CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenues	$ 236,049	$ 192,764	$ 653,875	$ 527,843
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	148,479	122,509	408,622	335,065
Selling, general and administrative expenses	55,431	42,875	158,345	113,905
Depreciation and amortization expense	4,393	5,510	12,496	14,650
Other operating (income)/ expenses, net	(30)	35	210	2,055
Income from operations	27,776	21,835	74,202	62,168
Interest and other income, net	865	1,261	3,322	3,401
Foreign exchange gain/ (loss)	32	(718)	(6,187)	(3,198)
Income before provision for income taxes	28,673	22,378	71,337	62,371
Provision for income taxes	5,800	3,338	14,519	11,153
Net income	22,873	19,040	56,818	51,218
Foreign currency translation adjustments	(8,341)	(8,260)	(7,397)	(8,943)
Comprehensive income	$ 14,532	$ 10,780	$ 49,421	$ 42,275
Net income per share:
Basic (in dollars per share)	$ 0.47	$ 0.40	$ 1.17	$ 1.09
Diluted (in dollars per share)	$ 0.44	$ 0.38	$ 1.10	$ 1.03
Shares used in calculation of net income per share:
Basic (in shares)	49,043	47,315	48,506	47,058
Diluted (in shares)	52,344	49,829	51,755	49,530