Cullen/Frost Bankers (CFR) 10-Q 27 Jul 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2017	Jul. 20, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	CFR
Entity Registrant Name	CULLEN/FROST BANKERS, INC.
Entity Central Index Key	39,263
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		64,229,805

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Assets:
Cash and due from banks	$ 542,475	$ 561,838
Interest-bearing deposits	3,040,148	3,560,865
Federal funds sold and resell agreements	123,692	18,742
Total cash and cash equivalents	3,706,315	4,141,445
Securities held to maturity, at amortized cost	1,596,262	2,250,460
Securities available for sale, at estimated fair value	10,783,737	10,203,277
Trading account securities	27,600	16,703
Loans, net of unearned discounts	12,512,338	11,975,392
Less: Allowance for loan losses	(149,558)	(153,045)
Net loans	12,362,780	11,822,347
Premises and equipment, net	520,253	525,821
Goodwill	654,952	654,952
Other intangible assets, net	5,880	6,776
Cash surrender value of life insurance policies	178,987	177,884
Accrued interest receivable and other assets	369,548	396,654
Total assets	30,206,314	30,196,319
Liabilities:
Non-interest-bearing demand deposits	10,707,365	10,513,369
Interest-bearing deposits	14,906,208	15,298,206
Total deposits	25,613,573	25,811,575
Federal funds purchased and repurchase agreements	924,867	976,992
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,155	136,127
Subordinated notes, net of unamortized issuance costs	98,473	99,990
Accrued interest payable and other liabilities	209,317	169,107
Total liabilities	26,982,385	27,193,791
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 at June 30, 2017 and December 31, 2016	144,486	144,486
Common stock, par value $0.01 per share; 210,000,000 shares authorized; 64,225,827 shares issued at June 30, 2017 and 63,632,464 shares issued at December 31, 2016	642	637
Additional paid-in capital	948,593	906,732
Retained earnings	2,078,898	1,985,569
Accumulated other comprehensive income, net of tax	51,310	(24,623)
Treasury stock, at cost; none at June 30, 2017 and 158,243 shares at December 31, 2016	0	(10,273)
Total shareholders’ equity	3,223,929	3,002,528
Total liabilities and shareholders’ equity	$ 30,206,314	$ 30,196,319

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
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	64,225,827	63,632,464
Treasury stock, shares	0	158,243
Series A Preferred Stock [Member]
Preferred stock liquidation preference value	$ 25	$ 25

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest income:
Loans, including fees	$ 131,073	$ 113,349	$ 253,673	$ 225,935
Securities:
Taxable	23,527	25,531	48,829	51,505
Tax-exempt	55,435	50,910	112,382	101,243
Interest-bearing deposits	9,076	3,602	15,912	7,255
Federal funds sold and resell agreements	163	59	270	117
Total interest income	219,274	193,451	431,066	386,055
Interest expense:
Deposits	2,173	1,773	4,041	3,560
Federal funds purchased and repurchase agreements	187	52	326	108
Junior subordinated deferrable interest debentures	962	803	1,870	1,553
Other long-term borrowings	1,164	321	1,532	608
Total interest expense	4,486	2,949	7,769	5,829
Net interest income	214,788	190,502	423,297	380,226
Provision for loan losses	8,426	9,189	16,378	37,689
Net interest income after provision for loan losses	206,362	181,313	406,919	342,537
Non-interest income:
Trust and investment management fees	27,727	26,021	54,197	51,355
Service charges on deposit accounts	21,198	19,865	41,967	40,229
Insurance commissions and fees	9,728	9,360	23,549	24,783
Interchange and debit card transaction fees	5,692	5,381	11,266	10,403
Other charges, commissions and fees	9,898	10,069	19,490	19,122
Net gain (loss) on securities transactions	(50)	0	(50)	14,903
Other	6,887	7,321	14,361	13,365
Total non-interest income	81,080	78,017	164,780	174,160
Non-interest expense:
Salaries and wages	80,995	78,106	163,507	157,403
Employee benefits	18,198	17,712	39,823	38,017
Net occupancy	19,153	18,242	38,390	35,429
Furniture and equipment	18,250	17,978	36,240	35,495
Deposit insurance	5,570	4,197	10,485	7,854
Intangible amortization	438	619	896	1,283
Other	45,447	42,591	86,625	83,123
Total non-interest expense	188,051	179,445	375,966	358,604
Income before income taxes	99,391	79,885	195,733	158,093
Income taxes	13,838	8,378	25,239	17,770
Net income	85,553	71,507	170,494	140,323
Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	$ 83,538	$ 69,492	$ 166,463	$ 136,292
Earnings per common share:
Basic	$ 1.30	$ 1.12	$ 2.59	$ 2.19
Diluted	$ 1.29	$ 1.11	$ 2.57	$ 2.19

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net income	$ 85,553	$ 71,507	$ 170,494	$ 140,323
Other comprehensive income (loss), before tax:
Change in net unrealized gain/loss on securities available for sale during the period	90,390	165,288	124,201	287,506
Change in net unrealized gain on securities transferred to held to maturity	(3,860)	(9,185)	(10,146)	(17,351)
Reclassification adjustment for net (gains) losses included in net income	50	0	50	(14,903)
Total securities available for sale and transferred securities, before tax amount	86,580	156,103	114,105	255,252
Defined-benefit post-retirement benefit plans:
Change in the net actuarial gain/loss	0	(862)	0	(862)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit)	1,358	1,740	2,715	3,293
Total defined-benefit post-retirement benefit plans	1,358	878	2,715	2,431
Other comprehensive income (loss), before tax	87,938	156,981	116,820	257,683
Deferred tax expense (benefit) related to other comprehensive income	30,778	54,943	40,887	90,189
Other comprehensive income (loss), net of tax	57,160	102,038	75,933	167,494
Comprehensive income (loss)	$ 142,713	$ 173,545	$ 246,427	$ 307,817

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity $ in Thousands	USD ($)
Total shareholders’ equity at beginning of period at Dec. 31, 2015	$ 2,890,343
Net income	140,323
Other comprehensive income (loss)	167,494
Stock option exercises/stock unit conversions (752,075 shares in 2017 and 67,075 shares in 2016)	3,586
Stock compensation expense recognized in earnings	5,477
Purchase of treasury stock (469 shares in 2017)	0
Cash dividends – preferred stock (approximately $0.67 per share in both 2017 and in 2016)	(4,031)
Cash dividends – common stock ($1.11 per share in 2017 and $1.07 per share in 2016)	(66,524)
Total shareholders’ equity at end of period at Jun. 30, 2016	3,136,668
Total shareholders’ equity at beginning of period at Dec. 31, 2016	3,002,528
Net income	170,494
Other comprehensive income (loss)	75,933
Stock option exercises/stock unit conversions (752,075 shares in 2017 and 67,075 shares in 2016)	44,149
Stock compensation expense recognized in earnings	6,291
Purchase of treasury stock (469 shares in 2017)	(42)
Cash dividends – preferred stock (approximately $0.67 per share in both 2017 and in 2016)	(4,031)
Cash dividends – common stock ($1.11 per share in 2017 and $1.07 per share in 2016)	(71,393)
Total shareholders’ equity at end of period at Jun. 30, 2017	$ 3,223,929

Consolidated Statements of Cha7

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Statement of Stockholders' Equity [Abstract]
Stock option exercises/stock unit conversions (shares)	752,075	67,075
Treasury stock, shares, acquired	469	0
Cash dividends declared on preferred stock, per share	$ 0.67	$ 0.67
Cash dividends declared on common stock, per share	$ 1.11	$ 1.07

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating Activities:
Net income	$ 170,494	$ 140,323
Adjustments to reconcile net income to net cash from operating activities:
Provision for loan losses	16,378	37,689
Deferred tax expense (benefit)	(4,173)	(9,633)
Accretion of loan discount	(7,403)	(8,185)
Securities premium amortization (discount accretion), net	43,652	38,806
Net (gain) loss on securities transactions	50	(14,903)
Depreciation and amortization	24,055	23,823
Net (gain) loss on sale/write-down of assets/foreclosed assets	(1,383)	(596)
Stock-based compensation	6,291	5,477
Net excess tax benefit from stock-based compensation	5,579	65
Earnings on life insurance policies	(1,565)	(1,745)
Net change in:
Trading account securities	(7,120)	177
Accrued interest receivable and other assets	(20,116)	(26,795)
Accrued interest payable and other liabilities	(36,277)	(4,664)
Net cash from operating activities	188,462	179,839
Investing Activities:
Securities held-to-maturity - Purchases	0	0
Securities held-to-maturity - Sales	0	135,610
Securities held to maturity: Maturities, calls and principal repayments	634,874	164,687
Securities available for sale:
Purchases	(8,825,545)	(1,514,263)
Sales	8,247,439	1,060,196
Maturities, calls and principal repayments	164,182	165,883
Proceeds from sale of loans	0	30,470
Net change in loans	(549,408)	(144,192)
Benefits received on life insurance policies	462	591
Proceeds from sales of premises and equipment	1,550	1,516
Purchases of premises and equipment	(14,481)	(23,459)
Proceeds from sales of repossessed properties	345	297
Net cash from investing activities	(340,582)	(122,664)
Financing Activities:
Net change in deposits	(198,002)	(56,144)
Net change in short-term borrowings	(52,125)	(160,362)
Proceeds from issuance of subordinated notes	98,434	0
Principal payments on subordinated notes	(100,000)	0
Proceeds from stock option exercises	44,149	3,586
Purchase of treasury stock	(42)	0
Cash dividends – preferred stock	(4,031)	(4,031)
Cash dividends – common stock	(71,393)	(66,524)
Net cash from financing activities	(283,010)	(283,475)
Net change in cash and cash equivalents	(435,130)	(226,300)
Cash and equivalents at beginning of period	4,141,445	3,591,523
Cash and equivalents at end of period	$ 3,706,315	$ 3,365,223

Significant Accounting Policies

Significant Accounting Policies	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	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 in this Quarterly Report on Form 10-Q 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. The consolidated financial statements in this Quarterly Report on Form 10-Q have not been audited by an independent registered public accounting firm, but in the opinion of management, reflect all adjustments necessary for a fair presentation of our financial position and results of operations. All such adjustments were of a normal and recurring nature. The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q adopted by the Securities and Exchange Commission (“SEC”). Accordingly, the financial statements do not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements and should be read in conjunction with our consolidated financial statements, and notes thereto, for the year ended December 31, 2016 , included in our Annual Report on Form 10-K filed with the SEC on February 3, 2017 (the “ 2016 Form 10-K”). Operating results for the interim periods disclosed herein are not necessarily indicative of the results that may be expected for a full year or any future period. Use of Estimates . The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements. Actual results could differ from those estimates. The allowance for loan losses and the fair values of financial instruments and the status of contingencies are particularly subject to change. Cash Flow Reporting . Additional cash flow information was as follows: Six Months Ended 2017 2016 Cash paid for interest $ 6,666 $ 5,770 Cash paid for income taxes 22,801 25,979 Significant non-cash transactions: Unsettled purchases of securities 80,586 306,564 Loans foreclosed and transferred to other real estate owned and foreclosed assets — 422 Accounting Changes, Reclassifications and Restatements. Certain items in prior financial statements have been reclassified to conform to the current presentation. As more fully described in our 2016 Form 10-K, during the third quarter of 2016, we elected to adopt the provisions of ASU 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” in advance of the required application date of January 1, 2017. Our financial statements for the three and six months ended June 30, 2016 have been restated to reflect the adoption of ASU 2016-09 as of January 1, 2016. As a result, compared to previously reported amounts, our consolidated income statement reflects decreases in income tax expense of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively, and corresponding increases in net income of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively. The increase in net income during the six months ended June 30, 2016 resulted in a $0.01 increase in previously reported diluted earnings per share.

Securities

Securities	6 Months Ended
	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Securities. A summary of the amortized cost and estimated fair value of securities, excluding trading securities, is presented below. June 30, 2017 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held to Maturity U.S. Treasury $ — $ — $ — $ — $ 249,889 $ 1,762 $ — $ 251,651 Residential mortgage-backed securities 3,992 32 24 4,000 4,511 39 — 4,550 States and political subdivisions 1,590,920 37,288 2,891 1,625,317 1,994,710 16,821 6,335 2,005,196 Other 1,350 — 2 1,348 1,350 — — 1,350 Total $ 1,596,262 $ 37,320 $ 2,917 $ 1,630,665 $ 2,250,460 $ 18,622 $ 6,335 $ 2,262,747 Available for Sale U.S. Treasury $ 4,203,901 $ 27,541 $ 7,188 $ 4,224,254 $ 4,003,692 $ 24,984 $ 8,945 $ 4,019,731 Residential mortgage-backed securities 681,364 25,693 1,436 705,621 756,072 30,388 1,293 785,167 States and political subdivisions 5,734,600 122,028 45,286 5,811,342 5,403,918 50,101 98,134 5,355,885 Other 42,520 — — 42,520 42,494 — — 42,494 Total $ 10,662,385 $ 175,262 $ 53,910 $ 10,783,737 $ 10,206,176 $ 105,473 $ 108,372 $ 10,203,277 All mortgage-backed securities included in the above table were issued by U.S. government agencies and corporations. At June 30, 2017 , approximately 98.1% of the securities in our municipal bond portfolio were issued by political subdivisions or agencies within the State of Texas, of which approximately 67.3% 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 $3.3 billion at June 30, 2017 and $3.9 billion at December 31, 2016 . During the fourth quarter of 2012, we reclassified certain securities from available for sale to held to maturity. The securities had an aggregate fair value of $2.3 billion with an aggregate net unrealized gain of $165.7 million ( $107.7 million , net of tax) on the date of the transfer. The net unamortized, unrealized gain on the remaining transferred securities included in accumulated other comprehensive income in the accompanying balance sheet as of June 30, 2017 totaled $17.6 million ( $11.4 million , net of tax). 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. As of June 30, 2017 , 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 Held to Maturity Residential mortgage-backed securities $ 2,191 $ 24 $ — $ — $ 2,191 $ 24 States and political subdivisions 20,127 83 118,937 2,808 139,064 2,891 Other 1,348 2 — — 1,348 2 Total $ 23,666 $ 109 $ 118,937 $ 2,808 $ 142,603 $ 2,917 Available for Sale U.S. Treasury $ 1,587,812 $ 7,188 $ — $ — $ 1,587,812 $ 7,188 Residential mortgage-backed securities 67,596 1,204 5,866 232 73,462 1,436 States and political subdivisions 1,450,982 38,138 142,507 7,148 1,593,489 45,286 Total $ 3,106,390 $ 46,530 $ 148,373 $ 7,380 $ 3,254,763 $ 53,910 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 June 30, 2017 , 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 bonds approach their maturity date or repricing date or if market yields for such investments decline. Management does not believe any of the securities are impaired due to reasons of credit quality. Accordingly, as of June 30, 2017 , 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 June 30, 2017 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 $ 329,237 $ 334,156 $ 57,171 $ 57,528 Due after one year through five years 170,170 177,977 4,818,303 4,845,635 Due after five years through ten years 349,324 357,485 362,030 375,143 Due after ten years 743,539 757,047 4,700,997 4,757,290 Residential mortgage-backed securities 3,992 4,000 681,364 705,621 Equity securities — — 42,520 42,520 Total $ 1,596,262 $ 1,630,665 $ 10,662,385 $ 10,783,737 Sales of Securities. As more fully discussed in our 2016 Form 10-K, during 2016, we sold certain securities issued by municipalities that, based upon our internal credit analysis, had experienced significant deterioration in creditworthiness. Some of the securities we sold were classified as held to maturity prior to their sale. Despite their classification as held to maturity, we believe the sale of these securities was merited and permissible under the applicable accounting guidelines because of the significant deterioration in the creditworthiness of the issuers. Sales of securities held to maturity were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Proceeds from sales $ — $ — $ — $ 135,610 Amortized cost — — — 131,840 Gross realized gains — — — 3,770 Gross realized losses — — — — Tax (expense) benefit of securities gains/losses — — — (1,319 ) Sales of securities available for sale were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Proceeds from sales $ 8,247,439 $ — $ 8,247,439 $ 1,060,196 Gross realized gains — — — 11,133 Gross realized losses (50 ) — (50 ) — Tax (expense) benefit of securities gains/losses 18 — 18 (3,897 ) Premiums and Discounts . Premium amortization and discount accretion included in interest income on securities was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Premium amortization $ (24,119 ) $ (22,219 ) $ (48,147 ) $ (44,559 ) Discount accretion 2,105 3,138 4,495 5,753 Net (premium amortization) discount accretion $ (22,014 ) $ (19,081 ) $ (43,652 ) $ (38,806 ) Trading Account Securities. Trading account securities, at estimated fair value, were as follows: June 30, December 31, U.S. Treasury $ 17,726 $ 16,594 States and political subdivisions 9,874 109 Total $ 27,600 $ 16,703 Net gains and losses on trading account securities were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Net gain on sales transactions $ 293 $ 351 $ 604 $ 653 Net mark-to-market gains (losses) (56 ) (2 ) (43 ) (1 ) Net gain (loss) on trading account securities $ 237 $ 349 $ 561 $ 652

