CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement [Abstract]
Revenues	$ 174,695	$ 133,184	$ 335,079	$ 257,382
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	110,102	83,547	212,556	161,484
Selling, general and administrative expenses	38,671	28,541	71,030	55,624
Depreciation and amortization expense	5,451	3,854	9,140	7,471
Other operating expenses, net	1,995	(293)	2,020	(268)
Income from operations	18,476	17,535	40,333	33,071
Interest and other income, net	1,164	769	2,140	1,399
Foreign exchange loss	(1,239)	(869)	(2,480)	(1,368)
Income before provision for income taxes	18,401	17,435	39,993	33,102
Provision for income taxes	3,587	3,317	7,815	6,304
Net income	14,814	14,118	32,178	26,798
Foreign currency translation adjustments	2,894	(1,045)	(683)	(3,388)
Comprehensive income	$ 17,708	$ 13,073	$ 31,495	$ 23,410
Net income per share:
Basic (in dollars per share)	$ 0.31	$ 0.31	$ 0.69	$ 0.59
Diluted (in dollars per share)	$ 0.30	$ 0.29	$ 0.65	$ 0.56
Shares used in calculation of net income per share:
Basic (in shares)	47,068	45,486	46,933	45,151
Diluted (in shares)	49,559	47,977	49,384	47,813