Cullen/Frost Bankers (CFR) 10-K 4 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ / shares in Units, $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 29, 2020	Jun. 30, 2019	Dec. 31, 2018
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-13221
Entity Registrant Name	CULLEN/FROST BANKERS, INC.
Entity Incorporation, State or Country Code	TX
Entity Tax Identification Number	74-1751768
Entity Address, Address Line One	111 W. Houston Street,
Entity Address, City or Town	San Antonio,
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78205
City Area Code	(210)
Local Phone Number	220-4011
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 5.6
Entity Common Stock, Shares Outstanding		62,677,154
Common stock, par value	$ 0.01			$ 0.01
Entity Central Index Key	0000039263
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Amendment Flag	false
Document Fiscal Period Focus	FY
Common Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $.01 Par Value
Trading Symbol	CFR
Security Exchange Name	NYSE
Preferred Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]
Entity Information [Line Items]
Title of 12(b) Security	5.375% Non-Cumulative Perpetual Preferred Stock, Series A
Trading Symbol	CFR.PRA
Security Exchange Name	NYSE

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Cash and due from banks	$ 581,857	$ 678,791
Interest-bearing deposits	2,849,950	2,641,971
Federal funds sold and resell agreements	356,374	635,017
Total cash and cash equivalents	3,788,181	3,955,779
Securities held to maturity, at amortized cost	2,030,005	1,106,057
Securities available for sale, at estimated fair value	11,269,591	11,387,321
Trading account securities	24,298	24,086
Loans, net of unearned discounts	14,750,332	14,099,733
Less: Allowance for loan losses	(132,167)	(132,132)
Net loans	14,618,165	13,967,601
Premises and equipment, net	1,011,947	552,330
Goodwill	654,952	654,952
Other intangible assets, net	2,481	3,649
Cash surrender value of life insurance policies	187,156	183,473
Accrued interest receivable and other assets	440,652	457,718
Total assets	34,027,428	32,292,966
Liabilities:
Non-interest-bearing demand deposits	10,873,629	10,997,494
Interest-bearing deposits	16,765,935	16,151,710
Total deposits	27,639,564	27,149,204
Federal funds purchased and repurchase agreements	1,695,342	1,367,548
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,299	136,242
Subordinated notes, net of unamortized issuance costs	98,865	98,708
Accrued interest payable and other liabilities	545,690	172,347
Total liabilities	30,115,760	28,924,049
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 2019 and 2018	144,486	144,486
Common stock, par value $0.01 per share; 210,000,000 shares authorized;64,236,306 shares issued at both December 31, 2019 and 2018	642	642
Additional paid-in capital	983,250	967,304
Retained earnings	2,667,534	2,440,002
Accumulated other comprehensive income, net of tax	267,370	(63,600)
Treasury stock, at cost; 1,567,302 shares in 2019 and 1,250,464 in 2018.	(151,614)	(119,917)
Total shareholders’ equity	3,911,668	3,368,917
Total liabilities and shareholders’ equity	$ 34,027,428	$ 32,292,966

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
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	64,236,306	64,236,306
Treasury stock, shares	1,567,302	1,250,464
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Loans, including fees	$ 741,747	$ 669,002	$ 534,804
Securities:
Taxable	117,082	86,370	92,979
Tax-exempt	233,842	233,358	222,620
Interest-bearing deposits	35,590	56,968	41,608
Federal funds sold and resell agreements	5,524	5,500	936
Total interest income	1,133,785	1,051,198	892,947
Interest expense:
Deposits	99,742	75,337	17,188
Federal funds purchased and repurchase agreements	19,675	8,021	1,522
Junior subordinated deferrable interest debentures	5,706	5,291	3,955
Other long-term borrowings	4,657	4,657	3,860
Total interest expense	129,780	93,306	26,525
Net interest income	1,004,005	957,892	866,422
Provision for loan losses	33,759	21,613	35,460
Net interest income after provision for loan losses	970,246	936,279	830,962
Non-interest income:
Trust and investment management fees	126,722	119,391	110,675
Service charges on deposit accounts	88,983	85,186	84,182
Insurance commissions and fees	52,345	48,967	46,169
Interchange and debit card transaction fees	14,873	13,877	23,232
Other charges, commissions and fees	37,123	37,231	39,931
Net gain (loss) on securities transactions	293	(156)	(4,941)
Other	43,563	46,790	37,222
Total non-interest income	363,902	351,286	336,470
Non-interest expense:
Salaries and wages	375,029	350,312	337,068
Employee benefits	86,230	77,323	74,575
Net occupancy	89,466	76,788	75,971
Technology, furniture and equipment	91,995	83,102	74,335
Deposit insurance	10,126	16,397	20,128
Intangible amortization	1,168	1,424	1,703
Other	180,665	173,538	175,289
Total non-interest expense	834,679	778,884	759,069
Income before income taxes	499,469	508,681	408,363
Income taxes	55,870	53,763	44,214
Net income	443,599	454,918	364,149
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	$ 435,536	$ 446,855	$ 356,086
Earnings per common share:
Basic (in dollars per share)	$ 6.89	$ 6.97	$ 5.56
Diluted (in dollars per share)	$ 6.84	$ 6.90	$ 5.51

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net income	$ 443,599	$ 454,918	$ 364,149
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss on securities available for sale during the period	418,556	(182,340)	157,016
Change in net unrealized gain on securities transferred to held-to-maturity	(1,292)	(8,818)	(16,193)
Reclassification adjustment for net (gains) losses included in net income	(293)	156	4,941
Total securities available for sale and transferred securities before tax amount	416,971	(191,002)	145,764
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss before tax amount	(3,644)	(7,225)	(597)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) before tax amount	5,623	5,002	5,429
Total defined-benefit post-retirement benefit plans	1,979	(2,223)	4,832
Reclassification adjustments for (gains) losses included in net income:
Other comprehensive income (loss), before tax	418,950	(193,225)	150,596
Deferred tax expense (benefit) related to other comprehensive income	87,980	(40,578)	46,461
Other comprehensive income (loss), net of tax	330,970	(152,647)	104,135
Comprehensive income	$ 774,569	$ 302,271	$ 468,284

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, 2016	$ 3,002,528	$ 144,486	$ 637	$ 906,732	$ 1,985,569	$ (24,623)	$ (10,273)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	364,149				364,149
Other comprehensive loss, net of tax	104,135					104,135
Proceeds from stock option exercises/stock unit conversions (399,244 shares, 548,238 shares, and 1,150,920 shares during 2019, 2018, and 2017, respectively)	67,746		5	33,616	(10,414)		44,539
Stock-based compensation expense recognized in earnings	13,013			13,013
Purchase of treasury stock (716,062 shares,1,037,982 shares, and 1,149,555 shares during 2019, 2018, and 2017, respectively)	(101,473)						(101,473)
Cash dividends paid on preferred stock (approximately $1.34 per share in 2019, 2018, and 2017)	(8,063)				(8,063)
Cash dividends – common stock ($2.80 per share, $2.58 per share, and $2.25 per share in 2019, 2018, and 2017, respectively)	(144,172)				(144,172)
Balance at Dec. 31, 2017	3,297,863	144,486	642	953,361	2,187,069	79,512	(67,207)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption	(2,285)				(2,285)
Stockholders' Equity, as adjusted at the beginning of period	3,295,578	144,486	642	953,361	2,184,784	79,512	(67,207)
Net income	454,918				454,918
Other comprehensive loss, net of tax	(152,647)					(152,647)
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act					(9,535)	9,535
Proceeds from stock option exercises/stock unit conversions (399,244 shares, 548,238 shares, and 1,150,920 shares during 2019, 2018, and 2017, respectively)	31,647				(16,653)		48,300
Stock-based compensation expense recognized in earnings	13,943			13,943
Purchase of treasury stock (716,062 shares,1,037,982 shares, and 1,149,555 shares during 2019, 2018, and 2017, respectively)	(101,010)						(101,010)
Cash dividends paid on preferred stock (approximately $1.34 per share in 2019, 2018, and 2017)	(8,063)				(8,063)
Cash dividends – common stock ($2.80 per share, $2.58 per share, and $2.25 per share in 2019, 2018, and 2017, respectively)	(165,449)				(165,449)
Balance at Dec. 31, 2018	3,368,917	144,486	642	967,304	2,440,002	(63,600)	(119,917)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption	(14,672)				(14,672)
Stockholders' Equity, as adjusted at the beginning of period	3,354,245	144,486	642	967,304	2,425,330	(63,600)	(119,917)
Net income	443,599				443,599
Other comprehensive loss, net of tax	330,970					330,970
Proceeds from stock option exercises/stock unit conversions (399,244 shares, 548,238 shares, and 1,150,920 shares during 2019, 2018, and 2017, respectively)	20,770				(16,326)		37,096
Stock-based compensation expense recognized in earnings	15,946			15,946
Purchase of treasury stock (716,062 shares,1,037,982 shares, and 1,149,555 shares during 2019, 2018, and 2017, respectively)	(68,793)						(68,793)
Cash dividends paid on preferred stock (approximately $1.34 per share in 2019, 2018, and 2017)	(8,063)				(8,063)
Cash dividends – common stock ($2.80 per share, $2.58 per share, and $2.25 per share in 2019, 2018, and 2017, respectively)	(177,006)				(177,006)
Balance at Dec. 31, 2019	$ 3,911,668	$ 144,486	$ 642	$ 983,250	$ 2,667,534	$ 267,370	$ (151,614)

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock option exercises/deferred stock unit conversions, shares	399,224	548,238	1,150,920
Purchase of treasury stock, shares	716,062	1,037,982	1,149,555
Approximate cash dividends declared on preferred stock, per share	$ 1.34	$ 1.34	$ 1.34
Cash dividends - common stock, per share	$ 2.80	$ 2.58	$ 2.25

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net income	$ 443,599	$ 454,918	$ 364,149
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	33,759	21,613	35,460
Deferred tax expense (benefit)	7,614	52,923	(14,493)
Accretion of loan discounts	(15,197)	(14,341)	(16,062)
Securities premium amortization (discount accretion), net	115,558	100,528	89,933
Net (gain) loss on securities transactions	(293)	156	4,941
Depreciation and amortization	54,091	50,172	47,812
Net (gain) loss on sale/write-down of assets/foreclosed assets	(5,712)	(5,272)	(4,697)
Stock-based compensation	15,946	13,943	13,013
Net tax benefit from stock-based compensation	2,447	3,865	9,062
Earnings on life insurance policies	(3,683)	(3,380)	(3,190)
Net change in:
Trading account securities	(212)	(2,658)	(3,842)
Lease right-of-use asset	20,124	0	0
Accrued interest receivable and other assets	(15,570)	(85,898)	(55,179)
Accrued interest payable and other liabilities	(18,381)	(24,181)	71,172
Net cash provided by (used in) operating activities	634,090	562,388	538,079
Investing Activities:
Securities held to maturity: Purchases	(649,326)	(1,500)	0
Securities held to maturity: Maturities, calls and principal repayments	81,762	300,632	783,176
Securities available for sale:
Purchases	(23,306,694)	(18,191,057)	(13,529,192)
Sales	18,660,147	16,806,062	11,963,359
Maturities, calls and principal repayments	4,694,927	221,906	1,328,143
Proceeds from sale of loans	24,036	21,318	0
Net change in loans	(693,587)	(1,008,789)	(1,187,631)
Benefits received on life insurance policies	0	384	597
Proceeds from sales of premises and equipment	8,038	13,628	4,525
Purchases of premises and equipment	(206,716)	(79,270)	(34,089)
Proceeds from sales of repossessed properties	663	3,366	517
Net cash provided by (used in) investing activities	(1,386,750)	(1,913,320)	(670,595)
Financing Activities:
Net change in deposits	490,360	276,815	1,060,814
Net change in short-term borrowings	327,794	219,724	170,832
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	(100,000)
Proceeds from stock option exercises	20,770	31,647	67,746
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	585,062	253,664	1,044,118
Net change in cash and cash equivalents	(167,598)	(1,097,268)	911,602
Cash and cash equivalents at beginning of year	3,955,779	5,053,047	4,141,445
Cash and cash equivalents at end of year	$ 3,788,181	$ 3,955,779	$ 5,053,047

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Nature of Operations . Cullen/Frost Bankers, Inc. (“Cullen/Frost”) is a financial holding company and a bank holding company headquartered in San Antonio, Texas that provides, through its subsidiaries, a broad array of products and services throughout numerous Texas markets. 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. Acquisitions are accounted for using the purchase method with the operating results of the acquired companies included with our results of operations since their respective dates of acquisition. We have evaluated subsequent events for potential recognition and/or disclosure through the date these consolidated financial statements were issued. Use of Estimates . The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses and the fair values of financial instruments and the status of contingencies are particularly subject to change. Concentrations and Restrictions on Cash and Cash Equivalents . 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 $918.0 million and $447.9 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2019 and 2018 . Additionally, as of December 31, 2019 and 2018 , we had $37.5 million and $10.0 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions. 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, 2019 2018 2017 Cash paid for interest $ 124,781 $ 89,270 $ 24,371 Cash paid for income tax 45,352 5,112 56,359 Significant non-cash transactions: Transfer of securities from available for sale to held to maturity 377,812 — — Unsettled purchases/sales of securities — 330 37,481 Loans foreclosed and transferred to other real estate owned and foreclosed assets 1,348 2,899 279 Loans to facilitate the sale of other real estate owned 847 — — Lease right-of-use assets obtained in exchange for lessee operating lease liabilities 319,286 — — 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 remains 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. Interest income on securities includes amortization of purchase premiums and discounts. Premiums and discounts on securities are generally amortized using the interest method with a constant effective yield without anticipating prepayments, except for mortgage-backed securities where prepayments are anticipated. Premiums on callable securities are amortized to their earliest call date. Prior to the adoption of a new accounting standard in 2019, as further discussed below, premiums on callable securities were amortized to their respective maturity dates unless such securities were included in pools for the purposes of assessing prepayment expectations. 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 3 - Loans. 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 3 - 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. We lease certain office facilities and office equipment under operating leases. We also own certain office facilities which we lease to outside parties under operating lessor leases; however, such leases are not significant. In 2019, we adopted certain accounting standard updates related to accounting for leases as further discussed below. Under the new standards, for operating leases other than those considered to be short-term, we recognize lease right-of-use assets and related lease liabilities. Such amounts are reported as components of premises and equipment and accrued interest payable and other liabilities, respectively, on our accompanying consolidated balance sheet. We do not recognize short-term operating leases on our balance sheet. A short-term operating lease has an original term of 12 months or less and does not have a purchase option that is likely to be exercised. In recognizing lease right-of-use assets and related lease liabilities, we account for lease and non-lease components (such as taxes, insurance, and common area maintenance costs) separately as such amounts are generally readily determinable under our lease contracts. Lease payments over the expected term are discounted using our incremental borrowing rate referenced to the Federal Home Loan Bank Secure Connect advance rates for borrowings of similar term. We also consider renewal and termination options in the determination of the term of the lease. If it is reasonably certain that a renewal or termination option will be exercised, the effects of such options are included in the determination of the expected lease term. Generally, we cannot be reasonably certain about whether or not we will renew a lease until such time the lease is within the last two years of the existing lease term. However, renewal options related to our regional headquarters facilities or operations centers are evaluated on a case-by-case basis, typically in advance of such time frame. When we are reasonably certain that a renewal option will be exercised, we measure/remeasure the right-of-use asset and related lease liability using the lease payments specified for the renewal period or, if such amounts are unspecified, we generally assume an increase (evaluated on a case-by-case basis in light of prevailing market conditions) in the lease payment over the final period of the existing lease term. 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 $1.1 million and $1.2 million at December 31, 2019 and 2018 . 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. See Note 5 - 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 5 - Goodwill and Other Intangible Assets. Revenue Recognition . In general, for revenue not associated with financial instruments, guarantees and lease contracts, we apply the following steps when recognizing revenue from contracts with customers: (i) identify the contract, (ii) identify the performance obligations, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations and (v) recognize revenue when a performance obligation is satisfied. Our contracts with customers are generally short term in nature, typically due within one year or less or cancellable by us or our customer upon a short notice period. Performance obligations for our customer contracts are generally satisfied at a single point in time, typically when the transaction is complete, or over time. For performance obligations satisfied over time, we primarily use the output method, directly measuring the value of the products/services transferred to the customer, to determine when performance obligations have been satisfied. We typically receive payment from customers and recognize revenue concurrent with the satisfaction of our performance obligations. In most cases, this occurs within a single financial reporting period. For payments received in advance of the satisfaction of performance obligations, revenue recognition is deferred until such time as the performance obligations have been satisfied. In cases where we have not received payment despite satisfaction of our performance obligations, we accrue an estimate of the amount due in the period our performance obligations have been satisfied. For contracts with variable components, only amounts for which collection is probable are accrued. We generally act in a principal capacity, on our own behalf, in most of our contracts with customers. In such transactions, we recognize revenue and the related costs to provide our services on a gross basis in our financial statements. In some cases, we act in an agent capacity, deriving revenue through assisting other entities in transactions with our customers. In such transactions, we recognize revenue and the related costs to provide our services on a net basis in our financial statements. These transactions recognized on a net basis primarily relate to insurance and brokerage commissions and fees derived from our customers' use of various interchange and ATM/debit card networks. Share-Based Payments . 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. Compensation expense for performance 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 over the service period of the award based upon the probable number of units expected to vest. 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. The fair value of performance stock units is generally the market price of our stock on the date of grant discounted by the present value of the dividends expected to be paid on our common stock during the service period of the award because dividend equivalent payments on performance stock units are deferred until such time that the units vest and shares are issued. The impact of forfeitures of share-based payment awards on compensation expense is recognized as forfeitures occur. 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. Although realization is not assured, management believes it is more likely than not that all of the deferred tax assets will be realized. Interest and/or penalties related to income taxes are reported as a component of income tax expense. The income tax effects related to settlements of share-based payment awards are reported in earnings as an increase (or decrease) to income tax expense (see Note 13 - Income Taxes). 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 10 - 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 and changes in the net actuarial gain/loss on defined benefit post-retirement benefit plans. See Note 14 - 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 17 - 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. Accounting Changes, Reclassifications and Restatements. Certain items in prior financial statements have been reclassified to conform to the current presentation. On January 1, 2019, we adopted certain accounting standard updates related to accounting for leases, primarily Accounting Standards Update (“ASU”) 2016-02 “Leases (Topic 842)” and subsequent updates. Among other things, these updates require lessees to recognize a lease liability, measured on a discounted basis, related to the lessee's obligation to make lease payments arising under a lease contract; and a right-of-use asset related to the lessee’s right to use, or control the use of, a specified asset for the lease term. The updates did not significantly change lease accounting requirements applicable to lessors and did not significantly impact our financial statements in relation to contracts whereby we act as a lessor. We adopted the updates using a modified-retrospective transition approach and recognized right-of-use lease assets and related lease liabilities totaling $170.5 million and $174.4 million , respectively, as of January 1, 2019. We elected to apply certain practical adoption expedients provided under the updates whereby we did not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) initial direct costs for any existing leases. We did not elect to apply the recognition requirements of the updates to any short-term leases. See Note 4 - Premises and Equipment and Lease Commitments. On January 1, 2019, we also adopted ASU 2017-08 “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities.” ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium to require such premiums to be amortized to the earliest call date unless applicable guidance related to certain pools of securities is applied to consider estimated prepayments. Under prior guidance, entities were generally required to amortize premiums on individual, non-pooled callable debt securities as a yield adjustment over the contractual life of the security. ASU 2017-08 does not change the accounting for callable debt securities held at a discount. Upon adoption, using a modified retrospective transition adoption approach, we recognized a cumulative effect reduction to retained earnings totaling $14.7 million . Premium amortization expense for 2019 was approximately $5.2 million higher than what would have been the case had we continued to amortize the affected securities to their respective maturity dates. On January 1, 2018, we adopted ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” In accordance with ASU 2018-02, we elected to reclassify certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act, which was enacted on December 22, 2017 (see Note 13 - Income Taxes), from accumulated other comprehensive income to retained earnings. Such amounts, which totaled $9.5 million , related to a net actuarial loss on defined benefit post-retirement plans and unrealized gains on securities available for sale and securities transferred to held to maturity. See Note 14 - Other Comprehensive Income (Loss). Notwithstanding this election made in accordance with ASU 2018-02, our policy is to release such income tax effects only when the entire portfolio to which the underlying transactions relate is liquidated, sold or extinguished. On January 1, 2018, we also adopted, ASU 2014-09, "Revenue from Contracts with Customers (Topic 606).” Using a modified retrospective transition approach for contracts that were not complete as of our adoption, we recognized a cumulative effect reduction to beginning retained earnings totaling $2.3 million . The amount was related to certain revenue streams within trust and investment management fees. Additionally, based on our underlying contracts, ASU 2014-09 requires us to report network costs associated with debit card and ATM transactions netted against the related fee income from such transactions. Previously, such network costs were reported as a component of other non-interest expense. For 2019 and 2018, gross interchange and debit card transaction fees totaled $27.8 million and $25.8 million , respectively, while related network costs totaled $12.9 million and $11.9 million , respectively. On a net basis, we reported $14.9 million and $13.9 million as interchange and debit card transaction fees in the accompanying Consolidated Statement of Income for 2019 and 2018, respectively. For 2017, we reported interchange and debit card transaction fees totaling $23.2 million on a gross basis in the accompanying Consolidated Statement of Income while related network cost totaling $11.9 million was reported as a component of other non-interest expense. ASU 2014-09 also required us to change the way we recognize certain recurring revenue streams reported as components of trust and investment management fees, insurance commissions and fees and other categories of non-interest income, however, such changes were not significant to our financial statements.

Securities

Securities	12 Months Ended
	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Securities. Year-end securities held to maturity and available for sale consisted of the following: 2019 2018 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: Residential mortgage-backed securities $ 530,861 $ 22 $ 9,365 $ 521,518 $ 2,737 $ 8 $ 85 $ 2,660 States and political subdivisions 1,497,644 28,909 896 1,525,657 1,101,820 11,525 552 1,112,793 Other 1,500 — — 1,500 1,500 — — 1,500 Total $ 2,030,005 $ 28,931 $ 10,261 $ 2,048,675 $ 1,106,057 $ 11,533 $ 637 $ 1,116,953 Available for Sale: U.S. Treasury $ 1,941,283 $ 18,934 $ 12,084 $ 1,948,133 $ 3,455,417 $ 1,772 $ 29,500 $ 3,427,689 Residential mortgage-backed securities 2,176,275 32,608 1,289 2,207,594 823,208 13,079 6,547 829,740 States and political subdivisions 6,717,344 353,857 204 7,070,997 7,089,132 70,760 72,690 7,087,202 Other 42,867 — — 42,867 42,690 — — 42,690 Total $ 10,877,769 $ 405,399 $ 13,577 $ 11,269,591 $ 11,410,447 $ 85,611 $ 108,737 $ 11,387,321 All mortgage-backed securities included in the above table were issued by U.S. government agencies and corporations. At December 31, 2019 , approximately 99.7% of the securities in our municipal bond portfolio were issued by the State of Texas or political subdivisions or agencies within the State of Texas, of which approximately 69.1% are either guaranteed by the Texas Permanent School Fund, which has a “triple-A” insurer financial strength rating, or are 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, 2019 and $3.8 billion December 31, 2018 . From time to time, we have reclassified certain securities from available for sale to held to maturity. During 2019 , we reclassified securities with an aggregate fair value of $377.8 million and an aggregate net unrealized gain of $3.3 million ( $2.6 million , net of tax) on the date of the transfer. The net unamortized, unrealized gain remaining on transferred securities, including those transferred in 2019 and in years prior, included in accumulated other comprehensive income in the accompanying balance sheet totaled $4.8 million ( $3.8 million , net of tax) at December 31, 2019 and $2.7 million ( $2.2 million , net of tax) at December 31, 2018 . 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. Unrealized Losses. 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 2019 Held to Maturity: Residential mortgage-backed securities $ 519,099 $ 9,361 $ 408 $ 4 $ 519,507 $ 9,365 States and political subdivisions 371,434 896 — — 371,434 896 Total $ 890,533 $ 10,257 $ 408 $ 4 $ 890,941 $ 10,261 Available for Sale: U.S. Treasury $ 636,999 $ 12,070 $ 199,980 $ 14 $ 836,979 $ 12,084 Residential mortgage-backed securities 276,249 782 31,456 507 307,705 1,289 States and political subdivisions 59,678 204 — — 59,678 204 Total $ 972,926 $ 13,056 $ 231,436 $ 521 $ 1,204,362 $ 13,577 Less than 12 Months More than 12 Months Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses 2018 Held to Maturity: Residential mortgage-backed securities $ — $ — $ 2,034 $ 85 $ 2,034 $ 85 States and political subdivisions 205,686 541 5,952 11 211,638 552 Total $ 205,686 $ 541 $ 7,986 $ 96 $ 213,672 $ 637 Available for Sale: U.S. Treasury $ — $ — $ 3,139,639 $ 29,500 $ 3,139,639 $ 29,500 Residential mortgage-backed securities 152,682 205 213,982 6,342 366,664 6,547 States and political subdivisions 1,136,322 7,026 2,058,048 65,664 3,194,370 72,690 Total $ 1,289,004 $ 7,231 $ 5,411,669 $ 101,506 $ 6,700,673 $ 108,737 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 expect to receive full value for the securities. Furthermore, as of December 31, 2019 , 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 due to increases in market interest rates over the yields available at the time the underlying securities were purchased. The fair value is expected to recover as the securities approach their maturity date or repricing date or if market yields for such investments decline. Management does not believe any of the securities are impaired due to reasons of credit quality. Accordingly, as of December 31, 2019 , management believes the impairments detailed in the table above are temporary and no impairment loss has been realized in our consolidated income statement. Contractual Maturities. The amortized cost and estimated fair value of securities, excluding trading securities, at December 31, 2019 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 $ 12,773 $ 12,847 $ 508,575 $ 509,404 Due after one year through five years 165,519 169,970 1,317,774 1,344,035 Due after five years through ten years 527,907 541,249 451,885 478,800 Due after ten years 792,945 803,091 6,380,393 6,686,891 Residential mortgage-backed securities 530,861 521,518 2,176,275 2,207,594 Equity securities — — 42,867 42,867 Total $ 2,030,005 $ 2,048,675 $ 10,877,769 $ 11,269,591 Sales of Securities. Sales of securities available for sale were as follows: 2019 2018 2017 Proceeds from sales $ 18,660,147 $ 16,806,062 $ 11,963,359 Gross realized gains 930 3 1 Gross realized losses (637 ) (159 ) (4,942 ) Tax benefit (expense) related to securities gains/losses (62 ) 33 1,729 Premiums and Discounts. Premium amortization and discount accretion included in interest income on securities was as follows: 2019 2018 2017 Premium amortization $ (120,785 ) $ (108,483 ) $ (97,841 ) Discount accretion 5,227 7,955 7,908 Net (premium amortization) discount accretion $ (115,558 ) $ (100,528 ) $ (89,933 ) Trading Account Securities. Year-end trading account securities, at estimated fair value, were as follows: 2019 2018 U.S. Treasury $ 24,298 $ 21,928 States and political subdivisions — 2,158 Total $ 24,298 $ 24,086 Net gains and losses on trading account securities were as follows: 2019 2018 2017 Net gain on sales transactions $ 2,173 $ 1,816 $ 1,408 Net mark-to-market gains (losses) (176 ) 105 (43 ) Net gain on trading account securities $ 1,997 $ 1,921 $ 1,365