Loans

Loans	6 Months Ended
	Jun. 30, 2017
Receivables [Abstract]
Loans	Loans Loans were as follows: June 30, Percentage of Total December 31, Percentage of Total Commercial and industrial $ 4,604,269 36.8 % $ 4,344,000 36.3 % Energy: Production 1,040,506 8.3 971,767 8.1 Service 183,543 1.5 221,213 1.8 Other 185,563 1.5 193,081 1.7 Total energy 1,409,612 11.3 1,386,061 11.6 Commercial real estate: Commercial mortgages 3,620,885 28.9 3,481,157 29.1 Construction 1,050,837 8.4 1,043,261 8.7 Land 322,130 2.6 311,030 2.6 Total commercial real estate 4,993,852 39.9 4,835,448 40.4 Consumer real estate: Home equity loans 355,744 2.8 345,130 2.9 Home equity lines of credit 283,344 2.3 264,862 2.2 Other 351,985 2.8 326,793 2.7 Total consumer real estate 991,073 7.9 936,785 7.8 Total real estate 5,984,925 47.8 5,772,233 48.2 Consumer and other 513,532 4.1 473,098 3.9 Total loans $ 12,512,338 100.0 % $ 11,975,392 100.0 % 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 June 30, 2017 , there were no concentrations of loans related to any single industry in excess of 10% of total loans other than energy loans, which totaled 11.3% of total loans. Unfunded commitments to extend credit and standby letters of credit issued to customers in the energy industry totaled $1.1 billion and $42.9 million , respectively, as of June 30, 2017 . 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 June 30, 2017 or December 31, 2016 . Non-Accrual and Past Due Loans. Non-accrual loans, segregated by class of loans, were as follows: June 30, December 31, Commercial and industrial $ 21,226 $ 31,475 Energy 55,464 57,571 Commercial real estate: Buildings, land and other 6,916 8,550 Construction — — Consumer real estate 2,543 2,130 Consumer and other 264 425 Total $ 86,413 $ 100,151 As of June 30, 2017 , non-accrual loans reported in the table above included $11.4 million related to loans that were restructured as “troubled debt restructurings” during 2017 . See the section captioned “Troubled Debt Restructurings” elsewhere in this note. Had non-accrual loans performed in accordance with their original contract terms, we would have recognized additional interest income, net of tax, of approximately $798 thousand and $1.6 million for the three and six months ended June 30, 2017 , compared to $936 thousand and $1.8 million for three and six months ended June 30, 2016 . An age analysis of past due loans (including both accruing and non-accruing loans), segregated by class of loans, as of June 30, 2017 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 $ 24,320 $ 26,149 $ 50,469 $ 4,553,800 $ 4,604,269 $ 10,768 Energy 5,991 6,430 12,421 1,397,191 1,409,612 2,902 Commercial real estate: Buildings, land and other 21,157 4,166 25,323 3,917,692 3,943,015 944 Construction — — — 1,050,837 1,050,837 — Consumer real estate 4,693 2,022 6,715 984,358 991,073 739 Consumer and other 3,508 740 4,248 509,284 513,532 650 Total $ 59,669 $ 39,507 $ 99,176 $ 12,413,162 $ 12,512,338 $ 16,003 Impaired Loans. 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 June 30, 2017 Commercial and industrial $ 27,709 $ 14,777 $ 4,040 $ 18,817 $ 1,780 Energy 59,771 36,162 19,215 55,377 350 Commercial real estate: Buildings, land and other 9,729 5,478 — 5,478 — Construction — — — — — Consumer real estate 1,203 1,203 — 1,203 — Consumer and other — — — — — Total $ 98,412 $ 57,620 $ 23,255 $ 80,875 $ 2,130 Unpaid Contractual Recorded Investment Recorded Investment Total Related December 31, 2016 Commercial and industrial $ 40,288 $ 19,862 $ 9,047 $ 28,909 $ 5,436 Energy 60,522 27,759 29,804 57,563 3,750 Commercial real estate: Buildings, land and other 11,369 6,866 — 6,866 — Construction — — — — — Consumer real estate 977 655 — 655 — Consumer and other 32 30 — 30 — Total $ 113,188 $ 55,172 $ 38,851 $ 94,023 $ 9,186 The average recorded investment in impaired loans was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial and industrial $ 21,347 $ 24,866 $ 23,867 $ 24,197 Energy 67,008 78,359 63,860 59,286 Commercial real estate: Buildings, land and other 5,966 20,533 6,266 24,497 Construction — 648 — 622 Consumer real estate 1,376 443 1,135 457 Consumer and other 12 27 18 18 Total $ 95,709 $ 124,876 $ 95,146 $ 109,077 Troubled Debt Restructurings . Troubled debt restructurings during the six months ended June 30, 2017 and June 30, 2016 are set forth in the following table. Six Months Ended Six Months Ended Balance at Restructure Balance at Period-End Balance at Restructure Balance at Period-End Commercial and industrial $ 784 $ 643 $ 510 $ 505 Energy 12,959 12,458 62,546 20,795 Commercial real estate: Buildings, land and other — — 1,456 1,456 Construction — — 243 224 $ 13,743 $ 13,101 $ 64,755 $ 22,980 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. As of June 30, 2017 , there were no loans restructured during the last year that were in excess of 90 days past due. During the six months ended June 30, 2017 , we recognized charge-offs totaling $10.0 million related to loans restructured during the third and fourth quarters of 2016. During the six months ended June 30, 2016 , we recognized a charge-off of $9.5 million related to a loan restructured during the first quarter of 2016. The loan was subsequently sold with proceeds from the sale totaling $30.5 million . 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 set forth in our 2016 Form 10-K. In monitoring credit quality trends in the context of assessing the appropriate level of the allowance for loan losses, we monitor portfolio credit quality by the weighted-average risk grade of each class of commercial loan. Individual relationship managers review updated financial information for all pass grade loans to 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. June 30, 2017 December 31, 2016 Weighted Loans Weighted Loans Commercial and industrial: Risk grades 1-8 6.00 $ 4,146,261 6.01 $ 3,989,722 Risk grade 9 9.00 222,108 9.00 106,988 Risk grade 10 10.00 78,696 10.00 115,420 Risk grade 11 11.00 135,978 11.00 100,245 Risk grade 12 12.00 19,446 12.00 25,939 Risk grade 13 13.00 1,780 13.00 5,686 Total 6.39 $ 4,604,269 6.35 $ 4,344,000 Energy Risk grades 1-8 6.32 $ 1,024,927 6.34 $ 854,688 Risk grade 9 9.00 43,415 9.00 78,524 Risk grade 10 10.00 115,913 10.00 150,872 Risk grade 11 11.00 169,893 11.00 244,406 Risk grade 12 12.00 55,114 12.00 53,821 Risk grade 13 13.00 350 13.00 3,750 Total 7.49 $ 1,409,612 7.95 $ 1,386,061 Commercial real estate: Buildings, land and other Risk grades 1-8 6.69 $ 3,590,525 6.67 $ 3,463,064 Risk grade 9 9.00 123,492 9.00 109,110 Risk grade 10 10.00 148,718 10.00 145,067 Risk grade 11 11.00 73,364 11.00 66,396 Risk grade 12 12.00 6,916 12.00 8,550 Risk grade 13 13.00 — 13.00 — Total 6.97 $ 3,943,015 6.95 $ 3,792,187 Construction Risk grades 1-8 7.03 $ 1,019,355 6.97 $ 1,023,194 Risk grade 9 9.00 22,632 9.00 15,829 Risk grade 10 10.00 5,116 10.00 2,889 Risk grade 11 11.00 3,734 11.00 1,349 Risk grade 12 12.00 — 12.00 — Risk grade 13 13.00 — 13.00 — Total 7.10 $ 1,050,837 7.01 $ 1,043,261 Net (charge-offs)/recoveries, segregated by class of loans, were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial and industrial $ (4,861 ) $ (3,966 ) $ (7,590 ) $ (5,098 ) Energy (6,236 ) (16,747 ) (10,461 ) (17,758 ) Commercial real estate: Buildings, land and other 460 481 502 542 Construction 3 2 6 9 Consumer real estate 111 74 207 173 Consumer and other (1,401 ) (1,199 ) (2,529 ) (1,702 ) Total $ (11,924 ) $ (21,355 ) $ (19,865 ) $ (23,834 ) 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, the components of which are more fully described in our 2016 Form 10-K, totaled 124.7 at May 31, 2017 (most recent date available) and 123.1 at December 31, 2016 . 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, which is more fully described in our 2016 Form 10-K, 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. 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. The following table presents details of the allowance for loan losses allocated to each portfolio segment as of June 30, 2017 and December 31, 2016 and detailed on the basis of the impairment evaluation methodology we used: Commercial and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Total June 30, 2017 Historical valuation allowances $ 28,504 $ 32,452 $ 17,975 $ 2,416 $ 5,455 $ 86,802 Specific valuation allowances 1,780 350 — — — 2,130 General valuation allowances 8,418 5,934 4,724 2,032 137 21,245 Macroeconomic valuation allowances 10,204 15,541 10,303 1,087 2,246 39,381 Total $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 Allocated to loans: Individually evaluated $ 1,780 $ 350 $ — $ — $ — $ 2,130 Collectively evaluated 47,126 53,927 33,002 5,535 7,838 147,428 Total $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 December 31, 2016 Historical valuation allowances $ 33,251 $ 34,626 $ 16,976 $ 2,225 $ 4,585 $ 91,663 Specific valuation allowances 5,436 3,750 — — — 9,186 General valuation allowances 6,708 3,769 5,004 1,506 (144 ) 16,843 Macroeconomic valuation allowances 7,520 18,508 8,233 507 585 35,353 Total $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Allocated to loans: Individually evaluated $ 5,436 $ 3,750 $ — $ — $ — $ 9,186 Collectively evaluated 47,479 56,903 30,213 4,238 5,026 143,859 Total $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Our recorded investment in loans as of June 30, 2017 and December 31, 2016 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 Consumer Consumer Total June 30, 2017 Individually evaluated $ 18,817 $ 55,377 $ 5,478 $ 1,203 $ — $ 80,875 Collectively evaluated 4,585,452 1,354,235 4,988,374 989,870 513,532 12,431,463 Total $ 4,604,269 $ 1,409,612 $ 4,993,852 $ 991,073 $ 513,532 $ 12,512,338 December 31, 2016 Individually evaluated $ 28,909 $ 57,563 $ 6,866 $ 655 $ 30 $ 94,023 Collectively evaluated 4,315,091 1,328,498 4,828,582 936,130 473,068 11,881,369 Total $ 4,344,000 $ 1,386,061 $ 4,835,448 $ 936,785 $ 473,098 $ 11,975,392 The following table details activity in the allowance for loan losses by portfolio segment for the three and six months ended June 30, 2017 and 2016 . 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 Three months ended: June 30, 2017 Beginning balance $ 45,583 $ 61,793 $ 34,009 $ 4,823 $ 6,848 $ 153,056 Provision for loan losses 8,184 (1,280 ) (1,470 ) 601 2,391 8,426 Charge-offs (5,579 ) (6,317 ) (14 ) (2 ) (3,623 ) (15,535 ) Recoveries 718 81 477 113 2,222 3,611 Net charge-offs (4,861 ) (6,236 ) 463 111 (1,401 ) (11,924 ) Ending balance $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 June 30, 2016 Beginning balance $ 45,084 $ 84,973 $ 23,587 $ 3,786 $ 4,450 $ 161,880 Provision for loan losses 6,460 (1,887 ) 2,993 75 1,548 9,189 Charge-offs (4,857 ) (16,749 ) (19 ) (23 ) (3,252 ) (24,900 ) Recoveries 891 2 502 97 2,053 3,545 Net charge-offs (3,966 ) (16,747 ) 483 74 (1,199 ) (21,355 ) Ending balance $ 47,578 $ 66,339 $ 27,063 $ 3,935 $ 4,799 $ 149,714 Six months ended: June 30, 2017 Beginning balance $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Provision for loan losses 3,581 4,085 2,281 1,090 5,341 16,378 Charge-offs (9,106 ) (10,595 ) (14 ) (13 ) (7,171 ) (26,899 ) Recoveries 1,516 134 522 220 4,642 7,034 Net charge-offs (7,590 ) (10,461 ) 508 207 (2,529 ) (19,865 ) Ending balance $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 June 30, 2016 Beginning balance $ 42,993 $ 54,696 $ 24,313 $ 4,659 $ 9,198 $ 135,859 Provision for loan losses 9,683 29,401 2,199 (897 ) (2,697 ) 37,689 Charge-offs (6,718 ) (17,760 ) (47 ) (177 ) (5,976 ) (30,678 ) Recoveries 1,620 2 598 350 4,274 6,844 Net charge-offs (5,098 ) (17,758 ) 551 173 (1,702 ) (23,834 ) Ending balance $ 47,578 $ 66,339 $ 27,063 $ 3,935 $ 4,799 $ 149,714

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	6 Months Ended
	Jun. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill and other intangible assets are presented in the table below. June 30, December 31, Goodwill $ 654,952 $ 654,952 Other intangible assets: Core deposits $ 4,636 $ 5,298 Customer relationships 1,188 1,410 Non-compete agreements 56 68 $ 5,880 $ 6,776 The estimated aggregate future amortization expense for intangible assets remaining as of June 30, 2017 is as follows: Remainder of 2017 $ 807 2018 1,424 2019 1,167 2020 918 2021 697 Thereafter 867 $ 5,880

Deposits

Deposits	6 Months Ended
	Jun. 30, 2017
Banking and Thrift [Abstract]
Deposits	Deposits Deposits were as follows: June 30, Percentage of Total December 31, Percentage of Total Non-interest-bearing demand deposits: Commercial and individual $ 10,076,475 39.3 % $ 9,670,989 37.5 % Correspondent banks 259,686 1.0 280,751 1.1 Public funds 371,204 1.5 561,629 2.2 Total non-interest-bearing demand deposits 10,707,365 41.8 10,513,369 40.8 Interest-bearing deposits: Private accounts: Savings and interest checking 6,349,462 24.8 6,436,065 24.9 Money market accounts 7,403,054 28.9 7,486,431 29.0 Time accounts of $100,000 or more 432,406 1.7 460,028 1.8 Time accounts under $100,000 327,228 1.3 338,714 1.3 Total private accounts 14,512,150 56.7 14,721,238 57.0 Public funds: Savings and interest checking 299,505 1.2 446,872 1.7 Money market accounts 77,361 0.3 113,669 0.4 Time accounts of $100,000 or more 16,426 — 15,748 0.1 Time accounts under $100,000 766 — 679 — Total public funds 394,058 1.5 576,968 2.2 Total interest-bearing deposits 14,906,208 58.2 15,298,206 59.2 Total deposits $ 25,613,573 100.0 % $ 25,811,575 100.0 % The following table presents additional information about our deposits: June 30, December 31, Deposits from foreign sources (primarily Mexico) $ 728,350 $ 776,003 Deposits not covered by deposit insurance 12,708,257 12,889,047

Borrowed Funds

Borrowed Funds	6 Months Ended
	Jun. 30, 2017
Debt Disclosure [Abstract]
Borrowed Funds	Borrowed Funds 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 $1.5 million at June 30, 2017 . Proceeds from sale of the notes were used for general corporate purposes. Our $100 million of 5.75% fixed-to-floating rate subordinated notes matured and were redeemed on February 15, 2017 . See Note 8 - Borrowed Funds in our 2016 Form 10-K for additional information about these notes.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments 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. As more fully discussed in our 2016 Form 10-K, 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. Financial instruments with off-balance-sheet risk were as follows: June 30, December 31, Commitments to extend credit $ 7,616,002 $ 7,476,420 Standby letters of credit 240,612 239,482 Deferred standby letter of credit fees 2,010 2,054 Lease Commitments . We lease certain office facilities and office equipment under operating leases. Rent expense for all operating leases totaled $7.5 million and $15.3 million during the three and six months ended June 30, 2017 and $7.3 million and $14.5 million during the three and six months ended June 30, 2016 . There has been no significant change in our expected future minimum lease payments since December 31, 2016 . See the 2016 Form 10-K for information regarding these commitments. 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	6 Months Ended
	Jun. 30, 2017
Banking and Thrift [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. 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 June 30, 2017 and December 31, 2016 includes $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 June 30, 2017 or December 31, 2016 . 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 $100.0 million of qualified subordinated debt at June 30, 2017 and $133.0 million of trust preferred securities at both June 30, 2017 and December 31, 2016 . The following table presents actual and required capital ratios 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 June 30, 2017 and December 31, 2016 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. See the 2016 Form 10-K for a more detailed discussion of the Basel III Capital Rules. Actual Minimum Capital Required - Basel III Phase-In Schedule Minimum Capital Required - Basel III Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio June 30, 2017 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,385,585 12.81 % $ 1,070,444 5.75 % $ 1,303,367 7.00 % $ 1,210,067 6.50 % Frost Bank 2,401,554 12.94 1,067,432 5.75 1,299,400 7.00 1,206,662 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,530,071 13.59 1,349,691 7.25 1,582,296 8.50 1,489,314 8.00 Frost Bank 2,401,554 12.94 1,345,892 7.25 1,577,843 8.50 1,485,123 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,912,629 15.65 1,722,019 9.25 1,954,601 10.50 1,861,642 10.00 Frost Bank 2,551,112 13.74 1,717,173 9.25 1,949,100 10.50 1,856,403 10.00 Leverage Ratio Cullen/Frost 2,530,071 8.61 1,174,957 4.00 1,174,910 4.00 1,468,696 5.00 Frost Bank 2,401,554 8.18 1,173,726 4.00 1,173,679 4.00 1,467,157 5.00 December 31, 2016 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,239,186 12.52 % $ 916,360 5.125 % $ 1,251,425 7.00 % $ 1,162,213 6.50 % Frost Bank 2,296,480 12.88 913,460 5.125 1,247,463 7.00 1,158,535 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,383,672 13.33 1,184,563 6.625 1,519,587 8.50 1,430,416 8.00 Frost Bank 2,296,480 12.88 1,180,814 6.625 1,514,776 8.50 1,425,889 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,669,717 14.93 1,542,168 8.625 1,877,137 10.50 1,788,020 10.00 Frost Bank 2,449,525 13.74 1,537,286 8.625 1,871,194 10.50 1,782,361 10.00 Leverage Ratio Cullen/Frost 2,383,672 8.14 1,171,682 4.00 1,171,573 4.00 1,464,602 5.00 Frost Bank 2,296,480 7.85 1,170,249 4.00 1,170,141 4.00 1,462,812 5.00 As of June 30, 2017 , capital levels at Cullen/Frost and Frost Bank exceed all capital adequacy requirements under the Basel III Capital Rules on a fully phased-in basis. Based on the ratios presented above, capital levels as of June 30, 2017 at Cullen/Frost and Frost Bank exceed the minimum levels necessary to be considered “well capitalized.” 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 June 30, 2017 , that Cullen/Frost and Frost Bank meet all capital adequacy requirements to which they are subject. 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 October 27, 2016 , our board of directors authorized a $100.0 million stock repurchase program, allowing us to repurchase shares of our common stock over a two -year period from time to time at various prices in the open market or through private transactions. As of June 30, 2017 , no shares have been repurchased under the plan. Dividend Restrictions . In the ordinary course of business, Cullen/Frost is dependent upon dividends from Frost Bank to provide funds for the payment of dividends to shareholders and to provide for other cash requirements. Banking regulations may limit the amount of dividends that may be paid. Approval by regulatory authorities is required if the effect of dividends declared would cause the regulatory capital of Frost Bank to fall below specified minimum levels. Approval is also required if dividends declared exceed the net profits for that year combined with the retained net profits for the preceding two years. Under the foregoing dividend restrictions and while maintaining its “well capitalized” status, at June 30, 2017 , Frost Bank could pay aggregate dividends of up to $420.6 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 our Series A Preferred Stock, in the event that we do not declare and pay dividends on our 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 our Series A Preferred Stock.

Derivative Financial Instrument

Derivative Financial Instruments	6 Months Ended
	Jun. 30, 2017
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 in our 2016 Form 10-K. The notional amounts and estimated fair values of interest rate derivative contracts 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. June 30, 2017 December 31, 2016 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 $ 40,089 $ 312 $ 41,818 $ 368 Loan/lease interest rate swaps – liabilities 14,921 (910 ) 18,812 (1,278 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps – assets 211,908 2,357 206,745 2,649 Loan/lease interest rate swaps – liabilities 681,298 (23,602 ) 694,965 (25,466 ) Loan/lease interest rate caps – assets 114,866 687 85,966 575 Customer counterparties: Loan/lease interest rate swaps – assets 681,298 23,602 694,965 25,467 Loan/lease interest rate swaps – liabilities 211,908 (2,357 ) 206,745 (2,649 ) Loan/lease interest rate caps – liabilities 114,866 (687 ) 85,966 (575 ) The weighted-average rates paid and received for interest rate swaps outstanding at June 30, 2017 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.34 % 1.17 % Non-hedging interest rate swaps – financial institution counterparties 3.99 % 2.77 % Non-hedging interest rate swaps – customer counterparties 2.77 % 3.99 % The weighted-average strike rate for outstanding interest rate caps was 3.07% at June 30, 2017 . 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. June 30, 2017 December 31, 2016 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil – assets Barrels 935 $ 4,684 227 $ 206 Oil – liabilities Barrels 178 (153 ) 944 (4,400 ) Natural gas – assets MMBTUs 1,061 109 — — Natural gas – liabilities MMBTUs 938 (85 ) 1,299 (1,357 ) Customer counterparties: Oil – assets Barrels 178 163 944 4,580 Oil – liabilities Barrels 935 (4,466 ) 227 (206 ) Natural gas – assets MMBTUs 938 87 1,299 1,393 Natural gas – liabilities MMBTUs 1,061 (103 ) — — 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: June 30, 2017 December 31, 2016 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts – assets EUR 497 $ 9 — $ — Forward contracts – assets GBP 217 5 — — Forward contracts – liabilities EUR 1,194 (9 ) 870 (9 ) Forward contracts – liabilities CAD 538 (3 ) 2,214 (21 ) Forward contracts – liabilities GBP 2,434 (20 ) 419 (3 ) Customer counterparties: Forward contracts – assets CAD 536 5 2,205 29 Forward contracts – liabilities EUR 500 (6 ) — — Forward contracts – liabilities GBP 219 (3 ) — — 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: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ (198 ) $ (388 ) $ (443 ) $ (726 ) Amount of (gain) loss included in other non-interest expense (2 ) (7 ) (3 ) (7 ) As stated above, we enter into non-hedge related derivative positions primarily to accommodate the business needs of our customers. Upon the origination of a derivative contract with a customer, we simultaneously enter into an offsetting derivative contract with a third party financial institution. We recognize immediate income based upon the difference in the bid/ask spread of the underlying transactions with our customers and the third party. Because we act only as an intermediary for our customer, subsequent changes in the fair value of the underlying derivative contracts for the most part offset each other and do not significantly impact our results of operations. Amounts included in the consolidated statements of income related to non-hedging interest rate, commodity and foreign currency derivative instruments are presented in the table below. Three Months Ended Six Months Ended 2017 2016 2017 2016 Non-hedging interest rate derivatives: Other non-interest income $ 607 $ 979 $ 977 $ 1,414 Other non-interest expense 2 — 1 — Non-hedging commodity derivatives: Other non-interest income 104 13 156 145 Non-hedging foreign currency derivatives: Other non-interest income 9 8 18 14 Counterparty Credit Risk. Our credit exposure relating to interest rate swaps, commodity swaps/options and foreign currency forward contracts with bank customers was approximately $23.5 million at June 30, 2017 . 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 $8.9 million at June 30, 2017 . 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 10 – Balance Sheet Offsetting and Repurchase Agreements for additional information regarding our credit exposure with upstream financial institution counterparties. The aggregate fair value of securities we posted as collateral related to derivative contracts totaled $13.1 million at June 30, 2017 . At such date, we also had $14.2 million in cash collateral on deposit with other financial institution counterparties.

