United Bankshares (UBSI) 10-K 1 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	UBSI
Entity Registrant Name	UNITED BANKSHARES INC/WV
Entity Central Index Key	729,986
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		105,041,766
Entity Public Float			$ 3,921,339,111

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and due from banks	$ 196,742	$ 175,468
Interest-bearing deposits with other banks	1,468,636	1,258,334
Federal funds sold	789	725
Total cash and cash equivalents	1,666,167	1,434,527
Securities available for sale at estimated fair value (amortized cost-$1,900,684 at December 31, 2017 and $1,277,639 at December 31, 2016)	1,888,756	1,259,214
Securities held to maturity (estimated fair value-$20,018 at December 31, 2017 and $31,178 at December 31, 2016)	20,428	33,258
Other investment securities	162,461	111,166
Loans held for sale (at fair value-$263,308 at December 31, 2017 and $0 at December 31, 2016)	265,955	8,445
Loans	13,027,337	10,356,719
Less: Unearned income	(15,916)	(15,582)
Loans net of unearned income	13,011,421	10,341,137
Less: Allowance for loan losses	(76,627)	(72,771)
Net loans	12,934,794	10,268,366
Bank premises and equipment	104,894	75,909
Goodwill	1,478,380	863,767
Accrued interest receivable	52,815	39,400
Other assets	484,309	414,840
TOTAL ASSETS	19,058,959	14,508,892
Deposits:
Noninterest-bearing	4,294,687	3,171,841
Interest-bearing	9,535,904	7,625,026
Total deposits	13,830,591	10,796,867
Borrowings:
Federal funds purchased	16,235	22,235
Securities sold under agreements to repurchase	311,352	237,316
Federal Home Loan Bank (FHLB) borrowings	1,271,531	897,707
Other long-term borrowings	242,446	224,319
Reserve for lending-related commitments	679	1,044
Accrued expenses and other liabilities	145,595	93,657
TOTAL LIABILITIES	15,818,429	12,273,145
Shareholders' Equity
Preferred stock, $1.00 par value; Authorized-50,000,000 shares; none issued	0	0
Common stock, $2.50 par value; Authorized-200,000,000 shares; issued- 105,069,821 and 81,068,252 at December 31, 2017 and 2016, respectively, including 29,173 and 28,278 shares in treasury at December 31, 2017 and 2016, respectively	262,675	202,671
Surplus	2,129,077	1,205,778
Retained earnings	891,816	872,990
Accumulated other comprehensive loss	(42,025)	(44,717)
Treasury stock, at cost	(1,013)	(975)
TOTAL SHAREHOLDERS' EQUITY	3,240,530	2,235,747
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 19,058,959	$ 14,508,892

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Securities available for sale, amortized cost	$ 1,900,684	$ 1,277,639
Securities held to maturity	20,018	31,178
Loans held for sale at fair value	$ 263,308	$ 0
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	105,069,821	81,068,252
Common stock, shares in treasury	29,173	28,278

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest income
Interest and fees on loans	$ 565,537	$ 430,738	$ 387,713
Interest on federal funds sold and other short-term investments	16,035	3,495	1,645
Interest and dividends on securities:
Taxable	36,715	32,357	30,744
Tax-exempt	5,519	3,751	3,528
Total interest income	623,806	470,341	423,630
Interest expense
Interest on deposits	49,726	29,125	28,023
Interest on short-term borrowings	1,579	1,584	834
Interest on long-term borrowings	23,504	14,301	10,649
Total interest expense	74,809	45,010	39,506
Net interest income	548,997	425,331	384,124
Provision for loan losses	28,406	24,509	22,574
Net interest income after provision for loan losses	520,591	400,822	361,550
Other income
Fees from trust and brokerage services	19,531	19,037	19,085
Fees from deposit services	33,622	32,858	37,962
Bankcard fees and merchant discounts	4,795	5,215	4,786
Other service charges, commissions, and fees	2,057	2,059	2,141
Income from bank-owned life insurance	5,110	5,794	5,557
Income from mortgage banking	58,907	3,450	2,507
Other income	2,039	1,339	1,433
Total other-than-temporary impairment losses	(60)	339	(113)
Portion of loss recognized in other comprehensive income	0	(372)	66
Net other-than-temporary impairment losses	(60)	(33)	(47)
Net gains on sales/calls of investment securities	5,644	313	202
Net investment securities gains (losses)	5,584	280	155
Total other income	131,645	70,032	73,626
Other expense
Employee compensation	164,247	93,281	88,123
Employee benefits	37,143	28,965	27,086
Net occupancy expense	39,067	27,529	24,301
Other real estate owned (OREO) expense	6,003	5,844	3,613
Equipment expense	10,528	8,622	9,034
Data processing expense	21,019	15,280	14,867
Bankcard processing expense	1,809	1,742	1,505
FDIC insurance expense	7,051	8,548	8,367
Other expense	80,542	58,385	54,791
Total other expense	367,409	248,196	231,687
Income before income taxes	284,827	222,658	203,489
Income taxes	134,246	75,575	65,530
Net income	$ 150,581	$ 147,083	$ 137,959
Earnings per common share:
Basic	$ 1.54	$ 2	$ 1.99
Diluted	1.54	1.99	1.98
Dividends per common share	$ 1.33	$ 1.32	$ 1.29
Average outstanding shares:
Basic	97,502,633	73,531,992	69,334,849
Diluted	97,890,078	73,893,127	69,625,531

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	$ 150,581	$ 147,083	$ 137,959
Change in net unrealized gain (loss) on available-for-sale (AFS) securities, net of tax									4,093	(7,782)	(4,068)
Accretion of the net unrealized loss on the transfer of AFS securities to held-to-maturity (HTM) securities, net of tax									5	6	5
Change in defined benefit pension plan, net of tax									(1,406)	1,271	1,615
Comprehensive income, net of tax									$ 153,273	$ 140,578	$ 135,511

Consolidated Statement of Chang

Consolidated Statement of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Cardinal Financial Corporation [Member]	Bank of Georgetown [Member]	Deferred Compensation Plan [Member]	Common Stock [Member]	Common Stock [Member]Cardinal Financial Corporation [Member]	Common Stock [Member]Bank of Georgetown [Member]	Common Stock [Member]Deferred Compensation Plan [Member]	Surplus [Member]	Surplus [Member]Cardinal Financial Corporation [Member]	Surplus [Member]Bank of Georgetown [Member]	Surplus [Member]Deferred Compensation Plan [Member]	Retained Earnings [Member]	Retained Earnings [Member]Cardinal Financial Corporation [Member]	Retained Earnings [Member]Bank of Georgetown [Member]	Retained Earnings [Member]Deferred Compensation Plan [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Cardinal Financial Corporation [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Bank of Georgetown [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Deferred Compensation Plan [Member]	Treasury Stock [Member]	Treasury Stock [Member]Cardinal Financial Corporation [Member]	Treasury Stock [Member]Bank of Georgetown [Member]	Treasury Stock [Member]Deferred Compensation Plan [Member]
Beginning Balance at Dec. 31, 2014	$ 1,656,160				$ 173,286				$ 742,960				$ 776,311				$ (35,764)				$ (633)
Beginning Balance, shares at Dec. 31, 2014					69,314,407
Net income	137,959				$ 0				0				137,959				0				0
Other comprehensive income, net of tax	(2,448)				0				0				0				(2,448)				0
Total comprehensive income, net of tax	135,511
Stock based compensation expense	2,484				0				2,484				0				0				0
Purchase of treasury stock	(1)				0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan				$ 1				$ 0				$ 0				$ 0				$ 0				$ 1
Issuance of treasury stock, shares								0																24
Cash dividends	(89,667)				0				0				(89,667)				0				0
Grant of restricted stock	0				$ 132				(132)				0				0				0
Grant of restricted stock, shares					53,071
Forfeiture of restricted stock	0				$ 0				187				0				0				(187)
Common stock options exercised	$ 8,147				$ 649				7,498				0				0				0
Common stock options exercised, shares	259,454				259,454
Ending Balance at Dec. 31, 2015	$ 1,712,635				$ 174,067				752,997				824,603				(38,212)				(820)
Ending Balance, shares at Dec. 31, 2015					69,626,932
Net income	147,083				$ 0				0				147,083				0				0
Other comprehensive income, net of tax	(6,505)				0				0				0				(6,505)				0
Total comprehensive income, net of tax	140,578
Stock based compensation expense	2,817				0				2,817				0				0				0
Issuance of common stock (4,330,000 shares)	199,916				$ 10,825				189,091				0				0				0
Acquisition, Values			$ 264,495				$ 16,319				$ 248,176				$ 0				$ 0				$ 0
Issuance of common stock (4,330,000 shares), shares					4,330,000
Acquisition, Shares							6,527,746
Purchase of treasury stock	(1)				$ 0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan	52			1	$ 0			$ 0	0			0	0			0	0			0	$ 52			$ 1
Issuance of treasury stock, shares					0			0													1,500			28
Cash dividends	(98,696)				$ 0				0				(98,696)				0				$ 0
Grant of restricted stock	0				$ 161				(161)				0				0				0
Grant of restricted stock, shares					64,092
Forfeiture of restricted stock	0				$ 0				207				0				0				(207)
Common stock options exercised	$ 13,950				$ 1,299				12,651				0				0				0
Common stock options exercised, shares	519,482				519,482
Ending Balance at Dec. 31, 2016	$ 2,235,747				$ 202,671				1,205,778				872,990				(44,717)				(975)
Ending Balance, shares at Dec. 31, 2016					81,068,252
Net income	150,581				$ 0				0				150,581				0				0
Other comprehensive income, net of tax	2,692				0				0				0				2,692				0
Total comprehensive income, net of tax	153,273
Stock based compensation expense	3,555				0				3,555				0				0				0
Acquisition, Values		$ 975,254				$ 59,226				$ 916,028				$ 0				$ 0				$ 0
Acquisition, Shares						23,690,589
Purchase of treasury stock	(1)				0				0				0				0				(1)
Distribution of treasury stock for deferred compensation plan				$ 1				$ 0				$ 0				$ 0				$ 0				$ 1
Issuance of treasury stock, shares								0																31
Cash dividends	(131,755)				0				0				(131,755)				0				0
Grant of restricted stock	0				$ 225				(225)				0				0				0
Grant of restricted stock, shares					90,075
Forfeiture of restricted stock	0				$ 0				38				0				0				(38)
Common stock options exercised	$ 4,456				$ 553				3,903				0				0				0
Common stock options exercised, shares	220,905				220,905
Ending Balance at Dec. 31, 2017	$ 3,240,530				$ 262,675				$ 2,129,077				$ 891,816				$ (42,025)				$ (1,013)
Ending Balance, shares at Dec. 31, 2017					105,069,821

Consolidated Statement of Chan7

Consolidated Statement of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash dividends per share	$ 1.33	$ 1.32	$ 1.29
Common stock options exercised, shares	220,905	519,482	259,454
Common Stock [Member]
Issuance of common stock, shares		4,330,000
Purchase of treasury stock, shares	0	0	0
Distribution of treasury stock for deferred compensation plan, shares		0
Cash dividends per share	$ 0
Grant of restricted stock, shares	90,075	64,092	53,071
Forfeiture of restricted stock, shares	840	5,955	5,294
Common stock options exercised, shares	220,905	519,482	259,454
Treasury Stock [Member]
Purchase of treasury stock, shares	86	16	17
Distribution of treasury stock for deferred compensation plan, shares		1,500
Deferred Compensation Plan [Member] | Common Stock [Member]
Distribution of treasury stock for deferred compensation plan, shares	0	0	0
Deferred Compensation Plan [Member] | Treasury Stock [Member]
Distribution of treasury stock for deferred compensation plan, shares	31	28	24
Cardinal Financial Corporation [Member] | Common Stock [Member]
Acquisition, Shares	23,690,589
Bank of Georgetown [Member] | Common Stock [Member]
Acquisition, Shares		6,527,746

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
OPERATING ACTIVITIES
Net income	$ 150,581	$ 147,083	$ 137,959
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	28,406	24,509	22,574
Depreciation, amortization and accretion	(21,567)	(8,720)	746
Loss (gain) on sales of bank premises, OREO and equipment	4,813	5,196	2,059
(Gain) loss on securities	(5,584)	(280)	(155)
Loans originated for sale	(2,373,622)	(154,335)	(145,836)
Proceeds from sales of loans	2,455,213	160,021	146,342
Gain on sales of loans	(58,907)	(3,450)	(2,507)
Stock-based compensation	3,555	2,817	2,484
Excess tax benefits from stock-based compensation arrangements	2,201	4,008	1,023
Deferred income tax expense	60,827	7,252	1,729
Increase in cash surrender value of bank-owned life insurance policies	(5,110)	(3,837)	(5,557)
Contribution to pension plan	(10,000)	0	0
Amortization of net periodic pension costs	3,310	5,156	4,380
Changes in:
Loans held for sale	(8,893)	0	0
Interest receivable	(2,024)	(755)	(3,467)
Other assets	32,924	(5,855)	14,349
Accrued expenses and other liabilities	(2,195)	(8,076)	(1,222)
Net Cash Provided by Operating Activities	253,928	170,734	174,901
INVESTING ACTIVITIES
Proceeds from maturities and calls of held to maturity securities	14,214	5,730	1,056
Purchases of held to maturity securities	(1,403)	0	(1,000)
Proceeds from sales of securities available for sale	247,131	103,440	7,316
Proceeds from maturities and calls of securities available for sale	439,181	410,550	183,950
Purchases of securities available for sale	(932,474)	(504,978)	(85,249)
Redemption of bank-owned life insurance policies	0	630	1,974
Purchases of bank premises and equipment	(14,357)	(7,271)	(5,263)
Proceeds from sales of bank premises and equipment	17	554	866
Acquisition of subsidiaries, net of cash paid	44,531	29,330	0
Proceeds from sales and redemptions of other investment securities	40,837	64,411	19,845
Purchases of other investment securities	(74,090)	(72,052)	(22,181)
Proceeds from sales of OREO properties	7,066	17,871	10,270
Net change in loans	496,025	(17,255)	(296,882)
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	266,678	30,960	(185,298)
FINANCING ACTIVITIES
Cash dividends paid	(121,354)	(96,351)	(88,864)
Acquisition of treasury stock	(1)	(1)	(1)
Proceeds from exercise of stock options	4,619	13,337	7,871
Proceeds from the issuance of common stock	0	199,916	0
Distribution of treasury stock for deferred compensation plan	0	1	1
Repayment of long-term Federal Home Loan Bank borrowings	(845,208)	(725,673)	(794,455)
Proceeds of long-term Federal Home Loan Bank borrowings	815,000	795,000	705,000
Changes in:
Time deposits	614,821	75,639	(135,674)
Other deposits	(928,665)	408,127	433,414
Federal funds purchased, securities sold under agreements to repurchase and other short-term borrowings	171,821	(294,497)	(12,624)
Net Cash Provided by (Used in) Financing Activities	(288,967)	375,498	114,668
INCREASE IN CASH AND CASH EQUIVALENTS	231,640	577,192	104,271
Cash and Cash Equivalents at Beginning of Year	1,434,527	857,335	753,064
CASH AND CASH EQUIVALENTS AT END OF YEAR	1,666,167	1,434,527	857,335
Supplemental information
Cash paid for interest	72,715	44,609	39,835
Cash paid for income taxes	73,096	61,905	52,319
Noncash investing activities:
Transfers of loans to OREO	$ 17,615	$ 21,776	$ 5,857

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE A—SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations: Operating Segments: Through its community banking segment, United offers a full range of banking products and services through various delivery channels. The mortgage banking segment engages primarily in the origination and acquisition of residential mortgages for sale into the secondary market though George Mason Mortgage, LLC (George Mason), an indirectly owned subsidiary of United. Basis of Presentation: The Cardinal acquisition was accounted for using the acquisition method and their results of operations have been included in the United’s consolidated financial statements as of the acquisition date (April 21, 2017). United determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (VIE) under U.S. generally accepted accounting principles. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. United consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE. United’s wholly owned and indirect wholly owned statutory trust subsidiaries are VIEs for which United is not the primary beneficiary. Accordingly, its accounts are not included in United’s consolidated financial statements. The accounting and reporting policies of United conform with U.S. generally accepted accounting principles. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. To conform to the 2017 presentation, certain reclassifications have been made to prior period amounts, which had no impact on net income, comprehensive income or shareholders’ equity. In the opinion of management, all adjustments necessary for a fair presentation of financial position and results of operations have been made. Such adjustments are of a normal and recurring nature. The Company has evaluated events and transactions subsequent to December 31, 2017 through the date these financial statements were issued. Based on definitions and requirements of generally accepted accounting principles for “Subsequent Events,” the Company has not identified any events that would require adjustments to, or disclosure in the financial statements. Cash and Cash Equivalents: Securities: value. Unrealized gains and losses on securities classified as available for sale are carried as a separate component of Accumulated Other Comprehensive Income (Loss), net of deferred income taxes. Gains or losses on sales of securities are recognized by the specific identification method and are reported in securities gains and losses within noninterest income of the Consolidated Statements of Income. United reviews available-for-sale held-to-maturity For equity securities, United evaluates the near-term prospects of the investment in relation to the severity and duration of any impairment and United’s ability and intent to hold these equity securities until a recovery of their fair value to at least the cost basis of the investment. Equity securities that are deemed to be other-than-temporarily impaired are written down to the fair value with the write-down recognized within noninterest income of the Consolidated Statements of Income. Certain security investments that do not have readily determinable fair values and for which United does not exercise significant influence are carried at cost and are classified as other investment securities on the balance sheet. These cost-method investments are reviewed for impairment at least annually or sooner if events or changes in circumstances indicate the carrying value may not be recoverable. Securities Purchased Under Resale Agreements and Securities Sold Under Agreements to Repurchase: Loans: Loans are designated as impaired when, in the opinion of management, based on current information and events, the collection of principal and interest in accordance with the loan contract is doubtful. Consistent with United’s existing method of income recognition for loans, interest on impaired loans, except those classified as nonaccrual, is recognized as income using the accrual method. United’s method of income recognition for impaired loans that are classified as nonaccrual is to recognize interest income on the cash basis or apply the cash receipt to principal when the ultimate collectibility of principal is in doubt. A loan is categorized as restructured if a concession is granted to provide for a reduction of either interest or principal due to a deterioration in the financial condition of the borrower. A loan classified as restructured will generally retain such classification until the loan is paid in full. However, a restructured one-to-four-family Loans Acquired Through Transfer: Loans Held for Sale: one-to-four Loans held for sale within the mortgage banking segment are recorded under the fair value option at a fair value measured using valuations from investors for loans with similar characteristics adjusted for the Company’s actual sales experience versus the investor’s indicated pricing. Loans held for sale within the community banking segment are carried at the lower of cost or fair value. The fair value is based on the price secondary markets are currently offering for similar loans using observable market data which is not materially different than cost due to the short duration between origination and sale. Gains and losses on sale of loans are recorded within income from mortgage banking activities. Allowance for Credit Losses: The allowance for loan losses is management’s estimate of the probable credit losses inherent in the loan portfolio. Management’s evaluation of the adequacy of the allowance for loan losses and the appropriate provision for credit losses is based upon a quarterly evaluation of the portfolio. This evaluation is inherently subjective and requires significant estimates, including the amounts and timing of estimated future cash flows, estimated losses on pools of loans based on historical loss experience, and consideration of current economic trends, all of which are susceptible to constant and significant change. The amounts allocated to specific credits and loan pools grouped by similar risk characteristics are reviewed on a quarterly basis and adjusted as necessary based upon subsequent changes in circumstances. In determining the components of the allowance for credit losses, management considers the risk arising in part from, but not limited to, charge-off charged-off In determining the adequacy of the allowance for loan losses, management makes allocations to specific commercial loans classified by management as to risk. Management determines the loan’s risk by considering the borrowers’ ability to repay, the collateral securing the credit and other borrower-specific factors that may impact collectibility. For impaired loans, specific allocations are based on the present value of expected future cash flows using the loan’s effective interest rate, or as a practical expedient, at the loan’s observable market price or the fair value of the collateral if the loan is collateral-dependent. Other commercial loans not specifically reviewed on an individual basis are evaluated based on loan pools, which are grouped by similar risk characteristics using management’s internal risk ratings. Allocations for these commercial loan pools are determined based upon historical loss experience adjusted for current environmental conditions and risk factors and the estimate period it takes for losses to result in a charge-off. Bank Premises and Equipment: Other Real Estate Owned Revenue Recognition Advertising Costs: Income Taxes: For uncertain income tax positions, United records a liability based on a recognition threshold of more-likely-than-not, United files a consolidated income tax return with its subsidiaries. Federal income tax expense or benefit has been allocated to subsidiaries on a separate return basis. Intangible Assets: Goodwill and intangible assets with indefinite lives (such as a trade name intangible) are not amortized, but are tested for impairment at least annually or sooner if indicators of impairment exist. Intangible assets with definite useful lives (such as core deposit intangibles) are amortized over their respective estimated useful lives to their estimated residual values, and reviewed for impairment at least annually or as indicators of impairment are identified. Based on the most recent goodwill impairment test, no impairment was noted. As of December 31, 2017, and 2016, total goodwill approximated $1,478,380,000 and $863,767,000, respectively. Derivative Financial Instruments: Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Derivative instruments designated in a hedge relationship to mitigate exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. For a fair value hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to the hedged financial instrument. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a fair value hedge are offset in current period earnings. For a cash flow hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to other comprehensive income within shareholders’ equity, net of tax. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a cash flow hedge are offset to other comprehensive income, net of tax. The portion of a hedge that is ineffective is recognized immediately in earnings. At inception of a hedge relationship, United formally documents the hedged item, the particular risk management objective, the nature of the risk being hedged, the derivative being used, how effectiveness of the hedge will be assessed and how the ineffectiveness of the hedge will be measured. United also assesses hedge effectiveness at inception and on an ongoing basis using regression analysis. Hedge ineffectiveness is measured by using the change in fair value method. The change in fair value method compares the change in the fair value of the hedging derivative to the change in the fair value of the hedged exposure, attributable to changes in the benchmark rate. United through George Mason enters into interest rate lock commitments to finance residential mortgage loans with its customers. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by United. Interest rate risk arises on these commitments and subsequently closed loans if interest rates change between the time of the interest rate lock and the delivery of the loan to the investor. Market risk on interest rate lock commitments and mortgage loans held for sale is managed using corresponding forward mortgage loan sales contracts. United is a party to these forward mortgage loan sales contracts to sell loans servicing released and short sales of mortgage-backed securities. When the interest rate is locked with the borrower, the rate lock commitment, forward sale agreement, and mortgage-backed security position are undesignated derivatives and marked to fair value through earnings. The fair value of the rate lock derivative includes the servicing premium and the interest spread for the difference between retail and wholesale mortgage rates. Income from mortgage banking activities includes the gain recognized for the period presented and associated elements of fair value. United sells mortgage loans on either a best efforts or mandatory delivery basis. For loans sold on a mandatory delivery basis, United enters into forward mortgage-backed securities (the “residual hedge”) to mitigate the effect of interest rate risk. Both the rate lock commitment for mandatory delivery loans and the residual hedge are recorded at fair value through earnings and are not designated as accounting hedges. At the closing of the loan, the loan commitment derivative expires and United records a loan held for sale at fair value and continues to mark these assets to market under the election of the fair value option. United closes out of the trading mortgage-backed securities assigned within the residual hedge and replaces the securities with a forward sales contract once a price has been accepted by an investor and recorded at fair value. For those loans selected to be sold under a best efforts delivery basis, at the closing of the loan, the rate lock commitment derivative expires and the Company records a loan held for sale at fair value under the election of fair value option and continues to be obligated under the same forward loan sales contract entered into at inception of the rate lock commitment. For derivatives that are not designated in a hedge relationship, changes in the fair value of the derivatives are recognized in earnings in the same period as the change in the fair value. Stock-Based Compensation Stock-based compensation expense was $3,555,000 in 2017, $2,817,000 in 2016, and $2,484,000 in 2015. Treasury Stock Trust Assets and Income: Earnings Per Common Share: two-class non-vested Under the two-class The reconciliation of the numerator and denominator of basic earnings per share with that of diluted earnings per share is presented as follows: Year Ended December 31 (Dollars in thousands, except per share) 2017 2016 2015 Distributed earnings allocated to common stock $ 131,527 $ 98,510 $ 89,497 Undistributed earnings allocated to common stock 18,816 48,317 48,218 Net earnings allocated to common shareholders $ 150,343 $ 146,827 $ 137,715 Average common shares outstanding 97,502,633 73,531,992 69,334,849 Dilutive effect of stock compensation 387,445 361,135 290,682 Average diluted shares outstanding 97,890,078 73,893,127 69,625,531 Earnings per basic common share $ 1.54 $ 2.00 $ 1.99 Earnings per diluted common share $ 1.54 $ 1.99 $ 1.98 Fair Value Measurements The Fair Value Measurements and Disclosures topic specifies a hierarchy of valuation techniques based on whether the inputs to those valuation techniques are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect United’s market assumptions. The three levels of the fair value hierarchy based on these two types of inputs are as follows: Level 1 - Valuation is based on quoted prices in active markets for identical assets and liabilities. Level 2 - Valuation is based on observable inputs including quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets and liabilities in less active markets, and model-based valuation techniques for which significant assumptions can be derived primarily from or corroborated by observable data in the market. Level 3 - Valuation is based on model-based techniques that use one or more significant inputs or assumptions that are unobservable in the market. When determining the fair value measurements for assets and liabilities, United looks to active and observable markets to price identical assets or liabilities whenever possible and classifies such items in Level 1. When identical assets and liabilities are not traded in active markets, United looks to market observable data for similar assets and liabilities and classifies such items as Level 2. Nevertheless, certain assets and liabilities are not actively traded in observable markets and United must use alternative valuation techniques using unobservable inputs to determine a fair value and classifies such items as Level 3. For assets and liabilities that are not actively traded, the fair value measurement is based primarily upon estimates that require significant judgment. Therefore, the results may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there are inherent weaknesses in any calculation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. The level within the fair value hierarchy is based on the lowest level of input that is significant in the fair value measurement. Recent Accounting Pronouncements In February 2018, the FASB issued ASU No. 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,” to help organizations address certain stranded income tax effects in accumulated other comprehensive income (AOCI) resulting from the Tax Cuts and Jobs Act (the “Tax Act”). This ASU provides financial statement preparers with an option to reclassify stranded tax effects within AOCI to retained earnings in each period in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Act (or portion thereof) is recorded. The amendments are effective for all organizations for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. Organizations should apply the proposed amendments either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Act is recognized. United expects to adopt ASU No. 2018-02 In August 2017, the FASB issued ASU No. 2017-12, No. 2017-12 No. 2017-12 In July 2017, the FASB issued ASU No. 2017-11, No. 2017-11 No. 2017-11 In May 2017, the FASB issued ASU No. 2017-09, non-substantive No. 2017-09 No. 2017-09 In March 2017, the FASB issued ASU 2017-07, 2017-07 2017-07 2017-07 In January 2017, the FASB issued ASU 2017-04, 2017-04 2017-04 In January 2017, the FASB issued ASU 2017-01, 2017-01 2017-01 In August 2016, the FASB issued ASU 2016-15, 2016-15 2016-15 2016-15 In June 2016, the FASB issued ASU 2016-13, 2016-13 available-for-sale 2016-13 2016-13 In March 2016, the FASB issued ASU 2016-09, 2016-09 2016-09 2016-09 tax-related 2016-09 In February 2016, the FASB issued ASU 2016-02, 2016-02 2016-02 right-of-use 2016-02 In January 2016, the FASB issued ASU 2016-01, 2016-01 2016-01 available-for-sale 2016-01 In May 2014, the FASB issued ASU 2014-09, 2014-09 2014-09 assessment of these revenue streams under the standard, management concluded that ASU 2014-09 2014-09

Mergers and Acquisitions

Mergers and Acquisitions	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Mergers and Acquisitions	NOTE B—MERGERS AND ACQUISITIONS Cardinal Financial Corporation On April 21, 2017 (Cardinal Acquisition Date), United acquired 100% of the outstanding common stock of Cardinal Financial Corporation (Cardinal), headquartered in Tysons Corner, Virginia. The acquisition of Cardinal expands United’s existing footprint in the Washington, D.C. Metropolitan Statistical Area. At consummation, Cardinal had assets of $4,136,008,000, loans of $3,313,033,000 and deposits of $3,344,740,000. Cardinal also operated George Mason Mortgage, LLC (George Mason), a residential mortgage lending company based in Fairfax, Virginia with offices located in Virginia, Maryland, North Carolina, South Carolina and the District of Columbia. As a result of the merger, George Mason became an indirectly-owned subsidiary of United. The merger was accounted for under the acquisition method of accounting. The results of operations of Cardinal are included in the consolidated results of operations from the Cardinal Acquisition Date. The aggregate purchase price was approximately $975,254,000, including common stock valued at $972,499, stock options assumed valued at $2,741,000, and cash paid for fractional shares of $14,000. The number of shares issued in the transaction was 23,690,589, which were valued based on the closing market price of $41.05 for United’s common shares on April 21, 2017. The preliminary purchase price has been allocated to the identifiable tangible and intangible assets resulting in preliminary additions to goodwill, core deposit intangibles and the George Mason trade name intangible of $613,286,000, $28,724,000 and $1,080,000, respectively. The core deposit intangibles are expected to be amortized over ten years. The George Mason trade name provides a source of market recognition to attract potential clients and retain existing relationships. United believes the George Mason trade name provides a competitive advantage and is likely going to be used into perpetuity and thus will not be subject to amortization, but rather be evaluated for impairment. Because the consideration paid was greater than the net fair value of the acquired assets and liabilities, the Company recorded goodwill as part of the acquisition. None of the goodwill from the Cardinal acquisition is expected to be deductible for tax purposes. United used an independent third party to help determine the fair values of the assets and liabilities acquired from Cardinal. As a result of the merger, United recorded preliminary fair value discounts of $144,434,000 on the loans acquired, $2,281,000 on leases and $8,738,000 on trust preferred issuances, respectively, and premiums of $4,408,000 on land acquired, $5,072,000 on interest-bearing deposits and $10,740,000 on long-term FHLB advances, respectively. The remaining discount and premium amounts are being accreted or amortized on an accelerated or straight-line basis over each asset’s or liability’s estimated remaining life at the time of acquisition except for loans and land. The discount on loans will be accreted into income based on the effective yield method. The premium on land will not be amortized. At December 31, 2017, the discounts on leases and trust preferred issuances had an average estimated remaining life of 5.75 years and 16.72 years, respectively, and the premiums on the interest-bearing deposits and the FHLB advances each had an average estimated remaining life of 4.75 years and 4.56 years, respectively. United assumed approximately $1,825,000 of liabilities to provide severance benefits to terminated employees of Cardinal, which has no remaining balance as of December 31, 2017. The estimated fair values of the acquired assets and assumed liabilities, including identifiable intangible assets and goodwill are preliminary as of December 31, 2017 and are subject to refinement as additional information relative to closing date fair values becomes available. Any subsequent adjustments to the fair values of acquired assets and liabilities assumed, identifiable intangible assets, or other purchase accounting adjustments will result in adjustments to goodwill within the measurement period following the date of acquisition. In many cases, determining the estimated fair value of the acquired assets and assumed liabilities required United to estimate cash flows expected to result from those assets and liabilities and to discount those cash flows at appropriate rates of interest. The most significant of those determinations related to the fair value of acquired loans. The fair value of the acquired loans was based on the present value of the expected cash flows. Periodic principal and interest cash flows were adjusted for expected losses and prepayments, then discounted to determine the present value and summed to arrive at the estimated fair value. For such loans, the excess of cash flows expected at acquisition over the estimated fair value is recognized as interest income over the remaining lives of the loans. The difference between contractually required payments at acquisition and the cash flows expected to be collected at acquisition reflects the impact of estimated credit losses and other factors, such as prepayments. In accordance with GAAP, there was no carry-over of Cardinal’s previously established allowance for loan losses. The acquired loans were divided into loans with evidence of credit quality deterioration, which are accounted for under ASC topic 310-30 310-20 In conjunction with the Cardinal merger, the acquired loan portfolio was accounted for at fair value as follows: (In thousands) April 21, 2017 Contractually required principal and interest at acquisition $ 4,211,734 Contractual cash flows not expected to be collected (56,176 ) Expected cash flows at acquisition 4,155,558 Interest component of expected cash flows (986,959 ) Basis in acquired loans at acquisition – estimated fair value $ 3,168,599 Included in the above table is information related to acquired impaired loans. Specifically, contractually required principal and interest, cash flows expected to be collected and estimated fair value of acquired impaired loans were $132,837,000, $108,275,000, and $86,696,000, respectively. The consideration paid for Cardinal’s common equity and the preliminary amounts of acquired identifiable assets and liabilities assumed as of the Cardinal Acquisition Date were as follows: (In thousands) Purchase price: Value of common shares issued (23,690,589 shares) $ 972,499 Fair value of stock options assumed 2,741 Cash for fractional shares 14 Total purchase price 975,254 Identifiable assets: Cash and cash equivalents 44,545 Investment securities 395,829 Loans held for sale 271,301 Loans 3,168,599 Premises and equipment 24,208 Core deposit intangibles 28,724 George Mason trade name intangible 1,080 Other assets 135,383 Total identifiable assets $ 4,069,669 Identifiable liabilities: Deposits $ 3,349,812 Short-term borrowings 96,215 Long-term borrowings 220,119 Unfavorable lease liability 2,281 Other liabilities 39,274 Total identifiable liabilities 3,707,701 Preliminary fair value of net assets acquired including identifiable intangible assets 361,968 Preliminary resulting goodwill $ 613,286 The operating results of United for year of December 31, 2017 include operating results of acquired assets and assumed liabilities subsequent to the Cardinal Acquisition Date. The operations of United’s metropolitan Washington D.C. geographic area, which primarily includes the acquired operations of Cardinal, provided $252,293,000 in total revenues, which represents net interest income plus other income, and $101,505,000 in net income from the period from the Cardinal Acquisition Date to December 31, 2017. These amounts are included in United’s consolidated financial statements as of and for the year ended December 31, 2017. Cardinal’s results of operations prior to the Cardinal Acquisition Date are not included in United’s consolidated financial statements. The following table presents certain unaudited pro forma information for the results of operations for the year ended December 31, 2017 and 2016, as if the Cardinal merger had occurred on January 1, 2017 and 2016, respectively. These results combine the historical results of Cardinal into United’s consolidated statement of income and, while certain adjustments were made for the estimated impact of certain fair valuation adjustments and other acquisition-related activity, they are not indicative of what would have occurred had the acquisition taken place on the indicated date nor are they intended to represent or be indicative of future results of operations. In particular, no adjustments have been made to eliminate the amount of Cardinal’s provision for credit losses for 2017 and 2016 that may not have been necessary had the acquired loans been recorded at fair value as of the beginning of 2017 and 2016. Additionally, United expects to achieve operating cost savings and other business synergies as a result of the acquisition which are not reflected in the pro forma amounts. Proforma Year Ended December 31 (In thousands) 2017 2016 Total Revenues (1) $ 763,807 $ 784,198 Net Income 153,810 216,335 (1) Represents net interest income plus other income Bank of Georgetown After the close of business on June 3, 2016 (BOG Acquisition Date), United acquired 100% of the outstanding common stock of Bank of Georgetown, a privately held community bank headquartered in Washington, D.C. With this transaction, United continues to expand its existing footprint in the D.C. Metro Region. The results of operations of Bank of Georgetown are included in the consolidated results of operations from the BOG Acquisition Date. At consummation, Bank of Georgetown had assets of $1,278,837,000, loans of $999,773,000, and deposits of $971,369,000. The transaction was accounted for under the acquisition method of accounting and accordingly, assets acquired, liabilities assumed and consideration exchanged were recorded at estimated fair value on the BOG Acquisition Date. The aggregate purchase price was $264,505,000, including common stock valued at $253,799,000, stock options assumed valued at $10,696,000, and cash paid for fractional shares of $10,000. The number of shares issued in the transaction was 6,527,746, which were valued based on the closing market price of $38.88 for United’s common shares on June 3, 2016. The purchase price has been allocated to the identifiable tangible and intangible assets resulting in additions to goodwill and core deposit intangibles of $152,845,000 and $9,058,000, respectively. The core deposit intangibles are being amortized over ten years. Because the consideration paid was greater than the net fair value of the acquired assets and liabilities, the Company recorded goodwill as part of the acquisition. None of the goodwill from the Bank of Georgetown acquisition is expected to be deductible for tax purposes. United used an independent third party to help determine the fair values of the assets and liabilities acquired from the Bank of Georgetown. As a result of the merger, United recorded fair value discounts of $43,072,000 on the loans acquired and $1,550,000 on leasehold improvements, respectively, and premiums on interest-bearing deposits acquired of $316,000 and a premium on long-term FHLB advances of $2,659,000. The remaining discount and premium amounts are being amortized or accreted on an accelerated basis over each asset’s or liability’s estimated remaining life at the time of acquisition. At December 31, 2017, the premium on the interest-bearing deposits and the FHLB advances had an estimated remaining life of 0.08 years and 7.67 years, respectively. United assumed approximately $300,000 of liabilities to provide severance benefits to terminated employees of Bank of Georgetown, which has no remaining balance as of December 31, 2017. The measurement period has closed and the estimated fair values of the acquired assets and assumed liabilities, including identifiable intangible assets were considered final as of June 3, 2017. In many cases, determining the estimated fair value of the acquired assets and assumed liabilities required United to estimate cash flows expected to result from those assets and liabilities and to discount those cash flows at appropriate rates of interest. The most significant of those determinations related to the fair valuation of acquired loans. The fair value of the acquired loans was based on the present value of the expected cash flows. Periodic principal and interest cash flows were adjusted for expected losses and prepayments, then discounted to determine the present value and summed to arrive at the estimated fair value. For such loans, the excess of cash flows expected at acquisition over the estimated fair value is recognized as interest income over the remaining lives of the loans. The difference between contractually required payments at acquisition and the cash flows expected to be collected at acquisition reflects the impact of estimated credit losses and other factors, such as prepayments. In accordance with GAAP, there was no carry-over of Bank of Georgetown’s previously established allowance for loan losses. In conjunction with the Bank of Georgetown merger, the acquired loan portfolio was accounted for at fair value as follows: (In thousands) June 3, 2016 Contractually required principal and interest at acquisition $ 1,275,398 Contractual cash flows not expected to be collected (33,980 ) Expected cash flows at acquisition 1,241,418 Interest component of expected cash flows (274,548 ) Basis in acquired loans at acquisition – estimated fair value $ 966,870 Included in the above table is information related to acquired impaired loans. Specifically, contractually required principal and interest, cash flows expected to be collected and estimated fair value of acquired impaired loans were $138,125,000, $117,564,000, and $95,570,000, respectively. The consideration paid for Bank of Georgetown’s common equity and the fair value of acquired identifiable assets and liabilities assumed as of the BOG Acquisition Date were as follows: (In thousands) Purchase price: Value of common shares issued (6,527,746 shares) $ 253,799 Fair value of stock options assumed 10,696 Cash for fractional shares 10 Total purchase price 264,505 Identifiable assets: Cash and cash equivalents 29,340 Investment securities 219,783 Loans 966,870 Premises and equipment 5,574 Core deposit intangibles 9,058 Other assets 31,605 Total identifiable assets $ 1,262,230 Identifiable liabilities: Deposits $ 971,685 Short-term borrowings 101,021 Long-term borrowings 67,659 Other liabilities 11,532 Total identifiable liabilities 1,151,897 Fair value of net assets acquired including identifiable intangible assets 110,333 Resulting goodwill $ 154,172

