Cullen/Frost Bankers (CFR) 10-K 4 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2015	Feb. 01, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	CULLEN/FROST BANKERS, INC.
Trading Symbol	CFR
Entity Central Index Key	39,263
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		61,982,333
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 4.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Assets:
Cash and due from banks	$ 532,824	$ 702,485
Interest-bearing deposits	2,991,782	3,630,846
Federal funds sold and resell agreements	66,917	30,792
Total cash and cash equivalents	3,591,523	4,364,123
Securities held to maturity, at amortized cost	2,663,009	2,926,486
Securities available for sale, at estimated fair value	9,206,358	8,461,254
Trading account securities	16,579	15,426
Loans, net of unearned discounts	11,486,531	10,987,535
Less: Allowance for loan losses	(135,859)	(99,542)
Net loans	11,350,672	10,887,993
Premises and equipment, net	559,124	442,170
Goodwill	654,668	654,668
Other intangible assets, net	8,800	12,125
Cash surrender value of life insurance policies	175,191	172,050
Accrued interest receivable and other assets	341,194	341,480
Total assets	28,567,118	28,277,775
Liabilities:
Non-interest-bearing demand deposits	10,270,233	10,149,061
Interest-bearing deposits	14,073,362	13,986,869
Total deposits	24,343,595	24,135,930
Federal funds purchased and repurchase agreements	893,522	803,119
Junior subordinated deferrable interest debentures	137,115	137,115
Other long-term borrowings	100,000	100,000
Accrued interest payable and other liabilities	202,543	250,208
Total liabilities	25,676,775	25,426,372
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 2015 and 2014	144,486	144,486
Common stock, par value $0.01 per share; 210,000,000 shares authorized; 63,632,464 shares issued in 2015 and 2014	637	637
Additional paid-in capital	897,350	886,476
Retained earnings	1,845,188	1,710,324
Accumulated other comprehensive income, net of tax	113,863	141,814
Treasury stock, at cost; 1,650,131 shares in 2015 and 483,041 in 2014.	(111,181)	(32,334)
Total shareholders’ equity	2,890,343	2,851,403
Total liabilities and shareholders’ equity	$ 28,567,118	$ 28,277,775

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
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	63,632,464
Treasury stock, shares	1,650,131	483,041
Series A Preferred Stock [Member]
Series A Preferred Stock, Liquidation preference value	$ 25	$ 25

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest income:
Loans, including fees	$ 433,872	$ 440,958	$ 415,230
Securities:
Taxable	112,601	93,087	97,873
Tax-exempt	194,793	156,618	122,031
Interest-bearing deposits	8,123	10,725	7,284
Federal funds sold and resell agreements	107	83	82
Total interest income	749,496	701,471	642,500
Interest expense:
Deposits	9,024	11,022	14,459
Federal funds purchased and repurchase agreements	167	134	121
Junior subordinated deferrable interest debentures	2,725	2,488	6,426
Other long-term borrowings	948	893	939
Total interest expense	12,864	14,537	21,945
Net interest income	736,632	686,934	620,555
Provision for loan losses	51,845	16,314	20,582
Net interest income after provision for loan losses	684,787	670,620	599,973
Non-interest income:
Trust and investment management fees	105,512	106,237	91,375
Service charges on deposit accounts	81,350	81,946	81,432
Insurance commissions and fees	48,926	45,115	43,140
Interchange and debit card transaction fees	19,666	18,372	16,979
Other charges, commissions and fees	37,551	36,180	34,185
Net gain (loss) on securities transactions	69	38	1,176
Other	35,656	32,256	34,531
Total non-interest income	328,730	320,144	302,818
Non-interest expense:
Salaries and wages	310,504	292,349	273,692
Employee benefits	69,746	60,151	62,407
Net occupancy	65,690	55,745	50,468
Furniture and equipment	64,373	62,087	58,443
Deposit insurance	14,519	13,232	11,682
Intangible amortization	3,325	3,520	3,141
Other	165,561	167,656	152,077
Total non-interest expense	693,718	654,740	611,910
Income before income taxes	319,799	336,024	290,881
Income taxes	40,471	58,047	53,015
Net income	279,328	277,977	237,866
Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	$ 271,265	$ 269,914	$ 231,147
Earnings per common share:
Basic (in dollars per share)	$ 4.31	$ 4.32	$ 3.82
Diluted (in dollars per share)	$ 4.28	$ 4.29	$ 3.80

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 279,328	$ 277,977	$ 237,866
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss during the period	(12,450)	103,044	(115,245)
Change in net unrealized gain on securities transferred to held-to-maturity	(33,601)	(35,441)	(35,682)
Reclassification adjustment for net (gains) losses included in net income	(69)	(38)	(1,176)
Total securities available for sale and transferred securities	(46,120)	67,565	(152,103)
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	3,118	(34,837)	35,293
Derivatives:
Change in the accumulated gain/loss on effective cash flow hedge derivatives	0	0	(49)
Reclassification adjustments for (gains) losses included in net income:
Interest rate swaps on variable-rate loans	0	(30,604)	(37,380)
Interest rate swap on junior subordinated deferrable interest debentures	0	0	4,064
Total derivatives	0	(30,604)	(33,365)
Other comprehensive income (loss), before tax	(43,002)	2,124	(150,175)
Deferred tax expense (benefit)	(15,051)	744	(52,561)
Other comprehensive income (loss), net of tax	(27,951)	1,380	(97,614)
Comprehensive income	$ 251,377	$ 279,357	$ 140,252

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	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, 2012	$ 2,417,482	$ 0	$ 615	$ 702,968	$ 1,475,851	$ 238,048	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,866				237,866
Other comprehensive loss, net of tax	(97,614)					(97,614)
Proceeds from stock option exercises	68,653		2	7,839	(12,097)		72,909
Tax benefits from stock-based compensation	2,293			2,293
Stock-based compensation expense recognized in earnings	11,963			11,963
Non-vested stock awards and stock units	0			(866)	0		866
Issuance of preferred stock	144,486	144,486
Purchase of treasury stock	(144,630)						(144,630)
Cash dividends paid on preferred stock	(6,719)				(6,719)
Cash dividends – common stock	(119,619)				(119,619)
Balance at Dec. 31, 2013	2,514,161	144,486	617	724,197	1,575,282	140,434	(70,855)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	277,977				277,977
Other comprehensive loss, net of tax	1,380					1,380
Proceeds from stock option exercises	29,158		0	(2,620)	(7,694)		39,472
Tax benefits from stock-based compensation	3,202			3,202
Stock-based compensation expense recognized in earnings	12,503			12,503
Non-vested stock awards and stock units	0			(506)	0		506
Common stock issued in acquisition of WNB Bancshares	149,720		20	149,700
Purchase of treasury stock	(1,457)						(1,457)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(127,178)				(127,178)
Balance at Dec. 31, 2014	2,851,403	144,486	637	886,476	1,710,324	141,814	(32,334)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	279,328				279,328
Other comprehensive loss, net of tax	(27,951)					(27,951)
Proceeds from stock option exercises	14,853		0	(2,248)	(4,240)		21,341
Tax benefits from stock-based compensation	1,434			1,434
Stock-based compensation expense recognized in earnings	12,737			12,737
Non-vested stock awards and stock units	0			(1,049)	0		1,049
Purchase of treasury stock	(101,237)						(101,237)
Cash dividends paid on preferred stock	(8,063)				(8,063)
Cash dividends – common stock	(132,161)				(132,161)
Balance at Dec. 31, 2015	$ 2,890,343	$ 144,486	$ 637	$ 897,350	$ 1,845,188	$ 113,863	$ (111,181)

Consolidated Statement of Chan7

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock option exercises/deferred stock unit conversions, shares	321,266	594,231	1,319,786
Non-vested stock awards, shares	15,790	7,620	13,040
Non-vested stock units, shares	38,200	24,430	24,970
Stock issued during period, shares, acquisitions	0	2,000,000	0
Issuance of preferred stock, shares	0	0	6,000,000
Purchase of treasury stock, shares	1,504,146	18,871	2,245,572
Approximate cash dividends declared on preferred stock, per share	$ 1.34	$ 1.34	$ 1.12
Cash dividends - common stock, per share	$ 2.10	$ 2.03	$ 1.98

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities:
Net income	$ 279,328	$ 277,977	$ 237,866
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	51,845	16,314	20,582
Deferred tax expense (benefit)	(19,059)	(4,130)	3,279
Accretion of loan discounts	(14,447)	(14,567)	(12,654)
Securities premium amortization (discount accretion), net	73,785	61,268	41,921
Net (gain) loss on securities transactions	(69)	(38)	(1,176)
Depreciation and amortization	41,960	39,694	38,471
Net (gain) loss on sale/write-down of assets/foreclosed assets	(1,765)	761	3,235
Stock-based compensation	12,737	12,503	11,963
Net tax benefit (deficiency) from stock-based compensation	45	19	(393)
Excess tax benefits from stock-based compensation	(1,389)	(3,183)	(2,686)
Earnings on life insurance policies	(3,585)	(3,218)	(3,103)
Net change in:
Trading account securities	(1,153)	972	14,686
Accrued interest receivable and other assets	(12,860)	(73,184)	(7,996)
Accrued interest payable and other liabilities	(11,902)	(24,518)	(170,389)
Net cash from operating activities	393,471	286,670	173,606
Investing Activities:
Securities held to maturity: Purchases	(1,350)	0	(257,571)
Securities held to maturity: Maturities, calls and principal repayments	209,425	153,523	14,891
Securities available for sale:
Purchases	(14,147,908)	(19,484,433)	(11,178,144)
Sales	12,683,169	12,151,287	10,056,060
Maturities, calls and principal repayments	658,199	4,987,629	1,311,643
Net change in loans	(500,990)	(800,120)	(317,987)
Net cash received (paid) in acquisitions	0	830,661	(1,896)
Benefits received on life insurance policies	444	0	0
Proceeds from sales of premises and equipment	2,538	49	18,481
Purchases of premises and equipment	(147,129)	(131,970)	(39,599)
Proceeds from sales of repossessed properties	4,682	11,281	8,200
Net cash from investing activities	(1,238,920)	(2,282,093)	(385,922)
Financing Activities:
Net change in deposits	207,665	1,823,101	1,191,420
Net change in short-term borrowings	90,403	84,677	107,192
Principal payments on long-term borrowings	0	0	(7)
Proceeds from stock option exercises	14,853	29,158	68,653
Excess tax benefits from stock-based compensation	1,389	3,183	2,686
Proceeds from issuance of preferred stock	0	0	144,486
Purchase of treasury stock	(101,237)	(1,457)	(144,630)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(6,719)
Cash dividends paid on common stock	(132,161)	(127,178)	(119,619)
Net cash from financing activities	72,849	1,803,421	1,243,462
Net change in cash and cash equivalents	(772,600)	(192,002)	1,031,146
Cash and cash equivalents at beginning of year	4,364,123	4,556,125	3,524,979
Cash and cash equivalents at end of year	$ 3,591,523	$ 4,364,123	$ 4,556,125

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
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 our subsidiaries, a broad array of products and services throughout numerous Texas markets. The terms “Cullen/Frost,” “the Corporation,” “we,” “us” and “our” mean Cullen/Frost Bankers, Inc. and its subsidiaries, when appropriate. In addition to general commercial and consumer banking, other products and services offered include trust and investment management, insurance, brokerage, mutual funds, leasing, treasury management, capital markets advisory 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. All significant intercompany balances and transactions have been eliminated in consolidation. The accounting and financial reporting policies we follow conform, in all material respects, to accounting principles generally accepted in the United States and to general practices within the financial services industry. We determine whether we have 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. We consolidate voting interest entities in which we have 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. Our wholly owned subsidiaries Cullen/Frost Capital Trust II and WNB Capital Trust I are VIEs for which we are not the primary beneficiary. Accordingly, the accounts of these trusts are not included in our consolidated financial statements. We have 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 our 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 us, 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, 2015 2014 2013 Cash paid for interest $ 12,982 $ 14,705 $ 22,449 Cash paid for income tax 57,086 62,976 49,514 Significant non-cash transactions: Unsettled purchases of securities 2,998 — 16,241 Loans foreclosed and transferred to other real estate owned and foreclosed assets 933 4,363 6,870 Premises and equipment transferred to other real estate owned and foreclosed assets — 1,740 — Loans to facilitate the sale of other real estate owned 20 102 678 Deferred gain on sale of building and parking garage — — 768 Concentrations and Restrictions on Cash and Cash Equivalents . We maintain 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 we are not exposed to any significant credit risks on cash and cash equivalents. We were required to have $188.9 million and $175.6 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2015 and 2014 . These deposits with the Federal Reserve Bank do not earn interest. Additionally, as of December 31, 2015 and 2014 , we had $16.9 million and $12.1 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions. Repurchase/Resell Agreements. We purchase 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. We also sell 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 our ability to retain our 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 our 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 we 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 inherent 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 our 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 $2.3 million and $5.3 million at December 31, 2015 and 2014 . 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 on October 1st, 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. Prior to 2015, we evaluated goodwill for possible impairment annually on September 30th. In 2015, we move the evaluation date back one day to coincide with our annual financial reporting cycle. 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. Our 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. We also receive contingent commissions from insurance companies as additional incentive for achieving specified premium volume goals and/or the loss experience of the insurance placed by us. Contingent commissions from insurance companies are recognized when determinable, which is generally when such commissions are received or when we receive data from the insurance companies that allows the reasonable estimation of these amounts. We maintain a reserve for commission adjustments based on estimated policy cancellations. This reserve was not significant at December 31, 2015 or 2014 . 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 us, 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 non-vested stock awards/stock units and deferred stock units is generally the market price of our 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. We file a consolidated income tax return with our 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. We have determined that our 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 our 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 . Our 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 our 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. We 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. We consider 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, we formally assess 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, we 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 our creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. See Note 18 - Fair Value Measurements. 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 us, (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) we do 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 our trust department, other than cash on deposit at Frost Bank, are not included in the accompanying financial statements because they are not our assets. Reclassifications and Restatement . Certain items in prior financial statements have been reclassified to conform to the current presentation. Additionally, certain items in prior financial statements have been restated to reflect adjustments to initially reported provisional amounts recognized in business combinations so that the prior financial statements are reported as if the adjusted amounts had been known as of the measurement date of the business combination. In that regard, during 2015, we made acquisition valuation adjustments impacting certain assets acquired in connection with the acquisition of WNB Bancshares, Inc. (See Note 2 - Mergers and Acquisitions). As a result of these adjustments, our consolidated balance sheet as of December 31, 2014 reflects a $718 thousand increase in goodwill and a $718 thousand decrease in premises and equipment.

Securities

Securities	12 Months Ended
	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Year-end securities held to maturity and available for sale consisted of the following: 2015 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held to Maturity: U.S. Treasury $ 249,441 $ 7,776 $ — $ 257,217 $ 249,009 $ 14,604 $ — $ 263,613 Residential mortgage-backed securities 6,456 63 4 6,515 8,012 92 — 8,104 States and political subdivisions 2,405,762 46,003 6,149 2,445,616 2,668,115 34,243 9,035 2,693,323 Other 1,350 — 13 1,337 1,350 — — 1,350 Total $ 2,663,009 $ 53,842 $ 6,166 $ 2,710,685 $ 2,926,486 $ 48,939 $ 9,035 $ 2,966,390 Available for Sale: U. S. Treasury $ 3,980,986 $ 22,041 $ 8,507 $ 3,994,520 $ 3,783,899 $ 30,594 $ 3,241 $ 3,811,252 Residential mortgage-backed securities 1,000,024 42,142 734 1,041,432 1,331,114 68,027 417 1,398,724 States and political subdivisions 3,996,113 133,305 1,459 4,127,959 3,104,563 104,500 156 3,208,907 Other 42,447 — — 42,447 42,371 — — 42,371 Total $ 9,019,570 $ 197,488 $ 10,700 $ 9,206,358 $ 8,261,947 $ 203,121 $ 3,814 $ 8,461,254 All mortgage-backed securities included in the above table were issued by U.S. government agencies and corporations. At December 31, 2015 , approximately 97.8% of the securities in our municipal bond portfolio were issued by political subdivisions or agencies within the State of Texas, of which approximately 62.4% 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 $3.9 billion at December 31, 2015 and $3.0 billion at December 31, 2014 . During 2012, we 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 $60.3 million ( $39.2 million , net of tax) at December 31, 2015 and $93.9 million ( $61.0 million , net of tax) at December 31, 2014 . 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 Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses 2015 Held to Maturity: Residential mortgage-backed securities $ 900 $ 4 $ — $ — $ 900 $ 4 States and political subdivisions 146,854 1,325 202,423 4,824 349,277 6,149 Other 1,337 13 — — 1,337 13 Total $ 149,091 $ 1,342 $ 202,423 $ 4,824 $ 351,514 $ 6,166 Available for Sale: U.S. Treasury $ 886,087 $ 8,507 $ — $ — $ 886,087 $ 8,507 Residential mortgage-backed securities 21,392 212 17,781 522 39,173 734 States and political subdivisions 120,782 1,237 18,485 222 139,267 1,459 Total $ 1,028,261 $ 9,956 $ 36,266 $ 744 $ 1,064,527 $ 10,700 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 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 our ability to retain our 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 we will receive full value for the securities. Furthermore, as of December 31, 2015 , 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 we 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, 2015 , management believes the impairments detailed in the table above are temporary and no impairment loss has been realized in our consolidated income statement. The amortized cost and estimated fair value of securities, excluding trading securities, at December 31, 2015 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 Cost Estimated Fair Value Amortized Cost Estimated Fair Value Due in one year or less $ 161,934 $ 163,320 $ 793,662 $ 796,452 Due after one year through five years 846,629 889,786 2,961,224 2,976,538 Due after five years through ten years 207,488 209,616 1,391,273 1,418,590 Due after ten years 1,440,502 1,441,448 2,830,940 2,930,899 Residential mortgage-backed securities 6,456 6,515 1,000,024 1,041,432 Equity securities — — 42,447 42,447 Total $ 2,663,009 $ 2,710,685 $ 9,019,570 $ 9,206,358 Sales of securities available for sale were as follows: 2015 2014 2013 Proceeds from sales $ 12,683,169 $ 12,151,287 $ 10,056,060 Gross realized gains 228 39 1,206 Gross realized losses (159 ) (1 ) (30 ) Tax (expense) benefit of securities gains/losses (24 ) (13 ) (412 ) Premium amortization and discount accretion included in interest income on securities was as follows: 2015 2014 2013 Premium amortization $ (84,467 ) $ (68,070 ) $ (49,112 ) Discount accretion 10,682 6,802 7,191 Net (premium amortization) discount accretion $ (73,785 ) $ (61,268 ) $ (41,921 ) Year-end trading account securities, at estimated fair value, were as follows: 2015 2014 U.S. Treasury $ 16,443 $ 15,339 States and political subdivisions 136 87 Total $ 16,579 $ 15,426 Net gains and losses on trading account securities were as follows: 2015 2014 2013 Net gain on sales transactions $ 1,109 $ 829 $ 878 Net mark-to-market gains (losses) (53 ) — (429 ) Net gain on trading account securities $ 1,056 $ 829 $ 449

Loans

Loans	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Loans	Loans Year-end loans, including leases net of unearned discounts, consisted of the following: 2015 2014 Commercial and industrial $ 4,120,522 $ 4,055,225 Energy: Production 1,249,678 1,160,404 Service 272,934 319,618 Other 235,583 293,923 Total energy 1,758,195 1,773,945 Commercial real estate: Commercial mortgages 3,285,041 2,999,082 Construction 720,695 624,888 Land 286,991 291,907 Total commercial real estate 4,292,727 3,915,877 Consumer real estate: Home equity loans 340,528 342,725 Home equity lines of credit 233,525 220,128 Other 306,696 286,198 Total consumer real estate 880,749 849,051 Total real estate 5,173,476 4,764,928 Consumer and other 434,338 393,437 Total loans $ 11,486,531 $ 10,987,535 Concentrations of Credit. Most of our 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 our loan portfolio consists of commercial and industrial and commercial real estate loans. As of December 31, 2015 and 2014 , there were no concentrations of loans related to any single industry in excess of 10% of total loans other than energy loans, which totaled 15.3% and 16.1% of total loans, respectively. Foreign Loans. We have 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, 2015 or 2014 . Overdrafts . Deposit account overdrafts reported as loans totaled $7.3 million and $7.7 million at December 31, 2015 and 2014 . Related Party Loans . In the ordinary course of business, we have 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 2015 is presented in the following table. Other changes were primarily related to changes in related-party status. Balance outstanding at December 31, 2014 $ 38,700 Principal additions 230,806 Principal reductions (200,867 ) Other changes 16,127 Balance outstanding at December 31, 2015 $ 84,766 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, we consider the borrower’s debt service capacity through the analysis of current financial information, if available, and/or current information with regards to our 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: 2015 2014 Commercial and industrial $ 25,111 $ 34,108 Energy 21,180 636 Commercial real estate: Buildings, land and other 34,519 19,639 Construction 569 2,792 Consumer real estate 1,862 2,212 Consumer and other 226 538 Total $ 83,467 $ 59,925 As of December 31, 2015 and 2014 , non-accrual loans reported in the table above included $536 thousand and $8.3 million related to loans that were restructured as “troubled debt restructurings” during 2015 and 2014 , respectively. See the section captioned “Troubled Debt Restructurings” elsewhere in this note. Had non-accrual loans performed in accordance with their original contract terms, we would have recognized additional interest income, net of tax, of approximately $1.6 million in 2015 , $1.5 million in 2014 and $2.2 million in 2013 . An age analysis of past due loans (including both accruing and non-accruing loans), segregated by class of loans, as of December 31, 2015 was as follows: Loans 30-89 Days Past Due Loans 90 or More Days Past Due Total Past Due Loans Current Loans Total Loans Accruing Loans 90 or More Days Past Due Commercial and industrial $ 27,777 $ 20,668 $ 48,445 $ 4,072,077 $ 4,120,522 $ 4,091 Energy 3,463 15,504 18,967 1,739,228 1,758,195 580 Commercial real estate: Buildings, land and other 43,090 5,307 48,397 3,523,635 3,572,032 1,642 Construction 1,149 569 1,718 718,977 720,695 — Consumer real estate 5,202 1,652 6,854 873,895 880,749 1,476 Consumer and other 3,781 382 4,163 430,175 434,338 319 Total $ 84,462 $ 44,082 $ 128,544 $ 11,357,987 $ 11,486,531 $ 8,108 Impaired Loans. Loans are considered impaired when, based on current information and events, it is probable we 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 us to reevaluate the fair value of collateral supporting impaired collateral dependent loans on at least an annual basis. While our policy is to comply with the regulatory guidelines, our general practice is to reevaluate the fair value of collateral supporting impaired collateral dependent loans on a quarterly basis. Thus, appraisals are generally not considered to be outdated, and we typically do not make any adjustments to the appraised values. The fair value of collateral supporting impaired collateral dependent loans is evaluated by our 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 Contractual Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Average Recorded Investment 2015 Commercial and industrial $ 26,067 $ 18,776 $ 4,084 $ 22,860 $ 2,378 $ 27,338 Energy 25,240 8,689 12,450 21,139 2,000 7,235 Commercial real estate: Buildings, land and other 37,126 32,425 — 32,425 — 18,211 Construction 793 569 — 569 — 1,320 Consumer real estate 755 485 — 485 — 664 Consumer and other — — — — — — Total $ 89,981 $ 60,944 $ 16,534 $ 77,478 $ 4,378 $ 54,768 2014 Commercial and industrial $ 42,212 $ 29,007 $ 2,853 $ 31,860 $ 1,613 $ 27,154 Energy 706 636 — 636 — 571 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 $ 31,429 $ 15,337 $ 7,004 $ 22,341 $ 4,140 $ 34,894 Energy 545 531 — 531 — 428 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 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 that occurred during 2015 , 2014 and 2013 are set forth in the following table. 2015 2014 2013 Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Commercial and industrial $ 709 $ 536 $ 5,795 $ 5,391 $ 6,334 $ 4,937 Energy — — — — 528 531 Commercial real estate: Buildings, land and other — — 3,121 2,948 7,964 5,747 Consumer — — — — 7 — $ 709 $ 536 $ 8,916 $ 8,339 $ 14,833 $ 11,215 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 our determination of the allowance for loan losses. As of December 31, 2015 , there was one loan totaling $259 thousand restructured during 2015 that was in excess of 90 days past due. During 2015 , we charged-off $88 thousand in connection with the restructuring of a commercial and industrial loan. A $277 thousand commercial and industrial loan restructured during 2015 was related to a loan relationship previously restructured during 2014 . During 2014, we charged off $627 thousand of commercial and industrial loans that were related to loans restructured during 2013. 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. During 2014, we also foreclosed upon certain commercial real estate loans that were restructured during 2013. We recognized $500 thousand of other real estate owned and no charge-offs in connection with these foreclosures. The aforementioned charge-offs and foreclosures during 2015 and 2014 did not significantly impact our determination of the allowance for loan losses. As of December 31, 2015 , $536 thousand of the loans restructured in 2015 were on non-accrual status, while as of December 31, 2014 , $8.3 million of the loans restructured in 2014 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 our 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. We utilize a risk grading matrix to assign a risk grade to each of our 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, we monitor 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, 2015 December 31, 2014 Weighted Average Risk Grade Loans Weighted Average Risk Grade Loans Commercial and industrial Risk grades 1-8 5.88 $ 3,869,203 5.93 $ 3,846,598 Risk grade 9 9.00 100,670 9.00 65,166 Risk grade 10 10.00 76,030 10.00 54,519 Risk grade 11 11.00 49,508 11.00 55,034 Risk grade 12 12.00 22,644 12.00 31,683 Risk grade 13 13.00 2,467 13.00 2,225 Total 6.13 $ 4,120,522 6.16 $ 4,055,225 Energy Risk grades 1-8 6.12 $ 1,385,749 5.37 $ 1,740,455 Risk grade 9 9.00 212,250 9.00 27,313 Risk grade 10 10.00 62,163 10.00 161 Risk grade 11 11.00 76,853 11.00 5,380 Risk grade 12 12.00 19,180 12.00 636 Risk grade 13 13.00 2,000 13.00 — Total 6.89 $ 1,758,195 5.45 $ 1,773,945 Commercial real estate: Buildings, land and other Risk grades 1-8 6.58 $ 3,280,435 6.53 $ 3,067,219 Risk grade 9 9.00 140,900 9.00 72,906 Risk grade 10 10.00 72,577 10.00 87,889 Risk grade 11 11.00 43,601 11.00 43,336 Risk grade 12 12.00 34,519 12.00 19,501 Risk grade 13 13.00 — 13.00 138 Total 6.85 $ 3,572,032 6.76 $ 3,290,989 Construction Risk grades 1-8 6.91 $ 696,229 6.91 $ 612,705 Risk grade 9 9.00 13,074 9.00 8,003 Risk grade 10 10.00 2,757 10.00 1,323 Risk grade 11 11.00 8,066 11.00 64 Risk grade 12 12.00 569 12.00 2,793 Risk grade 13 13.00 — 13.00 — Total 7.01 $ 720,695 6.97 $ 624,888 We have established maximum loan to value standards to be applied during the origination process of commercial and consumer real estate loans. We do 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, we reassess 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. We do not monitor loan-to-value ratios on a weighted-average portfolio-basis for commercial real estate loans having a calculated risk grade of 10 or higher as excess collateral from one borrower cannot be used to offset a collateral deficit for another borrower. When an individual consumer real estate loan becomes past due by more than 10 days, the assigned relationship manager will begin collection efforts. We only reassess 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, we do 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 our 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 we become 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 any event the charge-off must be taken within 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: 2015 2014 2013 Commercial and industrial $ (6,535 ) $ (2,911 ) $ (28,431 ) Energy (5,997 ) (1,237 ) (913 ) Commercial real estate: Buildings, land and other 314 (2,348 ) (381 ) Construction 18 348 256 Consumer real estate (91 ) (733 ) (719 ) Consumer and other (3,237 ) (2,329 ) (2,409 ) Total $ (15,528 ) $ (9,210 ) $ (32,597 ) 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 124.1 at November 30, 2015 (most recent date available) and 129.3 at December 31, 2014 . 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 inherent 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. Our 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, our 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. Our 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 our control, including, among other things, the performance of our loan portfolio, the economy, changes in interest rates and the view of the regulatory authorities toward loan classifications. We monitor 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 we experience over time. Our allowance for loan losses consists of: (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; (iii) general valuation allowances determined in accordance with ASC Topic 450 based on various risk factors that are internal to us; and (iv) macroeconomic valuation allowances determined in accordance with ASC Topic 450 based on general economic conditions and other risk factors that are external to us. 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. We calculate 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. Our pools of similar loans include similarly risk-graded groups of commercial and industrial loans, energy loans, commercial real estate loans, consumer real estate loans and consumer and other loans. General valuation allowances include allocations for groups of similar loans with similar risk characteristics that exceed certain concentration limits established by management and/or our 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 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). Our 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 by loan portfolio segment for the preceding four quarters, adjusted, when necessary, for expected future trends in recoveries. Prior to the second quarter of 2015, general valuation allowances included allocations for loan agreement monitoring exceptions related to credit and/or collateral for certain loans that exceeded specified risk grades. During the second quarter of 2015, we concluded that this risk was more appropriately captured within our loan risk grade matrix through the assignment of a higher risk grade for loans having these exceptions and thus included as a component of our historical valuation allowances. General valuation allowance allocations for loan agreement monitoring exceptions totaled $2.2 million at December 31, 2014 . There were no such general valuation allowance allocations as of December 31, 2015 as we have determined that these risks are now reflected in the historical valuation allowances. This change in our allowance methodology did not significantly impact the provision for loan losses recorded during 2015. The components of the macroeconomic valuation allowance include (i) reserves allocated as a result of applying an environmental risk adjustment factor to the base historical loss allocation, (ii) reserves allocated for loans to borrowers in distressed industries and (iii) reserves allocated based upon current economic trends and other quantitative and qualitative factors that could impact our loan portfolio segments. The aggregate sum of these components for each portfolio segment reflects management's assessment of current and expected economic conditions and other external factors that impact the inherent credit quality of loans in that portfolio segment. 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 our 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. Macroeconomic valuation allowances also include amounts allocated for loans to borrowers in distressed industries within our commercial loan portfolio segments. To determine the amount of the allocation for our commercial and industrial and commercial real estate loan portfolio segments, management calculates the wei