Balance Sheet Offsetting

Balance Sheet Offsetting	6 Months Ended
	Jun. 30, 2017
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 June 30, 2017 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized June 30, 2017 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,356 $ — $ 3,356 Commodity swaps and options 4,793 — 4,793 Foreign currency forward contracts 14 — 14 Total derivatives 8,163 — 8,163 Resell agreements 9,642 — 9,642 Total $ 17,805 $ — $ 17,805 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 24,512 $ — $ 24,512 Commodity swaps and options 238 — 238 Foreign currency forward contracts 32 — 32 Total derivatives 24,782 — 24,782 Repurchase agreements 919,017 — 919,017 Total $ 943,799 $ — $ 943,799 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount June 30, 2017 Financial assets: Derivatives: Counterparty A $ 413 $ (413 ) $ — $ — Counterparty B 1,896 (1,896 ) — — Counterparty C 979 (979 ) — — Counterparty D 1,610 (1,610 ) — — Other counterparties 3,265 (848 ) (2,028 ) 389 Total derivatives 8,163 (5,746 ) (2,028 ) 389 Resell agreements 9,642 — (9,642 ) — Total $ 17,805 $ (5,746 ) $ (11,670 ) $ 389 Financial liabilities: Derivatives: Counterparty A $ 9,644 $ (413 ) $ (9,231 ) $ — Counterparty B 3,737 (1,896 ) (1,841 ) — Counterparty C 1,260 (979 ) (9 ) 272 Counterparty D 8,004 (1,610 ) (6,394 ) — Other counterparties 2,137 (848 ) (1,278 ) 11 Total derivatives 24,782 (5,746 ) (18,753 ) 283 Repurchase agreements 919,017 — (919,017 ) — Total $ 943,799 $ (5,746 ) $ (937,770 ) $ 283 Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2016 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2016 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,592 $ — $ 3,592 Commodity swaps and options 206 — 206 Foreign currency forward contracts — — — Total derivatives 3,798 — 3,798 Resell agreements 9,642 — 9,642 Total $ 13,440 $ — $ 13,440 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 26,744 $ — $ 26,744 Commodity swaps and options 5,757 — 5,757 Foreign currency forward contracts 33 — 33 Total derivatives 32,534 — 32,534 Repurchase agreements 963,317 — 963,317 Total $ 995,851 $ — $ 995,851 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2016 Financial assets: Derivatives: Counterparty A $ 687 $ (687 ) $ — $ — Counterparty B 223 (223 ) — — Counterparty C 158 (158 ) — — Counterparty D 1,820 (1,820 ) — — Other counterparties 910 (677 ) (64 ) 169 Total derivatives 3,798 (3,565 ) (64 ) 169 Resell agreements 9,642 — (9,642 ) — Total $ 13,440 $ (3,565 ) $ (9,706 ) $ 169 Financial liabilities: Derivatives: Counterparty A $ 11,233 $ (687 ) $ (10,026 ) $ 520 Counterparty B 6,867 (223 ) (6,344 ) 300 Counterparty C 4,578 (158 ) (4,415 ) 5 Counterparty D 7,706 (1,820 ) (5,886 ) — Other counterparties 2,150 (677 ) (676 ) 797 Total derivatives 32,534 (3,565 ) (27,347 ) 1,622 Repurchase agreements 963,317 — (963,317 ) — Total $ 995,851 $ (3,565 ) $ (990,664 ) $ 1,622 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 June 30, 2017 and December 31, 2016 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 June 30, 2017 Repurchase agreements: U.S. Treasury $ 842,269 $ — $ — $ — $ 842,269 Residential mortgage-backed securities 76,748 — — — 76,748 Total borrowings $ 919,017 $ — $ — $ — $ 919,017 Gross amount of recognized liabilities for repurchase agreements $ 919,017 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2016 Repurchase agreements: U.S. Treasury $ 841,475 $ — $ — $ — $ 841,475 Residential mortgage-backed securities 121,842 — — — 121,842 Total borrowings $ 963,317 $ — $ — $ — $ 963,317 Gross amount of recognized liabilities for repurchase agreements $ 963,317 Amounts related to agreements not included in offsetting disclosures above $ —

Earnings Per Common Share

Earnings Per Common Share	6 Months Ended
	Jun. 30, 2017
Earnings Per Share [Abstract]
Earnings Per Common Share	Earnings Per Common Share Earnings per common share is computed using the two-class method as more fully described in our 2016 Form 10-K. 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. Three Months Ended Six Months Ended 2017 2016 2017 2016 Net income $ 85,553 $ 71,507 $ 170,494 $ 140,323 Less: Preferred stock dividends 2,015 2,015 4,031 4,031 Net income available to common shareholders 83,538 69,492 166,463 136,292 Less: Earnings allocated to participating securities 436 252 871 487 Net earnings allocated to common stock $ 83,102 $ 69,240 $ 165,592 $ 135,805 Distributed earnings allocated to common stock $ 36,545 $ 33,463 $ 71,020 $ 66,285 Undistributed earnings allocated to common stock 46,557 35,777 94,572 69,520 Net earnings allocated to common stock $ 83,102 $ 69,240 $ 165,592 $ 135,805 Weighted-average shares outstanding for basic earnings per common share 64,061,264 61,959,411 63,900,620 61,944,438 Dilutive effect of stock compensation 974,067 497,532 988,198 267,632 Weighted-average shares outstanding for diluted earnings per common share 65,035,331 62,456,943 64,888,818 62,212,070

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation 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 2016 was 29,240 . As of June 30, 2017 , there were 1,480,137 shares remaining available for grant for future stock-based compensation 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 Balance, 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 — — — — — — Exercised/vested (6,098 ) 62.29 (1,730 ) 76.07 — — (744,247 ) 59.32 Forfeited/expired — — (870 ) 76.07 — — (33,492 ) 69.35 Balance, June 30, 2017 53,008 $ 64.87 254,250 $ 73.40 43,860 $ 69.70 3,311,289 $ 63.36 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: Three Months Ended Six Months Ended 2017 2016 2017 2016 New shares issued from available authorized shares 310,021 — 593,363 — Issued from available treasury stock — 65,200 158,712 67,075 Total 310,021 65,200 752,075 67,075 Proceeds from stock option exercises $ 19,402 $ 3,490 $ 44,149 $ 3,586 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. Three Months Ended Six Months Ended 2017 2016 2017 2016 Stock options $ 1,573 $ 2,117 $ 3,360 $ 4,242 Non-vested stock awards/stock units 901 358 1,934 715 Director deferred stock units 519 520 519 520 Performance stock units 195 — 478 — Total $ 3,188 $ 2,995 $ 6,291 $ 5,477 Income tax benefit $ 1,116 $ 1,048 $ 2,202 $ 1,917 Unrecognized stock-based compensation expense at June 30, 2017 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. Stock options $ 8,694 Non-vested stock awards/stock units 8,413 Performance stock units 2,579 Total $ 19,686

Defined Benefit Plans

Defined Benefit Plans	6 Months Ended
	Jun. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Defined Benefit Plans	Defined Benefit Plans The components of the combined net periodic expense (benefit) for our defined benefit pension plans are presented in the table below. Three Months Ended Six Months Ended 2017 2016 2017 2016 Expected return on plan assets, net of expenses $ (2,780 ) $ (2,889 ) $ (5,559 ) $ (5,779 ) Interest cost on projected benefit obligation 1,548 1,749 3,095 3,498 Net amortization and deferral 1,358 1,553 2,715 3,106 SERP settlement costs — 187 — 187 Net periodic expense (benefit) $ 126 $ 600 $ 251 $ 1,012 Our non-qualified defined benefit pension plan is not funded. No contributions to the qualified defined benefit pension plan were made during the six months ended June 30, 2017 . We do not expect to make any contributions to the qualified defined benefit plan during the remainder of 2017 .

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Current income tax expense $ 13,710 $ 13,616 $ 29,412 $ 27,403 Deferred income tax expense (benefit) 128 (5,238 ) (4,173 ) (9,633 ) Income tax expense, as reported $ 13,838 $ 8,378 $ 25,239 $ 17,770 Effective tax rate 13.9 % 10.5 % 12.9 % 11.2 % Net deferred tax assets totaled $27.0 million at June 30, 2017 and $63.7 million at December 31, 2016 . No valuation allowance for deferred tax assets was recorded at June 30, 2017 as management believes it is more likely than not that all of the deferred tax assets will be realized because they were supported by recoverable taxes paid in prior years. The effective income tax rates differed from the U.S. statutory rate of 35% during the comparable periods primarily due to the effect of tax-exempt income from loans, securities and life insurance policies and the income tax effects associated with stock-based compensation. 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. 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 2013.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The before and after tax amounts allocated to each component of other comprehensive income (loss) are presented in the following table. Reclassification adjustments related to securities available for sale are included in net gain (loss) on securities transactions in the accompanying consolidated statements of income. Reclassification adjustments related to defined-benefit post-retirement benefit plans are included in the computation of net periodic pension expense (see Note 13 – Defined Benefit Plans). Three Months Ended Three Months Ended Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 90,390 $ 31,636 $ 58,754 $ 165,288 $ 57,851 $ 107,437 Change in net unrealized gain on securities transferred to held to maturity (3,860 ) (1,351 ) (2,509 ) (9,185 ) (3,215 ) (5,970 ) Reclassification adjustment for net (gains) losses included in net income 50 18 32 — — — Total securities available for sale and transferred securities 86,580 30,303 56,277 156,103 54,636 101,467 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss — — — (862 ) (302 ) (560 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 1,358 475 883 1,740 609 1,131 Total defined-benefit post-retirement benefit plans 1,358 475 883 878 307 571 Total other comprehensive income (loss) $ 87,938 $ 30,778 $ 57,160 $ 156,981 $ 54,943 $ 102,038 Six Months Ended Six Months Ended Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 124,201 $ 43,470 $ 80,731 $ 287,506 $ 100,627 $ 186,879 Change in net unrealized gain on securities transferred to held to maturity (10,146 ) (3,551 ) (6,595 ) (17,351 ) (6,073 ) (11,278 ) Reclassification adjustment for net (gains) losses included in net income 50 18 32 (14,903 ) (5,216 ) (9,687 ) Total securities available for sale and transferred securities 114,105 39,937 74,168 255,252 89,338 165,914 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss — — — (862 ) (302 ) (560 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 2,715 950 1,765 3,293 1,153 2,140 Total defined-benefit post-retirement benefit plans 2,715 950 1,765 2,431 851 1,580 Total other comprehensive income (loss) $ 116,820 $ 40,887 $ 75,933 $ 257,683 $ 90,189 $ 167,494 Activity in accumulated other comprehensive income (loss), net of tax, was as follows: Securities Available For Sale Defined Benefit Plans Accumulated Other Comprehensive Income Balance January 1, 2017 $ 16,153 $ (40,776 ) $ (24,623 ) Other comprehensive income (loss) before reclassifications 74,136 — 74,136 Amounts reclassified from accumulated other comprehensive income (loss) 32 1,765 1,797 Net other comprehensive income (loss) during period 74,168 1,765 75,933 Balance at June 30, 2017 $ 90,321 $ (39,011 ) $ 51,310 Balance January 1, 2016 $ 160,611 $ (46,748 ) $ 113,863 Other comprehensive income (loss) before reclassifications 175,601 (560 ) 175,041 Amounts reclassified from accumulated other comprehensive income (loss) (9,687 ) 2,140 (7,547 ) Net other comprehensive income (loss) during period 165,914 1,580 167,494 Balance at June 30, 2016 $ 326,525 $ (45,168 ) $ 281,357

Operating Segments

Operating Segments	6 Months Ended
	Jun. 30, 2017
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. See our 2016 Form 10-K for additional information regarding our operating segments. Summarized operating results by segment were as follows: Banking Frost Wealth Advisors Non-Banks Consolidated Revenues from (expenses to) external customers: Three months ended: June 30, 2017 $ 261,250 $ 36,712 $ (2,094 ) $ 295,868 June 30, 2016 237,444 32,225 (1,150 ) 268,519 Six months ended: June 30, 2017 $ 520,161 $ 71,300 $ (3,384 ) $ 588,077 June 30, 2016 492,717 63,948 (2,279 ) 554,386 Net income (loss): Three months ended: June 30, 2017 $ 81,529 $ 6,279 $ (2,255 ) $ 85,553 June 30, 2016 68,223 4,860 (1,576 ) 71,507 Six months ended: June 30, 2017 $ 162,398 $ 11,573 $ (3,477 ) $ 170,494 June 30, 2016 134,190 9,012 (2,879 ) 140,323

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2017
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 three-level 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. See our 2016 Form 10-K for additional information regarding the fair value hierarchy and a description of our valuation techniques. Financial Assets and Financial Liabilities. The table below summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of June 30, 2017 and December 31, 2016 , segregated by the level of the valuation inputs within the fair value hierarchy of ASC Topic 820 utilized to measure fair value. Level 1 Level 2 Level 3 Total Fair June 30, 2017 Securities available for sale: U.S. Treasury $ 4,224,254 $ — $ — $ 4,224,254 Residential mortgage-backed securities — 705,621 — 705,621 States and political subdivisions — 5,811,342 — 5,811,342 Other — 42,520 — 42,520 Trading account securities: U.S. Treasury 17,726 — — 17,726 States and political subdivisions — 9,874 — 9,874 Derivative assets: Interest rate swaps, caps and floors — 26,958 — 26,958 Commodity swaps and options — 5,043 — 5,043 Foreign currency forward contracts 19 — — 19 Derivative liabilities: Interest rate swaps, caps and floors — 27,556 — 27,556 Commodity swaps and options — 4,807 — 4,807 Foreign currency forward contracts 41 — — 41 December 31, 2016 Securities available for sale: U.S. Treasury $ 4,019,731 $ — $ — $ 4,019,731 Residential mortgage-backed securities — 785,167 — 785,167 States and political subdivisions — 5,355,885 — 5,355,885 Other — 42,494 — 42,494 Trading account securities: U.S. Treasury 16,594 — — 16,594 States and political subdivisions — 109 — 109 Derivative assets: Interest rate swaps, caps and floors — 29,059 — 29,059 Commodity swaps and options — 6,179 — 6,179 Foreign currency forward contracts 29 — — 29 Derivative liabilities: Interest rate swaps, caps and floors — 29,968 — 29,968 Commodity swaps and options — 5,963 — 5,963 Foreign currency forward contracts 33 — — 33 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. 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 during the reported periods. Six Months Ended Six Months Ended Level 2 Level 3 Level 2 Level 3 Carrying value of impaired loans before allocations $ — $ 21,686 $ — $ 11,183 Specific valuation allowance (allocations) reversals of prior allocations — (561 ) — (2,944 ) Fair value $ — $ 21,125 $ — $ 8,239 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. 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 following table presents foreclosed assets that were remeasured and reported at fair value during the reported periods: Six Months Ended 2017 2016 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ — $ 425 Charge-offs recognized in the allowance for loan losses — (3 ) Fair value $ — $ 422 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 89 $ — Write-downs included in other non-interest expense (16 ) — Fair value $ 73 $ — Financial Instruments Reported at Amortized Cost. The estimated fair values of financial instruments that are reported at amortized cost in our consolidated balance sheets, segregated by the level of the valuation inputs within the fair value hierarchy utilized to measure fair value, were as follows: June 30, 2017 December 31, 2016 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,706,315 $ 3,706,315 $ 4,141,445 $ 4,141,445 Securities held to maturity 1,596,262 1,630,665 2,250,460 2,262,747 Cash surrender value of life insurance policies 178,987 178,987 177,884 177,884 Accrued interest receivable 157,151 157,151 156,714 156,714 Level 3 inputs: Loans, net 12,362,780 12,384,234 11,822,347 11,903,956 Financial liabilities: Level 2 inputs: Deposits 25,613,573 25,608,770 25,811,575 25,812,039 Federal funds purchased and repurchase agreements 924,867 924,867 976,992 976,992 Junior subordinated deferrable interest debentures 136,155 137,115 136,127 137,115 Subordinated notes payable and other borrowings 98,473 102,280 99,990 100,000 Accrued interest payable 2,307 2,307 1,204 1,204

Accounting Standards Updates

Accounting Standards Updates	6 Months Ended
	Jun. 30, 2017
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Updates	Accounting Standards Updates Information about certain recently issued accounting standards updates is presented below. Also refer to Note 21 - Accounting Standards Updates in our 2016 Form 10-K for additional information related to previously issued 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. ASU 2014-09 was originally going to be effective for us on January 1, 2017; however, the FASB recently issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606) – Deferral of the Effective Date" which deferred the effective date of ASU 2014-09 by one year to January 1, 2018. Our revenue is comprised of net interest income on financial assets and financial liabilities, which is explicitly excluded from the scope of ASU 2014-09, and non-interest income. We expect that ASU 2014-09 will require us to change how we recognize certain recurring revenue streams within trust and investment management fees, insurance commissions and fees and other categories of non-interest income; however, we do not expect these changes to have a significant impact on our financial statements. We expect to adopt the standard in the first quarter of 2018 with a cumulative effect adjustment to opening retained earnings, if such adjustment is deemed to be significant. 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 early adoption permitted for interim or annual impairment tests beginning in 2017. ASU 2017-04 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 will be effective for us on January 1, 2018 and is not expected to 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. ASU 2017-08 will be effective for us on January 1, 2019, with early adoption permitted. We are currently evaluating the potential impact of ASU 2017-08 on our financial statements. 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 will be effective for us on January 1, 2018 and is not expected to have a significant impact on our financial statements.

Significant Accounting Polici27

Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2017
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 in this Quarterly Report on Form 10-Q 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. The consolidated financial statements in this Quarterly Report on Form 10-Q have not been audited by an independent registered public accounting firm, but in the opinion of management, reflect all adjustments necessary for a fair presentation of our financial position and results of operations. All such adjustments were of a normal and recurring nature. The consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with the instructions to Form 10-Q adopted by the Securities and Exchange Commission (“SEC”). Accordingly, the financial statements do not include all of the information and footnotes required by accounting principles generally accepted in the United States for complete financial statements and should be read in conjunction with our consolidated financial statements, and notes thereto, for the year ended December 31, 2016 , included in our Annual Report on Form 10-K filed with the SEC on February 3, 2017 (the “ 2016 Form 10-K”). Operating results for the interim periods disclosed herein are not necessarily indicative of the results that may be expected for a full year or any future period.
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.
Reclassification, Policy [Policy Text Block]	Reclassifications and Restatements. Certain items in prior financial statements have been reclassified to conform to the current presentation.
New Accounting Pronouncements, Policy [Policy Text Block]	As more fully described in our 2016 Form 10-K, during the third quarter of 2016, we elected to adopt the provisions of ASU 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” in advance of the required application date of January 1, 2017. Our financial statements for the three and six months ended June 30, 2016 have been restated to reflect the adoption of ASU 2016-09 as of January 1, 2016. As a result, compared to previously reported amounts, our consolidated income statement reflects decreases in income tax expense of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively, and corresponding increases in net income of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively. The increase in net income during the six months ended June 30, 2016 resulted in a $0.01 increase in previously reported diluted earnings per share. Accounting Standards Updates Information about certain recently issued accounting standards updates is presented below. Also refer to Note 21 - Accounting Standards Updates in our 2016 Form 10-K for additional information related to previously issued 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. ASU 2014-09 was originally going to be effective for us on January 1, 2017; however, the FASB recently issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606) – Deferral of the Effective Date" which deferred the effective date of ASU 2014-09 by one year to January 1, 2018. Our revenue is comprised of net interest income on financial assets and financial liabilities, which is explicitly excluded from the scope of ASU 2014-09, and non-interest income. We expect that ASU 2014-09 will require us to change how we recognize certain recurring revenue streams within trust and investment management fees, insurance commissions and fees and other categories of non-interest income; however, we do not expect these changes to have a significant impact on our financial statements. We expect to adopt the standard in the first quarter of 2018 with a cumulative effect adjustment to opening retained earnings, if such adjustment is deemed to be significant. 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 early adoption permitted for interim or annual impairment tests beginning in 2017. ASU 2017-04 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 will be effective for us on January 1, 2018 and is not expected to 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. ASU 2017-08 will be effective for us on January 1, 2019, with early adoption permitted. We are currently evaluating the potential impact of ASU 2017-08 on our financial statements. 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 will be effective for us on January 1, 2018 and is not expected to have a significant impact on our financial statements.

