STOCK-BASED COMPENSATION Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	$ 6,526	$ 5,789	$ 17,822	$ 15,217
Stock Options
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense				200
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	2,200	2,100	5,700	4,400
Restricted Stock Units (RSUs)
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	4,000	3,400	11,200	9,700
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	900	900
Cost of revenues
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	391	348	885	731
Research and development
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	2,173	1,934	6,158	5,343
Sales and marketing
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	1,441	1,303	3,727	3,229
General and administrative
Stock-based compensation expense for stock options, stock awards and employee stock purchases included in operations:
Stock-Based Compensation Expense	$ 2,521	$ 2,204	$ 7,052	$ 5,914