MarketAxess (MKTX) 10-K 20 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2018	Feb. 15, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	MKTX
Entity Registrant Name	MARKETAXESS HOLDINGS INC
Entity Central Index Key	1,278,021
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		40,585,293
Entity Public Float			$ 7.2

Consolidated Statements of Fina

Consolidated Statements of Financial Condition - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 246,322	$ 167,014
Investments, at fair value	240,105	239,521
Accounts receivable, net of allowance of $80 and $178 as of December 31, 2018 and 2017, respectively	57,535	52,636
Goodwill and intangible assets, net of accumulated amortization	62,675	63,059
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	63,010	38,548
Prepaid expenses and other assets	22,468	18,717
Deferred tax assets, net	3,424	1,737
Total assets	695,539	581,232
Liabilities
Accrued employee compensation	39,053	36,502
Income and other tax liabilities	16,432	13,061
Deferred revenue	2,810	2,660
Accounts payable, accrued expenses and other liabilities	29,366	14,241
Total liabilities	87,661	66,464
Commitments and Contingencies (Note 12)
Stockholders' equity
Additional paid-in capital	341,860	331,081
Treasury stock - Common stock voting, at cost, 2,900,432 and 2,781,323 shares as of December 31, 2018 and 2017, respectively	(184,962)	(159,791)
Retained earnings	463,252	353,583
Accumulated other comprehensive loss	(12,394)	(10,226)
Total stockholders' equity	607,878	514,768
Total liabilities and stockholders' equity	695,539	581,232
Undefined Preferred Stock [Member]
Stockholders' equity
Preferred stock
Series A Preferred Stock [Member]
Stockholders' equity
Preferred stock
Voting Common Stock [Member]
Stockholders' equity
Common stock	$ 122	$ 121

Consolidated Statements of Fi_2

Consolidated Statements of Financial Condition (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Allowance for accounts receivable	$ 80	$ 178
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	4,855,000	4,855,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.003	$ 0.003
Common stock, shares authorized	110,000,000	110,000,000
Common stock, shares issued	40,540,349	40,402,059
Common stock, shares outstanding	37,639,917	37,620,736
Treasury stock, shares	2,900,432	2,781,323
Series A Preferred Stock [Member]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	110,000	110,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common Stock Non-Voting [Member]
Common stock, par value	$ 0.003	$ 0.003
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Revenues	$ 435,565	$ 393,422	$ 367,730
Expenses
Employee compensation and benefits	109,117	102,313	96,625
Depreciation and amortization	23,080	19,274	17,838
Technology and communications	23,866	20,048	17,275
Professional and consulting fees	21,521	19,367	17,175
Occupancy	14,176	6,125	4,681
Marketing and advertising	12,114	9,762	8,934
Clearing costs	7,754	5,797	6,060
General and administrative	11,353	11,121	9,157
Total expenses	222,981	193,807	177,745
Operating income	212,584	199,615	189,985
Other income (expense)
Investment income	6,112	3,619	2,137
Other, net	(610)	(1,466)	(520)
Total other income	5,502	2,153	1,617
Income before income taxes	218,086	201,768	191,602
Provision for income taxes	45,234	53,679	65,430
Net income	$ 172,852	$ 148,089	$ 126,172
Net income per common share
Basic	$ 4.68	$ 4.02	$ 3.42
Diluted	4.57	3.89	3.34
Cash dividends declared per common share	$ 1.68	$ 1.32	$ 1.04
Weighted average shares outstanding
Basic	36,958	36,864	36,844
Diluted	37,855	38,038	37,738
Commissions [Member]
Revenues
Revenues	$ 390,834	$ 355,282	$ 332,307
Information Services [Member]
Revenues
Revenues	28,227	25,806	23,269
Post-trade Services [Member]
Revenues
Revenues	15,346	11,090	10,812
Other [Member]
Revenues
Revenues	$ 1,158	$ 1,244	$ 1,342

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 172,852	$ 148,089	$ 126,172
Net cumulative translation adjustment and foreign currency exchange hedge, net of tax of $1,290, $(2,807) and $5,407, respectively	(2,078)	2,236	(7,037)
Net unrealized (loss) gain on securities available-for-sale, net of tax of $(23), $(39), and $24, respectively	(90)	(234)	38
Comprehensive income	$ 170,684	$ 150,091	$ 119,173

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Foreign currency exchange hedge, tax expense (benefit)	$ 1,290	$ (2,807)	$ 5,407
Securities available-for-sale, tax expense (benefit)	$ (23)	$ (39)	$ 24

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock Voting [Member]	Additional Paid-In Capital [Member]	Treasury Stock - Common Stock Voting [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2015	$ 390,713	$ 121	$ 321,215	$ (93,405)	$ 168,011	$ (5,229)
Net income	126,172				126,172
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(7,037)					(7,037)
Unrealized net gain (loss) on securities available-for-sale, net of tax	38					38
Stock-based compensation	14,511		14,511
Exercise of stock options	2,299		2,299
Withholding tax payments on restricted stock vesting and stock option exercises	(5,173)	(1)	(5,172)
Excess tax benefits from stock-based compensation	9,458		9,458
Repurchases of common stock	(23,925)			(23,925)
Cash dividend on common stock	(39,043)				(39,043)
Ending Balance at Dec. 31, 2016	468,013	120	342,311	(117,330)	255,140	(12,228)
Net income	148,089				148,089
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	2,236					2,236
Unrealized net gain (loss) on securities available-for-sale, net of tax	(234)					(234)
Stock-based compensation	14,421		14,421
Exercise of stock options	1,972	1	1,971
Withholding tax payments on restricted stock vesting and stock option exercises	(27,691)		(27,691)
Repurchases of common stock	(42,461)			(42,461)
Cumulative effect of change in accounting for employee share-based payments	17		69		(52)
Cash dividend on common stock	(49,594)				(49,594)
Ending Balance at Dec. 31, 2017	514,768	121	331,081	(159,791)	353,583	(10,226)
Net income	172,852				172,852
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(2,078)					(2,078)
Unrealized net gain (loss) on securities available-for-sale, net of tax	(90)					(90)
Stock-based compensation	15,850		15,850
Exercise of stock options	2,973	1	2,972
Withholding tax payments on restricted stock vesting and stock option exercises	(8,043)		(8,043)
Repurchases of common stock	(25,171)			(25,171)
Cash dividend on common stock	(63,183)				(63,183)
Ending Balance at Dec. 31, 2018	$ 607,878	$ 122	$ 341,860	$ (184,962)	$ 463,252	$ (12,394)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income	$ 172,852	$ 148,089	$ 126,172
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	23,080	19,274	17,838
Stock-based compensation expense	15,850	14,421	14,511
Deferred taxes	(1,258)	6,590	(2,581)
Other	2,338	1,953	10,628
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(5,117)	(2,353)	(10,429)
(Increase) in prepaid expenses and other assets	(3,791)	(7,039)	(2,125)
Decrease (Increase) in trading securities	856	(17,081)	(74,195)
Increase in accrued employee compensation	2,551	1,719	5,487
Increase in income and other tax liabilities	2,965	5,770	3,221
Increase in deferred revenue	150	145	203
Increase (decrease) in accounts payable, accrued expenses and other liabilities	14,374	(1,614)	2,344
Net cash provided by operating activities	223,917	168,035	89,747
Cash flows from investing activities
Proceeds from maturities and sales, available-for-sale investments	333,791	187,794	46,347
Purchases, available-for-sale investments	(336,533)	(215,831)	(81,438)
Purchases of furniture, equipment and leasehold improvements	(35,888)	(12,086)	(6,385)
Capitalization of software development costs	(11,705)	(13,471)	(12,118)
Other	39	(59)	414
Net cash (used in) investing activities	(50,296)	(53,653)	(53,180)
Cash flows from financing activities
Cash dividend on common stock	(62,432)	(48,888)	(38,495)
Exercise of stock options	2,973	1,972	2,299
Withholding tax payments on restricted stock vesting and stock option exercises	(8,043)	(27,691)	(5,173)
Repurchases of common stock	(25,171)	(42,461)	(23,925)
Net cash (used in) financing activities	(92,673)	(117,068)	(65,294)
Effect of exchange rate changes on cash and cash equivalents	(1,640)	1,457	(2,758)
Cash and cash equivalents including restricted cash
Net increase (decrease) for the period	79,308	(1,229)	(31,485)
Beginning of period	168,150	169,379	200,864
End of period	247,458	168,150	169,379
Supplemental cash flow information:
Cash paid during the year for income taxes	47,208	43,997	58,268
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
Decrease (Increase) in trading securities	$ (933)	$ (1,839)	$ (1,327)

Organization and Principal Busi

Organization and Principal Business Activity	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Organization and Principal Business Activity	1. Organization and Principal Business Activity MarketAxess Holdings Inc. (the “Company” or “MarketAxess”) was incorporated in the State of Delaware on April 11, 2000. Through its subsidiaries, MarketAxess operates a leading electronic trading platform that enables fixed-income market participants to efficiently trade corporate bonds and other types of fixed-income instruments using MarketAxess’ patented trading technology. Over 1,500 institutional investor and broker-dealer firms are active users of the MarketAxess trading platform, accessing global liquidity in U.S. high-grade corporate bonds, emerging markets and high-yield bonds, European bonds, U.S. agency bonds, municipal bonds, credit default swaps and other fixed-income securities. Through its Open Trading TM ®