Loans

Loans	12 Months Ended
	Dec. 31, 2019
Receivables [Abstract]
Loans	Loans Year-end loans, including leases net of unearned discounts, consisted of the following: 2019 2018 Commercial and industrial $ 5,187,466 $ 5,111,957 Energy: Production 1,348,900 1,309,314 Service 192,996 168,775 Other 110,986 124,509 Total energy 1,652,882 1,602,598 Commercial real estate: Commercial mortgages 4,594,113 4,121,966 Construction 1,312,659 1,267,717 Land 289,467 306,755 Total commercial real estate 6,196,239 5,696,438 Consumer real estate: Home equity loans 375,596 353,924 Home equity lines of credit 354,671 337,168 Other 464,146 427,898 Total consumer real estate 1,194,413 1,118,990 Total real estate 7,390,652 6,815,428 Consumer and other 519,332 569,750 Total loans $ 14,750,332 $ 14,099,733 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, 2019 and 2018 , there were no concentrations of loans related to any single industry in excess of 10% of total loans other than energy loans, which totaled 11.2% and 11.4% of total loans at such dates, respectively. Unfunded commitments to extend credit and standby letters of credit issued to customers in the energy industry totaled $1.2 billion and $75.5 million , respectively, as of December 31, 2019 . 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, 2019 or 2018 . Overdrafts . Deposit account overdrafts reported as loans totaled $9.0 million and $8.5 million at December 31, 2019 and 2018 . 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”). Activity in related party loans during 2019 is presented in the following table. Other changes were primarily related to changes in related-party status. Balance outstanding at December 31, 2018 $ 256,056 Principal additions 304,407 Principal reductions (257,687 ) Other changes (4,248 ) Balance outstanding at December 31, 2019 $ 298,528 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: 2019 2018 Commercial and industrial $ 26,038 $ 9,239 Energy 65,761 46,932 Commercial real estate: Buildings, land and other 8,912 15,268 Construction 665 — Consumer real estate 922 892 Consumer and other 5 1,408 Total $ 102,303 $ 73,739 Had non-accrual loans performed in accordance with their original contract terms, we would have recognized additional interest income, net of tax, of approximately $3.9 million in 2019 , $5.2 million in 2018 and $3.7 million in 2017 . An age analysis of past due loans (including both accruing and non-accruing loans), segregated by class of loans, as of December 31, 2019 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 $ 25,474 $ 21,268 $ 46,742 $ 5,140,724 $ 5,187,466 $ 3,430 Energy 6,136 62,566 68,702 1,584,180 1,652,882 85 Commercial real estate: Buildings, land and other 12,384 2,725 15,109 4,868,471 4,883,580 967 Construction 195 1,066 1,261 1,311,398 1,312,659 402 Consumer real estate 7,442 2,129 9,571 1,184,842 1,194,413 1,425 Consumer and other 4,476 1,112 5,588 513,744 519,332 1,112 Total $ 56,107 $ 90,866 $ 146,973 $ 14,603,359 $ 14,750,332 $ 7,421 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 2019 Commercial and industrial $ 30,909 $ 11,588 $ 12,772 $ 24,360 $ 7,849 $ 14,913 Energy 87,103 2,764 62,480 65,244 20,246 53,563 Commercial real estate: Buildings, land and other 9,252 6,255 2,354 8,609 383 13,690 Construction 697 665 — 665 — 354 Consumer real estate 570 570 — 570 — 547 Consumer and other 5 — 5 5 5 1,285 Total $ 128,536 $ 21,842 $ 77,611 $ 99,453 $ 28,483 $ 84,352 2018 Commercial and industrial $ 9,094 $ 2,842 $ 4,287 $ 7,129 $ 2,558 $ 18,246 Energy 67,900 6,817 39,890 46,707 9,671 75,453 Commercial real estate: Buildings, land and other 15,774 2,168 12,517 14,685 2,599 12,799 Construction — — — — — — Consumer real estate 293 293 — 293 — 704 Consumer and other 1,475 — 1,407 1,407 1,407 925 Total $ 94,536 $ 12,120 $ 58,101 $ 70,221 $ 16,235 $ 108,127 2017 Commercial and industrial $ 60,781 $ 28,038 $ 15,722 $ 43,760 $ 7,553 $ 30,073 Energy 99,606 33,080 61,162 94,242 13,267 76,492 Commercial real estate: Buildings, land and other 10,795 6,394 — 6,394 — 6,164 Construction — — — — — — Consumer real estate 1,214 1,214 — 1,214 — 1,167 Consumer and other — — — — — 11 Total $ 172,396 $ 68,726 $ 76,884 $ 145,610 $ 20,820 $ 113,907 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 2019 , 2018 and 2017 are set forth in the following table. 2019 2018 2017 Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Commercial and industrial $ 3,845 $ 2,161 $ 2,203 $ — $ 4,026 $ 3,766 Energy — — 13,708 — 56,096 54,330 Commercial real estate: Buildings, land and other 9,457 9,393 — — — — Construction — — — — 388 388 Consumer real estate 124 120 — — — — $ 13,426 $ 11,674 $ 15,911 $ — $ 60,510 $ 58,484 Loan modifications are typically related to extending amortization periods, converting loans to interest only for a limited period of time, deferral of interest payments, waiver of certain covenants, consolidating notes and/or reducing collateral or interest rates. The modifications during the reported periods did not significantly impact our determination of the allowance for loan losses. Additional information related to restructured loans was as follows: 2019 2018 2017 Restructured loans past due in excess of 90 days at period-end: Number of loans 4 — 1 Dollar amount of loans $ 3,340 $ — $ 43,137 Restructured loans on non-accrual status at period end 5,576 — 53,622 Charge-offs of restructured loans: Recognized in connection with restructuring — — — Recognized on previously restructured loans 1,500 7,650 9,951 Proceeds from sale of restructured loans — 15,750 — 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, under the oversight of credit administration, review updated financial information for all pass grade loans to reassess the risk grade on at least an annual basis. When a loan has a 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 risk grade of 10 or higher, a special assets officer monitors the loan on an on-going basis. The following tables present weighted average risk grades for all commercial loans by class. December 31, 2019 December 31, 2018 Weighted Loans Weighted Loans Commercial and industrial Risk grades 1-8 6.17 $ 4,788,857 6.12 $ 4,862,275 Risk grade 9 9.00 247,212 9.00 112,431 Risk grade 10 10.00 71,472 10.00 58,328 Risk grade 11 11.00 53,887 11.00 69,684 Risk grade 12 12.00 18,189 12.00 6,681 Risk grade 13 13.00 7,849 13.00 2,558 Total 6.44 $ 5,187,466 6.30 $ 5,111,957 Energy Risk grades 1-8 5.90 $ 1,488,301 5.76 $ 1,451,673 Risk grade 9 9.00 32,163 9.00 35,565 Risk grade 10 10.00 51,898 10.00 43,001 Risk grade 11 11.00 14,760 11.00 25,427 Risk grade 12 12.00 45,514 12.00 37,261 Risk grade 13 13.00 20,246 13.00 9,671 Total 6.39 $ 1,652,882 6.22 $ 1,602,598 Commercial real estate: Buildings, land and other Risk grades 1-8 6.78 $ 4,523,271 6.76 $ 4,143,264 Risk grade 9 9.00 163,714 9.00 109,660 Risk grade 10 10.00 103,626 10.00 62,353 Risk grade 11 11.00 84,057 11.00 98,176 Risk grade 12 12.00 8,529 12.00 12,669 Risk grade 13 13.00 383 13.00 2,599 Total 7.01 $ 4,883,580 6.98 $ 4,428,721 Construction Risk grades 1-8 7.25 $ 1,274,098 7.13 $ 1,177,260 Risk grade 9 9.00 21,509 9.00 60,754 Risk grade 10 10.00 15,243 10.00 24,877 Risk grade 11 11.00 1,144 11.00 4,826 Risk grade 12 12.00 665 12.00 — Risk grade 13 13.00 — 13.00 — Total 7.31 $ 1,312,659 7.29 $ 1,267,717 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 impaired and 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 impaired and 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: 2019 2018 2017 Commercial and industrial $ (10,131 ) $ (22,388 ) $ (17,453 ) Energy (6,058 ) (13,121 ) (10,009 ) Commercial real estate: Buildings, land and other (830 ) (263 ) 735 Construction 24 13 11 Consumer real estate (2,457 ) (1,538 ) (506 ) Consumer and other (14,272 ) (7,548 ) (5,919 ) Total $ (33,724 ) $ (44,845 ) $ (33,141 ) 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 128.8 at November 30, 2019 (most recent date available) and 126.4 at December 31, 2018 . 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, consumer and other loans and overdrafts. 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. 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 macroeconomic 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 weighted-average risk grade for all loans to borrowers in distressed industries by loan portfolio segment. A multiple is then applied to the amount by which the weighted-average risk grade for loans to borrowers in distressed industries exceeds the weighted-average risk grade for all pass-grade loans within the loan portfolio segment to derive an allocation factor for loans to borrowers in distressed industries. The amount of the allocation for each loan portfolio segment is the product of this allocation factor and the outstanding balance of pass-grade loans within the identified distressed industries that have a risk grade of 6 or higher. Management identifies potential distressed industries by analyzing industry trends related to delinquencies, classifications and charge-offs as well as individual borrower financial information. The aforementioned methodology for allocating reserves for distressed industries within commercial and industrial and commercial real estate loan portfolio segments does not translate to our energy loan portfolio segment as the segment is made up of a single industry. For energy loans, management analyzes current economic trends, commodity prices and various other quantitative and qualitative factors that impact the inherent credit quality of our energy loan portfolio segment. If, based upon this analysis, management concludes that the prevailing conditions could have an adverse impact on the credit quality of our energy loan portfolio, management performs a sensitivity stress test on individual loans within our energy loan portfolio. The sensitivity stress test includes a commodity price shock to 75% of the commodity price deck. We also assess the financial strength of individual borrowers, the quality of collateral, the relative experience of the individual borrowers and their ability to withstand an economic downturn. The sensitivity stress test allows us to identify potential credit issues during p

Premises and Equipment

Premises and Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Premises and Equipment	Premises and Equipment and Lease Commitments Year-end premises and equipment were as follows: 2019 2018 Land $ 112,818 $ 104,045 Buildings 441,404 373,276 Technology, furniture and equipment 226,925 196,871 Leasehold improvements 156,144 83,320 Construction and projects in progress 44,251 45,456 Lease right-of-use assets 297,736 — 1,279,278 802,968 Less accumulated depreciation and amortization (267,331 ) (250,638 ) Total premises and equipment, net $ 1,011,947 $ 552,330 Depreciation of premises and equipment totaled $41.0 million in 2019 , $37.2 million 2018 and $36.3 million in 2017 . Amortization of lease right of use-assets totaled $27.6 million in 2019 . Lease Commitments. We lease certain office facilities and office equipment under operating leases. Rent expense for all operating leases totaled $42.1 million in 2019 , $31.1 million in 2018 and $30.5 million in 2017 . On January 1, 2019, we adopted a new accounting standard which required the recognition of certain operating leases on our balance sheet as lease right-of-use assets (reported as component of premises and equipment) and related lease liabilities (reported as a component of accrued interest payable and other liabilities). See Note 1 - Summary of Significant Accounting Policies. Rent expense includes amounts related to items that are not included in the determination of lease right-of-use assets including expenses related to short-term leases totaling $4.6 million in 2019 and non-lease components such as taxes, insurance, and common area maintenance costs totaling $9.9 million in 2019 . Lease payments under operating leases that were applied to our operating lease liability totaled $27.5 million during 2019. The following table reconciles future undiscounted lease payments due under non-cancelable operating leases (those amounts subject to recognition) to the aggregate operating lessee lease liability as of December 31, 2019 : Future lease payments 2020 $ 28,225 2021 30,813 2022 28,175 2023 26,661 2024 25,232 Thereafter 283,300 Total undiscounted operating lease liability 422,406 Imputed interest 98,718 Total operating lease liability included in the accompanying balance sheet $ 323,688 Weighted-average lease term in years 16.49 Weighted-average discount rate 3.17 % We lease certain buildings and branch facilities from various entities which are controlled by or affiliated with certain directors. Payments related to these leases totaled $5.9 million in 2019 , $464 thousand in 2018 and $1.4 million in 2017 . The increase in these lease payments during 2019 compared to 2018 was primarily related to the commencement of the lease of our new headquarters building during the second quarter of 2019. We recognized a right-of-use asset totaling $121.7 million and a related lease liability totaling $121.7 million in connection with this lease. The lease was a separate agreement under a comprehensive development agreement between us, the City of San Antonio and a third party controlled by one of our directors. We sold our old headquarters building to the City of San Antonio in 2016 and leased it back during the construction period of our new headquarters building. A portion of the gain from the sale of our old headquarters building was deferred and amortized to income over the term of the lease, which ended in the second quarter of 2019. Amortization of the deferred gain totaled $1.4 million in 2019, $2.8 million in 2018 and $2.9 million

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill . Year-end goodwill was as follows: 2019 2018 Goodwill $ 654,952 $ 654,952 Other Intangible Assets. Year-end other intangible assets were as follows: Gross Intangible Assets Accumulated Amortization Net Intangible Assets 2019 Core deposits $ 9,300 $ (7,257 ) $ 2,043 Customer relationships 3,388 (2,950 ) 438 $ 12,688 $ (10,207 ) $ 2,481 2018 Core deposits $ 9,300 $ (6,341 ) $ 2,959 Customer relationships 4,206 (3,534 ) 672 Non-compete agreements 74 (56 ) 18 $ 13,580 $ (9,931 ) $ 3,649 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 $1.2 million in 2019 , $1.4 million in 2018 , and $1.7 million in 2017 . The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2019 is as follows: 2020 $ 918 2021 697 2022 481 2023 282 2024 87 Thereafter 16 $ 2,481

Deposits

Deposits	12 Months Ended
	Dec. 31, 2019
Deposits [Abstract]
Deposits	Deposits Year-end deposits were as follows: 2019 2018 Non-interest-bearing demand deposits: Commercial and individual $ 10,212,265 $ 10,305,850 Correspondent banks 246,181 235,748 Public funds 415,183 455,896 Total non-interest-bearing demand deposits 10,873,629 10,997,494 Interest-bearing deposits: Private accounts: Savings and interest checking 7,147,327 6,977,813 Money market accounts 7,888,433 7,777,470 Time accounts of $100,000 or more 736,481 526,789 Time accounts under $100,000 347,418 331,511 Total private accounts 16,119,659 15,613,583 Public funds: Savings and interest checking 548,399 473,754 Money market accounts 73,180 59,953 Time accounts of $100,000 or more 24,672 4,332 Time accounts under $100,000 25 88 Total public funds 646,276 538,127 Total interest-bearing deposits 16,765,935 16,151,710 Total deposits $ 27,639,564 $ 27,149,204 The following table presents additional information about our year-end deposits: 2019 2018 Deposits from the Certificate of Deposit Account Registry Service (CDARS) $ 361 $ — Deposits from foreign sources (primarily Mexico) 805,828 752,658 Deposits not covered by deposit insurance 13,115,796 13,111,210 Deposits from certain directors, executive officers and their affiliates 197,919 199,321 Scheduled maturities of time deposits, including both private and public funds, at December 31, 2019 were as follows: 2020 $ 891,005 2021 217,591 $ 1,108,596 Scheduled maturities of time deposits in amounts of $100,000 or more, including both private and public funds, at December 31, 2019 , were as follows: Due within 3 months or less $ 191,563 Due after 3 months and within 6 months 140,654 Due after 6 months and within 12 months 271,209 Due after 12 months 157,727 $ 761,153

Borrowed Funds

Borrowed Funds	12 Months Ended
	Dec. 31, 2019
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 $27.2 million and $7.3 million at December 31, 2019 and 2018 . Securities sold under agreements to repurchase are secured short-term borrowings that typically mature overnight or 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 $1.7 billion and $1.4 billion at December 31, 2019 and 2018 . Subordinated Notes Payable. In March 2017, we issued $100 million of 4.50% subordinated notes that mature on March 17, 2027 . The notes, which qualify as Tier 2 capital for Cullen/Frost, bear interest at the rate of 4.50% per annum, payable semi-annually on each March 17 and September 17. The notes are unsecured and subordinated in right of payment to the payment of our existing and future senior indebtedness and structurally subordinated to all existing and future indebtedness of our subsidiaries. Unamortized debt issuance costs related to these notes, totaled approximately $1.1 million and $1.3 million December 31, 2019 and 2018 . Proceeds from sale of the notes were used for general corporate purposes. Our $100 million of 5.75% fixed-to-floating rate subordinated notes originally issued in February 2007 matured and were redeemed on February 15, 2017 . The notes qualified as Tier 2 capital for Cullen/Frost under the capital rules in effect prior to 2015. Prior to February 2012, the notes had a fixed interest rate of 5.75% per annum, after which the notes bore interest at a rate per annum equal to three-month LIBOR for the related interest period plus 0.53% ( 1.43% at December 31, 2016 ), paid quarterly. Junior Subordinated Deferrable Interest Debentures. At December 31, 2019 and 2018 , 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 totaled $816 thousand and $873 thousand at December 31, 2019 and 2018 . At December 31, 2019 and 2018 , 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 Bancshares, Inc. (“WNB”) in 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 $120.0 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 currently redeemable with the approval of the Federal Reserve Board in whole or in part at our option. 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 3.46% and 4.29% at December 31, 2019 and 2018 ) junior subordinated deferrable interest debentures issued by us, which have terms substantially similar to the trust preferred securities. 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 currently redeemable with the approval of the Federal Reserve Board in whole or in part at our option. 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 4.28% and 4.83% at December 31, 2019 and 2018 ) 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, 2019 and 2018 . See Note 9 - Capital and Regulatory Matters.

Off-Balance-Sheet Arrangements,

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies	12 Months Ended
	Dec. 31, 2019
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: 2019 2018 Commitments to extend credit $ 9,306,043 $ 8,369,721 Standby letters of credit 260,587 271,575 Deferred standby letter of credit fees 1,276 2,069 Credit Card Guarantees . We guarantee the credit card debt of certain customers to the merchant bank that issues the cards. At December 31, 2019 and 2018 , the guarantees totaled approximately $8.5 million and $8.1 million , of which amounts, $1.3 million and $1.4 million were fully collateralized. 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. 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, 2019
Broker-Dealer, Net Capital Requirement, SEC Regulation [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 designed 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, 2019 and 2018 included $144.5 million of 5.375% non-cumulative perpetual preferred stock. Frost Bank did not have any Additional Tier 1 capital beyond Common Equity Tier 1 at December 31, 2019 or 2018 . 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 both December 31, 2019 and 2018 , Cullen/Frost's Tier 2 capital included $133.0 million of trust preferred securities. At both December 31, 2019 and 2018 , Tier 2 Capital for Cullen/Frost also included $100.0 million related to the permissible portion of our aggregate $100 million of 4.50% subordinated notes. The permissible portion of qualified subordinated notes decreases 20% per year during the final five years of the term of the notes. The Common Equity Tier 1, 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. Fully phased in on January 1, 2019, the Basel III Capital Rules 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, effectively resulting in a minimum ratio of Common Equity Tier 1 capital to risk-weighted assets of at least 7.0% ), (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, effectively resulting in a minimum Tier 1 capital ratio of 8.5% ), (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, effectively resulting in a minimum total capital ratio of 10.5% ) 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 began on January 1, 2016 at the 0.625% level and was phased in over a four -year period (increasing by that amount on each subsequent January 1, until it reached 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 and the institution's “eligible retained income” (that is, four quarter trailing net income, net of distributions and tax effects not reflected in net income). The following table presents actual and required capital ratios as of December 31, 2019 and December 31, 2018 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, 2019 and December 31, 2018 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 Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2019 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,857,250 12.36 % $ 1,617,886 7.00 % $ 1,502,323 6.50 % Frost Bank 2,958,326 12.82 1,615,206 7.00 1,499,834 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 3,001,736 12.99 1,964,576 8.50 1,849,013 8.00 Frost Bank 2,958,326 12.82 1,961,322 8.50 1,845,950 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 3,367,403 14.57 2,426,829 10.50 2,311,266 10.00 Frost Bank 3,090,993 13.40 2,422,809 10.50 2,307,438 10.00 Leverage Ratio Cullen/Frost 3,001,736 9.28 1,293,188 4.00 1,616,485 5.00 Frost Bank 2,958,326 9.15 1,292,743 4.00 1,615,929 5.00 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 2018 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,642,475 12.27 % $ 1,372,573 6.375 % $ 1,507,139 7.00 % $ 1,399,486 6.50 % Frost Bank 2,743,973 12.78 1,368,701 6.375 1,502,887 7.00 1,395,538 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,786,961 12.94 1,695,532 7.875 1,830,098 8.50 1,722,445 8.00 Frost Bank 2,743,973 12.78 1,690,748 7.875 1,824,934 8.50 1,717,585 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 3,152,593 14.64 2,126,143 9.875 2,260,709 10.50 2,153,056 10.00 Frost Bank 2,876,605 13.40 2,120,144 9.875 2,254,331 10.50 2,146,982 10.00 Leverage Ratio Cullen/Frost 2,786,961 9.06 1,231,028 4.00 1,231,028 4.00 1,538,785 5.00 Frost Bank 2,743,973 8.93 1,229,650 4.00 1,229,650 4.00 1,537,062 5.00 Management believes that, as of December 31, 2019 , 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, 2019 , 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 repurchase of common stock. 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 July 24, 2019 , our board of directors authorized a $100.0 million stock repurchase program, allowing us to repurchase shares of our common stock over a one -year period from time to time at various prices in the open market or through private transactions. Under this plan, we repurchased 202,724 shares at a total cost of $17.2 million during 2019. Under a prior stock repurchase programs, we repurchased 496,307 shares at a total cost of $50.0 million during 2019, 1,027,292 shares at a total cost of $100.0 million during 2018 and 1,134,966 shares at a total cost of $100.0 million during 2017. Under the Basel III Capital Rules, Cullen/Frost may not repurchase its common stock (or repurchase or redeem any of its preferred stock or subordinated notes) without the prior approval of the Federal Reserve Board. 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, including to repurchase its common stock. 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, 2019 , Frost Bank could pay aggregate dividends of up to $682.9 million to Cullen/Frost without prior regulatory approval. Under the terms of the junior subordinated deferrable interest debentures that Cullen/Frost has issued to Cullen/Frost Capital Trust II and WNB Capital Trust I, Cullen/Frost has the right at any time during the term of the debentures to defer the payment of interest at any time or from time to time for an extension period not exceeding 20 consecutive quarterly periods with respect to each extension period. In the event that 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, 2019
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, deferred stock units and performance stock units (during the performance period), though no actual shares of common stock related to any type of stock unit 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. Holders of performance stock units receive dividend equivalent payments for dividends paid during the performance period at the vesting date of the award based upon the number of units that ultimately vest. 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. 2019 2018 2017 Net Income $ 443,599 $ 454,918 $ 364,149 Less: Preferred stock dividends 8,063 8,063 8,063 Net income available to common shareholders 435,536 446,855 356,086 Less: Earnings allocated to participating securities 3,687 3,169 2,016 Net earnings allocated to common stock $ 431,849 $ 443,686 $ 354,070 Distributed earnings allocated to common stock $ 175,540 $ 164,268 $ 143,356 Undistributed earnings allocated to common stock 256,309 279,418 210,714 Net earnings allocated to common stock $ 431,849 $ 443,686 $ 354,070 Weighted-average shares outstanding for basic earnings per common share 62,741,769 63,704,508 63,693,927 Dilutive effect of stock compensation 700,101 982,208 968,161 Weighted-average shares outstanding for diluted earnings per common share 63,441,870 64,686,716 64,662,088

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans Retirement Plans Profit Sharing Plans. Prior to 2019, we maintained a qualified defined contribution profit sharing plan that covered employees who had completed at least one year of service and were age 21 or older. The Plan was merged with and into our 401(k) plan effective January 1, 2019, as further discussed below. Expense related to this plan totaled $11.9 million in 2018 and $11.6 million in 2017 . We continue to maintain a separate non-qualified profit sharing plan for certain employees whose participation in the qualified profit sharing plan was limited. The plan offers such employees an alternative means of receiving comparable benefits. Expense related to this plan totaled $930 thousand in 2019 , $568 thousand in 2018 and $1.1 million in 2017 . 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: 2019 2018 2017 Change in plan assets: Fair value of plan assets at beginning of year $ 152,820 $ 168,450 $ 157,214 Actual return on plan assets 29,945 (7,739 ) 23,518 Employer contributions 1,163 1,077 1,049 Benefits paid (9,755 ) (8,968 ) (13,331 ) Fair value of plan assets at end of year 174,173 152,820 168,450 Change in benefit obligation: Benefit obligation at beginning of year 167,107 182,607 176,751 Interest cost 6,472 5,898 6,189 Actuarial (gain) loss 22,817 (12,430 ) 12,998 Benefits paid (9,755 ) (8,968 ) (13,331 ) Benefit obligation at end of year 186,641 167,107 182,607 Funded status of the plan at end of year and accrued benefit (liability) recognized $ (12,468 ) $ (14,287 ) $ (14,157 ) Accumulated benefit obligation at end of year $ 186,641 $ 167,107 $ 182,607 Certain disaggregated information related to our defined benefit pension plans as of year-end was as follows: Retirement Plan Restoration Plan 2019 2018 2019 2018 Projected benefit obligation $ 170,541 $ 152,035 $ 16,100 $ 15,072 Accumulated benefit obligation 170,541 152,035 16,100 15,072 Fair value of plan assets 174,173 152,820 — — Funded status of the plan at end of year and accrued benefit (liability) recognized 3,632 785 (16,100 ) (15,072 ) The components of the combined net periodic cost (benefit) for our defined benefit pension plans are presented in the table below. 2019 2018 2017 Expected return on plan assets, net of expenses $ (10,772 ) $ (11,916 ) $ (11,117 ) Interest cost on projected benefit obligation 6,472 5,898 6,189 Net amortization and deferral 5,623 5,002 5,429 Net periodic expense (benefit) $ 1,323 $ (1,016 ) $ 501 Amounts related to our defined benefit pension plans recognized as a component of other comprehensive income were as follows: 2019 2018 2017 Net actuarial gain (loss) $ 1,979 $ (2,223 ) $ 4,832 Deferred tax (expense) benefit (416 ) 466 (1,774 ) Other comprehensive income (loss), net of tax $ 1,563 $ (1,757 ) $ 3,058 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 $5.3 million of the net actuarial loss reported in the following table as of December 31, 2019 as a component of net periodic benefit cost during 2020 . 2019 2018 Net actuarial loss $ (57,964 ) $ (60,123 ) Deferred tax benefit 12,210 12,626 Amounts included in accumulated other comprehensive income/loss, net of tax (45,934 ) (47,497 ) 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. 2019 2018 2017 Benefit obligations: Discount rate 3.20 % 4.36 % 3.68 % Net periodic benefit cost: Discount rate 4.36 % 3.68 % 4.24 % Expected return on plan assets 7.25 7.25 7.25 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, 2019 , 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 64% invested in equity securities, approximately 32% invested in fixed income debt securities with any remainder invested in cash or short-term cash equivalents. The asset allocation optimization process provides portfolio allocations which best represent the potential risk associated with a given asset allocation over a full market cycle. This is used to help management determine an appropriate mix of assets in order to achieve the plan's long term investment goals. 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 17 - Fair Value Measurements). Our Restoration Plan is unfunded. 2019 2018 Level 1: Mutual funds $ 172,773 $ 152,477 Cash and cash equivalents 1,400 343 Total fair value of plan assets $ 174,173 $ 152,820 Mutual funds include various equity, fixed-income and blended funds with varying investment strategies. Approximately 68% of mutual fund investments consist of equity investments as of December 31, 2019 . 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. U.S. government agency securities include obligations of Ginnie Mae. 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 2019 . 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, 2019 , expected future benefit payments related to our defined benefit plans were as follows: 2020 $ 10,662 2021 10,968 2022 11,177 2023 11,423 2024 11,578 2025 through 2029 57,122 $ 112,930 We expect to contribute $1.2 million to the defined benefit plans during 2020 . Savings Plans 401(k) Plan and Thrift Incentive Plan. We maintain a 401(k) stock purchase plan that permits each participant to make before-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 30 days of service in order to enroll and vest in our matching contributions immediately. 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. In 2019, we merged our qualified profit sharing plan with and into the 401(k) plan. All profit 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. Profit sharing contributions are subject to withdrawal restrictions and participants vest in their allocated contributions after three years of service. Expense related to the plan totaled $28.9 million ( $16.3 million matching contributions and $12.6 million profit sharing) in 2019 , $15.0 million in 2018 , and $14.3 million in 2017 . 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 2019 , 2018 and 2017 . 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 award price, the duration of the award, the number of shares to which the award pertains, and such other provisions as the Committee determines. For stock options, 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 . As defined in the plans, outstanding awards may immediately vest upon a change-in-control of Cullen/Frost and, in the case of awards granted under the 2015 Plan, subsequent termination resulting from the change in control. A combined summary of activity in our active stock plans is presented in the table. Performance stock units outstanding are presented assuming attainment of the maximum payout rate as set forth by the performance criteria. The target award level for performance stock units granted in 2019 , 2018 and 2017 was 34,317 , 30,466 and 24,162 , respectively. As of December 31, 2019 , there were 1,105,616 shares remaining available for grant for future awards. Director Deferred Stock Units Outstanding Non-Vested Stock Awards/Stock Units Outstanding Performance Stock Units Outstanding Stock Options Outstanding Number of Units Weighted- Average Fair Value at Grant Number of Shares/Units Weighted- Average Fair Value at Grant Number of Units Weighted- Average Fair Value at Grant Number of Shares Weighted- Average Exercise Price January 1, 2017 53,659 $ 61.48 256,850 $ 73.43 43,860 $ 69.70 4,089,028 $ 62.67 Authorized — — — — — — — — Granted 5,447 95.37 99,833 98.90 36,246 92.27 — — Exercised/vested (6,098 ) 62.29 (39,740 ) 71.59 — — (1,118,122 ) 60.59 Forfeited/expired — — (4,287 ) 79.52 — — (53,764 ) 69.78 December 31, 2017 53,008 64.87 312,656 81.71 80,106 79.91 2,917,142 63.34 Authorized — — — — — — — — Granted 6,576 109.58 109,847 94.81 45,703 87.18 — — Exercised/vested (10,674 ) 63.68 (32,050 ) 78.92 — — (513,134 ) 61.68 Forfeited/expired — — (6,656 ) 87.60 — — (52,000 ) 70.42 December 31, 2018 48,910 71.14 383,797 85.59 125,809 82.55 2,352,008 63.55 Authorized — — — — — — — — Granted 7,592 102.70 127,091 93.46 51,479 85.74 — — Exercised/vested (1,132 ) 106.03 (53,990 ) 65.11 — — (359,892 ) 57.71 Forfeited/expired — — (16,251 ) 89.71 — — (11,250 ) 65.11 December 31, 2019 55,370 $ 74.76 440,647 $ 90.22 177,288 $ 83.48 1,980,866 $ 64.60 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. 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. Performance stock units represent shares potentially issuable in the future. Issuance is based upon the measure of our achievement of relative return on assets over a three-year performance period compared to an identified peer group's achievement of relative return on assets over the same three-year performance period. The ultimate number of shares issuable under each performance award is the product of the award target and the award payout percentage for the given level of achievement. The level of achievement is measured as the percentile rank of relative return on assets among the peer group. The award payout percentages by level of achievement are as follows: (i) less than 25th percentile pays out at 0% of target, (ii) 25th percentile pays out at 50% of target, (iii) 50th percentile pays out at 100% of target and (iv) 75th percentile or more pays out at 150% of target. Achievement between the aforementioned percentiles will result in an award payout percentage determined based on straight-line interpolation between the percentiles. Performance stock units are eligible to receive equivalent dividend payments as such dividends are declared on our common stock during the performance period. Equivalent dividend payments are based upon the ultimate number of shares issued under each performance award and are deferred until such time that the units vest and shares are issued. Other information regarding options outstanding and exercisable as of December 31, 2019 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 $ 50.00 238,055 $ 48.00 1.82 238,055 $ 48.00 50.01 to 55.00 464,009 53.75 2.04 464,009 53.75 65.01 to 70.00 526,096 65.11 5.67 526,096 65.11 70.01 to 75.00 275,654 71.39 3.80 275,654 71.39 75.01 to 80.00 477,052 78.95 4.71 477,052 78.95 Total 1,980,866 64.60 3.87 1,980,866 64.60 Total intrinsic value $ 65,725 $ 65,725 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: 2019 2018 2017 New shares issued from available authorized shares — — 603,842 Issued from available treasury stock 399,224 548,238 547,078 Total 399,224 548,238 1,150,920 Proceeds from stock option exercises $ 20,770 $ 31,647 $ 67,746 Intrinsic value of stock options exercised 13,713 23,292 38,275 Fair value of stock awards/units vested 5,192 4,212 4,578 Stock-based Compensation Expense. Stock-based compensation expense is recognized ratably over the requisite service period for all awards. For most stock option awards, the service period generally matches the vesting period. For stock options granted to certain executive officers and for non-vested stock units granted to all participants, the service period does not extend past the date the participant reaches 65 years of age. Deferred stock units granted to non-employee directors generally have immediate vesting and the related expense is fully recognized on the date of grant. For performance stock units, the service period generally matches the three-year performance period specified by the award, however, the service period does not extend past the date the participant reaches 65 years of age. Expense recognized each period is dependent upon our estimate of the number of shares that will ultimately be issued. Stock-based compensation expense and the related income tax benefit is presented in the following table. The service period for performance stock units granted each year begins on January 1 of the following year. 2019 2018 2017 Stock options $ 1,185 $ 3,652 $ 6,230 Non-vested stock awards/stock units 9,339 6,983 4,992 Deferred stock-units 780 721 519 Performance stock units 4,642 2,587 1,272 Total $ 15,946 $ 13,943 $ 13,013 Income tax benefit $ 2,359 $ 2,831 $ 4,555 Unrecognized stock-based compensation expense and the weighted-average period over which the expense is expected to be recognized at December 31, 2019 is presented in the table below. Unrecognized stock-based compensation expense related to performance stock units is presented assuming attainment of the maximum payout rate as set forth by the performance criteria. Unrecognized Expense Weighted-Average Number of Years for Expense Recognition Non-vested stock awards/stock units $ 18,882 2.81 Performance stock units 6,299 2.11 Total $ 25,181 Valuation of Stock-Based Compensation . For the purposes of recognizing stock-based compensation expense, the fair value of non-vested stock awards/stock units and deferred stock units is generally the market price of the stock on the measurement date, which, for us, is the date of the award. The fair value of performance stock units is determined in a similar manner except that the market price of the stock on the measurement date is discounted by the present value of the dividends expected to be paid on our common stock during the service period of the award because dividend equivalent payments on performance stock units are deferred until such time that the units vest and shares are issued. In applying this discount to the market price of our stock on the measurement date, we assumed we would pay a flat quarterly dividend during the service period equal to our most recent dividend payment, which was $0.71 , $0.67 and $0.57 in 2019 , 2018 , and 2017 respectively discounted at a weighted-average risk-free rate of 1.65% , 2.95% and 1.73% in 2019 , 2018 , and 2017 respectively. The fair value of 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. No

