EPAM Systems (EPAM) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 12, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	EPAM Systems, Inc.
Trading Symbol	EPAM
Entity Central Index Key	1,352,010
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		53,039,832
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Document Period End Date	Dec. 31, 2017
Document Type	10-K
Amendment Flag	false
Entity Public Float			$ 4,178

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 582,585	$ 362,025
Accounts receivable, net of allowance of $1,186 and $1,434, respectively	265,639	199,982
Unbilled revenues	86,500	63,325
Prepaid and other current assets, net of allowance of $45 and $644, respectively	23,196	18,493
Employee loans, current, net of allowance of $0 and $0, respectively	2,113	2,726
Total current assets	960,033	646,551
Property and equipment, net	86,419	73,616
Employee loans, noncurrent, net of allowance of $0 and $0, respectively	2,097	3,252
Intangible assets, net	44,511	51,260
Goodwill	119,531	109,289
Deferred tax assets	24,974	31,005
Other noncurrent assets, net of allowance of $140 and $132, respectively	12,691	10,838
Total assets	1,250,256	925,811
Current liabilities
Accounts payable	5,574	3,213
Accrued expenses and other current liabilities	89,812	49,895
Due to employees	38,757	32,203
Deferred compensation due to employees	5,964	5,900
Taxes payable, current	40,860	25,008
Total current liabilities	180,967	116,219
Long-term debt	25,033	25,048
Taxes payable, noncurrent	59,874	0
Other noncurrent liabilities	9,435	3,132
Total liabilities	275,309	144,399
Commitments and contingencies (Note 15)
Stockholders’ equity
Common stock, $0.001 par value; 160,000,000 authorized; 53,003,420 and 51,117,422 shares issued, 52,983,685 and 51,097,687 shares outstanding at December 31, 2017 and December 31, 2016, respectively	53	50
Additional paid-in capital	473,874	374,907
Retained earnings	518,820	444,320
Treasury stock	(177)	(177)
Accumulated other comprehensive loss	(17,623)	(37,688)
Total stockholders’ equity	974,947	781,412
Total liabilities and stockholders’ equity	$ 1,250,256	$ 925,811

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Accounts receivable allowance	$ 1,186	$ 1,434
Prepaid and other assets allowance	45	644
Employee loans current allowance	0	0
Noncurrent assets
Employee loans long-term allowance	0	0
Other long-term assets allowance	$ 140	$ 132
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	160,000,000	160,000,000
Common stock, shares issued	53,003,420	51,117,422
Common stock, shares outstanding	52,983,685	51,097,687

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Revenues	$ 1,450,448	$ 1,160,132	$ 914,128
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	921,352	737,186	566,913
Selling, general and administrative expenses	324,855	264,658	222,759
Depreciation and amortization expense	28,562	23,387	17,395
Other operating expenses, net	2,733	1,205	1,094
Income from operations	172,946	133,696	105,967
Interest and other income, net	4,601	4,848	4,731
Foreign exchange loss	(3,242)	(12,078)	(4,628)
Income before provision for income taxes	174,305	126,466	106,070
Provision for income taxes	101,545	27,200	21,614
Net income	72,760	99,266	84,456
Foreign currency translation adjustments	20,065	(2,538)	(13,096)
Comprehensive income	$ 92,825	$ 96,728	$ 71,360
Net income per share:
Basic (in dollars per share)	$ 1.40	$ 1.97	$ 1.73
Diluted (in dollars per share)	$ 1.32	$ 1.87	$ 1.62
Shares used in calculation of net income per share:
Basic (in shares)	52,077,011	50,309,362	48,720,844
Diluted (in shares)	54,984,173	53,215,392	51,985,873

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Common Stock2012 Directors Plan	Common StockRestricted Stock Units (RSUs)	Additional Paid-in Capital	Additional Paid-in CapitalRestricted Stock Units (RSUs)	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss)/ Income
Balance, beginning of period at Dec. 31, 2014	$ 464,050	$ 48			$ 229,501		$ 260,598		$ (22,054)
Balance, beginning of period (in shares) at Dec. 31, 2014		48,303,811
Treasury stock, beginning of period at Dec. 31, 2014								$ (4,043)
Treasury stock, beginning of period (in shares) at Dec. 31, 2014								444,487
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued in connection with acquisition (Note 3)	5,081				1,118			$ 3,963
Stock issued in connection with acquisition (Note 3) (in shares)		435,462						435,462
Forfeiture of stock issued in connection with acquisition					13			$ (13)
Forfeiture of stock issued in connection with acquisition (in shares)		(1,482)						1,482
Stock-based compensation expense	43,120				43,120
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock issued (in shares)			5,295
Stock units vested (in shares)				17,625
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested	574					$ 574
Proceeds from stock option exercises	20,675	$ 1			20,674
Proceeds from stock options exercises (in shares)		1,405,826
Excess tax benefits	8,363				8,363
Foreign currency translation adjustments	(13,096)								(13,096)
Net income	84,456						84,456
Balance, end of period at Dec. 31, 2015	613,223	$ 49			303,363		345,054		(35,150)
Balance, end of period (in shares) at Dec. 31, 2015		50,166,537
Treasury stock, end of period at Dec. 31, 2015								$ (93)
Treasury stock, end of period (in shares) at Dec. 31, 2015								10,507
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Forfeiture of stock issued in connection with acquisition					84			$ (84)
Forfeiture of stock issued in connection with acquisition (in shares)		(9,228)						9,228
Stock-based compensation expense	46,100				46,100
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock issued (in shares)			6,510
Stock units vested, net of shares withheld for employee taxes (in shares)				38,064
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units vested, net of shares withheld for employee taxes	2,069					2,069
Proceeds from stock option exercises	18,028	$ 1			18,027
Proceeds from stock options exercises (in shares)		895,804
Excess tax benefits	5,264				5,264
Foreign currency translation adjustments	(2,538)								(2,538)
Net income	99,266						99,266
Balance, end of period at Dec. 31, 2016	$ 781,412	$ 50			374,907		444,320		(37,688)
Balance, end of period (in shares) at Dec. 31, 2016	51,097,687	51,097,687
Treasury stock, end of period at Dec. 31, 2016								$ (177)
Treasury stock, end of period (in shares) at Dec. 31, 2016								19,735
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 48,173				48,173
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures [Abstract]
Stock units vested (in shares)				140,043
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures [Abstract]
Stock units withheld for employee taxes	(3,300)					$ (3,300)
Stock units withheld for employee taxes (in shares)				(43,479)
Proceeds from stock option exercises	54,097	$ 3			54,094
Proceeds from stock options exercises (in shares)		1,789,434
Foreign currency translation adjustments	20,065								20,065
Cumulative effect of the adoption of ASU	1,740
Cumulative effect of the adoption of ASU | ASU 2016-09	1,740
Net income	72,760						72,760
Balance, end of period at Dec. 31, 2017	$ 974,947	$ 53			$ 473,874		$ 518,820		$ (17,623)
Balance, end of period (in shares) at Dec. 31, 2017	52,983,685	52,983,685
Treasury stock, end of period at Dec. 31, 2017								$ (177)
Treasury stock, end of period (in shares) at Dec. 31, 2017								19,735

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 72,760	$ 99,266	$ 84,456
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	28,562	23,387	17,395
Bad debt expense	51	1,539	1,407
Deferred taxes	12,561	(3,304)	(15,328)
Stock-based compensation expense	52,407	49,244	45,833
Impairment charges and acquisition related adjustments	0	0	(1,183)
Excess tax benefit on stock-based compensation plans	0	(5,264)	(8,363)
Other	(4,010)	6,228	3,883
(Increase)/decrease in operating assets:
Accounts receivable	(58,745)	(30,612)	(47,694)
Unbilled revenues	(22,743)	34,777	(38,076)
Prepaid expenses and other assets	3,605	(4,791)	(574)
Increase/(decrease) in operating liabilities:
Accounts payable	1,221	741	(2,781)
Accrued expenses and other liabilities	37,282	(13,926)	25,694
Due to employees	1,933	5,261	2,752
Taxes payable	70,480	2,271	8,972
Net cash provided by operating activities	195,364	164,817	76,393
Cash flows used in investing activities:
Purchases of property and equipment	(29,806)	(29,317)	(13,272)
Payment for construction of corporate facilities	0	0	(4,692)
Employee housing loans issued	(648)	(2,006)	(2,054)
Proceeds from repayments of employee housing loans	2,565	2,177	2,249
Restricted cash and time deposits, net	8	29,595	(29,944)
Acquisition of businesses, net of cash acquired (Note 3)	(6,840)	(5,500)	(76,908)
Other investing activities, net	(1,452)	(4,271)	(873)
Net cash used in investing activities	(36,173)	(9,322)	(125,494)
Cash flows from financing activities:
Proceeds related to stock option exercises	53,984	17,996	20,675
Excess tax benefit on stock-based compensation plans	0	5,264	8,363
Payments of withholding taxes related to net share settlements of restricted stock units	(3,194)	(539)	0
Proceeds from debt (Note 12)	25,000	20,000	35,000
Repayment of debt (Note 12)	(25,103)	(30,129)	0
Acquisition of businesses, deferred consideration (Note 3)	0	(2,260)	(30,274)
Other financing activities, net	(941)	135	0
Net cash provided by financing activities	49,746	10,467	33,764
Effect of exchange rate changes on cash and cash equivalents	11,623	(3,386)	(5,748)
Net increase/(decrease) in cash and cash equivalents	220,560	162,576	(21,085)
Cash and cash equivalents, beginning of period	362,025	199,449	220,534
Cash and cash equivalents, end of period	582,585	362,025	199,449
Supplemental disclosures of cash flow information:
Income taxes	26,669	37,488	25,071
Bank interest	548	566	124
Supplemental disclosure of non-cash operating activities
Prepaid and other current assets write-off related to vendor advance	0	0	741
Supplemental disclosure of non-cash investing and financing activities
Deferred consideration payable	$ 0	$ 0	$ 603

NATURE OF BUSINESS AND SUMMARY

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES 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, media and entertainment, travel and hospitality, retail and distribution and life sciences and healthcare. The Company is incorporated in Delaware with headquarters in Newtown, PA. Principles of Consolidation — The consolidated financial statements include the financial statements of EPAM Systems, Inc. and its subsidiaries. All intercompany balances and transactions have been eliminated. Use of Estimates — The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions. These estimates and assumptions affect reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as revenues and expenses during the reporting period. The Company bases its estimates and judgments on historical experience, knowledge of current conditions and its beliefs of what could occur in the future, given available information. Actual results could differ from those estimates, and such differences may be material to the financial statements. Change in Presentation of Certain Financial Information — During the first quarter of 2017, the Company changed the presentation of geographic area information about its consolidated revenues. Historically, information about geographic location of revenues excluded reimbursable expenses and other revenues, which primarily consist of travel and entertainment costs that are chargeable to clients. Effective January 1, 2017, the Company began reporting reimbursable expenses and other revenues based on location of clients to which these costs are chargeable and allocating them to respective geographic locations. These changes did not result in adjustments to previously reported consolidated revenues in the Company’s financial statements and were applied retrospectively effective January 1, 2015. Comparative information for the years ended December 31, 2016 and 2015 follows: Year Ended December 31, 2016 As Reported After Reclassification (in thousands except percentages) United States $ 605,856 52.2 % $ 611,392 52.7 % United Kingdom 174,719 15.1 % 177,194 15.3 % Switzerland 122,399 10.6 % 122,919 10.6 % Canada 58,742 5.1 % 59,189 5.1 % Germany 43,216 3.7 % 43,621 3.8 % Russia 40,866 3.5 % 40,944 3.5 % Sweden 22,945 2.0 % 23,838 2.1 % Hong Kong 20,333 1.8 % 21,010 1.8 % Netherlands 16,762 1.4 % 17,521 1.5 % Belgium 8,505 0.7 % 8,627 0.7 % Ireland 5,152 0.4 % 5,167 0.4 % China 4,445 0.4 % 4,479 0.4 % Italy 3,970 0.3 % 4,052 0.3 % United Arab Emirates 3,486 0.3 % 3,615 0.3 % Other locations 16,215 1.4 % 16,564 1.5 % Reimbursable expenses and other revenues 12,521 1.1 % — — % Total $ 1,160,132 100.0 % $ 1,160,132 100.0 % Year Ended December 31, 2015 As Reported After Reclassification (in thousands except percentages) United States $ 427,433 46.8 % $ 431,992 47.3 % United Kingdom 164,301 18.0 % 166,418 18.2 % Switzerland 111,353 12.2 % 111,686 12.2 % Canada 57,643 6.3 % 58,319 6.4 % Germany 36,089 3.9 % 36,403 4.0 % Russia 36,506 4.0 % 36,585 4.0 % Sweden 10,589 1.2 % 10,775 1.2 % Hong Kong 23,117 2.5 % 23,285 2.5 % Netherlands 9,989 1.1 % 10,373 1.1 % Belgium 7,916 0.9 % 8,113 0.9 % Ireland 5,437 0.6 % 5,536 0.6 % Italy 2,318 0.3 % 2,342 0.3 % China 817 0.1 % 817 0.1 % Other locations 11,109 1.1 % 11,484 1.2 % Reimbursable expenses and other revenues 9,511 1.0 % — — % Total $ 914,128 100.0 % $ 914,128 100.0 % Revenue Recognition — The Company recognizes revenue when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred; (3) the sales price is fixed or determinable; and (4) collectability is reasonably assured. Determining whether and when some of these criteria have been satisfied often involves assumptions and judgments that can have a significant impact on the timing and amount of revenue reported. The Company derives its revenues from a variety of service offerings, which represent specific competencies of its IT professionals. Contracts for these services have different terms and conditions based on the scope, deliverables, and complexity of the engagement, which require management to make judgments and estimates in determining the appropriate revenue recognition. Fees for these contracts may be in the form of time-and-materials or fixed-price arrangements. If there is an uncertainty about the project completion or receipt of payment for the services, revenue is deferred until the uncertainty is sufficiently resolved. At the time revenue is recognized, the Company provides for any contractual deductions and reduces the revenue accordingly. 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 Company defers 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. Unbilled revenue is recorded when services have been provided but billed subsequent to the period end in accordance with the contract terms. The majority of the Company’s revenues ( 90.3% of revenues in 2017 , 88.2% in 2016 and 85.8% in 2015 ) are generated under time-and-material contracts where revenues are recognized as services are performed with the corresponding cost of providing those services reflected as cost of revenues. The majority of such revenues are billed using hourly, daily or monthly rates as actual time is incurred on the project. Revenues from fixed-price contracts ( 8.3% of revenues in 2017 , 10.4% in 2016 and 12.8% in 2015 ) include fixed-price maintenance and support arrangements, which may exceed one year in duration, as well as fixed-price application development arrangements. Revenues from maintenance and support arrangements are generally recognized ratably over the expected service period. Revenues from fixed-price application development arrangements are primarily determined using the proportional performance method. In cases where final acceptance of the product, system, or solution is specified by the client, and the acceptance criteria are not objectively determinable to have been met as the services are provided, revenues are deferred until all acceptance criteria have been met. In the absence of a sufficient basis to measure progress towards completion, revenue is recognized upon receipt of final acceptance from the client. Assumptions, risks and uncertainties inherent in the estimates used in the application of the proportional performance method of accounting could affect the amount of revenues, receivables and deferred revenues at each reporting period. Cost of Revenues (Exclusive of Depreciation and Amortization) — Consists principally of salaries, bonuses, fringe benefits, stock-based compensation expense, project related travel costs and fees for subcontractors that are assigned to client projects. Salaries and other compensation expenses of our revenue generating professionals are reported as cost of revenues regardless of whether the employees are actually performing client services during a given period. Selling, General and Administrative Expenses — Consists of expenses associated with promoting and selling our services and general and administrative functions of the business. These expenses include the costs of salaries, bonuses, fringe benefits, stock-based compensation expense, commissions, travel, legal and audit services, insurance, operating leases, advertising and other promotional activities. In addition, we pay a membership fee of 1% of revenues generated in Belarus to the administrative organization of the Belarus Hi-Tech Park. Furthermore, the Company has issued stock to the sellers and/or personnel in connection with business acquisitions and has been recognizing stock-based compensation expense in the periods after the closing of these acquisitions as part of selling, general and administrative expenses. Fair Value of Financial Instruments — The Company makes assumptions about fair values of its financial assets and liabilities in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 820, “Fair Value Measurement,” and utilizes the following fair value hierarchy in determining inputs used for valuation: Level 1 — Quoted prices for identical assets or liabilities in active markets. Level 2 — Inputs other than quoted prices within Level 1 that are observable either directly or indirectly, including quoted prices in markets that are not active, quoted prices in active markets for similar assets or liabilities, and observable inputs other than quoted prices such as interest rates or yield curves. Level 3 — Unobservable inputs reflecting management’s view about the assumptions that market participants would use in pricing the asset or liability. Where the fair values of financial assets and liabilities recorded in the consolidated balance sheets cannot be derived from an active market, they are determined using a variety of valuation techniques. These valuation techniques include a net present value technique, comparison to similar instruments with market observable inputs, option pricing models and other relevant valuation models. To the extent possible, observable market data is used as inputs into these models but when it is not feasible, a degree of judgment is required to establish fair values. The Company’s contingent liabilities measured at fair value on a recurring basis are comprised of performance-based awards issued to certain former owners of acquired businesses in exchange for future services. During a performance measurement period, performance-based awards are valued using significant inputs that are not observable in the market, which are defined as Level 3 inputs according to fair value measurement accounting. The Company estimates the fair value of contingent liabilities based on certain performance milestones of the acquired businesses and estimated probabilities of achievement, then discounts the liabilities to present value using the Company’s cost of debt for the cash component of contingent consideration, and a risk-free rate for the stock component of a contractual contingency. The Company believes its estimates and assumptions are reasonable, however, there is significant judgment involved. Changes in the fair value of contingent consideration liabilities primarily result from changes in the timing and amount of specific milestone estimates and changes in probability assumptions with respect to the likelihood of achieving the various earnout criteria. Changes in the fair value of these liabilities could cause a material impact to, and volatility in the Company’s operating results. See Note 16 “Fair Value Measurements.” Employee Loans — The Company issues employee housing loans in Belarus, relocation loans to assist employees with relocation needs in connection with intra-company transfers and loans for the purchase of automobiles in India. There are no loans issued to principal officers, directors, and their affiliates. The Company intends to hold all employee loans until their maturity. Interest income is reported using the effective interest method. Where applicable, loan origination fees, net of direct origination costs, are deferred and recognized in interest income over the life of the loan. The Employee Housing Program (the “Housing Program”) provides employees with loans to purchase housing in Belarus. The housing loans are measured using the Level 3 inputs within the fair value hierarchy because they are valued using significant unobservable inputs. These housing loans are measured at fair value upon initial recognition through the market approach under ASC Topic 820, “Fair Value Measurement” and subsequently carried at amortized cost less allowance for loan losses, if any. Any difference between the carrying value and the fair value of a loan upon initial recognition is charged to expense. Business Combinations — The Company accounts for its business combinations using the acquisition accounting method, which requires it to determine the fair value of net assets acquired and the related goodwill and other intangible assets in accordance with the FASB ASC Topic 805, “Business Combinations.” The Company identifies and attributes fair values and estimated lives to the intangible assets acquired and allocates the total cost of an acquisition to the underlying net assets based on their respective estimated fair values. Determining the fair value of assets acquired and liabilities assumed requires management’s judgment and involves the use of significant estimates, including projections of future cash inflows and outflows, discount rates, asset lives and market multiples. There are different valuation models for each component, the selection of which requires considerable judgment. These determinations will affect the amount of amortization expense recognized in future periods. The Company bases its fair value estimates on assumptions it believes are reasonable, but recognizes that the assumptions are inherently uncertain. All acquisition-related costs, other than the costs to issue debt or equity securities, are accounted for as expenses in the period in which they are incurred. Changes in fair value of contingent consideration arrangements that are not measurement period adjustments are recognized in earnings. Payments to settle contingent consideration, if any, are reflected in cash flows from financing activities and the changes in fair value are reflected in cash flows from operating activities in the Company’s consolidated statements of cash flows. The acquired assets typically consist of customer relationships, trade names, non-competition agreements, and workforce and as a result, a substantial portion of the purchase price is allocated to goodwill and other intangible assets. Cash and Cash Equivalents — Cash equivalents are short-term, highly liquid investments that are readily convertible into cash, with maturities of three months or less at the date acquired. As of December 31, 2017 and 2016 the Company had no cash equivalents. Accounts Receivable — Accounts receivable are stated net of allowance for doubtful accounts. Outstanding accounts receivable are reviewed periodically and allowances are provided when management believes it is probable that such balances will not be collected within a reasonable time. The allowance for doubtful accounts is determined by evaluating the relative creditworthiness of each client, historical collections experience and other information, including the aging of the receivables. Accounts receivable are generally written off when they are deemed uncollectible. Bad debts are recorded based on historical experience and management’s evaluation of accounts receivable. Property and Equipment — Property and equipment acquired in the ordinary course of the Company’s operations are stated at cost, net of accumulated depreciation. Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets generally ranging from two to fifty years. Leasehold improvements are amortized on a straight-line basis over the shorter of the term of the lease or the estimated useful life of the improvement. Maintenance and repairs are expensed as incurred. Long-Lived Assets — Long-lived assets, such as property and equipment and finite-lived intangible assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. When the carrying value of an asset is more than the sum of the undiscounted expected future cash flows, an impairment is recognized. An impairment loss is measured as the excess of the asset’s carrying amount over its fair value. Intangible assets that have finite useful lives are amortized over their estimated useful lives on a straight-line basis. Property and equipment held for disposal are carried at the lower of the current carrying value or fair value less estimated costs to sell. The Company did not incur any impairment of long-lived assets during the years ended December 31, 2017 , 2016 and 2015 . Goodwill and Other Indefinite-Lived Intangible Assets — Goodwill and other intangible assets that have indefinite useful lives are accounted for in accordance with the FASB ASC 350, “Intangibles — Goodwill and Other.” The Company conducts its evaluation of goodwill impairment at the reporting unit level on an annual basis as of October 31st, and more frequently if events or circumstances indicate that the carrying value of a reporting unit exceeds its fair value. A reporting unit is an operating segment or one level below. The Company does not have intangible assets other than goodwill that have indefinite useful lives. Income Taxes — The provision for income taxes includes federal, state, local and foreign taxes. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be reversed. Changes to enacted tax rates would result in either increases or decreases in the provision for income taxes in the period of changes. The realizability of deferred tax assets is primarily dependent on future earnings. The Company evaluates the realizability of deferred tax assets and recognizes a valuation allowance when it is more likely than not that all, or a portion of, deferred tax assets will not be realized. Any reduction in estimated forecasted results may require that we record valuation allowances against deferred tax assets. Once a valuation allowance has been established, it will be maintained until there is sufficient positive evidence to conclude that it is more likely than not that the deferred tax assets will be realized. A pattern of sustained profitability will generally be considered as sufficient positive evidence to reverse a valuation allowance. If the allowance is reversed in a future period, the income tax provision will be correspondingly reduced. Accordingly, the increase and decrease of valuation allowances could have a significant negative or positive impact on future earnings. See Note 10 “Income Taxes” for further information. Earnings per Share (“EPS”) — Basic EPS 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 restricted stock units (“RSUs”). The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method. Stock-Based Compensation — The Company recognizes the cost of its equity-classified stock-based incentive awards based on the fair value of the award at the date of grant, net of estimated forfeitures. The cost is expensed evenly over the service period. The service period is the period over which the employee performs the related services, which is normally the same as the vesting period. Quarterly, the forfeiture assumption is adjusted to the actual forfeiture rate and such change may affect the timing of the total amount of expense recognized over the vesting period. Equity-based awards that do not require future service are expensed immediately. Equity-based awards that do not meet the criteria for equity classification are recorded as liabilities and adjusted to fair value at the end of each reporting period. Off-Balance Sheet Financial Instruments — The Company uses the FASB ASC Topic 825, “Financial Instruments.” to identify and disclose off-balance sheet financial instruments, which include credit instruments, such as commitments to make employee loans and related guarantees, standby letters of credit and certain guarantees issued under customer contracts. The face amount for these items represents the exposure to loss, before considering available collateral or the borrower’s ability to repay. Loss contingencies arising from off-balance sheet financial instruments are recorded as liabilities when the likelihood of loss is probable and an amount or range of loss can be reasonably estimated. The Company does not believe such matters exist that would have a material effect on the financial statements. Foreign Currency Translation — Assets and liabilities of consolidated foreign subsidiaries whose functional currency is not the U.S. dollar are translated into U.S. dollars at period-end exchange rates and revenues and expenses are translated into U.S. dollars at daily exchange rates. The adjustment resulting from translating the financial statements of such foreign subsidiaries into U.S. dollars is reflected as a cumulative translation adjustment and reported as a component of accumulated other comprehensive income (loss). For consolidated foreign subsidiaries whose functional currency is the U.S. dollar, transactions and balances denominated in the local currency are foreign currency transactions. Foreign currency transactions and balances related to non-monetary assets and liabilities are remeasured to the functional currency of the subsidiary at historical exchange rates while monetary assets and liabilities are remeasured to the functional currency of the subsidiary at current exchange rates. Foreign currency exchange gains or losses from remeasurement are included in income in the period in which they occur. Risks and Uncertainties — As a result of its global operations, the Company may be subject to certain inherent risks. Concentration of Credit — Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash and cash equivalents, trade accounts receivable and unbilled revenues. The Company maintains cash and cash equivalents and short-term deposits with financial institutions. The Company determined that the Company’s credit policies reflect normal industry terms and business risk and there is no expectation of non-performance by the counterparties. As of December 31, 2017 , $240,148 of total cash, including time deposits and restricted cash, was held in CIS countries, with $196,656 of that total in Belarus. Banking and other financial systems in the CIS region are less developed and regulated than in some more developed markets, and bank deposits made by corporate entities in the CIS region are not insured. Changes in the market behavior or decisions of the Company’s clients could adversely affect the Company’s results of operations. During the years ended December 31, 2017 , 2016 and 2015 , revenues including reimbursable expenses and other revenues from our top five customers were $348,219 , $329,324 and $299,655 , respectively, representing 24.0% , 28.4% and 32.8% , respectively, of total revenues in the corresponding periods. Revenues including reimbursable expenses and other revenues from our top ten customers were $491,742 , $445,814 and $403,052 in 2017 , 2016 and 2015 , respectively, representing 33.9% , 38.4% and 44.1% , respectively, of total revenues in the corresponding periods. Foreign currency risk — The Company’s global operations are conducted predominantly in U.S. dollars. Other than U.S. dollars, the Company generates a significant portion of revenues in various currencies, principally, euros, British pounds sterling, Canadian dollars, Swiss francs and Russian rubles and incurs expenditures principally in Hungarian forints, Russian rubles, Polish zlotys, Swiss francs, British pounds, Indian rupees and China yuan renminbi associated with its delivery centers. The Company’s international operations expose it to foreign currency exchange rate changes that could impact translations of foreign denominated assets and liabilities into U.S. dollars and future earnings and cash flows from transactions denominated in different currencies. The Company is exposed to fluctuations in foreign currency exchange rates primarily related to accounts receivable and unbilled revenues from sales in foreign currencies and cash outflows for expenditures in foreign currencies. The Company’s results of operations, primarily revenues and expenses denominated in foreign currencies, can be affected if any of the currencies, which we use materially in our business, appreciate or depreciate against the U.S. dollar. Interest rate risk — The Company’s exposure to market risk is influenced primarily by changes in interest rates received on cash and cash equivalent deposits and paid on any outstanding balance on the Company’s revolving line of credit, which is subject to a variety of rates depending on the type and timing of funds borrowed (See Note 12 “Long-Term Debt”). The Company does not use derivative financial instruments to hedge the risk of interest rate volatility.

