EPAM Systems (EPAM) 10-Q 6 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 31, 2018
Document Documentand Entity Information [Abstract]
Entity Registrant Name	EPAM Systems, Inc.
Entity Central Index Key	1,352,010
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		53,781,973
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Document Period End Date	Jun. 30, 2018
Document Type	10-Q
Amendment Flag	false
Trading Symbol	EPAM

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 584,081	$ 582,585
Accounts receivable, net of allowance of $2,790 and $1,186, respectively	283,001	265,639
Unbilled revenues	123,434	86,500
Prepaid and other current assets, net of allowance of $42 and $45, respectively	31,919	23,196
Employee loans, current, net of allowance of $0 and $0, respectively	2,084	2,113
Total current assets	1,024,519	960,033
Property and equipment, net	98,450	86,419
Employee loans, noncurrent, net of allowance of $0 and $0, respectively	1,669	2,097
Intangible assets, net	55,201	44,511
Goodwill	144,667	119,531
Deferred tax assets	54,805	24,974
Other noncurrent assets, net of allowance of $130 and $140, respectively	12,884	12,691
Total assets	1,392,195	1,250,256
Current liabilities
Accounts payable	6,727	5,574
Accrued expenses and other current liabilities	72,443	89,812
Due to employees	50,374	38,757
Deferred compensation due to employees	4,338	5,964
Taxes payable	47,529	40,860
Total current liabilities	181,411	180,967
Long-term debt	25,020	25,033
Taxes payable, noncurrent	56,540	59,874
Other noncurrent liabilities	16,421	9,435
Total liabilities	279,392	275,309
Commitments and contingencies (Note 11)
Stockholders’ equity
Common stock, $0.001 par value; 160,000,000 authorized; 53,705,002 and 53,003,420 shares issued, 53,685,267 and 52,983,685 shares outstanding at June 30, 2018 and December 31, 2017, respectively	54	53
Additional paid-in capital	511,131	473,874
Retained earnings	633,950	518,820
Treasury stock	(177)	(177)
Accumulated other comprehensive loss	(32,155)	(17,623)
Total stockholders’ equity	1,112,803	974,947
Total liabilities and stockholders’ equity	$ 1,392,195	$ 1,250,256

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets
Accounts receivable allowance	$ 2,790	$ 1,186
Prepaid and other assets allowance	42	45
Employee loans current allowance	0	0
Assets, Noncurrent [Abstract]
Employee loans long-term allowance	0	0
Other long-term assets allowance	$ 130	$ 140
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, shares issued (in shares )	53,705,002	53,003,420
Common stock, shares outstanding (in shares)	53,685,267	52,983,685

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	289,175	220,132	566,809	427,862
Selling, general and administrative expenses	91,843	80,419	179,620	158,872
Depreciation and amortization expense	8,962	7,020	17,138	13,692
Other operating expenses, net	1,430	724	3,294	1,554
Income from operations	54,237	40,682	102,934	71,648
Interest and other income, net	1,052	802	501	1,386
Foreign exchange gain/(loss)	1,830	1,562	1,583	(1,393)
Income before provision for/(benefit from) income taxes	57,119	43,046	105,018	71,641
Provision for/(benefit from) income taxes	6,864	5,687	(9,655)	10,641
Net income	50,255	37,359	114,673	61,000
Foreign currency translation adjustments, net of tax	(15,834)	4,551	(12,525)	10,937
Unrealized net loss on cash-flow hedging instruments, net of tax	(2,076)	0	(2,007)	0
Comprehensive income	$ 32,345	$ 41,910	$ 100,141	$ 71,937
Net income per share:
Basic (in dollars per share)	$ 0.94	$ 0.72	$ 2.15	$ 1.19
Diluted (in dollars per share)	$ 0.89	$ 0.68	$ 2.03	$ 1.12
Shares used in calculation of net income per share:
Basic (in shares)	53,517,124	51,899,416	53,299,038	51,431,353
Diluted (in shares)	56,587,009	54,848,619	56,414,986	54,371,284

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 114,673	$ 61,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	17,138	13,692
Bad debt expense	1,529	102
Deferred taxes	(27,581)	(766)
Stock-based compensation expense	31,406	28,703
Other	(2,099)	(1,550)
(Increase)/decrease in operating assets:
Accounts receivable	(15,051)	(4,630)
Unbilled revenues	(35,334)	(44,133)
Prepaid expenses and other assets	(4,495)	973
Increase/(decrease) in operating liabilities:
Accounts payable	1,008	518
Accrued expenses and other liabilities	(15,861)	(3,333)
Due to employees	1,351	4,549
Taxes payable	105	4,208
Net cash provided by operating activities	66,789	59,333
Cash flows from investing activities:
Purchases of property and equipment	(19,303)	(11,441)
Employee housing loans issued	(214)	(512)
Proceeds from repayments of employee housing loans	919	1,315
Decrease in time deposits, net	418	13
Acquisition of businesses, net of cash acquired	(50,264)	(6,810)
Other investing activities, net	130	(190)
Net cash used in investing activities	(68,314)	(17,625)
Cash flows from financing activities:
Proceeds from stock option exercises	22,368	37,757
Payments of withholding taxes related to net share settlements of restricted stock units	(6,696)	(2,702)
Proceeds from debt (Note 6)	0	25,000
Repayment of debt (Note 6)	(3,478)	(25,059)
Other financing activities, net	(603)	(864)
Net cash provided by financing activities	11,591	34,132
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(7,645)	5,912
Net increase in cash, cash equivalents and restricted cash	2,421	81,752
Cash, cash equivalents and restricted cash, beginning of period	582,855	364,664
Cash, cash equivalents and restricted cash, end of period	$ 585,276	$ 446,416

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS CONDENSED CONSOLIDATED STATEMENT OF CASH FLOW (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Cash and cash equivalents	$ 584,081	$ 582,585
Restricted cash	1,195	270
Cash, cash equivalents, restricted cash and restricted cash equivalents	585,276	582,855
Prepaid and other current assets
Restricted cash	0	91
Other noncurrent assets
Restricted cash	$ 1,195	$ 179

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES EPAM Systems, Inc. (the “Company” or “EPAM”) is a leading global provider of digital platform engineering and software development services to clients located around the world, primarily in North America, Europe, Asia and Australia. The Company has expertise in various industries, including software and hi-tech, financial services, business information and media, travel and hospitality, retail and distribution and life sciences and healthcare. The Company is incorporated in Delaware and headquartered in Newtown, PA. Basis of Presentation — The accompanying unaudited condensed consolidated financial statements of EPAM have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and Article 10 of Regulation S-X under the Securities Exchange Act of 1934, as amended. The condensed consolidated financial statements include the financial statements of EPAM Systems, Inc. and its subsidiaries with all intercompany balances and transactions eliminated. These unaudited condensed consolidated financial statements and accompanying notes should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2017 included in its Annual Report on Form 10-K. The preparation of these condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in these condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates, and such differences may be material to the condensed consolidated financial statements. Operating results for the interim periods are not necessarily indicative of results that may be expected to occur for the entire year. In management’s opinion, all adjustments considered necessary for a fair presentation of the accompanying unaudited condensed consolidated financial statements have been included, and all adjustments are of a normal and recurring nature. Adoption of New Accounting Standards Unless otherwise discussed below, the adoption of new accounting standards did not have an impact on the Company’s consolidated financial position, results of operations, and cash flows. Revenue Recognition — Effective January 1, 2018, the Company adopted the new accounting standard ASU 2014-09, Revenue from Contracts with Customers (Topic 606) as amended using the modified retrospective method. The standard effectively replaced previously existing revenue recognition guidance (Topic 605) and requires entities to recognize revenue to depict the transfer of promised goods or services in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services as well as requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments. The following table summarizes the cumulative effect of adopting Topic 606 using the modified retrospective method of adoption as of January 1, 2018: Balance as of Adjustments Balance as of Balance Sheet Assets Unbilled revenues $ 86,500 $ (78 ) $ 86,422 Deferred tax assets $ 24,974 $ (173 ) $ 24,801 Liabilities Accrued expenses and other current liabilities $ 89,812 $ (708 ) $ 89,104 Stockholders’ equity Retained earnings $ 518,820 $ 457 $ 519,277 The Company applied a practical expedient to aggregate the effect of all contract modifications that occurred before the adoption date. See Note 7 “Revenues” in the condensed consolidated interim financial statements for additional information regarding revenues. Restricted cash and restricted cash equivalents — Effective January 1, 2018, the Company adopted Accounting Standard Update (“ASU”) No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash which requires the Company to include in its cash and cash equivalents balances presented in the statements of cash flows amounts that are deemed to be restricted in nature. As a result of the adoption, the Company restated its condensed consolidated statements of cash flows for all of the prior periods presented. The impact of adoption on the Company’s condensed consolidated statement of cash flows was as follows for the six months ended June 30, 2017: As Reported Restated Effect Cash flows from operating activities: Changes in operating assets and liabilities: Prepaid expenses and other assets $ 736 $ 973 $ 237 Net cash provided by operating activities $ 59,096 $ 59,333 $ 237 Cash flows from investing activities: Decrease in restricted cash and time deposits, net $ 94 $ 13 $ (81 ) Acquisition of businesses, net of cash acquired $ (6,840 ) $ (6,810 ) $ 30 Net cash used in investing activities $ (17,574 ) $ (17,625 ) $ (51 ) Effect of exchange rate changes on cash, cash equivalents, and restricted cash $ 5,822 $ 5,912 $ 90 Net increase in cash, cash equivalents and restricted cash $ 81,476 $ 81,752 $ 276 Cash, cash equivalents and restricted cash, beginning of period 362,025 364,664 2,639 Cash, cash equivalents and restricted cash, end of period $ 443,501 $ 446,416 $ 2,915 Derivatives and Hedging — Effective April 1, 2018, the Company early-adopted ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities . The new guidance is intended to simplify and amend hedge accounting and reporting to better align and disclose the economic results of an entity’s risk management activities in its financial statements. The ASU makes more financial and non-financial hedging strategies eligible for hedge accounting. It also changes how companies assess hedge effectiveness and amends the presentation and disclosure requirements by eliminating the requirement to separately measure and report hedge ineffectiveness and generally requires companies, for qualifying hedges, to present the entire change in the fair value of a hedging instrument in the same income statement line as the hedged item. The guidance also eases documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. The guidance requires entities to apply the amended presentation and disclosure guidance prospectively as of the period of adoption. The adoption of this guidance did not have any effect on the consolidated financial results. The Company enters into derivative financial instruments to manage exposure to fluctuations in certain foreign currencies. During 2018, for accounting purposes, these foreign currency forward contracts became designated as hedges, as defined under FASB ASC Topic 815, Derivatives and Hedging . The Company measures these foreign currency derivative contracts at fair value on a recurring basis utilizing Level 2 inputs. The Company records changes in the fair value of these hedges in accumulated other comprehensive income/(loss) in our consolidated balance sheet until the forecasted transaction occurs. When the forecasted transaction occurs, the related gain or loss on the cash flow hedge is reclassified to the same line item in the statement of income as the forecasted transaction is recorded. In the event the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the Company reclassifies the gain or loss on the underlying hedge from accumulated other comprehensive income/(loss) to foreign exchange gain/(loss) in the consolidated statement of income. The cash flow impact of derivatives identified as hedging instruments is reflected as cash flows from operating activities. The cash flow impact of derivatives not identified as hedging instruments is reflected as cash flows from investing activities. Pending Accounting Standards From time to time, new accounting pronouncements are issued by the FASB or other standards-setting bodies that the Company will adopt according to the various timetables the FASB specifies. Unless otherwise discussed below, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial position, results of operations and cash flows upon adoption. Leases — Effective January 1, 2019, the Company will be required to adopt the new guidance of ASC Topic 842, Leases (Topic 842) (with early adoption permitted effective January 1, 2018). This amendment supersedes previous accounting guidance (Topic 840) and requires all leases, with the exception of leases with a term of twelve months or less, to be recorded on the balance sheet as lease assets and lease liabilities. The standard allows for two methods of adoption to recognize and measure leases: retrospectively to each prior period presented in the financial statements with the cumulative effect of initially applying the guidance recognized at the beginning of the earliest comparative period presented or retrospectively at the beginning of the period of adoption with the cumulative effect of initially applying the guidance recognized at the beginning of the period in which the guidance is first applied. The adoption methods both include a number of optional practical expedients that entities may elect to apply. These practical expedients relate to the identification and classification of leases that commenced before the effective date, initial direct costs for leases that commenced before the effective date, and the ability to use hindsight in evaluating lessee options to extend or terminate a lease or to purchase the underlying asset. An entity that elects to apply the practical expedients will, in effect, continue to account for leases that commence before the effective date in accordance with previous GAAP unless the lease is modified, except that lessees are required to recognize a right-of-use asset and a lease liability for all operating leases based on the present value of the remaining minimum rental payments that were tracked and disclosed under previous GAAP. The transition guidance in Topic 842 also provides specific guidance for the amounts previously recognized in accordance with the business combinations guidance for leases. The Company has developed a transition plan, which includes making necessary changes to policies, processes, internal controls and system enhancements to generate the information necessary to comply with the new standard. The Company expects the new guidance will have a material impact on its consolidated balance sheet for the addition of right-of-use assets and lease liabilities principally due to its office space leases. EPAM does not expect the new guidance to have a material impact on its consolidated statement of income and comprehensive income or its consolidated statement of cash flows. The Company expects to adopt this standard on January 1, 2019 using the method of adoption whereby the cumulative effect of adoption is recognized at the beginning of the period of adoption. Measurement of Credit Losses on Financial Instruments — Effective January 1, 2020, the Company will be required to adopt the amended guidance of ASC Topic 326, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , (with early adoption permitted effective January 1, 2019.) The amendments in this update change how companies measure and recognize credit impairment for many financial assets. The new expected credit loss model will require companies to immediately recognize an estimate of credit losses expected to occur over the remaining life of the financial assets (including trade receivables) that are in the scope of the update. The update also made amendments to the current impairment model for held-to-maturity and available-for-sale debt securities and certain guarantees. Entities are required to adopt the standard using a modified-retrospective approach through a cumulative effect adjustment to retained earnings as of the beginning of the period of adoption. The Company has not yet completed its assessment of the impact of the new guidance on its consolidated financial statements or concluded on when it will adopt the standard.