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of Presentation The consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany transactions and balances have been eliminated. Accounting Pronouncements, Recently Adopted In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09”) requiring an entity to recognize revenue for the transfer of goods or services equal to the amount that it expects to be entitled to receive for those goods or services. The standard also requires new disclosure concerning contracts with customers, including the significant judgments made when applying the guidance. The Company adopted ASU 2014-09 effective January 1, 2018 using the modified retrospective transition approach. The adoption of this guidance did not have a material impact on the Company’s Consolidated Financial Statements. Effective January 1, 2017, the Company adopted ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects related to the accounting for share-based payment transactions, including the accounting for income taxes, statutory tax withholding requirements and classification on the statement of cash flows. Beginning January 1, 2017, the tax effects related to share-based payments were recorded through the income tax provision and the Company has elected to account for forfeitures as they occur. The adoption of ASU 2016-09 will cause volatility in the Company’s net income, effective tax rate and diluted earnings per share. The volatility in future periods will depend on the Company’s stock price at the vesting date for restricted stock awards or exercise date for stock options and the number of awards that vest or are exercised in each period. Under the guidance, excess tax benefits from share-based compensation are included as an operating activity in the Company’s Consolidated Statements of Cash Flows. Prior period cash flows have been adjusted to conform to the new presentation. Accounting Pronouncements, Not Yet Adopted as of December 31, 2018 In February 2016, the FASB issued ASU 2016-02, “Leases” (“ASU 2016-02”) requiring lessees to recognize lease assets and lease liabilities on the balance sheet for those leases previously classified as operating leases with lease terms greater than 12 months. ASU 2016-02 was effective for the Company beginning January 1, 2019. The Company expects to record new right-of-use assets of approximately $80.0 million, eliminate deferred rent of approximately $11.0 million and record lease liabilities associated with the future minimum payments required under operating leases of approximately $91.0 million. The presentation of occupancy expense and the pattern of expense recognition within the Consolidated Statements of Operations and Consolidated Statements of Cash Flows is expected to be consistent with the current lease accounting guidance. In January 2017, the FASB issued ASU 2017-04, “Intangibles-Goodwill and Other” (“ASU 2017-04”). ASU 2017-04 simplifies the testing for goodwill impairment. The guidance will be effective for the Company beginning January 1, 2020 and early adoption is permitted and should be applied prospectively. The adoption of this guidance is not expected to have a material effect on the Company’s Consolidated Financial Statements. Cash and Cash Equivalents Cash and cash equivalents includes cash and money market instruments that are primarily maintained at one major global bank. Given this concentration, the Company is exposed to certain credit risk in relation to its deposits at this bank. The Company defines cash equivalents as short-term interest-bearing investments with maturities at the time of purchase of three months or less. Investments The Company determines the appropriate classification of securities at the time of purchase which are recorded in the Consolidated Statements of Financial Condition on the trade date. Securities are classified as available-for-sale or trading. The Company’s available-for-sale investments are comprised of investment grade corporate debt securities. Available-for-sale investments are carried at fair value with the unrealized gains or losses reported in accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. Trading investments include investment grade corporate debt securities and U.S. Treasuries and are carried at fair value, with realized and unrealized gains or losses included in other income in the Consolidated Statements of Operations. The Company assesses whether an other-than-temporary impairment loss on the available-for-sale investments has occurred due to declines in fair value or other market conditions. The portion of an other-than-temporary impairment related to credit loss is recorded as a charge in the Consolidated Statements of Operations. The remainder is recognized in accumulated other comprehensive loss if the Company does not intend to sell the security and it is more likely than not that the Company will not be required to sell the security prior to recovery. No charges for other-than-temporary losses were recorded during the years ended December 31, 2018, 2017 and 2016. Fair Value Financial Instruments Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” A three-tiered hierarchy for determining fair value has been established that prioritizes inputs to valuation techniques used in fair value calculations. The three levels of inputs are defined as Level 1 (unadjusted quoted prices for identical assets or liabilities in active markets), Level 2 (inputs that are observable in the marketplace other than those inputs classified in Level 1) and Level 3 (inputs that are unobservable in the marketplace). The Company’s financial assets and liabilities measured at fair value on a recurring basis consist of its money market funds, securities available-for-sale, trading securities and foreign currency forward contracts. All other financial instruments are short-term in nature and the carrying amount is reported on the Consolidated Statements of Financial Condition at approximate fair value. Allowance for Doubtful Accounts All accounts receivable have contractual maturities of less than one year and are derived from trading-related fees and commissions and revenues from products and services. The Company continually monitors collections and payments from its customers and maintains an allowance for doubtful accounts. The allowance for doubtful accounts is based upon the historical collection experience and specific collection issues that have been identified. Additions to the allowance for doubtful accounts are charged to bad debt expense, which is included in general and administrative expense in the Company’s Consolidated Statements of Operations. The allowance for doubtful accounts was $0.1 million, $0.2 million and $0.1 million as of December 31, 2018, 2017 and 2016, respectively. The provision for bad debts was $0.2 million, $0.4 million and $0.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. Write-offs and other charges against the allowance for doubtful accounts were $0.2 million, $0.1 million and $0.1 million for the years ended December 31, 2018, 2017 and 2016, respectively. Depreciation and Amortization Fixed assets are carried at cost less accumulated depreciation. The Company uses the straight-line method of depreciation over three to seven years. The Company amortizes leasehold improvements on a straight-line basis over the lesser of the life of the improvement or the remaining term of the lease. Software Development Costs The Company capitalizes certain costs associated with the development of internal use software, including among other items, employee compensation and related benefits and third party consulting costs at the point at which the conceptual formulation, design and testing of possible software project alternatives have been completed. Once the product is ready for its intended use, such costs are amortized on a straight-line basis over three years. The Company reviews the amounts capitalized for impairment whenever events or changes in circumstances indicate that the carrying amounts of the assets may not be recoverable. Cash Provided as Collateral Cash is provided as collateral for broker-dealer clearing accounts. Cash provided as collateral is included in prepaid expenses and other assets in the Consolidated Statements of Financial Condition. Foreign Currency Translation and Forward Contracts Assets and liabilities denominated in foreign currencies are translated using exchange rates at the end of the period; revenues and expenses are translated at average monthly rates. Gains and losses on foreign currency translation are a component of accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. Transaction gains and losses are recorded in general and administrative expense in the Consolidated Statements of Operations. The Company enters into foreign currency forward contracts to hedge its net investment in its U.K. subsidiaries. Gains and losses on these transactions are included in accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. Revenue Recognition On January 1, 2018, the Company adopted ASU 2014-09 using the modified retrospective approach. The adoption of ASU 2014-09 did not have a material impact on the measurement or recognition of revenue in any prior or current reporting periods. The Company’s classification of revenues in the Consolidated Statements of Operations represents revenues from contracts with customers disaggregated by type of revenue. The Company has four revenue streams as described below. Commission Revenue. The Company charges its broker-dealer clients variable transaction fees for trades executed on its platform and, under certain plans, distribution fees or monthly minimum fees to use the platform for a particular product area. Variable transaction fees are generally calculated as a percentage of the notional dollar volume of bonds traded on the platform and vary based on the type, size, yield and maturity of the bond traded. Under the Company’s disclosed trading transaction fee plans, bonds that are more actively traded or that have shorter maturities generally generate lower commissions, while bonds that are less actively traded or that have longer maturities generally command higher commissions. Variable transaction fees, distribution fees and unused monthly fee commitments are invoiced and recorded on a monthly basis. For trades that the Company executes between and among institutional investor and broker-dealer clients on a matched principal basis by serving as counterparty to both the buyer and the seller, the Company earns its commission through the difference in price between the two trades. The commission is collected upon settlement of the trade, which typically occurs within one to two trading days after the trade date. The following table presents commission revenue by fee type for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Commission revenue by fee type Variable transaction fees Disclosed trading $ 228,004 $ 234,143 $ 230,319 Open Trading - matched principal trading 65,932 45,660 37,747 Total variable transaction fees 293,936 279,803 268,066 Distribution fees and unused minimum fees 96,898 75,479 64,241 Total commissions $ 390,834 $ 355,282 $ 332,307 Information services – Information services includes data licensed to the Company’s broker-dealer clients, institutional investor clients and data-only subscribers; professional and consulting services; technology software licenses; and maintenance and support services. The nature and timing of each performance obligation may vary as these contracts are either subscription based services transferred over time or one-time services that are transferred at a point in time. Revenues for services transferred over time are recognized ratably over the contract period as the Company’s performance obligation is met whereas revenues for services transferred at a point in time are recognized in the period the services are provided. Customers are generally billed monthly, quarterly, or annually; revenues billed in advance are deferred and recognized ratably over the contract period. The following table presents information services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Information services revenue by timing of recognition Services transferred over time $ 27,475 $ 25,242 $ 22,011 Services transferred at a point in time 752 564 1,258 Total information services revenues $ 28,227 $ 25,806 $ 23,269 Post-trade services – Post-trade services revenue is generated from regulatory transaction reporting, trade publication and trade matching services. Customers are generally billed monthly in arrears and revenue is recognized in the period transactions are processed. Revenues billed in advance are deferred and recognized ratably over the contract period. The Company also generates one-time implementation fees for onboarding clients which are invoiced and recognized in the period the implementation is completed. The following table presents post-trade services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Post-trade services revenue by timing of recognition Services transferred over time $ 15,013 $ 9,657 $ 10,812 Services transferred at a point in time 333 1,433 — Total post-trade services revenues $ 15,346 $ 11,090 $ 10,812 Other revenues – Other revenues primarily includes revenue from telecommunications line charges to broker-dealer clients. Contract liabilities consist of deferred revenues that the Company records when cash payments are received or due in advance of services to be performed. The revenue recognized from contract liabilities and the remaining balance is shown below: December 31, 2017 Payments received in advance of services to be performed Revenue recognized for services performed during the period Foreign Currency Translation December 31, 2018 (In thousands) Information services $ 1,763 $ 7,109 $ (6,913 ) $ — $ 1,959 Post-trade services 897 11,566 (11,561 ) (51 ) 851 Total deferred revenue $ 2,660 $ 18,675 $ (18,474 ) $ (51 ) $ 2,810 The majority of the Company’s contracts are short-term in nature with durations of less than one-year. For contracts extending beyond one year, the aggregate amount of the transaction price allocated to remaining performance obligations was $6.3 million as of December 31, 2018. The Company expects to recognize revenue associated with the remaining performance obligations over the next 18 months. Stock-Based Compensation The Company measures and recognizes compensation expense for all share-based payment awards based on their estimated fair values measured as of the grant date. These costs are recognized as an expense in the Consolidated Statements of Operations over the requisite service period, which is typically the vesting period, with an offsetting increase to additional paid-in capital. Effective upon the Company’s adoption of ASU 2016-09 on January 1, 2017, the Company accounts for forfeitures as they occur. Prior to the adoption of ASU 2016-09, expected forfeitures were included in determining share-based compensation expense. Income Taxes Income taxes are accounted for using the asset and liability method. Deferred income taxes reflect the net tax effects of temporary differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is recognized against deferred tax assets if it is more likely than not that such assets will not be realized in future years. The Company recognizes interest and penalties related to unrecognized tax benefits in general and administrative expenses in the Consolidated Statements of Operations. Effective upon the Company’s adoption of ASU 2016-09 all tax effects related to share-based payments are recorded through tax expense in the periods during which the awards are exercised or vest. On December 22, 2017, the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”) to address the application of U.S. generally accepted accounting principles (“GAAP”) related to the enactment of the Tax Cuts and Jobs Act (the “Tax Act”). SAB 118 allowed the Company to record a provisional amount when it did not have the necessary information available, prepared, or analyzed in reasonable detail to complete its accounting for the change in the tax law. The Company has completed its analysis within the one-year measurement period in accordance with SAB 118. Business Combinations, Goodwill and Intangible Assets Business combinations are accounted for under the purchase method of accounting. The total cost of an acquisition is allocated to the underlying net assets based on their respective estimated fair values. The excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. Determining the fair value of certain assets acquired and liabilities assumed is judgmental in nature and often involves the use of significant estimates and assumptions, including assumptions with respect to future cash flows, discount rates, growth rates and asset lives. The Company operates as a single reporting unit. Subsequent to an acquisition, goodwill no longer retains its identification with a particular acquisition, but instead becomes identifiable with the entire reporting unit. As a result, all of the fair value of the Company is available to support the value of goodwill. An impairment review of goodwill is performed on an annual basis, at year-end, or more frequently if circumstances change. Intangible assets with definite lives, including purchased technologies, customer relationships and other intangible assets, are amortized on a straight-line basis over their estimated useful lives, ranging from three to 15 years. Intangible assets are assessed for impairment when events or circumstances indicate the existence of a possible impairment. Earnings Per Share Basic earnings per share is computed by dividing the net income attributable to common stock by the weighted-average number of shares of common stock outstanding during the period. For purposes of computing diluted earnings per share, the weighted-average shares outstanding of common stock reflects the dilutive effect that could occur if convertible securities or other contracts to issue common stock were converted into or exercised for common stock. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Reclassifications Certain reclassifications have been made to the prior period’s Consolidated Financial Statements in order to conform to the current year presentation. The Company revised the format of the Consolidated Statements of Operations to separately present non-operating activities. Such activities include investment income, unrealized and realized gains (losses) on trading securities, foreign exchange gains (losses), investment advisory fees and other miscellaneous non-operating activities. Accordingly, the Company reclassified these amounts from the various revenue and expense line items to Other income (expense).

Net Capital Requirements

Net Capital Requirements	12 Months Ended
	Dec. 31, 2018
Net Capital [Abstract]
Net Capital Requirements	3. Net Capital Requirements Certain U.S. subsidiaries of the Company are registered as a broker-dealer or swap execution facility and therefore are subject to the applicable rules and regulations of the Securities and Exchange Commission and the Commodity Futures Trading Commission. These rules contain minimum net capital requirements, as defined in the applicable regulations, and also may require a significant part of the registrants’ assets be kept in relatively liquid form. Certain of the Company’s foreign subsidiaries are regulated by the Financial Conduct Authority in the U.K. or other foreign regulators and must maintain financial resources, as defined in the applicable regulations, in excess of the applicable financial resources requirement. As of December 31, 2018, each of the Company’s subsidiaries that are subject to these regulations had net capital or financial resources in excess of their minimum requirements. As of December 31, 2018, the Company’s subsidiaries maintained aggregate net capital and financial resources that were $162.8 million in excess of the required levels of $15.0 million. Each of the Company’s U.S. and foreign regulated subsidiaries are subject to local regulations which generally prohibit repayment of borrowings from the Company or affiliates, paying cash dividends, making loans to the Company or affiliates or otherwise entering into transactions that result in a significant reduction in regulatory net capital or financial resources without prior notification to or approval from such regulated entity’s principal regulator.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. Fair Value Measurements The following table summarizes the valuation of the Company’s assets and liabilities measured at fair value as categorized based on the hierarchy described in Note 2. Level 1 Level 2 Level 3 Total (In thousands) As of December 31, 2018 Money market funds $ 112,529 $ — $ — $ 112,529 Securities available-for-sale Corporate debt — 146,966 — 146,966 Trading securities Corporate debt — 71,861 — 71,861 U.S. Treasuries — 17,178 — 17,178 Mutual funds held in rabbi trust — 4,100 — 4,100 Foreign currency forward position — (1,021 ) — (1,021 ) Total $ 112,529 $ 239,084 $ — $ 351,613 As of December 31, 2017 Money market funds $ 88,562 $ — $ — $ 88,562 Securities available-for-sale Corporate debt — 145,052 — 145,052 Trading securities Corporate debt — 91,302 — 91,302 Mutual funds held in rabbi trust — 3,167 — 3,167 Foreign currency forward position — (702 ) — (702 ) Total $ 88,562 $ 238,819 $ — $ 327,381 Securities classified within Level 2 were valued using a market approach utilizing prices and other relevant information generated by market transactions involving comparable assets. The foreign currency forward contracts are classified within Level 2 as the valuation inputs are based on quoted market prices. The mutual funds held in a rabbi trust represent investments associated with the deferred cash incentive plan (see Note 14). There were no financial assets classified within Level 3 during the years ended December 31, 2018 and 2017. The Company enters into foreign currency forward contracts to hedge the net investment in the Company’s U.K. subsidiaries. The Company designates each foreign currency forward contract as a hedge and assesses the risk management objective and strategy, including identification of the hedging instrument, the hedged item and the risk exposure and how effectiveness is to be assessed prospectively and retrospectively. These hedges are for a one-month period and are used to limit exposure to foreign currency exchange rate fluctuations. The fair value of the asset is included in prepaid expenses and other assets and the fair value of the liability is included in accounts payable, accrued expenses and other liabilities in the Consolidated Statements of Financial Condition. Gains or losses on foreign currency forward contracts designated as hedges are included in accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. A summary of the foreign currency forward position is as follows: As of December 31, 2018 2017 (In thousands) Notional value $ 106,306 $ 84,422 Fair value of notional 107,327 85,124 Fair value of the (liability) $ (1,021 ) $ (702 ) The following is a summary of the Company’s investments: Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value (In thousands) As of December 31, 2018 Securities available-for-sale Corporate debt $ 147,556 $ 27 $ (617 ) $ 146,966 Trading securities Corporate debt 72,274 8 (421 ) 71,861 U.S. Treasuries 16,953 225 — 17,178 Mutual funds held in rabbi trust 4,347 — (247 ) 4,100 Total trading securities 93,574 233 (668 ) 93,139 Total investments $ 241,130 $ 260 $ (1,285 ) $ 240,105 As of December 31, 2017 Securities available-for-sale Corporate debt $ 145,526 $ 9 $ (483 ) $ 145,052 Trading securities Corporate debt 91,578 30 (306 ) 91,302 Mutual funds held in rabbi trust 2,729 438 — 3,167 Total trading securities 94,307 468 (306 ) 94,469 Total investments $ 239,833 $ 477 $ (789 ) $ 239,521 The following table summarizes the fair value of the investments based upon the contractual maturities: As of December 31, 2018 2017 (In thousands) Less than one year $ 134,255 $ 130,738 Due in 1 - 5 years 105,850 108,783 Total $ 240,105 $ 239,521 Proceeds from the sales and maturities of investments during the years ended December 31, 2018, 2017 and 2016 were $409.3 million, $219.2 million and $69.5 million, respectively. Net realized and unrealized gains or losses on trading securities were immaterial for the years ended December 31, 2018 and 2017. The following table provides fair values and unrealized losses on corporate debt investments and by the aging of the securities' continuous unrealized loss position as of December 31, 2018 and 2017 respectively: Less than Twelve Months Twelve Months or More Total Estimated fair value Gross unrealized losses Estimated fair value Gross unrealized losses Estimated fair value Gross unrealized losses (In thousands) As of December 31, 2018 Corporate debt $ 80,282 $ (256 ) $ 87,028 $ (782 ) $ 167,310 $ (1,038 ) As of December 31, 2017 Corporate debt $ 177,114 $ (536 ) $ 26,476 $ (253 ) $ 203,590 $ (789 )