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment Year-end premises and equipment were as follows: 2015 2014 Land $ 111,925 $ 102,334 Buildings 365,051 240,430 Furniture and equipment 136,983 102,885 Leasehold improvements 64,446 60,902 Construction in progress 81,991 118,367 760,396 624,918 Less accumulated depreciation and amortization (201,272 ) (182,748 ) Total premises and equipment, net $ 559,124 $ 442,170 Depreciation and amortization of premises and equipment totaled $28.5 million in 2015 , $23.5 million in 2014 and $22.5 million in 2013 .

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2015
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 tables below. During 2014, we recorded goodwill totaling $118.0 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: 2015 2014 Goodwill $ 654,668 $ 654,668 Other Intangible Assets. Year-end other intangible assets were as follows: Gross Intangible Assets Accumulated Amortization Net Intangible Assets 2015 Core deposits $ 39,410 $ (32,324 ) $ 7,086 Customer relationships 5,771 (4,214 ) 1,557 Non-compete agreements 725 (568 ) 157 $ 45,906 $ (37,106 ) $ 8,800 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 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 $3.3 million in 2015 , $3.5 million in 2014 , and $3.1 million in 2013 . The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2015 is as follows: 2016 $ 2,413 2017 1,619 2018 1,346 2019 1,102 2020 877 Thereafter 1,443 $ 8,800

Deposits

Deposits	12 Months Ended
	Dec. 31, 2015
Deposits [Abstract]
Deposits	Deposits Year-end deposits were as follows: 2015 2014 Non-interest-bearing demand deposits: Commercial and individual $ 9,251,463 $ 9,256,045 Correspondent banks 378,930 429,000 Public funds 639,840 464,016 Total non-interest-bearing demand deposits 10,270,233 10,149,061 Interest-bearing deposits: Private accounts: Savings and interest checking 5,149,905 4,743,963 Money market accounts 7,536,998 7,860,403 Time accounts of $100,000 or more 420,697 490,209 Time accounts under $100,000 405,726 454,220 Total private accounts 13,513,326 13,548,795 Public funds: Savings and interest checking 420,324 326,090 Money market accounts 93,969 57,145 Time accounts of $100,000 or more 44,941 53,684 Time accounts under $100,000 802 1,155 Total public funds 560,036 438,074 Total interest-bearing deposits 14,073,362 13,986,869 Total deposits $ 24,343,595 $ 24,135,930 The following table presents additional information about our year-end deposits: 2015 2014 Deposits from the Certificate of Deposit Account Registry Service (CDARS) $ 2,615 $ 22,229 Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB) 7,440 148,665 Deposits from foreign sources (primarily Mexico) 747,008 744,295 Deposits not covered by deposit insurance 11,953,367 12,056,180 Deposits from certain directors, executive officers and their affiliates 218,095 176,821 Scheduled maturities of time deposits, including both private and public funds, at December 31, 2015 were as follows: 2016 $ 736,480 2017 135,539 2018 88 2019 59 2020 — $ 872,166 Scheduled maturities of time deposits in amounts of $100,000 or more, including both private and public funds, at December 31, 2015 , were as follows: Due within 3 months or less $ 160,712 Due after 3 months and within 6 months 91,160 Due after 6 months and within 12 months 140,232 Due after 12 months 73,534 $ 465,638

Borrowed Funds

Borrowed Funds	12 Months Ended
	Dec. 31, 2015
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 $9.6 million and $12.0 million at December 31, 2015 and 2014 . 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. We may be required to provide additional collateral based on the fair value of the underlying securities. Securities sold under agreements to repurchase totaled $883.9 million and $791.1 million at December 31, 2015 and 2014 . Subordinated Notes Payable. In February 2007, we issued $100 million of 5.75% fixed-to-floating rate subordinated notes that mature on February 15, 2017 . The notes, which qualified as Tier 2 capital for Cullen/Frost under the capital rules in effect prior to 2015 (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% ( 0.89% and 0.76% at December 31, 2015 and 2014 ), payable quarterly on each February 15, May 15, August 15 and November 15. The notes are subordinated in right of payment to all of our senior indebtedness and effectively subordinated to all existing and future debt and all other liabilities of our subsidiaries. The notes cannot be accelerated except in the event of bankruptcy or the occurrence of certain other events of bankruptcy, insolvency or reorganization. We 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 $130 thousand and $250 thousand at December 31, 2015 and 2014 . 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, 2015 and 2014 , we 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 $1.0 million and $1.1 million at December 31, 2015 and 2014 . At December 31, 2015 and 2014 , we 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 we are not the primary beneficiary. As such, the accounts of Trust II and WNB Trust are not included in our consolidated financial statements. See Note 1 - Summary of Significant Accounting Policies for additional information about our consolidation policy. Details of our 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 our option 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 1.96% and 1.78% at December 31, 2015 and 2014 ) junior subordinated deferrable interest debentures issued by us, which have terms substantially similar to the trust preferred securities. In October 2008, we 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 our option 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 2.67% and 2.58% at December 31, 2015 and 2014 ) junior subordinated deferrable interest debentures issued by WNB, which have terms substantially similar to the trust preferred securities. We have 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 we have elected to defer interest on the debentures, we may not, with certain exceptions, declare or pay any dividends or distributions on our capital stock or purchase or acquire any of our capital stock. Payments of distributions on the trust preferred securities and payments on redemption of the trust preferred securities are guaranteed by us on a limited basis. We are 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. Our obligations 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 us 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 our 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 capital of Cullen/Frost for regulatory capital purposes as of December 31, 2015 and 2014 . See Note 10 - Capital and Regulatory Matters.

Off-Balance-Sheet Arrangements,

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies	12 Months Ended
	Dec. 31, 2015
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, we enter into various transactions, which, in accordance with generally accepted accounting principles are not included in our consolidated balance sheets. We enter into these transactions to meet the financing needs of our 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. We minimize our exposure to loss under these commitments by subjecting them to credit approval and monitoring procedures. We enter into contractual commitments to extend credit, normally with fixed expiration dates or termination clauses, at specified rates and for specific purposes. Substantially all of our 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 we issued 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, we would be required to fund the commitment. The maximum potential amount of future payments we could be required to make is represented by the contractual amount of the commitment. If the commitment were funded, we would be entitled to seek recovery from the customer. Our policies generally require that standby letter of credit arrangements contain security and debt covenants similar to those contained in loan agreements. We consider the fees collected in connection with the issuance of standby letters of credit to be representative of the fair value of our obligation undertaken in issuing the guarantee. In accordance with applicable accounting standards related to guarantees, we defer 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 our potential obligations under the standby letter of credit guarantees. Year-end financial instruments with off-balance-sheet risk were as follows: 2015 2014 Commitments to extend credit $ 8,246,698 $ 7,955,779 Standby letters of credit 279,147 248,360 Deferred standby letter of credit fees 2,115 1,942 Credit Card Guarantees . We guarantee the credit card debt of certain customers to the merchant bank that issues the cards. At December 31, 2015 and 2014 , the guarantees totaled approximately $7.9 million and $8.9 million , of which amounts, $1.2 million and $1.5 million were fully collateralized. Lease Commitments. We lease certain office facilities and office equipment under operating leases. Rent expense for all operating leases totaled $30.6 million in 2015 , $28.2 million in 2014 and $24.6 million in 2013 . Future minimum lease payments due under non-cancelable operating leases at December 31, 2015 were as follows: 2016 $ 22,489 2017 22,686 2018 21,913 2019 17,854 2020 15,041 Thereafter 106,926 $ 206,909 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, 2015 , were $588 thousand . We lease a branch facility from a partnership interest of a director. Payments related to this lease totaled $925 thousand in both 2015 and 2014 , and $871 thousand in 2013 . Change in Control Agreements . We have 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. Comprehensive Development Agreement. In July 2015, we entered into a comprehensive development agreement with the City of San Antonio and an independent third party whereby, under separate agreements, we will sell our current headquarters building to the City of San Antonio and various adjacent properties to the third party. The third party has agreed to build a new office building where we will be the primary tenant. The agreement to sell our headquarters building was finalized in July 2015 and is expected to close in the second half of 2016, subject to certain contingencies. Under the terms of the agreement, we will lease-back our headquarters building until such time that construction of the new building is completed, which is currently expected to be in 2018 or 2019. While significant gains or losses may be realized on the various individual property sales completed in connection with the comprehensive development agreement, we do not expect any such gains or losses in the aggregate to have a significant impact on our operations. Litigation . We are 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 our financial statements.

Capital and Regulatory Matters

Capital and Regulatory Matters	12 Months Ended
	Dec. 31, 2015
Regulatory Capital Requirements [Abstract]
Capital and Regulatory Matters	Capital and Regulatory Matters 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. The Basel III Capital Rules, a new comprehensive capital framework for U.S. banking organizations, became effective for Cullen/Frost and Frost Bank on January 1, 2015 (subject to a phase-in period for certain provisions). Quantitative measures established by the Basel III Capital Rules to ensure capital adequacy require the maintenance of minimum amounts and ratios (set forth in the table below) of Common Equity Tier 1 capital, Tier 1 capital and Total 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 Common Equity Tier 1 capital includes common stock and related paid-in capital, net of treasury stock, and retained earnings. In connection with the adoption of the Basel III Capital Rules, we elected to opt-out of the requirement to include most components of accumulated other comprehensive income in Common Equity Tier 1. Common Equity Tier 1 for both Cullen/Frost and Frost Bank is reduced by, goodwill and other intangible assets, net of associated deferred tax liabilities, and subject to transition provisions. Frost Bank's Common Equity Tier 1 is also reduced by its equity investment in its financial subsidiary, Frost Insurance Agency (“FIA”). Tier 1 capital includes Common Equity Tier 1 capital and additional Tier 1 capital. For Cullen/Frost, additional Tier 1 capital at December 31, 2015 includes $144.5 million of 5.375% non-cumulative perpetual preferred stock and the allowable portion of the $133.0 million of trust preferred securities issued by our unconsolidated subsidiary trusts. Under the Basel III Capital Rules, trust preferred securities do not qualify as Tier 1 capital instruments and must be phased-out of Tier 1 capital. At December 31, 2015 , $33.3 million of trust preferred securities were included in Cullen/Frost's additional Tier 1 capital. Beginning January 1, 2016, trust preferred securities may not be included in Tier 1 capital. Trust preferred securities excluded from additional Tier 1 capital may be included in Tier 2 capital, without limitation. Frost Bank did not have any additional Tier 1 capital beyond Common Equity Tier 1 as of December 31, 2015 . Total capital includes Tier 1 capital and Tier 2 capital. Tier 2 capital for both Cullen/Frost and Frost Bank includes a permissible portion of the allowance for loan losses. Tier 2 capital for Cullen/Frost also includes trust preferred securities that were excluded from Tier 1 capital and qualified subordinated debt. At December 31, 2015 , Cullen/Frost's Tier 2 capital included $99.8 million of trust preferred securities and the permissible portion of our aggregate $100 million of floating rate subordinated notes (which decreases 20% per year during the final five years of the term of the notes) totaling $20.0 million at December 31, 2015 . Our aggregate $100 million of floating rate subordinated notes mature on February 15, 2017 . No portion of these notes will be permissible as a component of Tier 2 capital subsequent to February 15, 2016 . Prior to January 1, 2015, under the capital rules then in effect, Cullen/Frost’s and Frost Bank’s Tier 1 capital included total shareholders’ equity excluding accumulated other comprehensive income and goodwill and other intangible assets, net of associated deferred tax liabilities. Tier 1 capital for Cullen/Frost also included $144.5 million of 5.375% non-cumulative perpetual preferred stock and $133.0 million of trust preferred securities issued by our unconsolidated subsidiary trusts. Tier 1 capital for Frost Bank was also reduced by a portion of its equity investment in its financial subsidiary, FIA. Cullen/Frost’s and Frost Bank’s Total capital included Tier 1 capital for each entity plus a permissible portion of the allowance for loan losses. Total capital for Cullen/Frost also included the permissible portion of our aggregate $100 million of floating rate subordinated notes which totaled $40.0 million at December 31, 2014 . Total capital for Frost Bank was also reduced by its equity investment in its financial subsidiary, FIA. The Common Equity Tier 1 (beginning in 2015), 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, with certain exclusions, allocated by risk weight category, and certain off-balance-sheet items, among other things. The leverage ratio is calculated by dividing Tier 1 capital by adjusted quarterly average total assets, which exclude goodwill and other intangible assets, among other things. When fully phased in on January 1, 2019, the Basel III Capital Rules will require Cullen/Frost and Frost Bank to maintain (i) a minimum ratio of Common Equity Tier 1 capital to risk-weighted assets of at least 4.5% , plus a 2.5% “capital conservation buffer” (which is added to the 4.5% Common Equity Tier 1 capital ratio as that buffer is phased in, effectively resulting in a minimum ratio of Common Equity Tier 1 capital to risk-weighted assets of at least 7.0% upon full implementation), (ii) a minimum ratio of Tier 1 capital to risk-weighted assets of at least 6.0% , plus the capital conservation buffer (which is added to the 6.0% Tier 1 capital ratio as that buffer is phased in, effectively resulting in a minimum Tier 1 capital ratio of 8.5% upon full implementation), (iii) a minimum ratio of Total capital (that is, Tier 1 plus Tier 2) to risk-weighted assets of at least 8.0% , plus the capital conservation buffer (which is added to the 8.0% total capital ratio as that buffer is phased in, effectively resulting in a minimum total capital ratio of 10.5% upon full implementation) and (iv) a minimum leverage ratio of 4.0% , calculated as the ratio of Tier 1 capital to average quarterly assets. The implementation of the capital conservation buffer will begin on January 1, 2016 at the 0.625% level and be phased in over a four -year period (increasing by that amount on each subsequent January 1, until it reaches 2.5% on January 1, 2019). The Basel III Capital Rules also provide for a “countercyclical capital buffer” that is applicable to only certain covered institutions and does not have any current applicability to Cullen/Frost or Frost Bank. The capital conservation buffer is designed to absorb losses during periods of economic stress and, as detailed above, effectively increases the minimum required risk-weighted capital ratios. Banking institutions with a ratio of Common Equity Tier 1 capital to risk-weighted assets below the effective minimum ( 4.5% plus the capital conservation buffer and, if applicable, the countercyclical capital buffer) will face constraints on dividends, equity repurchases and compensation based on the amount of the shortfall. The following table presents actual and required capital ratios as of December 31, 2015 for Cullen/Frost and Frost Bank under the Basel III Capital Rules. The minimum required capital amounts presented include the minimum required capital levels as of December 31, 2015 based on the phase-in provisions of the Basel III Capital Rules and the minimum required capital levels as of January 1, 2019 when the Basel III Capital Rules have been fully phased-in. Capital levels required to be considered well capitalized are based upon prompt corrective action regulations, as amended to reflect the changes under the Basel III Capital Rules. Actual Minimum Capital Required - Basel III Phase-In Schedule Minimum Capital Required - Basel III Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2015 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 1,986,200 11.37 % $ 786,344 4.50 % $ 1,222,837 7.00 % $ 1,135,830 6.50 % Frost Bank 2,131,360 12.24 783,727 4.50 1,218,766 7.00 1,132,049 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,163,936 12.38 1,048,458 6.00 1,484,874 8.50 1,397,944 8.00 Frost Bank 2,131,360 12.24 1,044,969 6.00 1,479,930 8.50 1,393,292 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,419,545 13.85 1,397,944 8.00 1,834,256 10.50 1,747,430 10.00 Frost Bank 2,267,219 13.02 1,393,292 8.00 1,828,149 10.50 1,741,615 10.00 Leverage Ratio Cullen/Frost 2,163,936 7.79 1,111,325 4.00 1,111,117 4.00 1,389,156 5.00 Frost Bank 2,131,360 7.68 1,110,143 4.00 1,109,935 4.00 1,387,679 5.00 The following table presents actual and required capital ratios as of December 31, 2014 for Cullen/Frost and Frost Bank under the regulatory capital rules then in effect. Actual Minimum Required for Capital Adequacy Purposes Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2014 Total Capital to Risk-Weighted Assets Cullen/Frost $ 2,325,818 14.55 % $ 1,278,797 8.00 % $ 1,598,496 10.00 % Frost Bank 2,071,012 12.99 1,275,858 8.00 1,594,823 10.00 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,186,276 13.68 639,398 4.00 959,098 6.00 Frost Bank 1,979,415 12.41 637,929 4.00 956,894 6.00 Leverage Ratio Cullen/Frost 2,186,276 8.16 1,072,035 4.00 1,340,043 5.00 Frost Bank 1,979,415 7.40 1,070,109 4.00 1,337,636 5.00 Management believes that, as of December 31, 2015 , 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 Board 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 our financial statements. Management believes, as of December 31, 2015 , that Cullen/Frost and Frost Bank meet all capital adequacy requirements to which they are subject. Preferred Stock. On February 15, 2013, we issued and sold 6,000,000 shares, or $150.0 million in aggregate liquidation preference, of our 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, our board of directors has authorized stock repurchase plans. In general, stock repurchase plans allow us to proactively manage our capital position and return excess capital to shareholders. Shares purchased under such plans also provide us with shares of common stock necessary to satisfy obligations related to stock compensation awards. On April 30, 2015 , our board of directors authorized a $100.0 million stock repurchase program, allowing us to repurchase shares of our common stock over a two -year period from time to time at various prices in the open market or through private transactions. Under the plan, we repurchased 1,485,493 shares at a total cost of $100.0 million during 2015 . Accelerated Share Repurchase . Concurrent with the issuance and sale of the Series A Preferred Stock discussed above, we entered into an accelerated share repurchase agreement (the “ASR agreement”) with Goldman, Sachs & Co. (“Goldman Sachs”). Under the ASR agreement, we paid $144.0 million to Goldman Sachs and received from Goldman Sachs 1,905,077 shares of our common stock, representing approximately 80% of the estimated total number of shares to be repurchased. Goldman Sachs borrowed such shares delivered to us 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 we received an additional 331,671 shares. The total number of shares that we repurchased was based on the volume-weighted-average price per share of our 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, 2015 , Frost Bank could pay aggregate dividends of up to $419.7 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 we have elected to defer interest on the debentures, we may not, with certain exceptions, declare or pay any dividends or distributions on our capital stock or purchase or acquire any of our capital stock. Under the terms of the Series A Preferred Stock, in the event that we do not declare and pay dividends on the Series A Preferred Stock for the most recent dividend period, we may not, with certain exceptions, declare or pay dividends on, or purchase, redeem or otherwise acquire, shares of our common stock or any of our securities that rank junior to the Series A Preferred Stock.

Earnings Per Common Share

Earnings Per Common Share	12 Months Ended
	Dec. 31, 2015
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 our 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. 2015 2014 2013 Net Income $ 279,328 $ 277,977 $ 237,866 Less: Preferred stock dividends 8,063 8,063 6,719 Net income available to common shareholders 271,265 269,914 231,147 Less: Earnings allocated to participating securities 941 1,001 850 Net earnings allocated to common stock $ 270,324 $ 268,913 $ 230,297 Distributed earnings allocated to common stock $ 131,702 $ 126,709 $ 119,177 Undistributed earnings allocated to common stock 138,622 142,204 111,120 Net earnings allocated to common stock $ 270,324 $ 268,913 $ 230,297 Weighted-average shares outstanding for basic earnings per common share 62,758,074 62,072,080 60,350,552 Dilutive effect of stock compensation 715,250 901,448 765,858 Weighted-average shares outstanding for diluted earnings per common share 63,473,324 62,973,528 61,116,410

