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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 140,150	$ 110,078	$ 397,532	$ 308,261
Segment Reporting Information [Line Items]
Income from operations	20,230	16,736	53,301	47,350
Other revenues	11	3	43	39
Stock-based compensation expense	(3,365)	(2,046)	(9,791)	(5,369)
Stock charge	0	0	0	(640)
Non-corporate taxes	(690)	(391)	(2,190)	(1,630)
Professional fees	(594)	(493)	(2,668)	(1,811)
Depreciation and amortization	(3,906)	(3,040)	(11,377)	(7,674)
Bank charges	(261)	(278)	(914)	(823)
Other corporate expenses	(1,736)	(1,769)	(5,752)	(4,785)
Interest and other income, net	846	486	2,245	1,422
Foreign exchange loss	(720)	(635)	(2,088)	(1,949)
Income before provision for income taxes	20,356	16,587	53,458	46,823
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	140,139	110,075	397,489	308,222
Segment Reporting Information [Line Items]
Income from operations	27,597	22,158	76,735	63,125
Unallocated Amounts [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	$ (732)	$ (448)	$ (2,162)	$ (756)