RECONCILIATION OF SEGMENT REVENUES AND OPERATING PROFIT TO CONSOLIDATED INCOME FROM OPERATIONS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 133,184	$ 103,800	$ 257,382	$ 198,183
Segment Reporting Information [Line Items]
Income from operations	17,535	16,830	33,071	30,614
Stock-based compensation expense	(3,850)	(1,773)	(6,426)	(3,323)
Depreciation and amortization	(3,854)	(2,423)	(7,471)	(4,634)
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
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	133,174	103,776	257,350	198,147
Segment Reporting Information [Line Items]
Income from operations	25,870	22,061	49,138	40,967
Unallocated Amounts [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	10	24	32	36
Segment Reporting Information [Line Items]
Other revenues	10	24	32	36
Stock-based compensation expense	(3,850)	(1,773)	(6,426)	(3,323)
Stock charge	0	0	0	(640)
Non-corporate taxes	(680)	(514)	(1,500)	(1,239)
Professional fees	(724)	(889)	(2,074)	(1,318)
Depreciation and amortization	(715)	(151)	(1,430)	(308)
Bank charges	(321)	(296)	(653)	(545)
Other corporate expenses	$ (2,055)	$ (1,632)	$ (4,016)	$ (3,016)