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	5. Goodwill and Intangible Assets Goodwill and intangible assets with indefinite lives was $59.7 million as of both December 31, 2018 and 2017. Intangible assets that are subject to amortization, including the related accumulated amortization, are comprised of the following: December 31, 2018 December 31, 2017 Cost Accumulated amortization Net carrying amount Cost Accumulated amortization Net carrying amount (In thousands) Technology $ 5,770 $ (5,770 ) $ — $ 5,770 $ (5,770 ) $ — Customer relationships 5,634 (2,672 ) 2,962 5,647 (2,301 ) 3,346 Non-competition agreements 380 (380 ) — 380 (380 ) — Tradenames 370 (370 ) — 370 (370 ) — Total $ 12,154 $ (9,192 ) $ 2,962 $ 12,167 $ (8,821 ) $ 3,346 Amortization expense associated with identifiable intangible assets was $0.4 million, $0.4 million and $ 0.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. Estimated total amortization expense is

Capitalized Software, Furniture

Capitalized Software, Furniture, Equipment and Leasehold Improvements	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Capitalized Software, Furniture, Equipment and Leasehold Improvements	6. Capitalized Software, Furniture, Equipment and Leasehold Improvements Capitalized software development costs, furniture, equipment and leasehold improvements, net of accumulated depreciation and amortization, are comprised of the following: As of December 31, 2018 2017 (In thousands) Software development costs $ 97,113 $ 86,129 Computer hardware and related software 42,705 35,945 Office hardware 5,909 4,575 Furniture and fixtures 5,385 2,347 Leasehold improvements 32,527 11,016 183,639 140,012 Accumulated depreciation and amortization (120,629 ) (101,464 ) Total $ 63,010 $ 38,548 During the years ended December 31, 2018 and 2017, software development costs totaling $11.7 million and $13.5 million, respectively, were capitalized. Non-capitalized software costs and routine maintenance costs are expensed as incurred and are included in employee compensation and benefits and professional and consulting fees in the Consolidated Statements of Operations.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	7. Income Taxes The provision for income taxes consists of the following: Year Ended December 31, 2018 2017 2016 (In thousands) Current: Federal $ 31,617 $ 36,045 $ 45,455 State and local 5,928 3,848 7,087 Foreign 8,862 7,234 6,166 Total current provision 46,407 47,127 58,708 Deferred: Federal (1,416 ) 6,171 5,884 State and local (272 ) 661 1,141 Foreign 515 (280 ) (303 ) Total deferred provision (1,173 ) 6,552 6,722 Provision for income taxes $ 45,234 $ 53,679 $ 65,430 Pre-tax income from U.S. operations was $168.5 million, $165.2 million and $161.9 million for the years ended December 31, 2018, 2017 and 2016, respectively. Pre-tax income from foreign operations was $49.6 million, $36.6 million and $29.7 million for the years ended December 31, 2018, 2017 and 2016, respectively. On December 22, 2017, the Tax Act was enacted into law. The Tax Act significantly revised the U.S. corporate income tax regime by, among other things, lowering the U.S. federal corporate income tax rate from 35% to 21%, implementing a territorial tax system and imposing a repatriation tax on deemed earnings of foreign subsidiaries. The Company recorded a provisional tax charge in 2017 of $11.7 million, composed of $6.7 million to re-measure U.S. deferred tax assets and $5.0 million for the repatriation tax on accumulated undistributed foreign earnings. In 2018, the Company reduced the provisional tax charge by $0.4 million as a result of new regulatory guidance and changes in interpretations and assumptions made by the Company. Pursuant to the Tax Act, all previously undistributed foreign earnings have now been subject to U.S. tax. Notwithstanding the U.S. taxation of these amounts, the Company considers its undistributed foreign earnings to be indefinitely reinvested outside of the U.S. and does not expect to incur any significant additional taxes related to such amounts. The difference between the Company’s reported provision for income taxes and the U.S. federal statutory rate of 21% is as follows: Year Ended December 31, 2018 2017 2016 U.S. federal tax at statutory rate 21.0 % 35.0 % 35.0 % State and local taxes - net of federal benefit 2.0 1.5 2.9 Credits and deductions related to research activities (0.3 ) (1.2 ) (1.3 ) Foreign rate differential benefit (0.5 ) (2.9 ) (2.3 ) Excess tax benefit from stock-based compensation (2.1 ) (11.6 ) — Tax Cuts and Jobs Act provisional tax charge (0.2 ) 5.8 — Other, net 0.8 — (0.2 ) Provision for income taxes 20.7 % 26.6 % 34.1 % The following is a summary of the Company’s net deferred tax assets: As of December 31, 2018 2017 (In thousands) Deferred tax assets: U.S. net operating loss carryforwards $ 603 $ 872 Capital loss carryforwards — 4,648 Stock compensation expense 4,967 4,534 Other 2,966 1,143 Total deferred tax assets 8,536 11,197 Valuation allowance — (4,648 ) Net deferred tax assets 8,536 6,549 Deferred tax liabilities: Depreciation and amortization (1,847 ) (1,369 ) Capitalized software development costs (3,776 ) (3,479 ) Intangible assets (898 ) (967 ) Deferred tax assets, net $ 2,015 $ 734 In 2001 and 2000, MarketAxess Holdings Inc. and MarketAxess Corporation had an ownership change within the meaning of Section 382 of the Internal Revenue Code. As of December 31, 2018, the Company had restricted U.S. federal net operating loss carryforwards of approximately $2.9 million related to the prior ownership change, which begin to expire in 2021. The Company’s net operating loss carryforwards may be subject to additional annual limitations if there is a 50% or greater change in the Company’s ownership, as determined over a rolling three-year period. The ultimate realization of deferred income tax assets is dependent upon the generation of future taxable income during the periods in which the temporary differences become deductible. If it is not more likely than not that some portion or all of the gross deferred income tax assets will be realized in future years, a valuation allowance is recorded. In October 2013, the Company recognized a $20.6 million capital loss on the sale of Greenline Financial Technologies, Inc. of which $1.2 million was carried back or otherwise utilized against current period capital gains. A full valuation allowance was provided against the remaining capital loss carryforward. The remaining capital loss carryforward expired as of December 31, 2018. A summary of the changes in the valuation allowance is as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Valuation allowance at beginning of year $ 4,648 $ 7,235 $ 7,294 (Decrease) to valuation allowance attributable to: Expiration of capital loss carryforwards (4,648 ) — — Federal and state tax rate changes — (2,587 ) (59 ) Valuation allowance at end of year $ — $ 4,648 $ 7,235 The Company or one of its subsidiaries files U.S. federal, state and foreign income tax returns. Income tax returns for U.S. Federal (through 2013), New York City (through 2003) and State (through 2009) and Connecticut State (through 2003) have been audited. An examination of the Company’s New York State income tax returns for 2010 through 2015 is currently underway. The Company cannot estimate when the examination will conclude or the impact such examinations will have on the Company’s Consolidated Financial Statements, if any. A reconciliation of the unrecognized tax benefits is as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Balance at beginning of year $ 2,650 $ 29 $ 265 Additions attributable to state and local apportionment 2,068 2,650 — Reductions for tax positions of prior years — (29 ) (236 ) Balance at end of year $ 4,718 $ 2,650 $ 29

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Common Stock As of December 31, 2018 and 2017, the Company had 110,000,000 authorized shares of voting common stock and 10,000,000 authorized shares of non-voting common stock. Voting common stock entitles the holder to one vote per share of common stock held. The following is a summary of the change in the Company’s outstanding shares of voting common stock: Year Ended December 31, 2018 2017 2016 (In thousands) Outstanding shares of voting common stock at the beginning of year 37,621 37,544 37,409 Exercise of stock options 121 262 181 Issuance of restricted stock, net of shares withheld for withholding tax payments and cancellations 22 39 104 Repurchases (124 ) (224 ) (150 ) Outstanding shares of voting common stock at the end of year 37,640 37,621 37,544 In January 2016, the Board of Directors authorized a share repurchase program for up to $25.0 million of the Company’s common stock. In October 2016, the Board of Directors approved a $50.0 million increase in the size of the repurchase program. This program expired in September 2017. In September 2017, the Board of Directors authorized a fifteen-month share repurchase program for up to $100.0 million that commenced in October 2017. The expiration date of this program was subsequently extended to March 31, 2019. In January 2019, the Board of Directors authorized a new two-year share repurchase program for up to $100.0 million. The Company expects the plan to commence in April 2019. Shares repurchased under each program will be held in treasury for future use. Dividends During 2018, 2017 and 2016, the Company paid quarterly cash dividends of $0.42 per share, $0.33 per share and $0.26 per share, respectively. Any future declaration and payment of dividends will be at the sole discretion of the Company’s Board of Directors. The Board of Directors may take into account such matters as general business conditions, the Company’s financial results, capital requirements, contractual obligations, legal, and regulatory restrictions on the payment of dividends to the Company’s stockholders or by the Company’s subsidiaries to their respective parent entities, and any such other factors as the Board of Directors may deem relevant.