Accounting Standards Updates Ac

Accounting Standards Updates Accounting Standards Updates (Policies)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
New Accounting Pronouncements, Policy [Policy Text Block]	As more fully described in our 2016 Form 10-K, during the third quarter of 2016, we elected to adopt the provisions of ASU 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” in advance of the required application date of January 1, 2017. Our financial statements for the three and six months ended June 30, 2016 have been restated to reflect the adoption of ASU 2016-09 as of January 1, 2016. As a result, compared to previously reported amounts, our consolidated income statement reflects decreases in income tax expense of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively, and corresponding increases in net income of $28 thousand and $65 thousand for the three and six months ended June 30, 2016 , respectively. The increase in net income during the six months ended June 30, 2016 resulted in a $0.01 increase in previously reported diluted earnings per share. Accounting Standards Updates Information about certain recently issued accounting standards updates is presented below. Also refer to Note 21 - Accounting Standards Updates in our 2016 Form 10-K for additional information related to previously issued 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. ASU 2014-09 was originally going to be effective for us on January 1, 2017; however, the FASB recently issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606) – Deferral of the Effective Date" which deferred the effective date of ASU 2014-09 by one year to January 1, 2018. Our revenue is comprised of net interest income on financial assets and financial liabilities, which is explicitly excluded from the scope of ASU 2014-09, and non-interest income. We expect that ASU 2014-09 will require us to change how we recognize certain recurring revenue streams within trust and investment management fees, insurance commissions and fees and other categories of non-interest income; however, we do not expect these changes to have a significant impact on our financial statements. We expect to adopt the standard in the first quarter of 2018 with a cumulative effect adjustment to opening retained earnings, if such adjustment is deemed to be significant. 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 early adoption permitted for interim or annual impairment tests beginning in 2017. ASU 2017-04 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 will be effective for us on January 1, 2018 and is not expected to 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. ASU 2017-08 will be effective for us on January 1, 2019, with early adoption permitted. We are currently evaluating the potential impact of ASU 2017-08 on our financial statements. 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 will be effective for us on January 1, 2018 and is not expected to have a significant impact on our financial statements.

Significant Accounting Polici29

Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2017
Accounting Policies [Abstract]
Additional Cash Flow Information	Additional cash flow information was as follows: Six Months Ended 2017 2016 Cash paid for interest $ 6,666 $ 5,770 Cash paid for income taxes 22,801 25,979 Significant non-cash transactions: Unsettled purchases of securities 80,586 306,564 Loans foreclosed and transferred to other real estate owned and foreclosed assets — 422

Securities (Tables)

Securities (Tables)	6 Months Ended
	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities	A summary of the amortized cost and estimated fair value of securities, excluding trading securities, is presented below. June 30, 2017 December 31, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value Held to Maturity U.S. Treasury $ — $ — $ — $ — $ 249,889 $ 1,762 $ — $ 251,651 Residential mortgage-backed securities 3,992 32 24 4,000 4,511 39 — 4,550 States and political subdivisions 1,590,920 37,288 2,891 1,625,317 1,994,710 16,821 6,335 2,005,196 Other 1,350 — 2 1,348 1,350 — — 1,350 Total $ 1,596,262 $ 37,320 $ 2,917 $ 1,630,665 $ 2,250,460 $ 18,622 $ 6,335 $ 2,262,747 Available for Sale U.S. Treasury $ 4,203,901 $ 27,541 $ 7,188 $ 4,224,254 $ 4,003,692 $ 24,984 $ 8,945 $ 4,019,731 Residential mortgage-backed securities 681,364 25,693 1,436 705,621 756,072 30,388 1,293 785,167 States and political subdivisions 5,734,600 122,028 45,286 5,811,342 5,403,918 50,101 98,134 5,355,885 Other 42,520 — — 42,520 42,494 — — 42,494 Total $ 10,662,385 $ 175,262 $ 53,910 $ 10,783,737 $ 10,206,176 $ 105,473 $ 108,372 $ 10,203,277
Securities, with Unrealized Losses Segregated by Length of Impairment	As of June 30, 2017 , 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 Held to Maturity Residential mortgage-backed securities $ 2,191 $ 24 $ — $ — $ 2,191 $ 24 States and political subdivisions 20,127 83 118,937 2,808 139,064 2,891 Other 1,348 2 — — 1,348 2 Total $ 23,666 $ 109 $ 118,937 $ 2,808 $ 142,603 $ 2,917 Available for Sale U.S. Treasury $ 1,587,812 $ 7,188 $ — $ — $ 1,587,812 $ 7,188 Residential mortgage-backed securities 67,596 1,204 5,866 232 73,462 1,436 States and political subdivisions 1,450,982 38,138 142,507 7,148 1,593,489 45,286 Total $ 3,106,390 $ 46,530 $ 148,373 $ 7,380 $ 3,254,763 $ 53,910
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 June 30, 2017 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 $ 329,237 $ 334,156 $ 57,171 $ 57,528 Due after one year through five years 170,170 177,977 4,818,303 4,845,635 Due after five years through ten years 349,324 357,485 362,030 375,143 Due after ten years 743,539 757,047 4,700,997 4,757,290 Residential mortgage-backed securities 3,992 4,000 681,364 705,621 Equity securities — — 42,520 42,520 Total $ 1,596,262 $ 1,630,665 $ 10,662,385 $ 10,783,737
Sales of Securities Held-to-Maturity	Sales of securities held to maturity were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Proceeds from sales $ — $ — $ — $ 135,610 Amortized cost — — — 131,840 Gross realized gains — — — 3,770 Gross realized losses — — — — Tax (expense) benefit of securities gains/losses — — — (1,319 )
Sales of Securities Available for Sale	Sales of securities available for sale were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Proceeds from sales $ 8,247,439 $ — $ 8,247,439 $ 1,060,196 Gross realized gains — — — 11,133 Gross realized losses (50 ) — (50 ) — Tax (expense) benefit of securities gains/losses 18 — 18 (3,897 )
Premium Amortization and Discount Accretion Included in Income on Securities [Table Text Block]	Premium amortization and discount accretion included in interest income on securities was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Premium amortization $ (24,119 ) $ (22,219 ) $ (48,147 ) $ (44,559 ) Discount accretion 2,105 3,138 4,495 5,753 Net (premium amortization) discount accretion $ (22,014 ) $ (19,081 ) $ (43,652 ) $ (38,806 )
Trading Account Securities, at Estimated Fair Value	Trading account securities, at estimated fair value, were as follows: June 30, December 31, U.S. Treasury $ 17,726 $ 16,594 States and political subdivisions 9,874 109 Total $ 27,600 $ 16,703
Net Gains and Losses on Trading Account Securities	Net gains and losses on trading account securities were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Net gain on sales transactions $ 293 $ 351 $ 604 $ 653 Net mark-to-market gains (losses) (56 ) (2 ) (43 ) (1 ) Net gain (loss) on trading account securities $ 237 $ 349 $ 561 $ 652

Loans (Tables)

Loans (Tables)	6 Months Ended
	Jun. 30, 2017
Receivables [Abstract]
Loans	Loans were as follows: June 30, Percentage of Total December 31, Percentage of Total Commercial and industrial $ 4,604,269 36.8 % $ 4,344,000 36.3 % Energy: Production 1,040,506 8.3 971,767 8.1 Service 183,543 1.5 221,213 1.8 Other 185,563 1.5 193,081 1.7 Total energy 1,409,612 11.3 1,386,061 11.6 Commercial real estate: Commercial mortgages 3,620,885 28.9 3,481,157 29.1 Construction 1,050,837 8.4 1,043,261 8.7 Land 322,130 2.6 311,030 2.6 Total commercial real estate 4,993,852 39.9 4,835,448 40.4 Consumer real estate: Home equity loans 355,744 2.8 345,130 2.9 Home equity lines of credit 283,344 2.3 264,862 2.2 Other 351,985 2.8 326,793 2.7 Total consumer real estate 991,073 7.9 936,785 7.8 Total real estate 5,984,925 47.8 5,772,233 48.2 Consumer and other 513,532 4.1 473,098 3.9 Total loans $ 12,512,338 100.0 % $ 11,975,392 100.0 %
Non-Accrual Loans, Segregated by Class of Loans	Non-accrual loans, segregated by class of loans, were as follows: June 30, December 31, Commercial and industrial $ 21,226 $ 31,475 Energy 55,464 57,571 Commercial real estate: Buildings, land and other 6,916 8,550 Construction — — Consumer real estate 2,543 2,130 Consumer and other 264 425 Total $ 86,413 $ 100,151
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 June 30, 2017 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 $ 24,320 $ 26,149 $ 50,469 $ 4,553,800 $ 4,604,269 $ 10,768 Energy 5,991 6,430 12,421 1,397,191 1,409,612 2,902 Commercial real estate: Buildings, land and other 21,157 4,166 25,323 3,917,692 3,943,015 944 Construction — — — 1,050,837 1,050,837 — Consumer real estate 4,693 2,022 6,715 984,358 991,073 739 Consumer and other 3,508 740 4,248 509,284 513,532 650 Total $ 59,669 $ 39,507 $ 99,176 $ 12,413,162 $ 12,512,338 $ 16,003
Impaired Loans	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 June 30, 2017 Commercial and industrial $ 27,709 $ 14,777 $ 4,040 $ 18,817 $ 1,780 Energy 59,771 36,162 19,215 55,377 350 Commercial real estate: Buildings, land and other 9,729 5,478 — 5,478 — Construction — — — — — Consumer real estate 1,203 1,203 — 1,203 — Consumer and other — — — — — Total $ 98,412 $ 57,620 $ 23,255 $ 80,875 $ 2,130 Unpaid Contractual Recorded Investment Recorded Investment Total Related December 31, 2016 Commercial and industrial $ 40,288 $ 19,862 $ 9,047 $ 28,909 $ 5,436 Energy 60,522 27,759 29,804 57,563 3,750 Commercial real estate: Buildings, land and other 11,369 6,866 — 6,866 — Construction — — — — — Consumer real estate 977 655 — 655 — Consumer and other 32 30 — 30 — Total $ 113,188 $ 55,172 $ 38,851 $ 94,023 $ 9,186
Average Recorded Investment In Impaired Loans	The average recorded investment in impaired loans was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial and industrial $ 21,347 $ 24,866 $ 23,867 $ 24,197 Energy 67,008 78,359 63,860 59,286 Commercial real estate: Buildings, land and other 5,966 20,533 6,266 24,497 Construction — 648 — 622 Consumer real estate 1,376 443 1,135 457 Consumer and other 12 27 18 18 Total $ 95,709 $ 124,876 $ 95,146 $ 109,077
Troubled Debt Restructurings	Troubled debt restructurings during the six months ended June 30, 2017 and June 30, 2016 are set forth in the following table. Six Months Ended Six Months Ended Balance at Restructure Balance at Period-End Balance at Restructure Balance at Period-End Commercial and industrial $ 784 $ 643 $ 510 $ 505 Energy 12,959 12,458 62,546 20,795 Commercial real estate: Buildings, land and other — — 1,456 1,456 Construction — — 243 224 $ 13,743 $ 13,101 $ 64,755 $ 22,980
Weighted Average Risk Grades for All Commercial Loans by Class	The following tables present weighted-average risk grades for all commercial loans by class. June 30, 2017 December 31, 2016 Weighted Loans Weighted Loans Commercial and industrial: Risk grades 1-8 6.00 $ 4,146,261 6.01 $ 3,989,722 Risk grade 9 9.00 222,108 9.00 106,988 Risk grade 10 10.00 78,696 10.00 115,420 Risk grade 11 11.00 135,978 11.00 100,245 Risk grade 12 12.00 19,446 12.00 25,939 Risk grade 13 13.00 1,780 13.00 5,686 Total 6.39 $ 4,604,269 6.35 $ 4,344,000 Energy Risk grades 1-8 6.32 $ 1,024,927 6.34 $ 854,688 Risk grade 9 9.00 43,415 9.00 78,524 Risk grade 10 10.00 115,913 10.00 150,872 Risk grade 11 11.00 169,893 11.00 244,406 Risk grade 12 12.00 55,114 12.00 53,821 Risk grade 13 13.00 350 13.00 3,750 Total 7.49 $ 1,409,612 7.95 $ 1,386,061 Commercial real estate: Buildings, land and other Risk grades 1-8 6.69 $ 3,590,525 6.67 $ 3,463,064 Risk grade 9 9.00 123,492 9.00 109,110 Risk grade 10 10.00 148,718 10.00 145,067 Risk grade 11 11.00 73,364 11.00 66,396 Risk grade 12 12.00 6,916 12.00 8,550 Risk grade 13 13.00 — 13.00 — Total 6.97 $ 3,943,015 6.95 $ 3,792,187 Construction Risk grades 1-8 7.03 $ 1,019,355 6.97 $ 1,023,194 Risk grade 9 9.00 22,632 9.00 15,829 Risk grade 10 10.00 5,116 10.00 2,889 Risk grade 11 11.00 3,734 11.00 1,349 Risk grade 12 12.00 — 12.00 — Risk grade 13 13.00 — 13.00 — Total 7.10 $ 1,050,837 7.01 $ 1,043,261
Net (Charge-Offs)/Recoveries, Segregated by Class of Loans	Net (charge-offs)/recoveries, segregated by class of loans, were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial and industrial $ (4,861 ) $ (3,966 ) $ (7,590 ) $ (5,098 ) Energy (6,236 ) (16,747 ) (10,461 ) (17,758 ) Commercial real estate: Buildings, land and other 460 481 502 542 Construction 3 2 6 9 Consumer real estate 111 74 207 173 Consumer and other (1,401 ) (1,199 ) (2,529 ) (1,702 ) Total $ (11,924 ) $ (21,355 ) $ (19,865 ) $ (23,834 )
Unallocated Portion of Allowance for Loan Losses	The following table presents details of the allowance for loan losses allocated to each portfolio segment as of June 30, 2017 and December 31, 2016 and detailed on the basis of the impairment evaluation methodology we used: Commercial and Industrial Energy Commercial Real Estate Consumer Real Estate Consumer and Other Total June 30, 2017 Historical valuation allowances $ 28,504 $ 32,452 $ 17,975 $ 2,416 $ 5,455 $ 86,802 Specific valuation allowances 1,780 350 — — — 2,130 General valuation allowances 8,418 5,934 4,724 2,032 137 21,245 Macroeconomic valuation allowances 10,204 15,541 10,303 1,087 2,246 39,381 Total $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 Allocated to loans: Individually evaluated $ 1,780 $ 350 $ — $ — $ — $ 2,130 Collectively evaluated 47,126 53,927 33,002 5,535 7,838 147,428 Total $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 December 31, 2016 Historical valuation allowances $ 33,251 $ 34,626 $ 16,976 $ 2,225 $ 4,585 $ 91,663 Specific valuation allowances 5,436 3,750 — — — 9,186 General valuation allowances 6,708 3,769 5,004 1,506 (144 ) 16,843 Macroeconomic valuation allowances 7,520 18,508 8,233 507 585 35,353 Total $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Allocated to loans: Individually evaluated $ 5,436 $ 3,750 $ — $ — $ — $ 9,186 Collectively evaluated 47,479 56,903 30,213 4,238 5,026 143,859 Total $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045
Investment in Loans Related to Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology	Our recorded investment in loans as of June 30, 2017 and December 31, 2016 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 Consumer Consumer Total June 30, 2017 Individually evaluated $ 18,817 $ 55,377 $ 5,478 $ 1,203 $ — $ 80,875 Collectively evaluated 4,585,452 1,354,235 4,988,374 989,870 513,532 12,431,463 Total $ 4,604,269 $ 1,409,612 $ 4,993,852 $ 991,073 $ 513,532 $ 12,512,338 December 31, 2016 Individually evaluated $ 28,909 $ 57,563 $ 6,866 $ 655 $ 30 $ 94,023 Collectively evaluated 4,315,091 1,328,498 4,828,582 936,130 473,068 11,881,369 Total $ 4,344,000 $ 1,386,061 $ 4,835,448 $ 936,785 $ 473,098 $ 11,975,392
Activity in Allowance for Loan Losses by Portfolio Segment	The following table details activity in the allowance for loan losses by portfolio segment for the three and six months ended June 30, 2017 and 2016 . 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 Three months ended: June 30, 2017 Beginning balance $ 45,583 $ 61,793 $ 34,009 $ 4,823 $ 6,848 $ 153,056 Provision for loan losses 8,184 (1,280 ) (1,470 ) 601 2,391 8,426 Charge-offs (5,579 ) (6,317 ) (14 ) (2 ) (3,623 ) (15,535 ) Recoveries 718 81 477 113 2,222 3,611 Net charge-offs (4,861 ) (6,236 ) 463 111 (1,401 ) (11,924 ) Ending balance $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 June 30, 2016 Beginning balance $ 45,084 $ 84,973 $ 23,587 $ 3,786 $ 4,450 $ 161,880 Provision for loan losses 6,460 (1,887 ) 2,993 75 1,548 9,189 Charge-offs (4,857 ) (16,749 ) (19 ) (23 ) (3,252 ) (24,900 ) Recoveries 891 2 502 97 2,053 3,545 Net charge-offs (3,966 ) (16,747 ) 483 74 (1,199 ) (21,355 ) Ending balance $ 47,578 $ 66,339 $ 27,063 $ 3,935 $ 4,799 $ 149,714 Six months ended: June 30, 2017 Beginning balance $ 52,915 $ 60,653 $ 30,213 $ 4,238 $ 5,026 $ 153,045 Provision for loan losses 3,581 4,085 2,281 1,090 5,341 16,378 Charge-offs (9,106 ) (10,595 ) (14 ) (13 ) (7,171 ) (26,899 ) Recoveries 1,516 134 522 220 4,642 7,034 Net charge-offs (7,590 ) (10,461 ) 508 207 (2,529 ) (19,865 ) Ending balance $ 48,906 $ 54,277 $ 33,002 $ 5,535 $ 7,838 $ 149,558 June 30, 2016 Beginning balance $ 42,993 $ 54,696 $ 24,313 $ 4,659 $ 9,198 $ 135,859 Provision for loan losses 9,683 29,401 2,199 (897 ) (2,697 ) 37,689 Charge-offs (6,718 ) (17,760 ) (47 ) (177 ) (5,976 ) (30,678 ) Recoveries 1,620 2 598 350 4,274 6,844 Net charge-offs (5,098 ) (17,758 ) 551 173 (1,702 ) (23,834 ) Ending balance $ 47,578 $ 66,339 $ 27,063 $ 3,935 $ 4,799 $ 149,714

Goodwill and Other Intangible32

Goodwill and Other Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill is presented in the table below. June 30, 2017 December 31, 2016 Goodwill $ 654,952 $ 654,952
Schedule of Other Intangible Assets	Other intangible assets are presented in the table below. Other intangible assets: Core deposits $ 4,636 $ 5,298 Customer relationship 1,188 1,410 Non-compete agreements 56 68 $ 5,880 $ 6,776
Estimated Aggregate Future Amortization Expense for Intangible Assets	The estimated aggregate future amortization expense for intangible assets remaining as of June 30, 2017 is as follows: Remainder of 2017 $ 807 2018 1,424 2019 1,167 2020 918 2021 697 Thereafter 867 $ 5,880

Deposits (Tables)

Deposits (Tables)	6 Months Ended
	Jun. 30, 2017
Banking and Thrift [Abstract]
Schedule of Deposits	Deposits were as follows: June 30, Percentage of Total December 31, Percentage of Total Non-interest-bearing demand deposits: Commercial and individual $ 10,076,475 39.3 % $ 9,670,989 37.5 % Correspondent banks 259,686 1.0 280,751 1.1 Public funds 371,204 1.5 561,629 2.2 Total non-interest-bearing demand deposits 10,707,365 41.8 10,513,369 40.8 Interest-bearing deposits: Private accounts: Savings and interest checking 6,349,462 24.8 6,436,065 24.9 Money market accounts 7,403,054 28.9 7,486,431 29.0 Time accounts of $100,000 or more 432,406 1.7 460,028 1.8 Time accounts under $100,000 327,228 1.3 338,714 1.3 Total private accounts 14,512,150 56.7 14,721,238 57.0 Public funds: Savings and interest checking 299,505 1.2 446,872 1.7 Money market accounts 77,361 0.3 113,669 0.4 Time accounts of $100,000 or more 16,426 — 15,748 0.1 Time accounts under $100,000 766 — 679 — Total public funds 394,058 1.5 576,968 2.2 Total interest-bearing deposits 14,906,208 58.2 15,298,206 59.2 Total deposits $ 25,613,573 100.0 % $ 25,811,575 100.0 %
Additional Information About Corporation's Deposits	The following table presents additional information about our deposits: June 30, December 31, Deposits from foreign sources (primarily Mexico) $ 728,350 $ 776,003 Deposits not covered by deposit insurance 12,708,257 12,889,047