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2015
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 our discretion and may be made without regard to current or accumulated profits. Contributions are allocated to eligible participants uniformly, 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. We also maintain 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 $11.3 million in 2015 , $10.8 million in 2014 and $11.4 million in 2013 . Retirement Plan and Restoration Plan. We maintain 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. Our funding policy is to contribute yearly, at least the amount necessary to satisfy the funding standards of the Employee Retirement Income Security Act (“ERISA”). Our 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 our contributions. We use a December 31 measurement date for our defined benefit plans. Combined activity in our defined benefit pension plans was as follows: 2015 2014 2013 Change in benefit obligation: Benefit obligation at beginning of year $ 199,637 $ 163,876 $ 178,158 Interest cost 8,210 8,002 7,341 Actuarial (gain) loss (6,489 ) 34,438 (15,333 ) Benefits paid (7,218 ) (6,679 ) (6,290 ) Benefit obligation at end of year 194,140 199,637 163,876 Change in plan assets: Fair value of plan assets at beginning of year 168,185 164,769 145,901 Actual return on plan assets 1,567 9,428 24,489 Employer contributions 736 667 669 Benefits paid (7,218 ) (6,679 ) (6,290 ) Fair value of plan assets at end of year 163,270 168,185 164,769 Funded status of the plan at end of year and accrued (benefit) liability recognized $ 30,870 $ 31,452 $ (893 ) Accumulated benefit obligation at end of year $ 194,140 $ 199,637 $ 163,876 Certain disaggregated information related to our defined benefit pension plans as of year-end was as follows: Retirement Plan Restoration Plan 2015 2014 2015 2014 Projected benefit obligation $ 174,429 $ 179,970 $ 19,711 $ 19,667 Accumulated benefit obligation 174,429 179,970 19,711 19,667 Fair value of plan assets 163,270 168,185 — — Funded status of the plan at end of year and accrued (benefit) liability recognized 11,159 11,785 19,711 19,667 The components of the combined net periodic cost (benefit) for our defined benefit pension plans were as follows: 2015 2014 2013 Expected return on plan assets, net of expenses $ (11,932 ) $ (12,514 ) $ (11,087 ) Interest cost on projected benefit obligation 8,210 8,002 7,341 Net amortization and deferral 6,995 2,687 6,558 Net periodic expense (benefit) $ 3,273 $ (1,825 ) $ 2,812 As of December 31, 2015, we changed the method we use to estimate the interest cost component of net periodic benefit cost for our defined benefit pension and other post-retirement benefit plans. Prior to the change, we estimated the interest cost component utilizing a single weighted-average discount rate derived from the yield curve used to measure our projected benefit obligation. Under the new method, we will utilize a full yield curve approach in the estimation of the interest cost component by applying the specific annual spot rates along the yield curve used in the measurement of our projected benefit obligation to the relevant projected cash flows. We view the full yield curve method as more representationally faithful of effective settlement rates as the interest cost component of the net periodic cost is measured more precisely, reflecting the difference in the timing of future benefit payment cash flows. This new method constitutes a change in an accounting estimate that is inseparable from a change in accounting principle and will be accounted for prospectively, with the resulting change impacting the recognition of net periodic benefit cost beginning January 1, 2016. While the change resulted in a decrease in the interest cost component of the net periodic benefit cost that will be recognized in 2016, the overall impact is not significant to our financial statements. Amounts related to our defined benefit pension plans recognized as a component of other comprehensive income were as follows: 2015 2014 2013 Net actuarial gain (loss) $ 3,118 $ (34,837 ) $ 35,293 Deferred tax (expense) benefit (1,091 ) 12,193 (12,353 ) Other comprehensive income (loss), net of tax $ 2,027 $ (22,644 ) $ 22,940 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 our defined benefit pension plans are presented in the following table. We expect to recognize approximately $6.2 million of the net actuarial loss reported in the following table as of December 31, 2015 as a component of net periodic benefit cost during 2016 . 2015 2014 Net actuarial loss $ (71,920 ) $ (75,038 ) Deferred tax benefit 25,172 26,263 Amounts included in accumulated other comprehensive loss, net of tax $ (46,748 ) $ (48,775 ) 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. 2015 2014 2013 Benefit obligations: Discount rate 4.55 % 4.20 % 5.00 % Net periodic benefit cost: Discount rate 4.20 % 5.00 % 4.20 % Expected return on plan assets 7.25 7.25 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, 2015 , management’s investment objective for our 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 our 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). Our Restoration Plan is unfunded. 2015 2014 Level 1: Mutual funds $ 162,379 $ 165,429 Cash and cash equivalents 322 1,447 Level 2: Corporate bonds and notes — 653 U.S. government agency securities 316 394 States and political subdivisions 253 262 Total fair value of plan assets $ 163,270 $ 168,185 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, 2015 . 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. Our investment strategies prohibit selling assets short and the use of derivatives. Additionally, our 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 7.25% in the determination of the net periodic benefit cost for 2015 . 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, 2015 , expected future benefit payments related to our defined benefit plans were as follows: 2016 $ 12,729 2017 9,421 2018 9,911 2019 10,365 2020 10,816 2021 through 2025 58,848 $ 112,090 We expect to contribute $4.9 million to the defined benefit plans during 2016 . Supplemental Executive Retirement Plan. We maintain 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 2015 , 2014 and 2013 . Savings Plans 401(k) Plan and Thrift Incentive Plan. We maintain 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. We match 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 our matching contributions immediately. Expense related to the plan totaled $13.3 million in 2015 , $12.3 million in 2014 , and $11.5 million in 2013 . Our matching contribution is initially invested in the Cullen/Frost common stock fund. However, employees may immediately reallocate our matching portion, as well as invest their individual contribution, to any of a variety of investment alternatives offered under the 401(k) Plan. We maintain 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 2015 , 2014 and 2013 . Stock Compensation Plans We have three active stock compensation plans (the 2005 Omnibus Incentive Plan, the 2007 Outside Directors Incentive Plan and the 2015 Omnibus Incentive Plan). All of the plans have been approved by our shareholders. During 2015, the 2015 Omnibus Incentive Plan (“2015 Plan”) was established to replace both the 2005 Omnibus Incentive Plan (“2005 Plan”) and the 2007 Outside Directors Incentive Plan (the “2007 Directors Plan”). All remaining shares authorized for grant under the superseded 2005 Plan and 2007 Directors Plan were transferred to the 2015 Plan. Our stock compensation plans were established to (i) motivate superior performance by means of performance-related incentives, (ii) encourage and provide for the acquisition of an ownership interest in our company by employees and non-employee directors and (iii) enable us to attract and retain qualified and competent persons as employees and to serve as members of our board of directors. Under the 2015 Plan, we may grant, among other things, nonqualified stock options, incentive stock options, stock awards, stock appreciation rights, restricted stock units, performance share units or any combination thereof to certain employees and non-employee directors. Any of the authorized shares may be used for any type of award allowable under the Plan. The Compensation and Benefits Committee (“Committee”) of our Board of Directors has sole authority to (i) establish the awards to be issued, (ii) select the employees and non-employee directors to receive awards, and (iii) approve the terms and conditions of each award contract. Each award under the stock 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 our active stock plans is presented in the following table. Director Deferred Stock Units Outstanding Non-Vested Stock Awards/Stock Units Outstanding Stock Options Outstanding Available for Grant Number of Units Weighted- Average Grant-Date Fair Value Number of Shares/Units Weighted- Average Grant-Date Fair Value Number of Shares Weighted- Average Exercise Price Balance at January 1, 2013 1,188,963 27,724 55.46 188,560 $ 51.67 5,513,516 $ 51.94 Authorized 2,293,660 — — — — — — Granted (635,360 ) 5,500 60.07 38,010 71.39 591,850 71.38 Stock options exercised — — — — — (1,319,786 ) 52.02 Stock awards/units vested — — — (26,830 ) 50.64 — — Forfeited/expired 46,890 — — — — (46,890 ) 46.05 Balance at December 31, 2013 2,894,153 33,224 56.22 199,740 55.32 4,738,690 54.35 Authorized — — — — — — — Granted (955,443 ) 5,643 78.04 32,050 78.92 917,750 78.93 Stock options exercised — — — — — (560,291 ) 52.04 Stock awards/units vested — — — (56,300 ) 52.46 — — Forfeited/expired 66,267 — — — — (66,267 ) 62.21 Balance at December 31, 2014 2,004,977 38,867 59.39 175,490 60.55 5,029,882 58.99 Authorized 515,000 — — — — — — Granted (951,506 ) 6,576 72.94 53,990 65.11 890,940 65.11 Stock options exercised — — — — — (287,326 ) 51.70 Stock awards/units vested — — — (56,300 ) 48.00 — — Forfeited/expired 21,256 — — — — (21,256 ) 66.72 Balance at December 31, 2015 1,589,727 45,443 61.35 173,180 $ 66.05 5,612,240 $ 60.30 Options awarded to employees generally have a ten -year life and vest in equal annual installments over a four -year period. Non-vested stock awards/stock units awarded to employees generally have a four -year-cliff vesting period. No options were awarded to non-employee directors during the reported periods. Deferred stock units awarded to non-employee directors generally have immediate vesting. Upon retirement from our board of directors, non-employee directors will receive one share of our common stock for each deferred stock unit held. Outstanding non-vested stock units and deferred stock units receive equivalent dividend payments as such dividends are declared on our common stock. Other information regarding options outstanding and exercisable as of December 31, 2015 is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life in Years Number of Shares Weighted- Average Exercise Price $ 45.01 to $ 50.00 898,753 $ 48.27 4.53 898,753 $ 48.27 50.01 to 55.00 2,065,524 52.74 4.78 1,885,777 52.58 55.01 to 60.00 296,150 57.63 0.89 296,150 57.63 65.01 to 70.00 890,940 65.11 9.83 — — 70.01 to 75.00 566,123 71.38 7.77 280,988 71.38 75.01 to 80.00 894,750 78.94 8.74 223,689 78.94 Total 5,612,240 60.30 6.27 3,585,357 55.03 The total intrinsic value of outstanding in-the-money stock options and outstanding in-the-money exercisable stock options was $26.2 million and $25.3 million at December 31, 2015 . 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: 2015 2014 2013 New shares issued from available authorized shares — — 153,275 Issued from available treasury stock 337,056 601,851 1,179,551 Total 337,056 601,851 1,332,826 Proceeds from stock option exercises $ 14,853 $ 29,158 $ 68,653 Intrinsic value of stock options exercised 5,766 13,714 20,506 Fair value of stock awards/units vested 3,728 4,346 1,918 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: 2015 2014 2013 Stock options $ 9,660 $ 9,142 $ 8,814 Non-vested stock awards/stock units 2,597 2,920 2,819 Deferred stock-units 480 441 330 Total $ 12,737 $ 12,503 $ 11,963 Income tax benefit $ 4,458 $ 4,376 $ 4,187 Unrecognized stock-based compensation expense at December 31, 2015 was as follows: Stock options $ 21,245 Non-vested stock awards/stock units 3,355 Total $ 24,600 The weighted-average period over which the remaining unrecognized stock-based compensation expense related to stock options is expected to be recognized was 2.9 years as of December 31, 2015 . 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 2.9 years as of December 31, 2015 . Valuation of Stock-Based Compensation . The fair value of our employee stock options granted is estimated on the measurement date, which, for us, 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 our stock price and other variables, and allows for the use of dynamic assumptions about interest rates and expected volatility. The weighted-average fair value of stock options granted during 2015 , 2014 and 2013 estimated using a binomial lattice-based valuation model, was $10.23 , $16.97 , and $13.74 . The assumptions used to determine the fair value of options granted are detailed in the table below. 2015 2014 2013 Weighted-average risk-free interest rate 2.05 % 2.33 % 2.65 % Dividend yield 3.02 2.71 2.92 Weighted-average expected market price volatility 26.48 26.66 24.20 Weighted-average expected term 5.7 years 7.1 years 6.7 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 our 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 us, is the date of the award.

Other Non-Interest Income and E

Other Non-Interest Income and Expense	12 Months Ended
	Dec. 31, 2015
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. 2015 2014 2013 Other non-interest income: Other $ 35,656 $ 32,256 $ 34,531 Total $ 35,656 $ 32,256 $ 34,531 Other non-interest expense: Advertising, promotions and public relations $ 28,858 $ 28,998 $ 26,232 Professional services 26,283 27,365 26,132 Travel/meals and entertainment 15,346 14,813 13,571 Check card expense 13,008 11,923 9,384 Other 82,066 84,557 76,758 Total $ 165,561 $ 167,656 $ 152,077

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense was as follows: 2015 2014 2013 Current income tax expense $ 59,530 $ 62,177 $ 49,736 Deferred income tax expense (benefit) (19,059 ) (4,130 ) 3,279 Income tax expense, as reported $ 40,471 $ 58,047 $ 53,015 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: 2015 2014 2013 Income tax expense computed at the statutory rate $ 111,930 $ 117,608 $ 101,808 Effect of tax-exempt interest (70,889 ) (58,761 ) (46,535 ) Bank owned life insurance income (1,255 ) (1,116 ) (1,086 ) Other 685 316 (1,172 ) Income tax expense, as reported $ 40,471 $ 58,047 $ 53,015 Year-end deferred taxes were as follows: 2015 2014 Deferred tax assets: Allowance for loan losses $ 47,551 $ 34,840 Net actuarial loss on defined benefit post-retirement benefit plans 25,172 26,263 Stock-based compensation 21,246 18,839 Alternative minimum tax carryforward 10,934 — Bonus accrual 5,832 6,118 Gain on sale of assets 2,044 2,139 Transaction costs 1,716 1,794 Partnerships 1,271 1,911 Other 4,447 5,272 Total gross deferred tax assets 120,213 97,176 Deferred tax liabilities: Net unrealized gain on securities available for sale and effective cash flow hedging derivatives (86,484 ) (102,626 ) Premises and equipment (23,038 ) (20,039 ) Defined benefit post-retirement benefit plans (14,089 ) (15,010 ) Intangible assets (8,940 ) (6,143 ) Leases (4,491 ) (4,952 ) Section 481(a) change in accounting method (tangible property) (3,387 ) — Prepaid expenses (1,702 ) (1,639 ) Reserve for medical insurance (211 ) (3,017 ) Other (352 ) (341 ) Total gross deferred tax liabilities (142,694 ) (153,767 ) Net deferred tax asset (liability) $ (22,481 ) $ (56,591 ) No valuation allowance for deferred tax assets was recorded at December 31, 2015 and 2014 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. We file income tax returns in the U.S. federal jurisdiction. We are no longer subject to U.S. federal income tax examinations by tax authorities for years before 2012.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2015
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 Amount Tax Expense, (Benefit) Net of Tax Amount 2015 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ (12,450 ) $ (4,358 ) $ (8,092 ) Change in net unrealized gain on securities transferred to held to maturity (33,601 ) (11,760 ) (21,841 ) Reclassification adjustment for net (gains) losses included in net income (69 ) (24 ) (45 ) Total securities available for sale and transferred securities (46,120 ) (16,142 ) (29,978 ) Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss 3,118 1,091 2,027 Total other comprehensive income (loss) $ (43,002 ) $ (15,051 ) $ (27,951 ) 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 ) Activity in accumulated other comprehensive income, net of tax, was as follows: Securities Available For Sale Defined Benefit Plans Derivatives Accumulated Other Comprehensive Income Balance January 1, 2015 $ 190,589 $ (48,775 ) $ — $ 141,814 Other comprehensive income (loss) before reclassification (29,933 ) 2,027 — (27,906 ) Amounts reclassified from accumulated other comprehensive income (loss) (45 ) — — (45 ) Net other comprehensive income (loss) during period (29,978 ) 2,027 — (27,951 ) Balance December 31, 2015 $ 160,611 $ (46,748 ) $ — $ 113,863 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

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2015
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. We utilize interest rate swaps, caps and floors to mitigate exposure to interest rate risk and to facilitate the needs of our customers. Our objectives for utilizing these derivative instruments are described below: We have entered into certain interest rate swap contracts that are matched to specific fixed-rate commercial loans or leases that we have entered into with our 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, we 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 our 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. We 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. In October 2008, we 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 our $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, we 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. We have 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 we enter 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 a third-party financial institution. In connection with each swap transaction, we agree 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, we agree to pay a third-party 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 our customer to effectively convert a variable rate loan to a fixed rate. Because we act as an intermediary for our customer, changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact our results of operations. The notional amounts and estimated fair values of interest rate derivative contracts outstanding at December 31, 2015 and 2014 are presented in the following table. We obtain dealer quotations to value our 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, 2015 December 31, 2014 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivatives designated as hedges of fair value: Financial institution counterparties: Loan/lease interest rate swaps - assets $ 49,927 $ 358 $ 31,614 $ 469 Loan/lease interest rate swaps - liabilities 31,038 (2,301 ) 37,672 (3,179 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps - assets 62,887 278 69,842 719 Loan/lease interest rate swaps - liabilities 768,182 (37,522 ) 765,979 (38,952 ) Loan/lease interest rate caps - assets 74,281 682 73,058 1,003 Customer counterparties: Loan/lease interest rate swaps - assets 780,082 37,630 765,979 38,910 Loan/lease interest rate swaps - liabilities 50,987 (188 ) 69,842 (719 ) Loan/lease interest rate caps - liabilities 74,281 (682 ) 73,058 (1,003 ) The weighted-average rates paid and received for interest rate swaps outstanding at December 31, 2015 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.36 % 0.37 % Non-hedging interest rate swaps - financial institution counterparties 4.14 2.01 Non-hedging interest rate swap - customer counterparties 2.01 4.14 The weighted-average strike rate for outstanding interest rate caps was 2.42% at December 31, 2015 . Commodity Derivatives. We enter into commodity swaps and option contracts that are not designated as hedging instruments primarily to accommodate the business needs of our customers. Upon the origination of a commodity swap or option contract with a customer, we simultaneously enter 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. We obtain dealer quotations and use internal valuation models with observable market data inputs to value our commodity derivative positions. December 31, 2015 December 31, 2014 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil - assets Barrels 1,184 $ 12,650 470 $ 14,357 Oil - liabilities Barrels 45 (352 ) 197 (1,670 ) Natural gas - assets MMBTUs 760 560 12,235 12,707 Natural gas - liabilities MMBTUs — — 16,755 (4,095 ) Customer counterparties: Oil - assets Barrels 45 354 197 1,670 Oil - liabilities Barrels 1,184 (12,454 ) 470 (14,318 ) Natural gas - assets MMBTUs — — 16,755 4,095 Natural gas - liabilities MMBTUs 760 (549 ) 12,235 (12,646 ) Foreign Currency Derivatives . We enter into foreign currency forward contracts that are not designated as hedging instruments primarily to accommodate the business needs of our customers. Upon the origination of a foreign currency denominated transaction with a customer, we simultaneously enter into an offsetting contract with a third party financial institution to negate the exposure to fluctuations in foreign currency exchange rates. We also utilize 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: December 31, 2015 December 31, 2014 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts - assets EUR 1,247 $ 13 936 $ 7 Forward contracts - assets CAD — — 24,724 659 Forward contracts - assets GBP 568 2 — — Forward contracts - liabilities EUR 572 (18 ) — — Forward contracts - liabilities CAD 1,440 (5 ) — — Forward contracts - liabilities GBP — — 544 (2 ) Customer counterparties: Forward contracts - assets EUR 575 22 — — Forward contracts - assets CAD 1,437 9 — — Forward contracts - liabilities EUR 343 (5 ) — — Forward contracts - liabilities CAD — — 24,680 (615 ) 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 were included in interest income on loans during 2014 and 2013 . 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 . 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: 2015 2014 2013 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ (1,796 ) $ (2,014 ) $ (2,437 ) Amount of (gain) loss included in other non-interest expense 11 3 4 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: 2015 2014 2013 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 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 Amount of gain (loss) recognized in other comprehensive income — — (49 ) 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 stated above, we enter into non-hedge related derivative positions primarily to accommodate the business needs of our customers. Upon the origination of a derivative contract with a customer, we simultaneously enter into an offsetting derivative contract with a third party financial institution. We recognize immediate income based upon the difference in the bid/ask spread of the underlying transactions with our customers and the third party. Because we act only as an intermediary for our customer, subsequent changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact our 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. 2015 2014 2013 Non-hedging interest rate derivatives: Other non-interest income $ 2,580 $ 1,786 $ 1,441 Other non-interest expense (43 ) (2 ) (96 ) Non-hedging commodity derivatives: Other non-interest income 208 118 496 Non-hedging foreign currency derivatives: Other non-interest income 78 162 175 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 our Asset/Liability Management Committee. Our credit exposure on interest rate swaps is limited to the net favorable value and interest payments of all swaps by each counterparty, while our 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 our 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. Our credit exposure relating to interest rate swaps, commodity swaps/options and foreign currency forward contracts with bank customers was approximately $37.7 million at December 31, 2015 . This credit exposure is partly mitigated as transactions with customers are generally secured by the collateral, if any, securing the underlying transaction being hedged. Our 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 $6.7 million at December 31, 2015 . This amount was primarily related to excess collateral we posted to counterparties. Collateral levels for upstream financial institution counterparties are monitored and adjusted as necessary. See Note 17 – Balance Sheet Offsetting and Repurchase Agreements for additional information regarding our credit exposure with upstream financial institution counterparties. The aggregate fair value of securities we posted as collateral related to derivative contracts totaled $17.5 million at December 31, 2015 . At such date, we also had $16.9 million in cash collateral on deposit with other financial institution counterparties.

Balance Sheet Offsetting

Balance Sheet Offsetting	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Balance Sheet Offsetting	Balance Sheet Offsetting and Repurchase Agreements Balance Sheet Offsetting. Certain financial instruments, including resell and repurchase agreements and derivatives, may be eligible for offset in the consolidated balance sheet and/or subject to master netting arrangements or similar agreements. Our 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, we do 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, 2015 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2015 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 1,318 $ — $ 1,318 Commodity swaps and options 13,210 — 13,210 Foreign currency forward contracts 15 — 15 Total derivatives 14,543 — 14,543 Resell agreements 13,442 — 13,442 Total $ 27,985 $ — $ 27,985 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 39,823 $ — $ 39,823 Commodity swaps and options 352 — 352 Foreign currency forward contracts 23 — 23 Total derivatives 40,198 — 40,198 Repurchase agreements 883,947 — 883,947 Total $ 924,145 $ — $ 924,145 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2015 Financial assets: Derivatives: Counterparty A $ 743 $ (743 ) $ — $ — Counterparty B 6,901 (5,795 ) (413 ) 693 Counterparty C 6,059 (3,447 ) (2,312 ) 300 Other counterparties 840 (840 ) — — Total derivatives 14,543 (10,825 ) (2,725 ) 993 Resell agreements 13,442 — (13,442 ) — Total $ 27,985 $ (10,825 ) $ (16,167 ) $ 993 Financial liabilities: Derivatives: Counterparty A $ 16,092 $ (743 ) $ (15,347 ) $ 2 Counterparty B 5,795 (5,795 ) — — Counterparty C 3,447 (3,447 ) — — Other counterparties 14,864 (840 ) (13,456 ) 568 Total derivatives 40,198 (10,825 ) (28,803 ) 570 Repurchase agreements 883,947 — (883,947 ) — Total $ 924,145 $ (10,825 ) $ (912,750 ) $ 570 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 Recognized Gross Amount Offset Net Amount Recognized December 31, 2014 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 Recognized Financial Instruments Collateral Net Amount December 31, 2014 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 Repurchase Agreements . We utilize securities sold under agreements to repurchase to facilitate the needs of our customers and to facilitate secured short-term funding needs. Securities sold under agreements to repurchase are stated at the amount of cash received in connection with the transaction. We monitor collateral levels on a continuous basis. We may be required to provide additional collateral based on the fair value of the underlying securities. Securities pledged as collateral under repurchase agreements are maintained with our safekeeping agents. The remaining contractual maturity of repurchase agreements in the consolidated balance sheets as of December 31, 2015 and December 31, 2014 is presented in the following tables. Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total December 31, 2015 Repurchase agreements: U.S. Treasury $ 664,419 $ — $ — $ — $ 664,419 Residential mortgage-backed securities 211,501 — 8,027 — 219,528 Total borrowings $ 875,920 $ — $ 8,027 $ — $ 883,947 Gross amount of recognized liabilities for repurchase agreements $ 883,947 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2014 Repurchase agreements: U.S. Treasury $ 427,402 $ — $ — $ — $ 427,402 Residential mortgage-backed securities 355,187 — 8,530 — 363,717 Total borrowings $ 782,589 $ — $ 8,530 $ — $ 791,119 Gross amount of recognized liabilities for repurchase agreements $ 791,119 Amounts related to agreements not included in offsetting disclosures above $ —

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
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, we utilize 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 our creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. Our 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 our 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 our 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, we obtain 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. We review 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, we do not purchase investment portfolio securities that are esoteric or that have a complicated structure. Our 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, we 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. We obtain dealer quotations and utilize internally developed valuation models to value commodity swaps/options. We utilize 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, we would obtain price verification from a third-party dealer. We utilize internal valuation models with observable market data inputs to estimate fair values of customer interest rate swaps, caps and floors. We also obtain 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 our derivative positions, we evaluate the credit risk of our counterparties as well as ours. Accordingly, we have considered factors such as the likelihood of our default and the default of our counterparties, our 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. We review our counterparty exposure on a regular basis, and, when necessary, appropriate business actions are taken to adjust the exposure. We also utilize this approach to estimate our own credit risk on derivative liability positions. To date, we have 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, 2015 and 2014 , segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value: Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value 2015 Securities available for sale: U.S. Treasury $ 3,994,520 $ — $ — $ 3,994,520 Residential mortgage-backed securities — 1,041,432 — 1,041,432 States and political subdivisions — 4,127,959 — 4,127,959 Other — 42,447 — 42,447 Trading account securities: U.S. Treasury 16,443 — — 16,443 States and political subdivisions — 136 — 136 Derivative assets: Interest rate swaps, caps and floors — 38,948 — 38,948 Commodity swaps and options — 13,564 — 13,564 Foreign currency forward contracts 46 — — 46 Derivative liabilities: Interest rate swaps, caps and floors — 40,693 — 40,693 Commodity swaps and options — 13,355 — 13,355 Foreign currency forward contracts 28 — — 28 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 There were no derivative assets measured at fair value using significant unobservable (Level 3) inputs as of December 31, 2015 . Derivative assets, measured at fair value on a recurring basis using significant unobservable (Level 3) inputs at December 31, 2014 consisted 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 related 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 was 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 , while 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: 2015 2014 2013 Level 2 Level 3 Level 2 Level 3 Level 2 Level 3 Carrying value of impaired loans before allocations $ — $ 14,921 $ — $ 2,715 $ 9,374 $ — Specific valuation allowance allocations — (2,765 ) — (1,475 ) (2,785 ) — Fair value $ — $ 12,156 $ — $ 1,240 $ 6,589 $ — Non-Financial Assets and Non-Financial Liabilities: We do not have any 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: 2015 2014 2013 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 1,102 $ 6,388 $ 7,580 Charge-offs recognized in the allowance for loan losses (169 ) (285 ) (710 ) Fair value $ 933 $ 6,103 $ 6,870 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 205 $ 5,026 $ 4,979 Write-downs included in other non-interest expense (36 ) (1,289 ) (895 ) Fair value $ 169 $ 3,737 $ 4,084 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 our provision for loan losses. Regulatory guidelines require us to reevaluate the fair value of other real estate owned on at least an annual basis. While our policy is to comply with the regulatory guidelines, our general practice is to reevaluate the fair value of collateral supporting impaired collateral dependent loans on a quarterly basis. Thus, appraisals are generally not considered to be outdated, and we typically do 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 our long-term relationships with depositors, commonly known as core deposit intangibles, which are separate intangible assets, and not considered financial instruments. Nonetheless, we would likely realize a core deposit premium if our 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 . Our 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 our 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, 2015 December 31, 2014 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,591,523 $ 3,591,523 $ 4,364,123 $ 4,364,123 Securities held to maturity 2,663,009 2,710,685 2,926,486 2,966,390 Cash surrender value of life insurance policies 175,191 175,191 172,050 172,050 Accrued interest receivable 139,986 139,986 128,436 128,436 Level 3 inputs: Loans, net 11,350,672 11,396,158 10,887,993 10,939,684 Financial liabilities: Level 2 inputs: Deposits 24,343,595 24,344,007 24,135,930 24,136,402 Federal funds purchased and repurchase agreements 893,522 893,522 803,119 803,119 Junior subordinated deferrable interest debentures 137,115 137,115 137,115 137,115 Subordinated notes payable and other borrowings 100,000 99,000 100,000 95,591 Accrued interest payable 1,014 1,014 1,132 1,132 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, we had no financial instruments measured at fair value under the fair value measurement option.

Operating Segments

Operating Segments	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Operating Segments	Operating Segments We are managed under a matrix organizational structure whereby our 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. We are 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 Insurance Agency and Frost Securities. 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. Prior to June 30, 2015, Frost Securities, Inc. provided advisory and private equity services to middle market companies. The operations of Frost Securities were discontinued and the entity was closed effective June 30, 2015. The Frost Wealth Advisors operating segment includes fee-based services within private trust, retirement services, and financial management services, including personal wealth management and securities 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 our banking and non-banking subsidiaries and the issuance of debt and equity. Our principal source of revenue is dividends from our subsidiaries. The accounting policies of each reportable segment are the same as those of our consolidated entity 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. We use a match-funded transfer pricing process to assess operating segment performance. The process helps us 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 Wealth Advisors Non-Banks Consolidated 2015 Net interest income (expense) $ 732,671 $ 7,634 $ (3,673 ) $ 736,632 Provision for loan losses 51,848 (3 ) — 51,845 Non-interest income 205,606 121,489 1,635 328,730 Non-interest expense 589,394 98,405 5,919 693,718 Income (loss) before income taxes 297,035 30,721 (7,957 ) 319,799 Income tax expense (benefit) 34,997 10,753 (5,279 ) 40,471 Net income (loss) 262,038 19,968 (2,678 ) 279,328 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 262,038 $ 19,968 $ (10,741 ) $ 271,265 Revenues from (expenses to) external customers $ 938,277 $ 129,123 $ (2,038 ) $ 1,065,362 Average assets (in millions) (1) $ 28,024 $ 36 $ 2 $ 28,062 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 (1) Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.7 billion , $30.5 billion and $29.0 billion at December 31, 2015 , 2014 and 2013 .

