OPERATING SEGMENTS, Reconciliation of Segment Revenues and Operating Profit to Consolidated Income From Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 236,049	$ 192,764	$ 653,875	$ 527,843
Segment Reporting Information [Line Items]
Income from operations	27,776	21,835	74,202	62,168
Stock-based compensation expense	(11,963)	(7,425)	(33,350)	(16,524)
Depreciation and amortization	(4,393)	(5,510)	(12,496)	(14,650)
One Time Charges	0	0	0	(2,000)
Interest and other income, net	865	1,261	3,322	3,401
Foreign exchange gain/ (loss)	32	(718)	(6,187)	(3,198)
Income before provision for income taxes	28,673	22,378	71,337	62,371
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	236,174	192,759	654,437	527,439
Segment Reporting Information [Line Items]
Income from operations	47,721	37,028	130,834	99,449
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	(125)	5	(562)	404
Segment Reporting Information [Line Items]
Other unallocated revenues/ (discounts)	(125)	5	(562)	404
Stock-based compensation expense	(11,963)	(7,425)	(33,350)	(16,524)
Non-corporate taxes	(1,120)	(789)	(2,858)	(1,944)
Professional fees	(1,572)	(839)	(5,423)	(3,380)
Depreciation and amortization	(1,312)	(2,589)	(3,919)	(5,470)
Bank charges	(340)	(708)	(1,021)	(1,211)
Other corporate expenses	$ (3,513)	$ (2,848)	$ (9,499)	$ (7,156)