v3.8.0.1
STOCK-BASED COMPENSATION - Valuation Assumptions (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Employee Stock Option        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years)   5 years 10 months 6 days   5 years 9 months 11 days
Expected volatility   53.18%   55.09%
Risk free interest rate   1.15%   1.49%
Market-Based Restricted Stock Unit [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility     46.36% 53.00%
Risk free interest rate     1.45% 1.07%
ESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility, minimum 34.00% 35.00% 34.00% 35.00%
Expected volatility, maximum 39.00% 55.30% 39.00% 55.30%
Risk free interest rate, minimum 0.60% 0.07% 0.60% 0.07%
Risk free interest rate, maximum 1.07% 0.51% 1.07% 0.51%
ESPP | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) 6 months 6 months 6 months 6 months
ESPP | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) 1 year 2 years 1 year 2 years