Condensed Financial Statements

Condensed Financial Statements of Parent Company	12 Months Ended
	Dec. 31, 2015
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, 2015 2014 Assets: Cash $ 6,434 $ 7,335 Resell agreements 200,100 286,660 Total cash and cash equivalents 206,534 293,995 Investment in subsidiaries 2,920,506 2,791,647 Accrued interest receivable and other assets 36,578 29,705 Total assets $ 3,163,618 $ 3,115,347 Liabilities: Junior subordinated deferrable interest debentures $ 137,115 $ 137,115 Subordinated notes payable 100,000 100,000 Accrued interest payable and other liabilities 36,160 26,829 Total liabilities 273,275 263,944 Shareholders’ Equity 2,890,343 2,851,403 Total liabilities and shareholders’ equity $ 3,163,618 $ 3,115,347 Condensed Statements of Income Year Ended December 31, 2015 2014 2013 Income: Dividend income paid by Frost Bank $ 126,375 $ 114,439 $ 144,642 Dividend income paid by non-banks 1,830 4,323 2,819 Interest and other income 82 69 79 Total income 128,287 118,831 147,540 Expenses: Interest expense 3,673 3,381 7,365 Salaries and employee benefits 1,376 1,218 1,175 Other 5,727 8,526 6,735 Total expenses 10,776 13,125 15,275 Income before income taxes and equity in undistributed earnings of subsidiaries 117,511 105,706 132,265 Income tax benefit 6,062 6,702 7,845 Equity in undistributed earnings of subsidiaries 155,755 165,569 97,756 Net income 279,328 277,977 237,866 Preferred stock dividends 8,063 8,063 6,719 Net income available to common shareholders $ 271,265 $ 269,914 $ 231,147 Condensed Statements of Cash Flows Year Ended December 31, 2015 2014 2013 Operating Activities: Net income $ 279,328 $ 277,977 $ 237,866 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed earnings of subsidiaries (155,755 ) (165,569 ) (97,756 ) Stock-based compensation 480 441 330 Excess tax benefits from stock-based compensation (161 ) (165 ) (155 ) Net change in other assets and other liabilities 2,621 (1,984 ) 2,372 Net cash from operating activities 126,513 110,700 142,657 Investing Activities: Redemption of investment in Frost Securities, Inc. 216 — — Net cash received in acquisitions — 830,661 — Capital contribution to subsidiaries — (879,730 ) — Net cash from investing activities 216 (49,069 ) — Financing Activities: Proceeds from stock option exercises 14,853 29,158 68,653 Proceeds from stock-based compensation activities of subsidiaries 12,257 12,062 11,633 Excess tax benefits from stock-based compensation 161 165 155 Proceeds from issuance of preferred stock — — 144,486 Purchase of treasury stock (101,237 ) (1,457 ) (144,630 ) Cash dividends paid on preferred stock (8,063 ) (8,063 ) (6,719 ) Cash dividends paid on common stock (132,161 ) (127,178 ) (119,619 ) Net cash from financing activities (214,190 ) (95,313 ) (46,041 ) Net change in cash and cash equivalents (87,461 ) (33,682 ) 96,616 Cash and cash equivalents at beginning of year 293,995 327,677 231,061 Cash and cash equivalents at end of year $ 206,534 $ 293,995 $ 327,677

Accounting Standards Updates

Accounting Standards Updates	12 Months Ended
	Dec. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Standards Updates	Accounting Standards Updates Accounting Standards Update (“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 us on January 1, 2013. See Note 17 – Balance Sheet Offsetting and Repurchase Agreements 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 us on January 1, 2013 and did not have a significant impact on our financial statements. 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 us on January 1, 2014 and did not have a significant impact on our 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 our 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 was originally going to be effective for us on January 1, 2017; however, the FASB recently issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606) – Deferral of the Effective Date" which deferred the effective date of ASU 2014-09 by one year to January 1, 2018. We are currently evaluating the potential impact of ASU 2014-09 on our 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 became effective for us on January 1, 2015 and did not have a significant impact on our financial statements. The new disclosures required by ASU 2014-11 are included in Note 17 - Balance Sheet Offsetting and Repurchase Agreements. 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 us beginning January 1, 2016, though early adoption is permitted. ASU 2015-01 is not expected to have a significant impact on our financial statements. ASU 2015-02, “Consolidation (Topic 810) – Amendments to the Consolidation Analysis.” ASU 2015-02 implements changes to both the variable interest consolidation model and the voting interest consolidation model. ASU 2015-02 (i) eliminates certain criteria that must be met when determining when fees paid to a decision maker or service provider do not represent a variable interest, (ii) amends the criteria for determining whether a limited partnership is a variable interest entity and (iii) eliminates the presumption that a general partner controls a limited partnership in the voting model. ASU 2015-02 will be effective for us on January 1, 2016 and is not expected to have a significant impact on our financial statements. ASU 2015-03, “Interest – Imputation of Interest (Subtopic 835-30) – Simplifying the Presentation of Debt Issuance Costs . ” ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by the amendments in ASU 2015-03. ASU 2015-03 will be effective for us on January 1, 2016, though early adoption is permitted. ASU 2015-03 is not expected to have a significant impact on our financial statements. ASU 2015-05, “Intangibles – Goodwill and Other - Internal-Use Software (Subtopic 350-40) – Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement.” ASU 2015-05 addresses accounting for fees paid by a customer in cloud computing arrangements such as (i) software as a service, (ii) platform as a service, (iii) infrastructure as a service and (iv) other similar hosting arrangements. ASU 2015-05 provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, then the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. ASU 2015-05 will be effective for us on January 1, 2016 and is not expected to have a significant impact on our financial statements. ASU 2015-15, “Interest – Imputation of Interest (Subtopic 835-30) – Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements. Amendments to SEC Paragraphs Pursuant to Staff Announcement at June 18, 2015 EITF Meeting." ASU 2015-15 adds SEC paragraphs pursuant to an SEC Staff Announcement that given the absence of authoritative guidance within ASU 2015-03 for debt issuance costs related to line-of-credit arrangements, the SEC staff would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-16, “Business Combinations (Topic 805) – Simplifying the Accounting for Measurement-Period Adjustments.” ASU 2015-16 requires that adjustments to provisional amounts that are identified during the measurement period of a business combination be recognized in the reporting period in which the adjustment amounts are determined. Furthermore, the income statement effects of such adjustments, if any, must be calculated as if the accounting had been completed at the acquisition date. The portion of the amount recorded in current-period earnings that would have been recorded in previous reporting periods if the adjustment to the provisional amounts had been recognized as of the acquisition date. Under previous guidance, adjustments to provisional amounts identified during the measurement period are to be recognized retrospectively. ASU 2015-16 will be effective for us on January 1, 2016 and is not expected to have a significant impact on our financial statements. ASU 2016-1, “No. 2016-01, Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. ASU 2016-1, among other things, (i) requires equity investments, with certain exceptions, to be measured at fair value with changes in fair value recognized in net income, (ii) simplifies the impairment assessment of equity investments without readily determinable fair values by requiring a qualitative assessment to identify impairment, (iii) eliminates the requirement for public business entities to disclose the methods and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet, (iv) requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes, (v) requires an entity to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when the entity has elected to measure the liability at fair value in accordance with the fair value option for financial instruments, (vi) requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset on the balance sheet or the accompanying notes to the financial statements and (viii) clarifies that an entity should evaluate the need for a valuation allowance on a deferred tax asset related to available-for-sale. ASU 2016-1 will be effective for us on January 1, 2018 and is not expected to have a significant impact on our financial statements.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Acquisition	Mergers and Acquisitions WNB Bancshares, Inc. On May 30, 2014 , we 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. We purchased all of the outstanding shares of WNB for approximately $198.8 million . The total purchase price included $149.7 million of our 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 our 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. Cash and cash equivalents $ 879,740 Securities available for sale 154,227 Loans 670,619 Premises and equipment 22,135 Core deposit intangible asset 9,300 Goodwill 118,019 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. Loans that were not deemed to be credit impaired at acquisition were subsequently considered as a part of our determination of the adequacy of the 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, we agreed with the Federal Reserve Board that before bringing it any further expansionary proposals, except for proposed branches serving majority minority areas within our existing markets, we would enhance certain compliance programs, including those related to fair lending. We are currently working on these enhancements. Kolkhorst Insurance Agency, Inc . On November 1, 2013, we acquired Kolkhorst Insurance Agency, Inc., a Houston-based insurance agency specializing in commercial lines insurance products. The acquisition did not significantly impact our financial statements.

Summary of Significant Accoun30

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
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 our subsidiaries, a broad array of products and services throughout numerous Texas markets. The terms “Cullen/Frost,” “the Corporation,” “we,” “us” and “our” mean Cullen/Frost Bankers, Inc. and its subsidiaries, when appropriate. In addition to general commercial and consumer banking, other products and services offered include trust and investment management, insurance, brokerage, mutual funds, leasing, treasury management, capital markets advisory 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. All significant intercompany balances and transactions have been eliminated in consolidation. The accounting and financial reporting policies we follow conform, in all material respects, to accounting principles generally accepted in the United States and to general practices within the financial services industry. We determine whether we have 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. We consolidate voting interest entities in which we have 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. Our wholly owned subsidiaries Cullen/Frost Capital Trust II and WNB Capital Trust I are VIEs for which we are not the primary beneficiary. Accordingly, the accounts of these trusts are not included in our consolidated financial statements. We have 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 our 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.
Cash Flow Reporting	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 us, federal funds sold and resell agreements. Net cash flows are reported for loans, deposit transactions and short-term borrowings.
Concentrations and Restrictions on Cash and Cash Equivalents	Concentrations and Restrictions on Cash and Cash Equivalents . We maintain 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 we are not exposed to any significant credit risks on cash and cash equivalents. We were required to have $188.9 million and $175.6 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2015 and 2014 . These deposits with the Federal Reserve Bank do not earn interest. Additionally, as of December 31, 2015 and 2014 , we had $16.9 million and $12.1 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions.
Repurchase/Resell Agreements	Repurchase/Resell Agreements. We purchase 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. We also sell 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 our ability to retain our 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 our 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 we 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	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 inherent 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 our 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 $2.3 million and $5.3 million at December 31, 2015 and 2014 .
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 on October 1st, 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. Prior to 2015, we evaluated goodwill for possible impairment annually on September 30th. In 2015, we move the evaluation date back one day to coincide with our annual financial reporting cycle. 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. Our 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. We also receive contingent commissions from insurance companies as additional incentive for achieving specified premium volume goals and/or the loss experience of the insurance placed by us. Contingent commissions from insurance companies are recognized when determinable, which is generally when such commissions are received or when we receive data from the insurance companies that allows the reasonable estimation of these amounts. We maintain a reserve for commission adjustments based on estimated policy cancellations. This reserve was not significant at December 31, 2015 or 2014 .
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 us, 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 non-vested stock awards/stock units and deferred stock units is generally the market price of our 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. We file a consolidated income tax return with our 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. We have determined that our 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 our 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 . Our 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 our 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. We 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. We consider 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, we formally assess 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, we 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 our creditworthiness, among other things, as well as unobservable parameters. Any such valuation adjustments are applied consistently over time. See Note 18 - Fair Value Measurements.
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 us, (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) we do 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 our trust department, other than cash on deposit at Frost Bank, are not included in the accompanying financial statements because they are not our assets.
Reclassifications	Reclassifications and Restatement . Certain items in prior financial statements have been reclassified to conform to the current presentation. Additionally, certain items in prior financial statements have been restated to reflect adjustments to initially reported provisional amounts recognized in business combinations so that the prior financial statements are reported as if the adjusted amounts had been known as of the measurement date of the business combination.

Summary of Significant Accoun31

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Additional Cash Flow Information	Additional cash flow information was as follows: Year Ended December 31, 2015 2014 2013 Cash paid for interest $ 12,982 $ 14,705 $ 22,449 Cash paid for income tax 57,086 62,976 49,514 Significant non-cash transactions: Unsettled purchases of securities 2,998 — 16,241 Loans foreclosed and transferred to other real estate owned and foreclosed assets 933 4,363 6,870 Premises and equipment transferred to other real estate owned and foreclosed assets — 1,740 — Loans to facilitate the sale of other real estate owned 20 102 678 Deferred gain on sale of building and parking garage — — 768

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2015
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: 2015 2014 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held to Maturity: U.S. Treasury $ 249,441 $ 7,776 $ — $ 257,217 $ 249,009 $ 14,604 $ — $ 263,613 Residential mortgage-backed securities 6,456 63 4 6,515 8,012 92 — 8,104 States and political subdivisions 2,405,762 46,003 6,149 2,445,616 2,668,115 34,243 9,035 2,693,323 Other 1,350 — 13 1,337 1,350 — — 1,350 Total $ 2,663,009 $ 53,842 $ 6,166 $ 2,710,685 $ 2,926,486 $ 48,939 $ 9,035 $ 2,966,390 Available for Sale: U. S. Treasury $ 3,980,986 $ 22,041 $ 8,507 $ 3,994,520 $ 3,783,899 $ 30,594 $ 3,241 $ 3,811,252 Residential mortgage-backed securities 1,000,024 42,142 734 1,041,432 1,331,114 68,027 417 1,398,724 States and political subdivisions 3,996,113 133,305 1,459 4,127,959 3,104,563 104,500 156 3,208,907 Other 42,447 — — 42,447 42,371 — — 42,371 Total $ 9,019,570 $ 197,488 $ 10,700 $ 9,206,358 $ 8,261,947 $ 203,121 $ 3,814 $ 8,461,254
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 Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses 2015 Held to Maturity: Residential mortgage-backed securities $ 900 $ 4 $ — $ — $ 900 $ 4 States and political subdivisions 146,854 1,325 202,423 4,824 349,277 6,149 Other 1,337 13 — — 1,337 13 Total $ 149,091 $ 1,342 $ 202,423 $ 4,824 $ 351,514 $ 6,166 Available for Sale: U.S. Treasury $ 886,087 $ 8,507 $ — $ — $ 886,087 $ 8,507 Residential mortgage-backed securities 21,392 212 17,781 522 39,173 734 States and political subdivisions 120,782 1,237 18,485 222 139,267 1,459 Total $ 1,028,261 $ 9,956 $ 36,266 $ 744 $ 1,064,527 $ 10,700 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
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, 2015 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 Cost Estimated Fair Value Amortized Cost Estimated Fair Value Due in one year or less $ 161,934 $ 163,320 $ 793,662 $ 796,452 Due after one year through five years 846,629 889,786 2,961,224 2,976,538 Due after five years through ten years 207,488 209,616 1,391,273 1,418,590 Due after ten years 1,440,502 1,441,448 2,830,940 2,930,899 Residential mortgage-backed securities 6,456 6,515 1,000,024 1,041,432 Equity securities — — 42,447 42,447 Total $ 2,663,009 $ 2,710,685 $ 9,019,570 $ 9,206,358
Sales of Securities Available for Sale	Sales of securities available for sale were as follows: 2015 2014 2013 Proceeds from sales $ 12,683,169 $ 12,151,287 $ 10,056,060 Gross realized gains 228 39 1,206 Gross realized losses (159 ) (1 ) (30 ) Tax (expense) benefit of securities gains/losses (24 ) (13 ) (412 )
Premium Amortization and Discount Accretion Included in Income on Securities	Premium amortization and discount accretion included in interest income on securities was as follows: 2015 2014 2013 Premium amortization $ (84,467 ) $ (68,070 ) $ (49,112 ) Discount accretion 10,682 6,802 7,191 Net (premium amortization) discount accretion $ (73,785 ) $ (61,268 ) $ (41,921 )
Year End Trading Account Securities, at Estimated Fair Value	Year-end trading account securities, at estimated fair value, were as follows: 2015 2014 U.S. Treasury $ 16,443 $ 15,339 States and political subdivisions 136 87 Total $ 16,579 $ 15,426
Net Gains and Losses on Trading Account Securities	Net gains and losses on trading account securities were as follows: 2015 2014 2013 Net gain on sales transactions $ 1,109 $ 829 $ 878 Net mark-to-market gains (losses) (53 ) — (429 ) Net gain on trading account securities $ 1,056 $ 829 $ 449

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2015
Receivables [Abstract]
Loans	Year-end loans, including leases net of unearned discounts, consisted of the following: 2015 2014 Commercial and industrial $ 4,120,522 $ 4,055,225 Energy: Production 1,249,678 1,160,404 Service 272,934 319,618 Other 235,583 293,923 Total energy 1,758,195 1,773,945 Commercial real estate: Commercial mortgages 3,285,041 2,999,082 Construction 720,695 624,888 Land 286,991 291,907 Total commercial real estate 4,292,727 3,915,877 Consumer real estate: Home equity loans 340,528 342,725 Home equity lines of credit 233,525 220,128 Other 306,696 286,198 Total consumer real estate 880,749 849,051 Total real estate 5,173,476 4,764,928 Consumer and other 434,338 393,437 Total loans $ 11,486,531 $ 10,987,535
Activities in Related Party Loans	Activity in related party loans during 2015 is presented in the following table. Other changes were primarily related to changes in related-party status. Balance outstanding at December 31, 2014 $ 38,700 Principal additions 230,806 Principal reductions (200,867 ) Other changes 16,127 Balance outstanding at December 31, 2015 $ 84,766
Non-Accrual Loans, Segregated by Class of Loans	Year-end non-accrual loans, segregated by class of loans, were as follows: 2015 2014 Commercial and industrial $ 25,111 $ 34,108 Energy 21,180 636 Commercial real estate: Buildings, land and other 34,519 19,639 Construction 569 2,792 Consumer real estate 1,862 2,212 Consumer and other 226 538 Total $ 83,467 $ 59,925
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, 2015 was as follows: Loans 30-89 Days Past Due Loans 90 or More Days Past Due Total Past Due Loans Current Loans Total Loans Accruing Loans 90 or More Days Past Due Commercial and industrial $ 27,777 $ 20,668 $ 48,445 $ 4,072,077 $ 4,120,522 $ 4,091 Energy 3,463 15,504 18,967 1,739,228 1,758,195 580 Commercial real estate: Buildings, land and other 43,090 5,307 48,397 3,523,635 3,572,032 1,642 Construction 1,149 569 1,718 718,977 720,695 — Consumer real estate 5,202 1,652 6,854 873,895 880,749 1,476 Consumer and other 3,781 382 4,163 430,175 434,338 319 Total $ 84,462 $ 44,082 $ 128,544 $ 11,357,987 $ 11,486,531 $ 8,108
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 Contractual Principal Balance Recorded Investment With No Allowance Recorded Investment With Allowance Total Recorded Investment Related Allowance Average Recorded Investment 2015 Commercial and industrial $ 26,067 $ 18,776 $ 4,084 $ 22,860 $ 2,378 $ 27,338 Energy 25,240 8,689 12,450 21,139 2,000 7,235 Commercial real estate: Buildings, land and other 37,126 32,425 — 32,425 — 18,211 Construction 793 569 — 569 — 1,320 Consumer real estate 755 485 — 485 — 664 Consumer and other — — — — — — Total $ 89,981 $ 60,944 $ 16,534 $ 77,478 $ 4,378 $ 54,768 2014 Commercial and industrial $ 42,212 $ 29,007 $ 2,853 $ 31,860 $ 1,613 $ 27,154 Energy 706 636 — 636 — 571 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 $ 31,429 $ 15,337 $ 7,004 $ 22,341 $ 4,140 $ 34,894 Energy 545 531 — 531 — 428 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
Troubled Debt Restructurings	Troubled debt restructurings that occurred during 2015 , 2014 and 2013 are set forth in the following table. 2015 2014 2013 Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Commercial and industrial $ 709 $ 536 $ 5,795 $ 5,391 $ 6,334 $ 4,937 Energy — — — — 528 531 Commercial real estate: Buildings, land and other — — 3,121 2,948 7,964 5,747 Consumer — — — — 7 — $ 709 $ 536 $ 8,916 $ 8,339 $ 14,833 $ 11,215
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, 2015 December 31, 2014 Weighted Average Risk Grade Loans Weighted Average Risk Grade Loans Commercial and industrial Risk grades 1-8 5.88 $ 3,869,203 5.93 $ 3,846,598 Risk grade 9 9.00 100,670 9.00 65,166 Risk grade 10 10.00 76,030 10.00 54,519 Risk grade 11 11.00 49,508 11.00 55,034 Risk grade 12 12.00 22,644 12.00 31,683 Risk grade 13 13.00 2,467 13.00 2,225 Total 6.13 $ 4,120,522 6.16 $ 4,055,225 Energy Risk grades 1-8 6.12 $ 1,385,749 5.37 $ 1,740,455 Risk grade 9 9.00 212,250 9.00 27,313 Risk grade 10 10.00 62,163 10.00 161 Risk grade 11 11.00 76,853 11.00 5,380 Risk grade 12 12.00 19,180 12.00 636 Risk grade 13 13.00 2,000 13.00 — Total 6.89 $ 1,758,195 5.45 $ 1,773,945 Commercial real estate: Buildings, land and other Risk grades 1-8 6.58 $ 3,280,435 6.53 $ 3,067,219 Risk grade 9 9.00 140,900 9.00 72,906 Risk grade 10 10.00 72,577 10.00 87,889 Risk grade 11 11.00 43,601 11.00 43,336 Risk grade 12 12.00 34,519 12.00 19,501 Risk grade 13 13.00 — 13.00 138 Total 6.85 $ 3,572,032 6.76 $ 3,290,989 Construction Risk grades 1-8 6.91 $ 696,229 6.91 $ 612,705 Risk grade 9 9.00 13,074 9.00 8,003 Risk grade 10 10.00 2,757 10.00 1,323 Risk grade 11 11.00 8,066 11.00 64 Risk grade 12 12.00 569 12.00 2,793 Risk grade 13 13.00 — 13.00 — Total 7.01 $ 720,695 6.97 $ 624,888
Net (Charge-Offs)/Recoveries, Segregated by Class of Loans	Net (charge-offs)/recoveries, segregated by class of loan, were as follows: 2015 2014 2013 Commercial and industrial $ (6,535 ) $ (2,911 ) $ (28,431 ) Energy (5,997 ) (1,237 ) (913 ) Commercial real estate: Buildings, land and other 314 (2,348 ) (381 ) Construction 18 348 256 Consumer real estate (91 ) (733 ) (719 ) Consumer and other (3,237 ) (2,329 ) (2,409 ) Total $ (15,528 ) $ (9,210 ) $ (32,597 )
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 and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Total December 31, 2015 Historical valuation allowances $ 25,428 $ 21,195 $ 15,544 $ 2,109 $ 12,813 $ 77,089 Specific valuation allowances 2,378 2,000 — — — 4,378 General valuation allowances 7,339 5,525 4,619 2,052 (6,932 ) 12,603 Macroeconomic valuation allowances 7,848 25,976 4,150 498 3,317 41,789 Total $ 42,993 $ 54,696 $ 24,313 $ 4,659 $ 9,198 $ 135,859 December 31, 2014 Historical valuation allowances $ 25,249 $ 7,172 $ 14,684 $ 2,017 $ 10,482 $ 59,604 Specific valuation allowances 1,613 — 67 — — 1,680 General valuation allowances 5,354 2,232 5,324 1,972 (6,263 ) 8,619 Macroeconomic valuation allowances 12,057 5,515 7,088 1,189 3,790 29,639 Total $ 44,273 $ 14,919 $ 27,163 $ 5,178 $ 8,009 $ 99,542
Activity in Allowance for Loan Losses by Portfolio Segment	The following table details activity in the allowance for loan losses by portfolio segment for 2015 , 2014 and 2013 . Allocation of a portion of the allowance to one category of loans does not preclude its availability to absorb losses in other categories. Commercial and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Unallocated Total 2015 Beginning balance $ 44,273 $ 14,919 $ 27,163 $ 5,178 $ 8,009 $ — $ 99,542 Provision for loan losses 5,255 45,774 (3,182 ) (428 ) 4,426 — 51,845 Charge-offs (11,092 ) (6,000 ) (657 ) (577 ) (11,246 ) — (29,572 ) Recoveries 4,557 3 989 486 8,009 — 14,044 Net charge-offs (6,535 ) (5,997 ) 332 (91 ) (3,237 ) — (15,528 ) Ending balance $ 42,993 $ 54,696 $ 24,313 $ 4,659 $ 9,198 $ — $ 135,859 Allocated to loans: Individually evaluated for impairment $ 2,378 $ 2,000 $ — $ — $ — $ — $ 4,378 Collectively evaluated for impairment 40,615 52,696 24,313 4,659 9,198 — 131,481 Ending balance $ 42,993 $ 54,696 $ 24,313 $ 4,659 $ 9,198 $ — $ 135,859 2014 Beginning balance $ 46,700 $ 6,090 $ 22,590 $ 5,230 $ 5,010 $ 6,818 $ 92,438 Provision for loan losses 484 10,066 6,573 681 5,328 (6,818 ) 16,314 Charge-offs (12,073 ) (1,747 ) (3,800 ) (1,097 ) (9,768 ) — (28,485 ) Recoveries 9,162 510 1,800 364 7,439 — 19,275 Net charge-offs (2,911 ) (1,237 ) (2,000 ) (733 ) (2,329 ) — (9,210 ) Ending balance $ 44,273 $ 14,919 $ 27,163 $ 5,178 $ 8,009 $ — $ 99,542 Allocated to loans: Individually evaluated for impairment $ 1,613 $ 67 $ — $ — $ — $ — $ 1,680 Collectively evaluated for impairment 42,660 14,852 27,163 5,178 8,009 — 97,862 Ending balance $ 44,273 $ 14,919 $ 27,163 $ 5,178 $ 8,009 $ — $ 99,542 2013 Beginning balance $ 46,585 $ 7,579 $ 29,346 $ 5,252 $ 3,507 $ 12,184 $ 104,453 Provision for loan losses 28,546 (576 ) (6,631 ) 697 3,912 (5,366 ) 20,582 Charge-offs (32,008 ) (924 ) (1,329 ) (1,047 ) (9,489 ) — (44,797 ) Recoveries 3,577 11 1,204 328 7,080 — 12,200 Net charge-offs (28,431 ) (913 ) (125 ) (719 ) (2,409 ) — (32,597 ) Ending balance $ 46,700 $ 6,090 $ 22,590 $ 5,230 $ 5,010 $ 6,818 $ 92,438 Allocated to loans: Individually evaluated for impairment $ 4,140 $ — $ 2,786 $ — $ — $ — $ 6,926 Collectively evaluated for impairment 42,560 6,090 19,804 5,230 5,010 6,818 85,512 Ending balance $ 46,700 $ 6,090 $ 22,590 $ 5,230 $ 5,010 $ 6,818 $ 92,438
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, 2015 and 2014 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 and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Total 2015 Individually evaluated $ 22,860 $ 21,139 $ 32,994 $ 485 $ — $ 77,478 Collectively evaluated 4,097,662 1,737,056 4,259,733 880,264 434,338 11,409,053 Total $ 4,120,522 $ 1,758,195 $ 4,292,727 $ 880,749 $ 434,338 $ 11,486,531 2014 Individually evaluated $ 31,860 $ 636 $ 20,499 $ 596 $ — $ 53,591 Collectively evaluated 4,023,365 1,773,309 3,895,378 848,455 393,437 10,933,944 Total $ 4,055,225 $ 1,773,945 $ 3,915,877 $ 849,051 $ 393,437 $ 10,987,535

