Stock-based Compensation - Allocation of Stock-based Compensation Expense (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Schedule of total stock-based compensation expense        
Total stock-based compensation expense $ 1,226 $ 683 $ 2,754 $ 1,862
Research and development [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense 691 318 1,392 860
Sales and marketing [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense 129 97 361 249
General and administrative [Member]
       
Schedule of total stock-based compensation expense        
Total stock-based compensation expense $ 406 $ 268 $ 1,001 $ 753