CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Revenues	$ 730,027	$ 555,117	$ 433,799
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	456,530	347,650	270,361
Selling, general and administrative expenses	163,666	116,497	85,868
Depreciation and amortization expense	17,483	15,120	10,882
Goodwill impairment loss	2,241	0	0
Other operating expenses/(income), net	3,924	(643)	682
Income from operations	86,183	76,493	66,006
Interest and other income, net	4,769	3,077	1,941
Change in fair value of contingent consideration	(1,924)	0	0
Foreign exchange loss	(2,075)	(2,800)	(2,084)
Income before provision for income taxes	86,953	76,770	65,863
Provision for income taxes	17,312	14,776	11,379
Net income	69,641	61,994	54,484
Foreign currency translation adjustments	(20,251)	(811)	2,493
Comprehensive income	49,390	61,183	56,977
Net income allocated to participating securities	0	0	(3,341)
Numerator for basic earnings per share	$ 69,641	$ 61,994	$ 51,143
Net income per share:
Basic (in dollars per share)	$ 1.48	$ 1.35	$ 1.27
Diluted (in dollars per share)	$ 1.40	$ 1.28	$ 1.17
Shares used in calculation of net income per share:
Basic (in shares)	47,189	45,754	40,190
Diluted (in shares)	49,734	48,358	43,821