-38,952	-32,469
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Caps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	73,058	53,058
Estimated Fair Value	1,003	1,309
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	765,979	626,980
Estimated Fair Value	38,910	32,426
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	69,842	195,234
Estimated Fair Value	-719	-9,573
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Caps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	73,058	53,058
Estimated Fair Value	($1,003)	($1,309)

Derivative_Financial_Instrumen4

Derivative Financial Instruments (Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding) (Detail)	Dec. 31, 2014
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	2.80%
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	0.16%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	4.05%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	1.67%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	1.67%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	4.05%

Derivative_Financial_Instrumen5

Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	bbl	bbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount	470,000	356,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$14,357	$1,004
Oil/Natural Gas Derivative Liabilities Notional Amount	197,000	1,574,000
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	-1,670	-2,704
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount	12,235,000	14,240,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	12,707	2,903
Oil/Natural Gas Derivative Liabilities Notional Amount	16,755,000	22,510,000
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	-4,095	-3,212
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount	197,000	1,574,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	1,670	2,818
Oil/Natural Gas Derivative Liabilities Notional Amount	470,000	356,000
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	-14,318	-991
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount	16,755,000	22,850,000
Oil/Natural Gas Derivative Assets, Estimated Fair Value	4,095	3,301
Oil/Natural Gas Derivative Liabilities Notional Amount	12,235,000	13,900,000
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	($12,646)	($2,805)

Derivative_Financial_Instrumen6

Derivative Financial Instruments Derivative Financial Instruments (Schedule of Notional Amount and Fair Value of Open Foreign Currency Forward Contract) (Details)

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2014

Dec. 31, 2013

In Thousands, unless otherwise specified

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Customer Counterparties [Member]

Customer Counterparties [Member]

Customer Counterparties [Member]

Customer Counterparties [Member]

Eurodollar Foreign Exchange Forward [Member] [Member]

Eurodollar Foreign Exchange Forward [Member] [Member]

Foreign Exchange Forward [Member]

Foreign Exchange Forward [Member]

Foreign Exchange Forward [Member]

Foreign Exchange Forward [Member]

GBP Foreign Exchange Forward [Member]

GBP Foreign Exchange Forward [Member]

Other Assets [Member]

Other Assets [Member]

Other Assets [Member]

Other Assets [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Other Assets [Member]

Other Assets [Member]

Other Liabilities [Member]

Other Liabilities [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Customer Counterparties [Member]

Customer Counterparties [Member]

Financial Institution Counterparties [Member]

Financial Institution Counterparties [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

Not Designated as Hedging Instrument [Member]

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

CAD

EUR (€)

CAD

EUR (€)

CAD

EUR (€)

GBP (£)

CAD

EUR (€)

GBP (£)

CAD

CAD

CAD

CAD

Derivative Counter Party [Line Items]

Forward Contracts - Assets, Notional Amount

24,724

€ 936

18,886

€ 1,175

0

14,055

Forward Contracts Liability, Notional Amount

0

0

544

14,078

494

0

24,680

18,859

Forward Contracts - Assets Estimated Fair Value

7

5

659

85

0

45

Forward Contracts, Liability Estimated Fair Value

$0

($4)

$0

($23)

($615)

($58)

($2)

$0

Derivative_Financial_Instrumen7

Derivative Financial Instruments (Schedule of Amounts Related to Interest Rate Derivatives Designated as Hedges of Fair Value) (Detail) (Designated as Hedging Instrument [Member], Commercial Loan/Lease Interest Rate Swaps [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Income on Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) included in income (expense)	($2,014)	($2,437)	($2,587)
Other Non-Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) included in income (expense)	$3	$4	$46

Derivative_Financial_Instrumen8

Derivative Financial Instruments (Schedule of Amounts Related to Interest Rate Derivatives Included in Income Designated as Hedges of Cash Flows) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in other comprehensive income		$19,900
Designated as Hedging Instrument [Member] | Interest Rate Swap On Junior Subordinated Deferrable Interest Debentures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in other comprehensive income	0	-49	-783
Designated as Hedging Instrument [Member] | Interest Income on Loans [Member] | Interest Rate Swaps On Variable-Rate Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount reclassified from accumulated other comprehensive income to interest	30,604	37,380	37,380
Designated as Hedging Instrument [Member] | Interest Expense [Member] | Interest Rate Swap On Junior Subordinated Deferrable Interest Debentures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount reclassified from accumulated other comprehensive income to interest	$0	$4,064	$4,224

