STOCKHOLDERS' EQUITY (Schedule of Shares Reserved for Issuance) (Details)	Dec. 31, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	21,505,313
Stock options outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	6,818,682
RSUs outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	6,563,863
Available for future stock option and restricted stock units and awards grants
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	6,046,518
Available for future ESPP offerings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	2,076,250