Business Combinations Purchase Price Allocation (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018	Jan. 05, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Acquired intangible assets, weighted average useful life		8 years
Goodwill acquired		$ 570,790
Customer contract and relationships		(23,900)		$ 0
SIlver Spring Networks, Inc. [Member]
Business Acquisition [Line Items]
Current Assets			$ 86,444
Property, plant, and equipment			27,670
Other long-term assets	[1]		(290)
Identifiable intangible assets			226,700
Total identified intangible assets			241,100
Goodwill acquired		$ 570,790
Current liabilities			(90,034)
Long-term liabilities			(2,565)
Total net assets acquired			809,215
Core Developed Technology [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			81,900
Acquired intangible assets, weighted average useful life		5 years
Customer Contracts And Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			134,000
Acquired intangible assets, weighted average useful life		10 years
Customer contract and relationships			(23,900)
Acquired finite-lived intangible liabilities, weighted average useful life		5 years
Trademarks and Trade Names [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			10,800
Acquired intangible assets, weighted average useful life		3 years
In Process Research and Development [Member]
Business Acquisition [Line Items]
Identifiable intangible assets			$ 14,400

[1] Reflects adjustments to deferred tax assets and liabilities, net as a result of the acquisition, and is classified as part of our overall consolidated deferred tax asset. This unfavorable deferred tax asset more than offsets the fair value of other noncurrent assets acquired.