Business Combinations - Narrative (Details)				1 Months Ended	12 Months Ended
	May. 09, 2014 USD ($) shares	Dec. 30, 2013 USD ($) $ / shares shares	Sep. 03, 2013 USD ($) $ / shares shares	May. 31, 2014 $ / shares shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					$ 307,493,000	$ 307,493,000
Estimated fair value of unvested awards to be expensed					494,700,000
Goodwill recognized						41,538,000
Amortization of intangible assets					47,100,000	45,200,000	$ 1,500,000
Finite-Lived Intangible Assets, Accumulated Amortization					92,933,000	45,868,000
Finite-Lived Intangible Assets, Net					214,560,000	261,625,000
Developed technology
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					78,193,000	78,193,000
Content
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					$ 128,600,000	128,600,000
Developed technology, content and contract backlog | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life					3 years
Developed technology, content and contract backlog | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life					10 years
Customer relationship and trade names | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life					4 years
Customer relationship and trade names | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life					8 years
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					$ 75,300,000	75,300,000
Contract backlog
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					13,000,000	13,000,000
Trade names
Finite-Lived Intangible Assets [Line Items]
Total intangible assets subject to amortization					$ 12,400,000	$ 12,400,000
nPulse Technologies
Finite-Lived Intangible Assets [Line Items]
Total purchase consideration	$ 56,600,000
Cash paid for acquisition	55,200,000
Shares issued for acquisition (in shares) | shares				295,681
Fair value of shares issued for acquisition	$ 1,300,000
Vesting period	3 years 6 months
Share price (usd per share) | $ / shares				$ 26.44
Goodwill deductible for income tax purposes	$ 0
nPulse Technologies | Maximum
Finite-Lived Intangible Assets [Line Items]
Shares issued for acquisition (in shares) | shares	54,319
nPulse Technologies | Developed technology
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	6 years
nPulse Technologies | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life	8 years
Mandiant, Inc.
Finite-Lived Intangible Assets [Line Items]
Total purchase consideration		$ 900,790,000
Cash paid for acquisition		106,538,000
Fair value of equity awards assumed		$ 89,838,000
Shares issued for acquisition (in shares) | shares		16,123,011
Share price (usd per share) | $ / shares		$ 5.22
Goodwill deductible for income tax purposes		$ 0
Share conversion ratio		0.8126
Estimated fair value of unvested awards to be expensed		$ 119,500,000
Fair values of vested equity based awards		$ 89,800,000
Pro forma net loss							$ 246,617,000
Mandiant, Inc. | Developed technology | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		4 years
Mandiant, Inc. | Developed technology | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		6 years
Mandiant, Inc. | Content
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		10 years
Mandiant, Inc. | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		8 years
Mandiant, Inc. | Contract backlog | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		1 year
Mandiant, Inc. | Contract backlog | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		3 years
Mandiant, Inc. | Trade names
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible asset, useful life		4 years
Secure DNA
Finite-Lived Intangible Assets [Line Items]
Total purchase consideration			$ 4,900,000
Cash paid for acquisition			$ 4,100,000
Shares issued for acquisition (in shares) | shares			50,000
Share price (usd per share) | $ / shares			$ 16.00
Contingent obligation determination period			2 years
Goodwill deductible for income tax purposes			$ 0
Business acquisition related costs			200,000
Goodwill recognized			2,300,000
Contingent consideration classified as equity | Secure DNA
Finite-Lived Intangible Assets [Line Items]
Contingent obligation maximum			$ 3,000,000.0
Contingent obligation of common stock (in shares) | shares			190,000
General and administrative | nPulse Technologies
Finite-Lived Intangible Assets [Line Items]
Acquisition costs	$ 500,000
General and administrative | Mandiant, Inc.
Finite-Lived Intangible Assets [Line Items]
Business acquisition related costs		$ 8,500,000
Unvested stock options and restricted stock | nPulse Technologies
Finite-Lived Intangible Assets [Line Items]
Fair value of equity awards assumed	$ 100,000