Goodwill and Intangible Assets (Amortization expense) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Amortization expense    
Amortization of intangible assets $ 1,230 $ 934
Cost of revenue    
Amortization expense    
Amortization of intangible assets 774 649
Research and development    
Amortization expense    
Amortization of intangible assets 48 40
Sales and marketing    
Amortization expense    
Amortization of intangible assets $ 408 $ 245