Investment Securities

Investment Securities	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investment Securities	NOTE C—INVESTMENT SECURITIES The following is a summary of the amortized cost and estimated fair values of securities available for sale. December 31, 2017 (In thousands) Amortized Gross Gross Estimated Cumulative (1) U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 114,735 $ 385 $ 362 $ 114,758 $ 0 State and political subdivisions 303,101 3,197 2,429 303,869 0 Residential mortgage-backed securities Agency 821,857 2,096 9,360 814,593 0 Non-agency 4,969 543 0 5,512 86 Commercial mortgage-backed securities Agency 457,107 1,059 3,309 454,857 0 Asset-backed securities 109,829 148 7 109,970 0 Trust preferred collateralized debt obligations 37,856 542 4,129 34,269 20,770 Single issue trust preferred securities 13,417 368 1,225 12,560 0 Other corporate securities 28,101 407 18 28,490 0 Marketable equity securities 9,712 179 13 9,878 0 Total $ 1,900,684 $ 8,924 $ 20,852 $ 1,888,756 $ 20,856 December 31, 2016 (In thousands) Amortized Gross Gross Estimated Cumulative (1) U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 95,247 $ 698 $ 159 $ 95,786 $ 0 State and political subdivisions 196,350 1,364 4,902 192,812 0 Residential mortgage-backed securities Agency 585,208 3,999 5,111 584,096 0 Non-agency 6,629 426 12 7,043 86 Commercial mortgage-backed securities Agency 304,635 1,948 1,242 305,341 0 Asset-backed securities 217 0 0 217 0 Trust preferred collateralized debt obligations 48,558 729 15,735 33,552 25,952 Single issue trust preferred securities 13,363 284 2,170 11,477 0 Other corporate securities 14,996 66 0 15,062 0 Marketable equity securities 12,436 1,398 6 13,828 0 Total $ 1,277,639 $ 10,912 $ 29,337 $ 1,259,214 $ 26,038 (1) Other-than-temporary impairment in accumulated other comprehensive income. Amounts are before-tax. The following is a summary of securities available for sale which were in an unrealized loss position at December 31, 2017 and 2016. Less than 12 months 12 months or longer (In thousands) Fair Value Unrealized Fair Unrealized December 31, 2017 U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 36,678 $ 230 $ 22,920 $ 132 State and political subdivisions 82,896 566 59,432 1,863 Residential mortgage-backed securities Agency 460,414 4,621 182,482 4,739 Non-agency 0 0 0 0 Commercial mortgage-backed securities Agency 282,858 2,386 70,763 923 Asset-backed securities 27,931 7 0 0 Trust preferred collateralized debt obligations 0 0 28,629 4,129 Single issue trust preferred securities 0 0 4,485 1,225 Other corporate securities 6,975 18 0 0 Marketable equity securities 0 0 363 13 Total $ 897,752 $ 7,828 $ 369,074 $ 13,024 Less than 12 months 12 months or longer (In thousands) Fair Unrealized Fair Unrealized December 31, 2016 U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 24,101 $ 159 $ 0 $ 0 State and political subdivisions 116,300 4,902 0 0 Residential mortgage-backed securities Agency 309,376 5,111 0 0 Non-agency 0 0 218 12 Commercial mortgage-backed securities Agency 162,479 1,242 0 0 Asset-backed securities 0 0 0 0 Trust preferred collateralized debt obligations 0 0 28,579 15,735 Single issue trust preferred securities 0 0 8,185 2,170 Marketable equity securities 357 6 0 0 Total $ 612,613 $ 11,420 $ 36,982 $ 17,917 Marketable equity securities consist mainly of equity securities of financial institutions and mutual funds within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers of United and its subsidiaries. The following table shows the proceeds from maturities, sales and calls of available for sale securities and the gross realized gains and losses on sales and calls of those securities that have been included in earnings as a result of any sales and calls. Gains or losses on sales and calls of available for sale securities were recognized by the specific identification method. The realized losses relate to sales of securities within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers and its subsidiaries. Year Ended (In thousands) 2017 2016 2015 Proceeds from maturities, sales and calls $ 686,312 $ 513,990 $ 191,266 Gross realized gains 3,274 268 143 Gross realized losses 1,400 13 10 At December 31, 2017, gross unrealized losses on available for sale securities were $20,852,000 on 463 securities of a total portfolio of 838 available for sale securities. Securities in an unrealized loss position at December 31, 2017 consisted primarily of pooled trust preferred collateralized debt obligations (Trup Cdos), single issue trust preferred securities and agency commercial and residential mortgage-backed securities. The Trup Cdos and the single issue trust preferred securities relate mainly to securities of financial institutions. The agency commercial and residential mortgage-backed securities relate to commercial and residential properties and provide a guaranty of full and timely payments of principal and interest by the issuing agency. In determining whether or not a security is other-than-temporarily impaired (OTTI), management considered the severity and the duration of the loss in conjunction with United’s positive intent and the more likely than not ability to hold these securities to recovery of their cost basis or maturity. State and political subdivisions United’s state and political subdivisions portfolio relates to securities issued by various municipalities located throughout the United States. The total amortized cost of available for sale state and political subdivision securities was $303,101,000 at December 31, 2017. As of December 31, 2017, approximately 75% of the portfolio was supported by the general obligation of the issuing municipality, which allows for the securities to be repaid by any means available to the municipality. The majority of the portfolio was rated AA or higher, and less than one percent of the portfolio was rated below investment grade as of December 31, 2017. In addition to monitoring the credit ratings of these securities, management also evaluates the financial performance of the underlying issuers on an ongoing basis. Based upon management’s analysis and judgment, it was determined that none of the state and political subdivision securities were other-than-temporarily impaired at December 31, 2017. Agency mortgage-backed securities United’s agency mortgage-backed securities portfolio relates to securities issued by Fannie Mae, Freddie Mac, and Ginnie Mae. The total amortized cost of available for sale agency mortgage-backed securities was $1,278,964,000 at December 31, 2017. Of the $1,278,964,000 amount, $457,107,000 was related to agency commercial mortgage-backed securities and $821,857,000 was related to agency residential mortgage-backed securities. Each of the agency mortgage-backed securities provides a guarantee of full and timely payments of principal and interest by the issuing agency. Based upon management’s analysis and judgment, it was determined that none of the agency mortgage-backed securities were other-than-temporarily impaired at December 31, 2017. Non-agency United’s non-agency non-agency non-agency non-agency Single issue trust preferred securities The majority of United’s single issue trust preferred portfolio consists of obligations from large cap banks (i.e. banks with market capitalization in excess of $10 billion). Management reviews each issuer’s current and projected earnings trends, asset quality, capitalization levels, and other key factors. Upon completing the review for the fourth quarter of 2017, it was determined that none of the single issue trust preferred securities were other-than-temporarily impaired. All single issue trust preferred securities are currently receiving interest payments. The amortized cost of available for sale single issue trust preferred securities as of December 31, 2017 consisted of $7,707,000 in investment grade bonds and $5,710,000 in unrated bonds. The investment grade bonds were rated either Baa3 or BBB-. Trust preferred collateralized debt obligations (Trup Cdos) In order to determine how and when the Company recognizes OTTI, the Company first assesses its intentions regarding any sale of securities as well as the likelihood that it would be required to sell prior to recovery of the amortized cost. As of December 31, 2017, the Company has determined that it does not intend to sell any pooled trust preferred security and that it is not more likely than not that the Company will be required to sell such securities before recovery of their amortized cost. To determine a net realizable value and assess whether other-than-temporary impairment existed, management performed detailed cash flow analysis to determine whether, in management’s judgment, it was more likely that United would not recover the entire amortized cost basis of the security. The Company discounts the security-specific cash flow projection at the security-specific interest rate and compares the present value to the amortized cost. Management’s cash flow analysis was performed for each security and considered the current deferrals and defaults within the underlying collateral, the likelihood that current deferrals would cure or ultimately default, potential future deferrals and defaults, potential prepayments, cash reserves, excess interest spread, credit analysis of the underlying collateral and the priority of payments in the cash flow structure. The underlying collateral analysis for each issuer took into consideration multiple factors including capital adequacy, earnings trends and asset quality. After completing its analysis of estimated cash flows, management determined that none of the Trup Cdos experienced an adverse change in cash flows during the fourth quarter of 2017, as the expected discounted cash flows from these particular securities were greater than or equal to the discounted cash flows originally expected at purchase or from the previous date of other-than-temporary impairment (cash flows are discounted at the contractual coupon rate for purposes of assessing OTTI). There was no credit-related other-than-temporary impairment recognized in earnings during 2017 and 2016 related to these securities. At December 31, 2017 and 2016, the balance of noncredit-related other-than-temporary impairment recognized on United’s Trup Cdo portfolio was $20,770,000 and $25,952,000, respectively. The amortized cost of available for sale Trup Cdos in an unrealized loss position for twelve months or longer as of December 31, 2017 consisted of $3,065,000 in investment grade bonds and $29,693,000 in below investment grade bonds. The following is a summary of the available for sale Trup Cdos as of December 31, 2017: (In thousands) Amortized Cost Class Amortized Cost Fair Value Unrealized (Gain) Investment Split Below Senior – Bank $ 4,863 $ 4,965 $ (102 ) $ 3,065 $ 0 $ 1,798 Mezzanine —Bank (now in senior position) 6,428 6,226 202 0 0 6,428 Mezzanine – Bank 22,668 19,967 2,701 0 0 22,668 Mezzanine – Bank & Insurance (combination) 3,897 3,111 786 0 0 3,897 Totals $ 37,856 $ 34,269 $ 3,587 $ 3,065 $ 0 $ 34,791 While a difference remains between the fair value and amortized cost, the Company believes the remaining unrealized losses are related to the illiquid market for Trup Cdos rather than an adverse change in expected cash flows. The expected future cash flow substantiates the return of the remaining amortized cost of the security. The Company believes the following evidence supports the position that the remaining unrealized loss is related to the illiquid market for Trup Cdos: • The market for new issuance of Trup Cdos was robust from 2000 to 2007 with an estimated $60 billion in new issuance. The new market issuances came to an abrupt halt in 2007. • The secondary market for Trup Cdos ultimately became illiquid and although the market has improved, trading activity remains limited on these securities. In making this determination, the Company holds discussions with institutional traders to identify trends in the number and type of transactions related to the Trup Cdos. • The presence of a below-investment grade rating severely limits the pool of available buyers and contributes to the illiquidity of the market. • Trup Cdos have a more complex structure than most debt instruments, making projections of tranche returns difficult for non-specialists • The variability of cash flows at the time the securities were originated was expected to be very limited. Due to the financial crisis, Trup Cdos have experienced more substantive variability of cash flows compared to expectations, resulting in a higher risk premium when evaluating discount rates. • The limited, yet relevant, observable inputs indicate that market yield requirements for Trup Cdos, on a credit-adjusted basis, remained very high relative to discount rates at purchase and compared to other similarly rated debt securities. Overall, the Company believes the lack of new issuances, illiquid secondary market, limited pool of buyers, below investment grade ratings, and complex structures are the key drivers of the remaining unrealized losses in the Company’s Trup Cdos and the robust expected cash flow analysis substantiates the return of the remaining amortized cost under ASC topic 320. Management also considered the ratings of the Company’s bonds in its portfolio and the extent of downgrades in United’s impairment analysis. However, management considered it imperative to independently perform its own credit analysis based on cash flows as described. The ratings of the investment grade Trup Cdos in the table above range from a low of AA to a high of Aaa. The below investment grade Trup Cdos range from a low of C to a high of Ba2. On the Trup Cdos that have not been deemed to be other-than-temporarily impaired, the collateralization ratios range from a low of 106.0% to a high of 461.3%, with a median of 283.6%, and a weighted average of 301.6%. The collateralization ratio is defined as the current performing collateral in a security, divided by the current balance of the specific tranche the Company owns, plus any debt which is senior or pari passu with the Company’s security’s priority level. Performing collateral excludes the balance of any issuer that has either defaulted or has deferred its interest payment. It is not uncommon for the collateralization of a security that is not other-than-temporarily impaired to be less than 100% due to the excess spread built into the securitization structure. Except for the debt securities that have already been deemed to be other-than-temporarily impaired, management does not believe any other individual security with an unrealized loss as of December 31, 2017 is other-than-temporarily impaired. For these securities, United believes the decline in value resulted from changes in market interest rates, credit spreads and liquidity, not a change in the expected contractual cash flows. Based on a review of each of the securities in the investment portfolio, management concluded that it expected to recover the amortized cost basis of the investment in such securities. Equity securities The cost of United’s equity securities was $9,712,000 at December 31, 2017. For equity securities, management has evaluated the near-term prospects of the investment in relation to the severity and duration of any impairment and based on that evaluation, management determined that no equity securities were other-than-temporarily impaired at December 31, 2017. Other investment securities (cost method) During the fourth quarter of 2017, United also evaluated all of its cost method investments to determine if certain events or changes in circumstances during the quarter had a significant adverse effect on the fair value of any of its cost method securities. United determined that there were no events or changes in circumstances during the fourth quarter of 2017 which would have an adverse effect on the fair value of any of its cost method securities. Therefore, no impairment was recorded. Below is a progression of the credit losses on securities which United has recorded other-than-temporary charges. These charges were recorded through earnings and other comprehensive income. (In thousands) Year Ended December 31 2017 2016 2015 Balance of cumulative credit losses at beginning of period $ 22,162 $ 23,773 $ 23,739 Additional credit losses on securities for which OTTI was previously recognized 0 33 34 Reductions for securities sold or paid off during the period (4,102) (1,644) 0 Balance of cumulative credit losses at end of period $ 18,060 $ 22,162 $ 23,773 The amortized cost and estimated fair value of securities available for sale at December 31, 2017 by contractual maturity are shown below. Expected maturities may differ from contractual maturities because the issuers may have the right to call or prepay obligations without penalties. Maturities of mortgage-backed securities with an amortized cost of $1,283,933,000 and an estimated fair value of $1,274,962,000 at December 31, 2017 are included below based upon contractual maturity. Estimated (In thousands) Amortized Fair Cost Value Due in one year or less $ 50,311 $ 50,212 Due after one year through five years 386,039 384,585 Due after five years through ten years 400,129 398,208 Due after ten years 1,054,493 1,045,873 Marketable equity securities 9,712 9,878 Total $ 1,900,684 $ 1,888,756 The following is a summary of the amortized cost and estimated fair values of securities held to maturity. December 31, 2017 (In thousands) Amortized Gross Gross Estimated U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 5,187 $ 308 $ 0 $ 5,495 State and political subdivisions 5,797 10 0 5,807 Residential mortgage-backed securities Agency 23 3 0 26 Single issue trust preferred securities 9,401 0 731 8,670 Other corporate securities 20 0 0 20 Total $ 20,428 $ 321 $ 731 $ 20,018 December 31, 2016 (In thousands) Amortized Gross Gross Estimated U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 5,295 $ 570 $ 0 $ 5,865 State and political subdivisions 8,598 17 0 8,615 Residential mortgage-backed securities Agency 30 5 0 35 Single issue trust preferred securities 19,315 0 2,672 16,643 Other corporate securities 20 0 0 20 Total $ 33,258 $ 592 $ 2,672 $ 31,178 Even though the market value of the held-to-maturity held-to-maturity held-to-maturity No gross realized gains and losses on calls and sales of held to maturity securities have been included in earnings for the years ended December 31, 2017, 2016 and 2015. The amortized cost and estimated fair value of debt securities held to maturity at December 31, 2017 by contractual maturity are shown below. Expected maturities may differ from contractual maturities because the issuers may have the right to call or prepay obligations with or without call or prepayment penalties. Maturities of mortgage-backed securities with an amortized cost of $23,000 and an estimated fair value of $26,000 at December 31, 2017 are included below based upon contractual maturity. Estimated (In thousands) Amortized Fair Cost Value Due in one year or less $ 0 $ 0 Due after one year through five years 9,344 9,660 Due after five years through ten years 5,663 5,343 Due after ten years 5,421 5,015 Total $ 20,428 $ 20,018 The carrying value of securities pledged to secure public deposits, securities sold under agreements to repurchase, and for other purposes as required or permitted by law, approximated $1,403,565,000 and $1,137,408,000 at December 31, 2017 and 2016, respectively. The fair value of mortgage-backed mortgage-backed The following table sets forth the maturities of all securities (based on amortized cost) at December 31, 2017, and the weighted-average After 1 But After 5 But (Dollars in thousands) Within 1 Year Within 5 Years Within 10 Years After 10 Years Amount Yield Amount Yield Amount Yield Amount Yield U.S. Treasury and other U.S. Government agencies and corporations $ 20,018 0.71 % $ 58,560 2.43 % $ 9,882 2.50 % $ 31,462 2.84 % States and political subdivisions (1) 20,711 2.76 % 68,543 2.53 % 45,399 2.97 % 174,245 3.72 % Residential mortgage-backed securities Agency 160 3.68 % 2,535 4.40 % 157,860 2.30 % 661,325 2.49 % Non-agency 121 5.01 % 547 5.00 % 0 0.00 % 4,301 5.84 % Commercial mortgage-backed Agency 9,300 1.11 % 258,207 2.03 % 168,964 2.57 % 20,636 2.81 % Asset-backed securities 0 0.00 % 0 0.00 % 0 0.00 % 109,829 2.03 % Trust preferred collateralized debt obligations 0 0.00 % 0 0.00 % 0 0.00 % 37,856 3.89 % Single issue trust preferred securities 0 0.00 % 0 0.00 % 9,687 2.70 % 13,131 4.72 % Marketable equity securities 0 0.00 % 0 0.00 % 0 0.00 % 9,712 0.27 % Other Corporate securities 0 0.00 % 6,993 2.32 % 14,000 5.21 % 7,128 0.75 % (1) Tax-equivalent There are no securities with a single issuer, other than the U.S. government and its agencies and corporations, the book value of which in the aggregate exceeds 10% of United’s total shareholders’ equity.

Loans

Loans	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Loans	NOTE D—LOANS Major classes of loans are as follows: December 31 (In thousands) 2017 2016 Commercial, financial, and agricultural Owner-occupied $ 1,361,629 $ 1,049,885 Nonowner-occupied 4,451,298 3,425,453 Other commercial 1,998,979 1,613,437 Total commercial, financial & agricultural 7,811,906 6,088,775 Residential real estate 2,996,171 2,403,437 Construction & land development 1,504,907 1,255,738 Consumer: Bankcard 10,314 14,187 Other Consumer 704,039 594,582 Less: Unearned interest (15,916) (15,582) Total Loans, net of unearned interest $ 13,011,421 $ 10,341,137 The table above does not include loans held for sale of $265,955,000 and $8,445,000 at December 31, 2017 and December 31, 2016, respectively. Loans held for sale consist of single-family residential real estate loans originated for sale in the secondary market. The outstanding balances in the table above include previously acquired impaired loans with a recorded investment of $210,521,000 or 1.62% of total gross loans at December 31, 2017 and $171,596,000 or 1.66% of total gross loans at December 31, 2016. The contractual principal in these acquired impaired loans was $285,964,000 and $231,096,000 at December 31, 2017 and December 31, 2016, respectively. The balances above do not include future accretable net interest (i.e. the difference between the undiscounted expected cash flows and the recorded investment in the loan) on the acquired impaired loans. Activity for the accretable yield for the year of 2017 follows. (In thousands) Accretable yield at the beginning of the period $ 29,165 Accretion (including cash recoveries) (15,490 ) Additions 17,444 Net reclassifications to accretable from non-accretable 13,424 Disposals (including maturities, foreclosures, and charge-offs) (5,445 ) Accretable yield at the ending of the period $ 39,098 At December 31, 2017 and 2016, loans-in-process United’s subsidiary bank has made loans, in the normal course of business, to the directors and officers of United and its subsidiaries, and to their associates. The aggregate dollar amount of these loans was $36,360,000 and $255,476,000 at December 31, 2017 and 2016, respectively. During 2017, $17,837,000 of new loans were made and repayments totaled $64,556,000. There was also a reduction of $172,397,000 in loans due to a merger of United’s banking subsidiaries in 2017 and the resulting change in the composition of the bank’s board of directors.

Credit Quality

Credit Quality	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Credit Quality	NOTE E—CREDIT QUALITY Management monitors the credit quality of its loans on an ongoing basis. Measurement of delinquency and past due status are based on the contractual terms of each loan. For all loan classes, past due loans are reviewed on a monthly basis to identify loans for nonaccrual status. Generally, when collection in full of the principal and interest is jeopardized, the loan is placed on nonaccrual status. The accrual of interest income on commercial and most consumer loans generally is discontinued when a loan becomes 90 to 120 days past due as to principal or interest. However, regardless of delinquency status, if a loan is fully secured and in the process of collection and resolution of collection is expected in the near term (generally less than 90 days), then the loan will not be placed on nonaccrual status. When interest accruals are discontinued, unpaid interest recognized in income in the current year is reversed, and unpaid interest accrued in prior years is charged to the allowance for loan losses. United’s method of income recognition for loans that are classified as nonaccrual is to recognize interest income on a cash basis or apply the cash receipt to principal when the ultimate collectibility of principal is in doubt. Nonaccrual loans will not normally be returned to accrual status unless all past due principal and interest has been paid and the borrower has evidenced their ability to meet the contractual provisions of the note. A loan is categorized as a troubled debt restructuring (TDR) if a concession is granted and there is deterioration in the financial condition of the borrower. TDRs can take the form of a reduction of the stated interest rate, splitting a loan into separate loans with market terms on one loan and concessionary terms on the other loan, receipts of assets from a debtor in partial or full satisfaction of a loan, the extension of the maturity date or dates at a stated interest rate lower than the current market rate for new debt with similar risk, the reduction of the face amount or maturity amount of the debt as stated in the instrument or other agreement, the reduction of accrued interest or any other concessionary type of renegotiated debt. As of December 31, 2017, United had TDRs of $50,129,000 as compared to $21,152,000 as of December 31, 2016. Of the $50,129,000 aggregate balance of TDRs at December 31, 2017, $30,868,000 was on nonaccrual, $95,000 were 90 days or more past due and $1,254,000 were 30 to 89 days past due. As of December 31, 2016, United had TDRs of $21,152,000. Of the $21,152,000 aggregate balance of TDRs at December 31, 2016, $11,106,000 was on nonaccrual status. All these amounts are included in the appropriate categories in the “Age Analysis of Past Due Loans” table on a subsequent page. As of December 31, 2017, there were no commitments to lend additional funds to debtors owing receivables whose terms have been modified in TDRs. At December 31, 2017, United had restructured loans in the amount of $2,001,000 that were modified by a reduction in the interest rate, $1,898,000 that were modified by a combination of a reduction in the interest rate and the principal and $46,230,000 that were modified by a change in terms. A loan acquired and accounted for under ASC topic 310-30 The following table sets forth United’s troubled debt restructurings that have been restructured during the year ended December 31, 2017 and 2016, segregated by class of loans: Troubled Debt Restructurings For the Year Ended December 31, 2017 December 31, 2016 Number of Pre- Modification Post- Number of Pre- Modification Post- Commercial real estate: Owner-occupied 1 $ 5,333 $ 5,327 1 $ 1,190 $ 1,178 Nonowner-occupied 0 0 0 0 0 0 Other commercial 13 32,211 29,411 7 2,803 2,213 Residential real estate 0 0 0 1 1,400 1,400 Construction & land development 1 1,456 1,383 0 0 0 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 0 0 0 0 0 0 Total 15 $ 39,000 $ 36,121 9 $ 5,393 $ 4,791 During 2017, $36,121,000 of restructured loans were modified by a change in terms. During 2016, $2,887,000 of restructured loans were modified by a change in loan terms and $1,904,000 of restructured loans were modified by a combination of a reduction in the interest rate and an extension of the maturity date. In some instances, the post-modification balance on a restructured loan is larger than the pre-modification The following table presents troubled debt restructurings, by class of loan, that had charge-offs during the year ended December 31, 2017 and 2016. These loans were restructured during the twelve months ended December 31, 2017 and 2016 and subsequently defaulted, resulting in principal charge-offs during the year of 2017 and 2016. Year Ended December 31, 2017 Year Ended December 31, 2016 (In thousands) Number of Recorded Number of Recorded Troubled Debt Restructurings Commercial real estate: Owner-occupied 0 $ 0 0 $ 0 Nonowner-occupied 0 0 0 0 Other commercial 1 1,495 1 37 Residential real estate 0 0 0 0 Construction & land development 0 0 0 0 Consumer: Bankcard 0 0 0 0 Other consumer 0 0 0 0 Total 1 $ 1,495 1 $ 37 The following table sets forth United’s age analysis of its past due loans, segregated by class of loans: Age Analysis of Past Due Loans As of December 31, 2017 (In thousands) 30-89 90 Days or Total Past Current & Total Financing Recorded Commercial real estate: Owner-occupied $ 7,968 $ 13,663 $ 21,631 $ 1,339,998 $ 1,361,629 $ 458 Nonowner-occupied 10,398 20,448 30,846 4,420,452 4,451,298 634 Other commercial 11,533 68,476 80,009 1,918,970 1,998,979 940 Residential real estate 35,300 28,637 63,937 2,932,234 2,996,171 6,519 Construction & land development 1,615 17,190 18,805 1,486,102 1,504,907 385 Consumer: Bankcard 449 186 635 9,679 10,314 186 Other consumer 9,288 968 10,256 693,783 704,039 775 Total $ 76,551 $ 149,568 $ 226,119 $ 12,801,218 $ 13,027,337 $ 9,897 (1) Other includes loans with a recorded investment of $210,521 acquired and accounted for under ASC topic 310-30 Age Analysis of Past Due Loans As of December 31, 2016 (In thousands) 30-89 90 Days or Total Past Current & Total Financing Recorded Commercial real estate: Owner-occupied $ 5,850 $ 3,981 $ 9,831 $ 1,040,054 $ 1,049,885 $ 94 Nonowner-occupied 9,288 20,847 30,135 3,395,318 3,425,453 172 Other commercial 15,273 42,766 58,039 1,555,398 1,613,437 2,518 Residential real estate 29,976 25,991 55,967 2,347,470 2,403,437 4,216 Construction & land development 3,809 7,779 11,588 1,244,150 1,255,738 33 Consumer: Bankcard 422 141 563 13,624 14,187 141 Other consumer 10,015 1,712 11,727 582,855 594,582 1,412 Total $ 74,633 $ 103,217 $ 177,850 $ 10,178,869 $ 10,356,719 $ 8,586 (1) Other includes loans with a recorded investment of $171,596 acquired and accounted for under ASC topic 310-30 The following table sets forth United’s nonaccrual loans, segregated by class of loans: Loans on Nonaccrual Status (In thousands) December 31, 2017 December 31, 2016 Commercial real estate: Owner-occupied $ 13,205 $ 3,887 Nonowner-occupied 19,814 20,675 Other commercial 67,536 40,248 Residential real estate 22,118 21,775 Construction & land development 16,805 7,746 Consumer: Bankcard 0 0 Other consumer 193 300 Total $ 139,671 $ 94,631 United assigns credit quality indicators of pass, special mention, substandard and doubtful to its loans. For United’s loans with a corporate credit exposure, United internally assigns a grade based on the creditworthiness of the borrower. For loans with a consumer credit exposure, United internally assigns a grade based upon an individual loan’s delinquency status. United reviews and updates, as necessary, these grades on a quarterly basis. Special mention loans, with a corporate credit exposure, have potential weaknesses that deserve management’s close attention. If left uncorrected, these potential weaknesses may result in deterioration of the repayment prospects for the loans or in the Company’s credit position at some future date. Borrowers may be experiencing adverse operating trends (declining revenues or margins) or an ill proportioned balance sheet (e.g., increasing inventory without an increase in sales, high leverage, tight liquidity). Adverse economic or market conditions, such as interest rate increases or the entry of a new competitor, may also support a special mention rating. Nonfinancial reasons for rating a credit exposure special mention include management problems, pending litigation, an ineffective loan agreement or other material structural weakness, and any other significant deviation from prudent lending practices. For loans with a consumer credit exposure, loans that are past due 30-89 A substandard loan with a corporate credit exposure is inadequately protected by the current sound worth and paying capacity of the obligor or of the collateral pledged, if any. Loans so classified have a well-defined weakness, or weaknesses, that jeopardize the liquidation of the debt by the borrower. They are characterized by the distinct possibility that the Company will sustain some loss if the deficiencies are not corrected. They require more intensive supervision by management. Substandard loans are generally characterized by current or expected unprofitable operations, inadequate debt service coverage, inadequate liquidity, or marginal capitalization. Repayment may depend on collateral or other credit risk mitigants. For some substandard loans, the likelihood of full collection of interest and principal may be in doubt and thus, placed on nonaccrual. For loans with a consumer credit exposure, loans that are 90 days or more past due or that have been placed on nonaccrual are considered substandard. A loan with corporate credit exposure is classified as doubtful if it has all the weaknesses inherent in one classified as substandard with the added characteristic that the weaknesses make collection in full, on the basis of currently existing facts, conditions, and values, highly questionable and improbable. A doubtful loan has a high probability of total or substantial loss, but because of specific pending events that may strengthen the loan, its classification as loss is deferred. Doubtful borrowers are usually in default, lack adequate liquidity or capital, and lack the resources necessary to remain an operating entity. Pending events can include mergers, acquisitions, liquidations, capital injections, the perfection of liens on additional collateral, the valuation of collateral, and refinancing. Generally, there are not any loans with a consumer credit exposure that are classified as doubtful. Usually, they are charged-off The following tables set forth United’s credit quality indicators information, by class of loans: Credit Quality Indicators Corporate Credit Exposure As of December 31, 2017 Commercial Real Estate (In thousands) Owner- Nonowner- Other Construction & Grade: Pass $ 1,276,088 $ 4,312,985 $ 1,848,868 $ 1,413,706 Special mention 20,165 57,618 55,564 5,196 Substandard 65,376 80,695 90,625 86,005 Doubtful 0 0 3,922 0 Total $ 1,361,629 $ 4,451,298 $ 1,998,979 $ 1,504,907 Credit Quality Indicators Corporate Credit Exposure As of December 31, 2016 Commercial Real Estate (In thousands) Owner- Nonowner- Other Construction & Grade: Pass $ 963,503 $ 3,284,497 $ 1,463,797 $ 1,126,742 Special mention 20,490 36,462 26,537 52,327 Substandard 65,892 104,494 122,893 76,669 Doubtful 0 0 210 0 Total $ 1,049,885 $ 3,425,453 $ 1,613,437 $ 1,255,738 Credit Quality Indicators Consumer Credit Exposure As of December 31, 2017 (In thousands) Residential Bankcard Other Grade: Pass $ 2,945,266 $ 9,679 $ 693,727 Special mention 18,025 449 9,334 Substandard 32,880 186 978 Doubtful 0 0 0 Total $ 2,996,171 $ 10,314 $ 704,039 As of December 31, 2016 (In thousands) Residential Bankcard Other Grade: Pass $ 2,348,017 $ 13,624 $ 582,704 Special mention 18,240 422 10,132 Substandard 36,995 141 1,746 Doubtful 185 0 0 Total $ 2,403,437 $ 14,187 $ 594,582 Loans are designated as impaired when, in the opinion of management, based on current information and events, the collection of principal and interest in accordance with the loan contract is doubtful. Typically, United does not consider loans for impairment unless a sustained period of delinquency (i.e. 90-plus smaller-balance The following table set forth United’s impaired loans information, by class of loans: Impaired Loans December 31, 2017 December 31, 2016 (In thousands) Recorded Unpaid Related Recorded Unpaid Related With no related allowance recorded: Commercial real estate: Owner-occupied $ 61,897 $ 62,661 $ 0 $ 46,575 $ 47,108 $ 0 Nonowner-occupied 107,476 107,927 0 92,654 93,104 0 Other commercial 86,477 90,610 0 46,064 48,308 0 Residential real estate 36,923 38,863 0 22,747 24,404 0 Construction & land development 76,845 79,110 0 19,863 21,746 0 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 59 59 0 36 36 0 With an allowance recorded: Commercial real estate: Owner-occupied $ 9,132 $ 9,132 $ 2,251 $ 1,787 $ 2,082 $ 815 Nonowner-occupied 3,957 3,956 1,592 17,938 17,938 2,524 Other commercial 60,471 74,792 16,721 43,774 46,188 13,441 Residential real estate 9,813 11,152 1,552 12,066 12,801 3,431 Construction & land development 1,383 5,881 229 4,940 7,899 3,206 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 0 0 0 0 0 0 Total: Commercial real estate: Owner-occupied $ 71,029 $ 71,793 $ 2,251 $ 48,362 $ 49,190 $ 815 Nonowner-occupied 111,433 111,883 1,592 110,592 111,042 2,524 Other commercial 146,948 165,402 16,721 89,838 94,496 13,441 Residential real estate 46,736 50,015 1,552 34,813 37,205 3,431 Construction & land development 78,228 84,991 229 24,803 29,645 3,206 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 59 59 0 36 36 0 Impaired Loans For the Year Ended December 31, 2017 December 31, 2016 (In thousands) Average Interest Average Interest With no related allowance recorded: Commercial real estate: Owner-occupied $ 56,202 $ 2,013 $ 36,800 $ 1,038 Nonowner-occupied 96,318 4,264 75,848 1,108 Other commercial 61,223 3,861 39,776 1,540 Residential real estate 23,618 986 25,964 538 Construction & land development 32,396 1,830 24,902 133 Consumer: Bankcard 0 0 0 0 Other consumer 36 0 33 0 With an allowance recorded: Commercial real estate: Owner-occupied $ 9,541 $ 610 $ 3,138 $ 97 Nonowner-occupied 12,593 539 11,920 564 Other commercial 63,963 2,208 36,511 1,615 Residential real estate 13,298 185 9,585 342 Construction & land development 2,597 85 8,994 83 Consumer: Bankcard 0 0 0 0 Other consumer 0 0 0 0 Total: Commercial real estate: Owner-occupied $ 65,743 $ 2,623 $ 39,938 $ 1,135 Nonowner-occupied 108,911 4,803 87,768 1,672 Other commercial 125,186 6,069 76,287 3,155 Residential real estate 36,916 1,171 35,549 880 Construction & land development 34,993 1,915 33,896 216 Consumer: Bankcard 0 0 0 0 Other consumer 36 0 33 0

Allowance for Credit Losses

Allowance for Credit Losses	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Allowance for Credit Losses	NOTE F--ALLOWANCE The allowance for loan losses is management’s estimate of the probable credit losses inherent in the loan portfolio. For purposes of determining the general allowance, the loan portfolio is segregated by product type to recognize differing risk profiles among categories. It is further segregated by credit grade for non-homogenous Loans deemed to be uncollectible are charged against the allowance for loan losses, while recoveries of previously charged-off charge-off charge-off charged-off charge-off For consumer loans, closed-end open-end charged-off. one-to-four open-end closed-end high-loan-to-value charges-off charged-off charged-off For loans acquired through the completion of a transfer, including loans acquired in a business combination, that have evidence of deterioration of credit quality since origination and for which it is probable, at acquisition, that United will be unable to collect all contractually required payment receivable are initially recorded at fair value (as determined by the present value of expected future cash flows) with no valuation allowance. The difference between the undiscounted cash flows expected at acquisition and the investment in the loan, or the “accretable yield,” is recognized as interest income on a level-yield method over the life of the loan. Contractually required payments for interest and principal that exceed the undiscounted cash flows expected at acquisition, or the “nonaccretable difference,” are not recognized as a yield adjustment or as a loss accrual or a valuation allowance. Increases in expected cash flows subsequent to the initial investment are recognized prospectively through adjustment of the yield on the loan over its remaining life. Decreases in expected cash flows are recognized as impairment. Valuation allowances on these impaired loans reflect only losses incurred after the acquisition (meaning the present value of all cash flows expected at acquisition that ultimately are not to be received). The amount of provision for loan losses related to loans acquired that have evidence of deterioration of credit quality resulted in a reversal of provision for loan losses expense of $1,106,000 for the year of 2017 and provision for loan losses expense of $1,676,000, and $5,321,000 for the years of 2016, and 2015, respectively. A progression of the allowance for loan losses, by portfolio segment, for the year ended December 31, 2017 and 2016 is summarized as follows: Allowance for Loan Losses and Carrying Amount of Loans For the Year Ended December 31, 2017 (In thousands) Commercial Real Other Residential Construction & Land Consumer Allowance Total Owner- Nonowner- Allowance for Loan Losses: Beginning balance $ 5,273 $ 6,883 $ 33,087 $ 13,770 $ 10,606 $ 2,805 $ 347 $ 72,771 Charge-offs 2,246 296 21,189 2,973 3,337 2,822 0 32,863 Recoveries 2,599 244 3,395 601 726 748 0 8,313 Provision (225) (462) 29,896 (1,471) (808) 1,750 (274) 28,406 Ending balance $ 5,401 $ 6,369 $ 45,189 $ 9,927 $ 7,187 $ 2,481 $ 73 $ 76,627 Ending Balance: individually evaluated for impairment $ 2,251 $ 1,592 $ 16,721 $ 1,552 $ 229 $ 0 $ 0 $ 22,345 Ending Balance: collectively evaluated for impairment $ 3,150 $ 4,777 $ 28,468 $ 8,375 $ 6,958 $ 2,481 $ 73 $ 54,282 Ending Balance: $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Financing receivables: Ending balance $ 1,361,629 $ 4,451,298 $ 1,998,979 $ 2,996,171 $ 1,504,907 $ 714,353 $ 0 $ 13,027,337 Ending Balance: individually evaluated for impairment $ 36,721 $ 21,851 $ 78,715 $ 14,316 $ 16,921 $ 0 $ 0 $ 168,524 Ending Balance: collectively evaluated for impairment $ 1,291,379 $ 4,320,997 $ 1,892,706 $ 2,967,666 $ 1,461,206 $ 714,338 $ 0 $ 12,648,292 Ending Balance: $ 33,529 $ 108,450 $ 27,558 $ 14,189 $ 26,780 $ 15 $ 0 $ 210,521 Allowance for Loan Losses and Carrying Amount of Loans For the Year Ended December 31, 2016 (In thousands) Commercial Real Other Residential Construction & Land Consumer Allowance Total Owner- Nonowner- Allowance for Loan Losses: Beginning balance $ 3,637 $ 5,309 $ 31,328 $ 15,148 $ 18,205 $ 1,995 $ 104 $ 75,726 Charge-offs 5,281 419 20,430 4,597 2,659 2,794 0 36,180 Recoveries 3,071 675 3,452 639 433 446 0 8,716 Provision 3,846 1,318 18,737 2,580 (5,373) 3,158 243 24,509 Ending balance $ 5,273 $ 6,883 $ 33,087 $ 13,770 $ 10,606 $ 2,805 $ 347 $ 72,771 Ending Balance: individually evaluated for impairment $ 815 $ 2,524 $ 13,441 $ 3,431 $ 3,206 $ 0 $ 0 $ 23,417 Ending Balance: collectively evaluated for impairment $ 4,458 $ 4,359 $ 19,646 $ 10,339 $ 7,400 $ 2,805 $ 347 $ 49,354 Ending Balance: $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Financing receivables: Ending balance $ 1,049,885 $ 3,425,453 $ 1,613,437 $ 2,403,437 $ 1,255,738 $ 608,769 $ 0 $ 10,356,719 Ending Balance: individually evaluated for impairment $ 18,976 $ 26,835 $ 56,091 $ 14,766 $ 8,152 $ 0 $ 0 $ 124,820 Ending Balance: collectively evaluated for impairment $ 1,005,999 $ 3,323,117 $ 1,527,479 $ 2,373,969 $ 1,221,006 $ 608,733 $ 0 $ 10,060,303 Ending Balance: $ 24,910 $ 75,501 $ 29,867 $ 14,702 $ 26,580 $ 36 $ 0 $ 171,596 United maintains an allowance for loan losses and a reserve for lending-related commitments such as unfunded loan commitments and letters of credit. The reserve for lending-related commitments of $679,000 and $1,044,000 at December 31, 2017 and December 31, 2016, respectively, is separately classified on the balance sheet and is included in other liabilities. The combined allowance for loan losses and reserve for lending-related commitments are referred to as the allowance for credit losses. A progression of the allowance for credit losses, which includes the allowance for loan losses and the reserve for lending-related commitments, for the periods presented is summarized as follows: Year Ended December 31 (In thousands) 2017 2016 2015 Balance of allowance for loan losses at beginning of period $ 72,771 $ 75,726 $ 75,529 Provision for loan losses 28,406 24,509 22,574 101,177 100,235 98,103 Loans charged off 32,863 36,180 25,499 Less recoveries (8,313) (8,716) (3,122) Net charge-offs 24,550 27,464 22,377 Balance of allowance for loan losses at end of period $ 76,627 $ 72,771 $ 75,726 Reserve for lending-related commitments 679 1,044 936 Balance of allowance for credit losses at end of period $ 77,306 $ 73,815 $ 76,662

Bank Premises and Equipment and

Bank Premises and Equipment and Leases	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Bank Premises and Equipment and Leases	NOTE G—BANK PREMISES AND EQUIPMENT AND LEASES Bank premises and equipment are summarized as follows: December 31 (In thousands) 2017 2016 Land $ 34,970 $ 24,238 Buildings and improvements 103,914 89,302 Leasehold improvements 44,684 33,194 Furniture, fixtures and equipment 99,232 65,598 282,799 212,332 Less allowance for depreciation and amortization 177,905 136,423 Net bank premises and equipment $ 104,894 $ 75,909 Depreciation expense was $8,914,000, $7,889,000, and $8,385,000 for years ending December 31, 2017, 2016 and 2015, respectively, while amortization expense was $122,000 for the year ended December 31, 2017 and $136,000 for the years ended December 31, 2016 and 2015, respectively. United and certain subsidiaries have entered into various noncancelable-operating leases. These noncancelable operating leases are subject to renewal options under various terms and some leases provide for periodic rate adjustments based on cost-of-living Future minimum lease payments, by year and in the aggregate, under noncancelable operating leases with initial or remaining terms of one year or more, for years subsequent to December 31, 2017, consisted of the following: Year Amount (In thousands) 2018 $ 14,753 2019 13,117 2020 11,249 2021 9,529 2022 6,400 Thereafter 14,796 Total minimum lease payments $ 69,844

Goodwill and Other Intangibles

Goodwill and Other Intangibles	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	NOTE H—GOODWILL AND OTHER INTANGIBLES The following is a summary of intangible assets subject to amortization and those not subject to amortization: December 31, 2017 Community Banking Mortgage Banking Total (In thousands) Gross Carrying Accumulated Gross Carrying Accumulated Gross Carrying Accumulated Amortized intangible assets: Core deposit intangible assets $ 98,359 ($ 54,453 ) $ 0 $ 0 $ 98,359 ($ 54,453) Non-amortized George Mason trade name $ 0 $ 1,080 $ 1,080 Goodwill not subject to amortization $ 1,473,265 $ 5,115 $ 1,478,380 December 31, 2016 Community Banking Total (In thousands) Gross Carrying Accumulated Gross Carrying Accumulated Amortized intangible assets: Core deposit intangible assets $ 69,635 ($ 46,681) $ 69,635 ($ 46,681) Goodwill not subject to amortization $ 863,767 $ 863,767 The following table provides a reconciliation of goodwill: (In thousands) Community Mortgage Total Goodwill at December 31, 2016 $ 863,767 $ 0 $ 863,767 Addition to goodwill from Bank of Georgetown acquisition 1,327 0 1,327 Preliminary addition to goodwill from Cardinal acquisition 608,171 5,115 613,286 Goodwill at December 31, 2017 $ 1,473,265 $ 5,115 $ 1,478,380 The following table sets forth the anticipated amortization expense for intangible assets for the years subsequent to 2017: Year Amount (In thousands) 2018 $ 8,039 2019 7,016 2020 6,309 2021 5,369 2022 and thereafter 17,173

Deposits

Deposits	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Deposits	NOTE I—DEPOSITS The book value of deposits consisted of the following: (In thousands) December 31 2017 2016 Demand deposits $ 4,294,687 $ 3,171,841 Interest-bearing checking 2,156,974 1,778,156 Regular savings 1,034,100 721,224 Money market accounts 3,756,259 3,151,896 Time deposits under $100,000 795,137 693,005 Time deposits over $100,000 1,793,434 1,280,745 Total deposits $ 13,830,591 $ 10,796,867 Included in time deposits over $100,000 at December 31, 2017 and 2016 were time deposits of $250,000 or more of $790,703,000 and $357,468,000, respectively. Interest paid on deposits approximated $48,887,000, $29,048,000, and $28,447,000 in 2017, 2016 and 2015, respectively. United’s subsidiary banks have received deposits, in the normal course of business, from the directors and officers of United and its subsidiaries, and their associates. Such related party deposits were accepted on substantially the same terms, including interest rates and maturities, as those prevailing at the time for comparable transactions with unrelated persons. The aggregate dollar amount of these deposits was $19,318,000 and $92,310,000 at December 31, 2017 and 2016, respectively. The decline was due mainly to a merger of United’s banking subsidiaries in 2017 and the resulting change in the composition of the bank’s board of directors.

Short-Term Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Short-Term Borrowings	NOTE J—SHORT-TERM BORROWINGS At December 31, 2017 and 2016, short-term borrowings and the related weighted-average interest rates were as follows: 2017 2016 Weighted- Weighted- (Dollars in thousands) Average Average Amount Rate Amount Rate Federal funds purchased $ 16,235 1.40 % $ 22,235 0.65 % Securities sold under agreements to repurchase 261,352 (1) 0.36 % (1) 187,316 (1) 0.25 % (1) Total $ 277,587 $ 209,551 (1) Excludes a wholesale security sold under an agreement to repurchase assumed in the Virginia Commerce merger of $50,000 with an interest rate of 4.37% at December 31, 2017 and 2016 and scheduled to mature in May of 2018. Federal funds purchased and securities sold under agreements to repurchase have been a significant source of funds for the company. United has various unused lines of credit available from certain of its correspondent banks in the aggregate amount of $180,000,000. These lines of credit, which bear interest at prevailing market rates, permit United to borrow funds in the overnight market, and are renewable annually subject to certain conditions. The following table shows the distribution of United’s federal funds purchased and securities sold under agreements to repurchase and the weighted-average interest rates thereon at the end of each of the last three years. Also provided are the maximum amount of borrowings and the average amounts of borrowings as well as weighted-average interest rates for the last three years. The table does not include the long-term wholesale security sold under an agreement to repurchase mentioned above assumed in the Virginia Commerce merger. (Dollars in thousands) Federal Funds Purchased Securities Sold Under To Repurchase At December 31: 2017 $ 16,235 $ 261,352 2016 22,235 187,316 2015 22,230 290,798 (Dollars in thousands) Federal Funds Purchased Securities Sold Under To Repurchase Weighted-average interest rate at year-end: 2017 1.40 % 0.36 % 2016 0.65 % 0.25 % 2015 0.25 % 0.15 % Maximum amount outstanding at any month’s end: 2017 $ 25,800 $ 377,687 2016 32,200 353,833 2015 52,000 379,818 Average amount outstanding during the year: 2017 $ 18,433 $ 287,663 2016 22,717 298,494 2015 38,526 283,011 Weighted-average interest rate during the year: 2017 0.88 % 0.33 % 2016 0.32 % 0.17 % 2015 0.21 % 0.10 % At December 31, 2017, all the repurchase agreements were in overnight accounts. The rates offered on these funds vary according to movements in the federal funds and short-term United has a $20,000,000 line of credit with an unrelated financial institution to provide for general liquidity needs. The line is an unsecured, revolving line of credit. The line is renewable on a 360 day basis and carries an indexed, floating-rate of interest. The line requires compliance with various financial and nonfinancial covenants. At December 31, 2017, United had no outstanding balance under this credit. Interest paid on short-term borrowings approximated $1,574,000, $1,587,000, and $835,000 in 2017, 2016 and 2015, respectively.

Long-Term Borrowings

Long-Term Borrowings	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Long-Term Borrowings	NOTE K—LONG-TERM BORROWINGS United’s subsidiary banks are members of the Federal Home Loan Bank (FHLB). Membership in the FHLB makes available short-term and long-term borrowings from collateralized advances. All FHLB borrowings are collateralized by a mix of single-family residential mortgage loans, commercial loans and investment securities. At December 31, 2017, the total carrying value of loans pledged as collateral for FHLB advances approximated $4,511,587,000. United had an unused borrowing amount as of December 31, 2017 of approximately $2,244,843,000 available subject to delivery of collateral after certain trigger points. Advances may be called by the FHLB or redeemed by United based on predefined factors and penalties. At December 31, 2017 and 2016, FHLB advances and the related weighted-average interest rates were as follows: 2017 2016 (Dollars in thousands) Amount Weighted- Weighted- Amount Weighted- Weighted- FHLB advances $ 1,271,531 1.60 % 1.60 % $ 897,707 0.72 % 0.72 % Overnight funds of $200,000,000 were included in the $1,271,531,000 above at December 31, 2017. No overnight funds were included in the $897,707,000 above at December 31, 2016. The weighted-average effective rate considers the effect of any interest rate swaps designated as fair value hedges outstanding at year-end A long-term wholesale security sold under an agreement to repurchase was assumed in the Virginia Commerce merger. At December 31, 2017 and 2016, the balance of the wholesale security sold under an agreement to repurchase was $50,000,000. The repurchase agreement had an interest rate of 4.37% at December 31, 2017 and 2016 and is scheduled to mature in May of 2018. At December 31, 2017, United had a total of fifteen statutory business trusts that were formed for the purpose of issuing or participating in pools of trust preferred capital securities (Capital Securities) with the proceeds invested in junior subordinated debt securities (Debentures) of United. The Debentures, which are subordinate and junior in right of payment to all present and future senior indebtedness and certain other financial obligations of United, are the sole assets of the trusts and United’s payment under the Debentures is the sole source of revenue for the trusts. At December 31, 2017 and 2016, the outstanding balance of the Debentures was $242,446,000 and $224,319,000, respectively, and was included in the category of long-term debt on the Consolidated Balance Sheets entitled “Other long-term borrowings.” The Capital Securities are not included as a component of shareholders’ equity in the Consolidated Balance Sheets. United fully and unconditionally guarantees each individual trust’s obligations under the Capital Securities. Under the provisions of the subordinated debt, United has the right to defer payment of interest on the subordinated debt at any time, or from time to time, for periods not exceeding five years. If interest payments on the subordinated debt are deferred, the dividends on the Capital Securities are also deferred. Interest on the subordinated debt is cumulative. For reporting periods prior to June 30, 2017, the Trust Preferred Securities qualified as Tier 1 regulatory capital under the “Basel III Capital Rules” as published by United’s primary federal regulator, the Federal Reserve, in July of 2013. The “Basel III Capital Rules” established a new comprehensive capital framework for U.S. banking organizations. Because United was less than $15 billion in total consolidated assets, the Basel III Capital Rules grandfathered United’s Trust Preferred Securities as Tier 1 capital under the limitations for restricted capital elements in the general risk-based capital rules. As a result, beginning in 2015 (the adoption date), United’s Trust Preferred Securities was subject to a limit of 25 percent of Tier 1 capital elements excluding any non-qualifying phase-out. Information related to United’s statutory trusts is presented in the table below: (Dollars in thousands) Description Issuance Date Amount of Interest Rate Maturity Date Century Trust March 23, 2000 $ 8,800 10.875% Fixed March 8, 2030 United Statutory Trust III December 17, 2003 $20,000 3-month LIBOR + 2.85% December 17, 2033 United Statutory Trust IV December 19, 2003 $25,000 3-month LIBOR + 2.85% January 23, 2034 United Statutory Trust V July 12, 2007 $50,000 3-month LIBOR + 1.55% October 1, 2037 United Statutory Trust VI September 20, 2007 $30,000 3-month LIBOR + 1.30% December 15, 2037 Premier Statutory Trust II September 25, 2003 $ 6,000 3-month LIBOR + 3.10% October 8, 2033 Premier Statutory Trust III May 16, 2005 $ 8,000 3-month LIBOR + 1.74% June 15, 2035 Premier Statutory Trust IV June 20, 2006 $14,000 3-month LIBOR + 1.55% September 23, 2036 Premier Statutory Trust V December 14, 2006 $10,000 3-month LIBOR + 1.61% March 1, 2037 Centra Statutory Trust I September 20, 2004 $10,000 3-month LIBOR + 2.29% September 20, 2034 Centra Statutory Trust II June 15, 2006 $10,000 3-month LIBOR + 1.65% July 7, 2036 Virginia Commerce Trust II December 19, 2002 $15,000 6-month LIBOR + 3.30% December 19, 2032 Virginia Commerce Trust III December 20, 2005 $25,000 3-month LIBOR + 1.42% February 23, 2036 Cardinal Statutory Trust I July 27, 2004 $20,000 3-month LIBOR + 2.40% September 15, 2034 UFBC Capital Trust I December 30, 2004 $ 5,000 3-month LIBOR + 2.10% March 15, 2035 At December 31, 2017 and 2016, the Debentures and their related weighted-average interest rates were as follows: 2017 2016 (Dollars in thousands) Amount Weighted- Amount Weighted- Century Trust $ 8,800 10.88 % $ 8,800 10.88 % United Statutory Trust III 20,619 4.45 % 20,619 3.84 % United Statutory Trust IV 25,774 4.23 % 25,774 3.74 % United Statutory Trust V 51,547 2.89 % 51,547 2.40 % United Statutory Trust VI 30,928 2.89 % 30,928 2.26 % Premier Statutory Trust II 6,186 4.46 % 6,186 3.98 % Premier Statutory Trust III 8,248 3.33 % 8,248 2.70 % Premier Statutory Trust IV 14,433 3.23 % 14,433 2.55 % Premier Statutory Trust V 10,310 3.09 % 10,310 2.54 % Centra Statutory Trust I 10,000 3.92 % 10,000 3.29 % Centra Statutory Trust II 10,000 3.01 % 10,000 2.53 % Virginia Commerce Trust II 12,014 5.14 % 11,784 4.62 % Virginia Commerce Trust III 16,216 2.87 % 15,690 2.34 % Cardinal Statutory Trust I 14,031 3.99 % 0 0.00 % UFBC Capital Trust I 3,340 3.69 % 0 0.00 % Total $ 242,446 $ 224,319 At December 31, 2017, the scheduled maturities of long-term borrowings were as follows: Year Amount (In thousands) 2018 $ 795,439 2019 186,404 2020 40,871 2021 51,453 2022 and thereafter 289,810 Total $ 1,363,977 Interest paid on long-term borrowings approximated $22,254,000, $13,974,000, and $10,553,000 in 2017, 2016 and 2015, respectively.