Other Non-Interest Income and E

Other Non-Interest Income and Expense	12 Months Ended
	Dec. 31, 2019
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. 2019 2018 2017 Other non-interest income: Other $ 43,563 $ 46,790 $ 37,222 Total $ 43,563 $ 46,790 $ 37,222 Other non-interest expense: Professional services $ 39,238 $ 35,941 $ 27,968 Advertising, promotions and public relations 38,001 32,514 29,337 Travel/meals and entertainment 16,459 15,030 15,066 Check card expense 5,947 4,744 16,501 Other 81,020 85,309 86,417 Total $ 180,665 $ 173,538 $ 175,289 As discussed in Note 1 - Summary of Significant Accounting Policies, a new accounting standard adopted in 2018 requires us to report network costs associated with debit card and ATM transactions netted against the related fee income from such transactions. Previously, such network costs were reported as a component of check card expense and included in other non-interest expense. In 2019 and 2018, network costs totaling $12.9 million and $11.9 million are reported as a component of interchange and debit card transaction fees in the accompanying Consolidated Statement of Income rather than as a component of check card expense in the table above. For 2017, network costs totaling $11.9 million were reported as a component of check card expense in the table above. In the ordinary course of business, we transact with certain directors and/or their affiliates. Payments for services provided totaled $567 thousand in 2019 , $568 thousand in 2018 and $833 thousand in 2017 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Tax Cuts and Jobs Act. The Tax Cuts and Jobs Act was enacted on December 22, 2017. Among other things, the new law (i) established a new, flat corporate federal statutory income tax rate of 21% , (ii) eliminated the corporate alternative minimum tax and allowed the use of any such carryforwards to offset regular tax liability for any taxable year, (iii) limited the deduction for net interest expense incurred by U.S. corporations, (iv) allowed businesses to immediately expense, for tax purposes, the cost of new investments in certain qualified depreciable assets, (v) eliminated or reduced certain deductions related to meals and entertainment expenses, (vi) modified the limitation on excessive employee remuneration to eliminate the exception for performance-based compensation and clarified the definition of a covered employee and (vii) limited the deductibility of deposit insurance premiums. The Tax Cuts and Jobs Act also significantly changes U.S. tax law related to foreign operations, however, such changes do not currently impact us. Income Taxes. Income tax expense was as follows: 2019 2018 2017 Current income tax expense $ 48,256 $ 840 $ 58,707 Deferred income tax expense (benefit) 7,614 52,923 (14,493 ) Income tax expense, as reported $ 55,870 $ 53,763 $ 44,214 Effective tax rate 11.2 % 10.6 % 10.8 % A reconciliation between reported income tax expense and the amounts computed by applying the U.S. federal statutory income tax rate of 21% in 2019 and 2018 and 35% in 2017 to income before income taxes is presented in the following table. 2019 2018 2017 Income tax expense computed at the statutory rate $ 104,888 $ 106,823 $ 142,927 Effect of tax-exempt interest (49,166 ) (49,700 ) (81,034 ) Tax benefit on dividends paid in our 401k plan (1,743 ) (1,551 ) (2,372 ) Bank owned life insurance income (774 ) (710 ) (1,116 ) Non-deductible compensation 1,708 210 158 Non-deductible FDIC premiums 1,267 1,771 — Non-deductible meals and entertainment 1,299 1,193 983 Net tax benefit from stock-based compensation (2,447 ) (3,865 ) (9,062 ) Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate — (231 ) (4,047 ) Correction for prior year tax-exempt interest — — (2,906 ) Other 838 (177 ) 683 Income tax expense, as reported $ 55,870 $ 53,763 $ 44,214 Income tax expense for 2017 was impacted by the adjustment of our deferred tax assets and liabilities related to the reduction in the U.S. federal statutory income tax rate to 21% under the Tax Cuts and Jobs Act. As a result of the new law, and as detailed in the table above, we recognized a provisional net tax benefit totaling $4.0 million in 2017 and an additional net tax benefit resulting from a finalization of those calculations totaling $231 thousand in 2018. Income tax expense for 2017 was also impacted by the correction of an over-accrual of taxes that resulted from incorrectly classifying certain tax-exempt loans as taxable for federal income tax purposes since 2013. As a result, we recognized tax benefits of $2.9 million in 2017 related to the 2013 through 2016 tax years, as detailed in the table above. There were no unrecognized tax benefits during any of the reported periods. Interest and/or penalties related to income taxes are reported as a component of income tax expense. Such amounts were not significant during the reported periods. Year-end deferred taxes are presented in the table below. Deferred taxes are based on the U.S. statutory federal income tax rate of 21% . 2019 2018 Deferred tax assets: Lease liabilities under operating leases $ 67,975 $ — Allowance for loan losses 27,755 27,748 Net actuarial loss on defined benefit post-retirement benefit plans 12,210 12,626 Stock-based compensation 11,211 10,622 Bonus accrual 5,055 4,586 Net unrealized loss on securities available for sale and transferred securities — 4,283 Deferred loan and lease origination fees 2,254 2,153 Other 2,163 4,761 Total gross deferred tax assets 128,623 66,779 Deferred tax liabilities: Net unrealized gain on securities available for sale and transferred securities (83,281 ) — Right-of-use assets under operating leases (63,463 ) — Premises and equipment (29,730 ) (23,859 ) Intangible assets (12,642 ) (10,726 ) Defined benefit post-retirement benefit plans (9,419 ) (9,452 ) Partnership interests (2,894 ) — Leases (1,572 ) (1,709 ) Other (1,440 ) (1,257 ) Total gross deferred tax liabilities (204,441 ) (47,003 ) Net deferred tax asset (liability) $ (75,818 ) $ 19,776 No valuation allowance for deferred tax assets was recorded at December 31, 2019 and 2018 as management believes it is more likely than not that all of the deferred tax assets will be realized against deferred tax liabilities and projected future taxable income. 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 2016.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2019
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 2019 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 418,556 $ 87,897 $ 330,659 Change in net unrealized gain on securities transferred to held to maturity (1,292 ) (271 ) (1,021 ) Reclassification adjustment for net (gains) losses included in net income (293 ) (62 ) (231 ) Total securities available for sale and transferred securities 416,971 87,564 329,407 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (3,644 ) (765 ) (2,879 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,623 1,181 4,442 Total defined-benefit post-retirement benefit plans 1,979 416 1,563 Total other comprehensive income (loss) $ 418,950 $ 87,980 $ 330,970 2018 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ (182,340 ) $ (38,292 ) $ (144,048 ) Change in net unrealized gain on securities transferred to held to maturity (8,818 ) (1,853 ) (6,965 ) Reclassification adjustment for net (gains) losses included in net income 156 33 123 Total securities available for sale and transferred securities (191,002 ) (40,112 ) (150,890 ) Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (7,225 ) (1,517 ) (5,708 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,002 1,051 3,951 Total defined-benefit post-retirement benefit plans (2,223 ) (466 ) (1,757 ) Total other comprehensive income (loss) $ (193,225 ) $ (40,578 ) $ (152,647 ) 2017 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 157,016 $ 48,626 $ 108,390 Change in net unrealized gain on securities transferred to held to maturity (16,193 ) (5,668 ) (10,525 ) Reclassification adjustment for net (gains) losses included in net income 4,941 1,729 3,212 Total securities available for sale and transferred securities 145,764 44,687 101,077 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (597 ) (126 ) (471 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,429 1,900 3,529 Total defined-benefit post-retirement benefit plans 4,832 1,774 3,058 Total other comprehensive income (loss) $ 150,596 $ 46,461 $ 104,135 Activity in accumulated other comprehensive income, net of tax, was as follows: Securities Available For Sale Defined Benefit Plans Accumulated Other Comprehensive Income Balance January 1, 2019 $ (16,103 ) $ (47,497 ) $ (63,600 ) Other comprehensive income (loss) before reclassification 329,638 (2,879 ) 326,759 Reclassification of amounts included in net income (231 ) 4,442 4,211 Net other comprehensive income (loss) during period 329,407 1,563 330,970 Balance December 31, 2019 $ 313,304 $ (45,934 ) $ 267,370 Balance January 1, 2018 $ 117,230 $ (37,718 ) $ 79,512 Other comprehensive income (loss) before reclassification (151,013 ) (5,708 ) (156,721 ) Reclassification of amounts included in net income 123 3,951 4,074 Net other comprehensive income (loss) during period (150,890 ) (1,757 ) (152,647 ) Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act to retained earnings 17,557 (8,022 ) 9,535 Balance December 31, 2018 $ (16,103 ) $ (47,497 ) $ (63,600 ) Balance January 1, 2017 $ 16,153 $ (40,776 ) $ (24,623 ) Other comprehensive income (loss) before reclassification 97,865 (471 ) 97,394 Reclassification of amounts included in net income 3,212 3,529 6,741 Net other comprehensive income (loss) during period 101,077 3,058 104,135 Balance December 31, 2017 $ 117,230 $ (37,718 ) $ 79,512

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2019
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. 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, 2019 and 2018 are presented in the following table. The fair values of interest rate derivative contracts are estimated utilizing internal valuation models with observable market data inputs, or as determined by the Chicago Mercantile Exchange (“CME”) for centrally cleared derivative contracts. CME rules legally characterize variation margin payments for centrally cleared derivatives as settlements of the derivatives' exposure rather than collateral. As a result, the variation margin payment and the related derivative instruments are considered a single unit of account for accounting and financial reporting purposes. Variation margin, as determined by the CME, is settled daily. As a result, derivative contracts that clear through the CME have an estimated fair value of zero as of December 31, 2019 and 2018 . December 31, 2019 December 31, 2018 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 $ 2,545 $ 6 $ 10,941 $ 207 Loan/lease interest rate swaps - liabilities 6,000 (138 ) 3,885 (199 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps - assets 122,788 67 496,887 2,384 Loan/lease interest rate swaps - liabilities 1,002,860 (19,483 ) 691,143 (8,921 ) Loan/lease interest rate caps - assets 107,835 266 122,791 509 Customer counterparties: Loan/lease interest rate swaps - assets 1,002,860 43,857 691,143 16,706 Loan/lease interest rate swaps - liabilities 122,788 (310 ) 496,887 (8,891 ) Loan/lease interest rate caps - liabilities 107,835 (266 ) 122,791 (509 ) The weighted-average rates paid and received for interest rate swaps outstanding at December 31, 2019 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.66 % 1.75 % Non-hedging interest rate swaps - financial institution counterparties 4.12 3.45 Non-hedging interest rate swaps - customer counterparties 3.45 4.12 The weighted-average strike rate for outstanding interest rate caps was 3.14% at December 31, 2019 . 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, 2019 December 31, 2018 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil - assets Barrels 1,214 $ 2,796 2,416 $ 24,332 Oil - liabilities Barrels 2,148 (6,916 ) 415 (646 ) Natural gas - assets MMBTUs 8,295 2,131 5,745 417 Natural gas - liabilities MMBTUs 2,689 (70 ) 9,314 (1,272 ) Customer counterparties: Oil - assets Barrels 2,172 7,208 415 646 Oil - liabilities Barrels 1,190 (2,652 ) 2,416 (24,009 ) Natural gas - assets MMBTUs 2,689 83 10,236 1,373 Natural gas - liabilities MMBTUs 8,295 (2,039 ) 4,823 (393 ) 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, 2019 December 31, 2018 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts - liabilities CAD 4,593 $ (33 ) 11,003 $ (13 ) Forward contracts - liabilities GBP — — 142 (2 ) Forward contracts - liabilities MXN — — 3,015 (132 ) Customer counterparties: Forward contracts - assets CAD 4,583 45 10,979 40 Forward contracts - assets GBP — — 145 4 Forward contracts - assets MXN — — 3,000 149 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 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: 2019 2018 2017 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ 86 $ 25 $ (726 ) Amount of (gain) loss included in other non-interest expense — (1 ) (14 ) 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, foreign currency and other derivative instruments are presented in the table below. 2019 2018 2017 Non-hedging interest rate derivatives: Other non-interest income $ 2,005 $ 4,112 $ 3,123 Other non-interest expense (1 ) — 1 Non-hedging commodity derivatives: Other non-interest income 503 795 440 Non-hedging foreign currency derivatives: Other non-interest income 51 246 300 Non-hedging other derivatives: Other non-interest income 750 — — 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 $47.1 million at December 31, 2019 . 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 $16.1 million at December 31, 2019 . 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 16 – Balance Sheet Offsetting and Repurchase Agreements for additional information regarding our credit exposure with upstream financial institution counterparties. At December 31, 2019 we had $37.5 million in cash collateral related to derivative contracts on deposit with other financial institution counterparties.

Balance Sheet Offsetting

Balance Sheet Offsetting	12 Months Ended
	Dec. 31, 2019
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, 2019 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2019 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 339 $ — $ 339 Commodity swaps and options 4,927 — 4,927 Total derivatives 5,266 — 5,266 Resell agreements 31,299 — 31,299 Total $ 36,565 $ — $ 36,565 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 19,621 $ — $ 19,621 Commodity swaps and options 6,986 — 6,986 Foreign currency forward contracts 33 — 33 Total derivatives 26,640 — 26,640 Repurchase agreements 1,668,142 — 1,668,142 Total $ 1,694,782 $ — $ 1,694,782 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2019 Financial assets: Derivatives: Counterparty A $ 39 $ (39 ) $ — $ — Counterparty B 1,650 (1,650 ) — — Counterparty C 1 (1 ) — — Other counterparties 3,576 (3,546 ) — 30 Total derivatives 5,266 (5,236 ) — 30 Resell agreements 31,299 — (31,299 ) — Total $ 36,565 $ (5,236 ) $ (31,299 ) $ 30 Financial liabilities: Derivatives: Counterparty A $ 5,192 $ (39 ) $ (5,153 ) $ — Counterparty B 7,424 (1,650 ) (5,774 ) — Counterparty C 135 (1 ) (134 ) — Other counterparties 13,889 (3,546 ) (10,343 ) — Total derivatives 26,640 (5,236 ) (21,404 ) — Repurchase agreements 1,668,142 — (1,668,142 ) — Total $ 1,694,782 $ (5,236 ) $ (1,689,546 ) $ — Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2018 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2018 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,100 $ — $ 3,100 Commodity swaps and options 24,749 — 24,749 Total derivatives 27,849 — 27,849 Resell agreements 11,642 — 11,642 Total $ 39,491 $ — $ 39,491 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 9,120 $ — $ 9,120 Commodity swaps and options 1,918 — 1,918 Foreign currency forward contracts 147 — 147 Total derivatives 11,185 — 11,185 Repurchase agreements 1,360,298 — 1,360,298 Total $ 1,371,483 $ — $ 1,371,483 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2018 Financial assets: Derivatives: Counterparty A $ 598 $ (598 ) $ — $ — Counterparty B 7,255 (3,380 ) (3,875 ) — Counterparty C 81 (81 ) — — Other counterparties 19,915 (2,084 ) (17,776 ) 55 Total derivatives 27,849 (6,143 ) (21,651 ) 55 Resell agreements 11,642 — (11,642 ) — Total $ 39,491 $ (6,143 ) $ (33,293 ) $ 55 Financial liabilities: Derivatives: Counterparty A $ 4,293 $ (598 ) $ (3,651 ) $ 44 Counterparty B 3,380 (3,380 ) — — Counterparty C 326 (81 ) (245 ) — Other counterparties 3,186 (2,084 ) (725 ) 377 Total derivatives 11,185 (6,143 ) (4,621 ) 421 Repurchase agreements 1,360,298 — (1,360,298 ) — Total $ 1,371,483 $ (6,143 ) $ (1,364,919 ) $ 421 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, 2019 and December 31, 2018 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, 2019 Repurchase agreements: U.S. Treasury $ 435,904 $ — $ — $ — $ 435,904 Residential mortgage-backed securities 1,232,238 — — — 1,232,238 Total borrowings $ 1,668,142 $ — $ — $ — $ 1,668,142 Gross amount of recognized liabilities for repurchase agreements $ 1,668,142 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2018 Repurchase agreements: U.S. Treasury $ 1,334,063 $ — $ — $ — $ 1,334,063 Residential mortgage-backed securities 26,235 — — — 26,235 Total borrowings $ 1,360,298 $ — $ — $ — $ 1,360,298 Gross amount of recognized liabilities for repurchase agreements $ 1,360,298 Amounts related to agreements not included in offsetting disclosures above $ —

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
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 tables summarize financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 , 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 2019 Securities available for sale: U.S. Treasury $ 1,948,133 $ — $ — $ 1,948,133 Residential mortgage-backed securities — 2,207,594 — 2,207,594 States and political subdivisions — 7,070,997 — 7,070,997 Other — 42,867 — 42,867 Trading account securities: U.S. Treasury 24,298 — — 24,298 Derivative assets: Interest rate swaps, caps and floors — 44,196 — 44,196 Commodity swaps and options — 12,218 — 12,218 Foreign currency forward contracts 45 — — 45 Derivative liabilities: Interest rate swaps, caps and floors — 20,197 — 20,197 Commodity swaps and options — 11,677 — 11,677 Foreign currency forward contracts 33 — — 33 2018 Securities available for sale: U.S. Treasury $ 3,427,689 $ — $ — $ 3,427,689 Residential mortgage-backed securities — 829,740 — 829,740 States and political subdivisions — 7,087,202 — 7,087,202 Other — 42,690 — 42,690 Trading account securities: U.S. Treasury 21,928 — — 21,928 States and political subdivisions — 2,158 — 2,158 Derivative assets: Interest rate swaps, caps and floors — 19,806 — 19,806 Commodity swaps and options — 26,768 — 26,768 Foreign currency forward contracts 193 — — 193 Derivative liabilities: Interest rate swaps, caps and floors — 18,520 — 18,520 Commodity swaps and options — 26,320 — 26,320 Foreign currency forward contracts 147 — — 147 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, oil and gas reserves, 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: 2019 2018 2017 Level 2 Carrying value of impaired loans before allocations $ 2,354 $ 12,517 $ — Specific valuation allowance allocations (383 ) (2,599 ) — Fair value $ 1,971 $ 9,918 $ — Level 3 Carrying value of impaired loans before allocations $ 65,176 $ 22,688 $ 75,435 Specific valuation allowance allocations (18,019 ) 9,260 (19,533 ) Fair value $ 47,157 $ 31,948 $ 55,902 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: 2019 2018 2017 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 1,348 $ 2,899 $ 279 Charge-offs recognized in the allowance for loan losses (76 ) — — Fair value $ 1,272 $ 2,899 $ 279 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ — $ 1,823 $ 89 Write-downs included in other non-interest expense — (473 ) (16 ) Fair value $ — $ 1,350 $ 73 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. 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, 2019 December 31, 2018 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,788,181 $ 3,788,181 $ 3,955,779 $ 3,955,779 Securities held to maturity 2,030,005 2,048,675 1,106,057 1,116,953 Cash surrender value of life insurance policies 187,156 187,156 183,473 183,473 Accrued interest receivable 183,850 183,850 188,989 188,989 Level 3 inputs: Loans, net 14,618,165 14,654,615 13,967,601 13,933,239 Financial liabilities: Level 2 inputs: Deposits 27,639,564 27,641,255 27,149,204 27,143,572 Federal funds purchased and repurchase agreements 1,695,342 1,695,342 1,367,548 1,367,548 Junior subordinated deferrable interest debentures 136,299 137,115 136,242 137,115 Subordinated notes payable and other borrowings 98,865 89,077 98,708 98,458 Accrued interest payable 12,393 12,393 7,394 7,394 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, 2019
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 and Frost Insurance Agency. Commercial banking services are provided to corporations and other business clients and include a wide array of lending and cash management products. Consumer banking services include direct lending and depository services. Frost Insurance Agency provides insurance brokerage services to individuals and businesses covering corporate and personal property and casualty products, as well as group health and life insurance products. 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. Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $37.8 billion , $33.3 billion and $32.8 billion at December 31, 2019 , 2018 and 2017 . Banking Frost Wealth Advisors Non-Banks Consolidated 2019 Net interest income (expense) $ 1,010,368 $ 4,001 $ (10,364 ) $ 1,004,005 Provision for loan losses 33,758 1 — 33,759 Non-interest income 218,447 145,905 (450 ) 363,902 Non-interest expense 703,121 124,622 6,936 834,679 Income (loss) before income taxes 491,936 25,283 (17,750 ) 499,469 Income tax expense (benefit) 55,520 5,308 (4,958 ) 55,870 Net income (loss) 436,416 19,975 (12,792 ) 443,599 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 436,416 $ 19,975 $ (20,855 ) $ 435,536 Revenues from (expenses to) external customers $ 1,228,815 $ 149,906 $ (10,814 ) $ 1,367,907 Average assets (in millions) $ 32,019 $ 56 $ 11 $ 32,086 Banking Frost Wealth Advisors Non-Banks Consolidated 2018 Net interest income (expense) $ 963,757 $ 4,083 $ (9,948 ) $ 957,892 Provision for loan losses 21,613 — — 21,613 Non-interest income 213,763 138,045 (522 ) 351,286 Non-interest expense 657,448 114,166 7,270 778,884 Income (loss) before income taxes 498,459 27,962 (17,740 ) 508,681 Income tax expense (benefit) 52,928 5,872 (5,037 ) 53,763 Net income (loss) 445,531 22,090 (12,703 ) 454,918 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 445,531 $ 22,090 $ (20,766 ) $ 446,855 Revenues from (expenses to) external customers $ 1,177,520 $ 142,128 $ (10,470 ) $ 1,309,178 Average assets (in millions) $ 30,964 $ 54 $ 12 $ 31,030 2017 Net interest income (expense) $ 856,593 $ 17,644 $ (7,815 ) $ 866,422 Provision for loan losses 35,460 — — 35,460 Non-interest income 207,810 128,819 (159 ) 336,470 Non-interest expense 644,072 108,931 6,066 759,069 Income (loss) before income taxes 384,871 37,532 (14,040 ) 408,363 Income tax expense (benefit) 37,837 13,137 (6,760 ) 44,214 Net income (loss) 347,034 24,395 (7,280 ) 364,149 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 347,034 $ 24,395 $ (15,343 ) $ 356,086 Revenues from (expenses to) external customers $ 1,064,403 $ 146,463 $ (7,974 ) $ 1,202,892 Average assets (in millions) $ 30,391 $ 43 $ 16 $ 30,450

Condensed Financial Statements

Condensed Financial Statements of Parent Company	12 Months Ended
	Dec. 31, 2019
Condensed Financial Information 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, 2019 2018 Assets: Cash $ 9,116 $ 11,397 Resell agreements 258,000 225,000 Total cash and cash equivalents 267,116 236,397 Investment in subsidiaries 3,896,962 3,362,474 Accrued interest receivable and other assets 2,545 9,122 Total assets $ 4,166,623 $ 3,607,993 Liabilities: Junior subordinated deferrable interest debentures, net of unamortized issuance costs $ 136,299 $ 136,242 Subordinated notes, net of unamortized issuance costs 98,865 98,708 Accrued interest payable and other liabilities 19,791 4,126 Total liabilities 254,955 239,076 Shareholders’ Equity 3,911,668 3,368,917 Total liabilities and shareholders’ equity $ 4,166,623 $ 3,607,993 Condensed Statements of Income Year Ended December 31, 2019 2018 2017 Income: Dividend income paid by Frost Bank $ 234,531 $ 223,371 $ 149,671 Dividend income paid by non-banks 1,822 953 915 Interest and other income 2,868 1,828 421 Total income 239,221 226,152 151,007 Expenses: Interest expense 10,363 9,948 7,815 Salaries and employee benefits 1,551 1,973 1,202 Other 7,033 7,016 6,373 Total expenses 18,947 18,937 15,390 Income before income taxes and equity in undistributed earnings of subsidiaries 220,274 207,215 135,617 Income tax benefit 5,135 5,218 7,092 Equity in undistributed earnings of subsidiaries 218,190 242,485 221,440 Net income 443,599 454,918 364,149 Preferred stock dividends 8,063 8,063 8,063 Net income available to common shareholders $ 435,536 $ 446,855 $ 356,086 Condensed Statements of Cash Flows Year Ended December 31, 2019 2018 2017 Operating Activities: Net income $ 443,599 $ 454,918 $ 364,149 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed earnings of subsidiaries (218,190 ) (242,485 ) (221,440 ) Stock-based compensation 780 721 519 Net tax benefit from stock-based compensation 240 304 318 Net change in other assets and other liabilities 22,216 (12,709 ) 7,665 Net cash from operating activities 248,645 200,749 151,211 Investing Activities: Net cash from investing activities — — — Financing Activities: Proceeds from issuance of subordinated notes — — 98,434 Principal payments on subordinated notes — — (100,000 ) Proceeds from stock option exercises 20,770 31,647 67,746 Proceeds from stock-based compensation activities of subsidiaries 15,166 13,222 12,494 Purchase of treasury stock (68,793 ) (101,010 ) (101,473 ) Cash dividends paid on preferred stock (8,063 ) (8,063 ) (8,063 ) Cash dividends paid on common stock (177,006 ) (165,449 ) (144,172 ) Net cash from financing activities (217,926 ) (229,653 ) (175,034 ) Net change in cash and cash equivalents 30,719 (28,904 ) (23,823 ) Cash and cash equivalents at beginning of year 236,397 265,301 289,124 Cash and cash equivalents at end of year $ 267,116 $ 236,397 $ 265,301

