SEGMENTS INFORMATION - Reconciliation of Segment Revenues and Operating Profit to Consolidated Income From Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 283,832	$ 217,781	$ 548,314	$ 417,826
Segment Reporting Information [Line Items]
Income from operations	32,080	23,606	62,411	46,426
Stock-based compensation expense			(23,694)	(21,387)
Depreciation and amortization	(6,123)	(3,903)	(11,225)	(8,103)
Interest and other income, net	1,138	1,299	2,349	2,457
Foreign exchange loss	(2,295)	(465)	(3,585)	(6,219)
Income before provision for income taxes	30,923	24,440	61,175	42,664
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	283,977	218,069	548,791	418,263
Segment Reporting Information [Line Items]
Income from operations	54,628	44,433	103,275	83,113
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	(145)	(288)	(477)	(437)
Segment Reporting Information [Line Items]
Other income	(145)	(288)	(477)	(437)
Stock-based compensation expense	(12,730)	(12,253)	(23,694)	(21,387)
Non-corporate taxes	(1,437)	(913)	(2,517)	(1,738)
Professional fees	(2,460)	(2,029)	(4,186)	(3,851)
Depreciation and amortization	(2,576)	(1,278)	(4,267)	(2,607)
Bank charges	(386)	(314)	(727)	(681)
One time charges	(307)	0	(307)	0
Other corporate expenses	$ (2,507)	$ (3,752)	$ (4,689)	$ (5,986)