Other Expense

Other Expense	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Expense	NOTE L—OTHER EXPENSE The following details certain items of other expense for the periods indicated: Year Ended December 31 (In thousands) 2017 2016 2015 Legal, consulting & other professional services $ 11,844 $ 9,763 $ 9,310 Franchise & other taxes not on income 12,586 7,778 7,055 Automated Teller Machine (ATM) expenses 6,686 7,365 7,107

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	NOTE M—INCOME TAXES The income tax provisions included in the consolidated statements of income are summarized as follows: (In thousands) Year Ended December 31 2017 2016 2015 Current (benefit) expense: Federal $ 65,459 $ 63,169 $ 58,373 State 7,960 5,154 5,428 Deferred expense: Federal 20,920 8,844 1,657 Tax Act remeasurement 37,732 0 0 State 2,175 (1,592 ) 72 Total income taxes $ 134,246 $ 75,575 $ 65,530 On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was signed into law. The Tax Act lowered the Federal corporate tax rate from 35% to 21% effective January 1, 2018 and made numerous other tax law changes. U.S. generally accepted accounting principles (GAAP) requires companies to recognize the effect of tax law changes in the period of enactment. As a result of the Tax Act, United was required to remeasure deferred tax assets and liabilities at the new tax rate and as a result, recorded deferred tax expense of $37,732,000 in the fourth quarter of 2017. Reasonable estimates were made based on the Company’s analysis of the Tax Act. This provisional amount may be adjusted in future periods during 2018 when additional information is obtained as provided for under Staff Accounting Bulletin (“SAB 118”). Additional information that may affect our provisional amount would include further clarification and guidance on how the IRS will implement tax reform, further clarification and guidance on how state taxing authorities will implement tax reform and the related effect on the Company’s state income tax returns, completion of United’s 2017 tax return filings, and the potential for additional guidance from the SEC or the FASB related to the Tax Act. Management continues to evaluate other potential impacts of the Tax Act. The Company did not identify items for which the income tax effects of the Tax Act have not been completed and a reasonable estimate could not be determined as of December 31, 2017. The following is a reconciliation of income tax expense to the amount computed by applying the statutory federal income tax rate to income before income taxes. Year Ended December 31 (Dollars in thousands) 2017 2016 2015 Amount % Amount % Amount % Tax on income before taxes at statutory federal rate $ 99,689 35.0% $ 77,930 35.0% $ 71,222 35.0% Plus: State income taxes net of federal tax benefits 6,207 2.2 4,084 1.8 3,516 1.7 105,896 37.2 82,014 36.8 74,738 36.7 Increase (decrease) resulting from: Tax-exempt (5,362 ) (1.9 ) (3,919 ) (1.8 ) (4,158 ) (2.0 ) Deferred taxes due to the Tax Act 37,732 13.2 0 0.0 0 0.0 Historic tax credit 0 0.0 0 0.0 (1,262 ) (0.6 ) Other items-net (4,020 ) (1.4 ) (2,520 ) (1.1 ) (3,788 ) (1.9 ) Income taxes $ 134,246 47.1% $ 75,575 33.9% $ 65,530 32.2% For years ended 2017, 2016 and 2015, United incurred federal income tax expense applicable to the sales and calls of securities of $2,088,000, $114,000, and $73,000, respectively. Income taxes paid approximated $73,096,000, $61,905,000, and $52,319,000 in 2017, 2016 and 2015, respectively. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. At December 31, 2017, United had no federal or state net operating loss carryforwards. Taxes not on income, which consists mainly of business franchise taxes, were $12,586,000, $7,778,000, and $7,055,000 for the years ended December 31, 2017, 2016 and 2015, respectively. These amounts are recorded in other expense in the Consolidated Statements of Income. Significant components of United’s deferred tax assets and liabilities (included in other assets in the Consolidated Balance Sheets) at December 31, 2017 and 2016 are as follows: (In thousands) 2017 2016 Deferred tax assets: Allowance for credit losses $ 18,012 $ 26,941 Accrued benefits payable 12,175 0 Other accrued liabilities 779 3,478 Unrecognized components of net periodic pension costs 13,443 20,166 Unrealized loss on securities available for sale 2,797 1,436 Premises and equipment 0 93 Other real estate owned 3,169 6,724 Deferred mortgage points 3,028 0 Purchase accounting intangibles 14,855 41,392 Total deferred tax assets 68,258 100,230 Deferred tax liabilities: Deferred mortgage points 2,994 3,608 Accrued benefits payable 0 4,061 Premises and equipment 0 0 Other 1,627 13,687 Total deferred tax liabilities 4,621 21,356 Net deferred tax assets $ 63,637 $ 78,874 At December 31, 2017 and 2016, United believes that all of the deferred tax amounts shown above are more likely than not to be realized based on an assessment of all available positive and negative evidence and therefore no valuation allowance has been recorded. In accordance with ASC topic 740, “Income Taxes,” United records a liability for uncertain income tax positions based on a recognition threshold of more-likely-than-not, Below is a reconciliation of the total amounts of unrecognized tax benefits: December 31 (In thousands) 2017 2016 Unrecognized tax benefits at beginning of year $ 2,442 $ 2,102 Increase in unrecognized tax benefits as a result of tax positions taken during the current period 972 673 Decreases in the unrecognized tax benefits as a result of a lapse of the applicable statute of limitations (520) (333) Unrecognized tax benefits at end of year $ 2,894 $ 2,442 The entire amount of unrecognized tax benefits, if recognized, would impact United’s effective tax rate. Over the next 12 months, the statute of limitations will close on certain income tax returns. However, at this time, United cannot reasonably estimate the amount of tax benefits, if any, it may recognize over the next 12 months. United is currently open to audit under the statute of limitations by the Internal Revenue Service for the years ended December 31, 2014, 2015 and 2016 and certain State Taxing authorities for the years ended December 31, 2014 through 2016. As of December 31, 2017 and 2016, the total amount of accrued interest related to uncertain tax positions was $670,000 and $569,000, respectively. United accounts for interest and penalties related to uncertain tax positions as part of its provision for federal and state income taxes. No interest or penalties were recognized in the results of operations for the years of 2017, 2016 and 2015.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employee Benefit Plans	NOTE N—EMPLOYEE BENEFIT PLANS United has a defined benefit retirement plan covering a majority of all employees. Pension benefits are based on years of service and the average of the employee’s highest five consecutive plan years of basic compensation paid during the ten plan years preceding the date of determination. Contributions by United are intended to provide not only for benefits attributed to service to date, but also for those expected to be earned in the future. In September of 2007, after a recommendation by United’s Pension Committee and approval by United’s Board of Directors, the United Bankshares, Inc. Pension Plan (the Plan) was amended to change the participation rules. The decision to change the participation rules for the Plan followed current industry trends, as many large and medium size companies have taken similar steps. The amendment provided that employees hired on or after October 1, 2007, will not be eligible to participate in the Plan. However, new employees will continue to be eligible to participate in United’s Savings and Stock Investment 401(k) plan. This change had no impact on current employees hired prior to October 1, 2007 as they will continue to participate in the Plan, with no change in benefit provisions, and will continue to be eligible to participate in United’s Savings and Stock Investment 401(k) Plan. As of December 31, 2016, United changed the method used to estimate the interest cost component of net periodic benefit cost for the Plan. Under the previous method, appropriate spot rates were used to discount the projected benefit obligation (PBO) cash flows based on date of measurement. Then, a single aggregated discount rate was calculated such that the present value of the PBO remained the same. This rate is technically a weighted-average of the spot rates. This single discount rate was applied to the interest and service costs as well. Under the full yield curve approach, separate discount rates are used to calculate the present value for each projected cash flow. That is, individual spot rates are applied to the cash flows in each time period. This does not have any impact on the present value of the PBO as the PBO was originally discounted with spot rates. The adoption of this method concerns the manner in which it affects interest and service costs. Interest costs typically decrease when using this method because of the different weightings applied to the cash flows; that is, interest costs closer to the current period will be discounted with a smaller rate than those further in the future based on a typical yield curve, and greater future Interest Costs values are discounted with greater longer-term spot rates. Similarly, service costs typically have longer durations and will thus be subject to longer-term spot rates, decreasing the present value of these costs. As a result, the full yield curve method is preferable as it provides a more granular, and thus a more accurate, determination of costs. This new method constitutes a change in an accounting estimate under the provisions of ASC topic 250, “Accounting Changes and Error Corrections,” that is inseparable from a change in accounting principle and was accounted for prospectively, with the resulting change impacting the recognition of net periodic pension cost beginning January 1, 2017. The impact of this accounting change on United’s net periodic pension cost for the year of 2017 was a decline of $1,000,000 in expense from the amount that would have been recorded under the previous method. Net consolidated periodic pension cost included the following components: (Dollars in thousands) Year Ended December 31, 2017 2016 2015 Service cost $ 2,146 $ 2,374 $ 2,787 Interest cost 5,149 5,950 5,902 Expected return on plan assets (8,538) (8,089) (9,290) Recognized net actuarial loss 4,553 4,921 4,980 Amortization of prior service cost 0 0 1 Net periodic pension cost $ 3,310 $ 5,156 $ 4,380 Weighted-Average Assumptions: Discount rate 4.49% 4.75% 4.35% Expected return on assets 7.00% 7.25% 7.50% Rate of Compensation Increase (prior to age 45) 3.50% 3.50% 3.50% Rate of Compensation Increase (otherwise) 3.00% 3.00% 3.00% Amounts related to the Plan recognized as a component of other comprehensive income were as follows: (In thousands) Year Ended December 31, 2017 2016 2015 Net actuarial loss $ 6,784 $ 2,914 $ 2,402 Amortization of: Prior service cost 0 0 (1) Actuarial loss (4,553) (4,921) (4,980) Total recognized in other comprehensive income $ 2,231 $ (2,007) $ (2,579) Included in accumulated other comprehensive income at December 31, 2017 are unrecognized actuarial losses of $56,222,000 ($35,420,000 net of tax) that have not yet been recognized in net periodic pension cost. The amortization of this item expected to be recognized in net periodic pension cost during the fiscal year ended December 31, 2018 is $4,653,000 ($2,932,000 net of tax). The reconciliation of the beginning and ending balances of the projected benefit obligation and the fair value of plan assets for the years ended December 31, 2017 and 2016 and the accumulated benefit obligation at December 31, 2017 and 2016 are as follows: (Dollars in thousands) December 31, 2017 2016 Change in Projected Benefit Obligation Projected Benefit Obligation at the Beginning of the Year $ 134,515 $ 125,403 Service Cost 2,146 2,374 Interest Cost 5,149 5,950 Actuarial Loss (Gain) 15,367 5,114 Benefits Paid (4,437 ) (4,326 ) Projected Benefit at the End of the Year $ 152,740 $ 134,515 Accumulated Benefit Obligation at the End of the Year $ 139,025 $ 121,548 Change in Plan Assets Fair Value of Plan Assets at the Beginning of the Year $ 119,711 $ 113,748 Actual Return on Plan Assets 17,121 10,289 Benefits Paid (4,437 ) (4,326 ) Employer Contributions 10,000 0 Fair value of plan assets at end of year $ 142,395 $ 119,711 Net Amount Recognized Funded Status $ (10,346 ) $ (14,804 ) Unrecognized Transition Asset 0 0 Unrecognized Prior Service Cost 0 0 Unrecognized Net Loss 56,222 53,991 Net Amount Recognized $ 45,876 $ 39,187 Weighted-Average Assumptions at the End of the Year Discount Rate 3.83 % 4.49 % Rate of Compensation Increase (prior to age 45) 3.50 % 3.50 % Rate of Compensation Increase (otherwise) 3.00 % 3.00 % Asset allocation for the defined benefit pension plan as of the measurement date, by asset category, is as follows: Plan Assets Target Allocation 2018 Allowable Allocation Range Percentage of Plan Assets at December 31, December 31, Equity Securities 68 % 50-70 % 71 % 71% Debt Securities 25 % 20-50 % 26 % 26% Other 7 % 3-15 % 3 % 3% Total 100 % 100% Equity securities include United common stock in the amounts of $3,677,000 (3%) at December 31, 2017 and $4,894,000 (4%) at December 31, 2016 . The policy, as established by the Pension Committee, primarily consisting of United’s Executive Management, is to invest assets based upon the target allocations stated above. The assets are reallocated periodically to meet the above target allocations. The investment policy is reviewed at least annually, subject to the approval of the Pension Committee, to determine if the policy should be changed. Prohibited investments include, but are not limited to, futures contracts, private placements, uncovered options, real estate, the use of margin, short sales, derivatives for speculative purposes, and other investments that are speculative in nature. In order to achieve a prudent level of portfolio diversification, the securities of any one company are not to exceed 10% of the total plan assets, and no more than the 15% of total plan assets is to be invested in any one industry (other than securities of U.S. Government or Agencies). Additionally, no more than 15% of the plan assets is to be invested in foreign securities, both equity and fixed. The expected long-term rate of return for the plan’s total assets is based on the expected return of each of the above categories, weighted based on the median of the target allocation for each class. United uses the corridor approach based on 10% of the greater of the projected benefit obligation and the market-related value of plan assets to amortize actuarial gains and losses. At December 31, 2017, the benefits expected to be paid in each of the next five fiscal years, and in the aggregate for the five years thereafter are as follows: Year Amount (In thousands) 2018 $ 5,314 2019 5,304 2020 5,632 2021 6,012 2022 6,377 2023 through 2027 36,991 During the third quarter of 2017, United made a discretionary contribution of $10,000,000.United did not contribute to the plan in 2016 and 2015 as no contributions were required by funding regulations or law. For 2018, no contributions to the plan are required by funding regulations or law. However, United may make a discretionary contribution in 2018, the amount of which cannot be reasonably estimated at this time. In accordance with ASC topic 715 and using the guidance contained in ASC topic 820, the following is a description of the valuation methodologies used to measure the plan assets at fair value. Cash and Cash Equivalents: Debt Securities Common and Preferred Stock: Mutual Funds: The following tables present the balances of the plan assets, by fair value hierarchy level, as of December 31, 2017 and 2016: Fair Value Measurements at December 31, 2017 Using (In thousands) Description Balance as of December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash equivalents $ 4,549 $ 4,549 $ 0 $ 0 Fixed Income Mutual Funds: Taxable 30,752 30,752 0 0 Alternative 6,302 6,302 0 0 Equity Securities: Common stock 24,003 24,003 0 0 Equity Mutual Funds: Domestic equity large cap 28,936 28,936 0 0 Domestic equity mid cap 13,108 13,108 0 0 Domestic equity small cap 9,520 9,520 0 0 Domestic equity other 0 0 0 0 International emerging equity 5,264 5,264 0 0 International equity developed 15,752 15,752 0 0 Alternative equity 4,209 4,209 0 0 Total $ 142,395 $ 142,395 $ 0 $ 0 Fair Value Measurements at December 31, 2016 Using (In thousands) Description Balance as of December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash equivalents $ 1,778 $ 1,778 $ 0 $ 0 Fixed Income Securities: Mortgage backed securities 47 0 47 0 Collateralized mortgage obligations 48 0 48 0 Municipal obligations 670 0 670 0 Corporate bonds 1,169 0 1,169 0 Foreign bonds, notes and debentures 96 0 96 0 Fixed Income Mutual Funds: Taxable 26,816 26,816 0 0 Alternative 3,898 3,898 0 0 Equity Securities: Common stock 20,629 20,629 0 0 Equity Mutual Funds: Domestic equity large cap 23,063 23,063 0 0 Domestic equity mid cap 6,457 6,457 0 0 Domestic equity small cap 13,087 13,087 0 0 Domestic equity other 910 910 0 0 International emerging equity 3,120 3,120 0 0 International equity developed 12,619 12,619 0 0 Alternative equity 3,456 3,456 0 0 Domestic Balanced Mutual Funds 1,848 1,848 0 0 Total $ 119,711 $ 117,681 $ 2,030 $ 0 Common stock investments are diversified amongst various industries with no industry representing more than 5% of the total plan assets. The United Bankshares, Inc. Savings and Stock Investment Plan (the Plan) is a defined contribution plan under Section 401(k) of the Internal Revenue Code. Each employee of United, who completes ninety (90) days of qualified service, is eligible to participate in the Plan. Each participant may contribute from 1% to 100% of compensation to his/her account, subject to Internal Revenue Service maximum deferral limits. United matches 100% of the first 4% of salary deferred with United stock. Vesting is 100% for employee deferrals and the company match at the time the employee makes his/her deferral. United’s expense relating to the Plan approximated $3,201,000, $2,069,000, and $1,894,000 in 2017, 2016 and 2015, respectively. The assets of United’s defined benefit plan and 401(k) Plan each include investments in United common stock. At December 31, 2017 and 2016, the combined plan assets included 998,041 and 893,440 shares, respectively, of United common stock with an approximate fair value of $34,682,000 and $41,322,000, respectively. Dividends paid on United common stock held by the plans approximated $1,218,000, $1,173,000, and $1,139,000 for the years ended December 31, 2017, 2016, and 2015, respectively. United has certain other supplemental deferred compensation plans covering various key employees. Periodic charges are made to operations so that the liability due each employee is fully recorded as of the date of their retirement. Amounts charged to expense have not been significant in any year.

Stock Based Compensation

Stock Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Based Compensation	NOTE O—STOCK BASED COMPENSATION On May 18, 2016, United’s shareholders approved the 2016 Long-Term Incentive Plan (2016 LTI Plan). The 2016 LTI Plan became effective as of May 18, 2016. An award granted under the 2016 LTI Plan may consist of any non-qualified non-employee non-employee S-8 The 2016 LTI Plan replaces the 2011 Long-Term Incentive Plan (2011 LTI Plan) which expired during the second quarter of 2016. During the year of 2017, a total of 255,217 non-qualified Stock Options United currently has options outstanding from various option plans other than the 2011 LTI Plan (the Prior Plans); however, no common shares of United stock are available for grants under the Prior Plans as these plans have expired. Awards outstanding under the Prior Plans will remain in effect in accordance with their respective terms. The maximum term for options granted under the plans is ten (10) years. The fair value of the options for 2017 was estimated at the date of grant using a binomial lattice option pricing model with the following weighted-average assumptions: risk-free interest rates of 2.13%; dividend yield of 3.00%; volatility factors of the expected market price of United’s common stock of 0.262; and a weighted-average expected option life of 6.98 years, respectively. The estimated fair value of the options at the date of grant was $8.85 for the options granted during 2017. ASC topic 718, “Compensation – Stock Compensation” defines a lattice model as a model that produces an estimated fair value based on the assumed changes in prices of a financial instrument over successive periods of time. A binomial lattice model assumes at least two price movements are possible in each period of time. A summary of activity under the United’s stock option plans as of December 31, 2017, and the changes during the year of 2017 are presented below: Year ended December 31, 2017 Weighted Average (Dollars in thousands, except per share data) Aggregate Remaining Intrinsic Contractual Exercise Shares Value Term (Yrs.) Price Outstanding at January 1, 2017 1,411,735 $ 28.05 Assumed in acquisition of subsidiary 153,602 21.47 Granted 255,217 45.20 Exercised (220,905 ) 22.00 Forfeited or expired (41,211 ) 27.38 Outstanding at December 31, 2017 1,558,438 $ 8,761 5.8 $ 31.09 Exercisable at December 31, 2017 1,050,567 $ 8,528 4.6 $ 26.86 The following table summarizes the status of United’s nonvested awards for the year ended December 31, 2017: Shares Weighted-Average Nonvested at January 1, 2017 430,278 $ 6.84 Granted 255,217 8.85 Vested (174,624 ) 6.69 Forfeited or expired (3,000 ) 8.85 Nonvested at December 31, 2017 507,871 $ 7.89 As of December 31, 2017, the total unrecognized compensation cost related to nonvested option awards was $2,597,000 with a weighted-average expense recognition period of 1.2 years. The total fair value of awards vested during the year ended December 31, 2017, was $1,168,000. Cash received from options exercised under the Plans for the years ended December 31, 2017, 2016 and 2015 was $4,619,000, $13,337,000, and $7,871,000, respectively. During 2017 and 2016, 220,905 and 519,482 shares, respectively, were issued in connection with stock option exercises. All shares issued in connection with stock option exercises for 2017 and 2016 were issued from authorized and unissued stock. The weighted-average grant-date fair value of options granted in the year of 2017, 2016, and 2015 was $8.85, $6.97, and $7.23, respectively. The total intrinsic value of options exercised under the Plans during the years ended December 31, 2017, 2016, and 2015 was $3,721,000, $11,001,000, and $2,380,000, respectively. ASC topic 230, “Statement of Cash Flows,” requires the benefits of tax deductions in excess of recognized compensation cost to be reported as an operating cash flow. This requirement reduces net operating cash flows. While the company cannot estimate what those amounts will be in the future (because they depend on, among other things, the date employees exercise stock options), United recognized cash flows used in operating activities of $2,201,000, $4,008,000, and $1,023,000 from excess tax benefits related to share-based compensation arrangements for the year of 2017, 2016 and 2015, respectively. Restricted Stock Under the 2011 LTI Plan, United may award restricted common shares to key employees and non-employee The following summarizes the changes to United’s restricted common shares for the year ended December 31, 2017: Number of Weighted-Average Outstanding at January 1, 2017 137,268 $ 33.61 Granted 90,075 45.21 Vested 56,007 32.48 Forfeited 840 45.30 Outstanding at December 31, 2017 170,496 $ 40.05

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	NOTE P—COMMITMENTS AND CONTINGENT LIABILITIES United is a party to financial instruments with off-balance-sheet United’s maximum exposure to credit loss in the event of nonperformance by the counterparty to the financial instrument for the loan commitments and standby letters of credit is the contractual or notional amount of those instruments. United uses the same policies in making commitments and conditional obligations as it does for on-balance Commitments to extend credit are agreements to lend to a customer as long as there is no violation of any condition established in the commitment contract. Commitments generally have fixed expiration dates or other termination clauses and may require the payment of a fee. Since many of the commitments are expected to expire without being drawn upon, the total commitment amounts do not necessarily, and historically do not, represent future cash requirements. The amount of collateral obtained, if deemed necessary upon the extension of credit, is based on management’s credit evaluation of the counterparty. United had approximately $4,224,719,000 and $2,823,396,000 of loan commitments outstanding as of December 31, 2017 and 2016, respectively, the majority of which contractually expire within one year. Included in the December 31, 2017 amount are commitments to extend credit of $229,630,000 related to George Mason’s mortgage loan funding commitments and are of a shot-term nature. Commercial and standby letters of credit are agreements used by United’s customers as a means of improving their credit standing in their dealings with others. Under these agreements, United guarantees certain financial commitments of its customers. A commercial letter of credit is issued specifically to facilitate trade or commerce. Typically, under the terms of a commercial letter of credit, a commitment is drawn upon when the underlying transaction is consummated as intended between the customer and a third party. As of December 31, 2017, United had no outstanding commercial letters of credit and $9,000 as of December 31, 2016. A standby letter of credit is generally contingent upon the failure of a customer to perform according to the terms of an underlying contract with a third party. United has issued standby letters of credit of $147,017,000 and $121,584,000 as of December 31, 2017 and 2016, respectively. In accordance with ASC topic 450, “Contingencies,” United has determined that substantially all of its letters of credit are renewed on an annual basis and the fees associated with these letters of credit are immaterial. George Mason provides for its estimated exposure to repurchase loans previously sold to investors for which borrowers failed to provide full and accurate information on their loan application or for which appraisals have not been acceptable or where the loan was not underwritten in accordance with the loan program specified by the loan investor, and for other exposure to its investors related to loan sales activities. United evaluates the merits of each claim and estimates its reserve based on actual and expected claims received and considers the historical amounts paid to settle such claims. During 2017, George Mason settled with investors on such loans for a total of $59,000. This reserve had a balance of $516,000 for the year ended December 31, 2017. No expense related to this reserve was recorded for the year ended December 31, 2017. George Mason had a reserve balance of $575,000 on the Cardinal Acquisition Date. United has derivative counter-party risk that may arise from the possible inability of George Mason’s third party investors to meet the terms of their forward sales contracts. George Mason works with third-party investors that are generally well-capitalized, are investment grade and exhibit strong financial performance to mitigate this risk. United does not expect any third-party investor to fail to meet its obligation. United and its subsidiaries are currently involved in various legal proceedings in the normal course of business. Management is vigorously pursuing all its legal and factual defenses and, after consultation with legal counsel, believes that all such litigation will be resolved with no material effect on United’s financial position.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	NOTE Q—DERIVATIVE FINANCIAL INSTRUMENTS United uses derivative instruments to help aid against adverse price changes or interest rate movements on the value of certain assets or liabilities and on future cash flows. These derivatives may consist of interest rate swaps, caps, floors, collars, futures, forward contracts, written and purchased options. United also executes derivative instruments with its commercial banking customers to facilitate its risk management strategies. United accounts for its derivative financial instruments in accordance with the Derivatives and Hedging topic of the FASB Accounting Standards Codification. The Derivatives and Hedging topic require all derivative instruments to be carried at fair value on the balance sheet. United has designated certain derivative instruments used to manage interest rate risk as hedge relationships with certain assets, liabilities or cash flows being hedged. Certain derivatives used for interest rate risk management are not designated in a hedge relationship. Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Derivative instruments designated in a hedge relationship to mitigate exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. For a fair value hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to the hedged financial instrument. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a fair value hedge are offset in current period earnings. For a cash flow hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to other comprehensive income within shareholders’ equity, net of tax. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a cash flow hedge are offset to other comprehensive income, net of tax. The portion of a hedge that is ineffective is recognized immediately in earnings. At inception of a hedge relationship, United formally documents the hedged item, the particular risk management objective, the nature of the risk being hedged, the derivative being used, how effectiveness of the hedge will be assessed and how the ineffectiveness of the hedge will be measured. United also assesses hedge effectiveness at inception and on an ongoing basis using regression analysis. Hedge ineffectiveness is measured by using the change in fair value method. The change in fair value method compares the change in the fair value of the hedging derivative to the change in the fair value of the hedged exposure, attributable to changes in the benchmark rate. The portion of a hedge that is ineffective is recognized immediately in earnings. United through George Mason enters into interest rate lock commitments to finance residential mortgage loans with its customers. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by United. Interest rate risk arises on these commitments and subsequently closed loans if interest rates change between the time of the interest rate lock and the delivery of the loan to the investor. Market risk on interest rate lock commitments and mortgage loans held for sale is managed using corresponding forward mortgage loan sales contracts. United is a party to these forward mortgage loan sales contracts to sell loans servicing released and short sales of mortgage-backed securities. When the interest rate is locked with the borrower, the rate lock commitment, forward sale agreement, and mortgage-backed security position are undesignated derivatives and marked to fair value through earnings. The fair value of the rate lock derivative includes the servicing premium and the interest spread for the difference between retail and wholesale mortgage rates. Income from mortgage banking activities includes the gain recognized for the period presented and associated elements of fair value. United sells mortgage loans on either a best efforts or mandatory delivery basis. For loans sold on a mandatory delivery basis, United enters into forward mortgage-backed securities (the “residual hedge”) to mitigate the effect of interest rate risk. Both the rate lock commitment under mandatory delivery and the residual hedge are recorded at fair value through earnings and are not designated as accounting hedges. At the closing of the loan, the loan commitment derivative expires and United records a loan held for sale at fair value and continues to mark these assets to market under the election of fair value option. United closes out of the trading mortgage-backed securities assigned within the residual hedge and replaces the securities with a forward sales contract once a price has been accepted by an investor and recorded at fair value. For those loans selected to be sold under best efforts delivery, at the closing of the loan, the rate lock commitment derivative expires and the Company records a loan held for sale at fair value under the election of fair value option and continues to be obligated under the same forward loan sales contract entered into at inception of the rate lock commitment. The derivative portfolio also includes derivative financial instruments not included in hedge relationships. These derivatives consist of interest rate swaps used for interest rate management purposes and derivatives executed with commercial banking customers to facilitate their interest rate management strategies. For derivatives that are not designated in a hedge relationship, changes in the fair value of the derivatives are recognized in earnings in the same period as the change in fair value. Gains and losses on other derivative financial instruments are included in noninterest income and noninterest expense, respectively. The following tables disclose the derivative instruments’ location on the Company’s Consolidated Balance Sheets and the notional amount and fair value of those instruments at December 31, 2017 and 2016. Asset Derivatives December 31, 2017 December 31, 2016 (In thousands) Balance Sheet Location Notional Amount Fair Value Balance Sheet Location Notional Amount Fair Value Derivatives designated as hedging instruments Fair Value Hedges: Interest rate swap contracts (hedging commercial loans) Other assets $ 71,831 $ 538 Other assets $ 74,783 $ 24 Total derivatives designated as hedging instruments $ 71,831 $ 538 $ 74,783 $ 24 Derivatives not designated as hedging instruments Interest rate swap contracts Other assets $ 0 $ 0 Other assets $ 14,583 $ 2,267 Forward loan sales commitments Other assets 31,024 2 Other assets 0 0 Interest rate lock commitments Other assets 148,866 4,559 Other assets 0 0 Total derivatives not designated as hedging instruments $ 179,890 $ 4,561 $ 14,583 $ 2,267 Total asset derivatives $ 251,721 $ 5,099 $ 89,366 $ 2,291 Liability Derivatives December 31, 2017 December 31, 2016 (In thousands) Balance Sheet Location Notional Amount Fair Value Balance Sheet Location Notional Amount Fair Value Derivatives designated as hedging instruments Fair Value Hedges: Interest rate swap contracts (hedging commercial loans) Other liabilities $ 18,795 $ 165 Other liabilities $ 19,799 $ 338 Total derivatives designated as hedging instruments $ 18,795 $ 165 $ 19,799 $ 338 Derivatives not designated as hedging instruments Interest rate swap contracts Other liabilities $ 0 $ 0 Other liabilities $ 14,583 $ 2,267 TBA mortgage-backed securities Other liabilities 236,500 312 Other liabilities 0 0 Interest rate lock commitments Other liabilities 0 0 Other liabilities 0 0 Total derivatives not designated as hedging instruments $ 236,500 $ 312 $ 14,583 $ 2,267 Total liability derivatives $ 255,295 $ 477 $ 34,382 $ 2,605 Derivative contracts involve the risk of dealing with both bank customers and institutional derivative counterparties and their ability to meet contractual terms. Credit risk arises from the possible inability of counterparties to meet the terms of their contracts. United’s exposure is limited to the replacement value of the contracts rather than the notional amount of the contract. The Company’s agreements generally contain provisions that limit the unsecured exposure up to an agreed upon threshold. Additionally, the Company attempts to minimize credit risk through certain approval processes established by management. The effect of United’s derivative financial instruments on its Consolidated Statements of Income for the years ended December 31, 2017, 2016 and 2015 is presented as follows: Year Ended (In thousands) Income Statement Location December 31, December 31, December 31, Derivatives in hedging relationships Fair Value Hedges: Interest rate swap contracts Interest income/ (expense) $ (781 ) $ (30 ) $ (813 ) Total derivatives in hedging relationships $ (781 ) $ (30 ) $ (813 ) Derivatives not designated as hedging instruments Forward loan sales commitments Income from Mortgage Banking Activities (426 ) 0 0 TBA mortgage-backed securities Income from Mortgage Banking Activities 1,547 0 0 Interest rate lock commitments Income from Mortgage Banking Activities (7,730 ) 0 0 Total derivatives not designated as hedging instruments $ (6,609) $ 0 $ 0 Total derivatives $ (7,390) $ (30) $ (813) For the years ended December 31, 2017, 2016 and 2015, changes in the fair value of any interest rate swaps attributed to hedge ineffectiveness were recorded, but not significant to United’s Consolidated Statements of Income.

Comprehensive Income

Comprehensive Income	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Comprehensive Income	NOTE R—COMPREHENSIVE INCOME The changes in accumulated other comprehensive income are as follows: For the Years Ended December 31 (In thousands) 2017 2016 2015 Net Income $ 150,581 $ 147,083 $ 137,959 Available for sale (“AFS”) securities: AFS securities with OTTI charges during the period (60) (77) (113) Related income tax effect 22 28 41 Income tax rate change 0 208 316 Less : OTTI charges recognized in net income 60 33 47 Related income tax benefit (22) (12) (17) Reclassification of previous noncredit OTTI to credit OTTI 0 415 0 Related income tax benefit 0 (150) 0 Net unrealized gains on AFS securities with OTTI 0 445 274 AFS securities – all other: Change in net unrealized (losses) gains on AFS securities arising during the period 8,371 (12,931) (6,672) Related income tax effect (3,097) 4,867 2,415 Net reclassification adjustment for gains included in net income (1,874) (255) (133) Related income tax expense 693 92 48 4,093 (8,227 ) (4,342 ) Net effect of AFS securities on other comprehensive income 4,093 (7,782) (4,068) Held to maturity (“HTM”) securities: Accretion on the unrealized loss for securities transferred from AFS to the HTM investment portfolio prior to call or maturity 8 9 8 Related income tax expense (3) (3) (3) Net effect of HTM securities on other comprehensive income 5 6 5 Defined benefit pension plan: Net actuarial loss during the period (6,784) (2,914) (2,402) Related income tax expense (benefit) 2,510 1,077 944 Amortization of prior service cost recognized in net income 0 0 1 Related income tax benefit 0 0 0 Amortization of net actuarial loss recognized in net income 4,553 4,921 4,980 Related income tax benefit (1,685) (1,813) (1,908) Net effect of change in defined benefit pension plan on other comprehensive income (1,406) 1,271 1,615 Total change in other comprehensive income, net of tax 2,692 (6,505 ) (2,448 ) Total Comprehensive Income $ 153,273 $ 140,578 $ 135,511 The components of accumulated other comprehensive income for the year ended December 31, 2017 are as follows: Changes in Accumulated Other Comprehensive Income (AOCI) by Component (a) For the Year Ended December 31, 2017 (Dollars in thousands) Unrealized Accretion Defined Items Total Balance at January 1, 2017 ($ 10,297 ) ($ 51 ) ($ 34,369 ) ($ 44,717 ) Other comprehensive income before reclassification 5,274 5 0 5,279 Amounts reclassified from accumulated other comprehensive income (1,181 ) 0 (1,406 ) (2,587 ) Net current-period other comprehensive income, net of tax 4,093 5 (1,406 ) 2,692 Balance at December 31, 2017 ($ 6,204 ) ($ 46 ) ($ 35,775 ) ($ 42,025 ) (a)All amounts are net-of-tax. Reclassifications out of Accumulated Other Comprehensive Income (AOCI) For the Year Ended December 31, 2017 (Dollars in thousands) Details about AOCI Components Amount Affected Line Item in the Statement Where Net Income is Presented Available for sale (“AFS”) securities: Reclassification of previous noncredit OTTI to credit OTTI $ 0 Total other-than-temporary impairment losses Net reclassification adjustment for losses (gains) included in net income (1,874 ) Net gains on sales/calls of investment (1,874 ) Total before tax Related income tax effect 693 Tax expense (1,181 ) Net of tax Pension plan: Net actuarial loss (6,784 )(a) Amortization of net actuarial loss 4,553 (b) (2,231 ) Total before tax Related income tax effect 825 Tax expense (1,406 ) Net of tax Total reclassifications for the period $ (2,587 ) (a) This AOCI component is included in the computation of changes in plan assets (see Note N, Employee Benefit Plans) (b) This AOCI component is included in the computation of net periodic pension cost (see Note N, Employee Benefit Plans)

United Bankshares, Inc. (Parent

United Bankshares, Inc. (Parent Company Only) Financial Information	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
United Bankshares, Inc. (Parent Company Only) Financial Information	NOTE S—UNITED BANKSHARES, INC. (PARENT COMPANY ONLY) FINANCIAL INFORMATION Condensed Balance Sheets December 31 (In thousands) 2017 2016 Assets Cash and due from banks $ 93,198 $ 130,304 Securities available for sale 22,066 4,881 Securities held to maturity 996 20 Other investment securities 163 100 Investment in subsidiaries: Bank subsidiaries 3,437,036 2,372,783 Nonbank subsidiaries 12,535 10,535 Goodwill (16,008 ) (10,453 ) Other assets 10,309 15,699 Total Assets $ 3,560,295 $ 2,523,869 Liabilities and Shareholders’ Equity Junior subordinated debentures of subsidiary trusts $ 242,446 $ 224,319 Accrued expenses and other liabilities 77,319 63,803 Shareholders’ equity (including other accumulated comprehensive loss of $42,025 and $44,717 at December 31, 2017 and 2016, respectively) 3,240,530 2,235,747 Total Liabilities and Shareholders’ Equity $ 3,560,295 $ 2,523,869 Condensed Statements of Income Year Ended December 31 (In thousands) 2017 2016 2015 Income Dividends from banking subsidiaries: Bank subsidiaries $ 115,000 $ 75,600 $ 70,500 Nonbank subsidiaries 58 10 433 Net interest income 437 86 76 Management fees: Bank subsidiaries 45,693 35,792 28,955 Nonbank subsidiaries 27 27 27 Other income 1,766 8 78 Total Income 162,981 111,523 100,069 Expenses Operating expenses 71,653 42,249 31,619 Income Before Income Taxes and Equity in Undistributed Net Income of Subsidiaries 91,328 69,274 68,450 Applicable income tax benefit (6,126 ) (3,061 ) (1,655 ) Income Before Equity in Undistributed Net Income of Subsidiaries 97,454 72,335 70,105 Equity in undistributed net income of subsidiaries: Bank subsidiaries 50,560 74,656 68,012 Nonbank subsidiaries 2,567 92 (158 ) Net Income $ 150,581 $ 147,083 $ 137,959 Condensed Statements of Cash Flows Year Ended December 31 (In thousands) 2017 2016 2015 Operating Activities Net income $ 150,581 $ 147,083 $ 137,959 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed net income of subsidiaries (53,127) (74,748) (67,854) Amortization of net periodic pension costs 228 393 384 Stock-based compensation 3,555 2,817 2,484 Excess tax benefits from stock-based compensation arrangements 2,201 4,008 1,023 Net gain on securities transactions (1,185) (8) (54) Net change in other assets and liabilities 8,764 (8,344) 7,420 Net Cash Provided by Operating Activities 111,017 71,201 81,362 Investing Activities Net purchases of securities (19,268) (234) (1,047) Net cash paid in acquisition of subsidiary 22,146 (10) 0 Increase in investment in subsidiaries (34,203) (100,000) 0 Change in other investment securities (63) 0 2 Net Cash Used in Investing Activities (31,388) (100,244) (1,045) Financing Activities Proceeds from issuance of common stock 0 199,916 0 Cash dividends paid (121,354) (96,351) (88,864) Acquisition of treasury stock (1) (1) (1) Proceeds from sale of treasury stock from deferred compensation plan 1 1 1 Proceeds from exercise of stock options 4,619 13,337 7,871 Net Cash Provided by (Used in) Financing Activities (116,735) 116,902 (80,993) Increase (Decrease) in Cash and Cash Equivalents (37,106) 87,859 (676) Cash and Cash Equivalents at Beginning of Year 130,304 42,445 43,121 Cash and Cash Equivalents at End of Year $ 93,198 $ 130,304 $ 42,445

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Regulatory Matters	NOTE T—REGULATORY MATTERS The subsidiary banks are required to maintain average reserve balances with their respective Federal Reserve Bank. The average amount of those consolidated reserve balances maintained and required for the year ended December 31, 2017, were approximately $1,251,806,000 and $471,763,000, respectively. The average amount of those consolidated reserve balances maintained and required for the year ended December 31, 2016, was approximately $606,898,000 and $361,521,000, respectively. The primary source of funds for the dividends paid by United to its shareholders is dividends received from its subsidiary banks. Dividends paid by United’s subsidiary banks are subject to certain regulatory limitations. Generally, the most restrictive provision requires regulatory approval if dividends declared in any year exceed that year’s net income, as defined, plus the retained net profits of the two preceding years. During 2018, the retained net profits available for distribution to United by United Bank as dividends without regulatory approval, are approximately $127,674,000, plus net income for the interim period through the date of declaration. Under Federal Reserve regulation, United Bank is also limited as to the amount they may loan to affiliates, including the parent company. Loans from United Bank to the parent company are limited to 10% of the banking subsidiaries’ capital and surplus, as defined, or $282,863,000 at December 31, 2017, and must be secured by qualifying collateral. United’s subsidiary banks are subject to various regulatory capital requirements administered by federal banking agencies. Pursuant to capital adequacy guidelines, United’s subsidiary banks must meet specific capital guidelines that involve various quantitative measures of the banks’ assets, liabilities, and certain off-balance-sheet As previously mentioned, the new Basel III Capital Rules became effective for United and United Bank on January 1, 2015 (subject to a phase-in At December 31, 2017, the most recent notification from its regulators, United and United Bank were categorized as well-capitalized. To be categorized as well-capitalized, United must maintain minimum total risk-based, Tier I risk-based, Common Tier I risk-based, and Tier I leverage ratios as set forth in the following table. There are no conditions or events since that notification that management believes would impact United’s well-capitalized status. United’s and United Bank, capital amounts (in thousands of dollars) and ratios are presented in the following table. (Dollars in thousands) Actual For Capital Adequacy Purposes To Be Well- Capitalized Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk- Weighted Assets): United Bankshares $ 2,093,369 14.2 % $ 1,177,952 ³ $ 1,472,439 ³ United Bank 2,013,852 13.7 % 1,174,099 ³ 1,467,624 ³ Tier I Capital (to Risk- Weighted Assets): United Bankshares $ 1,759,189 12.0 % $ 883,464 ³ $ 1,177,952 ³ United Bank 1,936,546 13.2 % 880,575 ³ 1,174,099 ³ Common Tier I Capital (to Risk Weighted Assets): United Bankshares $ 1,759,189 12.0 % $ 662,598 ³ $ 957,086 ³ United Bank 1,936,546 13.2 % 660,431 ³ 953,956 ³ Tier I Capital (to Average Assets): United Bankshares $ 1,759,189 10.1 % $ 698,388 ³ $ 872,985 ³ United Bank 1,936,546 11.0 % 702,311 ³ 877,888 ³ As of December 31, 2016: Total Capital (to Risk- Weighted Assets): United Bankshares $ 1,699,984 14.9 % $ 915,479 ³ $ 1,144,348 ³ United Bank 1,592,647 13.9 % 915,956 ³ 1,144,945 ³ Tier I Capital (to Risk- Weighted Assets): United Bankshares $ 1,625,543 14.2 % $ 686,609 ³ $ 915,479 ³ United Bank 1,518,831 13.3 % 686,967 ³ 915,956 ³ Common Tier I Capital (to Risk Weighted Assets): United Bankshares $ 1,393,743 12.2 % $ 514,957 ³ $ 743,826 ³ United Bank 1,518,831 13.3 % 515,225 ³ 744,214 ³ Tier I Capital (to Average Assets): United Bankshares $ 1,625,543 12.2 % $ 535,227 ³ $ 669,033 ³ United Bank 1,518,831 11.4 % 535,361 ³ 669,201 ³ United’s mortgage banking entity, George Mason, is subject to net worth requirements issued by the U.S. Department of Housing and Urban Development (HUD). Failure to meet minimum capital requirements of HUD can result in certain mandatory and possibly additional discretionary actions that, if undertaken, could have a direct material effect on George Mason’s operations. The minimum net worth requirement of HUD at December 31, 2017 was $2,500,000. George Mason’s net worth was $4,955,000 at December 31, 2017, which exceeded the HUD requirements.