Accounting Standards Updates

Accounting Standards Updates	12 Months Ended
	Dec. 31, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Standards Updates	Accounting Standards Updates Accounting Standards Update (“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. We adopted ASU 2014-09 effective January 1, 2018. See Note 1 - Summary of Significant Accounting Policies for additional information. ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities." ASU 2016-01, 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 securities. ASU 2016-01 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2016-02, “Leases (Topic 842).” ASU 2016-02 among other things, requires lessees to recognize a lease liability, which is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. We adopted ASU 2016-02, along with several other subsequent codification updates related to lease accounting, as of January 1, 2019. See Note 1 - Summary of Significant Accounting Policies for additional information. ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” ASU 2016-13 along with several other subsequent codification updates related to accounting for credit losses, requires the measurement of all expected credit losses for financial assets held at the reporting date based on historical experience, current conditions, and reasonable and supportable forecasts and requires enhanced disclosures related to the significant estimates and judgments used in estimating credit losses, as well as the credit quality and underwriting standards of an organization’s portfolio. In addition, ASU 2016-13 amends the accounting for credit losses on available-for-sale debt securities and purchased financial assets with credit deterioration. We currently expect the adoption of ASU 2016-13 will result in a combined 20.0% to 35.0% increase in our allowance for loan losses and our reserves for unfunded commitments. As we are currently finalizing the execution of our implementation controls and processes, the ultimate impact of the adoption of ASU 2016-13 as of January 1, 2020 could differ from our current expectation. The expected increase is a result of changing from an “incurred loss” model, which encompasses allowances for current known and inherent losses within the portfolio, to an “expected loss” model, which encompasses allowances for losses expected to be incurred over the life of the portfolio. Furthermore, ASU 2016-13 will necessitate that we establish an allowance for expected credit losses for certain debt securities and other financial assets; however, we do not expect these allowances to be significant. The adoption of ASU 2016-13 is not expected to have a significant impact on our regulatory capital ratios. ASU 2016-15, “Statement of Cash Flows (Topic 230) - Classification of Certain Cash Receipts and Cash Payments.” ASU 2016-15 provides guidance related to certain cash flow issues in order to reduce the current and potential future diversity in practice. ASU 2016-15 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2016-16, “Income Taxes (Topic 740) - Intra-Entity Transfers of Assets Other Than Inventory.” ASU 2016-16 provides guidance stating that an entity should recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. ASU 2016-16 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2016-18, “Statement of Cash Flows (Topic 230) - Restricted Cash.” ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2017-01, “Business Combinations (Topic 805) - Clarifying the Definition of a Business.” ASU 2017-01 clarifies the definition and provides a more robust framework to use in determining when a set of assets and activities constitutes a business. ASU 2017-01 is intended to provide guidance when evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. ASU 2017-01 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350) - Simplifying the Test for Goodwill Impairment.” ASU 2017-04 eliminates Step 2 from the goodwill impairment test which required entities to compute the implied fair value of goodwill. Under ASU 2017-04, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. ASU 2017-04 will be effective for us on January 1, 2020, with earlier adoption permitted and is not expected to have a significant impact on our financial statements. ASU 2017-05, “Other Income - Gains and Losses from the Derecognition of Nonfinancial Assets (Subtopic 610-20) - Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets.” ASU 2017-05 clarifies the scope of Subtopic 610-20 and adds guidance for partial sales of nonfinancial assets, including partial sales of real estate. Historically, U.S. GAAP contained several different accounting models to evaluate whether the transfer of certain assets qualified for sale treatment. ASU 2017-05 reduces the number of potential accounting models that might apply and clarifies which model does apply in various circumstances. ASU 2017-05 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2017-08, “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities.” ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium to require such premiums to be amortized to the earliest call date unless applicable guidance related to certain pools of securities is applied to consider estimated prepayments. Under prior guidance, entities were generally required to amortize premiums on individual, non-pooled callable debt securities as a yield adjustment over the contractual life of the security. ASU 2017-08 does not change the accounting for callable debt securities held at a discount. We adopted ASU 2017-08 effective January 1, 2019 and recognized a cumulative effect adjustment reducing retained earnings by $14.7 million . See Note 1 - Summary of Significant Accounting Policies for additional information. ASU 2017-09, “Compensation - Stock Compensation (Topic 718) - Scope of Modification Accounting.” ASU 2017-09 clarifies when changes to the terms or conditions of a share-based payment award must be accounted for as modifications. Under ASU 2017-09, an entity will not apply modification accounting to a share-based payment award if all of the following are the same immediately before and after the change: (i) the award's fair value, (ii) the award's vesting conditions and (iii) the award's classification as an equity or liability instrument. ASU 2017-09 became effective for us on January 1, 2018 and did not have a significant impact on our financial statements. ASU 2017-12, “Derivatives and Hedging (Topic 815) - Targeted Improvements to Accounting for Hedging Activities.” ASU 2017-12 amends the hedge accounting recognition and presentation requirements in ASC 815 to improve the transparency and understandability of information conveyed to financial statement users about an entity’s risk management activities to better align the entity’s financial reporting for hedging relationships with those risk management activities and to reduce the complexity of and simplify the application of hedge accounting. ASU 2017-12 became effective for us on January 1, 2019 and did not have a significant impact on our financial statements. ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” Under ASU 2018-02, entities may elect to reclassify certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act, which was enacted on December 22, 2017, from accumulated other comprehensive income to retained earnings. ASU 2018-02 also requires certain accounting policy disclosures. We elected to adopt the provisions of ASU 2018-02 as of January 1, 2018 in advance of the required application date of January 1, 2019. See Note 1 - Summary of Significant Accounting Policies for additional information. ASU 2018-05, “Income Taxes (Topic 740) - Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin (SAB) No. 118.” ASU 2018-05 amends the Accounting Standards Codification to incorporate various SEC paragraphs pursuant to the issuance of SAB 118. SAB 118 addresses the application of generally accepted accounting principles in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Cuts and Jobs Act. See Note 13 - Income Taxes. ASU 2018-13, “Fair Value Measurement (Topic 820) - Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement.” ASU 2018-13 modifies the disclosure requirements on fair value measurements in Topic 820. The amendments in this update remove disclosures that no longer are considered cost beneficial, modify/clarify the specific requirements of certain disclosures, and add disclosure requirements identified as relevant. ASU 2018-13 will be effective for us on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on our financial statements. ASU 2018-14, “Compensation - Retirement Benefits-Defined Benefit Plans-General (Subtopic 715-20).” ASU 2018-14 amends and modifies the disclosure requirements for employers that sponsor defined benefit pension or other post-retirement plans. The amendments in this update remove disclosures that no longer are considered cost beneficial, clarify the specific requirements of disclosures, and add disclosure requirements identified as relevant. ASU 2018-14 will be effective for us on January 1, 2021, with early adoption permitted, and is not expected to have a significant impact on our financial statements. ASU 2018-15, “Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) - Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract.” ASU 2018-15 clarifies certain aspects of ASU 2015-05, “Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement,” which was issued in April 2015. Specifically, ASU 2018-15 aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). ASU 2018-15 does not affect the accounting for the service element of a hosting arrangement that is a service contract. ASU 2018-15 will be effective for us on January 1, 2020, with early adoption permitted, and is not expected to have a significant impact on our financial statements. ASU 2018-16, “Derivatives and Hedging (Topic 815) - Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes.” The amendments in this update permit use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815 in addition to the interest rates on direct U.S. Treasury obligations, the LIBOR swap rate, the OIS rate based on the Fed Funds Effective Rate and the Securities Industry and Financial Markets Association (SIFMA) Municipal Swap Rate. ASU 2018-16 was effective for us on January 1, 2019 and did not have a significant impact on our financial statements. ASU 2019-12, “Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes.” The guidance issued in this update simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition for deferred tax liabilities for outside basis differences. ASU 2019-12 also simplifies aspects of the accounting for franchise taxes and enacted changes in tax laws or rates and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU 2019-12 will be effective for us on January 1, 2021, with early adoption permitted, and is not expected to have a significant impact on our financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations . Cullen/Frost Bankers, Inc. (“Cullen/Frost”) is a financial holding company and a bank holding company headquartered in San Antonio, Texas that provides, through its subsidiaries, a broad array of products and services throughout numerous Texas markets. 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. Acquisitions are accounted for using the purchase method with the operating results of the acquired companies included with our results of operations since their respective dates of acquisition. We have evaluated subsequent events for potential recognition and/or disclosure through the date these consolidated financial statements were issued.
Use of Estimates	Use of Estimates . The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses and the fair values of financial instruments and the status of contingencies are particularly subject to change.
Concentrations and Restrictions on Cash and Cash Equivalents	Concentrations and Restrictions on Cash and Cash Equivalents . 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 $918.0 million and $447.9 million of cash on hand or on deposit with the Federal Reserve Bank to meet regulatory reserve and clearing requirements at December 31, 2019 and 2018 . Additionally, as of December 31, 2019 and 2018 , we had $37.5 million and $10.0 million in cash collateral on deposit with other financial institution counterparties to interest rate swap transactions.
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. Additional cash flow information was as follows: Year Ended December 31, 2019 2018 2017 Cash paid for interest $ 124,781 $ 89,270 $ 24,371 Cash paid for income tax 45,352 5,112 56,359 Significant non-cash transactions: Transfer of securities from available for sale to held to maturity 377,812 — — Unsettled purchases/sales of securities — 330 37,481 Loans foreclosed and transferred to other real estate owned and foreclosed assets 1,348 2,899 279 Loans to facilitate the sale of other real estate owned 847 — — Lease right-of-use assets obtained in exchange for lessee operating lease liabilities 319,286 — —
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 remains 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. Interest income on securities includes amortization of purchase premiums and discounts. Premiums and discounts on securities are generally amortized using the interest method with a constant effective yield without anticipating prepayments, except for mortgage-backed securities where prepayments are anticipated. Premiums on callable securities are amortized to their earliest call date. Prior to the adoption of a new accounting standard in 2019, as further discussed below, premiums on callable securities were amortized to their respective maturity dates unless such securities were included in pools for the purposes of assessing prepayment expectations. 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 3 - Loans.
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 3 - 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 $1.1 million and $1.2 million at December 31, 2019 and 2018 .
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. See Note 5 - 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 5 - Goodwill and Other Intangible Assets.
Revenue Recognition	Revenue Recognition . In general, for revenue not associated with financial instruments, guarantees and lease contracts, we apply the following steps when recognizing revenue from contracts with customers: (i) identify the contract, (ii) identify the performance obligations, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations and (v) recognize revenue when a performance obligation is satisfied. Our contracts with customers are generally short term in nature, typically due within one year or less or cancellable by us or our customer upon a short notice period. Performance obligations for our customer contracts are generally satisfied at a single point in time, typically when the transaction is complete, or over time. For performance obligations satisfied over time, we primarily use the output method, directly measuring the value of the products/services transferred to the customer, to determine when performance obligations have been satisfied. We typically receive payment from customers and recognize revenue concurrent with the satisfaction of our performance obligations. In most cases, this occurs within a single financial reporting period. For payments received in advance of the satisfaction of performance obligations, revenue recognition is deferred until such time as the performance obligations have been satisfied. In cases where we have not received payment despite satisfaction of our performance obligations, we accrue an estimate of the amount due in the period our performance obligations have been satisfied. For contracts with variable components, only amounts for which collection is probable are accrued. We generally act in a principal capacity, on our own behalf, in most of our contracts with customers. In such transactions, we recognize revenue and the related costs to provide our services on a gross basis in our financial statements. In some cases, we act in an agent capacity, deriving revenue through assisting other entities in transactions with our customers. In such transactions, we recognize revenue and the related costs to provide our services on a net basis in our financial statements. These transactions recognized on a net basis primarily relate to insurance and brokerage commissions and fees derived from our customers' use of various interchange and ATM/debit card networks.
Stock Based Compensation	Share-Based Payments . 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. Compensation expense for performance 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 over the service period of the award based upon the probable number of units expected to vest. 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. The fair value of performance stock units is generally the market price of our stock on the date of grant discounted by the present value of the dividends expected to be paid on our common stock during the service period of the award because dividend equivalent payments on performance stock units are deferred until such time that the units vest and shares are issued. The impact of forfeitures of share-based payment awards on compensation expense is recognized as forfeitures occur.
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. Although realization is not assured, management believes it is more likely than not that all of the deferred tax assets will be realized. Interest and/or penalties related to income taxes are reported as a component of income tax expense. The income tax effects related to settlements of share-based payment awards are reported in earnings as an increase (or decrease) to income tax expense (see Note 13 - Income Taxes). 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 10 - 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 and changes in the net actuarial gain/loss on defined benefit post-retirement benefit plans. See Note 14 - 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 17 - 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.
Accounting Changes, Reclassifications and Restatement	Accounting Changes, Reclassifications and Restatements. Certain items in prior financial statements have been reclassified to conform to the current presentation. On January 1, 2019, we adopted certain accounting standard updates related to accounting for leases, primarily Accounting Standards Update (“ASU”) 2016-02 “Leases (Topic 842)” and subsequent updates. Among other things, these updates require lessees to recognize a lease liability, measured on a discounted basis, related to the lessee's obligation to make lease payments arising under a lease contract; and a right-of-use asset related to the lessee’s right to use, or control the use of, a specified asset for the lease term. The updates did not significantly change lease accounting requirements applicable to lessors and did not significantly impact our financial statements in relation to contracts whereby we act as a lessor. We adopted the updates using a modified-retrospective transition approach and recognized right-of-use lease assets and related lease liabilities totaling $170.5 million and $174.4 million , respectively, as of January 1, 2019. We elected to apply certain practical adoption expedients provided under the updates whereby we did not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases and (iii) initial direct costs for any existing leases. We did not elect to apply the recognition requirements of the updates to any short-term leases. See Note 4 - Premises and Equipment and Lease Commitments. On January 1, 2019, we also adopted ASU 2017-08 “Receivables - Nonrefundable Fees and Other Costs (Subtopic 310-20) - Premium Amortization on Purchased Callable Debt Securities.” ASU 2017-08 shortens the amortization period for certain callable debt securities held at a premium to require such premiums to be amortized to the earliest call date unless applicable guidance related to certain pools of securities is applied to consider estimated prepayments. Under prior guidance, entities were generally required to amortize premiums on individual, non-pooled callable debt securities as a yield adjustment over the contractual life of the security. ASU 2017-08 does not change the accounting for callable debt securities held at a discount. Upon adoption, using a modified retrospective transition adoption approach, we recognized a cumulative effect reduction to retained earnings totaling $14.7 million . Premium amortization expense for 2019 was approximately $5.2 million higher than what would have been the case had we continued to amortize the affected securities to their respective maturity dates. On January 1, 2018, we adopted ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220) - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income.” In accordance with ASU 2018-02, we elected to reclassify certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act, which was enacted on December 22, 2017 (see Note 13 - Income Taxes), from accumulated other comprehensive income to retained earnings. Such amounts, which totaled $9.5 million , related to a net actuarial loss on defined benefit post-retirement plans and unrealized gains on securities available for sale and securities transferred to held to maturity. See Note 14 - Other Comprehensive Income (Loss). Notwithstanding this election made in accordance with ASU 2018-02, our policy is to release such income tax effects only when the entire portfolio to which the underlying transactions relate is liquidated, sold or extinguished. On January 1, 2018, we also adopted, ASU 2014-09, "Revenue from Contracts with Customers (Topic 606).” Using a modified retrospective transition approach for contracts that were not complete as of our adoption, we recognized a cumulative effect reduction to beginning retained earnings totaling $2.3 million . The amount was related to certain revenue streams within trust and investment management fees. Additionally, based on our underlying contracts, ASU 2014-09 requires us to report network costs associated with debit card and ATM transactions netted against the related fee income from such transactions. Previously, such network costs were reported as a component of other non-interest expense. For 2019 and 2018, gross interchange and debit card transaction fees totaled $27.8 million and $25.8 million , respectively, while related network costs totaled $12.9 million and $11.9 million , respectively. On a net basis, we reported $14.9 million and $13.9 million as interchange and debit card transaction fees in the accompanying Consolidated Statement of Income for 2019 and 2018, respectively. For 2017, we reported interchange and debit card transaction fees totaling $23.2 million on a gross basis in the accompanying Consolidated Statement of Income while related network cost totaling $11.9 million was reported as a component of other non-interest expense. ASU 2014-09 also required us to change the way we recognize certain recurring revenue streams reported as components of trust and investment management fees, insurance commissions and fees and other categories of non-interest income, however, such changes were not significant to our financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Additional Cash Flow Information	Additional cash flow information was as follows: Year Ended December 31, 2019 2018 2017 Cash paid for interest $ 124,781 $ 89,270 $ 24,371 Cash paid for income tax 45,352 5,112 56,359 Significant non-cash transactions: Transfer of securities from available for sale to held to maturity 377,812 — — Unsettled purchases/sales of securities — 330 37,481 Loans foreclosed and transferred to other real estate owned and foreclosed assets 1,348 2,899 279 Loans to facilitate the sale of other real estate owned 847 — — Lease right-of-use assets obtained in exchange for lessee operating lease liabilities 319,286 — —

Securities (Tables)

Securities (Tables)	12 Months Ended
	Dec. 31, 2019
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: 2019 2018 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: Residential mortgage-backed securities $ 530,861 $ 22 $ 9,365 $ 521,518 $ 2,737 $ 8 $ 85 $ 2,660 States and political subdivisions 1,497,644 28,909 896 1,525,657 1,101,820 11,525 552 1,112,793 Other 1,500 — — 1,500 1,500 — — 1,500 Total $ 2,030,005 $ 28,931 $ 10,261 $ 2,048,675 $ 1,106,057 $ 11,533 $ 637 $ 1,116,953 Available for Sale: U.S. Treasury $ 1,941,283 $ 18,934 $ 12,084 $ 1,948,133 $ 3,455,417 $ 1,772 $ 29,500 $ 3,427,689 Residential mortgage-backed securities 2,176,275 32,608 1,289 2,207,594 823,208 13,079 6,547 829,740 States and political subdivisions 6,717,344 353,857 204 7,070,997 7,089,132 70,760 72,690 7,087,202 Other 42,867 — — 42,867 42,690 — — 42,690 Total $ 10,877,769 $ 405,399 $ 13,577 $ 11,269,591 $ 11,410,447 $ 85,611 $ 108,737 $ 11,387,321
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 2019 Held to Maturity: Residential mortgage-backed securities $ 519,099 $ 9,361 $ 408 $ 4 $ 519,507 $ 9,365 States and political subdivisions 371,434 896 — — 371,434 896 Total $ 890,533 $ 10,257 $ 408 $ 4 $ 890,941 $ 10,261 Available for Sale: U.S. Treasury $ 636,999 $ 12,070 $ 199,980 $ 14 $ 836,979 $ 12,084 Residential mortgage-backed securities 276,249 782 31,456 507 307,705 1,289 States and political subdivisions 59,678 204 — — 59,678 204 Total $ 972,926 $ 13,056 $ 231,436 $ 521 $ 1,204,362 $ 13,577 Less than 12 Months More than 12 Months Total Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses Estimated Fair Value Unrealized Losses 2018 Held to Maturity: Residential mortgage-backed securities $ — $ — $ 2,034 $ 85 $ 2,034 $ 85 States and political subdivisions 205,686 541 5,952 11 211,638 552 Total $ 205,686 $ 541 $ 7,986 $ 96 $ 213,672 $ 637 Available for Sale: U.S. Treasury $ — $ — $ 3,139,639 $ 29,500 $ 3,139,639 $ 29,500 Residential mortgage-backed securities 152,682 205 213,982 6,342 366,664 6,547 States and political subdivisions 1,136,322 7,026 2,058,048 65,664 3,194,370 72,690 Total $ 1,289,004 $ 7,231 $ 5,411,669 $ 101,506 $ 6,700,673 $ 108,737
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, 2019 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 $ 12,773 $ 12,847 $ 508,575 $ 509,404 Due after one year through five years 165,519 169,970 1,317,774 1,344,035 Due after five years through ten years 527,907 541,249 451,885 478,800 Due after ten years 792,945 803,091 6,380,393 6,686,891 Residential mortgage-backed securities 530,861 521,518 2,176,275 2,207,594 Equity securities — — 42,867 42,867 Total $ 2,030,005 $ 2,048,675 $ 10,877,769 $ 11,269,591
Sales of Securities Available for Sale	Sales of securities available for sale were as follows: 2019 2018 2017 Proceeds from sales $ 18,660,147 $ 16,806,062 $ 11,963,359 Gross realized gains 930 3 1 Gross realized losses (637 ) (159 ) (4,942 ) Tax benefit (expense) related to securities gains/losses (62 ) 33 1,729
Premium Amortization and Discount Accretion Included in Income on Securities	Premium amortization and discount accretion included in interest income on securities was as follows: 2019 2018 2017 Premium amortization $ (120,785 ) $ (108,483 ) $ (97,841 ) Discount accretion 5,227 7,955 7,908 Net (premium amortization) discount accretion $ (115,558 ) $ (100,528 ) $ (89,933 )
Year End Trading Account Securities, at Estimated Fair Value	Year-end trading account securities, at estimated fair value, were as follows: 2019 2018 U.S. Treasury $ 24,298 $ 21,928 States and political subdivisions — 2,158 Total $ 24,298 $ 24,086
Net Gains and Losses on Trading Account Securities	Net gains and losses on trading account securities were as follows: 2019 2018 2017 Net gain on sales transactions $ 2,173 $ 1,816 $ 1,408 Net mark-to-market gains (losses) (176 ) 105 (43 ) Net gain on trading account securities $ 1,997 $ 1,921 $ 1,365

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2019
Receivables [Abstract]
Loans	Year-end loans, including leases net of unearned discounts, consisted of the following: 2019 2018 Commercial and industrial $ 5,187,466 $ 5,111,957 Energy: Production 1,348,900 1,309,314 Service 192,996 168,775 Other 110,986 124,509 Total energy 1,652,882 1,602,598 Commercial real estate: Commercial mortgages 4,594,113 4,121,966 Construction 1,312,659 1,267,717 Land 289,467 306,755 Total commercial real estate 6,196,239 5,696,438 Consumer real estate: Home equity loans 375,596 353,924 Home equity lines of credit 354,671 337,168 Other 464,146 427,898 Total consumer real estate 1,194,413 1,118,990 Total real estate 7,390,652 6,815,428 Consumer and other 519,332 569,750 Total loans $ 14,750,332 $ 14,099,733
Activities in Related Party Loans	Activity in related party loans during 2019 is presented in the following table. Other changes were primarily related to changes in related-party status. Balance outstanding at December 31, 2018 $ 256,056 Principal additions 304,407 Principal reductions (257,687 ) Other changes (4,248 ) Balance outstanding at December 31, 2019 $ 298,528
Non-Accrual Loans, Segregated by Class of Loans	Year-end non-accrual loans, segregated by class of loans, were as follows: 2019 2018 Commercial and industrial $ 26,038 $ 9,239 Energy 65,761 46,932 Commercial real estate: Buildings, land and other 8,912 15,268 Construction 665 — Consumer real estate 922 892 Consumer and other 5 1,408 Total $ 102,303 $ 73,739
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, 2019 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 $ 25,474 $ 21,268 $ 46,742 $ 5,140,724 $ 5,187,466 $ 3,430 Energy 6,136 62,566 68,702 1,584,180 1,652,882 85 Commercial real estate: Buildings, land and other 12,384 2,725 15,109 4,868,471 4,883,580 967 Construction 195 1,066 1,261 1,311,398 1,312,659 402 Consumer real estate 7,442 2,129 9,571 1,184,842 1,194,413 1,425 Consumer and other 4,476 1,112 5,588 513,744 519,332 1,112 Total $ 56,107 $ 90,866 $ 146,973 $ 14,603,359 $ 14,750,332 $ 7,421
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 2019 Commercial and industrial $ 30,909 $ 11,588 $ 12,772 $ 24,360 $ 7,849 $ 14,913 Energy 87,103 2,764 62,480 65,244 20,246 53,563 Commercial real estate: Buildings, land and other 9,252 6,255 2,354 8,609 383 13,690 Construction 697 665 — 665 — 354 Consumer real estate 570 570 — 570 — 547 Consumer and other 5 — 5 5 5 1,285 Total $ 128,536 $ 21,842 $ 77,611 $ 99,453 $ 28,483 $ 84,352 2018 Commercial and industrial $ 9,094 $ 2,842 $ 4,287 $ 7,129 $ 2,558 $ 18,246 Energy 67,900 6,817 39,890 46,707 9,671 75,453 Commercial real estate: Buildings, land and other 15,774 2,168 12,517 14,685 2,599 12,799 Construction — — — — — — Consumer real estate 293 293 — 293 — 704 Consumer and other 1,475 — 1,407 1,407 1,407 925 Total $ 94,536 $ 12,120 $ 58,101 $ 70,221 $ 16,235 $ 108,127 2017 Commercial and industrial $ 60,781 $ 28,038 $ 15,722 $ 43,760 $ 7,553 $ 30,073 Energy 99,606 33,080 61,162 94,242 13,267 76,492 Commercial real estate: Buildings, land and other 10,795 6,394 — 6,394 — 6,164 Construction — — — — — — Consumer real estate 1,214 1,214 — 1,214 — 1,167 Consumer and other — — — — — 11 Total $ 172,396 $ 68,726 $ 76,884 $ 145,610 $ 20,820 $ 113,907
Troubled Debt Restructurings	Troubled debt restructurings that occurred during 2019 , 2018 and 2017 are set forth in the following table. 2019 2018 2017 Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Balance at Restructure Balance at Year-end Commercial and industrial $ 3,845 $ 2,161 $ 2,203 $ — $ 4,026 $ 3,766 Energy — — 13,708 — 56,096 54,330 Commercial real estate: Buildings, land and other 9,457 9,393 — — — — Construction — — — — 388 388 Consumer real estate 124 120 — — — — $ 13,426 $ 11,674 $ 15,911 $ — $ 60,510 $ 58,484
Restructured Loans Past Due in Excess of 90 Days on Financing Receivables [Table Text Block]	Additional information related to restructured loans was as follows: 2019 2018 2017 Restructured loans past due in excess of 90 days at period-end: Number of loans 4 — 1 Dollar amount of loans $ 3,340 $ — $ 43,137 Restructured loans on non-accrual status at period end 5,576 — 53,622 Charge-offs of restructured loans: Recognized in connection with restructuring — — — Recognized on previously restructured loans 1,500 7,650 9,951 Proceeds from sale of restructured loans — 15,750 —
Weighted Average Risk Grades for All Commercial Loans by Class	The following tables present weighted average risk grades for all commercial loans by class. December 31, 2019 December 31, 2018 Weighted Loans Weighted Loans Commercial and industrial Risk grades 1-8 6.17 $ 4,788,857 6.12 $ 4,862,275 Risk grade 9 9.00 247,212 9.00 112,431 Risk grade 10 10.00 71,472 10.00 58,328 Risk grade 11 11.00 53,887 11.00 69,684 Risk grade 12 12.00 18,189 12.00 6,681 Risk grade 13 13.00 7,849 13.00 2,558 Total 6.44 $ 5,187,466 6.30 $ 5,111,957 Energy Risk grades 1-8 5.90 $ 1,488,301 5.76 $ 1,451,673 Risk grade 9 9.00 32,163 9.00 35,565 Risk grade 10 10.00 51,898 10.00 43,001 Risk grade 11 11.00 14,760 11.00 25,427 Risk grade 12 12.00 45,514 12.00 37,261 Risk grade 13 13.00 20,246 13.00 9,671 Total 6.39 $ 1,652,882 6.22 $ 1,602,598 Commercial real estate: Buildings, land and other Risk grades 1-8 6.78 $ 4,523,271 6.76 $ 4,143,264 Risk grade 9 9.00 163,714 9.00 109,660 Risk grade 10 10.00 103,626 10.00 62,353 Risk grade 11 11.00 84,057 11.00 98,176 Risk grade 12 12.00 8,529 12.00 12,669 Risk grade 13 13.00 383 13.00 2,599 Total 7.01 $ 4,883,580 6.98 $ 4,428,721 Construction Risk grades 1-8 7.25 $ 1,274,098 7.13 $ 1,177,260 Risk grade 9 9.00 21,509 9.00 60,754 Risk grade 10 10.00 15,243 10.00 24,877 Risk grade 11 11.00 1,144 11.00 4,826 Risk grade 12 12.00 665 12.00 — Risk grade 13 13.00 — 13.00 — Total 7.31 $ 1,312,659 7.29 $ 1,267,717
Net (Charge-Offs)/Recoveries, Segregated by Class of Loans	Net (charge-offs)/recoveries, segregated by class of loan, were as follows: 2019 2018 2017 Commercial and industrial $ (10,131 ) $ (22,388 ) $ (17,453 ) Energy (6,058 ) (13,121 ) (10,009 ) Commercial real estate: Buildings, land and other (830 ) (263 ) 735 Construction 24 13 11 Consumer real estate (2,457 ) (1,538 ) (506 ) Consumer and other (14,272 ) (7,548 ) (5,919 ) Total $ (33,724 ) $ (44,845 ) $ (33,141 )
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, 2019 Historical valuation allowances $ 29,015 $ 7,873 $ 21,947 $ 2,690 $ 7,562 $ 69,087 Specific valuation allowances 7,849 20,246 383 — 5 28,483 General valuation allowances 9,840 5,196 4,201 904 (409 ) 19,732 Macroeconomic valuation allowances 4,889 4,067 4,506 519 884 14,865 Total $ 51,593 $ 37,382 $ 31,037 $ 4,113 $ 8,042 $ 132,167 December 31, 2018 Historical valuation allowances $ 25,351 $ 9,697 $ 20,817 $ 2,688 $ 6,845 $ 65,398 Specific valuation allowances 2,558 9,671 2,599 — 1,407 16,235 General valuation allowances 10,062 6,014 4,366 1,671 (13 ) 22,100 Macroeconomic valuation allowances 10,609 3,670 10,995 1,744 1,381 28,399 Total $ 48,580 $ 29,052 $ 38,777 $ 6,103 $ 9,620 $ 132,132
Investment in Loans Related to the Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology	Our recorded investment in loans related to each balance in the allowance for loan losses by portfolio segment and detailed on the basis of the impairment methodology we used was as follows: Commercial and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Total December 31, 2019 Individually evaluated $ 24,360 $ 65,244 $ 9,274 $ 570 $ 5 $ 99,453 Collectively evaluated 5,163,106 1,587,638 6,186,965 1,193,843 519,327 14,650,879 Total $ 5,187,466 $ 1,652,882 $ 6,196,239 $ 1,194,413 $ 519,332 $ 14,750,332 December 31, 2018 Individually evaluated $ 7,129 $ 46,707 $ 14,685 $ 293 $ 1,407 $ 70,221 Collectively evaluated 5,104,828 1,555,891 5,681,753 1,118,697 568,343 14,029,512 Total $ 5,111,957 $ 1,602,598 $ 5,696,438 $ 1,118,990 $ 569,750 $ 14,099,733
Activity in Allowance for Loan Losses by Portfolio Segment	The following table details activity in the allowance for loan losses by portfolio segment for 2019 , 2018 and 2017 . 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 Total 2019 Beginning balance $ 48,580 $ 29,052 $ 38,777 $ 6,103 $ 9,620 $ 132,132 Provision for loan losses 13,144 14,388 (6,934 ) 467 12,694 33,759 Charge-offs (14,117 ) (7,500 ) (1,025 ) (3,665 ) (24,725 ) (51,032 ) Recoveries 3,986 1,442 219 1,208 10,453 17,308 Net charge-offs (10,131 ) (6,058 ) (806 ) (2,457 ) (14,272 ) (33,724 ) Ending balance $ 51,593 $ 37,382 $ 31,037 $ 4,113 $ 8,042 $ 132,167 Allocated to loans: Individually evaluated for impairment $ 7,849 $ 20,246 $ 383 $ — $ 5 $ 28,483 Collectively evaluated for impairment 43,744 17,136 30,654 4,113 8,037 103,684 Ending balance $ 51,593 $ 37,382 $ 31,037 $ 4,113 $ 8,042 $ 132,167 2018 Beginning balance $ 59,614 $ 51,528 $ 30,948 $ 5,657 $ 7,617 $ 155,364 Provision for loan losses 11,354 (9,355 ) 8,079 1,984 9,551 21,613 Charge-offs (26,076 ) (13,940 ) (619 ) (2,143 ) (17,197 ) (59,975 ) Recoveries 3,688 819 369 605 9,649 15,130 Net charge-offs (22,388 ) (13,121 ) (250 ) (1,538 ) (7,548 ) (44,845 ) Ending balance $ 48,580 $ 29,052 $ 38,777 $ 6,103 $ 9,620 $ 132,132 Allocated to loans: Individually evaluated for impairment $ 2,558 $ 9,671 $ 2,599 $ — $ 1,407 $ 16,235 Collectively evaluated for impairment 46,022 19,381 36,178 6,103 8,213 115,897 Ending balance $ 48,580 $ 29,052 $ 38,777 $ 6,103 $ 9,620 $ 132,132 2017 Beginning balance $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Provision for loan losses 24,152 884 (11 ) 1,925 8,510 35,460 Charge-offs (20,619 ) (10,595 ) (86 ) (925 ) (15,579 ) (47,804 ) Recoveries 3,166 586 832 419 9,660 14,663 Net charge-offs (17,453 ) (10,009 ) 746 (506 ) (5,919 ) (33,141 ) Ending balance $ 59,614 $ 51,528 $ 30,948 $ 5,657 $ 7,617 $ 155,364 Allocated to loans: Individually evaluated for impairment $ 7,553 $ 13,267 $ — $ — $ — $ 20,820 Collectively evaluated for impairment 52,061 38,261 30,948 5,657 7,617 134,544 Ending balance $ 59,614 $ 51,528 $ 30,948 $ 5,657 $ 7,617 $ 155,364

