OPERATING SEGMENTS, 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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 174,695	$ 133,184	$ 335,079	$ 257,382
Segment Reporting Information [Line Items]
Income from operations	18,476	17,535	40,333	33,071
Stock-based compensation expense	(5,891)	(3,850)	(9,099)	(6,426)
Depreciation and amortization	(5,451)	(3,854)	(9,140)	(7,471)
Interest and other income, net	1,164	769	2,140	1,399
Foreign exchange loss	(1,239)	(869)	(2,480)	(1,368)
Income before provision for income taxes	18,401	17,435	39,993	33,102
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	174,683	133,174	334,680	257,350
Segment Reporting Information [Line Items]
Income from operations	32,542	25,870	62,421	49,138
Unallocated Amounts
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	12	10	399	32
Segment Reporting Information [Line Items]
Other revenues	12	10	399	32
Stock-based compensation expense	5,891	3,850	9,099	6,426
Non-corporate taxes	609	680	1,155	1,500
Professional fees	1,227	724	2,541	2,074
Depreciation and amortization	2,226	715	2,881	1,430
Bank charges	256	321	503	653
One Time Charges	(2,000)	0	(2,000)	0
Other corporate expenses	$ 1,869	$ 2,055	$ 4,308	$ 4,016