Derivative_Financial_Instrumen9

Derivative Financial Instruments (Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives) (Detail) (Not Designated as Hedging Instrument [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest Rate Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$1,786	$1,441	$4,722
Interest Rate Contract [Member] | Other Non-Interest Expense [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	-2	-96	-116
Commodity Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	118	496	124
Foreign Exchange Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$162	$175	$0

Balance_Sheet_Offsetting_Finan

Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	$29,921	$16,265
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	29,921	16,265
Gross Amount Recognized, Resell Agreements, Financial Assets	9,642	7,898
Gross Amount Offset, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Resell Agreements, Financial Assets	9,642	7,898
Gross Amount Recognized, Financial Assets	39,563	24,163
Gross Amount Offset, Financial Assets	0	0
Net Amount Recognized, Financial Assets	39,563	24,163
Gross Amount Recognized, Derivative, Financial Liabilities	47,898	42,603
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	47,898	42,603
Gross Amount Recognized, Repurchase Agreements, Financial Liabilities	791,119	668,053
Gross Amount Offset, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	791,119	668,053
Gross Amount Recognized, Financial Liabilities	839,017	710,656
Gross Amount Offset, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	839,017	710,656
Loan Lease Interest Rate Swaps And Caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	2,191	12,268
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	2,191	12,268
Commodity Swaps And Options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	27,064	3,907
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	27,064	3,907
Gross Amount Recognized, Derivative, Financial Liabilities	5,765	5,916
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	5,765	5,916
Foreign Currency Forward Contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	666	90
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	666	90
Gross Amount Recognized, Derivative, Financial Liabilities	2	27
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	2	27
Loan Lease Interest Rate Swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Liabilities	42,131	36,660
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	$42,131	$36,660

Balance_Sheet_Offsetting_Finan1

Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$29,921	$16,265
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	-20,436	-14,824
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	-6,035	-1,360
Net Amount, Derivatives, Financial Assets	3,450	81
Net Amount Recognized, Resell Agreements, Financial Assets	9,642	7,898
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	-9,642	-7,898
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	39,563	24,163
Gross Amounts Not Offset, Collateral, Financial Assets	-15,677	-9,258
Net Amount, Financial Assets	3,450	81
Net Amount Recognized, Derivatives, Financial Liabilities	47,898	42,603
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	-20,436	-14,824
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	-26,307	-27,012
Net Amount, Derivatives, Financial Liabilities	1,155	767
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	791,119	668,053
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	-791,119	-668,053
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	839,017	710,656
Gross Amounts Not Offset, Collateral, Financial Liabilities	-817,426	-695,065
Net Amount, Financial Liabilities	1,155	767
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	627	3,342
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	-627	-3,342
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	18,653	18,615
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	-627	-3,342
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	-17,626	-15,167
Net Amount, Derivatives, Financial Liabilities	400	106
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	17,308	8,196
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	-9,506	-8,196
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	-4,925	0
Net Amount, Derivatives, Financial Assets	2,877	0
Net Amount Recognized, Derivatives, Financial Liabilities	9,506	9,054
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	-9,506	-8,196
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	-613
Net Amount, Derivatives, Financial Liabilities	0	245
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	7,991	1,187
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	-7,539	-1,187
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	452	0
Net Amount Recognized, Derivatives, Financial Liabilities	7,539	10,870
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	-7,539	-1,187
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	-9,683
Net Amount, Derivatives, Financial Liabilities	0	0
Other Counterparties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	3,995	3,540
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	-2,764	-2,099
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	-1,110	-1,360
Net Amount, Derivatives, Financial Assets	121	81
Net Amount Recognized, Derivatives, Financial Liabilities	12,200	4,064
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	-2,764	-2,099
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	-8,681	-1,549
Net Amount, Derivatives, Financial Liabilities	$755	$416