Premises and Equipment (Tables)

Premises and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Premises and Equipment	Year-end premises and equipment were as follows: 2019 2018 Land $ 112,818 $ 104,045 Buildings 441,404 373,276 Technology, furniture and equipment 226,925 196,871 Leasehold improvements 156,144 83,320 Construction and projects in progress 44,251 45,456 Lease right-of-use assets 297,736 — 1,279,278 802,968 Less accumulated depreciation and amortization (267,331 ) (250,638 ) Total premises and equipment, net $ 1,011,947 $ 552,330
Future Minimum Lease Payments Due Under Non-Cancelable Operating Leases	The following table reconciles future undiscounted lease payments due under non-cancelable operating leases (those amounts subject to recognition) to the aggregate operating lessee lease liability as of December 31, 2019 : Future lease payments 2020 $ 28,225 2021 30,813 2022 28,175 2023 26,661 2024 25,232 Thereafter 283,300 Total undiscounted operating lease liability 422,406 Imputed interest 98,718 Total operating lease liability included in the accompanying balance sheet $ 323,688 Weighted-average lease term in years 16.49 Weighted-average discount rate 3.17 %

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill . Year-end goodwill was as follows: 2019 2018 Goodwill $ 654,952 $ 654,952
Schedule of Other Intangible Assets	Other Intangible Assets. Year-end other intangible assets were as follows: Gross Intangible Assets Accumulated Amortization Net Intangible Assets 2019 Core deposits $ 9,300 $ (7,257 ) $ 2,043 Customer relationships 3,388 (2,950 ) 438 $ 12,688 $ (10,207 ) $ 2,481 2018 Core deposits $ 9,300 $ (6,341 ) $ 2,959 Customer relationships 4,206 (3,534 ) 672 Non-compete agreements 74 (56 ) 18 $ 13,580 $ (9,931 ) $ 3,649
Estimated Aggregate Future Amortization Expense for Intangible Assets	The estimated aggregate future amortization expense for intangible assets remaining as of December 31, 2019 is as follows: 2020 $ 918 2021 697 2022 481 2023 282 2024 87 Thereafter 16 $ 2,481

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2019
Deposits [Abstract]
Schedule of Deposits	Year-end deposits were as follows: 2019 2018 Non-interest-bearing demand deposits: Commercial and individual $ 10,212,265 $ 10,305,850 Correspondent banks 246,181 235,748 Public funds 415,183 455,896 Total non-interest-bearing demand deposits 10,873,629 10,997,494 Interest-bearing deposits: Private accounts: Savings and interest checking 7,147,327 6,977,813 Money market accounts 7,888,433 7,777,470 Time accounts of $100,000 or more 736,481 526,789 Time accounts under $100,000 347,418 331,511 Total private accounts 16,119,659 15,613,583 Public funds: Savings and interest checking 548,399 473,754 Money market accounts 73,180 59,953 Time accounts of $100,000 or more 24,672 4,332 Time accounts under $100,000 25 88 Total public funds 646,276 538,127 Total interest-bearing deposits 16,765,935 16,151,710 Total deposits $ 27,639,564 $ 27,149,204
Additional Information About Corporation's Deposits	The following table presents additional information about our year-end deposits: 2019 2018 Deposits from the Certificate of Deposit Account Registry Service (CDARS) $ 361 $ — Deposits from foreign sources (primarily Mexico) 805,828 752,658 Deposits not covered by deposit insurance 13,115,796 13,111,210 Deposits from certain directors, executive officers and their affiliates 197,919 199,321
Scheduled Maturities of Time Deposits	Scheduled maturities of time deposits, including both private and public funds, at December 31, 2019 were as follows: 2020 $ 891,005 2021 217,591 $ 1,108,596
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, 2019 , were as follows: Due within 3 months or less $ 191,563 Due after 3 months and within 6 months 140,654 Due after 6 months and within 12 months 271,209 Due after 12 months 157,727 $ 761,153

Off-Balance-Sheet Arrangement_2

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Financial Instruments With Off-Balance-Sheet Risk	Year-end financial instruments with off-balance-sheet risk were as follows: 2019 2018 Commitments to extend credit $ 9,306,043 $ 8,369,721 Standby letters of credit 260,587 271,575 Deferred standby letter of credit fees 1,276 2,069

Capital and Regulatory Matters

Capital and Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2019
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Actual and Required Capital Ratios	The following table presents actual and required capital ratios as of December 31, 2019 and December 31, 2018 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, 2019 and December 31, 2018 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 Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio 2019 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,857,250 12.36 % $ 1,617,886 7.00 % $ 1,502,323 6.50 % Frost Bank 2,958,326 12.82 1,615,206 7.00 1,499,834 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 3,001,736 12.99 1,964,576 8.50 1,849,013 8.00 Frost Bank 2,958,326 12.82 1,961,322 8.50 1,845,950 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 3,367,403 14.57 2,426,829 10.50 2,311,266 10.00 Frost Bank 3,090,993 13.40 2,422,809 10.50 2,307,438 10.00 Leverage Ratio Cullen/Frost 3,001,736 9.28 1,293,188 4.00 1,616,485 5.00 Frost Bank 2,958,326 9.15 1,292,743 4.00 1,615,929 5.00 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 2018 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,642,475 12.27 % $ 1,372,573 6.375 % $ 1,507,139 7.00 % $ 1,399,486 6.50 % Frost Bank 2,743,973 12.78 1,368,701 6.375 1,502,887 7.00 1,395,538 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,786,961 12.94 1,695,532 7.875 1,830,098 8.50 1,722,445 8.00 Frost Bank 2,743,973 12.78 1,690,748 7.875 1,824,934 8.50 1,717,585 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 3,152,593 14.64 2,126,143 9.875 2,260,709 10.50 2,153,056 10.00 Frost Bank 2,876,605 13.40 2,120,144 9.875 2,254,331 10.50 2,146,982 10.00 Leverage Ratio Cullen/Frost 2,786,961 9.06 1,231,028 4.00 1,231,028 4.00 1,538,785 5.00 Frost Bank 2,743,973 8.93 1,229,650 4.00 1,229,650 4.00 1,537,062 5.00

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2019
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. 2019 2018 2017 Net Income $ 443,599 $ 454,918 $ 364,149 Less: Preferred stock dividends 8,063 8,063 8,063 Net income available to common shareholders 435,536 446,855 356,086 Less: Earnings allocated to participating securities 3,687 3,169 2,016 Net earnings allocated to common stock $ 431,849 $ 443,686 $ 354,070 Distributed earnings allocated to common stock $ 175,540 $ 164,268 $ 143,356 Undistributed earnings allocated to common stock 256,309 279,418 210,714 Net earnings allocated to common stock $ 431,849 $ 443,686 $ 354,070 Weighted-average shares outstanding for basic earnings per common share 62,741,769 63,704,508 63,693,927 Dilutive effect of stock compensation 700,101 982,208 968,161 Weighted-average shares outstanding for diluted earnings per common share 63,441,870 64,686,716 64,662,088

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
Retirement Benefits [Abstract]
Combined Activity in Corporations Defined Benefit Pension Plans	We use a December 31 measurement date for our defined benefit plans. Combined activity in our defined benefit pension plans was as follows: 2019 2018 2017 Change in plan assets: Fair value of plan assets at beginning of year $ 152,820 $ 168,450 $ 157,214 Actual return on plan assets 29,945 (7,739 ) 23,518 Employer contributions 1,163 1,077 1,049 Benefits paid (9,755 ) (8,968 ) (13,331 ) Fair value of plan assets at end of year 174,173 152,820 168,450 Change in benefit obligation: Benefit obligation at beginning of year 167,107 182,607 176,751 Interest cost 6,472 5,898 6,189 Actuarial (gain) loss 22,817 (12,430 ) 12,998 Benefits paid (9,755 ) (8,968 ) (13,331 ) Benefit obligation at end of year 186,641 167,107 182,607 Funded status of the plan at end of year and accrued benefit (liability) recognized $ (12,468 ) $ (14,287 ) $ (14,157 ) Accumulated benefit obligation at end of year $ 186,641 $ 167,107 $ 182,607
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 2019 2018 2019 2018 Projected benefit obligation $ 170,541 $ 152,035 $ 16,100 $ 15,072 Accumulated benefit obligation 170,541 152,035 16,100 15,072 Fair value of plan assets 174,173 152,820 — — Funded status of the plan at end of year and accrued benefit (liability) recognized 3,632 785 (16,100 ) (15,072 )
Net Periodic Benefit Cost (Benefit)	The components of the combined net periodic cost (benefit) for our defined benefit pension plans are presented in the table below. 2019 2018 2017 Expected return on plan assets, net of expenses $ (10,772 ) $ (11,916 ) $ (11,117 ) Interest cost on projected benefit obligation 6,472 5,898 6,189 Net amortization and deferral 5,623 5,002 5,429 Net periodic expense (benefit) $ 1,323 $ (1,016 ) $ 501
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: 2019 2018 2017 Net actuarial gain (loss) $ 1,979 $ (2,223 ) $ 4,832 Deferred tax (expense) benefit (416 ) 466 (1,774 ) Other comprehensive income (loss), net of tax $ 1,563 $ (1,757 ) $ 3,058
Defined Benefit Pension Plans Not Recognized as Component of Combined Net Period Benefit Cost	We expect to recognize approximately $5.3 million of the net actuarial loss reported in the following table as of December 31, 2019 as a component of net periodic benefit cost during 2020 . 2019 2018 Net actuarial loss $ (57,964 ) $ (60,123 ) Deferred tax benefit 12,210 12,626 Amounts included in accumulated other comprehensive income/loss, net of tax (45,934 ) (47,497 )
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. 2019 2018 2017 Benefit obligations: Discount rate 3.20 % 4.36 % 3.68 % Net periodic benefit cost: Discount rate 4.36 % 3.68 % 4.24 % Expected return on plan assets 7.25 7.25 7.25
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 17 - Fair Value Measurements). Our Restoration Plan is unfunded. 2019 2018 Level 1: Mutual funds $ 172,773 $ 152,477 Cash and cash equivalents 1,400 343 Total fair value of plan assets $ 174,173 $ 152,820
Expected Future Benefit Payments Related to Defined Benefit Plans	As of December 31, 2019 , expected future benefit payments related to our defined benefit plans were as follows: 2020 $ 10,662 2021 10,968 2022 11,177 2023 11,423 2024 11,578 2025 through 2029 57,122 $ 112,930
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	A combined summary of activity in our active stock plans is presented in the table. Performance stock units outstanding are presented assuming attainment of the maximum payout rate as set forth by the performance criteria. The target award level for performance stock units granted in 2019 , 2018 and 2017 was 34,317 , 30,466 and 24,162 , respectively. As of December 31, 2019 , there were 1,105,616 shares remaining available for grant for future awards. Director Deferred Stock Units Outstanding Non-Vested Stock Awards/Stock Units Outstanding Performance Stock Units Outstanding Stock Options Outstanding Number of Units Weighted- Average Fair Value at Grant Number of Shares/Units Weighted- Average Fair Value at Grant Number of Units Weighted- Average Fair Value at Grant Number of Shares Weighted- Average Exercise Price January 1, 2017 53,659 $ 61.48 256,850 $ 73.43 43,860 $ 69.70 4,089,028 $ 62.67 Authorized — — — — — — — — Granted 5,447 95.37 99,833 98.90 36,246 92.27 — — Exercised/vested (6,098 ) 62.29 (39,740 ) 71.59 — — (1,118,122 ) 60.59 Forfeited/expired — — (4,287 ) 79.52 — — (53,764 ) 69.78 December 31, 2017 53,008 64.87 312,656 81.71 80,106 79.91 2,917,142 63.34 Authorized — — — — — — — — Granted 6,576 109.58 109,847 94.81 45,703 87.18 — — Exercised/vested (10,674 ) 63.68 (32,050 ) 78.92 — — (513,134 ) 61.68 Forfeited/expired — — (6,656 ) 87.60 — — (52,000 ) 70.42 December 31, 2018 48,910 71.14 383,797 85.59 125,809 82.55 2,352,008 63.55 Authorized — — — — — — — — Granted 7,592 102.70 127,091 93.46 51,479 85.74 — — Exercised/vested (1,132 ) 106.03 (53,990 ) 65.11 — — (359,892 ) 57.71 Forfeited/expired — — (16,251 ) 89.71 — — (11,250 ) 65.11 December 31, 2019 55,370 $ 74.76 440,647 $ 90.22 177,288 $ 83.48 1,980,866 $ 64.60
Options Outstanding and Exercisable	Other information regarding options outstanding and exercisable as of December 31, 2019 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 $ 50.00 238,055 $ 48.00 1.82 238,055 $ 48.00 50.01 to 55.00 464,009 53.75 2.04 464,009 53.75 65.01 to 70.00 526,096 65.11 5.67 526,096 65.11 70.01 to 75.00 275,654 71.39 3.80 275,654 71.39 75.01 to 80.00 477,052 78.95 4.71 477,052 78.95 Total 1,980,866 64.60 3.87 1,980,866 64.60 Total intrinsic value $ 65,725 $ 65,725
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: 2019 2018 2017 New shares issued from available authorized shares — — 603,842 Issued from available treasury stock 399,224 548,238 547,078 Total 399,224 548,238 1,150,920 Proceeds from stock option exercises $ 20,770 $ 31,647 $ 67,746 Intrinsic value of stock options exercised 13,713 23,292 38,275 Fair value of stock awards/units vested 5,192 4,212 4,578
Stock-Based Compensation Expense	Stock-based compensation expense and the related income tax benefit is presented in the following table. The service period for performance stock units granted each year begins on January 1 of the following year. 2019 2018 2017 Stock options $ 1,185 $ 3,652 $ 6,230 Non-vested stock awards/stock units 9,339 6,983 4,992 Deferred stock-units 780 721 519 Performance stock units 4,642 2,587 1,272 Total $ 15,946 $ 13,943 $ 13,013 Income tax benefit $ 2,359 $ 2,831 $ 4,555
Unrecognized Stock-Based Compensation Expense	Unrecognized stock-based compensation expense and the weighted-average period over which the expense is expected to be recognized at December 31, 2019 is presented in the table below. Unrecognized stock-based compensation expense related to performance stock units is presented assuming attainment of the maximum payout rate as set forth by the performance criteria. Unrecognized Expense Weighted-Average Number of Years for Expense Recognition Non-vested stock awards/stock units $ 18,882 2.81 Performance stock units 6,299 2.11 Total $ 25,181

Other Non-Interest Income and_2

Other Non-Interest Income and Expense (Tables)	12 Months Ended
	Dec. 31, 2019
Other Income and Expenses [Abstract]
Other Non-Interest Income and Expense	2019 2018 2017 Other non-interest income: Other $ 43,563 $ 46,790 $ 37,222 Total $ 43,563 $ 46,790 $ 37,222 Other non-interest expense: Professional services $ 39,238 $ 35,941 $ 27,968 Advertising, promotions and public relations 38,001 32,514 29,337 Travel/meals and entertainment 16,459 15,030 15,066 Check card expense 5,947 4,744 16,501 Other 81,020 85,309 86,417 Total $ 180,665 $ 173,538 $ 175,289

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Tax Expense	Income tax expense was as follows: 2019 2018 2017 Current income tax expense $ 48,256 $ 840 $ 58,707 Deferred income tax expense (benefit) 7,614 52,923 (14,493 ) Income tax expense, as reported $ 55,870 $ 53,763 $ 44,214 Effective tax rate 11.2 % 10.6 % 10.8 %
Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate	A reconciliation between reported income tax expense and the amounts computed by applying the U.S. federal statutory income tax rate of 21% in 2019 and 2018 and 35% in 2017 to income before income taxes is presented in the following table. 2019 2018 2017 Income tax expense computed at the statutory rate $ 104,888 $ 106,823 $ 142,927 Effect of tax-exempt interest (49,166 ) (49,700 ) (81,034 ) Tax benefit on dividends paid in our 401k plan (1,743 ) (1,551 ) (2,372 ) Bank owned life insurance income (774 ) (710 ) (1,116 ) Non-deductible compensation 1,708 210 158 Non-deductible FDIC premiums 1,267 1,771 — Non-deductible meals and entertainment 1,299 1,193 983 Net tax benefit from stock-based compensation (2,447 ) (3,865 ) (9,062 ) Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate — (231 ) (4,047 ) Correction for prior year tax-exempt interest — — (2,906 ) Other 838 (177 ) 683 Income tax expense, as reported $ 55,870 $ 53,763 $ 44,214
Schedule of Deferred Tax Assets and Liabilities	Year-end deferred taxes are presented in the table below. Deferred taxes are based on the U.S. statutory federal income tax rate of 21% . 2019 2018 Deferred tax assets: Lease liabilities under operating leases $ 67,975 $ — Allowance for loan losses 27,755 27,748 Net actuarial loss on defined benefit post-retirement benefit plans 12,210 12,626 Stock-based compensation 11,211 10,622 Bonus accrual 5,055 4,586 Net unrealized loss on securities available for sale and transferred securities — 4,283 Deferred loan and lease origination fees 2,254 2,153 Other 2,163 4,761 Total gross deferred tax assets 128,623 66,779 Deferred tax liabilities: Net unrealized gain on securities available for sale and transferred securities (83,281 ) — Right-of-use assets under operating leases (63,463 ) — Premises and equipment (29,730 ) (23,859 ) Intangible assets (12,642 ) (10,726 ) Defined benefit post-retirement benefit plans (9,419 ) (9,452 ) Partnership interests (2,894 ) — Leases (1,572 ) (1,709 ) Other (1,440 ) (1,257 ) Total gross deferred tax liabilities (204,441 ) (47,003 ) Net deferred tax asset (liability) $ (75,818 ) $ 19,776

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2019
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 2019 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 418,556 $ 87,897 $ 330,659 Change in net unrealized gain on securities transferred to held to maturity (1,292 ) (271 ) (1,021 ) Reclassification adjustment for net (gains) losses included in net income (293 ) (62 ) (231 ) Total securities available for sale and transferred securities 416,971 87,564 329,407 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (3,644 ) (765 ) (2,879 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,623 1,181 4,442 Total defined-benefit post-retirement benefit plans 1,979 416 1,563 Total other comprehensive income (loss) $ 418,950 $ 87,980 $ 330,970 2018 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ (182,340 ) $ (38,292 ) $ (144,048 ) Change in net unrealized gain on securities transferred to held to maturity (8,818 ) (1,853 ) (6,965 ) Reclassification adjustment for net (gains) losses included in net income 156 33 123 Total securities available for sale and transferred securities (191,002 ) (40,112 ) (150,890 ) Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (7,225 ) (1,517 ) (5,708 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,002 1,051 3,951 Total defined-benefit post-retirement benefit plans (2,223 ) (466 ) (1,757 ) Total other comprehensive income (loss) $ (193,225 ) $ (40,578 ) $ (152,647 ) 2017 Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 157,016 $ 48,626 $ 108,390 Change in net unrealized gain on securities transferred to held to maturity (16,193 ) (5,668 ) (10,525 ) Reclassification adjustment for net (gains) losses included in net income 4,941 1,729 3,212 Total securities available for sale and transferred securities 145,764 44,687 101,077 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss (597 ) (126 ) (471 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 5,429 1,900 3,529 Total defined-benefit post-retirement benefit plans 4,832 1,774 3,058 Total other comprehensive income (loss) $ 150,596 $ 46,461 $ 104,135
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 Accumulated Other Comprehensive Income Balance January 1, 2019 $ (16,103 ) $ (47,497 ) $ (63,600 ) Other comprehensive income (loss) before reclassification 329,638 (2,879 ) 326,759 Reclassification of amounts included in net income (231 ) 4,442 4,211 Net other comprehensive income (loss) during period 329,407 1,563 330,970 Balance December 31, 2019 $ 313,304 $ (45,934 ) $ 267,370 Balance January 1, 2018 $ 117,230 $ (37,718 ) $ 79,512 Other comprehensive income (loss) before reclassification (151,013 ) (5,708 ) (156,721 ) Reclassification of amounts included in net income 123 3,951 4,074 Net other comprehensive income (loss) during period (150,890 ) (1,757 ) (152,647 ) Reclassification of certain income tax effects related to the change in the U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act to retained earnings 17,557 (8,022 ) 9,535 Balance December 31, 2018 $ (16,103 ) $ (47,497 ) $ (63,600 ) Balance January 1, 2017 $ 16,153 $ (40,776 ) $ (24,623 ) Other comprehensive income (loss) before reclassification 97,865 (471 ) 97,394 Reclassification of amounts included in net income 3,212 3,529 6,741 Net other comprehensive income (loss) during period 101,077 3,058 104,135 Balance December 31, 2017 $ 117,230 $ (37,718 ) $ 79,512

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding	December 31, 2019 December 31, 2018 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 $ 2,545 $ 6 $ 10,941 $ 207 Loan/lease interest rate swaps - liabilities 6,000 (138 ) 3,885 (199 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps - assets 122,788 67 496,887 2,384 Loan/lease interest rate swaps - liabilities 1,002,860 (19,483 ) 691,143 (8,921 ) Loan/lease interest rate caps - assets 107,835 266 122,791 509 Customer counterparties: Loan/lease interest rate swaps - assets 1,002,860 43,857 691,143 16,706 Loan/lease interest rate swaps - liabilities 122,788 (310 ) 496,887 (8,891 ) Loan/lease interest rate caps - liabilities 107,835 (266 ) 122,791 (509 )
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, 2019 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.66 % 1.75 % Non-hedging interest rate swaps - financial institution counterparties 4.12 3.45 Non-hedging interest rate swaps - customer counterparties 3.45 4.12
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, 2019 December 31, 2018 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil - assets Barrels 1,214 $ 2,796 2,416 $ 24,332 Oil - liabilities Barrels 2,148 (6,916 ) 415 (646 ) Natural gas - assets MMBTUs 8,295 2,131 5,745 417 Natural gas - liabilities MMBTUs 2,689 (70 ) 9,314 (1,272 ) Customer counterparties: Oil - assets Barrels 2,172 7,208 415 646 Oil - liabilities Barrels 1,190 (2,652 ) 2,416 (24,009 ) Natural gas - assets MMBTUs 2,689 83 10,236 1,373 Natural gas - liabilities MMBTUs 8,295 (2,039 ) 4,823 (393 )
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, 2019 December 31, 2018 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts - liabilities CAD 4,593 $ (33 ) 11,003 $ (13 ) Forward contracts - liabilities GBP — — 142 (2 ) Forward contracts - liabilities MXN — — 3,015 (132 ) Customer counterparties: Forward contracts - assets CAD 4,583 45 10,979 40 Forward contracts - assets GBP — — 145 4 Forward contracts - assets MXN — — 3,000 149
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: 2019 2018 2017 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ 86 $ 25 $ (726 ) Amount of (gain) loss included in other non-interest expense — (1 ) (14 )
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, foreign currency and other derivative instruments are presented in the table below. 2019 2018 2017 Non-hedging interest rate derivatives: Other non-interest income $ 2,005 $ 4,112 $ 3,123 Other non-interest expense (1 ) — 1 Non-hedging commodity derivatives: Other non-interest income 503 795 440 Non-hedging foreign currency derivatives: Other non-interest income 51 246 300 Non-hedging other derivatives: Other non-interest income 750 — —

