Equity Compensation (Expense) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Total stock-based compensation expense    
Total stock-based compensation expense $ 1,823 $ 1,849
Cost of revenue    
Total stock-based compensation expense    
Total stock-based compensation expense 43 47
Research and development    
Total stock-based compensation expense    
Total stock-based compensation expense 814 772
Sales and marketing    
Total stock-based compensation expense    
Total stock-based compensation expense 509 454
General and administrative    
Total stock-based compensation expense    
Total stock-based compensation expense 457 576
Stock options    
Total stock-based compensation expense    
Total unrecognized compensation cost related to non-vested stock option awards $ 10,200  
Weighted-average period over which unrecognized compensation cost will be recognized 2 years 2 months 12 days  
Restricted stock units    
Total stock-based compensation expense    
Total unrecognized compensation cost related to non-vested stock option awards   $ 10,200
Weighted-average period over which unrecognized compensation cost will be recognized   2 years 10 months 24 days