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Equity Incentive Plans -Stock Options Summary (Details) - Common stock options
12 Months Ended
Dec. 31, 2018
$ / shares
shares
Minimum  
Equity Incentive Plans  
Exercise prices of options granted through the end of the year (in dollars per share) $ 0.58
Maximum  
Equity Incentive Plans  
Exercise prices of options granted through the end of the year (in dollars per share) $ 285.71
1997 Plan and 2008 Plan  
Equity Incentive Plans  
Expiration period 10 years
Vesting period 4 years
2014 Equity Incentive Plan  
Equity Incentive Plans  
Shares available for grant | shares 1,988,069