REVENUE - Geographic Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 216,703	$ 203,263	$ 634,841	$ 635,224
Concentration Risk, Percentage	100.00%	100.00%	100.00%	100.00%
U.S.
Disaggregation of Revenue [Line Items]
Total revenue	$ 123,447	$ 103,075	$ 347,120	$ 327,409
Other Americas
Disaggregation of Revenue [Line Items]
Total revenue	11,748	10,424	49,450	37,766
United Kingdom (“U.K.”)
Disaggregation of Revenue [Line Items]
Total revenue	23,034	19,277	64,269	68,450
Europe (excluding U.K.), Middle East, and Africa
Disaggregation of Revenue [Line Items]
Total revenue	34,761	42,254	102,342	101,150
Asia-Pacific
Disaggregation of Revenue [Line Items]
Total revenue	$ 23,713	$ 28,233	$ 71,660	$ 100,449
Total revenue | U.S.
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	57.00%	51.00%	55.00%	51.00%
Total revenue | Other Americas
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	5.00%	5.00%	8.00%	6.00%
Total revenue | United Kingdom (“U.K.”)
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	11.00%	9.00%	10.00%	11.00%
Total revenue | Europe (excluding U.K.), Middle East, and Africa
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	16.00%	21.00%	16.00%	16.00%
Total revenue | Asia-Pacific
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	11.00%	14.00%	11.00%	16.00%