CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (Unaudited) [Abstract]
Revenues	$ 133,184	$ 103,800	$ 257,382	$ 198,183
Operating expenses:
Cost of revenues (exclusive of depreciation and amortization)	83,547	63,803	161,484	123,978
Selling, general and administrative expenses	28,541	20,711	55,624	38,338
Depreciation and amortization expense	3,854	2,423	7,471	4,634
Other operating (income)/ expenses, net	(293)	33	(268)	619
Income from operations	17,535	16,830	33,071	30,614
Interest and other income, net	769	460	1,399	936
Foreign exchange loss	(869)	(1,394)	(1,368)	(1,314)
Income before provision for income taxes	17,435	15,896	33,102	30,236
Provision for income taxes	3,317	2,575	6,304	4,816
Net income	14,118	13,321	26,798	25,420
Cumulative translation adjustment	(1,045)	(2,464)	(3,388)	(852)
Comprehensive income	13,073	10,857	23,410	24,568
Net income/ (loss) allocated to participating securities	0	0	0	(3,176)
Net income available for common stockholders	$ 14,118	$ 13,321	$ 26,798	$ 22,244
Net income per share of common stock:
Basic (common) (in dollars per share)	$ 0.31	$ 0.31	$ 0.59	$ 0.60
Diluted (common) (in dollars per share)	$ 0.29	$ 0.29	$ 0.56	$ 0.55
Shares used in calculation of net income per share of common stock:
Basic (common) (in shares)	45,486	42,475	45,151	36,987
Diluted (common) (in shares)	47,977	46,382	47,813	40,820