Fair Values of Financial Instru

Fair Values of Financial Instruments	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Values of Financial Instruments	NOTE U—FAIR VALUES OF FINANCIAL INSTRUMENTS In accordance with ASC topic 820, the following describes the valuation techniques used by United to measure certain financial assets and liabilities recorded at fair value on a recurring basis in the financial statements. Securities available for sale assumptions are derived primarily from or corroborated by observable market data. Using a market approach valuation methodology, third party vendors compile prices from various sources and may determine the fair value of identical or similar securities by using pricing models that considers observable market data (Level 2). Management internally reviews the fair values provided by third party vendors on a monthly basis. Management’s review consists of comparing fair values assigned by third party vendors to trades and offerings observed by management. The review requires some degree of judgment as to the number or percentage of securities to review on the part of management which could fluctuate based on results of past reviews and in comparison to current expectations. Exceptions that are deemed to be material are reviewed by management. Additionally, to assess the reliability of the information received from third party vendors, management obtains documentation from third party vendors related to the sources, methodologies, and inputs utilized in valuing securities classified as Level 2. Management analyzes this information to ensure the underlying assumptions appear reasonable. Management also obtains an independent service auditor’s report from third party vendors to provide reasonable assurance that appropriate controls are in place over the valuation process. Upon completing its review of the pricing from third party vendors at December 31, 2017, management determined that the prices provided by its third party pricing source were reasonable and in line with management’s expectations for the market values of these securities. Therefore, prices obtained from third party vendors that did not reflect forced liquidation or distressed sales were not adjusted by management at December 31, 2017. Management utilizes a number of factors to determine if a market is inactive, all of which may require a significant level of judgment. Factors that management considers include: a significant widening of the bid-ask available-for-sale Loans held for sale Derivatives For a fair value hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to the hedged financial instrument. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a fair value hedge are offset in current period earnings either in interest income or interest expense depending on the nature of the hedged financial instrument. For a cash flow hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to other comprehensive income within shareholders’ equity, net of tax. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a cash flow hedge are offset to other comprehensive income, net of tax. The portion of a hedge that is ineffective is recognized immediately in earnings. The Company records its interest rate lock commitments and forward loan sales commitments at fair value determined as the amount that would be required to settle each of these derivative financial instruments at the balance sheet date. In the normal course of business, George Mason enters into contractual interest rate lock commitments to extend credit to borrowers with fixed expiration dates. The commitments become effective when the borrowers “lock-in” For interest rate swap derivatives that are not designated in a hedge relationship, changes in the fair value of the derivatives are recognized in earnings in the same period as the change in the fair value. Unrealized gains and losses due to changes in the fair value of other derivative financial instruments not in hedge relationship are included in noninterest income and noninterest expense, respectively. The following table presents the balances of financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016, segregated by the level of the valuation inputs within the fair value hierarchy: Fair Value at December 31, 2017 Using (In thousands) Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Available for sale debt securities: U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 114,758 $ 0 $ 114,758 $ 0 State and political subdivisions 303,869 0 303,869 0 Residential mortgage-backed securities Agency 814,593 0 814,593 0 Non-agency 5,512 0 5,512 0 Commercial mortgage-backed securities Agency 454,857 0 454,857 0 Asset-backed securities 109,970 0 109,970 0 Trust preferred collateralized debt obligations 34,269 0 0 34,269 Single issue trust preferred securities 12,560 0 12,560 0 Other corporate securities 28,490 0 28,490 0 Total available for sale debt securities 1,878,878 0 1,844,609 34,269 Available for sale equity securities: Financial services industry 3,545 331 3,214 0 Equity mutual funds (1) 6,332 6,332 0 0 Other equity securities 1 1 0 0 Total available for sale equity securities 9,878 6,664 3,214 0 Total available for sale securities 1,888,756 6,664 1,847,823 34,269 Loans held for sale 263,308 0 0 263,308 Derivative financial assets: Interest rate swap contracts 538 0 538 0 Interest rate lock commitments 4,561 0 2 4,559 Total derivative financial assets 5,099 0 540 4,559 Liabilities Derivative financial liabilities: Interest rate swap contracts 165 0 165 0 TBA mortgage-backed securities 312 0 312 0 Total derivative financial liabilities 477 0 477 0 (1) The equity mutual funds are within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers of United and its subsidiaries. Fair Value at December 31, 2016 Using (In thousands) Description Balance as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Available for sale debt securities: U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 95,786 $ 0 $ 95,786 $ 0 State and political subdivisions 192,812 0 192,812 0 Residential mortgage-backed securities Agency 584,096 0 584,096 0 Non-agency 7,043 0 7,043 0 Asset-backed securities 217 0 217 0 Commercial mortgage-backed securities Agency 305,341 0 305,341 0 Trust preferred collateralized debt obligations 33,552 0 0 33,552 Single issue trust preferred securities 11,477 0 11,477 0 Other corporate securities 15,062 0 15,062 0 Total available for sale debt securities 1,245,386 0 1,211,834 33,552 Available for sale equity securities: Financial services industry 10,735 1,372 9,363 0 Equity mutual funds (1) 1,820 1,820 0 0 Other equity securities 1,273 1,273 0 0 Total available for sale equity securities 13,828 4,465 9,363 0 Total available for sale securities 1,259,214 4,465 1,221,197 33,552 Derivative financial assets: Interest rate contracts 2,291 0 2,291 0 Liabilities Derivative financial liabilities: Interest rate contracts 2,605 0 2,605 0 (1) The equity mutual funds are within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers of United and its subsidiaries. There were no transfers between Level 1, Level 2 and Level 3 for financial assets and liabilities measured at fair value on a recurring basis during the year ended December 31, 2017 and 2016. The following table presents additional information about financial assets and liabilities measured at fair value at December 31, 2017 and 2016 on a recurring basis and for which United has utilized Level 3 inputs to determine fair value: Available-for-sale (In thousands) Trust preferred collateralized debt obligations 2017 2016 Balance, beginning of year $ 33,552 $ 34,686 Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) 9 0 Included in other comprehensive income 8,757 (1,134 ) Purchases, issuances, and settlements 0 0 Sales (8,049 ) 0 Transfers in and/or out of Level 3 0 0 Balance, ending of year $ 34,269 $ 33,552 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date 0 0 (In thousands) Loans held for sale 2017 2016 Balance, beginning of period $ 0 $ 0 Acquired in Cardinal merger 271,301 0 Originations 2,333,927 0 Sales (2,408,945) 0 Total gains or losses during the period recognized in earnings 58,132 0 Transfers in and/or out of Level 3 8,893 0 Balance, end of period $ 263,308 $ 0 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date $ 0 $ 0 (In thousands) Derivative Financial Assets Interest Rate Lock Commitments 2017 2016 Balance, beginning of period $ 0 $ 0 Acquired in Cardinal merger 10,393 0 Transfers other (5,834 ) 0 Balance, end of period $ 4,559 $ 0 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date $ 0 $ 0 Certain financial assets are measured at fair value on a nonrecurring basis in accordance with GAAP. Adjustments to the fair value of these assets usually result from the application of lower-of-cost-or-market Fair Value Option United elected the fair value option for the loans held for sale in its mortgage banking segment to mitigate a divergence between accounting losses and economic exposure. The following table reflects the change in fair value included in earnings of financial instruments for which the fair value option has been elected: (In thousands) Description Year Ended December 31, 2017 Year Ended December 31, 2016 Assets Loans held for sale Income from mortgage banking activities $ (10,497 ) $ 0 The following table reflects the difference between the aggregate fair value and the remaining contractual principal outstanding for financial instruments for which the fair value option has been elected: December 31, 2017 December 31, 2016 (In thousands) Description Unpaid Fair Value Fair Value Unpaid Fair Fair Value Assets Loans held for sale $ 257,674 $ 263,308 $ 5,634 $ 0 $ 0 $ 0 Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis The following describes the valuation techniques used by United to measure certain financial assets recorded at fair value on a nonrecurring basis in the financial statements. Loans held for sale one-to-four Impaired Loans OREO bi-annual Intangible Assets: The following table summarizes United’s financial assets that were measured at fair value on a nonrecurring basis during the period: Carrying value at December 31, 2017 (In thousands) Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) YTD Losses Assets Loans held for sale $ 2,647 $ 0 $ 2,647 $ 0 $ 14 Impaired Loans 84,756 0 67,111 17,645 12,291 OREO 24,348 0 24,151 197 4,200 (In thousands) Description Balance as of December 31, Carrying value at December 31, 2016 YTD Losses Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Loans held for sale $ 8,445 $ 0 $ 8,445 $ 0 $ 4 Impaired Loans 80,505 0 27,609 52,896 5,119 OREO 31,510 0 31,510 0 2,086 Fair Value of Other Financial Instruments The following methods and assumptions were used by United in estimating its fair value disclosures for other financial instruments: Cash and Cash Equivalents: Securities held to maturity and other securities Loans: one-to-four Deposits: Short-term Borrowings: Long-term Borrowings: Summary of Fair Values for All Financial Instruments The estimated fair values of United’s financial instruments are summarized below: Fair Value Measurements (In thousands) Carrying Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 Cash and cash equivalents $ 1,666,167 $ 1,666,167 $ 0 $ 1,666,167 $ 0 Securities available for sale 1,888,756 1,888,756 6,664 1,847,823 34,269 Securities held to maturity 20,428 20,018 0 16,998 3,020 Other securities 162,461 154,338 0 0 154,338 Loans held for sale 265,955 265,955 0 2,647 263,308 Loans 12,934,794 12,437,797 0 0 12,437,797 Derivative financial assets 5,099 5,099 0 540 4,559 Deposits 13,830,591 14,024,720 0 14,024,720 0 Short-term borrowings 477,587 477,587 0 477,587 0 Long-term borrowings 1,363,977 1,338,754 0 1,338,754 0 Derivative financial liabilities 477 477 0 477 0 December 31, 2016 Cash and cash equivalents $ 1,434,527 $ 1,434,527 $ 0 $ 1,434,527 $ 0 Securities available for sale 1,259,214 1,259,214 4,465 1,221,197 33,552 Securities held to maturity 33,258 31,178 0 28,158 3,020 Other securities 111,166 105,608 0 0 105,608 Loans held for sale 8,445 8,445 0 8,445 0 Loans 10,268,366 10,122,486 0 0 10,122,486 Derivative financial assets 2,291 2,291 0 2,291 0 Deposits 10,796,867 10,785,294 0 10,785,294 0 Short-term borrowings 209,551 209,551 0 209,551 0 Long-term borrowings 1,172,026 1,142,782 0 1,142,782 0 Derivative financial liabilities 2,605 2,605 0 2,605 0

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	NOTE V—VARIABLE INTEREST ENTITIES Variable interest entities (VIEs) are entities that either have a total equity investment that is insufficient to permit the entity to finance its activities without additional subordinated financial support or whose equity investors lack the characteristics of a controlling financial interest (i.e., ability to make significant decisions, through voting rights, right to receive the expected residual returns of the entity, and obligation to absorb the expected losses of the entity). VIEs can be structured as corporations, trusts, partnerships, or other legal entities. United’s business practices include relationships with certain VIEs. For United, the business purpose of these relationships primarily consists of funding activities in the form of issuing trust preferred securities. United currently sponsors fifteen statutory business trusts that were created for the purpose of raising funds that qualify for Tier I regulatory capital. These trusts, of which several were acquired through bank acquisitions, issued or participated in pools of trust preferred capital securities to third-party investors with the proceeds invested in junior subordinated debt securities of United. The Company, through a small capital contribution, owns 100% of the voting equity shares of each trust. The assets, liabilities, operations, and cash flows of each trust are solely related to the issuance, administration, and repayment of the preferred equity securities held by third-party investors. United fully and unconditionally guarantees the obligations of each trust and is obligated to redeem the junior subordinated debentures upon maturity. The trusts utilized in these transactions are variable interest entities (VIEs) as the third-party equity holders lack a controlling financial interest in the trusts through their inability to make decisions that have a significant effect on the operations and success of the entities. United does not consolidate these trusts as it is not the primary beneficiary of these entities because United does not hold a controlling financial interest as evidenced by the power to direct the activities of the VIEs that most significantly impact their economic performance and the obligation to absorb losses of, or the right to receive benefits from, the VIEs that could potentially be significant to the VIEs. Information related to United’s statutory trusts is presented in Note K, Notes to Consolidated Financial Statements. United, through its banking subsidiaries, also makes limited partner equity investments in various low income housing and community development partnerships sponsored by independent third-parties. United invests in these partnerships to either realize tax credits on its consolidated federal income tax return or for purposes of earning a return on its investment. These partnerships are considered VIEs as the limited partners lack a controlling financial interest in the entities through their inability to make decisions that have a significant effect on the operations and success of the partnerships. United’s limited partner interests in these entities is immaterial, however; these partnerships are not consolidated as United is not deemed to be the primary beneficiary. The following table summarizes quantitative information about United’s significant involvement in unconsolidated VIEs: As of December 31, 2017 As of December 31, 2016 (In thousands) Aggregate Assets Aggregate Liabilities Risk Of Loss (1) Aggregate Assets Aggregate Liabilities Risk Of Loss (1) Trust preferred securities $ 266,669 $ 257,674 $ 8,995 $ 240,668 $ 232,583 $ 8,085 (1)   Represents investment in VIEs.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Information	NOTE W—SEGMENT INFORMATION As a result of the Cardinal acquisition, United now operates in two business segments: community banking and mortgage banking. Prior to the Cardinal acquisition, United’s business activities were confined to just one reportable segment of community banking. Through its community banking segment, United offers a full range of products and services through various delivery channels. In particular, the community banking segment includes both commercial and consumer lending and provides customers with such products as commercial loans, real estate loans, business financing and consumer loans. In addition, this segment provides customers with several choices of deposit products including demand deposit accounts, savings accounts and certificates of deposit as well as investment and financial advisory services to businesses and individuals, including financial planning, retirement/estate planning, and investment management. The mortgage banking segment engages primarily in the origination and acquisition of residential mortgages for sale into the secondary market though George Mason. The community banking segment provides the mortgage banking segment (George Mason) with short-term funds to originate mortgage loans through a warehouse line of credit and charges the mortgage banking segment interest based on the prime rate. These transactions are eliminated in the consolidation process. The Company does not have any operating segments other than those reported. The “Other” category consists of financial information not directly attributable to a specific segment, including interest income from investments and net securities gains or losses of parent companies and their non-banking non-segment Information about the reportable segments and reconciliation of this information to the consolidated financial statements at and for the years ended December 31, 2017, 2016 and 2015 is as follows: At and For the Year Ended December 31, 2017 (In thousands) Community Mortgage Other Consolidated Net interest income $ 558,622 $ (69 ) $ (9,556 ) $ 548,997 Provision for loans losses 28,406 0 0 28,406 Other income 69,615 58,532 3,498 131,645 Other expense 291,584 62,072 13,753 367,409 Income taxes 139,980 (901 ) (4,833 ) 134,246 Net income (loss) $ 168,267 $ (2,708 ) $ (14,978 ) $ 150,581 Total assets (liabilities) $ 18,761,508 $ 280,293 $ 17,158 $ 19,058,959 Average assets (liabilities) 17,385,448 212,212 19,769 17,617,429 At and For the Year Ended December 31, 2016 (In thousands) Community Other Consolidated Net interest income $ 433,140 $ (7,809 ) $ 425,331 Provision for loans losses 24,509 0 24,509 Other income 72,618 (2,586 ) 70,032 Other expense 249,894 (1,698 ) 248,196 Income taxes 78,640 (3,065 ) 75,575 Net income (loss) $ 152,715 $ (5,632 ) $ 147,083 Total assets (liabilities) $ 14,528,394 $ (19,502 ) $ 14,508,892 Average assets (liabilities) 13,398,861 (22,058 ) 13,376,803 At and For the Year Ended December 31, 2015 (In thousands) Community Other Consolidated Net interest income $ 390,775 $ (6,651 ) $ 384,124 Provision for loans losses 22,574 0 22,574 Other income 75,656 (2,030 ) 73,626 Other expense 235,644 (3,957 ) 231,687 Income taxes 67,109 (1,579 ) 65,530 Net income (loss) $ 141,104 $ (3,145 ) $ 137,959 Total assets (liabilities) $ 12,592,321 $ (14,377 ) $ 12,577,944 Average assets (liabilities) 12,277,023 (11,908 ) 12,265,115

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	NOTE X—QUARTERLY FINANCIAL DATA (UNAUDITED) Quarterly financial data for 2017 and 2016 is summarized below (dollars in thousands, except for per share data): (Dollars in thousands) 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter 2017 Interest income $ 120,758 $ 154,947 $ 171,583 $ 176,518 Interest expense 13,138 18,702 21,307 21,662 Net interest income 107,620 136,245 150,276 154,856 Provision for credit losses 5,899 8,251 7,279 6,977 Mortgage banking income 675 22,537 20,385 15,310 Securities gains (losses), net 3,940 747 467 430 Other noninterest income 15,531 17,222 17,377 17,024 Noninterest expense 62,842 112,137 96,652 95,778 Income taxes 20,216 19,304 27,836 66,890 Net income (1) 38,809 37,059 56,738 17,975 Per share data: Average shares outstanding (000s): Basic 80,902 99,198 104,760 104,808 Diluted 81,307 99,620 105,068 105,125 Net income per share: Basic $ 0.48 $ 0.37 $ 0.54 $ 0.17 Diluted $ 0.48 $ 0.37 $ 0.54 $ 0.17 Dividends per share $ 0.33 $ 0.33 $ 0.33 $ 0.34 2016 Interest income $ 108,496 $ 113,087 $ 123,137 $ 125,621 Interest expense 10,212 10,362 12,068 12,368 Net interest income 98,284 102,725 111,069 113,253 Provision for credit losses 4,035 7,667 6,988 5,819 Mortgage banking income 728 789 982 951 Securities losses, net 4 213 1 62 Other noninterest income 15,660 16,965 18,038 15,639 Noninterest expense 58,056 64,855 62,777 62,508 Income taxes 17,879 16,378 18,846 22,472 Net income (1) 34,706 31,792 41,479 39,106 Per share data: Average shares outstanding (000s): Basic 69,497 71,484 76,219 76,864 Diluted 69,714 71,809 76,648 77,303 Net income per share: Basic $ 0.50 $ 0.44 $ 0.54 $ 0.51 Diluted $ 0.50 $ 0.44 $ 0.54 $ 0.51 Dividends per share $ 0.33 $ 0.33 $ 0.33 $ 0.33 (1) For further information, see the related discussion “Quarterly Results” included in Management’s Discussion and Analysis.

Summary of Significant Accoun33

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations:
Operating Segments	Operating Segments: Through its community banking segment, United offers a full range of banking products and services through various delivery channels. The mortgage banking segment engages primarily in the origination and acquisition of residential mortgages for sale into the secondary market though George Mason Mortgage, LLC (George Mason), an indirectly owned subsidiary of United.
Basis of Presentation	Basis of Presentation: The Cardinal acquisition was accounted for using the acquisition method and their results of operations have been included in the United’s consolidated financial statements as of the acquisition date (April 21, 2017). United determines whether it has a controlling financial interest in an entity by first evaluating whether the entity is a voting interest entity or a variable interest entity (VIE) under U.S. generally accepted accounting principles. Voting interest entities are entities in which the total equity investment at risk is sufficient to enable the entity to finance itself independently and provides the equity holders with the obligation to absorb losses, the right to receive residual returns and the right to make decisions about the entity’s activities. United consolidates voting interest entities in which it has all, or at least a majority of, the voting interest. As defined in applicable accounting standards, VIEs are entities that lack one or more of the characteristics of a voting interest entity. A controlling financial interest in a VIE is present when an enterprise has both the power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and an obligation to absorb losses or the right to receive benefits that could potentially be significant to the VIE. The enterprise with a controlling financial interest, known as the primary beneficiary, consolidates the VIE. United’s wholly owned and indirect wholly owned statutory trust subsidiaries are VIEs for which United is not the primary beneficiary. Accordingly, its accounts are not included in United’s consolidated financial statements. The accounting and reporting policies of United conform with U.S. generally accepted accounting principles. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. To conform to the 2017 presentation, certain reclassifications have been made to prior period amounts, which had no impact on net income, comprehensive income or shareholders’ equity. In the opinion of management, all adjustments necessary for a fair presentation of financial position and results of operations have been made. Such adjustments are of a normal and recurring nature. The Company has evaluated events and transactions subsequent to December 31, 2017 through the date these financial statements were issued. Based on definitions and requirements of generally accepted accounting principles for “Subsequent Events,” the Company has not identified any events that would require adjustments to, or disclosure in the financial statements.
Cash and Cash Equivalents	Cash and Cash Equivalents:
Securities	Securities: value. Unrealized gains and losses on securities classified as available for sale are carried as a separate component of Accumulated Other Comprehensive Income (Loss), net of deferred income taxes. Gains or losses on sales of securities are recognized by the specific identification method and are reported in securities gains and losses within noninterest income of the Consolidated Statements of Income. United reviews available-for-sale held-to-maturity For equity securities, United evaluates the near-term prospects of the investment in relation to the severity and duration of any impairment and United’s ability and intent to hold these equity securities until a recovery of their fair value to at least the cost basis of the investment. Equity securities that are deemed to be other-than-temporarily impaired are written down to the fair value with the write-down recognized within noninterest income of the Consolidated Statements of Income. Certain security investments that do not have readily determinable fair values and for which United does not exercise significant influence are carried at cost and are classified as other investment securities on the balance sheet. These cost-method investments are reviewed for impairment at least annually or sooner if events or changes in circumstances indicate the carrying value may not be recoverable.
Securities Purchased Under Resale Agreements and Securities Sold Under Agreements to Repurchase	Securities Purchased Under Resale Agreements and Securities Sold Under Agreements to Repurchase:
Loans	Loans: Loans are designated as impaired when, in the opinion of management, based on current information and events, the collection of principal and interest in accordance with the loan contract is doubtful. Consistent with United’s existing method of income recognition for loans, interest on impaired loans, except those classified as nonaccrual, is recognized as income using the accrual method. United’s method of income recognition for impaired loans that are classified as nonaccrual is to recognize interest income on the cash basis or apply the cash receipt to principal when the ultimate collectibility of principal is in doubt. A loan is categorized as restructured if a concession is granted to provide for a reduction of either interest or principal due to a deterioration in the financial condition of the borrower. A loan classified as restructured will generally retain such classification until the loan is paid in full. However, a restructured one-to-four-family
Loans Acquired Through Transfer	Loans Acquired Through Transfer:
Loans Held for Sale	Loans Held for Sale: one-to-four Loans held for sale within the mortgage banking segment are recorded under the fair value option at a fair value measured using valuations from investors for loans with similar characteristics adjusted for the Company’s actual sales experience versus the investor’s indicated pricing. Loans held for sale within the community banking segment are carried at the lower of cost or fair value. The fair value is based on the price secondary markets are currently offering for similar loans using observable market data which is not materially different than cost due to the short duration between origination and sale. Gains and losses on sale of loans are recorded within income from mortgage banking activities.
Allowance for Credit Losses	Allowance for Credit Losses: The allowance for loan losses is management’s estimate of the probable credit losses inherent in the loan portfolio. Management’s evaluation of the adequacy of the allowance for loan losses and the appropriate provision for credit losses is based upon a quarterly evaluation of the portfolio. This evaluation is inherently subjective and requires significant estimates, including the amounts and timing of estimated future cash flows, estimated losses on pools of loans based on historical loss experience, and consideration of current economic trends, all of which are susceptible to constant and significant change. The amounts allocated to specific credits and loan pools grouped by similar risk characteristics are reviewed on a quarterly basis and adjusted as necessary based upon subsequent changes in circumstances. In determining the components of the allowance for credit losses, management considers the risk arising in part from, but not limited to, charge-off charged-off In determining the adequacy of the allowance for loan losses, management makes allocations to specific commercial loans classified by management as to risk. Management determines the loan’s risk by considering the borrowers’ ability to repay, the collateral securing the credit and other borrower-specific factors that may impact collectibility. For impaired loans, specific allocations are based on the present value of expected future cash flows using the loan’s effective interest rate, or as a practical expedient, at the loan’s observable market price or the fair value of the collateral if the loan is collateral-dependent. Other commercial loans not specifically reviewed on an individual basis are evaluated based on loan pools, which are grouped by similar risk characteristics using management’s internal risk ratings. Allocations for these commercial loan pools are determined based upon historical loss experience adjusted for current environmental conditions and risk factors and the estimate period it takes for losses to result in a charge-off.
Bank Premises and Equipment	Bank Premises and Equipment:
Other Real Estate Owned	Other Real Estate Owned
Advertising Costs	Advertising Costs:
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition
Income Taxes	Income Taxes: For uncertain income tax positions, United records a liability based on a recognition threshold of more-likely-than-not, United files a consolidated income tax return with its subsidiaries. Federal income tax expense or benefit has been allocated to subsidiaries on a separate return basis.
Intangible Assets	Intangible Assets: Goodwill and intangible assets with indefinite lives (such as a trade name intangible) are not amortized, but are tested for impairment at least annually or sooner if indicators of impairment exist. Intangible assets with definite useful lives (such as core deposit intangibles) are amortized over their respective estimated useful lives to their estimated residual values, and reviewed for impairment at least annually or as indicators of impairment are identified. Based on the most recent goodwill impairment test, no impairment was noted. As of December 31, 2017, and 2016, total goodwill approximated $1,478,380,000 and $863,767,000, respectively.
Derivative Financial Instruments	Derivative Financial Instruments: Derivative instruments designated in a hedge relationship to mitigate exposure to changes in the fair value of an asset, liability, or firm commitment attributable to a particular risk, such as interest rate risk, are considered fair value hedges. Derivative instruments designated in a hedge relationship to mitigate exposure to variability in expected future cash flows, or other types of forecasted transactions, are considered cash flow hedges. For a fair value hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to the hedged financial instrument. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a fair value hedge are offset in current period earnings. For a cash flow hedge, the fair value of the interest rate swap is recognized on the balance sheet as either a freestanding asset or liability with a corresponding adjustment to other comprehensive income within shareholders’ equity, net of tax. Subsequent adjustments due to changes in the fair value of a derivative that qualifies as a cash flow hedge are offset to other comprehensive income, net of tax. The portion of a hedge that is ineffective is recognized immediately in earnings. At inception of a hedge relationship, United formally documents the hedged item, the particular risk management objective, the nature of the risk being hedged, the derivative being used, how effectiveness of the hedge will be assessed and how the ineffectiveness of the hedge will be measured. United also assesses hedge effectiveness at inception and on an ongoing basis using regression analysis. Hedge ineffectiveness is measured by using the change in fair value method. The change in fair value method compares the change in the fair value of the hedging derivative to the change in the fair value of the hedged exposure, attributable to changes in the benchmark rate. United through George Mason enters into interest rate lock commitments to finance residential mortgage loans with its customers. These commitments, which contain fixed expiration dates, offer the borrower an interest rate guarantee provided the loan meets underwriting guidelines and closes within the timeframe established by United. Interest rate risk arises on these commitments and subsequently closed loans if interest rates change between the time of the interest rate lock and the delivery of the loan to the investor. Market risk on interest rate lock commitments and mortgage loans held for sale is managed using corresponding forward mortgage loan sales contracts. United is a party to these forward mortgage loan sales contracts to sell loans servicing released and short sales of mortgage-backed securities. When the interest rate is locked with the borrower, the rate lock commitment, forward sale agreement, and mortgage-backed security position are undesignated derivatives and marked to fair value through earnings. The fair value of the rate lock derivative includes the servicing premium and the interest spread for the difference between retail and wholesale mortgage rates. Income from mortgage banking activities includes the gain recognized for the period presented and associated elements of fair value. United sells mortgage loans on either a best efforts or mandatory delivery basis. For loans sold on a mandatory delivery basis, United enters into forward mortgage-backed securities (the “residual hedge”) to mitigate the effect of interest rate risk. Both the rate lock commitment for mandatory delivery loans and the residual hedge are recorded at fair value through earnings and are not designated as accounting hedges. At the closing of the loan, the loan commitment derivative expires and United records a loan held for sale at fair value and continues to mark these assets to market under the election of the fair value option. United closes out of the trading mortgage-backed securities assigned within the residual hedge and replaces the securities with a forward sales contract once a price has been accepted by an investor and recorded at fair value. For those loans selected to be sold under a best efforts delivery basis, at the closing of the loan, the rate lock commitment derivative expires and the Company records a loan held for sale at fair value under the election of fair value option and continues to be obligated under the same forward loan sales contract entered into at inception of the rate lock commitment. For derivatives that are not designated in a hedge relationship, changes in the fair value of the derivatives are recognized in earnings in the same period as the change in the fair value.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense was $3,555,000 in 2017, $2,817,000 in 2016, and $2,484,000 in 2015.
Treasury Stock	Treasury Stock
Trust Assets and Income	Trust Assets and Income:
Earnings Per Common Share	Earnings Per Common Share: two-class non-vested Under the two-class The reconciliation of the numerator and denominator of basic earnings per share with that of diluted earnings per share is presented as follows: Year Ended December 31 (Dollars in thousands, except per share) 2017 2016 2015 Distributed earnings allocated to common stock $ 131,527 $ 98,510 $ 89,497 Undistributed earnings allocated to common stock 18,816 48,317 48,218 Net earnings allocated to common shareholders $ 150,343 $ 146,827 $ 137,715 Average common shares outstanding 97,502,633 73,531,992 69,334,849 Dilutive effect of stock compensation 387,445 361,135 290,682 Average diluted shares outstanding 97,890,078 73,893,127 69,625,531 Earnings per basic common share $ 1.54 $ 2.00 $ 1.99 Earnings per diluted common share $ 1.54 $ 1.99 $ 1.98
Fair Value Measurements	Fair Value Measurements The Fair Value Measurements and Disclosures topic specifies a hierarchy of valuation techniques based on whether the inputs to those valuation techniques are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect United’s market assumptions. The three levels of the fair value hierarchy based on these two types of inputs are as follows: Level 1 - Valuation is based on quoted prices in active markets for identical assets and liabilities. Level 2 - Valuation is based on observable inputs including quoted prices in active markets for similar assets and liabilities, quoted prices for identical or similar assets and liabilities in less active markets, and model-based valuation techniques for which significant assumptions can be derived primarily from or corroborated by observable data in the market. Level 3 - Valuation is based on model-based techniques that use one or more significant inputs or assumptions that are unobservable in the market. When determining the fair value measurements for assets and liabilities, United looks to active and observable markets to price identical assets or liabilities whenever possible and classifies such items in Level 1. When identical assets and liabilities are not traded in active markets, United looks to market observable data for similar assets and liabilities and classifies such items as Level 2. Nevertheless, certain assets and liabilities are not actively traded in observable markets and United must use alternative valuation techniques using unobservable inputs to determine a fair value and classifies such items as Level 3. For assets and liabilities that are not actively traded, the fair value measurement is based primarily upon estimates that require significant judgment. Therefore, the results may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there are inherent weaknesses in any calculation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. The level within the fair value hierarchy is based on the lowest level of input that is significant in the fair value measurement.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2018, the FASB issued ASU No. 2018-02, “Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income,” to help organizations address certain stranded income tax effects in accumulated other comprehensive income (AOCI) resulting from the Tax Cuts and Jobs Act (the “Tax Act”). This ASU provides financial statement preparers with an option to reclassify stranded tax effects within AOCI to retained earnings in each period in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Act (or portion thereof) is recorded. The amendments are effective for all organizations for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. Early adoption is permitted. Organizations should apply the proposed amendments either in the period of adoption or retrospectively to each period (or periods) in which the effect of the change in the U.S. federal corporate income tax rate in the Tax Act is recognized. United expects to adopt ASU No. 2018-02 In August 2017, the FASB issued ASU No. 2017-12, No. 2017-12 No. 2017-12 In July 2017, the FASB issued ASU No. 2017-11, No. 2017-11 No. 2017-11 In May 2017, the FASB issued ASU No. 2017-09, non-substantive No. 2017-09 No. 2017-09 In March 2017, the FASB issued ASU 2017-07, 2017-07 2017-07 2017-07 In January 2017, the FASB issued ASU 2017-04, 2017-04 2017-04 In January 2017, the FASB issued ASU 2017-01, 2017-01 2017-01 In August 2016, the FASB issued ASU 2016-15, 2016-15 2016-15 2016-15 In June 2016, the FASB issued ASU 2016-13, 2016-13 available-for-sale 2016-13 2016-13 In March 2016, the FASB issued ASU 2016-09, 2016-09 2016-09 2016-09 tax-related 2016-09 In February 2016, the FASB issued ASU 2016-02, 2016-02 2016-02 right-of-use 2016-02 In January 2016, the FASB issued ASU 2016-01, 2016-01 2016-01 available-for-sale 2016-01 In May 2014, the FASB issued ASU 2014-09, 2014-09 2014-09 assessment of these revenue streams under the standard, management concluded that ASU 2014-09 2014-09

Summary of Significant Accoun34

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Reconciliation of Numerator and Denominator of Basic Earnings Per Share with that of Diluted Earnings Per Share	The reconciliation of the numerator and denominator of basic earnings per share with that of diluted earnings per share is presented as follows: Year Ended December 31 (Dollars in thousands, except per share) 2017 2016 2015 Distributed earnings allocated to common stock $ 131,527 $ 98,510 $ 89,497 Undistributed earnings allocated to common stock 18,816 48,317 48,218 Net earnings allocated to common shareholders $ 150,343 $ 146,827 $ 137,715 Average common shares outstanding 97,502,633 73,531,992 69,334,849 Dilutive effect of stock compensation 387,445 361,135 290,682 Average diluted shares outstanding 97,890,078 73,893,127 69,625,531 Earnings per basic common share $ 1.54 $ 2.00 $ 1.99 Earnings per diluted common share $ 1.54 $ 1.99 $ 1.98

Mergers and Acquisitions (Table

Mergers and Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Acquired Loans Accounted for at Fair Value	In conjunction with the Cardinal merger, the acquired loan portfolio was accounted for at fair value as follows: (In thousands) April 21, 2017 Contractually required principal and interest at acquisition $ 4,211,734 Contractual cash flows not expected to be collected (56,176 ) Expected cash flows at acquisition 4,155,558 Interest component of expected cash flows (986,959 ) Basis in acquired loans at acquisition – estimated fair value $ 3,168,599
Schedule of Fair Value of Acquired Identifiable Assets and Liabilities Assumed	The consideration paid for Bank of Georgetown’s common equity and the fair value of acquired identifiable assets and liabilities assumed as of the BOG Acquisition Date were as follows: (In thousands) Purchase price: Value of common shares issued (6,527,746 shares) $ 253,799 Fair value of stock options assumed 10,696 Cash for fractional shares 10 Total purchase price 264,505 Identifiable assets: Cash and cash equivalents 29,340 Investment securities 219,783 Loans 966,870 Premises and equipment 5,574 Core deposit intangibles 9,058 Other assets 31,605 Total identifiable assets $ 1,262,230 Identifiable liabilities: Deposits $ 971,685 Short-term borrowings 101,021 Long-term borrowings 67,659 Other liabilities 11,532 Total identifiable liabilities 1,151,897 Fair value of net assets acquired including identifiable intangible assets 110,333 Resulting goodwill $ 154,172
Cardinal Financial Corporation [Member]
Schedule of Acquired Loans Accounted for at Fair Value	In conjunction with the Bank of Georgetown merger, the acquired loan portfolio was accounted for at fair value as follows: (In thousands) June 3, 2016 Contractually required principal and interest at acquisition $ 1,275,398 Contractual cash flows not expected to be collected (33,980 ) Expected cash flows at acquisition 1,241,418 Interest component of expected cash flows (274,548 ) Basis in acquired loans at acquisition – estimated fair value $ 966,870
Schedule of Fair Value of Acquired Identifiable Assets and Liabilities Assumed	The consideration paid for Cardinal’s common equity and the preliminary amounts of acquired identifiable assets and liabilities assumed as of the Cardinal Acquisition Date were as follows: (In thousands) Purchase price: Value of common shares issued (23,690,589 shares) $ 972,499 Fair value of stock options assumed 2,741 Cash for fractional shares 14 Total purchase price 975,254 Identifiable assets: Cash and cash equivalents 44,545 Investment securities 395,829 Loans held for sale 271,301 Loans 3,168,599 Premises and equipment 24,208 Core deposit intangibles 28,724 George Mason trade name intangible 1,080 Other assets 135,383 Total identifiable assets $ 4,069,669 Identifiable liabilities: Deposits $ 3,349,812 Short-term borrowings 96,215 Long-term borrowings 220,119 Unfavorable lease liability 2,281 Other liabilities 39,274 Total identifiable liabilities 3,707,701 Preliminary fair value of net assets acquired including identifiable intangible assets 361,968 Preliminary resulting goodwill $ 613,286
Schedule of Business Acquisition Pro Forma Information	Additionally, United expects to achieve operating cost savings and other business synergies as a result of the acquisition which are not reflected in the pro forma amounts. Proforma Year Ended December 31 (In thousands) 2017 2016 Total Revenues (1) $ 763,807 $ 784,198 Net Income 153,810 216,335 (1) Represents net interest income plus other income

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2017
Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities	The following is a summary of the amortized cost and estimated fair values of securities available for sale. December 31, 2017 (In thousands) Amortized Gross Gross Estimated Cumulative (1) U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 114,735 $ 385 $ 362 $ 114,758 $ 0 State and political subdivisions 303,101 3,197 2,429 303,869 0 Residential mortgage-backed securities Agency 821,857 2,096 9,360 814,593 0 Non-agency 4,969 543 0 5,512 86 Commercial mortgage-backed securities Agency 457,107 1,059 3,309 454,857 0 Asset-backed securities 109,829 148 7 109,970 0 Trust preferred collateralized debt obligations 37,856 542 4,129 34,269 20,770 Single issue trust preferred securities 13,417 368 1,225 12,560 0 Other corporate securities 28,101 407 18 28,490 0 Marketable equity securities 9,712 179 13 9,878 0 Total $ 1,900,684 $ 8,924 $ 20,852 $ 1,888,756 $ 20,856 December 31, 2016 (In thousands) Amortized Gross Gross Estimated Cumulative (1) U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 95,247 $ 698 $ 159 $ 95,786 $ 0 State and political subdivisions 196,350 1,364 4,902 192,812 0 Residential mortgage-backed securities Agency 585,208 3,999 5,111 584,096 0 Non-agency 6,629 426 12 7,043 86 Commercial mortgage-backed securities Agency 304,635 1,948 1,242 305,341 0 Asset-backed securities 217 0 0 217 0 Trust preferred collateralized debt obligations 48,558 729 15,735 33,552 25,952 Single issue trust preferred securities 13,363 284 2,170 11,477 0 Other corporate securities 14,996 66 0 15,062 0 Marketable equity securities 12,436 1,398 6 13,828 0 Total $ 1,277,639 $ 10,912 $ 29,337 $ 1,259,214 $ 26,038 (1) Other-than-temporary impairment in accumulated other comprehensive income. Amounts are before-tax.
Summary of Securities Available for Sale in an Unrealized Loss Position	The following is a summary of securities available for sale which were in an unrealized loss position at December 31, 2017 and 2016. Less than 12 months 12 months or longer (In thousands) Fair Value Unrealized Fair Unrealized December 31, 2017 U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 36,678 $ 230 $ 22,920 $ 132 State and political subdivisions 82,896 566 59,432 1,863 Residential mortgage-backed securities Agency 460,414 4,621 182,482 4,739 Non-agency 0 0 0 0 Commercial mortgage-backed securities Agency 282,858 2,386 70,763 923 Asset-backed securities 27,931 7 0 0 Trust preferred collateralized debt obligations 0 0 28,629 4,129 Single issue trust preferred securities 0 0 4,485 1,225 Other corporate securities 6,975 18 0 0 Marketable equity securities 0 0 363 13 Total $ 897,752 $ 7,828 $ 369,074 $ 13,024 Less than 12 months 12 months or longer (In thousands) Fair Unrealized Fair Unrealized December 31, 2016 U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 24,101 $ 159 $ 0 $ 0 State and political subdivisions 116,300 4,902 0 0 Residential mortgage-backed securities Agency 309,376 5,111 0 0 Non-agency 0 0 218 12 Commercial mortgage-backed securities Agency 162,479 1,242 0 0 Asset-backed securities 0 0 0 0 Trust preferred collateralized debt obligations 0 0 28,579 15,735 Single issue trust preferred securities 0 0 8,185 2,170 Marketable equity securities 357 6 0 0 Total $ 612,613 $ 11,420 $ 36,982 $ 17,917
Summary of Gains or Losses on Proceeds from Maturities, Sales and Calls of Available for Sale Securities by Specific Identification Method	The realized losses relate to sales of securities within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers and its subsidiaries. Year Ended (In thousands) 2017 2016 2015 Proceeds from maturities, sales and calls $ 686,312 $ 513,990 $ 191,266 Gross realized gains 3,274 268 143 Gross realized losses 1,400 13 10
Summary of Unrealized Loss Positions of Available for Sale TRUP CDOs and Single Issue Trust Preferred Securities	The following is a summary of the available for sale Trup Cdos as of December 31, 2017: (In thousands) Amortized Cost Class Amortized Cost Fair Value Unrealized (Gain) Investment Split Below Senior – Bank $ 4,863 $ 4,965 $ (102 ) $ 3,065 $ 0 $ 1,798 Mezzanine —Bank (now in senior position) 6,428 6,226 202 0 0 6,428 Mezzanine – Bank 22,668 19,967 2,701 0 0 22,668 Mezzanine – Bank & Insurance (combination) 3,897 3,111 786 0 0 3,897 Totals $ 37,856 $ 34,269 $ 3,587 $ 3,065 $ 0 $ 34,791
Roll Forward of Credit Losses on Securities	Below is a progression of the credit losses on securities which United has recorded other-than-temporary charges. These charges were recorded through earnings and other comprehensive income. (In thousands) Year Ended December 31 2017 2016 2015 Balance of cumulative credit losses at beginning of period $ 22,162 $ 23,773 $ 23,739 Additional credit losses on securities for which OTTI was previously recognized 0 33 34 Reductions for securities sold or paid off during the period (4,102) (1,644) 0 Balance of cumulative credit losses at end of period $ 18,060 $ 22,162 $ 23,773
Summary of Amortized Cost and Estimated Fair Values of Securities Held to Maturity	The following is a summary of the amortized cost and estimated fair values of securities held to maturity. December 31, 2017 (In thousands) Amortized Gross Gross Estimated U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 5,187 $ 308 $ 0 $ 5,495 State and political subdivisions 5,797 10 0 5,807 Residential mortgage-backed securities Agency 23 3 0 26 Single issue trust preferred securities 9,401 0 731 8,670 Other corporate securities 20 0 0 20 Total $ 20,428 $ 321 $ 731 $ 20,018 December 31, 2016 (In thousands) Amortized Gross Gross Estimated U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 5,295 $ 570 $ 0 $ 5,865 State and political subdivisions 8,598 17 0 8,615 Residential mortgage-backed securities Agency 30 5 0 35 Single issue trust preferred securities 19,315 0 2,672 16,643 Other corporate securities 20 0 0 20 Total $ 33,258 $ 592 $ 2,672 $ 31,178
Maturities and Weighted-Average Yields of Securities	The following table sets forth the maturities of all securities (based on amortized cost) at December 31, 2017, and the weighted-average After 1 But After 5 But (Dollars in thousands) Within 1 Year Within 5 Years Within 10 Years After 10 Years Amount Yield Amount Yield Amount Yield Amount Yield U.S. Treasury and other U.S. Government agencies and corporations $ 20,018 0.71 % $ 58,560 2.43 % $ 9,882 2.50 % $ 31,462 2.84 % States and political subdivisions (1) 20,711 2.76 % 68,543 2.53 % 45,399 2.97 % 174,245 3.72 % Residential mortgage-backed securities Agency 160 3.68 % 2,535 4.40 % 157,860 2.30 % 661,325 2.49 % Non-agency 121 5.01 % 547 5.00 % 0 0.00 % 4,301 5.84 % Commercial mortgage-backed Agency 9,300 1.11 % 258,207 2.03 % 168,964 2.57 % 20,636 2.81 % Asset-backed securities 0 0.00 % 0 0.00 % 0 0.00 % 109,829 2.03 % Trust preferred collateralized debt obligations 0 0.00 % 0 0.00 % 0 0.00 % 37,856 3.89 % Single issue trust preferred securities 0 0.00 % 0 0.00 % 9,687 2.70 % 13,131 4.72 % Marketable equity securities 0 0.00 % 0 0.00 % 0 0.00 % 9,712 0.27 % Other Corporate securities 0 0.00 % 6,993 2.32 % 14,000 5.21 % 7,128 0.75 % (1) Tax-equivalent
Available-for-sale Securities [Member]
Summary of Maturities of Debt Securities Held to Maturity by Amortized Cost and Estimated Fair Value	Maturities of mortgage-backed securities with an amortized cost of $23,000 and an estimated fair value of $26,000 at December 31, 2017 are included below based upon contractual maturity. Estimated (In thousands) Amortized Fair Cost Value Due in one year or less $ 0 $ 0 Due after one year through five years 9,344 9,660 Due after five years through ten years 5,663 5,343 Due after ten years 5,421 5,015 Total $ 20,428 $ 20,018
Held-to-maturity Securities [Member]
Summary of Maturities of Debt Securities Held to Maturity by Amortized Cost and Estimated Fair Value	Maturities of mortgage-backed securities with an amortized cost of $1,283,933,000 and an estimated fair value of $1,274,962,000 at December 31, 2017 are included below based upon contractual maturity. Estimated (In thousands) Amortized Fair Cost Value Due in one year or less $ 50,311 $ 50,212 Due after one year through five years 386,039 384,585 Due after five years through ten years 400,129 398,208 Due after ten years 1,054,493 1,045,873 Marketable equity securities 9,712 9,878 Total $ 1,900,684 $ 1,888,756

