Goodwill and Intangible Assets (Amortization expense) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Amortization expense      
Amortization of intangible assets $ 4,598 $ 1,474 $ 491
Cost of revenue      
Amortization expense      
Amortization of intangible assets 3,052 1,392  
Research and development      
Amortization expense      
Amortization of intangible assets 188 $ 82  
Sales and marketing      
Amortization expense      
Amortization of intangible assets $ 1,358