STOCK-BASED COMPENSATION Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	$ 4,398	$ 6,526	$ 16,138	$ 17,822
Performance Based Awards and Long Term Performance based Units
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	(100)	2,200	2,600	5,700
Restricted Stock Units (RSUs)
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	4,200	4,000	12,400	11,200
Employee Stock Purchase Plan
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	300	300	1,100	900
Cost of revenues
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	243	391	784	885
Research and development
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	1,634	2,173	5,744	6,158
Sales and marketing
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	1,105	1,441	3,507	3,727
General and administrative
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	$ 1,416	$ 2,521	$ 6,103	$ 7,052