Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenues, net	$ 170,478	$ 155,621	$ 337,514	$ 299,131
Cost of revenues (exclusive of depreciation and amortization)	112,026	100,478	220,405	193,603
Gross profit	58,452	55,143	117,109	105,528
Operating expenses:
General and administrative expenses	21,148	19,990	41,766	38,611
Selling and marketing expenses	12,798	11,844	26,252	23,087
Depreciation and amortization	8,270	8,061	16,403	15,114
Total operating expenses	42,216	39,895	84,421	76,812
Income from operations	16,236	15,248	32,688	28,716
Other income/(expense) :
Foreign exchange gain	1,363	1,022	1,832	2,156
Other income, net	5,784	1,335	8,578	2,513
Income before income taxes	23,383	17,605	43,098	33,385
Income tax expense	7,008	5,531	12,903	11,744
Net income	$ 16,375	$ 12,074	$ 30,195	$ 21,641
Earnings per share:
Basic (in dollars per share)	$ 0.49	$ 0.36	$ 0.90	$ 0.65
Diluted (in dollars per share)	$ 0.47	$ 0.35	$ 0.88	$ 0.63
Weighted-average number of shares used in computing earnings per share:
Basic weighted average common shares outstanding (in shares)	33,621,444	33,417,079	33,500,736	33,327,169
Diluted weighted average common shares outstanding (in shares)	34,510,400	34,207,973	34,431,028	34,130,472