Balance Sheet Offsetting Balanc

Balance Sheet Offsetting Balance Sheet Offsetting (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2019 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 339 $ — $ 339 Commodity swaps and options 4,927 — 4,927 Total derivatives 5,266 — 5,266 Resell agreements 31,299 — 31,299 Total $ 36,565 $ — $ 36,565 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 19,621 $ — $ 19,621 Commodity swaps and options 6,986 — 6,986 Foreign currency forward contracts 33 — 33 Total derivatives 26,640 — 26,640 Repurchase agreements 1,668,142 — 1,668,142 Total $ 1,694,782 $ — $ 1,694,782 Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2018 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2018 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,100 $ — $ 3,100 Commodity swaps and options 24,749 — 24,749 Total derivatives 27,849 — 27,849 Resell agreements 11,642 — 11,642 Total $ 39,491 $ — $ 39,491 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 9,120 $ — $ 9,120 Commodity swaps and options 1,918 — 1,918 Foreign currency forward contracts 147 — 147 Total derivatives 11,185 — 11,185 Repurchase agreements 1,360,298 — 1,360,298 Total $ 1,371,483 $ — $ 1,371,483
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, 2019 Financial assets: Derivatives: Counterparty A $ 39 $ (39 ) $ — $ — Counterparty B 1,650 (1,650 ) — — Counterparty C 1 (1 ) — — Other counterparties 3,576 (3,546 ) — 30 Total derivatives 5,266 (5,236 ) — 30 Resell agreements 31,299 — (31,299 ) — Total $ 36,565 $ (5,236 ) $ (31,299 ) $ 30 Financial liabilities: Derivatives: Counterparty A $ 5,192 $ (39 ) $ (5,153 ) $ — Counterparty B 7,424 (1,650 ) (5,774 ) — Counterparty C 135 (1 ) (134 ) — Other counterparties 13,889 (3,546 ) (10,343 ) — Total derivatives 26,640 (5,236 ) (21,404 ) — Repurchase agreements 1,668,142 — (1,668,142 ) — Total $ 1,694,782 $ (5,236 ) $ (1,689,546 ) $ — Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2018 Financial assets: Derivatives: Counterparty A $ 598 $ (598 ) $ — $ — Counterparty B 7,255 (3,380 ) (3,875 ) — Counterparty C 81 (81 ) — — Other counterparties 19,915 (2,084 ) (17,776 ) 55 Total derivatives 27,849 (6,143 ) (21,651 ) 55 Resell agreements 11,642 — (11,642 ) — Total $ 39,491 $ (6,143 ) $ (33,293 ) $ 55 Financial liabilities: Derivatives: Counterparty A $ 4,293 $ (598 ) $ (3,651 ) $ 44 Counterparty B 3,380 (3,380 ) — — Counterparty C 326 (81 ) (245 ) — Other counterparties 3,186 (2,084 ) (725 ) 377 Total derivatives 11,185 (6,143 ) (4,621 ) 421 Repurchase agreements 1,360,298 — (1,360,298 ) — Total $ 1,371,483 $ (6,143 ) $ (1,364,919 ) $ 421
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, 2019 and December 31, 2018 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, 2019 Repurchase agreements: U.S. Treasury $ 435,904 $ — $ — $ — $ 435,904 Residential mortgage-backed securities 1,232,238 — — — 1,232,238 Total borrowings $ 1,668,142 $ — $ — $ — $ 1,668,142 Gross amount of recognized liabilities for repurchase agreements $ 1,668,142 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2018 Repurchase agreements: U.S. Treasury $ 1,334,063 $ — $ — $ — $ 1,334,063 Residential mortgage-backed securities 26,235 — — — 26,235 Total borrowings $ 1,360,298 $ — $ — $ — $ 1,360,298 Gross amount of recognized liabilities for repurchase agreements $ 1,360,298 Amounts related to agreements not included in offsetting disclosures above $ —

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on a Recurring Basis	The following tables summarize financial assets and financial liabilities measured at fair value on a recurring basis as of December 31, 2019 and 2018 , 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 2019 Securities available for sale: U.S. Treasury $ 1,948,133 $ — $ — $ 1,948,133 Residential mortgage-backed securities — 2,207,594 — 2,207,594 States and political subdivisions — 7,070,997 — 7,070,997 Other — 42,867 — 42,867 Trading account securities: U.S. Treasury 24,298 — — 24,298 Derivative assets: Interest rate swaps, caps and floors — 44,196 — 44,196 Commodity swaps and options — 12,218 — 12,218 Foreign currency forward contracts 45 — — 45 Derivative liabilities: Interest rate swaps, caps and floors — 20,197 — 20,197 Commodity swaps and options — 11,677 — 11,677 Foreign currency forward contracts 33 — — 33 2018 Securities available for sale: U.S. Treasury $ 3,427,689 $ — $ — $ 3,427,689 Residential mortgage-backed securities — 829,740 — 829,740 States and political subdivisions — 7,087,202 — 7,087,202 Other — 42,690 — 42,690 Trading account securities: U.S. Treasury 21,928 — — 21,928 States and political subdivisions — 2,158 — 2,158 Derivative assets: Interest rate swaps, caps and floors — 19,806 — 19,806 Commodity swaps and options — 26,768 — 26,768 Foreign currency forward contracts 193 — — 193 Derivative liabilities: Interest rate swaps, caps and floors — 18,520 — 18,520 Commodity swaps and options — 26,320 — 26,320 Foreign currency forward contracts 147 — — 147
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: 2019 2018 2017 Level 2 Carrying value of impaired loans before allocations $ 2,354 $ 12,517 $ — Specific valuation allowance allocations (383 ) (2,599 ) — Fair value $ 1,971 $ 9,918 $ — Level 3 Carrying value of impaired loans before allocations $ 65,176 $ 22,688 $ 75,435 Specific valuation allowance allocations (18,019 ) 9,260 (19,533 ) Fair value $ 47,157 $ 31,948 $ 55,902
Foreclosed Assets Remeasured and Reported at Fair Value	The following table presents foreclosed assets that were remeasured and reported at fair value: 2019 2018 2017 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 1,348 $ 2,899 $ 279 Charge-offs recognized in the allowance for loan losses (76 ) — — Fair value $ 1,272 $ 2,899 $ 279 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ — $ 1,823 $ 89 Write-downs included in other non-interest expense — (473 ) (16 ) Fair value $ — $ 1,350 $ 73
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, 2019 December 31, 2018 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,788,181 $ 3,788,181 $ 3,955,779 $ 3,955,779 Securities held to maturity 2,030,005 2,048,675 1,106,057 1,116,953 Cash surrender value of life insurance policies 187,156 187,156 183,473 183,473 Accrued interest receivable 183,850 183,850 188,989 188,989 Level 3 inputs: Loans, net 14,618,165 14,654,615 13,967,601 13,933,239 Financial liabilities: Level 2 inputs: Deposits 27,639,564 27,641,255 27,149,204 27,143,572 Federal funds purchased and repurchase agreements 1,695,342 1,695,342 1,367,548 1,367,548 Junior subordinated deferrable interest debentures 136,299 137,115 136,242 137,115 Subordinated notes payable and other borrowings 98,865 89,077 98,708 98,458 Accrued interest payable 12,393 12,393 7,394 7,394

Operating Segments (Tables)

Operating Segments (Tables)	12 Months Ended
	Dec. 31, 2019
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. Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $37.8 billion , $33.3 billion and $32.8 billion at December 31, 2019 , 2018 and 2017 . Banking Frost Wealth Advisors Non-Banks Consolidated 2019 Net interest income (expense) $ 1,010,368 $ 4,001 $ (10,364 ) $ 1,004,005 Provision for loan losses 33,758 1 — 33,759 Non-interest income 218,447 145,905 (450 ) 363,902 Non-interest expense 703,121 124,622 6,936 834,679 Income (loss) before income taxes 491,936 25,283 (17,750 ) 499,469 Income tax expense (benefit) 55,520 5,308 (4,958 ) 55,870 Net income (loss) 436,416 19,975 (12,792 ) 443,599 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 436,416 $ 19,975 $ (20,855 ) $ 435,536 Revenues from (expenses to) external customers $ 1,228,815 $ 149,906 $ (10,814 ) $ 1,367,907 Average assets (in millions) $ 32,019 $ 56 $ 11 $ 32,086 Banking Frost Wealth Advisors Non-Banks Consolidated 2018 Net interest income (expense) $ 963,757 $ 4,083 $ (9,948 ) $ 957,892 Provision for loan losses 21,613 — — 21,613 Non-interest income 213,763 138,045 (522 ) 351,286 Non-interest expense 657,448 114,166 7,270 778,884 Income (loss) before income taxes 498,459 27,962 (17,740 ) 508,681 Income tax expense (benefit) 52,928 5,872 (5,037 ) 53,763 Net income (loss) 445,531 22,090 (12,703 ) 454,918 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 445,531 $ 22,090 $ (20,766 ) $ 446,855 Revenues from (expenses to) external customers $ 1,177,520 $ 142,128 $ (10,470 ) $ 1,309,178 Average assets (in millions) $ 30,964 $ 54 $ 12 $ 31,030 2017 Net interest income (expense) $ 856,593 $ 17,644 $ (7,815 ) $ 866,422 Provision for loan losses 35,460 — — 35,460 Non-interest income 207,810 128,819 (159 ) 336,470 Non-interest expense 644,072 108,931 6,066 759,069 Income (loss) before income taxes 384,871 37,532 (14,040 ) 408,363 Income tax expense (benefit) 37,837 13,137 (6,760 ) 44,214 Net income (loss) 347,034 24,395 (7,280 ) 364,149 Preferred stock dividends — — 8,063 8,063 Net income (loss) available to common shareholders $ 347,034 $ 24,395 $ (15,343 ) $ 356,086 Revenues from (expenses to) external customers $ 1,064,403 $ 146,463 $ (7,974 ) $ 1,202,892 Average assets (in millions) $ 30,391 $ 43 $ 16 $ 30,450

Condensed Financial Statement_2

Condensed Financial Statements of Parent Company (Tables)	12 Months Ended
	Dec. 31, 2019
Condensed Financial Information Disclosure [Abstract]
Schedule of Condensed Balance Sheets	Condensed Balance Sheets December 31, 2019 2018 Assets: Cash $ 9,116 $ 11,397 Resell agreements 258,000 225,000 Total cash and cash equivalents 267,116 236,397 Investment in subsidiaries 3,896,962 3,362,474 Accrued interest receivable and other assets 2,545 9,122 Total assets $ 4,166,623 $ 3,607,993 Liabilities: Junior subordinated deferrable interest debentures, net of unamortized issuance costs $ 136,299 $ 136,242 Subordinated notes, net of unamortized issuance costs 98,865 98,708 Accrued interest payable and other liabilities 19,791 4,126 Total liabilities 254,955 239,076 Shareholders’ Equity 3,911,668 3,368,917 Total liabilities and shareholders’ equity $ 4,166,623 $ 3,607,993
Schedule of Condensed Statements of Income	Condensed Statements of Income Year Ended December 31, 2019 2018 2017 Income: Dividend income paid by Frost Bank $ 234,531 $ 223,371 $ 149,671 Dividend income paid by non-banks 1,822 953 915 Interest and other income 2,868 1,828 421 Total income 239,221 226,152 151,007 Expenses: Interest expense 10,363 9,948 7,815 Salaries and employee benefits 1,551 1,973 1,202 Other 7,033 7,016 6,373 Total expenses 18,947 18,937 15,390 Income before income taxes and equity in undistributed earnings of subsidiaries 220,274 207,215 135,617 Income tax benefit 5,135 5,218 7,092 Equity in undistributed earnings of subsidiaries 218,190 242,485 221,440 Net income 443,599 454,918 364,149 Preferred stock dividends 8,063 8,063 8,063 Net income available to common shareholders $ 435,536 $ 446,855 $ 356,086
Schedule of Condensed Statements of Cash Flows	Condensed Statements of Cash Flows Year Ended December 31, 2019 2018 2017 Operating Activities: Net income $ 443,599 $ 454,918 $ 364,149 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed earnings of subsidiaries (218,190 ) (242,485 ) (221,440 ) Stock-based compensation 780 721 519 Net tax benefit from stock-based compensation 240 304 318 Net change in other assets and other liabilities 22,216 (12,709 ) 7,665 Net cash from operating activities 248,645 200,749 151,211 Investing Activities: Net cash from investing activities — — — Financing Activities: Proceeds from issuance of subordinated notes — — 98,434 Principal payments on subordinated notes — — (100,000 ) Proceeds from stock option exercises 20,770 31,647 67,746 Proceeds from stock-based compensation activities of subsidiaries 15,166 13,222 12,494 Purchase of treasury stock (68,793 ) (101,010 ) (101,473 ) Cash dividends paid on preferred stock (8,063 ) (8,063 ) (8,063 ) Cash dividends paid on common stock (177,006 ) (165,449 ) (144,172 ) Net cash from financing activities (217,926 ) (229,653 ) (175,034 ) Net change in cash and cash equivalents 30,719 (28,904 ) (23,823 ) Cash and cash equivalents at beginning of year 236,397 265,301 289,124 Cash and cash equivalents at end of year $ 267,116 $ 236,397 $ 265,301

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash on hand or on deposit required	$ 918,000	$ 447,900
Cash collateral on deposit	37,500	10,000
Foreclosed assets	1,100	1,200
Operating lease, right-of-use asset	297,736	0		$ 170,500
Operating lease, liability				$ 174,400
Cumulative effect of new accounting principle in period of adoption		(14,672)	$ (2,285)
Additional premium amortization expense on securities	5,200
Gross interchange and debit card transaction fees	27,800	25,800	23,200
Gross cost related to interchange and debit card transactions	12,900	11,900	11,900
Interchange and debit card transaction fees	$ 14,873	13,877	23,232
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%
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		(14,672)	$ (2,285)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act		$ 9,500

Summary of Significant Accoun_5

Summary of Significant Accounting Policies (Additional Cash Flow Information) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash paid for interest	$ 124,781	$ 89,270	$ 24,371
Cash paid for income tax	45,352	5,112	56,359
Transfer of investment securities to held to maturity from available for sale	377,812	0	0
Unsettled purchases/sales of securities	0	330	37,481
Loans foreclosed and transferred to other real estate owned and foreclosed assets	1,348	2,899	279
Loans to facilitate the sale of other real estate owned	847	0	0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 319,286	$ 0	$ 0

Securities (Year End Securities

Securities (Year End Securities Held to Maturity and Available for Sale) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	$ 2,030,005	$ 1,106,057
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	28,931	11,533
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	10,261	637
Held to Maturity, Estimated Fair Value	2,048,675	1,116,953
Available for Sale, Amortized Cost	10,877,769	11,410,447
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	405,399	85,611
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	13,577	108,737
Available for Sale, Estimated Fair Value	11,269,591	11,387,321
US Treasury [Member]
Schedule of Investments [Line Items]
Available for Sale, Amortized Cost	1,941,283	3,455,417
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	18,934	1,772
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	12,084	29,500
Available for Sale, Estimated Fair Value	1,948,133	3,427,689
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	530,861	2,737
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	22	8
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	9,365	85
Held to Maturity, Estimated Fair Value	521,518	2,660
Available for Sale, Amortized Cost	2,176,275	823,208
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	32,608	13,079
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,289	6,547
Available for Sale, Estimated Fair Value	2,207,594	829,740
States and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,497,644	1,101,820
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	28,909	11,525
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	896	552
Held to Maturity, Estimated Fair Value	1,525,657	1,112,793
Available for Sale, Amortized Cost	6,717,344	7,089,132
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	353,857	70,760
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	204	72,690
Available for Sale, Estimated Fair Value	7,070,997	7,087,202
Other [Member]
Schedule of Investments [Line Items]
Held to Maturity, Amortized Cost	1,500	1,500
Debt Securities, Held-to-maturity, Accumulated Unrecognized Gain	0	0
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	0
Held to Maturity, Estimated Fair Value	1,500	1,500
Available for Sale, Amortized Cost	42,867	42,690
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	$ 42,867	$ 42,690

Securities (Narrative) (Detail)

Securities (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Marketable Securities [Line Items]
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas	99.70%
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas guaranteed by Texas permanent school fund	69.10%
Carry value of securities pledged	$ 3,900,000	$ 3,800,000
Securities available for sale, at estimated fair value	11,269,591	11,387,321
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, pre tax	4,800	2,700
Net unamortized, unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	3,800	$ 2,200
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	377,800
Available for sale securities reclassified to held to maturity, unrealized gain	3,300
Available for sale securities reclassified to held to maturity, unrealized gain net of tax	$ 2,600

Securities (Year End Securiti_2

Securities (Year End Securities with Unrealized Losses Segregated by Length of Impairment) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	$ 890,533	$ 205,686
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10,257	541
Held to Maturity, More than 12 Months, Estimated Fair Value	408	7,986
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4	96
Held to Maturity, Total Estimated Fair Value	890,941	213,672
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	10,261	637
Available for Sale, Less than 12 Months, Estimated Fair Value	972,926	1,289,004
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	13,056	7,231
Available for Sale, More than 12 Months, Estimated Fair Value	231,436	5,411,669
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	521	101,506
Available for Sale, Total Estimated Fair Value	1,204,362	6,700,673
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	13,577	108,737
US Treasury Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Available for Sale, Less than 12 Months, Estimated Fair Value	636,999	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12,070	0
Available for Sale, More than 12 Months, Estimated Fair Value	199,980	3,139,639
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	14	29,500
Available for Sale, Total Estimated Fair Value	836,979	3,139,639
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	12,084	29,500
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	519,099	0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9,361	0
Held to Maturity, More than 12 Months, Estimated Fair Value	408	2,034
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4	85
Held to Maturity, Total Estimated Fair Value	519,507	2,034
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	9,365	85
Available for Sale, Less than 12 Months, Estimated Fair Value	276,249	152,682
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	782	205
Available for Sale, More than 12 Months, Estimated Fair Value	31,456	213,982
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	507	6,342
Available for Sale, Total Estimated Fair Value	307,705	366,664
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,289	6,547
States and Political Subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	371,434	205,686
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	896	541
Held to Maturity, More than 12 Months, Estimated Fair Value	0	5,952
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	11
Held to Maturity, Total Estimated Fair Value	371,434	211,638
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	896	552
Available for Sale, Less than 12 Months, Estimated Fair Value	59,678	1,136,322
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	204	7,026
Available for Sale, More than 12 Months, Estimated Fair Value	0	2,058,048
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	65,664
Available for Sale, Total Estimated Fair Value	59,678	3,194,370
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	204	72,690
Other Investments [Member]
Schedule of Available-for-Sale Securities [Line Items]
Debt Securities, Held-to-maturity, Accumulated Unrecognized Loss	0	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, 2019	Dec. 31, 2018
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Due in one year or less, Amortized Cost	$ 12,773
Held to Maturity, Due after one year through five years, Amortized Cost	165,519
Held to Maturity, Due after five years through ten years, Amortized Cost	527,907
Held to Maturity, Due after ten years, Amortized Cost	792,945
Held to Maturity, Residential mortgage-backed securities, Amortized Cost	530,861
Held-to-maturity, Equity Securities, Amortized Cost	0
Held to Maturity, Amortized Cost	2,030,005	$ 1,106,057
Held to Maturity, Due in one year or less, Estimated Fair Value	12,847
Held to Maturity, Due after one year through five years, Estimated Fair Value	169,970
Held to Maturity, Due after five years through ten years, Estimated Fair Value	541,249
Held to Maturity, Due after ten years, Estimated Fair Value	803,091
Held to Maturity, Residential mortgage-backed securities, Estimated Fair Value	521,518
Held-to-maturity, Equity Securities, Estimated Fair Value	0
Held to Maturity, Estimated Fair Value	2,048,675	1,116,953
Available for Sale, Due in one year or less, Amortized Cost	508,575
Available for Sale, Due after one year through five years, Amortized Cost	1,317,774
Available for Sale, Due after five years through ten years, Amortized Cost	451,885
Available for Sale, Due after ten years, Amortized Cost	6,380,393
Available For Sale, Residential mortgage-backed securities, Amortized Cost	2,176,275
Available for Sale, Equity securities, Amortized Cost	42,867
Available for Sale, Amortized Cost	10,877,769	11,410,447
Available for Sale, Due in one year or less, Estimated Fair Value	509,404
Available for Sale, Due after one year through five years, Estimated Fair Value	1,344,035
Available for Sale, Due after five years through ten years, Estimated Fair Value	478,800
Available for Sale, Due after ten years, Estimated Fair Value	6,686,891
Available for Sale, Residential mortgage-backed securities, Estimated Fair Value	2,207,594
Available for Sale, Equity securities, Estimated Fair Value	42,867
Available for Sale, Estimated Fair Value	$ 11,269,591	$ 11,387,321

Securities (Sales of Securities

Securities (Sales of Securities Available for Sale) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 18,660,147	$ 16,806,062	$ 11,963,359
Gross realized gains	930	3	1
Gross realized losses	(637)	(159)	(4,942)
Tax benefit (expense) related to securities gains/losses	$ (62)	$ 33	$ 1,729

Securities Securities - (Premiu

Securities Securities - (Premium Amortization and Discount Accretion Included in Income on Securities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Premium amortization	$ (120,785)	$ (108,483)	$ (97,841)
Discount accretion	5,227	7,955	7,908
Net (premium amortization) discount accretion	$ (115,558)	$ (100,528)	$ (89,933)

Securities (Year End Trading Ac

Securities (Year End Trading Account Securities at Estimated Fair Value) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Trading account securities	$ 24,298	$ 24,086
US Treasury [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading account securities	24,298	21,928
States and Political Subdivisions [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading account securities	$ 0	$ 2,158

Securities (Net Gains and Losse

Securities (Net Gains and Losses on Trading Account Securities) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 2,173	$ 1,816	$ 1,408
Net mark-to-market gains (losses)	(176)	105	(43)
Net gain on trading account securities	$ 1,997	$ 1,921	$ 1,365

Loans (Narrative) (Detail)

Loans (Narrative) (Detail)	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Nov. 30, 2019
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	$ 9,000,000	$ 8,500,000
Minimum number of days to be considered past due	90 days
Interest income recognized subsequent to classification as impaired	$ 0	$ 0	$ 0
Number of days past due for payment of interest on loans, minimum	120 days
Texas Leading Index economic condition indicator		126.4		128.8
Maximum origination value of loans which were subject to further refinement of valuation methodology	$ 1,000,000
Sensitivity stress test price shock	75.00%
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of loans related to a single industry	11.20%	11.40%
Non Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additional interest that would have been recognized on non-accrual loans, net of tax	$ 3,900,000	$ 5,200,000	$ 3,700,000
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
Commitments to Extend Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	$ 1,200,000,000
Standby Letters of Credit [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	$ 75,500,000

Loans (Loans) (Detail)

Loans (Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 14,750,332	$ 14,099,733
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	5,187,466	5,111,957
Energy Production [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	1,348,900	1,309,314
Energy Service [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	192,996	168,775
Energy Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	110,986	124,509
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	1,652,882	1,602,598
Commercial mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	4,594,113	4,121,966
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	1,312,659	1,267,717
Commercial land loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	289,467	306,755
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	6,196,239	5,696,438
Home Equity Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	375,596	353,924
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	354,671	337,168
Other consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	464,146	427,898
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	1,194,413	1,118,990
Real Estate Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	7,390,652	6,815,428
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 519,332	$ 569,750

Loans (Activities in Related Pa

Loans (Activities in Related Party Loans) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Receivables [Abstract]
Balance outstanding at December 31, 2018	$ 256,056
Principal additions	304,407
Principal reductions	(257,687)
Other changes	(4,248)
Balance outstanding at December 31, 2019	$ 298,528

Loans (Non-Accrual Loans, Segre

Loans (Non-Accrual Loans, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 102,303	$ 73,739
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	26,038	9,239
Commercial and Industrial Total Energy Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	65,761	46,932
Commercial Real Estate, Buildings, Land and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	8,912	15,268
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	665	0
Total consumer real estate loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	922	892
Consumer Loan [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 5	$ 1,408

Loans (Age Analysis of Past Due

Loans (Age Analysis of Past Due Loans, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	$ 146,973
Current Loans	14,603,359
Total loans	14,750,332	$ 14,099,733
Accruing Loans 90 or More Days Past Due	7,421
Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	46,742
Current Loans	5,140,724
Total loans	5,187,466	5,111,957
Accruing Loans 90 or More Days Past Due	3,430
Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	68,702
Current Loans	1,584,180
Total loans	1,652,882	1,602,598
Accruing Loans 90 or More Days Past Due	85
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	15,109
Current Loans	4,868,471
Total loans	4,883,580	4,428,721
Accruing Loans 90 or More Days Past Due	967
Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	1,261
Current Loans	1,311,398
Total loans	1,312,659	1,267,717
Accruing Loans 90 or More Days Past Due	402
Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	9,571
Current Loans	1,184,842
Total loans	1,194,413	1,118,990
Accruing Loans 90 or More Days Past Due	1,425
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	5,588
Current Loans	513,744
Total loans	519,332	$ 569,750
Accruing Loans 90 or More Days Past Due	1,112
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	56,107
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	25,474
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	6,136
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	12,384
Financing Receivables, 30 to 89 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	195
Financing Receivables, 30 to 89 Days Past Due [Member] | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	7,442
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	4,476
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	90,866
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	21,268
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	62,566
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,725
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	1,066
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Total consumer real estate loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	2,129
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due Loans	$ 1,112

Loans (Impaired Loans) (Detail)

Loans (Impaired Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 128,536	$ 94,536	$ 172,396
Recorded Investment With No Allowance	21,842	12,120	68,726
Recorded Investment With Allowance	77,611	58,101	76,884
Total Recorded Investment	99,453	70,221	145,610
Related Allowance	28,483	16,235	20,820
Average Recorded Investment	84,352	108,127	113,907
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	30,909	9,094	60,781
Recorded Investment With No Allowance	11,588	2,842	28,038
Recorded Investment With Allowance	12,772	4,287	15,722
Total Recorded Investment	24,360	7,129	43,760
Related Allowance	7,849	2,558	7,553
Average Recorded Investment	14,913	18,246	30,073
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	87,103	67,900	99,606
Recorded Investment With No Allowance	2,764	6,817	33,080
Recorded Investment With Allowance	62,480	39,890	61,162
Total Recorded Investment	65,244	46,707	94,242
Related Allowance	20,246	9,671	13,267
Average Recorded Investment	53,563	75,453	76,492
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	9,252	15,774	10,795
Recorded Investment With No Allowance	6,255	2,168	6,394
Recorded Investment With Allowance	2,354	12,517	0
Total Recorded Investment	8,609	14,685	6,394
Related Allowance	383	2,599	0
Average Recorded Investment	13,690	12,799	6,164
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	697	0	0
Recorded Investment With No Allowance	665	0	0
Recorded Investment With Allowance	0	0	0
Total Recorded Investment	665	0	0
Related Allowance	0	0	0
Average Recorded Investment	354	0	0
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	570	293	1,214
Recorded Investment With No Allowance	570	293	1,214
Recorded Investment With Allowance	0	0	0
Total Recorded Investment	570	293	1,214
Related Allowance	0	0	0
Average Recorded Investment	547	704	1,167
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	5	1,475	0
Recorded Investment With No Allowance	0	0	0
Recorded Investment With Allowance	5	1,407	0
Total Recorded Investment	5	1,407	0
Related Allowance	5	1,407	0
Average Recorded Investment	$ 1,285	$ 925	$ 11

Loans (Troubled Debt Restructur

Loans (Troubled Debt Restructurings) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	$ 13,426	$ 15,911	$ 60,510
Balance at Year-end	11,674	0	58,484
Commercial Portfolio Segment [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	3,845	2,203	4,026
Balance at Year-end	2,161	0	3,766
Commercial and Industrial Total Energy Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	0	13,708	56,096
Balance at Year-end	0	0	54,330
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	9,457	0	0
Balance at Year-end	9,393	0	0
Construction Loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	0	0	388
Balance at Year-end	0	0	388
Total consumer real estate loans [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Balance at Restructure	124	0	0
Balance at Year-end	$ 120	$ 0	$ 0

Loans Loans (Restructured Loans

Loans Loans (Restructured Loans Past Due in Excess of 90 Days) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)Item	Dec. 31, 2018USD ($)Item	Dec. 31, 2017USD ($)Item
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loans restructured during the last year In excess of 90 days past due | Item	4	0	1
Dollar amount of loans previously restructured during the last year in excess of 90 days past due	$ 3,340	$ 0	$ 43,137
Restructured loans on non-accrual status at period end	5,576	0	53,622
Chare-offs of restrucured loans recognized in connection with restructuring	0	0	0
Charge-offs of restructured loans recognized on previously restructured loans	1,500	7,650	9,951
Proceeds from sale of restructured loans	$ 0	$ 15,750	$ 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, 2019USD ($)Grade	Dec. 31, 2018USD ($)Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned discounts	$ 14,750,332	$ 14,099,733
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.44	6.30
Loans, net of unearned discounts	$ 5,187,466	$ 5,111,957
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.39	6.22
Loans, net of unearned discounts	$ 1,652,882	$ 1,602,598
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.01	6.98
Loans, net of unearned discounts	$ 4,883,580	$ 4,428,721
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.31	7.29
Loans, net of unearned discounts	$ 1,312,659	$ 1,267,717
Risk Grade One To Eight [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.17	6.12
Loans, net of unearned discounts	$ 4,788,857	$ 4,862,275
Risk Grade One To Eight [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	5.90	5.76
Loans, net of unearned discounts	$ 1,488,301	$ 1,451,673
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	6.78	6.76
Loans, net of unearned discounts	$ 4,523,271	$ 4,143,264
Risk Grade One To Eight [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.25	7.13
Loans, net of unearned discounts	$ 1,274,098	$ 1,177,260
Risk Grade Nine [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans, net of unearned discounts	$ 247,212	$ 112,431
Risk Grade Nine [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans, net of unearned discounts	$ 32,163	$ 35,565
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, net of unearned discounts	$ 163,714	$ 109,660
Risk Grade Nine [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans, net of unearned discounts	$ 21,509	$ 60,754
Risk Grade Ten [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans, net of unearned discounts	$ 71,472	$ 58,328
Risk Grade Ten [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans, net of unearned discounts	$ 51,898	$ 43,001
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, net of unearned discounts	$ 103,626	$ 62,353
Risk Grade Ten [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans, net of unearned discounts	$ 15,243	$ 24,877
Risk Grade Eleven [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans, net of unearned discounts	$ 53,887	$ 69,684
Risk Grade Eleven [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans, net of unearned discounts	$ 14,760	$ 25,427
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, net of unearned discounts	$ 84,057	$ 98,176
Risk Grade Eleven [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans, net of unearned discounts	$ 1,144	$ 4,826
Risk Grade Twelve [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans, net of unearned discounts	$ 18,189	$ 6,681
Risk Grade Twelve [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans, net of unearned discounts	$ 45,514	$ 37,261
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, net of unearned discounts	$ 8,529	$ 12,669
Risk Grade Twelve [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans, net of unearned discounts	$ 665	$ 0
Risk Grade Thirteen [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans, net of unearned discounts	$ 7,849	$ 2,558
Risk Grade Thirteen [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans, net of unearned discounts	$ 20,246	$ 9,671
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, net of unearned discounts	$ 383	$ 2,599
Risk Grade Thirteen [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans, net of unearned discounts	$ 0	$ 0