ACQUISITIONS

ACQUISITIONS	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS Continuum — On March 15, 2018 , the Company acquired all of the outstanding equity of Continuum Innovation LLC together with its subsidiaries, (“Continuum”) to enhance the Company’s consulting capabilities as well as its digital and service design practices. Continuum, headquartered in Boston with offices located in Milan, Seoul, and Shanghai, focuses on four practices including strategy, physical and digital design, technology and its Made Real Lab. The acquisition of Continuum added approximately 125 design consultants to the Company’s headcount. In connection with the Continuum acquisition, the Company paid $52,515 as cash consideration, of which $5,410 was placed in escrow for a period of 9 to 15 months as security for the indemnification obligations of the sellers under the terms of the equity purchase agreement. Furthermore, subject to attainment of specified performance targets in the 12 months after the acquisition, the Company will make a cash earnout payment with a maximum amount payable of $3,135 . The Company recorded $2,400 related to this earnout payment as contingent consideration (Note 4 “Fair Value Measurements”). The following table summarizes the preliminary fair values of the assets acquired and liabilities assumed in connection with the acquisition of Continuum as originally reported and as adjusted as of June 30, 2018 : As Originally Reported As Adjusted Cash and cash equivalents $ 2,251 $ 2,251 Accounts receivable 6,676 6,676 Unbilled revenues 2,463 2,463 Prepaid and other current assets 942 936 Goodwill 29,805 26,293 Intangible assets 16,600 14,850 Property and equipment and other noncurrent assets 8,902 8,902 Total assets acquired $ 67,639 $ 62,371 Accounts payable, accrued expenses and other current liabilities $ 2,991 $ 2,745 Due to employees 1,001 1,001 Long-term debt (Note 6) 3,220 3,220 Other noncurrent liabilities 5,412 490 Total liabilities assumed $ 12,624 $ 7,456 Net assets acquired $ 55,015 $ 54,915 During the three months ended June 30, 2018, the Company updated the valuation of intangible assets acquired which resulted in an adjustment of initially recognized intangible assets and their useful lives as well as in recognition of an additional intangible asset in the form of a favorable lease. The Company removed a liability associated with an initially recognized unfavorable lease, which was classified as other noncurrent liabilities. These adjustments as well as the revaluation of contingent consideration resulted in a corresponding decrease in the value of acquired goodwill. The Company recorded $26 of amortization and $41 of rent expense during the three months ended June 30, 2018 that would have been recognized in a prior period if the adjustments to the preliminary amounts had been recognized as of the acquisition date. The Company is gathering additional information necessary to finalize the estimated fair values of the assets acquired and liabilities assumed. The fair values reflected are subject to change and such changes could be significant. The Company expects to finalize the valuation and complete the purchase price allocation as soon as practicable but no later than one year from the acquisition date. The following table presents the estimated fair values and useful lives of intangible assets acquired in connection with the acquisition of Continuum: Continuum Weighted Average Useful Life (in years) Amount Favorable lease 11.9 $ 5,900 Customer relationships 6.6 5,800 Contract royalties 8 1,900 Trade names 5 1,250 Total $ 14,850 The goodwill recognized as a result of the Continuum acquisition is attributable primarily to strategic and synergistic opportunities related to the consulting business, the assembled workforce of Continuum and other factors. The goodwill is expected to be deductible for income tax purposes. Revenues generated by Continuum totaled $8,470 and $10,224 during the three and six months ended June 30, 2018. Pro forma results of operations have not been presented because the effect of the Continuum acquisition on the Company’s condensed consolidated financial statements was not material.

GOODWILL

GOODWILL	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL	GOODWILL Goodwill by reportable segment was as follows: North America Europe Total Balance as of December 31, 2017 $ 77,290 $ 42,241 $ 119,531 Continuum acquisition (Note 2) 26,293 — 26,293 Effect of net foreign currency exchange rate changes (285 ) (872 ) (1,157 ) Balance as of June 30, 2018 $ 103,298 $ 41,369 $ 144,667 There were no accumulated impairment losses in the North America or Europe reportable segments as of June 30, 2018 or December 31, 2017 .

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company carries certain liabilities at fair value on a recurring basis on its consolidated balance sheets. The following table shows the fair values of the Company’s financial assets and liabilities measured at fair value on a recurring basis as of June 30, 2018 : As of June 30, 2018 Balance Level 1 Level 2 Level 3 Foreign exchange derivative assets $ 84 $ — $ 84 $ — Total assets measured at fair value on a recurring basis $ 84 $ — $ 84 $ — Contingent consideration $ 2,400 $ — $ — $ 2,400 Foreign exchange derivative liabilities 2,690 $ — 2,690 $ — Total liabilities measured at fair value on a recurring basis $ 5,090 $ — $ 2,690 $ 2,400 The Company had no material financial assets or liabilities measured at fair value on a recurring basis as of December 31, 2017. As of June 30, 2018 , contingent consideration included amounts payable in cash in connection with the acquisition of Continuum (Note 2 “Acquisitions”). The fair value of the contingent consideration is based on the expected future payments to be made to the sellers of the acquired business in accordance with the provisions outlined in the purchase agreement. In determining fair value, the Company considered a variety of factors, including future performance of the acquired businesses using financial projections developed by the Company and market risk assumptions that were derived for revenue growth and earnings before interest and taxes. The Company estimated future payments using the earnout formula and performance targets specified in the purchase agreement and adjusted those estimates to reflect the probability of their achievement. Those future payments were then discounted to present value using a rate based on the weighted-average cost of capital of guideline companies. The Company believes its estimates and assumptions are reasonable; however, there is significant judgment involved. Changes in financial projections, market risk assumptions, discount rates or probability assumptions related to achieving the various earnout criteria would result in a change in the fair value of the recorded contingent liability. Such changes, if any, are recorded within Interest and other income, net in the Company’s consolidated statement of income and comprehensive income. Our Level 2 foreign exchange derivatives are valued using pricing models and discounted cash flow methodologies based on observable foreign exchange data at the measurement date. See Note 5 for further information regarding the Company’s derivative financial instruments. A reconciliation of the beginning and ending balances of acquisition-related contractual contingent liabilities using significant unobservable inputs (Level 3) for the six months ended June 30, 2018 is as follows: Amount Contractual contingent liabilities at December 31, 2017 $ — Acquisition date fair value of contractual contingent liabilities — Continuum (Note 2) 2,400 Contractual contingent liabilities at June 30, 2018 $ 2,400 Estimates of fair value of financial instruments not carried at fair value on a recurring basis on the Company’s consolidated balance sheets are generally subjective in nature, and are determined as of a specific point in time based on the characteristics of the financial instruments and relevant market information. The Company uses the following methods to estimate the fair values of its financial instruments: • for financial instruments that have quoted market prices, those quoted prices are used to estimate fair value; • for financial instruments for which no quoted market prices are available, fair value is estimated using information obtained from independent third parties, or by discounting the expected cash flows using an estimated current market interest rate for the financial instrument; • for financial instruments for which no quoted market prices are available and that have no defined maturity, have a remaining maturity of 360 days or less, or reprice frequently to a market rate, the Company assumes that the fair value of these instruments approximates their reported value, after taking into consideration any applicable credit risk. The generally short duration of certain of the Company’s assets and liabilities results in a number of assets and liabilities for which fair value equals or closely approximates the amount recorded on the Company’s condensed consolidated balance sheets. These types of assets and liabilities which are reported on the Company’s consolidated balance sheet include: • cash and cash equivalents; • time deposits and restricted cash; • employee loans; • borrowings under the Company’s 2017 Credit Facility (Note 6 “Long-Term Debt”). The fair value of employee housing loans is estimated using information on the rates of return that market participants in Belarus would require when investing in unsecured U.S. dollar-denominated government bonds with similar maturities (a “risk-free rate”), after taking into consideration any applicable credit and liquidity risk. The following tables present the reported amounts and estimated fair values of the financial assets and liabilities for which disclosure of fair value is required, as they would be categorized within the fair value hierarchy, as of the dates indicated: Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 June 30, 2018 Financial Assets: Cash and cash equivalents $ 584,081 $ 584,081 $ 584,081 $ — $ — Restricted cash $ 1,195 $ 1,195 $ 1,195 $ — $ — Employee loans $ 3,753 $ 3,753 $ — $ — $ 3,753 Financial Liabilities: Borrowings under the 2017 Credit Facility $ 25,019 $ 25,019 $ — $ 25,019 $ — Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 December 31, 2017 Financial Assets: Cash and cash equivalents $ 582,585 $ 582,585 $ 582,585 $ — $ — Time deposits and restricted cash $ 673 $ 673 $ — $ 673 $ — Employee loans $ 4,210 $ 4,210 $ — $ — $ 4,210 Financial Liabilities: Borrowings under the 2017 Credit Facility $ 25,009 $ 25,009 $ — $ 25,009 $ —

DERIVATIVE FINANCIAL INSTRUMENT

DERIVATIVE FINANCIAL INSTRUMENTS	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE FINANCIAL INSTRUMENTS	DERIVATIVE FINANCIAL INSTRUMENTS The Company conducts a large portion of its operations in international markets that subject it to foreign currency fluctuations. To manage the risk of fluctuations in foreign currency exchange rates, during the six months ended June 30, 2018 , the Company implemented a hedging program whereby it entered into a series of foreign exchange forward contracts with durations of twelve months or less that are designated as cash flow hedges of forecasted Russian ruble, Polish zloty and Indian rupee transactions. The Company measures derivative instruments and hedging activities at fair value and recognizes them as either assets or liabilities in its consolidated balance sheets. Accounting for the gains and losses resulting from changes in fair value depends on the use of the derivative and whether it is designated and qualifies for hedge accounting. As of June 30, 2018 , all of the Company’s foreign exchange forward contracts were designated as hedges. To receive hedge accounting treatment, all hedging relationships are formally documented at the inception of the hedge, and the hedges must be highly effective in offsetting changes to future cash flows on hedged transactions. Derivatives may give rise to credit risks from the possible non-performance by counterparties. The Company has limited its credit risk by entering into derivative transactions only with highly-rated financial institutions and by conducting an ongoing evaluation of the creditworthiness of the financial institutions with which the Company does business. There is no financial collateral (including cash collateral) required to be posted by the Company related to the foreign exchange forward contracts. The fair value of derivative instruments on the Company’s consolidated balance sheets as of June 30, 2018 and December 31, 2017 were as follows: As of June 30, 2018 As of December 31, 2017 Balance Sheet Location Asset Derivatives Liability Derivatives Asset Derivatives Liability Derivatives Foreign exchange forward contracts - Designated as hedging instruments Prepaid and other current assets $ 84 $ — Accrued expenses and other current liabilities $ 2,690 $ — Foreign exchange forward contracts - Not designated as hedging instruments Prepaid and other current assets $ — $ 114 Accrued expenses and other current liabilities $ — $ — The Company records changes in the fair value of its cash flow hedges in accumulated other comprehensive income/(loss) in the consolidated balance sheet until the forecasted transaction occurs. When the forecasted transaction occurs, the Company reclassifies the related gain or loss on the cash flow hedge to cost of revenues (exclusive of depreciation and amortization). In the event the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the Company reclassifies the gain or loss on the related cash flow hedge from accumulated other comprehensive income/(loss) to foreign exchange gain/(loss) in the consolidated statement of income in that period. If the Company does not elect hedge accounting, or the contract does not qualify for hedge accounting treatment, the changes in fair value from period to period are recorded in foreign exchange gain/(loss) in the consolidated statement of income. The changes in the fair value of foreign currency derivative instruments in our unaudited condensed consolidated statements of income and comprehensive income for the three and six months ended June 30, 2018 and 2017 were as follows: Three Months Ended Six Months Ended 2018 2017 2018 2017 Foreign exchange forward contracts - Designated as hedging instruments: Change in fair value recognized in accumulated other comprehensive loss (2,696 ) — (2,606 ) — Net loss reclassified from accumulated other comprehensive loss into cost of revenues (exclusive of depreciation and amortization) (937 ) — (937 ) — Foreign exchange forward contracts - Not designated as hedging instruments: Net gain recognized in foreign exchange gain/(loss) — 20 44 159

LONG-TERM DEBT

LONG-TERM DEBT	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT Revolving Line of Credit — On May 24, 2017, the Company entered into an unsecured credit facility (the “2017 Credit Facility”) with PNC Bank, National Association; PNC Capital Markets LLC; Wells Fargo Bank, National Association; Santander Bank, N.A.; Fifth Third Bank and Citibank N.A. (collectively the “Lenders”). The 2017 Credit Facility provides for a borrowing capacity of $300,000 , with potential to increase the credit facility up to $400,000 if certain conditions are met. The 2017 Credit Facility matures on May 24, 2022 . Borrowings under the 2017 Credit Facility may be denominated in U.S. dollars or up to a maximum of $100,000 equivalent in British pounds sterling, Canadian dollars, euros or Swiss francs or other currencies as may be approved by the administrative agent and the Lenders. Borrowings under the 2017 Credit Facility bear interest at either a base rate or Euro-rate plus a margin based on the Company’s leverage ratio. The base rate is equal to the highest of (a) the Overnight Bank Funding Rate, plus 0.5% , (b) the Prime Rate, and (c) the Daily LIBOR Rate, plus 1.0% . As of June 30, 2018 , the Company’s outstanding borrowings are subject to a LIBOR-based interest rate which resets regularly at issuance, based on lending terms. The 2017 Credit Facility includes customary business and financial covenants that may restrict the Company’s ability to make or pay dividends (other than certain intercompany dividends) if a potential or an actual event of default has occurred or would be triggered. As of June 30, 2018 , the Company was in compliance with all covenants contained in the 2017 Credit Facility. The following table presents the outstanding debt and borrowing capacity of the Company under the 2017 Credit Facility: As of As of Outstanding debt $ 25,000 $ 25,000 Interest rate 3.1 % 2.6 % Irrevocable standby letters of credit $ 343 $ 1,294 Available borrowing capacity $ 274,657 $ 273,706 Current maximum borrowing capacity $ 300,000 $ 300,000 As part of the acquisition of Continuum, the Company assumed $3,448 of long-term debt associated with a leased facility and payable to Continuum’s landlord. The debt was payable in monthly installments through March 2029 and bore interest at a rate of 8% per annum. During March 2018, the Company paid $3,448 to settle this assumed long-term debt.