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Financial Instruments with Off-Balance-Sheet Risk	Financial instruments with off-balance-sheet risk were as follows: June 30, December 31, Commitments to extend credit $ 7,616,002 $ 7,476,420 Standby letters of credit 240,612 239,482 Deferred standby letter of credit fees 2,010 2,054

Capital and Regulatory Matters

Capital and Regulatory Matters (Tables)	6 Months Ended
	Jun. 30, 2017
Banking and Thrift [Abstract]
Actual and Required Capital Ratios	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 June 30, 2017 and December 31, 2016 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. See the 2016 Form 10-K for a more detailed discussion of the Basel III Capital Rules. Actual Minimum Capital Required - Basel III Phase-In Schedule Minimum Capital Required - Basel III Fully Phased-In Required to be Considered Well Capitalized Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio Capital Amount Ratio June 30, 2017 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,385,585 12.81 % $ 1,070,444 5.75 % $ 1,303,367 7.00 % $ 1,210,067 6.50 % Frost Bank 2,401,554 12.94 1,067,432 5.75 1,299,400 7.00 1,206,662 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,530,071 13.59 1,349,691 7.25 1,582,296 8.50 1,489,314 8.00 Frost Bank 2,401,554 12.94 1,345,892 7.25 1,577,843 8.50 1,485,123 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,912,629 15.65 1,722,019 9.25 1,954,601 10.50 1,861,642 10.00 Frost Bank 2,551,112 13.74 1,717,173 9.25 1,949,100 10.50 1,856,403 10.00 Leverage Ratio Cullen/Frost 2,530,071 8.61 1,174,957 4.00 1,174,910 4.00 1,468,696 5.00 Frost Bank 2,401,554 8.18 1,173,726 4.00 1,173,679 4.00 1,467,157 5.00 December 31, 2016 Common Equity Tier 1 to Risk-Weighted Assets Cullen/Frost $ 2,239,186 12.52 % $ 916,360 5.125 % $ 1,251,425 7.00 % $ 1,162,213 6.50 % Frost Bank 2,296,480 12.88 913,460 5.125 1,247,463 7.00 1,158,535 6.50 Tier 1 Capital to Risk-Weighted Assets Cullen/Frost 2,383,672 13.33 1,184,563 6.625 1,519,587 8.50 1,430,416 8.00 Frost Bank 2,296,480 12.88 1,180,814 6.625 1,514,776 8.50 1,425,889 8.00 Total Capital to Risk-Weighted Assets Cullen/Frost 2,669,717 14.93 1,542,168 8.625 1,877,137 10.50 1,788,020 10.00 Frost Bank 2,449,525 13.74 1,537,286 8.625 1,871,194 10.50 1,782,361 10.00 Leverage Ratio Cullen/Frost 2,383,672 8.14 1,171,682 4.00 1,171,573 4.00 1,464,602 5.00 Frost Bank 2,296,480 7.85 1,170,249 4.00 1,170,141 4.00 1,462,812 5.00

Derivative Financial Instrume36

Derivative Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding	The notional amounts and estimated fair values of interest rate derivative contracts 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. June 30, 2017 December 31, 2016 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 $ 40,089 $ 312 $ 41,818 $ 368 Loan/lease interest rate swaps – liabilities 14,921 (910 ) 18,812 (1,278 ) Non-hedging interest rate derivatives: Financial institution counterparties: Loan/lease interest rate swaps – assets 211,908 2,357 206,745 2,649 Loan/lease interest rate swaps – liabilities 681,298 (23,602 ) 694,965 (25,466 ) Loan/lease interest rate caps – assets 114,866 687 85,966 575 Customer counterparties: Loan/lease interest rate swaps – assets 681,298 23,602 694,965 25,467 Loan/lease interest rate swaps – liabilities 211,908 (2,357 ) 206,745 (2,649 ) Loan/lease interest rate caps – liabilities 114,866 (687 ) 85,966 (575 )
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 June 30, 2017 were as follows: Weighted-Average Interest Rate Paid Interest Rate Received Interest rate swaps: Fair value hedge loan/lease interest rate swaps 2.34 % 1.17 % Non-hedging interest rate swaps – financial institution counterparties 3.99 % 2.77 % Non-hedging interest rate swaps – customer counterparties 2.77 % 3.99 %
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. June 30, 2017 December 31, 2016 Notional Units Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Oil – assets Barrels 935 $ 4,684 227 $ 206 Oil – liabilities Barrels 178 (153 ) 944 (4,400 ) Natural gas – assets MMBTUs 1,061 109 — — Natural gas – liabilities MMBTUs 938 (85 ) 1,299 (1,357 ) Customer counterparties: Oil – assets Barrels 178 163 944 4,580 Oil – liabilities Barrels 935 (4,466 ) 227 (206 ) Natural gas – assets MMBTUs 938 87 1,299 1,393 Natural gas – liabilities MMBTUs 1,061 (103 ) — —
Notional Amounts and Fair Values of Open Foreign Currency Forward Contracts	The notional amounts and fair values of open foreign currency forward contracts were as follows: June 30, 2017 December 31, 2016 Notional Currency Notional Amount Estimated Fair Value Notional Amount Estimated Fair Value Financial institution counterparties: Forward contracts – assets EUR 497 $ 9 — $ — Forward contracts – assets GBP 217 5 — — Forward contracts – liabilities EUR 1,194 (9 ) 870 (9 ) Forward contracts – liabilities CAD 538 (3 ) 2,214 (21 ) Forward contracts – liabilities GBP 2,434 (20 ) 419 (3 ) Customer counterparties: Forward contracts – assets CAD 536 5 2,205 29 Forward contracts – liabilities EUR 500 (6 ) — — Forward contracts – liabilities GBP 219 (3 ) — —
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: Three Months Ended Six Months Ended 2017 2016 2017 2016 Commercial loan/lease interest rate swaps: Amount of gain (loss) included in interest income on loans $ (198 ) $ (388 ) $ (443 ) $ (726 ) Amount of (gain) loss included in other non-interest expense (2 ) (7 ) (3 ) (7 )
Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives	Amounts included in the consolidated statements of income related to non-hedging interest rate, commodity and foreign currency derivative instruments are presented in the table below. Three Months Ended Six Months Ended 2017 2016 2017 2016 Non-hedging interest rate derivatives: Other non-interest income $ 607 $ 979 $ 977 $ 1,414 Other non-interest expense 2 — 1 — Non-hedging commodity derivatives: Other non-interest income 104 13 156 145 Non-hedging foreign currency derivatives: Other non-interest income 9 8 18 14

Balance Sheet Offsetting (Table

Balance Sheet Offsetting (Tables)	6 Months Ended
	Jun. 30, 2017
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 June 30, 2017 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized June 30, 2017 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,356 $ — $ 3,356 Commodity swaps and options 4,793 — 4,793 Foreign currency forward contracts 14 — 14 Total derivatives 8,163 — 8,163 Resell agreements 9,642 — 9,642 Total $ 17,805 $ — $ 17,805 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 24,512 $ — $ 24,512 Commodity swaps and options 238 — 238 Foreign currency forward contracts 32 — 32 Total derivatives 24,782 — 24,782 Repurchase agreements 919,017 — 919,017 Total $ 943,799 $ — $ 943,799 Information about financial instruments that are eligible for offset in the consolidated balance sheet as of December 31, 2016 is presented in the following tables. Gross Amount Recognized Gross Amount Offset Net Amount Recognized December 31, 2016 Financial assets: Derivatives: Loan/lease interest rate swaps and caps $ 3,592 $ — $ 3,592 Commodity swaps and options 206 — 206 Foreign currency forward contracts — — — Total derivatives 3,798 — 3,798 Resell agreements 9,642 — 9,642 Total $ 13,440 $ — $ 13,440 Financial liabilities: Derivatives: Loan/lease interest rate swaps $ 26,744 $ — $ 26,744 Commodity swaps and options 5,757 — 5,757 Foreign currency forward contracts 33 — 33 Total derivatives 32,534 — 32,534 Repurchase agreements 963,317 — 963,317 Total $ 995,851 $ — $ 995,851
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 June 30, 2017 Financial assets: Derivatives: Counterparty A $ 413 $ (413 ) $ — $ — Counterparty B 1,896 (1,896 ) — — Counterparty C 979 (979 ) — — Counterparty D 1,610 (1,610 ) — — Other counterparties 3,265 (848 ) (2,028 ) 389 Total derivatives 8,163 (5,746 ) (2,028 ) 389 Resell agreements 9,642 — (9,642 ) — Total $ 17,805 $ (5,746 ) $ (11,670 ) $ 389 Financial liabilities: Derivatives: Counterparty A $ 9,644 $ (413 ) $ (9,231 ) $ — Counterparty B 3,737 (1,896 ) (1,841 ) — Counterparty C 1,260 (979 ) (9 ) 272 Counterparty D 8,004 (1,610 ) (6,394 ) — Other counterparties 2,137 (848 ) (1,278 ) 11 Total derivatives 24,782 (5,746 ) (18,753 ) 283 Repurchase agreements 919,017 — (919,017 ) — Total $ 943,799 $ (5,746 ) $ (937,770 ) $ 283 Gross Amounts Not Offset Net Amount Recognized Financial Instruments Collateral Net Amount December 31, 2016 Financial assets: Derivatives: Counterparty A $ 687 $ (687 ) $ — $ — Counterparty B 223 (223 ) — — Counterparty C 158 (158 ) — — Counterparty D 1,820 (1,820 ) — — Other counterparties 910 (677 ) (64 ) 169 Total derivatives 3,798 (3,565 ) (64 ) 169 Resell agreements 9,642 — (9,642 ) — Total $ 13,440 $ (3,565 ) $ (9,706 ) $ 169 Financial liabilities: Derivatives: Counterparty A $ 11,233 $ (687 ) $ (10,026 ) $ 520 Counterparty B 6,867 (223 ) (6,344 ) 300 Counterparty C 4,578 (158 ) (4,415 ) 5 Counterparty D 7,706 (1,820 ) (5,886 ) — Other counterparties 2,150 (677 ) (676 ) 797 Total derivatives 32,534 (3,565 ) (27,347 ) 1,622 Repurchase agreements 963,317 — (963,317 ) — Total $ 995,851 $ (3,565 ) $ (990,664 ) $ 1,622
Remaining Contractual Maturity of the Securities Sold Under Agreement [Table Text Block]	The remaining contractual maturity of repurchase agreements in the consolidated balance sheets as of June 30, 2017 and December 31, 2016 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 June 30, 2017 Repurchase agreements: U.S. Treasury $ 842,269 $ — $ — $ — $ 842,269 Residential mortgage-backed securities 76,748 — — — 76,748 Total borrowings $ 919,017 $ — $ — $ — $ 919,017 Gross amount of recognized liabilities for repurchase agreements $ 919,017 Amounts related to agreements not included in offsetting disclosures above $ — December 31, 2016 Repurchase agreements: U.S. Treasury $ 841,475 $ — $ — $ — $ 841,475 Residential mortgage-backed securities 121,842 — — — 121,842 Total borrowings $ 963,317 $ — $ — $ — $ 963,317 Gross amount of recognized liabilities for repurchase agreements $ 963,317 Amounts related to agreements not included in offsetting disclosures above $ —

Earnings Per Common Share (Tabl

Earnings Per Common Share (Tables)	6 Months Ended
	Jun. 30, 2017
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. Three Months Ended Six Months Ended 2017 2016 2017 2016 Net income $ 85,553 $ 71,507 $ 170,494 $ 140,323 Less: Preferred stock dividends 2,015 2,015 4,031 4,031 Net income available to common shareholders 83,538 69,492 166,463 136,292 Less: Earnings allocated to participating securities 436 252 871 487 Net earnings allocated to common stock $ 83,102 $ 69,240 $ 165,592 $ 135,805 Distributed earnings allocated to common stock $ 36,545 $ 33,463 $ 71,020 $ 66,285 Undistributed earnings allocated to common stock 46,557 35,777 94,572 69,520 Net earnings allocated to common stock $ 83,102 $ 69,240 $ 165,592 $ 135,805 Weighted-average shares outstanding for basic earnings per common share 64,061,264 61,959,411 63,900,620 61,944,438 Dilutive effect of stock compensation 974,067 497,532 988,198 267,632 Weighted-average shares outstanding for diluted earnings per common share 65,035,331 62,456,943 64,888,818 62,212,070

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Activity in Corporation's Active Stock Plans	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 Balance, 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 — — — — — — Exercised/vested (6,098 ) 62.29 (1,730 ) 76.07 — — (744,247 ) 59.32 Forfeited/expired — — (870 ) 76.07 — — (33,492 ) 69.35 Balance, June 30, 2017 53,008 $ 64.87 254,250 $ 73.40 43,860 $ 69.70 3,311,289 $ 63.36
Shares Issued in Connection with Stock Compensation Awards	Shares issued in connection with stock compensation awards along with other related information were as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 New shares issued from available authorized shares 310,021 — 593,363 — Issued from available treasury stock — 65,200 158,712 67,075 Total 310,021 65,200 752,075 67,075 Proceeds from stock option exercises $ 19,402 $ 3,490 $ 44,149 $ 3,586
Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]	Three Months Ended Six Months Ended 2017 2016 2017 2016 Stock options $ 1,573 $ 2,117 $ 3,360 $ 4,242 Non-vested stock awards/stock units 901 358 1,934 715 Director deferred stock units 519 520 519 520 Performance stock units 195 — 478 — Total $ 3,188 $ 2,995 $ 6,291 $ 5,477 Income tax benefit $ 1,116 $ 1,048 $ 2,202 $ 1,917
Unrecognized Stock-Based Compensation Expense	Stock options $ 8,694 Non-vested stock awards/stock units 8,413 Performance stock units 2,579 Total $ 19,686

Defined Benefit Plans (Tables)

Defined Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Net Periodic Cost (Benefit)	Three Months Ended Six Months Ended 2017 2016 2017 2016 Expected return on plan assets, net of expenses $ (2,780 ) $ (2,889 ) $ (5,559 ) $ (5,779 ) Interest cost on projected benefit obligation 1,548 1,749 3,095 3,498 Net amortization and deferral 1,358 1,553 2,715 3,106 SERP settlement costs — 187 — 187 Net periodic expense (benefit) $ 126 $ 600 $ 251 $ 1,012

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Tax Expense	Income tax expense was as follows: Three Months Ended Six Months Ended 2017 2016 2017 2016 Current income tax expense $ 13,710 $ 13,616 $ 29,412 $ 27,403 Deferred income tax expense (benefit) 128 (5,238 ) (4,173 ) (9,633 ) Income tax expense, as reported $ 13,838 $ 8,378 $ 25,239 $ 17,770 Effective tax rate 13.9 % 10.5 % 12.9 % 11.2 %

Other Comprehensive Income (L42

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Component of Other Comprehensive Income (Loss)	The before and after tax amounts allocated to each component of other comprehensive income (loss) are presented in the following table. Reclassification adjustments related to securities available for sale are included in net gain (loss) on securities transactions in the accompanying consolidated statements of income. Reclassification adjustments related to defined-benefit post-retirement benefit plans are included in the computation of net periodic pension expense (see Note 13 – Defined Benefit Plans). Three Months Ended Three Months Ended Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 90,390 $ 31,636 $ 58,754 $ 165,288 $ 57,851 $ 107,437 Change in net unrealized gain on securities transferred to held to maturity (3,860 ) (1,351 ) (2,509 ) (9,185 ) (3,215 ) (5,970 ) Reclassification adjustment for net (gains) losses included in net income 50 18 32 — — — Total securities available for sale and transferred securities 86,580 30,303 56,277 156,103 54,636 101,467 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss — — — (862 ) (302 ) (560 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 1,358 475 883 1,740 609 1,131 Total defined-benefit post-retirement benefit plans 1,358 475 883 878 307 571 Total other comprehensive income (loss) $ 87,938 $ 30,778 $ 57,160 $ 156,981 $ 54,943 $ 102,038 Six Months Ended Six Months Ended Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Before Tax Amount Tax Expense, (Benefit) Net of Tax Amount Securities available for sale and transferred securities: Change in net unrealized gain/loss during the period $ 124,201 $ 43,470 $ 80,731 $ 287,506 $ 100,627 $ 186,879 Change in net unrealized gain on securities transferred to held to maturity (10,146 ) (3,551 ) (6,595 ) (17,351 ) (6,073 ) (11,278 ) Reclassification adjustment for net (gains) losses included in net income 50 18 32 (14,903 ) (5,216 ) (9,687 ) Total securities available for sale and transferred securities 114,105 39,937 74,168 255,252 89,338 165,914 Defined-benefit post-retirement benefit plans: Change in the net actuarial gain/loss — — — (862 ) (302 ) (560 ) Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) 2,715 950 1,765 3,293 1,153 2,140 Total defined-benefit post-retirement benefit plans 2,715 950 1,765 2,431 851 1,580 Total other comprehensive income (loss) $ 116,820 $ 40,887 $ 75,933 $ 257,683 $ 90,189 $ 167,494
Schedule of Accumulated Other Comprehensive Income, Net of Tax	Activity in accumulated other comprehensive income (loss), net of tax, was as follows: Securities Available For Sale Defined Benefit Plans Accumulated Other Comprehensive Income Balance January 1, 2017 $ 16,153 $ (40,776 ) $ (24,623 ) Other comprehensive income (loss) before reclassifications 74,136 — 74,136 Amounts reclassified from accumulated other comprehensive income (loss) 32 1,765 1,797 Net other comprehensive income (loss) during period 74,168 1,765 75,933 Balance at June 30, 2017 $ 90,321 $ (39,011 ) $ 51,310 Balance January 1, 2016 $ 160,611 $ (46,748 ) $ 113,863 Other comprehensive income (loss) before reclassifications 175,601 (560 ) 175,041 Amounts reclassified from accumulated other comprehensive income (loss) (9,687 ) 2,140 (7,547 ) Net other comprehensive income (loss) during period 165,914 1,580 167,494 Balance at June 30, 2016 $ 326,525 $ (45,168 ) $ 281,357

Operating Segments (Tables)

Operating Segments (Tables)	6 Months Ended
	Jun. 30, 2017
Segment Reporting [Abstract]
Summary of Operating Results by Segment	Summarized operating results by segment were as follows: Banking Frost Wealth Advisors Non-Banks Consolidated Revenues from (expenses to) external customers: Three months ended: June 30, 2017 $ 261,250 $ 36,712 $ (2,094 ) $ 295,868 June 30, 2016 237,444 32,225 (1,150 ) 268,519 Six months ended: June 30, 2017 $ 520,161 $ 71,300 $ (3,384 ) $ 588,077 June 30, 2016 492,717 63,948 (2,279 ) 554,386 Net income (loss): Three months ended: June 30, 2017 $ 81,529 $ 6,279 $ (2,255 ) $ 85,553 June 30, 2016 68,223 4,860 (1,576 ) 71,507 Six months ended: June 30, 2017 $ 162,398 $ 11,573 $ (3,477 ) $ 170,494 June 30, 2016 134,190 9,012 (2,879 ) 140,323

