Goodwill and Intangible Assets (Amortization Expense) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Amortization expense    
Amortization of intangible assets $ 1,446 $ 1,230
Cost of revenue    
Amortization expense    
Amortization of intangible assets 921 774
Research and development    
Amortization expense    
Amortization of intangible assets 28 48
Sales and marketing    
Amortization expense    
Amortization of intangible assets $ 497 $ 408