REVENUES

REVENUES	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
REVENUES	REVENUES Adoption of ASC Topic 606, “Revenue from Contracts with Customers” and Change in Accounting Policies Effective January 1, 2018, the Company adopted ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) as amended. The Company adopted the new guidance using the modified retrospective method by recognizing the cumulative effect of adoption as an adjustment to retained earnings as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with Topic 605. The impact of adoption of the new guidance on the Company’s consolidated financial statements as of January 1, 2018 are presented in Note 1 “Summary of Significant Accounting Policies.” The Company recognizes revenues when control of goods or services is passed to a customer in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Such control may be transferred over time or at a point in time depending on satisfaction of obligations stipulated by the contract. Consideration expected to be received may consist of both fixed and variable components and is allocated to each separately identifiable performance obligation based on the performance obligation’s relative standalone selling price. Variable consideration is usually presented in the form of cash incentives or credits. Determining the estimated amount of such variable consideration involves assumptions and judgment that can have an impact on the amount of revenue reported. The Company derives its revenues from a variety of service offerings, which represent specific competencies of its IT professionals. Fees for these contracts may be in the form of time-and-materials or fixed-price arrangements. The majority of the Company’s revenues are generated under time-and-material contracts which are billed using hourly, daily or monthly rates to determine the amounts to be charged directly to the client. The Company applies a practical expedient and revenue related to time-and-material contracts is recognized based on the Company’s right to invoice for services performed. Fixed-price contracts include maintenance and support arrangements, which may exceed one year in duration, as well as application development arrangements. Maintenance and support arrangements generally relate to the provision of ongoing services. Revenues for such agreements are recognized ratably over the expected service period. Application development arrangements are accounted for using input or output methods for measuring the progress towards satisfaction of the performance obligation. Input methods are used only when there is a direct correlation between hours incurred and the end product delivered. Assumptions, risks and uncertainties inherent in the estimates used to measure progress could affect the amount of revenues, receivables and deferred revenues at each reporting period. Revenues from licenses which have significant stand-alone functionality are recognized at a point in time when control of the license is transferred to the customer. Revenues from licenses which do not have stand-alone functionality are recognized over time. If there is an uncertainty about the receipt of payment for the services, revenue is deferred until the uncertainty is sufficiently resolved. The Company applies a practical expedient and does not assess the existence of a significant financing component if the period between when the Company transfers the service to a customer and when the customer pays for that service is one year or less. The Company reports gross reimbursable “out-of-pocket” expenses incurred as both revenues and cost of revenues in the condensed consolidated statements of income and comprehensive income. The following tables summarize the impacts of changes in accounting policies after adoption of Topic 606 on the Company’s condensed consolidated financial statements for the three and six months ended June 30, 2018 , which primarily resulted from deferring the timing of revenue recognition for contracts that were previously recognized on a cash basis and recognizing revenues from certain license agreements at a point-in-time rather than over time: As of June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Balance Sheet Liabilities Accrued expenses and other current liabilities $ 72,443 $ 72,426 $ 17 Other noncurrent liabilities 16,421 16,424 (3 ) Stockholders’ equity Retained earnings $ 633,950 $ 633,964 $ (14 ) Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Income Statement Revenues $ 445,647 $ 444,951 $ 696 $ 869,795 $ 869,812 $ (17 ) Income from operations $ 54,237 $ 53,541 $ 696 $ 102,934 $ 102,951 $ (17 ) Provision for/(benefit from) income taxes $ 6,864 $ 6,728 $ 136 $ (9,655 ) $ (9,652 ) $ (3 ) Net income $ 50,255 $ 49,695 $ 560 $ 114,673 $ 114,687 $ (14 ) Disaggregation of Revenues The following tables show the disaggregation of the Company’s revenues by major client location, including a reconciliation of the disaggregated revenue with the reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Client Locations North America $ 250,273 $ 14,177 $ 14 $ 264,464 $ (13 ) $ 264,451 Europe 3,086 146,998 — 150,084 (280 ) 149,804 CIS 2,089 28 17,294 19,411 — 19,411 APAC 1,655 10,292 72 12,019 (38 ) 11,981 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Client Locations North America $ 476,343 $ 27,538 — $ 29 — $ 503,910 $ (13 ) $ 503,897 Europe 5,826 297,478 — 42 — 303,346 (457 ) 302,889 CIS 4,092 91 — 37,008 — 41,191 — 41,191 APAC 2,038 19,731 — 87 — 21,856 (38 ) 21,818 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 The following tables show the disaggregation of the Company’s revenues by industry vertical, including a reconciliation of the disaggregated revenue with the reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Industry Vertical Financial Services $ 26,732 $ 62,496 $ 14,091 $ 103,319 $ (331 ) $ 102,988 Travel & Consumer 47,104 52,120 1,792 101,016 — 101,016 Software & Hi-Tech 64,536 19,857 624 85,017 — 85,017 Business Information & Media 59,532 18,117 — 77,649 — 77,649 Life Sciences & Healthcare 32,876 5,649 — 38,525 — 38,525 Emerging Verticals 26,323 13,256 873 40,452 — 40,452 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Industry Vertical Financial Services $ 48,688 $ 128,314 $ 30,316 $ 207,318 $ (508 ) $ 206,810 Travel & Consumer 87,791 101,574 3,465 192,830 — 192,830 Software & Hi-Tech 125,100 40,151 1,388 166,639 — 166,639 Business Information & Media 116,869 36,987 — 153,856 — 153,856 Life Sciences & Healthcare 60,343 10,472 — 70,815 — 70,815 Emerging Verticals 49,508 27,340 1,997 78,845 — 78,845 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 The following tables show the disaggregation of the Company’s revenues by contract type including a reconciliation of the disaggregated revenue with the Company’s reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Contract Type Time-and-material $ 233,747 $ 156,637 $ 9,765 $ 400,149 $ — $ 400,149 Fixed-price 22,483 14,081 7,607 44,171 — 44,171 Licensing 638 327 1 966 — 966 Other revenues 235 450 7 692 (331 ) 361 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Contract Type Time-and-material $ 448,063 $ 316,103 $ 19,861 $ 784,027 $ — $ 784,027 Fixed-price 38,475 27,034 17,279 82,788 — 82,788 Licensing 1,300 946 11 2,257 — 2,257 Other revenues 461 755 15 1,231 (508 ) 723 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 Timing of Revenue Recognition The following tables show the timing of revenue recognition: Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Timing of Revenue Recognition Transferred at a point of time $ 294 $ 634 $ — $ 928 $ (331 ) $ 597 Transferred over time 256,809 170,861 17,380 445,050 — 445,050 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Timing of Revenue Recognition Transferred at a point of time $ 638 $ 1,062 $ 10 $ 1,710 $ (508 ) $ 1,202 Transferred over time 487,661 343,776 37,156 868,593 — 868,593 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 During the three and six months ended June 30, 2018 , the Company recognized $5,452 and $6,618 of revenues, respectively, from performance obligations satisfied in previous periods. The following table includes the estimated revenue expected to be recognized in the future related to performance obligations that are partially or fully unsatisfied as of June 30, 2018 . The Company applies a practical expedient and does not disclose the value of unsatisfied performance obligations for contracts that (i) have an original expected duration of one year or less and (ii) contracts for which it recognizes revenue at the amount to which it has the right to invoice for services provided: Less than 1 year 1 Year 2 Years 3 Years Total Contract Type Fixed-price $ 7,897 $ 580 $ 139 $ — $ 8,616 The Company applies a practical expedient and does not disclose the amount of the transaction price allocated to the remaining performance obligations nor provide an explanation of when the Company expects to recognize that amount as revenue. Contract Balances The following table provides information on the classification of contract assets and liabilities in the condensed consolidated balance sheets: As of As of Contract assets included in unbilled revenues $ 18,393 $ 7,901 Contract liabilities included in accrued expenses and other current liabilities $ 5,398 $ 4,498 Contract assets included in unbilled revenues are recorded when services have been provided but the Company does not have an unconditional right to receive consideration. The Company recognizes an impairment loss when the contract carrying amount is greater than the remaining consideration receivable, less directly related costs to be incurred. Contract assets have increased from December 31, 2017 primarily due to new contracts entered into in 2018 where the Company’s right to bill is contingent upon achievement of contractual milestones. Contract liabilities comprise amounts billed to its clients for revenues not yet earned. Such amounts are anticipated to be recorded as revenues when services are performed in subsequent periods. During the three and six months ended June 30, 2018 , the Company recognized $1,808 and $3,432 of revenue, respectively, that was included in Accrued expenses and other current liabilities at January 1, 2018.

INCOME TAXES

INCOME TAXES	6 Months Ended
	Jun. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES In determining its interim provision for/(benefit from) income taxes, the Company uses an estimated annual effective tax rate, which is based on expected annual profit before tax, statutory tax rates and tax planning opportunities available in the various jurisdictions in which the Company operates. Certain significant or unusual items are separately recognized in the quarter in which they occur and can be a source of variability in the effective tax rates from quarter to quarter. The Company’s worldwide effective tax rate for the three months ended June 30, 2018 and 2017 was 12.0% and 13.2% , respectively, and (9.2)% and 14.9% during the six months ended June 30, 2018 and 2017 , respectively. The interim provision for/(benefit from) income taxes in the three and six months ended June 30, 2018 was favorably impacted by the recognition of $706 and $25,340 , respectively, of net deferred tax assets as a result of the election to disregard as separate entities for U.S. tax purposes certain foreign subsidiaries of the Company. In addition, the Company recorded excess tax benefits upon vesting or exercise of stock-based awards of $5,440 and $4,138 during the three months ended June 30, 2018 and 2017 , respectively, and $10,130 and $5,832 during the six months ended June 30, 2018 and 2017 , respectively. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Cuts and Jobs Act (“U.S. Tax Act”), the Company has made reasonable estimates of the effects and recorded provisional amounts in its interim financial statements as of June 30, 2018 . As the Company collects and prepares necessary data and interprets the U.S. Tax Act and any additional guidance issued by the U.S. Treasury Department, the IRS, and other standard-setting bodies, and further refines the calculations, the Company may make adjustments to the provisional amounts recorded. During the three months ended March 31, 2018, the Company further refined its estimate and recorded a provisional $2,157 increase in its income taxes payable associated with the one-time transition tax on accumulated foreign subsidiary earnings not previously subject to U.S. income tax which now totals $66,478 . Of this amount, $55,841 is classified as Taxes payable, noncurrent as of June 30, 2018 . No adjustments were recorded to the provisional income tax payable associated with the one-time transition tax during the three months ended June 30, 2018 . The Company expects to complete its analysis during the second half of 2018. Any adjustments during this measurement period will be included in the provision for income taxes in the reporting period when such adjustments are determined. The U.S. Tax Act subjects a U.S. shareholder to tax on global intangible low-taxed income (“GILTI”) earned by certain foreign subsidiaries. The FASB Staff Q&A, Topic 740, No. 5, Accounting for Global Intangible Low-Taxed Income , states that an entity can make an accounting policy election to either recognize deferred taxes for temporary basis differences expected to reverse as GILTI in future years or provide for the tax expense related to GILTI in the year the tax is incurred. During the six months ended June 30, 2018 , the Company elected to provide for the tax expense related to GILTI in the year the tax is incurred. This election did not have a material impact on the interim financial statements for the three and six months ended June 30, 2018 .

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The following table summarizes the components of stock-based compensation expense recognized in the Company’s condensed consolidated statements of income and comprehensive income for the periods indicated: Three Months Ended Six Months Ended 2018 2017 2018 2017 Cost of revenues $ 7,054 $ 4,189 $ 15,343 $ 9,539 Selling, general and administrative expenses 7,756 8,738 16,063 19,164 Total $ 14,810 $ 12,927 $ 31,406 $ 28,703 Stock Options Stock option activity under the Company’s plans is set forth below: Number of Options Weighted Average Exercise Price Aggregate Intrinsic Value Weighted Average Remaining Contractual Term (in years) Options outstanding at January 1, 2018 4,901,748 $ 40.91 Options granted 157,133 $ 112.91 Options exercised (566,799 ) $ 39.34 Options forfeited/cancelled (27,583 ) $ 63.63 Options outstanding at June 30, 2018 4,464,499 $ 43.50 $ 360,830 5.8 Options vested and exercisable at June 30, 2018 3,530,693 $ 35.46 $ 313,776 5.3 Options expected to vest at June 30, 2018 879,470 $ 73.49 $ 44,709 7.7 As of June 30, 2018 , $19,733 of total remaining unrecognized stock-based compensation cost related to unvested stock options, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.1 years . As of June 30, 2018 , a total of 3,423 shares underlying options exercised through June 30, 2018 , were in transfer with the Company’s transfer agent. Effective January 1, 2018, the Company changed the methodology for estimating volatility used in the Black-Scholes option valuation model. Prior to January 1, 2018, the Company estimated the volatility of its common stock by using historical volatility of peer public companies including the Company’s historical volatility. In the first quarter of 2018, the Company began exclusively using its own historical volatility as it believes this is a more accurate estimate of future volatility of the price of the Company’s common stock. The Company did not change the methodology for estimating any other Black-Scholes option valuation model assumptions as disclosed in Note 13 “Stock-Based Compensation” to the audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 . Restricted Stock and Restricted Stock Units Service-Based Awards The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the six months ended June 30, 2018 . Equity-Classified Restricted Stock Equity-Classified Equity-Settled Restricted Stock Units Liability-Classified Cash-Settled Restricted Stock Units Number of Shares Weighted Average Grant Date Fair Value Per Share Number of Shares Weighted Average Grant Date Fair Value Per Share Number of Shares Weighted Average Grant Date Fair Value Per Share Unvested service-based awards outstanding at January 1, 2018 1,840 $ 54.37 688,012 $ 71.60 314,829 $ 72.50 Awards granted — $ — 330,717 $ 114.22 85,380 $ 112.65 Awards modified — $ — (2,299 ) $ 72.80 2,299 $ 116.63 Awards vested — $ — (202,569 ) $ 69.90 (91,052 ) $ 72.42 Awards forfeited/cancelled — $ — (27,460 ) $ 77.90 (4,761 ) $ 76.50 Unvested service-based awards outstanding at June 30, 2018 1,840 $ 54.37 786,401 $ 89.74 306,695 $ 83.97 As of June 30, 2018 , $56 of total remaining unrecognized stock-based compensation cost related to service-based restricted stock is expected to be recognized over the weighted-average remaining requisite service period of 1.1 years . As of June 30, 2018 , $56,843 of total remaining unrecognized stock-based compensation cost related to service-based equity-classified restricted stock units (“RSUs”), net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 3.0 years . As of June 30, 2018 , there were 3,894 restricted share units vested for which the holders elected to defer delivery of EPAM Systems, Inc. ordinary shares. During the first quarter of 2018, 44,228 RSUs were granted in connection with the acquisition of Continuum. As of June 30, 2018 , $29,706 of total remaining unrecognized stock-based compensation cost related to service-based liability-classified RSUs, net of estimated forfeitures, is expected to be recognized over the weighted-average remaining requisite service period of 2.7 years . The liability associated with the service-based liability-classified RSUs as of June 30, 2018 and December 31, 2017 , was $4,338 and $5,964 , respectively, and was classified as Deferred compensation due to employees in the condensed consolidated balance sheets. Performance-Based Awards The table below summarizes activity related to the Company’s equity-classified performance-based awards for the six months ended June 30, 2018 . Equity-Classified Equity-Settled Restricted Stock Units Number of Shares Weighted Average Grant Date Fair Value Per Share Unvested performance-based awards outstanding at January 1, 2018 — $ — Awards granted 45,375 $ 121.75 Awards vested — $ — Awards forfeited/cancelled — $ — Unvested performance-based awards outstanding at June 30, 2018 45,375 $ 121.75 As of June 30, 2018 , $5,128 of total remaining unrecognized stock-based compensation cost related to performance-based equity-classified restricted stock units is expected to be recognized over the weighted-average remaining requisite service period of 2.2 years . Performance-based equity-classified RSUs were granted during the period in connection with the acquisition of Continuum and have a variable vesting period, subject to satisfaction of the applicable performance conditions with each vesting portion having its own service inception date. The Company will periodically assess the probability of achievement of the performance criteria and adjust the amount of compensation expense accordingly. Compensation is recognized over the vesting period and adjusted for the probability of achievement of the performance criteria for each vesting portion separately.