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Premises and Equipment	Year-end premises and equipment were as follows: 2015 2014 Land $ 111,925 $ 102,334 Buildings 365,051 240,430 Furniture and equipment 136,983 102,885 Leasehold improvements 64,446 60,902 Construction in progress 81,991 118,367 760,396 624,918 Less accumulated depreciation and amortization (201,272 ) (182,748 ) Total premises and equipment, net $ 559,124 $ 442,170

Goodwill and Other Intangible35

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill . Year-end goodwill was as follows: 2015 2014 Goodwill $ 654,668 $ 654,668
Schedule of Other Intangible Assets	Other Intangible Assets. Year-end other intangible assets were as follows: Gross Intangible Assets Accumulated Amortization Net Intangible Assets 2015 Core deposits $ 39,410 $ (32,324 ) $ 7,086 Customer relationships 5,771 (4,214 ) 1,557 Non-compete agreements 725 (568 ) 157 $ 45,906 $ (37,106 ) $ 8,800 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
Estimated Aggregate Future Amortization Expense for Intangible Assets	The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2015 is as follows: 2016 $ 2,413 2017 1,619 2018 1,346 2019 1,102 2020 877 Thereafter 1,443 $ 8,800

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2015
Deposits [Abstract]
Schedule of Deposits	Year-end deposits were as follows: 2015 2014 Non-interest-bearing demand deposits: Commercial and individual $ 9,251,463 $ 9,256,045 Correspondent banks 378,930 429,000 Public funds 639,840 464,016 Total non-interest-bearing demand deposits 10,270,233 10,149,061 Interest-bearing deposits: Private accounts: Savings and interest checking 5,149,905 4,743,963 Money market accounts 7,536,998 7,860,403 Time accounts of $100,000 or more 420,697 490,209 Time accounts under $100,000 405,726 454,220 Total private accounts 13,513,326 13,548,795 Public funds: Savings and interest checking 420,324 326,090 Money market accounts 93,969 57,145 Time accounts of $100,000 or more 44,941 53,684 Time accounts under $100,000 802 1,155 Total public funds 560,036 438,074 Total interest-bearing deposits 14,073,362 13,986,869 Total deposits $ 24,343,595 $ 24,135,930
Additional Information About Corporation's Deposits	The following table presents additional information about our year-end deposits: 2015 2014 Deposits from the Certificate of Deposit Account Registry Service (CDARS) $ 2,615 $ 22,229 Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB) 7,440 148,665 Deposits from foreign sources (primarily Mexico) 747,008 744,295 Deposits not covered by deposit insurance 11,953,367 12,056,180 Deposits from certain directors, executive officers and their affiliates 218,095 176,821
Scheduled Maturities of Time Deposits	Scheduled maturities of time deposits, including both private and public funds, at December 31, 2015 were as follows: 2016 $ 736,480 2017 135,539 2018 88 2019 59 2020 — $ 872,166
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, 2015 , were as follows: Due within 3 months or less $ 160,712 Due after 3 months and within 6 months 91,160 Due after 6 months and within 12 months 140,232 Due after 12 months 73,534 $ 465,638

Off-Balance-Sheet Arrangement37

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Financial Instruments With Off-Balance-Sheet Risk	Year-end financial instruments with off-balance-sheet risk were as follows: 2015 2014 Commitments to extend credit $ 8,246,698 $ 7,955,779 Standby letters of credit 279,147 248,360 Deferred standby letter of credit fees 2,115 1,942
Future Minimum Lease Payments Due Under Non-Cancelable Operating Leases	Future minimum lease payments due under non-cancelable operating leases at December 31, 2015 were as follows: 2016 $ 22,489 2017 22,686 2018 21,913 2019 17,854 2020 15,041 Thereafter 106,926 $ 206,909

Capital and Regulatory Matters

Capital and Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2015
Regulatory Capital Requirements [Abstract]
Actual and Required Capital Ratios	Actual Minimum Capital Required - Basel III Phase-In Schedule Minimum Capital Required - Basel III Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2015 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 1,986,200 11.37 % $ 786,344 4.50 % $ 1,222,837 7.00 % $ 1,135,830 6.50 % Frost Bank 2,131,360 12.24 783,727 4.50 1,218,766 7.00 1,132,049 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,163,936 12.38 1,048,458 6.00 1,484,874 8.50 1,397,944 8.00 Frost Bank 2,131,360 12.24 1,044,969 6.00 1,479,930 8.50 1,393,292 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,419,545 13.85 1,397,944 8.00 1,834,256 10.50 1,747,430 10.00 Frost Bank 2,267,219 13.02 1,393,292 8.00 1,828,149 10.50 1,741,615 10.00 Leverage Ratio Cullen/Frost 2,163,936 7.79 1,111,325 4.00 1,111,117 4.00 1,389,156 5.00 Frost Bank 2,131,360 7.68 1,110,143 4.00 1,109,935 4.00 1,387,679 5.00 The following table presents actual and required capital ratios as of December 31, 2014 for Cullen/Frost and Frost Bank under the regulatory capital rules then in effect. Actual Minimum Required for Capital Adequacy Purposes Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2014 Total Capital to Risk-Weighted Assets Cullen/Frost $ 2,325,818 14.55 % $ 1,278,797 8.00 % $ 1,598,496 10.00 % Frost Bank 2,071,012 12.99 1,275,858 8.00 1,594,823 10.00 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,186,276 13.68 639,398 4.00 959,098 6.00 Frost Bank 1,979,415 12.41 637,929 4.00 956,894 6.00 Leverage Ratio Cullen/Frost 2,186,276 8.16 1,072,035 4.00 1,340,043 5.00 Frost Bank 1,979,415 7.40 1,070,109 4.00 1,337,636 5.00

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2015
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. 2015 2014 2013 Net Income $ 279,328 $ 277,977 $ 237,866 Less: Preferred stock dividends 8,063 8,063 6,719 Net income available to common shareholders 271,265 269,914 231,147 Less: Earnings allocated to participating securities 941 1,001 850 Net earnings allocated to common stock $ 270,324 $ 268,913 $ 230,297 Distributed earnings allocated to common stock $ 131,702 $ 126,709 $ 119,177 Undistributed earnings allocated to common stock 138,622 142,204 111,120 Net earnings allocated to common stock $ 270,324 $ 268,913 $ 230,297 Weighted-average shares outstanding for basic earnings per common share 62,758,074 62,072,080 60,350,552 Dilutive effect of stock compensation 715,250 901,448 765,858 Weighted-average shares outstanding for diluted earnings per common share 63,473,324 62,973,528 61,116,410

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Combined Activity in Corporations Defined Benefit Pension Plans	use a December 31 measurement date for our defined benefit plans. Combined activity in our defined benefit pension plans was as follows: 2015 2014 2013 Change in benefit obligation: Benefit obligation at beginning of year $ 199,637 $ 163,876 $ 178,158 Interest cost 8,210 8,002 7,341 Actuarial (gain) loss (6,489 ) 34,438 (15,333 ) Benefits paid (7,218 ) (6,679 ) (6,290 ) Benefit obligation at end of year 194,140 199,637 163,876 Change in plan assets: Fair value of plan assets at beginning of year 168,185 164,769 145,901 Actual return on plan assets 1,567 9,428 24,489 Employer contributions 736 667 669 Benefits paid (7,218 ) (6,679 ) (6,290 ) Fair value of plan assets at end of year 163,270 168,185 164,769 Funded status of the plan at end of year and accrued (benefit) liability recognized $ 30,870 $ 31,452 $ (893 ) Accumulated benefit obligation at end of year $ 194,140 $ 199,637 $ 163,876
Disaggregated Information Related to Corporations Defined Benefit Pension Plans	Certain disaggregated information related to our defined benefit pension plans as of year-end was as follows: Retirement Plan Restoration Plan 2015 2014 2015 2014 Projected benefit obligation $ 174,429 $ 179,970 $ 19,711 $ 19,667 Accumulated benefit obligation 174,429 179,970 19,711 19,667 Fair value of plan assets 163,270 168,185 — — Funded status of the plan at end of year and accrued (benefit) liability recognized 11,159 11,785 19,711 19,667
Net Periodic Benefit Cost (Benefit)	The components of the combined net periodic cost (benefit) for our defined benefit pension plans were as follows: 2015 2014 2013 Expected return on plan assets, net of expenses $ (11,932 ) $ (12,514 ) $ (11,087 ) Interest cost on projected benefit obligation 8,210 8,002 7,341 Net amortization and deferral 6,995 2,687 6,558 Net periodic expense (benefit) $ 3,273 $ (1,825 ) $ 2,812
Defined Benefit Pension Plans Recognized as Component of Other Comprehensive Income	Amounts related to our defined benefit pension plans recognized as a component of other comprehensive income were as follows: 2015 2014 2013 Net actuarial gain (loss) $ 3,118 $ (34,837 ) $ 35,293 Deferred tax (expense) benefit (1,091 ) 12,193 (12,353 ) Other comprehensive income (loss), net of tax $ 2,027 $ (22,644 ) $ 22,940
Defined Benefit Pension Plans Not Recognized as Component of Combined Net Period Benefit Cost	expect to recognize approximately $6.2 million of the net actuarial loss reported in the following table as of December 31, 2015 as a component of net periodic benefit cost during 2016 . 2015 2014 Net actuarial loss $ (71,920 ) $ (75,038 ) Deferred tax benefit 25,172 26,263 Amounts included in accumulated other comprehensive loss, net of tax $ (46,748 ) $ (48,775 )
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. 2015 2014 2013 Benefit obligations: Discount rate 4.55 % 4.20 % 5.00 % Net periodic benefit cost: Discount rate 4.20 % 5.00 % 4.20 % Expected return on plan assets 7.25 7.25 7.75
Fair Value of Plan Assets	The major categories of assets in our 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). Our Restoration Plan is unfunded. 2015 2014 Level 1: Mutual funds $ 162,379 $ 165,429 Cash and cash equivalents 322 1,447 Level 2: Corporate bonds and notes — 653 U.S. government agency securities 316 394 States and political subdivisions 253 262 Total fair value of plan assets $ 163,270 $ 168,185
Expected Future Benefit Payments Related to Defined Benefit Plans	As of December 31, 2015 , expected future benefit payments related to our defined benefit plans were as follows: 2016 $ 12,729 2017 9,421 2018 9,911 2019 10,365 2020 10,816 2021 through 2025 58,848 $ 112,090
Summary of Activity in Corporation's Active Stock Plans	A combined summary of activity in our active stock plans is presented in the following table. Director Deferred Stock Units Outstanding Non-Vested Stock Awards/Stock Units Outstanding Stock Options Outstanding Available for Grant Number of Units Weighted- Average Grant-Date Fair Value Number of Shares/Units Weighted- Average Grant-Date Fair Value Number of Shares Weighted- Average Exercise Price Balance at January 1, 2013 1,188,963 27,724 55.46 188,560 $ 51.67 5,513,516 $ 51.94 Authorized 2,293,660 — — — — — — Granted (635,360 ) 5,500 60.07 38,010 71.39 591,850 71.38 Stock options exercised — — — — — (1,319,786 ) 52.02 Stock awards/units vested — — — (26,830 ) 50.64 — — Forfeited/expired 46,890 — — — — (46,890 ) 46.05 Balance at December 31, 2013 2,894,153 33,224 56.22 199,740 55.32 4,738,690 54.35 Authorized — — — — — — — Granted (955,443 ) 5,643 78.04 32,050 78.92 917,750 78.93 Stock options exercised — — — — — (560,291 ) 52.04 Stock awards/units vested — — — (56,300 ) 52.46 — — Forfeited/expired 66,267 — — — — (66,267 ) 62.21 Balance at December 31, 2014 2,004,977 38,867 59.39 175,490 60.55 5,029,882 58.99 Authorized 515,000 — — — — — — Granted (951,506 ) 6,576 72.94 53,990 65.11 890,940 65.11 Stock options exercised — — — — — (287,326 ) 51.70 Stock awards/units vested — — — (56,300 ) 48.00 — — Forfeited/expired 21,256 — — — — (21,256 ) 66.72 Balance at December 31, 2015 1,589,727 45,443 61.35 173,180 $ 66.05 5,612,240 $ 60.30
Options Outstanding and Exercisable	Other information regarding options outstanding and exercisable as of December 31, 2015 is as follows: Options Outstanding Options Exercisable Range of Exercise Prices Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life in Years Number of Shares Weighted- Average Exercise Price $ 45.01 to $ 50.00 898,753 $ 48.27 4.53 898,753 $ 48.27 50.01 to 55.00 2,065,524 52.74 4.78 1,885,777 52.58 55.01 to 60.00 296,150 57.63 0.89 296,150 57.63 65.01 to 70.00 890,940 65.11 9.83 — — 70.01 to 75.00 566,123 71.38 7.77 280,988 71.38 75.01 to 80.00 894,750 78.94 8.74 223,689 78.94 Total 5,612,240 60.30 6.27 3,585,357 55.03
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: 2015 2014 2013 New shares issued from available authorized shares — — 153,275 Issued from available treasury stock 337,056 601,851 1,179,551 Total 337,056 601,851 1,332,826 Proceeds from stock option exercises $ 14,853 $ 29,158 $ 68,653 Intrinsic value of stock options exercised 5,766 13,714 20,506 Fair value of stock awards/units vested 3,728 4,346 1,918
Stock-Based Compensation Expense	Stock-based compensation expense and the related income tax benefit was as follows: 2015 2014 2013 Stock options $ 9,660 $ 9,142 $ 8,814 Non-vested stock awards/stock units 2,597 2,920 2,819 Deferred stock-units 480 441 330 Total $ 12,737 $ 12,503 $ 11,963 Income tax benefit $ 4,458 $ 4,376 $ 4,187
Unrecognized Stock-Based Compensation Expense	Unrecognized stock-based compensation expense at December 31, 2015 was as follows: Stock options $ 21,245 Non-vested stock awards/stock units 3,355 Total $ 24,600
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. 2015 2014 2013 Weighted-average risk-free interest rate 2.05 % 2.33 % 2.65 % Dividend yield 3.02 2.71 2.92 Weighted-average expected market price volatility 26.48 26.66 24.20 Weighted-average expected term 5.7 years 7.1 years 6.7 years

Other Non-Interest Income and41

Other Non-Interest Income and Expense (Tables)	12 Months Ended
	Dec. 31, 2015
Other Income and Expenses [Abstract]
Other Non-Interest Income and Expense	2015 2014 2013 Other non-interest income: Other $ 35,656 $ 32,256 $ 34,531 Total $ 35,656 $ 32,256 $ 34,531 Other non-interest expense: Advertising, promotions and public relations $ 28,858 $ 28,998 $ 26,232 Professional services 26,283 27,365 26,132 Travel/meals and entertainment 15,346 14,813 13,571 Check card expense 13,008 11,923 9,384 Other 82,066 84,557 76,758 Total $ 165,561 $ 167,656 $ 152,077

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Tax Expense	Income tax expense was as follows: 2015 2014 2013 Current income tax expense $ 59,530 $ 62,177 $ 49,736 Deferred income tax expense (benefit) (19,059 ) (4,130 ) 3,279 Income tax expense, as reported $ 40,471 $ 58,047 $ 53,015
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: 2015 2014 2013 Income tax expense computed at the statutory rate $ 111,930 $ 117,608 $ 101,808 Effect of tax-exempt interest (70,889 ) (58,761 ) (46,535 ) Bank owned life insurance income (1,255 ) (1,116 ) (1,086 ) Other 685 316 (1,172 ) Income tax expense, as reported $ 40,471 $ 58,047 $ 53,015
Schedule of Deferred Tax Assets and Liabilities	Year-end deferred taxes were as follows: 2015 2014 Deferred tax assets: Allowance for loan losses $ 47,551 $ 34,840 Net actuarial loss on defined benefit post-retirement benefit plans 25,172 26,263 Stock-based compensation 21,246 18,839 Alternative minimum tax carryforward 10,934 — Bonus accrual 5,832 6,118 Gain on sale of assets 2,044 2,139 Transaction costs 1,716 1,794 Partnerships 1,271 1,911 Other 4,447 5,272 Total gross deferred tax assets 120,213 97,176 Deferred tax liabilities: Net unrealized gain on securities available for sale and effective cash flow hedging derivatives (86,484 ) (102,626 ) Premises and equipment (23,038 ) (20,039 ) Defined benefit post-retirement benefit plans (14,089 ) (15,010 ) Intangible assets (8,940 ) (6,143 ) Leases (4,491 ) (4,952 ) Section 481(a) change in accounting method (tangible property) (3,387 ) — Prepaid expenses (1,702 ) (1,639 ) Reserve for medical insurance (211 ) (3,017 ) Other (352 ) (341 ) Total gross deferred tax liabilities (142,694 ) (153,767 ) Net deferred tax asset (liability) $ (22,481 ) $ (56,591 )

Other Comprehensive Income (L43

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2015
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 Amount Tax Expense, (Benefit) Net of Tax Amount 2015 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ (12,450 ) $ (4,358 ) $ (8,092 ) Change in net unrealized gain on securities transferred to held to maturity (33,601 ) (11,760 ) (21,841 ) Reclassification adjustment for net (gains) losses included in net income (69 ) (24 ) (45 ) Total securities available for sale and transferred securities (46,120 ) (16,142 ) (29,978 ) Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss 3,118 1,091 2,027 Total other comprehensive income (loss) $ (43,002 ) $ (15,051 ) $ (27,951 ) 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 )
Schedule of Accumulated Other Comprehensive Income, Net of Tax	Activity in accumulated other comprehensive income, net of tax, was as follows: Securities Available For Sale Defined Benefit Plans Derivatives Accumulated Other Comprehensive Income Balance January 1, 2015 $ 190,589 $ (48,775 ) $ — $ 141,814 Other comprehensive income (loss) before reclassification (29,933 ) 2,027 — (27,906 ) Amounts reclassified from accumulated other comprehensive income (loss) (45 ) — — (45 ) Net other comprehensive income (loss) during period (29,978 ) 2,027 — (27,951 ) Balance December 31, 2015 $ 160,611 $ (46,748 ) $ — $ 113,863 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

Derivative Financial Instrume44

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
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, 2015 and 2014 are presented in the following table. We obtain dealer quotations to value our 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, 2015 December 31, 2014 Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Derivatives designated as hedges of fair value: Financial institution counterparties: Loan/lease interest rate swaps - assets $ 49,927 $ 358 $ 31,614 $ 469 Loan/lease interest rate swaps - liabilities 31,038 (2,301 ) 37,672 (3,179 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps - assets 62,887 278 69,842 719 Loan/lease interest rate swaps - liabilities 768,182 (37,522 ) 765,979 (38,952 ) Loan/lease interest rate caps - assets 74,281 682 73,058 1,003 Customer counterparties: Loan/lease interest rate swaps - assets 780,082 37,630 765,979 38,910 Loan/lease interest rate swaps - liabilities 50,987 (188 ) 69,842 (719 ) Loan/lease interest rate caps - liabilities 74,281 (682 ) 73,058 (1,003 )
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, 2015 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.36 % 0.37 % Non-hedging interest rate swaps - financial institution counterparties 4.14 2.01 Non-hedging interest rate swap - customer counterparties 2.01 4.14
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. We obtain dealer quotations and use internal valuation models with observable market data inputs to value our commodity derivative positions. December 31, 2015 December 31, 2014 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil - assets Barrels 1,184 $ 12,650 470 $ 14,357 Oil - liabilities Barrels 45 (352 ) 197 (1,670 ) Natural gas - assets MMBTUs 760 560 12,235 12,707 Natural gas - liabilities MMBTUs — — 16,755 (4,095 ) Customer counterparties: Oil - assets Barrels 45 354 197 1,670 Oil - liabilities Barrels 1,184 (12,454 ) 470 (14,318 ) Natural gas - assets MMBTUs — — 16,755 4,095 Natural gas - liabilities MMBTUs 760 (549 ) 12,235 (12,646 )
Schedule of Foreign Exchange Contracts, Statement of Financial Position	The notional amounts and fair values of open foreign currency forward contracts were as follows: December 31, 2015 December 31, 2014 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts - assets EUR 1,247 $ 13 936 $ 7 Forward contracts - assets CAD — — 24,724 659 Forward contracts - assets GBP 568 2 — — Forward contracts - liabilities EUR 572 (18 ) — — Forward contracts - liabilities CAD 1,440 (5 ) — — Forward contracts - liabilities GBP — — 544 (2 ) Customer counterparties: Forward contracts - assets EUR 575 22 — — Forward contracts - assets CAD 1,437 9 — — Forward contracts - liabilities EUR 343 (5 ) — — Forward contracts - liabilities CAD — — 24,680 (615 )
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: 2015 2014 2013 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ (1,796 ) $ (2,014 ) $ (2,437 ) Amount of (gain) loss included in other non-interest expense 11 3 4
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: 2015 2014 2013 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 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 Amount of gain (loss) recognized in other comprehensive income — — (49 )
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. 2015 2014 2013 Non-hedging interest rate derivatives: Other non-interest income $ 2,580 $ 1,786 $ 1,441 Other non-interest expense (43 ) (2 ) (96 ) Non-hedging commodity derivatives: Other non-interest income 208 118 496 Non-hedging foreign currency derivatives: Other non-interest income 78 162 175

Balance Sheet Offsetting Balanc

Balance Sheet Offsetting Balance Sheet Offsetting (Tables)	12 Months Ended
	Dec. 31, 2015
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. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2014 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 Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2015 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2015 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 1,318 $ — $ 1,318 Commodity swaps and options 13,210 — 13,210 Foreign currency forward contracts 15 — 15 Total derivatives 14,543 — 14,543 Resell agreements 13,442 — 13,442 Total $ 27,985 $ — $ 27,985 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 39,823 $ — $ 39,823 Commodity swaps and options 352 — 352 Foreign currency forward contracts 23 — 23 Total derivatives 40,198 — 40,198 Repurchase agreements 883,947 — 883,947 Total $ 924,145 $ — $ 924,145
Financial Instruments Derivative Assets Liabilities And Resell Agreements Net Of Amount Not Offset	Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2015 Financial assets: Derivatives: Counterparty A $ 743 $ (743 ) $ — $ — Counterparty B 6,901 (5,795 ) (413 ) 693 Counterparty C 6,059 (3,447 ) (2,312 ) 300 Other counterparties 840 (840 ) — — Total derivatives 14,543 (10,825 ) (2,725 ) 993 Resell agreements 13,442 — (13,442 ) — Total $ 27,985 $ (10,825 ) $ (16,167 ) $ 993 Financial liabilities: Derivatives: Counterparty A $ 16,092 $ (743 ) $ (15,347 ) $ 2 Counterparty B 5,795 (5,795 ) — — Counterparty C 3,447 (3,447 ) — — Other counterparties 14,864 (840 ) (13,456 ) 568 Total derivatives 40,198 (10,825 ) (28,803 ) 570 Repurchase agreements 883,947 — (883,947 ) — Total $ 924,145 $ (10,825 ) $ (912,750 ) $ 570 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2014 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
Remaining Contractual Maturity of the Securities Sold Under Agreement	The remaining contractual maturity of repurchase agreements in the consolidated balance sheets as of December 31, 2015 and December 31, 2014 is presented in the following tables. Remaining Contractual Maturity of the Agreements Overnight and Continuous Up to 30 Days 30-90 Days Greater than 90 Days Total December 31, 2015 Repurchase agreements: U.S. Treasury $ 664,419 $ — $ — $ — $ 664,419 Residential mortgage-backed securities 211,501 — 8,027 — 219,528 Total borrowings $ 875,920 $ — $ 8,027 $ — $ 883,947 Gross amount of recognized liabilities for repurchase agreements $ 883,947 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2014 Repurchase agreements: U.S. Treasury $ 427,402 $ — $ — $ — $ 427,402 Residential mortgage-backed securities 355,187 — 8,530 — 363,717 Total borrowings $ 782,589 $ — $ 8,530 $ — $ 791,119 Gross amount of recognized liabilities for repurchase agreements $ 791,119 Amounts related to agreements not included in offsetting disclosures above $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
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, 2015 and 2014 , segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value: Level 1 Inputs Level 2 Inputs Level 3 Inputs Total Fair Value 2015 Securities available for sale: U.S. Treasury $ 3,994,520 $ — $ — $ 3,994,520 Residential mortgage-backed securities — 1,041,432 — 1,041,432 States and political subdivisions — 4,127,959 — 4,127,959 Other — 42,447 — 42,447 Trading account securities: U.S. Treasury 16,443 — — 16,443 States and political subdivisions — 136 — 136 Derivative assets: Interest rate swaps, caps and floors — 38,948 — 38,948 Commodity swaps and options — 13,564 — 13,564 Foreign currency forward contracts 46 — — 46 Derivative liabilities: Interest rate swaps, caps and floors — 40,693 — 40,693 Commodity swaps and options — 13,355 — 13,355 Foreign currency forward contracts 28 — — 28 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
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: 2015 2014 2013 Level 2 Level 3 Level 2 Level 3 Level 2 Level 3 Carrying value of impaired loans before allocations $ — $ 14,921 $ — $ 2,715 $ 9,374 $ — Specific valuation allowance allocations — (2,765 ) — (1,475 ) (2,785 ) — Fair value $ — $ 12,156 $ — $ 1,240 $ 6,589 $ —
Foreclosed Assets Remeasured and Reported at Fair Value	The following table presents foreclosed assets that were remeasured and reported at fair value: 2015 2014 2013 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 1,102 $ 6,388 $ 7,580 Charge-offs recognized in the allowance for loan losses (169 ) (285 ) (710 ) Fair value $ 933 $ 6,103 $ 6,870 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 205 $ 5,026 $ 4,979 Write-downs included in other non-interest expense (36 ) (1,289 ) (895 ) Fair value $ 169 $ 3,737 $ 4,084
Estimated Fair Values of Financial Instruments	The estimated fair values of financial instruments that are reported at amortized cost in our 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, 2015 December 31, 2014 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,591,523 $ 3,591,523 $ 4,364,123 $ 4,364,123 Securities held to maturity 2,663,009 2,710,685 2,926,486 2,966,390 Cash surrender value of life insurance policies 175,191 175,191 172,050 172,050 Accrued interest receivable 139,986 139,986 128,436 128,436 Level 3 inputs: Loans, net 11,350,672 11,396,158 10,887,993 10,939,684 Financial liabilities: Level 2 inputs: Deposits 24,343,595 24,344,007 24,135,930 24,136,402 Federal funds purchased and repurchase agreements 893,522 893,522 803,119 803,119 Junior subordinated deferrable interest debentures 137,115 137,115 137,115 137,115 Subordinated notes payable and other borrowings 100,000 99,000 100,000 95,591 Accrued interest payable 1,014 1,014 1,132 1,132

Operating Segments (Tables)

Operating Segments (Tables)	12 Months Ended
	Dec. 31, 2015
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 Wealth Advisors Non-Banks Consolidated 2015 Net interest income (expense) $ 732,671 $ 7,634 $ (3,673 ) $ 736,632 Provision for loan losses 51,848 (3 ) — 51,845 Non-interest income 205,606 121,489 1,635 328,730 Non-interest expense 589,394 98,405 5,919 693,718 Income (loss) before income taxes 297,035 30,721 (7,957 ) 319,799 Income tax expense (benefit) 34,997 10,753 (5,279 ) 40,471 Net income (loss) 262,038 19,968 (2,678 ) 279,328 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 262,038 $ 19,968 $ (10,741 ) $ 271,265 Revenues from (expenses to) external customers $ 938,277 $ 129,123 $ (2,038 ) $ 1,065,362 Average assets (in millions) (1) $ 28,024 $ 36 $ 2 $ 28,062 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 (1) Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.7 billion , $30.5 billion and $29.0 billion at December 31, 2015 , 2014 and 2013 .

