Business Combinations - Intangible Assets Acquired (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Mist Systems, Inc.
Business Acquisition [Line Items]
Total intangible assets acquired	$ 102.0
Mist Systems, Inc. | Existing technology
Business Acquisition [Line Items]
Acquired intangible asset, weighted average estimated useful life (in years)	5 years
Total intangible assets acquired	$ 81.0
Mist Systems, Inc. | Customer relationships
Business Acquisition [Line Items]
Acquired intangible asset, weighted average estimated useful life (in years)	5 years
Total intangible assets acquired	$ 15.0
Mist Systems, Inc. | Trade name
Business Acquisition [Line Items]
Acquired intangible asset, weighted average estimated useful life (in years)	5 years
Total intangible assets acquired	$ 6.0
HTBase
Business Acquisition [Line Items]
Total intangible assets acquired		$ 7.8
HTBase | Existing technology
Business Acquisition [Line Items]
Acquired intangible asset, weighted average estimated useful life (in years)		4 years
Total intangible assets acquired		$ 7.8
HTBase | Customer relationships
Business Acquisition [Line Items]
Total intangible assets acquired		0.0
HTBase | Trade name
Business Acquisition [Line Items]
Total intangible assets acquired		$ 0.0
Cyphort
Business Acquisition [Line Items]
Total intangible assets acquired			$ 15.4
Cyphort | Existing technology
Business Acquisition [Line Items]
Acquired intangible asset, weighted average estimated useful life (in years)			5 years
Total intangible assets acquired			$ 15.4
Cyphort | Customer relationships
Business Acquisition [Line Items]
Total intangible assets acquired			0.0
Cyphort | Trade name
Business Acquisition [Line Items]
Total intangible assets acquired			$ 0.0