RECENT ACCOUNTING PRONOUNCEMENT

RECENT ACCOUNTING PRONOUNCEMENTS RECENT ACCOUNTING PRONOUNCEMENTS	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Recent Accounting Pronouncements	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. Stock-Based Compensation — Effective January 1, 2017, the Company adopted Accounting Standard Update (“ASU”) No. 2016-09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . The provisions of the new guidance affecting the Company require excess tax benefits and tax deficiencies to be recorded in the income statement when stock-based awards vest or are settled; remove the requirement to include hypothetical excess tax benefits in the application of the treasury stock method when computing earnings per share; and provide for a new policy election to either: (1) continue applying forfeiture rate estimates in the determination of compensation cost, or (2) account for forfeitures as a reduction of share-based compensation cost as they occur. The new guidance also requires cash flows related to excess tax benefits to be classified as an operating activity in the statement of cash flows and now requires shares withheld for tax withholding purposes to be classified as a financing activity. As a result of this adoption: • the Company recognized a $1,740 increase in retained earnings as of January 1, 2017 for previously unrecognized tax benefits using the modified retrospective method of transition, as required by the standard; • the Company recognized discrete tax benefits of $9,307 in the provision for income taxes within the consolidated statement of income and comprehensive income during the year ended December 31, 2017, related to excess tax benefits upon vesting and exercise of stock-based awards; • the Company elected to adopt the cash flow presentation of the excess tax benefits prospectively where these benefits are classified along with other income tax cash flows as operating cash flows. Accordingly, prior period information has not been restated; • the Company elected to continue to estimate the number of stock-based awards expected to forfeit, rather than electing to account for forfeitures as they occur to determine the amount of compensation cost to be recognized in each period; and • the Company excluded the excess tax benefits from the assumed proceeds available to repurchase shares in the computation of diluted earnings per share for the year ended December 31, 2017. Simplifying the Measurement for Goodwill — Effective January 1, 2017, the Company early adopted the new accounting guidance simplifying the accounting for goodwill impairment. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The new guidance is adopted on a prospective basis. The adoption of this amended guidance did not have an impact on the Company’s financial results. 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. Revenue Recognition — In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . The core principle of Topic 606 is that an entity should 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. Topic 606 as amended, will replace most existing revenue recognition guidance in GAAP and requires expanded 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 standard allows for two methods of adoption: the full retrospective method, which requires the standard to be applied to each prior period presented, or the modified retrospective method, which requires the cumulative effect of adoption to be recognized as an adjustment to opening retained earnings in the period of adoption as well as incremental disclosure comparing results presented under Topic 606 to results that would have been presented utilizing current accounting. The Company adopted Topic 606 as amended on January 1, 2018 using the modified retrospective method. The Company completed its assessment of the impact of Topic 606 and implemented its transition plan, which included making necessary changes to policies, processes, internal controls and system enhancements to generate the information necessary to comply with the new standard. Based on the assessment procedures completed, the Company recognized a one-time immaterial adjustment to retained earnings as of January 1, 2018 and does not expect a significant change in the timing or pattern of revenue recognition after adoption. Due to the complexity of certain of the Company’s contracts, actual revenue recognition treatment required under the new standard depends on contract-specific terms and may vary from the accounting under the current guidance in some instances. For most of the Company’s time-and-materials contracts, EPAM expects to continue to recognize revenues as services are performed consistent with the Company’s current policy. For fixed-price contracts, the Company generally expects to continue to recognize revenues over time based on the measured progress of satisfaction of the performance obligations which is consistent with the Company’s current proportional performance method. The most impactful changes upon adoption included a delay in revenue recognition related to (1) cash collections on contracts when collectability is uncertain and (2) earlier recognition of revenue from certain software licenses. Beginning in the first quarter of 2018, EPAM expects to provide incremental disclosure in its consolidated financial statements related to revenue recognition including disaggregated information related to the Company’s key verticals, contract balances, remaining performance obligations, and significant judgments and estimates. Leases — Effective January 1, 2019, the Company will be required to adopt the new guidance of ASC Topic 842, Leases (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 requires lessees and lessors to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes 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 at each reporting date 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 expects to adopt this standard on January 1, 2019. The Company has not yet completed its assessment of the impact of the new guidance on its consolidated financial statements or concluded on whether it will elect to apply practical expedients. Derivatives and Hedging — Effective January 1, 2019, with early adoption permitted in any interim or annual period, the Company will be required to adopt 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 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 standard requires entities to apply the amended presentation and disclosure guidance only prospectively as of the period of adoption. Currently, the Company does not apply hedge accounting and has not yet concluded on when it will adopt the standard. 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	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
ACQUISITIONS	ACQUISITIONS The Company’s acquisitions allow it to expand into desirable geographic locations, complement its existing vertical markets, increase revenue and create new service offerings. Acquisitions were settled in cash and/or stock where a portion of the settlement price may have been deferred. For some transactions, purchase agreements contain contingent consideration in the form of an earnout obligation. During the years ended December 31, 2017 and 2016, the Company completed acquisitions with aggregated purchase prices of $6,980 and $5,580 , respectively. These acquisitions individually and in the aggregate are not material to the Company’s consolidated financial statements. NavigationArts — On July 10, 2015, the Company acquired all of the outstanding equity of NavigationArts, Inc. and its subsidiary, NavigationArts, LLC (collectively “NavigationArts”). The U.S.-based NavigationArts provided digital consulting, architecture and content solutions and was regarded as a leading user-experience agency. The acquisition of NavigationArts added approximately 90 design consultants to the Company’s headcount. In connection with the NavigationArts acquisition the Company paid $28,747 as cash consideration. In the first quarter of 2016, the Company made a 338(h)(10) election to treat the NavigationArts acquisition as an asset purchase for tax purposes. As a result, during the second quarter of 2016 the Company paid an additional $1,797 to the sellers of NavigationArts, as provided for in the stock purchase agreement. The acquired goodwill that is deductible for tax purposes was $23,794 as of the date of the acquisition. AGS — On November 16, 2015, the Company acquired all of the outstanding equity of Alliance Consulting Global Holdings, Inc including its wholly-owned direct and indirect subsidiaries Alliance Global Services, Inc., Alliance Global Services, LLC, companies organized under the laws of the U.S., and Alliance Global Services IT India, a company organized under the laws of India (collectively “AGS”). AGS provided software product development services and test automation solutions and had multiple locations in the United States and India. The acquisition of AGS added 1,151 IT professionals to the Company’s headcount in the United States and India. In connection with the AGS acquisition the Company paid $51,717 as cash consideration. The following is a summary of the fair values of the net assets acquired through each respective acquisition during the year ended December 31, 2015: NavigationArts AGS Total Cash and cash equivalents $ 1,317 $ 1,727 $ 3,044 Accounts receivable and other current assets 3,920 9,934 13,854 Property and equipment and other long-term assets 230 1,600 1,830 Deferred tax assets — 5,722 5,722 Acquired intangible assets 2,800 22,700 25,500 Goodwill 23,794 24,454 48,248 Total assets acquired 32,061 66,137 98,198 Accounts payable and accrued expenses 871 2,760 3,631 Bank loans and other long-term liabilities — 295 295 Deferred revenue 50 1,049 1,099 Due to employees 596 2,342 2,938 Deferred tax liabilities — 7,974 7,974 Total liabilities assumed 1,517 14,420 15,937 Net assets acquired $ 30,544 $ 51,717 $ 82,261 The following table presents the fair values and useful lives of intangible assets acquired through each respective acquisition during the year ended December 31, 2015: NavigationArts AGS Weighted Average Useful Life (in years) Amount Weighted Average Useful Life (in years) Amount Customer relationships 10 $ 2,800 10 $ 22,700 Total $ 2,800 $ 22,700

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS - NET	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS - NET	GOODWILL AND INTANGIBLE ASSETS — NET Goodwill by reportable segment was as follows: North America Europe Total Balance as of January 1, 2016 $ 81,464 $ 34,466 $ 115,930 NavigationArts purchase accounting adjustments 2,030 — 2,030 AGS purchase accounting adjustments (9,361 ) — (9,361 ) Other acquisitions 2,404 177 2,581 Other acquisitions purchase accounting adjustments 395 87 482 Effect of currency translation (120 ) (2,253 ) (2,373 ) Balance as of December 31, 2016 76,812 32,477 109,289 Other acquisitions 199 4,533 4,732 Other acquisitions purchase accounting adjustments (285 ) 2,100 1,815 Effect of currency translation 564 3,131 3,695 Balance as of December 31, 2017 $ 77,290 $ 42,241 $ 119,531 Excluded from the table above are the Russia and Other segments for which the allocated goodwill was fully impaired for the periods presented. The Russia segment had accumulated goodwill impairment losses of $2,241 as of December 31, 2017 , 2016 and 2015 . The Other segment had accumulated goodwill impairment losses of $1,697 as of December 31, 2017 , 2016 and 2015 . There were no accumulated goodwill impairment losses in the North America or Europe reportable segments as of December 31, 2017 , 2016 or 2015 . Intangible assets other than goodwill as of December 31, 2017 and 2016 were as follows: As of December 31, 2017 Weighted average life at acquisition (in years) Gross carrying amount Accumulated amortization Net carrying amount Customer relationships 10 $ 66,646 $ (22,200 ) $ 44,446 Trade names 5 4,099 (4,034 ) 65 Total $ 70,745 $ (26,234 ) $ 44,511 As of December 31, 2016 Weighted average life at acquisition (in years) Gross carrying amount Accumulated amortization Net carrying amount Customer relationships 10 $ 65,409 $ (15,133 ) $ 50,276 Trade names 5 5,622 (4,661 ) 961 Non-competition agreements 4 756 (733 ) 23 Total $ 71,787 $ (20,527 ) $ 51,260 All of the intangible assets other than goodwill have finite lives and as such are subject to amortization. Recognized amortization expense for each of the years ended December 31 is presented in the table below: For the Years Ended December 31, 2017 2016 2015 Customer relationships $ 6,643 $ 6,858 $ 3,961 Trade names 896 1,139 1,280 Non-competition agreements 23 173 175 Total $ 7,562 $ 8,170 $ 5,416 Estimated amortization expense related to the Company’s existing intangible assets for the next five years ending December 31 and thereafter is as follows: Amount 2018 $ 6,661 2019 6,661 2020 6,661 2021 6,661 2022 6,508 Thereafter 11,359 Total $ 44,511

PREPAID AND OTHER CURRENT ASSET

PREPAID AND OTHER CURRENT ASSETS	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
PREPAID AND OTHER CURRENT ASSETS	PREPAID AND OTHER CURRENT ASSETS Prepaid and other current assets consisted of the following: December 31, December 31, Taxes receivable $ 12,172 $ 6,054 Prepaid expenses 5,939 5,462 Other current assets, net of allowance of $45 and $644, respectively 5,085 6,977 Total $ 23,196 $ 18,493

EMPLOYEE LOANS AND ALLOWANCE FO

EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES	12 Months Ended
	Dec. 31, 2017
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES	EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES In 2012, the Board of Directors of the Company approved the Employee Housing Program (the “Housing Program”), which provides employees with loans to purchase housing in Belarus. The housing is sold directly to employees by independent third parties. The Housing Program was designed as a retention mechanism for the Company’s employees in Belarus and is available to full-time qualified employees who have been with the Company for at least three years . The aggregate maximum lending limit of the program is $10,000 , with no individual outstanding loans exceeding $50 . In addition to the housing loans, the Company issues relocation loans in connection with intra-company transfers, as well as certain other individual loans. During the year ended December 31, 2017 , loans issued by the Company under the Housing Program were denominated in U.S. dollars with a 5 -year term and carried an interest rate of 7.5% . As of December 31, 2017 and 2016, categories of employee loans included in the loan portfolio were as follows: December 31, December 31, Housing loans $ 3,513 $ 5,448 Relocation and other loans 697 530 Total employee loans 4,210 5,978 Less: Allowance for loan losses — — Total loans, net of allowance for loan losses $ 4,210 $ 5,978 Movement of employee loans balances during the years ended December 31, 2017 , 2016 and 2015 was as follows: Amount Employee loans at January 1, 2015 $ 6,515 Employee loans issued 3,427 Employee loans repaid (3,547 ) Employee loans written-off (7 ) Changes in interest and penalties accrued (32 ) Effect of net foreign currency exchange rate changes (18 ) Employee loans at December 31, 2015 $ 6,338 Employee loans issued 2,960 Employee loans repaid (3,273 ) Changes in interest and penalties accrued (35 ) Effect of net foreign currency exchange rate changes (12 ) Employee loans at December 31, 2016 $ 5,978 Employee loans issued 1,875 Employee loans repaid (3,615 ) Employee loans written-off (22 ) Changes in interest and penalties accrued (18 ) Effect of net foreign currency exchange rate changes 12 Employee loans at December 31, 2017 $ 4,210

PROPERTY AND EQUIPMENT - NET

PROPERTY AND EQUIPMENT - NET	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT - NET	PROPERTY AND EQUIPMENT — NET Property and equipment, net consisted of the following: Weighted Average Useful Life (in years) December 31, December 31, Computer hardware 3 $ 62,132 $ 49,599 Building 49 34,058 34,012 Furniture and fixtures 7 18,071 13,178 Leasehold improvements 6 13,186 7,944 Office equipment 7 10,825 9,416 Purchased computer software 3 8,379 4,601 Land improvements 20 1,474 1,467 148,125 120,217 Less accumulated depreciation and amortization (61,706 ) (46,601 ) Total $ 86,419 $ 73,616 Depreciation and amortization expense related to property and equipment was $21,000 , $15,217 and $11,979 during the years ended December 31, 2017 , 2016 and 2015 , respectively.

ACCRUED EXPENSES AND OTHER CURR

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES	ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities consisted of the following: December 31, December 31, Accrued compensation expense and related costs $ 67,034 $ 33,404 Deferred revenue 4,498 3,319 Other current liabilities and accrued expenses 18,280 13,172 Total $ 89,812 $ 49,895

TAXES PAYABLE

TAXES PAYABLE	12 Months Ended
	Dec. 31, 2017
Taxes Payable [Abstract]
TAXES PAYABLE	TAXES PAYABLE Current taxes payable consisted of the following: December 31, December 31, Income taxes payable $ 9,488 $ 4,000 Value added taxes payable 16,696 10,644 Payroll, social security, and other taxes payable 14,676 10,364 Total $ 40,860 $ 25,008 As a result of the U.S. Tax Cuts and Jobs Act enacted on December 22, 2017, the Company recorded income taxes payable of $64,321 to be paid over the next 8 years. Of this amount, $59,175 is classified as Taxes payable, noncurrent as of December 31, 2017 . See Note 10 “Income Taxes” for additional discussion of the impact of the Act. There were no noncurrent taxes payable as of December 31, 2016 .

