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Equity Incentive Plans and Stock-Based Compensation (Details 2) - Employee Stock Option [Member] - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Number of Shares    
Outstanding, at the beginning of the period (in shares) 4,310,361  
Options granted (in shares) 551,479 458,426
Options exercised (in shares) (158,351)  
Options forfeited (in shares) (150,588)  
Outstanding, at the end of the period (in shares) 4,552,901  
Vested or expected to vest at the end of the period (in shares) 4,476,226  
Options exercisable at the end of the period (in shares) 3,254,787  
Weighted Average Exercise Price    
Outstanding at the beginning of the year (in dollars per shares) $ 9.78  
Options granted (in dollars per share) 12.84  
Options exercised (in dollars per share) 7.23  
Options forfeited (in dollars per share) 18.32  
Outstanding at the end of the period (in dollars per shares) 9.96  
Vested or expected to vest at the end of the period (in dollars per share) 9.91  
Options exercisable at the end of the period (in dollars per share) $ 8.86  
Weighted Average Remaining Contractual Term    
Outstanding 5 years 11 months 19 days  
Vested or expected to vest 5 years 11 months 1 day  
Options exercisable 4 years 9 months 4 days  
Aggregate Intrinsic Value    
Outstanding $ 17,251  
Vested or expected to vest 17,199  
Options exercisable $ 16,232