Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenues, net	$ 628,492	$ 499,278	$ 478,452
Cost of revenues (exclusive of depreciation and amortization)	402,917	332,535	290,942
Gross profit	225,575	166,743	187,510
Operating expenses:
General and administrative expenses	77,293	65,381	58,797
Selling and marketing expenses	49,474	39,294	36,376
Depreciation and amortization	31,465	28,028	24,917
Total operating expenses	158,232	132,703	120,090
Income from operations	67,343	34,040	67,420
Other income/(expense) :
Foreign exchange gain/(loss), net	2,744	(5)	(4,990)
Other income, net	5,689	3,603	2,547
Income before income taxes	75,776	37,638	64,977
Income tax expense	24,211	5,193	16,880
Net income	$ 51,565	$ 32,445	$ 48,097
Earnings per share:
Basic (in dollars per share)	$ 1.55	$ 0.99	$ 1.47
Diluted (in dollars per share)	$ 1.51	$ 0.96	$ 1.42
Weighted-average number of shares used in computing earnings per share:
Basic (in shares)	33,298,104	32,804,606	32,750,178
Diluted (in shares)	34,178,340	33,636,593	33,842,938