Commitments and Contingencies - Contractual Obligations (Details) $ in Thousands			12 Months Ended
	Aug. 24, 2017 USD ($)	Apr. 21, 2017 USD ($) installment	Dec. 31, 2017 USD ($) installment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Investments [Line Items]
Purchase of intangible assets			$ 2,000	$ 0	$ 0
Avira, Inc.
Schedule of Investments [Line Items]
Sale of patent in license agreement		$ 3,900	$ 3,300
Number of quarterly installment payments | installment		12	10
Installment amount payable		$ 325
Fee receivable period		3 years
IBM | Patents
Schedule of Investments [Line Items]
Intangible assets acquired	$ 8,500
Purchase of intangible assets	2,000
Cash payable	$ 6,500
Weighted average useful life			4 years