INCOME TAXES

INCOME TAXES	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Income/(loss) before provision for income taxes Income before provision for income taxes included losses from domestic operations and income from foreign operations based on geographic location as disclosed in the table below: For the Years Ended December 31, 2017 2016 2015 Income/(loss) before provision for income taxes: Domestic $ (6,595 ) $ (9,300 ) $ (7,687 ) Foreign 180,900 135,766 113,757 Total $ 174,305 $ 126,466 $ 106,070 Provision for income taxes The provision for income taxes consists of the following: For the Years Ended December 31, 2017 2016 2015 Current Federal $ 65,571 $ 13,324 $ 19,851 State (204 ) (63 ) 2,563 Foreign 23,617 17,243 14,528 Deferred Federal 7,235 (3,581 ) (13,361 ) State (90 ) 312 (1,891 ) Foreign 5,416 (35 ) (76 ) Total $ 101,545 $ 27,200 $ 21,614 On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act (“U.S. Tax Act”). The U.S. Tax Act significantly changes U.S. corporate income tax laws including a reduction of the U.S. corporate income tax rate from 35.0% to 21.0% effective January 1, 2018 and the creation of a territorial tax system with a one-time transition tax on accumulated foreign subsidiary earnings not previously subject to U.S. income tax. In addition, the U.S. Tax Act creates new taxes on certain foreign-sourced earnings and certain related party payments, which are referred to as the global intangible low-taxed income tax (“GILTI”) and the base erosion and anti-abuse tax, respectively. Due to the timing of the enactment and the complexity involved in applying the provisions of the U.S. Tax Act, we have made reasonable estimates of the effects and recorded provisional amounts in our financial statements as of December 31, 2017 . As we collect and prepare necessary data and interpret 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 refine our calculations, we may make adjustments to the provisional amounts recorded. We expect to complete our 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 one-time transition tax on accumulated foreign subsidiary earnings not previously subject to U.S. income tax requires us to pay U.S. income tax at a rate of 15.5% to the extent of foreign cash and certain other net current assets and 8.0% on the remaining earnings. As a result, the Company recorded a provisional income tax expense and corresponding income taxes payable of $64,321 to be paid over the next 8 years. Of this amount, $59,175 is classified as Taxes payable, noncurrent as of December 31, 2017 . In addition, the Company provisionally reduced its net deferred tax assets by $10,311 reflecting the impact of the change in the U.S. statutory tax rate from 35.0% to 21.0% in the periods in which the net deferred tax assets are expected to be realized as a result of the U.S. Tax Act. The U.S. Tax Act subjects a U.S. shareholder to 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. Given the complexity of the GILTI provisions, we are still evaluating the effects of the GILTI provisions and have not yet determined our accounting policy. At December 31, 2017, because we are still evaluating the GILTI provisions and our analysis of future taxable income that is subject to GILTI, we are unable to make a reasonable estimate and have not reflected any adjustments related to GILTI in our financial statements. As of December 31, 2017 and in light of the U.S. Tax Act, the Company reassessed its accumulated foreign earnings and determined $97,000 of its accumulated earnings in Belarus are no longer indefinitely reinvested. As a result, the Company recorded a charge of $4,850 in its provision for income taxes during the year ended December 31, 2017 reflecting the withholding tax that will be payable to Belarus when the earnings are expatriated. As of December 31, 2017 , the Company has determined that all other accumulated foreign earnings of $642,149 are expected to be indefinitely reinvested. Due to the enactment of the U.S. Tax Act and the one-time transition tax on accumulated foreign subsidiary earnings, these accumulated foreign earnings are no longer expected to be subject to U.S. federal income tax if repatriated but could be subject to state and foreign income and withholding taxes. Effective tax rate reconciliation The reconciliation of the provision for income taxes at the federal statutory income tax rate to our effective income tax rate is as follows: For the Years Ended December 31, 2017 2016 2015 Provision for income taxes at federal statutory rate $ 61,007 $ 44,263 $ 37,125 Increase/ (decrease) in taxes resulting from: Impact from U.S. Tax Act 74,632 — — Foreign tax expense and tax rate differential (39,997 ) (33,477 ) (31,094 ) Effect of change in accounting for excess tax benefits relating to stock-based compensation (Note 2) (9,307 ) — — Stock-based compensation expense 6,908 9,535 7,591 Subsidiary withholding tax liability 4,850 — — Effect of permanent differences 3,205 5,042 7,314 Change in valuation allowance 783 — — Change in foreign tax rates 29 — 9 State taxes, net of federal benefit (116 ) 1,192 341 Other (449 ) 645 328 Provision for income taxes $ 101,545 $ 27,200 $ 21,614 The Company’s worldwide effective tax rate for years ended December 31, 2017 , 2016 and 2015 was 58.3% , 21.5% and 20.4% , respectively. The income tax in 2017 was unfavorably impacted by U.S. Tax Reform which was partially offset by the recognition of excess tax benefits following the adoption of ASU No. 2016-09 on January 1, 2017. See Note 2 “Recent Accounting Pronouncements” for further information. In Belarus, member technology companies of High-Technologies Park have a full exemption from Belarus income tax. This tax holiday was recently extended through January 2049 . The aggregate dollar benefits derived from this tax holiday approximated $15.5 million , $13.6 million and $20.8 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The benefit the tax holiday had on diluted net income per share approximated $0.28 , $0.26 and $0.40 for the years ended December 31, 2017 , 2016 and 2015 , respectively. Deferred Income Taxes Deferred income taxes reflect the net effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, December 31, Deferred tax assets: Property and equipment $ 170 $ 203 Intangible assets 1,456 1,525 Accrued expenses 4,392 9,172 Net operating loss carryforward 5,069 5,368 Deferred revenue 1,280 1,165 Stock-based compensation 16,197 19,701 Other assets 1,415 17 Deferred tax assets $ 29,979 $ 37,151 Less: valuation allowance (924 ) — Total deferred tax assets $ 29,055 $ 37,151 Deferred tax liabilities: Property and equipment $ 1,868 $ 1,735 Intangible assets 3,077 4,969 Accrued revenue and expenses 1,352 500 Subsidiary withholding tax liability 4,850 — Stock-based compensation 1,498 1,606 Other liabilities 239 314 Total deferred tax liabilities $ 12,884 $ 9,124 Net deferred tax assets $ 16,171 $ 28,027 As of December 31, 2017 and 2016 the Company classified $8,803 and $2,979 , respectively, of deferred tax liabilities as Other noncurrent liabilities in the consolidated balance sheet. Included in the stock-based compensation expense deferred tax asset at December 31, 2017 and 2016 is $8,512 and $11,471 , respectively that is related to acquisitions and is amortized for tax purposes over a 10 to 15 -year period. As of December 31, 2017 , our domestic and foreign net operating loss (“NOL”) carryforwards for income tax purposes were approximately $6,264 and $14,792 , respectively. If not utilized, the domestic NOL carryforwards will begin to expire in 2021. Our foreign NOL carryforwards include $2,454 from jurisdictions with no expiration date, $5,338 that will expire in various countries by 2026, as well as $1,183 and $5,817 , for which the Company has recorded a valuation allowance and will expire in 2021 and 2022, respectively. The valuation allowance maintained by the Company as of December 31, 2017 relates primarily to net operating loss carryforwards in certain non-U.S. jurisdictions that we believe are not likely to be realized. The net change in the valuation allowance in the current year was $924 . Uncertain Tax Positions The liability for unrecognized tax benefits is included in noncurrent taxes payable, within the consolidated balance sheets at December 31, 2017 and 2016 . At December 31, 2017 and 2016 , the total amount of gross unrecognized tax benefits (excluding the federal benefit received from state tax positions) was $699 and $66 , respectively. These amounts represent the amount of unrecognized tax benefits that, if recognized, would favorably affect the effective tax rate in future periods. The Company’s policy is to recognize interest and penalties related to uncertain tax positions as a component of its provision for income taxes. The Company accrued $148 of interest and penalties resulting from such unrecognized tax benefits at December 31, 2017 . There was no accrued interest and penalties resulting from such unrecognized tax benefits at December 31, 2016 and December 31, 2015 . The beginning to ending reconciliation of the gross unrecognized tax benefits is as follows: For the Years Ended December 31, 2017 2016 2015 Balance at January 1 $ 66 $ 62 $ 200 Increases in tax positions in current year 240 4 — Increases in tax positions in prior year 459 — — Decreases due to settlement (66 ) — (138 ) Balance at December 31 $ 699 $ 66 $ 62 There were no tax positions for which it was reasonably possible that unrecognized tax benefits will significantly increase or decrease within twelve months of the reporting date. The Company files income tax returns in the United States and in various state, local and foreign jurisdictions. The Company’s significant tax jurisdictions are the United States, Canada, Russia, Denmark, Germany, Ukraine, the United Kingdom, Hungary, Switzerland, and India. The tax years subsequent to 2014 remain open to examination by the Internal Revenue Service and generally, the tax years subsequent to 2014 remain open to examination by various state and local taxing authorities and various foreign taxing authorities.

EMPLOYEE BENEFITS

EMPLOYEE BENEFITS	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
EMPLOYEE BENEFITS	EMPLOYEE BENEFITS The Company offers a 401(k) retirement plan, which is a tax-qualified self-funded retirement plan covering substantially all of the Company’s U.S. employees. Under this plan, employees may elect to defer their current compensation up to the statutory limit defined by the Internal Revenue Service. The Company provides discretionary matching contributions to the plan of up to 2% of the employee’s eligible compensation as defined by the plan. Employer contributions are subject to a two -year vesting schedule. Employer contributions charged to expense for the years ended December 31, 2017 , 2016 and 2015 , were $2,331 , $1,934 and $740 , respectively. The Company does not maintain any defined benefit pension plans or any non-qualified deferred compensation plans.

LONG-TERM DEBT

LONG-TERM DEBT	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
LONG-TERM DEBT	LONG-TERM DEBT Revolving Line of Credit — On September 12, 2014, the Company entered into a revolving loan agreement (the “2014 Credit Facility”) with PNC Bank, National Association; Santander Bank, N.A; and Silicon Valley Bank (collectively the “Lenders”). Under the 2014 Credit Facility, the Company’s borrowing capacity was set at $100,000 , with potential to increase it to $200,000 if certain conditions were met. Borrowings under the 2014 Credit Facility were denominated in U.S. dollars or, up to a maximum of $50,000 in British pounds sterling, Canadian dollars, euros or Swiss francs (or other currencies as may be approved by the Lenders). Borrowings under the 2014 Credit Facility bore interest at either a base rate or Euro-rate plus a margin based on the Company’s leverage ratio. The base rate was equal to the highest of (a) the Federal Funds Open Rate, plus 0.5% , (b) the Prime Rate, and (c) the Daily LIBOR Rate, plus 1.0% . On May 24, 2017, the Company terminated the 2014 Credit Facility and entered into a new 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 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, or (c) the Daily LIBOR Rate, plus 1.0% . 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 December 31, 2017 , the Company was in compliance with all covenants contained in the 2017 Credit Facility. As of December 31, 2017 , the outstanding debt of the Company under the 2017 Credit Facility was $25,000 at an interest rate of 2.6% . As of December 31, 2016, the outstanding debt of the Company under the 2014 Credit Facility was $25,000 . Both borrowings are subject to a LIBOR-based interest rate, which resets regularly at issuance, based on lending terms. As of December 31, 2017 and 2016 , the Company had $1,294 and $942 irrevocable standby letters of credit, respectively. As of December 31, 2017 , the borrowing capacity of the Company under the 2017 Credit Facility was $273,706 . As of December 31, 2016, the borrowing capacity of the Company under the 2014 Credit Facility was $74,058 .

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The following costs related to the Company’s stock compensation plans were included in the consolidated statements of income and comprehensive income: For the Years Ended December 31, 2017 2016 2015 Cost of revenues $ 20,868 $ 16,619 $ 13,695 Selling, general and administrative expenses — Acquisition related 8,139 12,884 18,690 Selling, general and administrative expenses — All other 23,400 19,741 13,448 Total $ 52,407 $ 49,244 $ 45,833 Equity Plans 2015 Long-Term Incentive Plan — On June 11, 2015, the Company’s stockholders approved the 2015 Long-Term Incentive Plan (“2015 Plan”) to be used to issue equity awards to company personnel. As of December 31, 2017 , 5,818,622 shares of common stock remained available for issuance under the 2015 Plan. All of the awards issued pursuant to the 2015 Plan expire 10 years from the date of grant. 2012 Non-Employee Directors Compensation Plan — On January 11, 2012, the Company approved the 2012 Non-Employee Directors Compensation Plan (“2012 Directors Plan”) to be used to issue equity grants to its non-employee directors. The Company authorized 600,000 shares of common stock to be reserved for issuance under the plan. As of December 31, 2017 , 539,772 shares of common stock remained available for issuance under the 2012 Directors Plan. The 2012 Directors Plan will expire after 10 years and is administered by the Company’s Board of Directors. 2012 Long-Term Incentive Plan — On January 11, 2012, the Company approved the 2012 Long-Term Incentive Plan (“2012 Plan”) to be used to issue equity grants to Company personnel. In June 2015, the 2012 Plan was discontinued; however, outstanding awards remain subject to the terms of the 2012 Plan and any shares that are subject to an award that was previously granted under the 2012 Plan and that expire or terminate for any reason prior to exercise will become available for issuance under the 2015 Plan. All of the awards issued pursuant to the 2012 Plan expire 10 years from the date of grant. 2006 Stock Option Plan — Effective May 31, 2006, the Board of Directors of the Company adopted the 2006 Stock Option Plan (the “2006 Plan”) to grant stock options to directors, employees, and certain independent contractors. In January 2012, the 2006 Plan was discontinued; however, outstanding awards remain subject to the terms of the 2006 Plan and any shares that are subject to an option award that was previously granted under the 2006 Plan and that expire or terminate for any reason prior to exercise will become available for issuance under the 2015 Plan. All of the awards issued pursuant to the 2006 Plan expire 10 years from the date of grant. 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 Options outstanding at January 1, 2015 6,838,746 $ 20.98 $ 183,073 Options granted 2,219,725 $ 62.18 Options exercised (1,405,826 ) $ 14.70 Options forfeited/cancelled (201,731 ) $ 34.48 Options outstanding at December 31, 2015 7,450,914 $ 34.07 $ 331,938 Options granted 313,088 $ 70.27 Options exercised (895,804 ) $ 20.13 Options forfeited/cancelled (227,759 ) $ 47.89 Options expired (3,200 ) $ 1.52 Options outstanding at December 31, 2016 6,637,239 $ 37.20 $ 179,936 Options granted 261,373 $ 73.40 Options exercised (1,789,434 ) $ 30.23 Options forfeited/cancelled (200,210 ) $ 57.09 Options expired (7,220 ) $ 4.63 Options outstanding at December 31, 2017 4,901,748 $ 40.91 $ 326,064 6.2 Options vested and exercisable at December 31, 2017 3,068,917 $ 31.49 $ 233,054 5.5 Options expected to vest 1,764,538 $ 56.35 $ 90,133 7.3 The fair value of each option award is estimated on the date of grant using the Black-Scholes option valuation model. The Company recognizes the fair value of each option as compensation expense on a straight-line basis over the requisite service period (generally the vesting period). The Company estimates the volatility of its common stock at the date of grant using historical volatility of peer public companies. During 2014, the Company began including the historical volatility for the Company in conjunction with peer public companies to formulate estimated volatility regarding stock options. The expected term of the option is calculated using the simplified method of determining expected term as outlined in SEC Staff Accounting Bulletin 107 as the Company does not have sufficient history in order to develop a more precise estimate. The risk-free rate is based on the U.S. Treasury yield curve for periods equal to the expected term of the options in effect at the time of grant. The Company has not declared or paid any dividends on its common stock. The Company intends to retain any earnings to fund operations and future growth of its business and, therefore, does not anticipate paying any cash dividends in the foreseeable future. The grant-date fair value for stock options granted was determined using a Black-Scholes model incorporating the following average assumptions: For the Years Ended December 31, 2017 2016 2015 Expected volatility 30.5 % 31.9 % 34.1 % Expected term (in years) 6.25 6.24 6.25 Risk-free interest rate 2.1 % 1.5 % 1.8 % Expected dividends — % — % — % Additionally, the Company records share-based compensation expense only for those awards that are expected to vest. The Company applies an estimated forfeiture rate at the time of grant and adjusts those estimated forfeitures to reflect actual forfeitures quarterly. The weighted-average grant-date fair value of stock options granted during the years ended December 31, 2017 , 2016 and 2015 was $25.29 , $24.26 and $24.21 , respectively. The total intrinsic value of options exercised during the years ended December 31, 2017 , 2016 and 2015 was $91,148 , $39,577 and $89,860 , respectively. The options are typically scheduled to vest over four years from the time of grant, subject to the terms of the applicable plan and stock option agreement. In general, in the event of a participant’s termination of service for any reason, unvested options are forfeited as of the date of such termination without any payment to the participant. As of December 31, 2017 , total remaining unrecognized compensation cost related to unvested stock options, net of estimated forfeitures, was approximately $24,354 . The expense is expected to be recognized over a weighted-average period of 1.4 years . As of December 31, 2017 , a total of 4,354 shares underlying options exercised through December 31, 2017 , were in transfer with the Company’s transfer agent. Restricted Stock and Restricted Stock Units The Company grants restricted stock units (“RSUs”) to Company personnel and non-employee directors under the Company’s 2015 Plan (and prior to its approval, under the 2012 Plan) and 2012 Directors Plan, respectively. Prior to 2017, awards to non-employee directors were in the form of restricted stock. In addition, the Company has issued in the past, and may issue in the future, its equity securities to compensate employees of acquired businesses for future services. Equity-based awards granted in connection with acquisitions of businesses are generally issued in the form of service-based awards (dependent on continuing employment only) and performance-based awards, which are granted and vest only if certain specified performance conditions are met. The awards issued in connection with acquisitions of businesses are subject to the terms and conditions contained in the applicable award agreement and acquisition documents with typical vesting period of three years , with 33.3% of the awards granted vesting in equal installments on the first, second and third anniversaries of the grant. Service-Based Awards The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the years ended December 31, 2017 , 2016 and 2015 : Equity-Classified Equity-Settled 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, 2015 562,942 $ 37.42 70,500 $ 32.55 — $ — Awards granted 5,295 $ 70.79 108,319 $ 67.21 — $ — Awards vested (261,504 ) $ 33.74 (17,625 ) $ 32.55 — $ — Awards forfeited/cancelled 106 $ 36.57 (11,922 ) $ 34.49 — $ — Unvested service-based awards outstanding at December 31, 2015 306,839 $ 41.14 149,272 $ 57.55 — $ — Awards granted 6,510 $ 73.00 408,629 $ 70.39 207,586 $ 70.53 Awards vested (156,535 ) $ 42.64 (41,015 ) $ 55.60 — $ — Awards forfeited/cancelled (2,689 ) $ 45.32 (31,698 ) $ 70.44 (3,085 ) $ 70.52 Unvested service-based awards outstanding at December 31, 2016 154,125 $ 40.89 485,188 $ 67.69 204,501 $ 70.53 Awards granted — $ — 424,623 $ 73.89 170,295 $ 74.21 Awards modified — $ — (2,570 ) $ 26.85 2,570 $ 73.27 Awards vested (152,285 ) $ 43.39 (140,043 ) $ 66.54 (52,004 ) $ 70.56 Awards forfeited/cancelled — $ — (79,186 ) $ 70.30 (10,533 ) $ 71.72 Unvested service-based awards outstanding at December 31, 2017 1,840 $ 54.37 688,012 $ 71.60 314,829 $ 72.50 The fair value of vested service-based awards (measured at the vesting date) for the years ended December 31, 2017 , 2016 and 2015 was as follows: For the Years Ended December 31, 2017 2016 2015 Equity-classified equity-settled Restricted stock $ 12,607 $ 11,431 $ 19,305 Restricted stock units 10,620 2,932 1,092 Liability-classified cash-settled Restricted stock units 3,811 — — Total fair value of vested service-based awards $ 27,038 $ 14,363 $ 20,397 As of December 31, 2017 , $81 of total remaining unrecognized stock-based compensation costs related to service-based equity-classified restricted stock is expected to be recognized over the weighted-average remaining requisite service period of 1.6 years . As of December 31, 2017 , $32,100 of total remaining unrecognized stock-based compensation costs related to service-based equity-classified RSUs is expected to be recognized over the weighted-average remaining requisite service period of 1.9 years . As of December 31, 2017 , $19,691 of total remaining unrecognized stock-based compensation costs related to service-based liability-classified RSUs is expected to be recognized over the weighted-average remaining requisite service period of which is expected to be recognized over the next 1.9 years . The liability associated with our service-based liability-classified RSUs as of December 31, 2017 and 2016 was $5,964 and $2,111 , respectively, and was classified as Deferred compensation due to employees in the consolidated balance sheets. Performance -Based Awards In 2014, the Company granted performance-based awards in connection with the acquisitions completed during that year. The total number of the awards varied based on attainment of certain performance targets pursuant to the terms of the relevant transaction documents. No performance-based awards are outstanding as of December 31, 2017 . Summarized activity related to the Company’s performance-based awards for the years ended December 31, 2017 , 2016 and 2015 was as follows: Equity-Classified Liability-Classified Equity-Classified 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 performance-based awards outstanding at January 1, 2015 33,045 $ 38.44 338,465 $ 39.43 — $ — Awards granted — $ — — $ — 14,000 $ 70.22 Awards vested (12,145 ) $ 39.92 (105,604 ) $ 40.44 — $ — Awards forfeited/cancelled (1,360 ) $ 36.57 — $ — — $ — Changes in the number of awards expected to be delivered 2,550 $ 36.57 (21,655 ) $ 32.27 — $ — Unvested performance-based awards outstanding at December 31, 2015 22,090 $ 37.52 211,206 $ 39.65 14,000 $ 70.22 Awards granted — $ — — $ — — $ — Awards vested (9,978 ) $ 40.15 (105,604 ) $ 40.44 (4,666 ) $ 70.22 Awards forfeited/cancelled (6,539 ) $ 36.97 — $ — (4,667 ) $ 70.22 Unvested performance-based awards outstanding at December 31, 2016 5,573 $ 33.47 105,602 $ 38.86 4,667 $ 70.22 Awards granted — $ — — $ — — $ — Awards vested (5,573 ) $ 33.47 (105,602 ) $ 38.86 — $ — Awards forfeited/cancelled — $ — — $ — (4,667 ) $ 70.22 Unvested performance-based awards outstanding at December 31, 2017 — $ — — $ — — $ — The fair value of vested performance-based awards (measured at the vesting date) for the years ended December 31, 2017 , 2016 and 2015 was as follows: For the Years Ended December 31, 2017 2016 2015 Equity-classified equity-settled Restricted stock $ 452 $ 690 $ 789 Restricted stock units — 348 — Liability-classified equity-settled Restricted stock 8,633 7,955 7,363 Total fair value of vested performance-based awards $ 9,085 $ 8,993 $ 8,152

EARNINGS PER SHARE

EARNINGS PER SHARE	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Basic earnings per share is computed by dividing net 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 net 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: For the Years Ended December 31, 2017 2016 2015 Numerator for basic and diluted earnings per share: Net income $ 72,760 $ 99,266 $ 84,456 Numerator for basic and diluted earnings per share $ 72,760 $ 99,266 $ 84,456 Denominator for basic and diluted earnings per share: Basic weighted average common stock outstanding 52,077,011 50,309,362 48,720,844 Effect of dilutive securities: Stock options, equity-settled RSUs and performance-based awards 2,907,162 2,906,030 3,265,029 Diluted weighted average common stock outstanding 54,984,173 53,215,392 51,985,873 Earnings per share: Basic $ 1.40 $ 1.97 $ 1.73 Diluted $ 1.32 $ 1.87 $ 1.62 The amount of potential common stock that was excluded from the calculation of diluted earnings per share as their effect would be anti–dilutive was 883,350 , 2,324,667 and 1,637,048 for the years ended December 31, 2017 , 2016 and 2015 , respectively.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The Company leases office space under operating leases, which expire at various dates. Certain leases contain renewal provisions and generally require the Company to pay utilities, insurance, taxes, and other operating expenses. Rent expense under operating lease agreements for the years ended December 31, 2017 , 2016 and 2015 was $37,916 , $28,220 , and $20,065 respectively. Future minimum rental payments under operating leases that have initial or remaining lease terms in excess of one year as of December 31, 2017 were as follows: Year Ending December 31, Operating Leases 2018 $ 39,359 2019 27,739 2020 20,175 2021 15,517 2022 10,111 Thereafter 25,600 Total minimum lease payments $ 138,501 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 and intellectual property rights 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 historically had or would have a material effect on the 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 adverse effect on the Company’s business, financial condition, results of operations and cash flows.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS The Company had no material financial liabilities measured at fair value on a recurring basis as of December 31, 2017 . The following table shows the fair values of the Company’s financial liabilities measured at fair value on a recurring basis as of December 31, 2016 : As of December 31, 2016 Balance Level 1 Level 2 Level 3 Performance-based equity awards $ 3,789 $ 3,789 $ — $ — Total financial liabilities measured at fair value on a recurring basis $ 3,789 $ 3,789 $ — $ — Performance-based equity awards carried at fair value on a recurring basis represent contractual liabilities related to certain business combination transactions completed in 2014. All of these awards have vested as of December 31, 2017 and the related liabilities have been settled. Changes in the fair values of these awards were recorded within selling, general and administrative expenses on the Company’s consolidated statements of income and comprehensive income. A reconciliation of the beginning and ending balances of acquisition-related contractual contingent liabilities using significant unobservable inputs (Level 3) for the years ended December 31, 2016 and 2015, is as follows: Amount Contractual contingent liabilities at January 1, 2015 $ 40,623 Liability-classified stock-based awards 5,148 Changes in fair value of contractual contingent liabilities included in earnings 4,355 Effect of net foreign currency exchange rate changes 246 Settlements of contractual contingent liabilities (45,008 ) Contractual contingent liabilities at December 31, 2015 5,364 Acquisition date fair value of contractual contingent liabilities — other acquisitions 800 Liability-classified stock-based awards 5,148 Changes in fair value of contractual contingent liabilities included in earnings 1,232 Changes in fair value of contractual contingent liabilities recorded against goodwill 200 Settlements of contractual contingent liabilities (8,955 ) Reclassification of contractual contingent liabilities out of Level 3 (3,789 ) Contractual contingent liabilities at December 31, 2016 $ — There was no activity in contractual contingent liabilities during the year ended December 31, 2017. 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 significant number of assets and liabilities for which fair value equals or closely approximates the amount recorded on the Company’s consolidated balance sheets. The Company’s financial assets and liabilities that are not carried at fair value on a recurring basis on the Company’s consolidated balance sheets are as follows: • cash and cash equivalents; • restricted cash and time deposits; • employee loans and notes receivable; • long-term debt (Note 12 “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 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 2017 Credit Facility $ 25,009 $ 25,009 $ — $ 25,009 $ — Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 December 31, 2016 Financial Assets: Cash and cash equivalents $ 362,025 $ 362,025 $ 362,025 $ — $ — Time deposits and restricted cash $ 3,042 $ 3,042 $ — $ 3,042 $ — Employee loans $ 5,978 $ 5,978 $ — $ — $ 5,978 Financial Liabilities: Borrowings under 2014 Credit Facility $ 25,019 $ 25,019 $ — $ 25,019 $ —

