OPERATING SEGMENTS, Revenues from External Customers and Segment Operating Profit Before Unallocated Expenses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Customer	Mar. 31, 2013 Customer
Segment Reporting Information [Line Items]
Revenues	$ 160,384	$ 124,198
Operating profit	21,857	15,536
Number Of Customers Accounted For More Than Ten Percentage Of Revenue	1	0
UBS AG [Member]
Segment Reporting Information [Line Items]
Entity-Wide Revenue, Major Customer, Amount	20,024
Russia [Member]
Segment Reporting Information [Line Items]
Revenues	10,390	11,738
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues	159,997	124,176
Operating profit	29,879	23,268
Operating Segments [Member] | North America [Member]
Segment Reporting Information [Line Items]
Revenues	80,198	63,057
Operating profit	18,197	14,181
Operating Segments [Member] | Europe [Member]
Segment Reporting Information [Line Items]
Revenues	67,659	46,153
Operating profit	14,135	8,371
Operating Segments [Member] | Russia [Member]
Segment Reporting Information [Line Items]
Revenues	10,748	12,353
Operating profit	(1,135)	632
Operating Segments [Member] | Other Reportable Segments [Member]
Segment Reporting Information [Line Items]
Revenues	1,392	2,613
Operating profit	$ (1,318)	$ 84