EARNINGS PER SHARE

EARNINGS PER SHARE	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Basic earnings per share is computed by dividing income available to common shareholders by the weighted-average number of shares of common stock outstanding during the period. Diluted earnings per share is computed by dividing income available to common shareholders by the weighted-average number of shares of common stock outstanding during the period increased to include the number of additional shares of common stock that would have been outstanding if the potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, unvested restricted stock and unvested equity-settled RSUs. The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method. The following table sets forth the computation of basic and diluted earnings per share of common stock as follows: Three Months Ended Six Months Ended 2018 2017 2018 2017 Numerator for basic and diluted earnings per share: Net income $ 50,255 $ 37,359 $ 114,673 $ 61,000 Numerator for basic and diluted earnings per share $ 50,255 $ 37,359 $ 114,673 $ 61,000 Denominator: Weighted average common shares for basic earnings per share 53,517,124 51,899,416 53,299,038 51,431,353 Net effect of dilutive stock options, restricted stock units and restricted stock awards 3,069,885 2,949,203 3,115,948 2,939,931 Weighted average common shares for diluted earnings per share 56,587,009 54,848,619 56,414,986 54,371,284 Net income per share: Basic $ 0.94 $ 0.72 $ 2.15 $ 1.19 Diluted $ 0.89 $ 0.68 $ 2.03 $ 1.12 The number of shares underlying equity–based awards that was excluded from the calculation of diluted earnings per share as their effect would be anti–dilutive was 155,142 and 104,186 during the three and six months ended June 30, 2018 , respectively. The number of shares underlying equity–based awards that was excluded from the calculation of diluted earnings per share as their effect would be anti–dilutive was 654,435 and 1,463,156 during the three and six months ended June 30, 2017 , respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Indemnification Obligations — In the normal course of business, the Company is a party to a variety of agreements under which it may be obligated to indemnify the other party for certain matters. These obligations typically arise in contracts where the Company customarily agrees to hold the other party harmless against losses arising from a breach of representations or covenants for certain matters such as title to assets, intellectual property rights and data privacy matters associated with certain arrangements. The duration of these indemnifications varies, and in certain cases, is indefinite. The Company is unable to reasonably estimate the maximum potential amount of future payments under these or similar agreements due to the unique facts and circumstances of each agreement and the fact that certain indemnifications provide for no limitation to the maximum potential future payments under the indemnification. Management is not aware of any such matters that would have a material effect on the condensed consolidated financial statements of the Company. Litigation — From time to time, the Company is involved in litigation, claims or other contingencies arising in the ordinary course of business. The Company accrues a liability when a loss is considered probable and the amount can be reasonably estimated. When a material loss contingency is reasonably possible but not probable, the Company does not record a liability, but instead discloses the nature and the amount of the claim, and an estimate of the loss or range of loss, if such an estimate can be made. Legal fees are expensed as incurred. In the opinion of management, the outcome of any existing claims and legal or regulatory proceedings, if decided adversely, is not expected to have a material effect on the Company’s business, financial condition, results of operations or cash flows.

SEGMENTS INFORMATION

SEGMENTS INFORMATION	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION The Company determines its business segments and reports segment information in accordance with how the Company’s chief operating decision maker (“CODM”) organizes the segments to evaluate performance, allocate resources and make business decisions. Segment results are based on the segment’s revenues and operating profit, where segment operating profit is defined as income from operations before unallocated costs. Generally, operating expenses for each reportable segment have similar characteristics and are subject to similar factors, pressures and challenges. Expenses included in segment operating profit consist principally of direct selling and delivery costs as well as an allocation of certain shared services expenses. Certain corporate expenses are not allocated to specific segments as these expenses are not directly attributable to or controllable at the segment level. Such expenses include certain types of professional fees and recruitment and development expenses, non-corporate taxes, compensations to non-employee directors and certain other general and administrative expenses, including compensation of specific groups of non-production employees. In addition, the Company does not allocate amortization of acquisition-related intangible assets, goodwill and other assets impairment charges, stock-based compensation expenses, acquisition-related costs and certain other one-time charges. These unallocated amounts are combined with total segment operating profit to arrive at consolidated income from operations as reported below in the reconciliation of segment operating profit to consolidated income before provision for income taxes. The Company manages its business primarily based on the managerial responsibility for its client base. As managerial responsibility for a particular client relationship generally correlates with the client’s geographic location, there is a high degree of similarity between client locations and the geographic boundaries of the Company’s reportable segments. In some cases, managerial responsibility for a particular client is assigned to a management team in another region and is usually based on the strength of the relationship between client executives and particular members of EPAM’s senior management team. In such cases, the client’s activity would be reported through the management team’s reportable segment. Revenues from external customers and operating profit, before unallocated expenses, by reportable segments for the three and six months ended June 30, 2018 and 2017 , were as follows: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 Segment revenues: North America $ 257,103 $ 194,025 $ 488,299 $ 372,328 Europe 171,495 141,319 344,838 274,026 Russia 17,380 13,677 37,166 27,370 Total segment revenues $ 445,978 $ 349,021 $ 870,303 $ 673,724 Segment operating profit: North America $ 51,221 $ 43,622 $ 95,181 $ 80,714 Europe 26,568 20,658 55,458 40,469 Russia 2,321 1,895 7,668 5,444 Total segment operating profit $ 80,110 $ 66,175 $ 158,307 $ 126,627 Intersegment transactions were excluded from the above on the basis that they are neither included in the measure of a segment’s profit and loss results, nor considered by the CODM during the review of segment results. There were no customers that accounted for more than 10% of total revenues during the three and six months ended June 30, 2018 and 2017 . Accounts receivable and unbilled revenues are generally dispersed across the Company’s clients in proportion to their revenues. As of June 30, 2018 and December 31, 2017 , unbilled revenues from one customer, individually exceeded 10% and accounted for 10.2% and 13.0% of total unbilled revenues, respectively. There were no customers individually exceeding 10% of total accounts receivable as of June 30, 2018 and December 31, 2017 . Reconciliation of segment revenues to consolidated revenues and segment operating profit to consolidated income before provision for income taxes is presented below: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 Total segment revenues $ 445,978 $ 349,021 $ 870,303 $ 673,724 Other income included in segment revenues (331 ) (44 ) (508 ) (96 ) Revenues $ 445,647 $ 348,977 $ 869,795 $ 673,628 Total segment operating profit: $ 80,110 $ 66,175 $ 158,307 $ 126,627 Unallocated amounts: Other income included in segment revenues (331 ) (44 ) (508 ) (96 ) Stock-based compensation expense (14,810 ) (12,927 ) (31,406 ) (28,703 ) Non-corporate taxes (2,418 ) (1,795 ) (4,978 ) (5,246 ) Professional fees (1,400 ) (2,476 ) (3,316 ) (4,820 ) Depreciation and amortization expense (1,974 ) (1,905 ) (3,743 ) (3,880 ) Bank charges (579 ) (446 ) (1,168 ) (843 ) One-time charges and other acquisition-related expenses (1,241 ) (330 ) (1,861 ) (898 ) Other operating expenses (3,120 ) (5,570 ) (8,393 ) (10,493 ) Income from operations 54,237 40,682 102,934 71,648 Interest and other income, net 1,052 802 501 1,386 Foreign exchange gain/(loss) 1,830 1,562 1,583 (1,393 ) Income before provision for income taxes $ 57,119 $ 43,046 $ 105,018 $ 71,641 Geographic Area Information Long-lived assets include property and equipment, net of accumulated depreciation and amortization. Geographical information about the Company’s long-lived assets based on physical location of the assets is presented below: As of As of Belarus $ 48,426 $ 49,866 United States 11,541 3,371 Russia 10,521 9,617 India 7,472 2,698 Ukraine 6,818 6,995 Hungary 3,350 3,901 China 3,275 2,608 Other 7,047 7,363 Total $ 98,450 $ 86,419 The table below presents information about the Company’s revenues by client location for the three and six months ended June 30, 2018 and 2017 . Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 United States $ 246,831 $ 192,319 $ 470,514 $ 369,149 United Kingdom 50,103 46,112 101,833 92,706 Switzerland 34,268 28,119 69,872 57,215 Germany 20,111 14,144 39,599 26,238 Canada 17,620 13,649 33,383 26,143 Netherlands 17,254 12,556 34,903 21,227 Russia 16,909 13,326 36,321 26,535 Other locations 42,551 28,752 83,370 54,415 Total $ 445,647 $ 348,977 $ 869,795 $ 673,628

SUMMARY OF SIGNIFICANT ACCOUN19

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
	Jun. 30, 2018
Accounting Policies [Abstract]
Nature of Operations	EPAM Systems, Inc. (the “Company” or “EPAM”) is a leading global provider of digital platform engineering and software development services to clients located around the world, primarily in North America, Europe, Asia and Australia. The Company has expertise in various industries, including software and hi-tech, financial services, business information and media, travel and hospitality, retail and distribution and life sciences and healthcare. The Company is incorporated in Delaware and headquartered in Newtown, PA.
Basis of Presentation	Basis of Presentation — The accompanying unaudited condensed consolidated financial statements of EPAM have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and Article 10 of Regulation S-X under the Securities Exchange Act of 1934, as amended. The condensed consolidated financial statements include the financial statements of EPAM Systems, Inc. and its subsidiaries with all intercompany balances and transactions eliminated. These unaudited condensed consolidated financial statements and accompanying notes should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2017 included in its Annual Report on Form 10-K.
Use of Estimates	The preparation of these condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in these condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates, and such differences may be material to the condensed consolidated financial statements. Operating results for the interim periods are not necessarily indicative of results that may be expected to occur for the entire year. In management’s opinion, all adjustments considered necessary for a fair presentation of the accompanying unaudited condensed consolidated financial statements have been included, and all adjustments are of a normal and recurring nature.
Adoption of New Accounting Standards	Adoption of New Accounting Standards Unless otherwise discussed below, the adoption of new accounting standards did not have an impact on the Company’s consolidated financial position, results of operations, and cash flows. Revenue Recognition — Effective January 1, 2018, the Company adopted the new accounting standard ASU 2014-09, Revenue from Contracts with Customers (Topic 606) as amended using the modified retrospective method. The standard effectively replaced previously existing revenue recognition guidance (Topic 605) and requires entities to recognize revenue to depict the transfer of promised goods or services in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services as well as requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts, including significant judgments and changes in judgments. The following table summarizes the cumulative effect of adopting Topic 606 using the modified retrospective method of adoption as of January 1, 2018: Balance as of Adjustments Balance as of Balance Sheet Assets Unbilled revenues $ 86,500 $ (78 ) $ 86,422 Deferred tax assets $ 24,974 $ (173 ) $ 24,801 Liabilities Accrued expenses and other current liabilities $ 89,812 $ (708 ) $ 89,104 Stockholders’ equity Retained earnings $ 518,820 $ 457 $ 519,277 The Company applied a practical expedient to aggregate the effect of all contract modifications that occurred before the adoption date. See Note 7 “Revenues” in the condensed consolidated interim financial statements for additional information regarding revenues. Restricted cash and restricted cash equivalents — Effective January 1, 2018, the Company adopted Accounting Standard Update (“ASU”) No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash which requires the Company to include in its cash and cash equivalents balances presented in the statements of cash flows amounts that are deemed to be restricted in nature. As a result of the adoption, the Company restated its condensed consolidated statements of cash flows for all of the prior periods presented. The impact of adoption on the Company’s condensed consolidated statement of cash flows was as follows for the six months ended June 30, 2017: As Reported Restated Effect Cash flows from operating activities: Changes in operating assets and liabilities: Prepaid expenses and other assets $ 736 $ 973 $ 237 Net cash provided by operating activities $ 59,096 $ 59,333 $ 237 Cash flows from investing activities: Decrease in restricted cash and time deposits, net $ 94 $ 13 $ (81 ) Acquisition of businesses, net of cash acquired $ (6,840 ) $ (6,810 ) $ 30 Net cash used in investing activities $ (17,574 ) $ (17,625 ) $ (51 ) Effect of exchange rate changes on cash, cash equivalents, and restricted cash $ 5,822 $ 5,912 $ 90 Net increase in cash, cash equivalents and restricted cash $ 81,476 $ 81,752 $ 276 Cash, cash equivalents and restricted cash, beginning of period 362,025 364,664 2,639 Cash, cash equivalents and restricted cash, end of period $ 443,501 $ 446,416 $ 2,915 Derivatives and Hedging — Effective April 1, 2018, the Company early-adopted ASU 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities . The new guidance is intended to simplify and amend hedge accounting and reporting to better align and disclose the economic results of an entity’s risk management activities in its financial statements. The ASU makes more financial and non-financial hedging strategies eligible for hedge accounting. It also changes how companies assess hedge effectiveness and amends the presentation and disclosure requirements by eliminating the requirement to separately measure and report hedge ineffectiveness and generally requires companies, for qualifying hedges, to present the entire change in the fair value of a hedging instrument in the same income statement line as the hedged item. The guidance also eases documentation and assessment requirements and modifies the accounting for components excluded from the assessment of hedge effectiveness. The guidance requires entities to apply the amended presentation and disclosure guidance prospectively as of the period of adoption. The adoption of this guidance did not have any effect on the consolidated financial results. The Company enters into derivative financial instruments to manage exposure to fluctuations in certain foreign currencies. During 2018, for accounting purposes, these foreign currency forward contracts became designated as hedges, as defined under FASB ASC Topic 815, Derivatives and Hedging . The Company measures these foreign currency derivative contracts at fair value on a recurring basis utilizing Level 2 inputs. The Company records changes in the fair value of these hedges in accumulated other comprehensive income/(loss) in our consolidated balance sheet until the forecasted transaction occurs. When the forecasted transaction occurs, the related gain or loss on the cash flow hedge is reclassified to the same line item in the statement of income as the forecasted transaction is recorded. In the event the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the Company reclassifies the gain or loss on the underlying hedge from accumulated other comprehensive income/(loss) to foreign exchange gain/(loss) in the consolidated statement of income. The cash flow impact of derivatives identified as hedging instruments is reflected as cash flows from operating activities. The cash flow impact of derivatives not identified as hedging instruments is reflected as cash flows from investing activities. Pending Accounting Standards From time to time, new accounting pronouncements are issued by the FASB or other standards-setting bodies that the Company will adopt according to the various timetables the FASB specifies. Unless otherwise discussed below, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its consolidated financial position, results of operations and cash flows upon adoption. Leases — Effective January 1, 2019, the Company will be required to adopt the new guidance of ASC Topic 842, Leases (Topic 842) (with early adoption permitted effective January 1, 2018). This amendment supersedes previous accounting guidance (Topic 840) and requires all leases, with the exception of leases with a term of twelve months or less, to be recorded on the balance sheet as lease assets and lease liabilities. The standard allows for two methods of adoption to recognize and measure leases: retrospectively to each prior period presented in the financial statements with the cumulative effect of initially applying the guidance recognized at the beginning of the earliest comparative period presented or retrospectively at the beginning of the period of adoption with the cumulative effect of initially applying the guidance recognized at the beginning of the period in which the guidance is first applied. The adoption methods both include a number of optional practical expedients that entities may elect to apply. These practical expedients relate to the identification and classification of leases that commenced before the effective date, initial direct costs for leases that commenced before the effective date, and the ability to use hindsight in evaluating lessee options to extend or terminate a lease or to purchase the underlying asset. An entity that elects to apply the practical expedients will, in effect, continue to account for leases that commence before the effective date in accordance with previous GAAP unless the lease is modified, except that lessees are required to recognize a right-of-use asset and a lease liability for all operating leases based on the present value of the remaining minimum rental payments that were tracked and disclosed under previous GAAP. The transition guidance in Topic 842 also provides specific guidance for the amounts previously recognized in accordance with the business combinations guidance for leases. The Company has developed a transition plan, which includes making necessary changes to policies, processes, internal controls and system enhancements to generate the information necessary to comply with the new standard. The Company expects the new guidance will have a material impact on its consolidated balance sheet for the addition of right-of-use assets and lease liabilities principally due to its office space leases. EPAM does not expect the new guidance to have a material impact on its consolidated statement of income and comprehensive income or its consolidated statement of cash flows. The Company expects to adopt this standard on January 1, 2019 using the method of adoption whereby the cumulative effect of adoption is recognized at the beginning of the period of adoption. Measurement of Credit Losses on Financial Instruments — Effective January 1, 2020, the Company will be required to adopt the amended guidance of ASC Topic 326, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments , (with early adoption permitted effective January 1, 2019.) The amendments in this update change how companies measure and recognize credit impairment for many financial assets. The new expected credit loss model will require companies to immediately recognize an estimate of credit losses expected to occur over the remaining life of the financial assets (including trade receivables) that are in the scope of the update. The update also made amendments to the current impairment model for held-to-maturity and available-for-sale debt securities and certain guarantees. Entities are required to adopt the standard using a modified-retrospective approach through a cumulative effect adjustment to retained earnings as of the beginning of the period of adoption. The Company has not yet completed its assessment of the impact of the new guidance on its consolidated financial statements or concluded on when it will adopt the standard.

