OPERATING SEGMENTS, Reconciliation of Segment Revenues and Operating Profit to Consolidated Income From Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 160,384	$ 124,198
Segment Reporting Information [Line Items]
Income from operations	21,857	15,536
Other revenues	387	22
Stock-based compensation expense	(3,208)	(2,576)
Non-corporate taxes	(546)	(820)
Professional fees	(1,314)	(1,350)
Depreciation and amortization	(3,689)	(3,617)
Bank charges	(247)	(332)
Other corporate expenses	(2,439)	(1,961)
Interest and other income, net	976	630
Foreign exchange loss	(1,241)	(499)
Income before provision for income taxes	21,592	15,667
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	159,997	124,176
Segment Reporting Information [Line Items]
Income from operations	29,879	23,268
Unallocated Amounts [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	387	22
Segment Reporting Information [Line Items]
Depreciation and amortization	$ (655)	$ (715)