SEGMENT INFORMATION (Revenues by Customer Location) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 632,775	$ 588,103	$ 551,587	$ 521,333	$ 504,931	$ 468,186	$ 445,647	$ 424,148	$ 2,293,798	$ 1,842,912	$ 1,450,448
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									1,321,662	1,029,327	783,563
United Kingdom
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									290,039	200,918	188,995
Switzerland
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									152,710	144,398	123,281
Russia
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									89,941	71,181	61,222
Netherlands
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									88,488	70,274	51,556
Germany
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									82,441	80,787	60,158
Canada
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									68,304	69,836	57,129
Other locations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									$ 200,213	$ 176,191	$ 124,544