SEGMENT INFORMATION

SEGMENT INFORMATION	12 Months Ended
	Dec. 31, 2017
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. 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 expenses not directly attributable to or controllable at the segment level are not allocated to specific segments. Further, stock based compensation expense is not allocated to individual segments in internal management reports used by the CODM. 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 that management team’s reportable segment. The Company’s reportable segments are North America, Europe, Russia and Other. The revenues in the Other segment represented less than 1% of total segment revenues in 2015 due to the ending of certain customer relationships and contractual changes with other clients. As no substantial clients remained in the segment, during the first quarter of 2016, the Company shifted managerial responsibility for the remaining clients to the Russia segment. This change did not represent a change in the Company’s segments but rather a movement in responsibility for several clients that represented less than 1% of total segment revenues. Segment revenues from external customers and segment operating profit/(loss) for the North America, Europe, Russia and Other reportable segments were as follows: For the years ended December 31, 2017 2016 2015 Total segment revenues: North America $ 796,126 $ 642,216 $ 471,603 Europe 593,167 474,988 400,460 Russia 62,994 43,611 37,992 Other — — 4,911 Total segment revenues $ 1,452,287 $ 1,160,815 $ 914,966 Segment operating profit/(loss): North America $ 169,340 $ 143,021 $ 112,312 Europe 92,080 67,545 68,717 Russia 13,906 7,555 5,198 Other — — (94 ) Total segment operating profit $ 275,326 $ 218,121 $ 186,133 Intersegment transactions were excluded from the above on the basis that they are neither included into the measure of a segment’s profit and loss by the CODM, nor provided to the CODM on a regular basis. There were no customers individually exceeding 10% of our total segment revenues for the year ended December 31, 2017 . During the years ended December 31, 2016 and 2015 , segment revenues from one customer, UBS AG, were $138,124 and $130,605 , respectively and accounted for more than 10% of total segment revenues. Revenues from this customer are reported in the Company’s Europe segment. Accounts receivable and unbilled revenues are generally dispersed across our clients in proportion to their revenues. As of December 31, 2017 , unbilled revenues from one customer, individually exceeded 10% and accounted for 13.0% of our total unbilled revenues. As of December 31, 2016, unbilled revenues from two customers, individually exceeded 10% and accounted for 22.2% of our total unbilled revenues. There were no customers individually exceeding 10% of our accounts receivable as of December 31, 2017 and 2016 . Reconciliations of segment revenues to consolidated revenues and segment operating profit to consolidated income before provision for income taxes are presented below: For the Years Ended December 31, 2017 2016 2015 Total segment revenues $ 1,452,287 $ 1,160,815 $ 914,966 Other income included in segment revenues (1,839 ) (683 ) (838 ) Revenues $ 1,450,448 $ 1,160,132 $ 914,128 Total segment operating profit: $ 275,326 $ 218,121 $ 186,133 Unallocated amounts: Other income included in segment revenues (1,839 ) (683 ) (838 ) Stock-based compensation expense (52,407 ) (49,244 ) (45,833 ) Non-corporate taxes (9,659 ) (5,909 ) (4,274 ) Professional fees (8,032 ) (8,265 ) (7,104 ) Depreciation and amortization (7,632 ) (8,290 ) (5,581 ) Bank charges (1,969 ) (1,515 ) (1,352 ) One-time charges (1,741 ) (706 ) (747 ) Other corporate expenses (19,101 ) (9,813 ) (14,437 ) Income from operations 172,946 133,696 105,967 Interest and other income, net 4,601 4,848 4,731 Foreign exchange loss (3,242 ) (12,078 ) (4,628 ) Income before provision for income taxes $ 174,305 $ 126,466 $ 106,070 Geographic Area Information Long-lived assets include property and equipment, net of accumulated depreciation and amortization, and management has determined that it is not practical to allocate these assets by segment since such assets are used interchangeably among the segments. The Company’s long-lived assets based on physical location of the assets was as follows: December 31, December 31, December 31, 2015 Belarus $ 49,866 $ 46,011 $ 44,879 Russia 9,617 7,203 2,084 Ukraine 6,995 5,610 4,487 Hungary 3,901 3,485 2,485 United States 3,371 2,618 1,969 Poland 2,893 2,213 1,088 India 2,698 1,650 1,099 China 2,608 1,887 514 Bulgaria 922 722 317 Other 3,548 2,217 1,577 Total $ 86,419 $ 73,616 $ 60,499 The table below presents information about the Company’s revenues by client location including reimbursable expenses and other revenues, of $17,138 , $12,521 and $9,511 for the years ended 2017, 2016 and 2015. See Note 1 “Nature of Business and Summary of Significant Accounting Policies” for discussion on reclassifications to conform to the current presentation. Information about the Company’s revenues by client location is as follows: For the Years Ended December 31, 2017 2016 2015 United States $ 783,563 $ 611,392 $ 431,992 United Kingdom 188,995 177,194 166,418 Switzerland 123,281 122,919 111,686 Russia 61,222 40,944 36,585 Germany 60,158 43,621 36,403 Canada 57,129 59,189 58,319 Netherlands 51,556 17,521 10,373 Sweden 32,161 23,838 10,775 Hong Kong 19,795 21,010 23,285 United Arab Emirates 12,403 3,615 — Belgium 8,725 8,627 8,113 Ireland 8,674 5,167 5,536 China 7,379 4,479 817 Italy 6,505 4,052 2,342 Other locations 28,902 16,564 11,484 Revenues $ 1,450,448 $ 1,160,132 $ 914,128 Service Offering Information Information about the Company’s revenues by service offering is as follows: For the Years Ended December 31, 2017 2016 2015 Software development $ 1,060,286 $ 841,916 $ 644,732 Application testing services 276,270 223,010 174,259 Application maintenance and support 92,630 74,475 70,551 Licensing 3,529 3,141 3,764 Infrastructure services 595 5,069 11,311 Reimbursable expenses and other revenues 17,138 12,521 9,511 Revenues $ 1,450,448 $ 1,160,132 $ 914,128

QUARTERLY FINANCIAL DATA

QUARTERLY FINANCIAL DATA	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
QUARTERLY FINANCIAL DATA	QUARTERLY FINANCIAL DATA (UNAUDITED) Summarized quarterly results for the two years ended December 31, 2017 and 2016 were as follows: Three Months Ended 2017 March 31 June 30 September 30 December 31 Full Year Revenues $ 324,651 $ 348,977 $ 377,523 $ 399,297 $ 1,450,448 Operating expenses: Cost of revenues (exclusive of depreciation and amortization) 207,730 220,132 239,369 254,121 921,352 Selling, general and administrative expenses 78,453 80,419 81,190 84,793 324,855 Depreciation and amortization expense 6,672 7,020 7,174 7,696 28,562 Other operating expenses, net 830 724 542 637 2,733 Income from operations 30,966 40,682 49,248 52,050 172,946 Interest and other income, net 584 802 1,416 1,799 4,601 Foreign exchange (loss)/income (2,955 ) 1,562 (77 ) (1,772 ) (3,242 ) Income before provision for income taxes 28,595 43,046 50,587 52,077 174,305 Provision for income taxes 4,954 5,687 7,953 82,951 101,545 Net income/(loss) $ 23,641 $ 37,359 $ 42,634 $ (30,874 ) $ 72,760 Comprehensive income/(loss) $ 30,027 $ 41,910 $ 48,337 $ (27,449 ) $ 92,825 Basic net income/(loss) per share (1) $ 0.46 $ 0.72 $ 0.81 $ (0.58 ) $ 1.40 Diluted net income/(loss) per share (1)(2) $ 0.44 $ 0.68 $ 0.77 $ (0.58 ) $ 1.32 (1) Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis. (2) Due to the net loss during the three months ended December 31, 2017, zero incremental shares are included in the calculation of diluted earnings per share because of their antidilutive effect. Three Months Ended 2016 March 31 June 30 September 30 December 31 Full Year Revenues $ 264,482 $ 283,832 $ 298,293 $ 313,525 $ 1,160,132 Operating expenses: Cost of revenues (exclusive of depreciation and amortization) 167,381 180,782 190,797 198,226 737,186 Selling, general and administrative expenses 61,494 64,241 67,491 71,432 264,658 Depreciation and amortization expense 5,102 6,123 5,925 6,237 23,387 Other operating expenses, net 174 606 178 247 1,205 Income from operations 30,331 32,080 33,902 37,383 133,696 Interest and other income, net 1,211 1,138 1,067 1,432 4,848 Foreign exchange loss (1,290 ) (2,295 ) (1,728 ) (6,765 ) (12,078 ) Income before provision for income taxes 30,252 30,923 33,241 32,050 126,466 Provision for income taxes 6,353 6,493 7,067 7,287 27,200 Net income $ 23,899 $ 24,430 $ 26,174 $ 24,763 $ 99,266 Comprehensive income $ 28,598 $ 22,044 $ 26,532 $ 19,554 $ 96,728 Basic net income per share (1) $ 0.48 $ 0.49 $ 0.51 $ 0.49 $ 1.97 Diluted net income per share (1) $ 0.45 $ 0.46 $ 0.49 $ 0.46 $ 1.87 (1) Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis.

VALUATION AND QUALIFYING ACCOUN

VALUATION AND QUALIFYING ACCOUNTS VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2017, 2016 AND 2015 (U.S. dollars in thousands) Balance at Beginning of Year Additions Deductions/ Write offs Balance at End of Year Year ended December 31, 2017 Allowance for doubtful accounts for trade receivables $ 2,014 998 (1,826 ) $ 1,186 Valuation allowance on deferred tax assets $ — 924 — $ 924 Year ended December 31, 2016 Allowance for doubtful accounts for trade receivables $ 1,729 3,500 (3,215 ) $ 2,014 Year ended December 31, 2015 Allowance for doubtful accounts for trade receivables $ 2,181 $ 1,704 $ (2,156 ) $ 1,729

NATURE OF BUSINESS AND SIGNIFIC

NATURE OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Operations	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, media and entertainment, travel and hospitality, retail and distribution and life sciences and healthcare. The Company is incorporated in Delaware with headquarters in Newtown, PA.
Principles of Consolidation	Principles of Consolidation — The consolidated financial statements include the financial statements of EPAM Systems, Inc. and its subsidiaries. All intercompany balances and transactions have been eliminated.
Use of Estimates	Use of Estimates — The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions. These estimates and assumptions affect reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as revenues and expenses during the reporting period. The Company bases its estimates and judgments on historical experience, knowledge of current conditions and its beliefs of what could occur in the future, given available information. Actual results could differ from those estimates, and such differences may be material to the financial statements.
Changes in Presentation of Certain Financial Information	Change in Presentation of Certain Financial Information — During the first quarter of 2017, the Company changed the presentation of geographic area information about its consolidated revenues. Historically, information about geographic location of revenues excluded reimbursable expenses and other revenues, which primarily consist of travel and entertainment costs that are chargeable to clients. Effective January 1, 2017, the Company began reporting reimbursable expenses and other revenues based on location of clients to which these costs are chargeable and allocating them to respective geographic locations. These changes did not result in adjustments to previously reported consolidated revenues in the Company’s financial statements and were applied retrospectively effective January 1, 2015.
Revenue Recognition	Revenue Recognition — The Company recognizes revenue when the following criteria are met: (1) persuasive evidence of an arrangement exists; (2) delivery has occurred; (3) the sales price is fixed or determinable; and (4) collectability is reasonably assured. Determining whether and when some of these criteria have been satisfied often involves assumptions and judgments that can have a significant impact on the timing and amount of revenue reported. The Company derives its revenues from a variety of service offerings, which represent specific competencies of its IT professionals. Contracts for these services have different terms and conditions based on the scope, deliverables, and complexity of the engagement, which require management to make judgments and estimates in determining the appropriate revenue recognition. Fees for these contracts may be in the form of time-and-materials or fixed-price arrangements. If there is an uncertainty about the project completion or receipt of payment for the services, revenue is deferred until the uncertainty is sufficiently resolved. At the time revenue is recognized, the Company provides for any contractual deductions and reduces the revenue accordingly. 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 Company defers 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. Unbilled revenue is recorded when services have been provided but billed subsequent to the period end in accordance with the contract terms. The majority of the Company’s revenues ( 90.3% of revenues in 2017 , 88.2% in 2016 and 85.8% in 2015 ) are generated under time-and-material contracts where revenues are recognized as services are performed with the corresponding cost of providing those services reflected as cost of revenues. The majority of such revenues are billed using hourly, daily or monthly rates as actual time is incurred on the project. Revenues from fixed-price contracts ( 8.3% of revenues in 2017 , 10.4% in 2016 and 12.8% in 2015 ) include fixed-price maintenance and support arrangements, which may exceed one year in duration, as well as fixed-price application development arrangements. Revenues from maintenance and support arrangements are generally recognized ratably over the expected service period. Revenues from fixed-price application development arrangements are primarily determined using the proportional performance method. In cases where final acceptance of the product, system, or solution is specified by the client, and the acceptance criteria are not objectively determinable to have been met as the services are provided, revenues are deferred until all acceptance criteria have been met. In the absence of a sufficient basis to measure progress towards completion, revenue is recognized upon receipt of final acceptance from the client. Assumptions, risks and uncertainties inherent in the estimates used in the application of the proportional performance method of accounting could affect the amount of revenues, receivables and deferred revenues at each reporting period.
Cost of Revenues (Exclusive of Depreciation and Amortization)	Cost of Revenues (Exclusive of Depreciation and Amortization) — Consists principally of salaries, bonuses, fringe benefits, stock-based compensation expense, project related travel costs and fees for subcontractors that are assigned to client projects. Salaries and other compensation expenses of our revenue generating professionals are reported as cost of revenues regardless of whether the employees are actually performing client services during a given period.
Selling, General and Administrative Expenses	Selling, General and Administrative Expenses — Consists of expenses associated with promoting and selling our services and general and administrative functions of the business. These expenses include the costs of salaries, bonuses, fringe benefits, stock-based compensation expense, commissions, travel, legal and audit services, insurance, operating leases, advertising and other promotional activities. In addition, we pay a membership fee of 1% of revenues generated in Belarus to the administrative organization of the Belarus Hi-Tech Park. Furthermore, the Company has issued stock to the sellers and/or personnel in connection with business acquisitions and has been recognizing stock-based compensation expense in the periods after the closing of these acquisitions as part of selling, general and administrative expenses.
Fair Value of Financial Instruments	Fair Value of Financial Instruments — The Company makes assumptions about fair values of its financial assets and liabilities in accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 820, “Fair Value Measurement,” and utilizes the following fair value hierarchy in determining inputs used for valuation: Level 1 — Quoted prices for identical assets or liabilities in active markets. Level 2 — Inputs other than quoted prices within Level 1 that are observable either directly or indirectly, including quoted prices in markets that are not active, quoted prices in active markets for similar assets or liabilities, and observable inputs other than quoted prices such as interest rates or yield curves. Level 3 — Unobservable inputs reflecting management’s view about the assumptions that market participants would use in pricing the asset or liability. Where the fair values of financial assets and liabilities recorded in the consolidated balance sheets cannot be derived from an active market, they are determined using a variety of valuation techniques. These valuation techniques include a net present value technique, comparison to similar instruments with market observable inputs, option pricing models and other relevant valuation models. To the extent possible, observable market data is used as inputs into these models but when it is not feasible, a degree of judgment is required to establish fair values. The Company’s contingent liabilities measured at fair value on a recurring basis are comprised of performance-based awards issued to certain former owners of acquired businesses in exchange for future services. During a performance measurement period, performance-based awards are valued using significant inputs that are not observable in the market, which are defined as Level 3 inputs according to fair value measurement accounting. The Company estimates the fair value of contingent liabilities based on certain performance milestones of the acquired businesses and estimated probabilities of achievement, then discounts the liabilities to present value using the Company’s cost of debt for the cash component of contingent consideration, and a risk-free rate for the stock component of a contractual contingency. The Company believes its estimates and assumptions are reasonable, however, there is significant judgment involved. Changes in the fair value of contingent consideration liabilities primarily result from changes in the timing and amount of specific milestone estimates and changes in probability assumptions with respect to the likelihood of achieving the various earnout criteria. Changes in the fair value of these liabilities could cause a material impact to, and volatility in the Company’s operating results.
Employee Loans	Employee Loans — The Company issues employee housing loans in Belarus, relocation loans to assist employees with relocation needs in connection with intra-company transfers and loans for the purchase of automobiles in India. There are no loans issued to principal officers, directors, and their affiliates. The Company intends to hold all employee loans until their maturity. Interest income is reported using the effective interest method. Where applicable, loan origination fees, net of direct origination costs, are deferred and recognized in interest income over the life of the loan. The Employee Housing Program (the “Housing Program”) provides employees with loans to purchase housing in Belarus. The housing loans are measured using the Level 3 inputs within the fair value hierarchy because they are valued using significant unobservable inputs. These housing loans are measured at fair value upon initial recognition through the market approach under ASC Topic 820, “Fair Value Measurement” and subsequently carried at amortized cost less allowance for loan losses, if any. Any difference between the carrying value and the fair value of a loan upon initial recognition is charged to expense.
Business Combinations	Business Combinations — The Company accounts for its business combinations using the acquisition accounting method, which requires it to determine the fair value of net assets acquired and the related goodwill and other intangible assets in accordance with the FASB ASC Topic 805, “Business Combinations.” The Company identifies and attributes fair values and estimated lives to the intangible assets acquired and allocates the total cost of an acquisition to the underlying net assets based on their respective estimated fair values. Determining the fair value of assets acquired and liabilities assumed requires management’s judgment and involves the use of significant estimates, including projections of future cash inflows and outflows, discount rates, asset lives and market multiples. There are different valuation models for each component, the selection of which requires considerable judgment. These determinations will affect the amount of amortization expense recognized in future periods. The Company bases its fair value estimates on assumptions it believes are reasonable, but recognizes that the assumptions are inherently uncertain. All acquisition-related costs, other than the costs to issue debt or equity securities, are accounted for as expenses in the period in which they are incurred. Changes in fair value of contingent consideration arrangements that are not measurement period adjustments are recognized in earnings. Payments to settle contingent consideration, if any, are reflected in cash flows from financing activities and the changes in fair value are reflected in cash flows from operating activities in the Company’s consolidated statements of cash flows. The acquired assets typically consist of customer relationships, trade names, non-competition agreements, and workforce and as a result, a substantial portion of the purchase price is allocated to goodwill and other intangible assets.
Cash and Cash Equivalents	Cash and Cash Equivalents — Cash equivalents are short-term, highly liquid investments that are readily convertible into cash, with maturities of three months or less at the date acquired.
Accounts Receivable	Accounts Receivable — Accounts receivable are stated net of allowance for doubtful accounts. Outstanding accounts receivable are reviewed periodically and allowances are provided when management believes it is probable that such balances will not be collected within a reasonable time. The allowance for doubtful accounts is determined by evaluating the relative creditworthiness of each client, historical collections experience and other information, including the aging of the receivables. Accounts receivable are generally written off when they are deemed uncollectible. Bad debts are recorded based on historical experience and management’s evaluation of accounts receivable.
Property and Equipment	Property and Equipment — Property and equipment acquired in the ordinary course of the Company’s operations are stated at cost, net of accumulated depreciation. Depreciation is calculated on a straight-line basis over the estimated useful lives of the assets generally ranging from two to fifty years. Leasehold improvements are amortized on a straight-line basis over the shorter of the term of the lease or the estimated useful life of the improvement. Maintenance and repairs are expensed as incurred.
Long-Lived Assets	Long-Lived Assets — Long-lived assets, such as property and equipment and finite-lived intangible assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. When the carrying value of an asset is more than the sum of the undiscounted expected future cash flows, an impairment is recognized. An impairment loss is measured as the excess of the asset’s carrying amount over its fair value. Intangible assets that have finite useful lives are amortized over their estimated useful lives on a straight-line basis. Property and equipment held for disposal are carried at the lower of the current carrying value or fair value less estimated costs to sell.
Goodwill and Other Indefinite-Lived Intangible Assets	Goodwill and Other Indefinite-Lived Intangible Assets — Goodwill and other intangible assets that have indefinite useful lives are accounted for in accordance with the FASB ASC 350, “Intangibles — Goodwill and Other.” The Company conducts its evaluation of goodwill impairment at the reporting unit level on an annual basis as of October 31st, and more frequently if events or circumstances indicate that the carrying value of a reporting unit exceeds its fair value. A reporting unit is an operating segment or one level below. The Company does not have intangible assets other than goodwill that have indefinite useful lives.
Income Taxes	Income Taxes — The provision for income taxes includes federal, state, local and foreign taxes. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be reversed. Changes to enacted tax rates would result in either increases or decreases in the provision for income taxes in the period of changes. The realizability of deferred tax assets is primarily dependent on future earnings. The Company evaluates the realizability of deferred tax assets and recognizes a valuation allowance when it is more likely than not that all, or a portion of, deferred tax assets will not be realized. Any reduction in estimated forecasted results may require that we record valuation allowances against deferred tax assets. Once a valuation allowance has been established, it will be maintained until there is sufficient positive evidence to conclude that it is more likely than not that the deferred tax assets will be realized. A pattern of sustained profitability will generally be considered as sufficient positive evidence to reverse a valuation allowance. If the allowance is reversed in a future period, the income tax provision will be correspondingly reduced. Accordingly, the increase and decrease of valuation allowances could have a significant negative or positive impact on future earnings.
Earnings Per Share (EPS)	Earnings per Share (“EPS”) — Basic EPS 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 restricted stock units (“RSUs”). The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method.
Stock-based Compensation	Stock-Based Compensation — The Company recognizes the cost of its equity-classified stock-based incentive awards based on the fair value of the award at the date of grant, net of estimated forfeitures. The cost is expensed evenly over the service period. The service period is the period over which the employee performs the related services, which is normally the same as the vesting period. Quarterly, the forfeiture assumption is adjusted to the actual forfeiture rate and such change may affect the timing of the total amount of expense recognized over the vesting period. Equity-based awards that do not require future service are expensed immediately. Equity-based awards that do not meet the criteria for equity classification are recorded as liabilities and adjusted to fair value at the end of each reporting period.
Off-Balance Sheet Financial Instruments	Off-Balance Sheet Financial Instruments — The Company uses the FASB ASC Topic 825, “Financial Instruments.” to identify and disclose off-balance sheet financial instruments, which include credit instruments, such as commitments to make employee loans and related guarantees, standby letters of credit and certain guarantees issued under customer contracts. The face amount for these items represents the exposure to loss, before considering available collateral or the borrower’s ability to repay. Loss contingencies arising from off-balance sheet financial instruments are recorded as liabilities when the likelihood of loss is probable and an amount or range of loss can be reasonably estimated. The Company does not believe such matters exist that would have a material effect on the financial statements.
Foreign Currency Transaction	Foreign Currency Translation — Assets and liabilities of consolidated foreign subsidiaries whose functional currency is not the U.S. dollar are translated into U.S. dollars at period-end exchange rates and revenues and expenses are translated into U.S. dollars at daily exchange rates. The adjustment resulting from translating the financial statements of such foreign subsidiaries into U.S. dollars is reflected as a cumulative translation adjustment and reported as a component of accumulated other comprehensive income (loss). For consolidated foreign subsidiaries whose functional currency is the U.S. dollar, transactions and balances denominated in the local currency are foreign currency transactions. Foreign currency transactions and balances related to non-monetary assets and liabilities are remeasured to the functional currency of the subsidiary at historical exchange rates while monetary assets and liabilities are remeasured to the functional currency of the subsidiary at current exchange rates. Foreign currency exchange gains or losses from remeasurement are included in income in the period in which they occur.
Risks and Uncertainties	Risks and Uncertainties — As a result of its global operations, the Company may be subject to certain inherent risks. Concentration of Credit — Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash and cash equivalents, trade accounts receivable and unbilled revenues. The Company maintains cash and cash equivalents and short-term deposits with financial institutions. The Company determined that the Company’s credit policies reflect normal industry terms and business risk and there is no expectation of non-performance by the counterparties. As of December 31, 2017 , $240,148 of total cash, including time deposits and restricted cash, was held in CIS countries, with $196,656 of that total in Belarus. Banking and other financial systems in the CIS region are less developed and regulated than in some more developed markets, and bank deposits made by corporate entities in the CIS region are not insured. Changes in the market behavior or decisions of the Company’s clients could adversely affect the Company’s results of operations. During the years ended December 31, 2017 , 2016 and 2015 , revenues including reimbursable expenses and other revenues from our top five customers were $348,219 , $329,324 and $299,655 , respectively, representing 24.0% , 28.4% and 32.8% , respectively, of total revenues in the corresponding periods. Revenues including reimbursable expenses and other revenues from our top ten customers were $491,742 , $445,814 and $403,052 in 2017 , 2016 and 2015 , respectively, representing 33.9% , 38.4% and 44.1% , respectively, of total revenues in the corresponding periods. Foreign currency risk — The Company’s global operations are conducted predominantly in U.S. dollars. Other than U.S. dollars, the Company generates a significant portion of revenues in various currencies, principally, euros, British pounds sterling, Canadian dollars, Swiss francs and Russian rubles and incurs expenditures principally in Hungarian forints, Russian rubles, Polish zlotys, Swiss francs, British pounds, Indian rupees and China yuan renminbi associated with its delivery centers. The Company’s international operations expose it to foreign currency exchange rate changes that could impact translations of foreign denominated assets and liabilities into U.S. dollars and future earnings and cash flows from transactions denominated in different currencies. The Company is exposed to fluctuations in foreign currency exchange rates primarily related to accounts receivable and unbilled revenues from sales in foreign currencies and cash outflows for expenditures in foreign currencies. The Company’s results of operations, primarily revenues and expenses denominated in foreign currencies, can be affected if any of the currencies, which we use materially in our business, appreciate or depreciate against the U.S. dollar. Interest rate risk — The Company’s exposure to market risk is influenced primarily by changes in interest rates received on cash and cash equivalent deposits and paid on any outstanding balance on the Company’s revolving line of credit, which is subject to a variety of rates depending on the type and timing of funds borrowed (See Note 12 “Long-Term Debt”). The Company does not use derivative financial instruments to hedge the risk of interest rate volatility. Risks and Uncertainties — As a result of its global operations, the Company may be subject to certain inherent risks. Concentration of Credit — Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash and cash equivalents, trade accounts receivable and unbilled revenues. The Company maintains cash and cash equivalents and short-term deposits with financial institutions. The Company determined that the Company’s credit policies reflect normal industry terms and business risk and there is no expectation of non-performance by the counterparties. As of December 31, 2017 , $240,148 of total cash, including time deposits and restricted cash, was held in CIS countries, with $196,656 of that total in Belarus. Banking and other financial systems in the CIS region are less developed and regulated than in some more developed markets, and bank deposits made by corporate entities in the CIS region are not insured. Changes in the market behavior or decisions of the Company’s clients could adversely affect the Company’s results of operations. During the years ended December 31, 2017 , 2016 and 2015 , revenues including reimbursable expenses and other revenues from our top five customers were $348,219 , $329,324 and $299,655 , respectively, representing 24.0% , 28.4% and 32.8% , respectively, of total revenues in the corresponding periods. Revenues including reimbursable expenses and other revenues from our top ten customers were $491,742 , $445,814 and $403,052 in 2017 , 2016 and 2015 , respectively, representing 33.9% , 38.4% and 44.1% , respectively, of total revenues in the corresponding periods. Foreign currency risk — The Company’s global operations are conducted predominantly in U.S. dollars. Other than U.S. dollars, the Company generates a significant portion of revenues in various currencies, principally, euros, British pounds sterling, Canadian dollars, Swiss francs and Russian rubles and incurs expenditures principally in Hungarian forints, Russian rubles, Polish zlotys, Swiss francs, British pounds, Indian rupees and China yuan renminbi associated with its delivery centers. The Company’s international operations expose it to foreign currency exchange rate changes that could impact translations of foreign denominated assets and liabilities into U.S. dollars and future earnings and cash flows from transactions denominated in different currencies. The Company is exposed to fluctuations in foreign currency exchange rates primarily related to accounts receivable and unbilled revenues from sales in foreign currencies and cash outflows for expenditures in foreign currencies. The Company’s results of operations, primarily revenues and expenses denominated in foreign currencies, can be affected if any of the currencies, which we use materially in our business, appreciate or depreciate against the U.S. dollar. Interest rate risk — The Company’s exposure to market risk is influenced primarily by changes in interest rates received on cash and cash equivalent deposits and paid on any outstanding balance on the Company’s revolving line of credit, which is subject to a variety of rates depending on the type and timing of funds borrowed (See Note 12 “Long-Term Debt”). The Company does not use derivative financial instruments to hedge the risk of interest rate volatility.