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis	The table below summarizes financial assets and financial liabilities measured at fair value on a recurring basis as of June 30, 2017 and December 31, 2016 , segregated by the level of the valuation inputs within the fair value hierarchy of ASC Topic 820 utilized to measure fair value. Level 1 Level 2 Level 3 Total Fair June 30, 2017 Securities available for sale: U.S. Treasury $ 4,224,254 $ — $ — $ 4,224,254 Residential mortgage-backed securities — 705,621 — 705,621 States and political subdivisions — 5,811,342 — 5,811,342 Other — 42,520 — 42,520 Trading account securities: U.S. Treasury 17,726 — — 17,726 States and political subdivisions — 9,874 — 9,874 Derivative assets: Interest rate swaps, caps and floors — 26,958 — 26,958 Commodity swaps and options — 5,043 — 5,043 Foreign currency forward contracts 19 — — 19 Derivative liabilities: Interest rate swaps, caps and floors — 27,556 — 27,556 Commodity swaps and options — 4,807 — 4,807 Foreign currency forward contracts 41 — — 41 December 31, 2016 Securities available for sale: U.S. Treasury $ 4,019,731 $ — $ — $ 4,019,731 Residential mortgage-backed securities — 785,167 — 785,167 States and political subdivisions — 5,355,885 — 5,355,885 Other — 42,494 — 42,494 Trading account securities: U.S. Treasury 16,594 — — 16,594 States and political subdivisions — 109 — 109 Derivative assets: Interest rate swaps, caps and floors — 29,059 — 29,059 Commodity swaps and options — 6,179 — 6,179 Foreign currency forward contracts 29 — — 29 Derivative liabilities: Interest rate swaps, caps and floors — 29,968 — 29,968 Commodity swaps and options — 5,963 — 5,963 Foreign currency forward contracts 33 — — 33
Impaired Loans Remeasured And Reported At Fair Value Specific Valuation Allowance Allocation Method Of Underlying Collateral [Table Text Block]	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 during the reported periods. Six Months Ended Six Months Ended Level 2 Level 3 Level 2 Level 3 Carrying value of impaired loans before allocations $ — $ 21,686 $ — $ 11,183 Specific valuation allowance (allocations) reversals of prior allocations — (561 ) — (2,944 ) Fair value $ — $ 21,125 $ — $ 8,239
Foreclosed Assets Remeasured and Reported at Fair Value	The following table presents foreclosed assets that were remeasured and reported at fair value during the reported periods: Six Months Ended 2017 2016 Foreclosed assets remeasured at initial recognition: Carrying value of foreclosed assets prior to remeasurement $ — $ 425 Charge-offs recognized in the allowance for loan losses — (3 ) Fair value $ — $ 422 Foreclosed assets remeasured subsequent to initial recognition: Carrying value of foreclosed assets prior to remeasurement $ 89 $ — Write-downs included in other non-interest expense (16 ) — Fair value $ 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 the valuation inputs within the fair value hierarchy utilized to measure fair value, were as follows: June 30, 2017 December 31, 2016 Carrying Amount Estimated Fair Value Carrying Amount Estimated Fair Value Financial assets: Level 2 inputs: Cash and cash equivalents $ 3,706,315 $ 3,706,315 $ 4,141,445 $ 4,141,445 Securities held to maturity 1,596,262 1,630,665 2,250,460 2,262,747 Cash surrender value of life insurance policies 178,987 178,987 177,884 177,884 Accrued interest receivable 157,151 157,151 156,714 156,714 Level 3 inputs: Loans, net 12,362,780 12,384,234 11,822,347 11,903,956 Financial liabilities: Level 2 inputs: Deposits 25,613,573 25,608,770 25,811,575 25,812,039 Federal funds purchased and repurchase agreements 924,867 924,867 976,992 976,992 Junior subordinated deferrable interest debentures 136,155 137,115 136,127 137,115 Subordinated notes payable and other borrowings 98,473 102,280 99,990 100,000 Accrued interest payable 2,307 2,307 1,204 1,204

Significant Accounting Polici45

Significant Accounting Policies - Additional Cash Flow Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Accounting Policies [Abstract]
Cash paid for interest	$ 6,666	$ 5,770
Cash paid for income taxes	22,801	25,979
Unsettled purchases of securities	80,586	306,564
Loans foreclosed and transferred to other real estate owned and foreclosed assets	$ 0	$ 422

Significant Accounting Polici46

Significant Accounting Policies Significant Accounting Policies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income Tax Expense (Benefit)	$ (13,838)	$ (8,378)	$ (25,239)	$ (17,770)
Net Income (Loss) Available to Common Stockholders, Basic	$ 83,538	$ 69,492	$ 166,463	$ 136,292
Earnings Per Share, Diluted	$ 1.29	$ 1.11	$ 2.57	$ 2.19
Adjustments for New Accounting Pronouncement [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income Tax Expense (Benefit)		$ 28		$ 65
Net Income (Loss) Available to Common Stockholders, Basic		$ 28		$ 65
Earnings Per Share, Diluted				$ 0.01

Securities - Additional Informa

Securities - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2012
Schedule Of Marketable Securities [Line Items]
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas	98.10%
Percentage of municipal bond portfolio issued by political subdivision or agencies within the state of Texas guaranteed by Texas permanent school fund	67.30%
Securities Pledged as Collateral	$ 3,300,000	$ 3,900,000
Available for Sale, Estimated Fair Value	10,783,737	$ 10,203,277
Available for sale securities reclassified to held to maturity, unrealized gain			$ 165,700
Available for sale securities reclassified to held to maturity, unrealized gain net of tax			107,700
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income Pre Tax	17,600
Net unamortized unrealized gain on transferred securities included in accumulated other comprehensive income, net of tax	$ 11,400
Reclassified To Held To Maturity [Member]
Schedule Of Marketable Securities [Line Items]
Available for Sale, Estimated Fair Value			$ 2,300,000

Securities - Amortized Cost and

Securities - Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	$ 1,596,262	$ 2,250,460
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	37,320	18,622
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2,917	6,335
Held to Maturity, Estimated Fair Value	1,630,665	2,262,747
Available for Sale, Amortized Cost	10,662,385	10,206,176
Available for Sale, Gross Unrealized Gains	175,262	105,473
Available for Sale, Gross Unrealized Losses	53,910	108,372
Available for Sale, Estimated Fair Value	10,783,737	10,203,277
U.S. Treasury [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	0	249,889
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	1,762
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held to Maturity, Estimated Fair Value	0	251,651
Available for Sale, Amortized Cost	4,203,901	4,003,692
Available for Sale, Gross Unrealized Gains	27,541	24,984
Available for Sale, Gross Unrealized Losses	7,188	8,945
Available for Sale, Estimated Fair Value	4,224,254	4,019,731
Residential mortgage-backed securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	3,992	4,511
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	32	39
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	24	0
Held to Maturity, Estimated Fair Value	4,000	4,550
Available for Sale, Amortized Cost	681,364	756,072
Available for Sale, Gross Unrealized Gains	25,693	30,388
Available for Sale, Gross Unrealized Losses	1,436	1,293
Available for Sale, Estimated Fair Value	705,621	785,167
States and political subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,590,920	1,994,710
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	37,288	16,821
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2,891	6,335
Held to Maturity, Estimated Fair Value	1,625,317	2,005,196
Available for Sale, Amortized Cost	5,734,600	5,403,918
Available for Sale, Gross Unrealized Gains	122,028	50,101
Available for Sale, Gross Unrealized Losses	45,286	98,134
Available for Sale, Estimated Fair Value	5,811,342	5,355,885
Other [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Amortized Cost	1,350	1,350
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2	0
Held to Maturity, Estimated Fair Value	1,348	1,350
Available for Sale, Amortized Cost	42,520	42,494
Available for Sale, Gross Unrealized Gains	0	0
Available for Sale, Gross Unrealized Losses	0	0
Available for Sale, Estimated Fair Value	$ 42,520	$ 42,494

Securities - Securities, with U

Securities - Securities, with Unrealized Losses Segregated by Length of Impairment (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	$ 23,666
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	109
Held to Maturity, More than 12 Months, Estimated Fair Value	118,937
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,808
Held to Maturity, Total Estimated Fair Value	142,603
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2,917	$ 6,335
Available for Sale, Less than 12 Months, Estimated Fair Value	3,106,390
Available for Sale, Less than 12 Months, Unrealized Losses	46,530
Available for Sale, More than 12 Months, Estimated Fair Value	148,373
Available for Sale, More than 12 Months, Unrealized Losses	7,380
Available for Sale, Total Estimated Fair Value	3,254,763
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	53,910	108,372
Residential mortgage-backed securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	2,191
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	24
Held to Maturity, More than 12 Months, Estimated Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held to Maturity, Total Estimated Fair Value	2,191
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	24	0
Available for Sale, Less than 12 Months, Estimated Fair Value	67,596
Available for Sale, Less than 12 Months, Unrealized Losses	1,204
Available for Sale, More than 12 Months, Estimated Fair Value	5,866
Available for Sale, More than 12 Months, Unrealized Losses	232
Available for Sale, Total Estimated Fair Value	73,462
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,436	1,293
States and political subdivisions [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	20,127
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	83
Held to Maturity, More than 12 Months, Estimated Fair Value	118,937
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,808
Held to Maturity, Total Estimated Fair Value	139,064
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2,891	6,335
Available for Sale, Less than 12 Months, Estimated Fair Value	1,450,982
Available for Sale, Less than 12 Months, Unrealized Losses	38,138
Available for Sale, More than 12 Months, Estimated Fair Value	142,507
Available for Sale, More than 12 Months, Unrealized Losses	7,148
Available for Sale, Total Estimated Fair Value	1,593,489
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	45,286	98,134
Other Investments [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held to Maturity, Less than 12 Months, Estimated Fair Value	1,348
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2
Held to Maturity, More than 12 Months, Estimated Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held to Maturity, Total Estimated Fair Value	1,348
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	2	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
US Treasury Securities [Member]
Schedule of Available-for-Sale Securities [Line Items]
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Available for Sale, Less than 12 Months, Estimated Fair Value	1,587,812
Available for Sale, Less than 12 Months, Unrealized Losses	7,188
Available for Sale, More than 12 Months, Estimated Fair Value	0
Available for Sale, More than 12 Months, Unrealized Losses	0
Available for Sale, Total Estimated Fair Value	1,587,812
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 7,188	$ 8,945

Securities - Amortized Cost a50

Securities - Amortized Cost and Estimated Fair Value of Securities, Excluding Trading Securities, Presented by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Held to Maturity, Due in one year or less, Amortized Cost	$ 329,237
Held to Maturity, Due after one year through five years, Amortized Cost	170,170
Held to Maturity, Due after five years through ten years, Amortized Cost	349,324
Held to Maturity, Due after ten years, Amortized Cost	743,539
Held to Maturity, Residential mortgage-backed securities, Amortized Cost	3,992
Held-to-maturity Securities, Equity Securities, Amortized cost	0
Held to Maturity, Amortized Cost	1,596,262	$ 2,250,460
Held to Maturity, Due in one year or less, Estimated Fair Value	334,156
Held to Maturity, Due after one year through five years, Estimated Fair Value	177,977
Held to Maturity, Due after five years through ten years, Estimated Fair Value	357,485
Held to Maturity, Due after ten years, Estimated Fair Value	757,047
Held to Maturity, Residential mortgage-backed securities, Estimated Fair Value	4,000
Held-to-maturity Securities, Equity Securities, Fair Value	0
Held to Maturity, Estimated Fair Value	1,630,665	2,262,747
Available-for-sale Securities, Due in one year or less, Amortized Cost	57,171
Available for Sale, Due after one year through five years, Amortized Cost	4,818,303
Available for Sale, Due after five years through ten years, Amortized Cost	362,030
Available for Sale, Due after ten years, Amortized Cost	4,700,997
Available for Sale, Residential mortgage-backed securities, Amortized Cost	681,364
Available-for-sale Securities, Equity Securities, Amortized cost	42,520
Available for Sale, Amortized Cost	10,662,385	10,206,176
Available for Sale, Due in one year or less, Estimated Fair Value	57,528
Available for Sale, Due after one year through five years, Estimated Fair Value	4,845,635
Available for Sale, Due after five years through ten years, Estimated Fair Value	375,143
Available for Sale, Due after ten years, Estimated Fair Value	4,757,290
Available for Sale, Residential mortgage-backed securities, Estimated Fair Value	705,621
Available For Sale Securities Equity Securities Fair Value	42,520
Available for Sale, Estimated Fair Value	$ 10,783,737	$ 10,203,277

Securities Securities - Sales o

Securities Securities - Sales of Securities Held to Maturity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investment, Debt and Equity Securities [Abstract]
Proceeds from Sale of Held to Maturity Securities	$ 0	$ 0	$ 0	$ 135,610
Held to maturity securities sold amortized cost	0	0	0	131,840
Held-to-maturity Securities, Sold Security, Realized Gain (Loss)	0	0	0	3,770
Held to maturity securities sold security gross realized loss	0	0	0	0
Tax (expense) benefit of held to maturity securities gains/losses	$ 0	$ 0	$ 0	$ (1,319)

Securities - Sales of Securitie

Securities - Sales of Securities Available for Sale (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 8,247,439	$ 0	$ 8,247,439	$ 1,060,196
Gross realized gains	0	0	0	11,133
Gross realized losses	(50)	0	(50)	0
Tax (expense)benefit of securities gains/losses	$ 18	$ 0	$ 18	$ (3,897)

Securities Securities - Premium

Securities Securities - Premium Amortization and Discount Accretion Included in Income on Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Premium amortization	$ (24,119)	$ (22,219)	$ (48,147)	$ (44,559)
Discount accretion	2,105	3,138	4,495	5,753
Net (premium amortization) discount accretion	$ (22,014)	$ (19,081)	$ (43,652)	$ (38,806)

Securities - Trading Account Se

Securities - Trading Account Securities, at Estimated Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$ 27,600	$ 16,703
U.S. Treasury [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	17,726	16,594
States and political subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading account securities	$ 9,874	$ 109

Securities - Net Gains and Loss

Securities - Net Gains and Losses on Trading Account Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 293	$ 351	$ 604	$ 653
Net mark-to-market gains (losses)	(56)	(2)	(43)	(1)
Net gain (loss) on trading account securities	$ 237	$ 349	$ 561	$ 652

Loans - Additional Information

Loans - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017USD ($)Item	Jun. 30, 2016USD ($)	Jun. 30, 2017USD ($)Item	Jun. 30, 2016USD ($)	May 31, 2017	Dec. 31, 2016
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%
Percentage of total energy loans to total loans	11.30%		11.30%			11.60%
Troubled debt restructurings			$ 13,101	$ 22,980
Number Of Loans Restructured During The Last Year In Excess of 90 Days Past Due | Item	0		0
Minimum Number Of Days To Be Considered Past Due			90 days
Amount charged off of previously restructured loans			$ 10,000	9,500
Proceeds from sale of loans			0	30,470
Texas Leading Index economic condition indicator					124.7	123.1
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings			12,458	20,795
Non-Accrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings			11,400
Additional interest that would have been recognized on non-accrual loans, net of tax	$ 798	$ 936	1,649	$ 1,780
Commitments to Extend Credit [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	1,100,000		1,100,000
Standby Letters of Credit [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unfunded balances	$ 42,900		$ 42,900

Loans - Loans (Detail)

Loans - Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 4,604,269	$ 4,344,000
Energy:	1,409,612	1,386,061
Commercial mortgages	3,620,885	3,481,157
Construction	1,050,837	1,043,261
Land	322,130	311,030
Total commercial real estate	4,993,852	4,835,448
Home equity loans	355,744	345,130
Home equity lines of credit	283,344	264,862
Other	351,985	326,793
Total consumer real estate	991,073	936,785
Total real estate	5,984,925	5,772,233
Consumer and other	513,532	473,098
Total loans	$ 12,512,338	$ 11,975,392
Total commercial and industrial percentage of total loans	36.80%	36.30%
Percentage of total energy loans to total loans	11.30%	11.60%
Commercial mortgages percentage of total loans	28.90%	29.10%
Construction percentage of total loans	8.40%	8.70%
Land percentage of total loans	2.60%	2.60%
Total commercial real estate percentage of total loans	39.90%	40.40%
Home equity loans percentage of total loans	2.80%	2.90%
Home equity lines of credit percentage of total loans	2.30%	2.20%
Other percentage of total loans	2.80%	2.70%
Total consumer real estate percentage of total loans	7.90%	7.80%
Total real estate percentage of total loans	47.80%	48.20%
Total consumer and other percentage of total loans	4.10%	3.90%
Total loans percentage	100.00%	100.00%
Energy Production [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Energy:	$ 1,040,506	$ 971,767
Percentage of energy production loans to total loans	8.30%	8.10%
Energy Service [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Energy:	$ 183,543	$ 221,213
Percentage of energy service loans to total loans	1.50%	1.80%
Energy Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Energy:	$ 185,563	$ 193,081
Percentage of other energy loans to total loans	1.50%	1.70%

Loans - Non-Accrual Loans, Segr

Loans - Non-Accrual Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 86,413	$ 100,151
Commercial Portfolio Segment [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	21,226	31,475
Commercial and industrial, Energy [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	55,464	57,571
Commercial real estate, Buildings, land and other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	6,916	8,550
Construction Loans [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	0	0
Consumer Real Estate [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	2,543	2,130
Consumer and Other [Member]
Non Accrual Loans Segregated By Class Of Loans [Line Items]
Non-accrual loans	$ 264	$ 425

Loans - Age Analysis of Past Du

Loans - Age Analysis of Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 99,176
Current Loans	12,413,162
Total loans	12,512,338	$ 11,975,392
Accruing Loans 90 or More Days Past Due	16,003
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	50,469
Current Loans	4,553,800
Total loans	4,604,269
Accruing Loans 90 or More Days Past Due	10,768
Commercial and industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	12,421
Current Loans	1,397,191
Total loans	1,409,612
Accruing Loans 90 or More Days Past Due	2,902
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	25,323
Current Loans	3,917,692
Total loans	3,943,015
Accruing Loans 90 or More Days Past Due	944
Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	0
Current Loans	1,050,837
Total loans	1,050,837
Accruing Loans 90 or More Days Past Due	0
Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	6,715
Current Loans	984,358
Total loans	991,073
Accruing Loans 90 or More Days Past Due	739
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,248
Current Loans	509,284
Total loans	513,532
Accruing Loans 90 or More Days Past Due	650
Financing Receivables, 30 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	59,669
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	24,320
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial and industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	5,991
Financing Receivables, 30 to 89 Days Past Due [Member] | Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	21,157
Financing Receivables, 30 to 89 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	0
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,693
Financing Receivables, 30 to 89 Days Past Due [Member] | Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	3,508
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	39,507
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	26,149
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial and industrial, Energy [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	6,430
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	4,166
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	0
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	2,022
Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due Loans	$ 740

Loans - Impaired Loans (Detail)

Loans - Impaired Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 98,412	$ 113,188
Recorded Investment With No Allowance	57,620	55,172
Recorded Investment With Allowance	23,255	38,851
Total Recorded Investment	80,875	94,023
Related Allowance	2,130	9,186
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	27,709	40,288
Recorded Investment With No Allowance	14,777	19,862
Recorded Investment With Allowance	4,040	9,047
Total Recorded Investment	18,817	28,909
Related Allowance	1,780	5,436
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	59,771	60,522
Recorded Investment With No Allowance	36,162	27,759
Recorded Investment With Allowance	19,215	29,804
Total Recorded Investment	55,377	57,563
Related Allowance	350	3,750
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	9,729	11,369
Recorded Investment With No Allowance	5,478	6,866
Recorded Investment With Allowance	0	0
Total Recorded Investment	5,478	6,866
Related Allowance	0	0
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	0
Recorded Investment With No Allowance	0	0
Recorded Investment With Allowance	0	0
Total Recorded Investment	0	0
Related Allowance	0	0
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	1,203	977
Recorded Investment With No Allowance	1,203	655
Recorded Investment With Allowance	0	0
Total Recorded Investment	1,203	655
Related Allowance	0	0
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	0	32
Recorded Investment With No Allowance	0	30
Recorded Investment With Allowance	0	0
Total Recorded Investment	0	30
Related Allowance	$ 0	$ 0

Loans - Average Recorded Invest

Loans - Average Recorded Investment In Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 95,709	$ 124,876	$ 95,146	$ 109,077
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	21,347	24,866	23,867	24,197
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	67,008	78,359	63,860	59,286
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	5,966	20,533	6,266	24,497
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	0	648	0	622
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	1,376	443	1,135	457
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment	$ 12	$ 27	$ 18	$ 18

Loans - Troubled Debt Restructu

Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 13,743	$ 64,755
Balance at period end	13,101	22,980
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	784	510
Balance at period end	643	505
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	12,959	62,546
Balance at period end	12,458	20,795
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	0	1,456
Balance at period end	0	1,456
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	0	243
Balance at period end	$ 0	$ 224

