CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 99,266	$ 84,456	$ 69,641
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	23,387	17,395	17,483
Bad debt expense	1,539	1,407	817
Deferred taxes	(3,304)	(15,328)	(3,270)
Stock-based compensation expense	49,244	45,833	24,620
Impairment charges and acquisition related adjustments	0	(1,183)	7,907
Excess tax benefit on stock-based compensation plans	(5,264)	(8,363)	(3,776)
Other	6,228	3,883	735
(Increase)/decrease in operating assets:
Accounts receivable	(30,612)	(47,694)	(30,410)
Unbilled revenues	34,777	(38,076)	(11,134)
Prepaid expenses and other assets	(4,791)	(574)	565
Increase/(decrease) in operating liabilities:
Accounts payable	741	(2,781)	(2,603)
Accrued expenses and other liabilities	(13,926)	25,694	9,978
Due to employees	5,261	2,752	7,453
Taxes payable	2,271	8,972	16,868
Net cash provided by operating activities	164,817	76,393	104,874
Cash flows used in investing activities:
Purchases of property and equipment	(29,317)	(13,272)	(11,916)
Payment for construction of corporate facilities	0	(4,692)	(3,924)
Employee housing loans issued	(2,006)	(2,054)	(1,740)
Proceeds from repayments of employee housing loans	2,177	2,249	1,793
(Increase)/decrease in restricted cash and time deposits, net	29,595	(29,944)	1,430
Increase in other long-term assets, net	(4,327)	(708)	(1,479)
Acquisition of businesses, net of cash acquired (Note 3)	(5,500)	(76,908)	(37,093)
Other investing activities, net	56	(165)	0
Net cash used in investing activities	(9,322)	(125,494)	(52,929)
Cash flows from financing activities:
Proceeds related to stock options exercises	17,996	20,675	10,571
Excess tax benefit on stock-based compensation plans	5,264	8,363	3,776
Payments of withholding taxes related to net share settlements of restricted stock units	(539)	0	0
Proceeds from debt (Note 13)	20,000	35,000	0
Repayment of debt (Note 13)	(30,129)	0	0
Proceeds from government grants	135	0	0
Acquisition of businesses, deferred consideration (Note 3)	(2,260)	(30,274)	(4,000)
Net cash provided by financing activities	10,467	33,764	10,347
Effect of exchange rate changes on cash and cash equivalents	(3,386)	(5,748)	(10,965)
Net increase/(decrease) in cash and cash equivalents	162,576	(21,085)	51,327
Cash and cash equivalents, beginning of period	199,449	220,534	169,207
Cash and cash equivalents, end of period	362,025	199,449	220,534
Supplemental disclosures of cash flow information:
Income taxes	37,488	25,071	11,756
Bank interest	566	124	7
Supplemental disclosure of non-cash operating activities
Goodwill impairment loss	0	0	2,241
Contingent consideration fair value adjustment	0	0	1,924
Write off related to the construction of a building in Minsk, Belarus	0	0	3,742
Prepaid and other current assets write-off related to vendor advance	0	741	0
Supplemental disclosure of non-cash investing and financing activities
Deferred consideration payable	0	603	1,022
Contingent consideration payable	$ 0	$ 0	$ 36,322