Loans (Tables)

Loans (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Major Classes of Loans	Major classes of loans are as follows: December 31 (In thousands) 2017 2016 Commercial, financial, and agricultural Owner-occupied $ 1,361,629 $ 1,049,885 Nonowner-occupied 4,451,298 3,425,453 Other commercial 1,998,979 1,613,437 Total commercial, financial & agricultural 7,811,906 6,088,775 Residential real estate 2,996,171 2,403,437 Construction & land development 1,504,907 1,255,738 Consumer: Bankcard 10,314 14,187 Other Consumer 704,039 594,582 Less: Unearned interest (15,916) (15,582) Total Loans, net of unearned interest $ 13,011,421 $ 10,341,137
Activity for Accretable Yield	Activity for the accretable yield for the year of 2017 follows. (In thousands) Accretable yield at the beginning of the period $ 29,165 Accretion (including cash recoveries) (15,490 ) Additions 17,444 Net reclassifications to accretable from non-accretable 13,424 Disposals (including maturities, foreclosures, and charge-offs) (5,445 ) Accretable yield at the ending of the period $ 39,098

Credit Quality (Tables)

Credit Quality (Tables)	12 Months Ended
	Dec. 31, 2017
Text Block [Abstract]
Schedule of Troubled Debt Restructurings, Segregated by Class of Loans	The following table sets forth United’s troubled debt restructurings that have been restructured during the year ended December 31, 2017 and 2016, segregated by class of loans: Troubled Debt Restructurings For the Year Ended December 31, 2017 December 31, 2016 Number of Pre- Modification Post- Number of Pre- Modification Post- Commercial real estate: Owner-occupied 1 $ 5,333 $ 5,327 1 $ 1,190 $ 1,178 Nonowner-occupied 0 0 0 0 0 0 Other commercial 13 32,211 29,411 7 2,803 2,213 Residential real estate 0 0 0 1 1,400 1,400 Construction & land development 1 1,456 1,383 0 0 0 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 0 0 0 0 0 0 Total 15 $ 39,000 $ 36,121 9 $ 5,393 $ 4,791
Schedule of Charged-off Troubled Debt Restructurings on Financing Receivables	The following table presents troubled debt restructurings, by class of loan, that had charge-offs during the year ended December 31, 2017 and 2016. These loans were restructured during the twelve months ended December 31, 2017 and 2016 and subsequently defaulted, resulting in principal charge-offs during the year of 2017 and 2016. Year Ended December 31, 2017 Year Ended December 31, 2016 (In thousands) Number of Recorded Number of Recorded Troubled Debt Restructurings Commercial real estate: Owner-occupied 0 $ 0 0 $ 0 Nonowner-occupied 0 0 0 0 Other commercial 1 1,495 1 37 Residential real estate 0 0 0 0 Construction & land development 0 0 0 0 Consumer: Bankcard 0 0 0 0 Other consumer 0 0 0 0 Total 1 $ 1,495 1 $ 37
Schedule of Age Analysis of Past Due Loans, Segregated by Class of Loans	The following table sets forth United’s age analysis of its past due loans, segregated by class of loans: Age Analysis of Past Due Loans As of December 31, 2017 (In thousands) 30-89 90 Days or Total Past Current & Total Financing Recorded Commercial real estate: Owner-occupied $ 7,968 $ 13,663 $ 21,631 $ 1,339,998 $ 1,361,629 $ 458 Nonowner-occupied 10,398 20,448 30,846 4,420,452 4,451,298 634 Other commercial 11,533 68,476 80,009 1,918,970 1,998,979 940 Residential real estate 35,300 28,637 63,937 2,932,234 2,996,171 6,519 Construction & land development 1,615 17,190 18,805 1,486,102 1,504,907 385 Consumer: Bankcard 449 186 635 9,679 10,314 186 Other consumer 9,288 968 10,256 693,783 704,039 775 Total $ 76,551 $ 149,568 $ 226,119 $ 12,801,218 $ 13,027,337 $ 9,897 (1) Other includes loans with a recorded investment of $210,521 acquired and accounted for under ASC topic 310-30 Age Analysis of Past Due Loans As of December 31, 2016 (In thousands) 30-89 90 Days or Total Past Current & Total Financing Recorded Commercial real estate: Owner-occupied $ 5,850 $ 3,981 $ 9,831 $ 1,040,054 $ 1,049,885 $ 94 Nonowner-occupied 9,288 20,847 30,135 3,395,318 3,425,453 172 Other commercial 15,273 42,766 58,039 1,555,398 1,613,437 2,518 Residential real estate 29,976 25,991 55,967 2,347,470 2,403,437 4,216 Construction & land development 3,809 7,779 11,588 1,244,150 1,255,738 33 Consumer: Bankcard 422 141 563 13,624 14,187 141 Other consumer 10,015 1,712 11,727 582,855 594,582 1,412 Total $ 74,633 $ 103,217 $ 177,850 $ 10,178,869 $ 10,356,719 $ 8,586 (1) Other includes loans with a recorded investment of $171,596 acquired and accounted for under ASC topic 310-30
Schedule of Nonaccrual Loans, Segregated by Class of Loans	The following table sets forth United’s nonaccrual loans, segregated by class of loans: Loans on Nonaccrual Status (In thousands) December 31, 2017 December 31, 2016 Commercial real estate: Owner-occupied $ 13,205 $ 3,887 Nonowner-occupied 19,814 20,675 Other commercial 67,536 40,248 Residential real estate 22,118 21,775 Construction & land development 16,805 7,746 Consumer: Bankcard 0 0 Other consumer 193 300 Total $ 139,671 $ 94,631
Schedule of Credit Quality Indicators Information, by Class of Loans	The following tables set forth United’s credit quality indicators information, by class of loans: Credit Quality Indicators Corporate Credit Exposure As of December 31, 2017 Commercial Real Estate (In thousands) Owner- Nonowner- Other Construction & Grade: Pass $ 1,276,088 $ 4,312,985 $ 1,848,868 $ 1,413,706 Special mention 20,165 57,618 55,564 5,196 Substandard 65,376 80,695 90,625 86,005 Doubtful 0 0 3,922 0 Total $ 1,361,629 $ 4,451,298 $ 1,998,979 $ 1,504,907 Credit Quality Indicators Corporate Credit Exposure As of December 31, 2016 Commercial Real Estate (In thousands) Owner- Nonowner- Other Construction & Grade: Pass $ 963,503 $ 3,284,497 $ 1,463,797 $ 1,126,742 Special mention 20,490 36,462 26,537 52,327 Substandard 65,892 104,494 122,893 76,669 Doubtful 0 0 210 0 Total $ 1,049,885 $ 3,425,453 $ 1,613,437 $ 1,255,738 Credit Quality Indicators Consumer Credit Exposure As of December 31, 2017 (In thousands) Residential Bankcard Other Grade: Pass $ 2,945,266 $ 9,679 $ 693,727 Special mention 18,025 449 9,334 Substandard 32,880 186 978 Doubtful 0 0 0 Total $ 2,996,171 $ 10,314 $ 704,039 As of December 31, 2016 (In thousands) Residential Bankcard Other Grade: Pass $ 2,348,017 $ 13,624 $ 582,704 Special mention 18,240 422 10,132 Substandard 36,995 141 1,746 Doubtful 185 0 0 Total $ 2,403,437 $ 14,187 $ 594,582
Schedule of Impaired Loans Information by Class of Loans	The following table set forth United’s impaired loans information, by class of loans: Impaired Loans December 31, 2017 December 31, 2016 (In thousands) Recorded Unpaid Related Recorded Unpaid Related With no related allowance recorded: Commercial real estate: Owner-occupied $ 61,897 $ 62,661 $ 0 $ 46,575 $ 47,108 $ 0 Nonowner-occupied 107,476 107,927 0 92,654 93,104 0 Other commercial 86,477 90,610 0 46,064 48,308 0 Residential real estate 36,923 38,863 0 22,747 24,404 0 Construction & land development 76,845 79,110 0 19,863 21,746 0 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 59 59 0 36 36 0 With an allowance recorded: Commercial real estate: Owner-occupied $ 9,132 $ 9,132 $ 2,251 $ 1,787 $ 2,082 $ 815 Nonowner-occupied 3,957 3,956 1,592 17,938 17,938 2,524 Other commercial 60,471 74,792 16,721 43,774 46,188 13,441 Residential real estate 9,813 11,152 1,552 12,066 12,801 3,431 Construction & land development 1,383 5,881 229 4,940 7,899 3,206 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 0 0 0 0 0 0 Total: Commercial real estate: Owner-occupied $ 71,029 $ 71,793 $ 2,251 $ 48,362 $ 49,190 $ 815 Nonowner-occupied 111,433 111,883 1,592 110,592 111,042 2,524 Other commercial 146,948 165,402 16,721 89,838 94,496 13,441 Residential real estate 46,736 50,015 1,552 34,813 37,205 3,431 Construction & land development 78,228 84,991 229 24,803 29,645 3,206 Consumer: Bankcard 0 0 0 0 0 0 Other consumer 59 59 0 36 36 0 Impaired Loans For the Year Ended December 31, 2017 December 31, 2016 (In thousands) Average Interest Average Interest With no related allowance recorded: Commercial real estate: Owner-occupied $ 56,202 $ 2,013 $ 36,800 $ 1,038 Nonowner-occupied 96,318 4,264 75,848 1,108 Other commercial 61,223 3,861 39,776 1,540 Residential real estate 23,618 986 25,964 538 Construction & land development 32,396 1,830 24,902 133 Consumer: Bankcard 0 0 0 0 Other consumer 36 0 33 0 With an allowance recorded: Commercial real estate: Owner-occupied $ 9,541 $ 610 $ 3,138 $ 97 Nonowner-occupied 12,593 539 11,920 564 Other commercial 63,963 2,208 36,511 1,615 Residential real estate 13,298 185 9,585 342 Construction & land development 2,597 85 8,994 83 Consumer: Bankcard 0 0 0 0 Other consumer 0 0 0 0 Total: Commercial real estate: Owner-occupied $ 65,743 $ 2,623 $ 39,938 $ 1,135 Nonowner-occupied 108,911 4,803 87,768 1,672 Other commercial 125,186 6,069 76,287 3,155 Residential real estate 36,916 1,171 35,549 880 Construction & land development 34,993 1,915 33,896 216 Consumer: Bankcard 0 0 0 0 Other consumer 36 0 33 0

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2017
Receivables [Abstract]
Schedule of Allowance for Loan Losses and Carrying Amount of Loans	A progression of the allowance for loan losses, by portfolio segment, for the year ended December 31, 2017 and 2016 is summarized as follows: Allowance for Loan Losses and Carrying Amount of Loans For the Year Ended December 31, 2017 (In thousands) Commercial Real Other Residential Construction & Land Consumer Allowance Total Owner- Nonowner- Allowance for Loan Losses: Beginning balance $ 5,273 $ 6,883 $ 33,087 $ 13,770 $ 10,606 $ 2,805 $ 347 $ 72,771 Charge-offs 2,246 296 21,189 2,973 3,337 2,822 0 32,863 Recoveries 2,599 244 3,395 601 726 748 0 8,313 Provision (225) (462) 29,896 (1,471) (808) 1,750 (274) 28,406 Ending balance $ 5,401 $ 6,369 $ 45,189 $ 9,927 $ 7,187 $ 2,481 $ 73 $ 76,627 Ending Balance: individually evaluated for impairment $ 2,251 $ 1,592 $ 16,721 $ 1,552 $ 229 $ 0 $ 0 $ 22,345 Ending Balance: collectively evaluated for impairment $ 3,150 $ 4,777 $ 28,468 $ 8,375 $ 6,958 $ 2,481 $ 73 $ 54,282 Ending Balance: $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Financing receivables: Ending balance $ 1,361,629 $ 4,451,298 $ 1,998,979 $ 2,996,171 $ 1,504,907 $ 714,353 $ 0 $ 13,027,337 Ending Balance: individually evaluated for impairment $ 36,721 $ 21,851 $ 78,715 $ 14,316 $ 16,921 $ 0 $ 0 $ 168,524 Ending Balance: collectively evaluated for impairment $ 1,291,379 $ 4,320,997 $ 1,892,706 $ 2,967,666 $ 1,461,206 $ 714,338 $ 0 $ 12,648,292 Ending Balance: $ 33,529 $ 108,450 $ 27,558 $ 14,189 $ 26,780 $ 15 $ 0 $ 210,521 Allowance for Loan Losses and Carrying Amount of Loans For the Year Ended December 31, 2016 (In thousands) Commercial Real Other Residential Construction & Land Consumer Allowance Total Owner- Nonowner- Allowance for Loan Losses: Beginning balance $ 3,637 $ 5,309 $ 31,328 $ 15,148 $ 18,205 $ 1,995 $ 104 $ 75,726 Charge-offs 5,281 419 20,430 4,597 2,659 2,794 0 36,180 Recoveries 3,071 675 3,452 639 433 446 0 8,716 Provision 3,846 1,318 18,737 2,580 (5,373) 3,158 243 24,509 Ending balance $ 5,273 $ 6,883 $ 33,087 $ 13,770 $ 10,606 $ 2,805 $ 347 $ 72,771 Ending Balance: individually evaluated for impairment $ 815 $ 2,524 $ 13,441 $ 3,431 $ 3,206 $ 0 $ 0 $ 23,417 Ending Balance: collectively evaluated for impairment $ 4,458 $ 4,359 $ 19,646 $ 10,339 $ 7,400 $ 2,805 $ 347 $ 49,354 Ending Balance: $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Financing receivables: Ending balance $ 1,049,885 $ 3,425,453 $ 1,613,437 $ 2,403,437 $ 1,255,738 $ 608,769 $ 0 $ 10,356,719 Ending Balance: individually evaluated for impairment $ 18,976 $ 26,835 $ 56,091 $ 14,766 $ 8,152 $ 0 $ 0 $ 124,820 Ending Balance: collectively evaluated for impairment $ 1,005,999 $ 3,323,117 $ 1,527,479 $ 2,373,969 $ 1,221,006 $ 608,733 $ 0 $ 10,060,303 Ending Balance: $ 24,910 $ 75,501 $ 29,867 $ 14,702 $ 26,580 $ 36 $ 0 $ 171,596
Progression of Allowance for Credit Losses Including Allowance for Loan Losses and Reserve for Lending-Related Commitment	A progression of the allowance for credit losses, which includes the allowance for loan losses and the reserve for lending-related commitments, for the periods presented is summarized as follows: Year Ended December 31 (In thousands) 2017 2016 2015 Balance of allowance for loan losses at beginning of period $ 72,771 $ 75,726 $ 75,529 Provision for loan losses 28,406 24,509 22,574 101,177 100,235 98,103 Loans charged off 32,863 36,180 25,499 Less recoveries (8,313) (8,716) (3,122) Net charge-offs 24,550 27,464 22,377 Balance of allowance for loan losses at end of period $ 76,627 $ 72,771 $ 75,726 Reserve for lending-related commitments 679 1,044 936 Balance of allowance for credit losses at end of period $ 77,306 $ 73,815 $ 76,662

Bank Premises and Equipment a40

Bank Premises and Equipment and Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Bank Premises and Equipment	Bank premises and equipment are summarized as follows: December 31 (In thousands) 2017 2016 Land $ 34,970 $ 24,238 Buildings and improvements 103,914 89,302 Leasehold improvements 44,684 33,194 Furniture, fixtures and equipment 99,232 65,598 282,799 212,332 Less allowance for depreciation and amortization 177,905 136,423 Net bank premises and equipment $ 104,894 $ 75,909
Future Minimum Lease Payments	Future minimum lease payments, by year and in the aggregate, under noncancelable operating leases with initial or remaining terms of one year or more, for years subsequent to December 31, 2017, consisted of the following: Year Amount (In thousands) 2018 $ 14,753 2019 13,117 2020 11,249 2021 9,529 2022 6,400 Thereafter 14,796 Total minimum lease payments $ 69,844

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of Intangible Assets	The following is a summary of intangible assets subject to amortization and those not subject to amortization: December 31, 2017 Community Banking Mortgage Banking Total (In thousands) Gross Carrying Accumulated Gross Carrying Accumulated Gross Carrying Accumulated Amortized intangible assets: Core deposit intangible assets $ 98,359 ($ 54,453 ) $ 0 $ 0 $ 98,359 ($ 54,453) Non-amortized George Mason trade name $ 0 $ 1,080 $ 1,080 Goodwill not subject to amortization $ 1,473,265 $ 5,115 $ 1,478,380 December 31, 2016 Community Banking Total (In thousands) Gross Carrying Accumulated Gross Carrying Accumulated Amortized intangible assets: Core deposit intangible assets $ 69,635 ($ 46,681) $ 69,635 ($ 46,681) Goodwill not subject to amortization $ 863,767 $ 863,767
Reconciliation of Goodwill	The following table provides a reconciliation of goodwill: (In thousands) Community Mortgage Total Goodwill at December 31, 2016 $ 863,767 $ 0 $ 863,767 Addition to goodwill from Bank of Georgetown acquisition 1,327 0 1,327 Preliminary addition to goodwill from Cardinal acquisition 608,171 5,115 613,286 Goodwill at December 31, 2017 $ 1,473,265 $ 5,115 $ 1,478,380
Schedule of Anticipated Amortization Expense	The following table sets forth the anticipated amortization expense for intangible assets for the years subsequent to 2017: Year Amount (In thousands) 2018 $ 8,039 2019 7,016 2020 6,309 2021 5,369 2022 and thereafter 17,173

Deposits (Tables)

Deposits (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Book Value of Deposits	The book value of deposits consisted of the following: (In thousands) December 31 2017 2016 Demand deposits $ 4,294,687 $ 3,171,841 Interest-bearing checking 2,156,974 1,778,156 Regular savings 1,034,100 721,224 Money market accounts 3,756,259 3,151,896 Time deposits under $100,000 795,137 693,005 Time deposits over $100,000 1,793,434 1,280,745 Total deposits $ 13,830,591 $ 10,796,867

Short-Term Borrowings (Tables)

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Funds Purchased and Securities Sold Under Agreements to Repurchase and Weighted-Average Interest Rates	At December 31, 2017 and 2016, short-term borrowings and the related weighted-average interest rates were as follows: 2017 2016 Weighted- Weighted- (Dollars in thousands) Average Average Amount Rate Amount Rate Federal funds purchased $ 16,235 1.40 % $ 22,235 0.65 % Securities sold under agreements to repurchase 261,352 (1) 0.36 % (1) 187,316 (1) 0.25 % (1) Total $ 277,587 $ 209,551 (1) Excludes a wholesale security sold under an agreement to repurchase assumed in the Virginia Commerce merger of $50,000 with an interest rate of 4.37% at December 31, 2017 and 2016 and scheduled to mature in May of 2018.
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member]
Funds Purchased and Securities Sold Under Agreements to Repurchase and Weighted-Average Interest Rates	The following table shows the distribution of United’s federal funds purchased and securities sold under agreements to repurchase and the weighted-average interest rates thereon at the end of each of the last three years. Also provided are the maximum amount of borrowings and the average amounts of borrowings as well as weighted-average interest rates for the last three years. The table does not include the long-term wholesale security sold under an agreement to repurchase mentioned above assumed in the Virginia Commerce merger. (Dollars in thousands) Federal Funds Purchased Securities Sold Under To Repurchase At December 31: 2017 $ 16,235 $ 261,352 2016 22,235 187,316 2015 22,230 290,798 (Dollars in thousands) Federal Funds Purchased Securities Sold Under To Repurchase Weighted-average interest rate at year-end: 2017 1.40 % 0.36 % 2016 0.65 % 0.25 % 2015 0.25 % 0.15 % Maximum amount outstanding at any month’s end: 2017 $ 25,800 $ 377,687 2016 32,200 353,833 2015 52,000 379,818 Average amount outstanding during the year: 2017 $ 18,433 $ 287,663 2016 22,717 298,494 2015 38,526 283,011 Weighted-average interest rate during the year: 2017 0.88 % 0.33 % 2016 0.32 % 0.17 % 2015 0.21 % 0.10 %

Long-Term Borrowings (Tables)

Long-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
FHLB Advances and Related Weighted Average Interest Rates	At December 31, 2017 and 2016, FHLB advances and the related weighted-average interest rates were as follows: 2017 2016 (Dollars in thousands) Amount Weighted- Weighted- Amount Weighted- Weighted- FHLB advances $ 1,271,531 1.60 % 1.60 % $ 897,707 0.72 % 0.72 %
Information Related to Statutory Trusts	Information related to United’s statutory trusts is presented in the table below: (Dollars in thousands) Description Issuance Date Amount of Interest Rate Maturity Date Century Trust March 23, 2000 $ 8,800 10.875% Fixed March 8, 2030 United Statutory Trust III December 17, 2003 $20,000 3-month LIBOR + 2.85% December 17, 2033 United Statutory Trust IV December 19, 2003 $25,000 3-month LIBOR + 2.85% January 23, 2034 United Statutory Trust V July 12, 2007 $50,000 3-month LIBOR + 1.55% October 1, 2037 United Statutory Trust VI September 20, 2007 $30,000 3-month LIBOR + 1.30% December 15, 2037 Premier Statutory Trust II September 25, 2003 $ 6,000 3-month LIBOR + 3.10% October 8, 2033 Premier Statutory Trust III May 16, 2005 $ 8,000 3-month LIBOR + 1.74% June 15, 2035 Premier Statutory Trust IV June 20, 2006 $14,000 3-month LIBOR + 1.55% September 23, 2036 Premier Statutory Trust V December 14, 2006 $10,000 3-month LIBOR + 1.61% March 1, 2037 Centra Statutory Trust I September 20, 2004 $10,000 3-month LIBOR + 2.29% September 20, 2034 Centra Statutory Trust II June 15, 2006 $10,000 3-month LIBOR + 1.65% July 7, 2036 Virginia Commerce Trust II December 19, 2002 $15,000 6-month LIBOR + 3.30% December 19, 2032 Virginia Commerce Trust III December 20, 2005 $25,000 3-month LIBOR + 1.42% February 23, 2036 Cardinal Statutory Trust I July 27, 2004 $20,000 3-month LIBOR + 2.40% September 15, 2034 UFBC Capital Trust I December 30, 2004 $ 5,000 3-month LIBOR + 2.10% March 15, 2035
Debentures and Related Weighted Average Interest Rates	At December 31, 2017 and 2016, the Debentures and their related weighted-average interest rates were as follows: 2017 2016 (Dollars in thousands) Amount Weighted- Amount Weighted- Century Trust $ 8,800 10.88 % $ 8,800 10.88 % United Statutory Trust III 20,619 4.45 % 20,619 3.84 % United Statutory Trust IV 25,774 4.23 % 25,774 3.74 % United Statutory Trust V 51,547 2.89 % 51,547 2.40 % United Statutory Trust VI 30,928 2.89 % 30,928 2.26 % Premier Statutory Trust II 6,186 4.46 % 6,186 3.98 % Premier Statutory Trust III 8,248 3.33 % 8,248 2.70 % Premier Statutory Trust IV 14,433 3.23 % 14,433 2.55 % Premier Statutory Trust V 10,310 3.09 % 10,310 2.54 % Centra Statutory Trust I 10,000 3.92 % 10,000 3.29 % Centra Statutory Trust II 10,000 3.01 % 10,000 2.53 % Virginia Commerce Trust II 12,014 5.14 % 11,784 4.62 % Virginia Commerce Trust III 16,216 2.87 % 15,690 2.34 % Cardinal Statutory Trust I 14,031 3.99 % 0 0.00 % UFBC Capital Trust I 3,340 3.69 % 0 0.00 % Total $ 242,446 $ 224,319
Schedule of Maturities of Long-term Borrowings	At December 31, 2017, the scheduled maturities of long-term borrowings were as follows: Year Amount (In thousands) 2018 $ 795,439 2019 186,404 2020 40,871 2021 51,453 2022 and thereafter 289,810 Total $ 1,363,977

Other Expense (Tables)

Other Expense (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Expense	The following details certain items of other expense for the periods indicated: Year Ended December 31 (In thousands) 2017 2016 2015 Legal, consulting & other professional services $ 11,844 $ 9,763 $ 9,310 Franchise & other taxes not on income 12,586 7,778 7,055 Automated Teller Machine (ATM) expenses 6,686 7,365 7,107

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax Provisions Included in the Consolidated Statements of Income	The income tax provisions included in the consolidated statements of income are summarized as follows: (In thousands) Year Ended December 31 2017 2016 2015 Current (benefit) expense: Federal $ 65,459 $ 63,169 $ 58,373 State 7,960 5,154 5,428 Deferred expense: Federal 20,920 8,844 1,657 Tax Act remeasurement 37,732 0 0 State 2,175 (1,592 ) 72 Total income taxes $ 134,246 $ 75,575 $ 65,530
Reconciliation of Income Tax Expense to the Amount Computed by Applying the Statutory Federal Income Tax Rate	The following is a reconciliation of income tax expense to the amount computed by applying the statutory federal income tax rate to income before income taxes. Year Ended December 31 (Dollars in thousands) 2017 2016 2015 Amount % Amount % Amount % Tax on income before taxes at statutory federal rate $ 99,689 35.0% $ 77,930 35.0% $ 71,222 35.0% Plus: State income taxes net of federal tax benefits 6,207 2.2 4,084 1.8 3,516 1.7 105,896 37.2 82,014 36.8 74,738 36.7 Increase (decrease) resulting from: Tax-exempt (5,362 ) (1.9 ) (3,919 ) (1.8 ) (4,158 ) (2.0 ) Deferred taxes due to the Tax Act 37,732 13.2 0 0.0 0 0.0 Historic tax credit 0 0.0 0 0.0 (1,262 ) (0.6 ) Other items-net (4,020 ) (1.4 ) (2,520 ) (1.1 ) (3,788 ) (1.9 ) Income taxes $ 134,246 47.1% $ 75,575 33.9% $ 65,530 32.2%
Components of United's Deferred Tax Assets and Liabilities	Significant components of United’s deferred tax assets and liabilities (included in other assets in the Consolidated Balance Sheets) at December 31, 2017 and 2016 are as follows: (In thousands) 2017 2016 Deferred tax assets: Allowance for credit losses $ 18,012 $ 26,941 Accrued benefits payable 12,175 0 Other accrued liabilities 779 3,478 Unrecognized components of net periodic pension costs 13,443 20,166 Unrealized loss on securities available for sale 2,797 1,436 Premises and equipment 0 93 Other real estate owned 3,169 6,724 Deferred mortgage points 3,028 0 Purchase accounting intangibles 14,855 41,392 Total deferred tax assets 68,258 100,230 Deferred tax liabilities: Deferred mortgage points 2,994 3,608 Accrued benefits payable 0 4,061 Premises and equipment 0 0 Other 1,627 13,687 Total deferred tax liabilities 4,621 21,356 Net deferred tax assets $ 63,637 $ 78,874
Reconciliation of the Total Amounts of Unrecognized Tax Benefits	Below is a reconciliation of the total amounts of unrecognized tax benefits: December 31 (In thousands) 2017 2016 Unrecognized tax benefits at beginning of year $ 2,442 $ 2,102 Increase in unrecognized tax benefits as a result of tax positions taken during the current period 972 673 Decreases in the unrecognized tax benefits as a result of a lapse of the applicable statute of limitations (520) (333) Unrecognized tax benefits at end of year $ 2,894 $ 2,442

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Net Periodic Pension Cost	Net consolidated periodic pension cost included the following components: (Dollars in thousands) Year Ended December 31, 2017 2016 2015 Service cost $ 2,146 $ 2,374 $ 2,787 Interest cost 5,149 5,950 5,902 Expected return on plan assets (8,538) (8,089) (9,290) Recognized net actuarial loss 4,553 4,921 4,980 Amortization of prior service cost 0 0 1 Net periodic pension cost $ 3,310 $ 5,156 $ 4,380 Weighted-Average Assumptions: Discount rate 4.49% 4.75% 4.35% Expected return on assets 7.00% 7.25% 7.50% Rate of Compensation Increase (prior to age 45) 3.50% 3.50% 3.50% Rate of Compensation Increase (otherwise) 3.00% 3.00% 3.00%
Schedule of Amounts Related to Plan recognized as Component of Other Comprehensive Income	Amounts related to the Plan recognized as a component of other comprehensive income were as follows: (In thousands) Year Ended December 31, 2017 2016 2015 Net actuarial loss $ 6,784 $ 2,914 $ 2,402 Amortization of: Prior service cost 0 0 (1) Actuarial loss (4,553) (4,921) (4,980) Total recognized in other comprehensive income $ 2,231 $ (2,007) $ (2,579)
Reconciliation of the Beginning and Ending Balances of the Projected Benefit Obligation and the Fair Value of Plan Assets and the Accumulated Benefit Obligation	The reconciliation of the beginning and ending balances of the projected benefit obligation and the fair value of plan assets for the years ended December 31, 2017 and 2016 and the accumulated benefit obligation at December 31, 2017 and 2016 are as follows: (Dollars in thousands) December 31, 2017 2016 Change in Projected Benefit Obligation Projected Benefit Obligation at the Beginning of the Year $ 134,515 $ 125,403 Service Cost 2,146 2,374 Interest Cost 5,149 5,950 Actuarial Loss (Gain) 15,367 5,114 Benefits Paid (4,437 ) (4,326 ) Projected Benefit at the End of the Year $ 152,740 $ 134,515 Accumulated Benefit Obligation at the End of the Year $ 139,025 $ 121,548 Change in Plan Assets Fair Value of Plan Assets at the Beginning of the Year $ 119,711 $ 113,748 Actual Return on Plan Assets 17,121 10,289 Benefits Paid (4,437 ) (4,326 ) Employer Contributions 10,000 0 Fair value of plan assets at end of year $ 142,395 $ 119,711 Net Amount Recognized Funded Status $ (10,346 ) $ (14,804 ) Unrecognized Transition Asset 0 0 Unrecognized Prior Service Cost 0 0 Unrecognized Net Loss 56,222 53,991 Net Amount Recognized $ 45,876 $ 39,187 Weighted-Average Assumptions at the End of the Year Discount Rate 3.83 % 4.49 % Rate of Compensation Increase (prior to age 45) 3.50 % 3.50 % Rate of Compensation Increase (otherwise) 3.00 % 3.00 %
Asset Allocation for the Defined Benefit Pension Plan as of the Measurement Date, by Asset Category	Asset allocation for the defined benefit pension plan as of the measurement date, by asset category, is as follows: Plan Assets Target Allocation 2018 Allowable Allocation Range Percentage of Plan Assets at December 31, December 31, Equity Securities 68 % 50-70 % 71 % 71% Debt Securities 25 % 20-50 % 26 % 26% Other 7 % 3-15 % 3 % 3% Total 100 % 100%
Expected Benefit Payments	At December 31, 2017, the benefits expected to be paid in each of the next five fiscal years, and in the aggregate for the five years thereafter are as follows: Year Amount (In thousands) 2018 $ 5,314 2019 5,304 2020 5,632 2021 6,012 2022 6,377 2023 through 2027 36,991
Balances of the Plan Assets, by Fair Value Hierarchy Level	The following tables present the balances of the plan assets, by fair value hierarchy level, as of December 31, 2017 and 2016: Fair Value Measurements at December 31, 2017 Using (In thousands) Description Balance as of December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash equivalents $ 4,549 $ 4,549 $ 0 $ 0 Fixed Income Mutual Funds: Taxable 30,752 30,752 0 0 Alternative 6,302 6,302 0 0 Equity Securities: Common stock 24,003 24,003 0 0 Equity Mutual Funds: Domestic equity large cap 28,936 28,936 0 0 Domestic equity mid cap 13,108 13,108 0 0 Domestic equity small cap 9,520 9,520 0 0 Domestic equity other 0 0 0 0 International emerging equity 5,264 5,264 0 0 International equity developed 15,752 15,752 0 0 Alternative equity 4,209 4,209 0 0 Total $ 142,395 $ 142,395 $ 0 $ 0 Fair Value Measurements at December 31, 2016 Using (In thousands) Description Balance as of December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and Cash equivalents $ 1,778 $ 1,778 $ 0 $ 0 Fixed Income Securities: Mortgage backed securities 47 0 47 0 Collateralized mortgage obligations 48 0 48 0 Municipal obligations 670 0 670 0 Corporate bonds 1,169 0 1,169 0 Foreign bonds, notes and debentures 96 0 96 0 Fixed Income Mutual Funds: Taxable 26,816 26,816 0 0 Alternative 3,898 3,898 0 0 Equity Securities: Common stock 20,629 20,629 0 0 Equity Mutual Funds: Domestic equity large cap 23,063 23,063 0 0 Domestic equity mid cap 6,457 6,457 0 0 Domestic equity small cap 13,087 13,087 0 0 Domestic equity other 910 910 0 0 International emerging equity 3,120 3,120 0 0 International equity developed 12,619 12,619 0 0 Alternative equity 3,456 3,456 0 0 Domestic Balanced Mutual Funds 1,848 1,848 0 0 Total $ 119,711 $ 117,681 $ 2,030 $ 0

Stock Based Compensation (Table

Stock Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Plans	A summary of activity under the United’s stock option plans as of December 31, 2017, and the changes during the year of 2017 are presented below: Year ended December 31, 2017 Weighted Average (Dollars in thousands, except per share data) Aggregate Remaining Intrinsic Contractual Exercise Shares Value Term (Yrs.) Price Outstanding at January 1, 2017 1,411,735 $ 28.05 Assumed in acquisition of subsidiary 153,602 21.47 Granted 255,217 45.20 Exercised (220,905 ) 22.00 Forfeited or expired (41,211 ) 27.38 Outstanding at December 31, 2017 1,558,438 $ 8,761 5.8 $ 31.09 Exercisable at December 31, 2017 1,050,567 $ 8,528 4.6 $ 26.86
Status of United's Nonvested Stock Option Awards	The following table summarizes the status of United’s nonvested awards for the year ended December 31, 2017: Shares Weighted-Average Nonvested at January 1, 2017 430,278 $ 6.84 Granted 255,217 8.85 Vested (174,624 ) 6.69 Forfeited or expired (3,000 ) 8.85 Nonvested at December 31, 2017 507,871 $ 7.89
Changes to United's Restricted Common Shares	The following summarizes the changes to United’s restricted common shares for the year ended December 31, 2017: Number of Weighted-Average Outstanding at January 1, 2017 137,268 $ 33.61 Granted 90,075 45.21 Vested 56,007 32.48 Forfeited 840 45.30 Outstanding at December 31, 2017 170,496 $ 40.05

Derivative Financial Instrume49

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amount and Fair Value of Derivative Financial Instruments	The following tables disclose the derivative instruments’ location on the Company’s Consolidated Balance Sheets and the notional amount and fair value of those instruments at December 31, 2017 and 2016. Asset Derivatives December 31, 2017 December 31, 2016 (In thousands) Balance Sheet Location Notional Amount Fair Value Balance Sheet Location Notional Amount Fair Value Derivatives designated as hedging instruments Fair Value Hedges: Interest rate swap contracts (hedging commercial loans) Other assets $ 71,831 $ 538 Other assets $ 74,783 $ 24 Total derivatives designated as hedging instruments $ 71,831 $ 538 $ 74,783 $ 24 Derivatives not designated as hedging instruments Interest rate swap contracts Other assets $ 0 $ 0 Other assets $ 14,583 $ 2,267 Forward loan sales commitments Other assets 31,024 2 Other assets 0 0 Interest rate lock commitments Other assets 148,866 4,559 Other assets 0 0 Total derivatives not designated as hedging instruments $ 179,890 $ 4,561 $ 14,583 $ 2,267 Total asset derivatives $ 251,721 $ 5,099 $ 89,366 $ 2,291 Liability Derivatives December 31, 2017 December 31, 2016 (In thousands) Balance Sheet Location Notional Amount Fair Value Balance Sheet Location Notional Amount Fair Value Derivatives designated as hedging instruments Fair Value Hedges: Interest rate swap contracts (hedging commercial loans) Other liabilities $ 18,795 $ 165 Other liabilities $ 19,799 $ 338 Total derivatives designated as hedging instruments $ 18,795 $ 165 $ 19,799 $ 338 Derivatives not designated as hedging instruments Interest rate swap contracts Other liabilities $ 0 $ 0 Other liabilities $ 14,583 $ 2,267 TBA mortgage-backed securities Other liabilities 236,500 312 Other liabilities 0 0 Interest rate lock commitments Other liabilities 0 0 Other liabilities 0 0 Total derivatives not designated as hedging instruments $ 236,500 $ 312 $ 14,583 $ 2,267 Total liability derivatives $ 255,295 $ 477 $ 34,382 $ 2,605
Schedule of Derivative Financial Instruments on Statement of Income	The effect of United’s derivative financial instruments on its Consolidated Statements of Income for the years ended December 31, 2017, 2016 and 2015 is presented as follows: Year Ended (In thousands) Income Statement Location December 31, December 31, December 31, Derivatives in hedging relationships Fair Value Hedges: Interest rate swap contracts Interest income/ (expense) $ (781 ) $ (30 ) $ (813 ) Total derivatives in hedging relationships $ (781 ) $ (30 ) $ (813 ) Derivatives not designated as hedging instruments Forward loan sales commitments Income from Mortgage Banking Activities (426 ) 0 0 TBA mortgage-backed securities Income from Mortgage Banking Activities 1,547 0 0 Interest rate lock commitments Income from Mortgage Banking Activities (7,730 ) 0 0 Total derivatives not designated as hedging instruments $ (6,609) $ 0 $ 0 Total derivatives $ (7,390) $ (30) $ (813)

Comprehensive Income (Tables)

Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Components of Total Comprehensive Income	The changes in accumulated other comprehensive income are as follows: For the Years Ended December 31 (In thousands) 2017 2016 2015 Net Income $ 150,581 $ 147,083 $ 137,959 Available for sale (“AFS”) securities: AFS securities with OTTI charges during the period (60) (77) (113) Related income tax effect 22 28 41 Income tax rate change 0 208 316 Less : OTTI charges recognized in net income 60 33 47 Related income tax benefit (22) (12) (17) Reclassification of previous noncredit OTTI to credit OTTI 0 415 0 Related income tax benefit 0 (150) 0 Net unrealized gains on AFS securities with OTTI 0 445 274 AFS securities – all other: Change in net unrealized (losses) gains on AFS securities arising during the period 8,371 (12,931) (6,672) Related income tax effect (3,097) 4,867 2,415 Net reclassification adjustment for gains included in net income (1,874) (255) (133) Related income tax expense 693 92 48 4,093 (8,227 ) (4,342 ) Net effect of AFS securities on other comprehensive income 4,093 (7,782) (4,068) Held to maturity (“HTM”) securities: Accretion on the unrealized loss for securities transferred from AFS to the HTM investment portfolio prior to call or maturity 8 9 8 Related income tax expense (3) (3) (3) Net effect of HTM securities on other comprehensive income 5 6 5 Defined benefit pension plan: Net actuarial loss during the period (6,784) (2,914) (2,402) Related income tax expense (benefit) 2,510 1,077 944 Amortization of prior service cost recognized in net income 0 0 1 Related income tax benefit 0 0 0 Amortization of net actuarial loss recognized in net income 4,553 4,921 4,980 Related income tax benefit (1,685) (1,813) (1,908) Net effect of change in defined benefit pension plan on other comprehensive income (1,406) 1,271 1,615 Total change in other comprehensive income, net of tax 2,692 (6,505 ) (2,448 ) Total Comprehensive Income $ 153,273 $ 140,578 $ 135,511
Components of Accumulated Other Comprehensive Income	The components of accumulated other comprehensive income for the year ended December 31, 2017 are as follows: Changes in Accumulated Other Comprehensive Income (AOCI) by Component (a) For the Year Ended December 31, 2017 (Dollars in thousands) Unrealized Accretion Defined Items Total Balance at January 1, 2017 ($ 10,297 ) ($ 51 ) ($ 34,369 ) ($ 44,717 ) Other comprehensive income before reclassification 5,274 5 0 5,279 Amounts reclassified from accumulated other comprehensive income (1,181 ) 0 (1,406 ) (2,587 ) Net current-period other comprehensive income, net of tax 4,093 5 (1,406 ) 2,692 Balance at December 31, 2017 ($ 6,204 ) ($ 46 ) ($ 35,775 ) ($ 42,025 ) (a)All amounts are net-of-tax.
Reclassifications Out of Accumulated Other Comprehensive Income	Reclassifications out of Accumulated Other Comprehensive Income (AOCI) For the Year Ended December 31, 2017 (Dollars in thousands) Details about AOCI Components Amount Affected Line Item in the Statement Where Net Income is Presented Available for sale (“AFS”) securities: Reclassification of previous noncredit OTTI to credit OTTI $ 0 Total other-than-temporary impairment losses Net reclassification adjustment for losses (gains) included in net income (1,874 ) Net gains on sales/calls of investment (1,874 ) Total before tax Related income tax effect 693 Tax expense (1,181 ) Net of tax Pension plan: Net actuarial loss (6,784 )(a) Amortization of net actuarial loss 4,553 (b) (2,231 ) Total before tax Related income tax effect 825 Tax expense (1,406 ) Net of tax Total reclassifications for the period $ (2,587 ) (a) This AOCI component is included in the computation of changes in plan assets (see Note N, Employee Benefit Plans) (b) This AOCI component is included in the computation of net periodic pension cost (see Note N, Employee Benefit Plans)

United Bankshares, Inc. (Pare51

United Bankshares, Inc. (Parent Company Only) Financial Information (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Balance Sheets	Condensed Balance Sheets December 31 (In thousands) 2017 2016 Assets Cash and due from banks $ 93,198 $ 130,304 Securities available for sale 22,066 4,881 Securities held to maturity 996 20 Other investment securities 163 100 Investment in subsidiaries: Bank subsidiaries 3,437,036 2,372,783 Nonbank subsidiaries 12,535 10,535 Goodwill (16,008 ) (10,453 ) Other assets 10,309 15,699 Total Assets $ 3,560,295 $ 2,523,869 Liabilities and Shareholders’ Equity Junior subordinated debentures of subsidiary trusts $ 242,446 $ 224,319 Accrued expenses and other liabilities 77,319 63,803 Shareholders’ equity (including other accumulated comprehensive loss of $42,025 and $44,717 at December 31, 2017 and 2016, respectively) 3,240,530 2,235,747 Total Liabilities and Shareholders’ Equity $ 3,560,295 $ 2,523,869
Condensed Statements of Income	Condensed Statements of Income Year Ended December 31 (In thousands) 2017 2016 2015 Income Dividends from banking subsidiaries: Bank subsidiaries $ 115,000 $ 75,600 $ 70,500 Nonbank subsidiaries 58 10 433 Net interest income 437 86 76 Management fees: Bank subsidiaries 45,693 35,792 28,955 Nonbank subsidiaries 27 27 27 Other income 1,766 8 78 Total Income 162,981 111,523 100,069 Expenses Operating expenses 71,653 42,249 31,619 Income Before Income Taxes and Equity in Undistributed Net Income of Subsidiaries 91,328 69,274 68,450 Applicable income tax benefit (6,126 ) (3,061 ) (1,655 ) Income Before Equity in Undistributed Net Income of Subsidiaries 97,454 72,335 70,105 Equity in undistributed net income of subsidiaries: Bank subsidiaries 50,560 74,656 68,012 Nonbank subsidiaries 2,567 92 (158 ) Net Income $ 150,581 $ 147,083 $ 137,959
Condensed Statements of Cash Flows	Condensed Statements of Income Year Ended December 31 (In thousands) 2017 2016 2015 Income Dividends from banking subsidiaries: Bank subsidiaries $ 115,000 $ 75,600 $ 70,500 Nonbank subsidiaries 58 10 433 Net interest income 437 86 76 Management fees: Bank subsidiaries 45,693 35,792 28,955 Nonbank subsidiaries 27 27 27 Other income 1,766 8 78 Total Income 162,981 111,523 100,069 Expenses Operating expenses 71,653 42,249 31,619 Income Before Income Taxes and Equity in Undistributed Net Income of Subsidiaries 91,328 69,274 68,450 Applicable income tax benefit (6,126 ) (3,061 ) (1,655 ) Income Before Equity in Undistributed Net Income of Subsidiaries 97,454 72,335 70,105 Equity in undistributed net income of subsidiaries: Bank subsidiaries 50,560 74,656 68,012 Nonbank subsidiaries 2,567 92 (158 ) Net Income $ 150,581 $ 147,083 $ 137,959 Condensed Statements of Cash Flows Year Ended December 31 (In thousands) 2017 2016 2015 Operating Activities Net income $ 150,581 $ 147,083 $ 137,959 Adjustments to reconcile net income to net cash provided by operating activities: Equity in undistributed net income of subsidiaries (53,127) (74,748) (67,854) Amortization of net periodic pension costs 228 393 384 Stock-based compensation 3,555 2,817 2,484 Excess tax benefits from stock-based compensation arrangements 2,201 4,008 1,023 Net gain on securities transactions (1,185) (8) (54) Net change in other assets and liabilities 8,764 (8,344) 7,420 Net Cash Provided by Operating Activities 111,017 71,201 81,362 Investing Activities Net purchases of securities (19,268) (234) (1,047) Net cash paid in acquisition of subsidiary 22,146 (10) 0 Increase in investment in subsidiaries (34,203) (100,000) 0 Change in other investment securities (63) 0 2 Net Cash Used in Investing Activities (31,388) (100,244) (1,045) Financing Activities Proceeds from issuance of common stock 0 199,916 0 Cash dividends paid (121,354) (96,351) (88,864) Acquisition of treasury stock (1) (1) (1) Proceeds from sale of treasury stock from deferred compensation plan 1 1 1 Proceeds from exercise of stock options 4,619 13,337 7,871 Net Cash Provided by (Used in) Financing Activities (116,735) 116,902 (80,993) Increase (Decrease) in Cash and Cash Equivalents (37,106) 87,859 (676) Cash and Cash Equivalents at Beginning of Year 130,304 42,445 43,121 Cash and Cash Equivalents at End of Year $ 93,198 $ 130,304 $ 42,445

