Equity Compensation (Details 2) (Stock options, USD $)
3 Months Ended
Mar. 31, 2015
Options Outstanding  
Number of Underlying Shares 4,776,076
Options Exercisable  
Number of Underlying Shares 2,721,289
0.78-1.72  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 0.78
Range of Exercise Price, high end of range (in dollars per share) $ 1.72
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 1.10
Number of Underlying Shares 26,639
Weighted-Average Remaining Contractual Life 6 months
Options Exercisable  
Number of Underlying Shares 26,639
Weighted-Average Remaining Contractual Life 6 months
1.97-3.38  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 1.97
Range of Exercise Price, high end of range (in dollars per share) $ 3.38
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 2.57
Number of Underlying Shares 238,762
Weighted-Average Remaining Contractual Life 1 year 7 months 6 days
Options Exercisable  
Number of Underlying Shares 238,762
Weighted-Average Remaining Contractual Life 1 year 7 months 6 days
3.58-6.14  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 3.58
Range of Exercise Price, high end of range (in dollars per share) $ 6.14
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 5.66
Number of Underlying Shares 1,510,318
Weighted-Average Remaining Contractual Life 5 years 4 months 24 days
Options Exercisable  
Number of Underlying Shares 1,412,151
Weighted-Average Remaining Contractual Life 5 years 4 months 24 days
6.34-9.94  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 6.34
Range of Exercise Price, high end of range (in dollars per share) $ 9.94
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 8.29
Number of Underlying Shares 981,727
Weighted-Average Remaining Contractual Life 7 years
Options Exercisable  
Number of Underlying Shares 668,671
Weighted-Average Remaining Contractual Life 6 years 10 months 24 days
11.28-16.97  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 11.28
Range of Exercise Price, high end of range (in dollars per share) $ 16.97
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 13.91
Number of Underlying Shares 1,214,668
Weighted-Average Remaining Contractual Life 8 years 9 months 18 days
Options Exercisable  
Number of Underlying Shares 162,600
Weighted-Average Remaining Contractual Life 6 years 2 months 12 days
17.66-22.92  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 17.66
Range of Exercise Price, high end of range (in dollars per share) $ 22.92
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 21.00
Number of Underlying Shares 803,962
Weighted-Average Remaining Contractual Life 8 years 10 months 24 days
Options Exercisable  
Number of Underlying Shares 212,466
Weighted-Average Remaining Contractual Life 8 years 9 months 18 days