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Common Stock, Preferred Stock and Equity Plans - Stock and Option Plans (Details)
12 Months Ended
Dec. 31, 2017
vote
shares
Dec. 31, 2015
shares
Dec. 31, 2016
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock, shares authorized (shares) 500,000,000   500,000,000
Common stock, number of votes per share | vote 1    
Preferred stock, shares authorized (shares) 1,000,000   1,000,000
Preferred stock, shares issued (shares) 0   0
Preferred stock, shares outstanding (shares) 0   0
Awards outstanding (shares) 13,491,491    
Additional awards authorized for grant (shares) 11,427,114    
2013 Stock and Option Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards outstanding (shares) 10,388,723    
Additional awards authorized for grant (shares) 11,427,114    
Additional shares authorized (shares) 6,750,000 7,800,000  
2006 Stock and Option Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards outstanding (shares) 3,102,768    
Additional awards authorized for grant (shares) 0    
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expiration period 10 years