Stock-Based Compensation Plans

Stock-Based Compensation Plans	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation Plans	9. Stock-Based Compensation Plans The Company has a stock incentive plan which provides for the grant of stock options, stock appreciation rights, restricted stock, performance shares, performance units, or other stock-based awards as incentives and rewards to encourage employees, consultants and non-employee directors to participate in the long-term success of the Company. As of December 31, 2018, there were 304,965 shares available for grant under the stock incentive plan. Total stock-based compensation expense was as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Employees: Restricted stock and performance shares $ 12,559 $ 11,566 $ 12,459 Stock options 2,193 1,882 1,143 14,752 13,448 13,602 Non-employee directors: Restricted stock 1,098 973 909 Total stock-based compensation $ 15,850 $ 14,421 $ 14,511 The Company records stock-based compensation expense for employees in employee compensation and benefits and for non-employee directors in general and administrative expenses in the Consolidated Statements of Operations. Stock Options The exercise price of each option granted is equal to the market price of the Company’s common stock on the date of grant. Generally, option grants have provided for vesting over a three or five-year period. Options generally expire in six or ten years from the date of grant. The fair value of each option award is estimated on the date of grant using the Black-Scholes option-pricing model. The determination of fair value of share-based payment awards on the date of grant using an option-pricing model is affected by the Company’s stock price as well as assumptions regarding a number of highly complex and subjective variables, including the expected stock price volatility over the term of the awards, the risk-free interest rate, the expected dividend yield rate and the expected term. Expected volatilities are based on historical volatility of the Company’s stock. The risk-free interest rate is based on U.S. Treasury securities with a maturity value approximating the expected term of the option. The dividend yield rate is based on the expected annual dividends to be paid divided by the expected stock price. The expected term represents the period of time that options granted are expected to be outstanding based on actual and projected employee stock option exercise behavior. The weighted-average fair value for options granted during 2018, 2017 and 2016 was $56.11, $40.08 and $32.24, respectively. The following table represents the assumptions used for the Black-Scholes option-pricing model to determine the per share weighted-average fair value for options granted for the three years ended December 31, 2018: 2018 2017 2016 Expected life (years) 5.0 5.0 6.0 Risk-free interest rate 2.2 % 1.9 % 1.9 % Expected volatility 26.9 % 28.0 % 33.0 % Expected dividend yield 0.8 % 0.8 % 1.0 % In addition to the option grants above, 148,524 stock options were granted to the Company’s Chief Executive Officer in November 2018 with a grant date fair value of $5.5 million as determined by an independent third party using a Monte Carlo simulation model. The exercise price is $257.78 for 69,113 of the stock options and $278.40 for the remaining 79,411 stock options, which is equal to 125% and 135%, respectively, of the fair market value of the Company’s stock on the grant date. Subject to continued employment with the Company, the options will vest and become exercisable on November 8, 2023. The options expire on May 8, 2024. Key assumptions used for the Monte Carlo model included a risk free interest rate of 3.1%, volatility of 25.9% and a dividend yield of 0.8%. The following table reports stock option activity during the three years ended December 31, 2018 and the intrinsic value as of December 31, 2018: Number of Shares Weighted-Average Exercise Price ($) Remaining Contractual Term Intrinsic Value ($) (In thousands) Outstanding at December 31, 2015 939,036 $ 23.83 Granted 112,988 102.40 Canceled (874 ) 101.77 Exercised (195,410 ) 12.35 Outstanding at December 31, 2016 855,740 36.80 Granted 54,838 156.85 Canceled — — Exercised (380,967 ) 11.26 Outstanding at December 31, 2017 529,611 67.60 Granted 168,217 261.19 Canceled (1,676 ) 142.69 Exercised (120,588 ) 24.66 $ 21,823 Outstanding at December 31, 2018 575,564 132.93 3.2 53,651 Exercisable at December 31, 2018 203,564 53.49 2.1 32,126 The intrinsic value is the amount by which the closing price of the Company’s common stock on December 31, 2018 of $211.31 or the price on the day of exercise exceeds the exercise price of the stock options multiplied by the number of shares. As of December 31, 2018, there was $8.6 million of total unrecognized compensation cost related to non-vested stock options. That cost is expected to be recognized over a weighted-average period of 2.8 years. Restricted Stock and Performance Shares Restricted stock generally vests over a three or five-year period. Compensation expense is measured at the grant date and recognized ratably over the vesting period. Annual performance share awards are granted to certain officers and senior managers. Each performance share award is earned or forfeited based on the level of achievement by the Company of pre-tax operating income, as defined. The pay-out ranges from zero to 150% of the performance share award. For each performance share earned, a participant is awarded an equal number of shares of restricted stock. Any restricted stock awarded to a participant vests two equal installments on each of the second and third anniversaries of the date of grant of the applicable performance share award. Compensation expense for performance shares is measured at the grant date and recognized on a graded basis over the vesting period. Performance year: 2018 2017 2016 Share pay-out plan 10,479 12,971 15,390 Actual share pay-out in following year 10,479 8,094 21,423 Weighted average fair value per share on grant date $ 202.04 $ 155.53 $ 101.77 In addition to the grants above, 37,742 performance shares were granted to the Company’s Chief Executive Officer in November 2018 with a grant date fair value of $5.5 million as determined by an independent third party using a Monte Carlo simulation model. The performance share award provides that the number of shares earned will be based on the Company’s achievement of certain share price levels during the five-year performance period. The performance level is $257.78 for 17,942 of the performance shares and $278.40 for the remaining 19,800 performance shares, which is equal to 125% and 135%, respectively, of the fair market value of the Company’s stock on the grant date. Subject to continued employment with the Company, earned shares will vest on November 8, 2023. Key assumptions used for the Monte Carlo model included a risk free interest rate of 3.1%, volatility of 26.1% and a dividend yield of 0.8%. On April 1, 2017, the Company granted 9,367 multi-year performance shares to a certain officer. The performance share awards are earned or forfeited based on attaining certain cumulative operating income thresholds of the Company and select subsidiaries over the two-year period beginning January 1, 2017. The pay-out ranges from zero to 150% of the performance award value. Any restricted stock awarded will vest 50% on April 1, 2020 and 50% on April 1, 2021. The fair value per share of the awards on the grant date was $186.74. The actual share payout was 38.8% or 3,634 shares. In January 2016, the Company granted 33,509 multi-year performance shares to certain officers and senior managers. Each performance share award is earned or forfeited based on the level of achievement by the Company of aggregate operating income over the four-year period beginning January 1, 2016. The pay-out ranges from zero to 150% of the performance award value. Any restricted stock awarded will vest 50% on January 31, 2020 and 50% on January 31, 2021. The fair value per share of the awards on the grant date was $103.30. The estimated share payout as of December 31, 2018 was 106.0%. The following table reports restricted stock and performance share activity during the three years ended December 31, 2018: Number of Restricted Shares Weighted-Average Grant Date Fair Value Outstanding at December 31, 2015 432,138 $ 56.24 Granted 95,419 Performance share pay-out 61,936 Canceled (12,786 ) Vested (192,729 ) Outstanding at December 31, 2016 383,978 $ 71.50 Granted 61,434 Performance share pay-out 21,422 Canceled (4,590 ) Vested (142,645 ) Outstanding at December 31, 2017 319,599 $ 88.77 Granted 59,179 Performance share pay-out 8,094 Canceled (4,046 ) Vested (110,956 ) Outstanding at December 31, 2018 271,870 $ 112.47 As of December 31, 2018, there was $23.3 million of total unrecognized compensation expense related to non-vested restricted stock and performance shares. That cost is expected to be recognized over a weighted-average period of 1.7 years. Employee Stock Purchase Plan The Company offers a non-qualified employee stock purchase plan for non-executive employees. Under the plan, participants are granted the right to purchase shares of common stock based on the fair market value on the last day of the six-month offering period. On the purchase date, the Company grants to the participants a number of shares of common stock equal to 20% of the aggregate shares purchased by the participant. These matching shares vest over a one-year period. The Company issued 989, 1,034 and 1,190 matching shares in connection with the plan for the years ended December 31, 2018, 2017, and 2016, respectively.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	10. Earnings Per Share The following table sets forth basic and diluted weighted average shares outstanding used to compute earnings per share: Year Ended December 31, 2018 2017 2016 (In thousands) Basic weighted average shares outstanding 36,958 36,864 36,844 Dilutive effect of stock options and restricted stock 897 1,174 894 Diluted weighted average shares outstanding 37,855 38,038 37,738 Stock options and restricted stock totaling 83,718 shares, 31,766 shares and 84,052 shares for the years ended December 31, 2018, 2017 and 2016, respectively, were excluded from the computation of diluted earnings per share because their effect would have been antidilutive. The computation of diluted shares can vary among periods due, in part, to the change in the average price of the Company’s common stock.

Credit Agreement

Credit Agreement	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Credit Agreement	11. Credit Agreement In October 2015, the Company entered into a two-year amended and restated credit agreement (the “Credit Agreement”) that provided for revolving loans and letters of credit up to an aggregate of $100.0 million. The Company amended the Credit Agreement in October 2017 and extended the maturity date to October 2018. The amended Credit Agreement also provided for two additional one-year extension options and modified certain borrowing terms and covenants. In October 2018, the Company exercised its first option to extend the maturity date to October 2019. Subject to satisfaction of certain specified conditions, the Company is permitted to upsize the borrowing capacity under the Credit Agreement by an additional $50.0 million. As of December 31, 2018, the Company had $1.7 million in letters of credit outstanding and $98.3 million in available borrowing capacity under the Credit Agreement. Borrowings under the Credit Agreement will bear interest at a rate per annum equal to the base rate or adjusted LIBOR plus an applicable margin that varies with the Company’s consolidated total leverage ratio. The Credit Agreement requires that the Company satisfies certain covenants, which includes leverage ratios and minimum earnings before interest, tax, depreciation and amortization (“EBITDA”) requirements. The Company was in compliance with all applicable covenants at December 31, 2018 and December 31, 2017. The Company’s existing and future domestic subsidiaries (other than any regulated subsidiary) have guaranteed the Company’s obligations under the Credit Agreement. Subject to customary exceptions and exclusions, the Company’s borrowings under the Credit Agreement are collateralized by first priority pledges (subject to permitted liens) of substantially all of the Company’s personal property assets and the personal property assets of the Company’s domestic subsidiaries that have guaranteed the Credit Agreement, including the equity interests of the Company’s domestic subsidiaries and the equity interests of certain of the Company’s foreign subsidiaries (limited, in the case of the voting equity interests of the foreign subsidiaries, to a pledge of 65% of those equity interests). If an event of default occurs, including failure to pay principal or interest due on the loan balance, a voluntary or involuntary proceeding seeking liquidation, change in control of the Company, or one or more material judgments against the Company in excess of $10.0 million, the lenders would be entitled to accelerate the borrowings under the Credit Agreement and take various other actions, including all actions permitted to be taken by a secured creditor. If certain bankruptcy events of default occur, the borrowings under the Credit Agreement will automatically accelerate.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Lease Commitments The Company leases office space under non-cancelable lease agreements expiring at various dates through 2034. Office space leases are subject to escalation based on certain costs incurred by the landlord. Minimum rental commitments as of December 31, 2018 under such operating leases were as follows (in thousands): 2019 $ 9,764 2020 10,919 2021 10,114 2022 9,067 2023 8,738 2024 and thereafter 95,467 $ 144,069 Rental expense for the years ended December 31, 2018, 2017 and 2016 was $13.1 million, $5.3 million and $4.0 million, respectively, and is included in occupancy expense in the Consolidated Statements of Operations. Rental expense has been recorded based on the total minimum lease payments after giving effect to rent abatement and concessions, which are being amortized on a straight-line basis over the life of the lease. The total balance of rent abatements and concessions was $11.5 million and $2.7 as of December 31, 2018 and 2017, respectively, and is included in accounts payable, accrued expenses and other liabilities in the Company’s Consolidated Statement of Financial Condition. The Company is contingently obligated for standby letters of credit amounting to $1.7 million that were issued to landlords for office space. During 2016, the Company entered into a lease agreement for its new global headquarters in New York City. The Company relocated its headquarters to approximately 83,000 square feet of newly built office space at 55 Hudson Yards in January 2019. Rent expense recognition commenced upon acceptance of the premises in January 2018. The Company has entered into agreements that assign the Company’s lease obligations on two properties to third parties and is contingently liable should the third parties default on future lease obligations through the lease termination dates of November 2020 and February 2022. The aggregate amount of the future lease obligations under these arrangements is $5.8 million as of December 31, 2018. Legal In the normal course of business, the Company and its subsidiaries included in the consolidated financial statements may be involved in various lawsuits, proceedings and regulatory examinations. The Company assesses its liabilities and contingencies in connection with outstanding legal proceedings, if any, utilizing the latest information available. For matters where it is probable that the Company will incur a material loss and the amount can be reasonably estimated, the Company would establish an accrual for the loss. Once established, the accrual would be adjusted to reflect any relevant developments. When a loss contingency is not both probable and estimable, the Company does not establish an accrual. Based on currently available information, the outcome of the Company’s outstanding matters is not expected to have a material adverse impact on the Company’s financial position. It is not presently possible to determine the ultimate exposure to these matters and there is no assurance that the resolution of the outstanding matters will not significantly exceed any reserves accrued by the Company. Other The Company, through two regulated subsidiaries, executes certain bond transactions between and among institutional investor and broker-dealer clients on a matched principal basis by serving as counterparty to both the buyer and the seller in trades which settle through third-party clearing brokers. Settlement typically occurs within one to two trading days after the trade date. Cash settlement of the transaction occurs upon receipt or delivery of the underlying instrument that was traded. Under securities clearing agreements with third party clearing brokers, the Company maintains collateral deposits with each clearing broker in the form of cash. As of December 31, 2018 and 2017, the amount of the collateral deposits, which are disclosed in the Consolidated Statements of Cash Flows as restricted cash, and included in prepaid expenses and other assets in the Consolidated Statements of Financial Condition was $1.1 million and $1.2 million, respectively. The Company is exposed to credit risk in the event a counterparty does not fulfill its obligation to complete a transaction or if there is a miscommunication or other error in executing a matched principal transaction. Pursuant to the terms of the securities clearing agreements, each third-party clearing broker has the right to charge the Company for any losses they suffer resulting from a counterparty’s failure on any of the Company’s trades. The Company did not record any liabilities or losses with regard to this right for the years ended December 31, 2018, 2017 and 2016. In the normal course of business, the Company enters into contracts that contain a variety of representations, warranties and general indemnifications. The Company’s maximum exposure under these arrangements is unknown, as this would involve future claims that may be made against the Company that have not yet occurred. However, based on experience, the Company expects the risk of loss to be remote.

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment and Geographic Information	13. Segment and Geographic Information The Company operates an electronic multi-party platform for the trading of fixed-income securities and provides related data, analytics, compliance tools and post-trade services. The Company’s operations constitute a single business segment because of the highly integrated nature of these products and services, of the financial markets in which the Company competes and of the Company’s worldwide business activities. The Company believes that results by geographic region or client sector are not necessarily meaningful in understanding its business. For the years ended December 31, 2018, 2017 and 2016, the U.K. was the only individual foreign country in which the Company had a subsidiary that accounted for 10% or more of the total revenues or total long-lived assets. Revenues and long-lived assets are attributed to geographic area based on the location of the particular subsidiary. Long-lived assets are defined as furniture, equipment, leasehold improvements and capitalized software Year Ended December 31, 2018 2017 2016 (In thousands) Revenues United States $ 367,373 $ 332,982 $ 312,304 United Kingdom 66,241 58,991 53,865 Other 1,951 1,449 1,561 Total $ 435,565 $ 393,422 $ 367,730 As of December 31, 2018 2017 (In thousands) Long-lived assets, as defined United States $ 55,200 $ 27,990 United Kingdom 7,787 10,532 Other 23 26 Total $ 63,010 $ 38,548

Retirement and Deferred Compens

Retirement and Deferred Compensation Plans	12 Months Ended
	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Retirement and Deferred Compensation Plans	14. Retirement and Deferred Compensation Plans The Company, through its U.S. and U.K. subsidiaries, offers its employees the opportunity to invest in defined contribution plans. For the years ended December 31, 2018, 2017 and 2016, the Company contributed $2.6 million, $1.8 million and $1.9 million, respectively, to the plans. The Company offers a non-qualified deferred cash incentive plan to certain officers and other employees. Under the plan, eligible employees may defer up to 100% of their annual cash incentive pay. The Company has elected to fund its deferred compensation obligations through a rabbi trust. The rabbi trust is subject to creditor claims in the event of insolvency but such assets are not available for general corporate purposes. Assets held in the rabbi trust are invested in mutual funds, as selected by the participants, which are designated as trading securities and carried at fair value. As of December 31, 2018 and 2017, the fair value of the mutual fund investments and deferred compensation obligations were $4.1 million and $3.2 million, respectively. Changes in the fair value of securities held in the rabbi trust and offsetting increases or decreases in the deferred compensation obligation are recognized in other, net in the Company’s Consolidated Statements of Operations. For the years ended December 31, 2018, 2017 and 2016, the trading (losses) gains and changes in deferred compensation liability and expense were $ (

