OPERATING SEGMENTS - Major Customers (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)
Revenue, Major Customer [Line Items]
Revenues	$ 264,482	$ 200,045
Operating Segments
Revenue, Major Customer [Line Items]
Revenues	264,814	200,194
Operating Segments | Europe
Revenue, Major Customer [Line Items]
Revenues	$ 107,843	$ 91,152
Sales Revenue, Net | Customer Concentration Risk | Operating Segments | Europe | UBS AG
Revenue, Major Customer [Line Items]
Number of customers	1	1
Revenues	$ 35,669	$ 30,933
Accounts Receivable | Customer Concentration Risk | UBS AG | Billed Revenues
Revenue, Major Customer [Line Items]
Number of customers	1
Concentration percentage	15.20%
Accounts Receivable | Customer Concentration Risk | UBS AG | Unbilled Revenues
Revenue, Major Customer [Line Items]
Number of customers	1
Concentration percentage	17.20%