Loans - Weighted Average Risk G

Loans - Weighted Average Risk Grades for All Commercial Loans by Class (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017USD ($)Grade	Dec. 31, 2016USD ($)Grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,604,269	$ 4,344,000
Loans	4,993,852	4,835,448
Loans	$ 1,050,837	$ 1,043,261
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.39	6.35
Loans	$ 4,604,269	$ 4,344,000
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.49	7.95
Loans	$ 1,409,612	$ 1,386,061
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.97	6.95
Loans	$ 3,943,015	$ 3,792,187
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.10	7.01
Loans	$ 1,050,837	$ 1,043,261
Risk grades 1-8 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6	6.01
Loans	$ 4,146,261	$ 3,989,722
Risk grades 1-8 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.32	6.34
Loans	$ 1,024,927	$ 854,688
Risk grades 1-8 [Member] | Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	6.69	6.67
Loans	$ 3,590,525	$ 3,463,064
Risk grades 1-8 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	7.03	6.97
Loans	$ 1,019,355	$ 1,023,194
Risk grade 9 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans	$ 222,108	$ 106,988
Risk grade 9 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans	$ 43,415	$ 78,524
Risk grade 9 [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	$ 123,492	$ 109,110
Risk grade 9 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	9	9
Loans	$ 22,632	$ 15,829
Risk grade 10 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans	$ 78,696	$ 115,420
Risk grade 10 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans	$ 115,913	$ 150,872
Risk grade 10 [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	$ 148,718	$ 145,067
Risk grade 10 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	10	10
Loans	$ 5,116	$ 2,889
Risk grade 11 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans	$ 135,978	$ 100,245
Risk grade 11 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans	$ 169,893	$ 244,406
Risk grade 11 [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	$ 73,364	$ 66,396
Risk grade 11 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	11	11
Loans	$ 3,734	$ 1,349
Risk grade 12 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans	$ 19,446	$ 25,939
Risk grade 12 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans	$ 55,114	$ 53,821
Risk grade 12 [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	$ 6,916	$ 8,550
Risk grade 12 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	12	12
Loans	$ 0	$ 0
Risk grade 13 [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans	$ 1,780	$ 5,686
Risk grade 13 [Member] | Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans	$ 350	$ 3,750
Risk grade 13 [Member] | Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans	$ 0	$ 0
Risk grade 13 [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted Average Risk Grade | Grade	13	13
Loans	$ 0	$ 0

Loans - Net (Charge-Offs)_Recov

Loans - Net (Charge-Offs)/Recoveries, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	$ (11,924)	$ (21,355)	$ (19,865)	$ (23,834)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	(4,861)	(3,966)	(7,590)	(5,098)
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	(6,236)	(16,747)	(10,461)	(17,758)
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	460	481	502	542
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	3	2	6	9
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	111	74	207	173
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	$ (1,401)	$ (1,199)	$ (2,529)	$ (1,702)

Loans - Unallocated Portion of

Loans - Unallocated Portion of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 149,558	$ 153,056	$ 153,045	$ 149,714	$ 161,880	$ 135,859
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	2,130		9,186
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	147,428		143,859
Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	86,802		91,663
Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,130		9,186
General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	21,245		16,843
Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	39,381		35,353
Commercial Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	48,906	45,583	52,915	47,578	45,084	42,993
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	1,780		5,436
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	47,126		47,479
Commercial Portfolio Segment [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	28,504		33,251
Commercial Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,780		5,436
Commercial Portfolio Segment [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	8,418		6,708
Commercial Portfolio Segment [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	10,204		7,520
Commercial and industrial, Energy [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	54,277	61,793	60,653	66,339	84,973	54,696
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	350		3,750
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	53,927		56,903
Commercial and industrial, Energy [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	32,452		34,626
Commercial and industrial, Energy [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	350		3,750
Commercial and industrial, Energy [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,934		3,769
Commercial and industrial, Energy [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	15,541		18,508
Commercial Real Estate Portfolio Segment [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	33,002	34,009	30,213	27,063	23,587	24,313
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	33,002		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	17,975		16,976
Commercial Real Estate Portfolio Segment [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0		0
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	4,724		5,004
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	10,303		8,233
Consumer Real Estate [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,535	4,823	4,238	3,935	3,786	4,659
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	5,535		4,238
Consumer Real Estate [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,416		2,225
Consumer Real Estate [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0		0
Consumer Real Estate [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	2,032		1,506
Consumer Real Estate [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	1,087		507
Consumer and Other [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	7,838	$ 6,848	5,026	$ 4,799	$ 4,450	$ 9,198
Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment	0		0
Financing Receivable, Allowance for Credit Losses, Collectively Evaluated for Impairment	7,838		5,026
Consumer and Other [Member] | Historical Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	5,455		4,585
Consumer and Other [Member] | Specific Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	0		0
Consumer and Other [Member] | General Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	137		(144)
Consumer and Other [Member] | Macroeconomic Valuation Allowances [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Portion of allowance for loan losses	$ 2,246		$ 585

Loans - Investment in Loans Rel

Loans - Investment in Loans Related to Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	$ 4,604,269	$ 4,344,000
Energy:	1,409,612	1,386,061
Total commercial real estate	4,993,852	4,835,448
Total consumer real estate	991,073	936,785
Consumer and other	513,532	473,098
Total loans	12,512,338	11,975,392
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	18,817	28,909
Energy:	55,377	57,563
Total commercial real estate	5,478	6,866
Total consumer real estate	1,203	655
Consumer and other	0	30
Total loans	80,875	94,023
Loans Collectively Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial and industrial	4,585,452	4,315,091
Energy:	1,354,235	1,328,498
Total commercial real estate	4,988,374	4,828,582
Total consumer real estate	989,870	936,130
Consumer and other	513,532	473,068
Total loans	$ 12,431,463	$ 11,881,369

Loans - Activity in Allowance f

Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	$ 153,056	$ 161,880	$ 153,045	$ 135,859
Provision for loan losses	8,426	9,189	16,378	37,689
Charge-offs	(15,535)	(24,900)	(26,899)	(30,678)
Recoveries	3,611	3,545	7,034	6,844
Net charge-offs	(11,924)	(21,355)	(19,865)	(23,834)
Ending balance	149,558	149,714	149,558	149,714
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	45,583	45,084	52,915	42,993
Provision for loan losses	8,184	6,460	3,581	9,683
Charge-offs	(5,579)	(4,857)	(9,106)	(6,718)
Recoveries	718	891	1,516	1,620
Net charge-offs	(4,861)	(3,966)	(7,590)	(5,098)
Ending balance	48,906	47,578	48,906	47,578
Commercial and industrial, Energy [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	61,793	84,973	60,653	54,696
Provision for loan losses	(1,280)	(1,887)	4,085	29,401
Charge-offs	(6,317)	(16,749)	(10,595)	(17,760)
Recoveries	81	2	134	2
Net charge-offs	(6,236)	(16,747)	(10,461)	(17,758)
Ending balance	54,277	66,339	54,277	66,339
Commercial Real Estate Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	34,009	23,587	30,213	24,313
Provision for loan losses	(1,470)	2,993	2,281	2,199
Charge-offs	(14)	(19)	(14)	(47)
Recoveries	477	502	522	598
Net charge-offs	463	483	508	551
Ending balance	33,002	27,063	33,002	27,063
Consumer Real Estate [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	4,823	3,786	4,238	4,659
Provision for loan losses	601	75	1,090	(897)
Charge-offs	(2)	(23)	(13)	(177)
Recoveries	113	97	220	350
Net charge-offs	111	74	207	173
Ending balance	5,535	3,935	5,535	3,935
Consumer and Other [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Beginning balance	6,848	4,450	5,026	9,198
Provision for loan losses	2,391	1,548	5,341	(2,697)
Charge-offs	(3,623)	(3,252)	(7,171)	(5,976)
Recoveries	2,222	2,053	4,642	4,274
Net charge-offs	(1,401)	(1,199)	(2,529)	(1,702)
Ending balance	$ 7,838	$ 4,799	$ 7,838	$ 4,799

Goodwill and Other Intangible68

Goodwill and Other Intangible Assets - Schedule of Goodwill (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 654,952	$ 654,952

Goodwill and Other Intangible69

Goodwill and Other Intangible Assets - Schedule of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill)	$ 5,880	$ 6,776
Core deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill)	4,636	5,298
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill)	1,188	1,410
Non-compete agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Net (Excluding Goodwill)	$ 56	$ 68

Goodwill and Other Intangible70

Goodwill and Other Intangible Assets - Estimated Aggregate Future Amortization Expense for Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2017	$ 807
2,018	1,424
2,019	1,167
2,020	918
2,021	697
Thereafter	867
Future Amortization Expense, Total	$ 5,880	$ 6,776

Deposits - Schedule of Deposits

Deposits - Schedule of Deposits (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 10,707,365	$ 10,513,369
Total interest-bearing deposits	14,906,208	15,298,206
Total deposits	$ 25,613,573	$ 25,811,575
Total non-interest-bearing demand deposits, Percentage of Total	41.80%	40.80%
Total interest-bearing deposits, Percentage of Total	58.20%	59.20%
Total deposits, Percentage of Total	100.00%	100.00%
Commercial and Individual [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 10,076,475	$ 9,670,989
Total non-interest-bearing demand deposits, Percentage of Total	39.30%	37.50%
Correspondent Banks [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 259,686	$ 280,751
Total non-interest-bearing demand deposits, Percentage of Total	1.00%	1.10%
Private Accounts [Member]
Deposit [Line Items]
Savings and interest checking	$ 6,349,462	$ 6,436,065
Money market accounts	7,403,054	7,486,431
Time accounts of $100,000 or More	432,406	460,028
Time accounts under $100,000	327,228	338,714
Total private accounts	$ 14,512,150	$ 14,721,238
Savings and interest checking, Percentage of Total	24.80%	24.90%
Money market accounts, Percentage of Total	28.90%	29.00%
Time accounts of $100,000 or more, Percentage of Total	1.70%	1.80%
Time accounts under $100,000, Percentage of Total	1.30%	1.30%
Total private accounts, Percentage of Total	56.70%	57.00%
Public Funds [Member]
Deposit [Line Items]
Total non-interest-bearing demand deposits	$ 371,204	$ 561,629
Savings and interest checking	299,505	446,872
Money market accounts	77,361	113,669
Time accounts of $100,000 or More	16,426	15,748
Time accounts under $100,000	766	679
Total public funds	$ 394,058	$ 576,968
Total non-interest-bearing demand deposits, Percentage of Total	1.50%	2.20%
Savings and interest checking, Percentage of Total	1.20%	1.70%
Money market accounts, Percentage of Total	0.30%	0.40%
Time accounts of $100,000 or more, Percentage of Total	0.00%	0.10%
Time accounts under $100,000, Percentage of Total	0.00%	0.00%
Total public funds, Percentage of Total	1.50%	2.20%

Deposits - Additional Informati

Deposits - Additional Information About Corporation's Deposits (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Banking and Thrift [Abstract]
Deposits from foreign sources (primarily Mexico)	$ 728,350	$ 776,003
Deposits not covered by deposit insurance	$ 12,708,257	$ 12,889,047

Borrowed Funds (Narrative) (Det

Borrowed Funds (Narrative) (Details) - USD ($) $ in Thousands	Mar. 17, 2017	Feb. 15, 2017	Feb. 28, 2007	Jun. 30, 2017	Dec. 31, 2016
Subordinated Borrowing [Line Items]
Subordinated Debt				$ 98,473	$ 99,990
Subordinated Debt [Member]
Subordinated Borrowing [Line Items]
Unamortized Debt Issuance Expense				$ 1,500
Subordinated Debt	$ 100,000		$ 100,000
Subordinated Borrowing, Interest Rate	4.50%		5.75%
Debt Instrument, Maturity Date	Mar. 17, 2027	Feb. 15, 2017

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Rent expense for operating leases	$ 7.5	$ 7.3	$ 15.3	$ 14.5

Commitments and Contingencies75

Commitments and Contingencies - Financial Instruments with Off-Balance-Sheet Risk (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Standby Letters of Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 240,612	$ 239,482
Deferred Standby Letter Of Credit Fees [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	2,010	2,054
Commitments to Extend Credit [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Financial instruments with off- balance-sheet risk	$ 7,616,002	$ 7,476,420

Capital and Regulatory Matter76

Capital and Regulatory Matters - Additional Information (Detail) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2017USD ($)quartershares	Jun. 30, 2016shares	Dec. 31, 2016USD ($)	Oct. 27, 2016USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock Repurchase Program, Authorized Amount				$ 100,000
Stock Repurchase Program, Period in Force	2 years
Treasury stock, shares, acquired | shares	469	0
Preferred stock value issued include for regulatory tier one capital calculations	$ 144,500		$ 144,500
Preferred stock dividend rate percentage	5.375%		5.375%
Corporation's aggregate subordinated notes	$ 136,155		$ 136,127
Maximum dividends available without prior regulatory approval	$ 420,600
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 Preferred Securities Tier One Excluded Portion [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities	$ 133,000		$ 133,000
Floating Rate Subordinated Notes [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Corporation's aggregate subordinated notes	$ 100,000
Treasury Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, shares, acquired | shares	0

Capital and Regulatory Matter77

Capital and Regulatory Matters - Actual and Required Capital Ratios (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Cullen/Frost [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 to Risk-Weighted Assets, Actual, Capital Amount	$ 2,385,585	$ 2,239,186
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio	12.81%	12.52%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,070,444	$ 916,360
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	5.75%	5.125%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,303,367	$ 1,251,425
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased In, Ratio	7.00%	7.00%
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Capital Amount	$ 1,210,067	$ 1,162,213
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 2,530,071	$ 2,383,672
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	13.59%	13.33%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,349,691	$ 1,184,563
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	7.25%	6.625%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,582,296	$ 1,519,587
Tier 1 Capital 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	$ 1,489,314	$ 1,430,416
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	$ 2,912,629	$ 2,669,717
Total Capital to Risk-Weighted Assets, Actual, Ratio	15.65%	14.93%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,722,019	$ 1,542,168
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase - In Schedule, Ratio	9.25%	8.625%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,954,601	$ 1,877,137
Total Capital 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	$ 1,861,642	$ 1,788,020
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Leverage Ratio, Actual, Capital Amount	$ 2,530,071	$ 2,383,672
Leverage Ratio, Actual, Ratio	8.61%	8.14%
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,174,957	$ 1,171,682
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	4.00%	4.00%
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,174,910	$ 1,171,573
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,468,696	$ 1,464,602
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 1 to Risk-Weighted Assets, Actual, Capital Amount	$ 2,401,554	$ 2,296,480
Common Equity Tier 1 to Risk-Weighted Assets, Actual , Ratio	12.94%	12.88%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,067,432	$ 913,460
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	5.75%	5.125%
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,299,400	$ 1,247,463
Common Equity Tier 1 to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased In, Ratio	7.00%	7.00%
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Capital Amount	$ 1,206,662	$ 1,158,535
Common Equity Tier 1 to Risk-Weighted Assets, Required To Be Considered Well Capitalized, Ratio	6.50%	6.50%
Tier 1 Capital to Risk-Weighted Assets, Actual, Capital Amount	$ 2,401,554	$ 2,296,480
Tier 1 Capital to Risk-Weighted Assets, Actual, Ratio	12.94%	12.88%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,345,892	$ 1,180,814
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	7.25%	6.625%
Tier 1 Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,577,843	$ 1,514,776
Tier 1 Capital 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	$ 1,485,123	$ 1,425,889
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	$ 2,551,112	$ 2,449,525
Total Capital to Risk-Weighted Assets, Actual, Ratio	13.74%	13.74%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,717,173	$ 1,537,286
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Phase - In Schedule, Ratio	9.25%	8.625%
Total Capital to Risk-Weighted Assets, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,949,100	$ 1,871,194
Total Capital 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	$ 1,856,403	$ 1,782,361
Total Capital to Risk-Weighted Assets, Required to be Considered Well Capitalized, Ratio	10.00%	10.00%
Leverage Ratio, Actual, Capital Amount	$ 2,401,554	$ 2,296,480
Leverage Ratio, Actual, Ratio	8.18%	7.85%
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Capital Amount	$ 1,173,726	$ 1,170,249
Leverage Ratio, Minimum Capital Required - Basel III Phase-In Schedule, Ratio	4.00%	4.00%
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Capital Amount	$ 1,173,679	$ 1,170,141
Leverage Ratio, Minimum Capital Required - Basel III Fully Phased-In, Ratio	4.00%	4.00%
Leverage Ratio, Required to be Considered Well Capitalized, Capital Amount	$ 1,467,157	$ 1,462,812
Leverage Ratio, Required to be Considered Well Capitalized, Ratio	5.00%	5.00%

Derivative Financial Instrume78

Derivative Financial Instruments - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2017USD ($)
Derivative [Line Items]
Weighted-average strike rate for outstanding interest rate caps	3.07%
Approximate credit exposure related to swaps with bank customers	$ 23.5
Aggregate fair value of securities posted as collateral for derivative contracts	13.1
Cash collateral for borrowed securities deposited with other financial institutions	14.2
Interest rate swaps with upstream financial institution counterparties [Member]
Derivative [Line Items]
Approximate credit exposure related to swaps with bank customers	$ 8.9

Derivative Financial Instrume79

Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Interest Rate Derivative Contracts Outstanding (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Designated as Hedging Instrument [Member] | Financial institution counterparties Loan/lease interest rate swaps assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	$ 40,089	$ 41,818
Estimated Fair Value	312	368
Designated as Hedging Instrument [Member] | Financial institution counterparties Loan/lease interest rate swaps liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	14,921	18,812
Estimated Fair Value	(910)	(1,278)
Non Designated as Hedging Instrument [Member] | Financial institution counterparties Loan/lease interest rate swaps assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	211,908	206,745
Estimated Fair Value	2,357	2,649
Non Designated as Hedging Instrument [Member] | Financial institution counterparties Loan/lease interest rate swaps liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	681,298	694,965
Estimated Fair Value	(23,602)	(25,466)
Non Designated as Hedging Instrument [Member] | Financial institution counterparties Loan/lease interest-rate caps assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	114,866	85,966
Estimated Fair Value	687	575
Non Designated as Hedging Instrument [Member] | Customer counterparties Loan/lease interest rate swaps assets [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	681,298	694,965
Estimated Fair Value	23,602	25,467
Non Designated as Hedging Instrument [Member] | Customer counterparties Loan/lease interest rate swaps liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	211,908	206,745
Estimated Fair Value	(2,357)	(2,649)
Non Designated as Hedging Instrument [Member] | Customer counterparties Loan/lease interest rate caps liabilities [Member]
Derivatives, Fair Value [Line Items]
Notional Amount	114,866	85,966
Estimated Fair Value	$ (687)	$ (575)

Derivative Financial Instrume80

Derivative Financial Instruments - Schedule of Weighted-Average Rates Paid and Received for Interest Rate Swaps Outstanding (Detail)	Jun. 30, 2017
Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Fair value hedge loan/lease interest rate swaps	2.34%
Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Fair value hedge loan/lease interest rate swaps	1.17%
Financial Institution Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – financial institution counterparties	3.99%
Financial Institution Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – financial institution counterparties	2.77%
Customer Counterparties [Member] | Weighted Average Interest Rate Paid [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – customer counterparties	2.77%
Customer Counterparties [Member] | Weighted-Average Interest Rate Received [Member]
Weighted Average Discount Rate [Line Items]
Non-hedging interest rate swaps – customer counterparties	3.99%

Derivative Financial Instrume81

Derivative Financial Instruments - Schedule of Notional Amounts and Estimated Fair Values of Commodity Derivative Positions (Detail) bbl in Thousands, MMBTU in Thousands, $ in Thousands	Jun. 30, 2017USD ($)MMBTUbbl	Dec. 31, 2016USD ($)MMBTUbbl
Financial Institution Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | bbl	935	227
Oil/Natural Gas Derivative Liabilities, Notional Amount | bbl	178	944
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 4,684	$ 206
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (153)	$ (4,400)
Financial Institution Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | MMBTU	1,061	0
Oil/Natural Gas Derivative Liabilities, Notional Amount | MMBTU	938	1,299
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 109	$ 0
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (85)	$ (1,357)
Customer Counterparties [Member] | Oil Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | bbl	178	944
Oil/Natural Gas Derivative Liabilities, Notional Amount | bbl	935	227
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 163	$ 4,580
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (4,466)	$ (206)
Customer Counterparties [Member] | Natural Gas Commodity Derivative [Member]
Derivative Instruments [Line Items]
Oil/Natural Gas Derivative Assets, Notional Amount | MMBTU	938	1,299
Oil/Natural Gas Derivative Liabilities, Notional Amount | MMBTU	1,061	0
Oil/Natural Gas Derivative Assets, Estimated Fair Value	$ 87	$ 1,393
Oil/Natural Gas Derivative Liabilities, Estimated Fair Value	$ (103)	$ 0