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany transactions and balances have been eliminated.
Accounting Pronouncements, Recently Adopted	Accounting Pronouncements, Recently Adopted In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09”) requiring an entity to recognize revenue for the transfer of goods or services equal to the amount that it expects to be entitled to receive for those goods or services. The standard also requires new disclosure concerning contracts with customers, including the significant judgments made when applying the guidance. The Company adopted ASU 2014-09 effective January 1, 2018 using the modified retrospective transition approach. The adoption of this guidance did not have a material impact on the Company’s Consolidated Financial Statements. Effective January 1, 2017, the Company adopted ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects related to the accounting for share-based payment transactions, including the accounting for income taxes, statutory tax withholding requirements and classification on the statement of cash flows. Beginning January 1, 2017, the tax effects related to share-based payments were recorded through the income tax provision and the Company has elected to account for forfeitures as they occur. The adoption of ASU 2016-09 will cause volatility in the Company’s net income, effective tax rate and diluted earnings per share. The volatility in future periods will depend on the Company’s stock price at the vesting date for restricted stock awards or exercise date for stock options and the number of awards that vest or are exercised in each period. Under the guidance, excess tax benefits from share-based compensation are included as an operating activity in the Company’s Consolidated Statements of Cash Flows. Prior period cash flows have been adjusted to conform to the new presentation.
Accounting Pronouncements, Not Yet Adopted as of December 31, 2018	Accounting Pronouncements, Not Yet Adopted as of December 31, 2018 In February 2016, the FASB issued ASU 2016-02, “Leases” (“ASU 2016-02”) requiring lessees to recognize lease assets and lease liabilities on the balance sheet for those leases previously classified as operating leases with lease terms greater than 12 months. ASU 2016-02 was effective for the Company beginning January 1, 2019. The Company expects to record new right-of-use assets of approximately $80.0 million, eliminate deferred rent of approximately $11.0 million and record lease liabilities associated with the future minimum payments required under operating leases of approximately $91.0 million. The presentation of occupancy expense and the pattern of expense recognition within the Consolidated Statements of Operations and Consolidated Statements of Cash Flows is expected to be consistent with the current lease accounting guidance. In January 2017, the FASB issued ASU 2017-04, “Intangibles-Goodwill and Other” (“ASU 2017-04”). ASU 2017-04 simplifies the testing for goodwill impairment. The guidance will be effective for the Company beginning January 1, 2020 and early adoption is permitted and should be applied prospectively. The adoption of this guidance is not expected to have a material effect on the Company’s Consolidated Financial Statements.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents includes cash and money market instruments that are primarily maintained at one major global bank. Given this concentration, the Company is exposed to certain credit risk in relation to its deposits at this bank. The Company defines cash equivalents as short-term interest-bearing investments with maturities at the time of purchase of three months or less.
Investments	Investments The Company determines the appropriate classification of securities at the time of purchase which are recorded in the Consolidated Statements of Financial Condition on the trade date. Securities are classified as available-for-sale or trading. The Company’s available-for-sale investments are comprised of investment grade corporate debt securities. Available-for-sale investments are carried at fair value with the unrealized gains or losses reported in accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. Trading investments include investment grade corporate debt securities and U.S. Treasuries and are carried at fair value, with realized and unrealized gains or losses included in other income in the Consolidated Statements of Operations. The Company assesses whether an other-than-temporary impairment loss on the available-for-sale investments has occurred due to declines in fair value or other market conditions. The portion of an other-than-temporary impairment related to credit loss is recorded as a charge in the Consolidated Statements of Operations. The remainder is recognized in accumulated other comprehensive loss if the Company does not intend to sell the security and it is more likely than not that the Company will not be required to sell the security prior to recovery. No charges for other-than-temporary losses were recorded during the years ended December 31, 2018, 2017 and 2016.
Fair Value Financial Instruments	Fair Value Financial Instruments Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” A three-tiered hierarchy for determining fair value has been established that prioritizes inputs to valuation techniques used in fair value calculations. The three levels of inputs are defined as Level 1 (unadjusted quoted prices for identical assets or liabilities in active markets), Level 2 (inputs that are observable in the marketplace other than those inputs classified in Level 1) and Level 3 (inputs that are unobservable in the marketplace). The Company’s financial assets and liabilities measured at fair value on a recurring basis consist of its money market funds, securities available-for-sale, trading securities and foreign currency forward contracts. All other financial instruments are short-term in nature and the carrying amount is reported on the Consolidated Statements of Financial Condition at approximate fair value.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts All accounts receivable have contractual maturities of less than one year and are derived from trading-related fees and commissions and revenues from products and services. The Company continually monitors collections and payments from its customers and maintains an allowance for doubtful accounts. The allowance for doubtful accounts is based upon the historical collection experience and specific collection issues that have been identified. Additions to the allowance for doubtful accounts are charged to bad debt expense, which is included in general and administrative expense in the Company’s Consolidated Statements of Operations. The allowance for doubtful accounts was $0.1 million, $0.2 million and $0.1 million as of December 31, 2018, 2017 and 2016, respectively. The provision for bad debts was $0.2 million, $0.4 million and $0.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. Write-offs and other charges against the allowance for doubtful accounts were $0.2 million, $0.1 million and $0.1 million for the years ended December 31, 2018, 2017 and 2016, respectively.
Depreciation and Amortization	Depreciation and Amortization Fixed assets are carried at cost less accumulated depreciation. The Company uses the straight-line method of depreciation over three to seven years. The Company amortizes leasehold improvements on a straight-line basis over the lesser of the life of the improvement or the remaining term of the lease.
Software Development Costs	Software Development Costs The Company capitalizes certain costs associated with the development of internal use software, including among other items, employee compensation and related benefits and third party consulting costs at the point at which the conceptual formulation, design and testing of possible software project alternatives have been completed. Once the product is ready for its intended use, such costs are amortized on a straight-line basis over three years. The Company reviews the amounts capitalized for impairment whenever events or changes in circumstances indicate that the carrying amounts of the assets may not be recoverable.
Cash Provided as Collateral	Cash Provided as Collateral Cash is provided as collateral for broker-dealer clearing accounts. Cash provided as collateral is included in prepaid expenses and other assets in the Consolidated Statements of Financial Condition.
Foreign Currency Translation and Forward Contracts	Foreign Currency Translation and Forward Contracts Assets and liabilities denominated in foreign currencies are translated using exchange rates at the end of the period; revenues and expenses are translated at average monthly rates. Gains and losses on foreign currency translation are a component of accumulated other comprehensive loss in the Consolidated Statements of Financial Condition. Transaction gains and losses are recorded in general and administrative expense in the Consolidated Statements of Operations. The Company enters into foreign currency forward contracts to hedge its net investment in its U.K. subsidiaries. Gains and losses on these transactions are included in accumulated other comprehensive loss in the Consolidated Statements of Financial Condition.
Revenue Recognition	Revenue Recognition On January 1, 2018, the Company adopted ASU 2014-09 using the modified retrospective approach. The adoption of ASU 2014-09 did not have a material impact on the measurement or recognition of revenue in any prior or current reporting periods. The Company’s classification of revenues in the Consolidated Statements of Operations represents revenues from contracts with customers disaggregated by type of revenue. The Company has four revenue streams as described below. Commission Revenue. The Company charges its broker-dealer clients variable transaction fees for trades executed on its platform and, under certain plans, distribution fees or monthly minimum fees to use the platform for a particular product area. Variable transaction fees are generally calculated as a percentage of the notional dollar volume of bonds traded on the platform and vary based on the type, size, yield and maturity of the bond traded. Under the Company’s disclosed trading transaction fee plans, bonds that are more actively traded or that have shorter maturities generally generate lower commissions, while bonds that are less actively traded or that have longer maturities generally command higher commissions. Variable transaction fees, distribution fees and unused monthly fee commitments are invoiced and recorded on a monthly basis. For trades that the Company executes between and among institutional investor and broker-dealer clients on a matched principal basis by serving as counterparty to both the buyer and the seller, the Company earns its commission through the difference in price between the two trades. The commission is collected upon settlement of the trade, which typically occurs within one to two trading days after the trade date. The following table presents commission revenue by fee type for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Commission revenue by fee type Variable transaction fees Disclosed trading $ 228,004 $ 234,143 $ 230,319 Open Trading - matched principal trading 65,932 45,660 37,747 Total variable transaction fees 293,936 279,803 268,066 Distribution fees and unused minimum fees 96,898 75,479 64,241 Total commissions $ 390,834 $ 355,282 $ 332,307 Information services – Information services includes data licensed to the Company’s broker-dealer clients, institutional investor clients and data-only subscribers; professional and consulting services; technology software licenses; and maintenance and support services. The nature and timing of each performance obligation may vary as these contracts are either subscription based services transferred over time or one-time services that are transferred at a point in time. Revenues for services transferred over time are recognized ratably over the contract period as the Company’s performance obligation is met whereas revenues for services transferred at a point in time are recognized in the period the services are provided. Customers are generally billed monthly, quarterly, or annually; revenues billed in advance are deferred and recognized ratably over the contract period. The following table presents information services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Information services revenue by timing of recognition Services transferred over time $ 27,475 $ 25,242 $ 22,011 Services transferred at a point in time 752 564 1,258 Total information services revenues $ 28,227 $ 25,806 $ 23,269 Post-trade services – Post-trade services revenue is generated from regulatory transaction reporting, trade publication and trade matching services. Customers are generally billed monthly in arrears and revenue is recognized in the period transactions are processed. Revenues billed in advance are deferred and recognized ratably over the contract period. The Company also generates one-time implementation fees for onboarding clients which are invoiced and recognized in the period the implementation is completed. The following table presents post-trade services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Post-trade services revenue by timing of recognition Services transferred over time $ 15,013 $ 9,657 $ 10,812 Services transferred at a point in time 333 1,433 — Total post-trade services revenues $ 15,346 $ 11,090 $ 10,812 Other revenues – Other revenues primarily includes revenue from telecommunications line charges to broker-dealer clients. Contract liabilities consist of deferred revenues that the Company records when cash payments are received or due in advance of services to be performed. The revenue recognized from contract liabilities and the remaining balance is shown below: December 31, 2017 Payments received in advance of services to be performed Revenue recognized for services performed during the period Foreign Currency Translation December 31, 2018 (In thousands) Information services $ 1,763 $ 7,109 $ (6,913 ) $ — $ 1,959 Post-trade services 897 11,566 (11,561 ) (51 ) 851 Total deferred revenue $ 2,660 $ 18,675 $ (18,474 ) $ (51 ) $ 2,810 The majority of the Company’s contracts are short-term in nature with durations of less than one-year. For contracts extending beyond one year, the aggregate amount of the transaction price allocated to remaining performance obligations was $6.3 million as of December 31, 2018. The Company expects to recognize revenue associated with the remaining performance obligations over the next 18 months.
Stock-Based Compensation	Stock-Based Compensation The Company measures and recognizes compensation expense for all share-based payment awards based on their estimated fair values measured as of the grant date. These costs are recognized as an expense in the Consolidated Statements of Operations over the requisite service period, which is typically the vesting period, with an offsetting increase to additional paid-in capital. Effective upon the Company’s adoption of ASU 2016-09 on January 1, 2017, the Company accounts for forfeitures as they occur. Prior to the adoption of ASU 2016-09, expected forfeitures were included in determining share-based compensation expense.
Income Taxes	Income Taxes Income taxes are accounted for using the asset and liability method. Deferred income taxes reflect the net tax effects of temporary differences between the financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when such differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance is recognized against deferred tax assets if it is more likely than not that such assets will not be realized in future years. The Company recognizes interest and penalties related to unrecognized tax benefits in general and administrative expenses in the Consolidated Statements of Operations. Effective upon the Company’s adoption of ASU 2016-09 all tax effects related to share-based payments are recorded through tax expense in the periods during which the awards are exercised or vest. On December 22, 2017, the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”) to address the application of U.S. generally accepted accounting principles (“GAAP”) related to the enactment of the Tax Cuts and Jobs Act (the “Tax Act”). SAB 118 allowed the Company to record a provisional amount when it did not have the necessary information available, prepared, or analyzed in reasonable detail to complete its accounting for the change in the tax law. The Company has completed its analysis within the one-year measurement period in accordance with SAB 118.
Business Combinations, Goodwill and Intangible Assets	Business Combinations, Goodwill and Intangible Assets Business combinations are accounted for under the purchase method of accounting. The total cost of an acquisition is allocated to the underlying net assets based on their respective estimated fair values. The excess of the purchase price over the estimated fair values of the net assets acquired is recorded as goodwill. Determining the fair value of certain assets acquired and liabilities assumed is judgmental in nature and often involves the use of significant estimates and assumptions, including assumptions with respect to future cash flows, discount rates, growth rates and asset lives. The Company operates as a single reporting unit. Subsequent to an acquisition, goodwill no longer retains its identification with a particular acquisition, but instead becomes identifiable with the entire reporting unit. As a result, all of the fair value of the Company is available to support the value of goodwill. An impairment review of goodwill is performed on an annual basis, at year-end, or more frequently if circumstances change. Intangible assets with definite lives, including purchased technologies, customer relationships and other intangible assets, are amortized on a straight-line basis over their estimated useful lives, ranging from three to 15 years. Intangible assets are assessed for impairment when events or circumstances indicate the existence of a possible impairment.
Earnings Per Share	Earnings Per Share Basic earnings per share is computed by dividing the net income attributable to common stock by the weighted-average number of shares of common stock outstanding during the period. For purposes of computing diluted earnings per share, the weighted-average shares outstanding of common stock reflects the dilutive effect that could occur if convertible securities or other contracts to issue common stock were converted into or exercised for common stock.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Reclassifications	Reclassifications Certain reclassifications have been made to the prior period’s Consolidated Financial Statements in order to conform to the current year presentation. The Company revised the format of the Consolidated Statements of Operations to separately present non-operating activities. Such activities include investment income, unrealized and realized gains (losses) on trading securities, foreign exchange gains (losses), investment advisory fees and other miscellaneous non-operating activities. Accordingly, the Company reclassified these amounts from the various revenue and expense line items to Other income (expense).