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2017
Banking and Thrift [Abstract]
Capital Amounts and Ratios	United’s and United Bank, capital amounts (in thousands of dollars) and ratios are presented in the following table. (Dollars in thousands) Actual For Capital Adequacy Purposes To Be Well- Capitalized Amount Ratio Amount Ratio Amount Ratio As of December 31, 2017: Total Capital (to Risk- Weighted Assets): United Bankshares $ 2,093,369 14.2 % $ 1,177,952 ³ $ 1,472,439 ³ United Bank 2,013,852 13.7 % 1,174,099 ³ 1,467,624 ³ Tier I Capital (to Risk- Weighted Assets): United Bankshares $ 1,759,189 12.0 % $ 883,464 ³ $ 1,177,952 ³ United Bank 1,936,546 13.2 % 880,575 ³ 1,174,099 ³ Common Tier I Capital (to Risk Weighted Assets): United Bankshares $ 1,759,189 12.0 % $ 662,598 ³ $ 957,086 ³ United Bank 1,936,546 13.2 % 660,431 ³ 953,956 ³ Tier I Capital (to Average Assets): United Bankshares $ 1,759,189 10.1 % $ 698,388 ³ $ 872,985 ³ United Bank 1,936,546 11.0 % 702,311 ³ 877,888 ³ As of December 31, 2016: Total Capital (to Risk- Weighted Assets): United Bankshares $ 1,699,984 14.9 % $ 915,479 ³ $ 1,144,348 ³ United Bank 1,592,647 13.9 % 915,956 ³ 1,144,945 ³ Tier I Capital (to Risk- Weighted Assets): United Bankshares $ 1,625,543 14.2 % $ 686,609 ³ $ 915,479 ³ United Bank 1,518,831 13.3 % 686,967 ³ 915,956 ³ Common Tier I Capital (to Risk Weighted Assets): United Bankshares $ 1,393,743 12.2 % $ 514,957 ³ $ 743,826 ³ United Bank 1,518,831 13.3 % 515,225 ³ 744,214 ³ Tier I Capital (to Average Assets): United Bankshares $ 1,625,543 12.2 % $ 535,227 ³ $ 669,033 ³ United Bank 1,518,831 11.4 % 535,361 ³ 669,201 ³

Fair Values of Financial Inst53

Fair Values of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured at Fair Value	The following table presents the balances of financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016, segregated by the level of the valuation inputs within the fair value hierarchy: Fair Value at December 31, 2017 Using (In thousands) Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Available for sale debt securities: U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 114,758 $ 0 $ 114,758 $ 0 State and political subdivisions 303,869 0 303,869 0 Residential mortgage-backed securities Agency 814,593 0 814,593 0 Non-agency 5,512 0 5,512 0 Commercial mortgage-backed securities Agency 454,857 0 454,857 0 Asset-backed securities 109,970 0 109,970 0 Trust preferred collateralized debt obligations 34,269 0 0 34,269 Single issue trust preferred securities 12,560 0 12,560 0 Other corporate securities 28,490 0 28,490 0 Total available for sale debt securities 1,878,878 0 1,844,609 34,269 Available for sale equity securities: Financial services industry 3,545 331 3,214 0 Equity mutual funds (1) 6,332 6,332 0 0 Other equity securities 1 1 0 0 Total available for sale equity securities 9,878 6,664 3,214 0 Total available for sale securities 1,888,756 6,664 1,847,823 34,269 Loans held for sale 263,308 0 0 263,308 Derivative financial assets: Interest rate swap contracts 538 0 538 0 Interest rate lock commitments 4,561 0 2 4,559 Total derivative financial assets 5,099 0 540 4,559 Liabilities Derivative financial liabilities: Interest rate swap contracts 165 0 165 0 TBA mortgage-backed securities 312 0 312 0 Total derivative financial liabilities 477 0 477 0 (1) The equity mutual funds are within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers of United and its subsidiaries. Fair Value at December 31, 2016 Using (In thousands) Description Balance as of December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Available for sale debt securities: U.S. Treasury securities and obligations of U.S. Government corporations and agencies $ 95,786 $ 0 $ 95,786 $ 0 State and political subdivisions 192,812 0 192,812 0 Residential mortgage-backed securities Agency 584,096 0 584,096 0 Non-agency 7,043 0 7,043 0 Asset-backed securities 217 0 217 0 Commercial mortgage-backed securities Agency 305,341 0 305,341 0 Trust preferred collateralized debt obligations 33,552 0 0 33,552 Single issue trust preferred securities 11,477 0 11,477 0 Other corporate securities 15,062 0 15,062 0 Total available for sale debt securities 1,245,386 0 1,211,834 33,552 Available for sale equity securities: Financial services industry 10,735 1,372 9,363 0 Equity mutual funds (1) 1,820 1,820 0 0 Other equity securities 1,273 1,273 0 0 Total available for sale equity securities 13,828 4,465 9,363 0 Total available for sale securities 1,259,214 4,465 1,221,197 33,552 Derivative financial assets: Interest rate contracts 2,291 0 2,291 0 Liabilities Derivative financial liabilities: Interest rate contracts 2,605 0 2,605 0 (1) The equity mutual funds are within a rabbi trust for the payment of benefits under a deferred compensation plan for certain key officers of United and its subsidiaries.
Schedule of Additional Information about Financial Assets and Liabilities Measured at Fair Value Utilized Level 3	The following table presents additional information about financial assets and liabilities measured at fair value at December 31, 2017 and 2016 on a recurring basis and for which United has utilized Level 3 inputs to determine fair value: Available-for-sale (In thousands) Trust preferred collateralized debt obligations 2017 2016 Balance, beginning of year $ 33,552 $ 34,686 Total gains or losses (realized/unrealized): Included in earnings (or changes in net assets) 9 0 Included in other comprehensive income 8,757 (1,134 ) Purchases, issuances, and settlements 0 0 Sales (8,049 ) 0 Transfers in and/or out of Level 3 0 0 Balance, ending of year $ 34,269 $ 33,552 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date 0 0 (In thousands) Loans held for sale 2017 2016 Balance, beginning of period $ 0 $ 0 Acquired in Cardinal merger 271,301 0 Originations 2,333,927 0 Sales (2,408,945) 0 Total gains or losses during the period recognized in earnings 58,132 0 Transfers in and/or out of Level 3 8,893 0 Balance, end of period $ 263,308 $ 0 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date $ 0 $ 0 (In thousands) Derivative Financial Assets Interest Rate Lock Commitments 2017 2016 Balance, beginning of period $ 0 $ 0 Acquired in Cardinal merger 10,393 0 Transfers other (5,834 ) 0 Balance, end of period $ 4,559 $ 0 The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date $ 0 $ 0
Schedule of Changes in Fair Value Included in Earnings of Financial Instruments for which Fair Value Option has been Elected	The following table reflects the change in fair value included in earnings of financial instruments for which the fair value option has been elected: (In thousands) Description Year Ended December 31, 2017 Year Ended December 31, 2016 Assets Loans held for sale Income from mortgage banking activities $ (10,497 ) $ 0
Summary of Difference Between Aggregate Fair Value and Remaining Contractual Principal Outstanding for Financial Instruments for which Fair Value Option has been Elected	The following table reflects the difference between the aggregate fair value and the remaining contractual principal outstanding for financial instruments for which the fair value option has been elected: December 31, 2017 December 31, 2016 (In thousands) Description Unpaid Fair Value Fair Value Unpaid Fair Fair Value Assets Loans held for sale $ 257,674 $ 263,308 $ 5,634 $ 0 $ 0 $ 0
Summary of Financial Assets Measured at Fair Value on Nonrecurring Basis	The following table summarizes United’s financial assets that were measured at fair value on a nonrecurring basis during the period: Carrying value at December 31, 2017 (In thousands) Description Balance as of December 31, 2017 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) YTD Losses Assets Loans held for sale $ 2,647 $ 0 $ 2,647 $ 0 $ 14 Impaired Loans 84,756 0 67,111 17,645 12,291 OREO 24,348 0 24,151 197 4,200 (In thousands) Description Balance as of December 31, Carrying value at December 31, 2016 YTD Losses Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets Loans held for sale $ 8,445 $ 0 $ 8,445 $ 0 $ 4 Impaired Loans 80,505 0 27,609 52,896 5,119 OREO 31,510 0 31,510 0 2,086
Summary of Estimated Fair Values of Financial Instruments	The estimated fair values of United’s financial instruments are summarized below: Fair Value Measurements (In thousands) Carrying Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2017 Cash and cash equivalents $ 1,666,167 $ 1,666,167 $ 0 $ 1,666,167 $ 0 Securities available for sale 1,888,756 1,888,756 6,664 1,847,823 34,269 Securities held to maturity 20,428 20,018 0 16,998 3,020 Other securities 162,461 154,338 0 0 154,338 Loans held for sale 265,955 265,955 0 2,647 263,308 Loans 12,934,794 12,437,797 0 0 12,437,797 Derivative financial assets 5,099 5,099 0 540 4,559 Deposits 13,830,591 14,024,720 0 14,024,720 0 Short-term borrowings 477,587 477,587 0 477,587 0 Long-term borrowings 1,363,977 1,338,754 0 1,338,754 0 Derivative financial liabilities 477 477 0 477 0 December 31, 2016 Cash and cash equivalents $ 1,434,527 $ 1,434,527 $ 0 $ 1,434,527 $ 0 Securities available for sale 1,259,214 1,259,214 4,465 1,221,197 33,552 Securities held to maturity 33,258 31,178 0 28,158 3,020 Other securities 111,166 105,608 0 0 105,608 Loans held for sale 8,445 8,445 0 8,445 0 Loans 10,268,366 10,122,486 0 0 10,122,486 Derivative financial assets 2,291 2,291 0 2,291 0 Deposits 10,796,867 10,785,294 0 10,785,294 0 Short-term borrowings 209,551 209,551 0 209,551 0 Long-term borrowings 1,172,026 1,142,782 0 1,142,782 0 Derivative financial liabilities 2,605 2,605 0 2,605 0

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Quantitative Information Related to Significant Involvement in Unconsolidated Variable Interest Entities	The following table summarizes quantitative information about United’s significant involvement in unconsolidated VIEs: As of December 31, 2017 As of December 31, 2016 (In thousands) Aggregate Assets Aggregate Liabilities Risk Of Loss (1) Aggregate Assets Aggregate Liabilities Risk Of Loss (1) Trust preferred securities $ 266,669 $ 257,674 $ 8,995 $ 240,668 $ 232,583 $ 8,085 (1)   Represents investment in VIEs.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Summary of Segment Reporting Information	Information about the reportable segments and reconciliation of this information to the consolidated financial statements at and for the years ended December 31, 2017, 2016 and 2015 is as follows: At and For the Year Ended December 31, 2017 (In thousands) Community Mortgage Other Consolidated Net interest income $ 558,622 $ (69 ) $ (9,556 ) $ 548,997 Provision for loans losses 28,406 0 0 28,406 Other income 69,615 58,532 3,498 131,645 Other expense 291,584 62,072 13,753 367,409 Income taxes 139,980 (901 ) (4,833 ) 134,246 Net income (loss) $ 168,267 $ (2,708 ) $ (14,978 ) $ 150,581 Total assets (liabilities) $ 18,761,508 $ 280,293 $ 17,158 $ 19,058,959 Average assets (liabilities) 17,385,448 212,212 19,769 17,617,429 At and For the Year Ended December 31, 2016 (In thousands) Community Other Consolidated Net interest income $ 433,140 $ (7,809 ) $ 425,331 Provision for loans losses 24,509 0 24,509 Other income 72,618 (2,586 ) 70,032 Other expense 249,894 (1,698 ) 248,196 Income taxes 78,640 (3,065 ) 75,575 Net income (loss) $ 152,715 $ (5,632 ) $ 147,083 Total assets (liabilities) $ 14,528,394 $ (19,502 ) $ 14,508,892 Average assets (liabilities) 13,398,861 (22,058 ) 13,376,803 At and For the Year Ended December 31, 2015 (In thousands) Community Other Consolidated Net interest income $ 390,775 $ (6,651 ) $ 384,124 Provision for loans losses 22,574 0 22,574 Other income 75,656 (2,030 ) 73,626 Other expense 235,644 (3,957 ) 231,687 Income taxes 67,109 (1,579 ) 65,530 Net income (loss) $ 141,104 $ (3,145 ) $ 137,959 Total assets (liabilities) $ 12,592,321 $ (14,377 ) $ 12,577,944 Average assets (liabilities) 12,277,023 (11,908 ) 12,265,115

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	Quarterly financial data for 2017 and 2016 is summarized below (dollars in thousands, except for per share data): (Dollars in thousands) 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter 2017 Interest income $ 120,758 $ 154,947 $ 171,583 $ 176,518 Interest expense 13,138 18,702 21,307 21,662 Net interest income 107,620 136,245 150,276 154,856 Provision for credit losses 5,899 8,251 7,279 6,977 Mortgage banking income 675 22,537 20,385 15,310 Securities gains (losses), net 3,940 747 467 430 Other noninterest income 15,531 17,222 17,377 17,024 Noninterest expense 62,842 112,137 96,652 95,778 Income taxes 20,216 19,304 27,836 66,890 Net income (1) 38,809 37,059 56,738 17,975 Per share data: Average shares outstanding (000s): Basic 80,902 99,198 104,760 104,808 Diluted 81,307 99,620 105,068 105,125 Net income per share: Basic $ 0.48 $ 0.37 $ 0.54 $ 0.17 Diluted $ 0.48 $ 0.37 $ 0.54 $ 0.17 Dividends per share $ 0.33 $ 0.33 $ 0.33 $ 0.34 2016 Interest income $ 108,496 $ 113,087 $ 123,137 $ 125,621 Interest expense 10,212 10,362 12,068 12,368 Net interest income 98,284 102,725 111,069 113,253 Provision for credit losses 4,035 7,667 6,988 5,819 Mortgage banking income 728 789 982 951 Securities losses, net 4 213 1 62 Other noninterest income 15,660 16,965 18,038 15,639 Noninterest expense 58,056 64,855 62,777 62,508 Income taxes 17,879 16,378 18,846 22,472 Net income (1) 34,706 31,792 41,479 39,106 Per share data: Average shares outstanding (000s): Basic 69,497 71,484 76,219 76,864 Diluted 69,714 71,809 76,648 77,303 Net income per share: Basic $ 0.50 $ 0.44 $ 0.54 $ 0.51 Diluted $ 0.50 $ 0.44 $ 0.54 $ 0.51 Dividends per share $ 0.33 $ 0.33 $ 0.33 $ 0.33 (1) For further information, see the related discussion “Quarterly Results” included in Management’s Discussion and Analysis.

Summary of Significant Accoun57

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)Region	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of Metropolitan Statistical Areas | Region	5
Loan fees net of costs amortized and included in interest income	$ 44,475,000	$ 18,471,000	$ 15,798,000
Minimum days, related to accrual of interest on discontinued commercial and consumer loans	90 days
Maximum days, related to accrual of interest on discontinued commercial and consumer loans	120 days
Sustained period of repayment performance in restructured loans	6 months
Real estate acquired in foreclosure or other settlement of loans	$ 24,348,000	31,510,000
Recorded investment of consumer mortgage loans	873,000	660,000
Advertising expense	4,519,000	3,410,000	4,111,000
Amortization expense on intangible assets	7,772,000	3,944,000	3,420,000
Total goodwill	1,478,380,000	863,767,000
Stock based compensation expense	3,555,000	2,817,000	2,484,000
Increase to net cash from operating activity	253,928,000	170,734,000	174,901,000
Decrease to net cash from financing activities	$ (288,967,000)	375,498,000	114,668,000
ASU 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in income tax expense		1,048,000
Increase to net cash from operating activity		4,008,000	4,008,000
Decrease to net cash from financing activities		$ 1,023,000	$ 1,023,000
Minimum [Member] | Core Deposit Intangible Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Intangible assets amortization period	1 year
Maximum [Member] | Core Deposit Intangible Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Intangible assets amortization period	7 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Bank premises and equipment, useful life	3 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Bank premises and equipment, useful life	15 years
Buildings and Improvements [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Bank premises and equipment, useful life	5 years
Buildings and Improvements [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Bank premises and equipment, useful life	40 years

Summary of Significant Accoun58

Summary of Significant Accounting Policies - Reconciliation of Numerator and Denominator of Basic Earnings Per Share with that of Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Distributed earnings allocated to common stock									$ 131,527	$ 98,510	$ 89,497
Undistributed earnings allocated to common stock									18,816	48,317	48,218
Net earnings allocated to common shareholders									$ 150,343	$ 146,827	$ 137,715
Average common shares outstanding	104,808,000	104,760,000	99,198,000	80,902,000	76,864,000	76,219,000	71,484,000	69,497,000	97,502,633	73,531,992	69,334,849
Dilutive effect of stock compensation									387,445	361,135	290,682
Average diluted shares outstanding	105,125,000	105,068,000	99,620,000	81,307,000	77,303,000	76,648,000	71,809,000	69,714,000	97,890,078	73,893,127	69,625,531
Earnings per basic common share	$ 0.17	$ 0.54	$ 0.37	$ 0.48	$ 0.51	$ 0.54	$ 0.44	$ 0.50	$ 1.54	$ 2	$ 1.99
Earnings per diluted common share	$ 0.17	$ 0.54	$ 0.37	$ 0.48	$ 0.51	$ 0.54	$ 0.44	$ 0.50	$ 1.54	$ 1.99	$ 1.98

Mergers and Acquisitions - Addi

Mergers and Acquisitions - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Apr. 21, 2017	Jun. 03, 2016	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Total assets at consummation	$ 19,058,959,000			$ 19,058,959,000	$ 14,508,892,000
Loans at consummation	13,027,337,000			13,027,337,000	10,356,719,000
Deposits at consummation	13,830,591,000			13,830,591,000	10,796,867,000
Resulting goodwill	1,478,380,000			1,478,380,000	$ 863,767,000
Liabilities to provide severance benefits	$ 0			$ 0
Contractually required principal and interest at acquisition		$ 132,837,000	$ 138,125,000
Expected cash flows at acquisition		108,275,000	117,564,000
Estimated fair value of acquired impaired loans at acquisition		$ 86,696,000	95,570,000
Cardinal Financial Corporation [Member]
Business Acquisition [Line Items]
Acquisition completion date				Apr. 21, 2017
Outstanding common stock acquired		100.00%
Total assets at consummation		$ 4,136,008,000
Loans at consummation		3,313,033,000
Deposits at consummation		3,344,740,000
Common stock paid in cash		975,254,000
Common stock value		972,499,000
Stock options exchanged value		$ 2,741,000
Common stock, shares issued		23,690,589
Resulting goodwill		$ 613,286,000
Fractional shares cash paid per share		14,000
Goodwill from acquisition expected to be tax deductible		0
Fair value discounts on loans acquired		144,434,000
Fair value discounts on leases		2,281,000
Fair value adjustment on trust preferred issuances		8,738,000
Premiums on land acquired		4,408,000
Premiums on interest-bearing deposits acquired		5,072,000
Premium on long-term FHLB advances acquired		10,740,000
Estimated remaining life of discount on leases acquired	5 years 9 months
Estimated remaining life of discount on trust preferred issuances acquired	16 years 8 months 19 days
Estimated remaining life of premium on interest-bearing deposits acquired	4 years 9 months
Estimated remaining life of the FHLB advances acquired	4 years 6 months 21 days
Assumed liabilities to provide severance benefits		1,825,000
Contractually required principal and interest at acquisition		4,211,734,000
Expected cash flows at acquisition		4,155,558,000
Estimated fair value of acquired impaired loans at acquisition		3,168,599,000
Revenue since acquisition included in consolidated results				$ 252,293,000
Revenue since acquisition included in consolidated results				$ 101,505,000
Cardinal Financial Corporation [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock value		$ 972,499
Common stock, shares issued		23,690,589
Closing market price per common share		$ 41.05
Cardinal Financial Corporation [Member] | Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Purchase price allocation of Identifiable Intangible assets		$ 28,724,000
Estimated period of amortization of core deposit intangibles		10 years
Fractional shares cash paid per share		$ 14,000
Cardinal Financial Corporation [Member] | George Mason Trade Name Intangible [Member]
Business Acquisition [Line Items]
Purchase price allocation of Identifiable Intangible assets		$ 1,080,000
Bank of Georgetown [Member]
Business Acquisition [Line Items]
Outstanding common stock acquired	100.00%			100.00%
Total assets at consummation	$ 1,278,837,000			$ 1,278,837,000
Loans at consummation	999,773,000			999,773,000
Deposits at consummation	971,369,000			971,369,000
Common stock paid in cash			264,505,000
Common stock value			253,799,000
Stock options exchanged value			$ 10,696,000
Common stock, shares issued			6,527,746
Resulting goodwill			$ 154,172,000
Fractional shares cash paid per share			10,000
Goodwill from acquisition expected to be tax deductible			0
Fair value discounts on loans acquired			43,072,000
Fair value discounts on leases				1,550,000
Premiums on interest-bearing deposits acquired			316,000
Premium on long-term FHLB advances acquired	$ 2,659,000			2,659,000
Estimated remaining life of premium on interest-bearing deposits acquired	29 days
Estimated remaining life of the FHLB advances acquired	7 years 8 months 2 days
Assumed liabilities to provide severance benefits	$ 300,000			$ 300,000
Contractually required principal and interest at acquisition			1,275,398,000
Expected cash flows at acquisition			1,241,418,000
Estimated fair value of acquired impaired loans at acquisition			966,870,000
Bank of Georgetown [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Common stock value			$ 253,799,000
Common stock, shares issued			6,527,746
Closing market price per common share			$ 38.88
Bank of Georgetown [Member] | Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Purchase price allocation of Identifiable Intangible assets			$ 9,058,000
Estimated period of amortization of core deposit intangibles			10 years
Fractional shares cash paid per share			$ 10,000

Mergers and Acquisitions - Sche

Mergers and Acquisitions - Schedule of Acquired Loans Accounted for at Fair Value (Detail) - USD ($)	Apr. 21, 2017	Jun. 03, 2016
Business Acquisition [Line Items]
Contractually required principal and interest at acquisition	$ 132,837,000	$ 138,125,000
Expected cash flows at acquisition	108,275,000	117,564,000
Basis in acquired loans at acquisition - estimated fair value	86,696,000	95,570,000
Cardinal Financial Corporation [Member]
Business Acquisition [Line Items]
Contractually required principal and interest at acquisition	4,211,734,000
Contractual cash flows not expected to be collected	(56,176,000)
Expected cash flows at acquisition	4,155,558,000
Interest component of expected cash flows	(986,959,000)
Basis in acquired loans at acquisition - estimated fair value	$ 3,168,599,000
Bank of Georgetown [Member]
Business Acquisition [Line Items]
Contractually required principal and interest at acquisition		1,275,398,000
Contractual cash flows not expected to be collected		(33,980,000)
Expected cash flows at acquisition		1,241,418,000
Interest component of expected cash flows		(274,548,000)
Basis in acquired loans at acquisition - estimated fair value		$ 966,870,000

Mergers and Acquisitions - Sc61

Mergers and Acquisitions - Schedule of Fair Value of Acquired Identifiable Assets and Liabilities Assumed (Detail) - USD ($)	Apr. 21, 2017	Jun. 03, 2016	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Resulting goodwill			$ 1,478,380,000	$ 863,767,000
Cardinal Financial Corporation [Member]
Business Acquisition [Line Items]
Value of common shares issued	$ 972,499,000
Fair value of stock options assumed	2,741,000
Cash for fractional shares	14,000
Total purchase price	975,254,000
Cash and cash equivalents	44,545,000
Investment securities	395,829,000
Loans held for sale	271,301,000
Loans	3,168,599,000
Premises and equipment	24,208,000
Other assets	135,383,000
Total identifiable assets	4,069,669,000
Deposits	3,349,812,000
Short-term borrowings	96,215,000
Long-term borrowings	220,119,000
Unfavorable lease liability	2,281,000
Other liabilities	39,274,000
Total identifiable liabilities	3,707,701,000
Fair value of net assets acquired including identifiable intangible assets	361,968,000
Resulting goodwill	613,286,000
Cardinal Financial Corporation [Member] | Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Cash for fractional shares	14,000
Core deposit intangibles	28,724,000
Cardinal Financial Corporation [Member] | George Mason Trade Name Intangible [Member]
Business Acquisition [Line Items]
Core deposit intangibles	$ 1,080,000
Bank of Georgetown [Member]
Business Acquisition [Line Items]
Value of common shares issued		$ 253,799,000
Fair value of stock options assumed		10,696,000
Cash for fractional shares		10,000
Total purchase price		264,505,000
Cash and cash equivalents		29,340,000
Investment securities		219,783,000
Loans		966,870,000
Premises and equipment		5,574,000
Other assets		31,605,000
Total identifiable assets		1,262,230,000
Deposits		971,685,000
Short-term borrowings		101,021,000
Long-term borrowings		67,659,000
Other liabilities		11,532,000
Total identifiable liabilities		1,151,897,000
Fair value of net assets acquired including identifiable intangible assets		110,333,000
Resulting goodwill		154,172,000
Bank of Georgetown [Member] | Core Deposit Intangible Assets [Member]
Business Acquisition [Line Items]
Cash for fractional shares		10,000
Core deposit intangibles		$ 9,058,000

Mergers and Acquisitions - Sc62

Mergers and Acquisitions - Schedule of Fair Value of Acquired Identifiable Assets and Liabilities Assumed (Parenthetical) (Detail) - shares	Apr. 21, 2017	Jun. 03, 2016
Cardinal Financial Corporation [Member]
Business Acquisition [Line Items]
Common stock, shares issued	23,690,589
Bank of Georgetown [Member]
Business Acquisition [Line Items]
Common stock, shares issued		6,527,746

Mergers and Acquisitions - Sc63

Mergers and Acquisitions - Schedule of Business Acquisition Pro Forma Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Combinations [Abstract]
Total Revenues	$ 763,807	$ 784,198
Net Income	$ 153,810	$ 216,335

Investment Securities - Summary

Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Available for Sale Securities (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Amortized Cost	$ 1,900,684,000	$ 1,277,639,000
Gross Unrealized Gains	8,924,000	10,912,000
Gross Unrealized Losses	20,852,000	29,337,000
Estimated Fair Value	1,888,756,000	1,259,214,000
Cumulative OTTI in AOCI	20,856,000	26,038,000
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	114,735,000	95,247,000
Gross Unrealized Gains	385,000	698,000
Gross Unrealized Losses	362,000	159,000
Estimated Fair Value	114,758,000	95,786,000
Cumulative OTTI in AOCI	0	0
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Amortized Cost	303,101,000	196,350,000
Gross Unrealized Gains	3,197,000	1,364,000
Gross Unrealized Losses	2,429,000	4,902,000
Estimated Fair Value	303,869,000	192,812,000
Cumulative OTTI in AOCI	0	0
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	821,857,000	585,208,000
Gross Unrealized Gains	2,096,000	3,999,000
Gross Unrealized Losses	9,360,000	5,111,000
Estimated Fair Value	814,593,000	584,096,000
Cumulative OTTI in AOCI	0	0
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	4,969,000	6,629,000
Gross Unrealized Gains	543,000	426,000
Gross Unrealized Losses	0	12,000
Estimated Fair Value	5,512,000	7,043,000
Cumulative OTTI in AOCI	86,000	86,000
Commercial Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	457,107,000	304,635,000
Gross Unrealized Gains	1,059,000	1,948,000
Gross Unrealized Losses	3,309,000	1,242,000
Estimated Fair Value	454,857,000	305,341,000
Cumulative OTTI in AOCI	0	0
Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	109,829,000	217,000
Gross Unrealized Gains	148,000	0
Gross Unrealized Losses	7,000	0
Estimated Fair Value	109,970,000	217,000
Cumulative OTTI in AOCI	0	0
Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Investments [Line Items]
Amortized Cost	37,856,000	48,558,000
Gross Unrealized Gains	542,000	729,000
Gross Unrealized Losses	4,129,000	15,735,000
Estimated Fair Value	34,269,000	33,552,000
Cumulative OTTI in AOCI	20,770,000	25,952,000
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	13,417,000	13,363,000
Gross Unrealized Gains	368,000	284,000
Gross Unrealized Losses	1,225,000	2,170,000
Estimated Fair Value	12,560,000	11,477,000
Cumulative OTTI in AOCI	0	0
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized Cost	28,101,000	14,996,000
Gross Unrealized Gains	407,000	66,000
Gross Unrealized Losses	18,000	0
Estimated Fair Value	28,490,000	15,062,000
Cumulative OTTI in AOCI	0	0
Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	9,712,000	12,436,000
Gross Unrealized Gains	179,000	1,398,000
Gross Unrealized Losses	13,000	6,000
Estimated Fair Value	9,878,000	13,828,000
Cumulative OTTI in AOCI	$ 0	$ 0

Investment Securities - Summa65

Investment Securities - Summary of Securities Available for Sale in an Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	$ 897,752	$ 612,613
Less than 12 months, Unrealized Losses	7,828	11,420
12 months or longer, Fair Value	369,074	36,982
12 months or longer, Unrealized Losses	13,024	17,917
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	36,678	24,101
Less than 12 months, Unrealized Losses	230	159
12 months or longer, Fair Value	22,920	0
12 months or longer, Unrealized Losses	132	0
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	82,896	116,300
Less than 12 months, Unrealized Losses	566	4,902
12 months or longer, Fair Value	59,432	0
12 months or longer, Unrealized Losses	1,863	0
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	460,414	309,376
Less than 12 months, Unrealized Losses	4,621	5,111
12 months or longer, Fair Value	182,482	0
12 months or longer, Unrealized Losses	4,739	0
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	0	218
12 months or longer, Unrealized Losses	0	12
Commercial Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	282,858	162,479
Less than 12 months, Unrealized Losses	2,386	1,242
12 months or longer, Fair Value	70,763	0
12 months or longer, Unrealized Losses	923	0
Asset-Backed Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	27,931	0
Less than 12 months, Unrealized Losses	7	0
12 months or longer, Fair Value	0	0
12 months or longer, Unrealized Losses	0	0
Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	28,629	28,579
12 months or longer, Unrealized Losses	4,129	15,735
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	0
Less than 12 months, Unrealized Losses	0	0
12 months or longer, Fair Value	4,485	8,185
12 months or longer, Unrealized Losses	1,225	2,170
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	6,975
Less than 12 months, Unrealized Losses	18
12 months or longer, Fair Value	0
12 months or longer, Unrealized Losses	0
Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Less than 12 months, Fair Value	0	357
Less than 12 months, Unrealized Losses	0	6
12 months or longer, Fair Value	363	0
12 months or longer, Unrealized Losses	$ 13	$ 0

Investment Securities - Summa66

Investment Securities - Summary of Gains or Losses on Proceeds from Maturities, Sales and Calls of Available for Sale Securities by Specific Identification Method (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities, sales and calls	$ 686,312	$ 513,990	$ 191,266
Gross realized gains	3,274	268	143
Gross realized losses	$ 1,400	$ 13	$ 10

Investment Securities - Additio

Investment Securities - Additional Information (Detail)	12 Months Ended			96 Months Ended
	Dec. 31, 2017USD ($)Securities	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2007USD ($)
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	$ 20,852,000	$ 29,337,000
Available for sale securities in unrealized loss position | Securities	463
Available for sale securities in portfolio, number | Securities	838
Amortized cost of available for sale securities	$ 1,900,684,000	1,277,639,000
Capitalization of banks, equal to or greater than, in the single-issue trust preferred portfolio	10,000,000,000
Noncredit-related other-than-temporary impairment recognized	$ 20,856,000	26,038,000
New issuance of Preferred Stock estimated				$ 60,000,000,000
Security other-than-temporarily impaired	100.00%
Cost of equity securities	$ 9,712,000
Available-for-sale securities estimated fair value	1,888,756,000	1,259,214,000
Gross realized gains	0	0	$ 0
Gross realized losses	0	0	$ 0
Held-to-maturity securities amortized cost	20,428,000	33,258,000
Held-to-maturity securities estimated fair value	20,018,000	31,178,000
Carrying value of securities pledged	1,403,565,000	1,137,408,000
TRUP CDOs [Member]
Schedule of Investments [Line Items]
Credit-related other-than-temporary impairment recognized in earnings	0	0
Noncredit-related other-than-temporary impairment recognized	20,770,000	25,952,000
Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities amortized cost	1,283,933,000
Available-for-sale securities estimated fair value	1,274,962,000
Held-to-maturity securities amortized cost	23,000
Held-to-maturity securities estimated fair value	26,000
Net unrealized gains	8,968,000	13,000
SunTrust Bank [Member]
Schedule of Investments [Line Items]
Amortized cost of trust preferred securities	7,426,000
Royal Bank of Scotland [Member]
Schedule of Investments [Line Items]
Amortized cost of trust preferred securities	$ 976,000
Minimum [Member]
Schedule of Investments [Line Items]
Other-than-temporarily impaired, the collateralization ratios	106.00%
Maximum [Member]
Schedule of Investments [Line Items]
Other-than-temporarily impaired, the collateralization ratios	461.30%
Weighted Average [Member]
Schedule of Investments [Line Items]
Other-than-temporarily impaired, the collateralization ratios	301.60%
Median [Member]
Schedule of Investments [Line Items]
Other-than-temporarily impaired, the collateralization ratios	283.60%
Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale single issue trust preferred securities	$ 7,707,000
Investment Grade [Member] | TRUP CDOs [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	3,065,000
Below Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale single issue trust preferred securities	5,710,000
Below Investment Grade [Member] | TRUP CDOs [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	29,693,000
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	2,429,000	4,902,000
Amortized cost of available for sale securities	$ 303,101,000	196,350,000
Percent of portfolio with credit support	75.00%
Investment grade credit rate percentage	1.00%
Number of equity securities other-than-temporarily impaired | Securities	0
Noncredit-related other-than-temporary impairment recognized	$ 0	0
Available-for-sale securities estimated fair value	303,869,000	192,812,000
Held-to-maturity securities amortized cost	5,797,000	8,598,000
Held-to-maturity securities estimated fair value	5,807,000	8,615,000
Agency Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	1,278,964,000
Commercial Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	3,309,000	1,242,000
Amortized cost of available for sale securities	457,107,000	304,635,000
Noncredit-related other-than-temporary impairment recognized	0	0
Available-for-sale securities estimated fair value	454,857,000	305,341,000
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	9,360,000	5,111,000
Amortized cost of available for sale securities	821,857,000	585,208,000
Noncredit-related other-than-temporary impairment recognized	0	0
Available-for-sale securities estimated fair value	814,593,000	584,096,000
Held-to-maturity securities amortized cost	23,000	30,000
Held-to-maturity securities estimated fair value	26,000	35,000
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	0	12,000
Amortized cost of available for sale securities	4,969,000	6,629,000
Noncredit-related other-than-temporary impairment recognized	86,000	86,000
Available-for-sale securities estimated fair value	$ 5,512,000	7,043,000
Residential Mortgage-Backed Securities, Non-agency [Member] | Originated Prior to 2005 [Member]
Schedule of Investments [Line Items]
Percentage of portfolio of non-agency mortgage backed securities with collateral	17.00%
Residential Mortgage-Backed Securities, Non-agency [Member] | Originated in 2006 and 2007 [Member]
Schedule of Investments [Line Items]
Percentage of portfolio of non-agency mortgage backed securities with collateral	83.00%
Residential Mortgage-Backed Securities, Non-agency [Member] | Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	$ 546,000
Residential Mortgage-Backed Securities, Non-agency [Member] | Below Investment Grade [Member]
Schedule of Investments [Line Items]
Amortized cost of available for sale securities	4,423,000
Marketable Equity Securities [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	13,000	6,000
Amortized cost of available for sale securities	$ 9,712,000	12,436,000
Number of equity securities other-than-temporarily impaired | Securities	0
Noncredit-related other-than-temporary impairment recognized	$ 0	0
Available-for-sale securities estimated fair value	9,878,000	13,828,000
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Gross unrealized losses on available for sale securities	362,000	159,000
Amortized cost of available for sale securities	114,735,000	95,247,000
Noncredit-related other-than-temporary impairment recognized	0	0
Available-for-sale securities estimated fair value	114,758,000	95,786,000
Held-to-maturity securities amortized cost	5,187,000	5,295,000
Held-to-maturity securities estimated fair value	$ 5,495,000	$ 5,865,000
Aggregate book value percentage of securities to shareholders' equity	10.00%

Investment Securities - Summa68

Investment Securities - Summary of Unrealized Loss Positions of Available for Sale TRUP CDOs and Single Issue Trust Preferred Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Amortized Cost	$ 1,900,684	$ 1,277,639
Fair Value	1,888,756	$ 1,259,214
Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	37,856
Fair Value	34,269
Unrealized (Gain) Loss	3,587
Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	4,863
Fair Value	4,965
Unrealized (Gain) Loss	(102)
Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	6,428
Fair Value	6,226
Unrealized (Gain) Loss	202
Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	22,668
Fair Value	19,967
Unrealized (Gain) Loss	2,701
Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	3,897
Fair Value	3,111
Unrealized (Gain) Loss	786
Investment Grade [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	3,065
Investment Grade [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	3,065
Investment Grade [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Investment Grade [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Investment Grade [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Split Rated [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Split Rated [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Split Rated [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	0
Below Investment Grade [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	34,791
Below Investment Grade [Member] | Senior - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	1,798
Below Investment Grade [Member] | Mezzanine - Bank (now in senior position) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	6,428
Below Investment Grade [Member] | Mezzanine - Bank [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	22,668
Below Investment Grade [Member] | Mezzanine - Bank & Insurance (combination) [Member] | Trup CDOs and Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	$ 3,897

Investment Securities - Roll Fo

Investment Securities - Roll Forward of Credit Losses on Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Cumulative credit losses, Beginning Balance	$ 22,162	$ 23,773	$ 23,739
Additional credit losses on securities for which OTTI was previously recognized	0	33	34
Reductions for securities sold or paid off during the period	(4,102)	(1,644)	0
Cumulative credit losses, Ending Balance	$ 18,060	$ 22,162	$ 23,773

Investment Securities - Summa70

Investment Securities - Summary of Maturities of Securities Available for Sale by Amortized Cost and Estimated Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 50,311
Due after one year through five years, Amortized Cost	386,039
Due after five years through ten years, Amortized Cost	400,129
Due after ten years, Amortized Cost	1,054,493
Marketable equity securities, Amortized Cost	9,712
Amortized Cost	1,900,684	$ 1,277,639
Due in one year or less, Estimated Fair Value	50,212
Due after one year through five years, Estimated Fair Value	384,585
Due after five years through ten years, Estimated Fair Value	398,208
Due after ten years, Estimated Fair Value	1,045,873
Marketable equity securities, Estimated Fair Value	9,878
Total available for sale securities	$ 1,888,756	$ 1,259,214

Investment Securities - Summa71

Investment Securities - Summary of Amortized Cost and Estimated Fair Values of Securities Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Amortized Cost	$ 20,428	$ 33,258
Gross Unrealized Gains	321	592
Gross Unrealized Losses	731	2,672
Estimated Fair Value	20,018	31,178
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Investments [Line Items]
Amortized Cost	5,187	5,295
Gross Unrealized Gains	308	570
Gross Unrealized Losses	0	0
Estimated Fair Value	5,495	5,865
State and Political Subdivisions [Member]
Schedule of Investments [Line Items]
Amortized Cost	5,797	8,598
Gross Unrealized Gains	10	17
Gross Unrealized Losses	0	0
Estimated Fair Value	5,807	8,615
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Investments [Line Items]
Amortized Cost	23	30
Gross Unrealized Gains	3	5
Gross Unrealized Losses	0	0
Estimated Fair Value	26	35
Single Issue Trust Preferred Securities [Member]
Schedule of Investments [Line Items]
Amortized Cost	9,401	19,315
Gross Unrealized Gains	0	0
Gross Unrealized Losses	731	2,672
Estimated Fair Value	8,670	16,643
Corporate Bonds [Member]
Schedule of Investments [Line Items]
Amortized Cost	20	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 20	$ 20

Investment Securities - Summa72

Investment Securities - Summary of Maturities of Debt Securities Held to Maturity by Amortized Cost and Estimated Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 0
Due after one year through five years, Amortized Cost	9,344
Due after five years through ten years, Amortized Cost	5,663
Due after ten years, Amortized Cost	5,421
Amortized Cost	20,428	$ 33,258
Due in one year or less, Estimated Fair Value	0
Due after one year through five years, Estimated Fair Value	9,660
Due after five years through ten year, Estimated Fair Value	5,343
Due after ten years, Estimated Fair Value	5,015
Estimated Fair Value, Total	$ 20,018	$ 31,178

Investment Securities - Maturit

Investment Securities - Maturities and Weighted-Average Yields of Securities (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Securities matured After 1 But Within 5 Years, Amount	9,344
Securities matured After 5 But Within 10 Years, Amount	5,663
Securities matured After 10 Years, Amount	5,421
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 20,018
Weighted-average Within 1 Year, Yield	0.71%
Securities matured After 1 But Within 5 Years, Amount	$ 58,560
Weighted-average After 1 But Within 5 Years, Yield	2.43%
Securities matured After 5 But Within 10 Years, Amount	$ 9,882
Weighted-average After 5 But Within 10 Years, Yield	2.50%
Securities matured After 10 Years, Amount	$ 31,462
Weighted-average After 10 Years, Yield	2.84%
State and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 20,711
Weighted-average Within 1 Year, Yield	2.76%
Securities matured After 1 But Within 5 Years, Amount	$ 68,543
Weighted-average After 1 But Within 5 Years, Yield	2.53%
Securities matured After 5 But Within 10 Years, Amount	$ 45,399
Weighted-average After 5 But Within 10 Years, Yield	2.97%
Securities matured After 10 Years, Amount	$ 174,245
Weighted-average After 10 Years, Yield	3.72%
Residential Mortgage-Backed Securities, Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 160
Weighted-average Within 1 Year, Yield	3.68%
Securities matured After 1 But Within 5 Years, Amount	$ 2,535
Weighted-average After 1 But Within 5 Years, Yield	4.40%
Securities matured After 5 But Within 10 Years, Amount	$ 157,860
Weighted-average After 5 But Within 10 Years, Yield	2.30%
Securities matured After 10 Years, Amount	$ 661,325
Weighted-average After 10 Years, Yield	2.49%
Residential Mortgage-Backed Securities, Non-agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 121
Weighted-average Within 1 Year, Yield	5.01%
Securities matured After 1 But Within 5 Years, Amount	$ 547
Weighted-average After 1 But Within 5 Years, Yield	5.00%
Securities matured After 5 But Within 10 Years, Amount	$ 0
Weighted-average After 5 But Within 10 Years, Yield	0.00%
Securities matured After 10 Years, Amount	$ 4,301
Weighted-average After 10 Years, Yield	5.84%
Commercial Mortgage-backed Agency [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 9,300
Weighted-average Within 1 Year, Yield	1.11%
Securities matured After 1 But Within 5 Years, Amount	$ 258,207
Weighted-average After 1 But Within 5 Years, Yield	2.03%
Securities matured After 5 But Within 10 Years, Amount	$ 168,964
Weighted-average After 5 But Within 10 Years, Yield	2.57%
Securities matured After 10 Years, Amount	$ 20,636
Weighted-average After 10 Years, Yield	2.81%
Asset-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Weighted-average Within 1 Year, Yield	0.00%
Securities matured After 1 But Within 5 Years, Amount	$ 0
Weighted-average After 1 But Within 5 Years, Yield	0.00%
Securities matured After 5 But Within 10 Years, Amount	$ 0
Weighted-average After 5 But Within 10 Years, Yield	0.00%
Securities matured After 10 Years, Amount	$ 109,829
Weighted-average After 10 Years, Yield	2.03%
Trust Preferred Collateralized Debt Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Weighted-average Within 1 Year, Yield	0.00%
Securities matured After 1 But Within 5 Years, Amount	$ 0
Weighted-average After 1 But Within 5 Years, Yield	0.00%
Securities matured After 5 But Within 10 Years, Amount	$ 0
Weighted-average After 5 But Within 10 Years, Yield	0.00%
Securities matured After 10 Years, Amount	$ 37,856
Weighted-average After 10 Years, Yield	3.89%
Single Issue Trust Preferred Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Weighted-average Within 1 Year, Yield	0.00%
Securities matured After 1 But Within 5 Years, Amount	$ 0
Weighted-average After 1 But Within 5 Years, Yield	0.00%
Securities matured After 5 But Within 10 Years, Amount	$ 9,687
Weighted-average After 5 But Within 10 Years, Yield	2.70%
Securities matured After 10 Years, Amount	$ 13,131
Weighted-average After 10 Years, Yield	4.72%
Marketable Equity Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Weighted-average Within 1 Year, Yield	0.00%
Securities matured After 1 But Within 5 Years, Amount	$ 0
Weighted-average After 1 But Within 5 Years, Yield	0.00%
Securities matured After 5 But Within 10 Years, Amount	$ 0
Weighted-average After 5 But Within 10 Years, Yield	0.00%
Securities matured After 10 Years, Amount	$ 9,712
Weighted-average After 10 Years, Yield	0.27%
Corporate Bonds [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities matured Within 1 Year, Amount	$ 0
Weighted-average Within 1 Year, Yield	0.00%
Securities matured After 1 But Within 5 Years, Amount	$ 6,993
Weighted-average After 1 But Within 5 Years, Yield	2.32%
Securities matured After 5 But Within 10 Years, Amount	$ 14,000
Weighted-average After 5 But Within 10 Years, Yield	5.21%
Securities matured After 10 Years, Amount	$ 7,128
Weighted-average After 10 Years, Yield	0.75%

