Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies - Contractual Obligations (Details)

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Commitments and Contingencies - Contractual Obligations (Details)
$ in Thousands
12 Months Ended
Aug. 24, 2017
USD ($)
Apr. 21, 2017
USD ($)
installment
Dec. 31, 2018
USD ($)
installment
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Schedule of Investments [Line Items]          
Purchase of intangible assets     $ 1,000 $ 2,000 $ 0
Avira, Inc.          
Schedule of Investments [Line Items]          
Sale of patent in license agreement   $ 3,900 $ 2,000    
Number of quarterly installment payments | installment   12 6    
Installment amount payable   $ 325      
Fee receivable period   3 years      
IBM | Patents          
Schedule of Investments [Line Items]          
Fee receivable period     3 years    
Intangible assets acquired $ 8,500        
Purchase of intangible assets 2,000        
Cash payable $ 6,500   $ 5,500    
Weighted average useful life     4 years