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Commission Revenue by Fee Type	The following table presents commission revenue by fee type for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Commission revenue by fee type Variable transaction fees Disclosed trading $ 228,004 $ 234,143 $ 230,319 Open Trading - matched principal trading 65,932 45,660 37,747 Total variable transaction fees 293,936 279,803 268,066 Distribution fees and unused minimum fees 96,898 75,479 64,241 Total commissions $ 390,834 $ 355,282 $ 332,307
Summary of Information Services Revenue by Timing of Recognition	The following table presents information services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Information services revenue by timing of recognition Services transferred over time $ 27,475 $ 25,242 $ 22,011 Services transferred at a point in time 752 564 1,258 Total information services revenues $ 28,227 $ 25,806 $ 23,269
Summary of Post-Trade Services Revenue by Timing of Recognition	The following table presents post-trade services revenue by timing of recognition for the three years ended December 31, 2018: Year Ended December 31, 2018 2017 2016 (In thousands) Post-trade services revenue by timing of recognition Services transferred over time $ 15,013 $ 9,657 $ 10,812 Services transferred at a point in time 333 1,433 — Total post-trade services revenues $ 15,346 $ 11,090 $ 10,812
Summary of Revenue Recognized from Contract Liabilities and Remaining Balance	The revenue recognized from contract liabilities and the remaining balance is shown below: December 31, 2017 Payments received in advance of services to be performed Revenue recognized for services performed during the period Foreign Currency Translation December 31, 2018 (In thousands) Information services $ 1,763 $ 7,109 $ (6,913 ) $ — $ 1,959 Post-trade services 897 11,566 (11,561 ) (51 ) 851 Total deferred revenue $ 2,660 $ 18,675 $ (18,474 ) $ (51 ) $ 2,810

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Valuation of Company's Assets and Liabilities Measured at Fair Value	The following table summarizes the valuation of the Company’s assets and liabilities measured at fair value as categorized based on the hierarchy described in Note 2. Level 1 Level 2 Level 3 Total (In thousands) As of December 31, 2018 Money market funds $ 112,529 $ — $ — $ 112,529 Securities available-for-sale Corporate debt — 146,966 — 146,966 Trading securities Corporate debt — 71,861 — 71,861 U.S. Treasuries — 17,178 — 17,178 Mutual funds held in rabbi trust — 4,100 — 4,100 Foreign currency forward position — (1,021 ) — (1,021 ) Total $ 112,529 $ 239,084 $ — $ 351,613 As of December 31, 2017 Money market funds $ 88,562 $ — $ — $ 88,562 Securities available-for-sale Corporate debt — 145,052 — 145,052 Trading securities Corporate debt — 91,302 — 91,302 Mutual funds held in rabbi trust — 3,167 — 3,167 Foreign currency forward position — (702 ) — (702 ) Total $ 88,562 $ 238,819 $ — $ 327,381
Summary of Foreign Currency Forward Contracts	A summary of the foreign currency forward position is as follows: As of December 31, 2018 2017 (In thousands) Notional value $ 106,306 $ 84,422 Fair value of notional 107,327 85,124 Fair value of the (liability) $ (1,021 ) $ (702 )
Summary of Company's Investments	The following is a summary of the Company’s investments: Amortized cost Gross unrealized gains Gross unrealized losses Estimated fair value (In thousands) As of December 31, 2018 Securities available-for-sale Corporate debt $ 147,556 $ 27 $ (617 ) $ 146,966 Trading securities Corporate debt 72,274 8 (421 ) 71,861 U.S. Treasuries 16,953 225 — 17,178 Mutual funds held in rabbi trust 4,347 — (247 ) 4,100 Total trading securities 93,574 233 (668 ) 93,139 Total investments $ 241,130 $ 260 $ (1,285 ) $ 240,105 As of December 31, 2017 Securities available-for-sale Corporate debt $ 145,526 $ 9 $ (483 ) $ 145,052 Trading securities Corporate debt 91,578 30 (306 ) 91,302 Mutual funds held in rabbi trust 2,729 438 — 3,167 Total trading securities 94,307 468 (306 ) 94,469 Total investments $ 239,833 $ 477 $ (789 ) $ 239,521
Summary of Fair Value of Investments Based upon Contractual Maturities	The following table summarizes the fair value of the investments based upon the contractual maturities: As of December 31, 2018 2017 (In thousands) Less than one year $ 134,255 $ 130,738 Due in 1 - 5 years 105,850 108,783 Total $ 240,105 $ 239,521
Fair Values and Unrealized Losses on Corporate Debt Investments	The following table provides fair values and unrealized losses on corporate debt investments and by the aging of the securities' continuous unrealized loss position as of December 31, 2018 and 2017 respectively: Less than Twelve Months Twelve Months or More Total Estimated fair value Gross unrealized losses Estimated fair value Gross unrealized losses Estimated fair value Gross unrealized losses (In thousands) As of December 31, 2018 Corporate debt $ 80,282 $ (256 ) $ 87,028 $ (782 ) $ 167,310 $ (1,038 ) As of December 31, 2017 Corporate debt $ 177,114 $ (536 ) $ 26,476 $ (253 ) $ 203,590 $ (789 )

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Summary of Company's Intangible Assets	Goodwill and intangible assets with indefinite lives was $59.7 million as of both December 31, 2018 and 2017. Intangible assets that are subject to amortization, including the related accumulated amortization, are comprised of the following: December 31, 2018 December 31, 2017 Cost Accumulated amortization Net carrying amount Cost Accumulated amortization Net carrying amount (In thousands) Technology $ 5,770 $ (5,770 ) $ — $ 5,770 $ (5,770 ) $ — Customer relationships 5,634 (2,672 ) 2,962 5,647 (2,301 ) 3,346 Non-competition agreements 380 (380 ) — 380 (380 ) — Tradenames 370 (370 ) — 370 (370 ) — Total $ 12,154 $ (9,192 ) $ 2,962 $ 12,167 $ (8,821 ) $ 3,346

Capitalized Software, Furnitu_2

Capitalized Software, Furniture, Equipment and Leasehold Improvements (Tables)	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Capitalized Software Development Costs, Furniture, Equipment and Leasehold Improvements, Net of Accumulated Depreciation and Amortization	Capitalized software development costs, furniture, equipment and leasehold improvements, net of accumulated depreciation and amortization, are comprised of the following: As of December 31, 2018 2017 (In thousands) Software development costs $ 97,113 $ 86,129 Computer hardware and related software 42,705 35,945 Office hardware 5,909 4,575 Furniture and fixtures 5,385 2,347 Leasehold improvements 32,527 11,016 183,639 140,012 Accumulated depreciation and amortization (120,629 ) (101,464 ) Total $ 63,010 $ 38,548

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	The provision for income taxes consists of the following: Year Ended December 31, 2018 2017 2016 (In thousands) Current: Federal $ 31,617 $ 36,045 $ 45,455 State and local 5,928 3,848 7,087 Foreign 8,862 7,234 6,166 Total current provision 46,407 47,127 58,708 Deferred: Federal (1,416 ) 6,171 5,884 State and local (272 ) 661 1,141 Foreign 515 (280 ) (303 ) Total deferred provision (1,173 ) 6,552 6,722 Provision for income taxes $ 45,234 $ 53,679 $ 65,430
Difference Between the Company's Reported Provision for Income Taxes and the U.S. Federal Statutory Rate	The difference between the Company’s reported provision for income taxes and the U.S. federal statutory rate of 21% is as follows: Year Ended December 31, 2018 2017 2016 U.S. federal tax at statutory rate 21.0 % 35.0 % 35.0 % State and local taxes - net of federal benefit 2.0 1.5 2.9 Credits and deductions related to research activities (0.3 ) (1.2 ) (1.3 ) Foreign rate differential benefit (0.5 ) (2.9 ) (2.3 ) Excess tax benefit from stock-based compensation (2.1 ) (11.6 ) — Tax Cuts and Jobs Act provisional tax charge (0.2 ) 5.8 — Other, net 0.8 — (0.2 ) Provision for income taxes 20.7 % 26.6 % 34.1 %
Summary of Company's Net Deferred Tax Assets	The following is a summary of the Company’s net deferred tax assets: As of December 31, 2018 2017 (In thousands) Deferred tax assets: U.S. net operating loss carryforwards $ 603 $ 872 Capital loss carryforwards — 4,648 Stock compensation expense 4,967 4,534 Other 2,966 1,143 Total deferred tax assets 8,536 11,197 Valuation allowance — (4,648 ) Net deferred tax assets 8,536 6,549 Deferred tax liabilities: Depreciation and amortization (1,847 ) (1,369 ) Capitalized software development costs (3,776 ) (3,479 ) Intangible assets (898 ) (967 ) Deferred tax assets, net $ 2,015 $ 734
Summary of Changes in Valuation Allowance	A summary of the changes in the valuation allowance is as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Valuation allowance at beginning of year $ 4,648 $ 7,235 $ 7,294 (Decrease) to valuation allowance attributable to: Expiration of capital loss carryforwards (4,648 ) — — Federal and state tax rate changes — (2,587 ) (59 ) Valuation allowance at end of year $ — $ 4,648 $ 7,235
Reconciliation of the Unrecognized Tax Benefits	A reconciliation of the unrecognized tax benefits is as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Balance at beginning of year $ 2,650 $ 29 $ 265 Additions attributable to state and local apportionment 2,068 2,650 — Reductions for tax positions of prior years — (29 ) (236 ) Balance at end of year $ 4,718 $ 2,650 $ 29

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Summary of the Change in the Company's Outstanding Shares of Common Stock	Year Ended December 31, 2018 2017 2016 (In thousands) Outstanding shares of voting common stock at the beginning of year 37,621 37,544 37,409 Exercise of stock options 121 262 181 Issuance of restricted stock, net of shares withheld for withholding tax payments and cancellations 22 39 104 Repurchases (124 ) (224 ) (150 ) Outstanding shares of voting common stock at the end of year 37,640 37,621 37,544

Stock-Based Compensation Plans

Stock-Based Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation Expense	Total stock-based compensation expense was as follows: Year Ended December 31, 2018 2017 2016 (In thousands) Employees: Restricted stock and performance shares $ 12,559 $ 11,566 $ 12,459 Stock options 2,193 1,882 1,143 14,752 13,448 13,602 Non-employee directors: Restricted stock 1,098 973 909 Total stock-based compensation $ 15,850 $ 14,421 $ 14,511
Assumptions Used for the Black-Scholes Option-Pricing Model to Determine the Per Share Weighted Average Fair Value for Options Granted	The following table represents the assumptions used for the Black-Scholes option-pricing model to determine the per share weighted-average fair value for options granted for the three years ended December 31, 2018: 2018 2017 2016 Expected life (years) 5.0 5.0 6.0 Risk-free interest rate 2.2 % 1.9 % 1.9 % Expected volatility 26.9 % 28.0 % 33.0 % Expected dividend yield 0.8 % 0.8 % 1.0 %
Stock Option Activity	The following table reports stock option activity during the three years ended December 31, 2018 and the intrinsic value as of December 31, 2018: Number of Shares Weighted-Average Exercise Price ($) Remaining Contractual Term Intrinsic Value ($) (In thousands) Outstanding at December 31, 2015 939,036 $ 23.83 Granted 112,988 102.40 Canceled (874 ) 101.77 Exercised (195,410 ) 12.35 Outstanding at December 31, 2016 855,740 36.80 Granted 54,838 156.85 Canceled — — Exercised (380,967 ) 11.26 Outstanding at December 31, 2017 529,611 67.60 Granted 168,217 261.19 Canceled (1,676 ) 142.69 Exercised (120,588 ) 24.66 $ 21,823 Outstanding at December 31, 2018 575,564 132.93 3.2 53,651 Exercisable at December 31, 2018 203,564 53.49 2.1 32,126
Summary of Performance of Share Activity for Annual Awards	The following table reports performance share activity for annual awards for the three years ended December 31, 2018: Performance year: 2018 2017 2016 Share pay-out plan 10,479 12,971 15,390 Actual share pay-out in following year 10,479 8,094 21,423 Weighted average fair value per share on grant date $ 202.04 $ 155.53 $ 101.77
Restricted Stock and Performance Share Activity	The following table reports restricted stock and performance share activity during the three years ended December 31, 2018: Number of Restricted Shares Weighted-Average Grant Date Fair Value Outstanding at December 31, 2015 432,138 $ 56.24 Granted 95,419 Performance share pay-out 61,936 Canceled (12,786 ) Vested (192,729 ) Outstanding at December 31, 2016 383,978 $ 71.50 Granted 61,434 Performance share pay-out 21,422 Canceled (4,590 ) Vested (142,645 ) Outstanding at December 31, 2017 319,599 $ 88.77 Granted 59,179 Performance share pay-out 8,094 Canceled (4,046 ) Vested (110,956 ) Outstanding at December 31, 2018 271,870 $ 112.47

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Basic and Diluted Weighted Average Shares Outstanding Used to Compute Earnings Per Share	The following table sets forth basic and diluted weighted average shares outstanding used to compute earnings per share: Year Ended December 31, 2018 2017 2016 (In thousands) Basic weighted average shares outstanding 36,958 36,864 36,844 Dilutive effect of stock options and restricted stock 897 1,174 894 Diluted weighted average shares outstanding 37,855 38,038 37,738

