CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Revenues	$ 324,651	$ 264,482
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	207,730	167,381
Selling, general and administrative expenses	78,453	61,494
Depreciation and amortization expense	6,672	5,102
Other operating expenses, net	830	174
Income from operations	30,966	30,331
Interest and other income, net	584	1,211
Foreign exchange loss	(2,955)	(1,290)
Income before provision for income taxes	28,595	30,252
Provision for income taxes	4,954	6,353
Net income	23,641	23,899
Foreign currency translation adjustments	6,386	4,699
Comprehensive income	$ 30,027	$ 28,598
Net income per share:
Basic (in dollars per share)	$ 0.46	$ 0.48
Diluted (in dollars per share)	$ 0.44	$ 0.45
Shares used in calculation of net income per share:
Basic (in shares)	50,958	49,714
Diluted (in shares)	53,889	52,883