Unaudited Consolidated Statements of Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Revenues, net	$ 192,345	$ 171,200	$ 564,435	$ 508,714
Cost of revenues (exclusive of depreciation and amortization)	124,890	111,767	370,458	332,172
Gross profit	67,455	59,433	193,977	176,542
Operating expenses:
General and administrative expenses	26,870	21,854	75,809	63,620
Selling and marketing expenses	12,222	11,623	38,711	37,875
Depreciation and amortization	9,708	8,597	28,771	25,000
Total operating expenses	48,800	42,074	143,291	126,495
Income from operations	18,655	17,359	50,686	50,047
Foreign exchange gain, net	2,801	1,741	7,267	3,573
Interest expense	(482)	(295)	(1,379)	(1,023)
Other income, net	2,922	2,891	8,871	12,197
Income before income tax expense	23,896	21,696	65,445	64,794
Income tax expense	2,819	5,646	7,202	18,549
Net income	$ 21,077	$ 16,050	$ 58,243	$ 46,245
Earnings per share:
Basic (in dollars per share)	$ 0.62	$ 0.48	$ 1.72	$ 1.38
Diluted (in dollars per share)	$ 0.60	$ 0.46	$ 1.66	$ 1.34
Weighted-average number of shares used in computing earnings per share:
Basic (in shares)	33,838,374	33,624,401	33,834,392	33,542,258
Diluted (in shares)	35,043,987	34,675,485	35,048,672	34,512,815