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
Jun. 14, 2011
Dec. 31, 2013
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares of common stock previously reserved but unissued (in shares)     10,409,095 15,042,664
Employee stock        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares of common stock reserved for the issuance (in shares)   4,000,000    
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    
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        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period 4 years      
2011 Plan | Stock options | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expiration term (no more than) 10 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