Loans (Net (Charge-Offs)_Recove

Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (33,724)	$ (44,845)	$ (33,141)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(10,131)	(22,388)	(17,453)
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(6,058)	(13,121)	(10,009)
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(830)	(263)	735
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	24	13	11
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(2,457)	(1,538)	(506)
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (14,272)	$ (7,548)	$ (5,919)

Loans (Unallocated Portion of A

Loans (Unallocated Portion of Allowance for Loan Losses) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 132,167	$ 132,132	$ 155,364	$ 153,045
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	69,087	65,398
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	28,483	16,235
General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	19,732	22,100
Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	14,865	28,399
Commercial Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	51,593	48,580	59,614	52,915
Commercial Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	29,015	25,351
Commercial Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,849	2,558
Commercial Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	9,840	10,062
Commercial Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,889	10,609
Commercial And Industrial Energy Financing Receivable [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	37,382	29,052	51,528	60,653
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	7,873	9,697
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	20,246	9,671
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	5,196	6,014
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	4,067	3,670
Commercial Real Estate Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	31,037	38,777	30,948	30,213
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	21,947	20,817
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	383	2,599
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	4,201	4,366
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	4,506	10,995
Total consumer real estate loans [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	4,113	6,103	5,657	4,238
Total consumer real estate loans [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,690	2,688
Total consumer real estate loans [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0	0
Total consumer real estate loans [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	904	1,671
Total consumer real estate loans [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	519	1,744
Consumer Loan [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	8,042	9,620	$ 7,617	$ 5,026
Consumer Loan [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,562	6,845
Consumer Loan [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5	1,407
Consumer Loan [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	(409)	(13)
Consumer Loan [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 884	$ 1,381

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, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 14,750,332	$ 14,099,733
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,187,466	5,111,957
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,652,882	1,602,598
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,196,239	5,696,438
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,194,413	1,118,990
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	519,332	569,750
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	99,453	70,221
Loans Individually Evaluated for Impairment [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	24,360	7,129
Loans Individually Evaluated for Impairment [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	65,244	46,707
Loans Individually Evaluated for Impairment [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	9,274	14,685
Loans Individually Evaluated for Impairment [Member] | Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	570	293
Loans Individually Evaluated for Impairment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5	1,407
Loans Collectively Evaluated For Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	14,650,879	14,029,512
Loans Collectively Evaluated For Impairment [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	5,163,106	5,104,828
Loans Collectively Evaluated For Impairment [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,587,638	1,555,891
Loans Collectively Evaluated For Impairment [Member] | Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	6,186,965	5,681,753
Loans Collectively Evaluated For Impairment [Member] | Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	1,193,843	1,118,697
Loans Collectively Evaluated For Impairment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	$ 519,327	$ 568,343

Loans (Activity in Allowance fo

Loans (Activity in Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 132,132	$ 155,364	$ 153,045
Provision for loan losses	33,759	21,613	35,460
Charge-offs	(51,032)	(59,975)	(47,804)
Recoveries	17,308	15,130	14,663
Net charge-offs	(33,724)	(44,845)	(33,141)
Ending balance	132,167	132,132	155,364
Individually evaluated for impairment	28,483	16,235	20,820
Collectively evaluated for impairment	103,684	115,897	134,544
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	48,580	59,614	52,915
Provision for loan losses	13,144	11,354	24,152
Charge-offs	(14,117)	(26,076)	(20,619)
Recoveries	3,986	3,688	3,166
Net charge-offs	(10,131)	(22,388)	(17,453)
Ending balance	51,593	48,580	59,614
Individually evaluated for impairment	7,849	2,558	7,553
Collectively evaluated for impairment	43,744	46,022	52,061
Commercial And Industrial Energy Financing Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	29,052	51,528	60,653
Provision for loan losses	14,388	(9,355)	884
Charge-offs	(7,500)	(13,940)	(10,595)
Recoveries	1,442	819	586
Net charge-offs	(6,058)	(13,121)	(10,009)
Ending balance	37,382	29,052	51,528
Individually evaluated for impairment	20,246	9,671	13,267
Collectively evaluated for impairment	17,136	19,381	38,261
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	38,777	30,948	30,213
Provision for loan losses	(6,934)	8,079	(11)
Charge-offs	(1,025)	(619)	(86)
Recoveries	219	369	832
Net charge-offs	(806)	(250)	746
Ending balance	31,037	38,777	30,948
Individually evaluated for impairment	383	2,599	0
Collectively evaluated for impairment	30,654	36,178	30,948
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	6,103	5,657	4,238
Provision for loan losses	467	1,984	1,925
Charge-offs	(3,665)	(2,143)	(925)
Recoveries	1,208	605	419
Net charge-offs	(2,457)	(1,538)	(506)
Ending balance	4,113	6,103	5,657
Individually evaluated for impairment	0	0	0
Collectively evaluated for impairment	4,113	6,103	5,657
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	9,620	7,617	5,026
Provision for loan losses	12,694	9,551	8,510
Charge-offs	(24,725)	(17,197)	(15,579)
Recoveries	10,453	9,649	9,660
Net charge-offs	(14,272)	(7,548)	(5,919)
Ending balance	8,042	9,620	7,617
Individually evaluated for impairment	5	1,407	0
Collectively evaluated for impairment	$ 8,037	$ 8,213	$ 7,617

Premises and Equipment (Narrati

Premises and Equipment (Narrative) (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation		$ 41,000	$ 37,200	$ 36,300
Operating lease, right-of-use asset, amortization		27,600
Operating leases, rent expense, net		42,100	31,100	30,500
Short term operating lease rent expense		4,600
Non-operating lease components rent expense		9,900
Operating lease, payments		27,500
Recognition of right of use asset related to the new corporate headquarters facility	$ 121,700
Recognition of operating lease liability related to the new corporate headquarters facility	$ 121,700
Current period amortization of deferred gain		1,400	2,800	2,900
Partnership Interest [Member]
Property, Plant and Equipment [Line Items]
Operating leases, rent expense, net		$ 5,900	$ 464	$ 1,400

Premises and Equipment (Premise

Premises and Equipment (Premises and Equipment) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Land	$ 112,818		$ 104,045
Buildings	441,404		373,276
Technology, furniture and equipment	226,925		196,871
Leasehold improvements	156,144		83,320
Construction and projects in progress	44,251		45,456
Operating lease, right-of-use asset	297,736	$ 170,500	0
Premises and equipment, Gross	1,279,278		802,968
Less accumulated depreciation and amortization	(267,331)		(250,638)
Total premises and equipment, net	$ 1,011,947		$ 552,330

Premises and Equipment Future M

Premises and Equipment Future Minimum Lease Payments Due Under non-Cancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2019USD ($)
Property, Plant and Equipment [Line Items]
2020	$ 28,225
2021	30,813
2022	28,175
2023	26,661
2024	25,232
Thereafter	283,300
Total undiscounted operating lease liability	422,406
Imputed interest	98,718
Total operating lease liability included in the accompanying balance sheet	$ 323,688
Weighted-average lease term in years	16 years 5 months 26 days
Weighted-average discount rate	3.17%

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets (Schedule of Goodwill) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 654,952	$ 654,952

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets (Schedule of Other Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	$ 12,688	$ 13,580
Accumulated Amortization	(10,207)	(9,931)
Net Intangible Assets	2,481	3,649
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	9,300	9,300
Accumulated Amortization	(7,257)	(6,341)
Net Intangible Assets	2,043	2,959
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets	3,388	4,206
Accumulated Amortization	(2,950)	(3,534)
Net Intangible Assets	$ 438	672
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Intangible Assets		74
Accumulated Amortization		(56)
Net Intangible Assets		$ 18

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization expense related to intangible assets	$ 1,168	$ 1,424	$ 1,703
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	5 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets estimated lives, years	10 years

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets (Estimated Aggregate Future Amortization Expense for Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
2020	$ 918
2021	697
2022	481
2023	282
2024	87
Thereafter	16
Net Intangible Assets	$ 2,481	$ 3,649

Deposits (Schedule of Deposits)

Deposits (Schedule of Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deposit [Line Items]
Non-interest-bearing demand deposits:	$ 10,873,629	$ 10,997,494
Time Deposits, $100,000 or More	761,153
Total Interest-bearing deposits	16,765,935	16,151,710
Total deposits	27,639,564	27,149,204
Commercial And Individual [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	10,212,265	10,305,850
Correspondent Banks [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	246,181	235,748
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	7,147,327	6,977,813
Money market accounts	7,888,433	7,777,470
Time Deposits, $100,000 or More	736,481	526,789
Time accounts under $100,000	347,418	331,511
Total private accounts	16,119,659	15,613,583
Public Funds [Member]
Deposit [Line Items]
Non-interest-bearing demand deposits:	415,183	455,896
Savings and interest checking	548,399	473,754
Money market accounts	73,180	59,953
Time Deposits, $100,000 or More	24,672	4,332
Time accounts under $100,000	25	88
Total public funds	$ 646,276	$ 538,127

Deposits (Additional Informatio

Deposits (Additional Information About Corporation's Deposits) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deposits [Abstract]
Certificate Of Deposit Account Registry Service Cdars Deposits Held	$ 361	$ 0
Deposits from foreign sources (primarily Mexico)	805,828	752,658
Deposits not covered by deposit insurance	13,115,796	13,111,210
Deposits from certain directors, executive officers and their affiliates	$ 197,919	$ 199,321

Deposits (Scheduled Maturities

Deposits (Scheduled Maturities of Time Deposits) (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Deposits [Abstract]
2020	$ 891,005
2021	217,591
Time deposits, Total	$ 1,108,596

Deposits (Scheduled Maturitie_2

Deposits (Scheduled Maturities of Time Deposits in Amounts of $100,000 or More) (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Deposits [Abstract]
Due within 3 months or less	$ 191,563
Due after 3 months and within 6 months	140,654
Due after 6 months and within 12 months	271,209
Due after 12 months	157,727
Time deposits, $100,000 or more, total	$ 761,153

Borrowed Funds (Narrative) (Det

Borrowed Funds (Narrative) (Detail) $ in Thousands	Mar. 17, 2017USD ($)	Feb. 28, 2007USD ($)	Dec. 31, 2019USD ($)quarter	Dec. 31, 2018USD ($)	Dec. 31, 2016	Dec. 31, 2004USD ($)
Borrowed Funds [Line Items]
Federal funds purchased			$ 27,200	$ 7,300
Securities sold under agreements to repurchase			1,700,000	1,400,000
Subordinated notes			98,865	98,708
Junior subordinated deferrable interest debentures			$ 136,299	$ 136,242
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			3.46%	4.29%		1.55%
LIBOR plus margin						Three-month LIBOR plus a margin of 1.55%
Proceeds from Issuance of Trust Preferred Securities			$ 120,000	$ 120,000		$ 120,000
WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Maturity date						Jul. 23, 2034
Advances, variable-rate			4.28%	4.83%		2.35%
LIBOR plus margin						Three-month LIBOR plus a margin of 2.35%
Proceeds from Issuance of Trust Preferred Securities			$ 13,000	$ 13,000		$ 13,000
Subordinated Debt [Member]
Borrowed Funds [Line Items]
Subordinated notes	$ 100,000	$ 100,000
Subordinated notes interest rate	4.50%	5.75%
Maturity date	Mar. 17, 2027	Feb. 15, 2017
Advances, variable-rate		0.53%			1.43%
LIBOR plus margin		Three-month LIBOR plus a margin of 0.53%
Unamortized debt issuance cost related to note			1,100	1,300
Junior Subordinated Deferrable Interest Debenture [Member] | Trust II [Member]
Borrowed Funds [Line Items]
Unamortized debt issuance cost related to note			816	873
Junior subordinated deferrable interest debentures			123,700	123,700		123,700
Common equity securities						3,700
Junior Subordinated Deferrable Interest Debenture [Member] | WNB Capital Trust I [Member]
Borrowed Funds [Line Items]
Junior subordinated deferrable interest debentures			$ 13,400	$ 13,400		13,400
Common equity securities						$ 403
Federal Funds Purchased [Member] | Maximum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period			90 days
Federal Funds Purchased [Member] | Minimum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period			1 day
Securities Loaned or Sold under Agreements to Repurchase [Member] | Maximum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period			90 days
Securities Loaned or Sold under Agreements to Repurchase [Member] | Minimum [Member]
Borrowed Funds [Line Items]
Short term debt maturity period			30 days

Off-Balance-Sheet Arrangement_3

Off-Balance-Sheet Arrangements, Commitments, Guarantees and Contingencies (Financial Instruments With Off-Balance-Sheet Risk) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 260,587	$ 271,575
Deferred Standby Letter of Credit Fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	1,276	2,069
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 9,306,043	$ 8,369,721

Off-Balance Sheet Arrangements

Off-Balance Sheet Arrangements Commitments Guarantees and Contingencies (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Commitments And Guarantees [Line Items]
Credit card guarantees	$ 8.5	$ 8.1
Fully collateralized credit card guarantees	$ 1.3	$ 1.4

Capital and Regulatory Matter_2

Capital and Regulatory Matters (Narrative) (Detail)	Jul. 24, 2019USD ($)	Mar. 17, 2017USD ($)	Jan. 01, 2016	Feb. 15, 2013USD ($)$ / sharesshares	Feb. 28, 2007USD ($)	Dec. 31, 2019USD ($)quarter$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)shares	Jan. 01, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Subordinated notes						$ 98,865,000	$ 98,708,000
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
Share repurchase authorized amount	$ 100,000,000
Stock repurchase program, period in force	1 year
Treasury stock, shares, acquired | shares						716,062	1,037,982	1,149,555
Treasury Stock, Value, Acquired, Cost Method						$ (68,793,000)	$ (101,010,000)	$ (101,473,000)
Aggregate dividends available for payment without prior regulatory approval						$ 682,900,000
Maximum number of quarterly periods by which the corporation has the right to defer interest payments on junior subordinated deferrable interest debentures | quarter						20
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
Subordinated Debt [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Subordinated notes		$ 100,000,000			$ 100,000,000
Subordinated notes interest rate		4.50%			5.75%
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
Cullen/Frost [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Non-cumulative perpetual preferred stock						$ 144,500,000	$ 144,500,000
Non-cumulative perpetual preferred stock, dividend rate percentage						5.375%	5.375%
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio							6.375%		4.50%
Capital Conservation Buffer									2.50%
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation									7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets									6.00%
Effective tier one capital ratio, upon full implementation									8.50%
Minimum ratio of Total capital to risk weighted assets						14.57%	14.64%		8.00%
Minimum leverage ratio						9.28%	9.06%
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
Cullen/Frost [Member] | Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier one risk based capital to risk weighted assets, ratio upon full implementation									10.50%
Minimum leverage ratio									4.00%
Cullen/Frost [Member] | Trust Preferred Securities Tier Two Capital Allowable Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities						$ 133,000,000	$ 133,000,000
Cullen/Frost [Member] | Subordinated Debt [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Permissible portion of subordinated note included in total capital						100,000,000	100,000,000
Frost Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Additional Tier 1 Capital beyond Common Equity Tier 1						$ 0	$ 0
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio							6.375%		4.50%
Capital Conservation Buffer									2.50%
Effective common equity tier one capital to risk weighted assets, ratio upon full implementation									7.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets									6.00%
Effective tier one capital ratio, upon full implementation									8.50%
Minimum ratio of Total capital to risk weighted assets						13.40%	13.40%		8.00%
Minimum leverage ratio						9.15%	8.93%
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
Frost Bank [Member] | Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier one risk based capital to risk weighted assets, ratio upon full implementation									10.50%
Minimum leverage ratio									4.00%
stock repurchase 2019 plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury Stock, Value, Acquired, Cost Method						$ (17,200,000)
stock repurchase 2019 plan [Member] | Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares						202,724
stock repurchase 2017 plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury Stock, Value, Acquired, Cost Method						$ (50,000,000)	$ (100,000,000)
stock repurchase 2017 plan [Member] | Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares						496,307	1,027,292
stock repurchase 2016 plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury Stock, Value, Acquired, Cost Method								$ (100,000,000)
stock repurchase 2016 plan [Member] | Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares								1,134,966

Regulatory Matters (Actual and

Regulatory Matters (Actual and Required Capital Ratios) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Cullen/Frost [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one to risk-weighted assets, actual, capital amount	$ 2,857,250		$ 2,642,475
Common equity tier one to risk-weighted assets, actual, ratio	12.36%		12.27%
Common equity tier one to risk-weighted assets, minimum capital required basel III phase-in schedule, capital amount			$ 1,372,573
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio		4.50%	6.375%
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,617,886		$ 1,507,139
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	7.00%		7.00%
Common Equity Tier One Capital Required To Be Well Capitalized, Capital Amount	$ 1,502,323		$ 1,399,486
CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets, Ratio	6.50%		6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 3,001,736		$ 2,786,961
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.99%		12.94%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 1,695,532
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			7.875%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,964,576		$ 1,830,098
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	8.50%		8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,849,013		$ 1,722,445
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%		8.00%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 3,367,403		$ 3,152,593
Total Capital to Risk-Weighted Assets, Actual, Ratio	14.57%	8.00%	14.64%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 2,126,143
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			9.875%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 2,426,829		$ 2,260,709
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	10.50%		10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 2,311,266		$ 2,153,056
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%		10.00%
Leverage Ratio, Actual, Capital Amount	$ 3,001,736		$ 2,786,961
Leverage Ratio, Actual, Ratio	9.28%		9.06%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 1,231,028
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			4.00%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,293,188		$ 1,231,028
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Fully Phased In, Ratio	4.00%		4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,616,485		$ 1,538,785
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	$ 2,958,326		$ 2,743,973
Common equity tier one to risk-weighted assets, actual, ratio	12.82%		12.78%
Common equity tier one to risk-weighted assets, minimum capital required basel III phase-in schedule, capital amount			$ 1,368,701
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio		4.50%	6.375%
Common Equity Tier One Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,615,206		$ 1,502,887
Common Equity Tier One Risk Based Capital To Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	7.00%		7.00%
Common Equity Tier One Capital Required To Be Well Capitalized, Capital Amount	$ 1,499,834		$ 1,395,538
CommonEquityTierOneCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets, Ratio	6.50%		6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 2,958,326		$ 2,743,973
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.82%		12.78%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 1,690,748
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			7.875%
Tier One Risk Based Capital Required For Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,961,322		$ 1,824,934
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	8.50%		8.50%
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 1,845,950		$ 1,717,585
Tier 1 Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	8.00%		8.00%
Total Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 3,090,993		$ 2,876,605
Total Capital to Risk-Weighted Assets, Actual, Ratio	13.40%	8.00%	13.40%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 2,120,144
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			9.875%
Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 2,422,809		$ 2,254,331
Capital Required for Capital Adequacy to Risk Weighted Assets Minimum Capital Required Basel III Fully Phased In, Ratio	10.50%		10.50%
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Capital Amount	$ 2,307,438		$ 2,146,982
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%		10.00%
Leverage Ratio, Actual, Capital Amount	$ 2,958,326		$ 2,743,973
Leverage Ratio, Actual, Ratio	9.15%		8.93%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Phase In Schedule, Capital Amount			$ 1,229,650
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Phase In Schedule, Ratio			4.00%
Tier One Leverage Capital Required for Capital Adequacy Minimum Capital Required Basel III Fully Phased In, Capital Amount	$ 1,292,743		$ 1,229,650
Tier One Leverage Capital Required for Capital Adequacy to Average Assets Minimum Capital Required Basel III Fully Phased In, Ratio	4.00%		4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,615,929		$ 1,537,062
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 443,599	$ 454,918	$ 364,149
Less: Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	435,536	446,855	356,086
Less: Earnings allocated to participating securities	3,687	3,169	2,016
Distributed earnings allocated to common stock	175,540	164,268	143,356
Undistributed earnings allocated to common stock	256,309	279,418	210,714
Net earnings allocated to common stock	$ 431,849	$ 443,686	$ 354,070
Weighted-average shares outstanding for basic earnings per common share	62,741,769	63,704,508	63,693,927
Dilutive effect of stock compensation	700,101	982,208	968,161
Weighted-average shares outstanding for diluted earnings per common share	63,441,870	64,686,716	64,662,088

Employee Benefit Plans (Narrati

Employee Benefit Plans (Narrative) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost	$ 28,900,000
Net actuarial loss expected to be recognized	$ 5,300,000
Percentage of equity investments in mutual fund	68.00%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.25%
Expected defined benefit plans contribution within a year	$ 1,200,000
Number of stock plans	3
Share-based compensation arrangement by share-based payment award, number of shares available for grant	1,105,616
Dividends, share-based compensation	$ 0.71	$ 0.67	$ 0.57
Weighted-average risk-free interest rate	1.65%	2.95%	1.73%
Performance Shares [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Granted in period, number of shares/units	34,317	30,466	24,162
Award payout percentage at less than 25th percentile level of achievement	0.00%
Award payout percentage at the 25th percentile level of achievement	50.00%
Award payout percentage at the 50th percentile level of achievement	100.00%
Award payout percentage at the 75th percentile level of achievement	150.00%
Share-based Payment Arrangement, Option [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Options awarded during period	0	0	0	0
Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Target asset allocation percentage	64.00%
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	10 years	10 years
Vesting period of options awarded, years	4 years	4 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	10 years	10 years
Cliff vesting period, years	4 years	4 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	10 years
Vesting period of options awarded, years	4 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	10 years
Cliff vesting period, years	4 years	4 years	4 years
Maximum [Member] | Performance Shares [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Granted in period, number of shares/units	51,479	45,703	36,246
Deferred Profit Sharing [Member] | Qualified Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost	$ 12,600,000	$ 11,900,000	$ 11,600,000
Deferred Profit Sharing [Member] | Nonqualified Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost	930,000	568,000	1,100,000
Other Pension Plan [Member] | Qualified Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Defined contribution plan, cost	$ 16,300,000	$ 15,000,000	$ 14,300,000
Contribution percentage of eligible compensation	2.00%
Maximum annual contributions per employee, percent	50.00%
Participants contribution eligible for match	100.00%
Other Pension Plan [Member] | Qualified Plan [Member] | Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Employer matching contribution, percent of employees' gross pay	6.00%

Employee Benefit Plans (Combine

Employee Benefit Plans (Combined Activity in Corporations Defined Benefit Pension Plans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Fair value of plan assets at beginning of year	$ 152,820	$ 168,450	$ 157,214
Actual return on plan assets	29,945	(7,739)	23,518
Employer contributions	1,163	1,077	1,049
Benefits paid	(9,755)	(8,968)	(13,331)
Fair value of plan assets at end of year	174,173	152,820	168,450
Benefit obligation at beginning of year	167,107	182,607	176,751
Interest cost	6,472	5,898	6,189
Actuarial (gain) loss	22,817	(12,430)	12,998
Benefits paid	(9,755)	(8,968)	(13,331)
Benefit obligation at end of year	186,641	167,107	182,607
Funded status of the plan at end of year and accrued benefit (liability) recognized	(12,468)	(14,287)	(14,157)
Accumulated benefit obligation at end of year	$ 186,641	$ 167,107	$ 182,607

Employee Benefit Plans (Disaggr

Employee Benefit Plans (Disaggregated Information Related to Corporations Defined Benefit Pension Plans) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 186,641	$ 167,107	$ 182,607	$ 176,751
Accumulated benefit obligation	186,641	167,107	182,607
Fair value of plan assets	174,173	152,820	168,450	$ 157,214
Funded status of the plan at end of year and accrued benefit (liability) recognized	(12,468)	(14,287)	$ (14,157)
Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	170,541	152,035
Accumulated benefit obligation	170,541	152,035
Fair value of plan assets	174,173	152,820
Funded status of the plan at end of year and accrued benefit (liability) recognized	3,632	785
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	16,100	15,072
Accumulated benefit obligation	16,100	15,072
Fair value of plan assets	0	0
Funded status of the plan at end of year and accrued benefit (liability) recognized	$ (16,100)	$ (15,072)

Employee Benefit Plans (Net Per

Employee Benefit Plans (Net Periodic Benefit Cost (Benefit)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Expected return on plan assets, net of expenses	$ (10,772)	$ (11,916)	$ (11,117)
Interest cost on projected benefit obligation	6,472	5,898	6,189
Net amortization and deferral	5,623	5,002	5,429
Net periodic expense (benefit)	$ 1,323	$ (1,016)	$ 501

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net actuarial gain (loss)	$ 1,979	$ (2,223)	$ 4,832
Deferred tax (expense) benefit	(416)	466	(1,774)
Other comprehensive income (loss), net of tax	$ 1,563	$ (1,757)	$ 3,058

Employee Benefit Plans (Defin_2

Employee Benefit Plans (Defined Benefit Pension Plans not Recognized as Component of Combined Net Period Benefit Cost) (Detail) - Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (57,964)	$ (60,123)
Deferred tax benefit	12,210	12,626
Amounts included in accumulated other comprehensive loss, net of tax	$ (45,934)	$ (47,497)

Employee Benefit Plans (Weighte

Employee Benefit Plans (Weighted-Average Assumptions Used to Determine Benefit Obligations) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Benefit obligations, Discount rate	3.20%	4.36%	3.68%
Net periodic benefit cost, Discount rate	4.36%	3.68%	4.24%
Net periodic benefit cost, Expected return on plan assets	7.25%	7.25%	7.25%

Employee Benefit Plans (Fair Va

Employee Benefit Plans (Fair Value of Plan Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 174,173	$ 152,820	$ 168,450	$ 157,214
Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	172,773	152,477
Cash and Cash Equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,400	$ 343

Employee Benefit Plans (Expecte

Employee Benefit Plans (Expected Future Benefit Payments Related to Defined Benefit Plans) (Detail) $ in Thousands	Dec. 31, 2019USD ($)
Retirement Benefits [Abstract]
2020	$ 10,662
2021	10,968
2022	11,177
2023	11,423
2024	11,578
2025 through 2029	57,122
Total defined benefit plan expected future benefit payments	$ 112,930

Employee Benefit Plans (Summary

Employee Benefit Plans (Summary of Activity in Corporation's Active Stock Plans) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, number of shares	(399,224)	(548,238)	(1,150,920)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	55,370	48,910	53,008
Beginning balance, number of shares/units	48,910	53,008	53,659
Ending balance, weighted-average grant-date fair value	$ 74.76	$ 71.14	$ 64.87
Beginning balance, weighted-average grant-date fair value	$ 71.14	$ 64.87	$ 61.48
Granted in period, number of shares/units	7,592	6,576	5,447
Granted in period, weighted-average grant-date fair value	$ 102.70	$ 109.58	$ 95.37
Stock awards exercised/vested in period, number of shares	(1,132)	(10,674)	(6,098)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 106.03	$ 63.68	$ 62.29
Non-Vested Stock Awards/ Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	440,647	383,797	312,656
Beginning balance, number of shares/units	383,797	312,656	256,850
Ending balance, weighted-average grant-date fair value	$ 90.22	$ 85.59	$ 81.71
Beginning balance, weighted-average grant-date fair value	$ 85.59	$ 81.71	$ 73.43
Granted in period, number of shares/units	127,091	109,847	99,833
Granted in period, weighted-average grant-date fair value	$ 93.46	$ 94.81	$ 98.90
Stock awards exercised/vested in period, number of shares	(53,990)	(32,050)	(39,740)
Stock awards exercised/vested in period, weighted-average grant date fair value	$ 65.11	$ 78.92	$ 71.59
Forfeited/expired in period, number of shares/units	(16,251)	(6,656)	(4,287)
Forfeited/expired in period, weighted-average grant date fair value	$ 89.71	$ 87.60	$ 79.52
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted in period, number of shares/units	34,317	30,466	24,162
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares	1,980,866	2,352,008	2,917,142
Beginning balance, number of shares	2,352,008	2,917,142	4,089,028
Ending balance, weighted-average exercise price	$ 64.60	$ 63.55	$ 63.34
Beginning balance, weighted-average exercise price	$ 63.55	$ 63.34	$ 62.67
Stock options exercised, number of shares	(359,892)	(513,134)	(1,118,122)
Stock options exercised, weighted-average exercise price	$ 57.71	$ 61.68	$ 60.59
Forfeited/expired, number of shares	(11,250)	(52,000)	(53,764)
Forfeited/expired, weighted-average exercise price	$ 65.11	$ 70.42	$ 69.78
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, number of shares/units	177,288	125,809	80,106
Beginning balance, number of shares/units	125,809	80,106	43,860
Ending balance, weighted-average grant-date fair value	$ 83.48	$ 82.55	$ 79.91
Beginning balance, weighted-average grant-date fair value	$ 82.55	$ 79.91	$ 69.70
Granted in period, number of shares/units	51,479	45,703	36,246
Granted in period, weighted-average grant-date fair value	$ 85.74	$ 87.18	$ 92.27

