STOCKHOLDERS' EQUITY (Schedule of Shares Reserved for Issuance) (Details)	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	21,692,838
Options outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	7,078,932
Restricted stock units and awards outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for future issuance (in shares)	7,249,205
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)	4,845,772
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)	2,518,929