Condensed Financial Statement48

Condensed Financial Statements of Parent Company (Tables)	12 Months Ended
	Dec. 31, 2015
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Schedule of Condensed Balance Sheets	Condensed Balance Sheets December 31, 2015 2014 Assets: Cash $ 6,434 $ 7,335 Resell agreements 200,100 286,660 Total cash and cash equivalents 206,534 293,995 Investment in subsidiaries 2,920,506 2,791,647 Accrued interest receivable and other assets 36,578 29,705 Total assets $ 3,163,618 $ 3,115,347 Liabilities: Junior subordinated deferrable interest debentures $ 137,115 $ 137,115 Subordinated notes payable 100,000 100,000 Accrued interest payable and other liabilities 36,160 26,829 Total liabilities 273,275 263,944 Shareholders’ Equity 2,890,343 2,851,403 Total liabilities and shareholders’ equity $ 3,163,618 $ 3,115,347
Schedule of Condensed Statements of Income	Condensed Statements of Income Year Ended December 31, 2015 2014 2013 Income: Dividend income paid by Frost Bank $ 126,375 $ 114,439 $ 144,642 Dividend income paid by non-banks 1,830 4,323 2,819 Interest and other income 82 69 79 Total income 128,287 118,831 147,540 Expenses: Interest expense 3,673 3,381 7,365 Salaries and employee benefits 1,376 1,218 1,175 Other 5,727 8,526 6,735 Total expenses 10,776 13,125 15,275 Income before income taxes and equity in undistributed earnings of subsidiaries 117,511 105,706 132,265 Income tax benefit 6,062 6,702 7,845 Equity in undistributed earnings of subsidiaries 155,755 165,569 97,756 Net income 279,328 277,977 237,866 Preferred stock dividends 8,063 8,063 6,719 Net income available to common shareholders $ 271,265 $ 269,914 $ 231,147
Schedule of Condensed Statements of Cash Flows	Condensed Statements of Cash Flows Year Ended December 31, 2015 2014 2013 Operating Activities: Net income $ 279,328 $ 277,977 $ 237,866 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed earnings of subsidiaries (155,755 ) (165,569 ) (97,756 ) Stock-based compensation 480 441 330 Excess tax benefits from stock-based compensation (161 ) (165 ) (155 ) Net change in other assets and other liabilities 2,621 (1,984 ) 2,372 Net cash from operating activities 126,513 110,700 142,657 Investing Activities: Redemption of investment in Frost Securities, Inc. 216 — — Net cash received in acquisitions — 830,661 — Capital contribution to subsidiaries — (879,730 ) — Net cash from investing activities 216 (49,069 ) — Financing Activities: Proceeds from stock option exercises 14,853 29,158 68,653 Proceeds from stock-based compensation activities of subsidiaries 12,257 12,062 11,633 Excess tax benefits from stock-based compensation 161 165 155 Proceeds from issuance of preferred stock — — 144,486 Purchase of treasury stock (101,237 ) (1,457 ) (144,630 ) Cash dividends paid on preferred stock (8,063 ) (8,063 ) (6,719 ) Cash dividends paid on common stock (132,161 ) (127,178 ) (119,619 ) Net cash from financing activities (214,190 ) (95,313 ) (46,041 ) Net change in cash and cash equivalents (87,461 ) (33,682 ) 96,616 Cash and cash equivalents at beginning of year 293,995 327,677 231,061 Cash and cash equivalents at end of year $ 206,534 $ 293,995 $ 327,677

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2015
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	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. Cash and cash equivalents $ 879,740 Securities available for sale 154,227 Loans 670,619 Premises and equipment 22,135 Core deposit intangible asset 9,300 Goodwill 118,019 Other assets 33,644 Deposits (1,624,043 ) Other borrowings (63,592 ) Other liabilities (1,251 ) $ 198,798

Summary of Significant Accoun50

Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash on hand or on deposit required	$ 188,900	$ 175,600
Cash collateral on deposit	16,900	12,100
Foreclosed Assets	$ 2,300	5,300
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%
WNB Bancshares, Inc. [Member] | Goodwill [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, Purchase Accounting Adjustments		718
WNB Bancshares, Inc. [Member] | Property, Plant and Equipment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill, Purchase Accounting Adjustments		$ (718)

Summary of Significant Accoun51

Summary of Significant Accounting Policies (Additional Cash Flow Information) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Cash paid for interest	$ 12,982	$ 14,705	$ 22,449
Cash paid for income tax	57,086	62,976	49,514
Unsettled purchases of securities	2,998	0	16,241
Loans foreclosed and transferred to other real estate owned and foreclosed assets	933	4,363	6,870
Premises and equipment transferred to other real estate owned and foreclosed assets	0	1,740	0
Loans to facilitate the sale of other real estate owned	20	102	678
Deferred gain on sale of building and parking garage	$ 0	$ 0	$ 768

Securities (Year End Securities

Securities (Year End Securities Held to Maturity and Available for Sale) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	$ 2,663,009	$ 2,926,486
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	53,842	48,939
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	6,166	9,035
Held to Maturity, Estimated Fair Value	2,710,685	2,966,390
Available for Sale, Amortized Cost	9,019,570	8,261,947
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	197,488	203,121
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	10,700	3,814
Available for Sale, Estimated Fair Value	9,206,358	8,461,254
US Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	249,441	249,009
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	7,776	14,604
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held to Maturity, Estimated Fair Value	257,217	263,613
Available for Sale, Amortized Cost	3,980,986	3,783,899
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	22,041	30,594
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	8,507	3,241
Available for Sale, Estimated Fair Value	3,994,520	3,811,252
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	6,456	8,012
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	63	92
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	4	0
Held to Maturity, Estimated Fair Value	6,515	8,104
Available for Sale, Amortized Cost	1,000,024	1,331,114
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	42,142	68,027
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	734	417
Available for Sale, Estimated Fair Value	1,041,432	1,398,724
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	2,405,762	2,668,115
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	46,003	34,243
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	6,149	9,035
Held to Maturity, Estimated Fair Value	2,445,616	2,693,323
Available for Sale, Amortized Cost	3,996,113	3,104,563
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	133,305	104,500
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,459	156
Available for Sale, Estimated Fair Value	4,127,959	3,208,907
Other [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,350	1,350
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	13	0
Held to Maturity, Estimated Fair Value	1,337	1,350
Available for Sale, Amortized Cost	42,447	42,371
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Available for Sale, Estimated Fair Value	$ 42,447	$ 42,371

Securities (Narrative) (Detail)

Securities (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	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	97.80%
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas guaranteed by Texas permanent school fund	62.40%
Securities pledged as collateral	$ 3,900,000	$ 3,000,000
Securities available for sale, at estimated fair value	9,206,358	8,461,254
Available for sale securities reclassified to held to maturity, unrealized gain			$ 165,700
Available for sale securities reclassified to held to maturity, unrealized gain net of tax			107,700
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, pre tax	60,300	93,900
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	39,200	$ 61,000
Other than temporary impairment, credit losses recognized in earnings, credit losses on debt securities held	$ 0
Reclassified To Held To Maturity [Member]
Schedule Of Marketable Securities [Line Items]
Securities available for sale, at estimated fair value			$ 2,300,000

Securities (Year End Securiti54

Securities (Year End Securities with Unrealized Losses Segregated by Length of Impairment) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	$ 149,091	$ 68,024
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,342	144
Held to Maturity, More than 12 Months, Estimated Fair Value	202,423	683,251
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,824	8,891
Held to Maturity, Total Estimated Fair Value	351,514	751,275
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	6,166	9,035
Available for Sale, Less than 12 Months, Estimated Fair Value	1,028,261	1,093,531
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,956	3,439
Available for Sale, More than 12 Months, Estimated Fair Value	36,266	16,944
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	744	375
Available for Sale, Total Estimated Fair Value	1,064,527	1,110,475
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	10,700	3,814
US Treasury Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Available for Sale, Less than 12 Months, Estimated Fair Value	886,087	1,019,230
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8,507	3,241
Available for Sale, More than 12 Months, Estimated Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available for Sale, Total Estimated Fair Value	886,087	1,019,230
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	8,507	3,241
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	900
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4
Held to Maturity, More than 12 Months, Estimated Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held to Maturity, Total Estimated Fair Value	900
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	4	0
Available for Sale, Less than 12 Months, Estimated Fair Value	21,392	8,550
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	212	42
Available for Sale, More than 12 Months, Estimated Fair Value	17,781	16,944
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	522	375
Available for Sale, Total Estimated Fair Value	39,173	25,494
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	734	417
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	146,854	68,024
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,325	144
Held to Maturity, More than 12 Months, Estimated Fair Value	202,423	683,251
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,824	8,891
Held to Maturity, Total Estimated Fair Value	349,277	751,275
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	6,149	9,035
Available for Sale, Less than 12 Months, Estimated Fair Value	120,782	65,751
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,237	156
Available for Sale, More than 12 Months, Estimated Fair Value	18,485	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	222	0
Available for Sale, Total Estimated Fair Value	139,267	65,751
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,459	156
Other Investments [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	1,337
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	13
Held to Maturity, More than 12 Months, Estimated Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held to Maturity, Total Estimated Fair Value	1,337
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	13	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0	$ 0

Securities (Amortized Cost and

Securities (Amortized Cost and Estimated Fair Value of Securities Excluding Trading Securities Presented by Contractual Maturity) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Due in one year or less, Amortized Cost	$ 161,934
Held to Maturity, Due after one year through five years, Amortized Cost	846,629
Held to Maturity, Due after five years through ten years, Amortized Cost	207,488
Held to Maturity, Due after ten years, Amortized Cost	1,440,502
Held to Maturity, Residential mortgage-backed securities, Amortized Cost	6,456
Held-to-maturity, Equity Securities, Amortized Cost	0
Held to Maturity, Amortized Cost	2,663,009	$ 2,926,486
Held to Maturity, Due in one year or less, Estimated Fair Value	163,320
Held to Maturity, Due after one year through five years, Estimated Fair Value	889,786
Held to Maturity, Due after five years through ten years, Estimated Fair Value	209,616
Held to Maturity, Due after ten years, Estimated Fair Value	1,441,448
Held to Maturity, Residential mortgage-backed securities, Estimated Fair Value	6,515
Held-to-maturity, Equity Securities, Estimated Fair Value	0
Held to Maturity, Estimated Fair Value	2,710,685	2,966,390
Available for Sale, Due in one year or less, Amortized Cost	793,662
Available for Sale, Due after one year through five years, Amortized Cost	2,961,224
Available for Sale, Due after five years through ten years, Amortized Cost	1,391,273
Available for Sale, Due after ten years, Amortized Cost	2,830,940
Available For Sale, Residential mortgage-backed securities, Amortized Cost	1,000,024
Available for Sale, Equity securities, Amortized Cost	42,447
Available for Sale, Amortized Cost	9,019,570	8,261,947
Available for Sale, Due in one year or less, Estimated Fair Value	796,452
Available for Sale, Due after one year through five years, Estimated Fair Value	2,976,538
Available for Sale, Due after five years through ten years, Estimated Fair Value	1,418,590
Available for Sale, Due after ten years, Estimated Fair Value	2,930,899
Available for Sale, Residential mortgage-backed securities, Estimated Fair Value	1,041,432
Available for Sale, Equity securities, Estimated Fair Value	42,447
Available for Sale, Estimated Fair Value	$ 9,206,358	$ 8,461,254

Securities (Sales of Securities

Securities (Sales of Securities Available for Sale) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 12,683,169	$ 12,151,287	$ 10,056,060
Gross realized gains	228	39	1,206
Gross realized losses	(159)	(1)	(30)
Tax (expense) benefit of securities gains/losses	$ (24)	$ (13)	$ (412)

Securities Securities - (Premiu

Securities Securities - (Premium Amortization and Discount Accretion Included in Income on Securities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Premium amortization	$ (84,467)	$ (68,070)	$ (49,112)
Discount accretion	10,682	6,802	7,191
Net (premium amortization) discount accretion	$ (73,785)	$ (61,268)	$ (41,921)

Securities (Year End Trading Ac

Securities (Year End Trading Account Securities at Estimated Fair Value) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$ 16,579	$ 15,426
US Treasury [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	16,443	15,339
States and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$ 136	$ 87

Securities (Net Gains and Losse

Securities (Net Gains and Losses on Trading Account Securities) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 1,109	$ 829	$ 878
Net mark-to-market gains (losses)	(53)	0	(429)
Net gain on trading account securities	$ 1,056	$ 829	$ 449

Loans (Narrative) (Detail)

Loans (Narrative) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)Item	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Nov. 30, 2015	Dec. 31, 2012USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration of loans in a single industry in excess of ten percent	0.00%	0.00%
Maximum percentage loan related to single industry	10.00%	10.00%
Commercial and industrial loans related to overdraft for correspondent bank customer	$ 7,300	$ 7,700
Minimum number of days to be considered past due	90 days
Troubled debt restructurings	$ 536	8,339	$ 11,215
Number of loans restructured during the last year in excess of 90 days past due | Item	1
Previously restructured loans past due	$ 259
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 709	$ 8,916	14,833
Number of days past due for payment of interest on loans, minimum	120 days
Texas Leading Index economic condition indicator		129.3		124.1
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000
General valuation allowance allocations for loan agreement monitoring exceptions	$ 135,859	$ 99,542	92,438		$ 104,453
Sensitivity stress test price shock	75.00%
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
General valuation allowance allocations for loan agreement monitoring exceptions	$ 24,313	$ 27,163	22,590		29,346
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans related to a single industry	15.30%	16.10%
Troubled debt restructurings	$ 0	$ 0	531
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	0	528
General valuation allowance allocations for loan agreement monitoring exceptions	54,696	14,919	6,090		7,579
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	536	8,300
Additional interest that would have been recognized on non-accrual loans, net of tax	1,600	1,500	2,200
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	536	5,391	4,937
Financing Receivables, Impaired, Troubled Debt Restructuring, Write-down	88	627
Financing Receivable, Modifications, Pre-Modification Recorded Investment	709	5,795	6,334
General valuation allowance allocations for loan agreement monitoring exceptions	$ 42,993	44,273	46,700		$ 46,585
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]
Number of days past due for payment of interest on loans, minimum	180 days
Commercial Real Estate Buildings Land And Other Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings	$ 0	2,948	5,747
Financing Receivable, Modifications, Pre-Modification Recorded Investment	0	3,121	$ 7,964
Previously Restructured Loans Moved to OREO		500
Amount charged off related to loans restructured		0
Credit And Collateral Exceptions [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
General valuation allowance allocations for loan agreement monitoring exceptions	0	2,200
Commercial Borrower [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment		2,900
Commercial Borrower [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 277	$ 2,700

Loans (Loans) (Detail)

Loans (Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 4,120,522	$ 4,055,225
Total energy	1,758,195	1,773,945
Commercial mortgages	3,285,041	2,999,082
Construction	720,695	624,888
Land	286,991	291,907
Total commercial real estate	4,292,727	3,915,877
Home equity loans	340,528	342,725
Home equity lines of credit	233,525	220,128
Other	306,696	286,198
Total consumer real estate	880,749	849,051
Total real estate	5,173,476	4,764,928
Consumer and Other	434,338	393,437
Total loans	11,486,531	10,987,535
Energy Production [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total energy	1,249,678	1,160,404
Energy Service [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total energy	272,934	319,618
Energy Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total energy	$ 235,583	$ 293,923

Loans (Activities in Related Pa

Loans (Activities in Related Party Loans) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Receivables [Abstract]
Balance outstanding at December 31, 2014	$ 38,700
Principal additions	230,806
Principal reductions	(200,867)
Other changes	16,127
Balance outstanding at December 31, 2015	$ 84,766

Loans (Non-Accrual Loans, Segre

Loans (Non-Accrual Loans, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 83,467	$ 59,925
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	25,111	34,108
Commercial and Industrial, Energy [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	21,180	636
Commercial Real Estate, Buildings, Land and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	34,519	19,639
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	569	2,792
Residential Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	1,862	2,212
Consumer Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 226	$ 538

Loans (Age Analysis of Past Due

Loans (Age Analysis of Past Due Loans, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 128,544
Current Loans	11,357,987
Total loans	11,486,531	$ 10,987,535
Accruing Loans 90 or More Days Past Due	8,108
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	48,445
Current Loans	4,072,077
Total loans	4,120,522
Accruing Loans 90 or More Days Past Due	4,091
Commercial and Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	18,967
Current Loans	1,739,228
Total loans	1,758,195
Accruing Loans 90 or More Days Past Due	580
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	48,397
Current Loans	3,523,635
Total loans	3,572,032
Accruing Loans 90 or More Days Past Due	1,642
Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,718
Current Loans	718,977
Total loans	720,695
Accruing Loans 90 or More Days Past Due	0
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	6,854
Current Loans	873,895
Total loans	880,749
Accruing Loans 90 or More Days Past Due	1,476
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,163
Current Loans	430,175
Total loans	434,338
Accruing Loans 90 or More Days Past Due	319
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	84,462
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	27,777
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial and Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,463
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	43,090
Financing Receivables, 30 to 89 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,149
Financing Receivables, 30 to 89 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,202
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,781
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	44,082
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	20,668
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial and Industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	15,504
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,307
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	569
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	1,652
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 382

Loans (Impaired Loans) (Detail)

Loans (Impaired Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 89,981	$ 69,656	$ 61,007
Recorded Investment With No Allowance	60,944	50,473	32,588
Recorded Investment With Allowance	16,534	3,118	15,874
Total Recorded Investment	77,478	53,591	48,462
Related Allowance	4,378	1,680	6,926
Average Recorded Investment	54,768	49,636	71,741
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	26,067	42,212	31,429
Recorded Investment With No Allowance	18,776	29,007	15,337
Recorded Investment With Allowance	4,084	2,853	7,004
Total Recorded Investment	22,860	31,860	22,341
Related Allowance	2,378	1,613	4,140
Average Recorded Investment	27,338	27,154	34,894
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	25,240	706	545
Recorded Investment With No Allowance	8,689	636	531
Recorded Investment With Allowance	12,450	0	0
Total Recorded Investment	21,139	636	531
Related Allowance	2,000	0	0
Average Recorded Investment	7,235	571	428
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	37,126	22,919	27,792
Recorded Investment With No Allowance	32,425	17,441	15,697
Recorded Investment With Allowance	0	265	8,870
Total Recorded Investment	32,425	17,706	24,567
Related Allowance	0	67	2,786
Average Recorded Investment	18,211	20,339	34,633
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	793	3,007	0
Recorded Investment With No Allowance	569	2,793	0
Recorded Investment With Allowance	0	0	0
Total Recorded Investment	569	2,793	0
Related Allowance	0	0	0
Average Recorded Investment	1,320	739	634
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	755	812	907
Recorded Investment With No Allowance	485	596	745
Recorded Investment With Allowance	0	0	0
Total Recorded Investment	485	596	745
Related Allowance	0	0	0
Average Recorded Investment	664	674	804
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	0	334
Recorded Investment With No Allowance	0	0	278
Recorded Investment With Allowance	0	0	0
Total Recorded Investment	0	0	278
Related Allowance	0	0	0
Average Recorded Investment	$ 0	$ 159	$ 348

Loans (Troubled Debt Restructur

Loans (Troubled Debt Restructurings) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Modifications [Line Items]
Balance at Restructure	$ 709	$ 8,916	$ 14,833
Balance at Year-end	536	8,339	11,215
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	709	5,795	6,334
Balance at Year-end	536	5,391	4,937
Commercial and Industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	0	528
Balance at Year-end	0	0	531
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	3,121	7,964
Balance at Year-end	0	2,948	5,747
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	0	7
Balance at Year-end	$ 0	$ 0	$ 0

Loans (Weighted Average Risk Gr

Loans (Weighted Average Risk Grades for All Commercial Loans b Class) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)Grade	Dec. 31, 2014USD ($)Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans | $	$ 4,292,727	$ 3,915,877
Loans | $	$ 720,695	$ 624,888
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.13	6.16
Loans | $	$ 4,120,522	$ 4,055,225
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.89	5.45
Loans | $	$ 1,758,195	$ 1,773,945
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.85	6.76
Loans | $	$ 3,572,032	$ 3,290,989
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.01	6.97
Loans | $	$ 720,695	$ 624,888
Risk Grade One To Eight [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	5.88	5.93
Loans | $	$ 3,869,203	$ 3,846,598
Risk Grade One To Eight [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.12	5.37
Loans | $	$ 1,385,749	$ 1,740,455
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 | Grade	6.58	6.53
Loans | $	$ 3,280,435	$ 3,067,219
Risk Grade One To Eight [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.91	6.91
Loans | $	$ 696,229	$ 612,705
Risk Grade Nine [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans | $	$ 100,670	$ 65,166
Risk Grade Nine [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans | $	$ 212,250	$ 27,313
Risk Grade Nine [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans | $	$ 140,900	$ 72,906
Risk Grade Nine [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans | $	$ 13,074	$ 8,003
Risk Grade Ten [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans | $	$ 76,030	$ 54,519
Risk Grade Ten [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans | $	$ 62,163	$ 161
Risk Grade Ten [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans | $	$ 72,577	$ 87,889
Risk Grade Ten [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans | $	$ 2,757	$ 1,323
Risk Grade Eleven [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans | $	$ 49,508	$ 55,034
Risk Grade Eleven [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans | $	$ 76,853	$ 5,380
Risk Grade Eleven [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans | $	$ 43,601	$ 43,336
Risk Grade Eleven [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans | $	$ 8,066	$ 64
Risk Grade Twelve [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans | $	$ 22,644	$ 31,683
Risk Grade Twelve [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans | $	$ 19,180	$ 636
Risk Grade Twelve [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans | $	$ 34,519	$ 19,501
Risk Grade Twelve [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans | $	$ 569	$ 2,793
Risk Grade Thirteen [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans | $	$ 2,467	$ 2,225
Risk Grade Thirteen [Member] | Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans | $	$ 2,000	$ 0
Risk Grade Thirteen [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans | $	$ 0	$ 138
Risk Grade Thirteen [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans | $	$ 0	$ 0
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	1	1
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	8	8

Loans (Net (Charge-Offs)_Recove

Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (15,528)	$ (9,210)	$ (32,597)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(6,535)	(2,911)	(28,431)
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(5,997)	(1,237)	(913)
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	314	(2,348)	(381)
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	18	348	256
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(91)	(733)	(719)
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (3,237)	$ (2,329)	$ (2,409)

Loans (Unallocated Portion of A

Loans (Unallocated Portion of Allowance for Loan Losses) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 135,859	$ 99,542	$ 92,438	$ 104,453
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	77,089	59,604
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,378	1,680
General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	12,603	8,619
Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	41,789	29,639
Commercial Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	42,993	44,273	46,700	46,585
Commercial Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	25,428	25,249
Commercial Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,378	1,613
Commercial Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,339	5,354
Commercial Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,848	12,057
Commercial And Industrial Energy Financing Receivable [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	54,696	14,919	6,090	7,579
Commercial And Industrial Energy Financing Receivable [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	21,195	7,172
Commercial And Industrial Energy Financing Receivable [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,000	0
Commercial And Industrial Energy Financing Receivable [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,525	2,232
Commercial And Industrial Energy Financing Receivable [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	25,976	5,515
Commercial Real Estate Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	24,313	27,163	22,590	29,346
Commercial Real Estate Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	15,544	14,684
Commercial Real Estate Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	67
Commercial Real Estate Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,619	5,324
Commercial Real Estate Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,150	7,088
Residential Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,659	5,178	5,230	5,252
Residential Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,109	2,017
Residential Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	0
Residential Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,052	1,972
Residential Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	498	1,189
Consumer Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	9,198	8,009	$ 5,010	$ 3,507
Consumer Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	12,813	10,482
Consumer Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	0
Consumer Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(6,932)	(6,263)
Consumer Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 3,317	$ 3,790