DERIVATIVE FINANCIAL INSTRUME20

DERIVATIVE FINANCIAL INSTRUMENTS (Policies)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities	The Company measures derivative instruments and hedging activities at fair value and recognizes them as either assets or liabilities in its consolidated balance sheets. Accounting for the gains and losses resulting from changes in fair value depends on the use of the derivative and whether it is designated and qualifies for hedge accounting. As of June 30, 2018 , all of the Company’s foreign exchange forward contracts were designated as hedges. To receive hedge accounting treatment, all hedging relationships are formally documented at the inception of the hedge, and the hedges must be highly effective in offsetting changes to future cash flows on hedged transactions.
Reporting of Cash Flow Hedges	The Company records changes in the fair value of its cash flow hedges in accumulated other comprehensive income/(loss) in the consolidated balance sheet until the forecasted transaction occurs. When the forecasted transaction occurs, the Company reclassifies the related gain or loss on the cash flow hedge to cost of revenues (exclusive of depreciation and amortization). In the event the underlying forecasted transaction does not occur, or it becomes probable that it will not occur, the Company reclassifies the gain or loss on the related cash flow hedge from accumulated other comprehensive income/(loss) to foreign exchange gain/(loss) in the consolidated statement of income in that period.
Reporting of Derivative Activity	If the Company does not elect hedge accounting, or the contract does not qualify for hedge accounting treatment, the changes in fair value from period to period are recorded in foreign exchange gain/(loss) in the consolidated statement of income.

REVENUES (Policies)

REVENUES (Policies)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Effective January 1, 2018, the Company adopted ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) as amended. The Company adopted the new guidance using the modified retrospective method by recognizing the cumulative effect of adoption as an adjustment to retained earnings as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with Topic 605. The impact of adoption of the new guidance on the Company’s consolidated financial statements as of January 1, 2018 are presented in Note 1 “Summary of Significant Accounting Policies.” The Company recognizes revenues when control of goods or services is passed to a customer in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Such control may be transferred over time or at a point in time depending on satisfaction of obligations stipulated by the contract. Consideration expected to be received may consist of both fixed and variable components and is allocated to each separately identifiable performance obligation based on the performance obligation’s relative standalone selling price. Variable consideration is usually presented in the form of cash incentives or credits. Determining the estimated amount of such variable consideration involves assumptions and judgment that can have an impact on the amount of revenue reported. The Company derives its revenues from a variety of service offerings, which represent specific competencies of its IT professionals. Fees for these contracts may be in the form of time-and-materials or fixed-price arrangements. The majority of the Company’s revenues are generated under time-and-material contracts which are billed using hourly, daily or monthly rates to determine the amounts to be charged directly to the client. The Company applies a practical expedient and revenue related to time-and-material contracts is recognized based on the Company’s right to invoice for services performed. Fixed-price contracts include maintenance and support arrangements, which may exceed one year in duration, as well as application development arrangements. Maintenance and support arrangements generally relate to the provision of ongoing services. Revenues for such agreements are recognized ratably over the expected service period. Application development arrangements are accounted for using input or output methods for measuring the progress towards satisfaction of the performance obligation. Input methods are used only when there is a direct correlation between hours incurred and the end product delivered. Assumptions, risks and uncertainties inherent in the estimates used to measure progress could affect the amount of revenues, receivables and deferred revenues at each reporting period. Revenues from licenses which have significant stand-alone functionality are recognized at a point in time when control of the license is transferred to the customer. Revenues from licenses which do not have stand-alone functionality are recognized over time. If there is an uncertainty about the receipt of payment for the services, revenue is deferred until the uncertainty is sufficiently resolved. The Company applies a practical expedient and does not assess the existence of a significant financing component if the period between when the Company transfers the service to a customer and when the customer pays for that service is one year or less. The Company reports gross reimbursable “out-of-pocket” expenses incurred as both revenues and cost of revenues in the condensed consolidated statements of income and comprehensive income.
Unbilled Revenues	Contract assets included in unbilled revenues are recorded when services have been provided but the Company does not have an unconditional right to receive consideration.
Impairment Loss	The Company recognizes an impairment loss when the contract carrying amount is greater than the remaining consideration receivable, less directly related costs to be incurred.
Deferred Revenues	Contract liabilities comprise amounts billed to its clients for revenues not yet earned. Such amounts are anticipated to be recorded as revenues when services are performed in subsequent periods.

SUMMARY OF SIGNIFICANT ACCOUN22

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cummulative Effect of Adoption of ASU	The following tables summarize the impacts of changes in accounting policies after adoption of Topic 606 on the Company’s condensed consolidated financial statements for the three and six months ended June 30, 2018 , which primarily resulted from deferring the timing of revenue recognition for contracts that were previously recognized on a cash basis and recognizing revenues from certain license agreements at a point-in-time rather than over time: As of June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Balance Sheet Liabilities Accrued expenses and other current liabilities $ 72,443 $ 72,426 $ 17 Other noncurrent liabilities 16,421 16,424 (3 ) Stockholders’ equity Retained earnings $ 633,950 $ 633,964 $ (14 ) Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Income Statement Revenues $ 445,647 $ 444,951 $ 696 $ 869,795 $ 869,812 $ (17 ) Income from operations $ 54,237 $ 53,541 $ 696 $ 102,934 $ 102,951 $ (17 ) Provision for/(benefit from) income taxes $ 6,864 $ 6,728 $ 136 $ (9,655 ) $ (9,652 ) $ (3 ) Net income $ 50,255 $ 49,695 $ 560 $ 114,673 $ 114,687 $ (14 )
Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cummulative Effect of Adoption of ASU	The following table summarizes the cumulative effect of adopting Topic 606 using the modified retrospective method of adoption as of January 1, 2018: Balance as of Adjustments Balance as of Balance Sheet Assets Unbilled revenues $ 86,500 $ (78 ) $ 86,422 Deferred tax assets $ 24,974 $ (173 ) $ 24,801 Liabilities Accrued expenses and other current liabilities $ 89,812 $ (708 ) $ 89,104 Stockholders’ equity Retained earnings $ 518,820 $ 457 $ 519,277
ASU 2016-18
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cummulative Effect of Adoption of ASU	The impact of adoption on the Company’s condensed consolidated statement of cash flows was as follows for the six months ended June 30, 2017: As Reported Restated Effect Cash flows from operating activities: Changes in operating assets and liabilities: Prepaid expenses and other assets $ 736 $ 973 $ 237 Net cash provided by operating activities $ 59,096 $ 59,333 $ 237 Cash flows from investing activities: Decrease in restricted cash and time deposits, net $ 94 $ 13 $ (81 ) Acquisition of businesses, net of cash acquired $ (6,840 ) $ (6,810 ) $ 30 Net cash used in investing activities $ (17,574 ) $ (17,625 ) $ (51 ) Effect of exchange rate changes on cash, cash equivalents, and restricted cash $ 5,822 $ 5,912 $ 90 Net increase in cash, cash equivalents and restricted cash $ 81,476 $ 81,752 $ 276 Cash, cash equivalents and restricted cash, beginning of period 362,025 364,664 2,639 Cash, cash equivalents and restricted cash, end of period $ 443,501 $ 446,416 $ 2,915

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Fair Values of Net Assets Acquired	The following table summarizes the preliminary fair values of the assets acquired and liabilities assumed in connection with the acquisition of Continuum as originally reported and as adjusted as of June 30, 2018 : As Originally Reported As Adjusted Cash and cash equivalents $ 2,251 $ 2,251 Accounts receivable 6,676 6,676 Unbilled revenues 2,463 2,463 Prepaid and other current assets 942 936 Goodwill 29,805 26,293 Intangible assets 16,600 14,850 Property and equipment and other noncurrent assets 8,902 8,902 Total assets acquired $ 67,639 $ 62,371 Accounts payable, accrued expenses and other current liabilities $ 2,991 $ 2,745 Due to employees 1,001 1,001 Long-term debt (Note 6) 3,220 3,220 Other noncurrent liabilities 5,412 490 Total liabilities assumed $ 12,624 $ 7,456 Net assets acquired $ 55,015 $ 54,915
Fair Values and Useful Lives of Intangible Assets Acquired	The following table presents the estimated fair values and useful lives of intangible assets acquired in connection with the acquisition of Continuum: Continuum Weighted Average Useful Life (in years) Amount Favorable lease 11.9 $ 5,900 Customer relationships 6.6 5,800 Contract royalties 8 1,900 Trade names 5 1,250 Total $ 14,850

GOODWILL (Tables)

GOODWILL (Tables)	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill By Reportable Segment	Goodwill by reportable segment was as follows: North America Europe Total Balance as of December 31, 2017 $ 77,290 $ 42,241 $ 119,531 Continuum acquisition (Note 2) 26,293 — 26,293 Effect of net foreign currency exchange rate changes (285 ) (872 ) (1,157 ) Balance as of June 30, 2018 $ 103,298 $ 41,369 $ 144,667

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Financial Assers and Liabilities Measured at Fair Value on Recurring Basis	The following table shows the fair values of the Company’s financial assets and liabilities measured at fair value on a recurring basis as of June 30, 2018 : As of June 30, 2018 Balance Level 1 Level 2 Level 3 Foreign exchange derivative assets $ 84 $ — $ 84 $ — Total assets measured at fair value on a recurring basis $ 84 $ — $ 84 $ — Contingent consideration $ 2,400 $ — $ — $ 2,400 Foreign exchange derivative liabilities 2,690 $ — 2,690 $ — Total liabilities measured at fair value on a recurring basis $ 5,090 $ — $ 2,690 $ 2,400 The Company had no material financial assets or liabilities measured at fair value on a recurring basis as of December 31, 2017.
Acquisition-Related Contractual Contingent Liabilities Roll Forward	A reconciliation of the beginning and ending balances of acquisition-related contractual contingent liabilities using significant unobservable inputs (Level 3) for the six months ended June 30, 2018 is as follows: Amount Contractual contingent liabilities at December 31, 2017 $ — Acquisition date fair value of contractual contingent liabilities — Continuum (Note 2) 2,400 Contractual contingent liabilities at June 30, 2018 $ 2,400
Reported Amounts and Estimated Fair Values of the Financial Assets and Liabilities Requiring Fair Value Disclosure	The following tables present the reported amounts and estimated fair values of the financial assets and liabilities for which disclosure of fair value is required, as they would be categorized within the fair value hierarchy, as of the dates indicated: Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 June 30, 2018 Financial Assets: Cash and cash equivalents $ 584,081 $ 584,081 $ 584,081 $ — $ — Restricted cash $ 1,195 $ 1,195 $ 1,195 $ — $ — Employee loans $ 3,753 $ 3,753 $ — $ — $ 3,753 Financial Liabilities: Borrowings under the 2017 Credit Facility $ 25,019 $ 25,019 $ — $ 25,019 $ — Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 December 31, 2017 Financial Assets: Cash and cash equivalents $ 582,585 $ 582,585 $ 582,585 $ — $ — Time deposits and restricted cash $ 673 $ 673 $ — $ 673 $ — Employee loans $ 4,210 $ 4,210 $ — $ — $ 4,210 Financial Liabilities: Borrowings under the 2017 Credit Facility $ 25,009 $ 25,009 $ — $ 25,009 $ —

DERIVATIVE FINANCIAL INSTRUME26

DERIVATIVE FINANCIAL INSTRUMENTS (Tables)	6 Months Ended
	Jun. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Derivative Instruments	The fair value of derivative instruments on the Company’s consolidated balance sheets as of June 30, 2018 and December 31, 2017 were as follows: As of June 30, 2018 As of December 31, 2017 Balance Sheet Location Asset Derivatives Liability Derivatives Asset Derivatives Liability Derivatives Foreign exchange forward contracts - Designated as hedging instruments Prepaid and other current assets $ 84 $ — Accrued expenses and other current liabilities $ 2,690 $ — Foreign exchange forward contracts - Not designated as hedging instruments Prepaid and other current assets $ — $ 114 Accrued expenses and other current liabilities $ — $ —
Changes in the Fair Value of Derivative Instruments	The changes in the fair value of foreign currency derivative instruments in our unaudited condensed consolidated statements of income and comprehensive income for the three and six months ended June 30, 2018 and 2017 were as follows: Three Months Ended Six Months Ended 2018 2017 2018 2017 Foreign exchange forward contracts - Designated as hedging instruments: Change in fair value recognized in accumulated other comprehensive loss (2,696 ) — (2,606 ) — Net loss reclassified from accumulated other comprehensive loss into cost of revenues (exclusive of depreciation and amortization) (937 ) — (937 ) — Foreign exchange forward contracts - Not designated as hedging instruments: Net gain recognized in foreign exchange gain/(loss) — 20 44 159

LONG-TERM DEBT LONG-TERM DEBT (

LONG-TERM DEBT LONG-TERM DEBT (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Outstanding Dept And Borrowing Capacity under 2017 Credit Facility	The following table presents the outstanding debt and borrowing capacity of the Company under the 2017 Credit Facility: As of As of Outstanding debt $ 25,000 $ 25,000 Interest rate 3.1 % 2.6 % Irrevocable standby letters of credit $ 343 $ 1,294 Available borrowing capacity $ 274,657 $ 273,706 Current maximum borrowing capacity $ 300,000 $ 300,000

REVENUES (Tables)