Derivative Financial Instrume82

Derivative Financial Instruments - Notional Amount and Fair Value of Foreign Currency Forward Contract (Detail) € in Thousands, £ in Thousands, CAD in Thousands, $ in Thousands	Jun. 30, 2017USD ($)	Jun. 30, 2017CAD	Jun. 30, 2017EUR (€)	Jun. 30, 2017GBP (£)	Dec. 31, 2016USD ($)	Dec. 31, 2016CAD	Dec. 31, 2016EUR (€)	Dec. 31, 2016GBP (£)
Financial Institution Counterparties [Member] | Other Assets [Member] | Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount			€ 497	£ 217			€ 0	£ 0
Financial Institution Counterparties [Member] | Other Liabilities [Member] | Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Notional Amount		CAD 538	1,194	2,434		CAD 2,214	870	419
Customer Counterparties [Member] | Other Assets [Member] | Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Notional Amount | CAD		CAD 536				CAD 2,205
Customer Counterparties [Member] | Other Liabilities [Member] | Non Designated as Hedging Instrument [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Notional Amount			€ 500	£ 219			€ 0	£ 0
Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Estimated Fair Value	$ (3)				$ (21)
Foreign Exchange Forward [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	5				29
GBP Foreign Exchange Forward [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	5				0
Forward Contracts – Liability Estimated Fair Value	(20)				(3)
GBP Foreign Exchange Forward [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Estimated Fair Value	(3)				0
Eurodollar Future [Member] | Financial Institution Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Assets Estimated Fair Value	9				0
Forward Contracts – Liability Estimated Fair Value	(9)				(9)
Eurodollar Future [Member] | Customer Counterparties [Member]
Derivative Counter Party [Line Items]
Forward Contracts – Liability Estimated Fair Value	$ (6)				$ 0

Derivative Financial Instrume83

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	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest Income on Loans [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) included in income	$ (198)	$ (388)	$ (443)	$ (726)
Other Non-Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) included in income	$ (2)	$ (7)	$ (3)	$ (7)

Derivative Financial Instrume84

Derivative Financial Instruments - Schedule of Amounts Related to Non-Hedging Interest Rate and Commodity Derivatives (Detail) - Non Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Interest Rate Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$ 607	$ 979	$ 977	$ 1,414
Interest Rate Contract [Member] | Other Non-Interest Expense [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	2	0	1	0
Commodity Contract [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	104	13	156	145
Foreign Currency Derivative Contracts [Member] | Other Non-Interest Income [Member]
Other Non Interest Income Non Hedging Interest Rate Derivatives [Line Items]
Amount of gain (loss) included in income (expense)	$ 9	$ 8	$ 18	$ 14

Balance Sheet Offsetting - Fina

Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	$ 8,163	$ 3,798
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	8,163	3,798
Gross Amount Recognized, Resell agreements, Financial assets	9,642	9,642
Gross Amount Offset, Resell agreements, Financial assets	0	0
Net Amount Recognized, Resell agreements, Financial assets	9,642	9,642
Gross Amount Recognized, Financial assets	17,805	13,440
Gross Amount Offset, Financial assets	0	0
Net Amount Recognized, Financial assets	17,805	13,440
Gross Amount Recognized, Derivatives, Financial Liabilities	24,782	32,534
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	24,782	32,534
Gross Amount Recognized, Repurchase agreements, Financial liabilities	919,017	963,317
Gross Amount Offset, Repurchase agreements, Financial liabilities	0	0
Net Amount Recognized, Repurchase agreements, Financial liabilities	919,017	963,317
Gross Amount Recognized, Financial liabilities	943,799	995,851
Gross Amount Offset, Financial liabilities	0	0
Net Amount Recognized, Financial Liabilities	943,799	995,851
Loan/lease interest rate swaps and caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	3,356	3,592
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	3,356	3,592
Commodity swaps and options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	4,793	206
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	4,793	206
Gross Amount Recognized, Derivatives, Financial Liabilities	238	5,757
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	238	5,757
Foreign currency forward contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	14	0
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	14	0
Gross Amount Recognized, Derivatives, Financial Liabilities	32	33
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	32	33
Loan/lease interest rate swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Liabilities	24,512	26,744
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	$ 24,512	$ 26,744

Balance Sheet Offsetting - Fi86

Balance Sheet Offsetting - Financial Instruments Derivative Assets Liabilities and Resell Agreements Net of Amount Not Offset (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	$ 8,163	$ 3,798
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(5,746)	(3,565)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	(2,028)	(64)
Net Amount, Derivatives, Financial Assets	389	169
Net Amount Recognized, Resell agreements, Financial Assets	9,642	9,642
Gross Amounts Not Offset Financial Instruments, Resell Agreements	0	0
Gross Amounts Not Offset Collateral, Resell Agreements, Financial Assets	(9,642)	(9,642)
Net Amount, Financial Assets, Resell Agreements	0	0
Net Amount Recognized, Total Financial Assets	17,805	13,440
Gross Amounts Not Offset Collateral, Financial Assets	(11,670)	(9,706)
Net Amount, Financial Assets	389	169
Net Amount Recognized, Derivatives, Financial Liabilities	24,782	32,534
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(5,746)	(3,565)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(18,753)	(27,347)
Net Amount, Derivatives, Financial Liabilities	283	1,622
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	919,017	963,317
Gross Amounts Not Offset Financial Instruments, Repurchase Agreements, Financial Liabilities	0	0
Gross Amounts Not Offset Collateral, Repurchase Agreements, Financial Liabilities	(919,017)	(963,317)
Net Amount, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	943,799	995,851
Gross Amounts Not Offset Collateral, Financial Liabilities	(937,770)	(990,664)
Net Amount, Financial Liabilities	283	1,622
Counterparty A [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	413	687
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(413)	(687)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	9,644	11,233
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(413)	(687)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(9,231)	(10,026)
Net Amount, Derivatives, Financial Liabilities	0	520
Counterparty B [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	1,896	223
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(1,896)	(223)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	3,737	6,867
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(1,896)	(223)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(1,841)	(6,344)
Net Amount, Derivatives, Financial Liabilities	0	300
Counterparty C [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	979	158
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(979)	(158)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	1,260	4,578
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(979)	(158)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(9)	(4,415)
Net Amount, Derivatives, Financial Liabilities	272	5
Counterparty D [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Net Amount Recognized, Derivatives, Financial Assets	1,610	1,820
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(1,610)	(1,820)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	0	0
Net Amount, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivatives, Financial Liabilities	8,004	7,706
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(1,610)	(1,820)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(6,394)	(5,886)
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	3,265	910
Gross Amounts Not Offset, Financial Instruments, Total Derivatives, Financial Assets	(848)	(677)
Gross Amount Not Offset Collateral, Derivatives, Financial Assets	(2,028)	(64)
Net Amount, Derivatives, Financial Assets	389	169
Net Amount Recognized, Derivatives, Financial Liabilities	2,137	2,150
Gross Amounts Not Offset Financial Instruments, Total Derivatives, Financial Liabilities	(848)	(677)
Gross Amounts Not Offset Collateral, Derivatives, Financial Liabilities	(1,278)	(676)
Net Amount, Derivatives, Financial Liabilities	$ 11	$ 797

Balance Sheet Offsetting Balanc

Balance Sheet Offsetting Balance Sheet Offsetting - Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	$ 919,017	$ 963,317
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	919,017	963,317
Securities Sold under Agreements to Repurchase, Gross	919,017	963,317
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Securities	0	0
US Treasury Securities [Member]
Remaining Contractual Maturity of the Securities Sold Under Agreement to Repurchase [Line Items]
Remaining contractual maturity of the agreements overnight and continuous	842,269	841,475
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	842,269	841,475
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	76,748	121,842
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	$ 76,748	$ 121,842

Earnings Per Common Share - Bas

Earnings Per Common Share - Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income	$ 85,553	$ 71,507	$ 170,494	$ 140,323
Less: Preferred stock dividends	2,015	2,015	4,031	4,031
Net income available to common shareholders	83,538	69,492	166,463	136,292
Less: Earnings allocated to participating securities	436	252	871	487
Distributed earnings allocated to common stock	36,545	33,463	71,020	66,285
Undistributed earnings allocated to common stock	46,557	35,777	94,572	69,520
Net earnings allocated to common stock	$ 83,102	$ 69,240	$ 165,592	$ 135,805
Weighted-average shares outstanding for basic earnings per common share	64,061,264	61,959,411	63,900,620	61,944,438
Dilutive effect of stock compensation	974,067	497,532	988,198	267,632
Weighted-average shares outstanding for diluted earnings per common share	65,035,331	62,456,943	64,888,818	62,212,070

Stock-Based Compensation Stock-

Stock-Based Compensation Stock-Based Compensation - Narrative (Details) - shares	12 Months Ended
	Dec. 31, 2016	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		1,480,137
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	29,240

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity in Corporation's Active Stock Plans (Detail) - $ / shares	6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, Number of Shares	(752,075)	(67,075)
Director deferred stock units outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	53,659
Granted, Number of Units	5,447
Stock Awards Vested and Expected to Vest, Exercisable, Number	(6,098)
Ending Balance, Number of Shares	53,008		53,659
Beginning Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	$ 61.48
Granted, Directors Deferred, Weighted-Average Grant-Date Fair Value	95.37
Ending Balance, Director Deferred, Weighted-Average Grant-Date Fair Value	64.87		$ 61.48
Stock Award Vested, Weighted Average Grant Date Fair Value	$ 62.29
Non-Vested Stock Awards/Stock Units Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	256,850
Stock Awards Vested and Expected to Vest, Exercisable, Number	(1,730)
Ending Balance, Number of Shares	254,250		256,850
Forfeited/expired, Number of Shares	(870)
Stock Award Vested, Weighted Average Grant Date Fair Value	$ 76.07
Beginning Balance, Weighted-Average Grant-Date Fair Value	73.43
Ending Balance, Weighted-Average Grant-Date Fair Value	73.40		$ 73.43
Forfeited/expired, Weighted-Average Exercise Price	$ 76.07
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Units			29,240
Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	4,089,028
Ending Balance, Number of Shares	3,311,289		4,089,028
Stock options exercised, Number of Shares	(744,247)
Forfeited/expired, Number of Shares	(33,492)
Beginning Balance, Weighted-Average Exercise Price	$ 62.67
Stock options exercised, Weighted-Average Exercise Price	59.32
Forfeited/expired, Weighted-Average Exercise Price	69.35
Ending Balance, Weighted-Average Exercise Price	$ 63.36		$ 62.67
Maximum [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, Number of Shares	43,860
Ending Balance, Number of Shares	43,860		43,860
Beginning Balance, Weighted-Average Grant-Date Fair Value	$ 69.70
Ending Balance, Weighted-Average Grant-Date Fair Value	$ 69.70		$ 69.70

Stock-Based Compensation - Shar

Stock-Based Compensation - Shares Issued in Connection with Stock Compensation Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
New shares issued from available authorized shares	310,021	0	593,363	0
Issued from available treasury stock	0	65,200	158,712	67,075
Total	310,021	65,200	752,075	67,075
Proceeds from stock option exercises	$ 19,402	$ 3,490	$ 44,149	$ 3,586

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock options	$ 1,573	$ 2,117	$ 3,360	$ 4,242
Non-vested stock awards/stock units	901	358	1,934	715
Director deferred stock units	519	520	519	520
Performance stock units	195	0	478	0
Total	3,188	2,995	6,291	5,477
Income tax benefit	$ 1,116	$ 1,048	$ 2,202	$ 1,917

Stock-Based Compensation - Unre

Stock-Based Compensation - Unrecognized Stock-Based Compensation Expense (Detail) $ in Thousands	Jun. 30, 2017USD ($)
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock options	$ 8,694
Non-vested stock awards/stock units	8,413
Performance stock units	2,579
Total	$ 19,686

Defined Benefit Plans - Net Per

Defined Benefit Plans - Net Periodic Cost (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Compensation and Retirement Disclosure [Abstract]
Expected return on plan assets, net of expenses	$ (2,780)	$ (2,889)	$ (5,559)	$ (5,779)
Interest cost on projected benefit obligation	1,548	1,749	3,095	3,498
Net amortization and deferral	1,358	1,553	2,715	3,106
SERP settlement costs	0	187	0	187
Net periodic expense (benefit)	$ 126	$ 600	$ 251	$ 1,012

Defined Benefit Plans Additiona

Defined Benefit Plans Additional Information (Details)	6 Months Ended
	Jun. 30, 2017USD ($)
Compensation and Retirement Disclosure [Abstract]
Defined Benefit Plan, Expected Contributions in Current Fiscal Year	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Income Tax [Abstract]
Deferred Tax Assets, Net	$ 27	$ 63.7
Valuation allowance	$ 0
U.S. federal statutory income tax rate, percent	35.00%
Unrecognized tax benefits	$ 0

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Current income tax expense	$ 13,710	$ 13,616	$ 29,412	$ 27,403
Deferred income tax expense (benefit)	128	(5,238)	(4,173)	(9,633)
Income tax expense, as reported	$ 13,838	$ 8,378	$ 25,239	$ 17,770
Effective tax rate	13.90%	10.50%	12.90%	11.20%

Other Comprehensive Income (L98

Other Comprehensive Income (Loss) - Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ 90,390	$ 165,288	$ 124,201	$ 287,506
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(3,860)	(9,185)	(10,146)	(17,351)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	50	0	50	(14,903)
Total securities available for sale and transferred securities, before tax amount	86,580	156,103	114,105	255,252
Change in the net actuarial gain/loss,Before Tax Amount	0	(862)	0	(862)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income, before tax amount	1,358	1,740	2,715	3,293
Total defined-benefit post-retirement benefit plans	1,358	878	2,715	2,431
Total other comprehensive income (loss), before tax	87,938	156,981	116,820	257,683
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	31,636	57,851	43,470	100,627
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Tax Expense (Benefit)	(1,351)	(3,215)	(3,551)	(6,073)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	18	0	18	(5,216)
Total securities available for sale and transferred securities, Tax Expense (Benefit)	30,303	54,636	39,937	89,338
Change in the net actuarial gain/loss,Tax Expense (Benefit)	0	(302)	0	(302)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income, Tax Expense (Benefit)	475	609	950	1,153
Total defined-benefit post-retirement benefit plans, Tax Expense (Benefit)	475	307	950	851
Total other comprehensive income (loss), Tax Expense (Benefit)	30,778	54,943	40,887	90,189
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Net of Tax	58,754	107,437	80,731	186,879
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Net of Tax	(2,509)	(5,970)	(6,595)	(11,278)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Net of Tax	32	0	32	(9,687)
Total securities available for sale and transferred securities, Net of Tax	56,277	101,467	74,168	165,914
Change in the net actuarial gain/loss, Net of Tax	0	(560)	0	(560)
Reclassification adjustment for net amortization of actuarial gain/lloss included in net income, Net of Tax	883	1,131	1,765	2,140
Total defined-benefit post-retirement benefit plans, Net of Tax Amount	883	571	1,765	1,580
Other comprehensive income (loss), net of tax	$ 57,160	$ 102,038	$ 75,933	$ 167,494

Other Comprehensive Income - Sc

Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income, Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ (24,623)	$ 113,863
Other comprehensive income (loss) before reclassifications			74,136	175,041
Amounts reclassified from accumulated other comprehensive income (loss)			1,797	(7,547)
Other comprehensive income (loss), net of tax	$ 57,160	$ 102,038	75,933	167,494
Ending Balance	51,310	281,357	51,310	281,357
Securities Available For Sale [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			16,153	160,611
Other comprehensive income (loss) before reclassifications			74,136	175,601
Amounts reclassified from accumulated other comprehensive income (loss)			32	(9,687)
Other comprehensive income (loss), net of tax			74,168	165,914
Ending Balance	90,321	326,525	90,321	326,525
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			(40,776)	(46,748)
Other comprehensive income (loss) before reclassifications			0	(560)
Amounts reclassified from accumulated other comprehensive income (loss)			1,765	2,140
Other comprehensive income (loss), net of tax			1,765	1,580
Ending Balance	$ (39,011)	$ (45,168)	$ (39,011)	$ (45,168)

Operating Segments - Additional

Operating Segments - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2017Segment
Segment Reporting [Abstract]
Number of primary operating segments	2

Operating Segments - Summary of

Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 295,868	$ 268,519	$ 588,077	$ 554,386
Net income	85,553	71,507	170,494	140,323
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	261,250	237,444	520,161	492,717
Net income	81,529	68,223	162,398	134,190
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	36,712	32,225	71,300	63,948
Net income	6,279	4,860	11,573	9,012
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(2,094)	(1,150)	(3,384)	(2,279)
Net income	$ (2,255)	$ (1,576)	$ (3,477)	$ (2,879)

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	$ 10,783,737	$ 10,203,277
Trading account securities	27,600	16,703
Derivative assets	8,163	3,798
Derivative liabilities	24,782	32,534
Interest rate swaps, caps and floors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	26,958	29,059
Derivative liabilities	27,556	29,968
Commodity swaps and options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	5,043	6,179
Derivative liabilities	4,807	5,963
Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	19	29
Derivative liabilities	41	33
U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	4,224,254	4,019,731
Trading account securities	17,726	16,594
Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	705,621	785,167
States and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	5,811,342	5,355,885
Trading account securities	9,874	109
Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	42,520	42,494
Level 1 [Member] | Foreign Exchange Forward [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	19	29
Derivative liabilities	41	33
Level 1 [Member] | U.S. Treasury [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	4,224,254	4,019,731
Trading account securities	17,726	16,594
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	26,958	29,059
Derivative liabilities	27,556	29,968
Level 2 [Member] | Commodity swaps and options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	5,043	6,179
Derivative liabilities	4,807	5,963
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, estimated fair value	705,621	785,167
Level 2 [Member] | States and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	5,811,342	5,355,885
Trading account securities	9,874	109
Level 2 [Member] | Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, estimated fair value	$ 42,520	$ 42,494

Fair Value Measurements - Impai

Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 80,875	$ 94,023
Specific valuation allowance allocations	(2,130)	$ (9,186)
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	0		$ 0
Specific valuation allowance allocations	0		0
Loans receivable, fair value disclosure	0		0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	21,686		11,183
Specific valuation allowance allocations	(561)		(2,944)
Loans receivable, fair value disclosure	$ 21,125		$ 8,239

Fair Value Measurements - Forec

Fair Value Measurements - Foreclosed Assets Remeasured and Reported at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Jun. 30, 2016
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	$ 0	$ 425
Foreclosed Assets Remeasured at Initial Recognition Charge-offs recognized in the allowance for loan losses	0	(3)
Fair Value of Foreclosed Assets Remeasured at Initial Recognition	0	422
Foreclosed Assets Remeasured Subsequent to initial Recognition Carrying value of foreclosed assets prior to remeasurement	89	0
Foreclosed Assets Remeasured Subsequent to Initial Recognition Write-downs included in other non-interest expense	(16)	0
Fair Value of Foreclosed Assets remeasured subsequent to initial recognition	$ 73	$ 0

Fair Value Measurements - Estim

Fair Value Measurements - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 3,706,315	$ 4,141,445	$ 3,365,223	$ 3,591,523
Securities held to maturity	1,596,262	2,250,460
Loans, net	12,362,780	11,822,347
Deposits	25,613,573	25,811,575
Federal funds purchased and repurchase agreements	924,867	976,992
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,155	136,127
Subordinated Debt	98,473	99,990
Carrying Amount [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,706,315	4,141,445
Securities held to maturity	1,596,262	2,250,460
Cash surrender value of life insurance policies	178,987	177,884
Accrued interest receivable	157,151	156,714
Deposits	25,613,573	25,811,575
Federal funds purchased and repurchase agreements	924,867	976,992
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	136,155	136,127
Subordinated Debt	98,473	99,990
Accrued interest payable	2,307	1,204
Carrying Amount [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	12,362,780	11,822,347
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3,706,315	4,141,445
Securities held to maturity	1,630,665	2,262,747
Cash surrender value of life insurance policies	178,987	177,884
Accrued interest receivable	157,151	156,714
Deposits	25,608,770	25,812,039
Federal funds purchased and repurchase agreements	924,867	976,992
Junior subordinated deferrable interest debentures, net of unamortized issuance costs	137,115	137,115
Subordinated Debt	102,280	100,000
Accrued interest payable	2,307	1,204
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net	$ 12,384,234	$ 11,903,956