CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Income Statement [Abstract]
Revenues	$ 1,160,132		$ 914,128		$ 730,027
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	737,186		566,913		456,530
Selling, general and administrative expenses	264,658		222,759		163,666
Depreciation and amortization expense	23,387		17,395		17,483
Goodwill impairment loss	0		0		2,241
Other operating expenses, net	1,205		1,094		3,924
Income from operations	133,696		105,967		86,183
Interest and other income, net	4,848		4,731		4,769
Change in fair value of contingent consideration	0		0		(1,924)
Foreign exchange loss	(12,078)		(4,628)		(2,075)
Income before provision for income taxes	126,466		106,070		86,953
Provision for income taxes	27,200		21,614		17,312
Net income	99,266		84,456		69,641
Foreign currency translation adjustments	(2,538)		(13,096)		(20,251)
Comprehensive income	$ 96,728		$ 71,360		$ 49,390
Net income per share:
Basic (in dollars per share)	$ 1.97	[1]	$ 1.73	[1]	$ 1.48
Diluted (in dollars per share)	$ 1.87	[1]	$ 1.62	[1]	$ 1.40
Shares used in calculation of net income per share:
Basic (in shares)	50,309		48,721		47,189
Diluted (in shares)	53,215		51,986		49,734

[1] (1)Earnings per share amounts for each quarter may not necessarily total to the yearly earnings per share due to the weighting of shares outstanding on a quarterly and year to date basis.