REVENUES (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Impact of Changes After Adoption of Topic 606	The following tables summarize the impacts of changes in accounting policies after adoption of Topic 606 on the Company’s condensed consolidated financial statements for the three and six months ended June 30, 2018 , which primarily resulted from deferring the timing of revenue recognition for contracts that were previously recognized on a cash basis and recognizing revenues from certain license agreements at a point-in-time rather than over time: As of June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Balance Sheet Liabilities Accrued expenses and other current liabilities $ 72,443 $ 72,426 $ 17 Other noncurrent liabilities 16,421 16,424 (3 ) Stockholders’ equity Retained earnings $ 633,950 $ 633,964 $ (14 ) Three Months Ended June 30, 2018 Six Months Ended June 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) As Reported Balances Without Adoption of Topic 606 Effect of Change Higher/(Lower) Income Statement Revenues $ 445,647 $ 444,951 $ 696 $ 869,795 $ 869,812 $ (17 ) Income from operations $ 54,237 $ 53,541 $ 696 $ 102,934 $ 102,951 $ (17 ) Provision for/(benefit from) income taxes $ 6,864 $ 6,728 $ 136 $ (9,655 ) $ (9,652 ) $ (3 ) Net income $ 50,255 $ 49,695 $ 560 $ 114,673 $ 114,687 $ (14 )
Disaggregation of Revenues	The following tables show the disaggregation of the Company’s revenues by major client location, including a reconciliation of the disaggregated revenue with the reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Client Locations North America $ 250,273 $ 14,177 $ 14 $ 264,464 $ (13 ) $ 264,451 Europe 3,086 146,998 — 150,084 (280 ) 149,804 CIS 2,089 28 17,294 19,411 — 19,411 APAC 1,655 10,292 72 12,019 (38 ) 11,981 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Client Locations North America $ 476,343 $ 27,538 — $ 29 — $ 503,910 $ (13 ) $ 503,897 Europe 5,826 297,478 — 42 — 303,346 (457 ) 302,889 CIS 4,092 91 — 37,008 — 41,191 — 41,191 APAC 2,038 19,731 — 87 — 21,856 (38 ) 21,818 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 The following tables show the disaggregation of the Company’s revenues by industry vertical, including a reconciliation of the disaggregated revenue with the reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Industry Vertical Financial Services $ 26,732 $ 62,496 $ 14,091 $ 103,319 $ (331 ) $ 102,988 Travel & Consumer 47,104 52,120 1,792 101,016 — 101,016 Software & Hi-Tech 64,536 19,857 624 85,017 — 85,017 Business Information & Media 59,532 18,117 — 77,649 — 77,649 Life Sciences & Healthcare 32,876 5,649 — 38,525 — 38,525 Emerging Verticals 26,323 13,256 873 40,452 — 40,452 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Industry Vertical Financial Services $ 48,688 $ 128,314 $ 30,316 $ 207,318 $ (508 ) $ 206,810 Travel & Consumer 87,791 101,574 3,465 192,830 — 192,830 Software & Hi-Tech 125,100 40,151 1,388 166,639 — 166,639 Business Information & Media 116,869 36,987 — 153,856 — 153,856 Life Sciences & Healthcare 60,343 10,472 — 70,815 — 70,815 Emerging Verticals 49,508 27,340 1,997 78,845 — 78,845 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 The following tables show the disaggregation of the Company’s revenues by contract type including a reconciliation of the disaggregated revenue with the Company’s reportable segments (Note 12 “Segment Information”) for the three and six months ended June 30, 2018 : Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Contract Type Time-and-material $ 233,747 $ 156,637 $ 9,765 $ 400,149 $ — $ 400,149 Fixed-price 22,483 14,081 7,607 44,171 — 44,171 Licensing 638 327 1 966 — 966 Other revenues 235 450 7 692 (331 ) 361 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Contract Type Time-and-material $ 448,063 $ 316,103 $ 19,861 $ 784,027 $ — $ 784,027 Fixed-price 38,475 27,034 17,279 82,788 — 82,788 Licensing 1,300 946 11 2,257 — 2,257 Other revenues 461 755 15 1,231 (508 ) 723 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795 Timing of Revenue Recognition The following tables show the timing of revenue recognition: Three Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Timing of Revenue Recognition Transferred at a point of time $ 294 $ 634 $ — $ 928 $ (331 ) $ 597 Transferred over time 256,809 170,861 17,380 445,050 — 445,050 Revenues $ 257,103 $ 171,495 $ 17,380 $ 445,978 $ (331 ) $ 445,647 Six Months Ended June 30, 2018 Reportable Segments North America Europe Russia Total Segment Revenue Other Income Included in Segment Revenues Consolidated Revenues Timing of Revenue Recognition Transferred at a point of time $ 638 $ 1,062 $ 10 $ 1,710 $ (508 ) $ 1,202 Transferred over time 487,661 343,776 37,156 868,593 — 868,593 Revenues $ 488,299 $ 344,838 $ 37,166 $ 870,303 $ (508 ) $ 869,795
Revenue Expected to be Recognized in Future Related to Remaining Performance Obligations	The following table includes the estimated revenue expected to be recognized in the future related to performance obligations that are partially or fully unsatisfied as of June 30, 2018 . The Company applies a practical expedient and does not disclose the value of unsatisfied performance obligations for contracts that (i) have an original expected duration of one year or less and (ii) contracts for which it recognizes revenue at the amount to which it has the right to invoice for services provided: Less than 1 year 1 Year 2 Years 3 Years Total Contract Type Fixed-price $ 7,897 $ 580 $ 139 $ — $ 8,616
Contract Balances	The following table provides information on the classification of contract assets and liabilities in the condensed consolidated balance sheets: As of As of Contract assets included in unbilled revenues $ 18,393 $ 7,901 Contract liabilities included in accrued expenses and other current liabilities $ 5,398 $ 4,498

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	6 Months Ended
	Jun. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Costs Related to Stock Compensation Plans	The following table summarizes the components of stock-based compensation expense recognized in the Company’s condensed consolidated statements of income and comprehensive income for the periods indicated: Three Months Ended Six Months Ended 2018 2017 2018 2017 Cost of revenues $ 7,054 $ 4,189 $ 15,343 $ 9,539 Selling, general and administrative expenses 7,756 8,738 16,063 19,164 Total $ 14,810 $ 12,927 $ 31,406 $ 28,703
Stock Options Activity	Stock option activity under the Company’s plans is set forth below: Number of Options Weighted Average Exercise Price Aggregate Intrinsic Value Weighted Average Remaining Contractual Term (in years) Options outstanding at January 1, 2018 4,901,748 $ 40.91 Options granted 157,133 $ 112.91 Options exercised (566,799 ) $ 39.34 Options forfeited/cancelled (27,583 ) $ 63.63 Options outstanding at June 30, 2018 4,464,499 $ 43.50 $ 360,830 5.8 Options vested and exercisable at June 30, 2018 3,530,693 $ 35.46 $ 313,776 5.3 Options expected to vest at June 30, 2018 879,470 $ 73.49 $ 44,709 7.7
Service-based Awards Activity	The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the six months ended June 30, 2018 . Equity-Classified Restricted Stock Equity-Classified Equity-Settled Restricted Stock Units Liability-Classified Cash-Settled Restricted Stock Units Number of Shares Weighted Average Grant Date Fair Value Per Share Number of Shares Weighted Average Grant Date Fair Value Per Share Number of Shares Weighted Average Grant Date Fair Value Per Share Unvested service-based awards outstanding at January 1, 2018 1,840 $ 54.37 688,012 $ 71.60 314,829 $ 72.50 Awards granted — $ — 330,717 $ 114.22 85,380 $ 112.65 Awards modified — $ — (2,299 ) $ 72.80 2,299 $ 116.63 Awards vested — $ — (202,569 ) $ 69.90 (91,052 ) $ 72.42 Awards forfeited/cancelled — $ — (27,460 ) $ 77.90 (4,761 ) $ 76.50 Unvested service-based awards outstanding at June 30, 2018 1,840 $ 54.37 786,401 $ 89.74 306,695 $ 83.97
Performance-based Awards Activity	The table below summarizes activity related to the Company’s equity-classified performance-based awards for the six months ended June 30, 2018 . Equity-Classified Equity-Settled Restricted Stock Units Number of Shares Weighted Average Grant Date Fair Value Per Share Unvested performance-based awards outstanding at January 1, 2018 — $ — Awards granted 45,375 $ 121.75 Awards vested — $ — Awards forfeited/cancelled — $ — Unvested performance-based awards outstanding at June 30, 2018 45,375 $ 121.75

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings Per Share	The following table sets forth the computation of basic and diluted earnings per share of common stock as follows: Three Months Ended Six Months Ended 2018 2017 2018 2017 Numerator for basic and diluted earnings per share: Net income $ 50,255 $ 37,359 $ 114,673 $ 61,000 Numerator for basic and diluted earnings per share $ 50,255 $ 37,359 $ 114,673 $ 61,000 Denominator: Weighted average common shares for basic earnings per share 53,517,124 51,899,416 53,299,038 51,431,353 Net effect of dilutive stock options, restricted stock units and restricted stock awards 3,069,885 2,949,203 3,115,948 2,939,931 Weighted average common shares for diluted earnings per share 56,587,009 54,848,619 56,414,986 54,371,284 Net income per share: Basic $ 0.94 $ 0.72 $ 2.15 $ 1.19 Diluted $ 0.89 $ 0.68 $ 2.03 $ 1.12

SEGMENTS INFORMATION (Tables)

SEGMENTS INFORMATION (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Revenues from External Customers and Operating Profit/(Loss) Before Unallocated Expenses	Revenues from external customers and operating profit, before unallocated expenses, by reportable segments for the three and six months ended June 30, 2018 and 2017 , were as follows: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 Segment revenues: North America $ 257,103 $ 194,025 $ 488,299 $ 372,328 Europe 171,495 141,319 344,838 274,026 Russia 17,380 13,677 37,166 27,370 Total segment revenues $ 445,978 $ 349,021 $ 870,303 $ 673,724 Segment operating profit: North America $ 51,221 $ 43,622 $ 95,181 $ 80,714 Europe 26,568 20,658 55,458 40,469 Russia 2,321 1,895 7,668 5,444 Total segment operating profit $ 80,110 $ 66,175 $ 158,307 $ 126,627
Reconciliation of Segment Revenues to Consolidated Revenues and Segment Operating Profit to Consolidated Income Before Provision for Income Taxes	Reconciliation of segment revenues to consolidated revenues and segment operating profit to consolidated income before provision for income taxes is presented below: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 Total segment revenues $ 445,978 $ 349,021 $ 870,303 $ 673,724 Other income included in segment revenues (331 ) (44 ) (508 ) (96 ) Revenues $ 445,647 $ 348,977 $ 869,795 $ 673,628 Total segment operating profit: $ 80,110 $ 66,175 $ 158,307 $ 126,627 Unallocated amounts: Other income included in segment revenues (331 ) (44 ) (508 ) (96 ) Stock-based compensation expense (14,810 ) (12,927 ) (31,406 ) (28,703 ) Non-corporate taxes (2,418 ) (1,795 ) (4,978 ) (5,246 ) Professional fees (1,400 ) (2,476 ) (3,316 ) (4,820 ) Depreciation and amortization expense (1,974 ) (1,905 ) (3,743 ) (3,880 ) Bank charges (579 ) (446 ) (1,168 ) (843 ) One-time charges and other acquisition-related expenses (1,241 ) (330 ) (1,861 ) (898 ) Other operating expenses (3,120 ) (5,570 ) (8,393 ) (10,493 ) Income from operations 54,237 40,682 102,934 71,648 Interest and other income, net 1,052 802 501 1,386 Foreign exchange gain/(loss) 1,830 1,562 1,583 (1,393 ) Income before provision for income taxes $ 57,119 $ 43,046 $ 105,018 $ 71,641
Geographical Information of Long-Lived Assets Based on Physical Location	Geographical information about the Company’s long-lived assets based on physical location of the assets is presented below: As of As of Belarus $ 48,426 $ 49,866 United States 11,541 3,371 Russia 10,521 9,617 India 7,472 2,698 Ukraine 6,818 6,995 Hungary 3,350 3,901 China 3,275 2,608 Other 7,047 7,363 Total $ 98,450 $ 86,419
Revenues by Client Location	The table below presents information about the Company’s revenues by client location for the three and six months ended June 30, 2018 and 2017 . Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 United States $ 246,831 $ 192,319 $ 470,514 $ 369,149 United Kingdom 50,103 46,112 101,833 92,706 Switzerland 34,268 28,119 69,872 57,215 Germany 20,111 14,144 39,599 26,238 Canada 17,620 13,649 33,383 26,143 Netherlands 17,254 12,556 34,903 21,227 Russia 16,909 13,326 36,321 26,535 Other locations 42,551 28,752 83,370 54,415 Total $ 445,647 $ 348,977 $ 869,795 $ 673,628

SUMMARY OF SIGNIFICANT ACCOUN32

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Revenue Recognition) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Unbilled revenues	$ 123,434	$ 86,422	$ 86,500
Deferred tax assets	54,805	24,801	24,974
Liabilities
Accrued expenses and other current liabilities	72,443	89,104	89,812
Stockholders’ equity
Retained earnings	633,950	519,277	518,820
Balance under Revenue Guidance in Effect before Topic 606
Assets
Unbilled revenues			86,500
Deferred tax assets			24,974
Liabilities
Accrued expenses and other current liabilities	72,426		89,812
Stockholders’ equity
Retained earnings	633,964		$ 518,820
Topic 606 | Adjustments
Assets
Unbilled revenues		(78)
Deferred tax assets		(173)
Liabilities
Accrued expenses and other current liabilities	17	(708)
Stockholders’ equity
Retained earnings	$ (14)	$ 457

SUMMARY OF SIGNIFICANT ACCOUN33

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Restricted Cash and Restricted Cash Equivalents) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Changes in operating assets and liabilities:
Prepaid expenses and other assets	$ (4,495)	$ 973
Net cash provided by operating activities	66,789	59,333
Cash flows from investing activities:
Decrease in restricted cash and time deposits, net	418	13
Acquisition of businesses, net of cash acquired	(50,264)	(6,810)
Net cash used in investing activities	(68,314)	(17,625)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(7,645)	5,912
Net increase in cash, cash equivalents and restricted cash	2,421	81,752
Cash, cash equivalents and restricted cash, beginning of period	582,585
Cash, cash equivalents and restricted cash, beginning of period	582,855	364,664
Cash, cash equivalents and restricted cash, end of period	584,081
Cash, cash equivalents and restricted cash, end of period	$ 585,276	446,416
As Reported
Changes in operating assets and liabilities:
Prepaid expenses and other assets		736
Net cash provided by operating activities		59,096
Cash flows from investing activities:
Decrease in restricted cash and time deposits, net		94
Acquisition of businesses, net of cash acquired		(6,840)
Net cash used in investing activities		(17,574)
Effect of exchange rate changes on cash, cash equivalents, and restricted cash		5,822
Net increase in cash, cash equivalents and restricted cash		81,476
Cash, cash equivalents and restricted cash, beginning of period		362,025
Cash, cash equivalents and restricted cash, end of period		443,501
ASU 2016-18 | Effect
Changes in operating assets and liabilities:
Prepaid expenses and other assets		237
Net cash provided by operating activities		237
Cash flows from investing activities:
Decrease in restricted cash and time deposits, net		(81)
Acquisition of businesses, net of cash acquired		(30)
Net cash used in investing activities		(51)
Effect of exchange rate changes on cash, cash equivalents, and restricted cash		90
Net increase in cash, cash equivalents and restricted cash		276
Cash, cash equivalents and restricted cash, beginning of period		2,639
Cash, cash equivalents and restricted cash, end of period		$ 2,915