Employee Benefit Plans (Options

Employee Benefit Plans (Options Outstanding and Exercisable) (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares
$ 45.01 - $ 50.00 [Member]
Share-based Payment Arrangement, Option, 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 Payment Arrangement, Option, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	50.01
Range of Exercise Prices, Maximum	55
65.01 - 70.00 [Member]
Share-based Payment Arrangement, Option, 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 Payment Arrangement, Option, 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 Payment Arrangement, Option, Exercise Price Range [Line Items]
Range of Exercise Prices, Minimum	75.01
Range of Exercise Prices, Maximum	$ 80
Options Outstanding [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	1,980,866
Weighted-Average Exercise Price, Options Outstanding	$ 64.60
Weighted- Average Remaining Contractual Life in Years	3 years 10 months 13 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $	$ 65,725
Options Outstanding [Member] | $ 45.01 - $ 50.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	238,055
Weighted-Average Exercise Price, Options Outstanding	$ 48
Weighted- Average Remaining Contractual Life in Years	1 year 9 months 25 days
Options Outstanding [Member] | 50.01 - 55.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	464,009
Weighted-Average Exercise Price, Options Outstanding	$ 53.75
Weighted- Average Remaining Contractual Life in Years	2 years 14 days
Options Outstanding [Member] | 65.01 - 70.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	526,096
Weighted-Average Exercise Price, Options Outstanding	$ 65.11
Weighted- Average Remaining Contractual Life in Years	5 years 8 months 1 day
Options Outstanding [Member] | 70.01 - 75.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	275,654
Weighted-Average Exercise Price, Options Outstanding	$ 71.39
Weighted- Average Remaining Contractual Life in Years	3 years 9 months 18 days
Options Outstanding [Member] | 75.01 - 80.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Outstanding | shares	477,052
Weighted-Average Exercise Price, Options Outstanding	$ 78.95
Weighted- Average Remaining Contractual Life in Years	4 years 8 months 15 days
Options Exercisable [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	1,980,866
Weighted-Average Exercise Price, Options Exercisable	$ 64.60
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $	$ 65,725
Options Exercisable [Member] | $ 45.01 - $ 50.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	238,055
Weighted-Average Exercise Price, Options Exercisable	$ 48
Options Exercisable [Member] | 50.01 - 55.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	464,009
Weighted-Average Exercise Price, Options Exercisable	$ 53.75
Options Exercisable [Member] | 65.01 - 70.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	526,096
Weighted-Average Exercise Price, Options Exercisable	$ 65.11
Options Exercisable [Member] | 70.01 - 75.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	275,654
Weighted-Average Exercise Price, Options Exercisable	$ 71.39
Options Exercisable [Member] | 75.01 - 80.00 [Member]
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Number of Shares, Options Exercisable | shares	477,052
Weighted-Average Exercise Price, Options Exercisable	$ 78.95

Employee Benefit Plans (Shares

Employee Benefit Plans (Shares Issued in Connection with Stock Compensation Awards) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
New shares issued from available authorized shares	0	0	603,842
Issued from available treasury stock	399,224	548,238	547,078
Total	399,224	548,238	1,150,920
Proceeds from stock option exercises	$ 20,770	$ 31,647	$ 67,746
Intrinsic value of stock options exercised	13,713	23,292	38,275
Fair value of stock awards/units vested	$ 5,192	$ 4,212	$ 4,578

Employee Benefit Plans (Stock-B

Employee Benefit Plans (Stock-Based Compensation Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock options	$ 1,185	$ 3,652	$ 6,230
Non-vested stock awards/stock units	9,339	6,983	4,992
Deferred stock-units	780	721	519
Performance stock units	4,642	2,587	1,272
Total	15,946	13,943	13,013
Income tax benefit	$ 2,359	$ 2,831	$ 4,555

Employee Benefit Plans (Unrecog

Employee Benefit Plans (Unrecognized Stock-Based Compensation Expense) (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Non-vested stock awards/stock units	$ 18,882
Performance stock units	6,299
Total	$ 25,181
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 years 9 months 21 days
Employee service share-based compensation, Performance stock units,compensation cost not yet recognized,period for recognition	2 years 1 month 9 days

Other Non-Interest Income and_3

Other Non-Interest Income and Expense (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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%
Gross cost related to interchange and debit card transactions	$ 12,900	$ 11,900	$ 11,900
Payment for services provided by related party	$ 567	$ 568	$ 833

Other Non-Interest Income and_4

Other Non-Interest Income and Expense (Other Non-Interest Income and Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other	$ 43,563	$ 46,790	$ 37,222
Total other non-interest income	43,563	46,790	37,222
Professional services	39,238	35,941	27,968
Advertising, promotions and public relations	38,001	32,514	29,337
Travel/meals and entertainment	16,459	15,030	15,066
Check card expense	5,947	4,744	16,501
Other	81,020	85,309	86,417
Total other non-interest expense	$ 180,665	$ 173,538	$ 175,289

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Detail) - USD ($)	Dec. 22, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%	35.00%
Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate		$ 0	$ (231,000)	$ (4,047,000)
Correction for prior year tax-exempt interest		0	0	(2,906,000)
Valuation allowance		0	0	0
Unrecognized tax benefits		$ 0	$ 0	$ 0

Income Taxes (Income Tax Expens

Income Taxes (Income Tax Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 48,256	$ 840	$ 58,707
Deferred income tax expense (benefit)	7,614	52,923	(14,493)
Income tax expense, as reported	$ 55,870	$ 53,763	$ 44,214
Effective tax rate	11.20%	10.60%	10.80%

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense computed at the statutory rate	$ 104,888	$ 106,823	$ 142,927
Effect of tax-exempt interest	(49,166)	(49,700)	(81,034)
Tax benefit on dividends paid in our 401k plan	(1,743)	(1,551)	(2,372)
Bank owned life insurance income	(774)	(710)	(1,116)
Non-deductible compensation	1,708	210	158
Non-deductible FDIC premiums	1,267	1,771	0
Non-deductible meals and entertainment	1,299	1,193	983
Net tax benefit from stock-based compensation	(2,447)	(3,865)	(9,062)
Deferred tax adjustment related to reduction in U.S. federal statutory income tax rate	0	(231)	(4,047)
Correction for prior year tax-exempt interest	0	0	(2,906)
Other	838	(177)	683
Income tax expense, as reported	$ 55,870	$ 53,763	$ 44,214

Income Taxes (Schedule of Defer

Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Lease liabilities under operating leases	$ 67,975	$ 0
Allowance for loan losses	27,755	27,748
Net actuarial loss on defined benefit post-retirement benefit plans	12,210	12,626
Stock-based compensation	11,211	10,622
Bonus accrual	5,055	4,586
Net unrealized loss on securities available for sale and transferred securities	0	4,283
Deferred loan and lease origination fees	2,254	2,153
Other	2,163	4,761
Total gross deferred tax assets	128,623	66,779
Net unrealized gain on securities available for sale and transferred securities	(83,281)	0
Right-of-use assets under operating leases	(63,463)	0
Premises and equipment	(29,730)	(23,859)
Intangible assets	(12,642)	(10,726)
Defined benefit post-retirement benefit plans	(9,419)	(9,452)
Partnership interests	(2,894)	0
Leases	(1,572)	(1,709)
Other	(1,440)	(1,257)
Total gross deferred tax liabilities	(204,441)	(47,003)
Deferred Tax Liabilities, Net	$ (75,818)
Deferred Tax Assets, Net		$ 19,776

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, before tax amount	$ 418,556	$ (182,340)	$ 157,016
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, before tax amount	(1,292)	(8,818)	(16,193)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, before tax amount	(293)	156	4,941
Total securities available for sale and transferred securities before tax amount	416,971	(191,002)	145,764
Change in the net actuarial gain/loss before tax amount	(3,644)	(7,225)	(597)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) before tax amount	5,623	5,002	5,429
Total defined-benefit post-retirement benefit plans	1,979	(2,223)	4,832
Other comprehensive income (loss), before tax	418,950	(193,225)	150,596
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, tax expense (benefit)	87,897	(38,292)	48,626
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	(271)	(1,853)	(5,668)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, tax expense (benefit)	(62)	33	1,729
Total securities available for sale and transferred securities, tax expense (benefit)	87,564	(40,112)	44,687
Change in the net actuarial gain/loss, tax expense (benefit)	(765)	(1,517)	(126)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a componet of net periodic cost (benefit) , tax expense (benefit)	1,181	1,051	1,900
Total defined-benefit post-retirement benefit plans, tax expense (benefit)	416	(466)	1,774
Total other comprehensive income, tax expense (benefit)	87,980	(40,578)	46,461
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax amount	330,659	(144,048)	108,390
Securities available for sale and transferred securities. change in net unrealized gain on securities transfers to held-to-maturity, net of tax amount	(1,021)	(6,965)	(10,525)
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax amount	(231)	123	3,212
Total securities available for sale and transferred securities, net of tax amount	329,407	(150,890)	101,077
Change in the net actuarial gain/loss, net of tax amount	(2,879)	(5,708)	(471)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a componet of net periodic cost (benefit), net of tax amount	4,442	3,951	3,529
Total defined-benefit post-retirement benefit plans, net of tax amount	1,563	(1,757)	3,058
Other comprehensive income (loss), net of tax	$ 330,970	$ (152,647)	$ 104,135

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ (63,600)
Net other comprehensive income (loss) during period	330,970	$ (152,647)	$ 104,135
Ending Balance	267,370	(63,600)
Securities Available For Sale [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(16,103)	117,230	16,153
Other comprehensive income (loss) before reclassification	329,638	(151,013)	97,865
Reclassification of amounts included in net income	(231)	123	3,212
Net other comprehensive income (loss) during period	329,407	(150,890)	101,077
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act		17,557
Ending Balance	313,304	(16,103)	117,230
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(47,497)	(37,718)	(40,776)
Other comprehensive income (loss) before reclassification	(2,879)	(5,708)	(471)
Reclassification of amounts included in net income	4,442	3,951	3,529
Net other comprehensive income (loss) during period	1,563	(1,757)	3,058
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act		(8,022)
Ending Balance	(45,934)	(47,497)	(37,718)
AOCI Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(63,600)	79,512	(24,623)
Other comprehensive income (loss) before reclassification	326,759	(156,721)	97,394
Reclassification of amounts included in net income	4,211	4,074	6,741
Net other comprehensive income (loss) during period	330,970	(152,647)	104,135
Reclassification of certain income tax effects related to U.S. statutory federal income tax rate under the Tax Cuts and Jobs Act		9,535
Ending Balance	$ 267,370	$ (63,600)	$ 79,512

Derivative Financial Instrume_3

Derivative Financial Instruments (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Weighted-average strike rate for outstanding interest rate caps	3.14%
Approximate credit exposure related to swaps with bank customers	$ 47,100
Cash collateral on deposit with other financial institutions	37,500	$ 10,000
Interest Rate Swaps With Upstream Financial Institution Counterparties [Member]
Derivative [Line Items]
Approximate credit exposure related to swaps with bank customers	16,100
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivative [Line Items]
Estimated fair value of derivative contracts cleared through Chicago Mercantile Exchange	$ 0	$ 0

Derivative Financial Instrume_4

Derivative Financial Instruments (Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	$ 2,545	$ 10,941
Estimated Fair Value	6	207
Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	6,000	3,885
Estimated Fair Value	(138)	(199)
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	122,788	496,887
Estimated Fair Value	67	2,384
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	1,002,860	691,143
Estimated Fair Value	(19,483)	(8,921)
Not Designated as Hedging Instrument [Member] | Financial Institution Counterparties Loan Lease Interest Rate Caps Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	107,835	122,791
Estimated Fair Value	266	509
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Notional Amount	1,002,860	691,143
Estimated Fair Value	43,857	16,706
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Swaps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	122,788	496,887
Estimated Fair Value	(310)	(8,891)
Not Designated as Hedging Instrument [Member] | Customer Counterparties Loan Lease Interest Rate Caps Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Notional Amount	107,835	122,791
Estimated Fair Value	$ (266)	$ (509)

Derivative Financial Instrume_5

Derivative Financial Instruments (Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding) (Detail)	Dec. 31, 2019
Weighted Average Interest Rate Paid [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	2.66%
Weighted-Average Interest Rate Received [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Fair Value Hedge Loan Lease Interest Rate Swaps	1.75%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	4.12%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Non-hedging interest rate swaps - financial institution counterparties	3.45%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Non-hedging interest rate swaps - customer counterparties	3.45%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Short-duration Insurance Contracts, Discounted Liabilities [Line Items]
Non-hedging interest rate swaps - customer counterparties	4.12%

Derivative Financial Instrume_6

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, 2019USD ($)MMBTUbbl	Dec. 31, 2018USD ($)MMBTUbbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	1,214	2,416
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 2,796	$ 24,332
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	2,148	415
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (6,916)	$ (646)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	8,295	5,745
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 2,131	$ 417
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	2,689	9,314
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (70)	$ (1,272)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | bbl	2,172	415
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 7,208	$ 646
Oil/Natural Gas Derivative Liabilities Notional Amount | bbl	1,190	2,416
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (2,652)	$ (24,009)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets Notional Amount | MMBTU	2,689	10,236
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 83	$ 1,373
Oil/Natural Gas Derivative Liabilities Notional Amount | MMBTU	8,295	4,823
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (2,039)	$ (393)

Derivative Financial Instrume_7

Derivative Financial Instruments Derivative Financial Instruments (Schedule of Notional Amount and Fair Value of Open Foreign Currency Forward Contract) (Details) £ in Thousands, $ in Thousands, $ in Thousands, $ in Thousands	Dec. 31, 2019USD ($)	Dec. 31, 2019CAD ($)	Dec. 31, 2019MXN ($)	Dec. 31, 2019GBP (£)	Dec. 31, 2018USD ($)	Dec. 31, 2018CAD ($)	Dec. 31, 2018MXN ($)	Dec. 31, 2018GBP (£)
Financial Institution Counterparties [Member] | Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts Liability, Notional Amount		$ 4,593	$ 0	£ 0		$ 11,003	$ 3,015	£ 142
Customer Counterparties [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets, Notional Amount		$ 4,583	$ 0	£ 0		$ 10,979	$ 3,000	£ 145
Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts, Liability Estimated Fair Value	$ (33)				$ (13)
Foreign Exchange Forward [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	45				40
GBP Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts, Liability Estimated Fair Value	0				(2)
GBP Foreign Exchange Forward [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	0				4
MXN Foreign Exchange Forwards [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts, Liability Estimated Fair Value	0				(132)
MXN Foreign Exchange Forwards [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts - Assets Estimated Fair Value	$ 0				$ 149

Derivative Financial Instrume_8

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest Income on Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount included in income or expense	$ 86	$ 25	$ (726)
Other Non-Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount included in income or expense	$ 0	$ (1)	$ (14)

Derivative Financial Instrume_9

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, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 2,005	$ 4,112	$ 3,123
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	(1)	0	1
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	503	795	440
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	51	246	300
Other Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount included in income or expense	$ 750	$ 0	$ 0

Balance Sheet Offsetting - Fina

Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	$ 5,266	$ 27,849
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	5,266	27,849
Gross Amount Recognized, Resell Agreements, Financial Assets	31,299	11,642
Gross Amount Offset, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Resell Agreements, Financial Assets	31,299	11,642
Gross Amount Recognized, Financial Assets	36,565	39,491
Gross Amount Offset, Financial Assets	0	0
Net Amount Recognized, Financial Assets	36,565	39,491
Gross Amount Recognized, Derivative, Financial Liabilities	26,640	11,185
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	26,640	11,185
Gross Amount Recognized, Repurchase Agreements, Financial Liabilities	1,668,142	1,360,298
Gross Amount Offset, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	1,668,142	1,360,298
Gross Amount Recognized, Financial Liabilities	1,694,782	1,371,483
Gross Amount Offset, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,694,782	1,371,483
Loan Lease Interest Rate Swaps And Caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	339	3,100
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	339	3,100
Commodity Swaps And Options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	4,927	24,749
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	4,927	24,749
Gross Amount Recognized, Derivative, Financial Liabilities	6,986	1,918
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	6,986	1,918
Foreign Currency Forward Contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Liabilities	33	147
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	33	147
Loan Lease Interest Rate Swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Liabilities	19,621	9,120
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	$ 19,621	$ 9,120

Balance Sheet Offsetting - Fi_2

Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 5,266	$ 27,849
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(5,236)	(6,143)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(21,651)
Net Amount, Derivatives, Financial Assets	30	55
Net Amount Recognized, Resell Agreements, Financial Assets	31,299	11,642
Gross Amounts Not Offset, Financial Instruments, Resell Agreements, Financial Assets	0	0
Gross Amounts Not Offset, Collateral, Resell Agreements, Financial Assets	(31,299)	(11,642)
Net Amount, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Total Financial Assets	36,565	39,491
Gross Amounts Not Offset, Collateral, Financial Assets	(31,299)	(33,293)
Net Amount, Financial Assets	30	55
Net Amount Recognized, Derivatives, Financial Liabilities	26,640	11,185
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(5,236)	(6,143)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(21,404)	(4,621)
Net Amount, Derivatives, Financial Liabilities	0	421
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	1,668,142	1,360,298
Gross Amounts Not Offset, Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset, Collateral, Repurchase Agreements, Financial Liabilities	(1,668,142)	(1,360,298)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,694,782	1,371,483
Gross Amounts Not Offset, Collateral, Financial Liabilities	(1,689,546)	(1,364,919)
Net Amount, Financial Liabilities	0	421
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	39	598
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(39)	(598)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	5,192	4,293
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(39)	(598)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(5,153)	(3,651)
Net Amount, Derivatives, Financial Liabilities	0	44
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	1,650	7,255
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(1,650)	(3,380)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(3,875)
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	7,424	3,380
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(1,650)	(3,380)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(5,774)	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	1	81
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(1)	(81)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	135	326
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(1)	(81)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(134)	(245)
Net Amount, Derivatives, Financial Liabilities	0	0
Other Counterparties [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	3,576	19,915
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(3,546)	(2,084)
Gross Amounts Not Offset, Collateral, Derivatives, Financial Assets	0	(17,776)
Net Amount, Derivatives, Financial Assets	30	55
Net Amount Recognized, Derivatives, Financial Liabilities	13,889	3,186
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Liabilities	(3,546)	(2,084)
Gross Amounts Not offset, Collateral, Derivatives, Financial Liabilities	(10,343)	(725)
Net Amount, Derivatives, Financial Liabilities	$ 0	$ 377

Balance Sheet Offsetting Bala_2

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, 2019	Dec. 31, 2018
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	$ 1,668,142	$ 1,360,298
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	1,668,142	1,360,298
Securities Sold under Agreements to Repurchase, Gross	1,668,142	1,360,298
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	435,904	1,334,063
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	435,904	1,334,063
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	1,232,238	26,235
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	$ 1,232,238	$ 26,235

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments using fair value measurement option	$ 0	$ 0

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, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	$ 11,269,591	$ 11,387,321
Trading account securities	24,298	24,086
Derivative assets:	5,266	27,849
Derivative liabilities:	26,640	11,185
Interest Rate Swaps Caps And Floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	44,196	19,806
Derivative liabilities:	20,197	18,520
Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	12,218	26,768
Derivative liabilities:	11,677	26,320
Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	45	193
Derivative liabilities:	33	147
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	1,948,133	3,427,689
Trading account securities	24,298	21,928
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	2,207,594	829,740
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	7,070,997	7,087,202
Trading account securities		2,158
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	42,867	42,690
Level 1 [Member] | Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	45	193
Derivative liabilities:	33	147
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	1,948,133	3,427,689
Trading account securities	24,298	21,928
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:	44,196	19,806
Derivative liabilities:	20,197	18,520
Level 2 [Member] | Commodity Swaps And Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets:	12,218	26,768
Derivative liabilities:	11,677	26,320
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	2,207,594	829,740
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	7,070,997	7,087,202
Trading account securities		2,158
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	42,867	42,690
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	1,948,133	3,427,689
Trading account securities	24,298	21,928
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	2,207,594	829,740
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	7,070,997	7,087,202
Trading account securities	0	2,158
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at estimated fair value	$ 42,867	$ 42,690

Fair Value Measurements (Impair

Fair Value Measurements (Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 99,453	$ 70,221	$ 145,610
Specific valuation allowance allocations	(28,483)	(16,235)	(20,820)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	2,354	12,517	0
Specific valuation allowance allocations	(383)	(2,599)	0
Fair value	1,971	9,918	0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	65,176	22,688	75,435
Reversal of specific valuation allowance allocations		9,260
Specific valuation allowance allocations	(18,019)		(19,533)
Fair value	$ 47,157	$ 31,948	$ 55,902

Fair Value Measurements (Forecl

Fair Value Measurements (Foreclosed Assets Remeasured and Reported at Fair Value) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 1,348	$ 2,899	$ 279
Foreclosed Assets Remeasured at Initial Recognition Charge Offs Recognized In Allowance For Loan Losses	(76)	0	0
Fair Value of Foreclosed Assets Remeasured at Initial Recognition	1,272	2,899	279
Foreclosed Assets Remeasured Subsequent to Initial Recognition Carrying Value Of Foreclosed Assets Prior To Remeasurement	0	1,823	89
Foreclosed Assets Remeasured Subsequent to initial Recognition Write Downs Included In Other Non Interest Expense	0	(473)	(16)
Fair Value of Foreclosed Assets remeasured subsequent to initial recognition	$ 0	$ 1,350	$ 73

Fair Value Measurements (Estima

Fair Value Measurements (Estimated Fair Values of Financial Instruments) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 3,788,181	$ 3,955,779	$ 5,053,047	$ 4,141,445
Securities held to maturity	2,030,005	1,106,057
Loans, net	14,618,165	13,967,601
Deposits	27,639,564	27,149,204
Federal funds purchased and repurchase agreements	1,695,342	1,367,548
Junior subordinated deferrable interest debentures	136,299	136,242
Subordinated notes payable and other borrowings	98,865	98,708
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,788,181	3,955,779
Securities held to maturity	2,030,005	1,106,057
Cash surrender value of life insurance policies	187,156	183,473
Accrued interest receivable	183,850	188,989
Deposits	27,639,564	27,149,204
Federal funds purchased and repurchase agreements	1,695,342	1,367,548
Junior subordinated deferrable interest debentures	136,299	136,242
Subordinated notes payable and other borrowings	98,865	98,708
Accrued interest payable	12,393	7,394
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	14,618,165	13,967,601
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,788,181	3,955,779
Securities held to maturity	2,048,675	1,116,953
Cash surrender value of life insurance policies	187,156	183,473
Accrued interest receivable	183,850	188,989
Deposits	27,641,255	27,143,572
Federal funds purchased and repurchase agreements	1,695,342	1,367,548
Junior subordinated deferrable interest debentures	137,115	137,115
Subordinated notes payable and other borrowings	89,077	98,458
Accrued interest payable	12,393	7,394
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 14,654,615	$ 13,933,239

Operating Segments Operating Se

Operating Segments Operating Segments - Additional Information (Details) $ in Billions	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment Reporting [Abstract]
Number of operating segments | Segment	2
Fair value of off-balance sheet managed and custody assets | $	$ 37.8	$ 33.3	$ 32.8

Operating Segments (Summary of

Operating Segments (Summary of Operating Results by Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 1,004,005	$ 957,892	$ 866,422
Provision for loan losses	33,759	21,613	35,460
Non-interest income	363,902	351,286	336,470
Non-interest expense	834,679	778,884	759,069
Income before income taxes	499,469	508,681	408,363
Income tax expense (benefit)	55,870	53,763	44,214
Net income	443,599	454,918	364,149
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	435,536	446,855	356,086
Revenues from (expenses to) external customers	1,367,907	1,309,178	1,202,892
Average assets	32,086,000	31,030,000	30,450,000
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,010,368	963,757	856,593
Provision for loan losses	33,758	21,613	35,460
Non-interest income	218,447	213,763	207,810
Non-interest expense	703,121	657,448	644,072
Income before income taxes	491,936	498,459	384,871
Income tax expense (benefit)	55,520	52,928	37,837
Net income	436,416	445,531	347,034
Preferred stock dividends	0	0	0
Net income available to common shareholders	436,416	445,531	347,034
Revenues from (expenses to) external customers	1,228,815	1,177,520	1,064,403
Average assets	32,019,000	30,964,000	30,391,000
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	4,001	4,083	17,644
Provision for loan losses	1	0	0
Non-interest income	145,905	138,045	128,819
Non-interest expense	124,622	114,166	108,931
Income before income taxes	25,283	27,962	37,532
Income tax expense (benefit)	5,308	5,872	13,137
Net income	19,975	22,090	24,395
Preferred stock dividends	0	0	0
Net income available to common shareholders	19,975	22,090	24,395
Revenues from (expenses to) external customers	149,906	142,128	146,463
Average assets	56,000	54,000	43,000
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(10,364)	(9,948)	(7,815)
Provision for loan losses	0	0	0
Non-interest income	(450)	(522)	(159)
Non-interest expense	6,936	7,270	6,066
Income before income taxes	(17,750)	(17,740)	(14,040)
Income tax expense (benefit)	(4,958)	(5,037)	(6,760)
Net income	(12,792)	(12,703)	(7,280)
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	(20,855)	(20,766)	(15,343)
Revenues from (expenses to) external customers	(10,814)	(10,470)	(7,974)
Average assets	$ 11,000	$ 12,000	$ 16,000

Condensed Financial Statement_3

Condensed Financial Statements of Parent Company (Schedule of Condensed Balance Sheets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Cash	$ 581,857	$ 678,791
Resell agreements	356,374	635,017
Cash and cash equivalents	3,788,181	3,955,779	$ 5,053,047	$ 4,141,445
Total assets	34,027,428	32,292,966
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,299	136,242
Subordinated notes, net of unamortized issuance costs	98,865	98,708
Accrued interest payable and other liabilities	545,690	172,347
Total liabilities	30,115,760	28,924,049
Shareholders’ Equity	3,911,668	3,368,917	$ 3,297,863	$ 3,002,528
Total liabilities and shareholders’ equity	34,027,428	32,292,966
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Cash	9,116	11,397
Resell agreements	258,000	225,000
Cash and cash equivalents	267,116	236,397
Investment in subsidiaries	3,896,962	3,362,474
Accrued interest receivable and other assets	2,545	9,122
Total assets	4,166,623	3,607,993
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,299	136,242
Subordinated notes, net of unamortized issuance costs	98,865	98,708
Accrued interest payable and other liabilities	19,791	4,126
Total liabilities	254,955	239,076
Shareholders’ Equity	3,911,668	3,368,917
Total liabilities and shareholders’ equity	$ 4,166,623	$ 3,607,993

Condensed Financial Statement_4

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Total interest income	$ 1,133,785	$ 1,051,198	$ 892,947
Interest expense	129,780	93,306	26,525
Salaries and employee benefits	375,029	350,312	337,068
Other	180,665	173,538	175,289
Income before income taxes and equity in undistributed earnings of subsidiaries	499,469	508,681	408,363
Income tax benefit	(55,870)	(53,763)	(44,214)
Net income	443,599	454,918	364,149
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	435,536	446,855	356,086
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	234,531	223,371	149,671
Dividend income paid by non-banks	1,822	953	915
Interest and other income	2,868	1,828	421
Total interest income	239,221	226,152	151,007
Interest expense	10,363	9,948	7,815
Salaries and employee benefits	1,551	1,973	1,202
Other	7,033	7,016	6,373
Total expenses	18,947	18,937	15,390
Income before income taxes and equity in undistributed earnings of subsidiaries	220,274	207,215	135,617
Income tax benefit	5,135	5,218	7,092
Equity in undistributed earnings of subsidiaries	218,190	242,485	221,440
Net income	443,599	454,918	364,149
Preferred stock dividends	8,063	8,063	8,063
Net income available to common shareholders	$ 435,536	$ 446,855	$ 356,086

Condensed Financial Statement_5

Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income	$ 443,599	$ 454,918	$ 364,149
Stock-based compensation	15,946	13,943	13,013
Net tax benefit from stock-based compensation	2,447	3,865	9,062
Net cash provided by (used in) operating activities	634,090	562,388	538,079
Net cash provided by (used in) investing activities	(1,386,750)	(1,913,320)	(670,595)
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	(100,000)
Proceeds from stock option exercises	20,770	31,647	67,746
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	585,062	253,664	1,044,118
Net change in cash and cash equivalents	(167,598)	(1,097,268)	911,602
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	443,599	454,918	364,149
Equity in undistributed earnings of subsidiaries	(218,190)	(242,485)	(221,440)
Stock-based compensation	780	721	519
Net tax benefit from stock-based compensation	240	304	318
Net change in other assets and other liabilities	22,216	(12,709)	7,665
Net cash provided by (used in) operating activities	248,645	200,749	151,211
Net cash provided by (used in) investing activities	0	0	0
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	100,000
Proceeds from stock option exercises	20,770	31,647	67,746
Proceeds from stock-based compensation activities of subsidiaries	15,166	13,222	12,494
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	(217,926)	(229,653)	(175,034)
Net change in cash and cash equivalents	30,719	(28,904)	(23,823)
Cash and cash equivalents at beginning of year	236,397	265,301	289,124
Cash and cash equivalents at end of year	$ 267,116	$ 236,397	$ 265,301

Accounting Standards Updates Ac

Accounting Standards Updates Accounting Standards Update (Narrative) (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ (14,672)	$ (2,285)
Minimum [Member] | Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage increase in allowance for loan losses and reserve for unfunded commitments	20.00%
Maximum [Member] | Forecast [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage increase in allowance for loan losses and reserve for unfunded commitments	35.00%
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ (14,672)	$ (2,285)