Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenues, net	$ 171,200	$ 163,503	$ 508,714	$ 462,634
Cost of revenues (exclusive of depreciation and amortization)	111,767	103,198	332,172	296,801
Gross profit	59,433	60,305	176,542	165,833
Operating expenses:
General and administrative expenses	21,854	18,817	63,620	57,428
Selling and marketing expenses	11,623	12,682	37,875	35,769
Depreciation and amortization	8,597	8,057	25,000	23,171
Total operating expenses	42,074	39,556	126,495	116,368
Income from operations	17,359	20,749	50,047	49,465
Other income/(expense) :
Foreign exchange gain	1,741	191	3,573	2,347
Other income, net	2,596	1,787	11,174	4,300
Income before income taxes	21,696	22,727	64,794	56,112
Income tax expense	5,646	7,565	18,549	19,309
Net income	$ 16,050	$ 15,162	$ 46,245	$ 36,803
Earnings per share:
Basic (in dollars per share)	$ 0.48	$ 0.46	$ 1.38	$ 1.10
Diluted (in dollars per share)	$ 0.46	$ 0.44	$ 1.34	$ 1.08
Weighted-average number of shares used in computing earnings per share:
Basic weighted average common shares outstanding (in shares)	33,624,401	33,307,312	33,542,258	33,320,477
Diluted weighted average common shares outstanding (in shares)	34,675,485	34,180,635	34,512,815	34,147,120