ACQUISITIONS (Narrative) (Detai

ACQUISITIONS (Narrative) (Details) - Continuum $ in Thousands	Mar. 15, 2018USD ($)	Jun. 30, 2018USD ($)
Business Acquisition [Line Items]
Acquisition date	Mar. 15, 2018
Cash consideration	$ 52,515
Cash consideration placed in escrow	$ 5,410
Estimated future operating results, period	12 months
Earnout payment		$ 2,400
Minimum
Business Acquisition [Line Items]
Consideration placed in escrow, period	9 months
Maximum
Business Acquisition [Line Items]
Consideration placed in escrow, period	15 months
Earnout payment	$ 3,135
Design Consultants
Business Acquisition [Line Items]
Numbers of employees acquired	125

ACQUISITIONS (Fair Value of Net

ACQUISITIONS (Fair Value of Net Assets Acquired) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Unbilled revenues	$ 123,434		$ 86,422	$ 86,500
Goodwill	144,667			$ 119,531
Continuum
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Cash and cash equivalents	2,251	$ 2,251
Accounts receivable	6,676	6,676
Unbilled revenues	2,463	2,463
Prepaid and other current assets	936	942
Goodwill	26,293	29,805
Intangible assets	14,850	16,600
Property and equipment and other noncurrent assets	8,902	8,902
Total assets acquired	62,371	67,639
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Accounts payable, accrued expenses and other current liabilities	2,745	2,991
Due to employees	1,001	1,001
Long-term debt (Note 6)	3,220	3,220
Other noncurrent liabilities	490	5,412
Total liabilities assumed	7,456	12,624
Net assets acquired	$ 54,915	$ 55,015

ACQUISITIONS (Income Statement

ACQUISITIONS (Income Statement Effect) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Continuum
Business Acquisition [Line Items]
Revenues	8,470		$ 10,224
Continuum | Amortization expense
Business Acquisition [Line Items]
Adjustment related to incomplete initial accounting	26
Continuum | Rent expense
Business Acquisition [Line Items]
Adjustment related to incomplete initial accounting	$ 41

ACQUISITIONS (Fair Values and U

ACQUISITIONS (Fair Values and Useful Lives of Intangible Assets Acquired) (Details) - Continuum $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair value of intangible assets acquired	$ 14,850
Favorable lease
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	11 years 11 months
Estimated fair value of intangible assets acquired	$ 5,900
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	6 years 7 months
Estimated fair value of intangible assets acquired	$ 5,800
Contract royalties
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	8 years
Estimated fair value of intangible assets acquired	$ 1,900
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	5 years
Estimated fair value of intangible assets acquired	$ 1,250

GOODWILL (Goodwill Roll Forward

GOODWILL (Goodwill Roll Forward) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Goodwill [Roll Forward]
Balance as of December 31, 2017	$ 119,531
Effect of net foreign currency exchange rate changes	(1,157)
Balance as of June 30, 2018	144,667
North America
Goodwill [Roll Forward]
Balance as of December 31, 2017	77,290
Effect of net foreign currency exchange rate changes	(285)
Balance as of June 30, 2018	103,298
Europe
Goodwill [Roll Forward]
Balance as of December 31, 2017	42,241
Effect of net foreign currency exchange rate changes	(872)
Balance as of June 30, 2018	41,369
Continuum
Goodwill [Roll Forward]
Goodwill acquired	26,293
Balance as of June 30, 2018	26,293
Continuum | North America
Goodwill [Roll Forward]
Goodwill acquired	26,293
Continuum | Europe
Goodwill [Roll Forward]
Goodwill acquired	$ 0

GOODWILL (Goodwill Accumulated

GOODWILL (Goodwill Accumulated Impaitment Losses) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
North America
Goodwill [Line Items]
Accumulated impairment loss	$ 0	$ 0
Europe
Goodwill [Line Items]
Accumulated impairment loss	$ 0	$ 0

FAIR VALUE MEASUREMENTS (Financ

FAIR VALUE MEASUREMENTS (Financial Assets and Liabilities at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Continuum
Financial Liabilities:
Contingent consideration	$ 2,400
Recurring
Financial Assets:
Total assets measured at fair value on a recurring basis	84	$ 0
Financial Liabilities:
Total liabilities measured at fair value on a recurring basis	5,090	$ 0
Recurring | Foreign Exchange Contracts
Financial Assets:
Derivative assets	84
Financial Liabilities:
Derivative Liability	2,690
Recurring | Continuum
Financial Liabilities:
Contingent consideration	2,400
Recurring | Level 1
Financial Assets:
Total assets measured at fair value on a recurring basis	0
Financial Liabilities:
Total liabilities measured at fair value on a recurring basis	0
Recurring | Level 1 | Foreign Exchange Contracts
Financial Assets:
Derivative assets	0
Financial Liabilities:
Derivative Liability	0
Recurring | Level 1 | Continuum
Financial Liabilities:
Contingent consideration	0
Recurring | Level 2
Financial Assets:
Total assets measured at fair value on a recurring basis	84
Financial Liabilities:
Total liabilities measured at fair value on a recurring basis	2,690
Recurring | Level 2 | Foreign Exchange Contracts
Financial Assets:
Derivative assets	84
Financial Liabilities:
Derivative Liability	2,690
Recurring | Level 2 | Continuum
Financial Liabilities:
Contingent consideration	0
Recurring | Level 3
Financial Assets:
Total assets measured at fair value on a recurring basis	0
Financial Liabilities:
Total liabilities measured at fair value on a recurring basis	2,400
Recurring | Level 3 | Foreign Exchange Contracts
Financial Assets:
Derivative assets	0
Financial Liabilities:
Derivative Liability	0
Recurring | Level 3 | Continuum
Financial Liabilities:
Contingent consideration	$ 2,400

FAIR VALUE MEASUREMENTS (Acquis

FAIR VALUE MEASUREMENTS (Acquisition-Related Contractual Contingent Liabilities Roll Forward) (Details) - Level 3 $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contractual contingent liabilities at December 31, 2017	$ 0
Contractual contingent liabilities at June 30, 2018	2,400
Continuum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition date fair value of contractual contingent liabilities	$ 2,400

FAIR VALUE MEASUREMENTS (Fina42

FAIR VALUE MEASUREMENTS (Financial Assets and Liabilities Not Measured on Recurring Basis) (Details) - Nonrecurring - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Balance
Financial Assets:
Cash and cash equivalents	$ 584,081	$ 582,585
Restricted cash	1,195	673
Employee loans	3,753	4,210
Balance | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	25,019	25,009
Estimated Fair Value
Financial Assets:
Cash and cash equivalents	584,081	582,585
Restricted cash	1,195	673
Employee loans	3,753	4,210
Estimated Fair Value | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	25,019	25,009
Estimated Fair Value | Level 1
Financial Assets:
Cash and cash equivalents	584,081	582,585
Restricted cash	1,195	0
Employee loans	0	0
Estimated Fair Value | Level 1 | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	0	0
Estimated Fair Value | Level 2
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash	0	673
Employee loans	0	0
Estimated Fair Value | Level 2 | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	25,019	25,009
Estimated Fair Value | Level 3
Financial Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Employee loans	3,753	4,210
Estimated Fair Value | Level 3 | Revolving Credit Facility | Credit Facility 2017
Financial Liabilities:
Borrowings	$ 0	$ 0

DERIVATIVE FINANCIAL INSTRUME43

DERIVATIVE FINANCIAL INSTRUMENTS (Fair Value of Derivative Instruments) (Details) - Foreign Exchange Contracts - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Financial collateral posted	$ 0
Designated as hedging instruments | Cash Flow Hedging | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	84	$ 0
Designated as hedging instruments | Cash Flow Hedging | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	2,690	0
Not designated as hedging instruments | Prepaid and other current assets
Derivatives, Fair Value [Line Items]
Asset Derivatives	0	114
Not designated as hedging instruments | Accrued expenses and other current liabilities
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 0	$ 0

DERIVATIVE FINANCIAL INSTRUME44

DERIVATIVE FINANCIAL INSTRUMENTS (Changes in teh Fair Value of Derivative Instruments) (Details) - Foreign Exchange Contracts - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Designated as hedging instruments | Cash Flow Hedging | Accumulated Other Comprehensive Loss
Derivative Instruments, Gain (Loss) [Line Items]
Change in fair value	$ (2,696)	$ 0	$ (2,606)	$ 0
Designated as hedging instruments | Cash Flow Hedging | Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Net loss reclassified	(937)	0	(937)	0
Not designated as hedging instruments | Foreign Exchange Gain/(Loss)
Derivative Instruments, Gain (Loss) [Line Items]
Net gain recognized	$ 0	$ 20	$ 44	$ 159

LONG-TERM DEBT (Details)

LONG-TERM DEBT (Details) - USD ($) $ in Thousands	Mar. 15, 2018	May 24, 2017	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Continuum
Debt Instrument [Line Items]
Maturity date	Mar. 31, 2029
Long-term debt assumed	$ 3,448
Contractual interest rate	8.00%
Repayments of Debt			$ 3,448
Revolving Credit Facility | Credit Facility 2017
Debt Instrument [Line Items]
Maturity date		May 24, 2022
Revolving Credit Facility | Credit Facility 2017 | Federal Funds Open Rate
Debt Instrument [Line Items]
Variable interest rate spread		0.50%
Revolving Credit Facility | Credit Facility 2017 | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread		1.00%
Revolving Credit Facility | Credit Facility 2017 | U.S. dollars
Debt Instrument [Line Items]
Line of credit, current borrowing capacity		$ 300,000
Line of credit, maximum borrowing capacity		400,000
Outstanding debt				$ 25,000	$ 25,000
Interest rate				3.10%	2.60%
Available borrowing capacity				$ 274,657	$ 273,706
Revolving Credit Facility | Credit Facility 2017 | U.S. dollars | Maximum
Debt Instrument [Line Items]
Line of credit, current borrowing capacity				300,000	300,000
Revolving Credit Facility | Credit Facility 2017 | Other currencies, excluding U.S. dollars
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity		$ 100,000
Standby Letters of Credit | Credit Facility 2017
Debt Instrument [Line Items]
Irrevocable standby letters of credit				$ 343	$ 1,294

REVENUES (Impact of Changes Aft

REVENUES (Impact of Changes After Adoption of Topc 606) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Liabilities
Accrued expenses and other current liabilities	$ 72,443		$ 72,443		$ 89,104	$ 89,812
Other noncurrent liabilities	16,421		16,421			9,435
Stockholders’ equity
Retained earnings	633,950		633,950		519,277	518,820
Income Statement
Revenues	445,647	$ 348,977	869,795	$ 673,628
Income from operations	54,237	40,682	102,934	71,648
Provision for/(benefit from) income taxes	6,864	5,687	(9,655)	10,641
Net income	50,255	$ 37,359	114,673	$ 61,000
Balances Without Adoption of Topic 606
Liabilities
Accrued expenses and other current liabilities	72,426		72,426			89,812
Other noncurrent liabilities	16,424		16,424
Stockholders’ equity
Retained earnings	633,964		633,964			$ 518,820
Income Statement
Revenues	444,951		869,812
Income from operations	53,541		102,951
Provision for/(benefit from) income taxes	6,728		(9,652)
Net income	49,695		114,687
Effect of Change Higher/(Lower) | Topic 606
Liabilities
Accrued expenses and other current liabilities	17		17		(708)
Other noncurrent liabilities	(3)		(3)
Stockholders’ equity
Retained earnings	(14)		(14)		$ 457
Income Statement
Revenues	696		(17)
Income from operations	696		(17)
Provision for/(benefit from) income taxes	136		(3)
Net income	$ 560		$ (14)

REVENUES (Disaggregation of Rev

REVENUES (Disaggregation of Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	597		1,202
Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	445,050		868,593
Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	400,149		784,027
Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	44,171		82,788
Licensing
Disaggregation of Revenue [Line Items]
Revenues	966		2,257
Other revenues
Disaggregation of Revenue [Line Items]
Revenues	361		723
Financial Services
Disaggregation of Revenue [Line Items]
Revenues	102,988		206,810
Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	101,016		192,830
Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	85,017		166,639
Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	77,649		153,856
Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	38,525		70,815
Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	40,452		78,845
North America
Disaggregation of Revenue [Line Items]
Revenues	264,451		503,897
Europe
Disaggregation of Revenue [Line Items]
Revenues	149,804		302,889
CIS
Disaggregation of Revenue [Line Items]
Revenues	19,411		41,191
APAC
Disaggregation of Revenue [Line Items]
Revenues	11,981		21,818
North America
Disaggregation of Revenue [Line Items]
Revenues	257,103	194,025	488,299	372,328
North America | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	294		638
North America | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	256,809		487,661
North America | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	233,747		448,063
North America | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	22,483		38,475
North America | Licensing
Disaggregation of Revenue [Line Items]
Revenues	638		1,300
North America | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	235		461
North America | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	26,732		48,688
North America | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	47,104		87,791
North America | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	64,536		125,100
North America | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	59,532		116,869
North America | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	32,876		60,343
North America | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	26,323		49,508
North America | North America
Disaggregation of Revenue [Line Items]
Revenues	250,273		476,343
North America | Europe
Disaggregation of Revenue [Line Items]
Revenues	3,086		5,826
North America | CIS
Disaggregation of Revenue [Line Items]
Revenues	2,089		4,092
North America | APAC
Disaggregation of Revenue [Line Items]
Revenues	1,655		2,038
Europe
Disaggregation of Revenue [Line Items]
Revenues	171,495	141,319	344,838	274,026
Europe | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	634		1,062
Europe | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	170,861		343,776
Europe | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	156,637		316,103
Europe | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	14,081		27,034
Europe | Licensing
Disaggregation of Revenue [Line Items]
Revenues	327		946
Europe | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	450		755
Europe | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	62,496		128,314
Europe | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	52,120		101,574
Europe | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	19,857		40,151
Europe | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	18,117		36,987
Europe | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	5,649		10,472
Europe | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	13,256		27,340
Europe | North America
Disaggregation of Revenue [Line Items]
Revenues	14,177		27,538
Europe | Europe
Disaggregation of Revenue [Line Items]
Revenues	146,998		297,478
Europe | CIS
Disaggregation of Revenue [Line Items]
Revenues	28		91
Europe | APAC
Disaggregation of Revenue [Line Items]
Revenues	10,292		19,731
Russia
Disaggregation of Revenue [Line Items]
Revenues	17,380	13,677	37,166	27,370
Russia | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	0		10
Russia | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	17,380		37,156
Russia | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	9,765		19,861
Russia | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	7,607		17,279
Russia | Licensing
Disaggregation of Revenue [Line Items]
Revenues	1		11
Russia | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	7		15
Russia | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	14,091		30,316
Russia | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	1,792		3,465
Russia | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	624		1,388
Russia | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	0		0
Russia | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	0		0
Russia | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	873		1,997
Russia | North America
Disaggregation of Revenue [Line Items]
Revenues	14		29
Russia | Europe
Disaggregation of Revenue [Line Items]
Revenues	0		42
Russia | CIS
Disaggregation of Revenue [Line Items]
Revenues	17,294		37,008
Russia | APAC
Disaggregation of Revenue [Line Items]
Revenues	72		87
Total Segments
Disaggregation of Revenue [Line Items]
Revenues	445,978	$ 349,021	870,303	$ 673,724
Total Segments | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	928		1,710
Total Segments | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	445,050		868,593
Total Segments | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	400,149		784,027
Total Segments | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	44,171		82,788
Total Segments | Licensing
Disaggregation of Revenue [Line Items]
Revenues	966		2,257
Total Segments | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	692		1,231
Total Segments | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	103,319		207,318
Total Segments | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	101,016		192,830
Total Segments | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	85,017		166,639
Total Segments | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	77,649		153,856
Total Segments | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	38,525		70,815
Total Segments | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	40,452		78,845
Total Segments | North America
Disaggregation of Revenue [Line Items]
Revenues	264,464		503,910
Total Segments | Europe
Disaggregation of Revenue [Line Items]
Revenues	150,084		303,346
Total Segments | CIS
Disaggregation of Revenue [Line Items]
Revenues	19,411		41,191
Total Segments | APAC
Disaggregation of Revenue [Line Items]
Revenues	12,019		21,856
Other Income Included in Segment Revenues
Disaggregation of Revenue [Line Items]
Revenues	(331)		(508)
Other Income Included in Segment Revenues | Transferred at a point of time
Disaggregation of Revenue [Line Items]
Revenues	(331)		(508)
Other Income Included in Segment Revenues | Transferred over time
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Time-and-material
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Fixed-price
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Licensing
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	(331)		(508)
Other Income Included in Segment Revenues | Financial Services
Disaggregation of Revenue [Line Items]
Revenues	(331)		(508)
Other Income Included in Segment Revenues | Travel & Consumer
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Software & Hi-Tech
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Business Information & Media
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Life Sciences & Healthcare
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | Emerging Verticals
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | North America
Disaggregation of Revenue [Line Items]
Revenues	(13)		(13)
Other Income Included in Segment Revenues | Europe
Disaggregation of Revenue [Line Items]
Revenues	(280)		(457)
Other Income Included in Segment Revenues | CIS
Disaggregation of Revenue [Line Items]
Revenues	0		0
Other Income Included in Segment Revenues | APAC
Disaggregation of Revenue [Line Items]
Revenues	$ (38)		$ (38)

