CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 69,641,000	$ 61,994,000	$ 54,484,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17,483,000	15,120,000	10,882,000
Bad debt expense	817,000	335,000	662,000
Deferred taxes	(3,270,000)	41,000	(3,933,000)
Stock-based compensation expense	24,620,000	13,150,000	6,826,000
Impairment and acquisition related charges	7,907,000	0	0
Excess tax benefit on stock-based compensation plans	(3,776,000)	(6,201,000)	(3,297,000)
Non-cash stock charge	0	0	640,000
Other	735,000	1,199,000	(66,000)
(Increase)/ decrease in operating assets:
Accounts receivable	(30,410,000)	(17,302,000)	(12,664,000)
Unbilled revenues	(11,134,000)	(9,833,000)	(6,905,000)
Prepaid expenses and other assets	565,000	587,000	(1,339,000)
Increase/ (decrease) in operating liabilities:
Accounts payable	(2,603,000)	(2,900,000)	1,407,000
Accrued expenses and other liabilities	11,492,000	501,000	(5,825,000)
Deferred revenues	(1,514,000)	(2,325,000)	(767,000)
Due to employees	7,453,000	785,000	2,896,000
Taxes payable	16,868,000	3,074,000	5,498,000
Net cash provided by operating activities	104,874,000	58,225,000	48,499,000
Cash flows from investing activities:
Purchases of property and equipment	(11,916,000)	(13,360,000)	(13,376,000)
Payment for construction of corporate facilities	(3,924,000)	(2,560,000)	(13,701,000)
Employee housing loans	(1,740,000)	(7,982,000)	0
Proceeds from repayments of employee housing loans	1,793,000	2,189,000	0
Decrease in restricted cash and time deposits, net	1,430,000	429,000	470,000
Increase in other long-term assets, net	(1,479,000)	(516,000)	(69,000)
Acquisition of businesses, net of cash acquired (Note 2)	(37,093,000)	(20,000)	(32,951,000)
Net cash used in investing activities	(52,929,000)	(21,820,000)	(59,627,000)
Cash flows from financing activities:
Proceeds related to stock options exercises	10,571,000	9,300,000	4,951,000
Excess tax benefit on stock-based compensation plans	3,776,000	6,201,000	3,297,000
Net proceeds from issuance of common stock in initial public offering	0	0	32,364,000
Costs related to stock issue	0	0	(1,765,000)
Acquisition of business, deferred consideration	(4,000,000)	0	0
Net cash provided by financing activities	10,347,000	15,501,000	38,847,000
Effect of exchange rate changes on cash and cash equivalents	(10,965,000)	(811,000)	1,597,000
Net increase in cash and cash equivalents	51,327,000	51,095,000	29,316,000
Cash and cash equivalents, beginning of period	169,207,000	118,112,000	88,796,000
Cash and cash equivalents, end of period	220,534,000	169,207,000	118,112,000
Supplemental disclosures of cash paid:
Income taxes	11,756,000	10,207,000	13,065,000
Bank interest	7,000	26,000	14,000
Deferred consideration payable	1,022,000	0	0
Contingent consideration payable	36,322,000	0	0
Incurred but not paid costs	$ 0	$ 0	$ 96,000