CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenues	$ 283,832	$ 217,781	$ 548,314	$ 417,826
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	180,782	134,256	348,163	260,143
Selling, general and administrative expenses	64,241	55,976	125,735	102,914
Depreciation and amortization expense	6,123	3,903	11,225	8,103
Other operating expenses, net	606	40	780	240
Income from operations	32,080	23,606	62,411	46,426
Interest and other income, net	1,138	1,299	2,349	2,457
Foreign exchange loss	(2,295)	(465)	(3,585)	(6,219)
Income before provision for income taxes	30,923	24,440	61,175	42,664
Provision for income taxes	6,493	5,209	12,846	8,719
Net income	24,430	19,231	48,329	33,945
Foreign currency translation adjustments	(2,386)	3,674	2,313	944
Comprehensive income	$ 22,044	$ 22,905	$ 50,642	$ 34,889
Net income per share:
Basic (in dollars per share)	$ 0.49	$ 0.40	$ 0.97	$ 0.70
Diluted (in dollars per share)	$ 0.46	$ 0.37	$ 0.92	$ 0.66
Shares used in calculation of net income per share:
Basic (in shares)	50,211	48,584	49,688	48,237
Diluted (in shares)	53,271	51,917	52,803	51,461