Fair_Value_Measurements_Financ

Fair Value Measurements (Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	$8,461,254	$5,895,436
Trading account securities	15,426	16,398
Derivative assets:	29,921	16,265
Derivative liabilities:	47,898	42,603
US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,811,252	2,540,554
Trading account securities	15,339	15,389
US Government agencies/ corporations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		53,980
Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,398,724	1,776,016
States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,208,907	1,488,914
Trading account securities	87	1,009
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	42,371	35,972
Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	41,101	44,694
Derivative liabilities:	43,853	47,542
Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	32,829	10,026
Derivative liabilities:	32,729	9,712
Foreign Currency Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	666	135
Derivative liabilities:	617	85
Level 1 [Member] | US Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,811,252	2,540,554
Trading account securities	15,339	15,389
Level 1 [Member] | Foreign Currency Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	666	135
Derivative liabilities:	617	85
Level 2 [Member] | US Government agencies/ corporations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value		53,980
Level 2 [Member] | Residential Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	1,398,724	1,776,016
Level 2 [Member] | States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,208,907	1,488,914
Trading account securities	87	1,009
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	42,371	35,972
Level 2 [Member] | Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	40,931	44,520
Derivative liabilities:	43,853	47,542
Level 2 [Member] | Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	32,829	10,026
Derivative liabilities:	32,729	9,712
Level 3 [Member] | Interest Rate Swaps, Caps and Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	$170	$174

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Detail)	12 Months Ended
	Dec. 31, 2014
	Grade
Fair Value Disclosures [Abstract]
Weighted-average risk grade of loans underlying interest rate swaps measured at fair value	11
Default on the interest rate swaps, weighted average loss severity percentage	20.00%

Fair_Value_Measurements_Impair

Fair Value Measurements (Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$53,591	$48,462	$80,397
Specific valuation allowance allocations	-1,680	-6,926	-8,237
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	0	9,374	18,319
Specific valuation allowance allocations	0	-2,785	-3,634
Fair value	0	6,589	14,685
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	2,715	0	15,754
Specific valuation allowance allocations	-1,475	0	-2,911
Fair value	$1,240	$0	$12,843

Fair_Value_Measurements_Forecl

Fair Value Measurements (Foreclosed Assets Remeasured and Reported at Fair Value) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$5,300	$11,900
Foreclosed Assets Remeasured at Initial Recognition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of foreclosed assets prior to remeasurement	6,388	7,580	9,428
Charge-offs recognized in the allowance for loan losses	-285	-710	-1,611
Fair value	6,103	6,870	7,817
Foreclosed Assets Remeasured Subsequent to Initial Recognition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of foreclosed assets prior to remeasurement	5,026	4,979	12,126
Write-downs included in other non-interest expense	-1,289	-895	-2,093
Fair value	$3,737	$4,084	$10,033

Fair_Value_Measurements_Estima

Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$4,364,123,000	$4,556,125,000	$3,524,979,000
Securities held to maturity	2,926,486,000	3,139,748,000
Loans, net	10,887,993,000	9,423,262,000
Deposits	24,135,930,000	20,688,786,000
Federal funds purchased and repurchase agreements	803,119,000	668,253,000
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Subordinated notes payable and other borrowings	100,000,000	100,000,000
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,364,123,000	4,556,125,000
Securities held to maturity	2,926,486,000	3,139,748,000
Cash surrender value of life insurance policies	172,050,000	141,108,000
Accrued interest receivable	128,436,000	99,281,000
Deposits	24,135,930,000	20,688,786,000
Federal funds purchased and repurchase agreements	803,119,000	668,253,000
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Subordinated notes payable and other borrowings	100,000,000	100,000,000
Accrued interest payable	1,132,000	1,300,000
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	10,887,993,000	9,423,262,000
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	4,364,123,000	4,556,125,000
Securities held to maturity	2,966,390,000	3,029,663,000
Cash surrender value of life insurance policies	172,050,000	141,108,000
Accrued interest receivable	128,436,000	99,281,000
Deposits	24,136,402,000	20,689,323,000
Federal funds purchased and repurchase agreements	803,119,000	668,253,000
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Subordinated notes payable and other borrowings	95,591,000	92,552,000
Accrued interest payable	1,132,000	1,300,000
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$10,939,684,000	$9,582,734,000

Operating_Segments_Operating_S

Operating Segments Operating Segments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2014
	Segment
Segment Reporting [Abstract]
Number of Operating Segments	2