RECENT ACCOUNTING PRONOUNCEME27

RECENT ACCOUNTING PRONOUNCEMENTS RECENT ACCOUNTING PRONOUNCEMENTS (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Recent Accounting Pronouncements	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. Stock-Based Compensation — Effective January 1, 2017, the Company adopted Accounting Standard Update (“ASU”) No. 2016-09, Compensation — Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . The provisions of the new guidance affecting the Company require excess tax benefits and tax deficiencies to be recorded in the income statement when stock-based awards vest or are settled; remove the requirement to include hypothetical excess tax benefits in the application of the treasury stock method when computing earnings per share; and provide for a new policy election to either: (1) continue applying forfeiture rate estimates in the determination of compensation cost, or (2) account for forfeitures as a reduction of share-based compensation cost as they occur. The new guidance also requires cash flows related to excess tax benefits to be classified as an operating activity in the statement of cash flows and now requires shares withheld for tax withholding purposes to be classified as a financing activity. As a result of this adoption: • the Company recognized a $1,740 increase in retained earnings as of January 1, 2017 for previously unrecognized tax benefits using the modified retrospective method of transition, as required by the standard; • the Company recognized discrete tax benefits of $9,307 in the provision for income taxes within the consolidated statement of income and comprehensive income during the year ended December 31, 2017, related to excess tax benefits upon vesting and exercise of stock-based awards; • the Company elected to adopt the cash flow presentation of the excess tax benefits prospectively where these benefits are classified along with other income tax cash flows as operating cash flows. Accordingly, prior period information has not been restated; • the Company elected to continue to estimate the number of stock-based awards expected to forfeit, rather than electing to account for forfeitures as they occur to determine the amount of compensation cost to be recognized in each period; and • the Company excluded the excess tax benefits from the assumed proceeds available to repurchase shares in the computation of diluted earnings per share for the year ended December 31, 2017. Simplifying the Measurement for Goodwill — Effective January 1, 2017, the Company early adopted the new accounting guidance simplifying the accounting for goodwill impairment. The guidance removes Step 2 of the goodwill impairment test, which requires a hypothetical purchase price allocation. A goodwill impairment will now be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. The new guidance is adopted on a prospective basis. The adoption of this amended guidance did not have an impact on the Company’s financial results. 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. Revenue Recognition — In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . The core principle of Topic 606 is that an entity should 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. Topic 606 as amended, will replace most existing revenue recognition guidance in GAAP and requires expanded 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 standard allows for two methods of adoption: the full retrospective method, which requires the standard to be applied to each prior period presented, or the modified retrospective method, which requires the cumulative effect of adoption to be recognized as an adjustment to opening retained earnings in the period of adoption as well as incremental disclosure comparing results presented under Topic 606 to results that would have been presented utilizing current accounting. The Company adopted Topic 606 as amended on January 1, 2018 using the modified retrospective method. The Company completed its assessment of the impact of Topic 606 and implemented its transition plan, which included making necessary changes to policies, processes, internal controls and system enhancements to generate the information necessary to comply with the new standard. Based on the assessment procedures completed, the Company recognized a one-time immaterial adjustment to retained earnings as of January 1, 2018 and does not expect a significant change in the timing or pattern of revenue recognition after adoption. Due to the complexity of certain of the Company’s contracts, actual revenue recognition treatment required under the new standard depends on contract-specific terms and may vary from the accounting under the current guidance in some instances. For most of the Company’s time-and-materials contracts, EPAM expects to continue to recognize revenues as services are performed consistent with the Company’s current policy. For fixed-price contracts, the Company generally expects to continue to recognize revenues over time based on the measured progress of satisfaction of the performance obligations which is consistent with the Company’s current proportional performance method. The most impactful changes upon adoption included a delay in revenue recognition related to (1) cash collections on contracts when collectability is uncertain and (2) earlier recognition of revenue from certain software licenses. Beginning in the first quarter of 2018, EPAM expects to provide incremental disclosure in its consolidated financial statements related to revenue recognition including disaggregated information related to the Company’s key verticals, contract balances, remaining performance obligations, and significant judgments and estimates. Leases — Effective January 1, 2019, the Company will be required to adopt the new guidance of ASC Topic 842, Leases (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 requires lessees and lessors to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes 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 at each reporting date 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 expects to adopt this standard on January 1, 2019. The Company has not yet completed its assessment of the impact of the new guidance on its consolidated financial statements or concluded on whether it will elect to apply practical expedients. Derivatives and Hedging — Effective January 1, 2019, with early adoption permitted in any interim or annual period, the Company will be required to adopt 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 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 standard requires entities to apply the amended presentation and disclosure guidance only prospectively as of the period of adoption. Currently, the Company does not apply hedge accounting and has not yet concluded on when it will adopt the standard. 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.

NATURE OF BUSINESS AND SUMMAR28

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NATURE OF BUSINESS AND SIGNIFICANT ACCOUNTING POLICIES (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Reclassifications	Comparative information for the years ended December 31, 2016 and 2015 follows: Year Ended December 31, 2016 As Reported After Reclassification (in thousands except percentages) United States $ 605,856 52.2 % $ 611,392 52.7 % United Kingdom 174,719 15.1 % 177,194 15.3 % Switzerland 122,399 10.6 % 122,919 10.6 % Canada 58,742 5.1 % 59,189 5.1 % Germany 43,216 3.7 % 43,621 3.8 % Russia 40,866 3.5 % 40,944 3.5 % Sweden 22,945 2.0 % 23,838 2.1 % Hong Kong 20,333 1.8 % 21,010 1.8 % Netherlands 16,762 1.4 % 17,521 1.5 % Belgium 8,505 0.7 % 8,627 0.7 % Ireland 5,152 0.4 % 5,167 0.4 % China 4,445 0.4 % 4,479 0.4 % Italy 3,970 0.3 % 4,052 0.3 % United Arab Emirates 3,486 0.3 % 3,615 0.3 % Other locations 16,215 1.4 % 16,564 1.5 % Reimbursable expenses and other revenues 12,521 1.1 % — — % Total $ 1,160,132 100.0 % $ 1,160,132 100.0 % Year Ended December 31, 2015 As Reported After Reclassification (in thousands except percentages) United States $ 427,433 46.8 % $ 431,992 47.3 % United Kingdom 164,301 18.0 % 166,418 18.2 % Switzerland 111,353 12.2 % 111,686 12.2 % Canada 57,643 6.3 % 58,319 6.4 % Germany 36,089 3.9 % 36,403 4.0 % Russia 36,506 4.0 % 36,585 4.0 % Sweden 10,589 1.2 % 10,775 1.2 % Hong Kong 23,117 2.5 % 23,285 2.5 % Netherlands 9,989 1.1 % 10,373 1.1 % Belgium 7,916 0.9 % 8,113 0.9 % Ireland 5,437 0.6 % 5,536 0.6 % Italy 2,318 0.3 % 2,342 0.3 % China 817 0.1 % 817 0.1 % Other locations 11,109 1.1 % 11,484 1.2 % Reimbursable expenses and other revenues 9,511 1.0 % — — % Total $ 914,128 100.0 % $ 914,128 100.0 %

ACQUISITIONS (Tables)

ACQUISITIONS (Tables)	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Fair Values of Net Assets Acquired	The following is a summary of the fair values of the net assets acquired through each respective acquisition during the year ended December 31, 2015: NavigationArts AGS Total Cash and cash equivalents $ 1,317 $ 1,727 $ 3,044 Accounts receivable and other current assets 3,920 9,934 13,854 Property and equipment and other long-term assets 230 1,600 1,830 Deferred tax assets — 5,722 5,722 Acquired intangible assets 2,800 22,700 25,500 Goodwill 23,794 24,454 48,248 Total assets acquired 32,061 66,137 98,198 Accounts payable and accrued expenses 871 2,760 3,631 Bank loans and other long-term liabilities — 295 295 Deferred revenue 50 1,049 1,099 Due to employees 596 2,342 2,938 Deferred tax liabilities — 7,974 7,974 Total liabilities assumed 1,517 14,420 15,937 Net assets acquired $ 30,544 $ 51,717 $ 82,261
Fair Values and Useful Lives of Intangible Assets Acquired	The following table presents the fair values and useful lives of intangible assets acquired through each respective acquisition during the year ended December 31, 2015: NavigationArts AGS Weighted Average Useful Life (in years) Amount Weighted Average Useful Life (in years) Amount Customer relationships 10 $ 2,800 10 $ 22,700 Total $ 2,800 $ 22,700

GOODWILL AND INTANGIBLE ASSET30

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill By Reportable Segment	Goodwill by reportable segment was as follows: North America Europe Total Balance as of January 1, 2016 $ 81,464 $ 34,466 $ 115,930 NavigationArts purchase accounting adjustments 2,030 — 2,030 AGS purchase accounting adjustments (9,361 ) — (9,361 ) Other acquisitions 2,404 177 2,581 Other acquisitions purchase accounting adjustments 395 87 482 Effect of currency translation (120 ) (2,253 ) (2,373 ) Balance as of December 31, 2016 76,812 32,477 109,289 Other acquisitions 199 4,533 4,732 Other acquisitions purchase accounting adjustments (285 ) 2,100 1,815 Effect of currency translation 564 3,131 3,695 Balance as of December 31, 2017 $ 77,290 $ 42,241 $ 119,531
Components of Intangible Assets	Intangible assets other than goodwill as of December 31, 2017 and 2016 were as follows: As of December 31, 2017 Weighted average life at acquisition (in years) Gross carrying amount Accumulated amortization Net carrying amount Customer relationships 10 $ 66,646 $ (22,200 ) $ 44,446 Trade names 5 4,099 (4,034 ) 65 Total $ 70,745 $ (26,234 ) $ 44,511 As of December 31, 2016 Weighted average life at acquisition (in years) Gross carrying amount Accumulated amortization Net carrying amount Customer relationships 10 $ 65,409 $ (15,133 ) $ 50,276 Trade names 5 5,622 (4,661 ) 961 Non-competition agreements 4 756 (733 ) 23 Total $ 71,787 $ (20,527 ) $ 51,260
Intangible Assets Amortization Expense Recognized	Recognized amortization expense for each of the years ended December 31 is presented in the table below: For the Years Ended December 31, 2017 2016 2015 Customer relationships $ 6,643 $ 6,858 $ 3,961 Trade names 896 1,139 1,280 Non-competition agreements 23 173 175 Total $ 7,562 $ 8,170 $ 5,416
Estimated Amortization Expense	Estimated amortization expense related to the Company’s existing intangible assets for the next five years ending December 31 and thereafter is as follows: Amount 2018 $ 6,661 2019 6,661 2020 6,661 2021 6,661 2022 6,508 Thereafter 11,359 Total $ 44,511

PREPAID AND OTHER CURRENT ASS31

PREPAID AND OTHER CURRENT ASSETS (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid and Other Current Assets Components	Prepaid and other current assets consisted of the following: December 31, December 31, Taxes receivable $ 12,172 $ 6,054 Prepaid expenses 5,939 5,462 Other current assets, net of allowance of $45 and $644, respectively 5,085 6,977 Total $ 23,196 $ 18,493

EMPLOYEE LOANS AND ALLOWANCE 32

EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES (Tables)	12 Months Ended
	Dec. 31, 2017
Loans and Leases Receivable, Related Parties Disclosure [Abstract]
Categories of Employee Loans	As of December 31, 2017 and 2016, categories of employee loans included in the loan portfolio were as follows: December 31, December 31, Housing loans $ 3,513 $ 5,448 Relocation and other loans 697 530 Total employee loans 4,210 5,978 Less: Allowance for loan losses — — Total loans, net of allowance for loan losses $ 4,210 $ 5,978
Movement of Employee Loans	Movement of employee loans balances during the years ended December 31, 2017 , 2016 and 2015 was as follows: Amount Employee loans at January 1, 2015 $ 6,515 Employee loans issued 3,427 Employee loans repaid (3,547 ) Employee loans written-off (7 ) Changes in interest and penalties accrued (32 ) Effect of net foreign currency exchange rate changes (18 ) Employee loans at December 31, 2015 $ 6,338 Employee loans issued 2,960 Employee loans repaid (3,273 ) Changes in interest and penalties accrued (35 ) Effect of net foreign currency exchange rate changes (12 ) Employee loans at December 31, 2016 $ 5,978 Employee loans issued 1,875 Employee loans repaid (3,615 ) Employee loans written-off (22 ) Changes in interest and penalties accrued (18 ) Effect of net foreign currency exchange rate changes 12 Employee loans at December 31, 2017 $ 4,210

PROPERTY AND EQUIPMENT - NET (T

PROPERTY AND EQUIPMENT - NET (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and equipment, net consisted of the following: Weighted Average Useful Life (in years) December 31, December 31, Computer hardware 3 $ 62,132 $ 49,599 Building 49 34,058 34,012 Furniture and fixtures 7 18,071 13,178 Leasehold improvements 6 13,186 7,944 Office equipment 7 10,825 9,416 Purchased computer software 3 8,379 4,601 Land improvements 20 1,474 1,467 148,125 120,217 Less accumulated depreciation and amortization (61,706 ) (46,601 ) Total $ 86,419 $ 73,616

ACCRUED EXPENSES AND OTHER CU34

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Components of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, December 31, Accrued compensation expense and related costs $ 67,034 $ 33,404 Deferred revenue 4,498 3,319 Other current liabilities and accrued expenses 18,280 13,172 Total $ 89,812 $ 49,895

TAXES PAYABLE TAXES PAYABLE (Ta

TAXES PAYABLE TAXES PAYABLE (Tables)	12 Months Ended
	Dec. 31, 2017
Taxes Payable, Current [Abstract]
TaxesPayable	Current taxes payable consisted of the following: December 31, December 31, Income taxes payable $ 9,488 $ 4,000 Value added taxes payable 16,696 10,644 Payroll, social security, and other taxes payable 14,676 10,364 Total $ 40,860 $ 25,008 As a result of the U.S. Tax Cuts and Jobs Act enacted on December 22, 2017, the Company recorded income taxes payable of $64,321 to be paid over the next 8 years. Of this amount, $59,175 is classified as Taxes payable, noncurrent as of December 31, 2017 . See Note 10 “Income Taxes” for additional discussion of the impact of the Act. There were no noncurrent taxes payable as of December 31, 2016 .

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income before provision of income taxes	Income before provision for income taxes included losses from domestic operations and income from foreign operations based on geographic location as disclosed in the table below: For the Years Ended December 31, 2017 2016 2015 Income/(loss) before provision for income taxes: Domestic $ (6,595 ) $ (9,300 ) $ (7,687 ) Foreign 180,900 135,766 113,757 Total $ 174,305 $ 126,466 $ 106,070
Components of provision for income taxes	The provision for income taxes consists of the following: For the Years Ended December 31, 2017 2016 2015 Current Federal $ 65,571 $ 13,324 $ 19,851 State (204 ) (63 ) 2,563 Foreign 23,617 17,243 14,528 Deferred Federal 7,235 (3,581 ) (13,361 ) State (90 ) 312 (1,891 ) Foreign 5,416 (35 ) (76 ) Total $ 101,545 $ 27,200 $ 21,614
Effective tax rate reconciliation	The reconciliation of the provision for income taxes at the federal statutory income tax rate to our effective income tax rate is as follows: For the Years Ended December 31, 2017 2016 2015 Provision for income taxes at federal statutory rate $ 61,007 $ 44,263 $ 37,125 Increase/ (decrease) in taxes resulting from: Impact from U.S. Tax Act 74,632 — — Foreign tax expense and tax rate differential (39,997 ) (33,477 ) (31,094 ) Effect of change in accounting for excess tax benefits relating to stock-based compensation (Note 2) (9,307 ) — — Stock-based compensation expense 6,908 9,535 7,591 Subsidiary withholding tax liability 4,850 — — Effect of permanent differences 3,205 5,042 7,314 Change in valuation allowance 783 — — Change in foreign tax rates 29 — 9 State taxes, net of federal benefit (116 ) 1,192 341 Other (449 ) 645 328 Provision for income taxes $ 101,545 $ 27,200 $ 21,614
Components of deferred tax assets and liabilities	Significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, December 31, Deferred tax assets: Property and equipment $ 170 $ 203 Intangible assets 1,456 1,525 Accrued expenses 4,392 9,172 Net operating loss carryforward 5,069 5,368 Deferred revenue 1,280 1,165 Stock-based compensation 16,197 19,701 Other assets 1,415 17 Deferred tax assets $ 29,979 $ 37,151 Less: valuation allowance (924 ) — Total deferred tax assets $ 29,055 $ 37,151 Deferred tax liabilities: Property and equipment $ 1,868 $ 1,735 Intangible assets 3,077 4,969 Accrued revenue and expenses 1,352 500 Subsidiary withholding tax liability 4,850 — Stock-based compensation 1,498 1,606 Other liabilities 239 314 Total deferred tax liabilities $ 12,884 $ 9,124 Net deferred tax assets $ 16,171 $ 28,027
Gross unrecognized tax benefits	The beginning to ending reconciliation of the gross unrecognized tax benefits is as follows: For the Years Ended December 31, 2017 2016 2015 Balance at January 1 $ 66 $ 62 $ 200 Increases in tax positions in current year 240 4 — Increases in tax positions in prior year 459 — — Decreases due to settlement (66 ) — (138 ) Balance at December 31 $ 699 $ 66 $ 62

