Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenues, net	$ 685,988	$ 628,492	$ 499,278
Cost of revenues (exclusive of depreciation and amortization)	447,956	402,917	332,535
Gross profit	238,032	225,575	166,743
Operating expenses:
General and administrative expenses	88,648	77,293	65,381
Selling and marketing expenses	50,582	49,474	39,294
Depreciation and amortization	34,580	31,465	28,028
Total operating expenses	173,810	158,232	132,703
Income from operations	64,222	67,343	34,040
Other income/(expense) :
Foreign exchange gain/(loss), net	5,597	2,744	(5)
Interest expense	(1,343)	(1,338)	(369)
Other income, net	15,408	7,027	3,972
Income before income tax expense	83,884	75,776	37,638
Income tax expense	22,151	24,211	5,193
Net income	$ 61,733	$ 51,565	$ 32,445
Earnings per share:
Basic (in dollars per share)	$ 1.84	$ 1.55	$ 0.99
Diluted (in dollars per share)	$ 1.79	$ 1.51	$ 0.96
Weighted-average number of shares used in computing earnings per share:
Basic (in shares)	33,566,367	33,298,104	32,804,606
Diluted (in shares)	34,563,319	34,178,340	33,636,593