Investment Securities - Matur74

Investment Securities - Maturities and Weighted-Average Yields of Securities (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost and Fair Value Debt Securities [Abstract]
Tax on income before taxes at statutory federal rate, rate	35.00%	35.00%	35.00%

Loans - Major Classes of Loans

Loans - Major Classes of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Commercial, financial, and agricultural
Total commercial, financial & agricultural	$ 7,811,906	$ 6,088,775
Residential real estate	2,996,171	2,403,437
Construction & land development	1,504,907	1,255,738
Consumer:
Bankcard	10,314	14,187
Other Consumer	704,039	594,582
Less: Unearned interest	(15,916)	(15,582)
Loans net of unearned income	13,011,421	10,341,137
Owner-Occupied [Member]
Commercial, financial, and agricultural
Total commercial, financial & agricultural	1,361,629	1,049,885
Nonowner-Occupied [Member]
Commercial, financial, and agricultural
Total commercial, financial & agricultural	4,451,298	3,425,453
Other Commercial [Member]
Commercial, financial, and agricultural
Total commercial, financial & agricultural	$ 1,998,979	$ 1,613,437

Loans - Additional Information

Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Loans held for sale	$ 265,955,000	$ 8,445,000
Acquired impaired loans from merger	$ 13,027,337,000	$ 10,356,719,000
Percentage of acquired impaired loans from merger on total gross loans	1.62%	1.66%
Recorded investment in acquired impaired loans	$ 285,964,000	$ 231,096,000
Loans-in-process	37,738,000	38,591,000
Overdrafts from deposit accounts	24,714,000	7,971,000
Reduction of loans due to a merger	172,397,000
Directors and Officers [Member]
Related party loans	36,360,000	255,476,000
Additional amount of loan	17,837,000
Repayment of Loan	64,556,000
Loans Acquired with Deteriorated Credit Quality [Member]
Acquired impaired loans from merger	$ 210,521,000	$ 171,596,000

Loans - Activity for Accretable

Loans - Activity for Accretable Yield (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Accretable yield at the beginning of the period	$ 29,165
Accretion (including cash recoveries)	(15,490)
Additions	17,444
Net reclassifications to accretable from non-accretable	13,424
Disposals (including maturities, foreclosures, and charge-offs)	(5,445)
Accretable yield at the ending of the period	$ 39,098

Credit Quality - Additional Inf

Credit Quality - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Minimum days for discontinue of accrual interest on commercial and consumer loan	90 days
Maximum days for discontinue of accrual interest on commercial and consumer loan	120 days
Troubled debt restructuring	$ 50,129,000	$ 21,152,000
Restructured loans on nonaccrual status	30,868,000	11,106,000
Restructured loans modified by reduction in interest	1,898,000
Restructured loan and interest	2,001,000
Restructured loans modified by change in terms	46,230,000
Restructured loans modified by reduction in interest rate and change in terms	$ 36,121,000	2,887,000
Restructured loans modified by change in loan terms amount		$ 1,904,000
Minimum number of days required for special mention	30 days
Maximum number of days required for special mention	89 days
Number of days required for substandard	90 days
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Restructured loans on nonaccrual status	$ 95,000
Financing Receivables 30 To 89 Days Past Due [Member]
Restructured loans on nonaccrual status	$ 1,254,000

Credit Quality - Schedule of Tr

Credit Quality - Schedule of Troubled Debt Restructurings, Segregated by Class of Loans (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	15	9
Pre-Modification Outstanding Recorded Investment	$ 39,000	$ 5,393
Post-Modification Outstanding Recorded Investment	$ 36,121	$ 4,791
Construction & Land Development [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1	0
Pre-Modification Outstanding Recorded Investment	$ 1,456	$ 0
Post-Modification Outstanding Recorded Investment	$ 1,383	$ 0
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1	1
Pre-Modification Outstanding Recorded Investment	$ 5,333	$ 1,190
Post-Modification Outstanding Recorded Investment	$ 5,327	$ 1,178
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Pre-Modification Outstanding Recorded Investment	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	$ 0	$ 0
Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	13	7
Pre-Modification Outstanding Recorded Investment	$ 32,211	$ 2,803
Post-Modification Outstanding Recorded Investment	$ 29,411	$ 2,213
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	1
Pre-Modification Outstanding Recorded Investment	$ 0	$ 1,400
Post-Modification Outstanding Recorded Investment	$ 0	$ 1,400
Consumer [Member] | Bankcard [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Pre-Modification Outstanding Recorded Investment	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	$ 0	$ 0
Consumer [Member] | Other Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Pre-Modification Outstanding Recorded Investment	$ 0	$ 0
Post-Modification Outstanding Recorded Investment	$ 0	$ 0

Credit Quality - Schedule of Ch

Credit Quality - Schedule of Charged-off Troubled Debt Restructurings on Financing Receivables (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)Contract	Dec. 31, 2016USD ($)Contract
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1	1
Recorded Investment | $	$ 1,495	$ 37
Construction & Land Development [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0
Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	1	1
Recorded Investment | $	$ 1,495	$ 37
Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0
Consumer [Member] | Bankcard [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0
Consumer [Member] | Other Consumer [Member]
Financing Receivable, Modifications [Line Items]
Number of Contracts | Contract	0	0
Recorded Investment | $	$ 0	$ 0

Credit Quality - Schedule of Ag

Credit Quality - Schedule of Age Analysis of its Past Due Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	$ 76,551	$ 74,633
Loans, Total Past Due	226,119	177,850
Loans, Current & Other	12,801,218	10,178,869
Total Financing Receivables	13,027,337	10,356,719
Loans, Recorded Investment >90 Days & Accruing	9,897	8,586
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	149,568	103,217
Construction & Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	1,615	3,809
Loans, Total Past Due	18,805	11,588
Loans, Current & Other	1,486,102	1,244,150
Total Financing Receivables	1,504,907	1,255,738
Loans, Recorded Investment >90 Days & Accruing	385	33
Construction & Land Development [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	17,190	7,779
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	7,968	5,850
Loans, Total Past Due	21,631	9,831
Loans, Current & Other	1,339,998	1,040,054
Total Financing Receivables	1,361,629	1,049,885
Loans, Recorded Investment >90 Days & Accruing	458	94
Commercial Real Estate [Member] | Owner-Occupied [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	13,663	3,981
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	10,398	9,288
Loans, Total Past Due	30,846	30,135
Loans, Current & Other	4,420,452	3,395,318
Total Financing Receivables	4,451,298	3,425,453
Loans, Recorded Investment >90 Days & Accruing	634	172
Commercial Real Estate [Member] | Nonowner-Occupied [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	20,448	20,847
Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	11,533	15,273
Loans, Total Past Due	80,009	58,039
Loans, Current & Other	1,918,970	1,555,398
Total Financing Receivables	1,998,979	1,613,437
Loans, Recorded Investment >90 Days & Accruing	940	2,518
Other Commercial [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	68,476	42,766
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	35,300	29,976
Loans, Total Past Due	63,937	55,967
Loans, Current & Other	2,932,234	2,347,470
Total Financing Receivables	2,996,171	2,403,437
Loans, Recorded Investment >90 Days & Accruing	6,519	4,216
Residential Real Estate [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	28,637	25,991
Consumer [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	449	422
Loans, Total Past Due	635	563
Loans, Current & Other	9,679	13,624
Total Financing Receivables	10,314	14,187
Loans, Recorded Investment >90 Days & Accruing	186	141
Consumer [Member] | Bankcard [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	186	141
Consumer [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, 30-89 Days Past Due	9,288	10,015
Loans, Total Past Due	10,256	11,727
Loans, Current & Other	693,783	582,855
Total Financing Receivables	704,039	594,582
Loans, Recorded Investment >90 Days & Accruing	775	1,412
Consumer [Member] | Other Consumer [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans, Total Past Due	$ 968	$ 1,712

Credit Quality - Schedule of 82

Credit Quality - Schedule of Age Analysis of its Past Due Loans, Segregated by Class of Loans (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	$ 13,027,337	$ 10,356,719
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	210,521	171,596
Loans and Debt Securities Acquired with Deteriorated Credit Quality [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Acquired impaired loans from merger	$ 210,521	$ 171,596

Credit Quality - Schedule of No

Credit Quality - Schedule of Nonaccrual Loans, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	$ 139,671	$ 94,631
Construction & Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	16,805	7,746
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	13,205	3,887
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	19,814	20,675
Other Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	67,536	40,248
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	22,118	21,775
Consumer [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	0	0
Consumer [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans on Nonaccrual Status	$ 193	$ 300

Credit Quality - Schedule of Cr

Credit Quality - Schedule of Credit Quality Indicators Information, by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	$ 13,027,337	$ 10,356,719
Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	2,996,171	2,403,437
Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,998,979	1,613,437
Bankcard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	10,314	14,187
Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	704,039	594,582
Owner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,361,629	1,049,885
Nonowner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	4,451,298	3,425,453
Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,504,907	1,255,738
Pass [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	2,945,266	2,348,017
Pass [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,848,868	1,463,797
Pass [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	9,679	13,624
Pass [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	693,727	582,704
Pass [Member] | Owner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,276,088	963,503
Pass [Member] | Nonowner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	4,312,985	3,284,497
Pass [Member] | Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	1,413,706	1,126,742
Special Mention [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	18,025	18,240
Special Mention [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	55,564	26,537
Special Mention [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	449	422
Special Mention [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	9,334	10,132
Special Mention [Member] | Owner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	20,165	20,490
Special Mention [Member] | Nonowner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	57,618	36,462
Special Mention [Member] | Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	5,196	52,327
Substandard [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	32,880	36,995
Substandard [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	90,625	122,893
Substandard [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	186	141
Substandard [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	978	1,746
Substandard [Member] | Owner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	65,376	65,892
Substandard [Member] | Nonowner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	80,695	104,494
Substandard [Member] | Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	86,005	76,669
Doubtful [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	0	185
Doubtful [Member] | Other Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	3,922	210
Doubtful [Member] | Bankcard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	0	0
Doubtful [Member] | Other Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	0	0
Doubtful [Member] | Owner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	0	0
Doubtful [Member] | Nonowner-Occupied [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	0	0
Doubtful [Member] | Construction & Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable, credit quality indicators information	$ 0	$ 0

Credit Quality - Schedule of Im

Credit Quality - Schedule of Impaired Loans Information by Class of Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Construction & Land Development [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	$ 76,845	$ 19,863
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	79,110	21,746
Impaired Loans, Recorded Investment, With an allowance recorded	1,383	4,940
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	5,881	7,899
Impaired Loans, Related Allowance	229	3,206
Impaired Loans, Recorded Investment	78,228	24,803
Impaired Loans, Unpaid Principal Balance	84,991	29,645
Impaired Loans, Related Allowance	229	3,206
Impaired Loans, Average Recorded Investment, With no related allowance recorded	32,396	24,902
Impaired Loans, Interest Income Recognized, With no related allowance recorded	1,830	133
Impaired Loans, Average Recorded Investment, With an allowance recorded	2,597	8,994
Impaired Loans, Interest Income Recognized, With an allowance recorded	85	83
Impaired Loans, Average Recorded Investment	34,993	33,896
Impaired Loans, Interest Income Recognized	1,915	216
Bankcard [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Average Recorded Investment, With no related allowance recorded	0	0
Impaired Loans, Interest Income Recognized, With no related allowance recorded	0	0
Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Average Recorded Investment, With no related allowance recorded	36	33
Impaired Loans, Interest Income Recognized, With no related allowance recorded	0	0
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	61,897	46,575
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	62,661	47,108
Impaired Loans, Recorded Investment, With an allowance recorded	9,132	1,787
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	9,132	2,082
Impaired Loans, Related Allowance	2,251	815
Impaired Loans, Recorded Investment	71,029	48,362
Impaired Loans, Unpaid Principal Balance	71,793	49,190
Impaired Loans, Related Allowance	2,251	815
Impaired Loans, Average Recorded Investment, With no related allowance recorded	56,202	36,800
Impaired Loans, Interest Income Recognized, With no related allowance recorded	2,013	1,038
Impaired Loans, Average Recorded Investment, With an allowance recorded	9,541	3,138
Impaired Loans, Interest Income Recognized, With an allowance recorded	610	97
Impaired Loans, Average Recorded Investment	65,743	39,938
Impaired Loans, Interest Income Recognized	2,623	1,135
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	107,476	92,654
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	107,927	93,104
Impaired Loans, Recorded Investment, With an allowance recorded	3,957	17,938
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	3,956	17,938
Impaired Loans, Related Allowance	1,592	2,524
Impaired Loans, Recorded Investment	111,433	110,592
Impaired Loans, Unpaid Principal Balance	111,883	111,042
Impaired Loans, Related Allowance	1,592	2,524
Impaired Loans, Average Recorded Investment, With no related allowance recorded	96,318	75,848
Impaired Loans, Interest Income Recognized, With no related allowance recorded	4,264	1,108
Impaired Loans, Average Recorded Investment, With an allowance recorded	12,593	11,920
Impaired Loans, Interest Income Recognized, With an allowance recorded	539	564
Impaired Loans, Average Recorded Investment	108,911	87,768
Impaired Loans, Interest Income Recognized	4,803	1,672
Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	86,477	46,064
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	90,610	48,308
Impaired Loans, Recorded Investment, With an allowance recorded	60,471	43,774
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	74,792	46,188
Impaired Loans, Related Allowance	16,721	13,441
Impaired Loans, Recorded Investment	146,948	89,838
Impaired Loans, Unpaid Principal Balance	165,402	94,496
Impaired Loans, Related Allowance	16,721	13,441
Impaired Loans, Average Recorded Investment, With no related allowance recorded	61,223	39,776
Impaired Loans, Interest Income Recognized, With no related allowance recorded	3,861	1,540
Impaired Loans, Average Recorded Investment, With an allowance recorded	63,963	36,511
Impaired Loans, Interest Income Recognized, With an allowance recorded	2,208	1,615
Impaired Loans, Average Recorded Investment	125,186	76,287
Impaired Loans, Interest Income Recognized	6,069	3,155
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	36,923	22,747
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	38,863	24,404
Impaired Loans, Recorded Investment, With an allowance recorded	9,813	12,066
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	11,152	12,801
Impaired Loans, Related Allowance	1,552	3,431
Impaired Loans, Recorded Investment	46,736	34,813
Impaired Loans, Unpaid Principal Balance	50,015	37,205
Impaired Loans, Related Allowance	1,552	3,431
Impaired Loans, Average Recorded Investment, With no related allowance recorded	23,618	25,964
Impaired Loans, Interest Income Recognized, With no related allowance recorded	986	538
Impaired Loans, Average Recorded Investment, With an allowance recorded	13,298	9,585
Impaired Loans, Interest Income Recognized, With an allowance recorded	185	342
Impaired Loans, Average Recorded Investment	36,916	35,549
Impaired Loans, Interest Income Recognized	1,171	880
Consumer [Member] | Bankcard [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	0	0
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	0	0
Impaired Loans, Recorded Investment, With an allowance recorded	0	0
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	0	0
Impaired Loans, Related Allowance	0	0
Impaired Loans, Recorded Investment	0	0
Impaired Loans, Unpaid Principal Balance	0	0
Impaired Loans, Related Allowance	0	0
Impaired Loans, Average Recorded Investment, With an allowance recorded	0	0
Impaired Loans, Interest Income Recognized, With an allowance recorded	0	0
Impaired Loans, Average Recorded Investment	0	0
Impaired Loans, Interest Income Recognized	0	0
Consumer [Member] | Other Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired Loans, Recorded Investment, With no related allowance recorded	59	36
Impaired Loans, Unpaid Principal Balance, With no related allowance recorded	59	36
Impaired Loans, Recorded Investment, With an allowance recorded	0	0
Impaired Loans, Unpaid Principal Balance, With an allowance recorded	0	0
Impaired Loans, Related Allowance	0	0
Impaired Loans, Recorded Investment	59	36
Impaired Loans, Unpaid Principal Balance	59	36
Impaired Loans, Related Allowance	0	0
Impaired Loans, Average Recorded Investment, With an allowance recorded	0	0
Impaired Loans, Interest Income Recognized, With an allowance recorded	0	0
Impaired Loans, Average Recorded Investment	36	33
Impaired Loans, Interest Income Recognized	$ 0	$ 0

Allowance for Credit Losses - A

Allowance for Credit Losses - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Specific loss allocations are calculated for commercial loans in excess	$ 500,000
Number of days for collecting principal or interest on consumer loans	30 days
Minimum collection period for home equity loan or high loan to value loan	180 days
Retail credits amount deemed unrecoverable charged-off period	60 days
Retail credits charged off period after discovery of the fraud	90 days
Reversal of provision for loan losses related to loans acquired	$ 1,106,000	$ 1,676,000	$ 5,321,000
Reserve for lending-related commitments	$ 679,000	$ 1,044,000	$ 936,000
Closed-End Retail Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days delinquent from contractual due date	12 days
Open-End Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of days delinquent from contractual due date	180 days

Allowance for Credit Losses - S

Allowance for Credit Losses - Schedule of Allowance for Loan Losses and Carrying Amount of Loans (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	$ 72,771	$ 75,726
Charge-offs	32,863	36,180
Recoveries	8,313	8,716
Provision	28,406	24,509
Allowance for Loan Losses Ending balance	76,627	72,771
Allowance for Loan Losses, individually evaluated for impairment	22,345	23,417
Allowance for Loan Losses, collectively evaluated for impairment	54,282	49,354
Allowance for Loan Losses	76,627	72,771	$ 75,726	$ 75,529
Financing receivables	13,027,337	10,356,719
Financing receivables, individually evaluated for impairment	168,524	124,820
Financing receivables, collectively evaluated for impairment	12,648,292	10,060,303
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	210,521	171,596
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	10,606	18,205
Charge-offs	3,337	2,659
Recoveries	726	433
Provision	(808)	(5,373)
Allowance for Loan Losses Ending balance	7,187	10,606
Allowance for Loan Losses, individually evaluated for impairment	229	3,206
Allowance for Loan Losses, collectively evaluated for impairment	6,958	7,400
Financing receivables	1,504,907	1,255,738
Financing receivables, individually evaluated for impairment	16,921	8,152
Financing receivables, collectively evaluated for impairment	1,461,206	1,221,006
Construction & Land Development [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	26,780	26,580
Allowance for Estimated Imprecision [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	347	104
Charge-offs	0	0
Recoveries	0	0
Provision	(274)	243
Allowance for Loan Losses Ending balance	73	347
Allowance for Loan Losses, individually evaluated for impairment	0	0
Allowance for Loan Losses, collectively evaluated for impairment	73	347
Financing receivables	0	0
Financing receivables, individually evaluated for impairment	0	0
Financing receivables, collectively evaluated for impairment	0	0
Allowance for Estimated Imprecision [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	0	0
Commercial Real Estate [Member] | Owner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	5,273	3,637
Charge-offs	2,246	5,281
Recoveries	2,599	3,071
Provision	(225)	3,846
Allowance for Loan Losses Ending balance	5,401	5,273
Allowance for Loan Losses, individually evaluated for impairment	2,251	815
Allowance for Loan Losses, collectively evaluated for impairment	3,150	4,458
Financing receivables	1,361,629	1,049,885
Financing receivables, individually evaluated for impairment	36,721	18,976
Financing receivables, collectively evaluated for impairment	1,291,379	1,005,999
Commercial Real Estate [Member] | Owner-Occupied [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	33,529	24,910
Commercial Real Estate [Member] | Nonowner-Occupied [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	6,883	5,309
Charge-offs	296	419
Recoveries	244	675
Provision	(462)	1,318
Allowance for Loan Losses Ending balance	6,369	6,883
Allowance for Loan Losses, individually evaluated for impairment	1,592	2,524
Allowance for Loan Losses, collectively evaluated for impairment	4,777	4,359
Financing receivables	4,451,298	3,425,453
Financing receivables, individually evaluated for impairment	21,851	26,835
Financing receivables, collectively evaluated for impairment	4,320,997	3,323,117
Commercial Real Estate [Member] | Nonowner-Occupied [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	108,450	75,501
Other Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	33,087	31,328
Charge-offs	21,189	20,430
Recoveries	3,395	3,452
Provision	29,896	18,737
Allowance for Loan Losses Ending balance	45,189	33,087
Allowance for Loan Losses, individually evaluated for impairment	16,721	13,441
Allowance for Loan Losses, collectively evaluated for impairment	28,468	19,646
Financing receivables	1,998,979	1,613,437
Financing receivables, individually evaluated for impairment	78,715	56,091
Financing receivables, collectively evaluated for impairment	1,892,706	1,527,479
Other Commercial [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	27,558	29,867
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	13,770	15,148
Charge-offs	2,973	4,597
Recoveries	601	639
Provision	(1,471)	2,580
Allowance for Loan Losses Ending balance	9,927	13,770
Allowance for Loan Losses, individually evaluated for impairment	1,552	3,431
Allowance for Loan Losses, collectively evaluated for impairment	8,375	10,339
Financing receivables	2,996,171	2,403,437
Financing receivables, individually evaluated for impairment	14,316	14,766
Financing receivables, collectively evaluated for impairment	2,967,666	2,373,969
Residential Real Estate [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	14,189	14,702
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses Beginning balance	2,805	1,995
Charge-offs	2,822	2,794
Recoveries	748	446
Provision	1,750	3,158
Allowance for Loan Losses Ending balance	2,481	2,805
Allowance for Loan Losses, individually evaluated for impairment	0	0
Allowance for Loan Losses, collectively evaluated for impairment	2,481	2,805
Financing receivables	714,353	608,769
Financing receivables, individually evaluated for impairment	0	0
Financing receivables, collectively evaluated for impairment	714,338	608,733
Consumer [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for Loan Losses	0	0
Financing receivables	$ 15	$ 36

Allowance for Credit Losses - P

Allowance for Credit Losses - Progression of Allowance for Credit Losses Including Allowance for Loan Losses and Reserve for Lending-Related Commitments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Balance of allowance for loan losses at beginning of period				$ 72,771				$ 75,726	$ 72,771	$ 75,726	$ 75,529
Provision for loan losses	$ 6,977	$ 7,279	$ 8,251	$ 5,899	$ 5,819	$ 6,988	$ 7,667	$ 4,035	28,406	24,509	22,574
Financing receivable allowance and provisions for credit losses									101,177	100,235	98,103
Loans charged off									32,863	36,180	25,499
Less recoveries									(8,313)	(8,716)	(3,122)
Net charge-offs									24,550	27,464	22,377
Balance of allowance for loan losses at end of period	76,627				72,771				76,627	72,771	75,726
Reserve for lending-related commitments	679				1,044				679	1,044	936
Balance of allowance for credit losses at end of period	$ 77,306				$ 73,815				$ 77,306	$ 73,815	$ 76,662

Bank Premises and Equipment a89

Bank Premises and Equipment and Leases - Bank Premises and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 282,799	$ 212,332
Less allowance for depreciation and amortization	177,905	136,423
Bank premises and equipment, Net	104,894	75,909
Land [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	34,970	24,238
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	103,914	89,302
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	44,684	33,194
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Bank premises and equipment, Gross	$ 99,232	$ 65,598

Bank Premises and Equipment a90

Bank Premises and Equipment and Leases - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 8,914,000	$ 7,889,000	$ 8,385,000
Amortization expense	122,000	136,000	136,000
Rent expense related to properties owned by related parties	$ 24,740,000	$ 14,661,000	$ 12,528,000

Bank Premises and Equipment a91

Bank Premises and Equipment and Leases - Future Minimum Lease Payments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Property Plant and Equipment Useful Life and Values [Abstract]
2,018	$ 14,753
2,019	13,117
2,020	11,249
2,021	9,529
2,022	6,400
Thereafter	14,796
Total minimum lease payments	$ 69,844

Goodwill and Other Intangible92

Goodwill and Other Intangibles - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill not subject to amortization	$ 1,478,380	$ 863,767
Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	98,359	69,635
Accumulated Amortization	(54,453)	(46,681)
George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,080
Community Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill not subject to amortization	1,473,265	863,767
Community Banking [Member] | Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	98,359	69,635
Accumulated Amortization	(54,453)	(46,681)
Community Banking [Member] | George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0
Mortgage Banking [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill not subject to amortization	5,115	$ 0
Mortgage Banking [Member] | Core Deposit Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0
Accumulated Amortization	0
Mortgage Banking [Member] | George Mason Trade Name Intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 1,080

Goodwill and Other Intangible93

Goodwill and Other Intangibles - Reconciliation of Goodwill (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 863,767
Goodwill, Ending Balance	1,478,380
Bank of Georgetown [Member]
Goodwill [Line Items]
Addition to goodwill	1,327
Cardinal Financial Corporation [Member]
Goodwill [Line Items]
Addition to goodwill	613,286
Community Banking [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	863,767
Goodwill, Ending Balance	1,473,265
Community Banking [Member] | Bank of Georgetown [Member]
Goodwill [Line Items]
Addition to goodwill	1,327
Community Banking [Member] | Cardinal Financial Corporation [Member]
Goodwill [Line Items]
Addition to goodwill	608,171
Mortgage Banking [Member]
Goodwill [Line Items]
Goodwill, Beginning Balance	0
Goodwill, Ending Balance	5,115
Mortgage Banking [Member] | Bank of Georgetown [Member]
Goodwill [Line Items]
Addition to goodwill	0
Mortgage Banking [Member] | Cardinal Financial Corporation [Member]
Goodwill [Line Items]
Addition to goodwill	$ 5,115

Goodwill and Other Intangible94

Goodwill and Other Intangibles - Schedule of Anticipated Amortization Expense (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,018	$ 8,039
2,019	7,016
2,020	6,309
2,021	5,369
2022 and thereafter	$ 17,173

Deposits - Book Value of Deposi

Deposits - Book Value of Deposits (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deposits [Abstract]
Demand deposits	$ 4,294,687	$ 3,171,841
Interest-bearing checking	2,156,974	1,778,156
Regular savings	1,034,100	721,224
Money market accounts	3,756,259	3,151,896
Time deposits under $100,000	795,137	693,005
Time deposits over $100,000	1,793,434	1,280,745
Total deposits	$ 13,830,591	$ 10,796,867

Deposits - Additional Informati

Deposits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deposits [Line Items]
Time deposits over $250,000	$ 790,703,000	$ 357,468,000
Interest paid	72,715,000	44,609,000	$ 39,835,000
Deposits	13,830,591,000	10,796,867,000
Subsidiaries [Member]
Deposits [Line Items]
Deposits	19,318,000	92,310,000
Deposits [Member]
Deposits [Line Items]
Interest paid	$ 48,887,000	$ 29,048,000	$ 28,447,000

Short-Term Borrowings -Short-Te

Short-Term Borrowings -Short-Term Borrowings and the Related Weighted-Average Interest Rates (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Short-term borrowings	$ 277,587	$ 209,551
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Weighted-Average Rate	1.40%	0.65%	0.25%
Short-term borrowings	$ 16,235	$ 22,235	$ 22,230
Securities Sold Under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Weighted-Average Rate	0.36%	0.25%	0.15%
Short-term borrowings	$ 261,352	$ 187,316	$ 290,798

Short-Term Borrowings -Short-98

Short-Term Borrowings -Short-Term Borrowings and the Related Weighted-Average Interest Rates (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Long-term borrowings	$ 51,453,000
Virginia Commerce Merger [Member]
Short-term Debt [Line Items]
Long-term borrowings	$ 50,000,000	$ 50,000,000
Acquisition accounting adjustment to fair value, interest rate	4.37%	4.37%
Acquisition accounting adjustment to fair value, maturity period	2018-05	2018-05

Short-Term Borrowings - Additio

Short-Term Borrowings - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Unused lines of credit	$ 180,000,000
Interest paid	72,715,000	$ 44,609,000	$ 39,835,000
Short-Term Borrowings [Member]
Short-term Debt [Line Items]
Interest paid	1,574,000	$ 1,587,000	$ 835,000
Unrelated Financial Institution [Member]
Short-term Debt [Line Items]
Unused lines of credit	$ 20,000,000
Renewal period of line of credit	360 days
Amount of outstanding balance under line of credit	$ 0

Short-Term Borrowings - Funds P

Short-Term Borrowings - Funds Purchased and Securities Sold Under Agreements to Repurchase and Weighted-Average Interest Rates (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Short-term borrowings	$ 277,587	$ 209,551
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 16,235	$ 22,235	$ 22,230
Weighted-average interest rate at year-end	1.40%	0.65%	0.25%
Maximum amount outstanding at any month's end	$ 25,800	$ 32,200	$ 52,000
Average amount outstanding during the year	$ 18,433	$ 22,717	$ 38,526
Weighted-average interest rate during the year	0.88%	0.32%	0.21%
Securities Sold Under Agreements to Repurchase [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 261,352	$ 187,316	$ 290,798
Weighted-average interest rate at year-end	0.36%	0.25%	0.15%
Maximum amount outstanding at any month's end	$ 377,687	$ 353,833	$ 379,818
Average amount outstanding during the year	$ 287,663	$ 298,494	$ 283,011
Weighted-average interest rate during the year	0.33%	0.17%	0.10%

Long-Term Borrowings - Addition

Long-Term Borrowings - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017USD ($)Trust	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
Unused borrowing amount	$ 2,244,843,000
FHLB advances	1,271,531,000	$ 897,707,000
Overnight funds	200,000,000	0
Long-term borrowings	$ 51,453,000
Number of statutory business trusts | Trust	15
Outstanding balances of debentures	$ 242,446,000	224,319,000
Maximum time to defer payment of interest on subordinate debt	5 years
Interest paid	$ 72,715,000	44,609,000	$ 39,835,000
Long-Term Borrowings [Member]
Debt Instrument [Line Items]
Interest paid	22,254,000	13,974,000	$ 10,553,000
Virginia Commerce Merger [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 50,000,000	$ 50,000,000
Acquisition accounting adjustment to fair value, interest rate	4.37%	4.37%
Acquisition accounting adjustment to fair value, maturity period	2018-05	2018-05
Capital Securities [Member]
Debt Instrument [Line Items]
Number of statutory business trusts | Trust	15
Maximum [Member]
Debt Instrument [Line Items]
Risk based assets	$ 15,000,000,000
Federal Home Loan Bank Borrowings [Member]
Debt Instrument [Line Items]
Carrying value of loans pledged as collateral for FHLB advances	$ 4,511,587,000

Long-Term Borrowings - FHLB Adv

Long-Term Borrowings - FHLB Advances and Related Weighted Average Interest Rates (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
FHLB advances, Amount	$ 1,271,531	$ 897,707
FHLB advances, Weighted-Average Contractual Rate	1.60%	0.72%
FHLB advances, Weighted-Average Effective Rate	1.60%	0.72%

Long -Term Borrowings - Informa

Long -Term Borrowings - Information Related to Statutory Trusts (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Century Trust [Member]
Variable Interest Entity [Line Items]
Issuance Date	Mar. 23, 2000
Amount of Capital Securities Issued	$ 8,800
Interest Rate	10.875% Fixed
Maturity Date	Mar. 8, 2030
United Statutory Trust III [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 17, 2003
Amount of Capital Securities Issued	$ 20,000
Interest Rate	3-month LIBOR + 2.85%
Maturity Date	Dec. 17, 2033
United Statutory Trust IV [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 19, 2003
Amount of Capital Securities Issued	$ 25,000
Interest Rate	3-month LIBOR + 2.85%
Maturity Date	Jan. 23, 2034
United Statutory Trust V [Member]
Variable Interest Entity [Line Items]
Issuance Date	Jul. 12, 2007
Amount of Capital Securities Issued	$ 50,000
Interest Rate	3-month LIBOR + 1.55%
Maturity Date	Oct. 1, 2037
United Statutory Trust VI [Member]
Variable Interest Entity [Line Items]
Issuance Date	Sep. 20, 2007
Amount of Capital Securities Issued	$ 30,000
Interest Rate	3-month LIBOR + 1.30%
Maturity Date	Dec. 15, 2037
Premier Statutory Trust II [Member]
Variable Interest Entity [Line Items]
Issuance Date	Sep. 25, 2003
Amount of Capital Securities Issued	$ 6,000
Interest Rate	3-month LIBOR + 3.10%
Maturity Date	Oct. 8, 2033
Premier Statutory Trust III [Member]
Variable Interest Entity [Line Items]
Issuance Date	May 16, 2005
Amount of Capital Securities Issued	$ 8,000
Interest Rate	3-month LIBOR + 1.74%
Maturity Date	Jun. 15, 2035
Premier Statutory Trust IV [Member]
Variable Interest Entity [Line Items]
Issuance Date	Jun. 20, 2006
Amount of Capital Securities Issued	$ 14,000
Interest Rate	3-month LIBOR + 1.55%
Maturity Date	Sep. 23, 2036
Premier Statutory Trust V [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 14, 2006
Amount of Capital Securities Issued	$ 10,000
Interest Rate	3-month LIBOR + 1.61%
Maturity Date	Mar. 1, 2037
Centra Statutory Trust I [Member]
Variable Interest Entity [Line Items]
Issuance Date	Sep. 20, 2004
Amount of Capital Securities Issued	$ 10,000
Interest Rate	3-month LIBOR + 2.29%
Maturity Date	Sep. 20, 2034
Centra Statutory Trust II [Member]
Variable Interest Entity [Line Items]
Issuance Date	Jun. 15, 2006
Amount of Capital Securities Issued	$ 10,000
Interest Rate	3-month LIBOR + 1.65%
Maturity Date	Jul. 7, 2036
Virginia Commerce Trust II [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 19, 2002
Amount of Capital Securities Issued	$ 15,000
Interest Rate	6-month LIBOR + 3.30%
Maturity Date	Dec. 19, 2032
Virginia Commerce Trust III [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 20, 2005
Amount of Capital Securities Issued	$ 25,000
Interest Rate	3-month LIBOR + 1.42%
Maturity Date	Feb. 23, 2036
Cardinal Statutory Trust I [Member]
Variable Interest Entity [Line Items]
Issuance Date	Jul. 27, 2004
Amount of Capital Securities Issued	$ 20,000
Interest Rate	3-month LIBOR + 2.40%
Maturity Date	Sep. 15, 2034
UFBC Capital Trust I [Member]
Variable Interest Entity [Line Items]
Issuance Date	Dec. 30, 2004
Amount of Capital Securities Issued	$ 5,000
Interest Rate	3-month LIBOR + 2.10%
Maturity Date	Mar. 15, 2035

Long -Term Borrowings - Debentu

Long -Term Borrowings - Debentures and Related Weighted Average Interest Rates (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Amount	$ 242,446	$ 224,319
Century Trust [Member]
Debt Instrument [Line Items]
Amount	$ 8,800	$ 8,800
Weighted-Average Rate	10.88%	10.88%
United Statutory Trust III [Member]
Debt Instrument [Line Items]
Amount	$ 20,619	$ 20,619
Weighted-Average Rate	4.45%	3.84%
United Statutory Trust IV [Member]
Debt Instrument [Line Items]
Amount	$ 25,774	$ 25,774
Weighted-Average Rate	4.23%	3.74%
United Statutory Trust V [Member]
Debt Instrument [Line Items]
Amount	$ 51,547	$ 51,547
Weighted-Average Rate	2.89%	2.40%
United Statutory Trust VI [Member]
Debt Instrument [Line Items]
Amount	$ 30,928	$ 30,928
Weighted-Average Rate	2.89%	2.26%
Premier Statutory Trust II [Member]
Debt Instrument [Line Items]
Amount	$ 6,186	$ 6,186
Weighted-Average Rate	4.46%	3.98%
Premier Statutory Trust III [Member]
Debt Instrument [Line Items]
Amount	$ 8,248	$ 8,248
Weighted-Average Rate	3.33%	2.70%
Premier Statutory Trust IV [Member]
Debt Instrument [Line Items]
Amount	$ 14,433	$ 14,433
Weighted-Average Rate	3.23%	2.55%
Premier Statutory Trust V [Member]
Debt Instrument [Line Items]
Amount	$ 10,310	$ 10,310
Weighted-Average Rate	3.09%	2.54%
Centra Statutory Trust I [Member]
Debt Instrument [Line Items]
Amount	$ 10,000	$ 10,000
Weighted-Average Rate	3.92%	3.29%
Centra Statutory Trust II [Member]
Debt Instrument [Line Items]
Amount	$ 10,000	$ 10,000
Weighted-Average Rate	3.01%	2.53%
Virginia Commerce Trust II [Member]
Debt Instrument [Line Items]
Amount	$ 12,014	$ 11,784
Weighted-Average Rate	5.14%	4.62%
Virginia Commerce Trust III [Member]
Debt Instrument [Line Items]
Amount	$ 16,216	$ 15,690
Weighted-Average Rate	2.87%	2.34%
Cardinal Statutory Trust I [Member]
Debt Instrument [Line Items]
Amount	$ 14,031	$ 0
Weighted-Average Rate	3.99%	0.00%
UFBC Capital Trust I [Member]
Debt Instrument [Line Items]
Amount	$ 3,340	$ 0
Weighted-Average Rate	3.69%	0.00%

Long -Term Borrowings - Schedul

Long -Term Borrowings - Schedule of Maturities of Long-term Borrowings (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Debt Disclosure [Abstract]
2,018	$ 795,439
2,019	186,404
2,020	40,871
2,021	51,453
2022 and thereafter	289,810
Total	$ 1,363,977

Other Expense - Other Expense (

Other Expense - Other Expense (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Legal, consulting & other professional services	$ 11,844,000	$ 9,763,000	$ 9,310,000
Franchise & other taxes not on income	12,586,000	7,778,000	7,055,000
Automated Teller Machine (ATM) expenses	$ 6,686,000	$ 7,365,000	$ 7,107,000

Income Taxes - Income Tax Provi

Income Taxes - Income Tax Provisions Included in the Consolidated Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current (benefit) expense:
Federal									$ 65,459	$ 63,169	$ 58,373
State									7,960	5,154	5,428
Deferred expense:
Federal									20,920	8,844	1,657
Tax Act remeasurement									37,732	0	0
State									2,175	(1,592)	72
Total income taxes	$ 66,890	$ 27,836	$ 19,304	$ 20,216	$ 22,472	$ 18,846	$ 16,378	$ 17,879	$ 134,246	$ 75,575	$ 65,530

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Federal corporate tax rate			35.00%	35.00%	35.00%
Deferred tax expense due to the Tax Act	$ 37,732,000
Federal income tax expense applicable to sales and calls of securities			$ 2,088,000	$ 114,000	$ 73,000
Income taxes paid			73,096,000	61,905,000	52,319,000
Franchise & other taxes not on income			12,586,000	7,778,000	7,055,000
Valuation allowance recorded	0		$ 0	0
Estimate of unrecognized tax benefits, reasonable possible			United cannot reasonably estimate the amount of tax benefits, if any, it may recognize over the next 12 months.
Accrued interest related to uncertain tax positions	670,000		$ 670,000	569,000
Interest or penalties were recognized			0	$ 0	$ 0
Scenario, Forecast [Member]
Income Taxes [Line Items]
Federal corporate tax rate		21.00%
Federal [Member]
Income Taxes [Line Items]
State net operating loss carryforwards	0		0
State [Member]
Income Taxes [Line Items]
State net operating loss carryforwards	$ 0		$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Expense to the Amount Computed by Applying the Statutory Federal Income Tax Rate (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax on income before taxes at statutory federal rate									$ 99,689	$ 77,930	$ 71,222
Plus: State income taxes net of federal tax benefits									6,207	4,084	3,516
Income tax before adjustments									105,896	82,014	74,738
Tax-exempt interest income									(5,362)	(3,919)	(4,158)
Deferred taxes due to the Tax Act									37,732	0	0
Historic tax credit									0	0	(1,262)
Other items-net									(4,020)	(2,520)	(3,788)
Total income taxes	$ 66,890	$ 27,836	$ 19,304	$ 20,216	$ 22,472	$ 18,846	$ 16,378	$ 17,879	$ 134,246	$ 75,575	$ 65,530
Tax on income before taxes at statutory federal rate, rate									35.00%	35.00%	35.00%
Plus: State income taxes net of federal tax benefits, rate									2.20%	1.80%	1.70%
Income tax before adjustments, rate									37.20%	36.80%	36.70%
Increase (decrease) resulting from:
Tax-exempt interest income, rate									(1.90%)	(1.80%)	(2.00%)
Deferred taxes due to the Tax Act, rate									13.20%	0.00%	0.00%
Historic tax credit, rate									(0.00%)	(0.00%)	(0.60%)
Other items-net, rate									(1.40%)	(1.10%)	(1.90%)
Income taxes, rate									47.10%	33.90%	32.20%

Income Taxes - Components of Un

Income Taxes - Components of United's Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowance for credit losses	$ 18,012	$ 26,941
Accrued benefits payable	12,175	0
Other accrued liabilities	779	3,478
Unrecognized components of net periodic pension costs	13,443	20,166
Unrealized loss on securities available for sale	2,797	1,436
Premises and equipment	0	93
Other real estate owned	3,169	6,724
Deferred mortgage points	3,028	0
Purchase accounting intangibles	14,855	41,392
Total deferred tax assets	68,258	100,230
Deferred tax liabilities:
Deferred mortgage points	2,994	3,608
Accrued benefits payable	0	4,061
Premises and equipment	0	0
Other	1,627	13,687
Total deferred tax liabilities	4,621	21,356
Net deferred tax assets	$ 63,637	$ 78,874

Income Taxes - Reconciliatio111

Income Taxes - Reconciliation of the Total Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at beginning of year	$ 2,442	$ 2,102
Increase in unrecognized tax benefits as a result of tax positions taken during the current period	972	673
Decreases in the unrecognized tax benefits as a result of a lapse of the applicable statute of limitations	(520)	(333)
Unrecognized tax benefits at end of year	$ 2,894	$ 2,442

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost decline in expense		$ 1,000,000
Unrecognized actuarial gains (losses), before tax		56,222,000
Unrecognized actuarial gains (losses), net of tax		35,420,000
Amortization expected to be recognized		4,653,000
Amortization expected to be recognized, net of tax		2,932,000
Amount of United common stock held in the pension plan		$ 142,395,000	$ 119,711,000	$ 113,748,000
Percentage of equity securities include united common stock		100.00%	100.00%
Percentage of projected benefit obligation		10.00%
Employer discretionary contribution amount	$ 10,000,000
Minimum number of days required to be eligible for the participation in the plan		90 days
Percentage of salary deferred under condition one of contribution by company		100.00%
First percentage of salary deferred under condition one of contribution by company		4.00%
Vesting percentage of employee deferrals		100.00%
Cost related to savings and stock investment plan		$ 3,201,000	$ 2,069,000	1,894,000
Employer contribution in shares of common stock		998,041	893,440
Dividends paid on United common stock		$ 1,218,000	$ 1,173,000	$ 1,139,000
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage allowed as of contribution to respective accounts by participants		1.00%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage allowed as of contribution to respective accounts by participants		100.00%
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Amount of United common stock held in the pension plan		$ 24,003,000	$ 20,629,000
Percentage of equity securities include united common stock		3.00%	4.00%
Common Stock [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry			5.00%
Marketable Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Amount of United common stock held in the pension plan		$ 3,677,000	$ 4,894,000
Percentage of equity securities include united common stock		71.00%	71.00%
Maximum percentage limit of common stock to invest in portfolio for any industry		68.00%
Approximate fair value of plan assets		$ 34,682,000	$ 41,322,000
Marketable Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry		50.00%
Marketable Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry		70.00%
Individual Company [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry		10.00%
Industry [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry		15.00%
Securities of U.S. Government or Agencies [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Maximum percentage limit of common stock to invest in portfolio for any industry		15.00%

Employee Benefit Plans - Net Pe

Employee Benefit Plans - Net Periodic Pension Cost (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,146	$ 2,374	$ 2,787
Interest cost	5,149	5,950	5,902
Expected return on plan assets	(8,538)	(8,089)	(9,290)
Recognized net actuarial loss	4,553	4,921	4,980
Amortization of prior service cost	0	0	1
Net periodic pension cost	$ 3,310	$ 5,156	$ 4,380
Weighted-Average Assumptions:
Discount rate	4.49%	4.75%	4.35%
Expected return on assets	7.00%	7.25%	7.50%
Rate of Compensation Increase	3.00%	3.00%	3.00%
Prior to Age 45 [Member]
Weighted-Average Assumptions:
Rate of Compensation Increase	3.50%	3.50%	3.50%

Employee Benefit Plans - Schedu

Employee Benefit Plans - Schedule of Amounts Related to Plan recognized as Component of Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan [Abstract]
Net actuarial loss	$ 6,784	$ 2,914	$ 2,402
Prior service cost	0	0	(1)
Actuarial loss	(4,553)	(4,921)	(4,980)
Total recognized in other comprehensive income	$ 2,231	$ (2,007)	$ (2,579)

