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EMPLOYEE STOCK PLANS (Details) - shares
12 Months Ended
Apr. 26, 2017
Apr. 23, 2015
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Term of equity awards granted     10 years
Equity award vesting period     4 years
2009 Stock Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Additional shares of common stock reserved for issuance 1,500,000.0 2,500,000 1,500,000
Shares reserved for issuance     12,400,000
Term of equity awards granted     10 years
2009 Stock Plan | Period 1 | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options vesting rate     25.00%
Equity award vesting period     1 year
2009 Stock Plan | Period 1 | Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options vesting rate     25.00%
Equity award vesting period     1 year
2009 Stock Plan | Period 2 | Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Periodic vesting percentage     2.08333%
2009 Stock Plan | Period 2 | Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Periodic vesting percentage     12.50%
Employee Stock Purchase Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Additional shares of common stock reserved for issuance 1,500,000.0 1,000,000.0  
Shares reserved for issuance     4,800,000
Duration of offering period     6 months
Percentage of employee's total compensation (up to)     20.00%
Maximum shares per offering period     20,000
Percentage of fair market value of common stock     85.00%