Equity Compensation (Expense) (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Stock options        
Total stock-based compensation expense        
Total stock-based compensation expense $ 2,909 $ 2,127 $ 6,163 $ 3,950
Total unrecognized compensation cost related to non-vested stock option awards 4,200   $ 4,200  
Weighted-average period over which unrecognized compensation cost will be recognized     1 year 3 months 18 days  
Stock options | Cost of revenue        
Total stock-based compensation expense        
Total stock-based compensation expense 61 47 $ 119 90
Stock options | Research and development        
Total stock-based compensation expense        
Total stock-based compensation expense 1,050 890 2,179 1,704
Stock options | Sales and marketing        
Total stock-based compensation expense        
Total stock-based compensation expense 884 600 1,948 1,109
Stock options | General and administrative        
Total stock-based compensation expense        
Total stock-based compensation expense 914 $ 590 1,917 $ 1,047
Restricted stock units        
Total stock-based compensation expense        
Total unrecognized compensation cost related to non-vested restricted stock units $ 11,900   $ 11,900  
Weighted-average period over which unrecognized compensation cost will be recognized     2 years 1 month 6 days