Employee Benefit Plans - Reconc

Employee Benefit Plans - Reconciliation of the Beginning and Ending Balances of the Projected Benefit Obligation and the Fair Value of Plan Assets and the Accumulated Benefit Obligation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in Projected Benefit Obligation
Projected Benefit Obligation at the Beginning of the Year	$ 134,515	$ 125,403
Service cost	2,146	2,374	$ 2,787
Interest cost	5,149	5,950	5,902
Actuarial Loss (Gain)	15,367	5,114
Benefits Paid	(4,437)	(4,326)
Projected Benefit at the End of the Year	152,740	134,515	125,403
Accumulated Benefit Obligation at the End of the Year	139,025	121,548
Change in Plan Assets
Fair Value of Plan Assets at the Beginning of the Year	119,711	113,748
Actual Return on Plan Assets	17,121	10,289
Benefits Paid	(4,437)	(4,326)
Employer Contributions	10,000	0
Fair value of plan assets at end of year	142,395	119,711	$ 113,748
Net Amount Recognized
Funded Status	(10,346)	(14,804)
Unrecognized Transition Asset	0	0
Unrecognized Prior Service Cost	0	0
Unrecognized Net Loss	56,222	53,991
Net Amount Recognized	$ 45,876	$ 39,187
Weighted-Average Assumptions at the End of the Year
Discount Rate	3.83%	4.49%
Rate of Compensation Increase	3.00%	3.00%
Prior to Age 45 [Member]
Weighted-Average Assumptions at the End of the Year
Rate of Compensation Increase	3.50%	3.50%

Employee Benefit Plans - Asset

Employee Benefit Plans - Asset Allocation for the Defined Benefit Pension Plan as of the Measurement Date, by Asset Category (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets	100.00%	100.00%
Marketable Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	68.00%
Percentage of Plan Assets	71.00%	71.00%
Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	25.00%
Percentage of Plan Assets	26.00%	26.00%
Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	7.00%
Percentage of Plan Assets	3.00%	3.00%
Minimum [Member] | Marketable Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	50.00%
Minimum [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	20.00%
Minimum [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	3.00%
Maximum [Member] | Marketable Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	70.00%
Maximum [Member] | Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	50.00%
Maximum [Member] | Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	15.00%

Employee Benefit Plans - Expect

Employee Benefit Plans - Expected Benefit Payments (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Retirement Benefits [Abstract]
2,018	$ 5,314
2,019	5,304
2,020	5,632
2,021	6,012
2,022	6,377
2023 through 2027	$ 36,991

Employee Benefit Plans - Balanc

Employee Benefit Plans - Balances of the Plan Assets, by Fair Value Hierarchy Level (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	$ 142,395	$ 119,711	$ 113,748
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	4,549	1,778
Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		47
Collateralized Mortgage Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		48
Municipal Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		670
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		1,169
Foreign Bonds Notes and Debentures [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		96
Taxable Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	30,752	26,816
Fixed Income Funds Alternative [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	6,302	3,898
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	24,003	20,629
Equity Mutual Funds Domestic Equity Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	28,936	23,063
Equity Mutual Funds Domestic Equity Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	13,108	6,457
Equity Mutual Funds Domestic Equity Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	9,520	13,087
Equity Mutual Funds Domestic Equity Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	910
Equity Mutual Funds International Emerging Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	5,264	3,120
Equity Mutual Funds International Equity Developed [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	15,752	12,619
Equity Mutual Funds Alternative Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	4,209	3,456
Equity Mutual Funds Domestic Balanced Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		1,848
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	142,395	117,681
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	4,549	1,778
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Collateralized Mortgage Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign Bonds Notes and Debentures [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Taxable Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	30,752	26,816
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fixed Income Funds Alternative [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	6,302	3,898
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	24,003	20,629
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Domestic Equity Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	28,936	23,063
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Domestic Equity Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	13,108	6,457
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Domestic Equity Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	9,520	13,087
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Domestic Equity Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	910
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds International Emerging Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	5,264	3,120
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds International Equity Developed [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	15,752	12,619
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Alternative Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	4,209	3,456
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds Domestic Balanced Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		1,848
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	2,030
Significant Other Observable Inputs (Level 2) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		47
Significant Other Observable Inputs (Level 2) [Member] | Collateralized Mortgage Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		48
Significant Other Observable Inputs (Level 2) [Member] | Municipal Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		670
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		1,169
Significant Other Observable Inputs (Level 2) [Member] | Foreign Bonds Notes and Debentures [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		96
Significant Other Observable Inputs (Level 2) [Member] | Taxable Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Fixed Income Funds Alternative [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Domestic Equity Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Domestic Equity Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Domestic Equity Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Domestic Equity Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds International Emerging Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds International Equity Developed [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Alternative Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds Domestic Balanced Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member] | Collateralized Mortgage Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member] | Municipal Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member] | Foreign Bonds Notes and Debentures [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		0
Significant Unobservable Inputs (Level 3) [Member] | Taxable Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fixed Income Funds Alternative [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Domestic Equity Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Domestic Equity Mid Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Domestic Equity Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Domestic Equity Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds International Emerging Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds International Equity Developed [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Alternative Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value	$ 0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds Domestic Balanced Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Asset at fair value		$ 0

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Detail) - USD ($)	May 18, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized shares of stock, option plan, maximum	1,700,000
Aggregate number of shares issued in respect of restricted stock awards	500,000
Options available for award each plan year	1,200,000
Maximum number of shares of restricted stock or shares subject to a restricted stock units award granted		50,000
Maximum number of options and SARs		100,000
Maximum number of stock options and SARs awarded		10,000
Maximum number of Shares of restricted stock or shares subject to a restricted stock units award granted to individual non-employee director		5,000
Vesting period of awards		1/3 per year
Number of Options granted		255,217	967,285
Recognition of compensation expense		$ 3,555,000	$ 2,817,000	$ 2,484,000
Number of share available for grant for prior plans		0
Maximum term for awards granted (years)		10 years
Weighted average risk free interest rate		2.13%
Weighted average dividend yield		3.00%
Weighted average volatility factors of the expected market price of United's common stock		0.262%
Weighted-average expected option life		6 years 11 months 23 days
Estimated fair value of the options at the date of grant		$ 8.85
Total unrecognized compensation cost related to nonvested option awards		$ 2,597,000
Weighted-average expense recognition period		1 year 2 months 12 days
Total fair value of awards vested		$ 1,168,000
Cash received from options exercised under the plans		$ 4,619,000	$ 13,337,000	$ 7,871,000
Shares issued related stock option exercises		220,905	519,482	259,454
Weighted-average grant-date fair value of options granted		$ 8.85	$ 6.97	$ 7.23
Total intrinsic value of options exercised		$ 3,721,000	$ 11,001,000	$ 2,380,000
Excess tax benefits from stock-based compensation arrangements		$ 2,201,000	$ 4,008,000	$ 1,023,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted		90,075	289,637
Total unrecognized compensation cost related to nonvested option awards		$ 4,297,000
Weighted-average expense recognition period		1 year 3 months 19 days
Weighted-average grant-date fair value of options granted		$ 45.21
Vesting period		4 years

Stock Based Compensation - Summ

Stock Based Compensation - Summary of Stock Option Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Stock Options [Line Items]
Shares, Outstanding, Beginning balance	1,411,735
Shares, Granted	255,217	967,285
Shares, Exercised	(220,905)	(519,482)	(259,454)
Shares, Forfeited or expired	(41,211)
Shares, Outstanding, Ending balance	1,558,438	1,411,735
Shares, Exercisable at December 31, 2017	1,050,567
Aggregate Intrinsic Value, Outstanding at December 31, 2017	$ 8,761
Aggregate Intrinsic Value, Exercisable at December 31, 2017	$ 8,528
Weighted Average Remaining Contractual Term, Outstanding at December 31, 2017	5 years 9 months 18 days
Weighted Average Remaining Contractual Term, Exercisable at December 31, 2017	4 years 7 months 6 days
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 28.05
Weighted Average Exercise Price, Granted	45.20
Weighted Average Exercise Price, Exercised	22
Weighted Average Exercise Price, Forfeited or expired	27.38
Weighted Average Exercise Price, Outstanding, Ending balance	31.09	$ 28.05
Weighted Average Exercise Price, Exercisable	$ 26.86
Bank of Georgetown [Member]
Schedule Of Stock Options [Line Items]
Shares, Assumed in acquisition of subsidiary	153,602
Weighted Average Exercise Price, Exercisable	$ 21.47

Stock Based Compensation - Stat

Stock Based Compensation - Status of United's Nonvested Stock Option Awards (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares, Nonvested, Beginning balance	430,278
Shares, Granted	255,217	967,285
Shares, Vested	(174,624)
Shares, Forfeited or expired	(3,000)
Shares, Nonvested, Ending balance	507,871	430,278
Weighted-Average Grant Date Fair Value Per Share, Nonvested Beginning balance	$ 6.84
Weighted-Average Grant Date Fair Value Per Share, Granted	8.85
Weighted-Average Grant Date Fair Value Per Share, Vested	6.69
Weighted-Average Grant Date Fair Value Per Share, Forfeited or expired	8.85
Weighted-Average Grant Date Fair Value Per Share, Nonvested Ending balance	$ 7.89	$ 6.84

Stock Based Compensation - Chan

Stock Based Compensation - Changes to United's Restricted Common Shares (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value Per Share, Granted	$ 8.85	$ 6.97	$ 7.23
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning balance	137,268
Shares, Granted	90,075
Shares, Vested	56,007
Shares, Forfeited	840
Number of Shares, Outstanding, Ending balance	170,496	137,268
Weighted-Average Grant Date Fair Value Per Share, Outstanding, Beginning balance	$ 33.61
Weighted-Average Grant Date Fair Value Per Share, Granted	45.21
Weighted-Average Grant Date Fair Value Per Share, Vested	32.48
Weighted-Average Grant Date Fair Value Per Share, Forfeited	45.30
Weighted-Average Grant Date Fair Value Per Share, Outstanding, Ending balance	$ 40.05	$ 33.61

Commitments and Contingent L123

Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($)	Apr. 21, 2017	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Loan commitments outstanding		$ 4,224,719,000	$ 2,823,396,000
Loan commitments expiry period		1 year
George Mason [Member]
Loss Contingencies [Line Items]
Payments to investors to repurchase loans previously sold		$ 59,000
Reserve for possible losses due to the repurchase of loans previously sold to investors	$ 575,000	516,000
Expense related to the reserve for possible losses due to the repurchase of loans previously sold to investors		0
Commitments to Extend Credit [Member] | George Mason [Member] | Short-term Contract with Customer [Member]
Loss Contingencies [Line Items]
Additional commitments to extend credit		229,630,000
Commercial Letters of Credit [Member]
Loss Contingencies [Line Items]
Letters of credit issued		0	9,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Letters of credit issued		$ 147,017,000	$ 121,584,000

Derivative Financial Instrum124

Derivative Financial Instruments - Schedule of Notional Amount and Fair Value Derivative Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Asset derivatives, notional amount	$ 251,721	$ 89,366
Asset derivatives designated as hedging instruments	538	24
Liability derivatives, notional amount	255,295	34,382
Asset derivatives not designated as hedging instruments	4,561	2,267
Total asset derivatives	5,099	2,291
Liability derivatives designated as hedging instruments	165	338
Liability derivatives not designated as hedging instruments	312	2,267
Total liability derivatives	477	2,605
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives, notional amount	71,831	74,783
Liability derivatives, notional amount	18,795	19,799
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives, notional amount	179,890	14,583
Liability derivatives, notional amount	236,500	14,583
Other Assets [Member] | Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Asset derivatives not designated as hedging instruments	4,559	0
Other Assets [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Asset derivatives, notional amount	148,866	0
Other Liabilities [Member] | TBA Mortgage Backed Securities [Member]
Derivative [Line Items]
Liability derivatives not designated as hedging instruments	312	0
Other Liabilities [Member] | Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Liability derivatives not designated as hedging instruments	0	0
Other Liabilities [Member] | Not Designated as Hedging Instrument [Member] | TBA Mortgage Backed Securities [Member]
Derivative [Line Items]
Liability derivatives, notional amount	236,500	0
Other Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Liability derivatives, notional amount	0	0
Interest Rate Swap Contracts [Member] | Other Assets [Member]
Derivative [Line Items]
Asset derivatives not designated as hedging instruments	0	2,267
Interest Rate Swap Contracts [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives, notional amount	0	14,583
Interest Rate Swap Contracts [Member] | Other Assets [Member] | Fair Value Hedging [Member] | Hedged Commercial Loans [Member]
Derivative [Line Items]
Asset derivatives designated as hedging instruments	538	24
Interest Rate Swap Contracts [Member] | Other Assets [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Hedged Commercial Loans [Member]
Derivative [Line Items]
Asset derivatives, notional amount	71,831	74,783
Interest Rate Swap Contracts [Member] | Other Liabilities [Member]
Derivative [Line Items]
Liability derivatives not designated as hedging instruments	0	2,267
Interest Rate Swap Contracts [Member] | Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Liability derivatives, notional amount	0	14,583
Interest Rate Swap Contracts [Member] | Other Liabilities [Member] | Fair Value Hedging [Member] | Hedged Commercial Loans [Member]
Derivative [Line Items]
Liability derivatives designated as hedging instruments	165	338
Interest Rate Swap Contracts [Member] | Other Liabilities [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Hedged Commercial Loans [Member]
Derivative [Line Items]
Liability derivatives, notional amount	18,795	19,799
Forward Loan Sale Commitments [Member] | Other Assets [Member]
Derivative [Line Items]
Asset derivatives not designated as hedging instruments	2	0
Forward Loan Sale Commitments [Member] | Other Assets [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives, notional amount	$ 31,024	$ 0

Derivative Financial Instrum125

Derivative Financial Instruments - Schedule of Derivative Financial Instruments on Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivatives in hedging relationships	$ (7,390)	$ (30)	$ (813)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivatives in hedging relationships	(781)	(30)	(813)
Designated as Hedging Instrument [Member] | Interest Income/ (Expense) [Member] | Interest Rate Swap Contracts [Member] | Fair Value Hedging [Member]
Derivative [Line Items]
Derivatives in hedging relationships	(781)	(30)	(813)
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	(6,609)	0	0
Not Designated as Hedging Instrument [Member] | Income from Mortgage Banking Activities [Member] | TBA Mortgage Backed Securities [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	1,547	0	0
Not Designated as Hedging Instrument [Member] | Income from Mortgage Banking Activities [Member] | Interest Rate Lock Commitments [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	7,730	0	0
Not Designated as Hedging Instrument [Member] | Income from Mortgage Banking Activities [Member] | Forward Loan Sale Commitments [Member]
Derivative [Line Items]
Derivatives not designated as hedging instruments	$ 426	$ 0	$ 0

Comprehensive Income - Componen

Comprehensive Income - Components of Total Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	$ 150,581	$ 147,083	$ 137,959
AFS securities with OTTI charges during the period									(60)	(77)	(113)
Related income tax effect									22	28	41
Income tax rate change									0	208	316
Less : OTTI charges recognized in net income									60	33	47
Related income tax benefit									(22)	(12)	(17)
Reclassification of previous noncredit OTTI to credit OTTI									0	415	0
Related income tax benefit									0	(150)	0
Net unrealized gains on AFS securities with OTTI									0	445	274
Change in net unrealized (losses) gains on AFS securities arising during the period									8,371	(12,931)	(6,672)
Related income tax effect									(3,097)	4,867	2,415
Net reclassification adjustment for (gains) losses included in net income									(1,874)	(255)	(133)
Related income tax expense (benefit)									693	92	48
Total AFS securities - all other									4,093	(8,227)	(4,342)
Net effect of AFS securities on other comprehensive income									4,093	(7,782)	(4,068)
Accretion on the unrealized loss for securities transferred from AFS to the HTM investment portfolio prior to call or maturity									8	9	8
Related income tax expense									(3)	(3)	(3)
Net effect of HTM securities on other comprehensive income									5	6	5
Defined benefit pension plan:
Net actuarial loss during the period									(6,784)	(2,914)	(2,402)
Related income tax expense (benefit)									2,510	1,077	944
Amortization of prior service cost recognized in net income									0	0	1
Related income tax benefit									0	0	0
Amortization of net actuarial loss recognized in net income									4,553	4,921	4,980
Related income tax benefit									(1,685)	(1,813)	(1,908)
Net effect of change in defined benefit pension plan on other comprehensive income									(1,406)	1,271	1,615
Net current-period other comprehensive income, net of tax									2,692	(6,505)	(2,448)
Comprehensive income, net of tax									$ 153,273	$ 140,578	$ 135,511

Comprehensive Income - Compo127

Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 2,235,747	$ 1,712,635	$ 1,656,160
Net current-period other comprehensive income, net of tax	2,692	(6,505)	(2,448)
Ending Balance	3,240,530	2,235,747	1,712,635
Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(34,369)
Other comprehensive income before reclassification	0
Amounts reclassified from accumulated other comprehensive income	(1,406)
Net current-period other comprehensive income, net of tax	(1,406)
Ending Balance	(35,775)	(34,369)
Unrealized Gains/Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(10,297)
Other comprehensive income before reclassification	5,274
Amounts reclassified from accumulated other comprehensive income	(1,181)
Net current-period other comprehensive income, net of tax	4,093
Ending Balance	(6,204)	(10,297)
Accumulated Unrealized Loss On Securities Available For Sale Transferred To Held To Maturity [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(51)
Other comprehensive income before reclassification	5
Amounts reclassified from accumulated other comprehensive income	0
Net current-period other comprehensive income, net of tax	5
Ending Balance	(46)	(51)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(44,717)	(38,212)	(35,764)
Other comprehensive income before reclassification	5,279
Amounts reclassified from accumulated other comprehensive income	(2,587)
Net current-period other comprehensive income, net of tax	2,692	(6,505)	(2,448)
Ending Balance	$ (42,025)	$ (44,717)	$ (38,212)

Comprehensive Income - Reclassi

Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available for sale ("AFS") securities:
Net reclassification adjustment for losses (gains) included in net income									$ 5,644	$ 313	$ 202
Income before income taxes									284,827	222,658	203,489
Related income tax effect	$ (66,890)	$ (27,836)	$ (19,304)	$ (20,216)	$ (22,472)	$ (18,846)	$ (16,378)	$ (17,879)	(134,246)	(75,575)	(65,530)
Net income	17,975	56,738	37,059	38,809	39,106	41,479	31,792	34,706	150,581	147,083	137,959
Pension plan:
Net actuarial loss									(6,784)	(2,914)	(2,402)
Amortization of net actuarial loss									4,553	4,921	4,980
Income before income taxes									284,827	222,658	203,489
Related income tax effect	(66,890)	(27,836)	(19,304)	(20,216)	(22,472)	(18,846)	(16,378)	(17,879)	(134,246)	(75,575)	(65,530)
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	150,581	$ 147,083	$ 137,959
Reclassification out of Accumulated Other Comprehensive Income [Member]
Available for sale ("AFS") securities:
Net income									(2,587)
Pension plan:
Net income									(2,587)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains/Losses on AFS Securities [Member]
Available for sale ("AFS") securities:
Reclassification of previous noncredit OTTI to credit OTTI									0
Net reclassification adjustment for losses (gains) included in net income									(1,874)
Income before income taxes									(1,874)
Related income tax effect									693
Net income									(1,181)
Pension plan:
Income before income taxes									(1,874)
Related income tax effect									693
Net income									(1,181)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Available for sale ("AFS") securities:
Income before income taxes									(2,231)
Related income tax effect									825
Net income									(1,406)
Pension plan:
Net actuarial loss									(6,784)
Amortization of net actuarial loss									4,553
Income before income taxes									(2,231)
Related income tax effect									825
Net income									$ (1,406)

United Bankshares, Inc. (Par129

United Bankshares, Inc. (Parent Company Only) Financial Information - Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and due from banks	$ 196,742	$ 175,468
Securities available for sale	1,888,756	1,259,214
Securities held to maturity	20,018	31,178
Other investment securities	162,461	111,166
Goodwill	1,478,380	863,767
Other assets	484,309	414,840
TOTAL ASSETS	19,058,959	14,508,892
Accrued expenses and other liabilities	145,595	93,657
Shareholders' equity (including other accumulated comprehensive loss of $42,025 and $44,717 at December 31, 2017 and 2016, respectively)	3,240,530	2,235,747	$ 1,712,635	$ 1,656,160
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	19,058,959	14,508,892
United Bankshares [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and due from banks	93,198	130,304
Securities available for sale	22,066	4,881
Securities held to maturity	996	20
Other investment securities	163	100
Bank subsidiaries	3,437,036	2,372,783
Nonbank subsidiaries	12,535	10,535
Goodwill	(16,008)	(10,453)
Other assets	10,309	15,699
TOTAL ASSETS	3,560,295	2,523,869
Junior subordinated debentures of subsidiary trusts	242,446	224,319
Accrued expenses and other liabilities	77,319	63,803
Shareholders' equity (including other accumulated comprehensive loss of $42,025 and $44,717 at December 31, 2017 and 2016, respectively)	3,240,530	2,235,747
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 3,560,295	$ 2,523,869

United Bankshares, Inc. (Par130

United Bankshares, Inc. (Parent Company Only) Financial Information - Condensed Balance Sheets (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Accumulated other comprehensive loss	$ 42,025	$ 44,717
United Bankshares [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Accumulated other comprehensive loss	$ 42,025	$ 44,717

United Bankshares, Inc. (Par131

United Bankshares, Inc. (Parent Company Only) Financial Information - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Income Statements, Captions [Line Items]
Net interest income	$ 154,856	$ 150,276	$ 136,245	$ 107,620	$ 113,253	$ 111,069	$ 102,725	$ 98,284	$ 548,997	$ 425,331	$ 384,124
Income before income taxes									284,827	222,658	203,489
Applicable income tax benefit	66,890	27,836	19,304	20,216	22,472	18,846	16,378	17,879	134,246	75,575	65,530
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	150,581	147,083	137,959
United Bankshares [Member]
Condensed Income Statements, Captions [Line Items]
Bank subsidiaries									115,000	75,600	70,500
Nonbank subsidiaries									58	10	433
Net interest income									437	86	76
Bank subsidiaries									45,693	35,792	28,955
Nonbank subsidiaries									27	27	27
Other income									1,766	8	78
Total Income									162,981	111,523	100,069
Operating expenses									71,653	42,249	31,619
Income before income taxes									91,328	69,274	68,450
Applicable income tax benefit									(6,126)	(3,061)	(1,655)
Income Before Equity in Undistributed Net Income of Subsidiaries									97,454	72,335	70,105
Equity in undistributed net income of subsidiaries: Bank subsidiaries									50,560	74,656	68,012
Nonbank subsidiaries									2,567	92	(158)
Net income									$ 150,581	$ 147,083	$ 137,959

United Bankshares, Inc. (Par132

United Bankshares, Inc. (Parent Company Only) Financial Information - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	$ 150,581	$ 147,083	$ 137,959
Amortization of net periodic pension costs									3,310	5,156	4,380
Stock-based compensation									3,555	2,817	2,484
Excess tax benefits from stock-based compensation arrangements									2,201	4,008	1,023
Net gain on securities transactions	(430)	$ (467)	$ (747)	(3,940)	(62)	$ (1)	$ (213)	(4)	(5,584)	(280)	(155)
Net Cash Provided by Operating Activities									253,928	170,734	174,901
Net cash paid in acquisition of subsidiary									44,531	29,330	0
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES									266,678	30,960	(185,298)
Proceeds from issuance of common stock									0	199,916	0
Cash dividends paid									(121,354)	(96,351)	(88,864)
Acquisition of treasury stock									(1)	(1)	(1)
Proceeds from sale of treasury stock from deferred compensation plan									0	1	1
Proceeds from exercise of stock options									4,619	13,337	7,871
Net Cash Provided by (Used in) Financing Activities									(288,967)	375,498	114,668
Increase (Decrease) in Cash and Cash Equivalents									231,640	577,192	104,271
Cash and Cash Equivalents at Beginning of Year				1,434,527				857,335	1,434,527	857,335	753,064
CASH AND CASH EQUIVALENTS AT END OF YEAR	1,666,167				1,434,527				1,666,167	1,434,527	857,335
United Bankshares [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net income									150,581	147,083	137,959
Equity in undistributed net income of subsidiaries									(53,127)	(74,748)	(67,854)
Amortization of net periodic pension costs									228	393	384
Stock-based compensation									3,555	2,817	2,484
Excess tax benefits from stock-based compensation arrangements									2,201	4,008	1,023
Net gain on securities transactions									(1,185)	(8)	(54)
Net change in other assets and liabilities									8,764	(8,344)	7,420
Net Cash Provided by Operating Activities									111,017	71,201	81,362
Net purchases of securities									(19,268)	(234)	(1,047)
Net cash paid in acquisition of subsidiary									22,146	(10)	0
Increase in investment in subsidiaries									(34,203)	(100,000)	0
Change in other investment securities									(63)	0	2
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES									(31,388)	(100,244)	(1,045)
Proceeds from issuance of common stock									0	199,916	0
Cash dividends paid									(121,354)	(96,351)	(88,864)
Acquisition of treasury stock									(1)	(1)	(1)
Proceeds from sale of treasury stock from deferred compensation plan									1	1	1
Proceeds from exercise of stock options									4,619	13,337	7,871
Net Cash Provided by (Used in) Financing Activities									(116,735)	116,902	(80,993)
Increase (Decrease) in Cash and Cash Equivalents									(37,106)	87,859	(676)
Cash and Cash Equivalents at Beginning of Year				$ 130,304				$ 42,445	130,304	42,445	43,121
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 93,198				$ 130,304				$ 93,198	$ 130,304	$ 42,445

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Regulatory Matters [Line Items]
Average reserve balances to be maintained by subsidiary banks	$ 1,251,806,000	$ 606,898,000
Average reserve balances required by subsidiary banks	471,763,000	$ 361,521,000
Retained net profits available for distribution to United Bankshares, Inc. by its banking subsidiaries as dividends	$ 127,674,000
Maximum loan to parent company by subsidiaries as percentage it's of capital and surplus	10.00%
Maximum amount of loan to parent company by subsidiaries	$ 282,863,000
Minimum net worth requirement	2,500,000
George Mason [Member]
Regulatory Matters [Line Items]
Net worth	$ 4,955,000

Regulatory Matters - Capital Am

Regulatory Matters - Capital Amounts and Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
United Bankshares [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 2,093,369	$ 1,699,984
Tier 1 Capital to Risk-Weighted Assets, Actual Amount	1,759,189	1,625,543
Common Tier I Capital to Risk Weighted Assets, Actual Amount	1,759,189	1,393,743
Tier 1 Capital to Average Assets, Amount	$ 1,759,189	$ 1,625,543
Total Capital to Risk-Weighted Assets, Actual Ratio	14.20%	14.90%
Tier 1 Capital to Risk-Weighted Assets, Actual Ratio	12.00%	14.20%
Common Tier I Capital to Risk Weighted Assets,	12.00%	12.20%
Tier 1 Capital to Average Assets, Actual Ratio	10.10%	12.20%
Total Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Amount	$ 1,177,952	$ 915,479
Tier 1 Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Amount	883,464	686,609
Common Tier I Capital to Risk Weighted Assets,	662,598	514,957
Tier 1 Capital to Average Assets, For Capital Adequacy Purposes, Amount	$ 698,388	$ 535,227
Total Capital to Risk-Weighted Assets, For Capital Adequacy, Ratio	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Common Tier I Capital to Risk Weighted Assets,	4.50%	4.50%
Tier 1 Capital to Average Assets, For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Total Capital to Risk-Weighted Assets, To Be Well Capitalized, Amount	$ 1,472,439	$ 1,144,348
Tier 1 Capital to Risk-Weighted Assets, To Be Well Capitalized, Amount	1,177,952	915,479
Common Tier I Capital to Risk Weighted Assets,	957,086	743,826
Tier 1 Capital to Average Assets, To Be Well Capitalized, Amount	$ 872,985	$ 669,033
Total Capital to Risk-Weighted Assets, To Be Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets, To Be Well Capitalized, Ratio	8.00%	8.00%
Common Tier I Capital to Risk Weighted Assets,	6.50%	6.50%
Tier 1 Capital to Average Assets To Be Well Capitalized, Ratio	5.00%	5.00%
United Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Risk-Weighted Assets, Actual Amount	$ 2,013,852	$ 1,592,647
Tier 1 Capital to Risk-Weighted Assets, Actual Amount	1,936,546	1,518,831
Common Tier I Capital to Risk Weighted Assets, Actual Amount	1,936,546	1,518,831
Tier 1 Capital to Average Assets, Amount	$ 1,936,546	$ 1,518,831
Total Capital to Risk-Weighted Assets, Actual Ratio	13.70%	13.90%
Tier 1 Capital to Risk-Weighted Assets, Actual Ratio	13.20%	13.30%
Common Tier I Capital to Risk Weighted Assets,	13.20%	13.30%
Tier 1 Capital to Average Assets, Actual Ratio	11.00%	11.40%
Total Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Amount	$ 1,174,099	$ 915,956
Tier 1 Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Amount	880,575	686,967
Common Tier I Capital to Risk Weighted Assets,	660,431	515,225
Tier 1 Capital to Average Assets, For Capital Adequacy Purposes, Amount	$ 702,311	$ 535,361
Total Capital to Risk-Weighted Assets, For Capital Adequacy, Ratio	8.00%	8.00%
Tier 1 Capital to Risk-Weighted Assets, For Capital Adequacy Purposes, Ratio	6.00%	6.00%
Common Tier I Capital to Risk Weighted Assets,	4.50%	4.50%
Tier 1 Capital to Average Assets, For Capital Adequacy Purposes, Ratio	4.00%	4.00%
Total Capital to Risk-Weighted Assets, To Be Well Capitalized, Amount	$ 1,467,624	$ 1,144,945
Tier 1 Capital to Risk-Weighted Assets, To Be Well Capitalized, Amount	1,174,099	915,956
Common Tier I Capital to Risk Weighted Assets,	953,956	744,214
Tier 1 Capital to Average Assets, To Be Well Capitalized, Amount	$ 877,888	$ 669,201
Total Capital to Risk-Weighted Assets, To Be Well Capitalized, Ratio	10.00%	10.00%
Tier 1 Capital to Risk-Weighted Assets, To Be Well Capitalized, Ratio	8.00%	8.00%
Common Tier I Capital to Risk Weighted Assets,	6.50%	6.50%
Tier 1 Capital to Average Assets To Be Well Capitalized, Ratio	5.00%	5.00%

Fair Values of Financial Ins135

Fair Values of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount rates utilized, minimum	2.25%
Discount rates utilized, maximum	5.75%
Amount of decrease in fair value of securities	$ 6,177
Transfers from Level 1 to Level 3 for financial assets	0	$ 0
Transfers from Level 3 to Level 1 for financial assets	0	0
Transfers from Level 2 to Level 3 for financial assets	0	0
Transfers from Level 3 to Level 2 for financial assets	0	0
Transfers from Level 1 to Level 3 for financial liabilities	0	0
Transfers from Level 3 to Level 1 for financial liabilities	0	0
Transfers from Level 2 to Level 3 for financial liabilities	0	0
Transfers from Level 3 to Level 2 for financial liabilities	0	0
Nonrecurring fair value adjustments on loans held for sale	0
Fair value measurement of intangible assets	$ 0	$ 0
Loans Held For Sale [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.27%
Loans Held For Sale [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.40%
Loans Held For Sale [Member] | Weighted Average [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.37%
Derivatives [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.27%
Derivatives [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.40%
Derivatives [Member] | Weighted Average [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Sales price of loans held for sale increase percentage	0.37%
Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Decrease in fair value of securities	18.00%
Increase in discount rates, basis point	2.00%

Fair Values of Financial Ins136

Fair Values of Financial Instruments - Schedule of Financial Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	$ 9,878
Total available for sale securities	1,888,756	$ 1,259,214
Loans held for sale	265,955	8,445
Derivative financial assets	5,099	2,291
Derivative financial liabilities	477	2,605
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	1,878,878	1,245,386
Available for sale equity securities	9,878	13,828
Total available for sale securities	1,888,756	1,259,214
Loans held for sale	263,308
Derivative financial assets	5,099
Derivative financial liabilities	477
Fair Value, Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	4,561
Fair Value, Measurements, Recurring [Member] | TBA Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial liabilities	312
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	114,758	95,786
U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	114,758	95,786
State and Political Subdivisions [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	303,869	192,812
State and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	303,869	192,812
Residential Mortgage-Backed Securities, Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	814,593	584,096
Residential Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	814,593	584,096
Residential Mortgage-Backed Securities, Non-agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	5,512	7,043
Residential Mortgage-Backed Securities, Non-agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	5,512	7,043
Asset-Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	109,970	217
Asset-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	109,970	217
Commercial Mortgage-Backed Securities, Agency [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	454,857	305,341
Commercial Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	454,857	305,341
Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	34,269	33,552
Trust Preferred Collateralized Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	34,269	33,552
Single Issue Trust Preferred Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	12,560	11,477
Single Issue Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	12,560	11,477
Corporate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	28,490	15,062
Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	28,490	15,062
Financial Services Industry [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	3,545	10,735
Other Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	1	1,273
Interest Rate Swap Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	538	2,291
Derivative financial liabilities	165	2,605
Equity Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	6,332	1,820
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	6,664	4,465
Loans held for sale	0	0
Derivative financial assets	0	0
Derivative financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Available for sale equity securities	6,664	4,465
Total available for sale securities	6,664	4,465
Loans held for sale	0
Derivative financial assets	0
Derivative financial liabilities	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member] | TBA Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial liabilities	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | State and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Residential Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Residential Mortgage-Backed Securities, Non-agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Asset-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Trust Preferred Collateralized Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Single Issue Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Financial Services Industry [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	331	1,372
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	1	1,273
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Interest Rate Swap Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	0	0
Derivative financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	6,332	1,820
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	1,847,823	1,221,197
Loans held for sale	2,647	8,445
Derivative financial assets	540	2,291
Derivative financial liabilities	477	2,605
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	1,844,609	1,211,834
Available for sale equity securities	3,214	9,363
Total available for sale securities	1,847,823	1,221,197
Loans held for sale	0
Derivative financial assets	540
Derivative financial liabilities	477
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	2
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | TBA Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial liabilities	312
Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	114,758	95,786
Significant Other Observable Inputs (Level 2) [Member] | State and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	303,869	192,812
Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	814,593	584,096
Significant Other Observable Inputs (Level 2) [Member] | Residential Mortgage-Backed Securities, Non-agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	5,512	7,043
Significant Other Observable Inputs (Level 2) [Member] | Asset-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	109,970	217
Significant Other Observable Inputs (Level 2) [Member] | Commercial Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	454,857	305,341
Significant Other Observable Inputs (Level 2) [Member] | Trust Preferred Collateralized Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Single Issue Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	12,560	11,477
Significant Other Observable Inputs (Level 2) [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	28,490	15,062
Significant Other Observable Inputs (Level 2) [Member] | Financial Services Industry [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	3,214	9,363
Significant Other Observable Inputs (Level 2) [Member] | Other Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	0	0
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Swap Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	538	2,291
Derivative financial liabilities	165	2,605
Significant Other Observable Inputs (Level 2) [Member] | Equity Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	0	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total available for sale securities	34,269	33,552
Loans held for sale	263,308	0
Derivative financial assets	4,559	0
Derivative financial liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	34,269	33,552
Available for sale equity securities	0	0
Total available for sale securities	34,269	33,552
Loans held for sale	263,308
Derivative financial assets	4,559
Derivative financial liabilities	0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	4,559
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | TBA Mortgage Backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial liabilities	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury Securities and Obligations of U.S. Government Corporations and Agencies [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | State and Political Subdivisions [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage-Backed Securities, Non-agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Asset-Backed Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Commercial Mortgage-Backed Securities, Agency [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Trust Preferred Collateralized Debt Obligations [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	34,269	33,552
Significant Unobservable Inputs (Level 3) [Member] | Single Issue Trust Preferred Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale debt securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Financial Services Industry [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Other Equity Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Swap Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative financial assets	0	0
Derivative financial liabilities	0	0
Significant Unobservable Inputs (Level 3) [Member] | Equity Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available for sale equity securities	$ 0	$ 0

Fair Values of Financial Ins137

Fair Values of Financial Instruments - Schedule of Additional Information about Financial Assets and Liabilities Measured at Fair Value Utilized Level 3 (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Trust Preferred Collateralized Debt Obligations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	$ 33,552	$ 34,686
Included in earnings (or changes in net assets)	9	0
Included in other comprehensive income	8,757	(1,134)
Purchases, issuances, and settlements	0	0
Sales	(8,049)	0
Transfers in and/or out of Level 3	0	0
Balance, end of period	34,269	33,552
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Loans Held For Sale [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	0	0
Included in earnings (or changes in net assets)	(58,132)	0
Acquired in Cardinal merger	271,301	0
Originations	2,333,927	0
Sales	(2,408,945)	0
Transfers in and/or out of Level 3	8,893	0
Balance, end of period	263,308	0
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	0	0
Interest Rate Lock Commitments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Balance, beginning of period	0	0
Acquired in Cardinal merger	10,393	0
Transfers in and/or out of Level 3	(5,834)	0
Balance, end of period	4,559	0
The amount of total gains or losses for the period included in earnings (or changes in net assets) attributable to the change in unrealized gains or losses relating to assets still held at reporting date	$ 0	$ 0

Fair Values of Financial Ins138

Fair Values of Financial Instruments - Schedule of Changes in Fair Value Included in Earnings of Financial Instruments for which Fair Value Option has been Elected (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Mortgage Banking [Member]
Fair Value, Option, Qualitative Disclosures Related to Election [Line Items]
Income from mortgage banking activities	$ (10,497)	$ 0

Fair Values of Financial Ins139

Fair Values of Financial Instruments - Summary of Difference Between Aggregate Fair Value and Remaining Contractual Principal Outstanding for Financial Instruments for which Fair Value Option has been Elected (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Loans held for sale, unpaid principal balance	$ 257,674	$ 0
Loans held for sale, fair value	263,308	0
Loans held for sale, fair value over/(under) unpaid principal balance	$ 5,634	$ 0

Fair Values of Financial Ins140

Fair Values of Financial Instruments - Summary of Financial Assets Measured at Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	$ 14	$ 4
YTD Losses, Impaired Loans	12,291	5,119
YTD Losses, OREO	4,200	2,086
Loans held for sale	263,308	0
Impaired Loans	84,756	80,505
OREO	24,348	31,510
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	0	0
Impaired Loans	0	0
OREO	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	2,647	8,445
Impaired Loans	67,111	27,609
OREO	24,151	31,510
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	0	0
Impaired Loans	17,645	52,896
OREO	$ 197	$ 0

Fair Values of Financial Ins141

Fair Values of Financial Instruments - Summary of Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 1,666,167	$ 1,434,527	$ 857,335	$ 753,064
Securities available for sale	1,888,756	1,259,214
Securities held to maturity	20,428	33,258
Other securities	162,461	111,166
Loans held for sale	265,955	8,445
Loans	13,011,421	10,341,137
Derivative financial assets	5,099	2,291
Deposits	13,830,591	10,796,867
Derivative financial liabilities	477	2,605
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,666,167	1,434,527
Securities available for sale	1,888,756	1,259,214
Securities held to maturity	20,428	33,258
Other securities	162,461	111,166
Loans held for sale	265,955	8,445
Loans	12,934,794	10,268,366
Derivative financial assets	5,099	2,291
Deposits	13,830,591	10,796,867
Short-term borrowings	477,587	209,551
Long-term borrowings	1,363,977	1,172,026
Derivative financial liabilities	477	2,605
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,666,167	1,434,527
Securities available for sale	1,888,756	1,259,214
Securities held to maturity	20,018	31,178
Other securities	154,338	105,608
Loans held for sale	265,955	8,445
Loans	12,437,797	10,122,486
Derivative financial assets	5,099	2,291
Deposits	14,024,720	10,785,294
Short-term borrowings	477,587	209,551
Long-term borrowings	1,338,754	1,142,782
Derivative financial liabilities	477	2,605
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Securities available for sale	6,664	4,465
Securities held to maturity	0	0
Other securities	0	0
Loans held for sale	0	0
Loans	0	0
Derivative financial assets	0	0
Deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Derivative financial liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,666,167	1,434,527
Securities available for sale	1,847,823	1,221,197
Securities held to maturity	16,998	28,158
Other securities	0	0
Loans held for sale	2,647	8,445
Loans	0	0
Derivative financial assets	540	2,291
Deposits	14,024,720	10,785,294
Short-term borrowings	477,587	209,551
Long-term borrowings	1,338,754	1,142,782
Derivative financial liabilities	477	2,605
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Securities available for sale	34,269	33,552
Securities held to maturity	3,020	3,020
Other securities	154,338	105,608
Loans held for sale	263,308	0
Loans	12,437,797	10,122,486
Derivative financial assets	4,559	0
Deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Derivative financial liabilities	$ 0	$ 0

Variable Interest Entities - Ad

Variable Interest Entities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Trust
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of statutory business trusts	15
Percentage of equity shares of each trust owned by the company	100.00%

Variable Interest Entities - Su

Variable Interest Entities - Summary of Quantitative Information Related to Significant Involvement in Unconsolidated Variable Interest Entities (Detail) - Trust Preferred Securities [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Aggregate Assets	$ 266,669	$ 240,668
Aggregate Liabilities	257,674	232,583
Risk Of Loss	$ 8,995	$ 8,085

Segment Information - Additiona

Segment Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017Segment
Segment Reporting [Abstract]
Number of reportable segments	1
Number of business segment	2

Segment Information - Summary o

Segment Information - Summary of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 154,856	$ 150,276	$ 136,245	$ 107,620	$ 113,253	$ 111,069	$ 102,725	$ 98,284	$ 548,997	$ 425,331	$ 384,124
Provision for loans losses	6,977	7,279	8,251	5,899	5,819	6,988	7,667	4,035	28,406	24,509	22,574
Other income	17,024	17,377	17,222	15,531	15,639	18,038	16,965	15,660	131,645	70,032	73,626
Other expense	95,778	96,652	112,137	62,842	62,508	62,777	64,855	58,056	367,409	248,196	231,687
Income taxes	66,890	27,836	19,304	20,216	22,472	18,846	16,378	17,879	134,246	75,575	65,530
Net income	17,975	$ 56,738	$ 37,059	$ 38,809	39,106	$ 41,479	$ 31,792	$ 34,706	150,581	147,083	137,959
Total assets (liabilities)	19,058,959				14,508,892				19,058,959	14,508,892	12,577,944
Average assets (liabilities)									17,617,429	13,376,803	12,265,115
Operating Segments [Member] | Community Banking [Member]
Segment Reporting Information [Line Items]
Net interest income									558,622	433,140	390,775
Provision for loans losses									28,406	24,509	22,574
Other income									69,615	72,618	75,656
Other expense									291,584	249,894	235,644
Income taxes									139,980	78,640	67,109
Net income									168,267	152,715	141,104
Total assets (liabilities)	18,761,508				14,528,394				18,761,508	14,528,394	12,592,321
Average assets (liabilities)									17,385,448	13,398,861	12,277,023
Operating Segments [Member] | Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net interest income									(69)
Provision for loans losses									0
Other income									58,532
Other expense									62,072
Income taxes									(901)
Net income									(2,708)
Total assets (liabilities)	280,293								280,293
Average assets (liabilities)									212,212
Other [Member]
Segment Reporting Information [Line Items]
Net interest income									(9,556)	(7,809)	(6,651)
Provision for loans losses									0	0	0
Other income									3,498	(2,586)	(2,030)
Other expense									13,753	(1,698)	(3,957)
Income taxes									(4,833)	(3,065)	(1,579)
Net income									(14,978)	(5,632)	(3,145)
Total assets (liabilities)	$ 17,158				$ (19,502)				17,158	(19,502)	(14,377)
Average assets (liabilities)									$ 19,769	$ (22,058)	$ (11,908)

Quarterly Financial Data - Quar

Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 176,518	$ 171,583	$ 154,947	$ 120,758	$ 125,621	$ 123,137	$ 113,087	$ 108,496	$ 623,806	$ 470,341	$ 423,630
Interest expense	21,662	21,307	18,702	13,138	12,368	12,068	10,362	10,212	74,809	45,010	39,506
Net interest income	154,856	150,276	136,245	107,620	113,253	111,069	102,725	98,284	548,997	425,331	384,124
Provision for credit losses	6,977	7,279	8,251	5,899	5,819	6,988	7,667	4,035	28,406	24,509	22,574
Mortgage banking income	15,310	20,385	22,537	675	951	982	789	728
Securities gains (losses), net	430	467	747	3,940	62	1	213	4	5,584	280	155
Other noninterest income	17,024	17,377	17,222	15,531	15,639	18,038	16,965	15,660	131,645	70,032	73,626
Noninterest expense	95,778	96,652	112,137	62,842	62,508	62,777	64,855	58,056	367,409	248,196	231,687
Income taxes	66,890	27,836	19,304	20,216	22,472	18,846	16,378	17,879	134,246	75,575	65,530
Net income	$ 17,975	$ 56,738	$ 37,059	$ 38,809	$ 39,106	$ 41,479	$ 31,792	$ 34,706	$ 150,581	$ 147,083	$ 137,959
Average shares outstanding (000s):
Basic	104,808,000	104,760,000	99,198,000	80,902,000	76,864,000	76,219,000	71,484,000	69,497,000	97,502,633	73,531,992	69,334,849
Diluted	105,125,000	105,068,000	99,620,000	81,307,000	77,303,000	76,648,000	71,809,000	69,714,000	97,890,078	73,893,127	69,625,531
Net income per share:
Basic	$ 0.17	$ 0.54	$ 0.37	$ 0.48	$ 0.51	$ 0.54	$ 0.44	$ 0.50	$ 1.54	$ 2	$ 1.99
Diluted	0.17	0.54	0.37	0.48	0.51	0.54	0.44	0.50	1.54	1.99	1.98
Dividends per share	$ 0.34	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 1.33	$ 1.32	$ 1.29