SEGMENT INFORMATION (Major Customers) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Revenue, Major Customer [Line Items]
Revenues	$ 504,931	$ 468,186	$ 445,647	$ 424,148	$ 399,297	$ 377,523	$ 348,977	$ 324,651	$ 1,842,912	$ 1,450,448	$ 1,160,132
Accounts Receivable | Customer Concentration Risk | Billed Revenues
Revenue, Major Customer [Line Items]
Number of Customers									0	0
Operating Segments | Sales Revenue, Segment | Customer Concentration Risk
Revenue, Major Customer [Line Items]
Number of Customers									0	0
Operating Segments | Sales Revenue, Segment | Customer Concentration Risk | Europe | UBS AG
Revenue, Major Customer [Line Items]
Number of Customers											1
Revenues											$ 138,124