Annual report pursuant to Section 13 and 15(d)

Stock-based Compensation Plans and Awards - Stock compensation plans narrative (Details)

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Stock-based Compensation Plans and Awards - Stock compensation plans narrative (Details) - USD ($)
1 Months Ended 12 Months Ended
Jun. 14, 2011
Dec. 31, 2013
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock previously reserved but unissued (in shares)     18,500,050 10,409,095  
Shares issuable pursuant to the ESPP          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock reserved for the issuance (in shares)         10,000,000
Percentage of payroll deductions of eligible employees to purchase shares of common stock (up to)         15.00%
Maximum amount of payroll deductions eligible employees can use per calendar year   $ 25,000      
Offering period   6 months 6 months    
Exercise price as a percentage of the fair market value of the common stock   85.00%      
2011 Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock reserved for the issuance (in shares) 12,000,000        
Annual fixed increase alternative, increase in shares of common stock reserved for issuance (in shares) 10,000,000        
Annual percentage increase alternative, increase in common stock reserved for issuance as a percentage of common stock outstanding 4.00%        
2011 Plan | Stock options | Minimum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period 3 years        
2011 Plan | Stock options | Maximum          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Expiration term (no more than) 10 years        
Vesting period 4 years        
2004 Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares of common stock previously reserved but unissued (in shares) 1,506,424