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Costs Related to Stock Compensation Plans	The following costs related to the Company’s stock compensation plans were included in the consolidated statements of income and comprehensive income: For the Years Ended December 31, 2017 2016 2015 Cost of revenues $ 20,868 $ 16,619 $ 13,695 Selling, general and administrative expenses — Acquisition related 8,139 12,884 18,690 Selling, general and administrative expenses — All other 23,400 19,741 13,448 Total $ 52,407 $ 49,244 $ 45,833
Stock Option 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 Options outstanding at January 1, 2015 6,838,746 $ 20.98 $ 183,073 Options granted 2,219,725 $ 62.18 Options exercised (1,405,826 ) $ 14.70 Options forfeited/cancelled (201,731 ) $ 34.48 Options outstanding at December 31, 2015 7,450,914 $ 34.07 $ 331,938 Options granted 313,088 $ 70.27 Options exercised (895,804 ) $ 20.13 Options forfeited/cancelled (227,759 ) $ 47.89 Options expired (3,200 ) $ 1.52 Options outstanding at December 31, 2016 6,637,239 $ 37.20 $ 179,936 Options granted 261,373 $ 73.40 Options exercised (1,789,434 ) $ 30.23 Options forfeited/cancelled (200,210 ) $ 57.09 Options expired (7,220 ) $ 4.63 Options outstanding at December 31, 2017 4,901,748 $ 40.91 $ 326,064 6.2 Options vested and exercisable at December 31, 2017 3,068,917 $ 31.49 $ 233,054 5.5 Options expected to vest 1,764,538 $ 56.35 $ 90,133 7.3
Black-Scholes Model Valuation Assumptions	The grant-date fair value for stock options granted was determined using a Black-Scholes model incorporating the following average assumptions: For the Years Ended December 31, 2017 2016 2015 Expected volatility 30.5 % 31.9 % 34.1 % Expected term (in years) 6.25 6.24 6.25 Risk-free interest rate 2.1 % 1.5 % 1.8 % Expected dividends — % — % — %
Service-Based Awards Activity	The table below summarizes activity related to the Company’s equity-classified and liability-classified service-based awards for the years ended December 31, 2017 , 2016 and 2015 : Equity-Classified Equity-Settled 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, 2015 562,942 $ 37.42 70,500 $ 32.55 — $ — Awards granted 5,295 $ 70.79 108,319 $ 67.21 — $ — Awards vested (261,504 ) $ 33.74 (17,625 ) $ 32.55 — $ — Awards forfeited/cancelled 106 $ 36.57 (11,922 ) $ 34.49 — $ — Unvested service-based awards outstanding at December 31, 2015 306,839 $ 41.14 149,272 $ 57.55 — $ — Awards granted 6,510 $ 73.00 408,629 $ 70.39 207,586 $ 70.53 Awards vested (156,535 ) $ 42.64 (41,015 ) $ 55.60 — $ — Awards forfeited/cancelled (2,689 ) $ 45.32 (31,698 ) $ 70.44 (3,085 ) $ 70.52 Unvested service-based awards outstanding at December 31, 2016 154,125 $ 40.89 485,188 $ 67.69 204,501 $ 70.53 Awards granted — $ — 424,623 $ 73.89 170,295 $ 74.21 Awards modified — $ — (2,570 ) $ 26.85 2,570 $ 73.27 Awards vested (152,285 ) $ 43.39 (140,043 ) $ 66.54 (52,004 ) $ 70.56 Awards forfeited/cancelled — $ — (79,186 ) $ 70.30 (10,533 ) $ 71.72 Unvested service-based awards outstanding at December 31, 2017 1,840 $ 54.37 688,012 $ 71.60 314,829 $ 72.50
Fair Value of Service-Based Awards Vested	The fair value of vested service-based awards (measured at the vesting date) for the years ended December 31, 2017 , 2016 and 2015 was as follows: For the Years Ended December 31, 2017 2016 2015 Equity-classified equity-settled Restricted stock $ 12,607 $ 11,431 $ 19,305 Restricted stock units 10,620 2,932 1,092 Liability-classified cash-settled Restricted stock units 3,811 — — Total fair value of vested service-based awards $ 27,038 $ 14,363 $ 20,397
Performance-Based Awards Activity	Summarized activity related to the Company’s performance-based awards for the years ended December 31, 2017 , 2016 and 2015 was as follows: Equity-Classified Liability-Classified Equity-Classified 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 performance-based awards outstanding at January 1, 2015 33,045 $ 38.44 338,465 $ 39.43 — $ — Awards granted — $ — — $ — 14,000 $ 70.22 Awards vested (12,145 ) $ 39.92 (105,604 ) $ 40.44 — $ — Awards forfeited/cancelled (1,360 ) $ 36.57 — $ — — $ — Changes in the number of awards expected to be delivered 2,550 $ 36.57 (21,655 ) $ 32.27 — $ — Unvested performance-based awards outstanding at December 31, 2015 22,090 $ 37.52 211,206 $ 39.65 14,000 $ 70.22 Awards granted — $ — — $ — — $ — Awards vested (9,978 ) $ 40.15 (105,604 ) $ 40.44 (4,666 ) $ 70.22 Awards forfeited/cancelled (6,539 ) $ 36.97 — $ — (4,667 ) $ 70.22 Unvested performance-based awards outstanding at December 31, 2016 5,573 $ 33.47 105,602 $ 38.86 4,667 $ 70.22 Awards granted — $ — — $ — — $ — Awards vested (5,573 ) $ 33.47 (105,602 ) $ 38.86 — $ — Awards forfeited/cancelled — $ — — $ — (4,667 ) $ 70.22 Unvested performance-based awards outstanding at December 31, 2017 — $ — — $ — — $ —
Fair Value of Performance-Based Awards Vested	The fair value of vested performance-based awards (measured at the vesting date) for the years ended December 31, 2017 , 2016 and 2015 was as follows: For the Years Ended December 31, 2017 2016 2015 Equity-classified equity-settled Restricted stock $ 452 $ 690 $ 789 Restricted stock units — 348 — Liability-classified equity-settled Restricted stock 8,633 7,955 7,363 Total fair value of vested performance-based awards $ 9,085 $ 8,993 $ 8,152

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2017
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: For the Years Ended December 31, 2017 2016 2015 Numerator for basic and diluted earnings per share: Net income $ 72,760 $ 99,266 $ 84,456 Numerator for basic and diluted earnings per share $ 72,760 $ 99,266 $ 84,456 Denominator for basic and diluted earnings per share: Basic weighted average common stock outstanding 52,077,011 50,309,362 48,720,844 Effect of dilutive securities: Stock options, equity-settled RSUs and performance-based awards 2,907,162 2,906,030 3,265,029 Diluted weighted average common stock outstanding 54,984,173 53,215,392 51,985,873 Earnings per share: Basic $ 1.40 $ 1.97 $ 1.73 Diluted $ 1.32 $ 1.87 $ 1.62

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Future minimum rental payments under operating leases	Future minimum rental payments under operating leases that have initial or remaining lease terms in excess of one year as of December 31, 2017 were as follows: Year Ending December 31, Operating Leases 2018 $ 39,359 2019 27,739 2020 20,175 2021 15,517 2022 10,111 Thereafter 25,600 Total minimum lease payments $ 138,501

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Financial Liabilities Measured at Fair Value on a Recurring Basis	The following table shows the fair values of the Company’s financial liabilities measured at fair value on a recurring basis as of December 31, 2016 : As of December 31, 2016 Balance Level 1 Level 2 Level 3 Performance-based equity awards $ 3,789 $ 3,789 $ — $ — Total financial liabilities measured at fair value on a recurring basis $ 3,789 $ 3,789 $ — $ —
Reconciliation of Liabilities Measured on Recurring Basis, Unobservable Input	A reconciliation of the beginning and ending balances of acquisition-related contractual contingent liabilities using significant unobservable inputs (Level 3) for the years ended December 31, 2016 and 2015, is as follows: Amount Contractual contingent liabilities at January 1, 2015 $ 40,623 Liability-classified stock-based awards 5,148 Changes in fair value of contractual contingent liabilities included in earnings 4,355 Effect of net foreign currency exchange rate changes 246 Settlements of contractual contingent liabilities (45,008 ) Contractual contingent liabilities at December 31, 2015 5,364 Acquisition date fair value of contractual contingent liabilities — other acquisitions 800 Liability-classified stock-based awards 5,148 Changes in fair value of contractual contingent liabilities included in earnings 1,232 Changes in fair value of contractual contingent liabilities recorded against goodwill 200 Settlements of contractual contingent liabilities (8,955 ) Reclassification of contractual contingent liabilities out of Level 3 (3,789 ) Contractual contingent liabilities at December 31, 2016 $ — There was no activity in contractual contingent liabilities during the year ended December 31, 2017.
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 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 2017 Credit Facility $ 25,009 $ 25,009 $ — $ 25,009 $ — Fair Value Hierarchy Balance Estimated Fair Value Level 1 Level 2 Level 3 December 31, 2016 Financial Assets: Cash and cash equivalents $ 362,025 $ 362,025 $ 362,025 $ — $ — Time deposits and restricted cash $ 3,042 $ 3,042 $ — $ 3,042 $ — Employee loans $ 5,978 $ 5,978 $ — $ — $ 5,978 Financial Liabilities: Borrowings under 2014 Credit Facility $ 25,019 $ 25,019 $ — $ 25,019 $ —

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Segment Revenues from External Customers and Segment Operating Profit	evenues from external customers and segment operating profit/(loss) for the North America, Europe, Russia and Other reportable segments were as follows: For the years ended December 31, 2017 2016 2015 Total segment revenues: North America $ 796,126 $ 642,216 $ 471,603 Europe 593,167 474,988 400,460 Russia 62,994 43,611 37,992 Other — — 4,911 Total segment revenues $ 1,452,287 $ 1,160,815 $ 914,966 Segment operating profit/(loss): North America $ 169,340 $ 143,021 $ 112,312 Europe 92,080 67,545 68,717 Russia 13,906 7,555 5,198 Other — — (94 ) Total segment operating profit $ 275,326 $ 218,121 $ 186,133
Reconciliation of Segment Revenues and Operating Profit to Consolidated Income Before Provision for Income Taxes	Reconciliations of segment revenues to consolidated revenues and segment operating profit to consolidated income before provision for income taxes are presented below: For the Years Ended December 31, 2017 2016 2015 Total segment revenues $ 1,452,287 $ 1,160,815 $ 914,966 Other income included in segment revenues (1,839 ) (683 ) (838 ) Revenues $ 1,450,448 $ 1,160,132 $ 914,128 Total segment operating profit: $ 275,326 $ 218,121 $ 186,133 Unallocated amounts: Other income included in segment revenues (1,839 ) (683 ) (838 ) Stock-based compensation expense (52,407 ) (49,244 ) (45,833 ) Non-corporate taxes (9,659 ) (5,909 ) (4,274 ) Professional fees (8,032 ) (8,265 ) (7,104 ) Depreciation and amortization (7,632 ) (8,290 ) (5,581 ) Bank charges (1,969 ) (1,515 ) (1,352 ) One-time charges (1,741 ) (706 ) (747 ) Other corporate expenses (19,101 ) (9,813 ) (14,437 ) Income from operations 172,946 133,696 105,967 Interest and other income, net 4,601 4,848 4,731 Foreign exchange loss (3,242 ) (12,078 ) (4,628 ) Income before provision for income taxes $ 174,305 $ 126,466 $ 106,070
Geographical Information of Long-Lived Assets Based on Physical Location	he Company’s long-lived assets based on physical location of the assets was as follows: December 31, December 31, December 31, 2015 Belarus $ 49,866 $ 46,011 $ 44,879 Russia 9,617 7,203 2,084 Ukraine 6,995 5,610 4,487 Hungary 3,901 3,485 2,485 United States 3,371 2,618 1,969 Poland 2,893 2,213 1,088 India 2,698 1,650 1,099 China 2,608 1,887 514 Bulgaria 922 722 317 Other 3,548 2,217 1,577 Total $ 86,419 $ 73,616 $ 60,499
Revenues by Client Location	The table below presents information about the Company’s revenues by client location including reimbursable expenses and other revenues, of $17,138 , $12,521 and $9,511 for the years ended 2017, 2016 and 2015. See Note 1 “Nature of Business and Summary of Significant Accounting Policies” for discussion on reclassifications to conform to the current presentation. Information about the Company’s revenues by client location is as follows: For the Years Ended December 31, 2017 2016 2015 United States $ 783,563 $ 611,392 $ 431,992 United Kingdom 188,995 177,194 166,418 Switzerland 123,281 122,919 111,686 Russia 61,222 40,944 36,585 Germany 60,158 43,621 36,403 Canada 57,129 59,189 58,319 Netherlands 51,556 17,521 10,373 Sweden 32,161 23,838 10,775 Hong Kong 19,795 21,010 23,285 United Arab Emirates 12,403 3,615 — Belgium 8,725 8,627 8,113 Ireland 8,674 5,167 5,536 China 7,379 4,479 817 Italy 6,505 4,052 2,342 Other locations 28,902 16,564 11,484 Revenues $ 1,450,448 $ 1,160,132 $ 914,128
Revenues by Service Offering	Information about the Company’s revenues by service offering is as follows: For the Years Ended December 31, 2017 2016 2015 Software development $ 1,060,286 $ 841,916 $ 644,732 Application testing services 276,270 223,010 174,259 Application maintenance and support 92,630 74,475 70,551 Licensing 3,529 3,141 3,764 Infrastructure services 595 5,069 11,311 Reimbursable expenses and other revenues 17,138 12,521 9,511 Revenues $ 1,450,448 $ 1,160,132 $ 914,128

QUARTERLY FINANCIAL DATA (Table

QUARTERLY FINANCIAL DATA (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Summarized quarterly results for the two years ended December 31, 2017 and 2016 were as follows: Three Months Ended 2017 March 31 June 30 September 30 December 31 Full Year Revenues $ 324,651 $ 348,977 $ 377,523 $ 399,297 $ 1,450,448 Operating expenses: Cost of revenues (exclusive of depreciation and amortization) 207,730 220,132 239,369 254,121 921,352 Selling, general and administrative expenses 78,453 80,419 81,190 84,793 324,855 Depreciation and amortization expense 6,672 7,020 7,174 7,696 28,562 Other operating expenses, net 830 724 542 637 2,733 Income from operations 30,966 40,682 49,248 52,050 172,946 Interest and other income, net 584 802 1,416 1,799 4,601 Foreign exchange (loss)/income (2,955 ) 1,562 (77 ) (1,772 ) (3,242 ) Income before provision for income taxes 28,595 43,046 50,587 52,077 174,305 Provision for income taxes 4,954 5,687 7,953 82,951 101,545 Net income/(loss) $ 23,641 $ 37,359 $ 42,634 $ (30,874 ) $ 72,760 Comprehensive income/(loss) $ 30,027 $ 41,910 $ 48,337 $ (27,449 ) $ 92,825 Basic net income/(loss) per share (1) $ 0.46 $ 0.72 $ 0.81 $ (0.58 ) $ 1.40 Diluted net income/(loss) per share (1)(2) $ 0.44 $ 0.68 $ 0.77 $ (0.58 ) $ 1.32 (1) Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis. (2) Due to the net loss during the three months ended December 31, 2017, zero incremental shares are included in the calculation of diluted earnings per share because of their antidilutive effect. Three Months Ended 2016 March 31 June 30 September 30 December 31 Full Year Revenues $ 264,482 $ 283,832 $ 298,293 $ 313,525 $ 1,160,132 Operating expenses: Cost of revenues (exclusive of depreciation and amortization) 167,381 180,782 190,797 198,226 737,186 Selling, general and administrative expenses 61,494 64,241 67,491 71,432 264,658 Depreciation and amortization expense 5,102 6,123 5,925 6,237 23,387 Other operating expenses, net 174 606 178 247 1,205 Income from operations 30,331 32,080 33,902 37,383 133,696 Interest and other income, net 1,211 1,138 1,067 1,432 4,848 Foreign exchange loss (1,290 ) (2,295 ) (1,728 ) (6,765 ) (12,078 ) Income before provision for income taxes 30,252 30,923 33,241 32,050 126,466 Provision for income taxes 6,353 6,493 7,067 7,287 27,200 Net income $ 23,899 $ 24,430 $ 26,174 $ 24,763 $ 99,266 Comprehensive income $ 28,598 $ 22,044 $ 26,532 $ 19,554 $ 96,728 Basic net income per share (1) $ 0.48 $ 0.49 $ 0.51 $ 0.49 $ 1.97 Diluted net income per share (1) $ 0.45 $ 0.46 $ 0.49 $ 0.46 $ 1.87 (1) Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis.

VALUATION AND QUALIFYING ACCO43

VALUATION AND QUALIFYING ACCOUNTS VALUATION AND QUALIFYING ACCOUNTS (Tables)	12 Months Ended
	Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]
Allowance for Credit Losses on Financing Receivables [Table Text Block]	Balance at Beginning of Year Additions Deductions/ Write offs Balance at End of Year Year ended December 31, 2017 Allowance for doubtful accounts for trade receivables $ 2,014 998 (1,826 ) $ 1,186 Valuation allowance on deferred tax assets $ — 924 — $ 924 Year ended December 31, 2016 Allowance for doubtful accounts for trade receivables $ 1,729 3,500 (3,215 ) $ 2,014 Year ended December 31, 2015 Allowance for doubtful accounts for trade receivables $ 2,181 $ 1,704 $ (2,156 ) $ 1,729

NATURE OF BUSINESS AND SUMMAR44

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Change in Presentation of Certain Financial Information) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effect of Reclassification Adjustments [Line Items]
Revenues	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 1,450,448	$ 1,160,132	$ 914,128
Reimbursable expenses and other revenues
Effect of Reclassification Adjustments [Line Items]
Revenues									17,138	12,521	9,511
United States
Effect of Reclassification Adjustments [Line Items]
Revenues									783,563	611,392	431,992
United Kingdom
Effect of Reclassification Adjustments [Line Items]
Revenues									188,995	177,194	166,418
Switzerland
Effect of Reclassification Adjustments [Line Items]
Revenues									123,281	122,919	111,686
Canada
Effect of Reclassification Adjustments [Line Items]
Revenues									57,129	59,189	58,319
Germany
Effect of Reclassification Adjustments [Line Items]
Revenues									60,158	43,621	36,403
Russia
Effect of Reclassification Adjustments [Line Items]
Revenues									61,222	40,944	36,585
Sweden
Effect of Reclassification Adjustments [Line Items]
Revenues									32,161	23,838	10,775
Hong Kong
Effect of Reclassification Adjustments [Line Items]
Revenues									19,795	21,010	23,285
Netherlands
Effect of Reclassification Adjustments [Line Items]
Revenues									51,556	17,521	10,373
Belgium
Effect of Reclassification Adjustments [Line Items]
Revenues									8,725	8,627	8,113
Ireland
Effect of Reclassification Adjustments [Line Items]
Revenues									8,674	5,167	5,536
China
Effect of Reclassification Adjustments [Line Items]
Revenues									7,379	4,479	817
Italy
Effect of Reclassification Adjustments [Line Items]
Revenues									6,505	4,052	2,342
United Arab Emirates
Effect of Reclassification Adjustments [Line Items]
Revenues									12,403	3,615	0
Other locations
Effect of Reclassification Adjustments [Line Items]
Revenues									$ 28,902	16,564	11,484
As Reported
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 1,160,132	$ 914,128
Percent of Revenue										100.00%	100.00%
As Reported | Reimbursable expenses and other revenues
Effect of Reclassification Adjustments [Line Items]
Percent of Revenue										1.10%	1.00%
As Reported | United States
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 605,856	$ 427,433
Percent of Revenue										52.20%	46.80%
As Reported | United Kingdom
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 174,719	$ 164,301
Percent of Revenue										15.10%	18.00%
As Reported | Switzerland
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 122,399	$ 111,353
Percent of Revenue										10.60%	12.20%
As Reported | Canada
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 58,742	$ 57,643
Percent of Revenue										5.10%	6.30%
As Reported | Germany
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 43,216	$ 36,089
Percent of Revenue										3.70%	3.90%
As Reported | Russia
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 40,866	$ 36,506
Percent of Revenue										3.50%	4.00%
As Reported | Sweden
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 22,945	$ 10,589
Percent of Revenue										2.00%	1.20%
As Reported | Hong Kong
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 20,333	$ 23,117
Percent of Revenue										1.80%	2.50%
As Reported | Netherlands
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 16,762	$ 9,989
Percent of Revenue										1.40%	1.10%
As Reported | Belgium
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 8,505	$ 7,916
Percent of Revenue										0.70%	0.90%
As Reported | Ireland
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 5,152	$ 5,437
Percent of Revenue										0.40%	0.60%
As Reported | China
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 4,445	$ 817
Percent of Revenue										0.40%	0.10%
As Reported | Italy
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 3,970	$ 2,318
Percent of Revenue										0.30%	0.30%
As Reported | United Arab Emirates
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 3,486
Percent of Revenue										0.30%
As Reported | Other locations
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 16,215	$ 11,109
Percent of Revenue										1.40%	1.10%
After Reclassification
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 1,160,132	$ 914,128
Percent of Revenue										100.00%	100.00%
After Reclassification | Reimbursable expenses and other revenues
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 0	$ 0
Percent of Revenue										0.00%	0.00%
After Reclassification | United States
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 611,392	$ 431,992
Percent of Revenue										52.70%	47.30%
After Reclassification | United Kingdom
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 177,194	$ 166,418
Percent of Revenue										15.30%	18.20%
After Reclassification | Switzerland
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 122,919	$ 111,686
Percent of Revenue										10.60%	12.20%
After Reclassification | Canada
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 59,189	$ 58,319
Percent of Revenue										5.10%	6.40%
After Reclassification | Germany
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 43,621	$ 36,403
Percent of Revenue										3.80%	4.00%
After Reclassification | Russia
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 40,944	$ 36,585
Percent of Revenue										3.50%	4.00%
After Reclassification | Sweden
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 23,838	$ 10,775
Percent of Revenue										2.10%	1.20%
After Reclassification | Hong Kong
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 21,010	$ 23,285
Percent of Revenue										1.80%	2.50%
After Reclassification | Netherlands
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 17,521	$ 10,373
Percent of Revenue										1.50%	1.10%
After Reclassification | Belgium
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 8,627	$ 8,113
Percent of Revenue										0.70%	0.90%
After Reclassification | Ireland
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 5,167	$ 5,536
Percent of Revenue										0.40%	0.60%
After Reclassification | China
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 4,479	$ 817
Percent of Revenue										0.40%	0.10%
After Reclassification | Italy
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 4,052	$ 2,342
Percent of Revenue										0.30%	0.30%
After Reclassification | United Arab Emirates
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 3,615
Percent of Revenue										0.30%
After Reclassification | Other locations
Effect of Reclassification Adjustments [Line Items]
Revenues										$ 16,564	$ 11,484
Percent of Revenue										1.50%	1.20%

NATURE OF BUSINESS AND SUMMAR45

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Revenue Recognition) (Details) - Sales Revenue, Net - Product Concentration Risk	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Time-and-material contracts
Concentration Risk [Line Items]
Concentration percentage	90.30%	88.20%	85.80%
Fixed-price contracts
Concentration Risk [Line Items]
Concentration percentage	8.30%	10.40%	12.80%

NATURE OF BUSINESS AND SUMMAR46

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Employee Loans) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Accounting Policies [Abstract]
Loans issued to principal officers, directors, or their affiliates	$ 0

NATURE OF BUSINESS AND SUMMAR47

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Cash and Cash Equivalents) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash equivalents	$ 0	$ 0

NATURE OF BUSINESS AND SUMMAR48

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Property and Equipment) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	2 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	50 years

NATURE OF BUSINESS AND SUMMAR49

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Long-Lived Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Impairment of long-lived assets	$ 0	$ 0	$ 0

NATURE OF BUSINESS AND SUMMAR50

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Goodwill and Other Indefinite-Lived Intangible Assets) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Accounting Policies [Abstract]
Indefinite-lived intangible assets other than goodwill	$ 0