Loans (Activity in Allowance fo

Loans (Activity in Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 99,542	$ 92,438	$ 104,453
Provision for loan losses	51,845	16,314	20,582
Charge-offs	(29,572)	(28,485)	(44,797)
Recoveries	14,044	19,275	12,200
Net charge-offs	(15,528)	(9,210)	(32,597)
Ending balance	135,859	99,542	92,438
Individually evaluated for impairment	4,378	1,680	6,926
Collectively evaluated for impairment	131,481	97,862	85,512
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	44,273	46,700	46,585
Provision for loan losses	5,255	484	28,546
Charge-offs	(11,092)	(12,073)	(32,008)
Recoveries	4,557	9,162	3,577
Net charge-offs	(6,535)	(2,911)	(28,431)
Ending balance	42,993	44,273	46,700
Individually evaluated for impairment	2,378	1,613	4,140
Collectively evaluated for impairment	40,615	42,660	42,560
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	14,919	6,090	7,579
Provision for loan losses	45,774	10,066	(576)
Charge-offs	(6,000)	(1,747)	(924)
Recoveries	3	510	11
Net charge-offs	(5,997)	(1,237)	(913)
Ending balance	54,696	14,919	6,090
Individually evaluated for impairment	2,000	67	0
Collectively evaluated for impairment	52,696	14,852	6,090
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	27,163	22,590	29,346
Provision for loan losses	(3,182)	6,573	(6,631)
Charge-offs	(657)	(3,800)	(1,329)
Recoveries	989	1,800	1,204
Net charge-offs	332	(2,000)	(125)
Ending balance	24,313	27,163	22,590
Individually evaluated for impairment	0	0	2,786
Collectively evaluated for impairment	24,313	27,163	19,804
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,178	5,230	5,252
Provision for loan losses	(428)	681	697
Charge-offs	(577)	(1,097)	(1,047)
Recoveries	486	364	328
Net charge-offs	(91)	(733)	(719)
Ending balance	4,659	5,178	5,230
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	4,659	5,178	5,230
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	8,009	5,010	3,507
Provision for loan losses	4,426	5,328	3,912
Charge-offs	(11,246)	(9,768)	(9,489)
Recoveries	8,009	7,439	7,080
Net charge-offs	(3,237)	(2,329)	(2,409)
Ending balance	9,198	8,009	5,010
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	9,198	8,009	5,010
Unallocated [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	0	6,818	12,184
Provision for loan losses	0	(6,818)	(5,366)
Charge-offs	0	0	0
Recoveries	0	0	0
Net charge-offs	0	0	0
Ending balance	0	0	6,818
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	$ 0	$ 0	$ 6,818

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 ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 4,120,522	$ 4,055,225
Energy	1,758,195	1,773,945
Commercial Real Estate	4,292,727	3,915,877
Consumer Real Estate	880,749	849,051
Consumer and Other	434,338	393,437
Total loans	11,486,531	10,987,535
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	22,860	31,860
Energy	21,139	636
Commercial Real Estate	32,994	20,499
Consumer Real Estate	485	596
Consumer and Other	0	0
Total loans	77,478	53,591
Loans Collectively Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	4,097,662	4,023,365
Energy	1,737,056	1,773,309
Commercial Real Estate	4,259,733	3,895,378
Consumer Real Estate	880,264	848,455
Consumer and Other	434,338	393,437
Total loans	$ 11,409,053	$ 10,933,944

Premises and Equipment (Premise

Premises and Equipment (Premises and Equipment) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Land	$ 111,925	$ 102,334
Buildings	365,051	240,430
Furniture and equipment	136,983	102,885
Leasehold improvements	64,446	60,902
Construction in progress	81,991	118,367
Premises and equipment, Gross	760,396	624,918
Less accumulated depreciation and amortization	(201,272)	(182,748)
Total premises and equipment, net	$ 559,124	$ 442,170

Premises and Equipment (Narrati

Premises and Equipment (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization of premises and equipment, year to date	$ 28.5	$ 23.5	$ 22.5

Goodwill and Other Intangible74

Goodwill and Other Intangible Assets (Schedule of Goodwill) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 654,668	$ 654,668

Goodwill and Other Intangible75

Goodwill and Other Intangible Assets (Schedule of Other Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 45,906	$ 50,762
Accumulated Amortization	(37,106)	(38,637)
Net Intangible Assets	8,800	12,125
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	39,410	44,266
Accumulated Amortization	(32,324)	(34,591)
Net Intangible Assets	7,086	9,675
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	5,771	5,771
Accumulated Amortization	(4,214)	(3,643)
Net Intangible Assets	1,557	2,128
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	725	725
Accumulated Amortization	(568)	(403)
Net Intangible Assets	$ 157	$ 322

Goodwill and Other Intangible76

Goodwill and Other Intangible Assets (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 30, 2014
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 654,668	$ 654,668
Amortization expense related to intangible assets	$ 3,325	$ 3,520	$ 3,141
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
WNB Bancshares, Inc. [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill				$ 118,019
Core deposit intangible asset				$ 9,300

Goodwill and Other Intangible77

Goodwill and Other Intangible Assets (Estimated Aggregate Future Amortization Expense for Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
2,016	$ 2,413
2,017	1,619
2,018	1,346
2,019	1,102
2,020	877
Thereafter	1,443
Net Intangible Assets	$ 8,800	$ 12,125

Deposits (Schedule of Deposits)

Deposits (Schedule of Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deposit [Line Items]
Non-interest-bearing demand deposits:	$ 10,270,233	$ 10,149,061
Total Interest-bearing deposits	14,073,362	13,986,869
Total deposits	24,343,595	24,135,930
Commercial And Individual [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	9,251,463	9,256,045
Correspondent Banks [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	378,930	429,000
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	5,149,905	4,743,963
Money market accounts	7,536,998	7,860,403
Time accounts of $100,000 or more	420,697	490,209
Time accounts under $100,000	405,726	454,220
Total private accounts	13,513,326	13,548,795
Public Funds [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	639,840	464,016
Savings and interest checking	420,324	326,090
Money market accounts	93,969	57,145
Time accounts of $100,000 or more	44,941	53,684
Time accounts under $100,000	802	1,155
Total public funds	$ 560,036	$ 438,074

Deposits (Additional Informatio

Deposits (Additional Information About Corporation's Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deposits [Abstract]
Deposits from the Certificate of Deposit Account Registry Service (CDARS)	$ 2,615	$ 22,229
Deposits from the Promontory Interfinancial Network Insured Cash Sweep Service (acquired in the acquisition of WNB)	7,440	148,665
Deposits from foreign sources (primarily Mexico)	747,008	744,295
Deposits not covered by deposit insurance	11,953,367	12,056,180
Deposits from certain directors, executive officers and their affiliates	$ 218,095	$ 176,821

Deposits (Scheduled Maturities

Deposits (Scheduled Maturities of Time Deposits) (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Deposits [Abstract]
2,016	$ 736,480
2,017	135,539
2,018	88
2,019	59
2,020	0
Time deposits, Total	$ 872,166

Deposits (Scheduled Maturitie81

Deposits (Scheduled Maturities of Time Deposits in Amounts of $100,000 or More) (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Deposits [Abstract]
Due within 3 months or less	$ 160,712
Due after 3 months and within 6 months	91,160
Due after 6 months and within 12 months	140,232
Due after 12 months	73,534
Time deposits, $100,000 or more, total	$ 465,638

Borrowed Funds (Narrative) (Det

Borrowed Funds (Narrative) (Detail)	1 Months Ended		12 Months Ended
	Oct. 31, 2008	Feb. 28, 2007USD ($)	Dec. 31, 2015USD ($)quarter	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2004USD ($)
Borrowed Funds [Line Items]
Federal funds purchased			$ 9,600,000	$ 12,000,000
Securities sold under agreements to repurchase			883,900,000	791,100,000
Junior subordinated deferrable interest debentures			137,115,000	$ 137,115,000
Common equity securities					$ 144,486,000
Proceeds from Issuance of Trust Preferred Securities			$ 133,000,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter			20
Trust II [Member]
Borrowed Funds [Line Items]
Maturity date						Mar. 1, 2034
Advances, variable-rate			1.96%	1.78%		1.55%
LIBOR plus margin						Three-month LIBOR plus a margin of 1.55%
Proceeds from Issuance of Trust Preferred Securities			$ 120,000,000	$ 120,000,000		$ 120,000,000
WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Maturity date						Jul. 23, 2034
Advances, variable-rate			2.67%	2.58%		2.35%
LIBOR plus margin						Three-month LIBOR plus a margin of 2.35%
Proceeds from Issuance of Trust Preferred Securities			$ 13,000,000	$ 13,000,000		$ 13,000,000
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		Feb. 15, 2017
Advances, variable-rate		0.53%	0.89%	0.76%
LIBOR plus margin		Three-month LIBOR plus a margin of 0.53%
Percentage of redemption price			100.00%
Unamortized debt issuance cost related to note			$ 130,000	$ 250,000
Junior Subordinated Deferrable Interest Debenture [Member] | Trust II [Member]
Borrowed Funds [Line Items]
Derivative, term of contract	5 years
Unamortized debt issuance cost related to note			1,000,000	1,100,000
Junior subordinated deferrable interest debentures			123,712,000	123,712,000		123,712,000
Common equity securities						3,712,000
Junior Subordinated Deferrable Interest Debenture [Member] | WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Junior subordinated deferrable interest debentures			$ 13,403,000	$ 13,403,000		13,403,000
Common equity securities						$ 403,000

Off-Balance-Sheet Arrangement83

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Financial Instruments With Off-Balance-Sheet Risk) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 279,147	$ 248,360
Deferred Standby Letter of Credit Fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	2,115	1,942
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 8,246,698	$ 7,955,779

Off-Balance Sheet Arrangements

Off-Balance Sheet Arrangements Commitments Guarantees and Contingencies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments And Guarantees [Line Items]
Credit card guarantees	$ 7,900	$ 8,900
Fully collateralized credit card guarantees	1,200	1,500
Rent expense for operating leases	30,600	28,200	$ 24,600
Aggregate future minimum rentals to be received under non-cancelable subleases greater than one year	588
Partnership Interest of a Director [Member]
Commitments And Guarantees [Line Items]
Rent expense for operating leases	$ 925	$ 925	$ 871

Off-Balance-Sheet Arrangement85

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Future Minimum Lease Payments Due Under Non-Cancelable Operating Leases) (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,016	$ 22,489
2,017	22,686
2,018	21,913
2,019	17,854
2,020	15,041
Thereafter	106,926
Future minimum lease payments due, total	$ 206,909

Capital and Regulatory Matter86

Capital and Regulatory Matters (Narrative) (Detail)	Feb. 15, 2016USD ($)	Jan. 01, 2016	Aug. 13, 2013shares	Feb. 15, 2013USD ($)$ / sharesshares	Feb. 12, 2013USD ($)shares	Dec. 31, 2015USD ($)quarter$ / sharesshares	Dec. 31, 2014USD ($)$ / sharesshares	Dec. 31, 2013USD ($)shares	Jan. 01, 2019	Apr. 30, 2015USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock						$ 144,500,000
Non-cumulative perpetual preferred stock, dividend rate percentage						5.375%
Trust preferred securities						$ 133,000,000
Corporation's aggregate subordinated notes						$ 137,115,000	$ 137,115,000
Preferred stock, shares issued | shares						6,000,000	6,000,000
Preferred stock, par value | $ / shares						$ 0.01	$ 0.01
Proceeds from issuance of preferred stock				$ 144,500,000		$ 0	$ 0	$ 144,486,000
Accelerated share repurchase authorized amount										$ 100,000,000
Stock repurchase program, period in force						2 years
Treasury stock, shares, acquired | shares						1,504,146	18,871	2,245,572
Treasury stock, value, acquired, cost method						$ (101,237,000)	$ (1,457,000)	$ (144,630,000)
Amount paid under accelerated share repurchase agreement					$ 144,000,000
Shares repurchased under accelerated share repurchase program | shares			331,671		1,905,077
Accelerated Share Repurchase Program Repurchase Share Percent					80.00%
Aggregate dividends available for payment without prior regulatory approval						$ 419,700,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter						20
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule									4.50%
Capital Conservation Buffer									2.50%
Minimum ratio of Tier 1 capital to risk-weighted assets									6.00%
Minimum ratio of Total capital to risk weighted assets									8.00%
Two Thousand And Nineteen [Member] | Scenario, Forecast [Member] | Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation									7.00%
Effective tier one capital ratio, upon full implementation									8.50%
Tier one risk based capital to risk weighted assets, ratio upon full implementation									10.50%
Minimum leverage ratio									4.00%
Two Thousand And Sixteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier one capital conservation buffer to risk weighted assets required under regulatory		0.625%
Tier one risk based capital conservation buffer initial requirements phasing duration		4 years
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock, dividend rate percentage				5.375%
Preferred stock, shares issued | shares				6,000,000
Series A Preferred Stock, Liquidation preference value				$ 150,000,000		$ 25	25
Preferred stock, par value | $ / shares				$ 0.01
Liquidation preference per share | $ / shares				$ 25
Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares						1,485,493
Treasury stock, value, acquired, cost method						$ (100,000,000)
Trust Preferred Securities Tier One Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities						33,300,000
Trust Preferred Securities Tier Two Capital Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities						99,800,000
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						$ 20,000,000	$ 40,000,000
Floating Rate Subordinated Notes [Member] | Two Thousand And Sixteen [Member] | Scenario, Forecast [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Permissible portion of subordinated note included in total capital	$ 0

Regulatory Matters (Actual and

Regulatory Matters (Actual and Required Capital Ratios) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Cullen/Frost [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one to risk-weighted assets, actual, capital amount	$ 1,986,200
Common equity tier one to risk-weighted assets, actual, ratio	11.37%
Common equity tier one to risk-weighted assets, minimum capital required basel III phase-in schedule, capital amount	$ 786,344
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	4.50%
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,222,837
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	7.00%
Common Equity Tier One Capital Required To Be Well Capitalized	$ 1,135,830
CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	6.50%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 2,419,545	$ 2,325,818
Total Capital to Risk-Weighted Assets, Actual, Ratio	13.85%	14.55%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,397,944
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	8.00%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,834,256
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	10.50%
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,278,797
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio		8.00%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,747,430	$ 1,598,496
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	$ 2,163,936	$ 2,186,276
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.38%	13.68%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,048,458
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	6.00%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,484,874
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	8.50%
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 639,398
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio		4.00%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,397,944	$ 959,098
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%	6.00%
Leverage Ratio, Actual, Capital Amount	$ 2,163,936	$ 2,186,276
Leverage Ratio, Actual, Ratio	7.79%	8.16%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,111,325
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Phase In Schedule	4.00%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,111,117
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Fully Phased In	4.00%
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,072,035
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Ratio		4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,389,156	$ 1,340,043
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]
Common equity tier one to risk-weighted assets, actual, capital amount	$ 2,131,360
Common equity tier one to risk-weighted assets, actual, ratio	12.24%
Common equity tier one to risk-weighted assets, minimum capital required basel III phase-in schedule, capital amount	$ 783,727
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	4.50%
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,218,766
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	7.00%
Common Equity Tier One Capital Required To Be Well Capitalized	$ 1,132,049
CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets	6.50%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 2,267,219	$ 2,071,012
Total Capital to Risk-Weighted Assets, Actual, Ratio	13.02%	12.99%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,393,292
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	8.00%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,828,149
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	10.50%
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,275,858
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio		8.00%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,741,615	$ 1,594,823
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	$ 2,131,360	$ 1,979,415
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.24%	12.41%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,044,969
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule	6.00%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,479,930
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In	8.50%
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 637,929
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes, Ratio		4.00%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,393,292	$ 956,894
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%	6.00%
Leverage Ratio, Actual, Capital Amount	$ 2,131,360	$ 1,979,415
Leverage Ratio, Actual, Ratio	7.68%	7.40%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule	$ 1,110,143
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Phase In Schedule	4.00%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In	$ 1,109,935
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Fully Phased In	4.00%
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Capital Amount		$ 1,070,109
Leverage Ratio, Minimum Required for Capital Adequacy Purposes, Ratio		4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,387,679	$ 1,337,636
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 ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 279,328	$ 277,977	$ 237,866
Less: Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	271,265	269,914	231,147
Less: Earnings allocated to participating securities	941	1,001	850
Distributed earnings allocated to common stock	131,702	126,709	119,177
Undistributed earnings allocated to common stock	138,622	142,204	111,120
Net earnings allocated to common stock	$ 270,324	$ 268,913	$ 230,297
Weighted-average shares outstanding for basic earnings per common share	62,758,074	62,072,080	60,350,552
Dilutive effect of stock compensation	715,250	901,448	765,858
Weighted-average shares outstanding for diluted earnings per common share	63,473,324	62,973,528	61,116,410

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expense related to benefit plans	$ 11,300	$ 10,800	$ 11,400
Net actuarial loss expected to be recognized	$ 6,200
Modeling process confidence ratio	90.00%
Percentage of equity investments in mutual fund	71.00%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.75%
Expected defined benefit plans contribution within a year	$ 4,900
Target percentage of pay at age 55	45.00%
Target percentage of pay at age 60	60.00%
Stock purchase plan expense	$ 9,660	$ 9,142	$ 8,814
Number of stock plans	3
Intrinsic value of outstanding in-the-money stock options	$ 26,200
Outstanding in-the-money exercisable stock options	$ 25,300
Weighted-average period, unrecognized expense related to stock options, years	2 years 11 months 6 days
Weighted-average period, unrecognized expense related to non-vested stock awards, years	2 years 11 months
Weighted-average fair value of stock options granted	$ 10.23	$ 16.97	$ 13.74
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	$ 13,300	$ 12,300	$ 11,500
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%
Two Thousand Fifteen Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years	10 years
Vesting period of options awarded, years	4 years
Two Thousand Fifteen 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
Cliff vesting period, years	4 years
Two Thousand Five Plan [Member] | Stock Options [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Life period of options awarded, years		10 years	10 years
Vesting period of options awarded, years		4 years	4 years
Two Thousand Five 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
Cliff vesting period, 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 ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Benefit obligation at beginning of year	$ 199,637	$ 163,876	$ 178,158
Interest cost	8,210	8,002	7,341
Actuarial (gain) loss	(6,489)	34,438	(15,333)
Benefits paid	(7,218)	(6,679)	(6,290)
Benefit obligation at end of year	194,140	199,637	163,876
Fair value of plan assets at beginning of year	168,185	164,769	145,901
Actual return on plan assets	1,567	9,428	24,489
Employer contributions	736	667	669
Benefits paid	(7,218)	(6,679)	(6,290)
Fair value of plan assets at end of year	163,270	168,185	164,769
Funded status of the plan at end of year and accrued (benefit) liability recognized	30,870	31,452	(893)
Accumulated benefit obligation at end of year	$ 194,140	$ 199,637	$ 163,876

Employee Benefit Plans (Disaggr

Employee Benefit Plans (Disaggregated Information Related to Corporations Defined Benefit Pension Plans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 194,140	$ 199,637	$ 163,876	$ 178,158
Accumulated benefit obligation	194,140	199,637	163,876
Fair value of plan assets	163,270	168,185	164,769	$ 145,901
Funded status of the plan at end of year and accrued (benefit) liability recognized	30,870	31,452	$ (893)
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	174,429	179,970
Accumulated benefit obligation	174,429	179,970
Fair value of plan assets	163,270	168,185
Funded status of the plan at end of year and accrued (benefit) liability recognized	11,159	11,785
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	19,711	19,667
Accumulated benefit obligation	19,711	19,667
Fair value of plan assets	0	0
Funded status of the plan at end of year and accrued (benefit) liability recognized	$ 19,711	$ 19,667

Employee Benefit Plans (Net Per

Employee Benefit Plans (Net Periodic Benefit Cost (Benefit)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	$ (11,932)	$ (12,514)	$ (11,087)
Interest cost on projected benefit obligation	8,210	8,002	7,341
Net amortization and deferral	6,995	2,687	6,558
Net periodic expense (benefit)	$ 3,273	$ (1,825)	$ 2,812

Employee Benefit Plans (Defined

Employee Benefit Plans (Defined Benefit Pension Plans Recognized as Component of Other Comprehensive Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$ 3,118	$ (34,837)	$ 35,293
Deferred tax (expense) benefit	(1,091)	12,193	(12,353)
Other comprehensive income (loss), net of tax	$ 2,027	$ (22,644)	$ 22,940

Employee Benefit Plans (Defin94

Employee Benefit Plans (Defined Benefit Pension Plans not Recognized as Component of Combined Net Period Benefit Cost) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (71,920)	$ (75,038)
Deferred tax benefit	25,172	26,263
Amounts included in accumulated other comprehensive loss, net of tax	$ (46,748)	$ (48,775)

Employee Benefit Plans (Weighte

Employee Benefit Plans (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Benefit obligations, Discount rate	4.55%	4.20%	5.00%
Net periodic benefit cost, Discount rate	4.20%	5.00%	4.20%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.75%

Employee Benefit Plans (Fair Va

Employee Benefit Plans (Fair Value of Plan Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 163,270	$ 168,185	$ 164,769	$ 145,901
Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	162,379	165,429
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	322	1,447
Corporate Bonds And Notes [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	653
US Government Agency Securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	316	394
States and Political Subdivisions [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 253	$ 262

Employee Benefit Plans (Expecte

Employee Benefit Plans (Expected Future Benefit Payments Related to Defined Benefit Plans) (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Compensation and Retirement Disclosure [Abstract]
2,016	$ 12,729
2,017	9,421
2,018	9,911
2,019	10,365
2,020	10,816
2021 through 2025	58,848
Total defined benefit plan expected future benefit payments	$ 112,090

Employee Benefit Plans (Summary

Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Shares Available for Grant	2,004,977	2,894,153	1,188,963
Authorized, shares available for grant	515,000	0	2,293,660
Granted, Shares Available for Grant	(951,506)	(955,443)	(635,360)
Forfeited, Shares Available for Grant	21,256	66,267	46,890
Ending Balance, Shares Available for Grant	1,589,727	2,004,977	2,894,153
Stock options exercised, Number of Shares	(321,266)	(594,231)	(1,319,786)
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 16.97	$ 13.74
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 10.23	$ 16.97	$ 13.74
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	38,867	33,224	27,724
Granted, number of shares	6,576	5,643	5,500
Ending Balance, Number of Shares	45,443	38,867	33,224
Beginning Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 59.39	$ 56.22	$ 55.46
Granted, Weighted-Average Grant-Date Fair Value	72.94	78.04	60.07
Ending Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.35	$ 59.39	$ 56.22
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	175,490	199,740	188,560
Granted, number of shares	53,990	32,050	38,010
Stock awards vested, Number of Shares	(56,300)	(56,300)	(26,830)
Ending Balance, Number of Shares	173,180	175,490	199,740
Beginning Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 60.55	$ 55.32	$ 51.67
Granted, Weighted-Average Grant-Date Fair Value	65.11	78.92	71.39
Stock awards vested, Weighted-Average Grant-Date Fair Value	48	52.46	50.64
Ending Balance, Non-Vested Weighted-Average Grant-Date Fair Value	$ 66.05	$ 60.55	$ 55.32
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	5,029,882	4,738,690	5,513,516
Granted, number of shares	890,940	917,750	591,850
Stock options exercised, Number of Shares	(287,326)	(560,291)	(1,319,786)
Forfeited, Number of Shares	(21,256)	(66,267)	(46,890)
Ending Balance, Number of Shares	5,612,240	5,029,882	4,738,690
Beginning Balance, Weighted-Average Exercise Price	$ 58.99	$ 54.35	$ 51.94
Granted, Weighted-Average Exercise Price	65.11	78.93	71.38
Stock options exercised, Weighted-Average Exercise Price	51.70	52.04	52.02
Forfeited, Weighted-Average Exercise Price	66.72	62.21	46.05
Ending Balance, Weighted-Average Exercise Price	$ 60.30	$ 58.99	$ 54.35

Employee Benefit Plans (Options

Employee Benefit Plans (Options Outstanding and Exercisable) (Detail)	12 Months Ended
	Dec. 31, 2015$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Weighted- Average Remaining Contractual Life in Years	2 years 11 months 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
65.01 - 70.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	65.01
Range of Exercise Prices, Maximum	70
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 | shares	5,612,240
Weighted-Average Exercise Price, Options Outstanding	$ 60.30
Weighted- Average Remaining Contractual Life in Years	6 years 3 months 7 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 | shares	898,753
Weighted-Average Exercise Price, Options Outstanding	$ 48.27
Weighted- Average Remaining Contractual Life in Years	4 years 6 months 11 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 | shares	2,065,524
Weighted-Average Exercise Price, Options Outstanding	$ 52.74
Weighted- Average Remaining Contractual Life in Years	4 years 9 months 11 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 | shares	296,150
Weighted-Average Exercise Price, Options Outstanding	$ 57.63
Weighted- Average Remaining Contractual Life in Years	10 months 21 days
Options Outstanding [Member] | 65.01 - 70.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	890,940
Weighted-Average Exercise Price, Options Outstanding	$ 65.11
Weighted- Average Remaining Contractual Life in Years	9 years 9 months 29 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 | shares	566,123
Weighted-Average Exercise Price, Options Outstanding	$ 71.38
Weighted- Average Remaining Contractual Life in Years	7 years 9 months 7 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 | shares	894,750
Weighted-Average Exercise Price, Options Outstanding	$ 78.94
Weighted- Average Remaining Contractual Life in Years	8 years 8 months 27 days
Options Exercisable [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	3,585,357
Weighted-Average Exercise Price, Options Exercisable	$ 55.03
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 | shares	898,753
Weighted-Average Exercise Price, Options Exercisable	$ 48.27
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 | shares	1,885,777
Weighted-Average Exercise Price, Options Exercisable	$ 52.58
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 | shares	296,150
Weighted-Average Exercise Price, Options Exercisable	$ 57.63
Options Exercisable [Member] | 65.01 - 70.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	0
Weighted-Average Exercise Price, Options Exercisable	$ 0
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 | shares	280,988
Weighted-Average Exercise Price, Options 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 | shares	223,689
Weighted-Average Exercise Price, Options Exercisable	$ 78.94

Employee Benefit Plans (Shares

Employee Benefit Plans (Shares Issued in Connection with Stock Compensation Awards) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
New shares issued from available authorized shares	0	0	153,275
Issued from available treasury stock	337,056	601,851	1,179,551
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	337,056	601,851	1,332,826
Proceeds from stock option exercises	$ 14,853	$ 29,158	$ 68,653
Intrinsic value of stock options exercised	5,766	13,714	20,506
Fair value of stock awards/units vested	$ 3,728	$ 4,346	$ 1,918

Employee Benefit Plans (Stock-B

Employee Benefit Plans (Stock-Based Compensation Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Stock options	$ 9,660	$ 9,142	$ 8,814
Non-vested stock awards/stock units	2,597	2,920	2,819
Deferred stock-units	480	441	330
Total	12,737	12,503	11,963
Income tax benefit	$ 4,458	$ 4,376	$ 4,187

Employee Benefit Plans (Unrecog

Employee Benefit Plans (Unrecognized Stock-Based Compensation Expense) (Detail) $ in Thousands	Dec. 31, 2015USD ($)
Compensation and Retirement Disclosure [Abstract]
Stock options	$ 21,245
Non-vested stock awards/stock units	3,355
Total	$ 24,600

Employee Benefit Plans (Assumpt

Employee Benefit Plans (Assumptions to Determine Fair Value of Options Granted) (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Weighted-average risk-free interest rate	2.05%	2.33%	2.65%
Dividend yield	3.02%	2.71%	2.92%
Weighted-average expected market price volatility	26.48%	26.66%	24.20%
Weighted-average expected term	5 years 8 months 12 days	7 years 1 month 6 days	6 years 8 months 12 days

