Stock Option Plans - Options Outstanding (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Number of Options Outstanding 3,005,153 2,484,559
Weighted Average Remaining Contractual Term (in years), Outstanding 7 years 8 months 12 days  
Number of Options, Exercisable 1,883,201  
Weighted Average Remaining Contractual Term (in years), Exercisable 6 years 9 months 4 days  
Exercise Price $0.48 - $1.71    
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Exercise price range lower range limit 0.48  
Exercise price range upper range limit 1.71  
Number of Options Outstanding 51,898  
Weighted Average Remaining Contractual Term (in years), Outstanding 1 year 5 months 1 day  
Number of Options, Exercisable 51,898  
Weighted Average Remaining Contractual Term (in years), Exercisable 1 year 5 months 1 day  
Exercise Price $1.72- $2.94    
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Exercise price range lower range limit 1.72  
Exercise price range upper range limit 2.94  
Number of Options Outstanding 586,611  
Weighted Average Remaining Contractual Term (in years), Outstanding 4 years 10 months 2 days  
Number of Options, Exercisable 586,611  
Weighted Average Remaining Contractual Term (in years), Exercisable 4 years 10 months 2 days  
Exercise Price $5.40 - $7.86    
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Exercise price range lower range limit 5.40  
Exercise price range upper range limit 7.86  
Number of Options Outstanding 1,027,627  
Weighted Average Remaining Contractual Term (in years), Outstanding 7 years 6 months 22 days  
Number of Options, Exercisable 944,777  
Weighted Average Remaining Contractual Term (in years), Exercisable 7 years 6 months 15 days  
Exercise Price $7.87 - $13.71    
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Exercise price range lower range limit 7.87  
Exercise price range upper range limit 13.71  
Number of Options Outstanding 725,292  
Weighted Average Remaining Contractual Term (in years), Outstanding 8 years 10 months 24 days  
Number of Options, Exercisable 246,610  
Weighted Average Remaining Contractual Term (in years), Exercisable 8 years 9 months 18 days  
Exercise Price $23.51-$32.05    
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]    
Exercise price range lower range limit 23.51  
Exercise price range upper range limit 32.05  
Number of Options Outstanding 613,725  
Weighted Average Remaining Contractual Term (in years), Outstanding 9 years 9 months 15 days  
Number of Options, Exercisable 53,305  
Weighted Average Remaining Contractual Term (in years), Exercisable 9 years 9 months 4 days