OPERATING SEGMENTS, Reconciliation of Segment Revenues and Operating Profit to Consolidated Income From Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 217,781	$ 174,695	$ 417,826	$ 335,079
Segment Reporting Information [Line Items]
Income from operations	23,606	18,476	46,426	40,333
Stock-based compensation expense	(12,253)	(5,891)	(21,387)	(9,099)
Depreciation and amortization	(3,903)	(5,451)	(8,103)	(9,140)
One Time Charges	0	(2,000)	0	(2,000)
Interest and other income, net	1,299	1,164	2,457	2,140
Foreign exchange loss	(465)	(1,239)	(6,219)	(2,480)
Income before provision for income taxes	24,440	18,401	42,664	39,993
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	218,069	174,683	418,263	334,680
Segment Reporting Information [Line Items]
Income from operations	44,433	32,542	83,113	62,421
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	(288)	12	(437)	399
Segment Reporting Information [Line Items]
Other unallocated revenues/ (discounts)	(288)	12	(437)	399
Stock-based compensation expense	(12,253)	(5,891)	(21,387)	(9,099)
Non-corporate taxes	(913)	(609)	(1,738)	(1,155)
Professional fees	(2,029)	(1,227)	(3,851)	(2,541)
Depreciation and amortization	(1,278)	(2,226)	(2,607)	(2,881)
Bank charges	(314)	(256)	(681)	(503)
Other corporate expenses	$ (3,752)	$ (1,869)	$ (5,986)	$ (4,308)