Other Non-Interest Income an104

Other Non-Interest Income and Expense (Narrative) (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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 Non-Interest Income an105

Other Non-Interest Income and Expense (Other Non-Interest Income and Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Income and Expenses [Abstract]
Other	$ 35,656	$ 32,256	$ 34,531
Total other non-interest income	35,656	32,256	34,531
Advertising, promotions and public relations	28,858	28,998	26,232
Professional services	26,283	27,365	26,132
Travel/meals and entertainment	15,346	14,813	13,571
Check card expense	13,008	11,923	9,384
Other	82,066	84,557	76,758
Total other non-interest expense	$ 165,561	$ 167,656	$ 152,077

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
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 Expens

Income Taxes (Income Tax Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Current income tax expense	$ 59,530	$ 62,177	$ 49,736
Deferred income tax expense (benefit)	(19,059)	(4,130)	3,279
Income tax expense, as reported	$ 40,471	$ 58,047	$ 53,015

Income Taxes (Income Tax Comput

Income Taxes (Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income tax expense computed at the statutory rate	$ 111,930	$ 117,608	$ 101,808
Effect of tax-exempt interest	(70,889)	(58,761)	(46,535)
Bank owned life insurance income	(1,255)	(1,116)	(1,086)
Other	685	316	(1,172)
Income tax expense, as reported	$ 40,471	$ 58,047	$ 53,015

Income Taxes (Schedule of Defer

Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Allowance for loan losses	$ 47,551	$ 34,840
Net actuarial loss on defined benefit post-retirement benefit plans	25,172	26,263
Stock-based compensation	21,246	18,839
Alternative minimum tax carryforward	10,934	0
Bonus accrual	5,832	6,118
Gain on sale of assets	2,044	2,139
Transaction costs	1,716	1,794
Partnerships	1,271	1,911
Other	4,447	5,272
Total gross deferred tax assets	120,213	97,176
Net unrealized gain on securities available for sale and effective cash flow hedging derivatives	(86,484)	(102,626)
Premises and equipment	(23,038)	(20,039)
Defined benefit post-retirement benefit plans	(14,089)	(15,010)
Intangible assets	(8,940)	(6,143)
Leases	(4,491)	(4,952)
Section 481(a) change in accounting method (tangible property)	(3,387)	0
Prepaid expenses	(1,702)	(1,639)
Reserve for medical insurance	(211)	(3,017)
Other	(352)	(341)
Total gross deferred tax liabilities	(142,694)	(153,767)
Deferred Tax Liabilities, Net	$ (22,481)	$ (56,591)

Other Comprehensive Income (110

Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ (12,450)	$ 103,044	$ (115,245)
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(33,601)	(35,441)	(35,682)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	(69)	(38)	(1,176)
Total securities available for sale and transferred securities	(46,120)	67,565	(152,103)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	3,118	(34,837)	35,293
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	0	0	(49)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	0	(30,604)	(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	0	4,064
Total derivatives	0	(30,604)	(33,365)
Other comprehensive income (loss), before tax	(43,002)	2,124	(150,175)
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	(4,358)	36,065	(40,335)
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	(11,760)	(12,404)	(12,489)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	(24)	(13)	(412)
Total securities available for sale and transferred securities, Tax Expense (Benefit)	(16,142)	23,648	(53,236)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	1,091	(12,193)	12,353
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)			(17)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)		(10,711)	(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
Derivatives, Total derivatives, Tax Expense, (Benefit)			(11,678)
Total other comprehensive income, Tax Expense (Benefit)	(15,051)	744	(52,561)
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax	(8,092)	66,979	(74,910)
Securities available for sale and transferred securities. change in net unrealized gain on securities transfers to held-to-maturity, net of tax	(21,841)	(23,037)	(23,193)
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax	(45)	(25)	(764)
Total securities available for sale and transferred securities, net of tax	(29,978)	43,917	(98,867)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Net of Tax	2,027	(22,644)	22,940
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, net of tax			(32)
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swaps on variable-rate loans, net of tax		(19,893)	(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
Derivatives, Total derivatives, net of tax			(21,687)
Other comprehensive income (loss), net of tax	$ (27,951)	$ 1,380	$ (97,614)

Other Comprehensive Income (Sch

Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 141,814	$ 140,434	$ 238,048
Other comprehensive income (loss) before reclassification	(27,906)	21,298	(75,195)
Amounts reclassified from accumulated other comprehensive income (loss)	(45)	(19,918)	(22,419)
Net other comprehensive income (loss) during period	(27,951)	1,380	(97,614)
Ending Balance	113,863	141,814	140,434
Securities Available For Sale [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	190,589	146,672	245,539
Other comprehensive income (loss) before reclassification	(29,933)	43,942	(98,103)
Amounts reclassified from accumulated other comprehensive income (loss)	(45)	(25)	(764)
Net other comprehensive income (loss) during period	(29,978)	43,917	(98,867)
Ending Balance	160,611	190,589	146,672
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(48,775)	(26,131)	(49,071)
Other comprehensive income (loss) before reclassification	2,027	(22,644)	22,940
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Net other comprehensive income (loss) during period	2,027	(22,644)	22,940
Ending Balance	(46,748)	(48,775)	(26,131)
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	0	19,893	41,580
Other comprehensive income (loss) before reclassification	0	0	(32)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(19,893)	(21,655)
Net other comprehensive income (loss) during period	0	(19,893)	(21,687)
Ending Balance	$ 0	$ 0	$ 19,893

Derivative Financial Instrum112

Derivative Financial Instruments (Narrative) (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2007	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2008	Dec. 31, 2007
Derivative [Line Items]
Weighted-average strike rate for outstanding interest rate caps		2.42%
Approximate credit exposure related to swaps with bank customers		$ 37,700,000
Aggregate fair value of securities posted as collateral for derivative contracts		17,500,000
Cash collateral on deposit with other financial institutions		16,900,000	$ 12,100,000
Interest Rate Swaps With Upstream Financial Institution Counterparties [Member]
Derivative [Line Items]
Approximate credit exposure related to swaps with bank customers		6,700,000
Variable-Rate Loans Outstanding [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held						3
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%
Designated as Hedging Instrument [Member] | Interest Income [Member] | Variable-Rate Loans Outstanding [Member]
Derivative [Line Items]
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net		$ 0	$ 0	$ 0

Derivative Financial Instrum113

Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	$ 49,927	$ 31,614
Estimated Fair Value	358	469
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	31,038	37,672
Estimated Fair Value	(2,301)	(3,179)
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	62,887	69,842
Estimated Fair Value	278	719
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	768,182	765,979
Estimated Fair Value	(37,522)	(38,952)
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Caps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	74,281	73,058
Estimated Fair Value	682	1,003
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	780,082	765,979
Estimated Fair Value	37,630	38,910
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	50,987	69,842
Estimated Fair Value	(188)	(719)
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Caps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	74,281	73,058
Estimated Fair Value	$ (682)	$ (1,003)

Derivative Financial Instrum114

Derivative Financial Instruments (Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding) (Detail)	Dec. 31, 2015
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	2.36%
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	0.37%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	4.14%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	2.01%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	2.01%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swap - customer counterparties	4.14%

Derivative Financial Instrum115

Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions) (Detail) bbl in Thousands, MMBTU in Thousands, $ in Thousands	Dec. 31, 2015USD ($)MMBTUbbl	Dec. 31, 2014USD ($)MMBTUbbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	1,184	470
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 12,650	$ 14,357
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	45	197
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (352)	$ (1,670)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	760	12,235
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 560	$ 12,707
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	0	16,755
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ 0	$ (4,095)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	45	197
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 354	$ 1,670
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	1,184	470
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (12,454)	$ (14,318)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	0	16,755
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 0	$ 4,095
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	760	12,235
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (549)	$ (12,646)

Derivative Financial Instrum116

Derivative Financial Instruments Derivative Financial Instruments (Schedule of Notional Amount and Fair Value of Open Foreign Currency Forward Contract) (Details) € in Thousands, £ in Thousands, CAD in Thousands, $ in Thousands	Dec. 31, 2015USD ($)	Dec. 31, 2015CAD	Dec. 31, 2015EUR (€)	Dec. 31, 2015GBP (£)	Dec. 31, 2014USD ($)	Dec. 31, 2014CAD	Dec. 31, 2014EUR (€)	Dec. 31, 2014GBP (£)
Financial Institution Counterparties [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets, Notional Amount		CAD 0	€ 1,247	£ 568		CAD 24,724	€ 936	£ 0
Financial Institution Counterparties [Member] | Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts Liability, Notional Amount		1,440	572	£ 0		0	0	£ 544
Customer Counterparties [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets, Notional Amount		1,437	575			0	0
Customer Counterparties [Member] | Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts Liability, Notional Amount		CAD 0	€ 343			CAD 24,680	€ 0
Eurodollar Future [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	$ 13				$ 7
Forward Contracts, Liability Estimated Fair Value	(18)				0
Eurodollar Future [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	22				0
Forward Contracts, Liability Estimated Fair Value	(5)				0
Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	0				659
Forward Contracts, Liability Estimated Fair Value	(5)				0
Foreign Exchange Forward [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	9				0
Forward Contracts, Liability Estimated Fair Value	0				(615)
GBP Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	2				0
Forward Contracts, Liability Estimated Fair Value	$ 0				$ (2)

Derivative Financial Instrum117

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 ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest Income on Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount included in income or expense	$ (1,796)	$ (2,014)	$ (2,437)
Other Non-Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount included in income or expense	$ 11	$ 3	$ 4

Derivative Financial Instrum118

Derivative Financial Instruments (Schedule of Amounts Related to Interest Rate Derivatives Included in Income Designated as Hedges of Cash Flows) (Detail) - Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	$ 0	$ (49)
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	0	30,604	37,380
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	$ 0	$ 4,064

Derivative Financial Instrum119

Derivative Financial Instruments (Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives) (Detail) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest Rate Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount included in income or expense	$ 2,580	$ 1,786	$ 1,441
Interest Rate Contract [Member] | Other Non-Interest Expense [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount included in income or expense	(43)	(2)	(96)
Commodity Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount included in income or expense	208	118	496
Foreign Exchange Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount included in income or expense	$ 78	$ 162	$ 175

Balance Sheet Offsetting - Fina

Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	$ 14,543	$ 29,921
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	14,543	29,921
Gross Amount Recognized, Resell Agreements, Financial Assets	13,442	9,642
Gross Amount Offset, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Resell Agreements, Financial Assets	13,442	9,642
Gross Amount Recognized, Financial Assets	27,985	39,563
Gross Amount Offset, Financial Assets	0	0
Net Amount Recognized, Financial Assets	27,985	39,563
Gross Amount Recognized, Derivative, Financial Liabilities	40,198	47,898
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	40,198	47,898
Gross Amount Recognized, Repurchase Agreements, Financial Liabilities	883,947	791,119
Gross Amount Offset, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	883,947	791,119
Gross Amount Recognized, Financial Liabilities	924,145	839,017
Gross Amount Offset, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	924,145	839,017
Loan Lease Interest Rate Swaps And Caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	1,318	2,191
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	1,318	2,191
Commodity Swaps And Options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	13,210	27,064
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	13,210	27,064
Gross Amount Recognized, Derivative, Financial Liabilities	352	5,765
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	352	5,765
Foreign Currency Forward Contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	15	666
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	15	666
Gross Amount Recognized, Derivative, Financial Liabilities	23	2
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	23	2
Loan Lease Interest Rate Swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Liabilities	39,823	42,131
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	$ 39,823	$ 42,131

Balance Sheet Offsetting - F121

Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 14,543	$ 29,921
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(10,825)	(20,436)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(2,725)	(6,035)
Net Amount, Derivatives, Financial Assets	993	3,450
Net Amount Recognized, Resell Agreements, Financial Assets	13,442	9,642
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	(13,442)	(9,642)
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	27,985	39,563
Gross Amounts Not Offset, Collateral, Financial Assets	(16,167)	(15,677)
Net Amount, Financial Assets	993	3,450
Net Amount Recognized, Derivatives, Financial Liabilities	40,198	47,898
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(10,825)	(20,436)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(28,803)	(26,307)
Net Amount, Derivatives, Financial Liabilities	570	1,155
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	883,947	791,119
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	(883,947)	(791,119)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	924,145	839,017
Gross Amounts Not Offset, Collateral, Financial Liabilities	(912,750)	(817,426)
Net Amount, Financial Liabilities	570	1,155
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	743	627
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(743)	(627)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	16,092	18,653
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(743)	(627)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(15,347)	(17,626)
Net Amount, Derivatives, Financial Liabilities	2	400
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	6,901	17,308
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(5,795)	(9,506)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(413)	(4,925)
Net Amount, Derivatives, Financial Assets	693	2,877
Net Amount Recognized, Derivatives, Financial Liabilities	5,795	9,506
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(5,795)	(9,506)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	0
Net Amount, Derivatives, Financial Liabilities	0	0
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	6,059	7,991
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(3,447)	(7,539)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	(2,312)	0
Net Amount, Derivatives, Financial Assets	300	452
Net Amount Recognized, Derivatives, Financial Liabilities	3,447	7,539
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(3,447)	(7,539)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	0	0
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	840	3,995
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(840)	(2,764)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(1,110)
Net Amount, Derivatives, Financial Assets	0	121
Net Amount Recognized, Derivatives, Financial Liabilities	14,864	12,200
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(840)	(2,764)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(13,456)	(8,681)
Net Amount, Derivatives, Financial Liabilities	$ 568	$ 755

Balance Sheet Offsetting Bal122

Balance Sheet Offsetting Balance Sheet Offsetting - Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	$ 875,920	$ 782,589
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	8,027	8,530
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	883,947	791,119
Securities Sold under Agreements to Repurchase, Gross	883,947	791,119
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0	0
US Treasury [Member]
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	664,419	427,402
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	0	0
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	664,419	427,402
Residential Mortgage Backed Securities [Member]
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	211,501	355,187
Remaining contractual maturity of the agreements up to 30 Days	0	0
Remaining contractual maturity of the agreements 30 to 90 Days	8,027	8,530
Remaining contractual maturity of the agreements greater than 90 Days	0	0
Remaining contractual maturity of the agreements total	$ 219,528	$ 363,717

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)Grade	Dec. 31, 2014USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments using fair value measurement option	$ 0	$ 0
Weighted-average risk grade of loans underlying interest rate swaps measured at fair value | Grade	11
Default on the interest rate swaps, weighted average loss severity percentage	20.00%
Derivative assets:	$ 14,543	29,921
Interest Rate Swaps Caps And Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	38,948	41,101
Interest Rate Swaps Caps And Floors [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	$ 0	$ 170

Fair Value Measurements (Financ

Fair Value Measurements (Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	$ 9,206,358	$ 8,461,254
Trading account securities	16,579	15,426
Derivative assets:	14,543	29,921
Derivative liabilities:	40,198	47,898
Interest Rate Swaps Caps And Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	38,948	41,101
Derivative liabilities:	40,693	43,853
Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	13,564	32,829
Derivative liabilities:	13,355	32,729
Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	46	666
Derivative liabilities:	28	617
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,994,520	3,811,252
Trading account securities	16,443	15,339
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	1,041,432	1,398,724
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	4,127,959	3,208,907
Trading account securities	136	87
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	42,447	42,371
Level 1 [Member] | Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	46	666
Derivative liabilities:	28	617
Level 1 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	3,994,520	3,811,252
Trading account securities	16,443	15,339
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:	38,948	40,931
Derivative liabilities:	40,693	43,853
Level 2 [Member] | Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	13,564	32,829
Derivative liabilities:	13,355	32,729
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	1,041,432	1,398,724
Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	4,127,959	3,208,907
Trading account securities	136	87
Level 2 [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	42,447	42,371
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:	$ 0	$ 170

Fair Value Measurements (Impair

Fair Value Measurements (Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 77,478	$ 53,591	$ 48,462
Specific valuation allowance allocations	(4,378)	(1,680)	(6,926)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	0	0	9,374
Specific valuation allowance allocations	0	0	(2,785)
Fair value	0	0	6,589
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	14,921	2,715	0
Specific valuation allowance allocations	(2,765)	(1,475)	0
Fair value	$ 12,156	$ 1,240	$ 0

Fair Value Measurements (Forecl

Fair Value Measurements (Foreclosed Assets Remeasured and Reported at Fair Value) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreclosed Assets Remeasured at Initial Recognition Carrying Value Of Foreclosed Assets Prior To Remeasurement	$ 1,102	$ 6,388	$ 7,580
Foreclosed Assets Remeasured at Initial Recognition Charge Offs Recognized In Allowance For Loan Losses	(169)	(285)	(710)
Fair Value of Foreclosed Assets Remeasured at Initial Recognition	933	6,103	6,870
Foreclosed Assets Remeasured Subsequent to Initial Recognition Carrying Value Of Foreclosed Assets Prior To Remeasurement	205	5,026	4,979
Foreclosed Assets Remeasured Subsequent to initial Recognition Write Downs Included In Other Non Interest Expense	(36)	(1,289)	(895)
Fair Value of Foreclosed Assets remeasured subsequent to initial recognition	$ 169	$ 3,737	$ 4,084

Fair Value Measurements (Estima

Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 3,591,523	$ 4,364,123	$ 4,556,125	$ 3,524,979
Securities held to maturity	2,663,009	2,926,486
Loans, net	11,350,672	10,887,993
Deposits	24,343,595	24,135,930
Federal funds purchased and repurchase agreements	893,522	803,119
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	100,000	100,000
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,591,523	4,364,123
Securities held to maturity	2,663,009	2,926,486
Cash surrender value of life insurance policies	175,191	172,050
Accrued interest receivable	139,986	128,436
Deposits	24,343,595	24,135,930
Federal funds purchased and repurchase agreements	893,522	803,119
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	100,000	100,000
Accrued interest payable	1,014	1,132
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	11,350,672	10,887,993
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,591,523	4,364,123
Securities held to maturity	2,710,685	2,966,390
Cash surrender value of life insurance policies	175,191	172,050
Accrued interest receivable	139,986	128,436
Deposits	24,344,007	24,136,402
Federal funds purchased and repurchase agreements	893,522	803,119
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	99,000	95,591
Accrued interest payable	1,014	1,132
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 11,396,158	$ 10,939,684

Operating Segments Operating Se

Operating Segments Operating Segments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2015Segment
Segment Reporting [Abstract]
Number of Operating Segments	2

Operating Segments (Summary of

Operating Segments (Summary of Operating Results by Segment) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net interest income (expense)		$ 736,632	$ 686,934	$ 620,555
Provision for loan losses		51,845	16,314	20,582
Non-interest income		328,730	320,144	302,818
Non-interest expense		693,718	654,740	611,910
Income before income taxes		319,799	336,024	290,881
Income tax expense (benefit)		40,471	58,047	53,015
Net income		279,328	277,977	237,866
Preferred stock dividends		8,063	8,063	6,719
Net income available to common shareholders		271,265	269,914	231,147
Revenues from (expenses to) external customers		1,065,362	1,007,078	923,373
Average assets		28,062,000	25,768,000	22,752,000
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		732,671	683,579	621,333
Provision for loan losses		51,848	16,312	20,585
Non-interest income		205,606	193,883	190,767
Non-interest expense		589,394	549,812	513,909
Income before income taxes		297,035	311,338	277,606
Income tax expense (benefit)		34,997	51,881	50,823
Net income		262,038	259,457	226,783
Preferred stock dividends		0	0	0
Net income available to common shareholders		262,038	259,457	226,783
Revenues from (expenses to) external customers		938,277	877,462	812,100
Average assets	[1]	28,024,000	25,734,000	22,709,000
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		7,634	6,734	6,586
Provision for loan losses		(3)	2	(3)
Non-interest income		121,489	122,261	107,759
Non-interest expense		98,405	96,330	90,132
Income before income taxes		30,721	32,663	24,216
Income tax expense (benefit)		10,753	11,431	8,563
Net income		19,968	21,232	15,653
Preferred stock dividends		0	0	0
Net income available to common shareholders		19,968	21,232	15,653
Revenues from (expenses to) external customers		129,123	128,995	114,345
Average assets	[1]	36,000	32,000	31,000
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		(3,673)	(3,379)	(7,364)
Provision for loan losses		0	0	0
Non-interest income		1,635	4,000	4,292
Non-interest expense		5,919	8,598	7,869
Income before income taxes		(7,957)	(7,977)	(10,941)
Income tax expense (benefit)		(5,279)	(5,265)	(6,371)
Net income		(2,678)	(2,712)	(4,570)
Preferred stock dividends		8,063	8,063	6,719
Net income available to common shareholders		(10,741)	(10,775)	(11,289)
Revenues from (expenses to) external customers		(2,038)	621	(3,072)
Average assets	[1]	$ 2,000	$ 2,000	$ 12,000
[1]	Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.7 billion, $30.5 billion and $29.0 billion at December 31, 2015, 2014 and 2013.

Operating Segments (Summary 130

Operating Segments (Summary of Operating Results by Segment - Parenthetical) (Detail) - USD ($) $ in Billions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting [Abstract]
Fair value of off balance sheet managed and custody assets	$ 30.7	$ 30.5	$ 29

Condensed Financial Statemen131

Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Cash	$ 532,824	$ 702,485
Resell agreements	66,917	30,792
Cash and cash equivalents	3,591,523	4,364,123	$ 4,556,125	$ 3,524,979
Total assets	28,567,118	28,277,775
Junior subordinated deferrable interest debentures	137,115	137,115
Accrued interest payable and other liabilities	202,543	250,208
Total liabilities	25,676,775	25,426,372
Shareholders’ Equity	2,890,343	2,851,403	$ 2,514,161	$ 2,417,482
Total liabilities and shareholders’ equity	28,567,118	28,277,775
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	6,434	7,335
Resell agreements	200,100	286,660
Cash and cash equivalents	206,534	293,995
Investment in subsidiaries	2,920,506	2,791,647
Accrued interest receivable and other assets	36,578	29,705
Total assets	3,163,618	3,115,347
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable	100,000	100,000
Accrued interest payable and other liabilities	36,160	26,829
Total liabilities	273,275	263,944
Shareholders’ Equity	2,890,343	2,851,403
Total liabilities and shareholders’ equity	$ 3,163,618	$ 3,115,347

Condensed Financial Statemen132

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Total interest income	$ 749,496	$ 701,471	$ 642,500
Interest expense	12,864	14,537	21,945
Salaries and employee benefits	310,504	292,349	273,692
Other	165,561	167,656	152,077
Income before income taxes and equity in undistributed earnings of subsidiaries	319,799	336,024	290,881
Income tax benefit	(40,471)	(58,047)	(53,015)
Net income	279,328	277,977	237,866
Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	271,265	269,914	231,147
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	126,375	114,439	144,642
Dividend income paid by non-banks	1,830	4,323	2,819
Interest and other income	82	69	79
Total interest income	128,287	118,831	147,540
Interest expense	3,673	3,381	7,365
Salaries and employee benefits	1,376	1,218	1,175
Other	5,727	8,526	6,735
Total expenses	10,776	13,125	15,275
Income before income taxes and equity in undistributed earnings of subsidiaries	117,511	105,706	132,265
Income tax benefit	6,062	6,702	7,845
Equity in undistributed earnings of subsidiaries	155,755	165,569	97,756
Net income	279,328	277,977	237,866
Preferred stock dividends	8,063	8,063	6,719
Net income available to common shareholders	$ 271,265	$ 269,914	$ 231,147

Condensed Financial Statemen133

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	Feb. 15, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net income		$ 279,328	$ 277,977	$ 237,866
Stock-based compensation		12,737	12,503	11,963
Excess tax benefits from stock-based compensation		(1,389)	(3,183)	(2,686)
Net cash from operating activities		393,471	286,670	173,606
Net cash received in acquisitions		0	830,661	(1,896)
Net cash from investing activities		(1,238,920)	(2,282,093)	(385,922)
Proceeds from stock option exercises		14,853	29,158	68,653
Excess tax benefits from stock-based compensation		1,389	3,183	2,686
Proceeds from issuance of preferred stock	$ 144,500	0	0	144,486
Purchase of treasury stock		(101,237)	(1,457)	(144,630)
Cash dividends paid on preferred stock		(8,063)	(8,063)	(6,719)
Cash dividends paid on common stock		(132,161)	(127,178)	(119,619)
Net cash from financing activities		72,849	1,803,421	1,243,462
Net change in cash and cash equivalents		(772,600)	(192,002)	1,031,146
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income		279,328	277,977	237,866
Equity in undistributed earnings of subsidiaries		(155,755)	(165,569)	(97,756)
Stock-based compensation		480	441	330
Excess tax benefits from stock-based compensation		(161)	(165)	(155)
Net change in other assets and other liabilities		2,621	(1,984)	2,372
Net cash from operating activities		126,513	110,700	142,657
Redemption of investment in Frost Securities, Inc.		216	0	0
Net cash received in acquisitions		0	830,661	0
Capital contribution to subsidiaries		0	(879,730)	0
Net cash from investing activities		216	(49,069)	0
Proceeds from stock option exercises		14,853	29,158	68,653
Proceeds from stock-based compensation activities of subsidiaries		12,257	12,062	11,633
Excess tax benefits from stock-based compensation		161	165	155
Proceeds from issuance of preferred stock		0	0	144,486
Purchase of treasury stock		(101,237)	(1,457)	(144,630)
Cash dividends paid on preferred stock		(8,063)	(8,063)	(6,719)
Cash dividends paid on common stock		(132,161)	(127,178)	(119,619)
Net cash from financing activities		(214,190)	(95,313)	(46,041)
Net change in cash and cash equivalents		(87,461)	(33,682)	96,616
Cash and cash equivalents at beginning of year		293,995	327,677	231,061
Cash and cash equivalents at end of year		$ 206,534	$ 293,995	$ 327,677

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) - USD ($) $ in Thousands	May. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Non-interest expense expenditures related to the acquisition		$ 693,718	$ 654,740	$ 611,910
WNB Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Purchase price allocation	$ 198,798
Total value of stock issued for consideration	$ 149,700
Common stock number of shares issued for consideration	2,000,000
Amount of cash consideration	$ 49,100
Amortization period of intangible assets acquired		10 years
Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Non-interest expense expenditures related to the acquisition			$ 7,100	$ 1,400

Acquisitions - Schedule of Purc

Acquisitions - Schedule of Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	May. 30, 2014
Business Acquisition [Line Items]
Loans	$ 11,486,531	$ 10,987,535
Goodwill	654,668	654,668
Deposits	$ (24,343,595)	$ (24,135,930)
WNB Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 879,740
Securities available for sale			154,227
Loans			670,619
Premises and equipment			22,135
Core deposit intangible asset			9,300
Goodwill			118,019
Other assets			33,644
Deposits			(1,624,043)
Other borrowings			(63,592)
Other liabilities			(1,251)
Purchase price allocation			$ 198,798