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Business Acquisition Narratives (Details) - USD ($)
$ in Thousands
12 Months Ended
Feb. 29, 2016
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2015
Business Acquisition [Line Items]        
Goodwill   $ 237,279 $ 242,827 $ 197,781
TVN [Member]        
Business Acquisition [Line Items]        
Total purchase consideration $ 82,500 82,512    
Goodwill   $ 41,670