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Summary of Minimum Rental Commitments under Operating Leases	Minimum rental commitments as of December 31, 2018 under such operating leases were as follows (in thousands): 2019 $ 9,764 2020 10,919 2021 10,114 2022 9,067 2023 8,738 2024 and thereafter 95,467 $ 144,069

Segment and Geographic Inform_2

Segment and Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Summary of Revenue and Long-lived Assets	Information regarding revenue for the three years ended December 31, 2018, 2017 and 2016 and long-lived assets as of December 31, 2018 and 2017 follows: Year Ended December 31, 2018 2017 2016 (In thousands) Revenues United States $ 367,373 $ 332,982 $ 312,304 United Kingdom 66,241 58,991 53,865 Other 1,951 1,449 1,561 Total $ 435,565 $ 393,422 $ 367,730 As of December 31, 2018 2017 (In thousands) Long-lived assets, as defined United States $ 55,200 $ 27,990 United Kingdom 7,787 10,532 Other 23 26 Total $ 63,010 $ 38,548

Organization and Principal Bu_2

Organization and Principal Business Activity - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018Institutional_Investor_and_Broker-dealer_Firm
Accounting Policies [Line Items]
Date of incorporation	Apr. 11, 2000
Minimum [Member]
Accounting Policies [Line Items]
Number of institutional investor and broker-dealer firms	1,500

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018USD ($)Revenue	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Significant Accounting Policies [Line Items]
Future minimum payments required under operating leases	$ 144,069,000
Maximum maturity period for classification of investments as cash equivalents	3 months
Investments other-than-temporary losses	$ 0	$ 0	$ 0
Allowance for doubtful accounts	80,000	178,000	100,000
Provision for bad debts	200,000	400,000	200,000
Write-offs and other charges against the allowance for doubtful accounts	$ 200,000	$ 100,000	$ 100,000
Number of revenue streams | Revenue	4
Description of commission revenue	For trades that the Company executes between and among institutional investor and broker-dealer clients on a matched principal basis by serving as counterparty to both the buyer and the seller, the Company earns its commission through the difference in price between the two trades.
Settlement days of bond transaction	Within one to two trading days
Maximum [Member]
Significant Accounting Policies [Line Items]
Contractual maturities accounts receivable	1 year
Estimated useful life of fixed assets	7 years
Maximum [Member] | Business Combinations [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	15 years
Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life of fixed assets	3 years
Minimum [Member] | Business Combinations [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	3 years
Minimum [Member] | Internally Developed Software [Member]
Significant Accounting Policies [Line Items]
Estimated life of intangible assets	3 years
ASU 2016-02
Significant Accounting Policies [Line Items]
Future minimum payments required under operating leases	$ 91,000,000
Operating lease, right-of-use assets	80,000,000
Deferred rent	$ 11,000,000

Significant Accounting Polici_5

Significant Accounting Policies - Summary of Commission Revenue by Fee Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commission revenue by fee type
Revenues	$ 435,565	$ 393,422	$ 367,730
Commissions [Member]
Commission revenue by fee type
Disclosed trading	228,004	234,143	230,319
Open Trading - matched principal trading	65,932	45,660	37,747
Total variable transaction fees	293,936	279,803	268,066
Distribution fees and unused minimum fees	96,898	75,479	64,241
Revenues	$ 390,834	$ 355,282	$ 332,307

Significant Accounting Polici_6

Significant Accounting Policies - Summary of Information Services Revenue by Timing of Recognition (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Revenues	$ 435,565	$ 393,422	$ 367,730
Information Services [Member]
Significant Accounting Policies [Line Items]
Revenues	28,227	25,806	23,269
Information Services [Member] | Transferred over Time [Member]
Significant Accounting Policies [Line Items]
Revenues	27,475	25,242	22,011
Information Services [Member] | Transferred at a Point in Time [Member]
Significant Accounting Policies [Line Items]
Revenues	$ 752	$ 564	$ 1,258

Significant Accounting Polici_7

Significant Accounting Policies - Summary of Post-Trade Services Revenue by Timing of Recognition (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Significant Accounting Policies [Line Items]
Revenues	$ 435,565	$ 393,422	$ 367,730
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Revenues	15,346	11,090	10,812
Post-trade Services [Member] | Transferred over Time [Member]
Significant Accounting Policies [Line Items]
Revenues	15,013	9,657	$ 10,812
Post-trade Services [Member] | Transferred at a Point in Time [Member]
Significant Accounting Policies [Line Items]
Revenues	$ 333	$ 1,433

Significant Accounting Polici_8

Significant Accounting Policies - Summary of Revenue Recognized from Contract Liabilities and Remaining Balance (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	$ 2,660
Payments received in advance of services to be performed	18,675
Revenue recognized for services performed during the period	(18,474)
Foreign Currency Translation	(51)
Deferred revenues, ending balance	2,810
Information Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	1,763
Payments received in advance of services to be performed	7,109
Revenue recognized for services performed during the period	(6,913)
Deferred revenues, ending balance	1,959
Post-trade Services [Member]
Significant Accounting Policies [Line Items]
Deferred revenues, beginning balance	897
Payments received in advance of services to be performed	11,566
Revenue recognized for services performed during the period	(11,561)
Foreign Currency Translation	(51)
Deferred revenues, ending balance	$ 851

Significant Accounting Polici_9

Significant Accounting Policies - Additional Information (Detail 1) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2019-01-01 $ in Millions	Dec. 31, 2018USD ($)
Significant Accounting Policies [Line Items]
Aggregate amount of transaction price allocated to remaining performance obligations	$ 6.3
Expected time to recognize revenue for remaining performance obligation	18 months

Net Capital Requirements - Addi

Net Capital Requirements - Additional Information (Detail) $ in Millions	Dec. 31, 2018USD ($)
Brokers And Dealers [Abstract]
Aggregate net capital and financial resources in excess of required level	$ 162.8
Aggregate net capital and financial resources, minimum capital requirement	$ 15

Fair Value Measurements - Valua

Fair Value Measurements - Valuation of Company's Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	$ 112,529	$ 88,562
Trading securities	93,139	94,469
Assets Fair Value Total	351,613	327,381
Corporate Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale	146,966	145,052
Trading securities	71,861	91,302
U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	17,178
Mutual Funds Held In Rabbi Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	4,100	3,167
Foreign Currency Forward Position [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign currency forward position	(1,021)	(702)
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Money market funds	112,529	88,562
Assets Fair Value Total	112,529	88,562
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Fair Value Total	239,084	238,819
Level 2 [Member] | Corporate Debt [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Securities available-for-sale	146,966	145,052
Trading securities	71,861	91,302
Level 2 [Member] | U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	17,178
Level 2 [Member] | Mutual Funds Held In Rabbi Trust [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Trading securities	4,100	3,167
Level 2 [Member] | Foreign Currency Forward Position [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Foreign currency forward position	$ (1,021)	$ (702)

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Hedge derivative expiration period	1 month
Proceeds from the sales and maturities of securities available-for-sale	$ 409.3	$ 219.2	$ 69.5

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Foreign Currency Forward Contracts (Detail) - Foreign Currency Forward Position [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Notional value	$ 106,306	$ 84,422
Fair value of notional	107,327	85,124
Fair value of the (liability)	$ (1,021)	$ (702)

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Company's Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	$ 93,574	$ 94,307
Trading securities, Gross unrealized gains	233	468
Trading securities, Gross unrealized losses	(668)	(306)
Trading securities, Estimated fair value	93,139	94,469
Investments, Amortized cost	241,130	239,833
Investments, Gross unrealized gains	260	477
Investments, Gross unrealized losses	(1,285)	(789)
Investments, Estimated fair value	240,105	239,521
Corporate Debt [Member]
Schedule Of Available For Sale Securities [Line Items]
Securities available-for-sale, Amortized cost	147,556	145,526
Securities available-for-sale, Gross unrealized gains	27	9
Securities available-for-sale, Gross unrealized losses	(617)	(483)
Securities available-for-sale, Estimated fair value	146,966	145,052
Trading securities, Amortized cost	72,274	91,578
Trading securities, Gross unrealized gains	8	30
Trading securities, Gross unrealized losses	(421)	(306)
Trading securities, Estimated fair value	71,861	91,302
U.S. Treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	16,953
Trading securities, Gross unrealized gains	225
Trading securities, Estimated fair value	17,178
Mutual Funds Held In Rabbi Trust [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	4,347	2,729
Trading securities, Gross unrealized gains		438
Trading securities, Gross unrealized losses	(247)
Trading securities, Estimated fair value	$ 4,100	$ 3,167

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Fair Value of Investments Based upon Contractual Maturities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Less than one year	$ 134,255	$ 130,738
Due in 1 - 5 years	105,850	108,783
Total	$ 240,105	$ 239,521

Fair Value Measurements - Fair

Fair Value Measurements - Fair Values and Unrealized Losses on Corporate Debt Investments (Detail) - Corporate Debt [Member] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Less than Twelve Months, Estimated fair value	$ 80,282	$ 177,114
Less than Twelve Months, Gross unrealized losses	(256)	(536)
Twelve Months or More, Estimated fair value	87,028	26,476
Twelve Months or More, Gross unrealized losses	(782)	(253)
Estimated fair value, Total	167,310	203,590
Gross unrealized losses, Total	$ (1,038)	$ (789)

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 62,675	$ 63,059
Amortization expense associated with identifiable intangible assets	400	400	$ 700
Estimated total amortization expense 2019	400
Estimated total amortization expense 2020	400
Estimated total amortization expense 2021	400
Estimated total amortization expense 2022	400
Estimated total amortization expense 2023	300
Indefinite-lived Intangible Assets [Member]
Goodwill [Line Items]
Goodwill and intangible assets with indefinite lives	$ 59,700	$ 59,700

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Summary of Company's Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Cost	$ 12,154	$ 12,167
Accumulated amortization	(9,192)	(8,821)
Net carrying amount	2,962	3,346
Technology [Member]
Finite Lived Intangible Assets [Line Items]
Cost	5,770	5,770
Accumulated amortization	(5,770)	(5,770)
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Cost	5,634	5,647
Accumulated amortization	(2,672)	(2,301)
Net carrying amount	2,962	3,346
Non-Competition Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Cost	380	380
Accumulated amortization	(380)	(380)
Tradenames - Finite Life [Member]
Finite Lived Intangible Assets [Line Items]
Cost	370	370
Accumulated amortization	$ (370)	$ (370)

Capitalized Software, Furnitu_3

Capitalized Software, Furniture, Equipment and Leasehold Improvements - Capitalized Software Development Costs, Furniture, Equipment and Leasehold Improvements, Net of Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	$ 183,639	$ 140,012
Accumulated depreciation and amortization	(120,629)	(101,464)
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	63,010	38,548
Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	97,113	86,129
Computer Hardware and Related Software [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	42,705	35,945
Office Hardware [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	5,909	4,575
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	5,385	2,347
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Furniture, equipment, leasehold improvements and capitalized software, Gross	$ 32,527	$ 11,016

Capitalized Software, Furnitu_4

Capitalized Software, Furniture, Equipment and Leasehold Improvements - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Software development costs	$ 11.7	$ 13.5

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 31,617	$ 36,045	$ 45,455
State and local	5,928	3,848	7,087
Foreign	8,862	7,234	6,166
Total current provision	46,407	47,127	58,708
Deferred:
Federal	(1,416)	6,171	5,884
State and local	(272)	661	1,141
Foreign	515	(280)	(303)
Total deferred provision	(1,173)	6,552	6,722
Provision for income taxes	$ 45,234	$ 53,679	$ 65,430

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Pre Tax Income [Line Items]
Pre-tax income from U.S. operations	$ 168.5	$ 165.2	$ 161.9
U.S. federal tax at statutory rate	21.00%	35.00%	35.00%
Provisional tax charge recorded due to enactment of Tax Act	$ 11.7
Re-measurement of U.S. deferred tax assets	6.7
Repatriation taxes on accumulated undistributed foreign earnings	5
Reduction in provisional tax charge	$ 0.4
Additional annual limitations	50% or greater change
Percentage of change in ownership	50.00%
Additional annual limitations period	3 years
Capital loss on the sale	$ 20.6
Capital loss carried back	$ 1.2
New York State [Member] | Earliest Tax Year [Member]
Schedule Of Pre Tax Income [Line Items]
Income tax year under examination	2,010
New York State [Member] | Latest Tax Year [Member]
Schedule Of Pre Tax Income [Line Items]
Income tax year under examination	2,015
Foreign Country [Member]
Schedule Of Pre Tax Income [Line Items]
Pre-tax income from foreign operations	$ 49.6	$ 36.6	$ 29.7
US Country [Member]
Schedule Of Pre Tax Income [Line Items]
Net operating loss carryforwards related to prior ownership change	$ 2.9
Net operating loss carryforwards, expiration date	2,021

Income Taxes - Difference Betwe

Income Taxes - Difference Between the Company's Reported Provision for Income Taxes and the U.S. Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S. federal tax at statutory rate	21.00%	35.00%	35.00%
State and local taxes - net of federal benefit	2.00%	1.50%	2.90%
Credits and deductions related to research activities	(0.30%)	(1.20%)	(1.30%)
Foreign rate differential benefit	(0.50%)	(2.90%)	(2.30%)
Excess tax benefit from stock-based compensation	(2.10%)	(11.60%)
Tax Cuts and Jobs Act provisional tax charge	(0.20%)	5.80%
Other, net	0.80%		(0.20%)
Provision for income taxes	20.70%	26.60%	34.10%

