CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ 84,456,000	$ 69,641,000	$ 61,994,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17,395,000	17,483,000	15,120,000
Bad debt expense	1,407,000	817,000	335,000
Deferred taxes	(15,328,000)	(3,270,000)	41,000
Stock-based compensation expense	45,833,000	24,620,000	13,150,000
Impairment charges and acquisition related adjustments	(1,183,000)	7,907,000	0
Excess tax benefit on stock-based compensation plans	(8,363,000)	(3,776,000)	(6,201,000)
Other	3,883,000	735,000	1,199,000
(Increase)/ decrease in operating assets:
Accounts receivable	(47,694,000)	(30,410,000)	(17,302,000)
Unbilled revenues	(38,076,000)	(11,134,000)	(9,833,000)
Prepaid expenses and other assets	(574,000)	565,000	587,000
Increase/ (decrease) in operating liabilities:
Accounts payable	(2,781,000)	(2,603,000)	(2,900,000)
Accrued expenses and other liabilities	26,563,000	11,492,000	501,000
Deferred revenues	(869,000)	(1,514,000)	(2,325,000)
Due to employees	2,752,000	7,453,000	785,000
Taxes payable	8,972,000	16,868,000	3,074,000
Net cash provided by operating activities	76,393,000	104,874,000	58,225,000
Cash flows from investing activities:
Purchases of property and equipment	(13,272,000)	(11,916,000)	(13,360,000)
Payment for construction of corporate facilities	(4,692,000)	(3,924,000)	(2,560,000)
Employee housing loans	(2,054,000)	(1,740,000)	(7,982,000)
Proceeds from repayments of employee housing loans	2,249,000	1,793,000	2,189,000
Increase in restricted cash and time deposits, net	(29,944,000)	1,430,000	429,000
Increase in other long-term assets, net	(708,000)	(1,479,000)	(516,000)
Payments for foreign currency derivatives	(165,000)	0	0
Acquisition of businesses, net of cash acquired (Note 2)	(76,908,000)	(37,093,000)	(20,000)
Net cash used in investing activities	(125,494,000)	(52,929,000)	(21,820,000)
Cash flows from financing activities:
Proceeds related to stock options exercises	20,675,000	10,571,000	9,300,000
Excess tax benefit on stock-based compensation plans	8,363,000	3,776,000	6,201,000
Proceeds from borrowing under line of credit (Note 12)	35,000,000	0	0
Acquisition of business, deferred consideration (Note 2)	(30,274,000)	(4,000,000)	0
Net cash provided by financing activities	33,764,000	10,347,000	15,501,000
Effect of exchange rate changes on cash and cash equivalents	(5,748,000)	(10,965,000)	(811,000)
Net increase/ (decrease) in cash and cash equivalents	(21,085,000)	51,327,000	51,095,000
Cash and cash equivalents, beginning of period	220,534,000	169,207,000	118,112,000
Cash and cash equivalents, end of period	199,449,000	220,534,000	169,207,000
Supplemental disclosures of cash paid:
Income taxes	25,071,000	11,756,000	10,207,000
Bank interest	124,000	7,000	26,000
Goodwill impairment loss	0	2,241,000	0
Change in fair value of contingent consideration	0	1,924,000	0
Building construction, write off	3,742,000
Deferred consideration payable	603,000	1,022,000	0
Contingent consideration payable	$ 0	$ 36,322,000	$ 0