Operating_Segments_Summary_of_

Operating Segments (Summary of Operating Results by Segment) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Net interest income (expense)	$686,934,000		$620,555,000		$604,861,000
Provision for loan losses	16,314,000		20,582,000		10,080,000
Non-interest income	320,144,000		302,818,000		288,787,000
Non-interest expense	654,740,000		611,910,000		575,093,000
Income (loss) before income taxes	336,024,000		290,881,000		308,475,000
Income tax expense (benefit)	58,047,000		53,015,000		70,523,000
Net income	277,977,000		237,866,000		237,952,000
Preferred stock dividends	8,063,000		6,719,000		0
Net income available to common shareholders	269,914,000		231,147,000		237,952,000
Revenues from (expenses to) external customers	1,007,078,000		923,373,000		893,648,000
Average assets	25,768,000,000	[1]	22,752,000,000	[1]	20,827,000,000	[1]
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	683,579,000		621,333,000		605,330,000
Provision for loan losses	16,312,000		20,585,000		10,078,000
Non-interest income	193,883,000		190,767,000		188,440,000
Non-interest expense	549,812,000		513,909,000		485,302,000
Income (loss) before income taxes	311,338,000		277,606,000		298,390,000
Income tax expense (benefit)	51,881,000		50,823,000		69,078,000
Net income	259,457,000		226,783,000		229,312,000
Preferred stock dividends	0		0
Net income available to common shareholders	259,457,000		226,783,000
Revenues from (expenses to) external customers	877,462,000		812,100,000		793,770,000
Average assets	25,734,000,000	[1]	22,709,000,000	[1]	20,783,000,000	[1]
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	6,734,000		6,586,000		8,013,000
Provision for loan losses	2,000		-3,000		2,000
Non-interest income	122,261,000		107,759,000		96,577,000
Non-interest expense	96,330,000		90,132,000		82,744,000
Income (loss) before income taxes	32,663,000		24,216,000		21,844,000
Income tax expense (benefit)	11,431,000		8,563,000		7,646,000
Net income	21,232,000		15,653,000		14,198,000
Preferred stock dividends	0		0
Net income available to common shareholders	21,232,000		15,653,000
Revenues from (expenses to) external customers	128,995,000		114,345,000		104,590,000
Average assets	32,000,000	[1]	31,000,000	[1]	29,000,000	[1]
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	-3,379,000		-7,364,000		-8,482,000
Provision for loan losses	0		0		0
Non-interest income	4,000,000		4,292,000		3,770,000
Non-interest expense	8,598,000		7,869,000		7,047,000
Income (loss) before income taxes	-7,977,000		-10,941,000		-11,759,000
Income tax expense (benefit)	-5,265,000		-6,371,000		-6,201,000
Net income	-2,712,000		-4,570,000		-5,558,000
Preferred stock dividends	8,063,000		6,719,000
Net income available to common shareholders	-10,775,000		-11,289,000
Revenues from (expenses to) external customers	621,000		-3,072,000		-4,712,000
Average assets	$2,000,000	[1]	$12,000,000	[1]	$15,000,000	[1]
[1]	Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.5 billion, $29.0 billion and $26.2 billion at December 31, 2014, 2013 and 2012.

Operating_Segments_Summary_of_1

Operating Segments (Summary of Operating Results by Segment) (Parenthetical) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
In Billions, unless otherwise specified
Segment Reporting [Abstract]
Fair value of off balance sheet managed and custody assets	$30.50	$29	$26.20

Condensed_Financial_Statements2

Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Cash	$702,485,000	$885,121,000
Resell agreements	30,792,000	24,248,000
Total cash and cash equivalents	4,364,123,000	4,556,125,000	3,524,979,000
Total assets	28,277,775,000	24,312,939,000
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Accrued interest payable and other liabilities	250,208,000	218,027,000
Total liabilities	25,426,372,000	21,798,778,000
Shareholders’ Equity	2,851,403,000	2,514,161,000	2,417,482,000	2,283,537,000
Total liabilities and shareholders’ equity	28,277,775,000	24,312,939,000
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	7,335,000	7,477,000
Resell agreements	286,660,000	320,200,000
Total cash and cash equivalents	293,995,000	327,677,000
Investment in subsidiaries	2,791,647,000	2,409,433,000
Accrued interest receivable and other assets	29,705,000	19,038,000
Total assets	3,115,347,000	2,756,148,000
Junior subordinated deferrable interest debentures	137,115,000	123,712,000
Subordinated notes payable	100,000,000	100,000,000
Accrued interest payable and other liabilities	26,829,000	18,275,000
Total liabilities	263,944,000	241,987,000
Shareholders’ Equity	2,851,403,000	2,514,161,000
Total liabilities and shareholders’ equity	$3,115,347,000	$2,756,148,000