Income Taxes - Summary of Compa

Income Taxes - Summary of Company's Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Capital loss carryforwards		$ 4,648
Stock compensation expense	$ 4,967	4,534
Other	2,966	1,143
Total deferred tax assets	8,536	11,197
Valuation allowance		(4,648)	$ (7,235)	$ (7,294)
Net deferred tax assets	8,536	6,549
Deferred tax liabilities:
Depreciation and amortization	(1,847)	(1,369)
Capitalized software development costs	(3,776)	(3,479)
Intangible assets	(898)	(967)
Deferred tax assets, net	2,015	734
US Country [Member]
Deferred tax assets:
U.S. net operating loss carryforwards	$ 603	$ 872

Income Taxes - Summary of Chang

Income Taxes - Summary of Changes in Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Valuation allowance at beginning of year	$ 4,648	$ 7,235	$ 7,294
Expiration of capital loss carryforwards	$ (4,648)
Federal and state tax rate changes		(2,587)	(59)
Valuation allowance at end of year		$ 4,648	$ 7,235

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of the Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 2,650	$ 29	$ 265
Additions attributable to state and local apportionment	2,068	2,650
Reductions for tax positions of prior years		(29)	(236)
Balance at end of year	$ 4,718	$ 2,650	$ 29

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended												12 Months Ended
	Jan. 31, 2019	Sep. 30, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	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, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016	Jan. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized			110,000,000				110,000,000								110,000,000	110,000,000
Common stock entitles															One
Cash dividends declared per common share			$ 0.42	$ 0.42	$ 0.42	$ 0.42	$ 0.33	$ 0.33	$ 0.33	$ 0.33	$ 0.26	$ 0.26	$ 0.26	$ 0.26	$ 1.68	$ 1.32	$ 1.04
Share Repurchase Program [Member]
Class of Stock [Line Items]
Shares repurchase program period		15 months
Shares repurchase program authorized		$ 100,000,000						$ 100,000,000											$ 25,000,000
Shares repurchase program additional authorized amount																		$ 50,000,000
Commencement date		2017-10
Share Repurchase Program [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Shares repurchase program period	2 years
Shares repurchase program authorized	$ 100,000,000
Commencement date	2019-04
Common Stock Non-Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized			10,000,000				10,000,000								10,000,000	10,000,000
Common Stock Voting [Member]
Class of Stock [Line Items]
Common stock, shares authorized			110,000,000				110,000,000								110,000,000	110,000,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of the Companys Change in the Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	37,620,736
Exercise of stock options	120,588	380,967	195,410
Outstanding shares of voting common stock at the end of year	37,639,917	37,620,736
Voting Common Stock [Member]
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	37,621,000	37,544,000	37,409,000
Exercise of stock options	121,000	262,000	181,000
Issuance of restricted stock, net of shares withheld for withholding tax payments and cancellations	22,000	39,000	104,000
Repurchases	(124,000)	(224,000)	(150,000)
Outstanding shares of voting common stock at the end of year	37,640,000	37,621,000	37,544,000

Stock-Based Compensation Plan_2

Stock-Based Compensation Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Apr. 01, 2017	Nov. 30, 2018	Jan. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant under the stock incentive plans				304,965
Exercise price for the shares of the Company's common stock				$ 56.11	$ 40.08	$ 32.24
Grant date fair value				$ 21,823
Fair value assumptions, Dividend yield rate				0.80%	0.80%	1.00%
Closing price of common stock				$ 211.31
Unrecognized compensation costs related to non-vested				$ 8,600
Weighted-average period over which cost is expected to be recognized				2 years 9 months 18 days
Pay-out ranges, Minimum				0.00%
Pay-out ranges, Maximum				150.00%
Restricted Stock and Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs related to non-vested				$ 23,300
Weighted-average period over which cost is expected to be recognized				1 year 8 months 12 days
Employees Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period vested for option grants				1 year
Number of non-option equity instruments granted during the period				989	1,034	1,190
Percentage of shares grant to participants				20.00%
Chief Executive Officer [Member] | Incentive Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock option equity instruments granted during the period		148,524
Grant date fair value		$ 5,500
Share-based compensation arrangement by share-based payment award award vesting date		Nov. 8, 2023
Fair value assumptions, Risk free interest rate		3.10%
Fair value assumptions, Volatility rate		25.90%
Fair value assumptions, Dividend yield rate		0.80%
Share-based compensation arrangement by share-based payment award, options expiry date		May 8, 2024
Chief Executive Officer [Member] | Incentive Stock Options [Member] | Range One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price for the shares of the Company's common stock		$ 257.78
Number of stock option equity instruments granted during the period		69,113
Percentage of fair market value of the common stock on the grant date		125.00%
Chief Executive Officer [Member] | Incentive Stock Options [Member] | Range Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price for the shares of the Company's common stock		$ 278.40
Number of stock option equity instruments granted during the period		79,411
Percentage of fair market value of the common stock on the grant date		135.00%
Chief Executive Officer [Member] | Performance Based Share [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value		$ 5,500
Share-based compensation arrangement by share-based payment award award vesting date		Nov. 8, 2023
Fair value assumptions, Risk free interest rate		3.10%
Fair value assumptions, Volatility rate		26.10%
Fair value assumptions, Dividend yield rate		0.80%
Number of non-option equity instruments granted during the period		37,742
Performance period		2,005
Chief Executive Officer [Member] | Performance Based Share [Member] | Range One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period		17,942
Fair value per share on the grant date		$ 257.78
Percentage of fair market value of the common stock on the grant date		125.00%
Chief Executive Officer [Member] | Performance Based Share [Member] | Range Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of non-option equity instruments granted during the period		19,800
Fair value per share on the grant date		$ 278.40
Percentage of fair market value of the common stock on the grant date		135.00%
Officers and Senior Managers [Member] | Performance Based Share [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Expiration Period	2 years		4 years
Pay-out ranges, Minimum	0.00%		0.00%
Pay-out ranges, Maximum	150.00%		150.00%
Number of non-option equity instruments granted during the period	9,367		33,509
Fair value per share on the grant date	$ 186.74		$ 103.30
Share-based compensation arrangement by share-based payment award, actual share payout percent	38.80%
Share-based compensation arrangement by share-based payment award, actual share payout share	3,634
Estimated share payout percent				106.00%
Officers and Senior Managers [Member] | Performance Based Share [Member] | Share-based Compensation Award, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award award vesting date	Apr. 1, 2020		Jan. 31, 2020
Share-based compensation arrangement by share-based payment award, award vesting rights	50.00%		50.00%
Officers and Senior Managers [Member] | Performance Based Share [Member] | Share-based Compensation Award, Tranche Two [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award award vesting date	Apr. 1, 2021		Jan. 31, 2021
Share-based compensation arrangement by share-based payment award, award vesting rights	50.00%		50.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period vested for option grants				3 years
Options Expiration Period				6 years
Minimum [Member] | Restricted Stock and Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period vested for option grants				3 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period vested for option grants				5 years
Options Expiration Period				10 years
Maximum [Member] | Restricted Stock and Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Period vested for option grants				5 years

Stock-Based Compensation Plan_3

Stock-Based Compensation Plans - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 14,752	$ 13,448	$ 13,602
Employees [Member] | Restricted Stock and Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	12,559	11,566	12,459
Employees [Member] | Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	2,193	1,882	1,143
Non-Employee Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	15,850	14,421	14,511
Non-Employee Directors [Member] | Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation	$ 1,098	$ 973	$ 909

Stock-Based Compensation Plan_4

Stock-Based Compensation Plans - Assumptions Used for the Black-Scholes Option-Pricing Model to Determine the Per Share Weighted Average Fair Value for Options Granted (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected life (years)	5 years	5 years	6 years
Risk-free interest rate	2.20%	1.90%	1.90%
Expected volatility	26.90%	28.00%	33.00%
Expected dividend yield	0.80%	0.80%	1.00%

Stock-Based Compensation Plan_5

Stock-Based Compensation Plans - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	529,611	855,740	939,036
Number of Shares, Granted	168,217	54,838	112,988
Number of Shares, Canceled	(1,676)		(874)
Number of Shares, Exercised	(120,588)	(380,967)	(195,410)
Number of Shares, Ending Balance	575,564	529,611	855,740
Number of Shares, Exercisable	203,564
Weighted Average Exercise Price, Beginning Balance	$ 67.60	$ 36.80	$ 23.83
Weighted Average Exercise Price, Granted	261.19	156.85	102.40
Weighted Average Exercise Price, Canceled	142.69		101.77
Weighted Average Exercise Price, Exercised	24.66	11.26	12.35
Weighted Average Exercise Price, Ending Balance	132.93	$ 67.60	$ 36.80
Weighted Average Exercise Price, Exercisable	$ 53.49
Remaining Contractual Term, Outstanding at December 31, 2018	3 years 2 months 12 days
Remaining Contractual Term, Exercisable at December 31, 2018	2 years 1 month 6 days
Intrinsic Value, Exercised	$ 21,823
Intrinsic Value, Ending Balance	53,651
Intrinsic Value, Exercisable	$ 32,126

Stock-Based Compensation Plan_6

Stock-Based Compensation Plans - Summary of Performance of Share Activity for Annual Awards (Detail) - Performance Shares [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share pay-out plan	10,479	12,971	15,390
Actual share pay-out in following year	10,479	8,094	21,423
Weighted average fair value per share on grant date	$ 202.04	$ 155.53	$ 101.77

Stock-Based Compensation Plan_7

Stock-Based Compensation Plans - Restricted Stock and Performance Share Activity (Detail) - Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Restricted Shares, Beginning balance	319,599	383,978	432,138
Number of Restricted Shares, Granted	59,179	61,434	95,419
Number of Restricted Shares, Performance share pay-out	8,094	21,422	61,936
Number of Restricted Shares, Canceled	(4,046)	(4,590)	(12,786)
Number of Restricted Shares, Vested	(110,956)	(142,645)	(192,729)
Number of Restricted Shares, Ending balance	271,870	319,599	383,978
Weighted Average Grant Date Fair Value, Beginning balance	$ 88.77	$ 71.50	$ 56.24
Weighted Average Grant Date Fair Value, Ending balance	$ 112.47	$ 88.77	$ 71.50

Earnings Per Share - Basic and

Earnings Per Share - Basic and Diluted Weighted Average Shares Outstanding Used to Compute Earnings Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share Basic And Diluted [Abstract]
Basic weighted average shares outstanding	36,958	36,864	36,844
Dilutive effect of stock options and restricted stock	897	1,174	894
Diluted weighted average shares outstanding	37,855	38,038	37,738

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Options and Restricted Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Stock options and restricted stock excluded from the computation of diluted earnings per share	83,718	31,766	84,052

Credit Agreement - Additional I

Credit Agreement - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2015	Dec. 31, 2018
Line Of Credit Facility [Line Items]
Revolving loans and letters of credit			$ 100,000,000
Letter of credit outstanding				$ 1,700,000
Additional Credit Agreement			$ 50,000,000
Amount available under credit agreement				$ 98,300,000
Period of credit agreement			2 years
Equity interest				65.00%
Minimum [Member]
Line Of Credit Facility [Line Items]
Excess judgments against the company				$ 10,000,000
Credit Agreement [Member]
Line Of Credit Facility [Line Items]
Expiration period of credit agreement	Oct. 31, 2019	Oct. 31, 2018
Period of credit agreement		1 year

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)ft²AgreementSubsidiary	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Non-cancelable leases expiration date	Dec. 31, 2034
Rental expense	$ 13.1	$ 5.3	$ 4
Rent abatement and concessions	$ 11.5	2.7
Number of lease agreements assigned to third parties | Agreement	2
Future lease obligation under sublease arrangements	$ 5.8
Number of subsidiaries | Subsidiary	2
Settlement days of bond transaction	Within one to two trading days
Collateral deposits	$ 1.1	$ 1.2
Property One [Member]
Loss Contingencies [Line Items]
Lease termination dates	2020-11
Property Two [Member]
Loss Contingencies [Line Items]
Lease termination dates	2022-02
Lease Agreement [Member]
Loss Contingencies [Line Items]
Newly built office space | ft²	83,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Contingent obligation for standby letter of credit issued to Landlord	$ 1.7

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Minimum Rental Commitments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2,019	$ 9,764
2,020	10,919
2,021	10,114
2,022	9,067
2,023	8,738
2024 and thereafter	95,467
Operating Leases	$ 144,069

Segment and Geographic Inform_3

Segment and Geographic Information - Additional Information (Detail) - Segment	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues From External Customers And Long Lived Assets [Line Items]
Number of operating segment	1
Geographic Concentration Risk [Member] | Total Revenue and Long-lived Assets [Member] | United Kingdom [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Concentration Risk, Percentage	10.00%	10.00%	10.00%

Segment and Geographic Inform_4

Segment and Geographic Information - Summary of Revenue and Long-lived Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 435,565	$ 393,422	$ 367,730
Long-lived assets	63,010	38,548
United States [Member]
Segment Reporting Information [Line Items]
Revenues	367,373	332,982	312,304
Long-lived assets	55,200	27,990
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	66,241	58,991	53,865
Long-lived assets	7,787	10,532
Other [Member]
Segment Reporting Information [Line Items]
Revenues	1,951	1,449	$ 1,561
Long-lived assets	$ 23	$ 26

Retirement and Deferred Compe_2

Retirement and Deferred Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Contribution to defined plans	$ 2.6	$ 1.8	$ 1.9
Non-qualified deferred cash incentive plan maximum eligibility percentage of employees	100.00%
Mutual fund investments and deferred compensation obligation, at fair value	$ 4.1	3.2
Trading (losses) gains and changes in deferred compensation liability and expense	$ (0.2)	$ 0.4	$ 0.2