Goodwill and Intangible Assets (Amortization expense) (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Amortization expense        
Amortization of intangible assets $ 1,334 $ 1,221 $ 3,885 $ 3,393
Cost of revenue        
Amortization expense        
Amortization of intangible assets 802 800 2,367 2,266
Research and development        
Amortization expense        
Amortization of intangible assets 50 50 145 140
Sales and marketing        
Amortization expense        
Amortization of intangible assets $ 482 $ 371 $ 1,373 $ 987