NATURE OF BUSINESS AND SUMMAR51

NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Risks and Uncertainties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Revenues	$ 1,450,448	$ 1,160,132	$ 914,128
Customer Concentration Risk | Sales Revenue, Net | Top Five Customers
Concentration Risk [Line Items]
Concentration percentage	24.00%	28.40%	32.80%
Revenues	$ 348,219	$ 329,324	$ 299,655
Customer Concentration Risk | Sales Revenue, Net | Top Ten Customers
Concentration Risk [Line Items]
Concentration percentage	33.90%	38.40%	44.10%
Revenues	$ 491,742	$ 445,814	$ 403,052
CIS Countries | Geographic Concentration Risk | Assets, Total
Concentration Risk [Line Items]
Cash including time deposits and restricted cash	240,148
Belarus | Geographic Concentration Risk | Assets, Total
Concentration Risk [Line Items]
Cash including time deposits and restricted cash	$ 196,656

RECENT ACCOUNTING PRONOUNCEME52

RECENT ACCOUNTING PRONOUNCEMENTS RECENT ACCOUNTING PRONONCEMENTS - ASU 2016-09 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to retained earnings for previously unrecognized tax benefits	$ 1,740
Discrete tax benefit	9,307	$ 0	$ 0
ASU 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustment to retained earnings for previously unrecognized tax benefits	1,740
Discrete tax benefit	$ 9,307

ACQUISITIONS (Narrative) (Detai

ACQUISITIONS (Narrative) (Details) $ in Thousands	Nov. 16, 2015USD ($)	Jul. 10, 2015USD ($)	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition [Line Items]
Cash consideration				$ 6,980	$ 5,580
Cash consideration deferred				$ 0	$ 2,260	$ 30,274
NavigationArts
Business Acquisition [Line Items]
Cash consideration		$ 28,747
Cash consideration deferred			$ 1,797
Goodwill deductable for tax purposes		$ 23,794
NavigationArts | Design Consultant
Business Acquisition [Line Items]
Numbers of professionals acquired		90
AGS
Business Acquisition [Line Items]
Cash consideration	$ 51,717
AGS | IT professionals
Business Acquisition [Line Items]
Numbers of professionals acquired	1,151

ACQUISITIONS (Fair Values of Ne

ACQUISITIONS (Fair Values of Net Assets Acquired) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 119,531	$ 109,289	$ 115,930
2015 Acquisitions | Final Valuation
Business Acquisition [Line Items]
Cash and cash equivalents		3,044
Accounts receivable and other current assets		13,854
Property and equipment and other long-term assets		1,830
Deferred tax assets		5,722
Acquired intangible assets		25,500
Goodwill		48,248
Total assets acquired		98,198
Accounts payable and accrued expenses		3,631
Bank loans and other long-term liabilities		295
Deferred revenue		1,099
Due to employees		2,938
Deferred tax liabilities		7,974
Total liabilities assumed		15,937
Net assets acquired		82,261
2015 Acquisitions | Final Valuation | NavigationArts
Business Acquisition [Line Items]
Cash and cash equivalents		1,317
Accounts receivable and other current assets		3,920
Property and equipment and other long-term assets		230
Deferred tax assets		0
Acquired intangible assets		2,800
Goodwill		23,794
Total assets acquired		32,061
Accounts payable and accrued expenses		871
Bank loans and other long-term liabilities		0
Deferred revenue		50
Due to employees		596
Deferred tax liabilities		0
Total liabilities assumed		1,517
Net assets acquired		30,544
2015 Acquisitions | Final Valuation | AGS
Business Acquisition [Line Items]
Cash and cash equivalents		1,727
Accounts receivable and other current assets		9,934
Property and equipment and other long-term assets		1,600
Deferred tax assets		5,722
Acquired intangible assets		22,700
Goodwill		24,454
Total assets acquired		66,137
Accounts payable and accrued expenses		2,760
Bank loans and other long-term liabilities		295
Deferred revenue		1,049
Due to employees		2,342
Deferred tax liabilities		7,974
Total liabilities assumed		14,420
Net assets acquired		$ 51,717

ACQUISITIONS (Fair Values and U

ACQUISITIONS (Fair Values and Useful Lives of Intangible Assets Acquired) (Details) - 2015 Acquisitions $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
NavigationArts
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired, amount	$ 2,800
AGS
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired, amount	$ 22,700
Customer relationships | NavigationArts
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life (in years)	10 years
Finite-lived intangible assets acquired, amount	$ 2,800
Customer relationships | AGS
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life (in years)	10 years
Finite-lived intangible assets acquired, amount	$ 22,700

GOODWILL AND INTANGIBLE ASSET56

GOODWILL AND INTANGIBLE ASSETS - NET (Goodwill Roll Forward) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance beginning of period	$ 109,289	$ 115,930
Effect of currency translation	3,695	(2,373)
Balance end of period	119,531	109,289
North America
Goodwill [Roll Forward]
Balance beginning of period	76,812	81,464
Effect of currency translation	564	(120)
Balance end of period	77,290	76,812
Europe
Goodwill [Roll Forward]
Balance beginning of period	32,477	34,466
Effect of currency translation	3,131	(2,253)
Balance end of period	42,241	32,477
Russia
Goodwill [Roll Forward]
Balance beginning of period	0	0
Balance end of period	0	0
Other
Goodwill [Roll Forward]
Balance beginning of period	0	0
Balance end of period	0	0
NavigationArts
Goodwill [Roll Forward]
Purchase accounting adjustments		2,030
NavigationArts | North America
Goodwill [Roll Forward]
Purchase accounting adjustments		2,030
NavigationArts | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments		0
AGS
Goodwill [Roll Forward]
Purchase accounting adjustments		(9,361)
AGS | North America
Goodwill [Roll Forward]
Purchase accounting adjustments		(9,361)
AGS | Europe
Goodwill [Roll Forward]
Purchase accounting adjustments		0
Other Acquisitions
Goodwill [Roll Forward]
Acquisition	4,732	2,581
Purchase accounting adjustments	1,815	482
Other Acquisitions | North America
Goodwill [Roll Forward]
Acquisition	199	2,404
Purchase accounting adjustments	(285)	395
Other Acquisitions | Europe
Goodwill [Roll Forward]
Acquisition	4,533	177
Purchase accounting adjustments	$ 2,100	$ 87

GOODWILL AND INTANGIBLE ASSET57

GOODWILL AND INTANGIBLE ASSETS - NET (Goodwill Accumulated Impaitment Losses) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
North America
Goodwill [Line Items]
Accumulated impairment loss	$ 0	$ 0	$ 0
Europe
Goodwill [Line Items]
Accumulated impairment loss	0	0	0
Russia
Goodwill [Line Items]
Accumulated impairment loss	2,241	2,241	2,241
Other
Goodwill [Line Items]
Accumulated impairment loss	$ 1,697	$ 1,697	$ 1,697

GOODWILL AND INTANGIBLE ASSET58

GOODWILL AND INTANGIBLE ASSETS - NET (Intangible Assets Components and Amortization Expenses Recognized) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 70,745	$ 71,787
Accumulated amortization	(26,234)	(20,527)
Net carrying amount	44,511	51,260
Amortization of Intangible Assets	$ 7,562	$ 8,170	$ 5,416
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted average life at acquisition (in years)	10 years	10 years
Gross carrying amount	$ 66,646	$ 65,409
Accumulated amortization	(22,200)	(15,133)
Net carrying amount	44,446	50,276
Amortization of Intangible Assets	$ 6,643	$ 6,858	3,961
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted average life at acquisition (in years)	5 years	5 years
Gross carrying amount	$ 4,099	$ 5,622
Accumulated amortization	(4,034)	(4,661)
Net carrying amount	65	961
Amortization of Intangible Assets	896	$ 1,139	1,280
Non-competition agreements
Finite-Lived Intangible Assets [Line Items]
Weighted average life at acquisition (in years)		4 years
Gross carrying amount		$ 756
Accumulated amortization		(733)
Net carrying amount		23
Amortization of Intangible Assets	$ 23	$ 173	$ 175

GOODWILL AND INTANGIBLE ASSET59

GOODWILL AND INTANGIBLE ASSETS - NET (Estimated Amortization Expense) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	$ 6,661
2,019	6,661
2,020	6,661
2,021	6,661
2,022	6,508
Thereafter	11,359
Total	$ 44,511	$ 51,260

PREPAID AND OTHER CURRENT ASS60

PREPAID AND OTHER CURRENT ASSETS (Prepaid and other current assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Taxes receivable	$ 12,172	$ 6,054
Prepaid expenses	5,939	5,462
Other current assets, net of allowance of $45 and $644, respectively	5,085	6,977
Total	23,196	18,493
Other current assets allowance	$ 45	$ 644

EMPLOYEE LOANS AND ALLOWANCE 61

EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES (Narrative) (Details) - Housing loans $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Minimum service period for employee housing program	3 years
Loan term (in years)	5 years
Interest rate on loan (as a percent)	7.50%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans program lending limit	$ 10,000
Individual loan amount limit	$ 50

EMPLOYEE LOANS AND ALLOWANCE 62

EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES (Categories of Employee Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Employee loans, gross	$ 4,210	$ 5,978
Allowance for loan losses	0	0
Employee loans, net of allowance	4,210	5,978
Housing loans
Loans and Leases Receivable Disclosure [Line Items]
Employee loans, gross	3,513	5,448
Relocation and other loans
Loans and Leases Receivable Disclosure [Line Items]
Employee loans, gross	$ 697	$ 530

EMPLOYEE LOANS AND ALLOWANCE 63

EMPLOYEE LOANS AND ALLOWANCE FOR LOAN LOSSES (Employee Loans Rollforward) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Loans and Leases Receivable, Related Parties [Roll Forward]
Balance, beginning of period	$ 5,978	$ 6,338	$ 6,515
Employee loans issued	1,875	2,960	3,427
Employee loans repaid	(3,615)	(3,273)	(3,547)
Employee loans written-off	(22)		(7)
Changes in interest and penalties accrued	(18)	(35)	(32)
Effect of net foreign currency exchange rate changes	12	(12)	(18)
Balance, end of period	$ 5,978	$ 6,338	$ 6,515	$ 4,210

PROPERTY AND EQUIPMENT - NET (P

PROPERTY AND EQUIPMENT - NET (Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 148,125	$ 120,217
Less accumulated depreciation and amortization	(61,706)	(46,601)
Total	86,419	73,616	$ 60,499
Depreciation and amortization expenses	$ 21,000	15,217	$ 11,979
Computer hardware
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	3 years
Property and equipment, gross	$ 62,132	49,599
Building
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	49 years
Property and equipment, gross	$ 34,058	34,012
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	7 years
Property and equipment, gross	$ 18,071	13,178
Leasehold improvements
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	6 years
Property and equipment, gross	$ 13,186	7,944
Office equipment
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	7 years
Property and equipment, gross	$ 10,825	9,416
Purchased computer software
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	3 years
Property and equipment, gross	$ 8,379	4,601
Land improvements
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	20 years
Property and equipment, gross	$ 1,474	$ 1,467

ACCRUED EXPENSES AND OTHER CU65

ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES (Accrued expenses and other current liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued compensation expense and related costs	$ 67,034	$ 33,404
Deferred revenue	4,498	3,319
Other current liabilities and accrued expenses	18,280	13,172
Total	$ 89,812	$ 49,895

TAXES PAYABLE (Components of Ta

TAXES PAYABLE (Components of Taxes Payable) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Taxes Payable [Line Items]
Income taxes payable	$ 9,488	$ 4,000
Value added taxes payable	16,696	10,644
Payroll, social security, and other taxes payable	14,676	10,364
Total	40,860	25,008
Taxes payable, noncurrent	59,874	$ 0
Tax Cuts and Jobs Act
Schedule of Taxes Payable [Line Items]
Income tax payable, total	64,321
Taxes payable, noncurrent	$ 59,175

INCOME TAXES (Income_(Loss) bef

INCOME TAXES (Income/(Loss) before Provision for Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income/(loss) before provision for income taxes:
Domestic									$ (6,595)	$ (9,300)	$ (7,687)
Foreign									180,900	135,766	113,757
Income before provision for income taxes	$ 52,077	$ 50,587	$ 43,046	$ 28,595	$ 32,050	$ 33,241	$ 30,923	$ 30,252	$ 174,305	$ 126,466	$ 106,070

INCOME TAXES (Provision for Inc

INCOME TAXES (Provision for Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current
Federal									$ 65,571	$ 13,324	$ 19,851
State									(204)	(63)	2,563
Foreign									23,617	17,243	14,528
Deferred
Federal									7,235	(3,581)	(13,361)
State									(90)	312	(1,891)
Foreign									5,416	(35)	(76)
Total	$ 82,951	$ 7,953	$ 5,687	$ 4,954	$ 7,287	$ 7,067	$ 6,493	$ 6,353	$ 101,545	$ 27,200	$ 21,614

INCOME TAXES (U.S. Tax Act Effe

INCOME TAXES (U.S. Tax Act Effect) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Change in Tax Legislation [Line Items]
Statutory income tax rate		35.00%
Taxes payable, noncurrent		$ 59,874	$ 0
Provisional income tax expense		65,571	$ 13,324	$ 19,851
Accumulated foreign earnings indefinitely reinvested		$ 642,149
Tax Cuts and Jobs Act
Schedule of Change in Tax Legislation [Line Items]
Income tax rate on foreign cash and certain other net current assets		15.50%
Income tax rate on remaining earnings		8.00%
Income tax payable, total		$ 64,321
Taxes payable, noncurrent		59,175
Provisional income tax expense		64,321
Adjustment to deferred tax asset		10,311
Tax Cuts and Jobs Act | Belarus
Schedule of Change in Tax Legislation [Line Items]
Accumulated earnings that are no longer indefinitely reinvested		$ 97,000
Subsequent Event | Tax Cuts and Jobs Act
Schedule of Change in Tax Legislation [Line Items]
Statutory income tax rate	21.00%

INCOME TAXES (Effective Tax Rat

INCOME TAXES (Effective Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Provision for income taxes at federal statutory rate									$ 61,007	$ 44,263	$ 37,125
Increase/ (decrease) in taxes resulting from:
Impact from U.S. Tax Act									74,632	0	0
Foreign tax expense and tax rate differential									(39,997)	(33,477)	(31,094)
Effect of change in accounting for excess tax benefits relating to stock-based compensation (Note 2)									(9,307)	0	0
Stock-based compensation expense									6,908	9,535	7,591
Subsidiary withholding tax liability									4,850	0	0
Effect of permanent differences									3,205	5,042	7,314
Change in valuation allowance									783	0	0
Change in foreign tax rate									29	0	9
State taxes, net of federal benefit									(116)	1,192	341
Other									(449)	645	328
Total	$ 82,951	$ 7,953	$ 5,687	$ 4,954	$ 7,287	$ 7,067	$ 6,493	$ 6,353	$ 101,545	$ 27,200	$ 21,614
Effective tax rate									58.30%	21.50%	20.40%

INCOME TAXES (Income Tax Holida

INCOME TAXES (Income Tax Holiday) (Details) - Foreign - Belarus - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Holiday [Line Items]
Income tax holiday description	In Belarus, member technology companies of High-Technologies Park have a full exemption from Belarus income tax. This tax holiday was recently extended through January 2049 . The aggregate dollar benefits derived from this tax holiday approximated $15.5 million , $13.6 million and $20.8 million for the years ended December 31, 2017 , 2016 and 2015 , respectively. The benefit the tax holiday had on diluted net income per share approximated $0.28 , $0.26 and $0.40 for the years ended December 31, 2017 , 2016 and 2015 , respectively.
Income tax holiday termination date	1/1/2049
Aggregate dollar benefits from tax holiday	$ 15.5	$ 13.6	$ 20.8
Tax holiday benefit on diluted net income per share	$ 0.28	$ 0.26	$ 0.40

INCOME TAXES (Deferred Income T

INCOME TAXES (Deferred Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Gross [Abstract]
Property and equipment	$ 170	$ 203
Intangible assets	1,456	1,525
Accrued expenses	4,392	9,172
Net operating loss carryforward	5,069	5,368
Deferred revenue	1,280	1,165
Stock-based compensation	16,197	19,701
Other assets	1,415	17
Deferred tax assets	29,979	37,151
Less: valuation allowance	(924)	0
Total deferred tax assets	29,055	37,151
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	1,868	1,735
Intangible assets	3,077	4,969
Accrued revenue and expenses	1,352	500
Subsidiary withholding tax liability	4,850	0
Stock-based compensation	1,498	1,606
Other liabilities	239	314
Total deferred tax liabilities	12,884	9,124
Net deferred tax assets	16,171	28,027
Other noncurrent liabilities
Deferred Tax Liabilities, Classification [Abstract]
Deferred tax liabilities, noncurrent	8,803	2,979
Business acquisitions
Deferred Tax Assets, Gross [Abstract]
Stock-based compensation	$ 8,512	$ 11,471
Business acquisitions | Minimum
Deferred Tax Assets, Gross [Abstract]
Amortization period of stock-based compensation for tax	10 years
Business acquisitions | Maximum
Deferred Tax Assets, Gross [Abstract]
Amortization period of stock-based compensation for tax	15 years

INCOME TAXES (Operating Loss Ca

INCOME TAXES (Operating Loss Carryforwards) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Valuation Allowance Related to NOL Carryforwards
Operating Loss Carryforwards [Line Items]
Net change in teh valuation allowance	$ 924
Domestic
Operating Loss Carryforwards [Line Items]
Net operating loss	6,264
Foreign
Operating Loss Carryforwards [Line Items]
Net operating loss	14,792
Foreign | No expiry
Operating Loss Carryforwards [Line Items]
Net operating loss	2,454
Foreign | 2021
Operating Loss Carryforwards [Line Items]
Net operating loss	1,183
Foreign | 2022
Operating Loss Carryforwards [Line Items]
Net operating loss	5,817
Foreign | 2026
Operating Loss Carryforwards [Line Items]
Net operating loss	$ 5,338

INCOME TAXES (Unrecognized Tax

INCOME TAXES (Unrecognized Tax Benefit Narrative) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Total gross unrecognized tax benefit	$ 699	$ 66	$ 62	$ 200
Penalties and interest	148	0	$ 0
Taxes Payable, Noncurrent
Income Tax Contingency [Line Items]
Total gross unrecognized tax benefit	$ 699	$ 66

INCOME TAXES (Unrecognized Ta75

INCOME TAXES (Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 66	$ 62	$ 200
Increases in tax positions in current year	240	4	0
Increases in tax positions in prior year	459	0	0
Decreases due to settlement	(66)	0	(138)
Balance at end of period	$ 699	$ 66	$ 62

EMPLOYEE BENEFITS (Employee ben

EMPLOYEE BENEFITS (Employee benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Discretionary matching contribution to retirement plan by employer (as a percent)	2.00%
Vesting period	2 years
Employer contributions charged to expenses	$ 2,331	$ 1,934	$ 740

LONG-TERM DEBT (Revolving Line

LONG-TERM DEBT (Revolving Line of Credit) (Details) - USD ($) $ in Thousands	May 24, 2017	Sep. 12, 2014	Dec. 31, 2017	Dec. 31, 2016
Revolving Credit Facility | 2014 Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable rate spread		1.00%
Revolving Credit Facility | 2014 Credit Facility | Federal Funds Open Rate
Debt Instrument [Line Items]
Variable rate spread		0.50%
Revolving Credit Facility | 2014 Credit Facility | U.S. dollars
Debt Instrument [Line Items]
Line of credit, borrowing capacity		$ 100,000
Line of credit, maximum borrowing capacity		200,000
Line of credit, remaining borrowing capacity				$ 74,058
Revolving Credit Facility | 2014 Credit Facility | U.S. dollars | LIBOR
Debt Instrument [Line Items]
Outstanding debt				25,000
Revolving Credit Facility | 2014 Credit Facility | Other currencies, excluding U.S. dollars
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity		$ 50,000
Revolving Credit Facility | 2017 Credit Facility
Debt Instrument [Line Items]
Maturity date	May 24, 2022
Revolving Credit Facility | 2017 Credit Facility | LIBOR
Debt Instrument [Line Items]
Variable rate spread	1.00%
Revolving Credit Facility | 2017 Credit Facility | Federal Funds Open Rate
Debt Instrument [Line Items]
Variable rate spread	0.50%
Revolving Credit Facility | 2017 Credit Facility | U.S. dollars
Debt Instrument [Line Items]
Line of credit, borrowing capacity	$ 300,000
Line of credit, maximum borrowing capacity	400,000
Line of credit, remaining borrowing capacity			$ 273,706
Revolving Credit Facility | 2017 Credit Facility | U.S. dollars | LIBOR
Debt Instrument [Line Items]
Outstanding debt			$ 25,000
Line of credit, interest rate			2.56%
Revolving Credit Facility | 2017 Credit Facility | Other currencies, excluding U.S. dollars
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 100,000
Standby Letter of Credit | 2014 Credit Facility
Debt Instrument [Line Items]
Irrevocable standby letters of credit				$ 942
Standby Letter of Credit | 2017 Credit Facility
Debt Instrument [Line Items]
Irrevocable standby letters of credit			$ 1,294

STOCK-BASED COMPENSATION (Costs

STOCK-BASED COMPENSATION (Costs Related to Stock Compensation Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 52,407	$ 49,244	$ 45,833
Cost of revenues | Organic growth
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	20,868	16,619	13,695
Selling, general and administrative expenses | Organic growth
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	23,400	19,741	13,448
Selling, general and administrative expenses | Business acquisitions
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 8,139	$ 12,884	$ 18,690

STOCK-BASED COMPENSATION (Equit

STOCK-BASED COMPENSATION (Equity Plans) (Details) - shares	Jun. 11, 2015	Jan. 11, 2012	May 31, 2006	Dec. 31, 2017
2015 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (in shares)				5,818,622
Expiration period	10 years
2012 Directors Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (in shares)				539,772
Number of shares authorized for issuance (in shares)		600,000
Expiration period		10 years
2012 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
2006 Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period			10 years

STOCK-BASED COMPENSATION (Stock

STOCK-BASED COMPENSATION (Stock Option Activity) (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Options (in shares)
Options outstanding, beginning of period	6,637,239	7,450,914	6,838,746
Options granted	261,373	313,088	2,219,725
Options exercised	(1,789,434)	(895,804)	(1,405,826)
Options forfeited/cancelled	(200,210)	(227,759)	(201,731)
Options expired	(7,220)	(3,200)
Options outstanding, end of period	4,901,748	6,637,239	7,450,914
Options vested and exercisable at December 31, 2017	3,068,917
Options expected to vest	1,764,538
Weighted Average Exercise Price (in dollars per share)
Options outstanding, beginning of period	$ 37.20	$ 34.07	$ 20.98
Options granted	73.40	70.27	62.18
Options exercised	30.23	20.13	14.70
Options forfeited/cancelled	57.09	47.89	34.48
Options expired	4.63	1.52
Options outstanding, end of period	40.91	$ 37.20	$ 34.07
Options vested and exercisable at December 31, 2017	31.49
Options expected to vest	$ 56.35
Aggregate Intrinsic Value
Options outstanding, beginning of period	$ 179,936	$ 331,938	$ 183,073
Options outstanding, end of period	326,064	$ 179,936	$ 331,938
Options vested and exercisable at December 31, 2017	233,054
Options expected to vest	$ 90,133
Weighted Average Remaining Contractual Term (in years)
Options outstanding at December 31, 2017	6 years 2 months 11 days
Options vested and exercisable at December 31, 2017	5 years 6 months 6 days
Options expected to vest	7 years 3 months 29 days