Condensed_Financial_Statements3

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Total interest income	$701,471	$642,500	$631,612
Interest expense	14,537	21,945	26,751
Salaries and employee benefits	292,349	273,692	258,752
Other	167,656	152,077	139,469
Income before income taxes and equity in undistributed earnings of subsidiaries	336,024	290,881	308,475
Income tax benefit	-58,047	-53,015	-70,523
Net income	277,977	237,866	237,952
Less: Preferred stock dividends	8,063	6,719	0
Net income available to common shareholders	269,914	231,147	237,952
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	114,439	144,642	143,623
Dividend income paid by non-banks	4,323	2,819	3,077
Interest and other income	69	79	308
Total interest income	118,831	147,540	147,008
Interest expense	3,381	7,365	8,512
Salaries and employee benefits	1,218	1,175	1,167
Other	8,526	6,735	6,727
Total expenses	13,125	15,275	16,406
Income before income taxes and equity in undistributed earnings of subsidiaries	105,706	132,265	130,602
Income tax benefit	6,702	7,845	7,463
Equity in undistributed earnings of subsidiaries	165,569	97,756	99,887
Net income	277,977	237,866	237,952
Less: Preferred stock dividends	8,063	6,719	0
Net income available to common shareholders	$269,914	$231,147	$237,952

Condensed_Financial_Statements4

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income	$277,977	$237,866	$237,952
Stock-based compensation	12,503	11,963	12,836
Excess tax benefits from stock-based compensation	-3,183	-2,686	-171
Net cash from operating activities	286,670	173,606	299,999
Net cash received (paid) in acquisitions	830,661	-1,896	-7,199
Net cash from investing activities	-2,282,093	-385,922	-2,155,468
Proceeds from stock option exercises	29,158	68,653	10,516
Excess tax benefits from stock-based compensation	3,183	2,686	171
Proceeds from issuance of preferred stock	0	144,486	0
Purchase of treasury stock	-1,457	-144,630	-436
Cash dividends paid on preferred stock	-8,063	-6,719	0
Cash dividends paid on common stock	-127,178	-119,619	-116,853
Net cash from financing activities	1,803,421	1,243,462	2,472,856
Net change in cash and cash equivalents	-192,002	1,031,146	617,387
Cash and cash equivalents at beginning of year	4,556,125	3,524,979	2,907,592
Cash and cash equivalents at end of year		4,556,125	3,524,979
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	277,977	237,866	237,952
Equity in undistributed earnings of subsidiaries	-165,569	-97,756	-99,887
Stock-based compensation	441	330	330
Excess tax benefits from stock-based compensation	-165	-155	-133
Net change in other assets and other liabilities	-1,984	2,372	-2,256
Net cash from operating activities	110,700	142,657	136,006
Net cash received (paid) in acquisitions	830,661	0	0
Capital contribution to subsidiaries	-879,730	0	0
Net cash from investing activities	-49,069	0	0
Proceeds from stock option exercises	29,158	68,653	10,516
Proceeds from stock-based compensation activities of subsidiaries	12,062	11,633	12,506
Excess tax benefits from stock-based compensation	165	155	133
Proceeds from issuance of preferred stock	0	144,486	0
Purchase of treasury stock	-1,457	-144,630	-436
Cash dividends paid on preferred stock	-8,063	-6,719	0
Cash dividends paid on common stock	-127,178	-119,619	-116,853
Net cash from financing activities	-95,313	-46,041	-94,134
Net change in cash and cash equivalents	-33,682	96,616	41,872
Cash and cash equivalents at beginning of year	327,677	231,061	189,189
Cash and cash equivalents at end of year	$293,995	$327,677	$231,061

Acquisitions_Additional_Inform

Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended			9 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	30-May-14
Business Acquisition [Line Items]
Non-interest expense	$654,740,000	$611,910,000	$575,093,000
WNB Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Preliminary purchase price allocation					198,798,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned					149,700,000
Common stock number of shares issued for consideration	2,000,000
Amount of cash consideration	49,100,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life				10 years
Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Non-interest expense	$7,100,000	$1,400,000

Acquisitions_Schedule_of_Preli

Acquisitions - Schedule of Preliminary Purchase Price Allocation (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	30-May-14
In Thousands, unless otherwise specified
Business Acquisition [Line Items]
Loans	$10,987,535	$9,515,700
Goodwill	653,950	536,649
Deposits	-24,135,930	-20,688,786
WNB Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Cash and equivalents			879,740
Securities available for sale			154,227
Loans			670,619
Premises and equipment			22,853
Core deposit intangible assets			9,300
Goodwill			117,301
Other assets			33,644
Deposits			-1,624,043
Other borrowings			-63,592
Other liabilities			-1,251
Preliminary purchase price allocation			$198,798