REVENUES (Revenue Expected to b

REVENUES (Revenue Expected to be Recognized in Future Related to Remaining Performance Obligations) (Details) - Fixed-price $ in Thousands	Jun. 30, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenue related to partially or fully unsatisfied performance obligations	$ 8,616
Less than 1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenue related to partially or fully unsatisfied performance obligations	7,897
1 Year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenue related to partially or fully unsatisfied performance obligations	580
2 Years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenue related to partially or fully unsatisfied performance obligations	139
3 Years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Estimated revenue related to partially or fully unsatisfied performance obligations	$ 0

REVENUES (Contract Balances) (D

REVENUES (Contract Balances) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Schedule of Contract Balances [Line Items]
Unbilled revenues	$ 18,393	$ 18,393	$ 7,901
Change in Contract with Customer, Liability [Abstract]
Revenue recognized that was previously included in deferred revenues	1,808	3,432
Revenues from performance obligations satisfied in previous periods	5,452	6,618
Accrued expenses and other current liabilities
Schedule of Contract Balances [Line Items]
Deferred revenues	$ 5,398	$ 5,398	$ 4,498

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Components and Changes in Income Tax Expense (Benefit) and Respective Balance Sheet Items [Line Items]
Effective tax rate	12.00%		13.20%	(9.20%)	14.90%
Deferred income tax				$ (27,581)	$ (766)
Excess tax benefit	$ 5,440		$ 4,138	10,130	$ 5,832
Taxes payable, noncurrent	56,540			56,540		$ 59,874
Check the Box Election
Schedule of Components and Changes in Income Tax Expense (Benefit) and Respective Balance Sheet Items [Line Items]
Deferred income tax	706			25,340
Tax Cuts and Jobs Act
Schedule of Components and Changes in Income Tax Expense (Benefit) and Respective Balance Sheet Items [Line Items]
Provisional income tax expense	0	$ 2,157
Tax payable	66,478			66,478
Taxes payable, noncurrent	$ 55,841			$ 55,841

STOCK-BASED COMPENSATION - Cost

STOCK-BASED COMPENSATION - Costs Related To Stock Compensation Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 14,810	$ 12,927	$ 31,406	$ 28,703
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	7,054	4,189	15,343	9,539
Selling, general and administrative expenses
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,756	$ 8,738	$ 16,063	$ 19,164

STOCK-BASED COMPENSATION - Stoc

STOCK-BASED COMPENSATION - Stock Option Activity (Details) - Employee Stock Option $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)$ / sharesshares
Number of Options
Options outstanding at January 1, 2018 | shares	4,901,748
Options granted | shares	157,133
Options exercised | shares	(566,799)
Options forfeited/cancelled | shares	(27,583)
Options outstanding at June 30, 2018 | shares	4,464,499
Options vested and exercisable at June 30, 2018 | shares	3,530,693
Options expected to vest at June 30, 2018 | shares	879,470
Weighted Average Exercise Price
Options outstanding at January 1, 2018 | $ / shares	$ 40.91
Options granted | $ / shares	112.91
Options exercised | $ / shares	39.34
Options forfeited/cancelled | $ / shares	63.63
Options outstanding at June 30, 2018 | $ / shares	43.50
Options vested and exercisable at June 30, 2018 | $ / shares	35.46
Options expected to vest at June 30, 2018 | $ / shares	$ 73.49
Aggregate Intrinsic Value
Options outstanding at June 30, 2018 | $	$ 360,830
Options vested and exercisable at June 30, 2018 | $	313,776
Options expected to vest at June 30, 2018 | $	$ 44,709
Weighted Average Remaining Contractual Term (in years)
Options outstanding at June 30, 2018	5 years 10 months 6 days
Options vested and exercisable at June 30, 2018	5 years 4 months 2 days
Options expected to vest at June 30, 2018	7 years 8 months 26 days

STOCK-BASED COMPENSATION - St53

STOCK-BASED COMPENSATION - Stock Option Additional Information (Details) - Employee Stock Option $ in Thousands	6 Months Ended
	Jun. 30, 2018USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense | $	$ 19,733
Weighted-average remaining requisite service period	2 years 22 days
Number of options exercised in transfer | shares	3,423

STOCK-BASED COMPENSATION - Rest

STOCK-BASED COMPENSATION - Restricted Stock and Restricted Stock Units Activity (Details) - $ / shares	3 Months Ended	6 Months Ended
	Mar. 31, 2018	Jun. 30, 2018
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock
Number of Shares
Unvested awards outstanding at January 1, 2018	1,840	1,840
Awards granted		0
Awards modified		0
Awards vested		0
Awards forfeited/cancelled		0
Unvested awards outstanding at June 30, 2018		1,840
Weighted Average Grant Date Fair Value Per Share
Unvested awards outstanding at January 1, 2018	$ 54.37	$ 54.37
Awards granted		0
Awards modified		0
Awards vested		0
Awards forfeited/cancelled		0
Unvested awards outstanding at June 30, 2018		$ 54.37
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock Units
Number of Shares
Unvested awards outstanding at January 1, 2018	688,012	688,012
Awards granted		330,717
Awards modified		(2,299)
Awards vested		(202,569)
Awards forfeited/cancelled		(27,460)
Unvested awards outstanding at June 30, 2018		786,401
Weighted Average Grant Date Fair Value Per Share
Unvested awards outstanding at January 1, 2018	$ 71.60	$ 71.60
Awards granted		114.22
Awards modified		72.80
Awards vested		69.90
Awards forfeited/cancelled		77.90
Unvested awards outstanding at June 30, 2018		$ 89.74
Service Period | Liability Classified Award | Cash-Settled Award | Restricted Stock Units
Number of Shares
Unvested awards outstanding at January 1, 2018	314,829	314,829
Awards granted		85,380
Awards modified		2,299
Awards vested		(91,052)
Awards forfeited/cancelled		(4,761)
Unvested awards outstanding at June 30, 2018		306,695
Weighted Average Grant Date Fair Value Per Share
Unvested awards outstanding at January 1, 2018	$ 72.50	$ 72.50
Awards granted		112.65
Awards modified		116.63
Awards vested		72.42
Awards forfeited/cancelled		76.50
Unvested awards outstanding at June 30, 2018		$ 83.97
Performance Target | Equity Classified Award | Equity-Settled Award | Restricted Stock Units
Number of Shares
Unvested awards outstanding at January 1, 2018	0	0
Awards granted		45,375
Awards vested		0
Awards forfeited/cancelled		0
Unvested awards outstanding at June 30, 2018		45,375
Weighted Average Grant Date Fair Value Per Share
Unvested awards outstanding at January 1, 2018	$ 0	$ 0
Awards granted		121.75
Awards vested		0
Awards forfeited/cancelled		0
Unvested awards outstanding at June 30, 2018		$ 121.75
Continuum | Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock Units
Number of Shares
Awards granted	44,228

STOCK-BASED COMPENSATION - Re55

STOCK-BASED COMPENSATION - Restricted Stock and Restricted Stock Units Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability associated with RSUs	$ 4,338	$ 5,964
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 56
Weighted-average remaining requisite service period	1 year 1 month 17 days
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 56,843
Weighted-average remaining requisite service period	2 years 11 months 16 days
Vested RSUs with deferred delivery	3,894
Service Period | Liability Classified Award | Cash-Settled Award | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 29,706
Weighted-average remaining requisite service period	2 years 8 months 28 days
Performance Target | Equity Classified Award | Equity-Settled Award | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 5,128
Weighted-average remaining requisite service period	2 years 1 month 27 days
Deferred compensation due to employees | Service Period | Liability Classified Award | Cash-Settled Award | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability associated with RSUs	$ 4,338	$ 5,964

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator for basic and diluted earnings per share:
Net income	$ 50,255	$ 37,359	$ 114,673	$ 61,000
Numerator for basic and diluted earnings per share	$ 50,255	$ 37,359	$ 114,673	$ 61,000
Denominator:
Weighted average common shares for basic earnings per share	53,517,124	51,899,416	53,299,038	51,431,353
Effect of dilutive securities (in shares):
Net effect of dilutive stock options, restricted stock units and restricted stock awards	3,069,885	2,949,203	3,115,948	2,939,931
Weighted average common shares for diluted earnings per share	56,587,009	54,848,619	56,414,986	54,371,284
Net income per share:
Basic (in dollars per share)	$ 0.94	$ 0.72	$ 2.15	$ 1.19
Diluted (in dollars per share)	$ 0.89	$ 0.68	$ 2.03	$ 1.12
Anti-dilutive options not included in the calculation (in shares)	155,142	654,435	104,186	1,463,156

SEGMENTS INFORMATION - Revenues

SEGMENTS INFORMATION - Revenues from External Customers and Operating Profit/(Loss) Before Unallocated Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Operating profit	54,237	40,682	102,934	71,648
North America
Segment Reporting Information [Line Items]
Revenues	257,103	194,025	488,299	372,328
Operating profit	51,221	43,622	95,181	80,714
Europe
Segment Reporting Information [Line Items]
Revenues	171,495	141,319	344,838	274,026
Operating profit	26,568	20,658	55,458	40,469
Russia
Segment Reporting Information [Line Items]
Revenues	17,380	13,677	37,166	27,370
Operating profit	2,321	1,895	7,668	5,444
Operating Segments
Segment Reporting Information [Line Items]
Revenues	445,978	349,021	870,303	673,724
Operating profit	$ 80,110	$ 66,175	$ 158,307	$ 126,627

SEGMENTS INFORMATION - Major Cu

SEGMENTS INFORMATION - Major Customers (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2017
Revenue, Major Customer [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Operating Segments
Revenue, Major Customer [Line Items]
Revenues	$ 445,978	$ 349,021	$ 870,303	$ 673,724
Sales Revenue, Net | Customer Concentration Risk | Operating Segments
Revenue, Major Customer [Line Items]
Number of customers	0	0	0	0
Accounts Receivable | Customer Concentration Risk | Billed Revenues
Revenue, Major Customer [Line Items]
Number of customers			0		0
Accounts Receivable | Customer Concentration Risk | Unbilled Revenues
Revenue, Major Customer [Line Items]
Number of customers			1		1
Concentration percentage			10.20%		13.00%

SEGMENTS INFORMATION - Reconcil

SEGMENTS INFORMATION - Reconciliation of Segment Revenues to Consolidated Revenues and Segment Operating Profit to Consolidated Income Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
Segment Reporting Information [Line Items]
Income from operations	54,237	40,682	102,934	71,648
Stock-based compensation expense			(31,406)	(28,703)
Depreciation and amortization expense	(8,962)	(7,020)	(17,138)	(13,692)
Interest and other income, net	1,052	802	501	1,386
Foreign exchange gain/(loss)	1,830	1,562	1,583	(1,393)
Income before provision for income taxes	57,119	43,046	105,018	71,641
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	445,978	349,021	870,303	673,724
Segment Reporting Information [Line Items]
Income from operations	80,110	66,175	158,307	126,627
Other Income Included in Segment Revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	(331)	(44)	(508)	(96)
Segment Reporting Information [Line Items]
Other income included in segment revenues	(331)	(44)	(508)	(96)
Stock-based compensation expense	(14,810)	(12,927)	(31,406)	(28,703)
Non-corporate taxes	(2,418)	(1,795)	(4,978)	(5,246)
Professional fees	(1,400)	(2,476)	(3,316)	(4,820)
Depreciation and amortization expense	(1,974)	(1,905)	(3,743)	(3,880)
Bank charges	(579)	(446)	(1,168)	(843)
One-time charges and other acquisition-related expenses	(1,241)	(330)	(1,861)	(898)
Other operating expenses	$ (3,120)	$ (5,570)	$ (8,393)	$ (10,493)

SEGMENTS INFORMATION - Geograph

SEGMENTS INFORMATION - Geographical Information of Long-Lived Assets Based on Physical Location (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 98,450	$ 86,419
Belarus
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	48,426	49,866
United States
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	11,541	3,371
Russia
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	10,521	9,617
India
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	7,472	2,698
Ukraine
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	6,818	6,995
Hungary
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	3,350	3,901
China
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	3,275	2,608
Other
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 7,047	$ 7,363

SEGMENTS INFORMATION - Revenu61

SEGMENTS INFORMATION - Revenues by Client Location (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 445,647	$ 348,977	$ 869,795	$ 673,628
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	246,831	192,319	470,514	369,149
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	50,103	46,112	101,833	92,706
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	34,268	28,119	69,872	57,215
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	20,111	14,144	39,599	26,238
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	17,620	13,649	33,383	26,143
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	17,254	12,556	34,903	21,227
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	16,909	13,326	36,321	26,535
Other locations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 42,551	$ 28,752	$ 83,370	$ 54,415