STOCK-BASED COMPENSATION (Black

STOCK-BASED COMPENSATION (Black Scholes Model Valuation Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Expected volatility	30.50%	31.85%	34.07%
Expected term (in years)	6 years 3 months	6 years 2 months 27 days	6 years 2 months 29 days
Risk-free interest rate	2.10%	1.49%	1.83%
Expected dividends	0.00%	0.00%	0.00%

STOCK-BASED COMPENSATION (Sto82

STOCK-BASED COMPENSATION (Stock Options) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options exercised, in transfer (in shares)	4,354
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value	$ 25.29	$ 24.26	$ 24.21
Total intrinsic value of options exercised	$ 91,148	$ 39,577	$ 89,860
Vesting period (in years)	4 years
Unrecognized compensation cost net of forfeitures	$ 24,354
Unrecognized compensation cost, period for recognition	1 year 5 months

STOCK-BASED COMPENSATION (Retri

STOCK-BASED COMPENSATION (Retricted Stock and Restricted Stock Units Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock
Number of Shares
Unvested awards outstanding, beginning of period	154,125	306,839	562,942
Awards granted	0	6,510	5,295
Awards modified	0
Awards vested	(152,285)	(156,535)	(261,504)
Awards forfeited/cancelled	0	(2,689)	(106)
Unvested awards outstanding, end of period	1,840	154,125	306,839
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 40.89	$ 41.14	$ 37.42
Awards granted	0	73	70.79
Awards modified	0
Awards vested	43.39	42.64	33.74
Awards forfeited/cancelled	0	45.32	36.57
Unvested awards outstanding, end of period	$ 54.37	$ 40.89	$ 41.14
Service Period | Equity Classified Award | Equity-Settled Award | Restricted Stock Units (RSUs)
Number of Shares
Unvested awards outstanding, beginning of period	485,188	149,272	70,500
Awards granted	424,623	408,629	108,319
Awards modified	(2,570)
Awards vested	(140,043)	(41,015)	(17,625)
Awards forfeited/cancelled	(79,186)	(31,698)	(11,922)
Unvested awards outstanding, end of period	688,012	485,188	149,272
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 67.69	$ 57.55	$ 32.55
Awards granted	73.89	70.39	67.21
Awards modified	26.85
Awards vested	66.54	55.60	32.55
Awards forfeited/cancelled	70.30	70.44	34.49
Unvested awards outstanding, end of period	$ 71.60	$ 67.69	$ 57.55
Service Period | Liability Classified Award | Cash-Settled Award | Restricted Stock Units (RSUs)
Number of Shares
Unvested awards outstanding, beginning of period	204,501	0	0
Awards granted	170,295	207,586	0
Awards modified	2,570
Awards vested	(52,004)	0	0
Awards forfeited/cancelled	(10,533)	(3,085)	0
Unvested awards outstanding, end of period	314,829	204,501	0
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 70.53	$ 0	$ 0
Awards granted	74.21	70.53	0
Awards modified	73.27
Awards vested	70.56	0	0
Awards forfeited/cancelled	71.72	70.52	0
Unvested awards outstanding, end of period	$ 72.50	$ 70.53	$ 0
Performance Targets
Number of Shares
Unvested awards outstanding, end of period	0
Performance Targets | Equity Classified Award | Equity-Settled Award | Restricted Stock
Number of Shares
Unvested awards outstanding, beginning of period	5,573	22,090	33,045
Awards granted	0	0	0
Awards vested	(5,573)	(9,978)	(12,145)
Awards forfeited/cancelled	0	(6,539)	(1,360)
Changes in the number of awards expected to be delivered			2,550
Unvested awards outstanding, end of period	0	5,573	22,090
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 33.47	$ 37.52	$ 38.44
Awards granted	0	0	0
Awards vested	33.47	40.15	39.92
Awards forfeited/cancelled	0	36.97	36.57
Changes in the number of awards expected to be delivered			36.57
Unvested awards outstanding, end of period	$ 0	$ 33.47	$ 37.52
Performance Targets | Equity Classified Award | Equity-Settled Award | Restricted Stock Units (RSUs)
Number of Shares
Unvested awards outstanding, beginning of period	4,667	14,000	0
Awards granted	0	0	14,000
Awards vested	0	(4,666)	0
Awards forfeited/cancelled	(4,667)	(4,667)	0
Changes in the number of awards expected to be delivered			0
Unvested awards outstanding, end of period	0	4,667	14,000
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 70.22	$ 70.22	$ 0
Awards granted	0	0	70.22
Awards vested	0	70.22	0
Awards forfeited/cancelled	70.22	70.22	0
Changes in the number of awards expected to be delivered			0
Unvested awards outstanding, end of period	$ 0	$ 70.22	$ 70.22
Performance Targets | Liability Classified Award | Equity-Settled Award | Restricted Stock
Number of Shares
Unvested awards outstanding, beginning of period	105,602	211,206	338,465
Awards granted	0	0	0
Awards vested	(105,602)	(105,604)	(105,604)
Awards forfeited/cancelled	0	0	0
Changes in the number of awards expected to be delivered			(21,655)
Unvested awards outstanding, end of period	0	105,602	211,206
Weighted Average Grant Date Fair Value Per Share (in dollars per share)
Unvested awards outstanding, beginning of period	$ 38.86	$ 39.65	$ 39.43
Awards granted	0	0	0
Awards vested	38.86	40.44	40.44
Awards forfeited/cancelled	0	0	0
Changes in the number of awards expected to be delivered			32.27
Unvested awards outstanding, end of period	$ 0	$ 38.86	$ 39.65

STOCK-BASED COMPENSATION (Fair

STOCK-BASED COMPENSATION (Fair Value of Restricted Stock and Restricted Stock Units Vested) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	$ 27,038	$ 14,363	$ 20,397
Performance Targets
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	9,085	8,993	8,152
Equity Classified Award | Service Period | Equity-Settled Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	12,607	11,431	19,305
Equity Classified Award | Service Period | Equity-Settled Award | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	10,620	2,932	1,092
Equity Classified Award | Performance Targets | Equity-Settled Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	452	690	789
Equity Classified Award | Performance Targets | Equity-Settled Award | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	0	348	0
Liability Classified Award | Service Period | Cash-Settled Award | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	3,811	0	0
Liability Classified Award | Performance Targets | Equity-Settled Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested	$ 8,633	$ 7,955	$ 7,363

STOCK-BASED COMPENSATION (Ret85

STOCK-BASED COMPENSATION (Retricted Stock and Restricted Stock Units) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability associated with stock-based awardsurrent	$ 5,964,000	$ 5,900,000
Equity Classified Award | Service Period | Equity-Settled Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 81,000
Unrecognized compensation cost, period for recognition	1 year 7 months 16 days
Equity Classified Award | Service Period | Equity-Settled Award | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 32,100,000
Unrecognized compensation cost, period for recognition	1 year 10 months 21 days
Liability Classified Award | Service Period | Cash-Settled Award | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 19,691,000
Unrecognized compensation cost, period for recognition	1 year 10 months 29 days
Cash paid to settle awards	$ 3,811,000	0	$ 0
Liability Classified Award | Service Period | Cash-Settled Award | Restricted Stock Units (RSUs) | Deferred compensation due to employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Liability associated with stock-based awardsurrent	$ 5,964,000	$ 2,111,000
Business acquisitions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period (in years)	3 years
Year One | Business acquisitions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	33.30%
Year Two | Business acquisitions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	33.30%
Year Three | Business acquisitions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	33.30%

EARNINGS PER SHARE (Earning per

EARNINGS PER SHARE (Earning per share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator for basic and diluted earnings per share:
Net income	$ (30,874)		$ 42,634		$ 37,359		$ 23,641		$ 24,763		$ 26,174		$ 24,430		$ 23,899		$ 72,760	$ 99,266	$ 84,456
Numerator for basic and diluted earnings per share																	$ 72,760	$ 99,266	$ 84,456
Denominator for basic and diluted earnings per share:
Basic weighted average common stock outstanding (in shares)																	52,077,011	50,309,362	48,720,844
Stock options, equity-settled RSUs and performance-based awards (in shares)	0																2,907,162	2,906,030	3,265,029
Diluted weighted average common stock outstanding (in shares)																	54,984,173	53,215,392	51,985,873
Earnings per share:
Basic (in dollars per share)	$ (0.58)	[1],[2]	$ 0.81	[1]	$ 0.72	[1]	$ 0.46	[1]	$ 0.49	[1]	$ 0.51	[1]	$ 0.49	[1]	$ 0.48	[1]	$ 1.40	$ 1.97	$ 1.73
Diluted (in dollars per share)	$ (0.58)	[1],[2]	$ 0.77	[1]	$ 0.68	[1]	$ 0.44	[1]	$ 0.46	[1]	$ 0.49	[1]	$ 0.46	[1]	$ 0.45	[1]	$ 1.32	$ 1.87	$ 1.62
Anti-dilutive stock excluded from the calculation (in shares)																	883,350	2,324,667	1,637,048
[1]	(1)Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis.
[2]	(2)Due to the net loss during the three months ended December 31, 2017, zero incremental shares are included in the calculation of diluted earnings per share because of their antidilutive effect.

COMMITMENTS AND CONTINGENCIES87

COMMITMENTS AND CONTINGENCIES (Future Minimum Rental Payments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	$ 39,359
2,019	27,739
2,020	20,175
2,021	15,517
2,022	10,111
Thereafter	25,600
Total minimum lease payments	138,501
Operating lease expense	$ 37,916	$ 28,220	$ 20,065

FAIR VALUE MEASUREMENTS (Financ

FAIR VALUE MEASUREMENTS (Financial Liabilities at Fair Value on a Recurring Basis) (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities, Fair Value Disclosure [Abstract]
Total financial liabilities measured at fair value on a recurring basis	$ 0	$ 3,789
Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards		3,789
Level 1
Liabilities, Fair Value Disclosure [Abstract]
Total financial liabilities measured at fair value on a recurring basis		3,789
Level 1 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards		3,789
Level 2
Liabilities, Fair Value Disclosure [Abstract]
Total financial liabilities measured at fair value on a recurring basis		0
Level 2 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards		0
Level 3
Liabilities, Fair Value Disclosure [Abstract]
Total financial liabilities measured at fair value on a recurring basis		0
Level 3 | Restricted Stock
Liabilities, Fair Value Disclosure [Abstract]
Performance-based equity awards		$ 0

FAIR VALUE MEASUREMENTS (Contra

FAIR VALUE MEASUREMENTS (Contractual Contingent Liabilities Roll Forward) (Details) - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contractual contingent liabilities, beginning of period	$ 0	$ 5,364	$ 40,623
Liability-classified stock-based awards		5,148	5,148
Changes in fair value of contractual contingent liabilities included in earnings		1,232	4,355
Changes in fair value of contractual contingent liabilities recorded against goodwill	200
Settlements of contractual contingent liabilities		(8,955)	(45,008)
Effect of net foreign currency exchange rate changes			246
Reclassification of contractual contingent liabilities out of Level 3		(3,789)
Increase/(decrease) in contractual contingent liabilities	0
Contractual contingent liabilities, end of period	$ 0	$ 0	5,364
Other Acquisitions
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition date fair value of contractual contingent liabilities — other acquisitions			$ 800

FAIR VALUE MEASUREMENTS (Fina90

FAIR VALUE MEASUREMENTS (Financial Assets and Liabilities Not Measured on Recurring Basis) (Details) - Nonrecurring - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Balance
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 582,585	$ 362,025
Time Deposits and Restricted Cash and Cash Equivalents, Fair Value Disclosure	673	3,042
Loans Receivable, Fair Value Disclosure	4,210	5,978
Balance | Revolving Credit Facility | 2017 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings	25,009
Balance | Revolving Credit Facility | 2014 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings		25,019
Estimated Fair Value
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	582,585	362,025
Time Deposits and Restricted Cash and Cash Equivalents, Fair Value Disclosure	673	3,042
Loans Receivable, Fair Value Disclosure	4,210	5,978
Estimated Fair Value | Revolving Credit Facility | 2017 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings	25,009
Estimated Fair Value | Revolving Credit Facility | 2014 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings		25,019
Estimated Fair Value | Level 1
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	582,585	362,025
Time Deposits and Restricted Cash and Cash Equivalents, Fair Value Disclosure	0	0
Loans Receivable, Fair Value Disclosure	0	0
Estimated Fair Value | Level 1 | Revolving Credit Facility | 2017 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings	0
Estimated Fair Value | Level 1 | Revolving Credit Facility | 2014 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings		0
Estimated Fair Value | Level 2
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Time Deposits and Restricted Cash and Cash Equivalents, Fair Value Disclosure	673	3,042
Loans Receivable, Fair Value Disclosure	0	0
Estimated Fair Value | Level 2 | 2017 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings	25,009
Estimated Fair Value | Level 2 | 2014 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings		25,019
Estimated Fair Value | Level 3
Assets, Fair Value Disclosure [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Time Deposits and Restricted Cash and Cash Equivalents, Fair Value Disclosure	0	0
Loans Receivable, Fair Value Disclosure	4,210	5,978
Estimated Fair Value | Level 3 | Revolving Credit Facility | 2017 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings	$ 0
Estimated Fair Value | Level 3 | Revolving Credit Facility | 2014 Credit Facility
Liabilities, Fair Value Disclosure [Abstract]
Borrowings		$ 0

SEGMENT INFORMATION Schedule of

SEGMENT INFORMATION Schedule of Segment Revenues from External Customers and Segment Operating Profit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 1,450,448	$ 1,160,132	$ 914,128
Operating profit/(loss)	$ 52,050	$ 49,248	$ 40,682	$ 30,966	$ 37,383	$ 33,902	$ 32,080	$ 30,331	172,946	133,696	105,967
Russia
Segment Reporting Information [Line Items]
Revenues									61,222	40,944	36,585
Operating Segments
Segment Reporting Information [Line Items]
Revenues									1,452,287	1,160,815	914,966
Operating profit/(loss)									275,326	218,121	186,133
Operating Segments | North America
Segment Reporting Information [Line Items]
Revenues									796,126	642,216	471,603
Operating profit/(loss)									169,340	143,021	112,312
Operating Segments | Europe
Segment Reporting Information [Line Items]
Revenues									593,167	474,988	400,460
Operating profit/(loss)									92,080	67,545	68,717
Operating Segments | Russia
Segment Reporting Information [Line Items]
Revenues									62,994	43,611	37,992
Operating profit/(loss)									13,906	7,555	5,198
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues									0	0	4,911
Operating profit/(loss)									$ 0	$ 0	$ (94)

SEGMENT INFORMATION (Major Cust

SEGMENT INFORMATION (Major Customers) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Revenue, Major Customer [Line Items]
Revenues	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 1,450,448	$ 1,160,132	$ 914,128
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	2
Concentration percentage									13.00%	22.20%
Operating Segments
Revenue, Major Customer [Line Items]
Revenues									$ 1,452,287	$ 1,160,815	914,966
Operating Segments | Europe
Revenue, Major Customer [Line Items]
Revenues									$ 593,167	$ 474,988	$ 400,460
Operating Segments | Sales Revenue, Segment | Customer Concentration Risk
Revenue, Major Customer [Line Items]
Number of customers									0
Operating Segments | Sales Revenue, Segment | Customer Concentration Risk | Europe | UBS AG
Revenue, Major Customer [Line Items]
Number of customers										1	1
Revenues										$ 138,124	$ 130,605

SEGMENT INFORMATION (Reconcilia

SEGMENT INFORMATION (Reconciliation of Segment Revenues and Operating Profit to Consolidated Income Before Providion for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									$ 1,450,448	$ 1,160,132	$ 914,128
Segment Reporting Information [Line Items]
Total segment operating profit:	$ 52,050	$ 49,248	$ 40,682	$ 30,966	$ 37,383	$ 33,902	$ 32,080	$ 30,331	172,946	133,696	105,967
Stock-based compensation expense									(52,407)	(49,244)	(45,833)
Depreciation and amortization	(7,696)	(7,174)	(7,020)	(6,672)	(6,237)	(5,925)	(6,123)	(5,102)	(28,562)	(23,387)	(17,395)
Interest and other income, net	1,799	1,416	802	584	1,432	1,067	1,138	1,211	4,601	4,848	4,731
Foreign exchange loss	(1,772)	(77)	1,562	(2,955)	(6,765)	(1,728)	(2,295)	(1,290)	(3,242)	(12,078)	(4,628)
Income before provision for income taxes	$ 52,077	$ 50,587	$ 43,046	$ 28,595	$ 32,050	$ 33,241	$ 30,923	$ 30,252	174,305	126,466	106,070
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									1,452,287	1,160,815	914,966
Segment Reporting Information [Line Items]
Total segment operating profit:									275,326	218,121	186,133
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Other income included in segment revenues									(1,839)	(683)	(838)
Segment Reporting Information [Line Items]
Other income included in segment revenues									(1,839)	(683)	(838)
Stock-based compensation expense									(52,407)	(49,244)	(45,833)
Non-corporate taxes									(9,659)	(5,909)	(4,274)
Professional fees									(8,032)	(8,265)	(7,104)
Depreciation and amortization									(7,632)	(8,290)	(5,581)
Bank charges									(1,969)	(1,515)	(1,352)
One-time charges									(1,741)	(706)	(747)
Other corporate expenses									$ (19,101)	$ (9,813)	$ (14,437)

SEGMENT INFORMATION (Geographic

SEGMENT INFORMATION (Geographical Information of Long-Lived Assets Based on Physical Location) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 86,419	$ 73,616	$ 60,499
Belarus
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	49,866	46,011	44,879
Russia
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	9,617	7,203	2,084
Ukraine
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	6,995	5,610	4,487
Hungary
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	3,901	3,485	2,485
United States
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	3,371	2,618	1,969
Poland
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	2,893	2,213	1,088
India
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	2,698	1,650	1,099
China
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	2,608	1,887	514
Bulgaria
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	922	722	317
Other
Long-Lived Assets by Geographical Areas [Line Items]
Long-lived assets	$ 3,548	$ 2,217	$ 1,577

SEGMENT INFORMATION (Revenues b

SEGMENT INFORMATION (Revenues by Client Location) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 1,450,448	$ 1,160,132	$ 914,128
Reimbursable expenses and other revenues
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									17,138	12,521	9,511
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									783,563	611,392	431,992
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									188,995	177,194	166,418
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									123,281	122,919	111,686
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									61,222	40,944	36,585
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									60,158	43,621	36,403
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									57,129	59,189	58,319
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									51,556	17,521	10,373
Sweden
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									32,161	23,838	10,775
Hong Kong
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									19,795	21,010	23,285
United Arab Emirates
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									12,403	3,615	0
Belgium
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									8,725	8,627	8,113
Ireland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									8,674	5,167	5,536
China
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									7,379	4,479	817
Italy
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									6,505	4,052	2,342
Other locations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									$ 28,902	$ 16,564	$ 11,484

SEGMENT INFORMATION (Revenues96

SEGMENT INFORMATION (Revenues by Service Offering) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Revenues	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 313,525	$ 298,293	$ 283,832	$ 264,482	$ 1,450,448	$ 1,160,132	$ 914,128
Software development
Revenue from External Customer [Line Items]
Revenues									1,060,286	841,916	644,732
Application testing services
Revenue from External Customer [Line Items]
Revenues									276,270	223,010	174,259
Application maintenance and support
Revenue from External Customer [Line Items]
Revenues									92,630	74,475	70,551
Licensing
Revenue from External Customer [Line Items]
Revenues									3,529	3,141	3,764
Infrastructure services
Revenue from External Customer [Line Items]
Revenues									595	5,069	11,311
Reimbursable expenses and other revenues
Revenue from External Customer [Line Items]
Revenues									$ 17,138	$ 12,521	$ 9,511

QUARTERLY FINANCIAL DATA (Quate

QUARTERLY FINANCIAL DATA (Quaterly Financial Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 399,297		$ 377,523		$ 348,977		$ 324,651		$ 313,525		$ 298,293		$ 283,832		$ 264,482		$ 1,450,448	$ 1,160,132	$ 914,128
Cost of revenues (exclusive of depreciation and amortization)	254,121		239,369		220,132		207,730		198,226		190,797		180,782		167,381		921,352	737,186	566,913
Selling, general and administrative expenses	84,793		81,190		80,419		78,453		71,432		67,491		64,241		61,494		324,855	264,658	222,759
Depreciation and amortization expense	7,696		7,174		7,020		6,672		6,237		5,925		6,123		5,102		28,562	23,387	17,395
Other operating expenses, net	637		542		724		830		247		178		606		174		2,733	1,205	1,094
Total segment operating profit:	52,050		49,248		40,682		30,966		37,383		33,902		32,080		30,331		172,946	133,696	105,967
Interest and other income, net	1,799		1,416		802		584		1,432		1,067		1,138		1,211		4,601	4,848	4,731
Foreign exchange loss	(1,772)		(77)		1,562		(2,955)		(6,765)		(1,728)		(2,295)		(1,290)		(3,242)	(12,078)	(4,628)
Income before provision for income taxes	52,077		50,587		43,046		28,595		32,050		33,241		30,923		30,252		174,305	126,466	106,070
Provision for income taxes	82,951		7,953		5,687		4,954		7,287		7,067		6,493		6,353		101,545	27,200	21,614
Net income	(30,874)		42,634		37,359		23,641		24,763		26,174		24,430		23,899		72,760	99,266	84,456
Comprehensive income/(loss)	$ (27,449)		$ 48,337		$ 41,910		$ 30,027		$ 19,554		$ 26,532		$ 22,044		$ 28,598		$ 92,825	$ 96,728	$ 71,360
Basic net income/(loss) per share	$ (0.58)	[1],[2]	$ 0.81	[1]	$ 0.72	[1]	$ 0.46	[1]	$ 0.49	[1]	$ 0.51	[1]	$ 0.49	[1]	$ 0.48	[1]	$ 1.40	$ 1.97	$ 1.73
Diluted net income/(loss) per share	$ (0.58)	[1],[2]	$ 0.77	[1]	$ 0.68	[1]	$ 0.44	[1]	$ 0.46	[1]	$ 0.49	[1]	$ 0.46	[1]	$ 0.45	[1]	$ 1.32	$ 1.87	$ 1.62
Incremental shares (in shares)	0																2,907,162	2,906,030	3,265,029
[1]	(1)Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis.
[2]	(2)Due to the net loss during the three months ended December 31, 2017, zero incremental shares are included in the calculation of diluted earnings per share because of their antidilutive effect.

VALUATION AND QUALIFYING ACCO98

VALUATION AND QUALIFYING ACCOUNTS (Valuation and Qualifying Accounts) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Trade Receivables
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 2,014	$ 1,729	$ 2,181
Additions	998	3,500	1,704
Deductions/ Write offs	(1,826)	(3,215)	(2,156)
Balance at End of Year	1,186	2,014	$ 1,729
Valuation Allowance on Deferred Tax Assets
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	0
Additions	924
Deductions/ Write offs	0
Balance at End of Year	$ 924	$ 0