Equity Compensation (Details 4) (Stock options, USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Total stock-based compensation expense      
Total stock-based compensation expense $ 5,341,000 $ 3,760,000 $ 2,869,000
Total unrecognized compensation cost related to non-vested stock option awards 18,600,000    
Weighted-average period over which unrecognized compensation cost will be recognized 3 years 1 month 6 days    
Cost of revenue
     
Total stock-based compensation expense      
Total stock-based compensation expense 105,000 63,000 78,000
Research and development
     
Total stock-based compensation expense      
Total stock-based compensation expense 2,235,000 1,414,000 704,000
Sales and marketing
     
Total stock-based compensation expense      
Total stock-based compensation expense 1,110,000 743,000 580,000
General and administrative
     
Total stock-based compensation expense      
Total stock-based compensation expense $ 1,891,000 $ 1,540,000 $ 1,507,000