Equity Compensation (Range) (Details)
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Options Outstanding  
Number of Underlying Shares | shares 1,784,394
Options Exercisable  
Number of Underlying Shares | shares 1,649,277
4.89-7.49  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 4.89
Range of Exercise Price, high end of range (in dollars per share) 7.49
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 6.09
Number of Underlying Shares | shares 655,341
Weighted-Average Remaining Contractual Life 3 years 1 month 6 days
Options Exercisable  
Number of Underlying Shares | shares 647,967
Weighted-Average Remaining Contractual Life 3 years
8.16-12.93  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 8.16
Range of Exercise Price, high end of range (in dollars per share) 12.93
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 10.52
Number of Underlying Shares | shares 380,848
Weighted-Average Remaining Contractual Life 5 years 7 months 6 days
Options Exercisable  
Number of Underlying Shares | shares 305,478
Weighted-Average Remaining Contractual Life 5 years 3 months 18 days
12.98-19.56  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 12.98
Range of Exercise Price, high end of range (in dollars per share) 19.56
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 15.60
Number of Underlying Shares | shares 344,008
Weighted-Average Remaining Contractual Life 6 years 4 months 24 days
Options Exercisable  
Number of Underlying Shares | shares 291,635
Weighted-Average Remaining Contractual Life 6 years 4 months 24 days
20.91-22.92  
Equity compensation  
Range of Exercise Price, low end of range (in dollars per share) $ 20.91
Range of Exercise Price, high end of range (in dollars per share) 22.92
Options Outstanding  
Weighted Average Exercise Price (in dollars per share) $ 21.08
Number of Underlying Shares | shares 404,197
Weighted-Average Remaining Contractual Life 5 years 7 months 6 days
Options Exercisable  
Number of Underlying Shares | shares 404,197
Weighted-Average Remaining Contractual Life 5 years 7 months 6 days