OPERATING SEGMENTS, Reconciliation of Segment Revenues and Operating Profit to Consolidated Income From Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 192,764	$ 140,150	$ 527,843	$ 397,532
Segment Reporting Information [Line Items]
Income from operations	21,835	20,230	62,168	53,301
Stock-based compensation expense	(7,425)	(3,365)	(16,524)	(9,791)
Depreciation and amortization	(5,510)	(3,906)	(14,650)	(11,377)
Interest and other income, net	1,261	846	3,401	2,245
Foreign exchange loss	(718)	(720)	(3,198)	(2,088)
Income before provision for income taxes	22,378	20,356	62,371	53,458
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	192,759	140,139	527,439	397,489
Segment Reporting Information [Line Items]
Income from operations	37,028	27,597	99,449	76,735
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	5	11	404	43
Segment Reporting Information [Line Items]
Other revenues	5	11	404	43
Stock-based compensation expense	(7,425)	(3,365)	(16,524)	(9,791)
Non-corporate taxes	(789)	(690)	(1,944)	(2,190)
Professional fees	(839)	(594)	(3,380)	(2,668)
Depreciation and amortization	(2,589)	(732)	(5,470)	(2,162)
Bank charges	(708)	(261)	(1,211)	(914)
Asset impairment	0	0	(2,000)	0
Other corporate expenses	$ (2,848)	$ (1,736)	$ (7,156)	$ (5,752)