CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Revenues	$ 192,764	$ 140,150	$ 527,843	$ 397,532
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	122,509	88,539	335,065	250,023
Selling, general and administrative expenses	42,875	27,893	113,905	83,517
Depreciation and amortization expense	5,510	3,906	14,650	11,377
Other operating expenses, net	35	(418)	2,055	(686)
Income from operations	21,835	20,230	62,168	53,301
Interest and other income, net	1,261	846	3,401	2,245
Foreign exchange loss	(718)	(720)	(3,198)	(2,088)
Income before provision for income taxes	22,378	20,356	62,371	53,458
Provision for income taxes	3,338	3,919	11,153	10,223
Net income	19,040	16,437	51,218	43,235
Foreign currency translation adjustments	(8,260)	2,975	(8,943)	(413)
Comprehensive income	$ 10,780	$ 19,412	$ 42,275	$ 42,822
Net income per share:
Basic (in dollars per share)	$ 0.40	$ 0.36	$ 1.09	$ 0.95
Diluted (in dollars per share)	$ 0.38	$ 0.34	$ 1.03	$ 0.90
Shares used in calculation of net income per share:
Basic (in shares)	47,315	46,162	47,058	45,492
Diluted (in shares)	49,829	48,720	49,530	48,120