Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenues, net	$ 189,057	$ 170,478	$ 372,090	$ 337,514
Cost of revenues (exclusive of depreciation and amortization)	125,449	112,026	245,568	220,405
Gross profit	63,608	58,452	126,522	117,109
Operating expenses:
General and administrative expenses	24,715	21,148	48,939	41,766
Selling and marketing expenses	13,127	12,798	26,489	26,252
Depreciation and amortization	9,637	8,270	19,063	16,403
Total operating expenses	47,479	42,216	94,491	84,421
Income from operations	16,129	16,236	32,031	32,688
Foreign exchange gain, net	2,898	1,363	4,466	1,832
Interest expense	(465)	(343)	(897)	(728)
Other income, net	2,639	6,127	5,949	9,306
Income before income tax expense	21,201	23,383	41,549	43,098
Income tax expense	823	7,008	4,383	12,903
Net income	$ 20,378	$ 16,375	$ 37,166	$ 30,195
Earnings per share:
Basic (in dollars per share)	$ 0.60	$ 0.49	$ 1.10	$ 0.90
Diluted (in dollars per share)	$ 0.58	$ 0.47	$ 1.06	$ 0.88
Weighted-average number of shares used in computing earnings per share:
Basic (in shares)	33,819,320	33,621,444	33,833,153	33,500,736
Diluted (in shares)	34,993,226	34,510,400	35,051,767	34,431,028