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STOCK-BASED COMPENSATION - Schedule of Weighted-Average Assumptions for Options and ESPP Subscriptions Granted Granted (Details) - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Option Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk-free interest rate 1.80% 2.80% 2.30% 2.90%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility (as a percent) 29.70% 29.20% 29.60% 29.10%
Expected term 5 years 2 months 12 days 5 years 2 months 12 days 5 years 1 month 6 days 5 years
Fair value, per option (in dollars per share) $ 58.07 $ 46.37 $ 54.31 $ 42.44
ESPP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk-free interest rate 2.00% 2.20% 2.40% 1.70%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility (as a percent) 32.00% 34.30% 32.40% 32.80%
Expected term 21 days 21 days 18 days 18 days
Fair value, per option (in dollars per share) $ 57.31 $ 46.58 $ 49.29 $ 36.53