Stock-based Compensation - Allocation of Stock-based Compensation Expense (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Schedule of total stock-based compensation expense        
Total stock-based compensation expense $ 683 $ 520 $ 1,862 $ 1,503
Research and development [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense 318 146 860 373
Sales and marketing [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense 97 119 249 292
General and administrative [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense $ 268 $ 255 $ 753 $ 838